ABSTRACT:

The resource is a HEC-HMS model of a watershed for USGS Station 01665500. The station was used as a gage in ArcGIS to create a watershed. This watershed was then split into three smaller sub-watersheds and this was modeled in HEC-HMS. The original parameters for the watershed were determined using ArcMap. After the HEC-HMS model was created, it was calibrated with a storm event from May 1, 2013. The parameters were changed manually until a Nash-Sutcliffe value of 0.986 was obtained when simulated flows were compared to those observed at the USGS Station. Rainfall and Flow dss files were used for the HEC-HMS model and are included. The original storm used for calibration has the flow and rainfall data in RealDataHW1.dss. The second storm used to determine goodness of fit for the model is named Storm3-6-11.dss. The storm used for calibration had abnormally high discharge values for the amount of rainfall. It had a peak discharge of 13,500 cfs for 3 in. of rainfall while the second storm of similar size (2.7 in.) had a peak flow of only 4430 cfs. After using the HEC-HMS Optimization Tool and optimizing Initial Abstraction ratio, a Nash-Sutcliffe value of 0.992 was obtained for the first storm. The model was then updated with the new initial abstractions and run for the second storm. The Nash-Sutcliffe value dropped to -5.831 showing the model was inaccurate. This inaccuracy is believed to be due to due the model being calibrated for a storm with unusual discharge characteristics.