Sedimentation in Our Reservoirs

Sedimentation in Our Reservoirs
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Sedimentation in Our Reservoirs: Causes and Solutions
Sedimentation
in Our Reservoirs:
Causes and Solutions
Kansas Water Office
Kansas Water Resources Institute
Kansas Center for Agricultural Resources and the Environment
Kansas State University Agricultural Experiment Station
and Cooperative Extension Service
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Table of Contents
3
Reservoirs: Infrastructure for Our Future
Tracy Streeter
5
Sedimentation and the Future of Reservoirs in Kansas
W. L. Hargrove
Reservoirs in Kansas
7
Current State, Trend, and Spatial Variability
of Sediment in Kansas Reservoirs
9
Frank deNoyelles, Mark Jakubauskas
25
Methods for Assessing Sedimentation in Reservoirs
Mark Jakubauskas, Frank deNoyelles
35
Effects of Sedimentation on Biological Resources
Donald G. Huggins, Robert C. Everhart, Andrew Dzialowski, James Kriz, Debra S. Baker
Management Practices to Control Sediment
Loading From Agricultural Landscapes in Kansas
47
Daniel Devlin, Philip Barnes
57
Can Reservoir Management Reduce Sediment Deposition?
Debra Baker, Frank deNoyelles
Economic Issues of Watershed Protection
and Reservoir Rehabilitation
71
Jeff Williams, Craig Smith
Reusing Dredged Sediment:
Geochemical and Ecological Considerations
Margaret A. Townsend, Nathan O. Nelson, Deborah Goard, DeAnn Presley
103
Photo Credits
Dan Devlin, K-State Research and Extension:
Pages 25, 35, 51, 55, 67
Susan Brown, K-State Research and Extension:
Pages 18, 143
Jennifer Anderson, USDA NRCS PLANTS Database:
Page 127
U.S. Army Corps of Engineers: Pages 21, 33, 57, 70
John Charlton, Kansas Geological Survey: Back Cover
Kansas Water Office: Page 3
NOAA Restoration Center: Page 38
Scott Bauer, USDA ARS: Page 116
USDA NRCS: Pages 6, 9, 10, 15, 24, 26, 44, 46, 47, 58,
61, 64, 71, 73, 74, 79, 83, 84, 90, 93, 96, 97, 100, 107,
110, 119, 123, 137, 138
USDA NRCS PLANTS Database: Page 124
All other photos from K-State Research and Extension
files.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Reservoirs:
Infrastructure for Our Future
Federal reservoirs in Kansas serve as the source of municipal and industrial water
for more than two-thirds of the state’s population. They are recreational destinations and provide a reserve to supplement streamflow for water quality, aquatic
life, and related activities. These reservoirs were built from the 1940s through the
1980s by the U.S. Army Corps of Engineers and the Bureau of Reclamation primarily for flood control. State and local users saw value in adding water supply storage to
the purpose of those reservoirs.
Reservoirs are integral to Kansas’ water supply infrastructure, but like all infrastructure,
reservoirs age. By their nature, reservoirs act as settling basins; they gradually fill with sediment, which reduces their capacity to store water to meet our needs. Although erosion is
natural, our actions often accelerate this process. Human activities such as urbanization,
agriculture, and alteration of riparian and wetland habitats have changed flow regimes,
increasing the concentrations and rates at which sediment enters streams and rivers.
Kansas’ economic landscape is changing. A viable economy depends on well-managed natural resources. Too often we take for granted that the foundation of our lives and livelihoods
will be there forever. Future demand for water supply from federal reservoirs is projected
to increase. Increasing demands coupled with decreasing supplies will eventually result in
water supply shortages during severe drought conditions. Preliminary studies indicate that
if a multi-year, severe drought occurred in the foreseeable future, water supply shortages
could occur because of diminished storage in several basins. Models are currently being
developed to more effectively use available storage and optimize use of reservoir water to
meet current and future needs.
At the same time, study and research should be directed toward determining sources and
movement of sediment in our streams and rivers. This knowledge will allow resource
managers to improve the effectiveness of programs and practices to reduce sedimentation
rates, improve riparian and aquatic habitats, and derive the most value from dollars spent
and resources invested.
Protecting and making the best use of reservoirs and the streams and rivers that feed them
requires an investment today to assure they will be sustained for future generations. The
Kansas Water Office is committed to that investment.
Tracy Streeter
Director, Kansas Water Office
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
4
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Sedimentation and the Future
of Reservoirs in Kansas
The U.S. government made significant investments in building reservoirs in
the 1950s and 1960s, which changed much of the rural environment in Kansas.
Although many reservoirs were built with a projected lifespan of 150 to 200 years,
current projections indicate these lifespans could be cut short by 50 to 100 years.
Sedimentation is reducing water-storage capacity of these reservoirs, and deposited
sediments containing nutrients, trace metals, and endocrine disrupting compounds
are significantly affecting reservoir water quality. Scientists have documented changes
in sediment load and water quality, and citizens have watched reservoirs “shrink” over
past decades. Bridges that once spanned water now sit above a “mud flat” of sediment.
The Dust Bowl of the early 1900s had dramatic social, biological, and physical consequences in Texas, Oklahoma, and Kansas and resulted in dramatic technological changes in
land management. The “Mud Bowl” resulting from reservoir sedimentation poses an even
larger threat that demands corrective action based on sound science and practical, affordable technologies.
Protecting reservoirs from sedimentation will:
• result in overall water conservation (i.e., maximize reservoir water storage, minimize
water loss during storm events, and improve water conservation management);
• require widespread implementation of conservation measures; this requires us to evaluate,
understand, and influence producer management behaviors that affect implementation
of conservation measures as well as sedimentation and future functioning of reservoirs;
• involve participants from a variety of disciplines including agriculture, engineering,
hydrology, sociology, economics, and others;
• affect water savings on a large scale not only by conserving and protecting existing
reservoir resources but also by retaining more soil and water on land; and
• be crucial to agriculture and rural life, especially in Kansas, and encompass a variety of
community, economic, environmental, health, and social issues.
This publication brings together leading scientific knowledge from many academic
disciplines and identifies technological solutions that will protect and conserve federal
reservoirs. The following white papers evaluate threats to sustainability of federal reservoirs,
causative factors behind these threats, and technological solutions along with their scientific underpinnings and propose future research needed to improve sustainability of these
vital water resources and landscapes to which they are connected. Our aim is to advance
interdisciplinary science, research, collaboration, and problem solving to achieve a key goal:
sustaining supplies of abundant, clean water in Kansas.
W.L. Hargrove
Director, Kansas Center for Agricultural Resources and the Environment (KCARE)
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
6
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Reservoirs in Kansas
Harlan County
Swanson
CN
Keith
DC Sebelius NT
RA
PL
SM
Kirwin
SH
TH
SD
GH
RO
Webster
Lovewell
JW
Waconda
OB
GL
LG
WH
GO
SC
LE
TR
Cedar Bluff
NS
EL
RS
Sedimentation in Our Reservoirs: Causes and Solutions
KE
FI
HG
RH
ST
GT
RL
WY
GE
Wilson
BT
MP
WB
Wabaunsee
DK
LY
MN
Marion
CS
KW
HV
RN
Cheney
PR
KM
SG
Afton
Otis Creek
GW
BUEl Dorado
Fall
River
Olathe
JO
Cedar
Hillsdale
MI
Melvern
John CF
Redmond
PN
SF
SN
Clinton DG
Gardner
Pomona
OS
FR
Council
Grove
MR
EW
Kanopolis
FO
HS
Tuttle
Creek
OT
SA
ED
GY
CD
CY
Milford
RC
HM
WS
MC
LC
WA
RP
Pony
Creek
BR Hiawatha
DP
NM
MS
Mission
Atchison
Centralia Banner
County
AT
Creek
JA
PT
Perry
LV
JF
Crystal
AN
LN
WO
Toronto
AL
Bronson
BB
WL
NO
CR
EK
Big Hill
MT
SV
SW
ME
CA
CM
BA
HP
SU
CL
CQ
Elk City
MG
LB
CK
Empire
Map from USGS; Kansas Geological Survey. Adapted with permission.
Kansas has more than 120,000 impoundments ranging in size from small farm ponds to large reservoirs. The 24 federal reservoirs in Kansas range in size from 1,200 to 15,314 surface acres; 21
of these provide drinking water for more than half the state’s population. Smaller, state- and locally owned reservoirs are vital resources for drinking water, flood control, and recreation and
are distributed across nearly every county in the state.
This map shows the 24 federal reservoirs in Kansas and several smaller basins referenced throughout this publication.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
8
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Current State, Trend,
and Spatial Variability
of Sediment in Kansas Reservoirs
Frank deNoyelles, Deputy Director and Professor
Mark Jakubauskas, Research Associate Professor
Applied Science and Technology for Reservoir Assessment (ASTRA) Initiative
Kansas Biological Survey, University of Kansas
Introduction
The more than 300,000 acres of public and
private reservoirs and ponds constructed in
Kansas during the past century are steadily
filling with silt. These water resources were
constructed at great expense. For example,
cost of a typical Kansas reservoir (≈7000
acres in size) constructed in the 1970s was
$50 million to $60 million ($200 million to
$250 million in 2007 dollars). Yet, reservoirs provide significant economic value to
the state through flood control, irrigation,
recreation, wildlife support, power generation, and high-quality water for human and
livestock consumption. More than half the
U.S. and Kansas population receives some
drinking water from reservoirs.
It is becoming increasingly complicated
and costly to manage these crucial water
resources; inevitably, silt will fill these water
bodies entirely unless removed periodically. Silt removal will be an enormous task,
even more so than original construction,
but there is still time to prepare. Although
a number of state agencies are beginning
to examine this long term management
problem, new efforts must be directed at
controlling the currently declining quality
of aging reservoirs.
The Reservoir as a Resource
During the 20th century, more than 2 million reservoirs of all sizes, including smaller
ponds, were constructed in the United
States, and many more were constructed
worldwide. Nearly 1,000 U.S. reservoirs
are larger than 1,000 acres, and about half
of these are federally operated. The lower
half of the mid-continental United
States, particularly the central states of
Kansas, Missouri, Oklahoma, Arkansas,
and Texas, has the greatest number of
reservoirs. The National Recreation Lakes
Study Commission (1999) determined that
the 490 federal reservoirs larger than 1,000
acres had an annual economic impact of
$44 billion and provided employment for
637,000 persons. Several thousand smaller
reservoirs provide recreation opportunities, and all reservoirs provide flood control
that protects lives and property; economic
impacts of these benefits are incalculable.
Reservoirs and lakes are basins of standing water; flow of water through them is
slower than that in entering streams and
rivers. Reservoirs are constructed by human
means, but lakes form naturally. Both
range greatly in size, function similarly,
are affected by the same environmental
conditions, and provide similar resources.
Most reservoirs have a normal operation
depth and pool volume for recreation
and water supply with additional flood
control depth and pool volume above
the normal pool and below the spillway
to temporarily absorb floodwaters (i.e.,
minimize prolonged added pressure on the
dam). Reservoirs and lakes require similar
management and renovation practices, but
these efforts often are focused on reservoirs,
which typically are constructed to serve
particular continuing needs.
Reservoir problems requiring particular
management actions usually involve quality
of drinking water and recreation and water
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
storage capacity for flood control
and power generation. We build
reservoirs in areas with few natural
lakes, but we also recognize that
these environments do not support
reservoirs’ continued existence. Soils in
these areas are very erodible and can be
disturbed even more by human activities.
In the lower half of the mid-continental
United States, where many reservoirs have
been constructed, surface soils and clays are
deep. For thousands of years, these materials moved naturally into valleys and stream
channels; now they move into reservoirs.
Thus, reservoirs act as settling basins in
which the sedimentation process deposits
soil, clay, and smaller rock particles. The
upper regions of reservoirs, where streams
enter, fill with sediment three to five times
more rapidly than deeper areas. Expanding
shallow zones reduce quality of water and
wildlife habitat as well as operation storage
capacity for drinking water and recreation.
Sediment can fill the basin in 100 to 200
years, the projected life expectancy of most
reservoirs. In contrast, most natural lakes
exist for tens of thousands of years.
Two hundred of the largest reservoirs in the
United States are now more than 40 years
old. What will we do when most of our
existing reservoirs are filled enough to end
their useful life? We already built reservoirs
in nearly all of the best places. Excavating
old reservoirs will require moving 15 to 30,
even up to 100, times more material than
originally was moved to construct the dam.
We also need to find a location for the
removed material, ideally one that is nearby
and will withstand this environmental disturbance. Further, because urban and rural
development steadily surrounded our reservoirs, we cannot continually raise the height
of the original dam and the contained water
10
Sedimentation in Our Reservoirs: Causes and Solutions
level or build new reservoirs nearby. Obviously, we must develop and implement new
management strategies to maintain current reservoirs for their intended uses and
extend their life expectancy.
Kansas Reservoirs:
Number, Size, Distribution,
Ownership, Uses
Kansas has more than 120,000 impoundments, although most (> 80%) are farm
ponds smaller than 1 acre. Nearly 6,000
reservoirs are large enough to be regulated
by the state (Figure 1). Approximately
585 reservoirs are owned by state or local
governments; these average 30 years in age.
The 93 Kansas reservoirs used as water
supplies are an average of 51 years old; 63
of these are state or locally owned. The 21
federal reservoirs used for drinking water
in Kansas have watersheds that cover 23%
of the state and contain more than 4,000
miles of stream channels. Many reservoirs
serve multiple purposes (e.g., domestic
water supply, flood control, recreation, and
irrigation).
Responding to increasing occurrences of
water quality problems affecting use of
Kansas reservoirs is an enormous challenge.
The most pressing issue is ensuring the
quality of water received by drinking water
suppliers, who provide treated water to
more than 60% of Kansas residents. Flood
control, recreation, irrigation, and other
uses also must be protected. Sediment
accumulation and other factors continue
to create immediate problems for water
and habitat quality. But, siltation is just
one part of the problem; reservoirs experience many problems long before they are
completely filled (deNoyelleys et al., 1999).
For example, sedimentation produces
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
shallow water zones. This leads to increased
cyanobacteria (blue-green algae) production, which, in turn, often causes taste and
odor problems in drinking water (Figure
2). Numerous Kansas reservoirs are already
experiencing problems. Cheney Reservoir
(Smith et al., 2002; Wang et al., 2005b),
Clinton Lake (deNoyelles et al., 1999;
Mankin et al., 2003; Wang et al., 1999,
2005a), and Marion Lake (Linkov et al.,
2007) all experienced massive algae blooms
that triggered shutdowns of drinking water
intakes. The near-complete siltation of the
north end of Perry Lake (Figure 3) led to
abandoned recreation areas and boat ramps
and loss of fish habitat.
Particular Challenges of
Smaller Reservoirs
Smaller, state- and locally owned reservoirs
are vital resources for drinking water, flood
control, and recreation and are distributed
across nearly every county in the state
(Figure 4). Small reservoirs are more likely
than large reservoirs to exhibit serious
Figure 1. Reservoirs and impoundments in Kansas
Data analysis and map preparation: Kansas Biological Survey
Data source: USACE (200
Nutrients and light
Siltation
Shallow areas
Algal blooms
Taste and odor events
Figure 2. Sedimentation triggers a series of problems
Sedimentation in Our Reservoirs: Causes and Solutions
11
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
April 24, 1974
Figure 3. Siltation in Perry Lake, 1974-2001
An estimated 91.5 million cubic yards of sediment have accumulated
leading to loss of more than 1,000 acres of surface area
Images courtesy of Kansas Biological Survey
October 25, 2001
Figure 4. Reservoirs owned by the state of Kansas or local governments
Average age: 30 years; Average normal storage: 639 acre-feet
Data analysis and map preparation: Kansas Biological Survey
Data source: USACE (2005)
12
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
impairments in water quality and quantity
and wildlife habitat due to siltation. For
example, Cedar Lake in Johnson County
(54-acre surface area) lost 50% of its volume since its construction in 1938. Cedar
Lake is upstream from Lake Olathe, a water
supply for Johnson County, and intercepts
much of its sediment load.
Kansas currently is losing value, resources,
and benefits from all its impoundments
to varying degrees and will experience
more rapid losses in the future, but the
vast number of small reservoirs in Kansas
is a challenge for state agencies charged
with managing them. Unfortunately, most
nonfederal reservoirs are not mapped and
monitored for changes that could signal
the onset of conditions that lead to water
supply impairment. Water managers lack
basic physical and biological data that can
help identify impaired reservoirs, prioritize
reservoirs in terms of impairment and need
for renovation, or assess the current state of
a reservoir.
Current State, Trend,
and Conditions of
Sedimentation in Kansas
Reservoirs
Large Reservoirs
Current information on sedimentation
is not available for most large, federal
reservoirs in Kansas. In most cases, these
reservoirs have not been surveyed for 10 to
20 years (Table 1). Available information
(projected through 2005) indicates that
Table 1. Bathymetric surveys of 18 federal reservoirs in Kansas
Year of most
Reservoir
Year of closure
recent survey
Kanopolis
1948
1982
Marion
1968
1982
Wilson
1964
1984
Council Grove
1964
1985
Melvern
1972
1985
Pomona
1963
1989
Fall River
1949
1990
Toronto
1960
1990
Clinton
1977
1991
Big Hill
1981
1992
Elk City
1966
1992
Milford
1967
1994
Hillsdale
1981
1996
Cheney
1964
1998
Tuttle Creek
1962
2000
Perry
1969
2001
El Dorado
1981
2005
John Redmond
1964
2007
a
Years since most
recent surveya
25
25
23
22
22
18
17
17
16
15
15
13
11
9
7
6
2
0
As of 2007
Sedimentation in Our Reservoirs: Causes and Solutions
13
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
100%
90%
80%
Percent Loss
70%
60%
50%
40%
30%
20%
10%
Bi
g
H
il
W l
eb
ste
El
r
D
or
ad
o
M
elv
ern
Ch
en
ey
H
ill
sd
ale
Cl
in
t
C
ed on
ar
Bl
u
W ff
ac
on
da
M
ar
io
n
M
ilf
or
d
Po
C
m
ou
on
nc
a
il G
ro
ve
Pe
rr
El y
kC
i
Fa ty
ll R
ive
r
Tu
t
Ka tle
no
lo
pi
s
T
o
Jo
r
on
hn
Re to
dm
on
d
0%
Figure 5. Loss of multipurpose pool water-storage capacity in Kansas federal reservoirs
Data source: KWO (2008)
Table 2. Mean annual sediment yield and mean annual precipitation for selected reservoir
basins in Kansasa
Sediment yield (acre-feet/
Mean annual
Reservoir basin
square mile per year)
precipitation (in.)
Small reservoir basins
Mound City Lake
2.03
40
Crystal Lake
1.72
40
Mission Lake
1.42
35
Gardner City Lake
.85
39
Otis Creek Reservoir
.71
33
Lake Afton
.66
30
Large reservoir basins
Perry Lake
Hillsdale Lake
Tuttle Creek Lake
Cheney Reservoir
Webster Reservoir
a
14
Data source: Juracek (2004)
Sedimentation in Our Reservoirs: Causes and Solutions
1.59
.97
.40
.22
.03
37
41
30
27
21
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has been archived. Current information is available from http://www.ksre.ksu.edu.
multipurpose pool water-storage capacity
lost because of sedimentation ranges from
less than 10% for Cheney Reservoir, Hillsdale Lake, and Webster Reservoir to more
than 40% for the Tuttle Creek, Kanopolis,
Toronto, and John Redmond Reservoirs
(Figure 5; KWO, 2008). Approximately
18% of the original multipurpose pool of
Perry Reservoir, one of the largest reservoirs
in Kansas, which was constructed in 1969
with a 12,200-acre operation pool and a
25,300-acre flood control pool, has been
lost to sediment deposition (Figure 5).
Mean annual sediment yields from basins
of five large reservoirs range from 0.03
acre-feet/square mile for Webster Reservoir
to 1.59 acre-feet/square mile for Perry Lake
(Table 2; Juracek, 2004).
Small Reservoirs
Current information on sedimentation
also is lacking for most small reservoirs in
Kansas. However, the U.S. Army Corps of
Engineers recently completed a resurvey of
34 small reservoirs (KWA, 2001). Results
indicated that water-storage capacity lost
because of sedimentation ranged from
negligible for Wellington New City Lake
(4 years old at the time of the resurvey)
to 62% for Alma City Lake (34 years old
at the time of the resurvey) (Table 3). In
another study, Juracek (2004) determined
that mean annual sediment yields from six
small reservoirs ranged from 0.66 acrefeet/square mile for Lake Afton to 2.03
acre-feet/square mile for Mound City Lake
(Table 2).
Statewide Variability in
Reservoir Sedimentation
The combined influence of several factors
determines the sedimentation rate for a
given reservoir. Collins (1965) created a
generalized map of sediment yield
in Kansas using available information on areal geology, topography,
soil characteristics, precipitation,
runoff, reservoir sedimentation, and
measured suspended-sediment loads
in streams (Figure 6). In the Collins
map, mean annual sediment yields ranged
from less than 50 tons/square mile in parts
of southwestern and south-central Kansas
to more than 5,000 tons/square mile in
the extreme northeastern part of the state.
More than 4,000 of the nearly 6,000 major
reservoirs in the state are located in areas
with the three highest sediment yield
classes. A recent comparison of basin-specific sediment yields for eight reservoirs
using regional estimates provided by
Collins (1965) indicated that basin-specific
yields tended to be smaller. This difference
could be due to implemented conservation
practices and information used to estimate
yields (Juracek, 2004).
To explain differences in sediment yields
among reservoir basins in Kansas, Juracek
(2004) compared estimated mean annual
sediment yields for 11 reservoirs with factors that affect soil erosion—precipitation,
soil permeability, slope, and land use. Only
the relationship between mean annual
sediment yield and mean annual precipitation (Table 2) was statistically significant.
As mean annual precipitation increased,
mean annual sediment yield also increased.
For the 11 reservoirs studied, mean annual
precipitation was the best predictor of sediment yield. Given the pronounced decrease
in precipitation from east to west across
Kansas, a similar east to west decrease in
reservoir sedimentation rates is likely.
Sedimentation in Our Reservoirs: Causes and Solutions
15
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Table 3. Characteristics of small municipal reservoirs in Kansasa
Reservoir
Alma City Lake
Augusta City Lake
Blue Mound City Lake
Buffalo City Reservoir
Council Grove City Lake
Crystal Lake
Eureka Reservoir
Fort Scott City Lake
Gardner Lake
Harveyville City Lake
Herington Reservoir
Lake Kahola
Lake Miola
Louisburg City Lake
Lyndon City Lake
Madison City Lake
Mission Lake
Moline Reservoir
Mound City Lake
Olathe Lake
Parsons Lake
Pleasanton Reservoir
Polk Daniels Lake
Prairie Lake
Prescott City Lake
Richmond City Lake
Sedan City South Lake
Severy City Lake
Strowbridge Reservoir
Thayer New City Lake
Winfield City Lake
Wabaunsee Lake
Wellington New City Lake
Westphalia Lake
Yates Center City Lake
a
Data source: KWA (2001)
Community
served
Year built
Alma
Augusta
Blue Mound
Buffalo
Council Grove
Garnett
Eureka
Fort Scott
Gardner
Harveyville
Herington
Emporia
Paola
Louisburg
Lyndon
Madison
Horton
Moline
Mound City
Olathe
Parsons
Pleasanton
Howard
Holton
Prescott
Richmond
Sedan
Severy
Carbondale
Thayer
Winfield
Eskridge
Wellington
Anderson RWDc
Yates Center
1966
1940
1957
1960
1942
1879b
1939
1959
1940
1960
1982
1936
1957
1984
1966
1970
1924
1937
1979
1957
1938
1968
1935
1948
1964
1955
1965
1938
1966
1960
1970
1937
1996
1963
1990
b
c
16
Sedimentation in Our Reservoirs: Causes and Solutions
Original
capacity
(acre-feet)
1,013
2,358
----8,416
229
3,690
--2,301
235
5,759
6,600
2,960
--948
1,445
1,866
--1,773
3,330
10,050
--777
--138
--780
--3,371
--19,800
4,175
3,250
278
2,720
2000
capacity
(acre-feet)
383
2,100
165
1,631
7,346
104
3,125
7,200
2,020
222
5,750
5,500
2,760
3,750
930
1,333
940
1,590
1,525
3,300
8,500
1,180
640
495
--220
770
115
2,902
560
19,500
3,600
3,250
130
2,241
Date incorrectly listed as 1940 in KWA (2001)
RWD = rural water district
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Mean annual sediment yield, tons/sq. mile
< 50
50 - 300
300 - 750
750 - 2000
2000 - 5000
> 5000
Figure 6. Sediment yield regions in Kansas and 5,847 major Kansas reservoirs
Data analysis and map preparation: Kansas Biological Survey
Sediment map: Collins (1965); Reservoir data: USACE (2005)
Information Needs for
Reservoir Management
and Restoration
Estimates of Sediment
Volume, Mass, Load, and
Yield
Effective reservoir sedimentation management requires knowing the amount of
sediment deposited (i.e., volume and mass)
as well as the rate (i.e., load and yield) at
which sediment deposition is occurring.
This information provides a baseline to
assess changes in sedimentation and the
effectiveness of implemented sediment
reduction management practices. Federal
reservoirs are surveyed most frequently,
typically along range lines, and an increasing number of federal reservoirs have been
mapped using acoustic echosounding to
produce whole-reservoir maps of water
depth. However, most of the nearly 6,000
regulated reservoirs in Kansas do not have
bathymetric (lake bottom contour) data.
Data for state and local reservoirs in Kansas
are even rarer, collected on an as-needed or
ad-hoc basis, and often incomplete.
Estimates of Reservoir
Sediment Trap Efficiency
Reservoir sediment trap efficiency is a
measure of the effectiveness of a reservoir
for trapping and permanently storing the
inflowing sediment load. Trap efficiency
typically is greater than 90% for large reservoirs (Brune, 1953; Vanoni, 2006), less for
smaller reservoirs. For example, estimated
trap efficiency of Perry Lake is 99% (Juracek, 2003). Trap efficiency declines with
increasing sedimentation (Morris and Fan,
1998); therefore, obtaining trap efficiency
estimates is crucial, especially for reservoirs
that are rapidly filling with sediment.
Sedimentation in Our Reservoirs: Causes and Solutions
17
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Sediment Quality
Sediment quality is an environmental concern because sediment
can act as a sink for various
contaminants and, under certain
conditions, a source of contaminants
for the overlying water column and biota
(Baudo et al., 1990; Zoumis et al., 2001).
Examples of sediment-associated contaminants include phosphorus, trace elements,
certain pesticides, and polychlorinated
biphenyls. Once in the food chain, some
sediment-derived contaminants pose a
greater concern because of bioaccumulation. Even after the source of a particular
contaminant is eliminated from a basin,
it could take several decades before newly
deposited sediment recovers to baseline
contaminant concentrations (Van Metre
et al., 1998; Juracek and Ziegler, 2006).
When considering dredging as a sediment
management strategy, it is important to
ascertain the quality of reservoir bottom
sediment before determining where to store
dredged material (Morris and Fan, 1998).
Sediment quality information is available
for several large and small Kansas reservoirs
(Juracek and Mau, 2002; Juracek, 2003,
2004, 2006).
Sediment Sources
Nationally, billions of dollars have been
spent over the past several decades to
control erosion and mitigate its effects
(Pimentel et al., 1995; Morris and Fan,
1998). Determining sediment sources
is essential for designing cost-effective
sediment management strategies that will
achieve meaningful reductions in sediment
loads and yields (Walling, 2005). A fundamental question is whether the sediment
load in streams originates mostly from
erosion of channel banks or surface soils
18
Sedimentation in Our Reservoirs: Causes and Solutions
within a basin. Using a combination of
several chemical tracers, Juracek and Ziegler
(2007) determined that the majority of
sediment now being deposited in Perry
Lake originated from channel-bank sources.
Sedimentation Dynamics
Repeated bathymetric surveys can provide significant insight into the nature of
sedimentation within a reservoir (e.g., is
the rate of sedimentation a continuous or
episodic process?). Changes in reservoir
bottom topography can be monitored over
time to provide an overall estimate of the
sediment accumulation rate and a spatially
explicit representation of sediment accumulation and movement across a reservoir.
Similarly, bathymetric surveys before and
after major rain events can provide information on whether significant sediment
movement occurred.
Sedimentation Patterns
Similar to bathymetric data, sediment
thickness information for Kansas reservoirs
is limited. Federal reservoirs have the most
complete data sets, state and local reservoirs
have the poorest. Sediment thickness and
volume can be estimated by several direct or
indirect approaches (e.g., topographic and
acoustic differencing and sediment coring).
But even in the best cases, sediment thickness and distribution data likely are limited
to a few point samples or transects across
a reservoir, which provides a very limited
representation of actual sediment accumulation patterns and rates.
Statewide SuspendedSediment Monitoring
Network
A suspended-sediment monitoring network can provide valuable information
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for managing sediment loads in streams.
Information could include instantaneous
concentrations, long-term variability,
seasonality, and relation to streamflow
and turbidity. Moreover, data from the
monitoring network could be used to
document and explain differences among
sites and provide baseline information to
assess effectiveness of implemented erosion
control practices. A USGS suspended-sediment monitoring network provided data
for several sites from the 1950s through the
1980s (Jordan, 1985). However, at present,
few if any suspended-sediment data are
being collected routinely.
Reservoir Information
Systems for Decision Support
Multiple constituencies in Kansas need
or desire information from state agencies
on water depth, sediment accumulation,
and related conditions affecting reservoirs.
This need is expressed in many ways: a
fisherman desiring a reservoir depth map,
a neighborhood association faced with the
difficult decision of whether to dredge their
reservoir, and state officials grappling with
major issues of drinking water quality and
quantity in reservoirs.
Critical decisions about reservoir management must be made at numerous times
and places across the state, yet information
on the current status and trends of Kansas
reservoirs is not readily accessible and is
dispersed among federal, state, and local
entities. This prevents timely and efficient
identification of currently impaired reservoirs and reservoirs that could become
impaired. No comprehensive database
exists to identify these water bodies
and determine their size, age, location,
proximity to urban areas, current level of
impairment, or potential future physical or
chemical impairment; and existing data and
information are of little use unless accessible to a wide variety of users. Therefore, a
reservoir decision-support system should be
developed as a resource for Kansans. This
system should incorporate a suite of physical, chemical, geospatial, and other data
gathered from a variety of sources.
Reservoir Restoration:
Issues Related to
Sediment Removal
Unique Aspects of Sediment
Removal Projects
Removing sediment from a reservoir typically is performed by dredging. Unique
among earthmoving projects, dredging
requires removing material from beneath
a water surface. Excavated material is out
of sight of both the contractor and stakeholders until deposited on land. Generally,
dredging projects in Kansas involve pumping sediment from the reservoir bottom as a
slurry and placing it on land behind levees,
which allow water to drain back to the reservoir. It is difficult to quantify the amount
of excavated sediment and impossible to
determine if removal achieved the desired
reconfiguration of the reservoir bottom.
The end product of dredging is out of view
with only the spoils as evidence of progress
and completion.
Also unique to dredging is a basin of water
(with more water flowing in and out)
that is highly disturbed by the excavation
process. Observers, particularly those living
nearby, expect to see sediment deposits
on land. However, they will also witness
changes in the reservoir—waters becoming
increasingly cloudy, heavier than normal
growth of aquatic plants, and impaired
fishing and other activities. Failing to
Sedimentation in Our Reservoirs: Causes and Solutions
19
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has been archived. Current information is available from http://www.ksre.ksu.edu.
identify or address these effects and issues
can hinder satisfactory project completion.
Examples of potential problems include:
• Inability of stakeholders to adequately
develop project goals because they cannot accurately identify the extent and
location of sediment
• Higher bids from contractors to cover
contingencies because they are not able
to adequately assess sediment conditions beneath the water surface
• Stakeholder concerns including unexpected project costs, difficult-to-view
progress, and unexpected appearance of
site disturbances
• Impeded progress or equipment damage as unexpected rocks, tree stumps,
compacted sediment, or other impediments are encountered
• Uncertainty between contractors and
stakeholders regarding the new bottom configuration as each area of the
reservoir bottom is completed
• Disenchantment among financial
investors, particularly citizen stakeholders, due to continuing site disturbances
and perceived slow progress
• Disagreements between contractors
and stakeholders regarding project
completion resulting from contractors
judging contract commitments only by
rough estimates of removed materials
• Diminished credibility between contractors and stakeholders, whether
justified or not, leading to contentious
final contract completion settlement
• Lingering questions among stakeholders: Will the reservoir meet future
20
Sedimentation in Our Reservoirs: Causes and Solutions
expected needs? Was the investment
worth it?
• Dissatisfaction of stakeholders and
contractors leading to discouraging
projections for the future with no other
restoration options available
Managing These Issues
To address the above-mentioned issues and
resulting effects, a management plan should
be developed based on accurate mapping
of the reservoir bottom before, during, and
after the sediment removal project. The
Kansas Biological Survey, a state agency,
can provide this mapping service through
a newly developed bathymetric mapping
capability. Simultaneously measuring water
quality conditions can help address other
related issues. State and federal agencies
with expertise in measuring particular
water and sediment quality conditions of
interest can work together to provide this
information.
Before sediment removal. Of
primary importance are high-resolution
(less than 1 square meter) contour maps
of the bottom configuration for the entire
reservoir and for specific sites. Comparing
this information with pre-impoundment
contours and selected sediment coring to
verify thickness in certain locations will
enable stakeholders to develop well-defined
project goals and work plans to support
the bidding process. All interested contractors can receive clear project goals and an
accurate view and quantification of the
reservoir bottom contour conditions to be
reconfigured. This will minimize unknown
factors and encourage preparation of the
most accurate, cost-effective bids and most
mutually acceptable work plan.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
During sediment removal. Excavated
sediment can be quantified most accurately
with mapped contour changes at each
bottom site before and after excavation.
During the sediment removal process,
bottom configuration information should
be available immediately before the dredge
moves into a new area and immediately
after the new area is completed. Such data
allows contractors to more accurately quantify sediment removal continually during
the project, a determination that is difficult,
if not impossible, to make based only on
excavated slurry on land that might still be
combined with an undetermined volume
of water. Quantifying excavated sediment
will improve contractors’ sediment removal
efficiency and provides contractors and
stakeholders an ongoing measure of progress related to the original goals and work
plan.
Keeping Stakeholders Informed.
Other issues can be addressed by disseminating useful information (e.g., excavation
progress and changing water quality) to
stakeholders. State agencies should maintain an information network to continually
document progress and changing water
quality conditions resulting from excavation or water returning from the spoils
area. Periodic stakeholder meetings, some
on site, should be convened. However,
this level of oversight and communication
among all parties, particularly dredging
contractors who might not have previously
worked with this level of stakeholder input,
requires conscientious management to
ensure continued progress.
Summary
Many reservoirs have been constructed in locations where their
lifespans are threatened by natural
conditions as well as human land use
activities. It is impossible to expect that
we could someday restore or replace all
these reservoirs. Hundreds of reservoirs in
Kansas and thousands more throughout the
United States already require restoration or
replacement. Eventually, all reservoirs will
require some action to maintain, restore,
or replace their ability to provide resources
as intended. Most reservoirs worldwide
were constructed at about the same time
(post-1930s) and have similar lifespans.
This creates a time period for renovation or
replacement that is similarly condensed and
too short to ensure successful rehabilitation
of all reservoirs. Replacement is difficult
because reservoirs have already been
constructed in most of the best locations.
Raising dam height to compensate for lost
water storage is structurally impossible for
many reservoirs, and it is not feasible to lose
all of the urban development surrounding
many reservoirs. Renovation by dredging
requires moving material and will cost
15 to 100 times more than original dam
construction. Dredging one 7,000-acre
reservoir nearly filled with sediment would
cost about $1 billion today. We must
continue to preserve quality of reservoirs
and watersheds with better management
until renovation or replacement is feasible.
It is imperative that we protect these vital
public resources, first by responding to
immediate problems affecting water quality
and wildlife habitat and then by addressing
progressive siltation.
Sedimentation in Our Reservoirs: Causes and Solutions
21
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Recommendations
Reservoir management is an enormous task requiring considerable investment. Our
actions and procedures must be successful. Therefore, both now and in the future,
we should:
• Determine rates of sedimentation by bathymetric mapping, coring, and isotopic dating
• Manage reservoirs, their watersheds, and stream channels more
effectively to delay filling
• Address declining environmental quality of water and habitat in
reservoirs
• Identify and refine renovation or replacement strategies for particular reservoir situations
• Prioritize particular reservoirs for types of eventual treatments
• Explore alternative water collection, holding, and distribution
systems
• Accept that all reservoirs eventually will fill with sediment and
prepare to address the consequences
References
Baudo, R., Giesy, J.P., and Muntau, H. (Eds.). 1990. Sediments—Chemistry and toxicity of in-place pollutants.
