The CS-CRAB raster layer was created using a GIS spatial analysis model, unique for each county in Maryland. Coastal counties follow an analysis methodology that incorporates FEMA Stillwater wave action as it is understood from the FEMA identified VE zones. A Water Surface Elevation (WSE) and Still Water Elevation (SWEL) rasters are used as the baseline to identify existing water depths within each county. For all flood zones that are not classified as VE the WSE three feet was added to reflect a three-foot rise in the base flood elevations. For those WSEs falling within a FEMA floodplain identified V Zone, six feet was added (three feet for the increase in flood elevations for the CS-CRAB, and 3 feet to compensate for the minimum of 3 foot wave action typically mapped by FEMA) / wave heights greater than 3 feet were reduced to the 3 foot minimum for consistency across the shoreline. The newly calculated WSE plus three datasets were then converted to points and merged. Next, an Inverse Distance Weighted (IDW) Interpolation was used to compute the proportional weighted values between the WSE point locations based on proximity. The DEM for each county is then subtracted from the new IDW raster in order to show precise water locations as they relate to the land elevation, producing a freeboard depth grid representing the depth of flood waters above the existing ground elevation given a 3 foot increase in water level. A course resolution QAQC was applied to remove “islands” of data associated with DEM inaccuracies and other elevation anomalies.The analysis was run at a 1 ft x 1 ft raster resolution. The DEM accuracy for each county varies based what is currently available. Here the breakdown of DEM accuracy for each county used in this project: Anne Arundel County DEM year is 2017 and horizontal resolution is 1ft. Baltimore County DEM year is 2015 and horizontal resolution is 2.5ft. Baltimore City DEM year is 2015 and horizontal resolution is 0.7m. Calvert County DEM year is 2017 and horizontal resolution is 1ft. Caroline County DEM year is 2013 and horizontal resolution is 3.125ft. Cecil county DEM year is 2013 and horizontal resolution is 0.6m. Charles County DEM year is 2014 and horizontal resolution is 0.9m. Dorchester County DEM year is 2013 and horizontal resolution is 0.9m. Harford County DEM is 2013 and horizontal accuracy is 1.5m. Kent County DEM year is 2015 and horizontal resolution is 0.7m. Prince George’s County DEM year is 2014 and horizontal resolution is 0.7m. Queen Anne’s County DEM year is 2013 and horizontal resolution is 0.6m. Somerset County DEM year is 2012 and horizontal accuracy is 1m. St Mary’s County DEM year is 2014 and Horizontal accuracy is 0.9m. Talbot County DEM year is 2015 and Horizontal accuracy is 0.7m. Wicomico County DEM year is 2012 and horizontal accuracy is 1m. Worchester County DEM year is 2011 and horizontal accuracy is 1m.
The CS-CRAB raster layer was created using a GIS spatial analysis model, unique for each county in Maryland. Coastal counties follow an analysis methodology that incorporates FEMA Stillwater wave action as it is understood from the FEMA identified VE zones. A Water Surface Elevation (WSE) and Still Water Elevation (SWEL) rasters are used as the baseline to identify existing water depths within each county. For all flood zones that are not classified as VE the WSE three feet was added to reflect a three-foot rise in the base flood elevations. For those WSEs falling within a FEMA floodplain identified V Zone, six feet was added (three feet for the increase in flood elevations for the CS-CRAB, and 3 feet to compensate for the minimum of 3 foot wave action typically mapped by FEMA) / wave heights greater than 3 feet were reduced to the 3 foot minimum for consistency across the shoreline. The newly calculated WSE plus three datasets were then converted to points and merged. Next, an Inverse Distance Weighted (IDW) Interpolation was used to compute the proportional weighted values between the WSE point locations based on proximity. The DEM for each county is then subtracted from the new IDW raster in order to show precise water locations as they relate to the land elevation, producing a freeboard depth grid representing the depth of flood waters above the existing ground elevation given a 3 foot increase in water level. A course resolution QAQC was applied to remove “islands” of data associated with DEM inaccuracies and other elevation anomalies.The analysis was run at a 1 ft x 1 ft raster resolution. The DEM accuracy for each county varies based what is currently available. Here the breakdown of DEM accuracy for each county used in this project: Anne Arundel County DEM year is 2017 and horizontal resolution is 1ft. Baltimore County DEM year is 2015 and horizontal resolution is 2.5ft. Baltimore City DEM year is 2015 and horizontal resolution is 0.7m. Calvert County DEM year is 2017 and horizontal resolution is 1ft. Caroline County DEM year is 2013 and horizontal resolution is 3.125ft. Cecil county DEM year is 2013 and horizontal resolution is 0.6m. Charles County DEM year is 2014 and horizontal resolution is 0.9m. Dorchester County DEM year is 2013 and horizontal resolution is 0.9m. Harford County DEM is 2013 and horizontal accuracy is 1.5m. Kent County DEM year is 2015 and horizontal resolution is 0.7m. Prince George’s County DEM year is 2014 and horizontal resolution is 0.7m. Queen Anne’s County DEM year is 2013 and horizontal resolution is 0.6m. Somerset County DEM year is 2012 and horizontal accuracy is 1m. St Mary’s County DEM year is 2014 and Horizontal accuracy is 0.9m. Talbot County DEM year is 2015 and Horizontal accuracy is 0.7m. Wicomico County DEM year is 2012 and horizontal accuracy is 1m. Worchester County DEM year is 2011 and horizontal accuracy is 1m.
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