National Weather Service (NWS) customers and partners have identified inundation mapping as a high-priority service. Current procedures to create these maps require a hydraulic study and LiDAR-derived elevation data, both involving substantial time and financial resources to produce. Because only a few locations in the U.S. meet both of these requirements, maps can be developed at a small number of sites and only over a small geographic area around them. A simpler and less time-consuming method of mapping flood inundation has the potential to save significant cost and map many more areas.

The most important step in the development of flood inundation maps is the estimation of a water surface elevation profile. The land surface elevation is subtracted from this water surface profile to estimate inundation depth. Hydraulic models are used because they are assumed to provide accurate water surface profiles, although time and data requirements are substantial.

A GIS method to estimate water surface profiles was created at the NWS Weather Forecast Office (WFO) Des Moines and further developed at the NWS Lower Mississippi River Forecast Center. This method has been preliminarily tested at WFO Des Moines, IA, WFO Lake Charles, LA, and WFO Jackson, MS. This procedure has been tested on approximately a dozen river forecast points. Preliminary results presented here indicate that the tool performs best in areas with well-defined channels and steep-sloped topography. In these areas the resulting inundation extents have been very comparable to inundation extents developed using current NWS inundation mapping procedures.