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Dam Safety Assurance Program

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Waterbury Dam is located on the Little River 3 miles upstream from its junction with the Winooski River in Waterbury, Vermont. The dam consists of a rolled earth embankment approximately 1,850 feet long at its crest, 187 feet high at its maximum section above the original river channel, and approximately 1,000 feet wide at the maximum section. The spillway section is 261 feet long and consists of two components. The first is a 161-foot wide ungated concrete ogee weir section with a crest elevation of 617.5. The second section is 100-feet wide, contains 3 tainter gates, and has a sill elevation of 592. The gates are 26.5-feet high. Two of the gates are 20-feet wide and were part of the original dam construction. The third is 35-feet wide and was added in 1958 as part of a modification of the dam to satisfy updated hydrologic and hydraulic requirements.

The dam was designed by the Corps of Engineers as part of a regional flood damage reduction plan for the Winooski River basin. Construction was initiated in 1935 and completed in 1938 by the Civilian Conservation Corps under the Corps supervision. The dam was turned over to the State of Vermont for operation and maintenance as a flood damage reduction facility. The Corps modified the dam in 1959 increasing the dam height three feet and adding the third tainter gate to ensure that the dam could safely pass the probable maximum flood. The reservoir pool was lowered in 1981 due to concerns for the safety of the dam because of seepage and settlement in the embankment. In 1984, the Corps injected filter material, reconstructed a portion of the toe of the dam and installed grouting in the gorge area in the original river channel to remediate the seepage and settlement. A bypass conduit was also installed to increase the ability to draw down the reservoir. The reservoir was then refilled. The Corps conducted follow-up studies in 1987 to assess the work and in 1991 recommended that the State retain an engineering firm to perform periodic evaluations of the dam as the gorge area of the dam was considered suspect and should be further evaluated.

The firm, Gannett-Fleming, completed their evaluations in 1999 documenting that conditions existed in the gorge area which raised concern for the safety of the dam. Additional monitoring instruments were also installed as part of the evaluation process and recommendations were made to address the conditions in the gorge area. In July 2000, the State of Vermont lowered the reservoir pool as instruments in the dam indicated further concerns regarding the integrity of the dam. Based upon the 1999 evaluation, the State requested that the Corps conduct a dam safety assurance study on how to best address the conditions at the dam. The Dam Safety Assurance Program (DSAP) study was completed in August 2000 and approved by Corps Headquarters. Several alternatives were studied and evaluated from a cost, environmental, risk, and economic standpoint. The alternatives include complete removal of the dam, constructing a new dam, reconstructing the gorge area or constructing a cutoff wall. The recommended plan consisted of constructing a filter shaft and monitoring structure in the gorge area to correct to the seepage conditions in the gorge area and allow for monitoring of the gorge area. Construction was initiated on July 15, 2002. The first element of construction, the installation of filters on the outlet conduit, was completed in November 2002. Work in 2003 consisted of the initiation of construction of the secant cutoff wall and seepage control wells. Construction of the secant wall and dewatering system continued through 2004, 2005, and into 2006. The Fiscal Year 2004 Appropriations Bill directed the Corps to design and construct a repair for the concrete spillway and abutments supporting the tainter gates. The concrete was deteriorating due to an alkali aggregate reaction.

The spillway repair contract was awarded to Alltech Engineering on July 5, 2005 at a cost of $693,000 and construction work was successfully completed in December 2005.   The repairs were expected to extend the useful life of the spillway gates by ten to fifteen years.  As part of this effort a Design Report was prepared in 2006 for a full replacement of the spillway at a future date.  It should be noted that the operation of the gates is restricted in part due to structural deficiencies and the flood storage pool cannot be raised to the full height as intended. The mitigation contract was awarded to Fleet Environmental on August 23, 2005 at a price of $621,000 and work was completed in November 2006. Additional work to repair areas of the slope was performed on the mitigation site in the fall of 2007 and completed. The State of Vermont allowed the reservoir to refill in September 2006. The reservoir reached normal pool at the end of October 2006 and overall construction of the seepage control measures was substantially completed in January 2007 with punch list items completed in the fall of 2007 and formally turned over to the State of Vermont. An eighteen month performance and monitoring period followed the reservoir refill and demonstrated that the seepage control features continued to operate satisfactorily.  The completed project, including the Operation and Maintenance of the project, was turned over to the State in September 2010.  As noted above the operation is partly restricted for the flood pool. The dam is inspected annually by the Corps in cooperation with the State of Vermont under the Inspection of Completed Works Program.   

AUTHORIZATION: The original studies of the Winooski River were authorized in the Rivers and Harbors Act of 1927. The Director of Emergency Conservation Work authorized the construction of the dam in June 1933 and the construction was overseen by the Corps. The authority to modify the dam was made in the Flood Control Act of 1944 and subsequently under appropriations in the 1980’s. The most recent effort was conducted under the Dam Safety Assurance Program under the authority of Section 1203 of the Water Resource Development Act of 1986. Appropriations with directive bill language were made in subsequent years starting in 2001 by the Congress to implement the project as described. 

STATUS:  The FY17 Work Plan provided $400,000 for the Waterbury Dam Study under the Section 542 of WRDA 2000, which authorized the Secretary of the Army to establish a program for providing environmental assistance to non-Federal interests in the Lake Champlain Watershed through USACE. The goal of the Lake Champlain Watershed Environmental Assistance Program is to provide assistance with planning, designing and implementation of large scale projects that protect and enhance water quality, water supply, ecosystem integrity and other water related issues within the watershed. 

The study for Waterbury Dam can be initiated under Section 542, but construction would likely require a separate authority or a modification of this authority.  This study will be in accordance with ER 1110-2-1156 - Safety of Dams Policy and Procedures.  The team is currently drafting a PMP and prepping of all required PPA documents, all in coordination with the Lake Champlain Basin Program, USACE Dam Safety Office, and NAE Dam Safety center of expertise. 

 

CONTACT:  

Mr. Matthew Cosby Program Manager

U.S. Army Corps of Engineers, New York District

Phone: (917) 790-8080

E-mail: matthew.g.cosby@usace.army.mil  

26 Federal Plaza New York, NY 10278-0090  

 

CONGRESSIONAL DISTRICTS: Sen. Patrick Leahy, VT; Sen. Bernard Sanders, VT; Rep. Peter Welch, VT- At Large

 

Current as of February 2018