Ann Arbor, MI: Lewis.
Brune, G.M. 1953. Trap efficiency of reservoirs. Transactions of the American Geophysical Union, 34:407-448.
Collins, D.L. 1965, June. A general classification of source
areas of fluvial sediment in Kansas. Kansas Water
Resources Board Bulletin No. 8.
deNoyelles, F., Wang, S.H., Meyer, J.O., Huggins, D.G.,
Lennon, J.T., Kolln, W.S., et al. 1999. Water quality
issues in reservoirs: Some considerations from a study
of a large reservoir in Kansas. Proceedings of the 49th
Annual Environmental Engineering Conference.
Lawrence, KS. pp. 83-119.
Jordan, P.R. 1985. Design of a sediment data-collection
program in Kansas as affected by time trends. USGS
Water-Resources Investigations Report 85-4204.
22
Sedimentation in Our Reservoirs: Causes and Solutions
Juracek, K.E. 2003. Sediment deposition and occurrence
of selected nutrients, other chemical constituents, and
diatoms in bottom sediment, Perry Lake, northeast
Kansas, 1969-2001. USGS Water-Resources Investigations Report 03-4025.
Juracek, K.E. 2004. Sedimentation and occurrence and
trends of selected chemical constituents in bottom
sediment of 10 small reservoirs, eastern Kansas. USGS
Scientific Investigations Report 2004-5228.
Juracek, K.E. 2006. Sedimentation and occurrence and
trends of selected chemical constituents in bottom
sediment, Empire Lake, Cherokee County, Kansas,
1905-2005. USGS Scientific Investigations Report
2006-5307.
Juracek, K.E. and Mau, D.P. 2002. Sediment deposition
and occurrence of selected nutrients and other chemical constituents in bottom sediment, Tuttle Creek
Lake, northeast Kansas, 1962-1999. USGS WaterResources Investigations Report 02-4048.
Juracek, K.E. and Ziegler, A.C. 2006. The legacy of leaded
gasoline in bottom sediment of small rural reservoirs.
Journal of Environmental Quality, 35:2092-2102.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Juracek, K.E. and Ziegler, A.C. 2007. Estimation of
sediment sources using selected chemical tracers in
the Perry Lake and Lake Wabaunsee Basins, northeast Kansas. USGS Scientific Investigations Report
2007-5020.
[KWA] Kansas Water Authority. 2001. Executive
summary for House substitute for Senate Bill 287 mandates. Submitted to the Kansas Legislature on January
8. Topeka, KS. p. 3-14. Available at: http://www.kwo.
org/Reports%20%26%20Publications/HB287_executive_summary.pdf. Accessed April 2008.
[KWO] Kansas Water Office. 2008. Reservoir
information: Reservoir fact sheets. Available at:
http://www.kwo.org/ReservoirInformation/
Reservoir%20Information.htm. Accessed April 2008.
Linkov, I., Fristachi, A., Satterstrom, F.K., Shilfrin, A.,
Steevens, J., Clyde, Jr., G.A., et al. 2007. Harmful cyanobacteria blooms: Identifying data gaps and the need
for a management framework. Chapter 12 in I. Linkov,
G.A. Kiker, and R.J. Wenning (Eds.). Managing critical infrastructure risks. New York: Springer-Verlag.
Mankin, K.L., Wang, S.H., Koelliker, J.K., Huggins, D.G.,
and deNoyelles, Jr., F. 2003. Water quality modeling:
Verification and application. Journal of Soil and Water
Conservation, 58:188-197.
Morris, G.L. and Fan, J. 1998. Reservoir sedimentation
handbook. New York, NY: McGraw-Hill.
National Recreation Lakes Study Commission. 1999,
June. Reservoirs of opportunity. Final report of the
National Recreation Lakes Study. Washington, DC:
National Recreation Lakes Study Commission.
Pimentel, D., Harvey, C., Resosudarmo, P., Sinclair, K.,
Kurz, D., McNair, M., et al. 1995. Environmental
and economic costs of soil erosion and conservation
benefits. Science, 267:1117-1123.
Vanoni, V.A. (Ed.). 2006. Sedimentation engineering.
Reston, VA: American Society of Civil Engineers.
Walling, D.E. 2005. Tracing suspended sediment sources
in catchments and river systems. The Science of the
Total Environment, 344:159-184.
Wang, S.H., Huggins, D.G., deNoyelles, Jr., F., Feng, C.
1999. Public internet access for selected water quality
data in surface water of Clinton Lake, east-central
Kansas. Proceedings of the 24th Annual National
Association of Environmental Professionals Conference. June 20-24. Kansas City, MO. pp. 89-102.
Wang, S-H., Dzialowski, A.R., Meyer, J.O., deNoyelles,
Jr., F., Lim, N-C, Spotts, W., et al. 2005a. Relationships between cyanobacterial production and the
physical and chemical properties of a Midwestern
Reservoir, USA. Hydrobiologia, 541:29-43.
Wang, S.H., Huggins, D.G., Frees, L., Volkman, C.G.,
Lim, N.C., Baker, D.S., et al. 2005b. An integrated
modeling approach to watershed management: Water
and watershed assessment of Cheney Reservoir, Kansas, USA. Journal of Water, Air, and Soil Pollution,
164:1-19.
Zoumis, T., Schmidt, A., Grigorova, L., and Calmano, W.
2001. Contaminants in sediments—Remobilisation
and demobilization. The Science of the Total Environment, 266:195-202.
Additional Resources
ASTRA Initiative, Kansas Biological Survey: http://www.
kars.ku.edu/astra
USGS Reservoir Sediment Studies: http://ks.water.usgs.
gov/Kansas/studies/ressed/
Smith, V.H., Sieber-Denlinger, J., deNoyelles, Jr., F.,
Campbell, S., Pan, S., Randtke, S.J., et al. 2002. Managing taste and odor problems in a eutrophic drinking
water reservoir. Lake and Reservoir Management,
18:318-322.
[USACE] U.S. Army Corps of Engineers. 2005. National
inventory of dams. Available at: http://crunch.tec.
army.mil/nidpublic/webpages/nid.cfm. Accessed April
2008.
Van Metre, P.C., Wilson, J.T., Callender, E., and Fuller,
C.C. 1998. Similar rates of decrease of persistent,
hydrophobic and particle-reactive contaminants in
riverine systems. Environmental Science and Technology, 32:3312-3317.
Sedimentation in Our Reservoirs: Causes and Solutions
23
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Methods for Assessing
Sedimentation in Reservoirs
Mark Jakubauskas, Research Associate Professor
Frank deNoyelles, Deputy Director and Professor
Applied Science and Technology for Reservoir Assessment (ASTRA) Initiative
Kansas Biological Survey, University of Kansas
Introduction
Sediment accumulation and other factors
continue to create water quality problems
that affect the many uses of Kansas reservoirs. The most pressing issue is ensuring
the quality of drinking water supplies.
Flood control, recreation, irrigation, and
other reservoir uses also must be protected,
and renovation to ensure reservoirs’ longterm viability is becoming increasingly
necessary. Solving these problems is an
enormous challenge that requires gathering
crucial information about physical, chemical, and biological conditions in reservoirs
and watersheds. Bathymetric (lake bottom
contour) mapping and reservoir assessments are becoming particularly important
as federal, state, and local agencies contemplate and initiate sediment management
projects to renovate Kansas reservoirs.
Current State of the
Science: Bathymetric
Mapping
Traditional Approaches to
Water Depth Measurement
Information on water depth has been
important for thousands of years. Until the
20th century, water depth measurements
were obtained manually from the side of a
boat with a sounding line and lead weight
(Figure 1) or, in shallower waters, a pole
with depth markings. Sounding weights
and poles often were tipped with an
adhesive substance, such as wax or lard, to
capture a sample of sediment. The location
of each sounding (depth measurement) was
determined by estimation or direct measurement in smaller water bodies or harbors
and by celestial navigation (sextant or astrolabe) in oceans. Thus, horizontal accuracy
Figure 1. A 19th century sounding boat
Image from NOAA Central Library
Sedimentation in Our Reservoirs: Causes and Solutions
25
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has been archived. Current information is available from http://www.ksre.ksu.edu.
of these ad-hoc spot positions
generally was low. A measure
of control could be imposed in
areas where range lines could be
established between identifiable
landmarks on shore. This permitted
repeat visits to sounding positions over
time to monitor sedimentation or erosion.
Manual approaches to depth measurement are labor intensive, have relatively
low accuracy and precision, and have
considerable limitations, particularly
for mapping detailed bottom contours
or estimating whole-lake sedimentation
volumes, rates, and changes. Development
of acoustic echosounding systems that
use global positioning systems technology
for horizontal position location enabled
“whole-lake” approaches that build detailed
representations of depth contours based
on mathematical interpolation of thousands of geographically referenced depth
measurements.
D = ½ (S × T)
Where D = distance between sensor and
target, S = speed of sound in water, and T =
round-trip time.
To acquire information about the nature of
the target, intensity and characteristics of
the received signal also are measured. The
echosounder has four major components:
a transducer, which transmits and receives
the acoustic signal; a signal generation computer, which creates the electrical pulse; the
global positioning system, which provides
precise latitude/longitude coordinates; and
the control and logging computer. Typical
acoustic frequencies for environmental
work are:
• 420 kHz – plankton, submerged
aquatic vegetation
Whole-Lake Acoustic
Echosounding for Lake Depth
(Bathymetric) Mapping
• 200 kHz – bathymetry, bottom classification, submerged aquatic vegetation,
fish
By the 20th century, advances in acoustic
science and technology permitted development of sonar systems, originally used for
military purposes but adapted for civilian mapping operations. During the past
decade, acoustic echosounding systems
became sufficiently self-contained and
portable, allowing for use even on small
lakes and ponds.
• 120 kHz – fish, bathymetry, bottom
classification
Acoustic echosounding relies on accurate
measurement of time and voltage. A sound
pulse of known frequency and duration is
transmitted into the water, and the time
required for the pulse to travel to and from
26
a target (e.g., a submarine or the bottom
of a water body) is measured. The distance
between sensor and target can be calculated
using the following equation:
Sedimentation in Our Reservoirs: Causes and Solutions
• 70 kHz – fish
• 38 kHz – fish (marine), sediment
penetration
Prior to conducting a bathymetric survey,
geospatial data (including georeferenced
aerial photography) of the target lake are
acquired, and the lake boundary is digitized
as a polygon shapefile. Transect lines are
predetermined based on project needs and
reservoir size. Immediately before or after
the bathymetric survey, elevation of the
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has been archived. Current information is available from http://www.ksre.ksu.edu.
lake surface is determined. For large reservoirs (e.g., U.S. Army Corps of Engineers
or Bureau of Reclamation lakes), elevation
is determined using local gages. For smaller
reservoirs that are not gaged, a laser line is
established from a surveyed benchmark to
the water surface at the edge of the lake.
System parameters are set after boat launch
and echosounder initialization. Water
temperature at a depth of 1 to 2 meters
is recorded (°C) and used to calculate
the speed of sound in water for the given
temperature and depth. A ball check is
performed using a tungsten-carbide sphere,
which is supplied specifically for this
purpose with each transducer. The ball is
lowered to a known distance below the
transducer face. The position of the ball in
the water column (distance from the transducer face to the ball) is clearly visible on
the echogram, and the echogram distance
is compared with the known distance to
ensure parameters are set properly.
A typical survey procedure for smaller lakes
is to run the perimeter of the lake, maneuvering as close to shore as permitted by
boat draft, transducer depth, and shoreline
obstructions to establish near-shore lake
bottom dropoff. Then, predetermined
transect patterns are followed, and data are
automatically logged by the echosounding
system.
Raw acoustic data are processed through
proprietary software to generate ASCII
point files of latitude, longitude, and
depth. Point files are ingested to ArcGIS
and merged into a master point file, and
bad points and data dropouts are deleted.
Depths are converted to elevations of the
lake bottom based on the predetermined
lake elevation value. Lake bottom elevation
points are interpolated to a continuous
surface by generation of a triangulated,
irregular network or simple raster interpolation. Elevation of the digitized lake
perimeter is set to the predetermined
value and used in the interpolation as the
defining boundary of the lake. Then, areavolume-elevation tables can be computed
from the lake bottom surface model.
Current State of the
Science: Sediment
Classification and
Thickness Assessment
Acoustic Characterization of
Sediment Types
The acoustic echosounding system has a
proprietary software suite that classifies
reservoir bottom sediment (e.g., rock, sand,
silt, or mud) based on characteristics of
the acoustic return signal (Figure 2). Ideally, this process would be used to collect
acoustic data from known bottom types
to provide a “library” of Kansas-specific
classification data. Sediment sampling
and coring also provide bottom composition data for calibration and accuracy
assessment.
Figure 2. Acoustic signal classification for
bottom type mapping
Image courtesy of Mark Jakubauskas, Kansas Biological
Survey
Sedimentation in Our Reservoirs: Causes and Solutions
27
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Approaches for Estimating
Sediment Thickness
Estimating thickness of accumulated sediment in a reservoir is not a simple process.
Three techniques—sediment coring,
topographic differencing, and acoustic estimation—show promise for estimating the
spatial distribution, thickness, and volume
of accumulated sediment in Kansas reservoirs. Each technique has strengths and
limitations, and an ideal methodology uses
all three approaches in concert to calibrate
and cross-check results.
Sediment Coring. Sediment cores typically are taken from a boat using a gravity
corer or vibrational coring system. In either
case, an aluminum, plastic, or steel tube
is forced into the sediment, ideally until
pre-impoundment substrate is reached. The
tube is withdrawn and sliced longitudinally,
or the sample is carefully removed from
the tube, allowing for sediment thickness measurement and sample collection.
The interface between pre-impoundment
substrate and post-impoundment sediment
is fairly distinct in Kansas lake sediment
samples (Figure 3).
Several companies manufacture and
distribute sediment coring systems. However, most systems are intended for deep
water marine use in the ocean and are
not suitable for smaller, shallower lakes
and reservoirs. Sampling inland reservoirs
requires a portable, self-contained unit with
an independent power supply that is small
enough to fit on an outboard motorboat
or pontoon boat, which disqualifies pneumatic, hydraulic, or high-voltage systems
commonly used on larger marine vessels.
Smaller systems have been developed and
are used in Kansas (e.g., the VibeCore
System, Specialty Devices Inc., Texas).
Figure 3. Sediment core from Mission Lake in Brown County, Kansas, showing preimpoundment substrate (left) and post-impoundment sediment (right)
Photo courtesy of Kansas Biological Survey
28
Sedimentation in Our Reservoirs: Causes and Solutions
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has been archived. Current information is available from http://www.ksre.ksu.edu.
A benefit of the sediment coring approach
is that cored material can be preserved
and analyzed for sediment classification
or chemical composition. However, core
sampling is time and labor intensive; only a
small number (≈10 to 25) of point samples
can be taken per day. Although sediment
core data are likely highly accurate for
a given location, the overall result is an
incomplete and fragmentary representation
of sediment thickness and volume across
the reservoir.
Topographic Differencing. The
topographical approach computes the
difference between pre-impoundment
and present-day lake bottom topographic
data and uses that information to create
a spatially-explicit, three-dimensional
representation of sediment accumulation
(Figure 4). Data from archived topographic
maps, reservoir blueprints, or “as-built”
pre-impoundment topographic surveys are
used to create a pre-impoundment surface,
and data from new bathymetric surveys are
used to create a map of current reservoir
bottom topography. Unlike spot measurements of sediment thickness, topographic
differencing can display a “whole-lake”
representation of sediment accumulations,
facilitating estimates of sediment volume
(Figure 5).
However, quality of sediment thickness
data produced by this approach depends on
quality of data used to create pre-impoundment maps. Archival topographic data can
have one or more of the following limitations: no information on horizontal or
vertical projection of data used, referenced
to an arbitrary local elevation (i.e., nonstandard/nongeodetic vertical control), or
of inappropriate spatial scale to produce
meaningful comparisons with present-day
topographic data.
Figure 4. Topographic differencing of pre-impoundment and present-day reservoir topography
Left: 1923 engineering contour map of Mission Lake in Brown County, Kansas; Center: Digital elevation
model created from 1923 map; Right: Present-day lake bottom topography created from analysis of acoustic
echosounder data.
Images courtesy of Kansas Biological Survey
Sedimentation in Our Reservoirs: Causes and Solutions
29
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Figure 5. Elevation map of John Redmond Reservoir showing the difference between 2007
bathymetric survey data and a 1957 U.S. Army Corps of Engineers topographic map
Negative numbers indicate loss of material during the 50-year period; positive numbers indicate accumulated
material (siltation).
Image courtesy of Kansas Biological Survey
Acoustic Estimation. In the acoustic
approach, high-frequency and low-frequency transducers (200 kHz and 38 kHz)
are operated simultaneously during a lake
survey. Differencing acoustic returns from
high and low frequencies (reflecting off
the current reservoir bottom and the preimpoundment bottom, respectively) have
shown considerable promise for successful
sediment thickness mapping in inland
reservoirs (Figure 6; Dunbar et al., 2000).
Our results indicate that mapping the
base of sediment acoustically works
best in reservoirs that are dominated by
fine-grained deposition (clay and silt,
rather than silt and sand). Reservoirs
with fined-grained-deposition fill from
30
Sedimentation in Our Reservoirs: Causes and Solutions
the dam towards the backwater and
no delta forms at the tributary inlet.
As long as the water depth is greater
than the sediment thickness, the base
of sediment can be mapped without
interference from the water-bottom
multiple reflection, and the entire
reservoir can be surveyed from a boat.
Coarse-grained dominated reservoirs
fill from the backwater towards the
dam and form deltas in the backwater.
In the time [sic] the backwater region
cannot be surveyed, because it is dry
land. In these cases, the only option is
differing the bathymetry. (John Dunbar, personal communication, 2007)
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has been archived. Current information is available from http://www.ksre.ksu.edu.
a) 200 kHz
Depth (m)
7
8
9
10
b) 48 kHz
Depth (m)
7
8
9
10
c) 24 kHz
Depth (m)
7
8
9
10
d) 12 kHz
Depth (m)
7
8
9
10
e) 3.5 kHz
Depth (m)
7
8
9
10
0
100
200
300
400
500 m
Figure 6. Echograms of acoustic reflectance at multiple frequencies for reservoir sediments:
a) High frequency, showing strong discrimination of sediment-water interface; b through e)
Increasing penetration of post-impoundment sediments and increasing return from preimpoundment substrate with progressively lower frequencies.
Figure reprinted from Dunbar et al. (2000) with permission
Sedimentation in Our Reservoirs: Causes and Solutions
31
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Information Needs
Information needs related to lake bathymetry and reservoir assessment can be divided
into two broad categories: 1) reservoir-scale
information needs, which can be satisfied
by applying bathymetric technology in an
integrated reservoir assessment program,
and 2) technology-specific information
needs that explore strengths and limitations of bathymetric technology. Crucial
information is lacking, and many questions
remain.
Reservoir-Scale Information
Needs
What is the current depth and
volume of the state’s reservoirs?
Bathymetric data are not available for a
majority of the more than 5,000 regulated
reservoirs in Kansas. A review of 18 federal
reservoirs in Kansas showed that average
time since last bathymetric survey was 15
years (USGS, 2008), but an increasing
number of federal reservoirs have been
mapped using acoustic echosounding to
produce whole-lake maps of water depth.
Bathymetric data for state and local lakes
in Kansas are even more rare, collected on
an as-needed or ad-hoc basis, and often
incomplete.
How much and where has sediment accumulated in a given
reservoir? Like bathymetric data, sediment thickness information is limited in
Kansas. Federal reservoirs have the most
complete data sets, state and local reservoirs
have the poorest. Even in the best cases,
sediment thickness and distribution data
likely are limited to a few point samples or
transects and thus provide a very limited
representation of actual sediment accumulation patterns and rates.
32
Sedimentation in Our Reservoirs: Causes and Solutions
What is the rate of sedimentation,
and is sedimentation continuous
or episodic? Repeated bathymetric
surveys provide significant insight into
the nature of sedimentation in a reservoir.
Changes in reservoir bottom topography
can be monitored over time, allowing an
overall estimate of the rate of sediment
accumulation and a spatially explicit
representation of sediment accumulation
and movement across a reservoir. Bathymetric surveys before and after major rain
events can provide information on whether
significant sediment movement occurred.
Technology-Specific
Information Needs
To better understand data produced by
bathymetric surveying, research should
be conducted to explore strengths and
limitations of this technology. Answering
the following questions can help improve
speed, accuracy, and precision of data
acquisition, which is necessary for making
informed decisions about reservoir management and renovation.
Topographic and acoustic
sediment thickness estimation
techniques
• What are the possible sources of error
of this approach?
• What are the effects of sediment
composition on estimating sediment
thickness?
• What are the limitations to identifying
the pre-impoundment bottom contour
in acoustic data?
• What are the effects of scale (horizontal
and vertical resolution) on accuracy?
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has been archived. Current information is available from http://www.ksre.ksu.edu.
• What spatial error results from differences between pre-impoundment
published topographic data and “asbuilt” topographic conditions?
Processing acoustic data for
bathymetric and sediment
surveying
• What are the optimal interpolation
algorithms, in terms of speed, accuracy,
and precision, for bathymetry and sediment thickness estimation?
• Can advanced signal processing of
acoustic echosounder data accurately
identify pre-impoundment lake bottom
traces?
• Can advanced signal processing of
acoustic echosounder data coupled
with an “acoustic library” of Kansas
reservoir substrate signatures improve
bottom type classification?
Mapping and Assessment
Program
A long-range bathymetric mapping and
reservoir assessment program for Kansas
will have numerous benefits. Decision
makers will be able to easily assess current
conditions of a given reservoir and identify
and prioritize reservoirs based on sediment
load and need for renovation. Enhanced
knowledge of sediment deposition in
reservoirs will help determine effectiveness
of watershed protection practices. When
dredging appears to be the best alternative
to extend the life of a reservoir, sediment
deposition data will indicate how much
sediment needs to be removed and can help
determine how much was removed by the
dredger. Such a program should contain the
following elements:
Sustained ReservoirMapping Program
These surveys will provide a set
of baseline bathymetric elevations
and sediment data. One advantage
is that water quality and bathymetric
data can be measured simultaneously
from the same boat. Also, because surveys
will be conducted with the same equipment
and methods, it will be possible to compare
results among reservoirs and from the same
reservoir over time.
Change Detection Studies
These studies would involve revisiting previously mapped reservoirs, re-mapping the
bathymetry and cores, and comparing past
and present maps to identify sedimentation
locations and rates. This element likely
will not occur during the first few years
of the program but eventually could grow
into a major focus as baseline bathymetric
and sediment data are accumulated for
comparison.
Before/After Mapping,
Coring, and Sediment
Estimation
Comparing high-resolution contours of
bottom topography with pre-impoundment topography and selected sediment
coring to verify thickness in certain locations will enable stakeholders to develop
well-defined project goals and work plans.
Dredging contractors can receive an
accurate representation of reservoir bottom contours to be reconfigured. This will
minimize unknown factors and encourage
preparation of the most accurate and costeffective bids and the most mutually acceptable work plan.
Sedimentation in Our Reservoirs: Causes and Solutions
33
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Ad-hoc Mapping of Small
Reservoirs
Reservoir Information
System
In this capacity, the program can provide
timely, unbiased, impartial bathymetric
data and sediment estimates to help local
stakeholders make management decisions
relating to water quality, watershed management, and reservoir renovation.
Multiple constituencies in Kansas need or
desire information on water depth, sediment type, sediment accumulation, and
related conditions affecting reservoirs.
However, data and information are of little
use unless readily and easily accessible to a
wide variety of users.
Large-Scale Mapping and
Sediment Studies
Because of the intensive effort required and
large amount of data generated, we envision
this program mapping four to six federalsize reservoirs per year.
References
Dunbar, J.A., Allen, P.M., and Higley, P.D. 2000.
Color-encoding multifrequency acoustic data for nearbottom studies. Geophysics, 65:994-1002.
[USGS]. United States Geological Survey. 2008. Reservoir
sediment studies in Kansas. Available at: http://
ks.water.usgs.gov/Kansas/studies/ressed/. Accessed
March 31, 2008.
Concept for a Long-Range Bathymetric
Mapping and Reservoir Assessment
Program
• Sustained reservoir-mapping program that includes a number
(≈10 to 20) of bathymetric and coring surveys per year
• Change detection studies to estimate rates and locations of sediment accumulation
• Before/after bathymetric mapping, coring, and sediment volume
estimation for reservoir dredging projects
• Ad-hoc bathymetric mapping of small reservoirs for state, local, and
private entities
• Large-scale federal reservoir bathymetric mapping and sediment
studies
• Development of a reservoir information system
34
Sedimentation in Our Reservoirs: Causes and Solutions
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Effects of Sedimentation
on Biological Resources
Donald G. Huggins, Senior Aquatic Ecologist and Director
Robert C. Everhart, Graduate Research Assistant
Andrew Dzialowski, Post Doctoral Researcher
James Kriz, Graduate Research Assistant
Debra S. Baker, Assistant Director
Central Plains Center for BioAssessment, Kansas Biological Survey, University of Kansas
Summary
Sedimentation is a natural process, but
too much sediment in aquatic ecosystems
can cause loss or impairment of fish,
macroinvertebrates, and other aquatic
organisms. Our current ability to quantify
relationships among aquatic sediment
variables and aquatic biota in the Central
Plains is limited by available data and the
complexity of direct and indirect linkages
between resource components. At present,
turbidity appears to be the best indicator of
suspended sediment for defining biological impairment in flowing water systems.
Better coordination of existing and new
research, use and analysis of well-selected
indicators of suspended and deposited
sediment and ecosystem function, and
advanced statistical analyses will allow us
to more accurately identify and quantify
effects of sediment on aquatic ecosystems in
Kansas.
Introduction
Water from streams and rivers is used
for drinking, irrigation, waste dilution,
power generation, transportation, and
recreation and provides habitat for fish
and other aquatic organisms (Allan, 1995).
This water also contains sediment (e.g.,
eroded soil particles), which can be either
suspended in the water or deposited on the
bottom. Sedimentation is the process by
which sediment is transported and deposited in aquatic ecosystems.
In-stream sediments come from two
sources: runoff from surrounding areas
and erosion from both the sides and bed
of the channel. The complex interaction
of streams and the surrounding landscape
can be characterized to a large extent by
describing sediment movements. Erosion and sediment deposition affect many
stream characteristics including channel
depth, channel shape, substrate, flow
patterns, dissolved oxygen concentrations,
adjacent vegetation, and aquatic communities (Leopold et al., 1964; ASCE, 1992;
OMNR, 1994; Rosgen, 2006).
Sedimentation is a natural process that
occurs in most aquatic ecosystems, and
sediment-borne organic materials provide
the primary food source for a number of
filtering macroinvertebrates (Waters, 1995;
Wood and Armitage, 1997). However,
human activities such as urbanization,
agriculture, and alteration of riparian
habitat and flow regimes have increased
the concentrations and rates at which
sediment enters streams and rivers (Wood
and Armitage, 1997; USEPA, 2000; Zweig
and Rabeni, 2001; Angelo et al., 2002);
and losses of habitat, biota, and ecosystem
services due to sediment have caused severe
socioeconomic impacts (Duda, 1985). As
a result, sedimentation is listed as one of
the most common stream impairments in
the United States (USEPA, 2000, 2004),
occurring in almost one-third of the river
and stream miles recently assessed by the
U.S. Environmental Protection Agency
(USEPA; 2004).
Sedimentation in Our Reservoirs: Causes and Solutions
35
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Increased sedimentation and sediment
loading are also threatening the ecological integrity of other aquatic systems. For
example, sedimentation at higher than normal rates can reduce or impair habitat and
primary production in wetlands (Gleason
and Euliss Jr., 1998; USEPA, 2002; Gleason et al., 2003). Similar habitat reduction
has been observed in lakes; several Kansas
reservoirs are experiencing 10% to 40%
decreases in conservation-pool water-storage capacity. If sedimentation continues
at current rates, sediment pools of these
reservoirs will be filled by the 2020s (Juracek, 2006). In other reservoirs (e.g., Perry,
Tuttle Creek), increased sedimentation is
occurring primarily in the riverine upper
reaches, reducing both quality and quantity
of habitat.
WATER QUALITY
(Chemical and some
physical parameters)
“CLEAN” SEDIMENT
(Sediment transport curves, total suspended
solids, bedload, related variables)
Both “clean” and “dirty” sediment directly
and indirectly affect the structure and
function of all aquatic ecosystems (Figure
1). Clean sediment is free from additional
contaminants (e.g., volatile organics,
metals, or other toxic compounds), and
dirty sediment harbors these materials.
Effects of dirty sediment are due to the
nature and concentration of both sediment and contaminants, whereas effects of
clean sediment are due to the nature and
concentration of sediment particles alone.
Duration of exposure is also important. In
the environment, clean and dirty sediments
constantly interact as contaminants are
added, broken down, and removed. Because
both sediment types occur simultaneously,
clean and dirty sediment effects are difficult
to separate. To begin understanding sediment interactions, this white paper focuses
on effects of clean sediment.
FLOW
(Low flows, floods,
wet years, duration)
“DIRTY” SEDIMENT
(Media for contaminants)
GEOMORPHOLOGY
(Large and moderate scale factors
like sinuosity and channel shape)
BIOTA
(Fish, macroinvertebrates,
primary producers)
HABITAT
(Moderate to small scale factors or units
like riffle embeddedness and debris jams)
Figure 1. Conceptual framework showing interactions of sediment in aquatic ecosystems
Boxes illustrate important ecosystem units with examples, and arrows represent functional directions and links
between those units. Ultimate goals are to understand the links and quantify sediment effects on biota.
36
Sedimentation in Our Reservoirs: Causes and Solutions
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Although effects of sedimentation are
widespread, a comprehensive theory of
these effects on benthic communities does
not currently exist (Zweig and Rabeni,
2001). Appropriate management of aquatic
ecosystems in Kansas requires improving
our ability both to more accurately quantify relationships among aquatic sediment
variables and aquatic biota and to distinguish between natural and anthropogenic
sediment loading in this region. As a first
step in that process, this white paper summarizes current knowledge and provides
recommendations for future research.
State of the Art: Review
of Science to Date
Brief Literature Review
Most sedimentation research focuses on
cold water systems. Representative works
include basic research studies (Luedtke
and Brusven, 1976; Erman and Ligon,
1988; Lisle and Lewis, 1992; Goodin et
al., 1993; Maund et al., 1997; Simon et al.,
2003; Dodds and Whiles, 2004), literature
reviews (Cordone and Kelley, 1961; Foess,
1972; Newcombe and MacDonald, 1991;
Doisy and Rabeni, 2004), and books (Ford
et al., 1990; Waters, 1995). Previous studies report both direct and indirect effects
of sedimentation. Direct physical effects
include light interruption; smothering of
organisms; and coverage of sites used for
germination, feeding, spawning, and other
activities. Biotic effects include direct mortality; reduced fecundity; reduced disease
resistance; and inhibited feeding, growth,
and reproduction. Reviews by Newcombe
and MacDonald (1991) and Doisy and
Rabeni (2004) have also grouped direct
biotic effects into three categories:
• Lethal effects, which cause direct
mortality of organisms, reduce popula-
tions, or damage ecosystem capacity for
production
• Sublethal effects, which injure organism tissues or cause physiological stress,
both without causing mortality
• Behavioral effects, which alter the activity of affected organisms
Both suspended and deposited sediment
particles can affect aquatic ecosystems
(Waters, 1995; Zweig and Rabeni,
2001; Richardson and Jowett, 2002).
For example, increased suspended solid
concentrations can reduce primary production (Van Nieuwenhuyse and LaPerriere,
1986), disrupt feeding and respiration
rates of macroinvertebrates (Lemly, 1982),
and reduce growth and feeding rates of
many stream fish (Wood and Armitage,
1997). Both intensity (concentration) and
duration (time of exposure) of suspended
sediment loading contribute to biological
impairment, and models that consider both
are better predictors of impairment than
models that use either intensity or duration
alone (Newcombe and MacDonald, 1991).
Increased sediment deposition can reduce
the complexity of stream habitat (Allan,
1995) and smother aquatic organisms
including macroinvertebrates, fish, and
macrophytes (Waters, 1995; Wood and
Armitage, 1997).
In addition to the abundance of studies on
cold water systems, the majority of stream
sediment research has been conducted
in systems with either a naturally high
gradient (i.e., steep downhill slope) or
naturally low turbidity (Dodds et al. 2004).
However, aquatic systems in the Central
Plains—especially those in agriculturally
dominated areas like the Central Great
Plains, Western Corn Belt Plains, and,
Sedimentation in Our Reservoirs: Causes and Solutions
37
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to a lesser extent, the Central
Irregular Plains—generally are
characterized as warm water, lowgradient (i.e., mild downhill slope),
high-turbidity systems, though early
reports suggest that many Central
Plains streams that have been turbid for
the past 100 years might have been clear
prior to widespread plowing in the region
(Matthews, 1988). Compounding the
issue, many systems in the Central Plains
have sand as the natural substrate (Angelo
et al., 2002). In biological terms, sand-bottom streams are different than streams
with either large substrates (e.g., bedrock,
cobble, gravel) or fine substrates (e.g., silt,
mud, muck) because they provide different
structural and chemical characteristics that
affect aquatic life. Sand-bottom systems can
have significant movement of sand in the
channel bed (i.e., high bedload) under natural conditions. However, induced loading
of silt or mud can still impair sand-bottom
streams (Angelo et al., 2002). Distinguishing between natural sediment loading and
induced sediment loading in these systems
can be very difficult; significant regional
testing is required to understand how
anthropogenically altered sediment loading
can affect aquatic ecosystems.
Because of the need for regional testing and
current lack of a comprehensive theory of
sediment effects, a sediment workgroup
sponsored by USEPA Region VII developed
a conceptual framework for interactions of
sediment in lotic (i.e., flowing water) ecosystems (Figure 1). This framework provides
hypothesized direct and indirect linkages
among both clean and dirty sediments,
geomorphology, flow regimes, chemical and
physical water quality parameters, habitat
effects, and biotic components including primary producers, macroinvertebrates, and fish.
38
Sedimentation in Our Reservoirs: Causes and Solutions
Recent Regional Findings
To analyze complex systems, it often is
necessary to construct linked individual
relationships to depict indirect effects. Statistically significant relationships between
indicators (i.e., representative, measurable
components of the ecosystem) form the
links. For example, effects of clean sediment
(i.e., sediment only, without associated
nutrient or chemical loading considerations) on biology can be modeled by
relating a sediment loading indicator (e.g.,
total suspended solids) to a water quality
indicator (e.g., turbidity) then relating that
water quality indicator to a biological one
(e.g., number of fish species) (Figure 2).
Additional indirect effects are modeled in a
similar fashion.
A variety of potential sediment and erosion
indicators exist. USEPA uses water column
indicators (e.g., suspended sediment, bedload sediment, and turbidity), streambed
indicators (e.g., streambed particle size and
embeddedness), and riparian indicators
(e.g., buffer size and vegetation community
composition) to set criteria for allowable
loading of induced sediment (i.e., Total
Maximum Daily Loads for sediment;
USEPA, 1998). Several biological indicator
groups such as macroinvertebrates and fish
also respond to sediment-related effects
(Luedtke and Brusven, 1976; Culp et al.,
1986; Richards and Bacon, 1994; Rier and
King, 1996; Birtwell, 1999). However,
except for a study by Whiles and Dodds
(2002), linkages between sediment indicators and biological indicators both within
and between streams in the Central Plains
remain largely undocumented.
Sediment–Water Quality Links.
