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Located 35 miles southeast of Seattle, Washington, the Howard Hanson Dam protects a population of 75,000 people and the fourth-largest continuous warehousing district in the United States, as well as two major seaports handling 4,000,000 containers at $75 billion per year.

A DAm In CrIsIsIn January 2009, the dam’s water level reached a record high. Sediment-laden seepage through the embankment reached alarming levels, and investigators discovered two subsidences in the dam. The U.S. Army Corps of Engineers (USACE) reclassified the dam as high-risk, putting Howard Hanson in the top 10 dams at risk of failure in the U.S.—with an estimated failure probability of one in three. An emergency grout curtain was installed, but the dam quickly needed a permanent fix.

rounD-the-CloCk repAIrsThe project’s joint venture team contracted Kleinfelder to provide construction quality control, project administration, geotechnical support, and onsite laboratory services to mitigate seepage in the right abutment of the dam, along with the two subsidence areas. With two USACE-validated laboratories and three USACE-trained project managers, the team maintained an around-the-clock schedule to perform drilling operations, drain installations, soil and material testing, installation of temporary shoring, and soil excavation—all within 110 days of project notice.

proJeCt results

In February 2012—one

of the top ten rainfall

events in the area’s

history—the dam repairs

performed as designed and

constructed. One of the

first projects completed

in the new USACE DSAC

Risk Management System,

the dam validated the

ability of the new program

to prioritize repairs and

minimize public risk.

location:Seattle, Washington

owner:United State Army Corps of Engineers (USACE), Seattle Division

howard hanson Dam repair