News Release Archive

Reclamation to Reevaluate Seismic Hazards at Scoggins Dam in Oregon

Media Contact: John Redding, (208) 378-5212, jredding@pn.usbr.gov
Larry Wolf, lwolf@pn.usbr.gov

For Release: June 03, 2008

The Bureau of Reclamation announced today that a technical review of Scoggins Dam concluded that further onsite investigations are warranted in order to evaluate the dam's ability to withstand the forces of a major earthquake. These investigations were prompted by a recent reevaluation of the seismic hazard in the region.

Scoggins Dam, which impounds Henry Hagg Lake, is about 5 miles southwest of Forest Grove, Ore., and located within a seismic area known as the Cascadia Subduction Zone. This area has the potential to experience very large magnitude earthquakes with long durations of strong shaking.

"Scoggins Dam is safe under normal operating conditions," said Larry Wolf, Reclamation Safety of Dams program manager, "but our first priority is public safety, and our risk assessment report and Dam Safety Advisory Team review indicate that the potential seismic hazards at Scoggins Dam are serious enough to require us to take a detailed look at the structure, its foundation, and the geological makeup of the area."

Reclamation will work with the Tualatin Basin Water Supply Partners to develop and perform a field exploration program for Scoggins Dam to examine how the existing facility would perform during a major earthquake and what actions may be necessary for the proposed expansion of the lake. Drill rigs will be mobilized at the dam this summer to collect data for use in these studies.

The study findings will be shared with Reclamation's project water users and with the local partnership that is pursuing the Tualatin Basin Water Supply Project. The partners are studying options for raising the height of Scoggins Dam to meet future water supply needs, and also working on a proposal to transfer title for the Tualatin Project to local water supply and management agencies.

"We will coordinate the seismic safety assessment process with the Tualatin Valley Irrigation District, the Joint Water Commission, Clean Water Services, and the other partners involved in the dam raise and title transfer proposals," Wolf said.

When completed in 1975, Scoggins Dam was designed and constructed to then-current earthquake standards. The Scoggins Dam technical review and subsequent investigations are part of a Safety of Dams Program which routinely evaluates the structural integrity of Reclamation dams under various conditions to identify potential public safety risks.

Scoggins Dam is an earthfill structure that is operated and maintained by the Tualatin Valley Irrigation District. Reclamation owns the structure and provides safety assessments and coordinates potential repairs with the TVID, the Joint Water Commission, and Clean Water Services.

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