Effect prediction of rangeland condition changes on runoff by HEC-HMS model in Sarab-Sefid basin of Borujerd

Assessment of Watershed management practices is one of the main subjects for future planning of natural resources management and restoration projects. In terms of، there are no tools for assessment of watershed management practices in many basins of the country، and then distributed hydrological models can be used this purpose. The purpose of this study was evaluation of cover changes and it effect on runoff in Sarab Sefid basin in Borujerd county-Lorestan Province by HEC-HMS (Hydrologic Modeling System). For this purpose، based on the rainfall-runoff observed events، HEC-HMS model was optimized and calibrated. Then، to determination of rangeland condition changes، concentration time was measured after each scenario. Inputs of model were determined by SCS method and simulated runoff for available data from climatology stations. Criteria''s such as runoff pick and amount of flow determined for evaluation and measured in two situations of before and after land use. Results show that this model (HEC-HMS) is suitable for predicting and simulating of sun off in basin according to acceptable accuracy. Because of decreasing of Curve Number (CN) cause of plant cover increasing، the best scenarios to decreasing runoff are exclusion، available management of rangelands، conflagration and heavy grazing respectively. Therefore to decreasing of runoff must increase plant cover by any management tools even exclusion which it is the last way. Because of forestalling of natural hazardous and land degradation، orchards، built places beside of river and beside of Borujerd city.