Assessing environmental flows to secure ecosystem services in Benin

Developments planned for the Ouémé Delta in Benin will alter the hydrological regime of currently free-flowing rivers that enable important ecosystem services such as fisheries, fertile soils, flood retention and improved water quality. IUCN NL partner organisation Benin Environment and Education Society (BEES), research institution IHE Delft and the National Water Institute in Benin are carrying out an environmental flow assessment to determine how much water is needed for the ecosystems in and around the Ouémé Delta to remain intact.

Header photo: Ouémé River Basin in Benin © Elke Praagman

In the south of Benin, surrounding the important economic capital Cotonou and capital city Porto Novo, lies the delta of the Ouémé River and Lake Nokoué. The delta is an important aquatic ecosystem and supports the region’s largest wetland. The Ouémé River is one of the few remaining free-flowing rivers in the world, where the natural water course of the river has not been altered by large infrastructure such as dikes or dams. However, the wetland is under serious threat from urbanisation, encroachment, overexploitation and deteriorating water quality. In addition, several developments are envisaged in the delta, including dams upstream, which will alter the hydrological regime. These changes in the flow regime could severely impact important lake and wetland ecosystems.

Ensuring functioning ecosystems

It is imperative to know how much water is required to keep ecosystems healthy, as this can help authorities in their decision-making on water allocation and other developments in the river. ‘For example, if a large dam is planned upstream, it will alter the amount of water flowing downstream throughout the year,’ Maximin Djondo, Director of BEES explains. ‘In the rainy season, the downstream wetlands depend on flood water, for example for fish to spawn. If we know how much water is needed to sustain fish populations, we can influence decisions regarding upstream developments accordingly.’

To determine how much water is needed for the ecosystems to remain intact, BEES, IHE Delft and the National Water Institute in Benin are carrying out an environmental flow assessment in the Ouémé Delta. The assessment allows authorities to ensure the provision of goods and services, such as fisheries, fertile soils, flood retention and improved water quality, which the river, wetlands, lakes and swamps provide.

‘By mapping how much water is available during the year and how much is needed to sustain the different ecosystem services that people in the Ouémé Delta rely on, we can make recommendations to ensure those services are not compromised through future development,’ Djondo states.

Below film (in French) gives an impression of the kick-off training which introduced the concept of environmental flow assessment to a broad range of stakeholders including government, community representatives and other interested parties in Benin.

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