This project compares the implementation, acceptance, and progress of dam removal projects in France, using the example of the Sélune, and in the United States, where several similar removal projects have taken place.

In a nutshell: The food web project takes a broad look at the aquatic communities found in the Sélune River, ranging from microorganisms to fish, in both its tributaries and the river itself, from its source to where it flows into the estuary. The approach aims to study the interactions between these biological components, with the primary objective of understanding the overall functioning of the ecosystem. The goal is to understand the balances within aquatic ecosystems, from the headwaters of the watershed to the lower reaches of the river, both before (current state) and after (river restoration) the restoration of continuity through the removal of dams. Objective: to answer the following questions: · What role do dams and their reservoirs play in shaping aquatic communities within the river and in the functioning of this ecosystem? · How does the river ecosystem recover at the exact location of a dam reservoir after it has been drained? · What roles do certain key species (particularly amphihaline fish and invasive species) play in ecological balances? · What consequences can be expected from dam removal operations, from the headwaters to the estuary entrance, on these communities and the functioning of the river ecosystem reconnected to the ocean? Methods: inventories; physicochemical characterization; functional ecosystem analysis; stable isotope analysis; food web analysis Data: - Measurements of water’s physicochemical quality - Community inventories - Estimation of (1) the degradation of coarse organic matter (tree leaf litter) via the detritus pathway, and (2) the photosynthetic activity of microorganisms and biofilms in the algal pathway. - Data from isotopic analyses of communities; identification of energy sources (food, carbon cycle) in food webs - Role of keystone species (invasive crayfish and fish predators) - Analysis of food web structure

In 2020, scientific plots were set up, marked out on the ground with colored stakes. These plots are intended to facilitate scientific monitoring, particularly of renaturation. These plots represent privileged areas for scientists, where no sediment or vegetation disturbance is planned until the end of the Sélune program.

The removal of the dams on the Sélune River is the subject of a scientific program launched in 2012, in which environmental parameters are monitored in order to provide real feedback on this restoration operation. In 2019, a data observatory was set up to collect and process these parameters (biotic and abiotic). The data acquired from 2012 and at least until 2027 will be centralized through an information system (IS) called SISelune. SISelune aims to assist scientists associated with the Sélune program and make the data accessible to all. This layer shows the study area, based on hydrographic sub-basins for the continental part and the transitional water body for the Bay of Mont St-Michel.

Continuous monitoring stations for hydrological, physical, chemical, and sedimentary parameters have been installed on the Sélune River as part of the scientific program to monitor the removal of the Sélune dams. Measurements have been taken at least hourly since 2014. Since 2019, these stations have been under the responsibility of the Sélune Observatory, which is in charge of monitoring environmental parameters (biotic and abiotic). The physical and chemical parameters measured at all stations include turbidity, water level, and conductivity. At some stations, pH and dissolved oxygen or chlorophyll concentration are also measured. This layer provides the corrected measurements from the hydrological measurement stations. This layer provides corrected measurements from the SIGNY, LA-ROCHE-QUI-BOIT, VIREY, and DORIERE (only until October 2020) hydrological measuring stations.

In a nutshell: This research project focuses on the social and geographical dimensions of the ecological restoration of the Sélune River. Its objective is to assess the current state of the landscapes, land uses, and practices in the Sélune Valley (and more specifically in the gorge section) prior to the removal of the dams, and then to monitor the changes brought about by the removal: the state of both material transformations (land use, practices, visitor traffic) and conceptual transformations (perceptions, discourse) of the territory in order to assess the impacts of this project and thereby measure its success from the users’ perspective (quality of life, regional development, practices, etc.) to understand, using the example of the Sélune, the difficulties in gaining acceptance and ownership of such a project by various local stakeholders, as well as the challenges related to its definition and implementation. Methods used: surveys, questionnaires, analysis of the local press, photography Data: - A collection of photographs (~40) covering the entire Sélune Valley to track changes in the landscape - Historical photographs and postcards. Photographs will be annotated and geotagged - Inventory of land uses (fishing, recreation, lodging, etc.), analysis of visitor traffic in the gorges, and mapping - Semi-structured interviews will be conducted with representatives of user groups (to gather their opinions) - Text analysis (using Alceste or WordMapper software) of transcribed interviews - Collection of residents’ opinions and assessment of their satisfaction with the project - Corpus of articles published in the regional daily press to track the history of reactions - Collection of information disseminated via other media platforms such as blogs, forums, and websites by various stakeholder groups, particularly fishermen, environmentalists, and opponents of the clearing - Codification of the corpus followed by a lexical and semantic analysis using the TXM platform

