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

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

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methods: user hyetograph, user gage weighting, inverse-distance gage weighting,gridded precipitation, frequency storm, standard project storm, and the SCShypothetical storm. The first four methods are used for the analysis of historicalprecipitation datasets and the last three methods are designed for producingsynthetic precipitation events. The user specified hyetograph method may also beused for feeding a synthetic storm computed outside the HEC-HMS model. Theuser has then four options for defining historical events and four options fordefining synthetic events.At first, the gridded precipitation option seems to be the logical choice forthe ingestion of the precipitation records since the source of precipitation is<strong>NEXRAD</strong> data and that the radar values are estimated and remapped to a nationalsquare grid called the Hydrologic Analysis Project (HRAP) grid (Reed andMaidment, 1999). Under this grid-based option, quasi-distributed cell-basedhydrologic attributes can be used for the ModClark basin transform method in theHEC-HMS meteorologic definition.Even though the gridded precipation method was devised for using radarrainfall data inside HEC-HMS, for the <strong>Map</strong>2<strong>Map</strong> implementation the griddedprecipitation option was not used for a couple of reasons:• In HEC-HMS, gridded data must be at 1-hour intervals and the timeinterval in the control specifications must also be set to 1 hour. Thisposes a limitation on the resolution of the <strong>NEXRAD</strong> data that theapplication might ingest (specially for real-time applications withsmall time interval of 15 minutes or less) and a limitation on the93

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