Abstract:
Reservoir Sedimentation is the gradual accumulation of sediment from a river into the
reservoir. As part of a long-term optimal sediment management program, it is important to
predict sediment flow into the Grand Ethiopian Renaissance Dam, assess impacts on the
reservoir, and maintain dam capacity. The overall objective of this study was to estimate
sediment yield, map the watershed in terms of sediment production, and determine the most
suitable BMPs for the GERD Basin by using SWAT model. The watershed is delineated,
calibrated and validated at the El Deim station where the watershed area is 174,580.12 Km2
and by using the calibrated model simulate the sediment and flow at the GERD axis
(172,250 Km2
). For the model 45 metrological stations were used 42 is from NMI and the
other 3 is from NASAPOWER Website with appropriate bias correction and the LULC and
soil map is taken from ENTRO after comparing with the data’s available at ( FAO , Map
server Ethiopia, USGS. and Alaska Edu). Model calibration result for flow of (2002-2006)
gives coefficient of determination (R2
) and Nash-Sutcliffe simulation efficiency (NSE) 0.92
and 0.91 respectively and for validation period (2007-2010) the model gives 0.88 and 0.88
for R2
and ENS values respectively. Model Sediment calibration gives R2 and NSE 0.72
and 0.72 respectively and validation period gives R
2
and NSE 0.67 and 0.67 respectively.
This result indicates that the recorded values show good agreement with model simulated
value for both stream flow and sediment yield. The rainfall runoff and sediment yield
relationship of the catchment has been determined for each sub-basin of the watershed.
Also, the spatial distribution of sediment yield, the temporal distribution of rainfall runoff,
and sediment yields of the catchment were determined and the hotspot area that is sensitive
to soil erosion was identified. The model result indicates that the simulated annual average
sediment yield for the GERD Basin was 130.83 t/ha/yr. and the long-term average annual
sediment loads obtained from the SWAT model at EL Deim was 159.37 million ton/year.
This study reveals that 59.55% of the GERD Watershed area is classified as extremely
erosion prone, 1.32% and 6.68% as very high and high erosion prone, 3.44% as moderately
prone to erosion, and 20.01% as very low prone to erosion. Three different manage mencenario’s wear proposed from them Strip-cropping is found to be the best management
practice that needs to be employed on the selected hot spot areas in order to increase the
service life of the GERD Reservoir
