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Corps addresses poor water quality, increasing sediment at Northfield Brook Lake with proposed plan to de-water reservoir

Published Jan. 30, 2015

CONCORD, Mass. – The U.S. Army Corps of Engineers, New England District plans to take action to alleviate long-term negative water quality issues and reduce the ongoing sediment accumulation within the reservoir area (lake) of the Northfield Brook Dam in Thomaston, Conn.


The lake has been plagued with adverse water quality conditions requiring the Corps to routinely implement long-term closures of the swimming beach, often during the summer recreational season. The Corps believes the water quality conditions are increasing the potential for health concerns from waterborne illnesses as a result of high bacteria levels that exceed the state of Connecticut standards, and through the increasing incidents of cyanobacteria blooms.


The lake is on the Connecticut Impaired Waters List because it exceeds the water quality standards for recreational uses from elevated levels of E. coli from nonpoint and unknown source pollution. In addition, the sediment trapped behind the dam starves downstream aquatic habitats of needed naturally occurring sediment deposition and increases downstream erosion of the river channel. Increased sedimentation behind the dam reduces the storage capacity of the reservoir and must be removed. Historically, the Corps has needed to drain the lake to remove accumulated sediment.  


The Corps has the need to address the ongoing sediment buildup and the poor water quality issues within the reservoir area in a manner that will: 1) eliminate the impaired status of the impounded water within the reservoir area; 2) improve sediment management of the area behind the dam and allow a more natural run-of-the-river sediment transport; 3) increase the overall storage capability by eliminating the long term needs to remove sediment accumulation; 4) provide recreational opportunities; and 5) minimize the maintenance costs associated with management of adverse aquatic conditions within the federal flood control project.


The preferred method is to eliminate the permanent eight-acre lake (reservoir) behind the dam, and restore about 1,200 feet of the Northfield Brook within the reservoir area to a natural meandering channel. The action also would restore the riverbank to a riparian ecosystem and restore lost fisheries stream habitats. Following restoration of the waterbody, the remaining reservoir area would be established as recreational space for public use at the project.


Under flood conditions, the reservoir would be utilized for its authorized flood control purposes and store water to protect downstream communities from flood damage. The Corps would operate the project as a run-of-the-river flood control project during non-flood operations.


The alternative to permanently eliminating the lake is to temporarily dewater the lake and mechanically remove accumulated sediment. On completion of the sediment removal the lake would be allowed to refill and the project would continue to operate with a lake behind the dam. This would temporarily address the poor water quality conditions, but it is not a long-term solution and the lake would continue to act as a sediment trap. The lake conditions would deteriorate and the water quality issues and sediment accumulation would continue to be an ongoing resource management and recreational issue.   


The expected results of the Proposed Action would have short-term impacts to aquatic habitats from temporary increases of sediment loads into the water column as the water levels begin to reach the lower levels; and the eventual disposition of sediment onto fisheries habitat that exist immediately downstream.


The long-term impacts would be beneficial and result in re-establishing a flow regime closer to the original stream structure and restore the aquatic habitat to a natural riparian/riverine system after several decades of an artificial reservoir condition. It would eliminate the pool behind the dam which is an identified impaired waterbody. The action would result in beneficial impacts to river temperatures and oxygen levels for the Northfield Brook, and indirectly the Naugatuck River system, facilitate a more natural sediment transport, and restore habitat and downstream migration for fisheries, while allowing the Corps to continue to provide flood storage capabilities and recreational opportunities.


The Proposed Action is being coordinated with the following federal, state and local agencies: U.S. Fish and Wildlife Service; U.S. Department of Agriculture, Natural Resources Conservation Service; U.S. Environmental Protection Agency; Connecticut Department of Energy and Environmental Protection;  Connecticut Natural Resources Inland Fisheries Division; Connecticut State Historic Preservation Office; and the town of Thomaston Inland Wetlands and Watercourses Commission.


The Northfield Brook reservoir is two miles west of Thomaston on Route 254. The project stores Northfield Brook floodwaters and helps to lower flood stages in downstream communities along the Naugatuck River. Construction of the dam began in May 1963 and was completed in October 1965 at a cost of $2.9 million. The 810-foot-long, 118-foot-high dam has prevented flood damages of $75.8 million since it was built.  The flood storage area covers about 67 acres and extends 1.25 miles. The project and associated lands total 235 acres. Northfield Brook Lake can store up to 792 million gallons of water for flood control purposes. This is equivalent to eight inches of rain covering its drainage area of 5.7 square miles.


The Corps is soliciting public comments on the Environmental Assessment and Draft Finding of No Significant Impact of the Proposed Action. They are available for review at the Thomaston Public Library at 248 Main Street in Thomaston, Conn., and online at:

www.nae.usace.army.mil/Missions/ProjectsTopics/NorthfieldBrookDamConversion.aspx. Comments on the Proposed Action should be submitted by Feb. 28, 2015 to the U.S. Army Corps of Engineers, New England District, Engineering and Planning Division (Attn: Mr. Kirk Bargerhuff), 696 Virginia Road, Concord, MA 01742-2751 or by email to: kirk.e.bargerhuff@usace.army.mil. Questions on the proposal can be addressed to Northfield Brook Lake Project Manager Mr. Vincent Gualtieri at 978-318-8377 or to Study Manager Mr. Kirk Bargerhuff at 978-318-8029.

Tim Dugan

Release no. 2015-009