SWAT based runoff and sediment yield modelling: a case study of the Gumera watershed in the Blue Nile basin

Land degradation caused by soil erosion (sheet and rill erosion) and soil fertility decline is a serious threat in the Ethiopian highlands, especially in the Gumara watershed. In this study the SWAT (Soil and Water Assessment Tool) model was applied to the Gumara watershed to predict sediment yield and runoff, to establish the spatial distribution of sediment yield and to test the potential of watershed management measures to reduce sediment loadings from hotspot areas. The model was calibrated using five years of flow and sediment records and validated using data for the next three years. Out of 30 SWAT sub-basins, 18 sub-watersheds (72%) were identified as erosion prone areas contributing to a mean annual sediment load ranging from 11 to 22 t ha−1 yr−1. The model was used to evaluate the potential of vegetation filter strips of various widths to reduce sediment production from critical micro watersheds. The installation of vegetation filter strips on vulnerable land was shown to result in a 58 to 74% reduction in sediment yield for strip widths of 5 m and 10 m respectively.