A flow obstruction is a water-related structure that causes a change in surface water flow (in thalwegs, minor and major river beds, and marine inundation zones). Only artificial obstructions (resulting from human activity) are taken into account. The data presented is taken from the ObstEcoul_FXX data layer published by SANDRE, spatially restricted to the Sélune watershed. The data retrieved was updated on 07/30/2024 from the above-mentioned feed and reprocessed to complete the type of obstacle with a “nature” field representing an aggregation of the types identified on the following values: “Dam”, “Spout”, “Dike”, “Bridge”, ‘Weir’ and “Not specified”. The aggregation implemented to populate the “nature” field is as follows: 1/ retrieval of the types of obstacles present in the watershed (source data field “CdTypeOuvr”). 2/ Retrieve the associated labels in the SANDRE reference: https://api.sandre.eaufrance.fr/referentiels/v1/nsa/284.csv?outputSchema=SANDREv3.1 3/ Filter these labels to populate the new “nature” field: - if the label contains “dam” then ‘nature’ is initialized to “Dam” - if the label contains “buse” (pipe), then “nature” is initialized to ‘Buse’ - if the label contains “digue” (dyke), then “nature” is initialized to “Digue” - if the label contains “pont” (bridge), then ‘nature’ is initialized to “Pont” - if the label contains “weir,” then “nature” is initialized to ‘Weir’ - if the label contains “not specified” (initially empty code), then “nature” is initialized to “Not specified” The other fields offered in the dataset are taken from the original SANDRE feed but have been renamed. The correspondence is provided in the associated data dictionary.

This project aims to develop and apply a non-invasive method for monitoring migratory fish flows in the Sélune River. The development of this method is based on the analysis of images and videos taken by a hydroacoustic camera positioned in the watercourse.

Continuous monitoring stations for hydrological, physical, chemical, and sedimentary parameters have been installed on the Sélune River as part of the scientific program to monitor the removal of the Sélune dams. Measurements have been taken at least hourly since 2014. Since 2019, these stations have been under the responsibility of the Sélune Observatory, which is in charge of monitoring environmental parameters (biotic and abiotic). The physical and chemical parameters measured at all stations include turbidity, water level, and conductivity. At some stations, pH and dissolved oxygen or chlorophyll concentration are also measured. This layer provides raw measurements from the SIGNY, LA-ROCHE-QUI-BOIT, VIREY, and DORIERE (only until October 2020) hydrological measuring stations.

The re-establishment of the river continuum on the Sélune after the dams have been levelled will enable colonization of the upper reaches of the basin, which were previously inaccessible to eels. Before the dams were levelled, two main tributaries were used by amphihaline fish for reproduction, in addition to the main river: the Beuvron and the Oir. The eel population of the Sélune was monitored in the pre-flushing phase by abundance index campaigns carried out in 2013, 2015, 2019 on a network of stations covering the entire Sélune hydrographic network. Since 2021, this network of stations has evolved to monitor changes in the part of the watershed accessible following the dismantling of the 2 dams. These data enable us to estimate changes in eel abundance along the Sélune and its tributaries, as well as their size structure before and after the removal of the dams. The inventory is carried out in early September, every other year between 2013 and 2019, then every year since, using an electric fishing device and dip nets. Thirty thirty-second fishing stations are set up. A fishing station comprises approximately 100 meters of river. All eels caught are anaesthetized and biometric measurements are taken (weight, length, horizontal and vertical eye diameter, determination of yellow or silver stage). All eels are released directly at the fishing site. Two different protocols were implemented: the Eel Abundance Index (Pottier and Chapon, 2022) at 23 stations and exhaustion fishing at eight other stations (IAA01 to IAA08) on the Oir River and some of its tributaries, according to an internal protocol. This layer provides station abundances by fishing session.