An Assessment of Maryland's Vulnerability to Flood Damage

An Assessment of Maryland's Vulnerability to Flood Damage

The Maryland Department of the Environment (MDE) and the Eastern Shore Regional GIS Cooperative (ESRGC) at Salisbury University released a report: An Assessment of Maryland’s Vulnerability to Flood Damage in August, 2005.  Dr. Michael Scott at the ESRGC used the Federal Emergency Management Agency’s (FEMA’s) new hazard vulnerability modeling software program, HAZUS-MH FLOOD, to provide a systematic examination of Maryland’s built environment to both riverine and coastal flooding in each county and the City of Baltimore.  The model was used to provide an independent analysis to collaborate some of the Department’s flood hazard data and to test the usefulness of the new software.

The report documents the history of flooding in Maryland and the history of programs to mitigate against flood damage.  Strategies to mitigate the effects of flooding are outlined, including regulations, the State Model Floodplain Management Ordinance, local mitigation planning, the floodplain management database and repetitive loss project, mapping of risk, flood insurance, dam safety, stormwater management regulations, wetland regulations, growth management, sea level response strategy, and “no net adverse impact” watershed planning.  Some flood mitigation projects in Maryland are described, including those of the Comprehensive Flood Management Grant Program.  The report concludes with some recommendations to further flood mitigation in the State.

A level 1 analysis of the 100-year flood was conducted, which uses the 30 meter Digital Elevation Model (DEM), and the Census Bureau’s block building data from national datasets.  While this level analysis is not very accurate, it provides a consistent and comparable methodology to view statewide vulnerability for planning purposes.  Further, the user can modify input to the model to provide answers to such questions as how would flooding change if a flood wall or levee were built, what would happen if an area of the floodplain were filled, or what area would flood during a different frequency flood.  MDE had previously estimated that approximately 68,217 structures worth approximately $8 billion were exposed to the 100-year flood, and that amount of a county’s land area in the floodplain varies from 55.8% in Dorchester County to 4.6% in Garrett County.

The modeling showed that 13.4% of the State’s area is 100-year floodplain, varying from 61% in Dorchester County to 2.9% in Garrett County.  An estimated 44,755 buildings throughout the State would be damaged by the 100-year flood, with $8.12 billion in direct economic losses.  Only two counties, Anne Arundel and Worcester, made up more that 10% of the State’s buildings damaged.  Just three counties made up 40% of the State’s direct economic losses to buildings: Prince George’s, Worcester, and Anne Arundel.  Losses to residential buildings made up 86% of the total damages.  However, Somerset, Dorchester, St. Mary’s, and Calvert Counties were vulnerable to the largest percent of substantially damaged buildings. The data generated by the software compares reasonably well with data that had been complied by other methods.

A workshop was held on August 10, 2005, to introduce local planners and GIS specialists to the analysis, and copies of each county’s model were provided to the respective counties.  The report, the software runs for each county, maps depicting flooding and damage in each county and in the State, and the workshop presentation are all available on the Eastern Shore Regional GIS Cooperative’s website at www.esrgc.org/hazus.htm.

A very accurate Level 2 HAZUS-MH FLOOD analysis is being conducted for Ocean City.  This analysis will use the LiDAR data for very accurate topography and a GIS building inventory with the location and elevation of each building in Ocean City.  The resulting analysis should be able to accurately predict flooding and damage and will be evaluated by the Town for its usefulness.​