Sedimentation Modeling (Case Study, Gololcha Dam Reservoir, Upper Wabe Shebelle River Basin, Ethiopia)
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Date
2020-08
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Addis Ababa University
Abstract
Sedimentation of reservoirs is a critical problem that jeopardizes service life of hydraulic structures
by reducing their active storage capacity. This investigation is intended to estimate sediment yield
of Gololcha dam watershed, Wabe shebelle River basin, Ethiopia and to detect the sub basins that
are under severe sediment load and developing scenarios as intervention measures in reducing this
yield from catchment. The soil and water assessment tool is used in simulating Gololcha watershed
having catchment area of 841.463Km
. The model calibration and validation for flow and sediment
is done through isolating sensitive parameter. Slope length for lateral subsurface flow (SLSOIL)
was one of the sensitive parameter for flow and SCS runoff curve number (CN2) for sediment.
2
The model evaluation result showed that determination coefficient of 0.74, Nash-Sutcliffe of 0.73,
bias percentage of -9.1 for calibration of flow and determination coefficient of 0.61, Nash-Sutcliffe
of 0.6, bias percentage of -2.5 for validation of flow. For sediment calibration and validation, the
result obtained with determination coefficient of 0.79, Nash-Sutcliffe of 0.77, bias percentage of
0.7 and determination coefficient of 0.78, Nash-Sutcliffe of 0.52, bias percentage of 10.1,
respectively. Thus, the model found to be good in simulating the flow and sediment for the study
area. The estimated result indicated that the average annual sediment load at the dam site was
234,768 ton/yr. In this finding Spatial difference of sediment yield for Gololcha watershed
disclosed that sub basins 2,3,4,5 and 14 are the critical sub basins generating mean annual sediment
load varying from 5.48 ton/ha to 16.22 ton/ha.
Different Scenarios developed through land use refinement and operation management for the
critical sub basins identified for sediment reduction from the catchment. High amount of sediment
reduction observed when
intensively cultivated
land changed to
forest
mixed. In addition to this, the combination of contouring and terracing showed more effective
management practices than when they are practiced separately.
Description
Keywords
Gololcha watershed, sediment yield, calibration, validation, SWAT, SWAT-CUP