Abstract:
The Gilgel Abay reservoir, created by dam construction, faces sediment challenges due to
factors like steep terrain, poor land practices, and inadequate conservation measures,
leading to heightened soil erosion. This erosion negatively affects soil production, reservoir
lifespan, and regional projects. This research was utilized the SWAT model, aims to assess
sediment production and propose mitigation measures.
Simulation was carried out using meteorological and spatial data by dividing watershed
into 25 subbasins with 369 Hydrologic Response Units (HRUs). Model calibration (1999-
2011) and validation (2012-2018) Sequential Uncertainty Fitting (SUFI-2) was used as part
of the SWAT Calibration of Uncertainty Program (SWAT-CUP) for daily flow and
sediment data. For flow calibration and validation, the coefficient of determination (R2),
Nash-Sutcliffe model efficiency (ENS), and percent of bias (PBIAS) are 0.8, 0.79, -9.1,
and 0.79, 0.77,9.5, respectively. The percent of bias (PBIAS), the Nash-Sutcliffe model
efficiency (ENS), and the coefficient of determination (R2
) for sediment calibration and
validation are, respectively, 16, 0.72, 0.74, and 16.3 ,0.66, 0.67. Thus, in this research, the
model demonstrates very good assessment performance domain.
The magnitude of sediment yield from each sub basin area ranges between 1.1-194.09
tons/ha/yr and the catchment's hot spot area is, sub-basins 2, 1, 17, 9, 14, 13, 10, 25, 24 and
21 possess a range of spatial differences in sediment yield from 12.42 tons/ha/yr to 194.09
tons/ha/yr. Different scenarios through operation management, and sediment reduction
from the watershed were proposed for these crucial sub-basins. Therefore, combination of
contour farming and terracing practice was shown to be the most successful management
strategy among the scenarios.
