Effects of Digital Elevation Model (DEM) Spatial Resolution on the Recognition of Physiography Characteristics of the Basin )A Case Study of Shahrchai Watershed)

In recent years with developing geographic information systems tools, modeling and simulating methods has been developed quickly. Availability of accurate base maps is the basis of the cell sizes determination and preparing digital hydrologic models. Removing errors and minimizing of uncertainty factors in the digital models play the main role in improving the accuracy of the maps. The main purpose of this research is to produce GIS layers for Shaharchi river basin located in West Azerbaijan, according to the base maps of Iran and evaluating the accuracy of these maps. Physiographic parameters and hypsometric charts of the Shaharchai basin were estimated and drawn. Results showed that with increasing cell sizes, average, maximum and standard deviation of the slope decreased. The maximum slope is more dependent on cell sizes than the average and standard deviation. To calculate the watershed slope, at a scale of 1: 25000, a cell size of 15 meters and a scale of 1: 50000, a cell size of 40 meters and a scale of 1: 250,000, 90-meter cell size were distinguished as optimized cell sizes. After calculating the actual average slope of river profile and comparing with the slope amounts of each cell sizes and map scales it is concluded that for preparing river profiles the best cell size is 15 meters for 1:25000 map scale. The percent error of pits in the scale of 1:25000, increased slowly in the cell sizes smaller than 15 meters.