The Vergennes Hydroelectric Project is an existing licensed project (FERC No. 2674), located at river mile 7.6 on the Otter Creek in Addison County, Vermont. The project’s two powerhouses, intake structures, three dams, and tailrace lie within the City of Vergennes. The general project area extends from approximately 8.8 miles above the dam to just below the powerhouses. The project currently generates power using an average gross head of 37 feet developed between the project’s impoundment and tailwater.

Project Name Vergennes
LIHI Certificate No. 134
LIHI Certificate Term
December 30, 2016 –
December 30, 2021
Owner Green Mountain Power Corporation
State Vermont
Location Located on Otter Creek, a tributary to Lake Champlain, at river mile 7.6, in Vermont.
Installed Capacity 2.6 MW
Average Annual Generation 11,405 MWh
Facility Type Run-of-river
FERC No. P-2674 issued 1999, expires 2029

The Vergennes Project includes two powerhouses; Plant 9 located on the south bank of Otter Creek and Plant 9B located on the north bank. The two powerhouses are separated by three concrete spillway sections that are divided apart by two instream islands and one 29-foot-long non-overflow dam. Center Island divides the 9B Spillway from the Center Spillway and the Grist Mill Island divides the center spillway from the Plant 9 Spillway. Each of the spillways are approximately 10-feet-high, with a total length of 231 feet and a crest elevation of about 132.78 feet mean sea level (msl).

The Plant 9B station was originally constructed in 1943 and consists of a single 1,000 kw vertical Francis turbine directly connected to a generator. The runner for this plant was replaced in 1985. The Plant 9 station consisted of two identical 700 kw horizontal Francis turbines prior to the replacement of turbine #2 in 2005 and the replacement of turbine #1 in 2006. The upgraded Unit 2 began commercial operation on January 24, 2006, and Unit 1 came on-line on January 16, 2007. The plant was originally constructed in 1912. The runners were replaced in 1928 and the Unit No. 1 and No. 2 generators were rewound in 1946 and 1970, respectively.

The two existing Plant 9 turbines were replaced with new double discharge Francis turbines each rated at 1137 Hp and 35.5 ft of net head with a maximum hydraulic capacity of 363 cfs. The new modem design units will increase, mainly, the efficiency of the units with a moderate increase (13 cfs) in the hydraulic capacity of the units. The new installed capacity of the entire station is 2,600 kW; an increase of 200 kW since 2005.

The modern, high efficiency units will result in an estimated increase of 2,388 MWh of E-2 total annual net energy production at the facility over the Historic Generation Baseline. The drainage area above the Vergennes dam is approximately 866 square miles. GMP currently operates the Vergennes Project as a run-of-river project. Plant 9’s operating flow range is approximately 140 cfs to 726 cfs while the operating flow range for Plant 9B is approximately 200 cfs to 480 cfs. The total hydraulic capacity of the project turbines is approximately 1,206 cfs. The authorized installed capacity at the Project is 2,600 kW.

The Project operates in a strict run-of-river mode. GMP maintains spill over the spillways to support aesthetics and uses the following flow schedule:
April 1-Oct 31: 150 cfs daytime and 75 cfs nighttime
Nov 1-Dec 15: 100 cfs daytime and 50 cfs nighttime
Dec 16-Mar 31: No special flows.

Certification History

June 20, 2017: Having received no requests for appeal, the Vergennes Hydroelectric Project received a final decision on June 8th that the facility satisfies the LIHI Certification Criteria.

May 8, 2017: LIHI Executive Director Shannon Ames announced a Preliminary Certification Decision that the Vergennes Hydroelectric Project (FERC No. P-2674) satisfies the LIHI Certification Criteria. The certification includes one facility-specific condition, as follows:

Satisfied 2020. Condition 1.  The owner shall consult with the Vermont Department of Environmental Conservation to determine appropriate procedures to verify Run-of-River (RoR) operations at the Vergennes facility.  Within 180 days after certification, the owner shall provide LIHI with documentation describing the agreed-upon procedures and then implement those procedures within the first year of LIHI certification.  In the first annual compliance report to LIHI, the owner shall summarize the initial results from RoR verification.  If RoR verification activities continue beyond the first year of certification, then the owner shall report on the results annually.

As provided for in Section 4.2.5 of the LIHI 2nd Edition Handbook, the Preliminary Certification Decision, along with the Application Reviewer’s report and (if prepared) report of the Executive Director, will be posted on the Institute’s Web page for 30 days.  Notice of the posting will be provided to all individuals or organizations that commented on the initial Application Package.

Any Commenter may submit a letter to the Executive Director requesting an appeal within the 30-day period which ends on June 8, 2017.  The appeal request must state specific reasons why the hydropower facility should have failed one or more criteria.  Only individuals or organizations that commented on the initial Application Package may file an appeal.  Further information about the LIHI appeal process is available in the LIHI Handbook, available at

If no appeal is requested within the 30-day period, the Executive Director will issue LIHI Certification for the facility and post a notification of certification on the Institute’s website.  Once final, the effective certification date for the Vergennes Project is December 30, 2016 for a five (5) year term, which will expire on December 30, 2021.

January 6, 2016: On December 30, 2016, the Low Impact Hydropower Institute (LIHI) received a complete application from Green Mountain Power Corporation for the Low Impact Certification of the Vergennes hydroelectric project, located on Otter Creek, a tributary to Lake Champlain, at river mile 7.6 in Vermont.

LIHI is seeking public comment on this application. Specifically, we are interested in knowing whether you think the Vergennes project meets the LIHI Low Impact Certification Criteria. The Vergennes application is subject to review using the Criteria in the LIHI Certification Handbook of 2014.  Please review the program and criteria in LIHI’s 2014 Handbook and then review the Project’s 2016 application materials posted on the project page. Comments that are directly tied to specific LIHI criteria (flows, water quality, fish passage, etc.) will be most helpful, but all comments will be considered. Comments may be submitted to the Institute by e-mail at with “Vergennes Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, PO Box 194, Harrington Park, New Jersey 07640.  Comments must be received at the Institute on or before 5 pm Eastern time on March 12, 2017 to be considered. All comments will be posted to the web site and the applicant will have an opportunity to respond.  Any response will also be posted.