Using data from more than 500 samples in
16 small watersheds throughout the West-
350
240
280
180
120
n = 580
R2 = 0.99
p < 0.0001
60
0
Sediment Sensitive Macroinvert. Richness
Turbidity (NTU)
300
22
20
18
16
14
12
10
8
6
4
2
0
0
60
120
180
240
210
n = 560
R2 = 0.81
p < 0.0001
140
70
0
300
0
70
140
210
280
Inorganic Suspended Solids (mg/L)
Total Suspended Solids (mg/L)
(A)
(B)
350
100
Percent Sensitive Fish Species
Total Suspended Solids (mg/L)
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has been archived. Current information is available from http://www.ksre.ksu.edu.
n = 386
R2 = 0.298
p < 0.0001
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
n = 978
R2 = 0.145
p < 0.0001
86
71
57
43
29
14
0
-0.5
0.0
0.5
1.0
1.5
2.0
log (Average Turbidity)
log (Average Turbidity)
(C)
(D)
2.5
3.0
Figure 2. An example of relating sediment effects to biological responses using indirect effects
(A) Inorganic suspended solids, a measurement of the amount of mineral sediment particles floating in the water
column, is related to total suspended solids, a measure of the amount of all particles (both inorganic and organic)
floating in the water column. (B) Total suspended solids is related to turbidity, and turbidity is related both (C)
to the number of macroinvertebrate taxa that are known to be sensitive to sediment and (D) to the percentage
of fish species that are known to be sensitive to sediment. In this example, we relate “clean” sediment
(e.g., inorganic suspended solids and total suspended solids) to biological responses (e.g., sediment sensitive
macroinvertebrate richness and percentage of sensitive fish species) via the indirect effects of water quality (e.g.,
turbidity). Additional and more complicated analyses follow this general concept.
ern Corn Belt Plains, the Central Plains
Center for BioAssessment (CPCB; 1994)
found that inorganic suspended solids
(ISS) explained 99% of the variation in
total suspended solids (TSS) and that TSS
explained 81% of the variation in turbidity.
The USEPA Region VII Regional Technical Assistance Group (RTAG) found
that TSS explained 98% of the variation
in turbidity for more than 13,800 sites
throughout the Central Plains and across
ecoregions (RTAG, 2006); and Dodds
and Whiles (2004), using nationwide data,
found that TSS explained 89% of the variation in turbidity. Because turbidity is highly
correlated with TSS and, by extension, ISS,
turbidity measurements can be used as a
surrogate indicator for suspended clean
sediment in streams in the Central Plains.
Sedimentation in Our Reservoirs: Causes and Solutions
39
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40
Sediment/Water Quality–Biota
Links. In most biological systems, greater
diversity of organisms implies better or
“healthier” environmental conditions.
Models developed using RTAG (2006)
data suggest that macroinvertebrate richness (i.e., number of unique taxonomic
groups of macroinvertebrates) significantly
declines with increasing turbidity. Such
declines usually are associated with impairment or decreasing environmental quality.
However, statistical analysis and modeling
determined a “threshold range” of turbidity levels between 10 and 25 NTU above
which macroinvertebrate richness drops
very little. Even though turbidity can, and
often does, increase significantly beyond
this threshold range (the average turbidity level of 125 Central Plains streams
is 42 NTU), relatively few taxa are lost,
presumably because some ecological limit
of turbidity impairment has already been
reached. In other words, increased turbidity
has changed ecosystem function or structure (or both) such that more turbidity
does not elicit a biological response. Lack
of response could be because the sensitive species are gone because of death or
emigration or because the ecology has been
altered to a new state that cannot be further
degraded by turbidity. As a corollary,
reduction of turbidity might not result in a
significant increase of taxa unless turbidity
is reduced below the threshold range. Such
threshold ranges often are used as the basis
for developing benchmarks and criteria for
other types of impairments (e.g., nutrient
loading).
of sediment-sensitive fish also declined
with increasing turbidity. Data collected
during the National Wadeable Streams
Assessment (USEPA, 2004) from 125 sites
in Kansas, Nebraska, Iowa, Missouri, and
Oklahoma showed similar trends. Total
macroinvertebrate and EPT taxa richness
both decreased with increasing TSS. Richness of EPT taxa and macroinvertebrate
scrapers (i.e., macroinvertebrates that
scrape their food off substrates) decreased
as the percentage of fine substrates (i.e., silt
or mud but not sand) increased, but taxa
richness of macroinvertebrate shredders
(i.e., macroinvertebrates that shred larger
particles for food) and macroinvertebrate
predators (i.e., macroinvertebrates that eat
other macroinvertebrates) were generally
unaffected by changes in the percentage of
fine substrates. Three things are important
to note about these relationships. First,
evidence for impairment is consistent
across many ecological and taxonomic
groups because increasing sediment loading
correlates with decreasing diversity. Second,
though the relationships are significant, the
amount of variance in biological indicators
explained by changes in sediment indicators alone is relatively low (10% to 30%).
Advanced statistical techniques might
allow us to better understand the complexity of these relationships. Third, some
groups (e.g., macroinvertebrates as a whole,
EPT taxa, scrapers) are more impaired by
increased sediment loads than others (e.g.,
shredders and predators); this is consistent
with a priori expectations based on known
ecology of the organisms.
Regional RTAG (2006) data also revealed
that the taxa richness of three typically
habitat-sensitive orders of aquatic insects
(i.e., Ephemeroptera, Plecoptera, and
Trichoptera [EPT]) and the percentage
Habitat–Sediment/Biota Links.
Current data and quantification of interactions between small-scale habitat indicators
and both sediment and biology are limited.
One commonly measured habitat indicator,
Sedimentation in Our Reservoirs: Causes and Solutions
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“percent embeddedness,” is the degree to
which sediments fill spaces around rocks,
gravel, and other substrates at the bottom
of water bodies. When these spaces fill
with sediment, they can no longer provide
habitat or shelter for fish and macroinvertebrates. Data from the National
Wadeable Streams Assessment (USEPA,
2004) revealed that percent embeddedness explained about 12% of the variation
in turbidity and 26% of the variation in
percentage of fine substrates present. As
expected, total macroinvertebrate richness
and EPT taxa richness declined as percent
embeddedness increased (USEPA, 2004),
but the amount of explained variation
in richness was limited (13% and 10%,
respectively).
Geomorphology–Sediment/Habitat/Biota Links. Geomorphology
is the measure of the physical structure
and geometry of streams and rivers. Geomorphic variables include reach-scale
indicators (e.g., reach length, number and
length of riffles, sinuosity or “curviness”)
and channel-scale indicators (e.g., channel
depth, channel width, cross-sectional area).
Differences in scale make it difficult to
relate some ecosystem units (e.g., geomorphology) to others (e.g., habitat, biota) (see
Fausch et al., 2002, for a general overview).
Although geomorphology can be important
for describing particular aspects of streams
and rivers, more research is required to
relate these aspects to smaller-scale indicators of sediment, habitat, and biota in
the Central Plains. For example, though
Dauwalter et al. (2007) found that substrate type and geomorphology were related
to increased smallmouth bass density, the
streams they examined were cold water,
high-gradient, low-turbidity streams in the
Boston Mountain, Ouachita Mountain,
and Ozark Highland areas of
eastern Oklahoma, which are
not representative of the majority
of streams in the Central Plains.
Analysis of 53 geomorphic variables
from 16 stream reaches throughout
Kansas showed no statistical correlation
with any indicators of sediment, habitat,
or biota. Better understanding of scale (i.e.,
reach-scale vs. channel-scale vs. site-scale
measurements) and advanced statistical
techniques (e.g., principal components
analysis, regression trees) are required for
regional explanations of sediment links
with geomorphology, habitat, and biology.
Conclusions
Effects of sedimentation in low-gradient
aquatic systems are complex and difficult to
measure directly. Often, surrogate variables
are required to relate different ecosystem
components such as habitat, biota, water
quality, clean and dirty sediment, geomorphology, and flow. Based on Kansas and
regional data, turbidity appears to be a
reliable and easily measurable indicator for
clean sediment in lotic systems throughout
the Central Plains.
Although data indicate that increased
sediment has a negative effect on many biological variables, regional data are limited,
direct relationships are statistically weak,
and indirect relationships are difficult to
quantify (Figure 3). In addition, factors
other than sediment might contribute to
these relationships. Therefore, depiction
of direct and indirect sediment effects
via a hypothetical framework coupled
with advanced statistical analyses such as
multiple linear regression, principal components analysis, regression trees, and quartile
regression (Koenker, 1995, 2005; Cade
Sedimentation in Our Reservoirs: Causes and Solutions
41
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WATER QUALITY
Turbidity
“CLEAN” SEDIMENT
Inorganic suspended solids,
total suspended solids
GEOMORPHOLOGY
Few concurrent data, little
correlation, issues of scale
HABITAT
Mean embeddedness, % fine substrates
FLOW
Few concurrent data
“DIRTY” SEDIMENT
To be considered
in future studies
BIOTA
Macroinvertebrate total
richness, EPT richness,
% sensitive fish species,
sediment sensitive
taxa richness
Figure 3. Conceptual framework showing observed effects of sediment on aquatic biota
Boxes illustrate important ecosystem units, and arrows represent functional directions and links observed in this
study. Specific indicators used for each ecosystem unit are listed. Relative weights of the arrows indicate relative
strengths of relationships observed in this study.
and Noon, 2003) might lead to a better
understanding and quantification of complex sediment-biota relationships. Better
understanding leads to better management,
including more effective interventions and
better estimates of socioeconomic losses
associated with sediment impairment of
aquatic ecosystems.
Acknowledgments
This white paper is based on Report no.
146 of the Kansas Biological Survey,
“Effects of Sedimentation on Biological
Resources” (Huggins et al., in press), which
contains detailed descriptions of recent
regional findings including additional
figures, tables, and analyses. Kansas Biological Survey reports and other technical
publications are available at: http://www.
kbs.ku.edu/larc/tech/html/default.htm.
42
Sedimentation in Our Reservoirs: Causes and Solutions
Funding for portions of the unpublished
data used in this report was provided by the
following USEPA grants:
• Developing Regional Nutrient Benchmark Values for Streams, Rivers, and
Wetlands Occurring in USEPA Region
7. FED35840, X7-987401001.
• Acquisition and assessment of nutrient
data and biological criteria methods
gathered from historical sources, new
collections, and literature reviews.
FED23582, X7-98718201.
• Defining Relationships Among Indicators of Sediment, Erosion & Ecosystem
Health in Low Gradient Streams.
FED39410, X7-98749701.
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Recommendations for Future Research
We offer the following recommendations, based on reviews of available literature and
recent research results, to guide future research on the effects of sedimentation on
biological resources:
• Adopt a multidisciplinary approach. The complex nature
of sedimentation spans topics including hydrology, geomorphology,
aquatic ecology, water chemistry, soil and sediment chemistry, and
landscape-level phenomena (e.g., urban development and agriculture). Usually, sediment studies are approached from only one or
two of these points of view.
• Observe both sediment loading and biological
response. Surprisingly, little overlap exists between datasets on
sediment loading and biological indicators. Future studies should
emphasize concurrent collection of physical, chemical, geomorphic,
and biological data to gain a more comprehensive understanding of
complex and integrated relationships.
• Begin with gaged locations. Often, sediment loading rates
are the limiting factor in a multidisciplinary suite of sediment data.
To better estimate effects of sediment on biological resources, those
resources should be evaluated at locations where sediment loading
data is available. Typically, stream gaging stations provide available
loading data or opportunities to calculate sediment loads.
• Determine reference conditions for sedimentation.
To evaluate the extent of sedimentation effects on biological
resources (i.e., how “good” or “bad” a site is), a condition of high
quality must be established for comparison. Currently, there is
little agreement among hydrologic, geomorphic, and biological
definitions of this reference condition, making assessment of sediment-biological quality interactions problematic.
• Consider the regional context. In many cases, the full range
of geomorphic, hydrologic, and biological characteristics of certain
aquatic systems are not present in Kansas. However, such a range
might be observable at a regional or multi-state scale. Study of
related systems in other states is appropriate.
• Record both intensity and duration of sedimentation
events. Research shows that an ecotoxicological model (i.e., one
that considers both amount of sediment and length of sediment
exposure) better predicts effects of sedimentation. However, most
Sedimentation in Our Reservoirs: Causes and Solutions
43
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current studies report only sediment concentration (intensity).
Temporal cycling of sediment could be important for biological
systems.
• Distinguish between natural and induced sedimentation. Some low-gradient, high turbidity systems in the Central
Plains have elevated natural sediment loads as an ambient condition.
Discerning impairment in these systems could require significant
study.
• Use advanced statistical techniques. Interactions between
response and predictor variables in ecological systems are complex.
Statistical procedures used to analyze response data must be robust
to account for variation, and techniques such as multiple linear
regression, principal components analysis, regression trees, analysis
of covariance, quantile regression, and structural equation modeling
might be appropriate.
44
Sedimentation in Our Reservoirs: Causes and Solutions
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has been archived. Current information is available from http://www.ksre.ksu.edu.
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Sedimentation in Our Reservoirs: Causes and Solutions
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This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
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Management Practices to Control
Sediment Loading From Agricultural
Landscapes in Kansas
Daniel Devlin, Professor, Department of Agronomy
Philip Barnes, Associate Professor, Department of Biological and Agricultural Engineering
Kansas State University
Introduction
Suspended solids are the largest category
of water pollutants in Kansas (Devlin and
Powell, 1996). Almost all Kansas lakes
and streams contain undesirable levels of
suspended solids in the water and sediment
deposits in lake beds and stream channels. Suspended solids typically consist of
solid organic or mineral particles in water
suspension that have been detached and
transported (eroded) from their original
site. Sedimentation occurs when water
slows enough to allow particles to settle
out. The terms “suspended solids” and
“sediment” (or sedimentation) often are
used interchangeably. However, “sediment”
actually refers to particles that have settled
out of suspension to the bottom of streams,
rivers, or lakes.
Major sources of suspended solids in
agricultural landscapes include cropland,
grazing lands, livestock confinement operations, forest lands, roads and ditches, rural
homesites, and unstable stream beds and
channels. Several types of erosion occur
from these sites:
• Sheet erosion: a relatively uniform thin
layer of soil is removed by rainfall and
largely unchanneled surface runoff
• Rill erosion: numerous and randomly
occurring small channels only a few
inches deep with steep sides form on
sloping fields
• Ephemeral erosion: small channels
eroded by concentrated flow that can
be filled easily by normal tillage re-form
in the same location during subsequent
runoff events
• Gully erosion: accumulated
water repeatedly fills narrow
channels and, over short periods,
removes soil from this narrow area to
considerable depths resulting in channels that are too deep to correct easily
with farm tillage machinery
Implementing best management practices
(BMPs) to minimize erosion can improve
water quality. However, some studies
showed that despite implementation of
conservation practices, sediment yield in
many of our nation’s streams and lakes
remained constant for several decades
(Trimble, 1999). In many cases, this
continuing sediment yield comes from
additional erosion that occurs in streams
and lakes as channels and banks are eroded
by varying velocities of flowing water
(Simon and Rinaldi, 2006). This form of
erosion can be accelerated by channelization or modification of stream banks.
Sediment Sources from
Agricultural Lands
In Kansas, main sources of sediment from
agricultural landscapes are cropland fields,
grazing lands, streambeds and streambanks.
Runoff also occurs from livestock confinement operations, roads and roadway
ditches, forest lands, and rural homesites.
Previous research includes field measurements and modeled estimates of erosion
from crop fields, but few studies discuss
other sediment sources (Schnepf and Cox,
2006a, 2006b). Data from the National
Resources Inventory (NRI), a nationwide
survey conducted by the Natural Resources
Conservation Service (NRCS, 2007),
Sedimentation in Our Reservoirs: Causes and Solutions
47
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indicate that erosion from cropland and
pasturelands in Kansas declined over the
last 20 years (Table 1).
Table 1. Estimated erosion on nonfederal
lands in Kansas, 1982 to 2003a
Land Use
Cultivated PastureCRP
Year
Cropland
land
Landb
tons/acre per year
1982
2.7
0.8
--1987
2.6
0.8
2.3
1992
2.3
0.7
0.4
1997
2.2
0.7
0.3
2003
2.1
----a
b
Data source: NRCS (2007)
CRP = Conservation Reserve Program
Another NRCS (1992) study in northeast Kansas quantified sediment yields
from different sources for two watersheds
(Figure 1). In both the Missouri River and
Kansas River basins, unprotected croplands
contributed the majority of sediment
loads, more than 20 tons/acre per year in
the Kansas River basin. The second-largest
contributor was unprotected pasture, with
values near 5 tons/acre per year. Sheet and
rill erosion contributed more than 60% of
sediment loads, and ephemeral and classic
gullies each contributed around 10% to
20% (Figure 2).
Limitations in
Determining Agricultural
Contributions to
Reservoir Sedimentation
Erosion by water from croplands and
grazing lands is estimated with the Revised
Universal Soil Loss Equation (RUSLE),
which estimates sheet and rill erosion
occurring in an individual field, but the
model does not estimate ephemeral gully
48
Sedimentation in Our Reservoirs: Causes and Solutions
erosion or amount of sediment leaving the
field. Further, few studies have examined
relationships between in-field or edge-offield sediment losses and actual sediment
delivery into Kansas rivers and lakes.
Two terms, “sediment delivery ratio”
and “sediment yield,” are important for
determining the effect of erosion on
sedimentation of Kansas lakes. Sediment
delivery ratio is defined as the extent to
which eroded soil (sediment) is delivered
from the erosion source to the watershed
outlet and accounts for sediment deposition along the path from source to outlet.
Deposition areas include buffers, waterways, ponds, road ditches, fence rows, edges
of fields, and terraces. Sediment delivery
ratio is calculated using the following
equation:
SDR = sediment yield at outlet
total erosion
The larger the watershed, the smaller the
sediment delivery ratio (Figure 3). For
example, a watershed with a drainage area
of 1 square mile has a predicted delivery
ratio of 37%, but a watershed with a drainage area of 100 square miles has a predicted
delivery ratio of 11%. A large reservoir with
a large drainage area, such as the Tuttle
Creek Reservoir, might have a delivery ratio
as low as 3% or 4%.
Practices to Reduce
Erosion and
Sedimentation
Erosion Process
The first step in developing an erosion
management strategy is to understand the
three-stage erosion process. Implementing
BMPs can reduce erosion and sediment
yield at any or all of these stages:
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25
Missouri Basin
Tons/Acre
20
Kansas Basin
15
10
5
0
Crop
(P)
Crop
(U)
Pasture
(P)
Pasture
(UP)
Range
(P)
Range
(UP)
Forest
(P)
Forest
(UP)
Figure 1. Sediment load contribution from various sources in two northeast Kansas
watersheds
P = protected, UP = unprotected
Data source: NRCS (1992)
Figure adapted from McVay et al. (2005) with permission
80
70
Missouri Basin
Kansas Basin
% Contribution
60
50
40
30
20
10
0
Sheet & Rill
Ephemeral Gully
Classic Gully
Streambank
Figure 2. Sediment load contribution from various types of erosion in two northeast Kansas
watersheds
Data source: NRCS (1992)
Figure adapted from McVay et al. (2005) with permission
Sedimentation in Our Reservoirs: Causes and Solutions
49
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Sediment Delivery Ratio (%)
100
80
60
40
20
0
0.01
0.1
1
10
Drainage Area (Square Miles)
100
1000
Figure 3. Relationship between sediment delivery ratio and drainage area
Data source: NRCS (1992)
Detachment. Erosion starts with the
impact of a raindrop. Raindrops’ collisions
with the soil break the soil aggregate into
its component parts of sand, silt, and clay.
Moving water picks up smaller particles of
silt and clay. The force of flowing water also
detaches soil particles.
Transport. As initial water movement
into the soil slows, smaller particles settle
out, and finer particles start to plug pores
at the soil surface. Runoff occurs if rain
continues to fall at rates greater than what
the soil can absorb, and soil particles move
with runoff water.
Deposition. Soil particles are deposited
when water velocity slows enough that it
can no longer support them.
Best Management Practices
Although any soil surface left unprotected
is vulnerable to erosion, this paper focuses
on BMPs that reduce erosion from crop
fields and grazing lands, major sources of
sediment in Kansas. Strategies for reducing
erosion and sedimentation can be divided
into two categories: conservation structures
and management practices.
Conservation Structures. Conservation structures typically include an
engineering design and often have been
cost-shared through conservation districts
and the NRCS using state and federal
funds. Generally, these long-term practices
have an expected useful life span of at least
15 to 20 years. Examples of conservation
structures include:
• Terraces—gradient, level, tile outlet
• Grassed waterways
• Vegetative and riparian buffers/filters
• Grade stabilization structures
• Water and sediment control structures
50
Sedimentation in Our Reservoirs: Causes and Solutions
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Management Practices. These
practices generally are related to agronomic
practices and typically do not require an
engineering design. Examples of management practices include:
• No-till
• Reduced or minimum tillage
• Contour farming
• Crop rotations
Some strategies reduce soil erosion; others
trap sediment in the field. A system that
combines conservation structures and
management practices will be most effective at reducing soil erosion and sediment
yield. Several methods including in-field
and edge-of-field measurements, in-field
models, and watershed models have been
used to evaluate effectiveness of conservation structures and management practices.
Effectiveness of Selected
Practices
Terraces (gradient, level, or tile outlet) are
the backbone of conservation practices
in many Kansas fields. Although terraces
can be somewhat expensive, with onetime
installation costs of $30/acre to $40/acre
plus an annual cost of $13.60/acre (Devlin
et al., 2003), they also can be quite effective.
Terraces reduce erosion by breaking slopes
into segments, which reduces the speed of
runoff and amount of soil and adsorbed
pollutants that can be transported, and
reduce ephemeral and gully erosion by
safely transporting surface runoff to a
stable outlet. Some sediment deposition
will occur in the terrace channel. Kent
McVay (personal communication, September 1, 2005) used the RUSLE equation
to estimate soil erosion losses from four
different soil series in central
Kansas. In a field with a 6%
slope and 150-foot slope length,
soil erosion would be reduced
approximately 54% by using one
terrace and approximately 90% by
installing two terraces (Table 2). Field
studies in Kansas showed that terraces with
tile outlets or those draining into grassed
waterways reduced soil erosion approximately 30% (Devlin et al., 2003; Tables 3
and 4). McVay et al. (2005) used the Soil
and Water Assessment Tool (SWAT), a
watershed model, to examine the effect of
terraces and other management practices
in the Little Blue River watershed located
in Kansas and Nebraska and estimated that
terraces would reduce sediment loss by 89%
and 98% on conventional and no-till fields,
respectively (Table 5).
Table 2. Predicted terrace effectiveness
for reducing soil loss from four soil types
in a field with 6% slope and 150-foot slope
length in central Kansasa
Silty
Sandy
TerClay
clay
Loam
clay
races
loam
loam
loam
tons/acre per year
None
16.8
13.9
14.4
14.3
1
7.75
6.69
6.62
6.65
2
1.75
1.52
1.36
1.42
Data source: Kent McVay, personal
communication, 2005
a
Sedimentation in Our Reservoirs: Causes and Solutions
51
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Table 3. Effectiveness of BMPs for reducing
edge-of-field soil losses in conventionally
tilled fieldsa
Best Management
Reduction in
Practice
runoff (%)
Crop rotations
25
Establish vegetative buffer
50
strips
Conservation tillage
(>30% residue cover fol30
lowing planting)
No-till farming
75
Contour farming (without
35
terraces)
Terraces with tile outlets
30
Terraces with grass
waterways (with contour
30
farming)
a
Data source: Devlin et al. (2003)
Table 4. Effectiveness of BMPs for reducing
soil losses in no-till fieldsa
Best Management
Reduction in
Practice
runoff (%)
Crop rotations
25
Establish vegetative buffer
50
strips
Contour farming (without
20
terraces)
Terraces with tile outlets
30
Terraces with grass
waterways (with contour
30
farming)
a
Data source: Devlin et al. (2003)
Grassed waterways are also used widely in
Kansas. They serve as an outlet for excess
field runoff water and sediment, reducing
the potential for gully erosion and excessive
sedimentation. Grassed waterways often
are used as outlets for water from gradient
terraces or diversions. Vegetative cover in
the grassed waterways slows runoff water
52
Sedimentation in Our Reservoirs: Causes and Solutions
and allows for sediment deposition before
runoff water leaves the field. Grassed waterways can reduce sediment loss from crop
fields by 15% to 35% (Devlin et al., 2003).
Placing vegetative buffers on the downhill
slopes of crop fields or riparian buffers
next to streams are recommended practices
for removing sediment from runoff water
prior to the runoff water leaving the crop
field. Well-designed buffers can reduce
sediment loss by 50% (Tables 3 and 4), and
the SWAT model predicted that installing
a 20-meter buffer on the downhill side of
every field in the Little Blue River watershed would reduce sediment loss by 89% to
97% (Table 5).
No-till and minimum/reduced tillage
farming practices are being adopted rapidly
in Kansas (Figure 4) and, when adopted,
will significantly reduce sediment loss from
crop fields. In a continuous corn field in
Brown County, Kansas, converting from
conventional tillage with <10% residue
to no-till or minimum/reduced tillage
reduced sediment loss from 10.5 tons/acre
per year to 0.20 tons/acre per year and 0.53
tons/acre per year, respectively (B. Marsh,
personal communication, November 23,
1992). In a Franklin County, Kansas, field
with a grain sorghum/soybean rotation,
adopting no-till reduced sediment loss from
0.85 tons/acre per year to 0.23 tons/acre
per year (K. Janssen, personal communication, May 22, 2000). Devlin et al. (2003)
reported that adopting reduced/minimum
tillage (>30% residue cover following planting) and no-till reduced erosion by 30% and
75%, respectively (Table 3). The SWAT
model predicted that adopting no-till on all
crop fields in the Little Blue River watershed would reduce sediment loss from crop
fields by 77% (Table 5).
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Table 5. Estimated reductions in water flow and sediment loss due to BMP implementation
compared with a conventional tillage scenarioab
Water
Sediment
Tillage System
Best Management Practice
Discharge
Loss
% Reduction
Conventional
None
0.0
.0
10-m buffer
0.0
72
20-m buffer
0.0
89
contour
0.9
50
effective terraces
0.9
89.4
10-m buffer + contour
0.8
86
10-m buffer + contour + terraces
0.8
97
Conservation tillage
None
0.4
47
with 20% residue
Conservation tillage
None
0.8
63
with 50% residue
No-till
None
13
77
10-m buffer
13
93
20-m buffer
13
97
contour
20
90
effective terraces
20
98
10-m buffer + contour
20
97
10-m buffer + contour + terraces
20
99
Mixed grass
None
42
99
prairie/range
a
b
Table adapted from McVay et al. (2005) with permission
Based on SWAT model results in the Little Blue River basin of Kansas and Nebraska averaged over 22 years
Tilling and planting along the contour of
field slopes can reduce soil erosion. Contour farming is a recommended practice
for all sloping, erosive fields and is the only
acceptable method of farming in terraced
fields. Conducting tillage and planting
operations on the contour without terraces
reduced soil erosion by 35% (Devlin et
al., 2003; Table 3), and computer modeling with SWAT in the Little Blue River
watershed predicted contour farming
could reduce sediment loss by 50% to 90%
depending on tillage system (Table 5).
Sedimentation in Our Reservoirs: Causes and Solutions
53
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70
Corn
Oat
Winter Wheat
Soybean
Percent of Planted Acres
60
50
Double-Crop
Soybean
Cotton
Grain Sorghum
40
30
20
10
0
1990
1992
1994
1996
1998
2000
2002
2004
Figure 4. Rate of no-till adoption for various crops in Kansas
Data source: CTIC (2005)
Figure adapted from McVay et al. (2005) with permission
Recommendations
Because erosion is a natural process, there always will be some suspended solids in
streams. However, excessive soil erosion and sedimentation are negatively affecting
nearly all lakes and streams in Kansas. It is difficult to determine to what extent measured and predicted erosion actually affects sedimentation in rivers and lakes, but
minimizing erosion can improve water quality. A variety of BMPs, used separately or
together, can reduce erosion and sediment loss from agricultural lands, and the most
effective erosion reduction strategies include a combination of conservation structures and management practices.
We offer the following recommendations:
• Determine sediment sources and methods of sediment delivery
from agricultural lands to surface waters
• Determine effectiveness of cropland and grazing land erosion
control practices at both the field and watershed scale
• Develop an understanding of the lag period between implementation of erosion control practices and sediment delivery to surface
water bodies
• Develop methods that link changes in land cover with hydrologic
response, sediment-load response, and stream channel changes
• Determine the sediment load contributions of roads, urban sprawl,
and other nonagricultural activities in the rural landscape
54
Sedimentation in Our Reservoirs: Causes and Solutions
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has been archived. Current information is available from http://www.ksre.ksu.edu.
References
[CTIC] Conservation Technology Information Center.
2005. 2004 National crop residue management survey.
Available at: http://www2.ctic.purdue.edu/CTIC/
CRM.html. Accessed March 24, 2008.
Devlin, D. and Powell, M. 1996, March. Nonpoint source
pollution in Kansas. Publication MF-2204. Manhattan, KS: Kansas State University.
Devlin, D., Dhuyvetter, K., McVay, K., Kastens, T.,
Rice, C., Janssen, K., et al. 2003, February. Water
quality best management practices, effectiveness and
cost for reducing contaminant losses from cropland.
Publication MF-2572. Manhattan, KS: Kansas State
University.
Schnepf, M. and Cox, C. (Eds.). 2006a. Environmental
benefits of conservation practices on cropland: The
status of our knowledge. Ankeny, IA: Soil and Water
Conservation Society.
Schnepf, M. and Cox, C. (Eds.). 2006b. Managing
agricultural landscapes for environmental quality:
Strengthening the science base. Ankeny, IA: Soil and
Water Conservation Society.
Simon, A. and Rinaldi, M. 2006. Disturbance, stream
incision, and channel evolution: The roles of excess
transport capacity and boundary materials in controlling channel response. Geomorphology, 79:361-383.
Trimble, S. 1999. Decreased rates of alluvial sediment
storage in the Coon Creek Basin, Wisconsin, 1975-93.
Science, 285(5431):1244-1246.
McVay, K., Devlin, D., and Neel, J. 2005, July. Effects
of conservation practices on water quality: Sediment.
Publication MF-2682. Manhattan, KS: Kansas State
University.
[NRCS] Natural Resources Conservation Service. 1992.
Northeast Kansas erosion and sediment yield report.
1992. Salina, KS: USDA-Soil Conservation Service.
[NRCS] Natural Resources and Conservation Service.
2007. National resources inventory: 2003 annual NRI
– soil erosion. Washington, DC: NRCS.
Sedimentation in Our Reservoirs: Causes and Solutions
55
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has been archived. Current information is available from http://www.ksre.ksu.edu.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Can Reservoir Management
Reduce Sediment Deposition?
Debra Baker, Environmental Scientist, Kansas Water Office
Frank deNoyelles, Deputy Director and Professor, Applied Science and Technology
for Reservoir Assessment (ASTRA) Initiative, Kansas Biological Survey, University of Kansas
Introduction
This white paper describes why sedimentation in public water supply reservoirs
is cause for concern about both water
quantity and quality, proposes management options for reducing sedimentation
and strategies for implementing these
options, identifies needed resources, and
recommends assessment methods. We
focus on federal reservoirs because of their
large storage capacity, but similar problems
and solutions also apply to smaller, locally
owned reservoirs, commonly referred to as
lakes.
Thirteen federal reservoirs in Kansas are in
the state public water supply marketing and
assurance programs, both managed by the
Kansas Water Office (KWO). The marketing program allows public water suppliers
to purchase and withdraw state-owned
water stored in federal reservoirs. The assurance program allows public water suppliers
who draw water from streams downstream
from reservoirs to purchase stored water
that can be released during low flow conditions to supplement natural flows. About
50 smaller, mostly city-owned reservoirs
provide additional localized public water
supplies to municipalities and industries.
All these reservoirs are vital resources
because they provide regional sources of
stored, untreated water to public water
suppliers in Kansas for use in surrounding
communities and industries. Many Kansans
rely on the long-term availability of water
supplies. However, long-term planning to
ensure sustained water availability is lacking. Plans similar to those created for public
infrastructures, such as roads and bridges,
are needed for long-term protection
and maintenance of reservoirs.
Reservoir Construction
Natural lakes form through geologic processes, such as glacial melting or scouring.
Although often referred to as lakes, reservoirs do not occur naturally; they are
created by transforming part of a flowing
water body (lentic) into a still water body
(lotic) by building a dam to hold back the
water. Sediment transport occurs naturally
through streamflow, and reservoirs act as
settling basins for soil, clay, and smaller
rock particles deposited through sedimentation. Eventually, sediment will fill
all reservoirs unless removed or properly
redistributed. Reservoirs commonly are
constructed in areas with few natural lakes,
particularly locations south of the glaciated
area in middle latitudes. Soils in these areas
are inherently very erodible and can be
disturbed further by human activities. In
addition to receiving sediment deposited
through streamflow, most federal reservoirs
in Kansas experience shoreline erosion, due
to erodible soils, and constant maintenance
is required to stabilize shorelines.
Federal reservoirs were built and are owned
by either the U.S. Army Corps of Engineers
(USACE) or the Bureau of Reclamation
and were constructed at the direction and
authorization of Congress. Authorizations for use vary, but most reservoirs were
constructed primarily for flood control,
irrigation, water supply storage, aquatic
habitat, low flow supplementation, and
water quality maintenance. The USACE
also uses some reservoirs to maintain flows
Sedimentation in Our Reservoirs: Causes and Solutions
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for navigation in the Missouri
River. Congress has the final
authority to authorize reservoir
use or propose operational changes.
Many reservoirs were designed and
built based on a 100-year planning
framework. During this time, reservoirs
were expected to remain fully functional
and satisfy the needs and purposes for
which they were constructed. Now, nearly
half that time has passed. Federal reservoirs
in Kansas were built between 1946 and
1976. The oldest, Kanopolis, is 60 years old,
the youngest, Hillsdale, is 30 years old, and
the average age is about 44 years. Reservoir
designers assumed future stakeholders
would be better equipped, with new technologies and enhanced perspectives, to deal
with future water resource problems. But,
management strategies to ensure longer
reservoir lifespans have not been adequately
considered.
Sedimentation in
Reservoirs
Erosion
Reservoir sedimentation begins with runoff
and soil erosion. Various types of land
cover produce different runoff characteristics that, in turn, transform hydrology of
streams, and watersheds across the country
are dynamically adapting to continuous
land use changes. Original land cover in the
uplands of most watersheds draining into
federal reservoirs in Kansas was grassland,
the native, pre-settlement condition. Riparian forests occurred along most streams and
rivers, especially in floodplains. Prior to
human settlement, Kansas forests covered
about 8% of the landscape; today they
cover about 4% (Bob Atchison, Kansas
Forest Service, personal communication,
58
Sedimentation in Our Reservoirs: Causes and Solutions
2004). Historically, the prairie ecosystem
produced steady, prolonged runoff from
storms. Over hundreds of thousands of
years and long periods of climate change,
stream channels formed to accommodate
runoff during normal and extreme rainfall
events.
Watersheds gradually transformed from
expansive tallgrass prairie to a checkerboard
of rural communities, cropland, urban land,
and managed pastureland. Native prairie
and riparian woodlands were removed for
crop cultivation and building materials,
resulting in increased soil erosion from the
disturbed landscape. Land gradually became
less fertile as soil was lost, and maintaining
desired production levels required applying
additional nutrients. As erosion continued
on steeper slopes, added nutrients washed
into tributaries and rivers.
Runoff from cultivated and grazed land
occurs quickly, frequently, and intensely,
accelerating natural bank and channel
erosion. Other alterations, such as levees
that contain flood waters and prevent sediment from settling out on the floodplain,
constrictions due to road crossings, and
hundreds of dams forming small ponds,
affect stream channel stability and will
take many years to fully manifest. Urban
development results in increased impervious cover, further exacerbating erosion
and decreasing stability of watersheds and
stream systems.
Sedimentation
Soil particles eroded from land surfaces
(e.g., uplands, prairie, pasture, agricultural
fields, and streambanks) by wind and rain
become suspended in water that flows into
streams. Streamflow slows as it enters a
reservoir, and suspended particles begin
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to settle out. Eventually, all sediment will
settle to the bottom of a still pool of water,
but heavier sediment particles are deposited first. Sedimentation does not occur
uniformly; it is affected by many factors
including flow and volume of water produced by the incoming stream and size and
weight of sediment particles.
Regardless of rate or location, sediment
accumulation reduces reservoirs’ water
storage capacity. Therefore, reservoirs
were built larger than necessary for their
intended purposes, allowing sediment to
be collected behind the dam. Most Kansas
reservoirs were designed with a reserve
sediment storage pool that was projected to
fill with sediment over a 100-year period.
Designers expected that although sediment
would continue to accumulate beyond
this point, occupying space previously
available for water storage, aquatic habitat,
recreation, or other uses, reservoirs would
maintain flood control capacity for an
extended period of time and wetland and
marsh habitats would slowly form. Designers expected other forms of recreation, such
as waterfowl hunting and bird watching,
to develop but did not anticipate how
much communities and the state would
rely on reservoirs for public water supplies.
Although water supply is an authorized
reservoir use, designers gave the effects of
reduced water storage capacity little consideration and did not anticipate a need for
operating procedures or funding to address
this situation.
