LIHI Certificate #128 – Otter Creek Project, Vermont
The 22.807 megawatt (MW) Otter Creek Project (FERC No. 2558) includes three developments comprised of Proctor, Beldens, and Huntington Falls, and generates an average annual energy output of 49,117 MWh.
The Proctor Development is comprised of a masonry, concrete-capped dam constructed atop Southerland Falls. The dam is 13 ft-high by 128 ft-long and topped with a 3ft-high inflatable flashboard system. The development has a 100 ft-long by 17 ft-high by 45 ft-wide gated forebay-intake structure that contains trashracks with 1-inch clear bar spacing. Two penstocks: a 9 ft-diameter, riveted steel penstock (decreasing to 8 ft-diameter beyond the surge tank foundation) that extends 345 ft from the dam to a former surge tank and decreases to 8 ft in diameter for an additional 96 ft beyond the surge tank foundation; and a 7 ft-diameter spiral welded steel penstock extending 500 ft to the powerhouse.
The concrete and brick masonry powerhouse is 33 ft by 100 ft and contains four Francis turbine-generator units rated at 2,245 kW, 1,715 kW, 1,719 kW, and 1,714 kW, respectively. An attached 28 ft by 48 ft steel structure contains an additional 2,840-kW vertical Francis turbine-generator unit. The development has a total hydraulic capacity of 1188 cfs and a total authorized installed capacity of 10,233 kW. The development is also comprised of generator leads, two banks of 0.48/4.16 kV single-phase transformers and a 0.48/43.8 kV, three-winding transformer, and appurtenant facilities.
The 95 acre impoundment has a usable storage capacity of 275 acre-feet at a normal maximum water surface elevation of 469.5 feet msl. The reservoir has an average weighted depth of 6.6 feet and 12.2 miles of shoreline. The substrate of the impoundment is generally comprised of silt substrate with little to no vegetation.
The Proctor development operates in a modified run-of-river mode. When operating in run-of-river mode, the impoundment target elevation is 469.5 ft msl. GMP operates the development in a true run-of-river mode from July 1 through April 30, when inflow is less than 200 cfs, and from May 1 through June 30, when inflow is less than 400 cfs. At all other times, GMP operates the Proctor Development in a 1.5 ft drawdown/refill cycle (i.e., peaking mode).
During peaking operations, the impoundment is operated between elevations 469.5 ft msl and 468.0 ft msl. A bypass conservation flow of 60 cfs is additionally released at the dam at all times.
Beldens Dam is located on Otter Creek and consists of a concrete dam in two sections on either side of a ledge/bedrock island. The east dam is about 24 ft-high by 57 ft-long and has an excavated tailrace extending from the powerhouse about 120 ft downstream. The west dam is approximately 15 ft-high and 56 ft-long and discharges to the bypassed reach. The dam is equipped with 2.5 ft wooden flashboards. There are two intake structures at the development: one approximately 79 ft-long with a section of trash racks spaced 2 inches on center; the other approximately 35 ft-long with a section of trash racks spaced 1 1/8 inches on center.
There are two penstocks at the Project. The first penstock begins as a single 12 ft diameter steel penstock that bifurcates into two 10 ft-diameter sections about 30 ft long each leading to the original powerhouse (Powerhouse No. 1). A second 12 ft diameter by 45 ft-long concrete penstock connects to a newer powerhouse (Powerhouse No. 2). Powerhouse No. 1 is a 40 ft by 44 ft concrete and masonry structure housing two horizontal Francis turbine generator units, one rated at 800 kW and one at 949 kW. Powerhouse No. 2 is 40 ft by 75 ft concrete structure housing a 4,100 kW horizontal Kaplan turbine generator unit. The development has a total hydraulic capacity of 2,000 cfs and total authorized installed capacity of 5,849 kW. The development also includes generator leads, a 2.4/46 kV step-up transformer bank, and appurtenant facilities, such as a jib crane for moving equipment.
The 22 acre impoundment has a usable storage capacity of 253 acre-ft at a normal maximum water surface elevation of 283 ft msl. The impoundment has approximately 4.2 miles of shoreline and the substrate of the impoundment is generally comprised of silt with little vegetation.
The Development operates in a run-of-river mode with instantaneous inflows to the impoundment at all times. A bypass conservation flow of 35 cfs, with 10 cfs spilled over the east dam and 25 cfs over the west dam, is released at all times. The impoundment target elevation is 283.0 ft msl.
