Reservoir Operation for Optimal Water Use: A Case Study of Kabalega Reservoir in Uganda

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Addis Ababa University


Wambabya River catchment over the past years (since 2013) has been experiencing alterations in its upstream (forests cleared for agriculture) which may have resulted in seasonal variability in rainfall pattern. Temperatures have increased and thus high-water loss through evapotranspiration. River inflows into the reservoir have decreased thus affecting the power generation from Kabalega dam as evidenced by the operation below its capacity in most of the first quarter months of the year and thus being unable to meet the power demand and downstream ecological requirement. The study developed reservoir operation policies for optimal water use of Kabalega reservoir in order to meet the target demands. Australian Water Balance Model (AWBM) was used to simulate Wambabya River inflow into Kabalega reservoir. The model was calibrated with observed flow from 1990-2009 and validated with flow from 2010-2019. Nash & Sutcliff efficiency for calibration and validation is 0.758 and 0.67 respectively. HEC-ResSim model was used to optimize and develop new reservoir operating rules by calibrating and validating the model for 5 and 3 years which yielded Nash Sutcliff coefficient and correlation coefficient of 0.85 and 0.82 respectively. respectively. The reservoir system performance was further investigated by using statistical performance indices which are; reliability, vulnerability, resilience and sustainability index. Simulated releases were compared to the actual releases and generated/ simulated power compared to power demand and it was found that the system exhibits fewer deficits in terms of power supply, with minimal spill flows over the spillway found to occur compared to the original operation policy. The derived operation policies are thus recommended to serve as decision-making tools for operation of Kabalega reservoir to maximize the benefits.



Australian Water Balance Model, Hec-Ressim, Kabalega Reservoir, Operation Policy, Uganda