Recent USGS studies indicate that
decreases in conservation-pool water-storage capacity of federal reservoirs due to
sedimentation range from less than 10% for
Cheney Reservoir (south-central Kansas),
Hillsdale Lake (northeast Kansas), and
Webster Reservoir (north-central Kansas),
to about 25% to 40% for Perry Lake and
Tuttle Creek Lake (northeast Kansas). If
sedimentation continues at historical rates,
designed sediment pools in Perry Lake and
Tuttle Creek Lake will be filled by 2021
and 2023, respectively, and further sediment accumulation will encroach on water
supply storage intended for other purposes
(Juracek, 2006). Yet, KWO population
projections indicate that many communities that currently use these reservoirs
continue to grow and have increased
demand for municipal and industrial water
supplies. When reserve pools of existing
reservoirs fill with sediment, few viable
options will exist for maintaining resources
provided by reservoirs.
Eutrophication
Although this paper focuses primarily on
preservation of public water supply storage capacity, a related and more imminent
concern is the effect of sedimentation on
water quality. The main water quality issue
is eutrophication, the process that both
natural lakes and constructed reservoirs
undergo as they age. Eutrophic conditions
occur as sediment and nutrients attached to
sediment or suspended in water gradually
accumulate, leading to excessive aquatic
plant growth, especially algae. Most federal
reservoirs in Kansas already are in some
stage of eutrophication, and some are in
advanced stages.
Originally, most sediment was expected
to accumulate at the bottom of reservoirs
near dams. However, large quantities of
sediment are settling out in upper arms of
reservoirs, creating shallow flats and deltas.
Because inflow waters typically are nutrient rich, these shallow areas of still water
provide ideal conditions for algal growth
Sedimentation in Our Reservoirs: Causes and Solutions
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and dense growth of rooted aquatic plants.
When nutrient ratios are favorable, much
of the algal biomass is composed of bluegreen algae that produce geosmin. This
compound causes taste and odor problems
in drinking water, issues that can be difficult and expensive to treat. Additionally,
aquatic plant growth produces living and
decaying biomass that restricts boat access
and adds to taste and odor problems.
Managing Sedimentation
Current state and federal management
efforts focus on reducing sediment inputs
from the watershed landscape, including
streambanks and streambeds. However,
it also is necessary to manage sediment
already deposited in reservoirs. Reducing
sedimentation will extend the useful life
of reservoirs, particularly for water storage capacity, and reduce the amount of
nutrients entering reservoirs, slowing the
eutrophication process and reducing taste
and odor problems and associated treatment expenses.
Reservoir sedimentation management
strategies can include one or more of the
following techniques (Palmieri et al., 2003;
WOTS, 2004):
• Reducing sediment inflows
• Managing sediment in the reservoir
• Removing sediment from the reservoir
• Replacing lost storage
• De-commissioning the reservoir
Reducing Sediment Inflows
Techniques applied to the watershed
system before water enters the reservoir
include watershed management; upstream
60
Sedimentation in Our Reservoirs: Causes and Solutions
debris dams, sediment basins, and wetlands;
reservoir bypass, and off-channel storage.
Watershed Management. Erosion is a natural, geologic process but can
accelerate when the soil surface is exposed.
Implementing best management practices
(BMPs) that minimize soil exposure and
soil particle detachment can reduce soil
loss. Watershed BMPs are categorized
as rural/agricultural or urban/suburban
practices. Agricultural BMPs include conservation crop rotations, cover crops, and
conservation tillage. These BMPs improve
soil structure and increase soil organic matter content and surface roughness. Other
beneficial agricultural practices include
terraces that trap sediments and pond and
infiltrate water, waterways and filter strips
that slow water flow and trap sediment,
and buffers along streambanks that reduce
streambank erosion and trap nutrients and
sediment. Each farm enterprise is unique,
and encouraging widespread adoption of
appropriate BMPs requires one-on-one
interaction with producers (Birr and Mulla,
2006).
Urban/suburban BMPs include settling
basins, construction erosion control,
construction timing, buffers, and on-site
detention. These practices focus on preventing soils from leaving construction
sites. Other practices include swales, open
space detention, streambank protection, and on-site infiltration. These are
applicable in developed areas and focus
on preventing increased runoff and flows;
many are included as recommended practices in Phase 1 and 2 stormwater permits.
Agricultural BMPs are designed to be
effective for 24-hour storm events ranging
from 10- to 25- year recurrence intervals,
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but available data indicate that the greatest
sediment loads occur during storm events
that exceed these parameters. During
flows of this magnitude, watershed BMPs
have reduced effectiveness for containing
sediment. However, stable streambanks are
beneficial during flood events. During the
1993 flood in northeast Kansas, forested
riparian buffers along the main stem of
the Kansas River were considerably less
impacted (amount of bank loss) than areas
with streamside land cover of cropland or
grass (Geyer et al., 2003). Additionally,
streambank stabilization projects with
associated riparian buffer establishment are
effective at minimizing streambank erosion
and reducing sediment loads.
Where properly designed, installed, and
maintained, watershed landscape-level
BMPs (e.g., terraces, waterways, and filter
strips) are effective at reducing soil erosion on specific sites, which, theoretically,
should reduce reservoir sedimentation
rates. Unfortunately, research does not
support this. Studies estimate that reducing sediment yields by 10% to 20% might
require intensive conservation efforts
spanning several decades. Furthermore,
conservation measures often are considered
ineffective, from a reservoir sedimentation
management point of view, because of
the large time lag between when erosion
control measures are implemented and
when their effects on sediment reduction
are realized (Birr and Mulla, 2006).
A paired watershed study on effects of agricultural BMPs revealed that many factors,
including lag time, rate of BMP adoption,
mechanisms of nutrient transport, and
climatic variability, influence BMP evaluation at the watershed scale (Birr and Mulla,
2006). Current knowledge of watershed
processes and sediment transport
in rivers and how these relate does
not allow modeling to consistently
or adequately predict effects of
watershed management techniques
on sediment discharge in rivers. No
simple solution exists, and assessing
potential effects of optional watershed
management approaches requires detailed
study of watersheds under consideration
and thorough analysis of available data and
local knowledge.
Currently, the USGS is investigating sediment sources in the Perry Reservoir and
Lake Wabaunsee watersheds in Kansas.
The objective of this study is to determine,
by comparing composition of reservoir
bottom sediments and sources materials,
whether the majority of deposited sediment originated from surface soil erosion
or streambeds and streambanks. Understanding sediment sources will help target
future management efforts to achieve
meaningful reductions in sediment yield.
Preliminary results indicate that sediment
source is watershed specific and cannot be
generalized.
Good upland watershed management can
reduce sediment yields and produce many
associated benefits for agriculture, rural
and urban environments, food production,
forestry, and water availability. But during
the next 25 to 50 years, upland BMPs likely
will not have a large effect on reservoir
sedimentation.
Upstream Debris Dams, Sediment
Basins, and Wetlands. Debris dams
are used for streams in steep watersheds
and those with coarse-grained sediments.
Debris dams usually are located on one
or more tributaries upstream from the
Sedimentation in Our Reservoirs: Causes and Solutions
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reservoir, and sediments are removed
periodically from behind the dam. Ease of
access to remove sediment from the debris
dams and potential to reuse sediment make
debris dams a feasible option. Sediment
basins and constructed or enhanced wetlands in upstream tributaries use the same
concepts.
Reservoir Bypass. Installing conveyance structures (i.e., closing gates) upstream
from the reservoir diverts sediment-laden
flows around the reservoir, carrying away
large volumes of sediment that otherwise
would accumulate in the reservoir. This
technique limits flood control capability of
the reservoir, and floodplain development
might already have occurred downstream.
Often, bypassing is feasible only when
favorable hydrological and morphological
conditions exist. Operating costs of conveyance structures and benefits lost by not
capturing flood flows must be considered,
and this technique might require a change
in congressional authorization.
Off-Channel Storage. Off-channel
storage reservoirs are built adjacent to the
main river channel (e.g., a small tributary
or on the floodplain). Water from the
main river is routed into the reservoir when
sediment concentrations are low. This
option does not manage sediment in existing reservoirs but could be considered for
new projects. A variation of this technique
that can be applied in existing reservoirs is
construction of settling basins in tributaries; sediment can be periodically removed
from these basins.
62
Sedimentation in Our Reservoirs: Causes and Solutions
Managing Sediment in the
Reservoir
Techniques for preventing sediment from
settling once water enters the reservoir
include multilevel selective withdrawal,
changes in lake level management plans
(LLMPs), inflow routing, sluicing, and density current venting. These techniques are
most applicable in reservoirs that stratify
thermally. Because of their large size and
prevailing windy conditions that promote
mixing, most federal reservoirs in Kansas
do not thermally stratify for long periods of
time during the summer, which limits the
applicability of these methods.
Multilevel Selective Withdrawal.
Operating a multilevel withdrawal structure to manage sedimentation requires
considering numerous conditions and
constraints, most important of which is
thermal stratification. Selective withdrawal,
the capability to identify the vertical
distribution of withdrawal from a stratified
reservoir and use that capability to selectively release the desired quality of water,
can be used to determine the appropriate
or best available operation of a release
structure, design multilevel withdrawal
structures, or modify existing projects.
Lake Level Management Plans.
Many reservoir projects operate under some
type of LLMP that incorporates seasonal
changes in elevation. Modifying LLMPs
can enhance water quality and reduce
sedimentation. By changing the hydraulic
residence time of the reservoir, inflows can
be retained or routed quickly through the
reservoir. This allows the reservoir to retain
high quality water for later release or retain
poor quality water for treatment by in-reservoir processes.
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The KWO, in consultation with the Kansas Department of Wildlife and Parks, the
USACE, and the Bureau of Reclamation,
is responsible for annual development and
oversight of LLMPs. Planned variations in
operating level of each reservoir are published each year and cover the period from
October through September of the following year. Stakeholders can submit concerns
through a public input process.
Depending on project authorization, the
management plan might include large,
pool-level fluctuations on an annual basis.
For example, operation of a flood control
project usually involves drawing down the
reservoir level during fall and winter and
filling during spring and early summer,
resulting in a stable pool through summer
and early fall. Water quality might be a
concern when summer pool elevation is
kept relatively stable. Water quality components that could be affected include inflow
with undesirable qualities, nutrient loading
of the reservoir (and associated effects on
algal growth and fisheries), turbidity, and
sedimentation. For example, inflows with a
high sediment load might be delayed in the
upper reaches of a reservoir and settle out
before reaching the outlet works. Additionally, shoreline erosion can accelerate when
high elevations are maintained for long
periods of time. This results in sediment
accumulation around the edges of the
reservoir and contributes to formation of
flats and deltas, promoting unwanted algal
growth.
Inflow Routing. Poor inflow water
quality (e.g., high concentrations of nutrients, suspended solids, or other undesirable
constituents) can result in poor reservoir
water quality. Depending on volume of
inflow and retention time of the reservoir,
inflow constituents can settle and become
trapped in the reservoir, contributing to
eutrophication and increasing sediment
accumulation. If inflow quality is a concern,
it might be possible to route inflow through
the reservoir for downstream release without significantly affecting reservoir water
quality. Because inflow will seek its layer of
neutral density in a thermally or densitystratified reservoir, a density current will
develop and proceed through the reservoir.
Using the existing release structure and
operating within the existing water control
plan, undesirable water is routed through
the pool as quickly as possible.
Sluicing. Sluicing is an operational technique in which a substantial portion of the
incoming sediment load moves through the
reservoir and dam before sediment particles
can settle, reducing the reservoir’s trap
efficiency. In most cases, sluicing is accomplished by operating the reservoir at a lower
level during the flood season to maintain
higher flow velocity and sufficient sediment transport capacity of water flowing
through the reservoir. Increased sediment
transport capacity reduces the volume of
deposited sediment. After flood season,
the pool level in the reservoir is raised to
store relatively clear water. Effectiveness of
sluicing operations depends on availability
of excess runoff, grain size of sediment, and
reservoir morphology. In many cases, sluicing and flushing are used in combination.
If flood control is an authorized purpose of
a reservoir, use of sluicing might require a
change in congressional authorization.
Density Current Venting. Density
currents occur because the density of
sediment-carrying water flowing into a
reservoir is greater than the density of
clearer water impounded in a reservoir.
Sedimentation in Our Reservoirs: Causes and Solutions
63
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The increased density, increased
viscosity, and concomitant
reduction in turbulence intensity
result in a uniform current with
high sediment concentration that
dives underneath the clear water and
moves toward the dam. In reservoirs with
known density currents, installation and
operation of low-level gates allows sediment
currents to pass through the dam for downstream discharge. Density current venting is
an attractive option because, unlike flushing operations, it does not require lowering
the reservoir level. However, this approach
results in increased downstream sediment
loads that can degrade stream habitats. In
addition, dispersing sediment across large
areas makes it more difficult to eventually remove sediment from the watershed
system.
Removing Sediment from the
Reservoir
Techniques for removing accumulated
sediment include flushing, aeration, and
mechanical removal (e.g., dredging, dry
excavation, and hydro-suction).
Flushing. Flushing increases flow
velocities in a reservoir to the extent that
deposited sediments are resuspended and
transported through low-level outlets in the
dam. Flushing occurs in two ways: complete
draw-down flushing and partial draw-down
flushing. Complete draw-down flushing occurs when the reservoir is emptied
during flood season; this creates river-like
flow conditions in the reservoir. Deposited
sediment is remobilized and transported
through low-level gates to the river reach
downstream from the dam. Low-level gates
are closed toward the end of flood season to
capture clearer water for use during the dry
season.
64
Sedimentation in Our Reservoirs: Causes and Solutions
Partial draw-down flushing occurs when
the reservoir level is partially reduced.
Sediment transport capacity in the reservoir
increases only enough to allow sediment
from upstream locations to move farther
downstream, closer to the dam. Partial
draw-down flushing can clear more water
storage space upstream and transport
sediment to a more favorable location for
future complete draw-down flushing.
Artificial Lake Stirring and
Aeration. Dissolved oxygen (DO) is
an important component of reservoir
water quality and can affect drinking
water taste and odor, especially during
lake turnover events or when a fish die-off
occurs because of eutrophication and low
DO levels. In surface waters, DO occurs
naturally through two primary sources:
surface exchange with atmospheric oxygen
(adsorption) and algae that create oxygen
as a by-product of photosynthesis; DO is
removed from the water column by fish
respiration and decomposition of organic
matter by aerobic bacteria. An oxygen
shortage or depletion can occur when
photosynthesis ceases or is substantially
reduced during snow and ice cover or when
excessive biomass is present (e.g., in eutrophic lakes).
Several methods can supply DO artificially:
mechanical stirring by fountains, pumps,
and electric or wind-driven stirrers; compressed air supplied by oilless compressors
or blowers and diffusers; and chemical
oxidizers such as potassium permanganate. Each method varies in effectiveness.
Compressed air likely provides the best
long-term treatment, and potassium
permanganate provides the most immediate
results. The compressed air method also
promotes long-term organic matter decom-
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position and nutrient recycling that can
help correct eutrophication-related taste
and odor problems.
Compressed air is more efficient than
mechanical stirring or a water fountain
system at moving the oxygen-deprived
water column located in the bottom, or
hypolimnion, region of a lake (i.e., lake
turnover). Stirrers usually cannot reach the
lake bottom, and fountain intakes can plug
if mounted too close to bottom sediments.
Chemical oxidizers might be the best solution for providing DO immediately, but
this is a short-lived, temporary solution. In
addition to providing supplemental oxygen,
an aeration system can:
• Suspend organic matter in the water
column, allowing better oxidation and
fertilization of phytoplankton and zooplankton in the epilimnion, the upper
portion of water in the reservoir
• Resuspend and transfer sediment during water exchange events
• Partially restore lake depth and volume
One type of aeration system, the pipe venturi, can perform a specific type of dredging
called “air dredging” (Haag, 2006) and has
been used in wastewater lagoon systems to
move and aerate sludge. The pipe venturi is
approximately 3 feet in length and 6 inches
in diameter with holes cut in the bottom
and sides. It is placed vertically on the bottom of the reservoir in loosely compacted
sediments. Air is released at the bottom of
the pipe, and bubbles rise through the pipe
creating a suction, or venturi, effect. The
venturi disturbs the loosely compacted,
unconsolidated sediment, which becomes
resuspended in the epilimnion and then
moves out of the lake through the spillway
by flushing. The pipe venturi might be useful for dredging and redistributing organic
matter, clay particles, and nutrients in
eutrophic lakes. However, type and quality
of sediment must be quantified prior to
using this technique. Some sediment might
contain contaminants or unusually high
levels of nutrients that could have deleterious effects on water in the reservoir and
receiving stream.
Mechanical Removal. Mechanical
removal of deposited sediment occurs
through conventional dredging techniques,
dry excavation, and hydro-suction.
The process of excavating deposited
sediments from under water is termed
dredging. This is a highly specialized activity used mostly used for clearing navigation
channels in ports, rivers, and estuaries.
Dredging also can be used to reclaim
reservoir storage capacity lost to sediment deposition. However, conventional
hydraulic dredging often is much more
expensive than the cost of storage replacement and generally is not economically
viable or necessary. Excavating sediment
from existing reservoirs will require moving 20 to 50, even up to 100, times more
material than originally moved to construct
the dam. Costs of dredging larger reservoirs
in Kansas in their latter stages of filling
could be more than 100 times the original
construction cost, billions of dollars in
some cases. In addition, it will be necessary
to find a disposal location for the excavated
material, preferably close to the reservoir
to reduce transportation costs. Spreading
sediment uniformly over one square mile
in a one-foot-thick layer would dispose of
640 acre-feet of sediment, but sediment
accumulation in a reservoir can total tens of
thousands of acre-feet.
Sedimentation in Our Reservoirs: Causes and Solutions
65
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Disposing dredged material can cause
environmental problems, and solutions,
which can be quite expensive, have to be
developed on a case-by-case basis. Discharging high sediment concentrations
generally associated with dredging directly
downstream from the dam can be environmentally unacceptable. However, it
might be possible to reduce the sediment
concentration of water flowing in the river
by concurrently releasing clean water and
dredged material from the reservoir. If
dredged material is not deposited downstream, large expanses of landfill might be
required. Although dredged material can
be a liability, it also can be seen as an asset
(WOTS, 2004). Uses for dredged sediment
include habitat development, soil improvement for agriculture and forestry, and
construction (e.g., brick making).
Most Kansas reservoirs are about the same
age and fill at about the same rate. Excavating sediment-filled basins and finding a
place for the excavated material from all
these reservoirs is currently beyond our
means. Fortunately, we likely will not need
to dredge entire basins of most reservoirs.
Tactical dredging of upper arms of the
reservoir removes sediment from where it
is accumulating most rapidly. Excavating
upper basins deeper than their original
contour creates settling basins that serve as
sediment traps. Preserving an infrastructure
that allows access to these settling basins
will allow convenient redredging every 20
to 30 years, a possible long-term management strategy.
Dry excavation (i.e., trucking) requires lowering the reservoir during the dry season,
when reduced river flows can be adequately
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Sedimentation in Our Reservoirs: Causes and Solutions
controlled without interfering with excavation work. Sediment is excavated and
transported using traditional earth-moving
equipment. Excavation and disposal costs
are high; therefore, this technique generally
is used in relatively small reservoirs. Sediment from some reservoirs excavated using
this method has been used as engineered
landfill in hills adjacent to the reservoirs.
It can be difficult to dry the bottom of
the reservoir thoroughly enough for heavy
excavating equipment to operate on it.
A hydro-suction removal system is a variation of traditional dredging. Traditional
dredging uses pumps powered by electricity
or diesel. Hydro-suction uses energy from
the hydraulic head available at the dam.
Where sufficient head is available, operating costs for hydro-suction are substantially
lower than for traditional dredging.
Replacing Lost Storage
Lost storage can be replaced by constructing a new dam (upstream, downstream,
or on another river) or raising the existing
dam, but neither option can be accomplished easily. Raising the dam requires
conducting reallocation studies and
mitigation of additional flooded land and
recreational structures. A single reallocation study can cost more than $1 million.
Few good locations for large-scale new
dam development remain, and construction costs can be prohibitive. Urban and
rural development steadily surrounded
reservoirs, limiting our ability to raise dam
heights and flood additional land. Also,
environmental effects of large-scale dam
projects would be difficult to overcome
because of enhanced environmental protection regulations.
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Decommissioning the
Reservoir
Decommissioning should be regarded
as the last possible option. There are no
reported cases of decommissioning dams
higher than 40 meters. Decommissioning
large dams is problematic and needs careful
consideration, particularly when the reservoir behind the dam is full of sediment.
Other options to explore before decommissioning include maintaining the dam
at a lower level or using the silted reservoir
for ecological enhancement (e.g., wetland
habitat, farming, or recreation). However,
these options are site specific and still result
in lost water storage capacity.
Implementing Sediment
Management Strategies
Implementing sediment management
strategies requires collecting various data,
securing financial resources, and developing
a comprehensive plan with input from all
stakeholders.
Information
Sedimentation rate is the fundamental
problem in all reservoirs; all other reservoir
problems are linked, by various degrees,
to this issue. Therefore, determining a
reservoir’s sedimentation rate is necessary
for developing both short- and long-term
management strategies and will help determine the flow regimes under which most
sediment is delivered and deposited. This,
in turn, can guide design and placement of
appropriate BMPs.
To determine appropriate sediment management strategies for Kansas reservoirs, the
following questions should be answered:
• What are the sediment delivery ratios for
all watersheds above federal reservoirs?
• Does most sediment delivery occur during high-flow
events, or are cumulative
low-flow delivery ratios more
important?
• What are the stratification characteristics of the reservoir?
• How will dredging affect the usefulness
of the reservoir for water supply during
the dredging process? Would alternative water supplies be necessary for a
period of time? Does the infrastructure
exist to manage this?
• Which reservoirs have multilevel release
structures? Which could be modified to
incorporate these structures?
• What are the effects of discontinuing
flood control benefits in favor of water
supply capacity preservation? What is
the economic effect on properties that
would no longer be protected from
flooding? What is the cost to buy land
for floodplain preservation? What
other options for flood control are
available?
• What is the sediment quality?
• What are the costs and benefits of
various management techniques or
combinations of techniques?
• What is the true cost of providing
water via a reservoir if costs for longterm storage capacity maintenance are
included?
• Which reservoirs should be decommissioned first if this becomes necessary? If
a reservoir is decommissioned, how will
water storage, flood control, and other
needs be satisfied?
Sedimentation in Our Reservoirs: Causes and Solutions
67
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Resources
At typical dredging costs of $5,000/acrefoot to $6,000/acre-foot ($3/cubic yard
to $5/cubic yard) (deNoyelles et al, 2004)
and assuming a constant rate of sediment
deposition, removing the annual sediment
load deposited in Kansas reservoirs is cost
prohibitive. Estimated annual costs for four
reservoirs are (KWO, 2005):
• Clinton: $1.6 million
• John Redmond: $4.5 million
• Perry: $5.6 million
• Tuttle: $22.4 million
These costs alone are more than two
times the annual State Water Plan Fund.
Although BMPs can reduce sedimentation
and, ultimately, dredging costs, implementing these practices can be cost prohibitive.
To help defray costs of BMP implementation, landowners can participate in
government cost-share programs such
as the Natural Resources Conservation
Service (NRCS) Environmental Quality
Incentive Program. A recent report evaluating natural resource cost-share programs
summarized expenditures during recent
years for the two voluntary government
cost-share programs with greatest participation. The NRCS cost shared $89,450,451
to private landowners in Kansas from 2003
through 2005 for BMPs including terraces,
livestock production improvements, and
wetlands. The State Conservation Commission cost shared $12,972,721 from 2004
to 2006 for similar practices.
Planning
The original “design life” approach to
reservoir construction did not consider
what would happen to dams at the end
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Sedimentation in Our Reservoirs: Causes and Solutions
of their lifespan or how benefits could be
replaced. Future generations were left to
deal with substantial environmental, social,
economic, and safety issues. The conventional wisdom is to assume dams have a
finite ability to store water and accept that
this ability will diminish gradually because
of sedimentation. An alternative approach
is to view dams and reservoirs as sustainable
structures.
Sustainability requires that resources be
developed and used in a way that accounts
for interests of all stakeholders, including future generations. For infrastructure
projects, this means that future generations
should not be burdened with emergency
maintenance or decommissioning of assets
built to benefit their predecessors. The
ultimate goal of developing sustainable reservoirs is to maintain the major functions
of the dam through appropriate management and maintenance in perpetuity.
When this is not possible, decommissioning can be used as a last resort, provided
that this action is funded by an accumulating dam retirement fund. Sustainable
reservoir management will ensure that
current and future generations enjoy the
benefits of the facility and spread ownership, operation, and maintenance costs over
many generations.
With reservoir capacity and water quality
concerns looming, it is time to change the
paradigm of viewing reservoirs as projects
with a defined life span. We must develop
and implement sustainable strategies to
maintain and extend reservoirs’ useful life,
beginning by taking action to preserve
reservoir water supply infrastructures with
a phased plan that first address the most
crucial problems in the most important
reservoirs.
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Developing a Comprehensive Plan
We offer the following suggestions as a guide for developing comprehensive sediment
management plans for Kansas reservoirs:
• Establish goals or targets for reductions in sediment deposition for
each reservoir.
• Stabilize watersheds. Continue Watershed Restoration and Protection Strategy efforts and other watershed conservation work with
focus on public water supply (PWS) reservoirs and erosion control.
• Increase acres of cropland managed with no-till. Prioritize streams
for buffer installation and streambank stabilization. Provide costshare payments or cover the entire cost to ensure implementation
and maintenance. Develop means of monitoring and enforcing
BMP implementation.
• Prioritize reservoirs for maintenance and infrastructure development and upgrades. Determine which developments will have the
greatest effect on water supply infrastructure considering population served, water quality problems, demand, and location of
alternative supplies.
• Develop a dedicated state dredging/infrastructure upgrade and
maintenance fund.
• Complete a reservoir dredging pilot study. During the pilot study,
excavate deeper sedimentation basins in reservoir arms or tributaries
and establish maintenance infrastructures.
• Consider establishing critical water quality management areas above
PWS reservoirs, and direct funds to establish widespread erosion
control practices and streambank stabilization.
• Determine viable management options for in-reservoir water
manipulation.
• Establish maintenance infrastructures in priority reservoirs.
• Identify sediment disposal areas.
• Establish wetlands and riparian areas for use in conjunction with
sediment disposal sites.
• Increase number and size of wetlands to store flood waters and filter
sediment.
• Protect sites that have potential for new dam construction.
Sedimentation in Our Reservoirs: Causes and Solutions
69
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has been archived. Current information is available from http://www.ksre.ksu.edu.
References
Birr, A. and Mulla, D. 2006. Using paired watersheds to
evaluate the effects of agricultural best management
practices on water quality in south-central Minnesota.
Presentation at the Managing Agricultural Landscapes
for Environmental Quality Conference. Oct. 11-13.
Kansas City, MO.
deNoyelles, J., Jakubauskas, M., and Randke, S. 2004.
Reservoir management and restoration. Addressing
problems in multipurpose reservoir systems. Lawrence,
KS: Kansas Biological Survey.
Geyer, W., Brooks, K., and Neppl, T. 2003. Streambank
stability of two Kansas river systems during the 1993
flood in Kansas, USA. Transactions of the Kansas
Academy of Science, 106(1/2):48-53.
Haag, D.A. 2006. Supplemental aeration and oxidation
systems. Unpublished manuscript.
70
Sedimentation in Our Reservoirs: Causes and Solutions
Juracek, K.E. 2006. Sedimentation in Kansas reservoirs.
Abstract from the 23rd Annual Water and the Future
of Kansas Conference. March 16. Topeka, KS.
[KWO] Kansas Water Office, Evaluation and Assessment
Unit. 2005. Unpublished data.
Palmieri, A., Shah, F., Annandale, G., and Dinar, A. 2003.
Reservoir conservation volume I: The RESCON
approach. Washington, DC: World Bank.
[WOTS] Water Operations Technical Support
Program. 2004. The WES handbook on water quality
enhancement techniques for reservoirs and tailwaters.
Vicksburg, MS: U.S. Army Engineer Research and
Development Center. Waterways Experiment Station.
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Economic Issues of
Watershed Protection
and Reservoir Rehabilitation
Jeff Williams, Professor, Department of Agricultural Economics
Craig Smith, Watershed Economist, Department of Agricultural Economics
Kansas State University
Summary
Comprehensively analyzing economic
issues of watershed protection and reservoir rehabilitation projects is a somewhat
daunting task because of the extensive
effects of the costs and benefits of alternative management strategies. In addition,
data on economics of sediment control at
a watershed scale are lacking, and previous
studies have not evaluated whether dredging sediment or preventing sedimentation
is more economical. Many questions
remain unaddressed and unanswered.
Nevertheless, the economics of watershed
protection and reservoir rehabilitation is an
important topic. Although this white paper
is not a complete, comprehensive analysis,
it provides valuable insight into potential
watershed/reservoir management strategies,
the magnitude of costs, preferred analysis
approaches, and research needs.
In this white paper, we provide an overview
of costs of soil erosion and sedimentation
based on existing literature and review features and costs of common soil erosion and
sediment control methods. Appropriate
in-field soil erosion management practices
and their costs vary by site. Thus, we limit
our analysis to estimating potential savings
from implementing individual, in-field
erosion control methods in a watershed to
reduce future costs of dredging sediment
from a reservoir. Then, we compare potential savings with the cost of management
practices.
Our brief analysis indicates that in situations where the amount of accumulated
sediment has not reduced a reservoir’s use-
fulness, it could be more economical
for the government to fund expenditures for management practices that
reduce further erosion and sedimentation in a watershed than to rely on dredging
in the future. However, our economic
analysis is not complete because critical
data are not available. We do not know,
among other things, the source of sediment,
how suitable management practices are
for various locations in a watershed, or the
number of acres that, from a technical and
economic perspective, actually need these
practices applied. We also do not know
the benefits of reduced sedimentation.
Evaluating the best approach for reducing
additional sedimentation in watersheds
with reservoirs for which dredging is being
considered is a demanding task. A team
approach that integrates expertise from
various disciplines is essential for analyzing
sediment prevention, erosion management,
and reservoir rehabilitation. Ultimately,
a variety of models that incorporate both
physical and economic watershed characteristics are needed.
Soil Erosion and
Sedimentation Costs
Erosion of cropland and streambanks of
Kansas rivers increases sediment loads
deposited in downstream reservoirs, alters
fish and wildlife habits, and can cause
significant damage to fields bordering
streams, resulting in direct economic losses
for landowners and Kansas citizens. Soil
erosion causes loss of cropland, particularly
along streambanks and riverbanks, and
loss of soil productivity in crop fields and
pastures. Cropland erosion from high-flow
Sedimentation in Our Reservoirs: Causes and Solutions
71
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has been archived. Current information is available from http://www.ksre.ksu.edu.
events in floodplains can disrupt farming
operations. Soil erosion also has several offsite consequences (Figure 1); it can reduce
reservoirs’ water storage capacity, which
affects public water supplies, flood control
capability, and water availability for downstream navigation.
Suspended soil particles can affect viability
of aquatic life, reduce recreational value of
lakes and waterways, and increase operational costs for power plants, city water
supplies, and navigation. Deposited sediment causes extensive damage to aquatic
life, shortens reservoirs’ useful life, and
clogs navigation channels (Clark et al.,
1985). Sediment can fill drainage channels,
such as ditches and culverts, causing localized flooding if not removed. Sediment
also includes nutrients such as nitrogen
and phosphorus that alter water quality
and affect aquatic life. Other potential
contaminants in sediment include agricultural pesticides and dissolved solids such as
Resources
Leave the
Landscape
calcium, sodium, magnesium bicarbonate,
and chloride ions (Clark et al., 1985).
Sedimentation caused by soil erosion can
create significant societal costs (Mooney
and Williams, 2007). For example, sedimentation can affect the enjoyment people
derive from using waterways for recreation.
MacGregor (1988) estimated that increased
sedimentation at Ohio state park lakes
reduces the economic benefit of recreation
to out-of-state boaters by an average of
$0.49/ton of sediment. Bejranonda et al.
(1999) examined effects of sedimentation
on lakeside property values at 15 Ohio state
park lakes and found that homeowners
are willing to pay more for properties on
lakes with less sedimentation. A broader,
national estimate of the value of recreation loss attributable to sedimentation
is between $612 million and $3.6 billion
(2006$) (Tegtmeier and Duffy, 2004).
Amounts reported in 2006 dollars (2006$) or
2005 dollars (2005$) as indicated.
Physical
Effects
Water
Quality
Environmental Quality
and Economic Effects
Recreation
Drinking Water
Wildlife Habitat
Soil
Nutrients
Pesticides
Bacteria
Runoff
and
Erosion
Reservoir
Life
Property Values
Flood Control
Water Supply
On-site Crop
Productivity
Figure 1. General effects of soil erosion
72
Sedimentation in Our Reservoirs: Causes and Solutions
Fix or Replace
Reservoir
Yield Loss
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Hansen et al. (2002) examined costs of soil
erosion and sedimentation to downstream
navigation across different areas of the
United States. Their results suggest that
eroded soil poses no costs to navigation in
areas with no downstream shipping channels or harbors but can create costs up to
$5.67/ton of soil erosion (2006$) in areas
where navigation is affected (Hansen et
al., 2002). Tegtmeier and Duffy (2004)
estimated that costs of sedimentation
to shipping range from $345 million to
$383 million (2006$). Moore and McCarl
(1987) estimated effects of sediment on
municipal water treatment, road drainage
system maintenance, navigation channel
maintenance, reservoir capacity deterioration, and hydroelectric power plant costs in
Oregon. In this state alone, the total average cost of erosion for navigation channel
maintenance, municipal water treatment,
and country road and state highway maintenance is approximately $5.5 million
annually (Moore and McCarl, 1987). Tegtmeier and Duffy (2004) updated figures
from Ribaudo (1986); they estimated that
annual costs of sediment removal from
roadside ditches and irrigation channels
throughout the United States range from
$304 million to $895 million (2006$) and
annual costs of flood damage attributable to
erosion range from $215 million and $622
million (2006$). Nationally, estimates of
annual costs of dredging inland waterways
range from $282 million to $291 million,
and reservoir siltation costs range from
$274 million to $851 million (Clark et al.,
1985; Ribaudo, 1986; Hansen et al., 2002;
Tegtmeier and Duffy, 2004).
National Estimates
of Total Damage
from Water Erosion
Mooney and Williams (2007)
reviewed literature on water erosion
damages. They summarized work by
Clark et al. (1985), Ribaudo (1986), and
Tegtmeier and Duffy (2004), who provided
national estimates of total annual damages
attributable to water-based soil erosion
ranging from $2 billion to $31 billion
(2006$). These analyses included costs
related to recreation, navigation, water storage facilities, municipal and industrial water
users, water conveyance systems, and flooding. Estimated damages did not include all
sectors of the economy or all possible activities and thus represent a partial estimate of
the value of reduced soil erosion.
No comprehensive studies examining
damages attributable to water-based soil
erosion have been conducted since 1986
when Ribaudo calculated the value to
society of reducing soil erosion by one ton
based on potential annual damages from
erosion in 1983. Per-ton values ranged
from a low of $0.98/ton in the northern
Plains to $11.29/ton in the Northeast
(2006$). However, erosion of cropland
and other agricultural soil declined considerably during the past 20 years (NRCS,
2007b), partly because improved farming
practices and government programs such as
the Conservation Reserve Program (CRP)
retired highly erodible lands. According
to the 2003 National Resources Inventory (NRCS, 2007b), the average rate for
sheet and rill erosion on cropland declined
from 4.0 tons/acre per year in 1982 to 2.6
tons/acre per year in 2003. Wind erosion
rates dropped from 3.3 tons/acre per year
in 1982 to 2.1 tons/acre per year in 2003.
Sedimentation in Our Reservoirs: Causes and Solutions
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Damages created by soil erosion
probably changed over time, and
previous estimates likely are inaccurate now. Today, actual per-ton
damages depend on the value and
cost of downstream activities affected
by soil erosion.
Sediment Control Costs
Sediment source as well as type and effectiveness of erosion management strategies
affect costs of reducing sedimentation.
Sediment sources include upland landscape areas (e.g., cultivated fields, poorly
maintained pastures, construction sites,
and streambanks), sediment previously
deposited in floodplains, and in-stream
sources. Knowing the distribution of
sediment sources can help determine what
management strategies to use. For example,
if sediment occurs mainly from high-flow
events causing streambank erosion, it
might be economically efficient to target
streambanks rather than cultivated fields.
However, if most erosion and sedimentation occurs during infrequent but heavy
precipitation and water flow events, targeting erosion control strategies to these
events rather than to average rainfall events
might be useful. Presence of contaminants,
such as phosphorous or other chemicals, in
sediment also could influence source targeting decisions.
