نقش پوشش گیاهی در تولید رواناب و رسوب اراضی لسی گرگان

   Agricultural hillslopes with susceptible loess enters a large amount of runoff and sediment into the Gorgan city annually, due to the inappropriate drainage system which cause a lot of financial losses city. The purpose of this study was to investigate the effect of different vegetation scenarios on the runoff and sediment discharge from three hillslopes of catchment of ​​5.9 hectares. The runoff and sediment of the catchment were simulated for one year using WEPP model. In addition, eight vegetation scenarios include present condition, extremum potential vegetation scenario, existence and lack annual and permanent vegetation were simulated and compared in pairs. The total runoff volume and sediment yield for the current condition of the catchment was estimated at 1945 cubic meters per year and 1.5 tha-1, respectively The scenarios comparison indicated that the runoff and specific sediment rates were increased respectively from 1487 m3 meters per year and 0.4 tha-1, in the maximum potential vegetation scenario (more than 80%), to 5032 cubic meters per year and 64.5 tha-1 in the minimum vegetation scenario (fallow whit tillage). The difference of specific sediment rate between two scenarios of permanent vegetation cover and agriculture cover is equal to 8.1 tha-1, and this amount was calculated of ​​10.2 tha-1 for two scenarios of the lands under cultivation and fallow condition.