www.esrgc.org/hazus.htm

www.esrgc.org/hazus.htm
An Assessment Of
Maryland’s Vulnerability
To Flood Damage
John M. Joyce
Flood Hazard Mitigation Section
Maryland Department of the Environment
and
Michael S. Scott, PhD
Eastern Shore Regional GIS Cooperative
Salisbury University
August 2005
For more information, contact:
Maryland Department of the Environment
Flood Hazard Mitigation Section
1800 Washington Blvd.
Baltimore, MD 21230-1718
1-800-633-6101
Executive Summary ...........................................................................1
Part I. History of Flooding and Flood Mitigation .....6
History of Flood Hazard Mitigation in Maryland...............................................6
History of Flooding in Maryland ......................................................................10
Table 1. Flooding history of Maryland ....................................................................10
Flooding and the 100-year Floodplain in Maryland........................................12
Part II. Floodplain Development ..........................................16
Structures in the Floodplain ............................................................................16
Table 2. Structures and people in floodplains in Maryland ..........................................17
Structures Subject to Coastal Erosion ...........................................................18
State Buildings in the Floodplain ....................................................................19
State Schools Subject to Flooding..................................................................20
Other Critical Services and Local Public Buildings Subject to Flooding ....21
Table 3. Schools subject to flooding ......................................................................22
Part III. Modeled Flood Vulnerability Estimates.....23
Software.............................................................................................................24
Data Needed ......................................................................................................25
Procedures ........................................................................................................26
Flooding Scenarios and Damage Estimates ..................................................27
Table 4. Flood zone area versus total area of a subdivision in square miles ...................28
Table 5. Building damage by percent damaged in thousands of square feet ...................30
Map 1. Potential building damage resulting from riverine and coastal flooding in thousands of
square feet .......................................................................................................31
Table 6. Building damage by occupancy category in thousands of square feet ...............32
Map 2. Residential building damage in thousands of square feet .................................33
Map 3. Government building damage in thousands of square feet ................................34
Map 4. Commercial building damage in thousands of square feet ................................35
An Assessment of Maryland’s Vulnerability to Flooding
Page i
Map 5. Industrial building damage in thousands of square feet ....................................36
Table 7. Building damage by construction type category in thousands of square feet .......37
Map 6. Masonry building damage in thousands of square feet .....................................38
Map 7. Concrete building damage in thousands of square feet ....................................39
Map 8. Steel building damage in thousands of square feet .........................................40
Map 9. Wood building damage in thousands of square feet ........................................41
Table 8. Building damage by percent damaged in numbers of buildings ........................43
Map 10. Potential building damage resulting from riverine and coastal flooding by numbers
of buildings .......................................................................................................44
Table 9. Building damage by occupancy category in numbers of buildings .....................45
Map 11. Residential building damage in numbers of buildings .....................................46
Table 10. Building damage by construction type category in numbers of buildings ...........47
Map 12. Masonry building damage in numbers of buildings ........................................48
Map 13. Wood building damage in numbers of buildings ............................................49
Table 11. Direct economic losses from buildings in thousands of dollars .......................51
Map 14. Direct economic losses from building damage in thousands of dollars ...............52
Accuracy of Data...............................................................................................53
Improving Accuracy with Local Data ..............................................................53
Part IV. Mitigation Strategies..................................................55
Regulations .......................................................................................................55
Maryland Model Floodplain Management Ordinance ....................................55
Local Mitigation Planning ................................................................................57
Floodplain Management Database and Repetitive Loss Project ..................58
Table 12. Repetitive loss properties in Maryland by county as of November 30, 2004.......59
Mapping Risk – Floods and Tropical Storm Surges ......................................60
Flood Insurance ................................................................................................61
Dams and the State Dam Safety Program ......................................................62
Maryland Stormwater Management Regulations ...........................................63
Maryland Wetlands and Wetland Regulations................................................65
Growth Management – Critical Areas, Sensitive Areas, Smart Growth .......66
An Assessment of Maryland’s Vulnerability to Flooding
Page ii
Sea Level Rise Response Strategy .................................................................67
“No Net Adverse Impact” Watershed Planning .............................................68
Part V. Flood Mitigation Projects in Maryland.........71
State Projects ...................................................................................................71
Table 13. Comprehensive Flood Management Grant funds ........................................72
Table 14. Flood grant program acquisitions by county ...............................................73
Federal Projects ...............................................................................................75
Table 15. Major US Army Corps of Engineers flood protection projects in Maryland .........75
Part VI. Funding Mitigation ......................................................77
Sources of Funding for Mitigation ..................................................................77
Part VII. Recommendations .....................................................78
Flood Grant Program .......................................................................................78
Coordination .....................................................................................................78
No Adverse Impact ..........................................................................................78
Wetlands ...........................................................................................................79
Planning ............................................................................................................79
Tax Incentives ..................................................................................................79
Protection of Floodplains ................................................................................79
Sea-level Rise ...................................................................................................79
Acknowledgements .........................................................................80
References ...............................................................................................81
Appendix A ............................................................................................ A-1
100-year Flood Zone and Direct Economic Losses from Buildings by
Census Block for Each Subdivision in Maryland
An Assessment of Maryland’s Vulnerability to Flooding
Page iii
Appendix B ............................................................................................ B-1
Detailed HAZUS-MH Flood Vulnerability Modeling Results for Each
Subdivision in Maryland
Appendix C ............................................................................................ C-1
List of State-Owned Buildings in the 100-year Floodplain
An Assessment of Maryland’s Vulnerability to Flooding
Page iv
Executive Summary
History of Flooding and Flood Mitigation in Maryland
Maryland has had a long history of flood hazard mitigation. Since 1933,
Maryland has sought to assure public safety and avoid damage by regulating
development projects proposed for the floodplain. In its history, Maryland has
been subject to its share of major flooding events from the first recorded flood on
May 11, 1860 in Baltimore City along Jones Falls to the devastating floods
caused by the tidal surge of Hurricane Isabel in mid-September 2003.
The state is prone to three types of flooding: nontidal flooding (flooding
from rivers and streams), tidal flooding (flooding from tides and storm surges),
and coastal high hazard flooding (the addition of wave action to tidal flooding).
The area that has a 1% chance of being flooding in any given year (known as the
100-year floodplain) gets the most attention with regard to flood mitigation as this
area is regulated by local flood ordinances adopted by communities in the
National Flood Insurance Program (NFIP). In Maryland, the percent of land area
in each county that is floodplain varies from 55.8% in Dorchester County to 4.6%
in Garrett County, as estimated using the Q3 digital flood zone maps. However,
this statistic neither shows the amount of building stock exposure within that
floodplain, nor the varying dynamics of tidal versus nontidal flooding and their
impact on potential losses. Indeed, the average age of the Flood Insurance Rate
Maps (FIRM) in Maryland used to determine these floodplains was 19 years old.
Clearly, more up-to-date and accurate flood studies are needed.
Exposure of Maryland’s Built Environment to Flooding
To be vulnerable to flood damage, there must be a structure or some
other object of value in harm’s way as well as the possibility of flooding. Two
methods of estimating the degree of vulnerability of Maryland’s built environment
to flooding were used to tally the built environment exposure. In one,
communities were asked to estimate the number of structures within the 100year floodplain. In the other, digital floodplain maps were overlain with tax parcel
assessment information using MDProperty View. Using these methods, an
estimate of 68,217 structures are located within the floodplain in the state of
Maryland, with these buildings representing almost $8 billion in assessed value.
Coastal erosion is another important factor to consider when examining
the exposure of the built environment to flooding. Here, however, reports and
estimates conflict. In a 1994 Department of Natural Resources study, it was
estimated that 2,500 structures were subject to long-term erosion but that many
of these are located on bluffs and are not subject to flooding. On the other hand,
FEMA’s Evaluation of Erosion Hazards report estimates 25% of homes and other
An Assessment of Maryland’s Vulnerability to Flooding
Page 1
structures within 500 feet of the coast will fall victim to the effect of erosion within
the next 60 years.
More information on buildings and critical services located in the floodplain
can be found in the Maryland Hazard Mitigation Plan, prepared by the Maryland
Emergency Management Agency (MEMA).
Modeled Flood Vulnerability Estimates
In order to provide a systematic examination of the vulnerability of
Maryland’s built environment to riverine and coastal flooding, the Eastern Shore
Regional GIS Cooperative (ESRGC) at Salisbury University was asked to
undertake a vulnerability modeling effort. Using FEMA’s HAZUS-MH hazard
vulnerability analysis modeling software, the ESRGC sought to generate maps
and tables of Maryland’s potential for loss related to buildings from flooding on a
county-by-county basis. This potential for loss, or the degree of vulnerability,
was measured using four different factors: amount of county land area in
susceptible to a 100-year flood, the amount of square footage of buildings
potentially damaged, the number of buildings potential damaged, and the amount
of direct economic losses related to buildings. These four measures of loss help
give a more complete picture of the very complex issue of vulnerability to floods.
Completion of the HAZUS-MH vulnerability scenario modeling for every
county (and Baltimore City) in Maryland yielded a picture of varying degrees of
vulnerability to flooding throughout the state. Regarding the physical nature of
the flood zone, over 1,328 square miles of the state fall within the 100-year flood
zone. In other words, 13.4% of the land area of the state is vulnerable to a 100year flood event. These flood zone size estimates are comparable to those
completed using the Q3 digital flood zone maps (see above).
One measure generated by HAZUS-MH to express potential vulnerability
is the amount of square feet of damage to buildings in the event of a 100-year
flood. The results of the modeling effort reveal that 109,665,000 square feet of
Maryland building stock will potentially be damaged in the event of a 100-year
flood. Worcester County has the most building stock in harm’s way with over 21
million square feet or 19.4% of the total for the state. The other subdivisions that
are the most vulnerable with regard to buildings are Anne Arundel, Prince
George’s, Baltimore, and Baltimore City. The majority of damage to buildings in
the state of Maryland will be to residential buildings. In fact, about 86% of all the
potential damage from the 100-year flood comes from residential buildings. One
can also break down the potential building damage by the type of building
construction.
While construction types are much more widespread than
occupancy categories, wood (62%) and masonry (28%) dominate steel (7%) and
concrete (3%) in terms of damaged buildings.
An Assessment of Maryland’s Vulnerability to Flooding
Page 2
If one examines the level of vulnerability using the number of buildings
potentially damaged by a 100-year flood, rather than the amount of damaged
square feet, the pattern is similar but more evenly distributed. The county with
the most buildings damaged is Anne Arundel, followed by Worcester, Baltimore,
Prince George’s, and Washington. However, only Anne Arundel and Worcester
made up more than 10% of the state’s total number of buildings damaged
(44,755).
Finally, one can characterize the level of vulnerability from coastal and
riverine flooding in Maryland using the amount of direct economic losses related
to buildings. This measure includes monetary losses from the buildings
themselves (structural damage, contents damage, and inventory loss) as well as
monetary losses from the use or disuse of those buildings (losses related to
relocation, capital, wages, and rental income). The result of the HAZUS-MH
model for all the subdivisions in Maryland shows that $8.12 billion is vulnerable to
loss from a 100-year flood. Even more notable is that just 3 counties (Prince
George’s – $1.28B, Worcester – $1.03B, Anne Arundel – $0.92B) account for
almost 40% of the total direct economic losses related to buildings.
Strategies for Mitigating Flood Damage
Given the flood damage vulnerability potential for much of the state of
Maryland, it is prudent to adopt well-considered and appropriate measures to
mitigate the potential damage. The state agencies most involved with floodplain
hazard management, namely Maryland Department of the Environment (MDE),
Maryland Department of Natural Resources (MDNR), and Maryland Emergency
Management Agency (MEMA), have been collaborating for some time on a
variety of flood mitigation strategies. These include
•
•
•
•
•
•
•
•
•
•
•
Maryland Model Floodplain Management Ordinance
Local mitigation planning
Analysis of repetitive flood loss properties
Risk mapping exercises for floods and storm surges
National Flood Insurance Program
State Dam Safety Program
Stormwater management regulations
Wetlands regulations
Sea level rise response strategy
Growth management and,
“No Net Adverse Impact” watershed planning
An Assessment of Maryland’s Vulnerability to Flooding
Page 3
Maryland’s Efforts to Mitigate Flood Damage
The Comprehensive Flood Management Grant Program (CFMGP) has
been used to acquire structures, install flood-warning systems, construct flood
control projects, and other flood mitigation projects over the years. Between
1980 and 2002, a total of approximately $32 million in cost-share funding has
been provided by the state for flood management. This funding was used to
leverage up to 75% in Federal funds. In addition, beginning in 1946, federal
agencies have carried out major flood mitigation projects in Maryland. These
projects include dam, levee, and channel construction projects conducted by the
Army Corps of Engineers, removal of structures by the National Park Service,
and the restoration of waterways by the Natural Resource Conservation Service.
Report Recommendations
Therefore, given that Maryland’s predicted vulnerability to flooding impacts
tens of thousands of structures and multi-billion dollars in economic loss, more
must be done to mitigate the potential flooding impacts. Specifically, this report
makes nine policy recommendations:
1.
2.
3.
4.
5.
6.
The State’s Flood Management Grant Program needs to be able to
fund a wider range of activities than in the recent past. Although
acquisitions should remain the primary focus of the program, flood
studies, mapping, planning efforts, and other forms of mitigation should
also be considered for grant funds when appropriate and cost effective.
The State Flood Management Grant Program needs a reliable,
dedicated source of funding to fund mitigation projects. Other states
(Virginia, West Virginia) place a surcharge on flood insurance policies
of 1-5% to fund state mitigation efforts. A yearly surcharge of 3% on
Maryland flood insurance premiums would yield approximately
$500,000 per year for the program.
There needs to be better coordination of state agencies involved in
disaster mitigation and mitigation planning to prevent duplication of
effort and better use of state resources.
A “No Adverse Impact” policy should be implemented through the local
planning and permitting process with state assistance. Future
development would be predicated upon the principle that existing
development will not be harmed by greater flood heights from the
adverse impact of new development.
In conjunction with sea level rise and the preservation of wetlands, the
current policy of armoring shorelines needs to be examined.
Dynamic local planning will be important to lowering future vulnerability
to flooding. Much can be done at the local level to improve local
ordinances and policies to mitigate future disasters.
An Assessment of Maryland’s Vulnerability to Flooding
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7.
8.
9.
The state should provide support and strong tax and grant incentives
to individuals and communities that undertake measures that result in
proven future savings in disaster recovery costs.
Greater emphasis needs to be placed on maintaining riverine
floodplains and their associated wetlands and steep slopes in their
natural vegetation to maintain the vital functions of these important
ecosystems.
No state policy to deal with the consequences of sea level rise has
been articulated. The state needs to take action to articulate policies
to mitigate the effects of sea level rise. Among these should be
additional elevation of all new buildings (freeboard requirement) and
establishment of setback zones from eroding shorelines.
An Assessment of Maryland’s Vulnerability to Flooding
Page 5
Part I. History of Flooding and Flood Mitigation
History of Flood Hazard Mitigation in Maryland
Maryland has had a long history of flood hazard mitigation. The state saw
that it had a legitimate interest in assuring that floodplains are not unduly
restricted, and that it had a right and responsibility to regulate encroachment. A
program was initiated in 1933 by the enactment of the Waterway Construction
Law (Article 8-803 of the Natural Resources Article, Annotated Code of
Maryland) requiring that a person must obtain a permit if proposing any change
to the course, current, or cross section of any stream or body of water in the
state, except tidal waters. The primary objective of the permit program is to
assure the public safety and damage avoidance when projects are proposed in
the floodplain. In addition, the permit program addresses environmental and
living resource concerns. The permit program was administered under the Water
Resources Administration in the Department of Natural Resources for many
years, and, in 1992, the nontidal wetlands review was combined with the
floodplain review under the Nontidal Wetlands and Waterways Division. In 1995,
these functions were transferred to the Maryland Department of the Environment,
(COMAR 26.17.04). Originally, the requirement applied to the 50-year floodplain,
but the 100-year floodplain standard was adopted in 1976 to be consistent with
the federal requirements.