Stakeholders must consider several questions regarding effectiveness of soil erosion
management strategies. How effective
are the variety of in-field management
strategies at reducing soil erosion? If we
implement practices to reduce field erosion,
what is the effect on reservoir sedimentation? Will sediment already accumulated
in streambeds or low-lying areas continue
74
Sedimentation in Our Reservoirs: Causes and Solutions
negatively affecting water bodies even if
sediment loads from new sources decline?
It is likely that reducing sedimentation will
require a multi-strategy approach.
Strategies and Costs for
Reducing Soil Erosion and
Controlling Sediment
Sediment reduction strategies include
keeping sediment in place on upland landscapes, flood plain management, upstream
sediment traps, and dredging reservoirs
once sedimentation occurs. Landscape
management encompasses a variety of soil
conservation measures. For example, no-till
systems leave crop residue on fields to
reduce soil disturbance and erosion during wind and rainfall events. Alternatives
include cropping rotations that increase
crop and residue cover, vegetative buffers and CRP land, contour farming, and
terraces.
According to the 2003 National Resources
Inventory (NRCS, 2007b), soil erosion in
Kansas declined from 1987 to 1997 (Figure
2). Cultivated cropland remains the largest
erosion source; but, like other land use categories, erosion from this source is declining.
This decline likely is due to increased use
of conservation practices and enrollment
of land in the CRP. Still, we must ask: Has
reduced soil erosion decreased reservoir
sedimentation?
Putnam and Pope (2003) reported results
of time-trend tests from 1970 to 2002 for
sediment sampling sites in Kansas. Most
of the 14 sampling sites, including five
of the six sites upstream from reservoirs,
exhibited decreasing suspended sediment
concentrations, but only two sites had
trends that were statistically significant.
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6
Cropland
5
Pastureland
CRP Land
Total
Tons/Acre/Year
4
3
2
1
0
1982
1987
1992
Year
1997
2003
Figure 2. Soil erosion trends in Kansas
Data source: NRCS (2007b). Erosion rates for pastureland and CRP land were not reported in 2003.
Increasing suspended sediment concentrations occurred at three sites but were not
statistically significant. Both sites that
exhibited statistically significant decreasing
suspended sediment concentrations have a
large number of watershed impoundments
(i.e., structures designed to trap sediment)
in their respective drainage basins. The
relationship between percentage of the
watershed affected by impoundments and
suspended sediment concentration for
11 sites indicated that suspended sediment concentration decreases as number
of watershed impoundments increases.
Implementing other conservation practices,
such as terracing and contour farming,
could further reduce suspended sediment
concentrations.
The following sections contain rough cost
estimates of various erosion management
strategies; applicability and economic
viability of these strategies vary greatly by
location. The ultimate decision to adopt a
specific management strategy depends on
several factors including physical, biological, and economic characteristics of a site
and land managers’ capabilities and risk
preferences.
In-Field Strategies
Altering Residue Cover with Crop
Rotations. Plant residue management
is one strategy used to reduce soil erosion.
Crop rotations and tillage methods affect
the amount of plant residue left on the soil
surface. Al-Kaisi (2000) provided a relative
ranking of erosion from selected cropping
systems in Iowa. Fallow ground had the
highest rate of erosion followed by a cornsoybean rotation. Increasing the amount
of corn relative to beans in the cropping
rotation reduced erosion as did adding a
permanent cover crop or small grain crop,
such as oat. Devlin et al. (2003) reported
that the cost of using soil-conserving crop
Sedimentation in Our Reservoirs: Causes and Solutions
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rotations is $0.00/acre (Table 1). However,
actual costs of crop rotations vary by site,
and changes in commodity prices cause the
relative profitability of rotations to change
from year to year.
Contour Farming. Contour farming
uses field operations that follow the contour of the field rather than move straight
up and down field slopes. This method
requires additional labor and time and
Table 1. Cost for implementing sediment management practices
Practice
Cost
Altered crop rotations
$0.00/acre/yearb
Contour farming without terraces
$6.80/acre/yearb
Land retirement
$30 to more than $82/acre/yearf
No-till
$0.00/acreb
-$37.00 to more than $37.00/acreg
-$3.81 to $1.51/acred
Riparian forest buffer
$585/acre establishment plus annual loss of annual
income (land rent)h
Sediment trap
$1,300 establishment cost per acre of construction area
drainage to trapa
Streambank stabilization
$5,381 establishment cost per acre of CRP ($12.31/linear
foot)g
$3,252/acre of CRP after accounting for preserved land
value and incomeh
Terraces
$0.66 to $3.30/linear foot depending upon slopee
Terraces with tile outlet
$40 establishment cost per acre plus annual cost of
$13.60/acreb
$1.05/linear foote
Terraces with grassed waterways
$30 establishment per acre plus annual cost of $13.60/
and contour
acre in field plus loss of annual income (land rent)b
Vegetative buffers
$100 establishment cost per acre plus annual loss of land
rentb
$73 establishment cost per acre plus loss of annual
income (land rent) – Annualized cost $63.29/acrec
$104 establishment cost per acre plus annual loss of
annual income (land rent)j
Waterways (grass) including
$870 establishment cost per acre plus loss of annual
topsoiling
income (land rent)e
California Stormwater Quality Association (2003)
Devlin et al. (2003)
c
KSU-VegetativeBuffer estimate; Smith and Williams (2007)
d
Langemeier and Nelson (2006)
e
NRCS (2007a)
f
Taylor et al. (2004)
g
Williams et al. (2007)
h
Williams et al. (2004)
a
b
76
Sedimentation in Our Reservoirs: Causes and Solutions
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might necessitate using equipment with
reduced widths, which reduces efficiency.
Clark et al. (1985) reported that contour
farming practices reduced suspended
residue by 25% to 50%. Contour farming
costs a few dollars per acre on fields with
consistent contours and is significantly
more expensive on farms with variable field
topography; Devlin et al. (2003) reported
contour farming costs approximately
$6.80/acre (Table 1).
Land Retirement. The CRP and
other programs that retire land from crop
production and require establishment
of permanent cover can reduce soil erosion. The major cost of the CRP to land
managers is the value of lost production.
Therefore, the CRP pays an annual rental
rate to those who enroll land. Kansas
CRP payments range from $30/acre to
$82/acre (Table 1; Taylor et al., 2004).
Land not currently enrolled in CRP likely
is more profitable in crop production and
will require a larger incentive payment
than land currently enrolled. Cash rental
payments landlords received for renting
nonirrigated land in northeast Kansas in
2006 averaged $69/acre. The statewide
average is $39/acre and ranges from $26/
acre to $69/acre (Dhuyvetter and Kastens,
2006).
No-Till. No-till is a form of conservation
tillage in which chemicals are used in place
of tillage for weed control and seedbed
preparation. In a 100% no-till system, the
soil surface is never disturbed except for
planting or drilling operations. Two other
forms of tillage, reduced tillage and rotational no-till, involve light to moderate use
of tillage equipment. These methods also
control erosion and nutrient runoff but are
not as effective as 100% no-till.
Previous research shows that profitability
of no-till systems varies. Dhuyvetter et al.
(1996) reviewed nine studies including 23
comparisons between no-till and other tillage systems for various crops and rotations
in the Great Plains and found that no-till
had higher returns than conventional
tillage in eight comparisons. Most of these
comparisons were either wheat-fallow or
wheat-sorghum-fallow rotations. Williams
et al. (1990) found that net returns from
no-till for continuous corn and cornsoybean rotations were higher than from
conventional tillage in several government
commodity program designs. In contrast,
no-till had lower average net returns than
conventional tillage for continuous soybean. Similarly, average net returns from
no-till were less than from conventional
tillage for wheat and grain sorghum in
the central Plains (Williams et al., 2004).
In Texas, no-till had higher net returns
than conventional tillage for three cropping rotations: sorghum-wheat-soybean,
wheat-soybean, and continuous wheat, but
conventional tillage had higher net returns
for continuous sorghum and soybean
(Ribera et al., 2004).
Pendell et al. (2005) reported that net
returns for no-till were higher than for
conventional tillage for continuous corn
in northeast Kansas. A recent study (Williams et al., 2007) of five cropping systems
in northeast Kansas showed that returns
from no-till compared with conventional
tillage ranged from a negative $37.25/acre
to a positive $37.12/acre; compared with
reduced tillage, returns from no-till ranged
from a negative $40.10/acre to a positive
$21.14/acre depending on crop rotation
(Table 1). Langemeier and Nelson (2006)
reported that reducing tillage had a small
effect on production costs in northeast
Sedimentation in Our Reservoirs: Causes and Solutions
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Kansas but significantly reduced soil erosion. Changing from conservation tillage
to no-till for a corn-soybean rotation could
reduce production costs by $3.81/acre,
assuming no yield change, and soil erosion
by 15% to 42% depending on soil type;
changing to no-till in a sorghum-soybeanwheat rotation could increase production
costs by $1.51/acre and reduce soil erosion
by 2.1% to 26.9% (Langemeier and Nelson,
2006). Nationally, the percentage of planted
cropland in a no-till system increased from
6% in 1990 to 22% in 2004 (CTIC, 2005).
However, these data are just a snapshot of
the total no-till acres in a given year. The
number of continuous no-till acres, which
are important for soil erosion control, is
less than the total. Dhuyvetter and Kastens
(2005) summarized no-till adoption data
for Midwest crop production. In 2004,
no-till use was highest in soybean at 36.9%,
up from 26% in 1994, and next highest in
grain sorghum at 33.2%, up from 13.6%.
No-till use in corn and fall small grains was
17.8% and 18.5%, respectively. Overall
adoption of no-till in Kansas (21.2%) was
slightly less than in the Midwest region
(24.8%). In central and eastern Kansas,
no-till use is increasing primarily because of
lower costs, but higher yields and the associated revenue provide incentives for no-till
adoption in western Kansas (Dhuyvetter
and Kastens, 2005).
Large-scale adoption of no-till is relatively
slow, indicating many farm managers
regard it as unprofitable or that changing
tillage practices has high transaction costs.
We need to learn more about the types and
magnitude of incentives that could encourage farm managers not already using no-till
to adopt this practice.
78
Sedimentation in Our Reservoirs: Causes and Solutions
Riparian Forest Buffers. Riparian
forest buffers are areas of forested land
adjacent to streams, rivers, or other water
bodies. Shrubs and grasses often are located
upslope from the trees to reduce nutrient
and sediment losses from agricultural fields,
improve runoff water quality, and provide
wildlife habitat (Goard, 2006). Because of
these societal benefits, several federal and
state programs encourage installation and
maintenance of riparian forest buffers.
Establishment costs for a riparian forest
buffers with trees, shrubs, and grass range
from $243/acre to $970/acre with an average of $585/acre (Table 1; Williams et al.,
2004). Annual income is lost from land in
the buffer that can no longer be cropped,
but the cash rental rate for land in the area
is approximately the same as the amount of
lost income.
Sediment Traps. Sediment traps, or
basins, are excavated areas designed to
temporarily impound runoff water long
enough for suspended sediment to settle
out. Typically, these structures are temporary and used to control erosion from
construction sites. Sediment traps can be
constructed along a watercourse or between
a field and an outlet to a stream by excavating or forming an earthen embankment
across a drainage area or waterway. Limited
information is available on cost and effectiveness of these structures in agricultural
watersheds; however, the California Stormwater Quality Association (2003) reported
costs of $1,300/acre of drainage (Table 1).
Costs for sediment traps or impoundments
for agricultural erosion control vary by site
because of differences in area and characteristics of land from which runoff is collected;
removal and disposal of accumulated sediment add to the cost.
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Terraces. Terraces are embankments
constructed perpendicular to the slope of a
field; they reduce the length of a field slope,
catch water flowing off the slope, reduce
the rate of runoff, and allow soil particles
to settle out. Terraces can increase the time
needed complete field operations because
farm managers are unable to use larger or
wider equipment, and loss of some farmable land might occur depending on slope
and whether part of the terrace must be
seeded with grass. Terrace construction
costs include earth work for regrading land
and can be several hundred dollars per acre.
Carman (2006) reported construction costs
ranging from $1/linear foot to $6/linear
foot, and the NRCS (2007a) reported costs
of $.66/linear foot to $3.30/linear foot
depending on slope (Table 1).
Terraces with Grassed Waterways
and Contour Farming. Grassed waterways are used to prevent erosion and gully
formation and also function as outlets for
water from terraces. Vegetative cover slows
water flow and minimizes channel surface
erosion (Green and Haney, 2006). Grassed
waterways might require removing land
from production, which reduces potential
income, and also affect efficiency of field of
equipment, which increases time and cost
of field operations. Maintenance includes
harvesting and marketing forage, repairing
rills and gullies, and removing accumulated
sediment. Establishment costs include
field grading and vegetation establishment
and usually are less than costs for terraces.
Devlin et al. (2003) estimated that grassed
waterway costs include a onetime $30/acre
cost, $13.60/acre for all acres in the field,
and the annual loss of income from land in
the waterway (Table 1).
Vegetative Buffers. Vegetative buffers are land areas
maintained in permanent vegetation that reduce nutrient and
sediment losses from agricultural
fields, improve runoff water quality,
and provide wildlife habitat. Several
federal and state programs encourage
installation and maintenance of vegetative
buffers. Establishment costs for vegetative buffers average $104/acre (Table 1;
Williams et al., 2004) plus annual loss of
income from land in the buffer that can no
longer be cropped. We used the K-State
Vegetative Buffer Decision-Making Tool
(Smith and Williams, 2007) to estimate
annualized costs. Establishment costs for
a buffer using native grass are $73.12/acre
without any cost-share or incentive payments, and annualized costs including loss
of income are $63.29/acre (Table 1).
In-Stream Strategies
Streambank Stabilization and
Bendway Weirs. Various strategies are
used to reduce streambank degradation,
and several can be combined for effective
streambank stabilization. Willow posts can
be planted on the outer bend of smaller
streams to create a natural riparian zone
that slows water flow and dissipates energy
that will erode the bank toe. Posts usually
are 3 to 4 inches in diameter and 10 to 14
feet tall. Depending on bank height, three
to five rows are planted 4 feet apart. Other
strategies include bendway weirs, stone
toes, pools and riffles, and stream barbs.
These methods use rock structures to slow
or divert water flow and protect the bank
toe. Bendway weirs are jetties constructed
at an upstream angle of 10 to 25 degrees
that directs water toward the center of the
stream. Typically, they are less than half the
Sedimentation in Our Reservoirs: Causes and Solutions
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stream width in length and slightly higher
than low water. Sediment tends to collect
on the downstream side of weirs. Bendway weirs generally are suitable for larger
watercourses, such as sections of the Little
Blue River in Washington County, Kansas.
A stone toe is a row of large rocks along the
toe of the outside bank of a bend. Perpendicular “keys” are constructed at intervals
along the bank to protect against undercutting. In the pool and riffle method, a series
of riffles (i.e., rock and sand bars) are constructed across a stream. These slow stream
flow by breaking a steeply sloping stretch of
streambank into a series of gently sloping
sections (Johnson, 2003). Other methods
include placing tree revetments or riprap on
the outer bank of a bend. Tree revetment
involves securing cut trees, often cedars, at
the bank toe. The trees slow stream flow
and trap sediment from the eroding bank.
Eventually, willow and cottonwood seedlings will sprout and grow, re-establishing a
riparian zone. Riprap is large rocks placed
on the face of a bank to resist scouring from
water flow.
Williams et al. (2004) analyzed costs of
streambank stabilization based on actual
construction and establishment costs at
13 sites on a 35-mile stretch of the Little
Blue River in Washington County, Kansas
(Table 2). Each site required establishing a
125-foot-wide riparian buffer consisting
of trees, shrubs, and grass; 100 feet of the
width was CRP land (Figure 3). Land area
enrolled in the CRP ranged from .8 acres
to 4.6 acres with an average size of 3 acres.
Table 2. Construction and establishment costs of streambank stabilization by sitea
Percent
Length in
CRP
Total
Percent Cost per
Site
Equipment
c
Materials
Acred
feet
Acres
Costs
& Laborb
1
1,250
2.9
$18,261
32.5%
67.5%
$6,364
2
925
2.1
16,524
32.0%
68.0%
7,781
3
1,140
2.6
23,988
20.3%
79.7%
9,166
4
882
2.0
17,410
29.5%
70.5%
8,598
5
2,016
4.6
12,552
19.3%
80.7%
2,712
6
336
0.8
3,019
82.9%
17.1%
3,914
7
1,049
2.4
8,392
72.3%
27.7%
3,485
8
1,255
2.9
20,814
65.3%
34.7%
7,225
9
1,188
2.7
14,488
61.5%
38.5%
5,312
10
1,150
2.6
10,395
61.6%
38.4%
3,937
11
1,983
4.6
35,073
23.0%
77.0%
7,704
12
1,980
4.5
16,937
75.6%
24.4%
3,726
13
1,888
4.3
12,008
54.2%
45.8%
2,771
Average
1,311
3.0
$16,143
42.2%
57.8%
$5,592
Cost per
Linear
foot
$14.61
17.86
21.04
19.74
6.23
8.99
8.00
16.58
12.20
9.04
17.69
8.55
6.36
$12.31
Table adapted from Williams et al. (2004) with permission
Percentage of total costs for engineering and design, equipment, and labor to prepare the site including
planting grass seed
c
Percentage of total costs for material including rock, trees, shrubs, grass seed, tree shelters, and chemicals
d
Cost per acre in the CRP stabilization area
a
b
80
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CRP Area
B
River
25 ft
A
25 ft
.
C
D
50 ft.
25 ft.
Cropland
.
Figure 3. Streambank stabilization profile
A. Willow (4-foot spacing) and cottonwood (6-foot spacing)
B. Cottonwood, silver maple, and/or sycamore trees (8-foot spacing)
C. One row each of green ash, black walnut, and burr oak trees (10-foot by 12-foot spacing) and one row each
of choke cherry, fragrant sumac, and American plum shrubs (6-foot by 6-foot spacing)
D. Native grass mixtures of big bluestem, Indiangrass, switchgrass, sideoats grama, and western wheatgrass
Figure adapted from Williams et al. (2004) with permission
Construction equipment reshaped the
streambank so it rose 1 foot from stream
level to field level for every 3 feet of distance
from stream to field. Bank width from
stream level to field level was approximately
55 feet. Approximately every 175 feet,
bendway weirs were constructed from rock
boulders one-eighth ton to 1 ton in size
(Oertal, 2002). A typical weir was onethird the width of the stream at low water
and about 2 feet high, 18 feet wide at the
base, and 10 feet wide on top.
Per-site construction and establishment
costs ranged from $3,019 to $35,073 with
an average of $16,143. Cost per linear foot
of streambank ranged from $6.23 to $21.04
with an average of $12.31. Cost per acre,
based on acres in the 100-foot-wide stabilization portion, ranged from $2,712 to
$9,166 with an average of $5,592 (Table 2).
The annualized cost, using a 15-year period
and 6% interest rate, ranged from $279/acre
per year to $944/acre per year with an average of $576/acre per year. Landowners also
incurred some annual maintenance costs.
Landowners receive several benefits from
streambank stabilization including income
or rental payments from preserved cropland and market value of land saved from
erosion. Streambank stabilization projects
typically require that cropland be taken
out of production to install the vegetative
buffer but result in long-term net savings
of land. If the project can be enrolled in the
CRP, landowners will receive annual rental
payments. Cost-share payments, subsidies,
or other incentives also might be provided.
For purpose of cost calculations, the value
of CRP, cost-share, and other incentive
payments are not included in our analysis.
The present value of CRP payments over
15 years ranges from $724 to $3,602 with
an average of $1,907. Present value of rental
income not lost because of erosion over
15 years ranges from negative $1,211 to
$4,805 with an average of $474. Present
market value of cropland preserved after 15
years ranges from $990 to $16,985 with an
average of $6,121 (Table 3).
In-Reservoir Management
Dredging. Dredging is the removal of
accumulated sediment from bottoms of
lakes, reservoirs, or other water bodies by
mechanical, hydraulic, or pneumatic means
(Hudson, 1998). Sediments often are
removed from rivers and ports for navigation and boating purposes. Less frequently,
dredging is used in lakes and reservoirs to
reclaim water storage capacity. Dredging
Sedimentation in Our Reservoirs: Causes and Solutions
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Table 3. Present value and annualized present value of streambank stabilization costs
Average Site
$/acrea
Costs without potential landowner benefits:
– Total construction and establishment cost
–$16,143
–$5,381
– PV of annual maintenance costs over 15 years
–$206
–$69
= Present value of costs of project to land owner
–$16,349
–$5,450
b
Annualized present value of costs
–$1,670
–$557
Costs with potential landowner benefits:
– Total construction and establishment cost
– PV of annual maintenance costs over 15 years
+ PV of rental income effect over 15 years
+ PV of net land conserved in the terminal year (year 15)
= NPV of costs of project to land owner
Annualized present value of costs
a
b
–$16,143
–$206
+$474
+$6,121
–$9,754
–$997
–$5,381
–$69
+$158
+$2,040
–$3,252
–$332
Cost per acre in the CRP stabilization area
Annualized using a 5.81% discount rate
Table 4. Dredging costsa
Data Source
Corps of Engineersb
Iowa Minimumc
Iowa Maximumc
Kansas Minimumd
Kansas Maximumd
Cost per
cubic yard
$3.75
$2.55
$5.31
$3.00
$8.67
Tuttle Creek
Dredging and
Cost to remove
sediment deposdisposal cost per
sediment deposited as of 2005
acre-foot
ited by 2005
(acre-feet)
$6,049.99
165,000
$998,247,938
$4,115.58
165,000
$679,070,469
$8,574.48
165,000
$1,414,789,093
$4,839.99
165,000
$798,598,350
$13,983.22
165,000
$2,307,230,768
Costs provided in 2005 dollars
USACE (2005)
c
Iowa Department of Natural Resources (K. Jackson, personal communication, Nov. 1, 2006)
d
Kansas Water Office (2004)
a
b
costs provided by the Iowa Department of
Natural Resources (K. Jackson, personal
communication, Nov. 1, 2006), U.S. Army
Corps of Engineers (USACE; 2005), and
Kansas Water Office (2004) range from
$2.55/cubic yard to $8.67/cubic yard
(Table 4) and include dredging, equipment mobilization, and sediment disposal.
Mobilization costs represent a higher
percentage of overall costs in smaller proj82
Sedimentation in Our Reservoirs: Causes and Solutions
ects. Other organizations and companies
report hydraulic dredging costs ranging
from $4.00/cubic yard to $14/cubic yard
(Illinois Environmental Protection Agency,
2005; Kansas Biological Survey, 2005;
Dredging Specialists, 2007).
Other In-Reservoir. Information on
options for and economics of in-reservoir
sediment management strategies other
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than dredging is limited. Baker (2007)
reviewed some options for managing
sediment within a reservoir. However,
in-reservoir management strategies have
limited effectiveness for reducing sediment
loads introduced from the watershed and
transported via major tributaries. In some
areas, shoreline erosion control techniques
reduce sediment loading in reservoirs, but
sedimentation from shoreline erosion likely
is quite small compared with sedimentation
from off-site erosion.
One dredging alternative does not involve
sediment management; rather, it raises the
legal level of water storage elevation in the
lake. This approach is a temporary measure.
Costs for this strategy are very site specific
and can include purchasing additional land,
loss of income from cropland or other uses,
habitat loss on environmentally sensitive
sites, and relocation of roads, walks, ramps,
or other structures.
Huffaker and Hotchkiss (2006) grouped
sediment control strategies into three broad
approaches:
1. Reducing inflow by controlling erosion
in the catchment area (i.e., watershed)
2. Diverting sediment by routing it to offstream reservoirs or sluicing it through
a dam before it can settle
3. Removing accumulated sediment by
hydraulic flushing, hydraulic dredging,
or dry excavation.
They also examined another sediment
removal strategy called hydro suction
dredging, but their research was limited to
developing a theoretical economic model of
this process and determining the optimal
volume of reservoir water to allocate to
this sediment removal strategy. (Huffaker
and Hotchkiss, 2006). In hydro
suction dredging, one end of a
pipeline is located at the reservoir
bottom upstream from a dam. The
pipeline extends through the dam
to a downstream discharge point and
draws sediment-entrained water into
the pipe for transport downstream. This
sluicing process relies on the availability of
“surplus” water that drives suspended sediment beyond the reservoir. The “surplus” is
annual inflow beyond storage capacity that
is involuntarily spilled.
Targeting Best
Management Practice
Implementation
Identifying land in a watershed that should
be treated is crucial for reducing sedimentation. Because limited resources are
available to fund implementation of best
management practices (BMPs), it is most
cost-effective to target areas that contribute
most to sedimentation. Targeting attempts
to identify BMPs and land that have the
greatest sediment reduction benefits relative to cost.
Khanna et al. (2003) developed a framework that includes a hydrological model
that uses geographic information system
(GIS) data and an economic model to
determine cost-effectiveness of retiring land
using the Conservation Reserve Enhancement Program (CREP) to reduce sediment.
They applied the model to a 61,717-acre
Illinois watershed and assumed that sloping
cropland adjacent to a stream or riparian buffers within 900 feet of a stream
were eligible for land retirement using the
CREP. Model results revealed that 8,172
acres could be targeted. To achieve 20%
sediment reduction for a 5-year storm, 11%
Sedimentation in Our Reservoirs: Causes and Solutions
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of the acres in this area needed
to be in the CREP; this had an
average cost of $31/ton. With a
30% reduction goal, average cost
was $47/ton. Marginal costs rose
from $29/ton at a 10% reduction goal
to $117/ton at a 30% reduction goal. To
achieve a 20% sediment reduction goal, the
cost-effective land rental payment is $54/
ton times the tonnage of reduction per acre.
Results also showed that most land selected
for enrollment was from highly sloping and
highly erodible areas rather than less erodible flat floodplains.
…it is preferable to capture the sediment at the end of the flow channel by
retiring parcels adjacent to the water
body rather than reduce sediment
generated by retiring upslope parcels
that are farther from the water body.
Those parcels with high on-site erosion
and high sediment trapping effectiveness are also given priority. (Khanna et
al., 2003, p. 547-548)
Yang et al. (2003) used a similar approach
to examine CREP use across 12 contiguous
Illinois watersheds to reduce sedimentation
in the Illinois River by 20%. For a 5-year
storm event, a 20% reduction goal translated into a 32,000-ton sediment reduction
in the 617,763-acre region. However, only
a 900-foot-wide area along all streams and
tributaries was eligible for CREP establishment. To achieve 20% reduction at the
aggregate level (i.e., total watershed) at
least cost, sediment reduction in the 12
watersheds ranged from 4.1% to 33.3%. A
uniform standard applied to all 12 watersheds was more costly and required that
more cropland be placed in CREP.
Regardless of the variability across
watersheds, cropland selected for retirement in all watersheds is closer to water
84
Sedimentation in Our Reservoirs: Causes and Solutions
bodies, more sloping, more erosive, and
more likely to receive larger volumes of
upland sediment flows than the cropland not selected for retirement. (Yang
et al., 2003, p. 261)
This study focused on one management
practice and did not consider sediment
reduction benefits, optimal amount of sediment reduction, or dredging costs.
To extend research by Khanna et al. (2003)
and Yang et al. (2003), Yang and Weersink
(2004) examined cost-effectiveness of
targeting riparian buffers in a 36,077-acre
agricultural watershed in Ontario by combining economic and hydrologic models
with GIS data. Their model minimizes the
loss of economic return from crop production, which varies by watershed location
subject to fixed levels of sediment reduction
goals for a variety of buffer strip widths
in each sub-catchment of the watershed.
The model selects appropriate buffer strip
widths and locations for five separate sediment reduction goals but does not estimate
benefits of sediment reduction, determine
the optimal level of sediment to control,
suggest an optimal combination of management practices other than buffer strips, or
consider dredging. Results indicated that
cost-effective targeting results in buffer
strip locations that vary across the watershed and are not necessarily located on sites
adjacent to streams or having the greatest
slopes. Marginal costs of sediment control
increase as amount of land used for buffer strips and desired sediment reduction
increase.
Yang et al. (2005) used a similar approach
to examine spatial targeting of no-till to
improve water quality and carbon retention benefits in a 90,470-acre agricultural
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watershed in Ontario. They reported that
9.7%, 16.5%, 25.2%, and 39.6% of the
land must be in no-till to achieve 20%,
25%, 30%, and 35% sediment reduction,
respectively. Their study assumed a cornsoybean-wheat cropping system. Average
costs ranged from $10.89/acre per year
to $12.26/acre per year. As the sediment
reduction goal increased, additional no-till
acreage needed and costs also increased. As
expected, the percentage of land in no-till
varied across subwatersheds because of the
cost relative to amount of reduced sedimentation. Subwatersheds that required
a higher percentage of no-till cropland to
achieve the least-cost solution generally had
higher land slope and more erosive soils;
costs for using no-till were relatively lower
in these areas.
Within a watershed, the number of subwatersheds that might need to be modeled
affects the number of regions that can be
used to determine a cost-effective targeting
approach for sediment reduction. Using
data from Soil and Water Assessment Tool
(SWAT) models of four Iowa watersheds,
Jha et al. (2004) developed preliminary
guidelines for subdividing a watershed into
subwatersheds for modeling purposes. They
found that predicted sediment yields are
related to subwatershed size and delineation and suggested modeling studies should
include sensitivity analyses with various
subwatershed delineations to determine the
appropriate level for actual analysis.
These spatial targeting studies reveal an
important policy issue: How should BMPs
for sediment control be spatially distributed
to achieve optimal results (i.e., additional
costs of sediment control equal the additional benefits)?
Dredging Versus Best
Management Practices
We use Tuttle Creek Lake and its watershed as a preliminary case study to examine
the economics of watershed protection and
reservoir rehabilitation. Tuttle Creek Lake
is a 14,000-acre impoundment in northeast
Kansas at the lower end of the Big Blue
River. The 9,628-square-mile watershed
supplying the lake is largely agricultural.
The majority of the watershed extends
north into Nebraska, and the lower quarter
is in Kansas. The USACE built Tuttle
Creek Lake in 1962 for flood control,
irrigation, water supply, recreation, fish
and wildlife, low-flow augmentation, and
navigation-flow supplementation for Missouri River barge traffic. The lake provides
up to 50% of the Kansas River flow; this
river is a public water source for Topeka,
Lawrence, and Kansas City. Table 5 provides additional information about the lake
and watershed.
As of 2005, which was 43 years since the
reservoir was completed, Tuttle Creek Lake
contained 266,199,450 cubic yards of sediment. Although Table 4 shows a range of
dredging costs, we assume the cost of dredging is $5.00/cubic yard for the remainder
of our discussion. Total estimated cost of
removing sediment from Tuttle Creek
Lake at $5.00/cubic yard is $1,330,997,250
(which translates to $301/watershedacre). Calculating the annual payment on
a loan for the total dredging cost provides
perspective; assuming a 7% interest rate
and 43-year period, the loan payment is
$98,541,573/year or $22.28/acre of cropland in the watershed. Clearly, dredging is
an expensive option.
Sedimentation in Our Reservoirs: Causes and Solutions
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Table 5. Tuttle Creek Lake and watershed characteristics, dredging costs, and equivalent
per-acre expenditures
Characteristics
Original conservation storage pool (acre-feet)
425,000
Sediment deposited as of 2005 (acre-feet)
165,000
Sediment deposited as of 2005 (cubic yards)a
266,199,450
Drainage area (square miles)
9,600
Drainage area (acres)
6,144,000
Pastureland (%)
16%
Pastureland (acres)
983,040
Cropland (%)
72%
Cropland (acres)
4,423,680
Other (%)
12%
Other (acres)
737,280
Dredging Cost in 2005
Cost per cubic yard
Dredging and disposal cost per acre foot
Sediment deposited as of 2005 (acre-feet)a
Cost to remove sediment deposited until 2005
$5.00
$8,066.65
165,000
$1,330,997,250
Onetime Equivalent Costs
Cost per acre of cropland
a
Projected based on average annual sedimentation rate to 1999
Although dredging is effective at removing
sediment, it does not prevent sedimentation. If accumulated sediment has not
significantly reduced reservoir functions
and benefits, it might be reasonable to forgo
dredging and instead implement management practices that significantly reduce the
need for future dredging. This decision will
depend on sediment source, sedimentation
rate with and without management practices, effectiveness and cost of management
practices, dredging cost inflation, the planning horizon, and the discount rate used to
calculate present values.
86
$301
Sedimentation in Our Reservoirs: Causes and Solutions
A detailed analysis of this decision for
Tuttle Creek Lake or other reservoirs is
beyond the scope of this paper. A complete
study should consider costs, benefits, and
the optimal level of sediment control, and
determining the best approach to manage erosion and sediment requires a more
detailed economic analysis of the number
of acres within a watershed that can be
treated with a variety of practices. The following analysis does not consider all costs
and benefits. However, given a number of
assumptions, we estimate how many acres
of land can be treated with four individual
management practices: vegetative buffers, no-till, terraces, and streambank
stabilization.
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Our analysis examines how many acres a
management practice can be applied to if
savings generated from reduced dredging
finance the management practice (Figure
4). Estimated future savings from dredging costs avoided because of implementing
sediment reduction management practices
are a key component of this analysis. To
determine these values, we estimate the
reservoir sedimentation rate with and without management practices over a 20-year
planning period. We also estimate the cost
of dredging 20 years in the future based on
Select Management Practice
Determine Effectiveness of
Erosion and Sediment Reduction
Select Time Period for Analysis
Estimate Cost of Dredging
in a Future Year for Do Nothing
versus Management Practice
Calculate Future Savings
in Dredging Costs Due to
Management Practices
Adjust Savings to
Present Value and Annualize
Estimate Annualized
Cost of Management
Practice
Compare Savings to
Annualized Cost of
Management Practice
Calculate Number
of Acres Potentially
Applied
Figure 4. Method for comparing dredging
with management practices
the current rate of sedimentation versus
a reduced rate of sedimentation that will
result from implementing management
practices. Because we do not know the
specific effectiveness, cost, or combination of management practices that will be
appropriate for each area in the watershed,
we apply general assumptions to the entire
watershed. Our analysis is limited to costs;
therefore, we do not consider any benefits
resulting from reduced erosion and sedimentation (Smith et al., 2007).
In the following scenarios, we use characteristics of the Tuttle Creek Watershed
listed in Table 5. We examine four management strategies (i.e., vegetative buffers,
no-till, terraces, and streambank stabilization) to determine how many acres they
can potentially be applied to based on cost
savings from reduced dredging. Cost savings for all strategies, summarized in Table
6, are based on a 2005 dredging cost of
$5.00/cubic yard inflated at a 5.81% annual
inflation rate over the next 20 years and
a 7% annual discount rate for the present
value calculations (Appendix A). Dredging
cost inflation rate is based on historical data
(Figure 5).
In the first scenario, we assume vegetative buffers are 50% effective at reducing
erosion and the sedimentation rate (Devlin
et al., 2003). Compared with applying no
management practices, installing vegetative buffers will result in 61,906,849 fewer
cubic yards to dredge in 20 years. Estimated
dredging cost savings are $247,495,574
(2005$), equivalent to $55.95/cropland
acre. Average annual savings over the
20-year period are $5.28/cropland acre.
The interpretation of this value is that
spending $5.28/acre per year on every acre
of cropland in the watershed over the next
Sedimentation in Our Reservoirs: Causes and Solutions
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Table 6. Estimation of dredging cost savings from erosion reduction
Management Practice
Streambank
Do
Vegetative
No-Till
Terrace
Stabilizationab
Nothing
Buffera
Dredging inflation
5.81%
5.81%
5.81%
5.81%
5.81%
Initial dredge cost ($/cubic yard)
$5.00
$5.00
$5.00
$5.00
$5.00
Sediment rate based on 1962 to 2005
6,190,685
6,190,685
6,190,685
6,190,685
6,190,685
(cubic yards per year)
Reduction in sediment rate due to
0.00%
50.00%
75.00%
30.00%
90.00%
management practice
New sediment rate (cubic yards per
6,190,685
3,095,342
1,547,671
4,333,479
619,068
year)
Number of years at this new sediment
20
20
20
20
20
rate
Accumulated sediment over 20-year
123,813,698
61,906,849
30,953,424
86,669,588
12,381,370
period (cubic yards)
Reduction in sediment to dredge
61,906,849
92,860,273
37,144,109
111,432,328
compared with do nothing
Future dredging cost ($/cubic yard)
$15.47
$15.47
$15.47
$15.47
$15.47
Future dredge cost of 20-year
$1,915,459,554 $957,729,777 $478,864,888 $1,340,821,688 $191,545,955
accumulation
Future savings in dredging cost
$957,729,777 $1,436,594,665 $574,637,866 $1,723,913,598
Discount rate for present value
7.00%
7.00%
7.00%
7.00%
7.00%
calculations
$494,991,148 $247,495,574 $123,747,787 $346,493,803
$49,499,115
Present value of future dredging costc
Present value of dredging savings
$247,495,574 $371,243,361 $148,497,344 $445,492,033
compared with do nothingc
Annualized savings
$23,361,831
$35,042,747
$14,017,099
$42,051,296
Onetime savings per acre
Savings per acre of cropland
Savings per acre of 50% of cropland
$55.95
$111.90
$83.92
$167.84
$33.57
$67.14
$100.71
$201.41
Annualized savings per acre over
selected year period
Savings per acre of cropland
Savings per acre of 50% of cropland
$5.28
$10.56
$7.92
$15.84
$3.17
$6.34
$9.51
$19.01
$65.00
8,985,320
203.12%
$10.00
3,504,275
79.22%
$20.00
700,855
15.84%
$332.04
3,166,132
71.57%
Management practice cost $/acre/year
Potential crop acres applied
Percentage of cropland in watershed
Management practice cost $/streambank mile/year
Potential streambank miles
We assume 1 acre of buffer treats 25 aces of cropland
Cost for streambank stabilization includes an adjustment for landowner benefits (Refer to Table 3)
c
Amounts reported in 2005 dollars
a
b
88
Sedimentation in Our Reservoirs: Causes and Solutions
$4,024.73
10,448
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$4.00
$3.50
Cost/Cubic Yard
$3.00
$2.50
$2.00
$1.50
$1.00
$0.50
$0.00
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
Year
Figure 5. Historical dredging costs in nominal dollars
Data source: USACE (2005). Average annual increase is 5.8%.
