John Day Dam Seismic Evaluations
John Day Dam was built between 1958 and 1971 as part of the Columbia River Basin system of dams. This major hydroelectric dam (2,160MW) spans the Columbia River east of The Dalles, Ore. The dam includes 16 turbine units totaling 2,160MW, a 1200-foot-long spillway with a capacity of over 2 million cfs, a 100-foot-high navigation lock - the highest lift in the United States - as well as fish ladders along both sides.
HDR geotechnical and structural experts were assembled to perform a Seismic Safety Review (SSR) for John Day Dam. Several structures were identified as potentially deficient and the SSR recommended additional evaluations occur for these structures. The team worked with USACE to prioritize the features for further evaluation and requested that a Phase 1 evaluation be performed on identified structures to assure the continued safe operation of the dam following an earthquake for the next 50 years of the structure life.
The Phase I Special Studies, Seismic Safety Evaluation was performed to determine if the project features identified in the SSR would survive a maximum credible earthquake (MCE) event without collapse. The work tasks included a site-specific seismicity review and ground motion development; and seismic stability analyses for various facility features including the North Embankment, a Navigation Lock (Navlock) downstream gate monolith, a Navlock gravity monolith, a Navlock downstream gate tower, the North Non-overflow Dam, a typical spillway monolith, and the powerhouse superstructure.