assessment of tasoki-rigchah critical area in wind erosion production in sistan plain

in order to determine the source and critical areas of wind erosion, sistan plain, irifr-e.a method was applied. according to geomorphological investigations, the studied area consists of the following two main units namely: pediment with 1 type and 8 geomorphological facies, and playa with 2 types of flatland and desert type that includes 9 geomorphological facies. on the basis of sediment, the facies in piedmont were divided into 3 groups so that, 2 facies (1-1-4, 1-1-3) have sediment delivery by 500-1500 tons/km²/y while, 4 facies (1-1-2, 1-1-8, 1-1-11) have 1500-6000 tons/km²/y sediment delivery, and 3 facies of covered pediment (1-1-5, 1-1-6, 1-1-7) have more than 6000 tons/km²/y sediment delivery. therefore, the mean sediment delivery of piedmont (covered pediment type) is about 5500-39000 tons/km²/y. in playa unit, four facies (2-1-4, 2-1-5, 2-1-6 and 2-1-8) have 500-1500 tons/km²/y sediment load and three facies (1-1-2, 2-1-3, 2-1-7) carry 1500-6000 tons/km²/y, and two facies (2-1-2, 2-2-1) have more than 6000 tons/km²/y sediment load and total sediment load is 8000-30000 tons/km²/y. morphoscopic study and investigation of the relationship between sediment grain diameter (d) and transport distance in 18 cases, it was shown that all samples except of one, transport distance is 5-20 km. therefore the source of sediment is close to the sedimentation area. dominant and erosive winds in the study area are from north and nw. also due to drought, the erosive winds carry a considerable amount of sand especially during the summer and spring seasons and it has been intensified considering that, hamoon and hirman rivers are dry.