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

Figure 4.13 DSS2GDB Model ComponentLocations of flow data change points are usually defined at the upstreamend of each reach where flow source points are defined by tributaries entering anadditional flow hydrograph to the main river. This is so because the reachdefinition is done by having in mind all the existing confluence points (tributariesentering the main river channel) and all the existing divergence points (flow splitpoints). It is possible however to define a flow change location inside a reach ifthe reach segmentation missed a source point.The hydrologic simulation in HEC-HMS is responsible for providing therunoff hydrographs for all the flow change location points that import streamflowinto the main channel subject to hydraulic analysis. In general, every single reachlocation receiving flow (the most upstream end and all the tributary confluencepoints) from subbasins inside the watershed under study must be treated as flowchange location points in HEC-RAS and the entering flow must be definedthrough the steady flow data component. By doing this, the hydraulic routing willbe properly affected by those flow additions.Since the runoff hydrographs generated by the output of HEC-HMS arestored in a HEC-DSS file, the flow values must somehow be extracted from DSS110