Huntington Falls Development
The dam at the Huntington Falls Development is 187 ft-long with a maximum height of about 31 ft, topped with a 2.5 ft inflatable flashboard system. The development tailrace continues from Powerhouse No. 1 for 120 ft downstream. The Development has a 40 ft-wide by 20 ft-high intake with 13 ft-high by 26 ft-wide trashracks with bar spacing of 1.125 inches. The second intake structure is 38 ft-high by 40 ft-wide with 16 ft high by 30 ft-wide trashracks with 2 inch clear bar spacing. The Development has three penstocks. Two are 10 ft-diameter steel penstocks, each approximately 30 ft-long, leading to the original powerhouse (Powerhouse No. 1). A third penstock, 12 ft diameter by 75 ft-long, leads to the newer powerhouse (Powerhouse No. 2). Powerhouse No. 1 is brick masonry, measuring 42 ft by 60 ft, and houses two horizontal Francis turbine generating units, with a combined installed capacity of 2,625 kW. Powerhouse No. 2 measures 40 ft by 75 ft, and houses a 4,100 kW horizontal Kaplan turbine generator. The development has a total hydraulic capacity of 2,250 cfs and a total authorized installed capacity of 6,725 kW. In addition, the development has generator leads, a 2.4/46 kV step-up transformer bank, and appurtenant facilities.
|Project Name||Otter Creek|
|LIHI Certificate No.||128|
|LIHI Certificate Term||January 7, 2016 - January 7, 2021, extended to May 31, 2021|
|Owner||Green Mountain Power Corporation|
|Location||Located between river mile 21 and 64.2 on Otter Creek in west-central Vermont within Addison and Rutland Counties, near the communities of Proctor, Middlebury, and Weybridge, Vermont.|
|Installed Capacity||22.807 MW|
|Average Annual Generation||49,117 MWh|
|Facility Type||Proctor: modified run-of-river Belden: run-of-river Huntingon Falls: run-of-river|
|FERC No.||P-2558 issued 2014, expires 2054|
The 23 acre impoundment has a usable storage capacity of 234.16 acre-ft at a normal maximum water surface elevation of 217.8 ft msl. The impoundment has approximately 1.2 miles of shoreline and the substrate of the impoundment is generally comprised of silt with little to no vegetation.
The facility is operated in a run-of-river mode with instantaneous inflows to the impoundment at all times. Under the 2014 License an increased bypass conservation flow of 66 cfs was approved. Before the facility is able to provide a bypass flow of 66 cfs, physical modifications to the site are needed in order to provide increased flows. Modifications are planned for 2016/2017 and in the interim a bypass conservation flow of 48 cfs is voluntarily released at all times at two locations at the dam. The impoundment target level is 217.8 ft msl.
August 22, 2016 – LIHI Executive Director Michael J. Sale has issued a Certification Decision that the Otter Creek Hydroelectric Project (FERC No. P-2558) satisfies the LIHI Certification Criteria. This certification decision is based on a unanimous vote of the Governing Board members present at the June 21, 2016, Technical Committee meeting. A Preliminary Decision was announced on July 11, 2016, and a 30-day appeal period was open until August 13, 2016. No requests for appeal were received. This Certification Decision includes two facility-specific conditions, as follows:
- Condition satisfied in 2017. Condition 1. The owner shall complete construction of the new gate for minimum flow releases at Huntington Falls and fully implement the release of the 66-cfs minimum flow required at that facility. The owner shall send LIHI a letter report no later than December 31, 2016, describing the status of this implementation, and if it has not yet been completed, define and commit to remediation measures that will ensure it is completed as soon as possible.
- Condition satisfied in 2017. Condition 2. The owner shall complete all elements of the recreational plan at Huntington Falls, including the acquisition of necessary easements, and send LIHI a letter report no later than December 31, 2016 confirming that all elements have been completed. If there are any part of the Recreation Plan unfinished at that time, the owner shall explain the reasons why and actions planned to complete them.
The effective certification date for the Otter Creek Project is January 7, 2016 for a five (5) year term, which will expire on January 7, 2021.
January 8, 2016 – On January 7, 2016, the Low Impact Hydropower Institute (LIHI) received a complete application from Kleinschmidt Associates, on behalf of the Green Mountain Power Corporation, for the Low Impact Certification of the Otter Creek Project, FERC P-2558, located on Otter Creek in west-central Vermont within Addison and Rutland counties, near the communities of Proctor, Middlebury, and Weybridge, Vermont.
LIHI is seeking public comment on this application. Specifically, we are interested in knowing whether you think the Otter Creek Project meets the LIHI Low Impact Certification Criteria. Please review the program and criteria in LIHI’s revised Handbook and then review the Project’s application materials posted 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 firstname.lastname@example.org with “Otter Creek 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 8, 2016 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.