Every year, the U.S. Army Corps of Engineers pulls submerged debris from under the surface of Foster Lake at the dam.
This year, the Corps discovered a bigger problem than usual and has had to approach the cleanup in an unusual way €“ by putting a barge and crane onto the lake.
Normally, like it does at the other 12 dams in the Willamette Project, the Corps places a crane on top of the dam and dips debris out along the face of the dam, but an overabundance of debris this winter meant that debris had to be collected from the lake itself east of Foster Dam.
“We are doing a normal operations and maintenance project, a new approach to a normal business process,” Special Projects Coordinator Dianne Luiz said.
In the intake area of the dam are a pair of “pinstacks.” They are approximately 235 feet long. The pinstacks are pipes, 13 1/2 feet in diameter, running from the face of the dam to the power generators.
At the dam, the pinstacks are covered by “trash racks,” vertical bars spaced 6 inches apart. The trash racks prevent debris from entering the opening to the power generators.
Last year, Corps officials learned “shear pins” were breaking in the power generators, Luiz said. The shear pins are designed to break and close “wicket gates” when debris gets into the pipes.
The Corps has to shut down the generators to repair the system, Luiz said. The costs of the shutdowns include labor and lost power generation.
With repeated breakages, Luiz said, Corps officials determined something was going on and hired Northwest Maritime Industrial to complete a sonar survey and tell the Corps what is going on.
Northwest Maritime is an enterprise of Siletz Business Corporation, a branch of the Siletz Tribe.
“They said, ‘You have a pretty significant debris field in your forebay,'” Luiz said. The forebay is the area on the lake side of the dam.
The Corps hired Northwest Maritime to clean up the debris field beginning on March 2, Luiz said. The company will finish its in-water work on Thursday. Northwest Maritime used a crane to place pieces of the barge into the lake at Shea Point.
The crew placed large logs between the barge and shore, Luiz said. The barge was tied down, with a tug pushing from behind to keep the platform and logs steady while the crane moved onto the barge.
As of Friday, Northwest Maritime had removed four barges full of debris, equivalent to 30 dump truck loads at 8 cubic yards, Luiz said. It is stored temporarily at the north end of the dam.
In January, U.S. Army dive staff dropped a remote submersible into the lake to examine the trash rack, Luiz said. “We had some suspicions, but we just did that to get clear a picture.”
Friday, a Navy crew was able to get a submersible into the lake and get a look at the trash rack, Luiz said. The clarity was better, and officials were able to see two of the vertical bars were missing from the pinstack, explaining how debris was getting into the pinstacks and disrupting power generation.
Corps officials are working on a plan to fix the structure.
“This is the first time we’ve actually extended into the forebay,” Luiz said. “We will continue to monitor the success and results of this operation.”
The Corps is hoping an ounce of prevention now will prevent further unscheduled outages at the powerhouse, she said. “To get this amount (of debris), it should take years.”
“We do a great job of maintaining our facilities,” Luiz said. The Corps keeps its equipment running and maintains downstream stream levels well.
“Yet this debris field has been one of those things that’s not visible,” she said. Just like more visible maintenance, this “is an extension of our operation and maintenance of this facility, meeting our goals of flood damage reduction, power generation, recreation and fish and wildlife water quality.”
In addition to the usual wood debris, Northwest Maritime also has pulled out one bicycle, five tires, “a crazy amount” of different kinds of beer bottles, an anti-freeze bottle and car windshields.