Exploring Trade-offs in Reservoir Operations through Many Objective Optimisation: Case of Nile River Basin

Abstract

Water storage and diversion capacity of reservoirs in the Nile Basin are benefited for various purposes including agricultural irrigation and hydro-energy production. Filling and operation of the recently constructed Grand Ethiopian Renaissance Dam (GERD) have been subject to heated debate for its implications on downstream countries Sudan and Egypt. In this study, we investigated trade-offs between the objectives of the three countries by formulating the problem as many objective optimisation. To this end, we built a simulation model conforming to the evolutionary multi-objective direct policy search (EMODPS) framework. Based on the optimisation results, we discovered two scenarios under which trade-offs exhibit diverging patterns. Our findings suggest that 1) aggressive filling strategies create evident trade-offs between the hydro-energy generation objective of Ethiopia and consumptive uses of Sudan and Egypt, 2) growing demand in the long-term brings the dilemma
of maintaining dams operational versus satisfying the demand and 3) increased demand pressure reinforces trade-offs between Egypt’s aggregate deficit minimisation and Ethiopia’s hydropower maximisation objectives. Our results highlight the potential of compromise policies in managing the objectives of all stakeholders without imposing heavy sacrifices. These policies represent an opportunity for cooperative operation of the dams through which multiple challenges facing the basin can be addressed.