20 years will equal savings from reduced
dredging due to implementing buffer strips
that are considered 50% effective. If only
50% of crop acres actually need management practices, $10.56/acre can be spent
each year. If we assume the annualized cost
of a vegetative buffer is $65/acre per year
and each acre of vegetative buffer treats
25 acres (Smith, 2004), savings will cover
costs when buffers are applied on up to
8,985,320 acres. This is more than twice
(203%) the number of cropland acres in the
watershed. Under these assumptions, using
vegetative buffers appears more economical
than dredging.
yards to dredge in 20 years. Estimated
dredging cost savings are $371,243,361
(2005$), equivalent to $83.92/cropland
acre. Average annual savings over the 20year period are $7.92/cropland acre. If only
50% of crop acres actually need management practices, $15.84/acre can be spent
each year. At $10/acre per year, no-till can
be used on 3,504,275 acres (79% of crop
acres) in addition to any acres already under
no-till. If no-till needs to be applied to less
than 79% of cropland acres, savings from
reduced dredging will pay for the cost of a
program that provides $10/acre per year to
use no-till.
The second scenario examines no-till,
which is considered 75% effective at
reducing erosion and the sedimentation
rate (Devlin et al., 2003). Compared with
applying no management practices, using
no-till will result in 92,860,273 fewer cubic
The third scenario examines farmable terraces, which are considered 30% effective
at reducing erosion and the sedimentation rate (Devlin et al., 2003). Compared
with applying no management practices,
installing farmable terraces will result in
Sedimentation in Our Reservoirs: Causes and Solutions
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37,144,109 fewer cubic yards
to dredge in 20 years. Estimated dredging cost savings are
$148,497,344 (2005$), equivalent
to $33.57/cropland acre. Average
annual savings over the 20-year period
are $3.17/cropland acre. If only 50% of
crop acres actually need management practices, $6.34/acre can be spent each year. We
assume 223 linear feet of terrace are applied
to each acre requiring terracing. Using
the lowest establishment cost reported in
Table 1 ($.66/linear foot), terrace establishment costs $147.18/acre. Annualizing this
cost using a 10-year life and 6% interest
rate results in a $20/acre per year cost. At
this cost, terraces can be used on 700,855
acres (15.8% of crop acres) in addition to
any acres that already have terraces. Fully
evaluating whether establishing terraces is
more economical than dredging requires
determining how many acres of terraces are
needed to reduce sedimentation.
In the final scenario, we assume streambanks are stabilized as described previously
(Williams et al., 2004) and include buffer
strips that are 90% effective at reducing erosion and the sedimentation rate.
Compared with applying no management
practices, streambank stabilization will
result in 111,432,328 fewer cubic yards to
dredge in 20 years. Estimated dredging cost
savings are $445,492,033 (2005$), equivalent to $100.71/cropland acre. Average
annual savings over the 20-year period are
$9.51/cropland acre. If only 50% of crop
acres actually need management practices,
$19.01/acre can be spent each year. We
assume that 100 linear feet of buffer width
are required for each linear foot of streambank requiring stabilization. Therefore, 1
acre of land is required for every 436 feet
of streambank stabilized. Costs for stream90
Sedimentation in Our Reservoirs: Causes and Solutions
bank stabilization are very site specific, but
given the average costs reported in Table
3, annualized cost for a 15-year period is
$332/acre excluding any cost-share and
annual incentive payments but including
benefits to the landowner in the form of
annual income from and asset value of
preserved land (Williams et al, 2004). At
this cost, streambank stabilization can be
used on 10,448 streambank miles. Assuming each acre of vegetative buffer in the
stabilization area treats 25 acres (Smith,
2004), the stabilization project can treat
3,166,132 acres (71.6% of crop acres). If
each stabilization acre treated only 10 acres,
dredging cost savings could be used to treat
1,266,453 acres (29.6% of crop acres). Fully
evaluating whether streambank stabilization is more economical than dredging
requires determining how many streambank miles need to be stabilized to reduce
sedimentation.
Our calculations do not reflect the
optimum number of acres to which management practices should be applied. We do
not know, from a technical and economic
perspective, how suitable no-till, terraces,
vegetative buffers, or streambank stabilization might be for various locations in the
watershed or the number of acres or miles
that actually need these practices applied.
Numbers presented represent only the
potential area to which these management
practices can be applied based solely on
cost savings from reduced dredging. The
more expensive or less effective the practice,
the fewer acres to which it can be applied.
Estimates provide some perspective on
dredging versus use of soil erosion management practices. Our brief analysis indicates
that in situations where the amount of
accumulated sediment has not reduced
a reservoir’s usefulness, it could be more
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economical for the government to fund
expenditures for management practices that
reduce further erosion and sedimentation
in a watershed than to rely on dredging in
the future.
From an economic perspective, the optimal
level of sedimentation control is when the
marginal (additional) benefits of control
practices equal the marginal costs of implementing those practices. Because data on
costs and benefits of sediment management
practices are significantly limited, this paper
provides only a rough analysis and does not
consider benefits of BMPs versus dredging.
Further, none of the articles we reviewed
presented a model for or attempted a
comprehensive analysis. In previous literature, alternative levels of sedimentation
reduction simply are assumed. Although
we do not attempt to quantify benefits
of BMPs or dredging, we recognize that
in-field BMPs might provide benefits, in
addition to reduced sediment loads, that
need to be accounted for in a comprehensive in-field versus in-reservoir management
Sensitivity Analysis
Although many variables in our analysis are
unknown, we perform sensitivity analyses on three variables that can affect the
analysis: sedimentation rate, dredging cost,
and discount rate. Because BMPs such as
CRP land, terraces, and no-till have been
established over time in the watershed,
simply averaging sedimentation rates over
the time period since the impoundment
was constructed might overstate the future
sedimentation rate. Therefore, we use
alternative sedimentation rates (110%,
100%, 90%, 80%, and 70% of the original)
in a sensitivity analysis (Figure 6). The
Streambank Stabilization
No-Till
Vegetative Buffer
Terrace
$50,000,000
$45,000,000
$40,000,000
Annualized Savings
strategy comparison. For example, if an
in-field strategy keeps more soil on a field,
productivity of that field will be greater
over time; this benefit is not realized as
much through in-reservoir strategies. Other
benefits associated with in-field strategies
include reduced nutrient and pesticide
loads entering the reservoir and increased
wildlife habitat.
$35,000,000
$30,000,000
$25,000,000
$20,000,000
$15,000,000
$10,000,000
$5,000,000
$0
70%
80%
90%
100%
110%
% of estimated sedimentation rate
Figure 6. Annualized savings as a function of sedimentation rate
Annualized savings are avoided dredging costs that can be spent on BMPs. Annualized cost savings from reduced
dredging at the original sedimentation rate for each management practice are reported in Table 7 and range from
$14 million for terraces to $42 million for streambank stabilization. These values are represented at the 100%
level in this figure.
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original rate is 6,190,685 cubic yards/year.
If the expected sedimentation rate without
management practices is lower than the
original rate, annualized savings decline.
A lower sedimentation rate means fewer
dredging costs are avoided by using BMPs.
As a result, savings from reduced dredging
costs cover application of BMPs on fewer
acres or stream miles (Table 7).
Original dredging cost is $5.00/cubic
yard (2005$). Future dredging costs are
unknown and could be lower because of
technological improvements. Therefore, we
performed a sensitivity analysis using various dredging costs inflated at an annual rate
of 5.81% (Figure 7). If dredging costs less in
the future, annualized savings from reduced
dredging decline and will cover application
of BMPs on fewer acres or stream miles
(Table 7). Alternatively, if dredging costs
are higher than expected, annualized savings increase.
Table 7. Sensitivity of percentage of acres or potential streambank miles to which BMPs
could be applied based on dredging savings for various sedimentation rates, dredging costs,
and discount rates
Sedimentation rate (% of original)
70%
80%
90%
100%
110%
Percentage of cropland in watershed
Vegetative buffer
142.2% 162.5% 182.8% 203.1% 223.4%
No-till
55.4%
63.4%
71.3%
79.2%
87.1%
Terrace
11.1%
12.7%
14.3%
15.8%
17.4%
Potential streambank miles
Streambank stabilization
7,314
8,359
9,403
10,448
11,493
Dredging cost
Percentage of cropland in watershed
Vegetative buffer
No-till
Terrace
Potential streambank miles
Streambank stabilization
Discount rate
Percentage of cropland in watershed
Vegetative buffer
No-Till
Terrace
Potential streambank miles
Streambank stabilization
92
Sedimentation in Our Reservoirs: Causes and Solutions
$3.00
$4.00
$5.00
$6.00
$7.00
121.9%
47.5%
9.5%
162.5%
63.4%
12.7%
203.1%
79.2%
15.8%
243.7%
95.1%
19.0%
284.4%
110.9%
22.2%
6,269
8,359
10,448
12,538
14,628
4%
5%
6%
7%
8%
279.6%
109.1%
21.8%
251.8%
98.2%
19.6%
226.4%
88.3%
17.7%
203.1%
79.2%
15.8%
182.0%
71.0%
14.2%
14,384
12,954
11,644
10,448
9,360
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Discount rate also affects the analysis. The
original discount rate is 7% per year. A
lower discount rate discounts future values
less. Therefore, future values discounted
to the present are worth more (in 2005$)
or are larger (Figure 8). The lower the
Streambank Stabilization
No-Till
Vegetative Buffer
Terrace
$70,000,000
$60,000,000
Annualized Savings
discount rate, the larger the
annualized savings from reduced
future dredging. These larger
savings can be used to implement
BMPs on more acres or streambank
miles (Table 7).
$50,000,000
$40,000,000
$30,000,000
$20,000,000
$10,000,000
$0
$3.00
$4.00
$5.00
$6.00
$7.00
Dredging Cost per cubic yard
Figure 7. Annualized savings as a function of dredging cost
Annualized savings are avoided dredging costs that can be spent on BMPs. Annualized cost savings from reduced
dredging at the original dredging cost for each management practice are reported in Table 7 and correspond to
the $5.00 level in this figure.
Streambank Stabilization
No-Till
Vegetative Buffer
Terrace
$70,000,000
Annualized Savings
$60,000,000
$50,000,000
$40,000,000
$30,000,000
$20,000,000
$10,000,000
$0
4%
5%
6%
7%
8%
Discount Rate
Figure 8. Annualized savings as a function of discount rate
Annualized savings are avoided dredging costs that can be spent on BMPs.
Sedimentation in Our Reservoirs: Causes and Solutions
93
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has been archived. Current information is available from http://www.ksre.ksu.edu.
A Potential Process
for Evaluating the Best
Approach for Sediment
Reduction and Reservoir
Rehabilitation
Evaluating the best approach for reducing
additional sedimentation in watersheds
with reservoirs for which dredging is being
considered is a large and demanding task
that is beyond the scope of this paper.
Many issues require discussion and analysis:
determining important sediment sources,
effectiveness of management practices for
these sources, effectiveness of management practices under heavy rainfall and
high stream flow events, and location and
amount of and appropriate management
practices for acres needing treatment.
Many questions remain: Is there an acceptable level of sedimentation? What levels
of sedimentation are acceptable before
dredging is the only option? What is the
appropriate combination of management
practices and dredging? What are the
environmental, flood control, irrigation,
water supply, recreation, fish and wildlife,
low-flow augmentation, and navigationflow supplementation costs and benefits of
alternative management approaches? What
time period should be considered? What
is the quality of sediment and is any of it
marketable?
We need to know more about management
practice costs, which vary by site and with
commodity price changes. The following outline provides a general research
approach for a more detailed analysis of
these issues and questions; it is not inclusive
of the entire decision-making process. Figure 9 provides an overview of this approach.
94
Sedimentation in Our Reservoirs: Causes and Solutions
1. Sediment Source Identification
2. Data Collection
- Watershed characteristics
- Rates of sedimentation and erosion
- Extent and types of management
practices currently in place
- Potential management practices
3. Modeling
- Develop baseline watershed model
- Evaluate erosion and sedimentation
changes under alternative manage ment scenarios
4. Economic Analysis
- Evaluate effects of erosion and
sedimentation on stakeholders
- Determine costs of alternative
practices modeled at field and
watershed scale
- Evaluate sediment reduction cost effectiveness using spatial targeting
approaches
- Estimate benefits of alternative
scenarios for land managers,
producers, and watershed users
Available Tools and Tool
Development
Livestock and cropland BMPs can benefit
society as a whole, but it also is important
to consider how these BPMs affect producers and land managers who decide whether
to adopt the practices and are responsible
for implementing them. To facilitate this
analysis, several spreadsheet-based decision-assistance tools are currently under
development in the Department of Agricultural Economics at Kansas State University.
These tools are designed to analyze BMPs
based on economic benefits and costs at
the individual field or farm level (societal
benefits and costs are not included in the
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Establish Watershed Characteristics
and Management Practices
Identify Erosion Rates and Sources
Develop Baseline Watershed Model
Identify Alternative BMPs
for Each Erosion Problem
Determine Effectiveness of
Erosion and Sediment Reduction
Select Time Period for Analysis
Evaluate Erosion and Sedimentation
Change under Alternative BMPs
Estimate Costs and Benefits of Each BMP
Combination at Watershed Level
Estimate Cost of Dredging in a
Future Year for Do Nothing Scenario
Compare Alternatives
Figure 9. Preferred approach for comparing
dredging with sedimentation BMPs
analysis) and will allow producers or land
managers to identify sediment- and nutrient-reducing BMPs, determine costs and
benefits of BMPs for their operations, and
identify available cost-share funding.
The K-State Vegetative Buffer DecisionMaking Tool (Smith and Williams, 2007)
is designed to answer the following questions: What are the benefits and costs of
vegetative buffers, and does it make sense
to install a buffer on my operation? This
spreadsheet tool provides information,
specific to vegetative buffers, about three
factors: economic benefits, costs, and available financial programs and incentives. The
tool also compares net benefits of buffers
with net benefits from cropping. Other
decision-making tools currently under
consideration will focus on economics of
alternative tillage (e.g., reduced tillage or
no-till), riparian forest buffers, streambank
stabilization projects, and various livestock
and rangeland management strategies.
Research Issues
and Opportunities
Predicting effects of management practices
on erosion and sedimentation requires
development of detailed watershed models.
These models must include information
about sediment source because source location will influence the type of management
practices used to reduce the sedimentation rate. Type of management practices
selected influences the cost of sediment
reduction and overall costs and benefits
of sediment reduction versus dredging.
Even if watershed models can be designed
to determine the technically best sediment reduction management practices,
site-specific costs will influence selection
Sedimentation in Our Reservoirs: Causes and Solutions
95
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of the most economical management practices. Currently, we can
assign only a general cost to each
management practice even though
different managers can have different costs for implementing the same
practice. Two possible approaches for
gaining additional information about costs
of implementing management practices are
Water Quality Trading (WQT) programs
and BMP auctions.
96
active sulfur dioxide market for air emissions, the emissions target was achieved for
less than half its originally estimated cost
(NCEE, 2001).
Water Quality Trading programs create a
market for “water quality credits.” Farmers
generate income by selling these credits and
then are obligated to implement certain
BMPs on their farms. A recent report
(Breetz et al., 2004) identified more than
70 WQT programs operating in the United
States, and additional WQT programs are
being adopted rapidly to manage a variety
of water quality problems. Most existing
WQT programs aim to reduce nutrient
concentrations, primarily nitrogen and
phosphorous, in streams and lakes. In a
typical program, point source polluters
(mainly municipal wastewater treatment
plants) buy water quality credits from
nonpoint source polluters (farmers). Point
sources polluters use credits to offset some
of their current nutrient discharges to meet
regulatory discharge limits. In essence, they
purchase nutrient reductions from farmers
instead of installing potentially costly treatment technologies.
Although current programs target nutrient reduction, WQT programs for erosion
control can be structured similarly. Eligible
BMPs in nutrient trading programs also
reduce sedimentation because a large portion of discharged nutrients are dissolved in
soil particles. In an erosion control WQT
program, each credit represents a specified
amount of erosion reduction (e.g., one ton
of soil loss). A schedule delineating the
number of credits generated by each BMP
will need to be developed from watershed
modeling simulations, which already are
being developed for various watersheds in
Kansas (Mankin, 2005). Credits generated
by a particular BMP can vary across different subwatersheds depending on soil and
topographic features. Landowners across
the watershed will be eligible to sell credits,
and likely buyers include state agencies,
local municipalities, recreation entities, and
concerned environmental groups. Buyers
will set prices based on financial gain from
reduced dredging, improved recreation
opportunities, and other benefits. Essentially, sellers will be providing cost estimates
for controlling erosion and sediment to
various degrees, allowing more accurate
identification of erosion and sediment
reduction costs.
Economists often favor market approaches
to environmental management because
these approaches ensure cost-effectiveness.
If certain conditions are met, active markets ensure the environmental quality
target is met at the lowest possible cost for
the watershed as a whole (Atkinson and
Tietenberg, 1991). For example, in the
A BMP auction is another market-based
program with potential to accurately identify sediment reduction costs. In a BMP
auction, agricultural producers compete
by submitting bids to supply the buyer
(i.e., project sponsor) with water quality
improvements through BMP implementation. Bids are ranked by amount of water
Sedimentation in Our Reservoirs: Causes and Solutions
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quality improvement generated per dollar.
Buyers contract first with the producer
who can offer water quality improvement
at the lowest price. This process is repeated
until a predetermined point is reached (e.g.,
funds are exhausted or bids no longer meet
a certain water quality improvement/price
ratio target). These auctions allow buyers to
identify and purchase the most cost-effective water quality improvements with a
specified budget.
A unique characteristic of BMP auctions
is that if existing incentives (e.g., cost-share
or incentive payments) are insufficient
to induce cooperation for high-priority,
high-impact improvements, a producer can
“reveal” the price required to undertake the
desired action. In the marketplace, numerous producers provide such information,
and project sponsors can select among
competing bids to purchase the most
cost-effective bundle of pollution reduction
investments. Further, the totality of information provides valuable insight into the
incentive levels required to induce producers to adopt various desirable practices.
Research Needs
Additional research should be conducted to determine:
1. Sources of sediment and rates of
sedimentation
2. Effectiveness of sedimentreducing BMPs in high- and
low-runoff events
3. Costs and returns of alternative
BMPs
4. Future dredging costs
5. Environmental and economic
effects of alternative watershed
protection and reservoir rehabilitation strategies
Sedimentation in Our Reservoirs: Causes and Solutions
97
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Appendix A: Selecting a Discount Rate
Selecting an appropriate discount rate reflects the time value of money. A dollar
received today is valued more than a guarantee today of a dollar to be received in
the future because the future payment implies forgone consumption or investment
opportunities today. Many agree that a discount rate should be based on the minimum acceptable rate of return or the opportunity cost of dollars invested in private
investments. Raising taxes to pay for public projects removes dollars from private
investments that earn a rate of return for investors. Selecting a discount rate can be
difficult and controversial because higher discount rates place less emphasis on future
benefits and costs. Choice of discount rate is further complicated if both private and
public funds are involved in projects because of the nature of who pays and benefits
from the projects over time.
Discounting is necessary for economic analysis of projects that have benefits and
costs over many years. Discounting benefits, savings, and costs transforms dollar
flows occurring in different time periods to a common measure of time value for
analysis and comparison, but discount rate affects results. In this study, present values
are calculated in 2005 dollars.
One alternative is to calculate a discount rate according to the following formula:
i = (r + 1)(1 + f) - 1
where: i = nominal discount rate or minimum acceptable rate of return on the investment of dollars, r = real rate of return or discount rate, and f = inflation rate.
A reasonable real rate of return for a risk-free investment is 2.0% to 3.5% (AAEA,
2000). Inflation rate can be measured by the average rate of change in the Personal
Consumption Expenditure Index. The long-run average annual rate from 1960 to
2007 was approximately 3.6% (Bureau of Economic Analysis, 2007). Thus, the real
rate of return (r) at the midpoint of the suggested range is 2.75%, and an inflation
rate (f) of 3.6% gives a resulting discount rate (i) of 6.45%. The Office of Management and Budget suggests using a 7% rate for benefit-cost
analysis of projects (National Center for Environmental Decision-Making Research,
2007), but those who place more emphasis on the future and are in favor of larger
government investments in public projects will argue for a lower discount rate. Those
who favor less government expenditures and place more emphasis on the present will
favor a higher discount rate. The USACE (2002) recently used 6.875% and 3.5%
discount rates. The NRCS provides discount rates used for projects since 1957 at:
http://www.economics.nrcs.usda.gov/cost/discountrates.html. Since 1990, rates
ranged from 4.875% to 8.875%. We used a 7% rate to calculate present values and
amortized or annualized present values.
98
Sedimentation in Our Reservoirs: Causes and Solutions
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Acknowledgments
We thank the following individuals for contributing
knowledge, data, references, or reviews:
Phil Balch, Watershed Institute, Topeka, KS
Nick Brozović, Department of Agricultural and Consumer Economics, University of Illinois
Dan Devlin, Department of Agronomy, Kansas State
University
Allen Featherstone, John Leatherman, Richard Llewelyn, and Jeff Peterson, Department of Agricultural
Economics, Kansas State University
Paul Gallagher and Larry Kuder, National Resources
Conservation Service, Salina, KS
Kyle Juracek, United States Geological Survey, Lawrence,
KS
Steve Nolen, Chief Environmental Branch, Planning
Division, U.S. Army Corps of Engineers
Waite Osterkamp, United States Department of the Interior—United States Geological Survey, Tucson, AZ
Thomas Roth, National Resources Conservation Service,
Clay Center, KS
Kerry Wedel, Kansas Water Office, Topeka, KS
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has been archived. Current information is available from http://www.ksre.ksu.edu.
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Reusing Dredged Sediment:
Geochemical and Ecological
Considerations
Margaret A. Townsend, Kansas Geological Survey, University of Kansas
Nathan O. Nelson, Department of Agronomy, Kansas State University
Deborah Goard, Kansas Forest Service
DeAnn Presley, Department of Agronomy, Kansas State University
Introduction
Options for rehabilitating federal reservoirs
and water-supply lakes filling because of
excess sedimentation include controlling
pollutant and sediment inputs, decommissioning dams, renovating dams or building
them higher, and dredging (Peterson, 1982;
Caldwell, 2007). In Kansas, dredging
sediments is one of several methods being
considered for reservoir restoration. However, many issues need to be addressed prior
to pursuing this option: dredging cost,
finding sites on which to apply dredged
sediments, transporting sediments to
those sites, effects on aquatic biota due to
sediment resuspension, effects on reservoir
water quality due to release of trace elements from sediment during the dredging
process, and effects on aquatic and land
biota due to chemical changes in landapplied sediment. In this white paper, we
focus on the last issue and provide an overview of possible sediment chemistry effects
associated with dredging Kansas reservoirs.
Chemistry of reservoir sediment is of
concern because of 1) effects on reservoir
water quality during the dredging process,
particularly if the reservoir is a primary
drinking-water source, and 2) effects of
remobilized metals, trace elements, or
nutrients on aquatic and land biota and
water resources. If large quantities of chemical constituents of concern are present,
potential chemical effects of land-applied
sediment can be important for elements
such as lead, zinc, chromium, cadmium,
arsenic, or selenium and nutrients such as
nitrogen and phosphorus.
Estimates of chemicals deposited in
sediments from eight Kansas reservoirs
range from approximately 9,720 to 3
million lb/year of phosphorus; 19,000 to
7.6 million lb/year of nitrogen; 96 to 2,700
lb/year of selenium; 620 to 58,000 lb/year
of arsenic; 330 to 85,000 lb/year of lead;
1,400 to 366,000 lb/year of zinc; and 340
to 100,000 lb/year of copper (Appendix
A-1). These trace elements and nutrients
may be mobile or immobile when sediment
is moved from reservoirs to land. However,
these estimates imply that large quantities
of trace elements and nutrients are associated with reservoir sediment and may cause
problems if land application is used as a
sediment disposal method (see Appendix
A-2 for estimates of total sediment and
chemical loads in eight reservoirs).
Overview of Dredging
and Sediment Disposal
Options
Dredging is used to remove sediments from
lakes or reservoirs to restore storage area,
reduce eutrophication, remove aquatic
plants and algae buildup along lake edges,
and improve water quality by reducing
nutrient sources, especially phosphorus
(Ryding, 1982; Darmody et al., 2004; Sigua,
2005). Most literature on dredging deals
with harbor or canal remediation in areas
of high shipping traffic, such as the Great
Lakes or oceanic ports, and many studies involve toxic chemical concentrations
higher than those found in Kansas environments. The keys to removing polluted
sediments are minimizing disruption of
Sedimentation in Our Reservoirs: Causes and Solutions
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the sediment-water interface, containing
polluted, dredged materials until they are
remediated, and treating water accompanying the sediment (Peterson, 1982). Prior to
dredging, sediment should be characterized
for deposited thickness, particle size, bulk
density, organic and nutrient content, and
potential contaminant concentrations.
can seal the diked area, preventing draining
and delaying remediation (Dunst, 1987).
Lack of storage space can cause flooding
overflow from the CDF, and excess nutrients, sediment, and other contaminants
could return to the lake if the CDF is
located nearby.
Typically, dredged sediment is disposed of
by either placement in a confined disposal
facility (CDF) or application to agricultural
land, grasslands, brownfields, strip mines,
highway borders, and other areas, provided
that the chemistry of the sediment will not
harm the soil or environment (Skogerboe
et al., 1987; Darmody et al, 2004; Kelly et
al., 2007). CDFs are used for contaminated
sediments, those with metal concentrations
above environmental toxicity levels recommended by the USEPA (1997), and in
areas with river or lake contamination from
mining or industrial waste (Darmody et al.,
2004).
Issues associated with land application of
dredged sediment include compatibility
of sediment with the host soil with respect
to leaching, stability of the land for use of
heavy machinery, and overland flow of sediments and contaminants back to the lake
(Cooke et al., 1986). Land application of
dredged sediments is frequently used when
chemistry of the sediments is not potentially toxic to aquatic or plant life and areas
are located away from the dredged lake.
Dredged material that has low metal or
contaminant toxicities generally is suitable
for various land uses including strip mine
reclamation, brownfields, construction
areas, agriculture, forestry, wetland areas,
parks, beaches, and landscaping (Darmody
and Marlin, 2002; Machesky et al., 2005).
Confined Disposal Facilities
(CDFs)
CDFs are diked enclosures in which sediment or sediment slurries are deposited
to permit water mixed with the sediment
to leach or evaporate. Disposing dredged
sediment in a CDF can be problematic
if the facility is too small. Factors such
as sediment volume, water content, and
underlying soil type need to be considered
in the CDF design phase (Myers, 1996).
Freshwater sediments have a high water-tosediment ratio and are slow to settle. Slow
settling can cause diked areas to fill faster
because of the volume of water accumulating with the sediment; usable retention area
decreases until water has either evaporated
or drained from the sediment (Peterson,
1982). Settling of fine-grained sediments
104
Sedimentation in Our Reservoirs: Causes and Solutions
Land Application
Work by Kelly et al. (2007) showed that
mixing dredged sediment from the Illinois
River with wastewater biosolids increased
organic and nutrient content of the sediments, had a positive effect on microbial
biomass of the soil, and resulted in usable
farmland. In another study, using manure
as an amendment to dredged sediments
helped retain metals in the sediment and
enhanced removal of metals by plants (i.e.,
phytoremediation; Skogerboe et al., 1987).
Work by Sigua et al. (2004a, 2004b)
showed that sediments from Lake Panasoffkee, FL, had 82% calcium carbonate
content. When combined with agricultural
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soil, these sediments had the same favorable effects as liming, including enhanced
phosphorus and micronutrient availability, nitrification, nitrogen fixation, and
soil physical conditions (Nelson, 1981).
All trace element contents of reservoir
sediments were below USEPA sediment
toxicity values (USEPA, 1997); therefore,
agricultural or livestock industries could
use the sediments to produce forages. In
addition, sediment properties improved the
level of local soil compaction and structure.
One Sigua et al. (2004b) study showed that
grass yield from amended fields was greater
than that from control sites, and forage
from amended fields had increased crude
protein content. These studies show that
freshwater sediments with low levels of
trace elements can be used by agricultural
industries with no obvious side effects.
elements currently stored in and annually
moving into Kansas lakes are large (Appendices A-1, A-2). Chemistry, soil physical
properties, and potential contaminant hazards of dredged material must be evaluated
prior to land disposal (Cooke et al., 1986;
USACE, 1987).
A study by Darmody and Marlin (2002)
indicated that dredged, fine-grained lake
sediment is suitable for agriculture if
allowed to drain sufficiently to support
heavy machinery. In that study, dredged
sediment was applied to nearby agricultural
land. Heavy metal composition of the soil
was below USEPA toxicity values (USEPA,
1997), and nutrient values were sufficient
to encourage plant growth and survival.
Bramley and Rimmer (1988) showed that
with proper remediation by drainage,
mixing with manure or biosolids, and use
of phytoremediation and other methods,
contaminated Rhine River sediments were
usable for landscaping, agriculture, and
other material-fill situations.
Resuspension also can cause water-quality
problems, particularly in Kansas where
many rivers, streams, and lakes have Total
Maximum Daily Loads (TMDLs) of suspended sediments and nutrients above the
recommended limits adopted by the Kansas
Department of Health and Environment
(2008). Chemical effects associated with
fine-grained sediment include: 1) adsorption of phosphorus species to fine sediment
particles and subsequent transport into
lakes, 2) recycling of phosphorus in water
with potential increased eutrophication if
sediment is disturbed, 3) increased total
inorganic nitrogen concentrations in water
from conversion of ammonium-nitrogen in
the sediment to nitrate-nitrogen in water,
and 4) release of adsorbed trace elements
because of an environmental change from
an anaerobic (low oxygen) to an aerobic
(oxygenated) environment (Barnard, 1978;
Cooke et al., 1986).
Economics of dredged sediment transportation and availability of sufficient
land for disposal must be addressed before
land application can be used in Kansas.
Estimated volumes of sediment and trace
Environmental Effects of
Dredging Sediment
Much of the sediment in freshwater lakes
is fine grained, generally silt and/or clay.
Dredging this type of material, regardless
of the depth of sediment removed, results
in resuspension of some sediment. Resuspended sediment can interfere with light
and food needs of benthic communities and
is a major concern associated with reservoir
dredging.
Sedimentation in Our Reservoirs: Causes and Solutions
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Physical Effects of
Reusing Dredged
Sediment on Land
Soil physical properties determine how
liquids, gases, and heat move through a soil
profile, thereby affecting internal drainage
and aeration of the soil profile. However,
sediment that is dredged from reservoirs
is not soil and lacks many of the properties present in natural soils (SSSA, 2001).
Vermuelen et al. (2003) estimated that 70%
(by volume) of recently dredged sediment
is water. To use dredged sediment on land
for growing vegetation, several physical
properties must be modified. This section
provides a brief review of selected physical
properties that should be considered prior
to land application of dredged, dewatered
sediments.
Particle-Size Distribution
Particle-size distribution, also referred to
as texture, influences sediment use. For
example, sandy sediments can be used in
beach construction, whereas clayey material might make a liner material for ponds
or lagoons. Sediment with a loamy texture
often is the best choice for supporting
vegetation, whether in cropland, residential
areas, or reclamation of degraded land.
Reservoir sediment reflects local geography
and soils but generally is composed of finergrained sizes such as silt and clay (Darmody
and Marlin, 2002).
Organic matter is important for supporting
vegetation; it provides nutrient storage and
cycling (cation exchange capacity), waterholding capacity (important in coarser
sediments), and increased aggregation
(ability for particles to combine; Tisdall
and Oades, 1982). Sediment with minimal
organic matter content has reduced useful106
Sedimentation in Our Reservoirs: Causes and Solutions
ness. However, organic matter content can
be improved by adding amendments such
as compost, waste-treatment biosolids, or
manure.
Applied sediment should have a texture
similar to that of the original underlying
material; a layered system of contrasting textures is undesirable. The different
textures affect sediment-soil permeability
and movement of water vertically and horizontally in both unsaturated and saturated
conditions (Hillel, 1998). Incorporating
organic amendments such as compost
decreases textural differences and improves
overall permeability (Burden and Sims,
1999).
Soil Strength
Soil strength is the measure of the capacity of a soil mass to withstand stresses.
Soil strength is most affected by changes
in soil-water content and bulk density,
although other factors including texture,
mineralogy, cementation, cation composition, and organic matter content also affect
soil strength (SSSA, 2001). In agricultural
settings, increases in strength and bulk
density usually result in decreased plant
emergence, decreased soil aeration, and
increased compaction (Unger and Kaspar,
1994). In Florida pastures, incorporating
carbonate-rich, dredged sediment increased
overall soil permeability and reduced soil
compaction (Sigua et al., 2006). Freshly
deposited, dredged sediments usually have
low soil strength and need modification by
amendments, plants, and/or drainage to
facilitate their future use (Darmody and
Marlin, 2002). At sites in Illinois, sediment
soil strength increased after addition of
amendments, use of water-loving plants,
and drainage of excess water (Darmody and
Marlin, 2002).
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Structural Properties
Structure is the arrangement of individual
soil particles into aggregates, groups of
primary soil particles that cohere more
strongly to each other than to other surrounding particles (SSSA, 2001). Soil
structure can be difficult to assess and
quantify. However, soil structural characteristics are important because they control
movement of gases and solutes as well as a
variety of other biological, chemical, and
physical processes (for specific examples, see
Diaz-Zorita et al., 2002, p. 5). Immediately
after dewatering, dredged sediment contains no structure or aggregation.
Soil aggregation is a function of organic
matter content, clay mineralogy, concentration and ratio of ions, vegetation type
and abundance, and soil biology (Bronick
and Lal, 2005). Soil aggregates develop as
a function of five soil-forming factors: climate, organisms, parent material, relief, and
time (Jenny, 1941). Aggregate stability is
the ability of an aggregate to retain its shape
when wetted. The degree of both structure
and aggregate development affect entry
and movement of water and air through
soil. Plants cause changes in soil structure
through penetration of roots, modification
of the soil-water regime, enmeshment of
soil particles and micro-aggregates by roots,
and deposition of carbon below ground;
microbes alter soil structure by increasing
soil stability (Angers and Caron, 1998).
Soil aggregates and soil structure develop
with time, vegetative growth, and wettingdrying and freeze-thaw cycles. Presence of
water-stable aggregates decreases soil erodibility (Tisdall and Oades, 1982).
Initial development of internal drainage
is referred to as conditioning or ripening. Vermuelen et al. (2003) categorized
the development of sediments
into soil into three processes:
physical, biological, and chemical.
The physical process of forming
structure occurs through desiccation
and the resulting formation of cracks.
During this process, sediment bulk
density decreases and void space increases,
thereby increasing internal drainage of the
sediments. However, physical formation of
structure occurs only in sediments with clay
content greater than 8% and/or organic
matter content greater than 3% (Vermuelen et al., 2003).
Growing aquatic plants in draining
sediment aids development of physical
properties by creating root cavities. These
cavities allow oxygen to penetrate soil,
leading to microbe growth and increased
aggregation and permeability (Loser and
Zehnsdorf, 2002). Terrestrial plants are
introduced naturally from seeds transported by wind and birds (Vermuelen et
al., 2003). Soil fauna such as bacteria, fungi,
and earthworms decompose fresh organic
matter and produce humus, a more stable
form of organic matter that increases binding of soil particles into aggregates.
