Using of Geographic Information System in estimating of soil erosion and sediment production on Nojian watershed )Southeast of Khorramabad city)

Abstract
Soil erosion is one of the most important factors causing decline of soil fertility, siltation of different kinds of waterways, reduction of reservoir capacity, increase in destructive risk of flooding and other environmental degradations. In order to mitigate the negative effects of soil erosion and sediment production in watersheds, determining amount and source of sediment is imperative. Since most of Iran’s watersheds are ungauged, use of erosion and sediment estimation models are needed. But for selection of applicable model the models first have to be tested and/or evaluated. In order to achieve to this goal, a research study was carried out to evaluate MPSIAC model in GIS environment based on the observed data of sediment of the Nojian sub-watershed located in southeast of Khorram Abad city in the Lorestan province-Iran. In so doing, to run the selected model after introducing the information layers into the GIS program and combining the layers in MPSIAC model, the given catchments were divided into 527 homogenous units. Then, erosion rate and sediment yield were estimated in these homogenous units. The amount of estimated sediment yield by using MPSIAC model was 489372.2 T/y. For comparison of the model results, the amount of measured sediment in hydrometric station was considered as the control level, which was 812410 T/y. The outcome of the research showed that estimating sediment by using MPSIAC model in comparison to measured sediment was 0.602. The results of the assessment on observed differences show that calibration of the empirical models is needed first to resolve the limitation of the models in correspondence to the existing condition of the watersheds. It can be concluded that in order to accept or reject the result of the sediment yield estimation using the MPSIAC model with high confidence, the model first should be calibrated based on the existing condition of the Iran’s watershed.