Application of HYPE Model for Reservoir Operation Optimization: A Case Study of Koka Reservoir, Awash Basin, Ethiopia
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Date
2025-11
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Addis Ababa University
Abstract
Water scarcity increasingly threatens agricultural productivity in Ethiopia, exacerbated by ineffective reservoir operation policies that contribute to the misuse of available water resources. The suboptimal operating policy of the Koka Reservoir represents a critical and common challenge. The developed Et-HYPEv2.0 model demonstrated good and satisfactory performance during calibration and validation, as measured by the Nash-Sutcliffe Efficiency (NSE) and Relative Volume Error (RE%).This thesis focuses on optimizing the operation of the Koka Dam Reservoir within the Awash Sub-Basin, Ethiopia, through the application of the Et-HYPEv2.0 model. The model is built using daily inflow data from two stations (Hombole and Mojo River), daily precipitation, water Storage data, monthly reservoir surface evaporation, and physical characteristics of the Koka Dam and Reservoir, spanning a twenty-one-year period (1990-2010) for inflow and precipitation at the reservoir surface. A monthly reservoir optimization strategy, implemented to prioritize irrigation demands, significantly altered seasonal flow patterns to achieve a stable, year-round downstream release. The optimized operation reduced the average wet-season flow by 27% (from 62.25 m³/s to 45.4 m³/s) and increased the average dry-season flow by 46% (from 31 m³/s to 45.4 m³/s) there by improving year round flow stability. This balanced approach effectively mitigates extreme seasonal variations, providing reliable water availability for multiple downstream uses including irrigation and power generation. The total area currently located downstream of Koka Reservoir under irrigation encompasses 715.894 km². The annual water requirements for the monoculture optimization scenario were calculated as 957.49 MCM for sugarcane and 287.62 MCM for wheat. Under the multi-crop optimization scenario, the total annual water requirement was estimated at 449.05 MCM.
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Keywords
IWR, HYPE, Optimization, Reservoir, Operation, Rule Curve