Surface soils containing stable aggregates
resist formation of a surface soil crust and
allow water to enter (infiltration) and move
through (permeability) the soil profile.
Darmody and Marlin (2002) showed that
the rate of aggregate formation in dredged
sediments used for agriculture became
similar to that of native soils over a 10-year
period.
Exposure of dredged sediments to air is
termed chemical ripening. Exposure to oxygen results in oxidation of metals occurring
as reduced species such as iron or selenium
Sedimentation in Our Reservoirs: Causes and Solutions
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and either decreased or increased mobility
of these elements. Also, mineral weathering of primary soil minerals can increase
secondary (clay) minerals and change the
cation exchange capacity, thereby affecting
soil solution concentrations (Vermuelen
et al., 2003). Chemical changes affecting
selected trace elements and nutrients are
described in more detail in the remainder of
this paper.
Sediment Chemistry
Studies in Kansas
Reservoirs
Studies of sediment chemistry in Kansas
reservoirs are mainly limited to studies
performed by the USGS (2008a). These
studies assessed a variety of nutrients
and trace elements to determine which
reservoirs have potential contamination
problems. Information obtained from these
studies provides a background database that
can be used for future comparison of trace
elements if reservoirs are dredged and sediment is disposed of by land application.
The USGS sediment data presented in this
review are from eight of 24 federal reservoirs and 14 of the many freshwater lakes in
Kansas. The studies provide information on
measured concentrations, potential nutrient sources, trace elements, and pesticides
and the volume of sediment, trace elements,
and nutrients deposited at selected lakes
(USGS, 2008a). Results are summarized
in Appendices A-1, A-2, A-3, B-1, and B-2
and cited throughout this paper.
Sediment quality guidelines adopted by
the USEPA allow assessment of reservoir
sediment with respect to level-of-concern
concentrations of various trace elements
and organochlorine compounds, including
108
Sedimentation in Our Reservoirs: Causes and Solutions
polychlorinated biphenyls and several pesticides (Smith et al., 1996; USEPA, 1997;
USEPA, 2004). Two such level-of-concern
concentrations are the threshold-effects
level (TEL) and the probable-effects level
(PEL). The TEL represents the concentration below which toxic biological effects
rarely occur. In the range between the TEL
and PEL, toxic effects occasionally occur.
The PEL represents the concentration
above which toxic effects usually or frequently occur. These guidelines are used by
the USEPA as screening tools and are not
enforceable (Sigua et al., 2004a; USEPA,
2004).
As of 2006, the USGS used a combination
of the USEPA level-of-concern concentrations and the consensus-based sediment
quality guidelines developed by MacDonald
et al. (2000), which consist of a thresholdeffect concentration and a probable-effect
concentration. Much of the USGS
sediment work prior to 2006 reported levelof-concern concentrations using TELs and
PELs; thus, those levels are reported in this
paper to provide a level of comparison.
Of the trace elements and pesticides
evaluated in Kansas lakes, six contaminants
typically exceeded TELs: arsenic, chromium, copper, lead, nickel, and zinc (Table
1). No TEL is established for selenium. In
addition, DDE, a daughter product of the
pesticide DDT, was measured in a number
of the tested reservoirs and lakes. Typically,
pesticides concentrations are less than
the TELs (USGS, 2008a). Most national
studies had similar results, with variation
occurring because of different metal sources
and varying depths of collected samples.
Christensen and Juracek (2001) observed
an increase in arsenic, selenium, and stron-
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Table 1. Kansas reservoirs with trace elements above USEPA TELsa
Trace Elements and TELs
Arsenic Chromium Copper
Lead
Reservoir
Nickel
(7.24 mg/kg) (52.3 mg/kg) (18.7 mg/kg) (30.2 mg/kg) (15.9 mg/kg)
Swanson
Harlan County
Milford
Kirwin
Webster
Waconda
Tuttle Creek
Perry
Centralia
Mission
Pony Creek
Cheney
Lake Afton
Hillsdale
Cedar Lake
Lake Olathe
Gardner
Bronson
Crystal
Otis Creek
a
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
o
o
o
x
Zinc
(124 mg/kg)
x
x
x
x
x
x
x
x
x
x
x
o
x
x
x
x
x
x
x
x
o
x
x
x
x
x
x
x
x
x
x
x
x
Data source: USGS (2008a)
ο = Value above USEPA PEL
TEL = threshold-effects level
PEL = probable-effects level
tium in several reservoirs in the Republican
and Solomon River basins. The increase
might be related to increased irrigation
throughout the two basins. Arsenic and
copper values often exceeded TELs, but
overall, other trace elements (i.e., cadmium,
nickel, lead, zinc, and chromium) tested in
the basins did not.
Empire Lake in Cherokee County in southeastern Kansas is the most contaminated
lake examined by the USGS in Kansas
(Juracek, 2006). This lake is affected by
lead and zinc mining that occurred in the
tri-state area of Missouri and Kansas beginning in 1870 (Brosius and Sawin, 2001).
Concentrations of lead, zinc, and cadmium,
an element that occurs with lead and zinc,
are above PELs (Appendix B-1). Concentrations decreased over time, but present
surface sediment concentrations are still
above PELs of concern for aquatic life.
Other Kansas reservoirs have various
metals above TELs but not PELs. In most
Kansas reservoirs and lakes studied by the
Sedimentation in Our Reservoirs: Causes and Solutions
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USGS, arsenic, copper, and nickel
were measured above TELs; at
a few of the lakes and reservoirs,
chromium, lead, and zinc were
measured above TELs; and at all
the reservoirs and lakes, cadmium
and mercury were below TELs (USGS,
2008a). Use of total concentrations implies
the amount of constituent measured in the
sediment. It does not imply that this total
quantity is available for mobility or use by
plants if sediment is dredged. However,
total quantity does report the amount of
the constituent that is stored and could be
mobilized under certain chemical conditions or change when sediment is dredged
and removed from the lake environment.
Chemical Changes in
Dredged Sediment
Much literature on dredged-sediment
disposal on upland areas describes chemical
changes that occur when sediment from the
bottom of a lake is brought into an oxidizing situation. Many studies focused on
one or more trace elements, nutrients, and
organic matter. This section of the paper
focuses on trace elements typically found
in Kansas reservoirs above TELs: arsenic,
chromium, copper, lead, nickel, and zinc
(Table 1). Potential sources and effects of
mercury, methylmercury, and selenium are
also included because of possible biogeochemical effects of these compounds on fish
and other aquatic life.
Work by Delfino et al. (1969) and Nrigau
(1968) showed a strong relationship
between water depth and increased concentrations of nitrogen, phosphorus, iron, and
total- and sulfide-sulfur in Lake Mendota,
WI. This trend was mirrored in observations made by Iskandar and Keeney (1974),
110
Sedimentation in Our Reservoirs: Causes and Solutions
who also found that post-cultural sediment
(from 1818-1970) showed increased levels
of chromium, copper (related to the use of
copper sulfate for algal control in the lakes),
lead, and cadmium in the more recent
sediments (1970s) of five hard-water and
five soft-water Wisconsin lakes. Sources for
these metals were sewage effluent, chemical
treatment for algae, and vehicular traffic;
trace-element concentrations increased
overall because of human activities.
Chemical results from selected USGS studies conducted in Kansas (USGS, 2008a)
are summarized in Appendices A-1 and
A-2. Appendix A-3 shows the mercury
concentration in the few lakes where it
was detected, and ranges of concentrations
observed in cores from selected lakes are
presented in Appendices B-1 and B-2.
Reduction-Oxidation
Chemistry
Reduction-oxidation (redox) potential describes the chemical reactions in
sedimentary environments that occur
with changes in dissolved oxygen levels.
When dissolved oxygen in reservoir sediments decreases to a very small amount,
redox potential decreases and the system
is described as anoxic or anaerobic. Some
elements such as arsenic, iron, manganese,
and phosphorus are more mobile in an
anaerobic environment and can move with
pore water. If sediments become exposed
to oxygen, these elements can become
oxidized and coprecipitate with other elements, forming compounds such as iron- or
manganese-hydroxides or oxides (Forstner,
1977). Coprecipitated oxides and hydroxides also can serve as adsorptive surfaces,
thereby increasing adsorption of other
potential contaminants (e.g., phosphorus).
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Increased redox potential (i.e., more oxygen
is available) can result in decomposition
of organic material and transformation of
redox-sensitive elements, such as copper,
zinc, cadmium, and nickel, to oxidized
states. These dissolved metals can coprecipitate as oxides or oxyhydroxides (DeLaune
and Smith, 1985; Brannon et al., 1994;
Rognerud and Fjeld, 2001; Davidson et
al., 2005). Increased aeration of silt/clay
sediment in a Mississippi reservoir resulted
in decreased concentrations of copper, zinc,
cadmium, and nickel in water and increased
coprecipitation of these elements with iron,
forming solid amorphous oxides (Davidson
et al., 2005). Oxidizing conditions generally favor metal insolubility, and reducing
conditions favor metal solubility or mobility (Miao et al., 2006).
Organic Carbon Cycling
Rate and extent of organic matter cycling
in a lake help determine oxygen levels and
redox-potential levels in the water column
and sediments (Avnimelech et al., 1984).
Lake sediments generally contain greater
concentrations of organic matter and
nutrients than the overlying water. Organic
matter decomposition also contributes to
nutrient recycling in sediment and water.
During dredging, microbial transformations of nutrients to more mobile forms
and trace elements to less mobile forms
occurs if sufficient organic carbon is present and the sediment environment changes
from anaerobic to aerobic.
In cores, organic carbon often decreases
with increasing depth, indicating organic
matter degradation and changes in sediment chemistry with depth. However, the
organic-carbon concentration in several
Kansas lakes is uniform throughout the
profile, suggesting rapid sedimentation
with few chemical or biological changes
with depth (Callender, 2000; Mahler et al.,
2006; Juracek, personal communication,
2007).
Estimated total organic carbon loads
from the Kansas lake studies included in
this literature survey range from 19,300
to 928,000 tons (Appendix A-2). Total
organic carbon measured from specific
cores ranged from 0.7 to 3.9 mg/kg in
many of the lakes; Webster, Kirwin, and
Waconda had unusually high values ranging from 3,440 to 16,200 mg/kg (Appendix
B-1). This large volume of organic carbon
suggests that microbial transformations of
trace elements are likely if dredging is used
as a remediation method in Kansas. Because
availability of organic carbon and oxygen
affects mobility of trace elements and nutrients, potential changes that could occur in
Kansas require further study.
Contaminants of Interest
Final use of land where dredged sediment is applied depends on the amount
of contamination in the sediment. When
contaminants are present at high levels, vegetative growth on the deposited sediment
can be harmed or completely restricted.
Sediment in a number of Kansas reservoirs
is contaminated with trace elements and
nutrients, but contaminant levels are
relatively low compared with other parts of
the country.
Lead, zinc, copper, cadmium, arsenic,
selenium, nickel, dissolved salts, DDE, and
nutrients are the contaminants of most
interest in Kansas lake sediments. Lead,
zinc, copper, cadmium, arsenic, and nickel
are found above TELs for sediment qualSedimentation in Our Reservoirs: Causes and Solutions
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ity in Kansas (USGS, 2008a). These trace
elements, DDE, and the nutrient content
of sediment are of concern because of
resuspension of sediment (Peterson, 1982),
effects on drinking water quality, and
ecological effects if sediment is applied on
agricultural land (Skogerboe et al., 1987;
Darmody et al., 2004; Kelly et al., 2007).
Mercury is also of concern because it has
potentially deleterious biological effects if
resuspended with sediment or dissolved in
lake water during dredging.
toxic to fish; it also bioaccumulates, which
can affect human health.
Mercury. Atmospheric deposition,
agricultural chemicals, power-plant and
waste-incineration emissions, and decomposition of terrestrial litter are potential
sources of mercury in Kansas. Forest fires as
well as industrial sources such as mining or
coal-fired power plants can also add mercury to the environment (Wiedinmyer and
Friedli, 2007).
Organic carbon has a strong connection
to presence of mercury or methylmercury
in the environment. Several studies show
that water movement through wetlands
and peat bogs, which have relatively high
dissolved organic carbon concentrations,
increases methylmercury formation and
transport (Jackson, 1989; Kelly et al., 1995;
Krabbenhoft et al, 1995; Rudd, 1995).
Methylation increases when sulfate and
salinity levels are low and concentrations
of organic fermentation products are high
(Kongchum et al., 2006). Jackson (1989)
demonstrated that quantity and type of
clay minerals, oxides, and humic matter
also affects methylmercury production in
sediments.
Total mercury was measured in only a few
of the Kansas lakes and reservoirs evaluated
by the USGS (Appendix A-3). All mean
and median values were below the USEPA
TEL of 0.13 mg/kg, except Empire Lake
in southeast Kansas, which had one core
with values above the TEL (Juracek, 2003,
2004). Several lakes in northeast Kansas
had mean annual net loads for mercury
ranging from 0.39 to 317 lb/year (Juracek,
2003, 2004; Juracek and Mau, 2002).
Although the majority of lakes studied
had mercury values below USEPA TELs,
because of mercury’s potential ecological
effects and the presence of measurable
mercury in some lakes, sediment should be
tested for mercury prior to dredging.
Methylmercury. Methylmercury is a
neurotoxin that is harmful to both aquatic
and terrestrial biota. This compound is
112
Sedimentation in Our Reservoirs: Causes and Solutions
Methylmercury is formed by sulfate-reducing bacteria in anaerobic environments,
particularly lake sediments and wetlands.
Bacteria metabolize mercury into methylmercury. Sources of methylmercury
include mercury sources mentioned previously as well as terrestrial runoff and direct
atmospheric deposition onto a lake surface
(Rudd, 1995).
Land uses such as agriculture, forestry, or
mining also affect occurrence of methylmercury in surface water, sediments,
and fish (Brumbaugh et al., 2001). The
increased quantities of plant matter,
organic carbon, and sediment transported
to rivers or lakes during storms enhance
the potential formation of methylmercury
within a lake or river system (Rudd, 1995).
Most sampled lakes in Kansas had mercury
values below the TEL, but methylmercury
sediment-core pore waters were not evaluated. Because a large volume of organic
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carbon and sediment enters Kansas lakes
and reservoirs, it is likely that methylmercury could form in the sediment or mercury
could dissolve in lake water if sediment is
resuspended during dredging. This issue
warrants further research.
drainage. Lead needs to be evaluated prior to dredging because
it has potential environmental
effects and occurs, sometimes at
high levels, in most lakes studied in
Kansas.
Lead. Lead concentrations in lake and
river sediment cores are directly related
to exhaust from vehicles that use leaded
gasoline (Callender and Van Metre, 1997;
Machesky et al., 2005). A study of 10
small lakes in Kansas (Juracek and Ziegler,
2006) showed strong relationships between
observed lead concentration and traffic
volume, reservoir size, and basin size. Lead
profiles showed an increasing concentration trend related to leaded gasoline use
from 1940 to 1970 and a decreasing trend
after lead was removed from gasoline in
1972. Over time, lead concentrations in
sediment might return to baseline conditions. However, the buried, high lead
concentrations (often above both TELs
and PELs) could cause future concerns if
reservoirs are dredged, dams are removed,
or dams fail. Zinc. Zinc is present at levels between
TELs and PELs in Kansas lakes (Table 1,
Appendices A-1, A-2, B-2). At high concentrations, zinc causes a range of biological
and toxic responses in a variety of aquatic
organisms (Mullis et al., 1996; Lefcort et
al., 1998). Atmospheric deposition of zinc
occurs from metal production, waste-incineration and fossil fuel emissions, phosphate
fertilizer use, and cement production.
Water-contamination sources include deicing salts; automotive exhaust; and wear
and tear of rubber tires, brake linings,
and galvanized metal parts (Councell et
al., 2004). There is a strong relationship
between traffic density and zinc concentrations in sediment cores in Georgia and
Florida lakes (Callender and Rice, 2000).
The estimated mean annual net lead load
of lead for Empire Lake is 6,500 lb/year,
and approximately 650,000 lb of lead have
been deposited in the lake since the dam
was closed (Appendices A-1, A-2). Lead
concentrations in younger sediments have
decreased over time, but the present surface
sediment concentrations are still above
PELs of concern for aquatic and plant
life (Appendix B-2). Lead concentrations
in lake sediments can remobilize if pH
and oxygen levels change (Telmer et al.,
2006). If Empire Lake is dredged, lead in
sediments could affect the environment
because of chemical changes in the sediment caused by exposure to oxygen and
Estimated annual zinc loads for the Kansas
lakes studied range from 1,363 to 366,000
lb/year, and estimated total chemical loads
of zinc range from 84,506 to 11.7 million lb
(Appendices A-1, A-2). Ecological effects of
and phytoremediation possibilities for zinc
should be evaluated prior to dredging.
Arsenic. Arsenic is of environmental concern in freshwater lakes, surface water, and
groundwater (Huang et al., 1982). Potential sources of arsenic include past use of
arsenical pesticides (banned in the 1970s),
smelters, coal-fired power plants, erosion
caused by intensive land use, leaching from
lumber pressure treated with chromated
copper arsenate, mineral weathering, high
evaporation rates in arid environments,
Sedimentation in Our Reservoirs: Causes and Solutions
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and irrigation-return flows (Huang et al.,
1982; Welch et al., 2000; Rice et al., 2002;
Smedley and Kinniburgh, 2002). Arsenic
is strongly sorbed to surfaces of aluminum
and iron oxides and edges of clay minerals
under oxidizing conditions (Kneebone and
Hering, 2000).
Arsenic in solution exists as either arsenite
(As+3, toxic form) or arsenate (As+5, nontoxic form). In a laboratory experiment
conducted by Oscarson et al. (1980),
manganese and iron compounds of clay
particle size (0.002 mm) in sediment
affected oxidation of arsenite (As+3) to
arsenate (As+5). This suggests that presence of manganese and iron compounds in
freshwater sediments could help detoxify
arsenic concentrations.
Arsenic in lake-sediment pore water is
generally present as arsenite, which is toxic
in anaerobic conditions. Dredging permits
mixing of arsenite in the water column
until oxidation or sorption remove it or
render it nontoxic (Brannon and Patrick,
1987). Disposal of arsenic-rich sediment
in a CDF could result in pulses of toxic
(arsenite) and nontoxic (arsenate) forms of
arsenic in leachate depending on whether
oxidizing or anaerobic conditions are present. Precipitation reactions occurring at the
site could result in pH changes at both the
surface and at depth, which could affect the
form of arsenic present in sediment (Brannon and Patrick, 1987; Kneebone and
Hering, 2000).
Arsenic is an issue in Kansas lakes where it
is present above TELs (Table 1, Appendix
B-2). In lakes where arsenic was measured,
annual chemical loads ranged from 619 to
57,800 lb/year with total chemical loads
ranging from 24,760 to 1.8 million lb
114
Sedimentation in Our Reservoirs: Causes and Solutions
(Appendices A-1, A-2). Arsenic should be
evaluated prior to using land application of
dredged material for remediation.
Selenium. Selenium is derived primarily
from weathering of rocks. In the northern
Great Plains, Cretaceous-aged Pierre Shale
is a primary source of seleniferous soils.
Other sources include volcanic activity
and fossil fuel combustion. Selenium often
occurs in colloid- and sulfide-rich lake and
river sediments and in organic- and ironrich soil layers. Selenium is more likely to
leach in sediments with low organic matter
and clay content and an alkaline pH (above
7) and in calcareous soils (Sarma and Singh,
1983). Processes that affect selenium transport include soil leaching, groundwater
transport, metabolic uptake and release by
plants and animals, sorption and desorption, chemical or bacterial reduction and
oxidation, and mineral formation (Juracek
and Ziegler, 1998).
Selenium is generally inert under reducing
conditions. In an oxidized environment,
several forms of selenium exist: selenate (Se+6),
selenite (Se+4), and an organic form of selenium (Se-2) (USEPA, 1996). Because selenium can coexist in several forms, the USEPA
set the toxicity limit for total selenium and
not separate forms of the element. Selenium
concentrations equal to or greater than 4.0
mg/kg in sediment are of concern for fish
and wildlife because of food-chain bioaccumulation (Lemly and Smith, 1987).
Selenium is of particular concern in rivers
and lakes in western Kansas because of
geologic sources from the Pierre Shale and
other Upper Cretaceous strata and from
evapoconcentration of irrigation water.
Estimated mean annual net chemical loads
deposited in the few Kansas lakes where
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selenium was measured range from 96 to
2,730 lb/year with estimated total loads in
bottom sediments ranging from 3,856 to
87,360 lb (Appendices A-1, A-2, B-2).
If selenium-containing dredged soils are
land applied, selenium likely will be immobilized in soils amended with manure or
compost because it binds well with organic
matter and clays (Geering et al., 1968). The
potential for selenium to become remobilized in lake water during the dredging
process is of more concern. If dredging
occurs in lakes used for public drinkingwater supply, the USEPA drinking-water
limit of 0.05 mg/L selenium will need to be
carefully monitored.
In a number of Kansas lakes, copper values
exceeded the TEL; in a few lakes, cores
showed copper values above the PEL (Table
1, Appendix B-2). Estimated mean annual
net loads of copper in Kansas lakes range
from 336 to 100,000 lb/year; estimated
total loads range from 19,845 to 3.2 million
lb (Appendices A-1, A-2, B). Copper can
pose disposal problems because changes
from an anaerobic to aerobic environment
during dredging or when sediment is deposited on land can permit remobilization
(Baccini and Joller, 1981).
Copper. Copper is a micronutrient and
toxin. It strongly adsorbs to organic matter, carbonates, and clay, which reduces
its bioavailability. Copper is highly toxic
in aquatic environments and affects fish,
invertebrates, and amphibians; all three
groups are equally sensitive to chronic
toxicity (USEPA, 2007a). Cu+2 is the oxidation state of copper generally encountered
in water. When Cu+2 occurs in the environment, the ion typically binds to inorganic
and organic materials contained in water,
soil, and sediments (ATSDR, 2004).
Cadmium. Sources of cadmium are generally associated with industrial processes,
wastewater, or emissions. Atmospheric
sources include waste incineration, fossil
fuel combustion, mining, and smelting of
zinc ore for galvanized roofing (Mahler
et al., 2006). Additional sources include
application of phosphate fertilizers, biosolids, or manure on fields; weathering of
rocks and soils; and leaching from landfills.
Major factors governing cadmium speciation, adsorption, and distribution in soils
are pH, soluble organic matter content,
hydrous metal oxide content, clay content
and type, presence of organic and inorganic
ligands, and competition from other metal
ions (UN, 2006).
The most obvious copper source, particularly in Kansas lakes, is use of copper sulfate
to control algal blooms. The compound is
used in smaller ponds and lakes, where algae
problems are most severe (Peterson and
Lee, 2005; D.E. Peterson, KSU Agronomy
Dept., personal communication, 2007).
Copper in lake sediments also comes from
leaching from animal waste and pressuretreated lumber, atmospheric deposition
by precipitation, and road wear of brake
linings (Rice et al., 2002).
Relative to more industrialized areas of
the country, Kansas lakes have minimal
cadmium concentrations that generally are
below the TEL (Appendix B-2). Estimated
mean annual net loads of cadmium in
selected Kansas reservoirs range from 3.2
to 1,520 lb/year, and stored quantity
estimates range from 171 to 48,640 lb
(Appendices A-1, A-2). However, remobilization of cadmium from sediments in lakes
with higher concentrations, such as Empire
Lake in southeastern Kansas, can affect
Sedimentation in Our Reservoirs: Causes and Solutions
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aquatic life and plants (USEPA,
2001).
Chromium. Chromium is found
in rocks, animals, plants, soil, and
volcanic dust and gases. The concentration of naturally occurring chromium
in U.S. soils ranges from 1 ppm to 2,000
ppm (USEPA, 2007b). Chromium is present in the environment in several different
forms. Its valence states range from +2 to +6,
but in natural environments, it is generally found as trivalent chromium (Cr+3)
or hexavalent chromium (Cr+6). Trivalent chromium occurs naturally in many
fresh vegetables, fruits, meat, grains, and
yeast and is added to vitamins as a dietary
supplement. However, release of Cr+3 to
the environment can be toxic because of
conversion to Cr+6. Hexavalent chromium
is most often produced from industrial
sources such as coal-fired power plants, steel
making, leather tanning, chrome plating,
dyes and pigments, and wood preservation
and can indicate environmental contamination. This form of chromium exists in
oxidizing conditions and can move through
soil to underlying groundwater. Hexavalent
chromium is the more toxic form and is a
threat to aquatic life and human health if
ingested (ATSDR, 2001).
Chromium enters air, water, and soil
mostly in the trivalent (Cr+3) and hexavalent (Cr+6) forms. In air, chromium
compounds are present mostly as fine dust
particles that eventually settle over land and
water. Chromium concentrations are generally low, but the metal often concentrates
in hydrous manganese and iron oxides or
adsorbs to clay-size particles in sediment.
The clay-size fraction is the particle size
most likely to be transported to lakes,
particularly during floods or in areas where
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Sedimentation in Our Reservoirs: Causes and Solutions
streambank erosion is high (Whittemore
and Switek, 1977; ATSDR, 2001).
Chromium was detected at concentrations
exceeding the TEL at some Kansas reservoirs (Table 1; Appendix B-2). Estimated
mean annual net loads of chromium for
selected Kansas lakes range from 864 to
302,000 lb/year; estimated total chemical
loads range from 52,740 to 9.6 million
lb (Appendices A-1, A-2). Because of the
potential for environmental and human
harm, chromium in lake sediment needs
to be evaluated prior to dredging and land
application.
Nickel. Some anthropogenic sources of
nickel include oil combustion, oil-burning
and coal-fired power plants, trash incinerators, treated wastewater, car exhaust,
abrasion of nickel-containing automobile
parts, and animal waste (Lagerwerff and
Specht, 1970; ATSDR, 2005). Because of
the density of agricultural land use near
lakes and reservoirs, the most likely anthropogenic sources of nickel for Kansas lakes
are wastewater and animal waste.
Nickel strongly adsorbs to soil or sediment
containing iron or manganese. However,
nickel becomes more mobile if water or
sediment pH becomes more acidic, such as
in an anaerobic environment. Nickel does
not appear to accumulate in fish or other
animals used as food but is a known carcinogen and toxic to humans and animals
when maximum tolerable amounts are
exceeded (ATSDR, 2005; LENNTECH,
2008).
Nickel occurs at levels between TELs and
PELs in Kansas lakes (Table 1; Appendices
A-1, A-2, B-2). Estimated mean annual net
loads range from 355 to 152,000 lb/year;
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estimated total net loads range from 22,000
to 4.8 million lb. Phytoremediation possibilities for nickel should be evaluated prior
to dredging.
DDE and DDD. DDE and DDD are
degradation products from the pesticide
DDT, which was used extensively in agriculture during the 1950s and 1960s until
it was banned in 1972 (USGS, 2008a).
Sources of DDT, DDE, and DDD include
runoff from agricultural fields and deposition on lakes, streams, and land of soil
particles carried by wind (Rapaport et al.,
1985).
Detection of DDE and DDD in recently
deposited sediments of eight Kansas
reservoirs (Appendix B-1) indicates that
DDT use was widespread in eastern Kansas
(Juracek, 2004). DDT, with a half-life of 2
to 15 years, lasts for years in soil (ATSDR,
2002). Detection of the daughter products
DDD and DDE in upper parts of cores
indicates that DDT breakdown products
are continuing to enter Kansas lakes,
probably from eroding soils in upstream
watersheds.
Salinity. Salinity affects both mobilization and biological availability of metal
contaminants. Lakes in semi-arid or arid
environments can have increased salinity
in both water and sediments because of
evaporation or inflow of soils affected by
evapotranspiration upgradient. Disposing
of saline sediments in upland, unconfined
areas could result in increased remobilization of many metals; subsequently, these
metals could be taken up by plants, leach
into groundwater, or run off to surface
water (Francingues et al., 1985). Additional
information on salinity is presented in the
next section.
Nutrient
Transformations
and Salinity Effects
Land application of dredged sediments
has potential benefits. Even if minimally
contaminated with trace elements or toxic
organic compounds, lake sediments can
support crop growth and even improve
agricultural soils. Woodard (1999) found
that amending soil with dredged sediment had minimal effects on growth of
soybean, corn, and sunflower but increased
growth and nutrient concentrations in big
bluestem. Sigua et al. (2004b) reported
increased growth and nutrient uptake of
bahiagrass forage when grown on soils
amended with dredged lake sediment.
Dredged lake sediments can have higher
nutrient concentrations than the originating soil. This phenomenon, known as
sediment enrichment, is caused by selective
transport and deposition of fine particles
(silt and clay) to which nutrients are
attached (Sigua, 2005). Studies by Mau
(2001), Pope et al. (2002), and Juracek
and Ziegler (2007) showed that sediments
from several Kansas lakes have higher
total phosphorus concentrations than
soils in contributing watersheds (Table 2).
Furthermore, sediment transport from an
anaerobic lake bottom to aerobic surface
soils can result in nutrient transformations
associated with changes in redox potential.
Therefore, sediment properties and nutrient transformations should be considered
when evaluating agronomic and environmental sustainability of land application of
dredged sediments.
Sedimentation in Our Reservoirs: Causes and Solutions
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Nitrogen
Total nitrogen concentrations of lake
sediments are generally similar to those of
contributing watershed soils (Juracek and
Ziegler, 2007). Although the majority of
nitrogen in lake sediments likely is organicnitrogen (non-plant available), various
forms of nitrogen in sediment samples are
rarely determined. Nitrogen transformations in soils and sediments are dynamic
and highly influenced by oxygen supply
(Figure 1). These transformations influence
plant availability, transport, and potential
environmental effects of nitrogen.
Organic-nitrogen forms must be mineralized before they are available to plants.
Nitrogen mineralization occurs in anaerobic sediments, but the rate nearly doubles
when sediments are subjected to an aerobic
environment (Moore et al., 1992). Nitrification, conversion of nitrogen from
ammonium (NH4+) to nitrate (NO3-), is
strictly an aerobic process (Figure 1). Nitrification is particularly important from an
N2
environmental standpoint because nitrate is
subject to leaching loss. Moore et al. (1992)
found that pore-water nitrate-nitrogen
concentrations increased to greater than 30
mg/L of nitrogen during the first 15 days in
an aerobic environment. This indicates that
there can be a sudden flush of nitrate following land application of lake sediments;
however, nitrate leaching from dredged
sediments has not been studied. Aerobic
conditions followed by anaerobic conditions could convert much of the nitrate to
nitrogen gas through denitrification (Figure
1). Soil-water content, water flux, and plant
uptake influence nitrate losses. Proper management could minimize nitrate losses, but
additional research is needed to confirm
this supposition.
Measured nitrogen in sediment cores
ranges from 30 to 5,200 mg/kg depending
on the lake (Appendix B-1). This variation
in nitrogen availability reflects different
source areas and land uses near the sampled
lakes. Estimated mean annual net loads
FIXATION
NH3(g)
N2O
VOLATILIZATION
DENITRIFICATION
UPTAKE
NO ANAEROBIC
NO2
Root
Zone
NH3
PROCESS
MINERALIZATION
Plant available N
NO3-
NO3-
LEACHING
NITRIFICATION
AEROBIC PROCESS
NO3-
Figure 1. General nitrogen cycle in soils
Red lines emphasize aerobic or anaerobic processes
118
Sedimentation in Our Reservoirs: Causes and Solutions
NH4+
Organic N
IMMOBILIZATION
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of nitrogen available in sediments from
selected Kansas lakes range from 19,200 to
7.6 million lb/year; estimated stored chemical loads range from 1.2 million to 243
million lb (Appendices A-1, A-2). In Kansas lakes, the volume of nitrogen available
for transformation when sediment redox
conditions change is large and needs to be
considered when selecting a disposal area
and plants for use in phytoremediation.
Phosphorus
Total phosphorus concentrations in lake
sediment generally are higher than average
phosphorus concentrations in soils in contributing watersheds (Table 2). Although
elevated phosphorus concentrations in
sediment are not a concern for crop production, high phosphorus concentrations
are an environmental concern. Increases
in lake sediment phosphorus content are
correlated to increased phosphorus loss
through erosion and runoff (Sharpley,
1995). Implementing best management
practices to control erosion and capture
eroded sediment before it reaches
surface water bodies is an important component of plans for land
application of dredged sediments.
Loss of dissolved phosphorus can
have environmental effects even when
erosion is controlled. Phosphorus cycling
in soils is generally governed by inorganic
phosphorus reactions, such as adsorption
and precipitation. Phosphorus desorption
and dissolution release sediment-bound
phosphorus into soil solution or runoff
water (Figure 2). Changes in redox status
of the soil, which occur during dredging
and land application of sediment, affect
adsorption/desorption and precipitation/
dissolution reactions (Sharpley, 1995; Miao
et al., 2006).
The majority of research on redox effects
on phosphorus sorption reactions has
been conducted on either agricultural soils
that are flooded or in situ lake-bottom
sediments. Under reduced conditions,
Table 2. Total phosphorus concentrations in lake sediments and corresponding watershed
soils for several Kansas lakes
Upstream
Downstream
Watershed
Lake/Watershed
sediments
sediments
soils
Mean Total Phosphorus Concentration (mg/kg)
a
Atchison County Lake
800
1000
520
a
Banner Creek Reservoir
770
860
740
a
Mission Lake
670
1100
620
a
Perry Lake
810
930
610
a
Lake Wabaunsee
620
870
550
Cheney Lakebc
Out-of-channel
In-channel
430
630
Nonagricultural
(cemetery)
245
Juracek and Ziegler (2007)
Pope et al. (2002)
c
Mau (2001)
a
b
Sedimentation in Our Reservoirs: Causes and Solutions
119
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UPTAKE
Adsorbed P
MINERALIZATION
ADSORPTION
DESORPTION
Organic P
IMMOBILIZATION
Plant available P
H2PO4- / HPO42-
Root
Zone
PRECIPITATION
Secondary
Mineral P
DISSOLUTION
DISSOLUTION
LEACHING
Primary
Mineral P
Figure 2. Phosphorus transformations and reactions in soil environments
phosphorus sorption is greater at high
phosphorus concentrations and lower at
low phosphorus concentrations compared
with oxidized soils (Khalid et al., 1977;
Vadas and Sims, 1998). Therefore, predicted phosphorus release patterns resulting
from oxidizing reduced sediments depend
on the phosphorus status of soils.
Oxidizing sediments with low phosphorus
concentrations would decrease soluble
phosphorus, but oxidizing sediments with
high phosphorus concentrations could
increase soluble phosphorus release. Reactions can be further complicated if soils
undergo repeated cycles of oxidation and
reduction. A general increase in phosphorus release has been observed in soils
that are reduced, oxidized, and reduced
again (Young and Ross, 2001; Shenker et
al., 2005). Chen et al. (2003) found that
pore-water phosphate concentrations did
not increase following initial application
of dredged sediment to soil surface but
increased 10-fold over the control following the first drying and wetting cycle.
Measured phosphorus in sediment cores
ranges from 422 to 1,300 mg/kg depending
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Sedimentation in Our Reservoirs: Causes and Solutions
on the lake (Appendix B-1). This variation
in phosphorus availability reflects different
source areas and land uses near the sampled
lakes. Estimated mean annual net loads of
phosphorus available in sediments from
selected Kansas lakes range from 9,720 to
3.4 million lb/year; estimated stored chemical loads range from 437,400 to 109 million
lb (Appendices A-1, A-2). In Kansas lakes,
the volume of phosphorus available for
transformation when sediment redox
conditions change is large (Appendix B-1)
and needs to be considered when selecting a
disposal area. Because of the complex redox
effects on phosphorus sorption and lack of
phosphorus-loss data from soils amended
with dredged sediments, additional research
is needed to fully characterize phosphorus
loss risks from land application of dredged
sediments.
Salinity
Salinity of land-applied dredged sediments
is a concern (USACE, 1987); however,
most salinity problems cited are due to
sediments taken from brackish or saltwater
waterways (Winger et al., 2000; Novak and
Trapp, 2005). Data on potential salinity
issues in land-applied sediments dredged
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from freshwater Kansas reservoirs are lacking; therefore, the following information is
based on reservoir water analyses.
Salinity of Kansas reservoirs varies because
of the precipitation gradient and variety
of drainage-basin geology found across
the state (Table 3). In general, reservoir
salinity increases from east to west in the
state, as indicated by increases in electrical conductivity of the water. Soil salinity
is determined by measuring electrical
conductivity of a saturated paste extract
(ECse); ECse is an approximation or relative index of the electrical conductivity of
soil water (Zhang et al., 2005). Assuming
that sediment pore water is in equilibrium
with reservoir water, sediment ECse can be
approximated by determining electrical
conductivity of reservoir water.
