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

Thus, the time period for the entire simulation must be large enough toencompass the full range of streamflow magnitudes that may occur during thestorm event, from the baseflow values to the peak flow values and back to thebaseflow values to capture the entire rise and recession of the hydrograph’s shape.One approximation for this is to define a simulation time window thatencompasses the entire rainfall event duration plus the hydrologic response timeof the entire watershed plus the hydraulic response time of the channel system.This total duration is then the storm duration plus the travel time of the watershedup to the outlet. The storm duration can be read from the time series realization ofthe event, but in principle the travel time of the watershed has to be selected withcare and consideration for the intensity of the storm, the initial moistureconditions, the level of development of the watershed, etc. Thus, in practice, thetotal simulation time window is obtained by incrementing the starting date andtime of the simulated storm event with the storm duration plus a reasonableestimate for the travel time of water within the watershed.The simulation time interval (computational time step) determines theresolution of the model results computed during a run. The entered gage data islinearly interpolated to the selected time interval (from hourly gage data to 15minute time steps in this case study). The analyst must define at what timeinterval the computed flow hydrographs will be written to HEC-DSS. In general,this time interval should be selected to give an adequate number of points to fullydefine the shape of the computed hydrographs (rise and fall) without losing keyinformation about the flow peaks or volume of the hydrographs. To make sure99