| چکیده انگلیسی مقاله |
Soil water erosion and sediment yield are among most important factors threat sustainable agriculture and the health environment conditions inducing serious economic and social problem especially in mountainous arid and semiarid regions. Studies have shown in many parts of the world that rainfall erosivity has a high correlation with soil erosion. Snow melt runoff can has important role in rainfall-runoff erosivity in mountain basins where snowmelt is a major runoff factor. Though contribution of snowmelt in total annual erosivity has been documented in few studies, the knowledge on monthly rainfall-runoff erosivity is still lacking. This study was aimed to predict daily snow accumulation and melting, predicting half month rainfall-runoff erosivity and evaluate the relationship between half-month erosivity and sediment yield in Latian watershed. Latian is a typical rocky mountain catchment, 360 km2, located on the southern parts of the Alborz Mountain. The elevation of the catchment ranges from 1800 m a.m.s.l. to 4250 m a.m.s.l. Latian watershed has shown high flood risk due to its mountainous condition, especially in early spring during the ground warm up and the melting of snow. In this study, the degree-day model was used to evaluate the snowmelt erosivity of R factor of the Revised Universal Soil Loss Equation (RUSLE). The results revealed that snowmelt runoff erosivity comprises about 75% of total erosivity across the watershed on average. This result means that neglecting snowmelt erosivity in similar watershed may results in under prediction of soil erosion hazards. Evaluation of the half-month cycles of rainfall-runoff erosivity and suspended sediment yield showed a similar trend, but the peak of erosivity occurred in the first half of April and the suspended sediment peak occurred in the second half of May. As a result, the seasonal cycle of the suspended sediment showed a lag in compare to the seasonal cycle of rainfall-runoff erosivity. Based on the watershed average of erosivity, erodibility, vegetation, slope length and steepness and management factors of the RUSLE which were 453 MJ. m-1 ha-1 yr-1, 0.017 ton ha. MJ-1 ha-1mm-1, 0.83, 20 and 1, respectively, the soil erosion risk of the watershed was estimated to be 146 ton. ha-1 yr-1. |
