Sensitivity Analysis of Soil Parameters of WEPP Model (Case Study: Haji Abad Watershed)

Estimate of erosion, sediment and runoff in a watershed are an important target of researchers in areas without data. Also aware of the model sensitivity to the input factors can be used in cases where there is no time or resources to measure all the parameters, will help in selecting the most effective parameters. In this study because the high efficiency and a wide range of input parameters of the WEPP model the sensitivity of soil parameters WEPP model were investigated. In order to run this model, information on soil type, management, topographic and climatic characteristics and properties of waterways of the area studied is required. Climate data were extracted from the station Birjand. The topographical properties via GeoWEPP model and using DEM and factors of management and channel properties measured in the field and were entered into the model. Finally, the parameters of the soil contains clay, silt, gravel, sand, organic matter, cation exchange capacity and soil depth was entered into the model. Depending on the type of soil in the area, to determine the sensitivity, each soil factor was changed separately and the effect on the mean runoff, sediment yield and soil loss were calculated. The results showed that the amount of silt and sand have had the greatest and cation exchange capacity and soil depth the least impact on the amount of runoff, erosion and sediment. Also amount of runoff and sediment yield increased with increasing clay. But impact of sand, organic matter, cation exchange capacity and soil depth on the amount of sediment and soil loss was not clear.