Abstract
Soil erosion is exacerbated by unsustainable land-use activities and poor management practices, undermining reservoir storage capacity. To this effect, appropriate estimation of sediment would help to adopt sustainable land-use activities and best management practices that lead to efficient reservoir operations. This paper aims to investigate the spatial variability of sediment yield, amount of sediment delivery into the reservoir, and reservoir sedimentation in the Koga Reservoir using the Soil and Water Assessment Tool (SWAT). Sediment yield and the amount entered into the reservoir were also estimated using a rating curve, providing an alternative approach to spatially referenced SWAT generated suspended sediment load. SWAT was calibrated from 1991 to 2000 and validated from 2002 to 2007 using monthly observations. Model performance indicators showed acceptable values using Nash-Sutcliffe efficiency (NSE) correlation coefficient (R2), and percent bias (PBIAS) for flow (NSE = 0.75, R2 = 0.78, and PBIAS = 11.83%). There was also good agreement between measured and simulated sediment yields, with NSE, R2, and PBIAS validation values of 0.80, 0.79, and 6.4%, respectively. The measured rating curve and SWAT predictions showed comparable mean annual sediment values of 62,610.08 ton/yr and 58,012.87 ton/yr, respectively. This study provides an implication for the extent of management interventions required to meet sediment load targets to a receiving reservoir, providing a better understanding of catchment processes and responses to anthropogenic and natural stressors in mixed land use temperate climate catchments. Findings would benefit policymakers towards land and water management decisions and serve as a prototype for other catchments where management interventions may be implemented. Specifically, validating SWAT for the Koga Reservoir is a first step to support policymakers, who are faced with implementing land and water management decisions.
Highlights
The construction of dams to create an artificial impounded reservoir changes the stream’s natural conditions by reducing streamflow velocity
This paper aims to determine major sediment sources in the Ethiopian highlands by quantifying geographic variability in sediment output from a medium-sized watershed and assessing future environmental implications by implementing methods to estimate the total amount of sediment yield into the reservoir and reservoir sedimentation rate
Soil and Water Assessment Tool (SWAT) is used to estimate soil erosion driven by rainfall runoff processes in a continuous time step using Modified Universal Soil Loss Equation (MUSLE), an inbuilt algorithm for simulating erosion
Summary
The construction of dams to create an artificial impounded reservoir changes the stream’s natural conditions by reducing streamflow velocity. Distributed hydrological models with input parameters representing different land surface characteristics have been applied to assess anthropogenic impacts on runoff and changes in sediment dynamics [25] These models can identify sediment source areas and prioritize catchments and subcatchments to make informed policy decisions regarding land use planning and future catchment management [26]. In addition to the rating curve method, a basin-scale distributed hydrological model, the Soil and Water Assessment Tool (SWAT; [27]), was used to estimate streamflow and sediment load in a medium-sized hillslope-dominated watershed. This paper aims to determine major sediment sources in the Ethiopian highlands by quantifying geographic variability in sediment output from a medium-sized watershed and assessing future environmental implications by implementing methods to estimate the total amount of sediment yield into the reservoir and reservoir sedimentation rate. The specific objective of the study was to (1) assess the spatial variability of sediment yield and identify vulnerable sub-watersheds for erosion and sediment yield, (2) quantify the amount of sediment inflow into the reservoir, and (3) predict the total amount of sediment in the reservoir
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