Estimation of sediment yield and effectiveness of level stone bunds to reduce sediment loss in the Gumara-Maksegnit watershed, Nile Basin, Ethiopia

Abstract

Soil erosion is one of the most significant environmental problems in the Ethiopian highlands. The study was conducted in the main Gumara-Maksegnit watershed and at the sub-catchment scale with and without soil and water conservation (SWC) measures to estimate event-based sediment yield and evaluate the effectiveness of level stone bunds on sediment reduction. The runoff volume and peak discharge were recorded manually with the help of a time series of pictures using the DOERR digital camera. The sediment concentration was determined from manual runoff samples and grid-based soil samples were collected at 162 points. The slope map and satellite image were obtained from the USGS Earth Explorer database with 30-m and 15-m spatial resolutions, respectively. Finally, all six-model factors were combined using the raster calculator in map algebra through the MUSLE framework. The paired t test parametric procedures were applied to test whether the means of event-based predicted and observed sediment yield values are different. The average event-based observed and estimated sediment yields were 0.5581 and 0.4031 Mg ha−1 for the Gumara-Maksegnit watershed, 0.5125 and 0.4194 Mg ha−1 for the treated (with SWC) sub-catchment, and 1.0694 and 1.0150 Mg ha−1 for the untreated (without SWC) sub-catchment, respectively. The observed and estimated sediment losses within the main watershed and sub-catchments were not significantly different. However, comparing the treated and untreated sub-catchments, the sediment losses were highly significantly different and the stone bunds have a capacity for reducing sediment loss by 58.8%. In general, the MUSLE model performed well to estimate sediment yield in the study area with R2 values of 0.62, 0.72, and 0.7 and NSE values of 0.53, 0.71, and 0.34 for treated, untreated, and the main Gumara-Maksegnit watershed, respectively. The results showed that stone bunds have a capacity for reducing sediment loss by 58.8% as compared with untreated sub-catchment. Therefore, successful implementation of stone bunds in the study area, as well as similar agro-ecologies, has a great benefit to enhance land productivity. Meanwhile, the MUSLE model was well suited for reliable applications of sediment yield estimation in the study area.