Woody Debris for Salmon Habitat

The Value of Woody Debris in our Rivers

The Alouette River Management Society is working with many partners to replace some of the woody debris that has been lost over the last century. As of 1998, a total of 48 instream large woody debris structures have been place in the Alouette River from Allco Park to the Alouette Reservoir Dam. An additional 7 structures were installed in the lower Alouette as well. This work has developed 3,440 square meters of large woody debris covered habitat that was not previously available to juvenile fish.

An assessment of these structures later showed that both coho and steelhead parr were using this new habitat. In fact, coho were nin times more adbundant under the woody debris than in untreated open areas of the river, while Steelhead were twice as abundant.

Figure 1. Image of woody debris installed along the Alouette River

Figure 2. Image of the scale and size of some woody debris that is installed

Figure 3. Image of woody debris installed in the upper Alouette River

Figure 4. Image of woody debris installed in Coniagas Channel

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

One of the most critical components of salmonoid 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. Salmonoid 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.

Historically, the Alouette River was seen to produce large numbers of various species of salmon. Significant declines of these populations occurred subsequent to the forestry, damming, channelization and urbanization of the watershed. Coho, chum, pink, steelhead and cutthroat salmon still return to the Alouette River. Sockeye and chinook eventually became extinct in the river after the impoundment of the upper Alouette River and Alouette Lake for hydro-electric power. (Chinook were reintroduced in 1997).

Replacing what was lost

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. Trees 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.

Figure 5. Image of woody debris installed at Golden Pond

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

In 2005, the Georgia Basin Steelhead Recovery Program was funded through BC Hydro’s Bridge Coastal Fish and Wildlife Restoration Program to assess the habitat and write prescriptions for the installation of large woody debris within the “Corrections” reach of the Alouette River.  A copy of this assessment can be found at www.bchydro.com//projects/docs/bridge_river/05.Al.01.pdf.

The Georgia Basin Steelhead Recovery Program was successful in their 2006 application to and the instream work was completed during the summer and fall of 2006.  ARMS provided assistance to this team to ensure its success.  A link to this report will be provided when the completed. In 2006, Shaun Korman, Katharine Scotton and Dave Taylor, three BCIT Fish and Wildlife students, conducted further studies to determine the effect of the 1997 and 1998 LWD placement in the upper reaches of the Alouette River.  While not conclusive, it would appear through this study that these “aquatic condos” are being well utilized in our river.

A graph of the winter LWD Habitat can be seen to the right.

Winter Habitat Usage – Comparison of Species

For a review of the power point presentation by Korman, Taylor and Stotten NOTHING PROVIDED