Estimating runoff at Ruckersville, VA using HEC-HMS, calibrating and validating the model

This is a HEC-HMS model for runoff estimation from a 115 sq-mile watershed at Ruckersville, VA and the work was done for Hydrology class project at University of Virginia for Fall 2017. The watershed has 3 subbasins where subbasin 1 and 2 discharge to reach-1 via junction-1, and reach 1 and subbasin-3 discharge to outlet (junction-2). Precipitation from NOAA weather station “Piedmont” at Orange County was used to generate flow from this watershed. Modeled flow was then compared with observed flow at USGS Station “Rapidan River near Ruckersville, VA” (Station 01665500) with Latitude 38°16'50\" and Longitude 78°20'25\". For original model, a rain event from May 2013 was used and for validation, two events from Mar 2011 and Oct 2012 were chosen. The original model was calibrated first without adding baseflow to any subbasins and the model simulation after the hydrograph peak wasn’t satisfactory. Then, baseflow was added to subbasin-2 as that creates best match for the modeled flow with the observed one. This calibration shows nearly perfect goodness of fit with Nash-Sutcliffe efficiency (E) of 0.938. In addition, 2 other rain events from Oct 2012 and May 2013 were used for model validation which produced very weak goodness of fit with negative E. This difference might result in due to weather, soil moisture condition, peak flow etc. Overall, the HEC-HMS model was calibrated perfectly for about 14,000 cfs peak flow in May but the validation result was not satisfactory, so the model needs further verification to become representative for the watershed for a wide range of peak flow and season.