Remeandring
Life Program Objectives
11 km of streams restored in 5 Natura 2000 sites
Travaux réalisés pendant le programme
Reméandrement du Nanchez et du Trémontagne (39)
Objectif : rétablir le fonctionnement morphodynamique du cours d'eau et restaurer les échanges avec la nappe en supprimant l'effet drainant du cours d'eau à l'étiage.
Etapes :
- Broyage de la végétation empêchant l'accès des machines au site;
- Piquetage des méandres;
- Creusement du futur lit;
- Recharge du lit guide;
- Mise en place de fascines d'épicéa;
- Comblement du lit rectifié;
- Comblement des fossés de drainage.
Maitre d'ouvrage : Parc naturel régional du Haut-Jura.
Entreprises : Jura Natura Services et Goyard TP.
Assistance à maîtrise d'oeuvre : ECOGEA.
Pêches de sauvetage : Fédération du Jura pour la Pêche et la protection du milieu aquatique.
Budget : 278 000 euros HT de prestation auquels il faut ajouter le coût de personnel pour le montage et le suivi du projet.
As for drainage, correction of rivers causes a disruption in the natural morpho-dynamic of the stream.
Techniques
Specifically, this includes either the reactivation of the old meandering bed or the creation of a new one.
The design of the new bed should be adapted to its regime. If it is recreated from scratch, its route must be adapted to the topography of the area (usually in a swamp, its length is multiplied by 1.7 to 2, compared to a straight bed).
Once the new bed is recreated, it is necessary to seal the old straight one, by the resumption of the barricade from its dredging and by filling with suitable materials. Downstream, it is often necessary to install a bottom rail to maintain the water level and stop any regressive erosion. A "sedimentary recharge" can also be performed in the new bed, to accelerate the re-creation of a varied substrate and restart the erosive dynamic, guaranteeing a major morphological and ecological diversity.
In some cases, it is not possible to completely restore the watercourse. A partial rehabilitation may be a tightening of the minor bed or laying background ramps to raise the water level.
Consequences
In general, the vocation of a stream restoration is to restore the morpho-dynamic functionning of the stream and restore exchange table / streams by reactivating or recreating a meandering bed, with dimensions and at an altitude adapted on the ground. The table is then significantly enhanced, leading to a definite improvement in the conservation status of marsh habitats.