Investigation of the results of soil erosion and sediment yield studies over the past three decades in the watersheds of West Azerbaijan Province

Since most of soil erosion studies in the watersheds are conducted by consultant and executive companies (as contractors) using the semi-quantitative MPSIAC model under the supervision of provincial natural resources and watershed administrations (as employers), so in this study, the results and findings of the aforesaid studies in West Azerbaijan Province were considered. Analysis of the studies showed that in the last three decades a total of 76 watersheds of the province with an approximate area of 4100 km2 have been studied in terms of soil erosion and sediment yield states using the MPSIAC Model. Estimated mean annual soil erosion was 13.95, 16.30, and 15.59 t.ha−1.yr−1 for northern, central, and southern sections, respectively. Meanwhile, based on the model, the mean sediment yield of mentioned sections has been calculated equal to 5.39, 5.64, and 6.09 t.ha−1.yr−1. Nevertheless, a detailed investigation based on the resistance of different lithology units to erosion in the studied watersheds, as well as land use and vegetation cover as the two most important factors of the MPSIAC Model showed less reliability of the reported results. It seems one of most important reasons for such unreliable results refers to one of the most important weaknesses of the MPSIAC model which estimation of the soil erosion is depended on the estimated amounts of sediment yields and sediment delivery ratio. According to our findings, it can be concluded and suggested that the Forests, Rangelands, and Watershed Management Organization should replace the MPSIAC Model, with USLE family models, especially RUSLE, at least in estimating the soil erosion, in the services description of consultant and executive companies. Implementation of this change should also be taken seriously by the provincial natural resources and watershed management administrations.