Sean C. Morgan
Foster Lake will be a couple of feet shy of a full pool this summer.
The U.S. Army Corps of Engineers announced last week that the lake will be held near an elevation of 635 feet above sea level throughout the summer. It’s usually a foot or two higher.
This operation is part of a yearlong study that will help the Corps determine how to better operate Foster Dam to improve the survival of spring Chinook, winter steelhead and other fish species in the South Santiam River Basin. The study will collect information about fish behavior, density and movement in the reservoir, and fish passage through the dam.
Most particularly, the steelhead appear to migrate out June through September, based on an Oregon Department of Fish and Wildlife study, said Corps Spokesman Scott Clemans. That means the Corps needs the weir, a notched wall segment installed in one of the dam’s spillways to direct the passage of fish, in place during the summer to study migration.
As part of the study, the Corps also has installed detectors and sonar transducers to monitor the reservoir, to find out when the salmonids, steelhead in particular, begin showing up, what they do and how they do it, whether they choose to go over the weir or through the turbines, Clemans said.
“The main reason we need to keep it a foot or two low, we just don’t have the resources to operate the fish weir at full pool,” Clemans said. The Corps doesn’t have enough stop logs to get the fish weir high enough for full pool.
“We can almost make it but not quite,” Clemans said.
The Corps anticipates very little impact to recreation users. All boat ramps and Edgewater Marina will still be accessible. Linn County Parks will install extra dock sections at the Sunnyside and Lewis Creek moorages to extend them into deeper water.
At all water levels, but especially when below normal, boaters should be aware of and watch carefully for underwater hazards.
For many years the Corps has conducted a special operation at Foster Dam in April and May. Reservoir regulators hold the water level between 613 and 616 feet, allowing the surface water where juvenile steelhead usually swim to gently spill through the weir installed in one of the dam’s spillway bays.
However, recent Oregon Department of Fish and Wildlife research in the South Santiam River shows that many juvenile fish – particularly steelhead – are migrating downriver outside of that April to May period. Corps juvenile passage tests in May 2012 also proved that fish can very successfully use the weir when the reservoir is at or near its usual summer elevation.
“We hope this study will give us a better sense of how we can best operate the dam to ensure those fish survive passing the dam as they journey to the sea, and return to the South Santiam Basin as adults in a few years,” said Corps fishery biologist Fenton Khan, who is leading the study. “We appreciate the understanding and support of the local community and reservoir users as we work to achieve that goal.”
What happens in the future will depend on what researchers find, Clemans said. Likely, the Corps will probably add more stop logs and test at full pool.