| Abstract/Description or Keywords |
The impact of fine sediments on salmonid egg incubation habitat in the Cowichan River is an ongoing concern among members of the Cowichan Stewardship Roundtable. High inputs of fine sediments, typically from excessive bank erosion, may infiltrate the interstices of the riverbed spawning gravel and reduce egg-to-fry survivals. Although sediment inputs from naturally eroding banks are apparent along the mainstem, several sites stand out as having larger areas of fine sediments and which are or have the potential to be significant sources of fine sediments to the river. For example, Stoltz Bluff has been identified as the most significant single source of fine sediments to the river (LGL and KWL 2005; KWL 2005). Rehabilitation measures were constructed at Stoltz Bluff in 2006 to stabilize the toe of the Bluff thereby reducing sediment inputs from this chronic erosion site. Significant erosion sites have also been identified further upstream above Skutz Falls but an evaluation on the composition of these eroding banks, the mechanism of bank failure, the relative rate of bank erosion, and the feasibility of constructing rehabilitative works to stabilize the sites and reduce the erosion rate has not been considered in detail. The purpose of this report is to summarize the existing information on previous investigations examining the sediment source issue, including the implications of sediment on incubation success for Cowichan River salmonids, and to develop a list of sites with their priority and rationale for implementing rehabilitative measures. For this project, the area under consideration is restricted to the Cowichan River mainstem and bounded primarily between the Cowichan Lake weir and Skutz Falls. This project was co-funded by Living Rivers-Georgia Basin/Vancouver Island (2006-11), a program of the BC Living Rivers Trust Fund. |
