Runoff and suspended sediment yield and implications for watershed management

Improper implementation of conservation structures in the Ethiopian highlands in general and in the Yewoll watershed, in particular, enabled the existence of soil erosion at an aggressive rate. This research aimed to enable a better understanding of the hydrological processes of the Yewoll watershed in the upper Blue Nile basin, Ethiopia. Rainfall, runoff, and suspended sediment load data were collected for 2 years, and stage-discharge curves were developed. Suspended sediment load from runoff samples, soil infiltration rate, and shallow groundwater level were measured using a Whatman filter paper, double-ring infiltrometer, and piezometers, respectively. A high rate of soil water infiltration (greater than 250 mm/h) was observed at upland steep slope areas. The shallow groundwater level was closer to the surface for most of the rainy season in the valleys and bottoms of the hillslope areas. At the outlet of the watershed, it takes a longer time to drain the runoff after a rainstorm than the gentle slope and hillslope areas of the upstream area. The upstream watershed (a drainage area of 52.5 km(2)) received a maximum annual rainfall of 689 mm, while it was 647 mm for the whole watershed (a drainage area of 68.7 km(2)). The presence of an abundance of gullies in the sub-watershed located between the two gauging sites as opposed to the upstream steep sloppy area is the main source of annual runoff and generation of sediment loads representing hot spots areas for soil erosion, hence require priority investment in managing Yewoll watershed.