Simulation of Daily Suspended Sediment and Investigation of the Impact of land Use Change in GolGol Watershed, Ilam

In this study, the ability of spatially distributed hydrological WetSpa model for simulation of suspended sediment concentration in a daily time step was investigated. Hydro-climate daily data for a period of 7 years including: precipitation, temperature, evaporation, discharge and suspended sediment and three basic basic digital maps of DEM, soil texture and land use, with the cell size of 25 meters was used. Also, with the implementation of the model by changing the land use map, we determined the impact of land use change on sediment of GolGol watershed. The results showed that the WetSpa model has potential to simulate suspended sediment concentration at the daily time step based on Nash-Sutcliffe (%67.45) as an important evaluation index. Moreover, the change detection of land use showed that by changes in forest and irrigated agriculture-garden from 1988 to 2013 there is a reduction amount of 3322.5 and 3934.3 hectares respectively, while, for rangeland and dry farming increased 3942.99 and 3313.9 hectares respectively. The results showed that the mean daily sediment concentration, annual specific sediment and annual suspended sediment yield by changing land use from 1988 to 2013 has increased. Statistical analysis results showed that the land use changes have effect on suspended sediment concentration in 1% significant level in the study area, so that the mean annual sediment concentration of 1.141 g/l in 1988 increased to 1.171 g/l in 2013. Finally the yearly average of sediment yield increased 63.8189 kilograms per hectares.