woody debriThe Value of Woody Debris in our Rivers

The Alouette River Management Society works with many partners to replace some of the woody debris that has been lost over the last century.

One of the most critical components of salmonid habitat is cover, particularly for rearing juveniles. Rearing fish tend to occupy covered habitats for extended periods of time. They rarely leave these areas except for short foraging and feeding excursions into more exposed stream habitats.

Loss of Woody Debris contributes to the reduction of fish populations.

stumpsSalmonid streams should contain a diversity of cover types. Submerged cover such as large woody debris, boulders, rubble and aquatic vegetation afford protection from predators, while overhead cover such as floating debris, undercut banks, turbulence and overhanging vegetation provide shade as well as protection from predators.

Root wads, trash bundles and trees can be secured at key locations within a stream to increase the amount of submerged and overhead cover for rearing fish. Cedar is the preferred species, but other species are acceptable due to their high resin content. Fast rotting species such as alder or cottonwood are avoided.

Stumps remnant from valleys flooded for hydroelectric dams are often used on LWD Projects

trees in riverTrees and root wads are anchored in a manner that avoids damming the flow. Trees are placed with the branches trailing downstream with the butt section steel cabled and anchored to engineered standards along the streambank.

Loose root wads can also be placed in protected pools, like those behind beaver dams, where there isn’t any danger of them washing downstream.

During 1997 to 1998 a total of 48 instream large woody debris structures were placed in the Alouette River from Allco Park to the Alouette Reservoir Dam. An additional 7 structures were installed in the lower Alouette as well by a private property owner. This work has developed 3,440 square meters of large woody debris covered habitat that was not previously available to juvenile fish.

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