GLES was retained by the Nipigon District of MNR to design a walleye spawning bed on Bass Creek just north of Nipigon. The bed was to be located immediately downstream of a small (2m high) falls at the point where the creek flows into the Nipigon River just downstream of Ontario Power Generation’s Alexander Generating Station. During the May spawning period, high flows in the Nipigon River cause water to back up against the falls which results in a reduction in the local water velocity and a deposition of suspended soil particles on top of the existing spawning habitat located immediately downstream of the falls. Both have a direct impact on the spawning success of walleye at this site.

After conducting a site visit, obtaining a bathymetric survey (through Tulloch) and researching available flow and water level records a solution was proposed. The preferred alternative was to install a 10m wide defined channel immediately downstream of the falls.

The channel was confined with larger 1.2m diameter perimeter boulders. A base layer of broken rock, filled with Granular A was placed within the new channel to provide support for the actual spawning bed. A 500mm thick layer of preferred walleye spawning gravel/cobble was then placed over top of this layer. The top of the spawning bed was set at an elevation that would provide the ideal depth range for spawning walleye at the long term average May water level in the Nipigon River. The 10m width was chosen to provide ideal velocity conditions for spawning walleye at the water level imposed by the Nipigon River in May and the average May flow from Bass Creek. The May average flow for Bass Creek was estimated by comparing known historic flows from an adjacent gauged watershed and modifying them based on drainage areas.

In addition, low and high water level beds were included to accept spawning walleye under a range of water level conditions. Projects such as this require a variety of skills including biology, engineering and surveying to successfully complete. GLES has completed the design of various other spawning beds which have been successfully constructed and are currently in use by many fish species.