Developing Real-Time Inundation Mapping for Harris County and Vicinity

By: Abebe S. Gebregiorgis, PhD, PE, CFM | Ataul Hannan, PE, CFM | Todd Ward, PE, CFM

Realtime Flood Mapping

We present the development of the Real-Time Flood Inundation Mapping Tool (FIMT-RT),

designed to provide instantaneous inundation maps based on real-time water surface gage data. The primary objective of FIMT-RT is to enhance flood preparedness and response within Harris County by leveraging its dense gage and remote water level monitoring network, administered by the Harris County Flood Control District (HCFCD). FIMT-RT seamlessly retrieves real-time observation data from approximately 180 gages directly through the Harris County flood warning system (fws - https://www.harriscountyfws.org). The tool processes this data to compute water surface elevations (WSEL) at predefined cross-sections along watercourses, subsequently generating maps that illustrate the extent and depth of riverine flooding within the gage channels.

These inundation maps are made available to the public on the fws website in near-real-time, bolstering community flood awareness and response. The methodology employed involves estimating the annual exceedance probability (AEP) of observed WSEL data, utilizing FEMA effective HEC-RAS profiles at established gage locations through linear interpolation and logarithmic best-fit techniques. Estimated AEPs are then interpolated along the channels cross-sections and translated into corresponding WSEL values for specific events. The culmination of this process is the creation of an inundation raster, which represents the WSEL of the event across multiple cross-sections. Notably, the output raster is generated at 3 to 5ft resolution within a 5 to 10-minute timeframe following the collection of gage readings. Extensive validation exercises involving historical events have showcased the robust performance of the FIMT-RT model. Additionally, the tool was subjected to testing during the historic Harvey event in August 2017, further affirming its efficacy. Currently, the FIMT-RT product is hosted on the fws website, actively contributing to public accessibility and awareness of flood risks in the region.