UNLOCK - Assessing the multiple impacts of dam removal on biodiversity, water quality and the landscape

UNLOCK - Assessing the multi-faceted consequences of dam removal for biodiversity, water quality and territorial transitions

Coordinator(s)

Jean-Marc Roussel and Laura Soissons

Scientific context

Aquatic ecosystems are essential to biodiversity and human well-being, but they face growing threats such as pollution, climate change and the construction of dams. Dam construction is a controversial issue for aquatic ecosystems: whilst it enables the generation of hydroelectricity and creates new land-use opportunities, it affects water quality, biodiversity and ecosystem functioning. The removal of dams has gained momentum in current policies as a solution to mitigate these impacts and to restore the ecological health of watercourses. However, cases of restoration through the complete dam removal are relatively rare, and knowledge of the mechanisms involved remains even more limited. It is essential to understand the benefits and trade-offs associated with dam removal in order to inform decisions on river management.

Subject(s) of study

Taking a cross-disciplinary approach, this project examines the consequences—both positive and negative—of the removal of the Sélune dams on water quality, biodiversity, landscapes and associated land uses.

Objectives

The main objective of the UNLOCK project is to assess the ecological and territorial impacts of the removal of the Sélune dams. The analysis will focus on biodiversity, water quality and the societal aspects of this restoration.

1. Firstly, a PhD project (2026–2029) will examine various components of the Sélune ecosystem to identify recovery mechanisms, with a particular focus on sediment dynamics, water quality and the functional characteristics of aquatic and riparian communities.
2. At the same time, a postdoctoral project (2026–2028) will focus on two objectives. Firstly, it will assess how local residents and users interact with the landscape that has been transformed following the removal of the dams, and how they may benefit from it. This will take into account social relationships and attachment to the environment. Secondly, it will seek to create a comprehensive historical inventory of the valley in order to understand changes in ecological connectivity and biodiversity, focusing on the mapping of landscape units at the valley scale.
3. Ultimately, the UNLOCK project will play a central role in developing explicit, multidimensional spatial indicators to assess the impact of the Sélune valley's restoration. The results of the UNLOCK project will provide valuable insights into the consequences of restoring ecological continuity in rivers, as well as guidance for stakeholders that can be applied to similar scenarios worldwide.

Methods

The aim of this project is to utilise data collected since 2012 on the Sélune river and its valley, both before and after the removal of the dams. This data, which is available in the SISélune information system, will be analysed and modelled in a transdisciplinary approach, drawing on the scientific literature.

A whole range of existing data will be utilised:

• For the PhD research: data from the Sélune Observatory, and research projects focusing on aquatic and terrestrial biodiversity and river dynamics.
• For the postdoctoral research: high-resolution aerial photography campaigns of the former dried-up area using drones; historical aerial photographs; GIS data collected as part of the scientific programme (footpaths, viewpoints, recreational areas, social gathering spots, jetties and hangars, residential areas with lake views, photographic landscape observatory).

Meanwhile, new field studies, as well as individual surveys (interviews, questionnaires) and group surveys (focus groups), will provide a better understanding of the links between landscape reorganisation and the ways in which landscapes are used.

Laboratorie involved

• DECOD - UMR Dynamique et Durabilité des Ecosystèmes: de la source à l'océan, INRAE/Institut Agro/Ifremer, Rennes
• MNHN – Station marine de Dinard, Dinard
• UMR Geosciences Rennes, OSEREN, Rennes
• INRAE UMR SAS, Rennes
• LETG-Rennes UMR 6554 CNRS-Univ. Rennes 2, Rennes
• Laboratoire Mosaïques LAVUE UMR 7218 CNR, Univ. Paris-Nanterre, Nanterre
•  Univ. Paris Est Creteil et Laboratoire Géographie Physique (LGP) CNRS, Paris
• ECOBIO UMR 6553, Univ. Rennes 1-CNRS, Rennes
• OFB
• AESN
• Hub des sciences participatives, programme IRIS-E, Univ. Rennes, Rennes