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

esolution of the output runoff hydrographs that may miss the flowpeaks and accurate volume amounts.• To preserve the original HEC-HMS model configuration as it wasprovided by the local agencies in San Antonio. In fact, most of thehydrologic model configurations are developed with the user-specifiedhyetograph option and simulations from them should be kept as closeas possible to the original setup.In light of the aforementioned reasons, the user defined hyetograph option,as selected in the original configuration of the HMS model was employed toassign the rainfall hyetographs to each subbasin as the first alternative to beimplemented for the Map2Map application.The user-specified hyetograph option allows the user to enter/define thedepth and temporal distribution of a historical or hypothetical storm event. Inpractice, in HEC-HMS the rainfall values for each subbasin are entered andinterpreted as if it were rainfall at a gage. The model, however, applies that “pointrainfall measurement” over the entire subbasin for the hydrologic simulations (alumped approach).For most of the options available to ingest rainfall into the HMS model,the final goal is to have a rainfall hyetograph assigned to each subbasin element asdefined in the segmentation of the basin under study. The gridded precipitationoption on the other hand assigns a hyetograph to each grid-cell and the modelperforms transformation functions at the grid-cell level also.94