In 1968, Congress passed the National Flood Act, which established the
National Flood Insurance Program (NFIP). This act made specified amounts of
flood insurance, previously unavailable from private insurers, available under
federal auspices. At this time, the Federal Insurance Administration (FIA) of the
U. S. Department of Housing and Community Development administered the
NFIP. A community could join the program by applying for coverage and
agreeing to adopt land use control measures intended to reduce future flood
losses. However, the FIA was slow in producing the flood insurance studies
necessary to delineate the 100-year floodplain and set actuarial insurance rates.
When Hurricane Camille hit in August 1969, only four communities had qualified
for the program. In response, the Emergency Flood Insurance Program was
enacted in 1969 to allow communities to immediately enter the program without a
detailed study, making flood insurance available if they agreed to adopted land
use measures to reduce flood losses. Using data at hand, flood hazard
boundary maps were produced depicting the approximate 100-year floodplain to
give communities some idea of the areas they must regulate. Later, flood
insurance studies were conducted, using detailed methods to delineate the 100year floodplain and set actuarial premium rates. The Act was not very effective
in restricting development in floodplains, since people felt they would receive
disaster relief and did not need flood insurance. Also, the FIA was slow in
making the flood hazard boundary maps available.
An Assessment of Maryland’s Vulnerability to Flooding
Page 6
The NFIP was further enhanced by the passage of the Flood Disaster
Protection Act of 1973. The Act increased the limits of coverage, extended the
emergency program, and set a requirement for purchase of flood insurance for all
federally supervised lending institutions making loans for construction in flood
prone areas. Persons in nonparticipating communities were denied federal
assistance in the form of grants, loans, and mortgages on buildings in the flood
hazard area. The requirement for flood insurance is implemented through
lenders, who, to receive any federal assistance, must secure the loans with flood
insurance. Flood prone communities were identified, notified of their eligibility to
participate, and given until December 31, 1975, to apply. However, the program
was still slow to catch on because many local officials did not understand the
value of the NFIP or the process to apply and adopt regulations.
In 1973, Maryland passed the Flood Disaster Protection Act in response to
the devastation caused by Hurricane Agnes in June of 1972. It established the
Flood Disaster Coordinating Office within the Department of State Planning to
coordinate state recovery planning from Agnes. Its role was to coordinate the
recovery effort and agencies conducting studies and investigations of flooding
problems in Maryland, including the Federal Insurance Administration (FIA), U. S.
Army Corps of Engineers, U. S. Geological Survey, U. S. Soil Conservation
Service, and the Maryland Department of Natural Resources.
By 1973, many of the riverine watersheds in Maryland having serious
flooding problems were in some phase of study. Studies were done on a
watershed basis, not on a jurisdictional basis as required by the FIA. However,
the issue of coastal flooding and tidal inundation was not addressed. An Army
Corps survey of the Chesapeake Bay was made in 1963, but contained no
provisions to do any studies, although it noted the entire shoreline was
vulnerable to damage from abnormal tides and wave action from severe storms.
A State Soil Conservation Committee was established in 1937 under the
State Board of Agriculture, and moved to the Maryland Department of Agriculture
when it was established in 1972. The Committee worked with the 24 Soil
Conservation District offices in Maryland on soil and water problems, including
watershed protection and flood prevention projects, as well as river basin studies.
By 1974, 41 projects had been approved, including 19 dams and 22 flood
prevention and drainage ditch projects. The Soil Conservation Service also
completed flood insurance studies for the FIA, while the U. S. Geological Survey
did the Flood Hazard Boundary Maps.
The Water Resources Administration (WRA) in the Maryland Department
of Natural Resources (DNR) was responsible for water resource management
activities. In addition to permitting responsibilities, DNR was charged with a
program to control the waters of the state and cooperate with federal agencies in
matters pertaining to flood control under COMAR 8-901. Included was providing
assistance to local governments in drafting land use regulations pertaining to
An Assessment of Maryland’s Vulnerability to Flooding
Page 7
areas subject to flooding and conducting floodplain studies to support this effort.
DNR was to act as the State Coordinating Office for the NFIP.
As of March 27, 1974, 39 Maryland jurisdictions were eligible for
emergency coverage in the NFIP. Two jurisdictions, Prince George's County and
Ocean City, were in the regular program. However, preliminary flood hazard
boundary maps had been issued to only six jurisdictions.
Maryland passed the Flood Control and Watershed Management Act of
1976 to provide the foundation for watershed planning for flood management.
Five goals were established:
(1) reduction of existing flood hazards,
(2) prevention of future flood hazards,
(3) adequate emergency preparedness,
(4) preservation of the environmental quality of watersheds, and
(5) reduction of economic and social losses.
The Act also stated the need for better coordination among agencies having
flood hazard mitigation responsibilities. It mandated the development of a list of
priority watersheds to be studied for the 100-year flood and the preparation of
local flood management plans. The Act created a comprehensive flood
management grant program (CFMGP) within DNR which could use proceeds
from state debt, upon approval of the Board of Public Works, to fund watershed
studies and flood control and watershed management capital projects. However,
no funding was provided until 1980.
The Act was amended in 1980 to authorize $7.5 million in bond revenue
for implementation of capital projects. Amendments in 1981 allowed this money
to be used for technical studies. As the technical studies and flood management
plans were completed, the need for capital projects became apparent, as well as
the need for additional funding. The law and implementing regulations encourage
acquisition and removal of flood prone structures, while recognizing that
structural control measures may be required in certain circumstances. In 1982,
the General Assembly authorized an additional $1.5 million in bond funding for
the CFMGP. The state funded almost $30 million to the CFMGP for cost shared
grants in the period 1980 - 1991, after which the flood grant program was
suspended due to budgetary constraints. However, after two major flooding
events in 1996, the program became active again, with funding in 1998 until
2003.
The development of the Storm Surge Model for the Chesapeake Bay by
the Virginia Institute of Marine Sciences in 1978, allowed the development of tidal
water surface elevations for different frequency floods by generating a model
storm surge up the Chesapeake Bay. The Federal Emergency Management
Agency (FEMA), which had taken over the FIA, developed WHAFIS, a computer
An Assessment of Maryland’s Vulnerability to Flooding
Page 8
program to determine wave height elevations for coastal areas in 1981. These
technologies advanced the development of Flood Insurance Studies for coastal
areas in Maryland, which were completed by WRA in the early 1980's.
In 1981, the General Assembly created the Emergency Management
Advisory Council, including representatives from state agencies, county and
municipal representatives, and emergency managers, to advise the Governor on
emergency management matters. The Department of State Planning had
previously been given a coordinating role after Hurricane Agnes in 1972 for flood
recovery planning and prevention programs within various state and local
agencies. The State Hazard Mitigation Office was delegated to WRA in DNR by
FEMA, and tasked with a variety of pre-disaster and post-disaster
responsibilities. Included was leading the State Hazard Mitigation Team,
preparing federally required hazard mitigation plans, and identifying mitigation
projects. In 1995, the State Hazard Mitigation Office was moved to the Maryland
Emergency Management Agency (MEMA), which now leads the state's
involvement in post-flood response and mitigation activities. It is responsible for
preparing the preliminary damage estimates for the Governor to request a
Disaster Declaration and serves as the Governor's Authorized Representative
during disasters.
The state of Maryland, through WRA, worked closely with FEMA in
coordinating the NFIP at the local level.
When the Community Assistance
Program - State Support Services Element (CAP-SSSE) was created in 1980 as
part of the National Flood Insurance Act, FEMA delegated responsibility to WRA
to implement the NFIP in the state of Maryland. The Governor delegated the
functions of the State Coordinator for the NFIP to WRA. Regular funding was
created by 1985 to provide technical assistance to communities for adopting and
implementing floodplain management ordinances. Planning funds were provided
in the early 1980's for developing a master plan of mitigation and public
education activities. Currently, the State Coordinating Office, now in Water
Management Administration of the Maryland Department of the Environment,
serves 116 communities participating in the NFIP in the state.
The Coordinating Office visits participating communities every 2-3 years to
assure adequate implementation and enforcement of local floodplain
management ordinances. In 1989, FEMA determined that a resolution to accept
the state's permit in lieu of local ordinances was not sufficient. This resolution
had been used in a number of small towns for years. In 1990, a State Model
Floodplain Management Ordinance was developed incorporating both the NFIP
and state requirements, and a major effort began to have all communities adopt
a new ordinance over the next two years. The Coordinating Office provides
general technical assistance to citizens about flood insurance, flood mitigation,
building standards, flood mapping, and flood safety.
An Assessment of Maryland’s Vulnerability to Flooding
Page 9
History of Flooding in Maryland
Table 1 lists the major historical flooding events in Maryland:
Table 1. Flooding history of Maryland
Year
Date
Description
1860
May 11
First recorded flood occurred along Jones Falls with heavy damage
to the City's business district and bridges over Jones Falls.
1868
July 24
Jones Falls again flooded Baltimore City with heavy loss of life and
property. Patapsco River flooded Ellicott City.
1876
1889
Unknown
June
1911
1923
August 4
July 23
1924
March 28-30
"Centennial Storm" noted in Wicomico County.
Susquehanna and Potomac Rivers largest flood of record to date
(50 to more than 100-year recurrence interval).
Herring Run through Baltimore County and City.
Patapsco River flooded greater than in 1868. Ellicott City
under water.
Potomac was 20 feet above normal due to snowmelt and intense
rainfall, devastating parts of Cumberland (recurrence interval 20 to
more than 100-year).
Potomac flooded Cumberland; Antietam Creek flooded Hagerstown.
May
1933
August 23-24
1934
March 4
July 9
1936
1937
September
March 17-19
January
April
October
1942
August
October
1945
1948
1949
July
July
Flooding on Eastern Shore due to hurricane. Thirteen deaths, $12.3
million damage (recurrence interval 10 to more than 100-year).
Spring thaw floods Carroll and Howard Counties.
Aberdeen, Havre de Grace, and Elkton flooded; Roads and bridges
in Southern Maryland washed out.
Federalsburg flooded 9 feet above normal.
Snow melt and heavy rainfall causes most extensive flooding of
Potomac and Susquehanna Rivers, especially Cumberland,
Hancock, Williamsport, Point of Rocks, Port Deposit, and Havre de
Grace. Losses of $5 million. (Recurrence interval 20 to greater than
100-year).
Potomac floods Hancock
"Northeaster" causes extensive flooding statewide. Damage to
Cumberland, Williamsport, Baltimore, Dundalk, Washington, DC,
Chestertown, Salisbury, and southern Maryland.
Anacostia River floods Hyattsville, Bladensburg, and other parts of
Prince George's County. Gwynns Falls and Patuxent River cause
minor floods. A week later Potomac floods Cumberland and
Hancock and parts of Southern Maryland flooded.
Rains flood Dundalk, Parkton, and southern Maryland.
Potomac floods Cumberland, Hancock, Williamsport, and Point of
Rocks. Washington, DC had floods 17.6 above normal. Patapsco
floods Ellicott City.
Minor flooding throughout state due to extended rainfall.
Minor flooding on Eastern Shore
Minor flooding in Hagerstown, Frederick, and Baltimore Counties.
An Assessment of Maryland’s Vulnerability to Flooding
Page 10
Year
Date
1954
October 1416
1955
August 12-13
1958
August 26
1960
1962
July
August
September
12-13
March 6-7
1966
1967
1970
1971
September
August
April
August 1-2
Sept. 11-12
1972
June 21-24
1974
Dec. 1
1975
September
23-26
1979
Feb. 24-26
Sept. 5-6
1984
March 28-29
August 13
1985
Aug. 18
Sept. 27
Nov. 4-7
Description
Hurricane Hazel dumped heavy rains on North Branch of the
Potomac River, causing flooding from Cumberland to Washington,
DC. Savage River Dam, built in 1951 prevents more extensive
damage. Other areas of state suffer damage. Winds of over 100
mph reported on Eastern Shore. Six deaths; $11.5 million damage.
Recurrence interval 25 to greater than 100-year storm.
Hurricane Connie dumps heavy rains on Eastern Shore of over 10
inches. Baltimore - Washington area flooding.
Heavy rains cause dam failure on Marshyhope Creek, flooding
Federalsburg.
Tropical storm Brenda causes flooding in St. Mary's County.
Potomac and Wills Creek flood Cumberland.
Hurricane Donna causes flooding on Eastern Shore, especially to
Ocean City. Two deaths.
"Northeaster" causes extensive flooding on Eastern Shore. Called
the most destructive extra-tropical storm experienced on East Coast.
Two thirds of Ocean City's population evacuated, with one death.
Minor flooding throughout state of 10-year frequency.
Federalsburg and Greensboro severely flooded.
Minor flash flooding in Cumberland.
Heavy flooding in Laurel, Westminster, Ellicott City, and Baltimore as
a result of thunderstorms. Fourteen deaths and $6.5 million in
losses. Recurrence interval 25 to more than 100-year.
Heavy rains in Central Maryland, especially Howard County cause
$4 million in losses.
Hurricane Agnes, the worst flood in 36 years, and estimated to be
the 100-year flood in many places, floods many parts of state.
Damage estimated to be several hundred million dollars and 19 lives
lost. Severe damage in Ellicott City, Port Deposit, Cumberland,
Williamsport, Point of Rocks, and Baltimore City and County.
Deaths -19; losses $80 million; recurrence interval 50 to greater than
100-year.
Storms and tidal surges cause damage statewide, especially on the
Western Shore of the Bay.
Hurricane Eloise causes flooding especially in Monocacy and
Patapsco River basins with $6.2 million damages. Recurrence
interval 10 to greater than 100-year storm.
Snowmelt and intense rainfall causes flooding especially in
Pocomoke River - 50 -100-year storm.
Hurricane David floods Rock Creek, Jones Falls, East Branch
Herbert Run. Recurrence interval 50 to greater than 100-years.
Statewide flooding and intense coastal erosion, especially along
lower Chesapeake Bay. Two deaths.
Heavy thunderstorms from Harford to Frederick Counties, especially
in Baltimore area.
Remnants of Hurricane Danny flood St. Mary's Co with 10
inches of rain.
Hurricane Gloria floods Eastern Shore with storm surge, especially
Ocean City.
Hurricane Juan combined with stationary front causes flooding
statewide, but especially in Potomac river basin. One death and $5
million (nontidal) and $16 million (tidal) damages. Recurrence
interval 2 - more than 100-year.
An Assessment of Maryland’s Vulnerability to Flooding
Page 11
Year
Date
Description
1989
June 23
July 6
August 20
Thunderstorms cause flash flooding in Allegany Co.
Statewide flooding, but most severe in Elkton.
Thunderstorms dump 10 inches of rain in Pocomoke River area.
1992
Jan. 4
Northeaster caused severe beach erosion in Ocean City Assateague area. West Ocean City area experiences floods (Snug
Harbor, Eagle's Nest, Frontier Town).
Heavy rains in Cecil Co. cause flooding especially of Main Street in
Elkton by Big Elk Creek
Heavy rains (5 inches) cause flooding in Frederick area (Monacacy
River).
Thunderstorms in Westernport, Allegany Co. cause runoff from
surrounding mountains.
Heavy rains and snow melt cause widespread flooding in Western
MD (AL, GA, WA, FR counties) and in Cecil County, esp. Port
Deposit and Farr Creek.
Isolated thunderstorms flood parts of Frederick Co. especially
Emmitsburg.
Remnants of Hurricane Fran cause widespread flooding in Western
MD, especially George's Creek. $1.7 million in damages.
Hurricane Floyd causes widespread flooding on Eastern Shore,
especially in northern portions. Damages $14 million, and greater
than 500 year flood in places.
Local thunderstorms flood SW Cumberland from stormwater off
Haystack Mountain.
Remnants of Hurricane Isabel cause widespread tidal surge
flooding, esp. in middle portion of Bay. Close to 100-year flooding.
Riverine flooding minor.
Local thunderstorms cause isolated flooding in Baltimore City and
Harford Co, especially Havre de Grace.
