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Open Access Publications from the University of California

Reservoir Management in Mediterranean Climates through the European Water Framework Directive


While the problem of sedimentation slowly filling dams and reservoirs is innate to the structures, it is especially significant in Mediterranean climates that rely on reservoir storage to mitigate out-of-phase water availability and demand. Reservoirs and their impounding structures have significant impacts on in-stream and riparian ecosystems. Several preventative and mitigation measures have been designed by engineers to limit sediment accumulation and the ecological impacts of reservoirs. Dam removal has been documented to have significant environmental benefits for restoration of aquatic ecosystems and native fisheries but may also lead to eroded floodplains, impaired downstream habitat and loss of flood control capacity. The European Water Framework Directive (WFD) establishes goals and guidance designating “heavily modified water bodies” and achieving “good ecological potential,” but definitions of these terms are not clearly defined. In addition, sediment management is not explicitly addressed in WFD guidance, thus contributing to limited guidance on how reservoir sedimentation should be managed in Mediterranean climates. As a European Union member state and a Mediterranean-climate country, surface water and reservoir management in Portugal is undergoing several changes through actions to achieve WFD goals. We examine how WFD management guidance for reservoirs and their ecological status is currently being considered throughout Europe and in Portugal specifically.

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