Water Stewardship Information Sources
| Citation | Robertson Environmental Services Ltd. 2010. Tyson Creek Hydroelectric Project: Sediment Impact Assessment. Prepared for BC Ministry of Environment. |
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| Organization | Ministry of Environment |
| URL | https://a100.gov.bc.ca/appsdata/epic/documents/p313/d34839/1345584202610_fbbafe7b2834d79d2caa1ffaa7095de2206cf5409f83f6ffa5b8982d5f07cc09.pdf |
| Abstract/Description or Keywords | In February 2010, the Tyson Creek Hydroelectric Project experienced a sedimentation incident related to erosion of a delta by channels feeding Tyson Lake. While the incident was not witnessed as the lake surface was ice covered, high turbidity in Tyson Creek was noted during an overflight of the area by the Ministry of Forests and Range. The erosion appeared to take place while the lake was drawn down to 10 m below natural levels. The incident resulted in water exceeding BC Ambient Water Quality Guidelines being discharged from the tailrace for a short time into Tyson Creek, which then flowed into the Tzoonie River and Narrows Inlet estuary. As a result, the project was shut down to allow water quality to improve within Tyson Lake and to allow the lake to refill. The project began operating within natural lake levels in late May 2010. The Ministry of Environment, Water Stewardship Division, requested that an assessment of the impacts of the sedimentation incident be completed. Field work to assess impacts was completed for some species/groups of concern in 2010. This report includes the results of the field work and an assessment of the impacts of the incident to terrain, fish, amphibians, birds, mammals, plants and the marine environment. The following is a brief summary of the work that has been undertaken to aid in the assessment of impacts and a summary of the key findings. Terrain Tyson Lake was visited on March 23 and August 26, 2010 and a description of the geologic setting and mechanism of the February 2010 event was presented. The sedimentation event was found to be due to gully erosion in the lakehead delta following the initial drawdown of Tyson Lake. Fish, Water Quality and Plankton Data have been collected on Tyson Lake, Tyson Creek and the Tzoonie River since the incident. Assessments have included: 1. Assessment of salmonid spawning area and sampling of in-gravel conditions on the Tzoonie River mainstem below Tyson Creek; 2. Identification of any resulting deposition and build-up of settled fines in areas that may impede/degrade salmonid and invertebrate habitats; 3. Addressing suspended sediment concentrations within the lake basin using vertical profile sampling. Some of the results have already been submitted to MOE and DFO in a memo (Bates 2010). No increased deposition of fine sands and silts within gravels downstream of Tyson Lake was noted. Observations of the material from the Tyson Lake event suggest the materials suspended and discharged were small and likely stayed in suspension as the discharge waters were mixed and transported downstream. There was no evidence that supports the hypothesis that this material “dropped” or settled out of suspension in significant and potentially detrimental volumes. Fish rearing habitats showed no outward signs of degradation that may have been related to the Tyson Lake turbidity event. There was no observed, measurable build-up of fines downstream of the Tyson Creek confluence that could be directly linked to Tyson Creek Hydro. It was concluded that any initial, settled inputs would have been mobilized and removed from the area with increased river discharge. Vertical profile sampling in Tyson Lake in August 2010 showed that the concentration of total suspended solids was below the minimum detectable level within all profiles. Plankton hauls were completed in August 2010 and showed that the lake continues to support a zooplankton community dominated by Leptodiaptomus spp. |
| Information Type | report |
| Regional Watershed | Howe Sound & Sunshine Coast |
| Sub-watershed if known | Tyson Lake |
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| Comments | |
| Project status | complete |
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