SALMONID DISTRIBUTION IN RELATION TO STREAM TEMPERATURES IN FORTUNE CREEK, BRITISH COLUMBIA – THE INFLUENCE OF SURFACE AND GROUNDWATER INTERACTIONS

Surface water and groundwater interaction in a stream can greatly influence the physical and chemical characteristics of stream water (i.e. temperature, dissolved oxygen etc.), and consequently aquatic biology. In an attempt to quantify whether surface water and groundwater interaction affects salmonid use of Fortune Creek in the North Okanagan, British Columbia, the relationship between water temperatures and salmonid occurrences was explored. Over the summer of 2008, temperature data were collected at 22 sites along the creek, and weekly salmonid counting was conducted at eight sites. Piezometers were installed in the streambed in a known groundwater upwelling area to examine how the hydraulic gradient changes over the summer as streamflow is reduced and groundwater pumping pressure increases.

Temperatures at the salmonid count sites were measured at 30–minute intervals in the air, the water, and at two depths below the streambed. The measurements in the streambed were intended to verify the presence of cool groundwater upwelling through the gravel. Piezometers were equipped with water level loggers and installed in the stream with the screen at 3 m below the streambed. In addition, a water level logger was installed in a nearby agricultural well to determine how pumping affects the hydraulic gradient in the creek. Water releases from a reservoir located on the headwaters of Fortune Creek were tracked along the length of the creek to assess whether they had an impact on stream temperatures. This data, together with water chemistry samples, was used to quantify mixing ratios of surface water and groundwater at several selected sites.

Salmonid counts of juvenile coho (Oncorhynchus kisutch) and Chinook salmon (Oncorhynchus tshawytscha) and rainbow trout (Oncorhynchus mykiss) were conducted weekly with baited minnow traps set over night. Preliminary results indicate that salmonids are absent in the lower valley bottom reaches of the creek during periods of high stream temperatures. Upper reaches of the creek, where temperatures are cooler, showed abundant salmonid numbers throughout the summer.