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Howard Hanson Dam

Howard Hanson Dam And The Green River Reservoir

Howard Hanson Dam spans the Green River approximately three miles upstream from Tacoma Water’s Headworks diversion dam, where water from the Green River is diverted by Tacoma Water. The Howard Hanson Dam was built in 1961. The U.S. Army Corps of Engineers (Corps) operates the dam, controls water levels in the reservoir, and regulates flow in the Green River for flood control in the winter and flow-augmentation during low-flow periods (typically late summer through fall).

Tacoma Water, the Regional Water Supply System (RWSS) and the Corps are working in cooperation on the Howard Hanson Additional Water Storage Project. This project – a component of the Second Supply Project – increased the amount of water stored behind Howard Hanson Dam for use as municipal supply by increasing the surface elevation from 1,147 feet (above sea level) to 1,167 feet. The stored volume of water increased by about 75%.

Concurrent with this increased storage volume, a new downstream fish passage facility is being constructed to enhance survival and passage of out-migrating juvenile fish. This facility will allow juvenile salmon to safely pass downstream following their natural outmigration pattern. The downstream fish passage facility is a challenging project, and the Corps  – with involvement from key regulatory agencies and Tacoma Water  – continues to evaluate the best solution to address these challenges. 

The completion date for the downstream fish passage is not yet known, however construction is tentatively scheduled for 2018. With Tacoma and its partners' fulfillment of obligations under the Additional Water Storage Project and the Corps and resource agencies' approval, storage for municipal use began in 2007.  This water has been used as a critical part of the water supply of Tacoma and the RWSS, ensuring water is available to the region when it is most needed.

More information 
U.S. Army Corps of Engineers
Howard Hanson Dam 
Additional Water Storage Project
Green River Basin Map