SWAT model-based quantification of the impact of land use change on sediment yield in the Fincha watershed, Ethiopia

Abstract

In recent years, Ethiopia is facing problems due to soil erosion, mainly because of the conversion of natural vegetation cover into cultivated land. Soil erosion is also affecting dam reservoirs, which are threatened by an increase in sediment yield entering the lake. The present study focuses on the Ethiopian Fincha watershed and takes advantage of the potentiality of SWAT, to investigate how land use land cover changes impact soil erosion and the consequent sediment yield entering the Fincha Dam, eventually suggesting potential management strategies. The SWAT model was calibrated and validated using time series data of stream flow and sediment from 1986 – 2008 years, and its performance was evaluated by looking at the coefficient of determination, Nash-Sutcliffe simulation efficiency, and per cent bias. Once validated, the SWAT model was applied to derive sediment yield for the future thirty years, based on forecasted land use land cover conditions. The results show that the mean annual soil loss rate increased from 32.51 t ha-1 in 1989 to 34.05 t ha-1 in 2004, reaching 41.20 t ha-1 in 2019. For the future, a higher erosion risk should be expected, with the annual soil loss rate forecasted to be 46.20 t ha-1 in 2030, 51.19 t ha-1 in 2040, and 53.98 t ha-1 in 2050. This soil erosion means that sediments transported to the Fincha Dam, located at the watershed outlet, increased significantly in the last thirty years (from 1.44 in 1989 to 2.75 mil t in 2019) and will have the same trend in the future (3.08 to 4.42 mil t in 2019 and 2050, respectively), therefore highly affecting the Fincha reservoir services in terms of reduction of water volume for irrigation and hydroelectric power generation.