Overview of Fish and Fish Habitat Resources, and Aquatic Ecosystem Flow Requirements in Trout Creek
Chilibeck, B. (2005). Trout Creek Water Use Plan Fisheries Report . Northwest Hydraulic Consultants Ltd. . Vancouver: Ministry of Environment.
Trout Creek, as the second largest tributary watershed to Okanagan Lake, provides domestic and agricultural water supply, as well supporting important sport fish – notably rainbow trout and kokanee. Water storage and intake water diversion result in altered stream flows. As a result, there are over 13 km of stream channel in the lower reaches of the creek below the Summerland intake which have reduced stream flows. These reduced flows decrease the amount of suitable, available habitat which can result in reduced productivity and overall numbers of fish.
Historical water use practices resulted in conflicts between the District of Summerland, and Fisheries and Oceans Canada and the Ministry of Water, Land and Air Protection Fisheries staff. Using the provincial water use planning process, a supportable documented plan has been developed to ensure fish and fish habitat are protected, and a secure water supply is ensured. Part of the process has been to examine available data, analyze and determine functional relationships between measures and conduct a comparative study or trade-off analysis. For Trout Creek, the primary measures are water and fish habitat.
In order to provide a rationale for the assessment of stream flows for fish in the Okanagan, fundamental flow principals have been developed. These detail naturalized, conservation, optimum and baseflows which are important measures relating back to productivity of fish habitat. Estimates for naturalized and conservation flows at the District of Summerland intake were developed in previous studies and optimal and base flow results were developed based on the analysis of test sections of habitat in lower Trout Creek. The primary fish performance measure was rainbow parr 1+ rearing habitat which was estimated using weighted usable widths (WUW), and a secondary measure was kokanee spawning and incubation habitat.
Naturalized stream flows have been calculated for the Trout Creek Watershed in previous studies as ranging from 2.5 m3/s to 2.9 m3/s, with the applicable naturalized mean annual discharge (MAD) at the District of Summerland water system intake being estimated at 2.54 m3/s. Conservation flows are based on percentages of MAD and are estimated to be between 5.09 and 0.51 m3/s depending on the month of the year.
Weighted usable width (WUWdv) and % weighted usable width (%WUWdv) were calculated for the range of transect flows. Stream flows from 0.019-2.811 m3/s at the canyon site and from 0.022-4.909 m3/s at the lower channel site for rainbow parr habitat were used. Flows ranging from 0.015-1.664 m3/s at the canyon sites and from 0.032-3.251 m3/s at lower channel were examined for kokanee spawning-incubation habitat.
Correlations for all sites were strong and good functional relationships were developed through regression and curve-fitting techniques for the rainbow trout 1+ rearing habitat. A stream flow that appears to maximize available habitat was estimated at 1.4-1.5 m3/s, approximately 48-52% MAD, for the range of stream flows investigated. The correlation and functional relationships for WUW and stream flow were also strong for the kokanee spawning habitat. However, an optimum flow for kokanee spawning-incubation habitat could not be identified for the canyon site. An optimum flow for kokanee spawning and incubation is estimated at 0.8 m3/s, approximately 28% MAD, over the range of flows surveyed for the lower channel site.
Camp Creek is a tributary of Trout Creek with a relatively natural flow regime and a real- time Water Survey of Canada hydrometric gauging station near its mouth. This provides an opportunity to estimate naturalized flows in Trout Creek on a real-time basis by using a multiplier to scale up from the relatively small Camp Creek sub-basin to the larger Trout Creek Watershed. Multipliers between 6 to 14:1 were reviewed to examine their representativeness of estimated naturalized flows for the Trout Creek watershed, as well as potential reduction in habitat as estimated by WUW.
Results indicate that the lesser of either a 10:1 Camp Creek multiplier or the conservation flow standard will provide similar amounts of habitat at either site. Reductions to lower Camp Creek multipliers will reduce the amount of suitable habitat for rainbow parr in Trout Creek. Absolute quantitative losses of habitat resulting from changes within the envelope of expected minimum flows in the proposed Trout Creek water use plan could be relatively large. These losses in WUW depend solely on multipliers selected during contemplated in- season flow adjustments. At the riffle site in the lower reach, losses of suitable rearing habitat are significant, but more importantly, reduced migration flows for kokanee may develop that would limit their access to spawning habitat.
As noted, weighted usable width and other measures are simple metrics for productive fish habitat, and other factors potentially influenced by stream flow should be considered along with physical habitat. Considerable negative impacts to habitat quality and productivity could result from reduced stream flows in Trout Creek. These impacts include increased solar heating and temperature impacts, loss of productive benthic invertebrate habitat and reduced drift (food), reduced cover and increased predation, increased stress and disease with reduced survival. Quantitative fish biology and synoptic study of individual fish, their growth and health is required to better assess the critical elements of physical habitat, food and nutrients, and water quality that constitute productive fish habitat in Trout Creek, and how these habitat elements are interrelated and affected by stream flow.
The water use planning process used limited biological and hydrological data. No directed biological studies were undertaken to determine actual fish utilization in lower Trout Creek (e.g. rainbow trout parr), and considerable uncertainty surrounds the spawning distribution and habitat use of kokanee. A critical shortcoming of the assessment and analysis of fish habitat is the reliance on the habitat characteristics and analysis results of a single riffle site in each of the canyon reach and the channelized reach of the lower system. Additional sites should be selected and monitoring stations benchmarked for consistent application of sites and sections. Analyses should also investigate natural, undisturbed pool-riffle macrohabitat features in the middle watershed above the intake and below Thirsk reservoir to develop flow-habitat measures for these reaches. Physical and flow-related barriers in the creek should be reviewed to ensure adequate access or extended access to utilize all available habitats – especially for kokanee which may have flow-limited access to spawning habitats.
In concert with the biological work, a hydrometric station to collect real-time stream flow and temperature data should be installed in the lower reaches of the creek below the water intake. Consistent gauging and flow records are vital if meaningful flow-habitat investigations are to be considered in the future. Finally, water quality improvements specifically related to reducing suspended sediment from the continual seepage-related slides within the upper canyon reach should be reviewed, and concepts and costs prepared to remediate the issue.