Dec. 11
1993
Nov. 28
1995
June
1996
Jan. 19-20
June
Sept. 6
1999
Sept. 16
2000
Sept.
2003
Sept. 18-19
2004
July
Flooding and the 100-year Floodplain in Maryland
Land adjacent to any water body is subject to flooding. Flooding is a
result of unusually high water levels associated with meteorological events.
Flood is defined under the NFIP regulations as "a general and temporary
condition of partial or complete inundation of normally dry land areas from the
overflow of inland or tidal waters or the unusual and rapid accumulation or runoff
of surface waters from any source". The term "flood stage" refers to the level at
which waters begin to rise above riverbanks. High water is generally not
considered to be a problem until it begins to adversely affect people or their
property.
There are three general classifications of types of flooding:
•
Nontidal Flooding - flooding from rivers, streams, etc., with gravity flow
downstream.
An Assessment of Maryland’s Vulnerability to Flooding
Page 12
•
•
Tidal Flooding - flooding by slowing rising water from tides and storm
surges.
Coastal High Hazard Flooding - flooding from static tidal flooding with
the addition of waves of at least three feet.
Most of Maryland's inland nontidal watersheds are relatively small in area.
Prolonged or intense rains run off quickly, accumulating in tributary streams and
main channels within hours. The waters typically rise quickly often resulting in
flash flooding, but fall just a quickly as the water moves on downstream. Studied
nontidal floodplains have designated floodways, where the deepest and high
velocity waters will flow during the 100-year flood. A few watersheds are
extensive enough that waters may stay above flood stage for several days to a
week. These include the Potomac, Susquehanna, and Monocacy Rivers.
Waters in tidal areas often rise and fall much more slowly and predictably,
and may be influenced by tidal cycles, extensive low-pressure weather systems,
and strong prolonged onshore winds. Although more extensive areas may be
flooded, flow is not as strong as nontidal rivers experience, since large gradients
do not exist. Erosive forces are not as strong, unless high wave energies are
experienced. Tidal flooding affects extensive areas of low relief along the
Chesapeake Bay and its tributaries and the back bays behind the Atlantic coast.
Flooding along the Atlantic coast and the Chesapeake Bay caused by tropical
storms, hurricanes, and northeasters may be very severe with high waves on top
of strong tidal surges.
The 100-year floodplain is the one percent chance per year flood area
mapped by the Federal Emergency Agency (FEMA). Since this is a probability
statement, it should be understood "100-year floods" may occur more frequently
than once every 100 years. The 100-year floodplain is the area regulated by
local floodplain ordinances adopted by communities that are in the National
Flood Insurance Program (NFIP). Technically, only the outer edge of the 100year floodplain has a 1% risk of flooding. The risk rises for sites closer to the
flooding source and at lower elevations. There are areas within the mapped 100year floodplain that may flood more frequently and to greater depths than others,
even though people think of the entire 100-year floodplain as having the same
risk.
Flood maps and elevations are based on estimates of the 100-year flood
discharge, determined by a number of techniques and based on a point in time.
Factors such as the size of the watershed, the availability of stream gage
records, and the level of detail used in the mapping and the model contribute to
the uncertainty of the 100-year discharge estimates. Subsequent changes in
land use in the watershed and to the stream channel and its floodplain will
contribute further uncertainty. After a flood discharge rate is determined, a
hydraulic model computes the elevation of the 100-year flood within an accuracy
of 0.5 to 2.0 feet, depending on the accuracy of the topography, frictional losses,
An Assessment of Maryland’s Vulnerability to Flooding
Page 13
and hydrology used. Once the elevation of the 100-year flood is determined, it is
mapped on a topographical map, which again varies in precision and level of
detail.
The accuracy of the 100-year floodplain boundary is influenced most
strongly by the quality of the 100-year discharge estimates. The next most
significant factor is the quality of the topographic mapping. The Galloway Report
estimated that probable nationwide standard error for base flood elevation
mapping is 23% of the base flood depth. This value, translated into an average
depth, amounts to about 3 feet. Thus, the floodplain line shown on a map is not
absolute; structures located within several feet vertically of the 100-year flood
elevation may be at risk. In flat areas, structures located within several hundred
feet or more horizontally of the 100-year floodplain line also may be at risk.
The standard error is increased by the age of the Flood Insurance Studies
(FIS), and the fact that they were based on the existing development at the time
of the study. A FIS provides the technical documentation to support flood
elevations printed on the Flood Insurance Rate Maps (FIRMs). Any area that
has experienced significant watershed and/or floodplain development may
experience flooding different from that predicted by the study. In 2004, the
average age of FIRMs in Maryland was 19 years, indicating a great need to
update the studies and maps. Better technology is available today to more
accurately evaluate the risk, and it should be used in updating the older studies.
The 100-year floodplain in Maryland is shown in the figure below. The
percent of land area in each county that is floodplain varies from 55.8% in
Dorchester County down to 4.6% in Garrett County. However, the percentages
do not reflect the seriousness of the flooding problems. Tidal areas have
extensive flat areas flooded by shallow waters with little or no current, but may be
much more extensive. Riverine areas may have steep gradients where water
flows at very high velocities and to greater depths, with extreme erosive forces.
Coastal high hazard areas have enough fetch over large water bodies to create
waves of 3 feet or more. These different flooding scenarios will result in different
flooding problems and damages.
An Assessment of Maryland’s Vulnerability to Flooding
Page 14
An Assessment of Maryland’s Vulnerability to Flooding
Page 15
Part II. Floodplain Development
Structures in the Floodplain
Estimates of the built environment have been made using two methods,
shown in Table 2. One was taken from the Community Assistance Visit (CAV)
records, in which communities are asked to estimate the number of structures in
their floodplains. County estimates may not be accurate, and in many cases we
do not know how they were derived. A few counties were unable to provide any
estimates. Another estimate was taken by overlaying the Q3 digital floodplain
lines onto parcel information from MDProperty View, which does provide a
consistent methodology throughout the state. There are a number of problems
with the overlay, namely that the fit is not always good, and we are not sure
where the improvements are on the parcel of land. However, we do have
concrete data on the types of improvements and more importantly, the value of
the improvements. The community estimates were significantly lower than those
provided by the overlays. The population estimates were taken from applying the
average number of persons per household in each county from 2000 census
data to the number of improvements in the floodplain. However, it should be
noted that not all the improved structures are residential, so the method would
provide an over-estimate of floodplain population. Approximately 30% of flood
insurance policies nationally are written for areas outside the 100-year floodplain.
It would seem to be reasonable to average the two results (57,795 +
78,638)/2 to estimate the total number of structures in the floodplain for
Maryland, which gives a result of 68,217 structures.
The percent of property in Maryland covered by flood insurance policies is
nearly 74%, which is far above the national average of about 30%. The
insurance policy count is higher than expected, but is likely to be skewed by the
fact that over half the policies in Maryland are in Worcester County, mainly
Ocean City. In multiple occupancy units, there may be a number of policies per
building. Some policies may cover the building, while others cover the contents
of each unit within the building. Thus, one building would have multiple flood
insurance policies. If the data from Worcester County is eliminated, the policy
coverage drops to 47% statewide. Analysis of the data indicates that the more
developed counties with more housing stock also have higher rates of flood
insurance coverage, while in some of the rural counties rates may drop below
30%.
An Assessment of Maryland’s Vulnerability to Flooding
Page 16
Table 2. Structures and people in floodplains in Maryland
2420
10088
2973
16067
3983
1265
6063
$76,947,040
$691,534,340
Flood
Insurance
Policies
(2002)
419
4406
6000
4000
1672
1653
$640,920,560
900
54.4
16323
1523
390
2288
5096
1098
6550
682
104
1960
1740
750
10300
15213
3300
1608
1352
6179
1739
7264
3672
1211
4504
2520
2756
5559
7491
6712
579
158
1103
2210
1037
2750
294
31
741
956
4
277
4045
6184
1134
609
481
2280
608
2761
1350
475
1656
930
1183
2090
2734
$630,154,881
$123,665,770
$46,807,801
$58,158,060
$171,198,955
$76,642,190
$237,910,750
$366,260,240
$41,959,550
$184,647,550
$179,293,170
$110,788,300
$577,218,670
$479,081,120
2962
558
185
146
823
275
1179
321
139
608
339
445
1059
984
47.9
49.2
30.4
30.4
36.1
45.2
38.3
23.8
29.3
36.7
36.5
37.6
50.7
36.0
2800
7829
1205
2988
$344,088,796
1878
62.9
2705
7900
5273
2900
17500
3411
10523
4503
2221
3003
74913
1105
316
2228
1051
2
6375
1254
4440
1941
903
1187
32152
$109,075,140
$243,355,070
$311,748,620
$109,596,840
$110,272,270
$2,068,494,400
592
1488
1822
264
401
28792
47.2
33.5
62.9
29.2
33.8
89.5
133097*
193813
57795*
78638
$7,989,820,083
50394
64.1
People
County
Allegany
Anne
Arundel
Baltimore
City
Baltimore
Calvert
Caroline
Carroll
Cecil
Charles
Dorchester
Frederick
Garrett
Harford
Howard
Kent
Montgomery
Prince
George's
Queen
Anne's
Saint Mary's
Somerset
Talbot
Washington
Wicomico
Worcester
TOTALS
CAV
Structures
Overlay
CAV
Overlay
Value of
Improvements
(2001)
Percent
Policies
33.1
72.7
Note * indicates totals data is adjusted by adding the average number of people and structures
for the missing counties.
Lastly, the value of the improvements on improved land in the 100-year
floodplain was calculated from overlays of the floodplain lines on MDProperty
View data by county. The total gross value of all the improvements exposed to
flooding is close to $8 billion. However, this figure does not reflect the amount of
damage that would occur from the 100-year flood. The actual damages would
depend on the depth of flooding, the elevation of buildings, presence of
An Assessment of Maryland’s Vulnerability to Flooding
Page 17
basement, and other factors, such as erosion, and would be based on depthdamage curves for different building uses.
Structures Subject to Coastal Erosion
In 1994, the Department of Natural Resources estimated that
approximately 2,500 structures are subject to long-term erosion. Many of the
structures are located on bluffs and are not subject to flooding. The report noted
that lack of consistent erosion zone delineations makes it difficult to estimate the
number of buildings in Maryland reasonably expected to be subject to coastal
erosion over a 30-year period. The estimate is based on the fact that of the
3,700 miles of shoreline of the Chesapeake Bay in Maryland, less than 8%, or
273 miles, is deemed to be eroding at rates of 2 feet/year. The estimate does
not include Ocean City because the joint town, state, and Army Corps protection
project there is expected to protect structures from 100-year erosive forces. The
report estimated that approximately 127,500 buildings are subject to flood
damage, which is double the more recent estimate above of 68,217 structures.
Coastal erosion is a natural process; sandy beaches naturally migrate
inland. Structures built on them will be lost over time unless expensive measures
are taken to preserve them. Ocean City is built on a barrier island, part of a
system of barrier islands that protect the East Coast from the ocean waves. The
natural process is for the dunes to retreat as sea level rises or the land subsides.
Fenwick Island has migrated an average of 2 feet per year landward. With
houses in the way, there is no place for the dunes to migrate. Ocean City is
maintained by an expensive process of beach nourishment, or pumping sand
from out in the ocean back onto the beach as it is lost. In other areas, retreat is
more likely the solution to coastal erosion.
A national report, Evaluation of Erosion Hazards, provides a
comprehensive assessment of coastal erosion and its impact on people and
property. The report, prepared by the Heinz Center for Science, Economics and
the Environment for FEMA, projects that approximately 25% of homes and other
structures within 500 feet of the U.S. coastline will fall victim to the effect of
erosion in the next 60 years. Thus, long- term erosion will likely affect areas like
Ocean City.
Especially hard hit will be Atlantic and Gulf of Mexico coastlines, which are
expected to account for 60% of the losses nationwide. Costs will average half a
billion dollars per year, and could be considerably higher if additional
development is allowed in high erosion areas, according to the report.
The report recommends that FEMA develop maps identifying coastal
erosion hazard areas and include the cost of expected erosion losses when
setting flood insurance rates, based on measured erosion rates. Coastal High
An Assessment of Maryland’s Vulnerability to Flooding
Page 18
Hazard Zones would include risk factors for both flood and erosion, with premium
surcharges for erosion. In addition, setback standards would be established and
communities would be required to impose standards for new development.
Under the recommendations, erosion insurance could be provided to bluff areas.
Currently, only Calvert County has any regulations governing setbacks
from the edge of cliffs.
State Buildings in the Floodplain
State buildings on state land in the floodplain are not subject to local
review, but must submit plans for floodplain review under the State Waterway
Construction Permit process. This is supposed to insure that state development
will meet at least the minimum requirements of the NFIP. Otherwise, any state
development should be submitted for local floodplain review and approval. The
local permit should satisfy the requirements of the NFIP.
Based on a 1987 legal opinion regarding flood management review of
state projects, it was noted that the state DNR had review authority of flood
control measures in state construction projects under Section 8-905 of Natural
Resources Article until its repeal in 1984. The new Subtitle 9A Flood Control and
Watershed Management replaced it. Section 8-9A-04 (a) provides that DNR
"assure that state construction projects meet the requirements of this subtitle".
This was interpreted to mean that DNR will assure that state construction
projects comply with state flood control law. In other words, plan approval for
correct elevation in a floodplain lies within DNR by state law, thus exempting
these projects from local review. Therefore, the state review would have to
incorporate the minimum NFIP standards, and more stringent local standards
would not apply. State permit jurisdiction does not extend into tidal floodplain
areas, however.
The adequacy of the state project review process was called into question
by FEMA in 1990, after permits were issued by the state for construction in the
FEMA floodway. The state defended its permit review process, maintaining that
in many respects the review exceeds NFIP requirements by requiring an analysis
based on ultimate development, that structures be elevated one foot above the
100-year flood elevation, and the "no rise" rule on improved property. The state
admitted that their regulations do not explicitly reference the floodway delineated
on the FEMA maps. Although no changes were made to the state regulations, a
policy was instituted to resolve any floodway issues to be consistent with the
NFIP requirements.
At the same time, it was noted that state construction within tidal
floodplains is guided by policies within each constructing agency. DNR pledged
to work with state agencies to put in place clear standards for the tidal floodplains
An Assessment of Maryland’s Vulnerability to Flooding
Page 19
comparable to the nontidal floodplain requirements. The two largest construction
agencies, the Department of General Services and the State Highway
Administration have worked to assure that that their projects either avoid the
floodplain or are consistent with NFIP requirements. Other agencies have
volunteered to send plans for floodplain review. Often plans are submitted to
local jurisdictions for review, as well.
Any projects receiving federal funding must comply with Executive Order
11988, issued in May 1977. It charged federal agencies to assert leadership in
reducing flood losses by avoiding actions located in or adversely affecting
floodplains, unless there is no practicable alternative, or to mitigate losses if
avoidance is not practicable. Guidelines were established in an eight step review
process: (1) determine if proposed action is in floodplain, (2) provide public
review, (3) identify and evaluate alternatives to floodplain, (4) identify impacts, (5)
minimize threats to life and property and preserve and restore natural and
beneficial floodplain values, (6) reevaluate alternatives, (7) issue findings, and (8)
implement the action. Federal actions that increase annual losses from floods or
adversely affect floodplains are contrary to EO 11988 and should not be funded
or undertaken. If a practicable alternative exists outside the floodplain, the
proposed action must not be located in the 100-year floodplain (or 500-year
floodplain for critical actions.)
In 1990, a project was undertaken by Water Resources Administration,
DNR to inventory all state owned structures in the 100-year floodplain. This was
undertaken in conjunction with the General Services Administration to assure
that state buildings were adequately insured and if any mitigation measures
might be employed to protect them. The resulting database is shown in
Appendix C. Where possible, elevations of the lowest floor or entry point of
floodwaters were obtained and compared to the 100-year water surface
elevations.
