Customizing Hydrologic Basin Shapefiles to Improve National Weather Service Flash Flood Warnings and Statements

Recent flash flood events in the Nashville Metro area have highlighted the need for more specific information regarding the locations being impacted by flood waters. The National Weather Service maintains situational awareness during flash flooding, using specialized software called Flash Flood Monitoring and Prediction (FFMP). This program displays estimates of rainfall rates and amounts for areas within a GIS shapefile that contains hundreds of small hydrologic basins to highlight where flash flooding may be occurring. These basins often have an uncommon or incorrect naming structure, and may not reflect the actual drainage of the creek or stream.

The current shapefile used in FFMP to monitor and diagnose flash flooding in the NWS Nashville County Warning Area makes it difficult for forecasters to quickly identify well-known areas that would be impacted by flooding. We determined that reconfiguring the basins around the Nashville Metropolitan area would improve forecaster situational awareness and shorten the flash flood warning process.

The basin reconfiguration process involved reshaping drainage basins based on their relative location to streams, lakes, and other topographical features, and renaming them to include recognizable names of cities, neighborhoods, and creeks. This was accomplished by altering several basin attributes using a combination of GIS applications. In addition to better-worded warnings and statements, these changes will allow for customized Flash Flood Guidance values to be assigned to the new basins. This poster will show how this process will lead to an increased quality and usefulness of the Flash Flood Warnings issued, and an improved understanding of the specific areas impacted.