2025

This layer shows the location of the points making up the Sélune scientific programme reference system. These points can be used to uniquely designate a location within the study area, regardless of the discipline or research project.

Free use subject to the following compulsory mention on all distribution documents: “Source: UMR DECOD INRAE - Agrocampus Ouest”.

Open license: https://www.etalab.gouv.fr/licence-ouverte-open-licence

No public access restrictions

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Secteur hydrographique "I9" (correspondant à la Sélune de sa source à l'embouchure)

The points are created on the watercourses, using a “Kilometre Point” approach. Points are created along watercourses, every 100m, from upstream to downstream. Each of these points has a unique code, corresponding to the combination of the watercourse (designated by a short code) and the distance to the source or confluence.

Since 2025, each of these points has also been characterized by its position in the watershed (downstream, upstream, ...) in relation to the zone determined by the former dams and their reservoirs, as well as their distance from the sea in 2 forms (LTM: Limite Transversale à la mer / Transverse Sea Limit and LSE: Limite Salaison des eaux / Salted Water Limit).

The categorization of the point's position in the watershed was carried out manually by spatial selection in order to position the following values

- UPSTREAM: point located UPSTREAM OF THE VEZINS RETENTION (SELUNE ET AFFLUENTS)

- DOWNSTREAM: point located DOWNSTREAM OF THE ROCHE QUI BOIT DAM (SELUNE ET AFFLUENTS)

- RETENUE_R: point located in the RETENUE LA ROCHE QUI BOIT area (SELUNE)

- RETENUE_V: point located in the RETENUE DE VEZINS SUR LA SELUNE (SELUNE) zone

- RETENUE_AF: point located on one of the AFFLUENTS SE JET DES LES 2 RETENUES

Points are created on watercourses, with a "Kilometre point" approach. Points are created along watercourses, every 100m, from upstream to downstream. Each of these points has a unique code, corresponding to the combination of the watercourse (designated by a short code) and the distance to the source or confluence.

Two different distances to the sea have been listed in this dataset: the distance to the sea with reference to the Limite Transversale à la Mer (LTM) or the Limite de Salure des Eaux (LSE).

The LTM distance-to-sea value was calculated as follows:

Step 1: determination of one (or more) reference point(s) for the sea/freshwater environment change in order to calculate this distance to the sea.

Step 2: identification of the associated reference point(s) in order to assign them a distance to the sea equal to 0

Step 3: each reference point being separated by 100 m from its predecessor and successor and already possessing a distance-to-source attribute. The distance to the sea is calculated from nearest to nearest.

The LSE distance to sea is calculated by difference with the reference value of 1500m.

Limitation: the reference frame was created from the sources (distance to source = 0) and then positioned with a point every 100 meters. When the reference frame is traversed from the sea, there may therefore be offsets and distances between 2 points of less than 100m (particularly in the presence of numerous confluence points and/or “parallel” channels). As a result, distance-to-sea information is all the more reliable the higher the associated Strahler number (a river with a low Strahler number is a small tributary river, with several confluences scattered along its course to the sea; each confluence can introduce an uncertainty of between 50 and 100m on the distance between 2 points). Despite this limitation, the distance to the sea calculated in this way provides global information on the watershed that is relevant at this scale.

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ISO 19115

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