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LEARN: Impact of dam removal on hyporheic flows and groundwater-river exchanges in the Selune river

Coordinator(s)

Alain Crave

Scientific context

Restoring the continuity of the Selune by removing its dams will have a major impact on hydrology and the transfer of sediment in the river. This may also lead to the unclogging of the upstream bed and the clogging of the downstream bed. The restoration of the Selune valley provides a unique opportunity in Europe to study the vertical and lateral continuity of water flows between the river, the hyporheic zone, the banks and the groundwater. There are a number of fundamental questions that have yet to be explored, including :

• What are the physico-chemical gradients at the water/sediment interface resulting from water flows on and in the riverbed matrix, biofilms and water flows between the river and groundwater?
• What is the potential impact of clogging of the Selune on the water resources of the Canton of Ducey?
• What is the spatial distribution of clogging and its dynamics?
• What is the impact of lowering the water level on the hydrogeology of the catchment?

Subject(s) of study

The project deals with exchanges between the groundwater and the river. The physico-chemical and biological properties of the water are also considered.

Objectives

The first objective of the project is to document and understand the functioning of the hyporheic zone in a context of hydrological variations (flood waves, variations in the water table) and sedimentary variations (clogging, variations in roughness and compactness).
The second objective will be to develop a numerical model (based on bio-geochemical models proposed in the literature) of hyporheic functioning as a function of the river's hydraulic and sedimentary boundary conditions. This model will be capable of predicting the variability of physico-chemical conditions and associated microbial activity.

Methods

A major part of the project is devoted to implementing innovative metrology, derived from national and European research programmes, to measure in situ water flows and dissolved gas concentrations within the riverbed matrix. All the data will be used to calibrate and validate flow models at different scales, redox processes and bacterial activity within the hyporheic zone. As such, this project is based on a partnership between several teams involved in national and international study programmes on groundwater/river exchanges and the hyporheic zone.

Laboratories involved

• Geosciences, Université de Rennes 1, Rennes
• ECOBIO - Ecosystems, Biodiversity, Evolution, Rennes
• ARMINES Centre of géosciences
• BRGM