InFRM Flood Inundation Mapping

Science Center Objects

The purpose of this flood inundation mapping effort will be to meet the needs of real-time emergency managers by bridging the gap between the NWS's river forecasts and FEMA's available hydraulic modeling and mapping. 

During the recent Texas floods of 2015 and 2016, state and local emergency managers were searching for real-time inundation mapping from any and all available sources in order to help guide their emergency response efforts. Accurate inundation mapping can help guide emergency responders to the locations of impending road closures and homes or businesses that need to be evacuated for the protection of human life.

By law, the National Weather Service (NWS) is the federal agency tasked with the mission of issuing river and flood forecasts for the nation, which includes real-time inundation mapping. However, the current availability of NWS real-time inundation mapping from the West Gulf River Forecast Center (WGRFC) is limited to the immediate reaches surrounding a select few of their river forecast points.

The Federal Emergency Management Agency (FEMA) Region VI, on the other hand, maintains an inventory of hundreds of thousands of river miles of inundation mapping in its mission to administer the National Flood Insurance Program (NFIP). However, FEMA's Flood Insurance Rate Maps (FIRMs) generally only map one or two flood scenarios, typically the 1% and 0.2% annual chance exceedance events.

The purpose of this flood inundation mapping effort will be to meet the needs of real-time emergency managers by bridging the gap between the NWS's river forecasts and FEMA's available hydraulic modeling and mapping. This will be accomplished by taking existing detailed hydraulic models from FEMA's FIRMs and running a series of steady flow discharges through those models, ranging from just below the channel banks to a stage higher than the flood of record and/or the 0.2% annual chance flood event, in order to produce a series of inundation maps for each river reach.

Discharges will be entered that correlate to every one foot of stage. Each inundation map will then be correlated to a stage at the nearest WGRFC forecast point, where available, so that as the NWS updates its river forecast, the corresponding inundation map can be shared with local emergency managers in real-time.

The USGS Texas Water Science Center has developed a web based inundation map viewer to host the library of inundation maps that will be developed under this project. The inundation map viewer will allow emergency managers to have immediate access to real-time inundation mapping for areas not presently available through the NWS or other entities.