State Schools Subject to Flooding
Out of approximately 1,200 public schools in Maryland, only a few are in
the floodplain. In 1985, the Oldtown School in Allegany County received
extensive damage when high discharges from the South Branch of the Potomac
River created a blockage which caused the main stem of the Potomac to back up
rapidly and flood the school with approximately 8 feet of water, along with several
homes in Oldtown. As a result of negotiations with FEMA, this school was the
only presidentially declared disaster for a single building in FEMA history. The
state agreed to develop a plan to assess the flood risk of all public schools in the
state and the procedure by which local school boards select future school sites.
The plan developed guidelines to insure adequate identification of floodplains
and wetlands in the school site selection process. The NFIP State Coordinator
must comment on the proposed school sites prior to the commitment of funding.
An Assessment of Maryland’s Vulnerability to Flooding
Page 20
The effort also identified schools in the state subject to flooding. Of those
identified, 7 were considered to have flood risks from moderate to severe, and 6
others to be marginally affected. A few only had athletic fields or access routes
subject to flooding. The three that have the most severe flood risk are the
Oldtown School, the Westernport School, and the Flintstone School (situated
less than 5 feet from the eroding stream bank of Flintstone Creek). A plan to
move vital records to the second floor for permanent storage and to move
damageable equipment to the second floor if floods threaten was developed for
the Oldtown School. The warning and response plan included an inward opening
door to escape a flood (since the last adults to leave had difficulty getting the
outward opening doors to open). Fire codes require all doors to open outward,
which could constitute a hazard during flooding. The Westernport School
received a state grant of $100,000 to floodproof the lower level, which included
flood shields over the windows and doors. However, the school received
significant damage in the September 1996, flood, even though the shields were
in place, since the seals on the closures had not been maintained. The rubber
gaskets exposed to sunlight will deteriorate and must be replaced periodically.
A plan to place gabion protection along the eroding stream bank at Flintstone
School was never implemented.
The Cross County Elementary School in Baltimore underwent extensive
renovations and incorporated much flood protection into the design. Other
schools may have had renovations to reduce the potential flood damages and
risks because of the increased awareness. No known new schools have been
built in the floodplain since the procedures were implemented.
Table 3 lists the schools in Maryland that are known to be subject to
flooding by being in the 100-year floodplain or have flooded in the past.
Other Critical Services and Local Public Buildings Subject to
Flooding
Maryland Emergency Management Agency (MEMA) has prepared the
Maryland Hazard Mitigation Plan. This plan includes data on state and local
buildings in the 100-year floodplain, including hospitals, fire, police, and other
local critical services. The plan can be accessed on the MEMA website at
www.mema.state.md.us/programs/mitigation. The data have been
georeferenced and located on maps by county. Chapters 8, 9, and 10 are
devoted to flooding from flash and riverine flooding, coastal storms, and dam
failure respectively. Building values were estimated from MDProperty View and
contents from the agency occupying the building to determine total exposure.
An Assessment of Maryland’s Vulnerability to Flooding
Page 21
Table 3. Schools subject to flooding
County
Allegany
Baltimore City
Baltimore Co.
Dorchester
Garrett
Harford
Kent
Prince
George’s
Somerset
School
Westernport
Elementary
Oldtown School
Flintstone School
Northeast Elementary
Bel Air Elementary
Beechfield Elementary
#246
Cross Country
Elementary 247
Southeastern Tech
South Dorchester K-8
Friendsville
Elementary
Havre de Grace
Elementary
Rock Hall Middle
Paint Branch
Elementary
Forest Heights
Elementary
Tylerton School
Ewell Elementary
Crisfield Elementary
Comments
First floor floodproofed in 1990. Damage in Sept.
1996. History of frequent flooding -Potomac River
Extensive damage 11/85 - Potomac River
Close to Flintstone Creek. Has flooded.
Dry Run Tributary
Riverine - Unnamed tributary of Potomac
Riverine - Maidens Choice. History of frequent
flooding
Riverine - Western Run
Tidal flooding- Peach Orchard Cr.
Tidal flooding
Riverine - Youghiogheny River
Riverine - Lilly Run
Fringe of tidal
Riverine - Paint Branch
Riverine - Oxen Run
Tidal flooding
Tidal flooding
Tidal flooding
MEMA is working with Towson University to develop the Emergency
Management Mapping Application (EMMA) to enable the emergency
management community to access and display relevant and real-time information
on a map before, during, and after an incident occurs. Built using ESRI's ArcIMS
software, EMMA is a secure, content and tool-rich, Web-based GIS application
that enables the emergency responders to identify incident locations from the
field, generate location-specific reports, visualize incident locations via a map,
perform site-specific analysis, and coordinate response efforts. Using a simple
Web browser, such as Internet Explorer, EMMA provides basic and advanced
tools for map visualization, location analysis, and report generation.
An Assessment of Maryland’s Vulnerability to Flooding
Page 22
Part III. Modeled Vulnerability Estimates
In order to provide a systematic examination of the vulnerability of
Maryland’s built environment to riverine and coastal flooding, the Eastern Shore
Regional GIS Cooperative (ESRGC) at Salisbury University was asked to
undertake a vulnerability modeling effort. Using FEMA’s HAZUS-MH hazard
vulnerability analysis modeling software (see below), the ESRGC sought to
generate maps and tables of Maryland’s potential for loss related to buildings
from flooding on a county-by-county basis. This potential for loss, or the degree
of vulnerability, was measured using four different factors: amount of county land
area in susceptible to a 100-year flood, the amount of square footage of buildings
potentially damaged, the number of buildings potential damaged, and the amount
of direct economic losses related to buildings. These four measures of loss help
give a more complete picture of the very complex issue of vulnerability to floods.
Software
FEMA developed a hazard vulnerability analysis
software package, HAZUS-MH, which can be used to
estimate the potential losses from earthquakes, wind,
and floods. There are three levels of analysis that can be performed for floods.
Level 1 is the most basic level of analysis. Supplied datasets can be used for
this type of analysis. A Level 2 analysis is a slightly more detailed analysis that
requires more accurate building information. Finally, a Level 3 analysis is the
most detailed level of analysis.
To do the flood analysis, FEMA developed software components to
support HAZUS-MH. The Flood Information Tool (FIT) was designed to support
the integration of local data. InCAST is a building inventory tool that allows the
user to prepare building information for entry into HAZUS. The Building
Information Tool (BIT) was developed to take large databases and extract
information needed for HAZUS. For example, MDProperty View information
could be imported for use in HAZUS using the BIT.
An Assessment of Maryland’s Vulnerability to Flooding
Page 23
Data Needed
To perform the Level 1 flood vulnerability analysis using HAZUS-MH, the
only datasets needed are those either provided by FEMA on the HAZUS
distribution disks or by the USGS via The National Map. Specifically, a Level 1
flood vulnerability analysis requires block-level census data containing building
stock, employment profiles, and population counts, stream gauge locations and
flow volumes, and lifeline locations, all provided on the data disks that
accompany the HAZUS-MH program. In addition, users must download the 30meter digital elevation model (DEM) data from the USGS. The National Map has
a seamless distribution module that allows users to enter a set of coordinates
and have a continuous elevation layer downloaded to their computer.
Procedures
Starting in December 2004, the staff at the ESRGC at Salisbury University
undertook the task of running the HAZUS-MH loss estimation software for each
county in Maryland (plus Baltimore City). Originally, we ran version 1.0 of the
HAZUS software on the ArcGIS 8 platform. Unfortunately, this version not only
ran extremely slowly but generated a large number of errors. After HAZUS-MH
version 1.1 was released in mid-January 2005, we upgraded our GIS to ArcGIS
9.0.1 and began to have much more success. There were still some lingering
issues but with the help of FEMA, NIBS (National Institute of Building Sciences),
An Assessment of Maryland’s Vulnerability to Flooding
Page 24
and ABS Consulting (the author of the software), we were able to solve almost all
of them.
The first step of a vulnerability model run is to create a new study area,
which involves choosing the correct hazard (flood), state, and county from a
series of dialog boxes. Only a county level analysis is available when examining
a flood hazard; this is not the case with other hazards. Once a county study area
has been created, we open it and launch HAZUS-MH.
Once in HAZUS-MH, the first step is to determine if a county should be
examined for riverine flooding vulnerability, coastal flooding vulnerability, or both.
In Maryland, nine counties (Allegany, Caroline, Carroll, Frederick, Garrett,
Howard, Montgomery, Prince George’s, & Washington) are subject to riverine
flooding only. The other 14 (plus Baltimore City) are subject to both coastal and
riverine flooding.
Next, the extent of the digital elevation model (DEM) for the study area
needed to be determined, and the dataset downloaded.
We used the
coordinates generated by HAZUS-MH as the minimum bounding rectangle to
select the DEM from The National Map at seamless.usgs.gov. This selected
DEM then downloaded automatically as a ZIP file, which was uncompressed in
the working directory of the study area and HAZUS-MH was pointed to its
location.
The third step is one of the more crucial decisions in the execution of the
vulnerability model – the selection of an appropriate minimum stream drainage
area size (in square miles). The minimum stream drainage area size essentially
functions as a “resolution” setting in the model. The potential range of area size
runs from 0.25 sq miles (local scale) to 400 sq miles (regional scale). As with
any resolution, the trade-off is size versus detail. A small stream drainage area
size will encompass many small streams and creeks and examine them for their
flooding potential. However, it is easy to overwhelm the software with too much
detail, making a model run difficult to finish. On the other hand, choosing a large
stream drainage area size ensures the model will finish easily, as there may be
only a few drainage areas that meet the size criteria. Unfortunately if the area
size is too large, many important streams reaches may be omitted, thus underreporting the level of vulnerability.
Our strategy to select the minimum stream drainage area size was to
choose the smallest possible size without creating an overwhelming number of
reaches. Through empirical testing, we found that a reasonable number of
reaches was between 60 and 80 total reaches. For most of the counties in
Maryland, this yielded a minimum drainage basin size of around 4 to 6 square
miles. They ranged, however, from 1 square mile in Baltimore City to 10 square
miles in Frederick County. In our limited experimentation, we found that dropping
the minimum stream drainage area below 4 square miles for a county of
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“average” size created many more very small reaches without having a large
impact on vulnerability results.
The fourth step of a HAZUS-MH model run is the creation of a study case.
Within a given study area (like a county), one can have multiple study cases,
each examining different drainage basins, municipalities, or some other pertinent
subdivision. For this analysis, we created one study case per county that
contained all of the river reaches and coastline segments (if appropriate)
available. This study case would contain all of the results for a given county, and
yield vulnerability maps of the county as a whole.
Subsequently, we completed the hydrologic analysis for all of the river
reaches in the study area. This process is more completely outlined in the
HAZUS-MH Flood Model Technical Manual, included with the HAZUS-MH
software release. The major steps involve automatically delineating the drainage
area for each stream reach, determining the stream gauges that are either
upstream or downstream of each reach, and finally calculation the flow volume
for the entire set of stream reaches in the study case.
Sixth, in order to correctly calculate the extent of the 100-year coastal
flood hazard zone, we characterized the shoreline in each county that fronts
either the Chesapeake Bay or the Atlantic Ocean. Characterization of the
shoreline involves picking the type of coast and the flooding characteristics for
each coastline segment. The type of coast consists of both the degree of wave
exposure (from sheltered to full exposure) and the shoreline morphology (from
rocky to small dunes to large dunes to flood protection structure). The flooding
characteristics involve recording the 10-year, 50-year, 100-year, and 500-year
flood height, plus any wave heights (if available). This data was taken from the
most recent flood study completed for each Maryland subdivision.
Next, we calculated the extent and degree of the 100-year flood hazard.
The calculation of the riverine and coastal flood hazard are accomplished in
separate processes. For the riverine flood hazard, a hydraulics analysis is
completed, the details of which are best explained by the HAZUS-MH Flood
Model Technical Manual. To summarize the important methodological steps of
the riverine hydraulics analysis: the model approximates the floodplain
associated with a stream reach, finds the upstream and downstream limits of that
approximated floodplain, generates a set of cross-sections, and associates those
cross-sections with flood elevations and discharge values.
The process to assess the coastal flood hazard depth and extent is
different than the riverine case but similar to the approach used by FEMA to
determine coastal flood zones. The two generalized steps are drawing transects
perpendicular to the shoreline and running one or more of three FEMA models
(dune/bluff erosion, wave height, and wave run-up) to calculate flood depths and
extents. The decision of which models are to be run is a function of the shoreline
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characteristics and the wave conditions. The result of both the coastal and the
riverine flood hazard determination is two flood depth grids for a particular
recurrence interval that can be used to intersect the demographic data to
estimate loss. When examining both coastal and riverine flooding in the same
county, the model picks the “predominant” flooding mechanism and its
associated flood depth when intersecting the flood zone with the demographic
data.
Eighth, we ran five different analyses of the potential flood vulnerability
namely count of damaged buildings by type, count of damaged buildings by
occupancy, amount of building damage (in square feet) by type, amount of
building data by occupancy, and the amount of direct economic losses from
damage to buildings (in dollars). These analyses intersect the census block data
with the flood depth information to create an estimate of amount and degree of
damage to buildings as well as the resulting potential economic losses. These
analyses suffer from similar caveats as any polygon interpolation process.
Certainly, any analysis will be dependent on good quality input data. In HAZUSMH, the quality of input census data is not known but is probably similar to the
US Bureau of the Census itself. More importantly however, the location of
buildings within a census block is not known. Therefore, any block that is not
completely contained in the flood zone must be assumed to have its
characteristics evenly distributed throughout it – often an incorrect assumption.
What follows is a summary of those analysis results, examining the extent
of the flooding vulnerability in the state of Maryland on a county-by-county basis.
For a more detailed discussion of a given county’s results, please see Appendix
B (downloadable from www.esrgc.org). For even more detail, the actual HAZUSMH scenario model may also be downloaded from the same site.
Flooding Scenarios and Damage Estimates
Completion of the HAZUS-MH vulnerability scenario modeling for every
county (and Baltimore City) in Maryland yielded a picture of varying degrees of
vulnerability to flooding throughout the state. Regarding the physical nature of
the flood zone, over 1,328 square miles of the state fall within the 100-year flood
zone (Table 4). In other words, 13.4% of the land area of the state is vulnerable
to a 100-year flood event. The county with the largest flood zone according to
HAZUS-MH is Dorchester (353.1 sq miles) while the county/city with the smallest
flood zone is Baltimore City (5.2 sq miles). As a percentage of the overall area of
the county, the largest flood zone area is also Dorchester County with 61% of the
county defined as 100-year flood zone. Only one other county has more than
half of its total area in the 100-year flood zone (Somerset) but several other
counties, such as Worcester, Wicomico, Montgomery, and Talbot counties have
significant (more than 15% of total area) expanses of flood zone.
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Table 4. Flood zone area versus total area of a subdivision in square miles
County
Allegany
Anne Arundel
Baltimore City
Baltimore
Calvert
Caroline
Carroll
Cecil
Charles
Dorchester
Frederick
Garrett
Harford
Howard
Kent
Montgomery
Prince George's
Queen Anne's
Somerset
St. Mary's
Talbot
Washington
Wicomico
Worcester
TOTAL
Flood Zone
Area
(sq mi)
17.76
42.12
5.19
41.56
13.73
14.96
20.30
25.00
36.64
353.10
41.02
19.09
47.13
13.74
17.51
84.86
33.05
23.86
191.14
28.07
43.87
42.98
63.56
108.11
1,328.35
Total Area
(sq mi)
430.54
417.98
81.03
607.67
216.87
324.24
452.37
355.31
461.55
578.54
667.50
657.56
445.05
253.51
281.66
507.19
487.87
374.12
329.42
363.84
270.98
467.85
380.52
476.39
9,889.57
% of
Total
4.1%
10.1%
6.4%
6.8%
6.3%
4.6%
4.5%
7.0%
7.9%
61.0%
6.1%
2.9%
10.6%
5.4%
6.2%
16.7%
6.8%
6.4%
58.0%
7.7%
16.2%
9.2%
16.7%
22.7%
13.4%
Of course, the size of the flood zone is but one measure of vulnerability.
