Investigating the Role of Buffer Strips in Reducing Erosion and Sediment Using the WEPP Model: A Case Study of a Loess Hillslope in Erfan Suburb –Gorgan, Iran

Existence of susceptible agricultural lands with loess deposits in the South and West of Gorgan, with plowing in down-slope direction and failure in promoting contour plowing based methods have led to use alternative control practices such as cultivating buffers in the marginal lands. The under-studied hillslope with an area of 5.1 hectares includes four long agricultural lands and three permanent vegetation buffer strips between them with an average width of 7 meters and a field under fallow with 55 meters length located in the down slope. In this study, the climate files of the WEPP model were built by using the BPCDG software for the year 2015 based on the data of the recording rain-gauge in the Hashem Abad synoptic station. To increase the accuracy of the model, the slope file was created using a digital survey camera with a resolution of 0.2 meter. In order to verify the WEPP model, the plot observation data of a rainfall simulator were used. Then two cases of lack and existence of current buffer strips in the hillslope were evaluated by the WEPP model. WEPP model estimated the amount of erosion and the specific sediment for the existing buffers modes in hillslope to be 27.36 and 18.08 tons per hectare per year respectively, and for the scenario of a lack of buffer strips, they were estimated to be 37.11 and 35.28 tons per hectare per year, respectively. Also, the model estimated runoff rate for the existence and lack of buffer strip scenarios to be 32.66 and 40.54 mm, respectively. The results showed that the buffer zones in the under-studied hillslope have decreased the amount of erosion and sediment to 9.75 and 17.20 tons per hectare per year respectively, as well as reduce the runoff rate 7.88 millimeter per year. Therefore, the buffer zones were able to control a significant amount of sediment (49 percent), which cause remarkable damages in the downward.