Converting a NEXRAD Rainfall Map into a Flood Inundation Map by ...

contours (isohyetals) or by interpolating point values to generate iso-surfacesrepresenting precipitation values for a given frequency and storm duration.The execution of the aforementioned procedure over a region produces acollection of synthetic precipitation events that can be used for regulatorypurposes and to promote standard and comparable engineering practices. Thesetypes of studies have been developed over the U.S. by the National WeatherService and used as a national reference. These studies have been presented in theform of reports that serve as the standard in the U.S. The U.S. Weather Bureautechnical paper no. 40, also known as NWS TP-40, for durations from 30 minutesto 24 hours and developed by Hershfield in 1961. The need for inclusion of biggerstorm durations prompted supplemental studies in 1964 that included stormdurations for 2 days to 10 days, reported as NWS TP-49. The need for smallerstorm durations of 30 minutes or less (in urban drainage design or storm sewerdesign) prompted another study by the National Weather Service in 1977commonly known as Hydro-35 for storm events having durations from 5 minutesto 60 minutes.A digital rainfall atlas for Texas (containing raster isohyetal maps ofdesign rainfall depth for various event durations and for standard return periods)was made available for this study by Halff Associates, Inc. based on the threereports mentioned above (TP-40, TP-49, Hydro-35). This digital atlas containsraster isohyetal maps for storm durations of 5 minutes, 15 minutes, 30 minutes, 60minutes, 2 hours, 3 hours, 6 hours, 12 hours, 24 hours, 2 days, and 4 days. Foreach of the listed durations the series of frequency values corresponds to 1-year,179