Les barrages sont à l’origine de modifications significatives du régime hydrologique, de la température de l’eau et des flux biologiques et biogéochimiques. C’est le cas des barrages de Vezins et de la Roche qui Boit, présents sur le cours principal de la Sélune, et d’autres plus petits obstacles qui fragmentent le bassin versant de la Sélune. Cette couche représente les barrages hydroélectriques de la Sélune, avec les batiments associés, en lien avec la production électrique. La géométrie de ces polygones est issue de plusieurs sources : BD Topo, OpenStreetMap (de 2019), complétée par photointerprétation. Des informations extraites du livre « Quand les rivières reprennent leur cours – Notes sur l’effacement de barrages et de seuils, sur la Sélune et ailleurs » ont été ajoutées pour décrire l'état (en service ou arasé), la nature et les caractérisques physiques de ces barrages.

In partnership with ANR Reppaval, the Syndicat Mixte du bassin de la Sélune has begun implementing a photographic observatory of the landscapes of the Sélune basin. This is a photographic itinerary consisting of viewpoints spread across the entire territory, where photographs will be taken regularly. The aim is to monitor changes in the landscape, particularly in relation to the Sélune restoration project. The layer shows the location of the sites on the photographic itinerary that are directly affected by the Sélune restoration work: lakes and dams.

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 hydrographic sections, which make up the waterways, were extracted from the Topage database covering the study area.

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 using an information system (IS) called SISelune. SISelune aims to assist scientists associated with the Sélune program and make the data accessible to all. Watercourses are linear hydrographic entities, linked to a main place name and broken down into hydrographic sections. These watercourses are extracted from the Topage database covering the study area. Codes that can be used within the Sélune program have been added, as well as codes from the former hydrographic reference system (Carthage database).

The opening of the dams will have a significant impact on trout populations in the Sélune. Restoring the river's ecological continuity will alter population flows by allowing amphihaline sea trout to migrate further upstream and native trout to move downstream and upstream of the dams. The trout population is monitored at a network of stations covering the entire Sélune basin using an abundance index, which is carried out every two years. The field campaigns comply with the Vigitruite® fishing protocol, developed by INRA and intended for use throughout France. This abundance index, relative to the area of favorable habitats in the watercourse, makes it possible to assess the quantity of young trout present in the river, resulting from natural reproduction in previous years. This table provides individual data on trout caught according to the year of study.

Stations for continuous measurement of hydrological, physical, chemical and sediment parameters have been installed on the Sélune river, as part of the scientific program to monitor the leveling of the Sélune dams. Measurements have been taken on at least an hourly basis since 2014 at the latest. Since 2019, these stations have been part of the Sélune Observatory, which is responsible for monitoring environmental parameters (biotic and abiotic). All stations measure turbidity, water level and conductivity. Some stations measure additional physico-chemical parameters such as pH, dissolved oxygen and chlorophyll concentration. Samples are also taken at upstream (Pont de Virey) and downstream (Pont de Signy) stations, for laboratory chemical analysis. This layer shows the location of flow measurement stations.

The spawning grounds of the sea lamprey (Petromyzon marinus) are located within the perimeter of the Sélune Observatory. As this species is migratory, its colonisation of the Sélune river and its tributaries will probably be influenced by the removal of the Sélune dams. The spawning grounds are characterised by a depression accompanied by a sediment ejection dome immediately downstream. The stones returned to the dome are lighter, making the nests easily visible and identifiable for up to several weeks after spawning. This data is available for the years 2015, 2019, 2020, 2021, 2022, 2023, 2024 and 2025. The Sélune Observatory's activity reports (see attached links) give details of the prospecting conditions.

The opening of the dams should impact the functioning of Atlantic salmon populations migrating up the Sélune River and its tributaries. Restoring the river's ecological continuity will alter population flows by allowing amphihaline sea trout to migrate further upstream and native trout to move downstream and upstream of the dams. The trout population is monitored at a network of stations covering the entire Sélune basin using an abundance index, which is carried out every two years before 2021 and every year since then. Field campaigns comply with the fishing protocol developed by INRAE and OFB. The aim of this method is to estimate the abundance of juvenile Atlantic salmon (Salmo salar) at a station (or sector). This protocol targets juveniles of the year (aged 0+) whose abundance reflects the renewal of generations within the population (or recruitment) and survival after the embryonic development phases under gravel and the first months of life in the open environment. Field campaigns are carried out by INRAE and the Manche and Ille-et-Vilaine Federations for Fishing and the Protection of the Aquatic Environment (FDAAPPMA50 and FDAAPPMA35). This dataset provides abundance data for Atlantic salmon (0+, 1+, 2+ and cumulative) as well as the salmon abundance index (PAS) by station and fishing session.