Water Stewardship Information Sources
| ID | 1244 |
|---|---|
| Citation | McHugh and Soverel, 2013. Lower Bridge River Aquatic Monitoring. Year 2012 Data Report. Bridge Seton Water Use Plan. Prepared for St'at'imc Eco Resources, Ltd. and BC Hydro for submission to the Deputy Comptroller of Water Rights, August 2013. |
| Organization | BC Hydro |
| URL | https://www.bchydro.com/content/dam/BCHydro/customer-portal/documents/corporate/environment-sustainability/water-use-planning/lower-mainland/brgmon-1-yr1-2013-07-31.pdf |
| Abstract/Description or Keywords | Historically, the Bridge River Valley was a thriving, productive river valley that harbored a rich and abundant diversity of aquatic and terrestrial life. This diversity contributed vast benefits to local and regional culture, society and the environment. These benefits were partially the result of interconnectedness between the headwaters of the Bridge River and the confluence of the Fraser River. In 1948, the interconnectedness was broken by the building of Mission Dam, and in 1960 the system was fully fragmented by the finalization of Terzaghi Dam. Terzaghi dam blocked off all flow into the Lower Bridge River (LBR) between 1960 and 2000, converting approximately 4km of its uppermost reach from aquatic to terrestrial habitat. During this time period, the St’at’imc First Nation and the Bridge River Band and others raised environmental concerns about the lack of water released from Terzaghi Dam. To address these concerns, a long term monitoring program was designed that would test two main flow releases (Trials 1 and 2) against a zero-flow baseline scenario, which represented the previous 40 years. The zero flow was classified as a Pre-Trial baseline and data were collected from 1996-2000. Trial 1 was an annual water budget of 3 m3 s-1, which was implemented from August 2000 to April 2011; Trial 2 is an annual water budget of 6 m3 s-1, which was initiated in May 2011 and will be implemented for 4 years (until April, 2015). Data from this monitoring program is used to inform the management of the Lower Bridge River flow regime, and a future water use decision. Following the flow trials, St’át’imc Nation, the Bridge River Band, BC Hydro, regulatory agencies and other stakeholders will work together to determine a long term flow release strategy for the LBR. A quantitative comparison of the two flow releases relative to the baseline will occur, with the optimal hydrograph being chosen. This process will begin in April, 2015. The existing LBR aquatic monitoring program is scheduled for an additional 6 years, however this is conditional on the outcome of an interim review). following the water use decision and implementation of the flow release strategy. In order to inform any management decisions, a suite of biotic and abiotic aquatic indicators were chosen and are explained in detail within this report. The main purpose of the program in 2012 was to continue monitoring the influence of the flow release from Terzaghi Dam on fish resources and the aquatic environment in Reaches 2, 3 and 4 of the Lower Bridge River. Four monitoring activities were conducted as part of the monitoring program: 1) constant temperature and water stage recording; 2) water chemistry, aquatic invertebrate diversity and periphyton accrual during fall; 3) sampling to monitor juvenile salmonid growth; and 4) a fall standing stock assessment for fish distribution and relative abundance indices. In addition, a rampdown monitoring component was integrated into the Lower Bridge River Aquatic Monitoring Program during the summer and fall seasons. The main findings from this year are consistent with past years in the flow trial experiment. Broadly, the continual water release from Carpenter Reservoir has altered the physical habitat and associated ecological, social and cultural benefits. Relative to pre-release (i.e., baseline) conditions, the seasonal temperature regime was modified, and the wetted area of the river was observed to be larger. Since the flow trial began, these effects were observed most acutely in the upper reaches (i.e., Reaches 3 and 4) and less in Reach 2 due to the influence of the Yalakom River inflows , groundwater and the differing channel morphology. Specifically, water chemistry parameters for 2012 were similar to those reported in previous non-pink salmon spawning years (across the flow trials) and concentrations were within the water quality guidelines established by British Columbia. Periphyton accrual increased as the fall season progressed, and a sharp increase in periphyton biovolume was observed in November. The invasive algal species rock snot (Didymosphenia geminate) was prevalent within the LBR at this time and may explain this increase. An increase in aquatic invertebrate biodiversity during 2012 versus other study years suggests a flow regime change may have positively affected the invertebrate community structure. The mean size of fish for each reach was analyzed during the late summer and fall seasons. Size was slightly smaller than 2011, but was overall similar to flow Trial 1 (for non-pink years). Fish density, relative abundance and spatial distribution derived from standing stock data followed similar patterns across the reaches in 2012 as during the previous flow trials. However, salmonid biomass was on the low side of the ranges observed within the 3 m3 s-1 and 6 m3 s-1 trials. Reach 4 had the highest biomass estimate for the eleventh consecutive year since the flow trials began. Reach 3 had a higher biomass estimate than Reach 2, but was lower than biomass estimates observed under baseline (no flow) conditions. This trend has also been observed since the flow trials began. The reasons for these observed parameter changes and the differences between flow trials are varied and uncertain. However, they are likely influenced by the changed thermal regime of the river, habitat alterations due to differing flow regimes, and nutrient inputs from pink salmon spawners. In addition, there are certainly other influences upon the aquatic ecosystem that are outside the scope of this monitoring program. |
| Information Type | report |
| Regional Watershed | Fraser |
| Sub-watershed if known | Bridge River |
| Aquifer # | |
| Comments | |
| Project status | complete |
| Contact Name | Coldstream Ecology Ltd |
| Contact Email | [email protected] |