An Assessment Of Maryland s Vulnerability To Flood Damage

Transcription

1 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

2 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

3 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, 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

4 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 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

5 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

6 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 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 100- year 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

7 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 100- year 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

8 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

9 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. 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. 2. 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. 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. 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. 5. In conjunction with sea level rise and the preservation of wetlands, the current policy of armoring shorelines needs to be examined. 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. An Assessment of Maryland s Vulnerability to Flooding Page 4

10 7. 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. 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. 9. 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

11 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 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 ). 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 100- year 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

12 The NFIP was further enhanced by the passage of the Flood Disaster Protection Act of 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 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 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 Included was providing assistance to local governments in drafting land use regulations pertaining to An Assessment of Maryland s Vulnerability to Flooding Page 7

13 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 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 , 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 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

14 program to determine wave height elevations for coastal areas in 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

15 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 July 24 Jones Falls again flooded Baltimore City with heavy loss of life and property. Patapsco River flooded Ellicott City Unknown "Centennial Storm" noted in Wicomico County June Susquehanna and Potomac Rivers largest flood of record to date (50 to more than 100-year recurrence interval) August 4 Herring Run through Baltimore County and City July 23 Patapsco River flooded greater than in Ellicott City under water March Potomac was 20 feet above normal due to snowmelt and intense rainfall, devastating parts of Cumberland (recurrence interval 20 to more than 100-year). May Potomac flooded Cumberland; Antietam Creek flooded Hagerstown August Flooding on Eastern Shore due to hurricane. Thirteen deaths, $12.3 million damage (recurrence interval 10 to more than 100-year) March 4 Spring thaw floods Carroll and Howard Counties. July 9 Aberdeen, Havre de Grace, and Elkton flooded; Roads and bridges in Southern Maryland washed out. September Federalsburg flooded 9 feet above normal March 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) January Potomac floods Hancock April "Northeaster" causes extensive flooding statewide. Damage to Cumberland, Williamsport, Baltimore, Dundalk, Washington, DC, Chestertown, Salisbury, and southern Maryland. October 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 August Rains flood Dundalk, Parkton, and southern Maryland. October Potomac floods Cumberland, Hancock, Williamsport, and Point of Rocks. Washington, DC had floods 17.6 above normal. Patapsco floods Ellicott City July Minor flooding throughout state due to extended rainfall Minor flooding on Eastern Shore 1949 July Minor flooding in Hagerstown, Frederick, and Baltimore Counties. An Assessment of Maryland s Vulnerability to Flooding Page 10

16 Year Date Description 1954 October 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 August Hurricane Connie dumps heavy rains on Eastern Shore of over 10 inches. Baltimore - Washington area flooding August 26 Heavy rains cause dam failure on Marshyhope Creek, flooding Federalsburg July Tropical storm Brenda causes flooding in St. Mary's County. August Potomac and Wills Creek flood Cumberland. September Hurricane Donna causes flooding on Eastern Shore, especially to Ocean City. Two deaths March 6-7 "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 September Minor flooding throughout state of 10-year frequency August Federalsburg and Greensboro severely flooded April Minor flash flooding in Cumberland August 1-2 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. Sept Heavy rains in Central Maryland, especially Howard County cause $4 million in losses June 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 Dec. 1 Storms and tidal surges cause damage statewide, especially on the 1975 September 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. Feb Snowmelt and intense rainfall causes flooding especially in Pocomoke River year storm. Sept. 5-6 Hurricane David floods Rock Creek, Jones Falls, East Branch Herbert Run. Recurrence interval 50 to greater than 100-years. March Statewide flooding and intense coastal erosion, especially along lower Chesapeake Bay. Two deaths. August 13 Heavy thunderstorms from Harford to Frederick Counties, especially in Baltimore area. Aug. 18 Remnants of Hurricane Danny flood St. Mary's Co with 10 Sept. 27 Nov. 4-7 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

17 Year Date Description 1989 June 23 Thunderstorms cause flash flooding in Allegany Co. July 6 Statewide flooding, but most severe in Elkton. August 20 Thunderstorms dump 10 inches of rain in Pocomoke River area Jan. 4 Dec. 11 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 1993 Nov. 28 Heavy rains (5 inches) cause flooding in Frederick area (Monacacy River) June Thunderstorms in Westernport, Allegany Co. cause runoff from surrounding mountains Jan 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. June Isolated thunderstorms flood parts of Frederick Co. especially Sept. 6 Emmitsburg. Remnants of Hurricane Fran cause widespread flooding in Western MD, especially George's Creek. $1.7 million in damages Sept. 16 Hurricane Floyd causes widespread flooding on Eastern Shore, especially in northern portions. Damages $14 million, and greater than 500 year flood in places Sept. Local thunderstorms flood SW Cumberland from stormwater off Haystack Mountain Sept Remnants of Hurricane Isabel cause widespread tidal surge flooding, esp. in middle portion of Bay. Close to 100-year flooding. Riverine flooding minor July Local thunderstorms cause isolated flooding in Baltimore City and Harford Co, especially Havre de Grace. 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

18 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 100- year 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 100- year 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

19 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

20 An Assessment of Maryland s Vulnerability to Flooding Page 15

21 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, ,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

22 Table 2. Structures and people in floodplains in Maryland People Structures County CAV Overlay CAV Overlay Value of Improvements (2001) Flood Insurance Policies (2002) Percent Policies Allegany $76,947, Anne $691,534, Arundel Baltimore $640,920, City Baltimore $630,154, Calvert $123,665, Caroline $46,807, Carroll $58,158, Cecil $171,198, Charles $76,642, Dorchester $237,910, Frederick $366,260, Garrett $41,959, Harford $184,647, Howard $179,293, Kent $110,788, Montgomery $577,218, Prince $479,081, George's Queen $344,088, Anne's Saint Mary's $109,075, Somerset $243,355, Talbot $311,748, Washington $109,596, Wicomico $110,272, Worcester $2,068,494, TOTALS * * $7,989,820, 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

23 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

24 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 of Natural Resources Article until its repeal in 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