Foster fix to start in 2 weeks

Sean C. Morgan

Of The New Era

The U.S. Army Corps of Engineers last week outlined its plans to repair the spillway gates in Foster Dam.

The Corps will hold a public meeting to present this information and answer questions from 5:30 to 7:30 p.m. on Oct. 28 at the Sweet Home Senior Center, 880 18th Ave.

The public can expect Foster Dam Road to be closed the week of Nov. 3 for an unspecified period, Public Affairs Specialist Amy Echols said. The public can also expect high water in the South Santiam River.

Foster Dam was completed in 1968 to function primarily as a re-regulation dam for Green Peter, said Erik Petersen, operations manager for the Willamette Valley Project. The dam also provides some storage capability and 20 megawatts of electricity.

Water mainly flows through the dam’s two turbines, passing through approximately 3,000 cubic feet of water per second each.

necessary, he said. The gates swing up and down on hinges called trunions.

The trunions are greased annually, and the gates are opened and closed to work the grease into the trunion, Petersen said. Every five years, the gates receive a more in-depth inspection.

“Engineers literally climb up and down those gates,” Petersen said. They take measurements and look down the structural beams for deformities. They inspect two gates at a time, so the cycle is 10 years.

In June, engineers discovered that the trunions were warping and buckling, Eriksen said, so the Corps scheduled additional inspections. In mid-July, the Corps lowered the lake level to winter pool, 613 feet above sea level, for further inspection and initial repairs.

The trunions were greased and the gates exercised to make sure the grease was uniformly distributed, he said.

The Corps was unable to run the inspections earlier in the year, Petersen said.

“In January, we might need those gates for flood damage protection,” he said. “We haven’t, in the past, discovered problems. We didn’t expect problems.”

The best time for inspections is when weather is dry, he said.

The Corps has two schools of thought on why the structural members are warping, Petersen said. One is that there may be “differentiated friction,” which means the two trunions that make up the hinges of a gate may have different levels of friction as they rotate, twisting the gate and structural beams as it opens or closes.

The thought is that “the original structural members were not designed considering trunion friction,” he said.

The second school of thought is that they weren’t designed to account for static or dynamic load levels on the gates.

Static load is the weight of the water in the lake pressing against the gates, he said. The dynamic load is the force applied to the gate when it is moved.

In a short period of time, the Corps has essentially reengineered the gate design to account for trunion friction and static and dynamic loading, he said. The Corps evaluated the stresses and will replace the structural beams with steel that can bear the anticipated loads.

The old structural beams will be cut out of the gates and the replacements welded into place, he said.

The contract for Gate One, the furthest north, has been awarded to Knight Construction of Dear Park, Wash.

“It was a firm that was able to demonstrate their ability to move in very quickly,” Petersen said. Speed is key as the Corps prepares for the coming winter season.

“Our initial phase is kind of two-fold,” Petersen said. “We’re acquiring three more stop logs as quickly as we can.”

Stop logs are metal beams lowered into the dam behind the gates. They are used to hold back lake water while a gate is open. The Corps already has four for Foster Dam. The stop logs will allow the Corps to open and repair a gate while keeping the lake at full summer pool of 637 feet above sea level.

Even during repairs, the Corps intends to operate the lake at full pool next summer, Petersen said.

Officials have been hesitant to promise this in case of something unforeseen.

“If everything goes as planned, I anticipate full pool,” Petersen said. “We’re working hard to that end.”

The Corps’ top concern is getting a gate working by January when the risk of flooding gets stars rising substantially.

The Corps will not be holding water back in Foster Lake during the repair period, Public Affairs Specialist Amy Echols said. Gates two through four will be opened enough to allow water to flow straight through at a pool level of 604 feet.

The river level will rise as the uncontrolled South Santiam River feeds the lake, Echols said. Green Peter is being drawn lower than usual to help slow the flow from the Quartzville area.

The South Santiam River will rise almost to the levels of the flood of 1996, approximately 30,000 cubic feet per second at Waterloo, Echols said, though, she added, it won’t cause the problems it did during that flood, with just the Santiam rising.

The February 1996 flood was a conjunction of a variety of factors, including saturated ground, warm wind, rain and melting ice and snow at low elevations.

Gate One will be functional by January and operating normally by late January when this kind of storm is more likely, Petersen said.

Among the valley’s other 13 dams, the Corps has similar problems at Dexter, where a couple of the dam’s seven gates are affected, Petersen said. Green Peter, with its greaseless bushings, shouldn’t have this problem though, he said.

The Foster repairs are costly in many ways, he said, including the price of the new stop logs, the hydropower that won’t be produced and the actual repairs.

Counting the work so far, the initial repairs will cost between $3 and $4 million, he said. The rest of the gates will take the cost up to $6 to $8 million.

Petersen said he is often asked why the Corps didn’t catch this sooner, he said, but “really it’s evidence our program works.”

The problems were found before it became an emergency, he said.