Estimation of Erosion Intensity and Sedimentation of Ivar Watershed Using MPSIAC Empirical Methods

Erosion and sedimentation is one of the major problems in the management of watersheds of the country. Erosion and its resulting consequences, by increasing the human utilization of the nature from the early times of the twentieth century, has caused its negative effects on the ecosystem. Studies of soil erosion has a great and considerable importance due to adverse environmental and economical consequences, gradual salinity of land, loss of vegetation cover, reduced soil fertility, increased erosion and sedimentation, chemical pollution of soil and adverse effects on the sustainable management of land. For estimating the erosion and sedimentation rate in sub watersheds and Ivar watershed in South Khorasan Province, ​​MPSIAC model was used based on nine factors including geology, soil, climate, run off , ups and downs, land cover, condition of surface erosion, river erosion and sedimentation delivery. So that, after determining the working unit plan, the points relating to the nine factor's model in each working unit was estimated and also amount of sediment was calculated. Then by the weighted average of working units , the sedimentation amount for each sub watersheds and all the watersheds was estimated and finally by calculating SDR for watersheds and sub watersheds, the amount of erosion was calculated. According to the obtained results , the average erosion rate of the all area is 7.01 tons /year and the sub watersheds of I'10 and I'9 with about 14 ton annual soil erosion, have the greatest amount of erosion. Among geomorphologic faces, Masil faces with an erosion value of equivalent with 45.32 tones / hectare has a great difference with other faces. Sub watersheds I'10 and I'9 with deposition values of over 7 tons / hectare in a year have the highest amount of sediment production. The average amount of deposition in all parts of the region is 2.95 tons /hectare in a year and average deposition class has the highest proportion of the watershed area. Geology units Qal (river bed) have the highest value of erosion. Erosion value, due to high level of precipitation in high areas is increased in comparison with the outlet points and lower areas of the watershed.By increasing the runoff volume especially in the lower parts of the watershed, the erosion will increase severely. Type of the geology formation and sediment production in Ivar watershed especially in the outlet parts are the most important factors of erosion and sediment production . The existence of the sensitive formation of marl, which has appeared in all surfaces of the land, are the reason of natural erosion in the area. In outlet areas of the watershed, erosion amount is increased and are placed in great and very great classes.