Assessing the amount of sediment yield in watershed scale using MPSIAC model: (A case study in Nojian watershed)

MPSIAC is a model for estimating erosion and sediment yield used in many countries particularly in Iran for so many years. The model have been widespreadly applied ungauged watershed of the country in comparison to other erosion and sediment estimation models due to the simplicity of collecting needed data and evaluating factors used in the model. According to the some research studies in terms of M. Sc thesis the accuracy of MPSIAC model was not approved all over the country. The research studies in Iran have shown that there are many reasons that affect the accuracy of the model. Because of result gained based on the research studies the reason turn back to weighting procedure of the model, which has to been tested in representative watershed of the country. In order to evaluate and test the result of previous studies, the study have been conducted to check the result of the MPSIAC in comparison to two other erosion and sediment estimation models on a representative watershed in west of Iran. In this study, erosion and sediment yield rates was estimated by MPSIAC model using geographic information system(GIS) in the Nojian watershed basin. In order to run the model, the watershed area was divided to 527 homogenous units and the nine factors used in model, were assist in each unit. The results of this study indicate that amount of sediment yield in the study area is about 489372 Th center dot y (-1). Considering the amount of the observed sediment yield of the watershed, which is about 812410 Ton center dot y(-1), the amount of estimated sediment yield is significantly differs by 323038 Ton center dot y(-1). The observed difference can not consider as this mean that the model should or should not be employed in watershed projects. It seems that there must be a rational reason( s) for difference between the observed and estimated amount of sediment yield. The results of the evaluation on the observed difference were shown that it should has the root in structure of the model as well as its related tables for rating and weighting of the factors included in the model. Because it appears that, the tables of the model used for rating and weighting of the included factors are not complete and can not be used in areas were the characteristics of given watershed are not similar to the development area of the model. 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.