Multi-objective trade-off analysis in operating dams for the environment: The case of the Lower Volta River

Historically, overcoming energy deficits or increasing water security has translated into a demand for more dams. However, the construction and conventional operation of dams have had contradictory outcomes, negatively impacting natural riverine ecosystems and riparian communities. In the Lower Volta River Basin in Ghana, the construction of the Akosombo dam, with a residence time of 3.9 years, led to the formation of the largest artificial lake by surface area and the resettlement of 80,000 people. Furthermore, the riverine ecosystem changed, as did the lives of the downstream communities who lost their traditional livelihoods. In contrast, the Akosombo dam is credited for powering Ghana’s industrialization and making it one of the more developed countries in West Africa. Thein lies the issue: there exists a trade-off between anthropogenic water demands such hydropower, irrigation or recreation on the one hand, and water for river ecosystems and services on the other. A transparent approach to managing these trade-offs between multiple water users is therefore needed to operate dams equitably. In this study, an Evolutionary Multi-Objective Direct Policy Search (EMODPS) is applied to case of the Lower Volta River Basin to identify the multi-sectorial trade-offs that exists between water users.  A designer environmental flow is incorporated as an objective rather than as a constraint and additionally, different policy framings and scenarios encompassing climate change and varying energy futures are investigated. This study highlights the challenges faced by dam operators in balancing water demands, and also identifies synergies and opportunities for compromise in the Lower Volta River.