Effect of spatial resolution on watershed characteristics and the ANSWERS model hydrological simulations for a small watershed

Abstract

The present study was undertaken to investigate the effect of cell size variation on watershed characteristics and hydrological simulations of the physically based distributed parameter Areal Non point Source Watershed Environment Response Simulation (ANSWERS) model. The study is carried out in Banha watershed located in Upper Damodar catchment, Jharkhand, India having 16.13 km 2 area (with average slope of 1.91%.) using Digital Elevation Model (DEM), GIS and remote sensing techniques for automatic extraction of the model input parameters. The spatial resolution (cell size) variation from 30m to 150m with incremental step of 30m influences the accuracy of watershed characteristics extracted from DEM. The flow path length and average watershed slope decreased by 53.71% and 20.94% respectively due to variation in cell size. Important watershed parameters such as drainage area, stream network, slope etc. were extracted most accurately automatically with variations less than 10% using DEM of 30m resolution through EASI/PACE and IDRISI GIS. Land use and land cover information generated from Indian Remote Sensing Satellite (IRS-1B, LISS-II) data at 30 m resolution resulted in overall classification accuracy greater than 88%. The watershed hydrological data from fifteen storms of 1995 and 1996 were used for the ANSWERS model cell size sensitivity study. The runoff, peak flow and sediment yield simulations by the model decrease as cell size increases from 30 m to 150 m. The model simulated peak flow at acceptable accuracy for 30 m cell size. The runoff and sediment yield simulations are not observed to be significantly different from the observed values up to 120 m cell size.