Dam to get temporary fix
March 22, 2010 · 4:47 PM
By Steve Hunter
For The Courier-Herald
The U.S. Army Corps of Engineers revealed plans Thursday to extend a grout curtain as a temporary fix for the next several years as engineers design and construct a permanent fix to stop a leak through a damaged abutment next to Howard Hanson Dam.
The corps still needs to acquire federal funds for the proposed $44 million project that would add 650 feet in length to the grout curtain installed last fall to the dam north of Enumclaw on the Green River. The dam helps protect the cities of Kent, Auburn, Renton and Tukwila from river flooding. The corps spent $8.9 million last fall on the grout curtain.
“We may be looking at another flood season or more before we complete this,” said Col. Anthony Wright, commander of the Seattle district of the Corps of Engineers.
Wright presented an update about the Hanson Dam to local elected officials and the media at corps district headquarters in Seattle.
Local officials emphasized in a press conference after Wright’s presentation that Congress needs to act quickly to fund the extended grout curtain.
“Time is of the essence,” said King County Executive Dow Constantine. “Congress must address the need to move more quickly than what might be standard procedure for the corps.”
The corps expects to have the design for a permanent fix, such as a concrete cutoff barrier, by the end of June in order to apply for funding from Congress in 2012 to start the project.
“We’ll have perhaps another five flood seasons before it is complete,” Wright said about a permanent fix.
Wright said the expanded grout curtain would allow the corps to store more water in the Eagle Gorge reservoir behind the dam and could return the odds of flooding in the Green River Valley to the 1 in 140 chance when the dam operates at full capacity.
Wright emphasized the grout curtain would only serve as a temporary fix for the next several years and that a permanent fix still would be needed.
The abutment was formed nearly 10,000 years ago by a landslide. The federal government built the rock-and earth-fill Howard Hanson dam in 1961 next to the abutment to control major flooding in the Green River Valley.
Problems with water storage behind the dam were discovered by the corps when a 10-foot-wide depression formed on the embankment next to the dam after heavy rain in January 2009. The corps stored a record amount of water in the reservoir during that storm to prevent flooding.
The lack of heavy rainstorms this winter has kept the Green River from flooding.
Several alternatives are being looked at as far as permanent fixes. Wright said a design for a permanent fix would be ready in late June in order to meet deadlines by Congress to consider the project for funding in 2012. Wright did not yet have an exact cost for a permanent fix or an exact timeline of when construction would be completed. He estimated a permanent fix would cost several hundred million dollars.
“All the solutions we are looking at have a fairly lengthy construction period once funds are appropriated,” Wright said. “It would take several years for the fixes to be complete.”