Restore salmon habitat at Les Marais pool, Causapscal River, phase 1

Since 2018, the flow in breach no. 1 lets an important part of the flow bypass the pool. In 2018, 2019 et 2020, the deterioration of the habitat continued, the current velocity and the flow in Les Marais pool are now insufficient and coarse sediments have filled most of this important pool: its average depth diminished drastically, at such a point that since 2019, this fish habitat is no longer optimal as a salmon holding pool. Soon, this situation will cause the loss of this essential feature for the protection and conservation of the salmon population of Causapscal River.

Rehabilitation work of salmon habitat was separated in two phases. This proposal is for phase 1 and includes the following work and developments (see plans and specifications):

1- Access road and culvert
2- Stop log, water diversion and sediments management
3- Reprofiling the sediment bar (2,500 square meters)
4- Consolidating, rebuilding and reprofiling the bank before stabilization (stones type mg-80 and recovered stones on the sediment bar)
5- Stabilizing the left bank on 80 to 90 linear meters (geotextile and stones)
6- Stabilizing breaches and secondary channels on the left bank by installing thresholds.

Phase 2 which will follow will complete the work and will be detailed in a future proposal. But briefly, it will consist in completing the stabilization of the left bank on a last section of 90 linear meters, in stabilizing the bank opposite to the exhibition center and consolidating the existing stabilization opposite to the pool, cleaning and removing accumulated sediments from the pool.

Le site de la fosse Les Marais permet d’assurer une surveillance et une protection en continue des saumons en contention dans la fosse. La distance riveraine entre les deux barrières de contention protégeant la fosse est d’environ 260 mètres. Les faciès d’écoulement au site de la fosse Les Marais (rapide-seuil-fosse) sont insérés dans une succession de deux méandres.
Il importe d’insister sur le fait qu’au cours des dernières débâcles printanières (2007 à 2020), la crue a parfois été soudaine et intense, charriant des quantités anormalement élevées de sédiments semi-grossiers (cailloux et galets). Or, une partie de ces sédiments se déposent et s’accumulent au niveau de la rive droite convexe du méandre en amont de la fosse. À cet endroit, l’accumulation de sédiments a rétréci la largeur du lit du cours d’eau et dirige le débit de la rivière sur la rive opposée (rive gauche). Des chenaux d’écoulements secondaires s’y sont formés, dont le plus imposant, soit le canal no. 1.

Contact:

Michelle Levesque

michelle.levesque@cgrmp.com

418 756 6174