Location of the three catchment areas covered by the ISABEL project in the Haute-Vienne department
© BRGM
The need
Limousin is a major livestock farming region, but in order to maintain and develop this activity, water resources of suitable quality for livestock watering must be available in sufficient quantities. However, the lack of surface water on some farms means that farmers have to rely on the drinking water network to water their livestock. In addition, watering on rivers and streams has a direct impact (by damaging banks), and livestock trampling also affects wetlands.
To address these issues, and contribute to the search for water autonomy, the ISABEL project (Identification de Solutions adaptées à l'Abreuvement du Bétail et limitation de la pression sur l'hydrosystème En Limousin) aims to provide the knowledge needed to exploit the resource available in the loose alterite deposits, using the technique of filtering points (shallow catchment structures). With the aim of ensuring quantity and quality, this operation must fit into a context of balanced management, without conflicts of use.
Ten-metre weathering profile developed on diorites cut by brecciated dykes, Saint-Hilaire-Bonneval (Haute-Vienne)
© BRGM
The results
The cross-disciplinary ISABEL project brings together hydrogeologists, soil scientists, naturalists and farmers. The first phase of the project involved characterising three selected catchment areas in the Haute-Vienne département. In addition to the characteristics obtained from the analysis of digital terrain models (contours of sub-catchment areas, slopes, landscape classification, etc.), BRGM mapped the presence of weathering-deposit formations by means of field surveys. In collaboration with the Kermap consultancy, satellite images were processed to produce an initial index characterising soils with persistent moisture.
Concomitantly, the Chamber of Agriculture carried out field surveys to characterise the type of watering (directly from rivers or streams, use of the drinking water network with or without transport, etc.), the distribution of large livestock units and the volumes consumed. By cross-referencing watering requirements and the presence of weathering-deposits, it was then possible to select a pilot site within each catchment.
At each pilot site, as well as the characterisation of the wetlands, which was carried out by the Conservatoire Botanique National du Massif Central, the University of Limoges used geophysical methods (electrical conductivity mapping) to help choose the sites for installing piezometers. The piezometers (3 per pilot site) installed in the first half of 2023 will be equipped with a water level recorder to monitor the recharge/drainage dynamics of the weathering-deposit surface reservoirs. Analyses of surface and groundwater will add to our knowledge of local hydro systems.
Using the results
The aim of the project is to develop a reproducible and transferable methodology for extracting resources from weathering-deposits, while respecting the following stages and criteria:
- Characterisation of a little-known and little-exploited resource, whose flow may be sustained by underlying aquifers;
- Definition of favourable areas on the basis of scientific criteria: water abstraction must not alter the functioning of wetlands and watercourses;
- Suitability for operators' needs (filtering-point abstractions);
Regulations and monitoring of facilities.
The partners
- Haute-Vienne Chamber of Agriculture
- University of Limoges - E2Lim Laboratory
- National Botanical Conservatory of the Massif Central
- Kermap
- Agence de l’Eau Loire-Bretagne (Loire-Brittany Water Agency)
- New Aquitaine Region
