Simulation of scenarios urbanization impacts on and sediment using WetSpa model in Ziarat watershed, Iran

Erosion and sediment transport is a complex process that is influenced by soil texture, topography, regional climate, land use, human activities such as farming systems and soil conservation measures. This study examines the effects of changes in land use and residential development on erosion and sedimentation in Ziarat watershed in Iran.. In this study, the basic WetSpa model inputs were the maps of a digital elevation model (DEM), land use and soil type in GIS raster format, and hydrometeorological data including hourly precipitation, evapotranspiration and temperature for 4 years (2007-2010). Hourly discharge and suspended sediment at the watershed outlet were used for the model calibration and validation. The accuracy of flow simulations based on the Nash - Sutcliffe model efficiency was 67.02% respectively. The evaluation of suspended sediment simulations for the calibration period based on the Nash – Sutcliffe criteria was 63.08% and 72.22 % for the suspended sediment concentration and sediment yield, respectively. Then, the residential development and land use change scenarios were developed in GIS environment and were used as input maps for the calibrated model. Comparison of the components of erosion and sediment transport results showed that by increasing the residential areas, suspended sediment concentration changed from 0.23 g/l for current situation (zero scenario) to 2.27 g/l in Scenario IV(100% increase in residential areas). Also the amount of suspended sediment yield increased from 253 g/s in current situation to 1143 g/s.