Evaluating discharge and sediment load in a gullying watershed in the highlands of Ethiopia
摘要
Soil erosion is one of the most serious environmental issues, which worsens land degradation. Land degradation and gully formation in the Ethiopian Highlands result in increasing sediment loads in rivers, and negatively affect the environment. This research aimed to investigate event-based discharge and sediment concentration and yield patterns in the northwestern highlands of Ethiopia. The 414 ha Ene-Chilala watershed was selected for this study. Three nested watersheds (W1, W2, W3) and the entire watershed (W4) were monitored. Rainfall, discharge, and sediment concentration data were measured during the main rainy seasons between June and September from 2013 to 2016. A total of 502 storm events were collected in the four years. W1 did not have an active gully. Gullies in W2 and W3 were rehabilitated during the four years. The result indicates the mean annual runoff coefficients of 11% for W1 and 19% for W2. In all watersheds, suspended sediment concentrations were higher at the onset of the rainy season and gradually decline over time. The yearly mean sediment yield was the lowest for W1 (5.9 t ha−1 yr−1) and highest for W3 (15.2 t ha−1 yr−1). The significant differences in sediment yield among watersheds were with the prevalence of gullies and extensive implementation of land management practices in the watershed. Rehabilitating gullies, soil loss and runoff depth were reduced. The Mann‐Kendall trend test indicates a statistically significant negative trend (p < 0.005) in annual and seasonal sediment yield from the entire watershed (W4). Land management practices in the valley bottom gullies and uplands significantly reduced runoff and sediment yields at the watershed scale, hence, increased agricultural productivity and environmental sustainability. Therefore, these practices should be scaled up and integrated into national strategic plans for landscape restoration and climate resilience.