Sean C. Morgan
Of The New Era
The timing of the U.S. Army Corps of Engineers’ inspection of Foster Dam in June mostly had to do with flood season, the local Corps manager told local residents and business owners last week.
“We have to do it at a time of year we won’t be needing to use those spillway gates,” said Erik Petersen, operations manager for the Willamette Valley Project.
Petersen gave an update and answered questions about the Foster Dam repair project at the regular Rotary Club meeting on Aug. 12.
In response to questions, he explained why the Corps inspected the dam in June, during the recreational season, instead of another part of the year when the lake level is lower. The June inspection uncovered damage to the dam’s spillway gates. As a result, the Corps had to draw down the lake in mid-July to more closely inspect the gates and grease the trunnion bearings that serve as hinges for the gates. That action effectively ended the season for many local waterskiers and other boating enthusiasts.
While down, the boat ramp at Sunnyside Park was barely usable while the ramps at Gedney Creek and Calkins Park were above the waterline.
After the inspection and repair work earlier this month, the Corps was able to increase the lake levels high enough to allow the use of the ramps at Sunnyside and Gedney Creek. The Calkins Park ramp remains out of service.
In June, the likelihood of needing to use Foster’s spillway gates is minimal, Petersen said. The lake has low inflow, and the Corps can lock out a gate during inspection. The inspection is made about once every five years at a cost of approximately $40,000. During the inspection, the Corps brings in experts who look at the hydraulics, the steel structure, bulkheads, the operating gates, the spillway gates and more.
Petersen said he is often asked why the dam hasn’t been maintained, but the bottom line is that the Corps has maintained the dam.
“We know a lot more now than we knew back in 1968,” Petersen said. If the dam were designed today, it would be designed differently.
Combined with the aging infrastructure, the main cause of the breakdown at Foster Dam is a lack of even lubrication in the trunnion bearings along with structural members that weren’t as strong as they needed to be, he said.
The top structural members of three of the four gates have buckled, most likely as a result of friction in the trunnion bearing, Petersen said. That has compromised the load-bearing capacity of the gates.
“Living with the gates in the condition they’re in was unacceptable,” he said. Two of the gates are now completely out of service.
With the intermediate maintenance and repairs, with little risk, the dam can handle a lake level of 622 feet above sea level, he said. The Corps’ goal was “to try to salvage the recreation season, whatever we could.”
Full pool is 637 feet above sea level.
Full repairs will cost about $7 million, Petersen said. The Corps has secured about $4 million to cut out the top structural beams on each gate and replace them with stronger metal.
Petersen is confident that the rest of the repairs will be funded at the beginning of the fiscal year, Oct. 1, he said. With that funding, he hopes to have the dam repaired before the beginning of the flood season in the winter.
Foster Dam is a re-regulation dam that provides up to 20 megawatts of electrical power and will soon provide drinking water to Sweet Home. It has two electrical generation units and four spillways. The Willamette Project’s 12 dams include a total of 17 generation units with 28 spillways.
Foster Lake ranks third among the Willamette Project dams for recreation, behind Detroit and Fern Ridge reservoirs, Petersen said, but summer recreation is just one of the Corps’ missions.
“Around the valley, our biggest mission is flood damage reduction,” Petersen said. The dams prevent upward of $1 billion per year in flood damage. Without it, the valley would look much different than it does now.