Salmon jump the overshot gates at the McIntyre Dam, B.C.
A project by Associated Engineering is great news for sockeye salmon. For 90 years the fish migrating in from the Pacific Ocean and attempting to reach spawning grounds upstream in the Okanagan Riveo have been stopped at the McIntyre Dam.
Located near Oliver, the dam is a 1.7-metre high gated control structure that was built in 1954 to reduce flood impacts in the Okanagan watershed. It replaced a weir constructed in 1918.
In an effort to restore the salmon populations, the Okanagan Nation Alliance asked a team led by Associated Engineering to look at how the McIntyre Dam might be modified to allow the salmon to pass through to reach spawning habitat. The dam had undershot gates that were preventing fish from getting through, as was the force of the water. The dam was retrofitted with five automated overshot gates which create a waterfall effect and make it easier for the fish to leap the dam.
Studies show that adult salmon need water to be at a depth of 1.24 metres in order to jump one metre. As it was, the river below the McIntyre Dam did not provide enough depth so the solution was to construct a 1.8 metre rock riffle to impound water downstream of the dam. This pool gave the salmon enough depth to make the jump, and it also lowered the height of the jump.
Even while the new gates were just being commissioned in October 2009, salmon were already starting to accumulate around the foot of the dam, eager to prolong their journey. When the first two overshot gates were operated for a brief one-hour period, Rod MacLean, project manager at Associated Engineering, and his team saw five salmon successfully jumping over the gates. The next day the gates were tested for three hours and the engineers saw 100 salmon jump the dam. By the end of the week, 4,000 salmon had succeeded in commandeering the barrier and were free to reach new spawning habitat upstream.
In preparing the design for the changes to the dam, MacLean visited local museums, archives and government files to find information on how the original dam was constructed in 1917.