KAHLOTUS, Wash. – Recent routine inspections at Lower Monumental Lock and Dam resulted in an important dam safety discovery, a trunnion on Spillway Gate 3 had friction levels outside of the safe operating range.
Trunnions are pivots that allow the spillway gates to open and close. They are integral to the operation of a dam’s spillway gates, which in turn is integral to the safe operation of a dam. If too much friction exists, it puts extra stress on the gate when it is moved. If trunnion friction levels are too high, it can lead to a failure of the spillway gate. As a result, Gate 3 was taken out of service to continue the safe operation of the dam.
Upon this discovery, an inspection was ordered for the remaining seven spillway gates at Lower Monumental. The inspection discovered that four additional gates (1,2,6 and 7) were experiencing the same issue, and subsequentially taken out of service. Engineers and maintenance crews have developed a remedy by drilling grease ports on the trunnions. These ports will allow crews to grease internal bearings that were originally designed to be greaseless. This remedy was applied and tested on Gate 3 which lowered friction levels to a safe operating range.
Currently, work crews are drilling grease ports on the trunnions of the remaining affected spillway gates. This work is projected to be completed by May 30, 2022. As a result, we have closed dam crossings for the safety of both work crews and the public. While the work is ongoing, Lower Monumental will adjust spill operations for fish passage and use the remaining spillway gates to safely pass juvenile salmon. Due to the cold start to the spring, very few fish are migrating at this time. This provides the opportunity to perform the required maintenance on the gates with minimal impacts to fish. As the gates are repaired they will be returned to service.
As professional operators of multipurpose civil works infrastructure, the engineering and science behind our ability to predict, maintain and repair is constantly increasing. This is one example where we are taking lessons learned from across the industry and proactively heading off potential dam safety issues so we can continue to deliver value to the Nation.
Public dam crossings are currently available at Lower Granite Lock and Dam and Little Goose Lock and Dam.
For more information about dam crossing visit https://www.nww.usace.army.mil/Missions/Recreation/Dam-Crossing/ or call 1-888-AM-INFO (1-888-326-4636).
Release no. 22-027