Pending Application - Bolton Falls Project, Vermont

Project Name Bolton Falls
LIHI Certificate No.
Pending #201
LIHI Certificate Term
Owner Green Mountain Power
State Vermont
Location River Mile 43 – Winooski River.
Installed Capacity 6.96 MW
Average Annual Generation 26,301 MWh
Facility Type Run-of-river
FERC No. P-2879. License issued October 5, 2022, expiring September 30, 2062.

The Bolton Falls Hydroelectric Project is located on the Winooski River in Washington County, Vermont.  Most of the infrastructure associated with the Project, including the intake, penstocks, bypass pipe, and powerhouse, is located within the town of Duxbury, Vermont. The right abutment of the Project dam is in the town of Waterbury, Vermont.

The Project dam is located on the Winooski River at approximately river mile (RM) 43.  The total drainage area is approximately 821 square miles, which is approximately 76% of the drainage area at the Winooski River’s mouth where it enters Lake Champlain. The Project dam is the fourth dam upstream of Lake Champlain on the Winooski River.  It is 33 miles upstream of Winooski One/Chace Mill (LIHI #16), and about 25 miles upstream of Essex 19 (LIHI #146).  It is located about 17 miles downstream of Winooski No. 8 (LIHI #77).

The Project dam is 92 feet tall and 275 feet long, and consists of a timber crib dam buttressed with a masonry wall on the downstream face. The dam spillway is capped with a 196-foot-long reinforced concrete overflow spillway, and a 5-foot-high inflatable rubber dam. Redevelopment of the project in the 1980s initially included 5-foot wooden flashboards atop the dam crest; these were replaced by the current 5-foot-high inflatable rubber dam system in 1991. The foundation of the dam is below the normal tailrace elevation, with the deepest section found at approximately elevation 320 feet and approximately 25 feet below the normal tailwater elevation.

The project dam was originally constructed in 1898 as a rock-filled timber crib dam. Electricity generation began in 1899 with its two turbine-generator units. During 1899, the dam deflected and to strengthen it, an ashlar-faced stone dam was constructed in 1900 against the downstream face of the timber crib structure. In 1905-1906, a third turbine generator unit was added, utilizing the large landward-side penstock for the supply of water. The new generating unit (No. 3) was in a powerhouse structure at the end of the powerhouse, which housed Units 1 and 2. However, by 1938, the Project had fallen into disrepair, and it was taken off-line. The Project dam and powerhouse were redeveloped in 1985-1986 under the previous FERC license, which was issued in February 1982. Construction began in May 1985 with power first generated in October 1986. As a result of this redevelopment, the remnants of the previous powerhouses were removed and a new powerhouse containing two equally sized turbine generator units was constructed.

The left abutment includes a concrete-capped masonry tower as well as a lower pad on the upstream face of the left abutment that allows access to the trash rake and penstock gates. The right abutment consists of a concrete cap atop the masonry wall to which the rubber dam is attached.

The dam includes two sluiceways into the masonry buttress section for drainage of the timber crib dam. The sluiceways are 4.0 feet wide by 4.5 feet high.

A section of the former (destroyed) powerhouse masonry foundation wall near the dam’s left abutment was stabilized with a reinforced concrete facing and anchored to bedrock with post-tensioned anchors in 1992-1993.

The Project forebay consists of two separate concrete intakes for each penstock. The bottom of the intakes are at elevation 360.0 feet, approximately 37 feet below the normal pond elevation. The top of the intakes are at elevation 389.1 feet, approximately 8 feet below the normal pond elevation. The intake structure is equipped with trashracks with 3-inch clear spacing and a trash raking system. The trashrack dimensions are 27 feet wide by 43 feet high and angled 70 degrees from the horizontal plane. The penstocks are each 10-foot-diameter and 120-foot-long and are made of steel encased in concrete.

The Project impoundment is approximately 59 acres in surface area at a pool elevation of 397.0 feet, with an effective storage of 210 acre-ft and a gross storage capacity of 300 acre-feet.. The Project impoundment has 4.2 miles of shoreline.

The powerhouse, located on river left downstream of the dam’s left abutment, is a reinforced concrete structure approximately 73 feet long by 57 feet wide.

Following flooding in spring 1987 when water levels came within three feet of overtopping the powerhouse roof, the parapet walls around the powerhouse roof were raised several feet. Raising these walls appeared to greatly reduce (but not eliminate) the amount of damage sustained by the powerhouse following the August 2011 Hurricane Irene flooding.

There is also a 75-foot-long, 36-inch-diameter water bypass pipe that discharges water directly adjacent to the dam’s left abutment on the left edge of the spillway. The invert for the bypass pipe intake is at approximately elevation 383 feet, approximately 14 feet below the normal pond elevation.

A 130-foot long, 5-kV underground transmission line ties the powerhouse to an adjacent switchyard. The generator main leads are connected to a 34.5/4.16 kV transformer in the switchyard. Station service power can either be tapped from the generators or supplied separately by GMP. There is also a 34.5 kV transmission line that is approximately 600 feet long that runs from the switchyard mentioned above to a second switchyard with a 34.5/4.16 kV transformer.

The Project has a short, 150-foot-long bypassed reach and the tailrace is approximately 90 feet wide and 60 feet long.

The Project also includes various turbine governors, generator exciters, batteries, control panels, and circuit breakers.

Certification History

April 19, 2024: The Low Impact Hydropower Institute (LIHI) has preliminarily approved Low Impact Certification for the Bolton Falls (pending LIHI #201) Hydroelectric Project, FERC# P-2879. The project is located on the Winooski River in Vermont. The full application and reviewer’s report are available below.

This decision is preliminary pending the 30-day appeal window. Only those who commented on the initial applications during the 60-day comment period are eligible to file an appeal. Such appeal needs to include an explanation as to how the Projects do not meet the LIHI criteria. Appeal requests can be submitted by email to with “Bolton Falls” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 1167 Massachusetts Ave, Arlington, MA 02476. All requests will be posted to the website. The applicant will have an opportunity to respond and any response will also be posted. Requests must be received by 5 pm Eastern time on May 19, 2024. If no appeal requests are received the certification terms will be January 26, 2024 through January 25, 2034.

January 30, 2024: The Low Impact Hydropower Institute has received a complete application for Low Impact Certification of the Bolton Falls Hydroelectric Project.  LIHI is seeking public comment on this application.  Specifically, we are interested in knowing whether you think the Project meets the LIHI Low Impact Certification Criteria, as revised in the 2nd Edition Handbook.  Please review the program and criteria in LIHI’s revised Handbook and then review the Project’s application materials below. 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 “Bolton Falls Project Comments” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 1167 Massachusetts Avenue, Arlington, MA 02476. Comments must be received on or before 5 pm Eastern time on March 30, 2024 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.

Certification Files

Key Documents