Drains neutralization
Life Program Objectives
16 km of drains neutralized spread over 14 Natura 2000 sites
Travaux réalisés pendant le programme
Bas-marais de Mont de Voyon aux Granges-Narboz (25)
Objectif : Ralentir les écoulements et recharger en eau le marais et in fine la nappe qui profitera du ralentissement des écoulements.
Réalisation :
- neutralisation de 6 petits fossés avec panneaux de bois et sciure;
- neutralisation d'un gros fossé avec 8 palissades en madriers de bois.
Cette neutralisation de 1520 m de fossés au total a été réalisée par l'entreprise Jura Natura Services sous maitrise d'ouvrage du SMMAHD.
Budget : 62 912 euros de prestation auquels il faut ajouter le coût de personnel pour le montage et le suivi du projet.
Much of peatlands in the Jura massif was drained. The resulting drying affects all habitats and almost all species of community interest housed. The only way to restore the peatland is to restore the hydrology of the site.
Techniques
The configuration of the drainage ditches varies from one site to another. Their width as their depth can vary from 0.5 m to 4 m, the length of ten to several hundred meters. Their slope may also vary widely (from almost 0 to a few percent).
The optimal response is to completely clog the drain with peat or an equivalent material. This technique allows to raise the level of water saturation throughout the dried surface, completely canceling the functioning of gullies. It requires a significant amount of materials whose quality must be in line with the trophic conditions of the restoration site:
- peat (usually taken nearby);
- spruce sawdust (interesting alternative solution);
- small diameter trees ground and mixed with peat or sawdust.
If it is impossible to achieve a total filler, an alternative technique is to create dams covered with peat. The number of these structures is highly dependent on the slope: the more it is, the greater the number and design will be important.
Consequences
Neutralizing a drain induced a rise in the water table, which again allows to absorb water walks near the surface and promotes communities return called "peat producing", that is to say capable of producing peat. Conservation states habitats and species of Community interest are thus improved.