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 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 as hydropower or irrigation on the other. In this study, an Evolutionary Multi-Objective Direct Policy Search (EMODPS) is used to explore the multi-sectoral trade-offs that exist in the Lower Volta River basin. Three environmental flows, previously determined for the Lower Volta, are incorporated separately as environmental objectives. 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 the 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 as this scenario makes more water available for users. Furthermore, climate change resulting in decreased annual inflows provides 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. @en

For most of the 20th century, the design and operation of dams prioritized traditional economic considerations such as hydropower generation, flood risk reduction and provision of water for irrigation and domestic use. This resulted in altered river flow regimes, degraded riverine ecosystems and ecosystem services, and biodiversity loss. Implementation of environmental flows (e-flows), freshwater flows for the environment, is a means to restore some of the benefits of naturally flowing rivers and halt the rapid deterioration of freshwater and estuarine habitats, flora and fauna. Since its early days in the 1940s, e-flows science has grown and there now exists a wide array of methodologies for establishing flow-ecology relationships. The concept of e-flows also has a firm place in many national water laws and policies across the world. Despite this progress, actual implementation of e-flows has not followed suit and remains limited. This research was aimed at generating insights into how e-flows evolve from recommendation into practice and the trade-offs that are identified between conventional water uses and e-flows during conception or implementation. The study focused in particular on e-flows implementation through the re-operation of existing dams. This study addressed two major shortcomings in e-flows science, specifically, the lack of a global record of e-flows implementation and the lack of insight into why certain e-flow recommendations have been implemented while others have not. The research followed an exploratory, sequential, mixed methods approach beginning with a systematic literature review and a global survey of practical cases of dam re-operation for e-flows. A logic model of the process was used to develop a conceptual framework of how e-flows are implemented in practice. While the systematic literature review identified the inputs, activities and outputs of dam re-operation in successful cases, the global survey of stakeholders with first-hand experience in dam re-operation attempts revealed how stalled attempts at dam re-operation significantly differed from successful attempts through a comparison of the survey responses for the two groups using statistical methods. This extensive research phase looking at cases of dam re-operation across the globe formed the first part of this research and was then followed by a case study to investigate the synergies and trade-offs between water users when dam operations are changed to implement e-flows. The Akosombo and Kpong dams in the Lower Volta River, Ghana, were chosen as the case study. The choice of case study was partly informed by the findings from the systematic literature review and survey. Attempts at dam re-operation in this location have stalled despite it possessing some of the key characteristics of successful cases. It thus presented an interesting case for further investigation. While past studies had already developed e-flows for the Lower Volta, these were based on the natural flow paradigm: an e-flows design approach based on the natural, pre-dam flow regime of a river. An additional e-flow was designed based on the designer e-flows paradigm whereby components of a river’s hydrograph are compiled to meet a desired ecological outcome. Owing to the data scarce situation in the case study, a Bayesian Belief Network (BBN) was used to link river flows to the state of the Volta clam fishery, an important artisanal industry in the basin. Finally, a simulation-optimisation technique, Evolutionary Multi-Objective Direct Policy Search (EMODPS), was applied to the case study to determine the trade-offs and synergies between the environment and key water users in the Lower Volta Basin. The new e-flow recommendation developed for the Lower Volta River, together with the past recommendations based on the natural flow of the river, served as inputs to this trade-off analysis. This research reveals that e-flow recommendations are usually implemented through a collaborative analytical process which makes use of existing supporting frameworks such as legislation, but also takes advantage of opportunities that may arise to advance the process of dam re-operation for e-flows such as flow experiments. The process is usually non-linear and it is important to emphasize the local context which makes each process of dam re-operation unique. A global database of successful e-flow implementations through dam re-operation has also been created. This records the inputs, activities, and outputs as well as the stakeholders involved and the e-flows implementation approaches in successful cases. Moreover, in regard to stalled re-operation attempts, four hypotheses were derived for further study on why some attempts at dam re-operation are at an impasse, namely: 1. In undertaking scientific studies for determination of e-flows, first a consensus on the priorities, knowledge gap, and solutions must be reached together with local stakeholders. 2. Genuine, carefully designed consultations and negotiations between stakeholders can overcome hurdles encountered in the process 3. Local-level legislation and policy on e-flows provide the enabling environment for dam reoperation for e-flows. 4. Scientists are important stakeholders in the process of dam re- operation, but should play a supportive role rather than drive the process. Through the in-depth context-dependent examination of a unique stalled case, the Lower Volta, this research demonstrated that a parsimonious ecologically grounded, designer e-flows assessment method using a BBN can be applied successfully in data scarce areas. This resulted in an alternative designer e-flow recommendation for the Lower Volta River for low flow releases during the Volta clam veliger larva and recruitment life stages from November to March. Two other complementary management strategies were also recommended for the Lower Volta: annual full breaching of the sandbar which regularly builds up at the Volta Estuary and prohibition of sand winning from the river bed. The multi-objective trade-off analysis of water users in the Lower Volta highlighted the dominance of hydropower in the river basin and quantified the amount by which firm hydropower demand from the Akosombo and Kpong dams would have to decrease for the implementation of e-flows under current and future climate scenarios. Notably, and curiously, both an increase and a decrease in annual inflows to the Akosombo Dam reduce the trade-off and create synergies between e-flows and hydropower generation. This is because climate change leading to increased annual inflows to the Akosombo Dam results in increased water availability for both hydropower and e-flows while climate change resulting in lower inflows provides the opportunity to strategically deliver dry season e-flows, that is, reduce flows sufficiently to meet low flow requirements for key ecosystem services such as the clam fishery. This research has generated knowledge on the process of dam re-operation for e-flows implementation; the enabling factors for successful dam re-operation; the hurdles typically encountered and how they have been overcome in successful cases; as well as inter-sectoral trade-offs that must be made between e-flows and conventional water uses in delivering e-flows in a unique case study. These insights inform attempts to scale up efforts in e-flows implementation through the sustainable and equitable operation of dams for people and the environment. @en

