Water Stewardship Information Sources
| Citation | Northwest Hydraulic Consultants Ltd. 2011. Effects of gravel removal on flood levels: Results of Hydraulic modelling. Prepared for Cowichan Valley Regional District. |
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| Organization | Cowichan Valley Regional District |
| URL | http://www.cvrd.bc.ca/DocumentCenter/Home/View/7998 |
| Abstract/Description or Keywords | Northwest Hydraulic Consultants (NHC) was retained by the Cowichan Valley Regional District CVRD to assess the hydraulic effects of removing gravel from two sites on the Cowichan River downstream of Somenos Creek using the Mike Flood hydrodynamic model developed for NHC’s Integrated Flood Management Plan (IFMP) in 2008 - 20091 . The gravel removal scenarios were identified between July 8th and July 12th in consultation with the CVRD. The following information on the river’s overall sediment budget is condensed from NHC (2009). Comparison of cross sections surveyed in 1977 and 2008 indicated there was a total net deposition of 251,000 cubic metres on the Cowichan River downstream of Highway 1. During this period gravel was periodically removed from a number of different sites, including between the railway bridge and Major Jimmy’s channel and along the North Branch of the Cowichan. Accounting for these removals, the net overall sedimentation volume was estimated at 450,000 cubic metres. This volume is equivalent to an influx of gravel of 14,500 cubic metres/year upstream of the Allenby Bridge. For illustrative purposes, an estimate of the thickness of deposition was made by spreading the volume uniformly over the length of the channel. Based on this assumption, it was found that the average bed level rise amounted to 0.7 m over the 31 year period (22.5 mm/year). |
| Information Type | report |
| Regional Watershed | Vancouver Island South |
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| Contact Name | Kate Miller |
| Contact Email | [email protected] |