As it is the intersection of the potential hazard and the social system that creates
the potential for loss, a more accurate method for expressing the level of
vulnerability is to report the potential damage from a 100-year flood event. One
such measure is the amount of square feet of damage to buildings in the event of
a 100-year flood. The results of the HAZUS-MH modeling effort reveal that
109,665,000 square feet of Maryland building stock will be potentially damaged
in the event of a 100-year flood (Table 5). As one can see from the table and the
resulting map (Map 1), Worcester County has the most building stock in harm’s
way with over 21 million square feet or 19.4% of the total for the state. The other
subdivisions that are the most vulnerable with regard to buildings are Anne
Arundel, Prince George’s, Baltimore, and Baltimore City. Those subdivisions that
are least vulnerable are Carroll, Caroline, Kent, and Garrett. Another important
statistic to notice from Table 5 is the ratio of substantial damage to total
damaged. For instance, Somerset County’s overall amount of building damage
is moderately high (6th in the state) but 68% of the damage is predicted to be
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“substantial” (more than 50% damaged). Other counties with a large amount of
potential substantial damage are Dorchester, Washington, St. Mary’s and
Calvert.
As we break down the total square feet of potential building damage by
county into different categories of occupancy, a clearer picture of the dimensions
of the flood vulnerability emerges (Table 6). First, of the occupancy categories
tracked by HAZUS-MH (agricultural, commercial, educational, governmental,
industrial, religious/non-profit, and residential), only commercial, governmental,
industrial, and residential categories garnered more that 0.5% of the overall total
damage. The others are insignificant in terms of either their exposure to the 100year flood zone or in their distribution generally. Next, one will quickly realize
that the majority of damage to buildings in the state of Maryland will be to
residential buildings. In fact, about 86% of all the potential damage from the 100year flood comes from residential buildings. Spatially, the residential damage
pattern looks similar to the total damage (Map 2). Looking at other categories
yields somewhat different results. For example, the distribution of governmental
building damage (Map 3) shows the importance of the public service sector in
Prince George’s County. The distribution of commercial building damage (Map
4) shows Baltimore City more vulnerable. Actually, Cecil, Allegany, Frederick,
and Garrett counties and Baltimore City have the distinction of having less than
80% of their damage amount coming from residential impacts. Finally, mapping
the damage to industrial buildings shows Anne Arundel, Prince George’s,
Washington, and Baltimore City as the location of many vulnerable industrial
areas (Map 5).
One can also break down the potential building damage by the type of
building construction. While construction types are much more widespread than
occupancy categories, wood (62%) and masonry (28%) dominate steel (7%) and
concrete (3%) (Table 7). In general when these patterns are mapped (Maps 6, 7,
8, and 9), the overall distribution of vulnerability remains the same with certain
jurisdictions showing different anomalies. Examples are Baltimore City having
more exposure with steel buildings than its neighbors (Map 8) but relatively less
wood buildings in the floodplain (Map 9).
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If one examines the level of vulnerability using the number of buildings
potentially damaged by a 100-year flood, rather than the amount of damaged
square feet, the pattern is similar but more evenly distributed (Table 8). The
county with the most buildings damaged is Anne Arundel, followed by Worcester,
Baltimore, Prince George’s, and Washington (Map 10). However, only Anne
Arundel and Worcester made up more than 10% of the state’s total number of
buildings damaged (44,755). Again, several counties had a large number of
buildings vulnerable to substantial damage including Somerset (72%),
Dorchester, St. Mary’s, and Calvert.
Once we break down the total number of buildings damaged into their
occupancy categories, we were surprised to learn that only the residential
category accounted for more than 0.5% of the total number of buildings (Table
9). Thus, agricultural, commercial, governmental, industrial, and religious/nonprofit buildings each represented less than 0.5% of the total. This shows much
more about the uncertainty of the HAZUS-MH model results than it does the
profile of Maryland’s vulnerability.
Because the “number of buildings”
calculations are subject to significant rounding errors (i.e. trying to avoid having
0.524 of a building), the model will generate thousands of square feet of damage
(see Table 6 above) but no “whole” buildings to count. For what it’s worth, the
map (Map 11) of residential building counts shows a very similar pattern to the
map of the total number of damaged building map (Map 10). This should be
expected as residential buildings make up 99.5% of the total building count.
Separating the building counts into their construction type yields yet more
insight into the distribution of building vulnerability to the 100-year flood in
Maryland (Table 10). Although only the masonry and wood constructions types
had results that were more than 0.5% of the total (28% and 72% respectively),
the maps (Maps 12 and 13) show that construction techniques in the floodplain
do vary around the state. One is much more likely to find a masonry house in the
flood zone in the Midstate than on the Eastern Shore, for example (Map 12).
Wood construction accounts for vulnerable buildings throughout the state (Map
13).
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Table 9. Building damage by occupancy category in numbers of buildings. Only categories
representing more that 0.5% of the total damage are reported.
County
Allegany
Anne Arundel
Baltimore City
Baltimore
Calvert
Caroline
Carroll
Cecil
Charles
Dorchester
Frederick
Garrett
Harford
Howard
Kent
Montgomery
Prince George's
Queen Anne's
Somerset
St. Mary's
Talbot
Washington
Wicomico
Worcester
TOTAL
Residential
Substantial Total
8
727
606
7,013
194
2,352
315
3,993
181
1,008
10
105
1
138
4
558
17
531
424
1,247
106
2,181
35
276
35
1,622
0
1,628
13
146
40
2,184
146
3,810
14
647
1,944
2,678
158
781
61
869
454
3,606
42
438
593
6,007
5,401 44,545
All
Substantial
8
606
200
315
181
10
1
4
17
424
106
35
35
0
13
40
146
14
1,946
158
61
457
42
593
5,412
Total
731
7,038
2,384
3,999
1,008
105
138
561
533
1,247
2,191
276
1,631
1,633
146
2,189
3,855
647
2,680
781
869
3,623
438
6,052
44,755
An Assessment of Maryland’s Vulnerability to Flooding
%
Substantial
1.1%
8.6%
8.4%
7.9%
18.0%
9.5%
0.7%
0.7%
3.2%
34.0%
4.8%
12.7%
2.1%
0.0%
8.9%
1.8%
3.8%
2.2%
72.6%
20.2%
7.0%
12.6%
9.6%
9.8%
12.1%
% of
Total
1.6%
15.7%
5.3%
8.9%
2.3%
0.2%
0.3%
1.3%
1.2%
2.8%
4.9%
0.6%
3.6%
3.6%
0.3%
4.9%
8.6%
1.4%
6.0%
1.7%
1.9%
8.1%
1.0%
13.5%
100.0%
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Finally, one can characterize the level of vulnerability from coastal and
riverine flooding in Maryland using the amount of direct economic losses related
to buildings (Table 11). This measure includes monetary losses from the
buildings themselves (structural damage, contents damage, and inventory loss)
as well as monetary losses from the use or disuse of those buildings (losses
related to relocation, capital, wages, and rental income). The result of the
HAZUS-MH model for all the subdivisions in Maryland shows that $8.12 billion is
vulnerable to loss from a 100-year flood. Even more notable is that just 3
counties (Prince George’s – $1.28B, Worcester – $1.03B, Anne Arundel –
$0.92B) account for almost 40% of the total direct economic losses related to
buildings. Examining Table 11, one can see that while all have significant losses,
their components are different. In Prince George’s County, a large number of
commuters to Washington, DC would be displaced in the event of a major flood,
causing significant wage losses. On the other hand, nearly half of Worcester
County’s loss stems from structural damage to the buildings themselves. Finally,
examination of the map (Map 14) shows that the middle portion of the state has
somewhat higher potential for economic loss in the event of a 100-year flood
than either Western Maryland (except Washington), Southern Maryland, or the
Eastern Shore (except Worcester).
The summation of the results of the HAZUS-MH flood vulnerability
modeling effort is only one part of the story and generalizes a very complex
interplay between natural system and sociodemographic structure. Included in
Appendix A is the 100-year flood zone and direct economic losses by block for
each subdivision in the state of Maryland. Through these 48 maps, one can not
only examine the potential impact of flood waters on large swaths of the land
surface around the Chesapeake Bay and the Atlantic Ocean (i.e. Dorchester
County, Map A19 and Somerset County, Map A37) but also the unfortunate
location of increasing levels of development in flood-prone areas like Anne
Arundel (Map A4), Queen Anne’s (Map A36), and Worcester Counties (Map
A48). Indeed, the spread of our urban areas into suburban counties (Baltimore
County, Map A8; Montgomery County, Map A32; and Prince George’s County,
Map A34) brings the potential damage to structures, contents, and livelihoods to
existing flood zones. Some solace may be taken in that many of the counties on
the Eastern Shore with extensive 100-year flood zones have not yet significantly
developed, leaving the door open to structural mitigation techniques (i.e. elevated
foundations).
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Accuracy of Data
The accuracy of this study and its results are a major concern. The
source of concern about the accuracy of the results is threefold: the HAZUS-MH
modeling software, the underlying processing assumptions and the underlying
data. First, the path to completing this study was fraught with significant, often
fatal errors within HAZUS-MH. Although the authors and distributors of the
software were most gracious in their attempt to fix all of the major errors we
encountered, it is only reasonable to assume that other non-fatal (and therefore
undetected) errors have occurred within the program’s algorithms. Just looking
at some of the specific results such as Talbot County’s maximum flood depth
being almost 70 feet when the highest elevation found in the county is only 77
feet (Map A41) or the general results regarding numbers of damaged buildings
versus the amount of damaged square feet of buildings are enough to give one
pause.
Second, some of the underlying processing assumptions are worrisome.
For example, because of a lack of high-quality network of stream gauges in many
parts of Maryland, often the hydrologic profile for a stream reach is being
interpolated from one stream gauge, perhaps not even on the reach being
modeled. While this may work, there has not been enough independent field
research to conclude that the method is consistently accurate.
Third, one has to assume the data underlying the analysis is error-free in
order to conclude the results are accurate. One can almost guarantee that the
data input to the model, particularly those collected as part of huge national data
collection efforts, are not error-free. One can actually see this in some of the
flood zone maps (i.e. Montgomery County, Map A31), where the model is
creating a very deep flooded area along a river. This is almost assuredly the
underlying DEM including the height of a bridge over the river as the actual land
surface height, thus creating a “dam” where none exists. Census block data, for
all the valiant efforts of the US Bureau of the Census, contains some errors in
their raw counts. Unfortunately, it is very difficult to determine the location and
significance of these errors, particularly when examining the output of a complex
modeling process like that used in HAZUS-MH.
Improving Accuracy with Local Data
The potential exists, however, to significantly increase the accuracy and
the precision of this research. This study completed a HAZUS-MH Level 1
Analysis of the 100-year flood vulnerability in the state of Maryland, meaning that
only existing and available national datasets were used to calculate results. This
manifests itself most significantly in the use of a digital elevation model with 30meter cells and generalized census block enumerations. HAZUS-MH has the
ability to dig much deeper and generate much more accurate and precise
vulnerability calculations using local datasets. For example, using the highlyAn Assessment of Maryland’s Vulnerability to Flooding
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precise and highly-accurate LiDAR (Light Detection And Ranging) elevation data
should generate much more accurate stream reaches and stream profiles. Using
information on assessed taxable properties from the Maryland Department of
Planning and the Maryland Department of Taxation and Assessment rather than
generic building information should refine the results considerably.
There are some caveats, however, when considering the use of local data.
First, not all types of data (like LiDAR elevations) are available throughout the
state, making statewide comparisons difficult. Second, as one increases the
resolution of the data, the size of the data balloons. Using LiDAR as an example,
the 2-meter DEM of Somerset County alone is over 1.2 GB in size. This will
considerably increase the amount of time it takes to run a simulation. Third, local
data may not be in an appropriate form. The MDP/MDAT assessed property
locations are stored as property centroids. It is probable that many properties
would be considered out of the floodplain because the centroid does not fall
within the flood polygon, yet a majority of the property may indeed fall within the
hazard zone.
All of this points to the use of a HAZUS-MH Level 2 Analysis (using local
data) as a refinement of the initial Level 1 analysis. For example, Ocean City,
Maryland is a well-known, national example of the potential folly of building a
major tourist destination on a mobile barrier island. Despite tremendous efforts
at the federal, state, and local level, the Level 1 analysis suggests that much of
Ocean City is still vulnerable to a 100-year flood (Map A47). These results beg
for further exploration with a more accurate and precise Level 2 Analysis to
further refine the exact location and characteristics of Ocean City’s flooding
vulnerability
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Part IV. Mitigation Strategies
Regulations
Neither state nor federal regulations preclude development in the 100-year
floodplain. The minimum NFIP requirements address how to build in the
floodplain to prevent damage to structures, but not that structures should not be
placed in the floodplain. Performance standards allow use of land while
minimizing hazards to human life and property damage.
The minimum
requirements would allow a building in the floodway, if it did not increase flood
heights. Floodplains of waters that flow downhill under gravity are regulated by
both the state and local jurisdictions.
The state's program focuses on
engineering analysis to show that new floodplain development will not increase
hazards on existing improved property. State jurisdiction does not extend into
tidal floodplains. However, flood maps depict the source of flooding, and a
number of areas that are normally considered tidal would be overwhelmed by
riverine flooding during the 100-year flood, and would come under state
jurisdiction. In tidal areas, only the local permit, issued under the local floodplain
management ordinance, is required.
An excellent source of information for construction in the coastal V Zone is
FEMA 55: Coastal Construction Manual, which was revised June, 2000. In the
body of this technical document are the regulations for the proper techniques for
building in the Coastal V Zone. It is advisable to use the techniques in this
manual for construction in A-zones subject to wave action, as well.
Maryland Model Floodplain Management Ordinance
The Maryland Model Floodplain Management Ordinance, adopted by most
local jurisdictions in the NFIP, is more restrictive than the minimum NFIP
regulations. The ordinance clearly states that new buildings and fill are not to be
permitted in floodways. Any floodway development must receive a Conditional
Letter of Map Revision (CLOMR) from FEMA and meet the following conditions:
(1) no reasonable alternative must exist outside the floodway,
(2) encroachment into the floodway in the minimum necessary,
(3) the development will be able to withstand the 100-year flood with
minimal damage, and
(4) the development will not increase downstream or upstream flooding or
erosion.
The amount of fill allowed in the floodplain is limited to 600 cubic yards per
lot to discourage disruption of drainage patterns and diversion of runoff onto
neighboring properties, since issuance of the local permit may not increase
flooding onto neighboring properties.
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Subdivision regulations in the Model Ordinance prohibit the subdivision of
new lots in nontidal floodplains unless a building pad outside the floodplain can
be identified for each lot. In tidal floodplains, the subdivision plan must show that
the higher land is considered for development before floodplain lots may be
considered. High priority should be given to clustering development out of the
floodplain. Floodplains should be reserved as natural areas in the open space
requirements for subdivisions, if at all possible. Preserving floodplains as natural
areas preserves the natural beneficial functions they provide and has high
amenity value to the community. It is important to note that structures built in the
floodplain are not only subject to damage from flooding, but development in the
floodplain reduces flood storage capacity, increasing flood heights, and
increasing downstream flooding.
One of the most important, but least used, provisions in the Model
Ordinance is the "Avoidance and Minimization” clause which directs local
permitting officials to work with applicants to move a proposed structure out of
the floodplain, if possible. If it must be in the floodplain, then the impacts to the
floodplain should be minimized.
In Coastal High Hazard Areas (V-zones) the Model Ordinance requires an
alternatives analysis that requires the applicant to demonstrate that:
(1) no reasonable alternative exists outside the V-zone,
(2) the encroachment on the V-zone is the minimum necessary,
(3) the development will withstand the 100-year wind and water loads
without damage,
(4) the development will not create an additional hazard to existing
structures, and
(5) any natural dune system will not be disturbed.
