Assessment of reservoir response to flood conditions to optimize hydropower operations – Isimba HPP Uganda

Lake Victoria is the largest tropical lake in the world and the source of river Nile, the longest river in the world. Due to prolonged precipitation above the average over the past two years, the lake water levels have increased surpassing the highest ever recorded of 13.41m in 1964. To mitigate the negative impacts on the people, navigation and developments in the flood zones, lake outflows were gradually increased from 1000cumecs to 2400cumecs. Isimba Hydropower Plant (HPP) with a reservoir capacity of 170 million cubic meters is the fourth hydropower plant along the upper Nile cascade with a design flood level of 1055m above sea level. Reservoir operation is constrained by the bridge construction and ferry operation works downstream which are affected by the increased discharges. There is also uncertainty of the incoming discharge magnitude and travel time due to lack of an upstream gauging station. This paper seeks to assess the reservoir response to the increasing flood conditions using Hydrologic Engineering software for flood routing and to model an operation water level (OWL) that optimizes power production and flood control whilst ensuring public safety of the downstream activities through real-time forecasts in the short term.