Oregon needs to raise Hagg Lake dam for fear of earthquakes

Published 14 May 2009

In Oregon they expect the Big One — a massive earthquake — sometime in the next fifty years; one measure of preparation is to raise the height of dams so that earthquake-generated waves in the reservoirs behind the dams would not spill over and flood the neighboring territory

A massive earthquake that might not hit the Pacific Northwest for fifty years could cost Washington County, Oregon, residents a lot of money much sooner.

This is because the earthquake prediction is affecting the cost of raising Scoggins Dam at Henry Hagg Lake, where most of the county plans to turn to for water over the next fifty years.

The Oregonian’s Jill Rehkopf Smith writes that a consultant’s report will soon provide cost estimates for four new dam-raise options, said Tom VanderPlaat of Clean Water Services, which is leading the project. Any of these options will be more expensive than originally expected, he said.

Last spring, new studies led scientists to predict that a level-9 quake would occur in the Pacific Northwest sometime in the next 300 years, with a 10 to 14 percent chance it will happen in the next 50. The Bureau of Reclamation, which operates Scoggins Dam, began studying how it would hold up during such a quake and will have a report ready in October. A conceptual dam-raise design it had created earlier was inadequate, VanderPlaat said.

Meanwhile, the Tualatin Basin Water Supply Project Partners hired Kleinfelder — an engineering, environmental, and construction management firm — to come up with alternative, earthquake-proof designs for raising the dam. The partners include Beaverton, Hillsboro, Tualatin Valley Water District, and Clean Water Services, which is beginning to notify the public about the change in plans. Representatives have met with Community Participation Organizations about the four dam designs being considered.