Policy discussion paper "Linking e-Flows to sediment dynamics"

Fluvial communities and their ecological integrity are the result of their evolutionary adaptation to river habitats. Flowing water is the main driver for development and maintenance of these habitats, which is why environmental flows (e-Flows) are needed where societal demands are depleting water resources. Fluvial habitats are not only the result of water flow, however, but are shaped by the combined interaction of water, sediments woody/organic material, and riparian vegetation. Water abstraction, flow regulation by dams, gravel pits or siltation by fine sediments eroded from hillslopes are pressures that can disturb interactions among water, sediments, and other constituents that create the habitats needed by fluvial communities. 

Present e-Flow design criteria are based only on water flow requirements. Here we argue that sediment dynamics need to be considered when specifying instream flows, thereby expanding the environmental objectives and definition of e-Flows to include sediments (extended e-Flows).

We recognize that currently used biological assessment systems and metrics are not sufficiently sensitive indicators of ecological status of water bodies impacted by sediment and flow management. To overcome current limitations of available metrics that use biological quality elements (BQEs) in assessing flow related impacts, we are proposing alternative assessment criteria that include hydromorphological (HYMO) aspects. Our broadened definition of extended e-flows requires a broader set of protocols and tools derived from specific HYMO approaches (e.g. REFORM multiscale hymo framework). 

To this aim, a framework for e-Flows assessment and identification of best strategies for fluvial restoration, including the context of rivers regulated by large dams, is presented.

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