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.

Usage libre sous réserve des mentions obligatoires sur tout document de diffusion : "Source : UMR DECOD INRAE - Agrocampus Ouest"

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

Pas de restriction d’accès public

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

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

Since 2025, each of these points has also been characterized by its position on the watershed (downstream, upstream, etc.) in relation to the area determined by the old dams and their reservoirs, as well as their distance from the sea in two forms (LTM: Transverse Limit to the Sea and LSE: Water Salinity Limit).

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

- UPSTREAM: point located UPSTREAM OF THE VEZINS RESERVOIR (SELUNE AND TRIBUTARIES)

- DOWNSTREAM: point located DOWNSTREAM OF THE LA ROCHE QUI BOIT DAM (SELUNE AND TRIBUTARIES)

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

- RETENUE_V: point located in the VEZINS SUR LA SELUNE RESERVOIR area (SELUNE)

- RETENUE_AF: point located on one of the TRIBUTARIES FLOWING FROM THE TWO RESERVOIRS

Two different distances to the sea have been listed in this dataset: the distance to the sea with reference to the Transverse Limit to the Sea (LTM) or the Salinity Limit of Water (LSE).

Two different distances to the sea have been recorded in this dataset: the distance to the sea with reference to the Transverse Sea Limit (LTM) or the Salinity Limit (LSE).

The LTM sea distance value was calculated as follows:

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

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 is separated by 100 m from its predecessor and successor and already has a distance attribute to the source. The distance to the sea is calculated step by step.

The LSE distance to the sea was calculated by difference with the reference value of 1,500 m.

Limitations: the reference system was created using sources (distance to source = 0) and then positioning a point every 100 meters. Therefore, when the reference system is traversed from the sea, there may be discrepancies and thus distances between two points of less than 100 meters (particularly in the presence of numerous confluence points and/or “parallel” channels). As a result, the distance to the sea information is more reliable when the associated Strahler number is high (a watercourse with a low number is a small tributary, and several confluences dot the route to the sea; each confluence can introduce an uncertainty of between 50 and 100 meters in the distance between two points). Despite this limitation, the distance to the sea calculated in this way provides comprehensive information on the watershed that is relevant at this scale.

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ISO 19115

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