Investigating Parameters of Geomorphic Direct Runoff Hydrograph Models¹

Abstract—Formulation of rainfall runoff models and identification of their parameters is difficult step especially for catchments having scanty or no data. Parameters of geomorphic instantaneous unit hydrograph (GIUH) models have been investigated in this research. Recorded data of Shahpur Dam Catchment, Pakistan was used for developing direct runoff hydrograph model. Satellite imageries of the catchment were processed using ArcGIS 10.1 to estimate geomorphologic parameters. The rainfall and runoff data for 10 events was collected from Meteorological Department Lahore and from Small Dam Organization, Rawalpindi, Pakistan. Rainfall data was analyzed and excess rainfall was estimated using Percent Runoff Method. Using estimated geomorphologic parameters the ordinates of GIUH- Nash Model were obtained by standard equations of Nash instantaneous unit hydrograph (IUH). These ordinates of Nash-IUH, were converted into the ordinates of direct runoff hydrographs through their convolution with the excess rainfall. The results of model were evaluated on the basis of their deviation from the observed runoff data. Statistical parameter Nash-Sutcliffe Coefficient and percent error between observed and simulated direct runoff were used for this purpose. The impact of using digital elevation models (DEM) of two different resolutions; 30 and 90 m, was then investigated. It is observed that the geomorphic parameters are affected due to DEM’s resolution. Hence the resolution of DEM impacts the direct runoff as well.