Environmental Flows Assessment Based on the Coupling of Water Level and Salinity Requirements for Maintaining Biodiversity: A Case Study from the Ouémé delta in West Africa

The present study carried out on the Ouémé delta in West Africa, addresses the implementation of the BBM approach for the determination e-flows in a context of high data limitation. It also highlights the potential challenges for the implementation of the recommended e-flows in West Africa countries. To do this, we first established the current ecological status of the delta based on data collection, measurements and scientists’ observations. Then, we formulated ecological objectives for e-flows based on the environmental management vision for the delta. And finally, we determined the water requirements for the sustainability of the biodiversity and ecosystem services using a simple 2D hydrodynamic model. The results indicate that 100 and 50% of the average natural flows are required respectively in low-water and high-water periods (3.4 billion m³ per year) to maintain the Ouémé Delta in its current environmental management class. This recommendation for e-flows allocation is in direct competition with the water requirements for the economic development of the delta, which is estimated to be over 3.0 billion m³ per year in the Master Plan for Water Development and Management. While it is clear that the establishment of e-flows recommendations must be accompanied by measures to limit the degradation of ecological habitats, it is even more clear that the economic development remained the main concern of policymakers. The integration of environmental flows into water resources management policies in developing countries requires linking water needs for economic development with water needs for the ecological sustainability of rivers and their associated ecosystems.