Howard A. Hanson Dam

Howard A. Hanson Dam
Howard A. Hanson Dam (rear)
Location	King County, Washington, USA
Construction began	1959
Opening date	1961
Operator(s)	U.S. Army Corps of Engineers
Dam and spillways
Impounds	Green River
Height	235 ft (72 m)
Length	675 ft (206 m)
Width (crest)	23 ft (7 m)
Width (base)	960 ft (292 m)
Spillway type	Service, controlled
Spillway capacity	107,000 cubic feet per second (3,000 m3/s)
Reservoir
Creates	Howard A. Hanson Reservoir/Pool
Total capacity	106,000 acre·ft (131,000,000 m3)
Catchment area	220 square miles (570 km2)

Howard A. Hanson Dam is an earthen embankment dam on the Green River, 21 miles (34 km) east of Auburn, Washington. The dam was completed in 1961 and its primary purpose is flood control along with water supply for Tacoma, Washington.

After the dam's reservoir reached record levels in January 2009, the U.S. Army Corps of Engineers discovered seepage in the right abutment of the dam, leading to efforts to mitigate a potential flood. Improved drainage works were completed in October 2011 and although studies are still underway, the dam was declared safe to maintain its maximum reservoir level.

The Green River Valley was settled in the 1850s and became a notable farming area, until an aphid infestation destroyed the large hop crop in 1890. Since then, the area mainly consisted of dairy and berry farms, but farmers had to cope with yearly floods. These floods would lead to log jams, redirecting the Green and other rivers. Sometimes farmers would clear log jams with dynamite which led to the flooding of other farms. To deal with the matter, the Associated Improvement Clubs of South King County was formed in 1926. The association created several dikes and repaired river courses but they would soon realize more help was needed.

It was not until 1936 that community leaders, citizens and with additional effort by Congress, the U.S. Army Corps of Engineers (USACE), Seattle District began to search for a suitable flood control project site on the Green River. The selection was delayed by the Second World War and finally in 1949, Eagle Gorge was recommended to Congress as a site for a dam and reservoir project.

In 1955, funds were appropriated for the project; Congress gave $37 million, Washington State $1.5 million and King County provided $500,000. Construction on the dam which included the relocation of 13 miles (21 km) of the Northern Pacific Railway began in February 1959. During construction in December 1959, the last devastating flood occurred on the Green River; damaging homes and removing topsoil from farms. Despite this, the dam was completed almost five months ahead of time on Christmas Day, 1961. The completion of the dam ended a 70-year era of flooding in the Green River Valley and by 1996, the dam had prevented an estimated $694 million in flood damages.