Module 5: Coastal Flooding

The purpose of this module was to explore procedures for coastal flooding and storm surge analyses using elevation models, overlay analyses for vectors and rasters, and spatial queries.

The first data set was for an area in New Jersey that was impacted by Hurricane Sandy. I converted LAS files from pre- and post- Sandy for the coastline area were to TINs and then rasters. I subtracted the two rasters from each other using the Calculate Raster tool and analyzed the resulting shapefile was for damage with a 2019 building overlay. There are several areas in the study area that show significant erosion (red areas) that have not been rebuilt. The map below shows the overall results of this analysis.
The second data set was also for New Jersey. A DEM was provided and I reclassified it into areas that would flood based on the Hurricane Sandy storm surge of 2 meters. I then converted the raster to a polygon and examined the result for Cape Map County. Based on the analysis, about 52% of Cape May County, New Jersey would be at risk to a storm surge of 2 meters. The screen shot below shows the storm surge area in red from this analysis.



The third and final data set was for Collier County Florida. For this analysis, I compared a traditional USGS DEM and a DEM derived from Lidar assuming a storm surge of 1 meter. I reclassified the rasters based on the storm surge of 1 meter and used the Region Group tool to identify areas connected to open water. I then used the Extract by Attributes tool to extract only those areas in each raster connect to water and converted the rasters to polygons. Each polygon was overlay-ed with a buildings shape file with a spatial join and queried with Select by Attributes to get a count of each of the different building types in each floodzone (either USGS or Lidar). I also determined the agreement between these results under the assumption that the Lidar data was more accurate. I used a combination of spatial query and overlay tools to determine the errors of omission and commission. My analysis resulted in the Lidar storm surge area being contained entirely within the USGS flood areas – probably because the USGS DEM was coarser and more created a wider area, whereas the Lidar data is finer and resulted in a narrower area. This means that if the Lidar is taken as the true scenario, then there were no areas of omission, however the commission errors are very high (because the USGS flood area is so much greater). The map below shows the results of the Storm Surge Analysis for Collier County, Florida, including the analysis results table.



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