The Sediment yield potential estimation of Kashmar urban watershed using MPSIAC model in the GIS framework

Abstract:
With due attention to the relatively suitable compatibility of MPSIAC model with the arid and semiarid conditions of Iran and lack of hydrometric station in region, in order to estimating of sediment yield and providing sediment yield and erosion intensity map in this watershed, we used modified PSIAC model. At first to enter the available raw data into the GIS framework we digitized topography, geology, geomorphology, land capability, soil hydrologic groups and plant cover maps using on-screen method. In the second stage digitized maps were encoded based on the values of geology, soil erodibility, climate, land cover, land use, present status of erosion and channel erosion and sediment transport factors. Using the DEM layer, slope and rain (using the rain gradient equation) maps were provided and consequently topographic and runoff (using the logical method) factors maps were prepared. Then these factors maps were summed together and finally sedimentation score map was provided. We applied following equation on the sedimentation score map and therefore sedimentation map was obtained:
Q_s=38.77e^0.0353R
Where:
Q_s: specific sediment (m³/km²/y)
R: sediment yield score

And then with the applying Sediment Delivery Ratio (SDR) on the sedimentation map, erosion intensity map was obtained. Also to obtain the work unit map, we used geology, geomorphology and hydrologic units maps and with overlaying this maps work unit map was obtained. Considering the upper part of this basin is rocky, the small work units were eliminated, and at last 28 work unit was obtained. Then by Spatial Analyst module facilities in the ArcView 3.2 software, the average of sediment yield, erosion and in any work unit and subbasin was obtained. To mapping erosion forms was used from aerial photos interpretation and field surveying and 4 erosion forms (E1, R1, R2, S) was distinguished. For the relatively high effect of slope and landuse factors on increasing of sediment yield specially in the upper part of basin, to decrease the effect of these factors, was applied the average filter (size: 100m*100m) on the slope map and also the score of landuse factor was adjusted. Considering the urban watershed of Kashmar has soil only in the lower part of watershed and the most part of that is rocky, 55.6% of watershed area was categorized in the third class (a class with medium erosion), 42.7% in the second class (a class with low erosion), 1.7% in the fourth class (a class with relatively high erosion) .The class of high erosion there is in the lower part of this basin because this part has more sensitive formation. Also in this basin there is two sediment yield class.79.4% of this basin was classified in the second class (a class with low sediment yield) and 20.6% in the third class (a class with medium sediment yield).