The provision of flows for the environment, e-flows, is a means to restore the benefits of naturally flowing rivers. Despite the development of numerous methodologies to determine e-flows and optimize dam releases, actual implementation is relatively limited. Examples of successful e-flows implementation through dam reoperation exist in scientific literature; however, there is a missing narrative on cases where dam reoperation has been attempted but not successfully implemented. This study explores this impasse narrative and presents four hypotheses for further research on this subject: (1) Scientists are important stakeholders in the process of dam reoperation, but should play a supportive role rather than drive the process; (2) In undertaking scientific studies for determination of e-flows, a consensus on the priorities, knowledge gap, and solutions must be reached together with local stakeholders; (3) Local-level legislation and policy on e-flows provide the enabling environment for dam reoperation for e-flows; and (4) Genuine, carefully designed consultations of, and negotiations between, stakeholders can overcome hurdles encountered in the process of dam reoperation for e-flows implementation. @en

The Volta clam, Galatea paradoxa, is a freshwater macrobenthic bivalve which is endemic to the Lower Volta River in Ghana. The range of occurrence of the clam has been influenced by the flow regime in the Lower Volta which is in turn controlled by operation of two dams located upstream. Previous research has documented the changes to the Lower Volta due to the dams and attempts have been made to design environmental flows (e-flows), freshwater flows to sustain ecosystems, to inform the re-operation of the dams. The past attempts were based on the pre-dam, natural flow regime of the Lower Volta. In this study, a designer e-flow approach is explored using the Volta clam as an indicator species. Using knowledge garnered from various sources on the lifecycle, habitat and the local conditions corresponding to historical and current states of the Volta clams, the factors influencing its extent are visualized and quantified in a Bayesian belief network (BBN). Based on this BBN, an e-flow recommendation for the Lower Volta is for low flows, between 50 m3/s and 330 m3/s, for four months during the Volta clam veliger larva and recruitment life stages which occur in November to March. In addition, it is recommended that full breaching of the sandbar which regularly builds up at the Volta Estuary is done annually and that sand winning on the river bed is prohibited. These e-flow and management recommendations will have consequences for other water users and these have to be investigated, for instance by flow experiments and trade-off analysis. The results show that a BBN is potentially suitable for modelling the linkages between flows, management practices and the status of ecological indicators for the development of e-flows for highly modified rivers in data scarce regions.@en

Dam construction and operation are known to alter the hydrology of rivers and degrade riverine ecosystems. In recent decades, the call to reverse these negative impacts by re-operating dams has become stronger. Dams can support riverine ecosystems by releasing environmental flows (e-flows). Unfortunately, despite the development of numerous methodologies to determine e-flows and optimise dam releases, actual implementation has not followed suit. Integrating e-flow requirements in the design of new dams is relatively easier than changing operations of existing dams; however, re-operating existing dams is essential to restore ecosystems and ecosystem services that have already been affected by the construction and operation of dams. This study provides insights into how e-flows evolve from recommendation to practice through a systematic literature review on practical experiences to integrate e-flows in dam operations. Sixty-nine cases of successful dam re-operation have been identified, ranging from the well-documented case of the Glen Canyon Dam in the United States to less known cases such as the Katse Dam in Lesotho. We find that the most important factors that facilitate the successful implementation of e-flows are the existence of e-flows legislation or policy, the development of a research base in the form of an environmental impact study, and then flow experimentation. Illustrations of the important role of collaboration between various stakeholders and set timelines for implementation of recommendations are also given. These insights will inform how existing dams can be re-operated and governed more equitably and sustainably for both humans and the environment.

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