Topographically Derived High-Water Thresholds for Flood Inundation Mapping

Topographically Derived High-Water Thresholds for Flood Inundation Mapping

Day 2 Session 2 (1:30PM)

Operational flood forecasting by the National Water Center relies on the identification of high-water thresholds for the initiation of Flood Inundation Mapping (FIM). More accurate representation of high-water thresholds at scale will result in more accurate triggers for FIM generation, a key public-facing OWP product, and response activation. Furthermore, paired high-water stage and flow thresholds can improve HAND-FIM performance through the calibration of synthetic rating curves. This workshop introduces “INFLection-based Elevations from Channel Topography” (INFLECT), a python application for identifying high-water thresholds from topographic data, and provides training on how to apply INFLECT to improve HAND-FIM performance. Using data from an example watershed, attendees will: 1) apply INFLECT to identify high-water thresholds at the hydrofabric segment scale, 2) calculate corresponding bankfull flow and recurrence interval values from nearest USGS gage flow records, 3) use the identified bankfull stage and flow as a calibration point to adjust a HAND-derived synthetic rating curve, and 4) compare flood inundation maps before and after calibration. The course will be facilitated through a Python Jupyter notebook, preloaded with results so attendees may perform all processing steps or simply inspect sample results along each step of the workshop.