Surface water and groundwater interaction in the Fortune Creek watershed: implications for fish protection and water management (Year 3)

Fortune Creek is a regulated system that supplies water to approximately 4,500 residences in Armstrong and the Spallumcheen Valley. The creek provides habitat for resident rainbow trout, juvenile coho and Chinook salmon. Due to low flows in the summer, water temperature often becomes lethally warm to salmonids. A three-year project was approved in principle by the Pacific Salmon Foundation in May 2007. The objectives were:

1) to understand surface water and groundwater interactions, and their relationship to fish needs; and

2) to assess impacts of various management strategies on fish protection and human needs.

Work in the first year (2007/08) used several techniques to quantify surface water and groundwater interactions. The objective in the second year (2008/09) and the third year (2009/2010) was to assess the relationships between groundwater flow regimes and specific fish habitat and population indicators. Fish habitat quality indicated by flow rate, temperature, cover and water chemistry were monitored along the whole creek. Fish enumerations were used to quantify temporal variations in fish populations, and their relations to groundwater discharge and water temperatures. Statistical analysis of salmonid distribution in relation to habitat indicators indicated that high water temperatures limit juvenile salmonid use of Fortune Creek. Low and erratic stream flows limit rearing by drying out the shaded upper reaches and causing water temperatures to escalate in the lower reaches. Groundwater discharges to the stream throughout the valley bottom. However, no localized thermal refugia were identified and groundwater cooling of the stream is too small to provide thermal relief for salmonids. Maintaining thermally suitable habitat for salmonids could be achieved with increase shade, especially on select reaches. Several options exist for using in-stream flow to maintain temperatures ranging from using flows above 0.1 m3/s in the absence of shading, to potentially lower values with strategic shading.