Existing buildings in V-zones shall not be substantially improved or
expanded horizontally or vertically unless the entire foundation system is certified
by a professional engineer or architect as being capable of supporting the
existing building and the proposed improvement during the 100-year storm.
There is a requirement to track cumulative improvements, so that this provision
will be implemented.
The state model incorporates a one-foot freeboard requirement on new
buildings. This is consistent with the state permit requirement in nontidal areas.
In tidal areas, communities may wish to consider a greater freeboard requirement
on new construction in light of sea level rise projections of approximately three
feet over the next century. Implementing a greater freeboard requirement now
will avert much more costly mitigation in the future to save structures that will be
flooded more frequently than present.
An Assessment of Maryland’s Vulnerability to Flooding
Page 56
Some local regulations are more restrictive than others concerning
floodplain development. For example, Anne Arundel, Baltimore, Caroline,
Carroll, Frederick, Harford, Howard, Montgomery, and Prince George's Counties
do not allow new buildings in their nontidal floodplains. A few communities
prohibit any new development in the floodplain, such as Fruitland and
Chesapeake City.
Some communities have adopted greater freeboard
requirements, such as Ocean City and Carroll County. On the other hand, some
communities have failed to adopt any freeboard requirement, including
Dorchester, Somerset, and Worcester Counties.
Local Mitigation Planning
Until recently, local mitigation planning efforts had been in response to
requirements for both federal and state funding, and were used to justify a project
for which the local jurisdiction was seeking funding. A comprehensive plan of
how the county intended to make itself resistant to flooding was not a likely
result. However, FEMA has been evolving toward adopting a comprehensive
planning requirement as a requirement for federal funding, first under the Flood
Mitigation Assistance Program, now for the Hazard Mitigation Grant Program and
for new pre-disaster mitigation programs.
MDE and MEMA sponsored a workshop on October 6, 1999, to begin the
process of local planning to mitigate all hazards to which the local jurisdiction
may be subject. Planners, Emergency Managers, and NFIP Coordinators
attended and were encouraged to work together to develop and implement all
hazard plans for their county. The Maryland Hazard Mitigation Manual was
presented to participating counties, which closely parallels North Carolina's
recent effort, with their permission.
Maryland and North Carolina both
experience similar hazards, and North Carolina was ahead of Maryland in
mitigation planning. The Manual describes how to develop a plan and gives a
number of tools and techniques for mitigating natural hazards.
MEMA published the Maryland Hazard Analysis in January 2000, which
outlined potential hazards, vulnerabilities and risks for each county in the state,
based on frequency and severity of the hazard. From this, a relative risk was
derived for 15 different hazards. The hazards that were assigned the highest risk
potential for Maryland are:
(1) flash or riverine flooding,
(2) hurricane and tropical cyclone,
(3) winter weather, and
(4) fire and explosion.
The Disaster Mitigation Act, passed by Congress in 2000, amended the
Robert T. Stafford Disaster Relief and Emergency Assistance Act by adding a
An Assessment of Maryland’s Vulnerability to Flooding
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mitigation planning requirement. It requires local governments to develop and
submit compliant mitigation plans as a condition of receiving Hazard Mitigation
Grant Program (HMGP) project grants after a disaster declaration. Prior to this,
only Flood Mitigation Assistance project funding required a flood mitigation plan.
Also, states with approved Enhanced State Mitigation Plans could qualify for
additional mitigation funding. For disasters declared after November, 2004,
HMGP funds will not be available to local jurisdictions without approved hazard
mitigation plans.
MEMA has been assisting local jurisdictions in developing mitigation plans
to meet these requirements. MDE supplied the repetitive loss data it generated
to incorporate into the plans to identify some viable projects. DNR supplied
information on sea level rise.
Floodplain Management Database and Repetitive Loss Project
To assist local planning efforts, MDE has compiled data useful in
floodplain management planning, using funding from FEMA received through
MEMA. The data was compiled in ArcView format and consists of data layers,
which can be overlain on digitized and orthorectified quarter quadrangle aerial
photography (DOQQ). Layers used include MDProperty View and the Q3 digital
floodplain line. This has allowed the development of guidance maps for local
planning which have been distributed to many of the small towns whose flood
maps were out of date or insufficient due to annexations or other reasons.
Some data analysis in this report and in our newsletter to local floodplain
managers is derived from this database. Examples include the percent of land
area that is floodplain in each county, the number of parcels in the floodplain,
improvements in the floodplain, and the repetitive loss data. ArcView software
was used by MDE to show the areas that were flooded during Hurricane Floyd to
determine if waters reached beyond the 100-year flood lines.
With a grant from FEMA, a Corvallis Microtechnology, Inc. CMT-Z33 dualfrequency Global Positioning System (GPS) was purchased in 2000. It is an allpurpose high precision GPS for surveying and GIS data collection. It consists of
a base station in one backpack system and a rover unit in another backpack, with
a radio link between the two GPS receivers, and a field data recorder for each.
In addition, a laser range finder was added to the system to allow readings to
remote points not accessible to the GPS equipment, due to loss of satellite
coverage under trees and near structures. This equipment allows accurate
determination of elevation and position, for the repetitive loss project, high water
marks, etc.
The repetitive loss project was undertaken to provide a statewide list of
priority projects for mitigation funding. The repetitive loss data was supplied by
the National Flood Insurance Program and is a list of properties experiencing two
An Assessment of Maryland’s Vulnerability to Flooding
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or more flood insurance claims of at least $1,000 within a 10-year period since
1978.
Data was collected on each repetitive loss property in the state, including
elevation and latitude/longitude information, the source and type of flooding, the
depth of flooding, the lowest point of entry of water, the date the structure was
built and whether or not it has a basement. We will use the GIS database to
target areas of high repetitive loss and set priorities for funding. We can use it to
immediately justify proposed projects - all information to develop the benefit/cost
analysis will be in the database. It should help determine when community or
area wide solutions are more appropriate than individual solution. Table 12 is a
listing of the number of repetitive loss properties in Maryland by county. A
number of repetitive loss properties have been added to the repetitive loss list as
a result of damage by Isabel in 2003, after the project was completed in 2002.
The additional properties have not been visited, but many were mitigated by
elevating the property.
Table 12. Repetitive Loss Properties in Maryland by County as of November 30, 2004
TOTAL
FEMA Mitigated FEMA Non-mitigated
County
per County
Repetitive Losses Repetitive Losses
Allegany
Anne Arundel
Baltimore City
Baltimore
Calvert
Caroline
Carroll
Cecil
Charles
Dorchester
Frederick
Garrett
Harford
Howard
Kent
Montgomery
Prince George's
Queen Anne's
Somerset
St. Mary's
Talbot
Washington
Wicomico
Worcester
TOTAL
7
0
4
7
2
0
0
0
0
0
3
1
4
0
0
0
1
0
1
0
0
6
0
48
84
19
70
39
111
30
0
12
36
8
32
22
16
8
4
6
36
0
21
12
5
13
57
2
75
634
An Assessment of Maryland’s Vulnerability to Flooding
26
70
43
118
32
0
12
36
8
32
25
17
12
4
6
36
1
21
13
5
13
63
2
123
718
Page 59
Mapping Risk - Floods and Tropical Storm Surges
Maryland's flood risk was originally mapped in the 1970's on the Flood
Hazard Boundary Maps distributed by the Department of Housing and Urban
Development based on the best available information at the time, although a few
local studies had been undertaken.
The maps were designed to give
communities who wished to join the Emergency Phase of the National Flood
Insurance Program (NFIP) some guidance as to the hazard areas they needed to
regulate to be in the program. In most cases, flood insurance studies using
hydrologic and hydraulic methods were later conducted to refine the risk and to
allow communities to enter the Regular Program. When studies were completed,
new Flood Insurance Rate Maps (FIRMS) and Flood Boundary and Floodway
Maps (FBFM) were issued by the Federal Emergency Management Agency, who
took over the NFIP. These used the best available base maps at the time,
usually the U. S. Geologic Survey quadrangle topographic maps, often with a 20foot contour interval. In studies and maps issued since January 1985, the
Floodway information is included on the FIRM and only one map is issued. Also,
the vertical datum used is being converted from National Geodetic Vertical
Datum of 1929 (NGVD) to the North American Vertical Datum of 1988, with 1991
revision (NAVD 88,91).
Under the NFIP regulations, once the floodway is delineated by a detailed
study, no encroachment is allowed which would cause any increase in the 100year flood elevation. This area is reserved for the discharge of the 100-year
flood without impediment. Floodplain areas outside the floodway may be
developed under the provisions of the ordinance adopted by the local jurisdiction
to be in the NFIP. A large number of areas were not studied by costly detailed
methods. These approximate floodplain areas show the extent of the floodplain,
based on best available methods, but no 100-year flood elevations are available.
Currently, most studies are outdated, with the average age of flood
insurance studies in Maryland being 19 years old. New studies are now provided
in a digital format, called a countywide D-FIRM. By 2005, only two countywide
D-FIRMs have been produced in Maryland: Harford County and St. Mary’s
County. Further refinement of the flood hazard hinges on replacement of the
current topographic base maps with more refined topography - down to 2-foot
contour intervals. Where discharges and riverine characteristics have changed,
restudy may be necessary. The development of accurate digital topography is
critical to better refinement of the flood risk through the use of current hydrologic
and hydraulic modeling and the refinement of floodplain lines.
FEMA has been lobbying Congress to appropriate additional funding to
update the flood maps. Up to now, funding to update maps has been severely
limited, and very little has been accomplished. FEMA's Map Modernization effort
calls for substantial funding. A bill was proposed for Congress to appropriate an
additional $300 million per year for 3 years, starting in 2003, for this effort;
An Assessment of Maryland’s Vulnerability to Flooding
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however, Congress reduced the amount to $150 million for 2003 and 2004. The
2005 budget is for $200 million and the time frame has been extended to at least
5 years.
The State Coordinating Office is trying to promote the development of
improved topographical modeling using LIDAR technology to support FEMA's
Map Modernization effort. If the better topography is available, it will be used by
FEMA in creating the new D-FIRMs and will be critical to better definition of
flooding risk. Although we have been unable to obtain state funding to support
this effort, we have been trying to coordinate local, federal, and state efforts to
assure that any data generated will meet Map Modernization standards.
Hurricane inundation maps were created for the Chesapeake Bay and
Atlantic Coastal areas of Maryland to show areas that would be inundated by the
storm surge from different categories of hurricanes in 1988. The project was a
cooperative effort among the National Oceanic and Atmospheric Administration
(NOAA), the Army Corps, and DNR. NOAA supplied the data for the maps, the
Army Corps produced the maps, and DNR distributed the 18 maps to the 16
coastal counties, Baltimore City, and Ocean City. The maps predict the
inundation zones for Saffir-Simpson Category 1 through 4 hurricanes. Storm
surges range in height from 3-5 feet for a Category 1 storm to 13-18 feet for a
Category 4 storm.
Hurricane inundation maps are now available in a digital format that can
be overlain in a Geographical Information System (GIS). Maps are provided in
the Maryland Hazard Analysis.
Flood Insurance
Any resident of a community participating in the National Flood Insurance
Program (NFIP) can purchase flood insurance. It is a good way to protect from
property losses in areas subject to flooding. Flood insurance can be purchased
on both the building and contents. For example, a tenant may purchase content
coverage, while the landlord may purchase a policy on the building. Any
participating insurance agency may sell and service a flood insurance policy, but
all policies go through the NFIP.
The mandatory purchase of flood insurance requirement is implemented
through the lender. Federal law requires that all loans written on structures in
designated flood hazard areas be secured by flood insurance, at least up to the
value of the loan, or, if the loan exceeds the maximum amount of flood coverage
available, to the maximum flood insurance coverage available. If the lender does
not meet the requirement during an audit, fines can be levied. The lender is
responsible for making a flood determination for each loan, but may delegate this
responsibility to a flood determination company. The buyer of the property has
An Assessment of Maryland’s Vulnerability to Flooding
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the opportunity to purchase flood insurance, but if they fail to do so, the lender
can "force place" flood insurance. This allows the lender to purchase a policy
from any source (not necessarily the NFIP) and charge the cost to the
homeowner.
The cost of a flood insurance policy is based on a number of factors, such
as when a structure was built, the flood zone it is in, its elevation, and if a
basement is present. All structures are classified as either pre-FIRM or postFIRM. A pre-FIRM structure was built prior to the local jurisdiction adopting any
regulations and joining the NFIP. These structures are placed in a subsidized
pool in which the risk is unknown. The premium is based on the flood zone and
presence of a basement. Structures built after the adoption of floodplain
regulations by the local jurisdiction must submit an elevation certificate in which a
surveyor or engineer certifies the elevation of the lowest floor and that the
structures is in compliance with floodplain regulations. The premium will be
based on the actuarial risk from the elevation certificate. If the lowest floor is
above the 100-year elevation, premiums will be reduced, if it is below, premiums
will be much greater. Structures in coastal high hazard areas or V-zones, where
waves are a factor, pay higher rates than structures that are in A-zones.
Structures that are outside flood hazard areas (C- or X-zones) can purchase
flood insurance at much lower premiums.
In order to collect on a claim, there must have been a general condition of
flooding, that is, other properties in the immediate vicinity must have flooded. If
an isolated flooding incident occurs, flood insurance may be denied. Coverage
for sewage and drain backup may be purchased as a rider on homeowner's
policies. Property owners who have received federal disaster assistance aid
must carry flood insurance to cover future losses, since no aid will be allowed in
the future, except that provided by flood insurance.
Dams and the State Dam Safety Program
The Maryland Waterway Construction Act, passed in 1933, also governed
the construction and operation of dams in Maryland. It placed on the dam owner
the responsibility of constructing and maintaining a safe facility, as well as a
requirement for a state permit, currently under COMAR 26.17.04. It also gave
the Water Resources Commission authority to require the owner of a reservoir,
dam, or waterway obstruction to remove or repair any structure deemed to be
unsafe. In 1964, the Department of Water Resources assumed these duties, and
in 1973, the Department of Natural Resources was formed and the functions
were moved to the Water Resources Administration. In 1995, the functions were
moved to Maryland Department of the Environment.
Federal legislation didn't come until the 1972 National Dam Inspection Act
to inventory and inspect nonfederal dams to protect human life and property.
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However, it was not until 1977 that funding became available to the Army Corps
to inspect dams, starting with the 9,000 "high" hazard nonfederal dams identified.
In 1979, this function was shifted to the Federal Emergency Management
Agency.
The Dam Safety Division in the Water Management Administration of
MDE currently oversees dams in Maryland, issuing permits and inspecting dams.
Maryland has a total of 376 dams, characterized based on the potential damage
that could occur if the dam were to fail. There are 56 "high" hazard (loss of life
and extensive property damage likely), 79 "significant" hazard (extensive
property damage but no loss of life likely), or 235 "low" hazard (no loss of life or
significant property damage likely).
Downstream development in the danger
reach affects the dam's classification and is not advised. Dams must develop
emergency warning and evacuation plans to mitigate the effects of a dam failure.
Most dams (72%) in Maryland are small earthen dams.
The Dam Safety Division is in the process of producing digital dam break
flood maps for all the high hazard dams in the state. These will be available to
local jurisdictions to use to prevent development in these high hazard areas.
Maryland Stormwater Management Regulations
Stormwater management regulations have as one of the goals to help
prevent flooding, but the design standards are geared to the water quality effects
of the 2-year and 10-year flood. The stormwater devices are not usually designed
to accommodate the really big floods. Design standards specify that the devices
must pass the 100-year flood safely, however. Many are designed with
additional capacity to retain floodwaters. The new regulations are stressing
proper construction, and requiring as-built documentation, as well as periodic
inspection and maintenance. Many of the past failures had to do with insufficient
maintenance, although improper construction was a factor.
The new regulations de-emphasize the flood control function, in favor of
water quality and channel erosion control functions. However, the regulations
allow more environmentally friendly nonstructural Best Management Practices,
such as natural area conservation, buffers, infiltration, reduction of impervious
cover, and environmentally sensitive development. Keeping as much of the
runoff on the site and allowing it to infiltrate does have a flood attenuating
function. By reducing the impervious surfaces, keeping the runoff on site, and
allowing it to infiltrate the soil, we are helping to prevent flood damage.