Soils with ECse greater than 1 dS/m are
referred to as having high salts, and soils
with ECse greater than 4 dS/m are classified
as “saline,” or severely limited because of
salts. Effects of salinity on crop growth are
evaluated by comparing ECse with cropspecific threshold values. Yield loss or plant
growth problems occur when ECse exceeds
threshold values. Most major Kansas crops
will tolerate low levels of salinity (Table 4).
Salinity is not an issue for land application
of sediment dredged from the majority of
Kansas lakes. Some lakes in western Kansas,
such as Wilson Lake, probably have sediment with a high dissolved salt content,
but the predicted ECse of sediments from
these lakes is less than threshold values
for sorghum, soybean, and wheat. Corn
production, however, could be limited on
dredged sediments from Wilson Lake. Correcting soil-salinity problems can be costly.
Therefore, salinity of material dredged
from lakes with electrical conductivities
greater than 1 dS/m should be confirmed
with sediment analysis before land-application. Field or greenhouse research trials
can help quantify effects of saline sediment
applications on crop growth.
Table 3. Electrical conductivity of lake water in Kansas reservoirsa
Mean
Number
First
Last
electrical
Standard
b
Reservoir
of
sampling sampling Longitude
conductivity deviation
samples
date
date
(dS/cm)
Olathe Lake
0.539
0.105
103
6/21/00 9/30/05 94°50´ W
Perry Lake
0.308
0.034
15
5/1/92
8/30/93 95°27´ W
Tuttle Creek Lake
0.348
0.131
9
5/5/92
9/1/93 96°38´ W
Milford Lake
0.518
0.086
9
5/5/92
9/1/93 96°55´ W
Cheney Reservoir
0.835
0.056
148
10/7/70 6/13/07 97°50´ W
Kanopolis Lake
1.097
0.339
39
12/28/49 9/3/93 98°00´ W
Waconda Lake
0.766
0.104
8
5/6/92
9/2/93 98°21´ W
Wilson Lake
2.649
0.428
258
8/16/66
9/2/93 98°33´ W
Cedar Bluff Reservoir
1.317
0.255
27
10/23/75 8/9/82 99°47´ W
a
b
Data source: USGS (2008b)
Reservoirs sorted from east to west
Sedimentation in Our Reservoirs: Causes and Solutions
121
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Table 4. Salt Tolerance Ratings for Various Field and Forage Cropsa
Sensitive
Moderately Tolerant
Tolerant
b
(0-4 dS/m)
(4-6 dS/m)
(6-8 dS/m)
Field beans (dry)
Corn
Wheat
Red clover
Grain sorghum
Oat
Ladino clover
Soybean
Triticale
Alsike clover
Bromegrass
Sunflower
Sudangrass
Alfalfa
Sorghum-Sudans
Tall fescue
Sweet clovers
Highly Tolerant
(8-12 dS/m)
Barley
Rye
Bermudagrass
Crested Wheatgrass
Table adapted from Lamond and Whitney (1992) with permission
dS/m = deciSiemens per meter, a measure of electrical conductivity of a soil solution. Soils with electrical
conductivity of 4 dS/m or greater are considered saline.
a
b
Phytoremediation
Processes and Methods
Contamination in land-applied dredged
sediment is a concern. However, some
contaminants can be contained, degraded,
or removed through phytoremediation,
a process in which plants remediate contamination by taking up contaminated
water (USGS, 2008c). Phytoremediation is
useful because plants survive higher concentrations of hazardous wastes than most
microorganisms used for bioremediation.
Phytoremediation works best when soil
contaminants are less than 5 meters deep
(Schnoor et al., 1995).
Types of phytoremediation include
phytoextraction, phytostabilization,
rhizofiltration, phytodegradation, phytovolatilization, rhizosphere degradation, and
phytorestoration (Salt et al., 1998; Peer et
al., 2005). In Kansas, phytostabilization
and phytoextraction are most applicable
because of generally low trace-element
concentrations in lake sediments, the
likelihood of dredged sediments being land
applied, and the variety of plant species
(many with rooting depths less than the
122
Sedimentation in Our Reservoirs: Causes and Solutions
5 meters recommended by Schnoor et al.,
1995) available in the state for treatment of
different contaminants.
Metal Uptake
One part of the phytoremediation process
is uptake of metals through plant roots.
Heavy metals can be taken up without
negatively affecting plant growth, but the
quantity taken up depends on several factors including soil characteristics and plant
species. Only some forms of metals in the
soil are available for uptake, and availability
of different metals is affected by soil pH,
organic matter, soil water content, and
presence of other metals (Madejon and
Lepp, 2006). As water drains out of soil,
oxidation can lower soil pH. Lower pH
levels increase availability, solubility, and
mobility of most metals, which increases
their availability to plants (Borgegard
and Rydin, 1989; Turner and Dickinson,
1993). Arsenic is an exception; its mobility
is lower at lower pH levels (Madejon and
Lepp, 2006). Plant-available arsenic could
decrease as soil acidity increases with plant
growth. This requires further research,
especially for Kansas lake sediments with
arsenic concentrations that exceed the TELs.
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Usually, dredged material is anaerobic, has a
pH around 7.0, and has a moisture content
greater than 40%. In these conditions,
heavy metals are tightly bound to sediment
and not available to vegetation (Skogerboe
et al., 1987). As dredged material dries and
is oxidized, heavy metals become more
soluble and are of concern to the environment because they are more mobile in
surface runoff and more available to vegetation (Skogerboe et al., 1987).
Contaminated soil becomes less so as plant
roots take up metals and translocate them
to other parts of the plant. After uptake,
many metals are immobilized in roots
and not translocated to other plant parts
(Cunningham and Lee, 1995). Metals that
immobilize in tree roots include chromium,
mercury, lead, aluminum, tin, and vanadium. Metals that are translocated include
boron, cadmium, cobalt, copper, molybdenum, nickel, selenium, arsenic, manganese,
and zinc (Pulford and Dickinson, 2005).
Not every heavy metal is mobilized the
same way. Uptake and retention of many
heavy metals available to trees follows the
pattern of roots > leaves > bark > wood
(Pulford and Dickinson, 2005). Copper
uptake by weeping willow (Salix spp.)
occurred in the roots > wood > new stems
> leaves (Punshon and Dickinson 1997).
Sycamore maple (Acer pseudoplatanus L.)
concentrated lead and zinc in roots, then
lead translocated to stems, and zinc moved
to leaves (Turner and Dickinson, 1993).
Only cadmium and zinc accumulate in
above-ground tree tissues at concentrations
sufficiently high enough for phytoremediation to be useful (Pulford and Dickinson,
2005). Other commonly studied metals
(e.g., chromium, copper, nickel, and lead)
are either poorly bioavailable in
soil or not translocated out of
roots.
Phytostabilization
According to Raskin and Ensley
(2000), the purposes of phytostabilization are to: 1) stabilize waste so no wind
or water erosion occurs, 2) stop leaching
of contaminants to groundwater, and 3)
immobilize contaminants both physically
and chemically by making them bind to
roots and organic matter. Phytostabilization is best used on soils with low
contaminant levels (Raskin and Ensley,
2000; McCutcheon and Schnoor, 2003). Vegetation reduces wind and water erosion in several ways. Accumulation of leaf
litter forms a barrier over the surface of
contaminated soil, which provides physical
stabilization by reducing splash erosion.
Roots of grasses, shrubs, and trees bind
and stabilize soil as water runs over it. The
litter layer and binding of soil by roots also
help reduce wind erosion. Reducing wind
erosion with vegetation also lowers human
exposure because of reduced potential for
inhalation of contaminated soil and ingestion of contaminated foods (Schnoor et al.,
1995).
Vegetation also takes up large amounts
of water that are lost from leaf surfaces
through transpiration. Tree species such as
poplar, willow, and cottonwood are good at
taking up water from the top 2 to 3 meters
of soil (Raskin and Ensley, 2000). This
large amount of water moving through the
plant from the soil to the atmosphere can
decrease the potential for metals to leach
from the soil (Schnoor et al., 1995).
Sedimentation in Our Reservoirs: Causes and Solutions
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Madejon and Lepp (2006)
studied three contaminated sites
that were naturally revegetated
with mosses, ferns, and herbaceous
and woody plant species suitable for
phytostabilization. They found that
arsenic was taken up and immobilized
in roots with little transfer to stems and
leaves. Root uptake of arsenic in herbaceous
and woody plants ranged from 0.66 to 18.3
mg/kg and 1.37 to 5.54 mg/kg, respectively.
Amount of arsenic translocated to stems
and leaves in herbaceous and woody species
was less than 2 mg/kg. These data show
that the species tested would work well for
phytostabilization because little arsenic was
translocated out of roots.
Another study in the southern United
States noted successful use of Bermudagrass
for phytostabilization on dredged material
containing low amounts of zinc (Best et
al., 2003). Bermudagrass responded to an
increase in zinc levels by increasing bioaccumulation of zinc until a decrease of plant
mass occurred at a zinc phytotoxicity level
of 324 mg/kg. Red fescue (Festuca rubra)
also is metal tolerant and has been used in
grazing-management strategies on highly
contaminated soils (Cunningham and Lee,
1995).
Species native to a particular area are best
for phytostabilization because they are
most likely adapted to the climate, insects,
and diseases present (Peer et al., 2005). The
U.S. Army Corps of Engineers (1987) published a list of vegetation that can be used
on dredged material; Appendix C contains
a condensed version that lists 161 species
found in the mid-Plains.
124
Sedimentation in Our Reservoirs: Causes and Solutions
Phytoextraction
Phytoextraction removes contaminants
from the system by immobilizing them in
soil or biomass (Peer et al., 2005; Pulford
and Dickinson, 2005). Vegetation such as
grasses and trees can be harvested, which
helps permanently remove contaminants
from soil. Dried, ashed, and composted
plant material can be isolated as hazardous
waste or recycled as a metal ore (Kumar
Nanda et al., 1995).
Hyperaccumulator plants are good for
phytoextraction of metals and include
herbs, shrubs, and trees. To be labeled a
hyperaccumulator, a plant must take up
more than 10,000 µg/g (ppm) of zinc and
1,000 µg/g of copper, nickel, chromium,
and lead (Baker and Brooks, 1989). More
than 300 of the approximately 400 species
of hyperaccumulators accumulate nickel
(Brown, 1995). Table 5 compares amounts
of selected metals taken up by hyperaccumulators with amounts normally found in
plant leaves and soil.
Metals present in Kansas reservoir sediments at concentrations greater than TELs
include arsenic, chromium, copper, lead,
nickel, selenium, and zinc (Appendix B-2).
Examples of hyperaccumulator species that
take up these metals are shown in Table
6. Most plants that accumulate metals are
slow-growing, small, weedy plants that have
a low biomass, but some herbaceous hyperaccumulators such as Brassica juncea have a
high biomass (Kumar Nanda et al., 1995).
Plants with higher biomass can remove
greater amounts of contamination and
have more uses when harvested (Pulford
and Dickinson, 2005). For a more complete list of hyperaccumulators, see Baker
and Brooks (1989) and McCutcheon and
Schnoor (2003).
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Compared with herbaceous hyperaccumulators, trees are advantageous for several
reasons (Pulford and Dickinson, 2005):
• Certain tree species have high-yielding
biomass that would only need to take
up moderate amounts of metal to be
effective.
• Trees have more uses when harvested
than most hyperaccumulators.
• A greater genetic diversity of fast growing, short-rotational trees such as Salix
spp. and Populus spp. are available. This
allows for selection of traits for resistance to high metal concentrations as
well as genotypes that have high or low
metal uptake.
• Woody plant biomass use is well
established.
• Short-rotation, fast growing coppice
trees have a high economic value.
• Trees on highly contaminated land are
visually aesthetic.
• Trees protect soil surfaces from wind
and water erosion because their roots
stabilize substrate and their leaves produce organic matter when they drop.
• Uptake of water and transpiration
through leaves helps limit leaching of
heavy metals from soils and protects
groundwater and surface waters from
contamination.
Sites most favorable for timber growth
include marginal land or abandoned
disposal sites on which dredged, dewatered
material has been deposited (Best et al.,
2003). An additional benefit of using trees
is that dredged materials can be applied in
thicker layers because tree roots descend
farther than herbaceous plant roots. This
allows marginal land to be made more productive. And, trees can be used to produce a
variety of beneficial products. Tree species
suitable for use on dredged material include
eastern cottonwood, American sycamore,
eucalyptus, green ash, water oak, and sweet
gum on periodically flooded sites; and longleaf pine, slash pine, loblolly pine, black
walnut, white ash, pecan, and several oak
and hickory species on upland sites (Best et
Table 5. Comparison of amounts of heavy metals normally found in plant leaves and soil with
the minimum amounts required for plants to be considered hyperaccumulators
Normal Range of
Normal Range of Metal Minimum Amount of
Metal
Element Concentrations Concentration in Soil Metal Taken up to be a
in Dried Plant Leavesa
(United States)b
Hyperaccumulatorc
(mg/kg)
Arsenic
--3.6-8.8
--Chromium
0.2-5
14-29
1,000
Copper
5-25
20-85
1,000
Nickel
1-10
13-30
1,000
Lead
0.1-5
17-26
1,000
Selenium
0.05-1
----Zinc
20-400
34-84
10,000
Raskin and Ensley (2000)
Sandia National Laboratory (2007)
c
Baker and Brooks (1989)
a
b
Sedimentation in Our Reservoirs: Causes and Solutions
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Table 6. Hyperaccumulator species used to remove metals present in Kansas reservoir
sediments
Metal
Arsenic
Copper
Chromium
Nickel
Lead
Selenium
Zinc
Scientific Name
Pteris vittataa
Pteris creticaa
Pteris longifoliab
Pteris umbrosab
Holcus lanatusb
Salix spp.b
Brassica junceaac
Helianthus annuusd
Avena sativae
Hordeum vulgaree
Salix spp.a
Betula spp.a
Salsola kalia
Brassica junceac
Brassica junceacd
Helianthus annuuse
Brassica junceaacd
Brassica spp. (others)a
Helianthus annuusd
Astragalus bisulcatusa
Brassica junceaa
Thlaspi caerulescensad
Brassica junceaacd
Helianthus annuusd
Avena sativae
Hordeum vulgaree
Peer et al. (2005)
Baker and Brooks (1989)
c
Kumar Nanda et al. (1995)
d
McCutcheon and Schnoor (2003)
e
Ebbs and Kochian (1998)
*Natural or introduced to Kansas
a
b
126
Sedimentation in Our Reservoirs: Causes and Solutions
Common Name
Family
Ladder brake
Pteridadeae
Cretan brake
Pteridadeae
Long-Leaved brake
Pteridadeae
Jungle brake
Pteridadeae
Common velvetgrass
Poaceae
Willow species
Salicaceae
Indian mustard
Brassicaceae
Common sunflower
Asteraceae
Oat
Poaceae
Barley
Poaceae
Willow species
Salicaceae
Birch species
Betulaceae
Russian thistle
Chenopodiaceae
Indian mustard
Brassicaceae
Indian mustard
Brassicaceae
Common sunflower
Asteraceae
Indian mustard
Brassicaceae
--Brassicaceae
Common sunflower
Asteraceae
Two-grooved milk vetch
Fabaceae
Indian mustard
Brassicaceae
Alpine pennycress
Brassicaceae
Indian mustard
Brassicaceae
Common sunflower
Asteraceae
Oat
Poaceae
Barley
Poaceae
Location
USA
USA
USA
USA
USA*
USA*
USA*
USA*
USA*
USA*
USA*
USA*
USA
USA*
USA*
USA*
USA*
USA
USA*
USA*
USA*
USA
USA*
USA*
USA*
USA*
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al., 2003). However, not all are suitable for
Kansas.
Using trees for phytoextraction also has
disadvantages. Because trees take longer to
mature, the time period between sediment
disposals is longer than if herbaceous plants
are used (Best et al., 2003). Disposing additional dredged sediment around planted
trees limits the quantity of oxygen available
to the roots and can result in death of the
trees. Trees also tend to acidify soil, which
could cause increased bioavailability of
metals.
Phytoextraction and phytostablization have
method-specific advantages and disadvantages (PRC, 1997). Phytoextraction by
trees has high biomass production but is
disadvantageous because of the potential
for off-site migration and transportation
of metals to the leaf surface. Phytoextration by grasses has high accumulation but
low biomass production and a slow growth
rate. A disadvantage for both methods is
that metals concentrated in plant biomass
must eventually be disposed of. Phytostabilization does not require disposal of
contaminated biomass but does necessitate
long-term maintenance.
The main disadvantage of all phytoremediation methods is that they are cyclical
and occur only during the growing season.
Some sites might require additional soil
amendments such as manure, sawdust,
and lime or the addition of chemicals to
increase solubility of metals (Brown, 1995;
Murray, 2003). An additional concern is
whether plants take up enough contaminants to make a difference or if it will take
thousands of years to clean soil to acceptable contaminant levels (Pulford and
Dickinson, 2005).
Summary
Dredging and land-applying
sediments pose a variety of concerns including costs, locations
of disposal sites, economics, and
transportation. From a chemical standpoint, dredging and subsequent disposal
of sediments as a means to renovate Kansas
reservoirs appears viable. Contaminants
of concern in most Kansas reservoir sediments evaluated in USGS studies are not
analytically detectable or are present at
concentrations below USEPA TELs.
A few metals (e.g., lead, arsenic, selenium,
copper, nickel, chromium, and zinc) will be
issues in some parts of the state. Whether
lead will create problems depends on depth
of sediment dredged, lake location, and
source of lead. Sediments from Empire
Lake in southeastern Kansas are most likely
to have disposal-related problems because
of high concentrations of cadmium, lead,
and zinc. Other reservoirs have higher
concentrations of lead in deeper sediments
because of past use of leaded gasoline and
will need to be evaluated if dredging is
considered as a remediation option.
Phytoremediation is a natural process that
can be beneficial, especially on sediments
with low contamination levels, such as
those found in many Kansas reservoirs.
Many vegetation species, including some
native to Kansas, are appropriate for
phytoremediation. Although phytoremediation requires further research, it is viable
for Kansas and should be considered along
with land application of dredged sediment
as part of an overall reservoir dredging
evaluation.
Sedimentation in Our Reservoirs: Causes and Solutions
127
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Questions and Research Needs
Chemical Issues
Although contaminants in Kansas reservoir sediments generally are below TELs,
changes that could occur when sediment is removed and placed on land have not been
evaluated. Research should examine:
• Redox potential and pH of sediment
• Potential changes in concentrations of metals and nutrients due to
land disposal
• Leaching of lake sediment in combination with disposal site soil:
Are contaminants of interest mobile or retained in the soil matrix?
• Retention of trace elements in soil: Do amendments (biosolids and
liming) prevent trace-element mobility and/or uptake by plants?
• Quantity of manganese- and iron-oxides and hydroxides and content and type of clay present in combined soils at disposal sites:
What combination will optimize retention of metals?
• Leaching of nitrate and other contaminants from land-applied
dredged sediments
• Management of dredged sediment to minimize nitrate losses
• Phosphorus loss risks from land-applied dredged sediments due to
complex redox effects on phosphorus sorption
• Sediment from lakes with high electrical conductivity (field or
greenhouse research trials) prior to dredging; correcting soil-salinity
problems can be costly
• Methylmercury content in sediment pore-water
Phytoremediation
Successful establishment of vegetation for phytoremediation depends on physical
qualities of dredged materials, contaminants present, soil water, soil structure, and
salinity. Questions to ask prior to using phytoremediation on dredged sediments
include:
• What are the risks of metal uptake by plants and potential transmission up the food chain?
• What can or should be done with material after it accumulates in
plant tissue? Can woody material be used if it contains heavy metals?
What other disposal possibilities exist?
128
Sedimentation in Our Reservoirs: Causes and Solutions
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• What volume of metals is removed by phytoremediation, and what
is the rate of uptake?
• What are the economic effects of phytoremediation compared with
other remediation methods?
• Will species currently used for phytostabilization and phytoextraction be successful in Kansas? Many species used for
phytoremediation are short-rotation, hybrid, fast-growing woody
species; are they feasible here?
• Should controlled, pre-trial experiments be conducted to determine
likelihood of success before various plant species are used on dredged
materials?
Sedimentation in Our Reservoirs: Causes and Solutions
129
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Mean net load (lb/year) based on values reported for period of study
Reservoir characteristics
Appendix A-1. Estimated annual sediment deposition and chemical loads for selected Kansas reservoirs
Reservoir (year completed)
Tuttle
Perry Hillsdale
Cheney Webster Empire
Lake
Cedar
Creek
Lake
Lake
Reservoir Reservoir Lake
Olathe
Lake
Lake
e
fc
g
h
h
(1969)a (1981)bc
(1964)
(1956)
(1906)
(1956)
(1938)
(1962)d
Drainage areai, mi2
1,117
144
9,628
933
1,150
2,500
16.9*
16.9*
32
15
37
33
40
100
45
62
56,700
2,100
142,000
7,100
1,267
1,000
317
338
3,040
million
265
million
1,633
million
453
million
7.8
million
24
million
12.6
million
9.6
million
3.4
million
154,000
2.5
million
226,000
29,400
---
9,720
14,700
(Total organic-N
+ Ammonia-N)
Nitrogen
7.6
million
---
672,000
840,000
129,000
---
29,610
19,200
Total organic
carbon
58
million
---
33
million
---
966,000
---
---
---
Selenium
2,730
---
1,324
190
96
---
---
---
Arsenic
57,800
---
22,861
15,800
619
---
---
---
Lead
85,100
---
40,824
8,640
---
6,500
416
326
Zinc
366,000
---
196,000
37,500
---
120,000
1,966
1,363
Copper
100,000
---
55,000
7,940
---
830
441
336
Chromium
302,000
---
132,450
31,740
---
1,591
1,172
864
Cadmium
1,520
---
717
146
---
780
3.8
3.2
152,000
---
62,143
13,830
---
840
441
355
Years since dam
closurei
Total deposition,
acre-ft
Mean Annual
Sediment
Deposition, lb/yr
Phosphorus
Nickel
Juracek (2003)
Juracek (1997)
c
Mau and Christensen (2000)
d
Juracek and Mau (2002)
e
Mau (2001)
a
b
130
Sedimentation in Our Reservoirs: Causes and Solutions
Christensen (1999)
Juracek (2006)
h
Mau (2002)
i
USGS (2008a)
*Watershed includes both Lake Olathe and Cedar Lake
f
g
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has been archived. Current information is available from http://www.ksre.ksu.edu.
Total estimated load (lb) based on values reported for period of study
Reservoir characteristics
Appendix A-2. Estimated total sediment deposition and chemical loads for selected Kansas reservoirs
Reservoir (year completed)
Tuttle
Perry Hillsdale
Cheney Webster Empire
Lake
Creek
Lake
Lake
Reservoir Reservoir Lake
Olathe
Lake
(1969)a (1981)bc
(1964)e
(1956)fc (1906)g (1956)h
(1962)d
Drainage areai, mi2
1,117
144
9,628
933
1,150
2,500
16.9*
16.9*
32
15
37
33
40
100
45
62
56,700
2,100
142,000
7,100
1,267
1,000
317
338
48.6
million
1.9
million
30.2
million
7.5
million
156,000
1.2
million
283,500
297,500
109
million
2.3
million
93
million
7.5
million
1.1
million
---
437,400
911,400
243
million
---
24.8
million
27.7
million
5 million
---
1.3
million
1.2
million
Total organic
carbon
928,000
---
610,000
---
19,300
---
---
---
Selenium
87,360
---
48,988
6,270
3,856
---
---
---
---
845,868
521,400
24,760
---
---
---
285,120
---
650,000
18,720
20,212
1.2
million
---
12
million
88,470
84,506
Years since dam
closurei
Total deposition,
acre-ft
Total estimated
sediment deposition since dam
closure, tons
Phosphorus
Nitrogen
(Total organic-N
+ Ammonia-N)
Arsenic
Lead
Zinc
Copper
Chromium
b
1.8
million
2.7
million
11.7
million
3.2
million
9.6
million
-----
1.5
million
7.25
million
---
825,000
262,020
---
83,040
19,845
20,832
---
4.9
million
1 million
---
159,110
52,740
53,568
Cadmium
48,640
---
26,517
4,818
---
78,000
171
198
Nickel
4.8
million
---
2.3
million
456,390
---
84,000
19,845
22,010
Juracek (2003)
Juracek (1997)
c
Mau and Christensen (2000)
d
Juracek and Mau (2002)
e
Mau (2001)
a
Cedar
Lake
(1938)h
Christensen (1999)
Juracek (2006)
h
Mau (2002)
i
USGS (2008a)
*Watershed includes both Lake Olathe and Cedar Lake
f
g
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Appendix A-3. Mercury values from sediment cores at selected Kansas reservoirs and estimated mean annual
net loads
Reservoir
e
Gardner
Lake
Mission Perry Tuttle Cedar Hiawatha Lake Empire Lake (one core)
City
Aftona
Lakea Lakeb Creekc Laked
Lakea
Olathed Top Middle Bottom
Lakea
Number of
------19/19 41/41
------------samples
Measured
----------------0.12
.029
.022
value
Minimum,
0.03
0.05
0.02
0.01 <0.02 0.05
0.1
--------mg/kg
Mean,
0.04
0.06
0.02
----0.07
0.04
0.06
------mg/kg
Median,
0.04
0.06
0.04
0.05
0.04
------------mg/kg
Maximum,
0.04
0.07
0.04
0.07
1.4
0.14
0.06
--------mg/kg
TEL
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
0.13
PEL
0.696
0.696
0.696
0.696
0.696
0.696
0.696
0.696
0.696
0.696
0.696
0.46
0.39
0.93
69
144
---
---
---
---
---
---
0.35
0.33
0.93
152
317
---
---
---
---
---
---
Mean
annual net
load, kg/yrf
Mean
annual net
load, lb/yrf
TEL = threshold-effects level
PEL = probable-effects level; values given for comparison
a
Juracek (2004)
b
Juracek (2003)
c
Juracek and Mau (2002)
132
Sedimentation in Our Reservoirs: Causes and Solutions
Mau (2002)
Juracek (2006)
f
Values calculated using median concentration, bulk densities,
and annual sediment loads reported in studies cited
d
e
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Appendix B-1. Nutrient and pesticide concentrations in sediment cores from selected Kansas reservoirs
Nutrients
Pesticides
Organic
Total
Total
Total
carbon
DDD
DDE
DDT
nitrogen
carbon
phosphorus
(TOC)
μg/kg
μg/kg
μg/kg
mg/kg
mg/kg
%
mg/kg
TEL
PEL
Reservoir
Websterb
Kirwinb
Waconda Lakeb
Tuttle Creekc
Cedar Laked
Lake Olathed
Pony Creeke
Otis Creeke
Mission Lakee
Lake Aftone
Hiawathae
Gardner Lakee
Edgerton Citye
Crystal Lakee
Centraliae
Bronsone
Perry Lakef
Empire Lakeg
Cheney Lakeh
Hillsdale Lakei
Milford Lakej
Range
Range
Range
Range
Range
Median
Range
Median
Range
Range
Range
Range
Range
Range
Range
Range
Median
Median
Range
Mean
Range
Range
Range
TEL = threshold-effects level
PEL = probable-effects level
a
USEPA (2004)
b
Christensen (1999)
US EPA TELs and PELsa
-------------
-----
30-1,910
1,200-1,980
704-3,210
600-5,200
2,000-2,700
2,350
1,300-2,700
2,000
3,000- 3,400
2,200-2,400
1,900-2,400
2,200-2,600
1,000-1,700
1,600-3,100
1,000-2,200
2,600-4,300
2,400
3,700
1,300-2,800
1,250
1,400-2,400
-----
1.22
7.81
2.07
374
Values from Sampled Sediment Cores
251-692 10,600-16,200
--<0.2
<0.2
422-795
8,310-13,600
--<0.2
<0.2
281-904
3,440-19,900
------198-952
0.84-2
0.93-2.2 <0.50
<0.2
1,370-1,810
--------1,540
--1,540
<0.2
<0.2
588-1,030
--------774
----<0.50
0.2
1,100-1,200
2.6-2.8
3.2-3.5
----600-640
2-2.3
3.5-3.7
----750-1,200
2.1-2.6
1.9-2.3
<0.50
1.86
740-840
1.9-2.4
2-2.5
<1.25
0.22
400-680
1.1-2.4
1.1-2.6
1.19
1.99
1,100-1,300
3.2-3.4
3-3.9
0.46
<0.50
480-610
0.7-2.1
0.6-2
<0.50
0.22
690-1,300
2.6-3.9
2.7-6.1
<0.50
4.76
1,300
2.7
2.7
<0.50
0.27
1,100
3.6
3.9
<0.50
0.52
630-1,300
1-2.1
1-2.3 <0.5-0.55 <0.2-0.8
610
1.35
1.7
----495-647
--------410-810
------------------Juracek and Mau (2002)
Mau (2002)
e
Juracek (2004)
f
Juracek (2003)
1.19
4.77
<0.2
<0.2
--<0.50
--<0.2
--<0.50
----<0.50
<1.25
<0.50
--<0.50
<0.50
<0.50
<0.50
<0.50
---------
Juracek (2006)
Mau (2001)
i
Juracek (1997)
j
Christensen and Juracek (2001)
c
g
d
h
Sedimentation in Our Reservoirs: Causes and Solutions
133
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Appendix B-2. Trace element concentrations in sediment cores from selected Kansas reservoirs
Trace Elements
Arsenic Cadmium Chromium Copper
Lead
Nickel Selenium Zinc
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg
mg/kg mg/kg mg/kg
TEL
PEL
Reservoir
Websterb
Kirwinb
Waconda Lakeb
Tuttle Creekc
Cedar Laked
Lake Olathed
Pony Creeke
Otis Creeke
Mission Lakee
Lake Aftone
Hiawathae
Gardner Lakee
Edgerton Citye
Crystal Lakee
Centraliae
Bronsone
Perry Lakef
Empire Lakeg
Cheney Lakeh
Hillsdale Lakei
Milford Lakej
0.676
4.21
15.9
42.8
-----
Values from Sampled Sediment Cores
Range
8-15
<3.0
<6-26
19-29
16-32
<12-30 0.5-2.7
Range 4.6-10 <2.7-3.7
9-33
17-28
14-26
<11-24 <0.5-2.2
Range 5.4-13.1
<5.1
<10 - 17
7-27
<14-25
<21
<0.6 - 3.6
Range 6.9-18 0.26-0.6
48-120
20-44
16-160
19-77 0.34-1.5
Range
13-16 0.23-0.36
90-98
32-45
32-35
32-39 0.86-1.1
Median
14
0.31
90
32
33
34
0.99
Range
15-18 0.27-0.41
88-94
32-38
28-40
35-39 0.95-1.2
Median
16
0.33
89
36
36
37
0.99
Range
13-17
0.4-0.5
70-77
26-29
24-25
35-38
0.8-0.9
Range
10-13
0.4-0.6
76-82
21-22
23-24
35-39
1-1.2
Range
12-16
0.3
74-84
28-35
24-31
37-41
0.8-0.9
Range 9.9-15
0.6-0.8
69-74
32-35
34-54
37-40
0.7
Range 8.2-12
0.5-0.9
43-54
14-20
21-58
21-26
0.4-0.6
Range 7.3-15
0.6-1
83-100
39-210 1,300-1,600 1.3-1.6 130-150
Range 7.3-15
0.1-0.4
48-61
14-19
21-24
19-24
0.7-1.1
Range
14-21
0.5-1.4
67-93
25-1600
28-65
32-43
0.8-1.2
Median
18
0.8
77
30
19
40
0.8
Median
15
0.7
74
200
34
37
0.9
Range
8-25
0.2-0.6
59-100
18-35
18-30
22-54
0.4-1
Mean
4.6
29
66.3
34.6
270
25
0.8
Range 5.9-10 0.24-0.40
55-100
12-24
14-24
18-43 0.31-0.52
Range
--------------Range 6.1-9.9 ≈0.9-1.5
34-46
21-30
<33-53
29-38
0.2-2.2
TEL = threshold-effects level
PEL = probable-effects level
a
USEPA (2004)
b
Christensen (1999)
134
7.24
41.6
USEPA TELs and PELsa
52.3
18.7
30.2
160
108
112
Juracek and Mau (2002)
Mau (2002)
e
Juracek (2004)
f
Juracek (2003)
c
d
Sedimentation in Our Reservoirs: Causes and Solutions
Juracek (2006)
Mau (2001)
i
Juracek (1997)
j
Christensen and Juracek (2001)
g
h
124
271
----35-137
65-150
150-170
150
140-150
140
170-200
66-74
120-140
120-140
58-250
<.50
58-76
130-250
110
150
58-140
4,900
58-120
--29-38
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Appendix C. Vegetation used to remediate dredged materialsa
Plant Name
Natural Planted
Grasses
Barley
Barnyard grass
Beaked panic grass
Big bluestem
Bromegrass
Bromesedge
Corn
Deertongue
Fall panic grass
Foxtail millet
Goose grass
Green bristlegrass
Johnson grass
Jungle rice
Large crabgrass
Oat
Orchardgrass
Panic grass
Prairie cordgrass
Quackgrass
Red fescue
Redtop
Red canary grass
Rice cutgrass
Rye
Sand dropseed
Sixweeks fescue
Smooth crabgrass
Sorghum
Sudan grass
Switchgrass
Timothy
Wheat
Wild rye
Yellow bristlegrass
Plant Name
Natural Planted
Herbs
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Alfalfa
Alsike clover
Arrow-leafed tearthumb
Black medic
Black nightshade
Blackseed plantain
Bracted plantain
Broadleaf plantain
Chufa
Common chickweed
Common lambsquarters
Common mullein
Common purslane
Common ragweed
Common spikerush
Common threesquare
Cow pea
Crimson clover
Curly dock
Dwarf spikerush
Flowering spurge
Giant ragweed
Goosefoot
Hairy vetch
Hardstem bulrush
Hop clover
Horseweed
Japanese clover
Jerusalem artichoke
Korean clover
Ladino clover
Ladysthumb
Lespedeza
Malta starthistle
Mapleleaf goosefoot
Marsh pea
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
Sedimentation in Our Reservoirs: Causes and Solutions
135
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Plant Name
Natural Planted
Marsh pepper
x
Maximillian’s sunflower
Mexican tea
x
Narrowleaf vetch
x
Nodding smartweed
x
Nutsedge
x
Pennsylvania smartweed
x
Pokeberry
x
Prostrate knotweed
x
Prostrate spurge
Purple nutsedge
x
Purple vetch
x
Red clover
x
Redroot pigweed
x
Schweinitz’s nutsedge
x
Sea blite
x
Seaside dock
x
Sericea lespedeza
Sheep sorrel
x
Soybean
x
x
Spotted burclover
Spotted spurge
x
Squarestem spikerush
x
Sunflower
x
Tansy mustard
Tumbleweed
x
Virginia pepperweed
x
Western ragweed
x
White clover
x
x
Wild bean
x
Wild buckwheat
x
Wild sensitive pea
Wild strawberry
Wooly croton
x
Wooly indianwheat
x
136
Sedimentation in Our Reservoirs: Causes and Solutions
Plant Name
Vines
Common greenbrier
Fringed catbrier
Japanese honeysuckle
Kudzu
Muscadine grape
Peppervine
Virginia creeper
Natural Planted
x
x
x
x
x
x
Plant Name
Natural Planted
Shrubs and small trees
American elderberry
x
American hornbeam
American plum
x
Black raspberry
x
Carolina ash
Carolina rose
x
Eastern hophornbeam
x
Gray dogwood
x
Halberd-leaved willow
x
Multiflora rose
x
Poison ivy
x
Possumhaw
x
Rough-leafed dogwood
x
Russian olive
x
x
Sandbar willow
x
Shining sumac
x
Silky dogwood
x
Smooth sumac
x
Squaw huckleberry
Staghorn sumac
x
Tartarian honeysuckle
x
Thorny eleagnus
x
Wild apple
x
Witch hazel
Shining sumac
x
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service
has been archived. Current information is available from http://www.ksre.ksu.edu.
Plant Name
Natural Planted
Large Trees
American sycamore
x
Black cherry
x
Black gum
x
Black locust
x
b
Black walnut
x
b
Black willow
x
b
Eastern redcedar
x
Green ash
x
Hackberry
x
Honeylocust
x
Mockernut hickory
Peachleaf willow
x
Pecan
Persimmon
x
Pignut hickory
Red maple
x
Red mulberry
x
River birch
x
Sassafras
x
Sugarberry
x
Sugar Maple
x
White ash
x
White oak
White poplar
a
b
Data source: USACE (1987)
Not listed as in mid-Plains, but is present in Kansas
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