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 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.

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.

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.

Macrophytes are a group of aquatic plants. They are at the base of the food chain and can provide a habitat for many other species. As part of the Sélune Observatory, pilot stations have been set up along the main course of the Sélune, distributed from upstream to downstream of the hydroelectric dams. Three stations are located in the former reservoirs of the dams, while the other two, known as the reference stations, are outside the area of influence of the former dams (one downstream and the other upstream). At these stations, the aquatic biocenoses (including benthic macroinvertebrates, biofilms, macrophytes, etc.) are monitored. The parameters monitored are the specific composition and cover, at 8 stations in the main course located upstream, downstream and in the neolotic zones of the macrophyte communities. The monitoring frequency consists of one annual campaign for stations outside reservoirs (S0, S1 and S5) and two annual campaigns (spring/autumn) for neolotic stations (S2, S3.4, S4.1 and S6). The protocol used is the sampling protocol for macrophytes and bryophytes in accordance with standard NF T90-395 (October 2003), which defines the IBMR. The taxa are sampled for laboratory identification. This layer shows the location of the study sectors used for macrophyte monitoring, as well as the campaigns carried out and the mesology identified during these different campaigns.

The restoration of the Sélune river continuum after the dams were demolished will allow colonization of the upper reaches of the basin, which were previously inaccessible to eels. Before the demolition, 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-demolition phase by abundance index campaigns carried out in 2013, 2015, 2019, and then every year since 2021, on a network of stations covering the entire Sélune river system. These data make it possible to estimate changes in eel abundance along the Sélune and its tributaries and their size structure before and after the destruction of the dams. The inventory is carried out in early September, every other year, then every year since 2021, using electric fishing equipment and landing nets. Thirty fishing points are carried out for a minimum of 30 seconds. A fishing station covers approximately 100 meters of river. All eels caught are anesthetized and undergo biometric measurements (weight, length, horizontal and vertical eye diameter, determination of yellow or silver stage). All eels are released directly at the fishing site. This sheet refers to two layers, one showing only the study areas and their location, and the other specifying the concept of capture sessions.

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.