Quantifying the trade-offs in re-operating dams for the environment in the Lower Volta River

Abstract. The construction of the Akosombo and Kpong dams in the Lower Volta River Basin in Ghana changed the downstream riverine ecosystem and affected the lives of downstream communities, particularly those who lost their traditional livelihoods. In contrast to the costs borne by those in the vicinity of the river, Ghana as a whole, has enjoyed vast economic benefits from the affordable hydropower, irrigation schemes and lake tourism that developed after construction of the dams. Herein lies the challenge; there exists a trade-off between water for river ecosystems and related services on the one hand, and anthropogenic water demands such hydropower or irrigation on the other. In this study, an Evolutionary Multi-Objective Direct Policy Search (EMODPS) is used to identify the multi-sectorial trade-offs that exist in the Lower Volta River Basin. Three environmental flows, previously determined for the Lower Volta are incorporated separately as an environmental objective. The results highlight the dominance of hydropower production in the Lower Volta, but show that there is room for providing environmental flows under current climatic and water use conditions if firm energy requirement from Akosombo Dam reduces by 12 % to 38 % depending on the environmental flow regime that is implemented. There is uncertainty in climate change effects on runoff in this region, however multiple scenarios are investigated. It is found that climate change leading to increased annual inflows to the Akosombo Dam reduces the trade-off between hydropower and the environment while climate change resulting in lower inflows provide the opportunity to strategically provide dry season environmental flows, that is, reduce flows sufficiently to meet low flow requirements for key ecosystem services such as the clam fishery. This study not only highlights the challenges in balancing anthropogenic water demands and environmental considerations in managing existing dams, but also identifies opportunities for compromise in the Lower Volta River.