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West Thompson Lake Flood Risk Management Project

West Thompson LakeThe dam at West Thompson Lake is located in Thompson on the Quinebaug River, about 1,000 feet upstream from the junction of the Quinebaug and French rivers. It is three miles north of Putnam on Route 12. The project consists of an earthfill dam with stone slope protection 2,550 feet long and 70 feet high; an earthfill dike with stone slope protection measuring 1,650 feet long and 30 feet high; a gated horseshoe shaped concrete conduit 254 feet long and 12 feet in diameter; and a side channel concrete chute spillway with a 320-foot-long L-shaped concrete weir. The weir’s crest elevation is 19 feet lower than the top of the dam.

Construction started in August 1963 and was completed in October 1965. The relocation of 3.3 miles of town roads was required. The cost of the project was $7 million. The project has prevented $56.4 million in flood damages since it was built (as of September 2011).

West Thompson Lake contains a 200-acre conservation pool that has a maximum depth of 13 feet. The flood storage area of the project, which is normally empty and is only utilized to store floodwaters, totals 1,250 acres and extends seven miles upstream. The project and associated lands cover 2,033 acres in both Thompson and Dudley, Massachusetts. West Thompson Lake can store up to 8.34 billion gallons of water for flood control purposes. This is equivalent to 6.5 inches of water covering its drainage area of 173.5 square miles.

The Reservoir Control Center (RCC) is the "nerve center" for the New England flood control dams such as West Thompson Dam. Using radio and satellite communications, the team constantly monitors river levels and weather conditions that influence flood control decisions.

Corps personnel, in conjunction with RCC regulate the amount of water released downstream by raising or lowering the two gates located in the control tower at the dam. In a time of high water, the gates are lowered in order to hold back the water, only to be released when downstream river conditions begin to recede. The Reservoir Control Center provides information about river flows, dam operations, snow depths, recreational water releases, and more.

For more information call (860) 923-2982 or visit the website at:

- Updated: May 4, 2021