The Essex 19 Hydroelectric Project is owned by Green Mountain Power Corp (GMP) and is located at river mile (RM) 17.6 on the mainstem of the Winooski River, in the townships of Essex Junction and Williston, Chittenden County, Vermont.  The Winooski River flows to the northwest into Lake Champlain.

Project Description

The dam is built at the Hubble Falls and was constructed between 1913 and 1917, however a dam has been at this location since the late 18th century.  The original dam washed out in 1798, and another dam was built just upstream of the current location. Sometime after 1830 a timber dam was built just downstream of the current dam location.

The Project includes a 495-foot-long concrete gravity dam with a 345-foot-long by 45-foot-high uncontrolled spillway section topped with 5-foot-high inflatable flashboards, and an 84-foot-long by 45-foot-high tip section topped with 6.5-foot-high inflatable flashboards.  Two 3-foot-diameter steel/diversion penstocks and four 9-foot-diameter steel/diversion penstocks extend from the dam to the powerhouse.

The powerhouse contains four horizontal Francis-type turbines with an installed capacity of 2,223 kW each, and four horizontal shaft General Electric generators rated at 1,800 kW each, as well as a minimum flow unit located in an old unused exciter unit bay, which is a double horizontal Francis-type turbine with an installed capacity of 874 kW connected to a generator rated at 850 kW.

The Project impounds 352 acres at a normal maximum water surface elevation with a gross storage capacity of about 1, 950 acre-feet. A usable storage capacity of 905 acre-feet is available between normal impoundment operating elevations of 272 to 275 feet USGS.

GMP operates the Project largely as a modified peaking facility with seasonal run-of-river operations, seasonal minimum flow releases, low-flow restrictions, and ramping rates.

Project Name Essex 19
LIHI Certificate Number 146
LIHI Effective and
Expiration Dates
October 31, 2018 – October 30, 2023
Owner Green Mountain Power Corporation
State Vermont
Location River mile 17.6 on the mainstem of the Winooski River in the townships of Essex Junction and Williston, Chittenden County, Vermont.
Installed Capacity 8.05 MW
Average Annual Generation 42,925 MWh

(2010 – 2014)

Facility Type Modified peaking
FERC No. 2513
  • From May 16 – June 15, GMP provides a minimum flow of 1,000 cfs, or inflow if less, for the protection of Atlantic sturgeon spawning and incubation habitat. The Project is operated as run-of-river when flows are less than 1,000 cfs and in peaking mode with ramping rates when flows are higher.
  • From June 16 – September 30, GMP provides a minimum flow of 450 cfs, or inflow if less, for the protection of salmonid habitat. Peaking flows in this timeframe are limited to 500 cfs and may only occur when river flows are greater than or equal to 450 cfs.
  • The minimum flow from October 1 – March 31 remains 450 cfs, but peaking operations can occur if flows allow.
  • From April 1 – May 15 GMP operates the Project in a run-of-river mode with a minimum flow of 50 cfs or inflow if less, into the bypassed reach via the fish passage facility (since installment of the minimum flow unit, GMP releases all flows less than 100 cfs to the bypassed reach via the downstream fish passage facility). Outflow approximates inflow on an instantaneous basis for the protection of walleye spawning and incubation habitat.
  • When river flow is greater than 275 cfs GMP operates flows through both the bypass (via the downstream fish passage facility) and existing units. When river flows are greater than 100 cfs flows are operated through both the bypass and the minimum flow unit, and when flows are below 100 cfs flows are operated through the bypass.


Certification History

December 18, 2018: The decision to certify the Essex 19 Hydroelectric Project is final. No appeals were received during the appeal period which closed on December 16, 2018. The new certification term for the Project is from October 31, 2018 through October 30, 2023.

November 16, 2018: The Low Impact Hydropower Institute (LIHI) preliminarily approved Low Impact Certification for the Essex 19 Hydroelectric Project, with the following two conditions:

Condition 1: The facility Owner shall continue to work collaboratively with VDEC to determine any additional needs for ongoing monitoring and reporting of operations and flows, update the Project’s operations compliance plan in consultation with resource agencies, and upon agency concurrence, file that plan with FERC. The Owner shall file quarterly updates with LIHI on the status of these efforts until the final plan has been filed with and approved by FERC.

Condition 2:  The facility Owner shall complete installation during the 2019 construction season of the permanent weir enhancements, including any needed plunge pool or rock modifications in consultation with VDEC and USFWS.  The Owner shall file the revised downstream passage standard operating procedure (SOP) and agency-requested spring passage timing adjustment with FERC and provide a copy to LIHI. Upon commencement of passage operations and in consultation with resource agencies, the Owner shall implement the downstream passage monitoring and effectiveness testing in accordance with license Article 410 or associated updated requirements.  The Owner shall report on the status of downstream passage in annual compliance statements submitted to LIHI.

This decision is preliminary pending the 30-day appeal window. Only those who commented on the initial application during the 60-day comment period are eligible to file an appeal. Such appeal needs to include an explanation as to how the Project does not meet the LIHI criteria. Appeal requests can be submitted by email to with “Essex 19 Hydroelectric Project” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 329 Massachusetts Ave, Suite 2, Lexington, MA 02420. 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 December 16, 2018.  The full application and reviewers report are available below.  If no appeal requests are received and the decision becomes final, the Certification term for the Essex 19 Project will be October 31, 2018 through October 30, 2023.

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 Essex 19 Hydroelectric project, located at river mile 17.6 on the mainstem of the Winooski River in the townships of Essex Junction and Williston, Chittenden County, Vermont.


2018 Certification