New regulations governing stormwater management (SWM) programs
were implemented statewide by July 1, 2001, under COMAR 26.17.02. The goal
is to maintain the predevelopment characteristics of runoff as nearly as possible
after development, and to reduce stream channel erosion, pollution, siltation and
An Assessment of Maryland’s Vulnerability to Flooding
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sedimentation, and local flooding. The 2000 Maryland Stormwater Design
Manual, Vol. I and II has been adopted as the official guide for stormwater
principles, methods, and practices. The regulations offer greater flexibility in
methods while attaining better management of runoff.
The Water Management
Administration
in
MDE
is
responsible for the program
statewide, but local jurisdictions
must implement it by adopting
compliant
ordinances
and
implementing
acceptable
programs. Basically, a grading or
building permit may not be issued
unless a SWM plan has been
approved for all development that
will disturb over 5,000 square feet
of land area.
If a site is
redeveloped,
the
existing
impervious area of the site must be
reduced by at least 20%, or runoff
reduced by a combination of SWM
practices and reduced impervious
surfaces.
Best Management Practices
(BMPs) for SWM include both
structural
and
nonstructural
methods.
Structural methods
include
SWM
ponds,
SWM
wetlands, SWM infiltration, SWM
filtering systems, and SWM open
channel systems.
Nonstructural
methods include natural area
conservation, disconnection of
rooftop runoff, disconnection of
nonrooftop runoff, sheet flow to
buffers, grass channels, and
environmentally
sensitive
development. They can be used in
combination to reduce runoff to the required standard, but nonstructural methods
should be used in preference to structural ones when possible.
In the design of BMPs, the Eastern Shore counties must require that the
recharge volume, water quality volume, and overbank flood protection volume for
the 2-year frequency storm be used. In other parts of the state, control of the 10-
An Assessment of Maryland’s Vulnerability to Flooding
Page 64
year frequency storm is required. (The 2-year frequency storm is about 3.3
inches of rain in 24 hours, while the 10-year would be associated with 5.2 inches
in 24 hours, but varies somewhat by county.) Development in watersheds
designated as interjurisdictional flood hazard watersheds (Carroll Creek, Gwynns
Fall, and Jones Falls and their tributaries) may not increase the downstream
peak discharge of the 100-year frequency storm event (about 7.4 inches in 24
hours).
All ordinances must provide for periodic inspections and maintenance of
all completed stormwater management devices to insure proper functioning.
Enforcement procedures must be in place to ensure that deficiencies indicated
by inspections are rectified.
Maryland Wetlands and Wetland Regulations
Maryland has roughly 600,000 acres of wetlands (10% of the land area),
based on a 1982 survey, approximately 50% of the pre-settlement estimate of
1.2 million acres. Of this, 250,000 acres of salt and brackish water wetlands, and
340,000 acres of palustrine (mainly nontidal) wetlands were identified. Wetlands
are extremely important for the many functions they provide: habitat for wildlife,
enhance water quality, flood control, water recharge, and recreation and
aesthetics. Some wetlands fall among the world's most productive ecosystems
and the productivity of the Chesapeake Bay depends on the input of detritus from
wetlands. Wetlands provide significant water storage during periods of flooding
and release the water stored slowly to lower peak flows and maintain base flows.
Emergent wetlands protect many shorelines from erosion.
Historically viewed as wastelands to be filled in, the attitude towards
wetlands has changed since the 1970s to be viewed as valuable natural
resources to be preserved. Significant wetland losses were associated with
human activities until regulations were instituted in the 1980s. Passage of the
Maryland Nontidal Wetlands Act in 1989 greatly reduced wetland losses from
human activity. However, wetland losses continue to occur as a result of sea
level rise and land subsidence. For example, studies by the University of
Maryland on the Blackwater Wildlife Refuge show that approximately 3,460 acres
of marsh were converted to open water between 1938 and 1989. These losses
will continue to result from natural causes and are exacerbated by man-made
barriers preventing wetlands from migrating landward as sea level rises.
The 1970 Tidal Wetlands Act regulates "state" wetlands (all lands lying
below the mean high water line) and "private" wetlands (lands extending
shoreward from mean high water line, subject to periodic tidal flooding, and
support aquatic growth) under COMAR 26.24 Tidal wetlands are delineated on
maps showing the state's jurisdiction. Property owners have the right to control
erosion and gain access to navigable waters from their land.
An Assessment of Maryland’s Vulnerability to Flooding
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The Nontidal Wetlands Act of 1989 requires that a permit be obtained after
1990 for any impact to a wetland or its 25-foot buffer under COMAR 26.23. The
goal is no net loss, and a gain in wetlands. The applicant must demonstrate that
the impact cannot be avoided, and if any wetlands are destroyed, the applicant
must create additional wetlands or pay into a state wetland creation fund.
Growth Management - Critical Areas, Sensitive Areas, Smart
Growth
In 1984, the Critical Area Law passed the state legislature. The Act
established a 1000-foot strip of land around the Chesapeake Bay and its tidal
tributaries for special protection efforts to help prevent further degradation of the
water quality and resources of the Bay. In Maryland, 60 counties and
municipalities lie within the Critical Area. The Critical Area Commission
established requirements that would be implemented at the local level. Most
important among these was the extra protection afforded by maintaining a natural
vegetated 100-foot buffer along the shoreline of tidal waters, wetlands, and
tributary streams. Development is severely limited in the buffer and natural
vegetation maintained or planted. In the Critical Area, zoning overlays of
Intensely Developed Areas (IDA), Limited Development Areas (LDA), and
Resource Conservation Areas (RCA) were established, based on current
development on December 1, 1985. Resource Conservation Areas were
afforded the highest protection, allowing only one residence per 20 acres.
Regulations adopted limit impervious surfaces and stormwater runoff, as well as
provide for storage to achieve water quality goals by maintaining predevelopment runoff.
In 2002, the Legislature passed the Atlantic Coastal Bays Protection Act,
which added the coastal bays to the Chesapeake Bay Critical Area Program.
This extended similar protections to the coastal bays behind Ocean City and
Assateague. Like the Critical Areas Program, a local protection program
consistent with the state law is implemented in Worcester County.
The Maryland Economic Growth, Resource Protection, and Planning Act
of 1992 required, among other requirements, that local jurisdictions incorporate a
sensitive area component into their comprehensive plans. The sensitive area
component had to contain "goals, objectives, principles, policies, and standards
to protect from the adverse effects of development, sensitive areas, including the
following: (1) streams and their buffers, (2) 100-year floodplains, (3) habitats of
threatened and endangered species, and (4) steep slopes." The act encouraged
local jurisdictions to adopt plans and regulations to prevent development in
stream valleys and floodplains and give a high priority to their protection. The
Act helped local floodplain management ordinances by adding additional reasons
to prevent floodplain development and maintain the natural beneficial functions of
An Assessment of Maryland’s Vulnerability to Flooding
Page 66
floodplains. Other tools to prevent development in sensitive areas, such as
transferable development rights, clustering, and flexible regulations, were
suggested.
This Act also implemented the "Smart Growth" provisions designed to
promote growth in established developed areas of the state to prevent sprawl.
State agencies with permitting and funding responsibilities are to review
proposed development to ascertain that smart grow provisions are met. Among
these is that all environmental permits are reviewed to ascertain that sensitive
areas are protected.
Sea Level Rise Response Strategy
The Coastal Zone Management Program in the Department of Natural
Resources (DNR), released a document in 2000, which sets forth the policy and
implemental framework for reducing Maryland's vulnerability to sea level rise in
the coming years. The report notes that sea level rise rates along Maryland's
coastline of approximately one foot in the last century are nearly twice those of
the global average.
Global
warming
could
increase the rate to as much as 3
feet over the next century. It is
difficult to separate the effects of
sea level rise from those of land
subsidence, but both contribute to
greater flooding of low-lying lands.
In addition to increasing the rate of
sea level rise, global warming is
expected to increase the severity
and frequency of storms. Coastal
flooding will increase, submerging
tidal wetlands, increasing erosion of shorelines, and damaging structures in lowlying areas.
Sea level response planning is needed in Maryland; the state's current
capabilities do not adequately address the three primary impacts of sea level rise
(erosion, flooding, and wetland loss), and little is being done to prevent adverse
effects. The report refers to sea level planning as the "ultimate planning
challenge". Maryland's vulnerability should be assessed, and strategies need to
be developed to accommodate for the expected effects of this sea level rise.
Additional freeboard, establishment of coastal erosion setback zones, and further
preservation of low-lying wetland areas are some possible strategies to
accommodate. The policy of armoring coastlines needs to be re-evaluated. A
"do nothing" attitude will lead to unwise decisions and increased risk over time.
An Assessment of Maryland’s Vulnerability to Flooding
Page 67
The report is authored by Zoe Johnson, and is available from the Coastal Zone
Management Program at DNR (410) 260-8730 or on the web at
www.dnr.state.md.us/bay/czm/index/html
An article in the Natural Hazard Observer by Klaus H. Jacob of the
Lament-Doherty Earth Observatory at Columbia University focuses on futuristic
hazard and risk assessment. The author comments that the latest scientific
knowledge must be applied when estimating future hazards and risks. He notes
that this is not the case for flood zones mapped decades ago, and no attempt is
made to evaluate future risk exposures.
The East Coast will be exposed to an increasing frequency of coastal
storm surge floods, attributed to global warming and sea level rise. The U.S.
Global Climatic Change Program models predict sea level increases of 1-3 feet
by the year 2100. These estimates take into account local land subsidence,
melting of alpine glaciers and icecaps, and the thermal expansion of warming
oceans. More surprising, the 1-3 feet of sea level rise will cause storm surges
less than 20 feet in height 2-10 times more often, with an average of 3 times
more often, by the year 2100.
If billions of dollars are invested in new structures without accounting for
sea level rise, hundreds of billions of dollars in future losses will occur. The
author concludes that the best mitigation is to avoid placing new or refurbished
structures and assets at too low an elevation. This will require planning, with
flood elevations that will protect the housing stock into the future, as well as
tough zoning enforcement. With proper execution, critical components will be
placed at sufficiently high elevation to protect them into the future and prevent
staggering losses.
“No Net Adverse Impact” Watershed Planning
Citing the fact that annual flood losses in the United States continue to
worsen, now totaling $6 billion, in spite of federal flood control and the National
Flood Insurance Program, a new approach is being proposed by Larry Larson
and Doug Plasencia. In an article entitled: No Adverse Impact: A New Direction
in Floodplain Management Policy, they suggest a new “no adverse impact”
floodplain policy. The Association of State Floodplain Manager's supports the
concept.
A "no adverse impact floodplain" is one in which the action of one property
owner or community does not adversely affect the flood risks for other properties
or communities as measured by the increased flood stages, increased flood
velocity, increased flows, or the increased potential for erosion and
sedimentation, unless the impact is mitigated as provided for in a community or
watershed based plan. It requires anyone proposing new development to
An Assessment of Maryland’s Vulnerability to Flooding
Page 68
mitigate the effect so that no increased harm will result to existing development.
This policy will decrease the creation of new flood damages and promote wise
use of floodplains. Alternatively, if a watershed management plan allows and
compensates for the development, such as through a regional stormwater
management facility, the development may be permitted.
Current federal policy has not come to grips with how to prevent new
development from creating flooding problems on existing development. While
the NFIP debates how to construct in the floodplain, it does not consider whether
the development itself is making flooding conditions more severe. Little attention
is paid to the pushing of flood waters onto other land when floodplains are filled,
or when the watershed outside the floodplain is developed and the newly
increased runoff is allowed to flow freely downhill. The NFIP allows new
development to cause an increase in the level of future floods, but ignores that
level for the next development. When a building is constructed in the floodplain,
its lowest floor elevation is based on data that is 15 years or older, regardless of
the amount of development in the interim, and could be well below the current
true 100-year flood elevation.
The cumulative effects of floodplain and
watershed development over these years could drastically increase flood heights,
but the building is only required to be elevated to the flood elevation existing at
the time the study was done.
Using future development conditions in floodplain mapping is one strategy.
The report cites a study in Mecklenberg County, NC. By updating the FEMA
map computer models to 2000 land use conditions, flood heights increased 2-3
feet. However, when ultimate land use in the watershed was loaded into the
models, flood height increased another 2-3 feet. The maps will not keep up with
development, and new buildings will not be protected from flooding, using the
federal requirements. A study done on McAlpine Creek estimated that investing
$250,000 in ultimate floodplain studies and basing regulations on better data,
prevented $16 million in flood damage.
An Assessment of Maryland’s Vulnerability to Flooding
Page 69
The no adverse impact floodplain, based on no increased flood risk, as
measured by flood stages, flood velocity, flow, and erosion and sedimentation, is
being espoused as a new national standard for all programs affecting floodplains.
It promotes local planning initiatives that would insure that future development in
both the floodplain and the watershed are part of a locally adopted plan. The
effects of the development must be mitigated by the plan, or it could not be
permitted.
This program is highly recommended for consideration to prevent future
flooding problems from development.
An Assessment of Maryland’s Vulnerability to Flooding
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Part V. Flood Mitigation Projects in Maryland
State Projects
The Comprehensive Flood Management Grant Program (CFMGP) has
been used to acquire structures, install flood-warning systems, construct flood
control projects, and other flood mitigation projects over the years. Initially, the
focus was on completing flood studies to define the hazard. In addition,
watershed-wide flood management plans are required to justify projects. In order
to approve a project, the state requires that a flood management plan be
submitted by the local jurisdiction, which defined the flooding problem and
outlined the proposed project as the best solution to the problem. In some
cases, the state shared in the cost of the plan.
State funds are leveraged by federal mitigation funds, which are available
after a Disaster Declaration and generally pay up to 75% of the project cost, if
approved. After a disaster declaration, a fund equal to 15% of the total disaster
expenditures by FEMA is made available to the state for mitigation. In these
An Assessment of Maryland’s Vulnerability to Flooding
Page 71
cases, the CFMGP will pay half of the 25% local share of the project cost. The
program has paid up to 50% of the cost of projects until a regulatory change in
1999, which increased the state payment up to a maximum of 75% when no
federal cost share is available.
Communities are asked to submit a yearly list of proposed projects, which
are rated in priority by the state in May and funded as Program funds permit.
Funding for the program has varied widely year to year as interest in flood
mitigation has waxed and waned. Flood events generally increase funding, while
years of budget deficits and no major flooding have caused Program funding to
decrease or the Program to become inactive. As of the beginning of 2003, a total
of approximately $32 million has been funded by the state for the cost share
program, as shown in Table 13.
Table 13. Comprehensive Flood Management Grant funds
Funding Source
Amount
Comprehensive Flood Management Loan of 1980
Comprehensive Flood Management Loan of 1982
Comprehensive Flood Management Loan of 1983
Comprehensive Flood Management Loan of 1984
Comprehensive Flood Management Loan of 1986
Comprehensive Flood Management Loan of 1987
Comprehensive Flood Management Loan of 1988
Comprehensive Flood Management Loan of 1989
MD Consolidated Capital Bond Loan - 1990
MD Consolidated Capital Bond Loan - 1991
MD Consolidated Capital Bond Loan - 1998
MD Consolidated Capital Bond Loan - 1999
Hurricane Floyd Disaster Assistance - PAYGO - 2001
$ 7,500,000
$ 1,500,000
$ 3,500,000
$ 1,000,000
$ 1,500,000
$ 1,500,000
$ 3,000,000
$ 4,000,000
$ 2,500,000
$ 2,900,000
$ 969,000
$
33,000
$ 283,323
MD Consolidated Capital Bond Loan - 2001
MD Consolidated Capital Bond Loan - 2002
$ 1,250,000
$ 667,000
TOTAL
$32,102,323
After the initial investment in studies and mapping to define the flood risk
in conjunction with the NFIP, the Program has turned to seeking solutions to
flooding problems. The primary focus is to acquire flood prone structures in the
100-year flood plain and remove them. The structures are removed and the
land must be dedicated to open space uses after acquisition. To qualify, a
structure must have a history of flooding above the 1st floor or get a least a foot of
flooding around the foundation. The program has authority to do emergency
acquisitions of flood-damaged homes immediately after a flood.
