|Citation||Gaboury, M, Robichaud, D and Damborg, J. 2012. Effectiveness monitoring of Stotlz Bluff stabilization works, Cowichan River, Final Report. Prepared for BC Conservation Foundation and Pacific Salmon Commission.|
|Organization||BC Conservation Foundation|
|Abstract/Description or Keywords||The impact of fine sediments on salmonid egg incubation habitat in the Cowichan River has
been an ongoing concern among members of the Cowichan Stewardship Roundtable. The
concern relates to the impact of fine sediments, typically generated from excessive bank
erosion, infiltrating the interstices of the riverbed spawning gravel and reducing egg-to-fry
survival. Although sediment inputs from naturally eroding banks are apparent along the
mainstem, several sites stand out as generating large volumes 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). The sediment contribution from
Stoltz Bluff was estimated at ~10,000-28,000 m3
annually between 1993 and 2004.
Suspended sediment from Stoltz Bluff also represented from 35-45% of the total suspended
load measured at Vimy Road, ~15 km further downstream. To address this significant
sediment source, 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. Two key
rehabilitation objectives for the Stoltz Bluff stabilization project were:
1. To reduce the erosion and the generation of sediment loads from Stoltz Bluff to the
lower river; and
2. To improve salmon egg-to-fry survival in spawning habitats downstream of Stoltz
This final report presents results of a two year study of the effectiveness of rehabilitation
works constructed at Stoltz Bluff to determine if these rehabilitation objectives are being met.
Project Goal and Objectives
The goal of this project is to report back to the Stoltz Bluff rehabilitation project funding
partners, Cowichan Stewardship Roundtable and Cowichan Watershed Board on the status of
fish habitat (particularly spawning conditions), following successful implementation of a
major sediment control project (i.e., capital cost >$1M). The project objectives were:
1. Develop an appropriate experimental design that will produce repeatable and testable
results at the 0.05 level of significance.
2. Establish a series of water quality, substrate permeability, test egg incubator and
hydraulic egg sampling sites on the Cowichan River, downstream of Lake Cowichan,
closely matching those conducted in baseline years, prior to Stoltz Bluff remediation.
The sites will most likely include Greendale (control), Riverside Cabins (control),
Greendale Trestle (control), ~200 m above Stoltz Bluff (control), Stoltz Bluff side
channel (control), Wildwood, Stoltz Pool, Sandy Pool and the Catalyst Paper mill
pump house. Sampling targeted August 2010 to March 2012.
3. Measure substrate permeability with standpipe piezometers using a constant gradient
test at four of the above sites, where suitable salmon spawning habitat presently exists. Continuously measure in situ turbidity using YSI 600 OMS meters at 5 sites
embracing both control and treated (impacted) reaches from October to March.
Additional turbidity data to be provided by Catalyst Paper from water extracted at
their intake site in Duncan.
5. Collect turbidity and TSS water samples at up to six sites. The focus will be on
ascending limbs of the seasonal flood hydrograph from November to February.
Standard chemical analysis will be conducted at a certified water analysis laboratory.
6. Install approximately 50 standpipe incubators of DFO (M. Sheng) design with ~60
eyed Chinook eggs at 4 sampling sites (~5-15 incubators/site) with five incubators
remaining in the hatchery to act as controls.
7. Conduct hydraulic sampling at salmon egg incubation sites. Approximately 10-15
samples will be obtained at each of up to ~5 sites.
8. Prepare interim 2010-11 and final 2011/12 reports incorporating assessment results,
conclusions and recommendations.
|Regional Watershed||Vancouver Island South|
|Sub-watershed if known||Cowichan|