Creating this map and doing the analysis required to complete the lab has been the most challenging assignment so far in my GIS Certificate Program. Above is a map comparing a LiDAR-based DEM and USGS DEM to display a 1-meter storm surge in Florida. My main task was to calculate how many buildings would be impacted at each elevation model. After the DEMs were converted from feet to meters, I used a Region Group Tool to separate the areas so that the analysis was only focused on the areas directly connected to the coastline. Then, I completed the Raster to Polygon tool to get polygons for the expected flood areas for each DEM.
To determine which buildings were impacted, I added fields to the buildings layer for LiDAR and USGS and Categorized them into 4 categories - 0, 1, 2, 3, 4.
0 = No impact from either DEM
1 = Building is impacted in both DEMs
2 = Building is impacted just by LiDAR DEM
3 = Building is impacted by just USGS DEM
We then were instructed to find the errors of omission and errors of commission where omission is the buildings flooded in LiDAR but missed in USGS and commission is the buildings flooded in USGS but missed in LiDAR. We did these calculations for all four building types - commercial, residential, shed, and garage. The calculations were difficult for me to conceptualize what each number represented in the formula and why it was important.
The assignment also had us reflecting on what would make this model more realistic. This analysis assumes a flat, uniform 1-meter storm surge across the study area but surge heights can vary based on many factors like wind speed, coastline shape, and buildings and vegetation obstruction. Also, it does not consider rainfall runoff or backflow from rivers. It doesn’t include flow direction, slope, or water pressure in the analysis either. To make it more realistic, we would need to incorporate flow connectivity and use flow direction of where the water would travel even to the disconnected low-lying areas. We would need to add infrastructure layers that include flood control structures like storm drains. I would also include storm surge models that have rainfall / runoff.
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