An Assessment of Maryland’s Vulnerability to Flooding
Page 72
In addition to the acquisition of flood prone buildings, the CFGMP has
funded flood-warning systems in Allegany County, Baltimore City, Baltimore
County, Howard County, and Prince George’s County. Structural solutions to
flooding that have been funded include levees and floodwall, detention
structures, channel improvements, dam repairs, and flood gates and valves.
The most involved and costly project undertaken by the CFMGP was the
Carroll Creek Project in the City of Frederick. The flood control project is
designed to prevent flooding in downtown Frederick by diverting up to 100-year
floodwaters through a 1.3 mile long underground conduit system. A small portion
of the streamflow is diverted to an above ground channel that is the centerpiece
of a linear urban greenway through the City. This project began in 1983 and was
completed in the late 90s at a cost of approximately $60 million. Final removal of
the protected area from the floodplain did not occur until 2002.
Table 14 lists the acquisition projects that have been undertaken with the
grant program:
Table 14. Flood grant program acquisitions by county
County
Year
Watershed Number
Type
Location
ALLEGANY
1983 Fairgo
3 Homes
Moss Ave, Ellerslie
ALLEGANY
1986 Wills Creek
8 Homes
Locust Grove
ALLEGANY
1987 Wills Creek II
6 Homes
Locust Grove
ALLEGANY
1989 Wills Creek II
5 Homes
Locust Grove
ALLEGANY
1997 George's Creek
13 Homes
ALLEGANY
1997 George's Creek
9 Homes
ALLEGANY
1999 Wills, Bradford
12 Homes
Cumberland-LaVale, Locust Grove
ALLEGANY
2000 Dry Run I
16 Homes
Valley Road, Cumberland
ALLEGANY
2000 George's Creek
ALLEGANY
2000 Dry Run 2
18 Homes
Valley Road, Cumberland
ALLEGANY
2001 George's Creek
20 Homes
Various, mainly Gilmore
ALLEGANY
2001 Dry Run
ALLEGANY
2002 George's Creek
ANNE ARUNDEL
1984 Patapsco
ANNE ARUNDEL
1985 Brooklyn Park
2 Homes
1 Homes
11 Homes
6 Homes
19 Townhomes
Nikep, Pekin. Barton, Midland
Lonaconing
Barton, Moscow
Valley Rd
Midland, Lonaconing, Nikep
Lakeview Ave.
Meadow & Old Riverside Rd
BALTIMORE CITY
1983 Gwynns Falls
15 Homes
Maisel St., Hollins Ferry Rd
BALTIMORE CITY
1984 Jones Falls
40 Homes
Falls, Asbury Rd, Mattfeldt
BALTIMORE CITY
1984 Jones Falls
1 Industrial
Rockland Ind.
BALTIMORE CITY
1987 Jones Falls
1 Industrial
MD Bolt & Nut
BALTIMORE
1981 Patapsco
11 Homes
Landsdown - Research Ave.
BALTIMORE
1981 Roland Run
25 Homes
Cliffedge Rd.,
BALTIMORE
1982 Roland Run
12 Homes
Morris Ave.
BALTIMORE
1982 Brien Run
12 Homes
Victory Villa - Runway Ct
BALTIMORE
1982 Red House Run
1 Home
BALTIMORE
1982 Roland Run
2 Homes
W. Seminary Ave.
An Assessment of Maryland’s Vulnerability to Flooding
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County
Year
Watershed Number
Type
3 Homes
Location
BALTIMORE
1983 Brien Run
BALTIMORE
1983 Herbert Run
BALTIMORE
1983 Gwynns
8 Homes
BALTIMORE
1983 Gwynns
10 Homes
BALTIMORE
1983 Little Falls
BALTIMORE
1983 Moores Run
8 Homes
E. Biddle St, 62nd St.
BALTIMORE
1984 Moores Run
12 Homes
Same area as above
BALTIMORE
1986 Gunpowder
20 Homes
CALVERT
1986 North Beach
2 Homes
Bay Ave. @ 5th St.
CALVERT
2001 Chesapeake Bay
1 Home
Webster Drive, Cove Pt.
CAROLINE
2001 Choptank
5 Homes
Sunset Ave, Greensboro
CARROLL
2001 Pipe Creek
1 Commercial
Junk yard in Detour
CECIL
2001 Big Elk Creek
13 Homes
FREDERICK
1998 Potomac River
5 Homes
Homes - Point of Rocks
FREDERICK
2001 Potomac River
1 Home
Home - Point of Rocks
FREDERICK
2002 Potomac River
10 Homes
Homes - Point of Rocks
12 Homes
7 Homes
Victory Villa - Runway Ct.
Leeds Ave, Ridge Dr.
Queen Anne Rd.
Same area as above
Parkton - York Rd & Hyde Rd
Ensor Mill Rd
Farr Creek, Elkton
GARRETT
1998 Potomac River
6 Homes
Homes - Shallmar
GARRETT
1999 Youghiogheny
1 Home
2527 Hutton Rd, Crellin
1 Home
450 Liberty Rd, Oakland
GARRETT
1999 Bradley Run
GARRETT
2000 Youghiogheny
HARFORD
1986 Deer Creek
2 Homes
Walters Mill Rd.
HARFORD
1990 Grays Creek
3 Homes
Montreal Ave, Phila. Rd
HARFORD
1990 Bynum Run
3 Homes
Wheel Rd, Cedar La
HARFORD
1999 James Run
2 Homes
4125-7 Philadelphia Rd
HARFORD
1999 Plumtree
1 Home
3203 Shawnee La.
HOWARD
1990 Patapsco
3 Homes
Tiber/Hudson
HOWARD
1990 Patapsco
2 Taverns
Sykesville taverns
HOWARD
2002 Deep Run
2 Homes
Harwood Park
KENT
2000 Chester River
3 Homes
Millington, Montabello Lake
MONTGOMERY
1982 Rock Creek
8 Homes
Various locations in watershed
PRINCE GEORGE'S
1983 Bald Hill
6 Homes
Good Luck Rd.
PRINCE GEORGE'S
1986 SW Branch
4 Homes
Homes
PRINCE GEORGE'S
1986 Piscataway
22 Homes
Clinton Acres
PRINCE GEORGE'S
1986 Henson
35 Homes
Homes
PRINCE GEORGE'S
1986 NW Branch
PRINCE GEORGE'S
1986 Tinkers
2 Homes
Coolidge Dr.
PRINCE GEORGE'S
1987 Folly Branch
2 Homes
Glendale
PRINCE GEORGE'S
1999 Various
3 Homes
Hyattsville, Bowie
17 Homes
Crellin
9 Duplex Homes 38th St., Hyattsville
QUEEN ANNE'S
2002 Chester River
1 Home
Sassafrass St, Millington
ST. MARY'S
1997 St. Mary's River
1 Home
Great Mills
WASHINGTON
2001 Potomac River
5 Homes
Main St., Hancock
TOTAL
531
An Assessment of Maryland’s Vulnerability to Flooding
Page 74
The greatest success story of federal, state, and local government
cooperation occurred in Westernport, MD. In September 1996, George's Creek
overflowed its blocked channel onto Front Street and ran down Main Street. An
estimated 27 structures were substantially damaged. Quickly, Allegany County,
State Highway Administration, and Natural Resource Conservation Service
responded with a plan and the funding to acquire and remove those homes
within 5 months. Now, a Town park is where flood prone homes used to be.
Federal Projects
Federal agencies have carried out some major flood mitigation projects in
Maryland. The Army Corps of Engineers has been involved in a number of
projects and are listed in Table 15. Typically, the Corps of Engineers funds and
builds structural projects such as levees, floodwalls, dams, and stream channel
stabilization. Due to differences in how their benefit to cost ratio is calculated
compared to FEMA’s, the Corp does not generally fund acquisition of structures,
but can fund floodproofing. The Corps is charged with the responsibility of
regulating wetlands and navigable waterways and wetland mitigation is a product
of their accomplishments.
Table 15. Major U.S. Army Corps of Engineers flood protection projects in Maryland
Project
Date
Description
Kitzmiller Levee
County
GA
1963
5,800 ft of levee; 30 ft of retaining wall; 4,700 ft channel
improvements along Potomac River.
Bloomington Lake
GA
1962
Savage River
GA
1949
Cumberland
AL
1946
Anacostia
PG
1954
Anacostia
PG
1972
Oxon Run
PG
1962
Upper Marlboro
PG
1963
Dam 2,130 feet across valley of North Branch Potomac
River; 296 feet high; storage of 130,900 acre-feet, of
which 32,200 acre-feet is flood control.
Dam 1,050 feet long and 184 feet high. Storage
capacity 20,000 acre-feet; seasonally used for flood
control.
Channelization of Wills Creek for 1.6 miles. Channel
improvements of Potomac River of 1,7 miles. Levees
and floodwalls along Potomac; pumping stations,
pressure conduits, and small dam.
Levees along 28,100 feet of Anacostia River and
Northeast and Northwest Branch. Flood control
channels of 14,400 feet; pumping stations.
Upstream of previous project; included channel
improvements by realigning, widening and deepening
channels of Northwest Br (5,610 ft.), Northeast Br
(7,200 ft), Indian Creek (7,600 ft).
Channel improvements of 4,160 feet; drop structure at
upstream end; and approximately 1,500 feet of earth
levee to protect Town of Forest Heights.
Channel improvements of Western Branch (4,028 ft of
channel improvement, 1,350 ft of earth levee, 160 ft of
floodwall) and Collington Branch (1,335 ft of channel
improvements, 500 ft of levee, 150 ft of floodwall) of the
Patuxent River.
An Assessment of Maryland’s Vulnerability to Flooding
Page 75
The National Park Service (NPS),
under the U.S. Department of Interior, has
been proficient in removing structures from
the floodplain that fall within the C&O
Canal National Historical Park. Nearly half
of the structures removed by the Park
Service appear on the state repetitive loss
list.
County
Allegany
Montgomery
Washington
TOTALS
No. Structures
Repetitive
Removed
Loss
1
1
1
0
22
10
24
11
Another federal agency that has been active in the acquisition of homes
and the restoration of waterways is the Natural Resource Conservation Service
(NRCS), under the U.S. Department of Agriculture. NRCS has contributed nearly
$2 million to restoring the Dry Run watershed, and was a major contributor to the
Westernport acquisition project in Allegany County.
An Assessment of Maryland’s Vulnerability to Flooding
Page 76
Part VI. Funding Mitigation
Sources of Funding for Mitigation
Federal
• Federal Emergency Management Agency
o Hazard Mitigation Grant Program
o Flood Mitigation Assistance Program
• National Park Service
o Rivers and Trails Assistance Program
• Natural Resources Conservation Service
• U.S. Army Corps of Engineers
• Department of Housing
o Community Development Block Grant
State
• Maryland Department of the Environment
o Comprehensive Flood Management Grant Program
o Nontidal Wetlands and Waterways Mitigation
• Department of Housing and Community Development
o Community Development Block Grant Program
• Maryland Emergency Management Agency
Administers FEMA Program in the state
• Maryland Department of Planning
Local (County)
• County Commissioners or County Council
• Department of Emergency Services
• Department of Planning and Zoning
• Department of Public Works
Local (Municipal)
• Mayor and City/Town Council
• Town Planning or Engineering Dept.
An Assessment of Maryland’s Vulnerability to Flooding
Page 77
Part VII. Recommendations
Flood Grant Program
1. The State’s Flood Management Grant Program needs to be able to fund a
wider range of activities than in the recent past. Although acquisitions
should remain the primary focus of the program, flood studies, mapping,
planning efforts, and other forms of mitigation should also be considered
for grant funds when appropriate and cost effective. Internal Revenue
Service policy dictates that bond funds can no longer be used to fund
projects that are not capital projects, so alternative funding will be
required.
2. The State Flood Management Grant Program needs a reliable, dedicated
source of funding to fund mitigation projects. Currently, funding waxes
and wanes with flood events and budget crunches. Other states (Virginia,
West Virginia) place a surcharge on flood insurance policies of 1-5% to
fund state mitigation efforts. A yearly surcharge of 3% on Maryland flood
insurance premiums would yield approximately $500,000 per year for the
program. We urge the legislature to consider such a dedicated source of
funding for the future of the program, in addition to bond funds.
Coordination
3. There needs to be better coordination of state agencies involved in
disaster mitigation and mitigation planning to prevent duplication of effort
and better use of state resources. The roles of each agency should be
defined and agencies need to communicate and work together to gain a
consensus and articulate a consistent state policy. A state agency that
can communicate and coordinate effectively with other agencies should be
tasked with the coordinating role and given the necessary authority and
resources.
“No Adverse Impact”
4. A “No Adverse Impact” policy should be implemented through the local
planning and permitting process with state assistance.
Future
development would be predicated upon the principle that existing
development will not be harmed by greater flood heights from the adverse
impact of new development. Stormwater management planning will
become an integral part of future permits and will need to be
strengthened. In obtaining future permits, applicants would have to
demonstrate no adverse impact, work with the local jurisdiction to alleviate
the impact, or be denied the permit.
An Assessment of Maryland’s Vulnerability to Flooding
Page 78
Wetlands
5. In conjunction with sea level rise and the preservation of wetlands, the
current policy of armoring shorelines needs to be examined. Wetlands are
currently being lost to open waters and will need to have the ability to
migrate inland to persevere, or their vital functions will be lost.
Planning
6. Dynamic local planning will be important to lowering future vulnerability to
flooding. Much can be done at the local level to improve local ordinances
and policies to mitigate future disasters. The minimal present cost of
implementing hazard area zoning, freeboard requirements, better building
practices, etc., will prevent overwhelming losses in the future, if the local
jurisdiction is serious about making itself disaster resistant.
Tax Incentives
7. The state should provide support and strong incentives to individuals and
communities that undertake measures that result in proven future savings
in disaster recovery costs. Tax incentives and grants should be awarded
to individuals and communities that implement proven technologies and
methods.
Protection of Floodplains
8. Greater emphasis needs to be placed on maintaining riverine floodplains
and their associated wetlands and steep slopes in their natural vegetation
to maintain the vital functions of these important ecosystems. Currently,
neither the regulations nor the costs of altering these sensitive areas are
great enough to prevent destruction of many vital floodplain functions to
the state.
Sea-level Rise
9. Sea level rise is a fairly predictable phenomenon with predictable
consequences for failure to take appropriate actions. However, no state
policy to deal with the consequences of sea level rise has been
articulated. The state needs to take action to articulate policies to mitigate
the effects of sea level rise. Among these should be additional elevation
of all new buildings (freeboard requirement) and establishment of setback
zones from eroding shorelines.
An Assessment of Maryland’s Vulnerability to Flooding
Page 79
Acknowledgements
The authors would like to thank the many people that made the completion of
this report possible. Mr. Joyce would like to thank Kevin G. Wagner for
assistance in analysis of some of the data, production of graphics and tables,
and review of the text. Dr. Scott would like to thank Melissa Berry for her tireless
pursuit of a clean HAZUS-MH model run and Suzanne McArdle for her creation
of many of the high-quality cartographic products found in this document.
Additionally, thanks go to Cliff Oliver of FEMA, Philip Schneider of the National
Institute of Building Sciences, and Neil Blais of ABS Consulting for their response
to our pleas for help regarding the HAZUS-MH software. Hopefully, by working
together, we helped create a better user experience for HAZUS users in the
future.
An Assessment of Maryland’s Vulnerability to Flooding
Page 80
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Sharing the
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Johnson, Z.P. 2000. A Sea Level Response Strategy for Maryland, Report for
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An Assessment of Maryland’s Vulnerability to Flooding
Page 81
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An Assessment of Maryland’s Vulnerability to Flooding
Page 82
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