LIHI Certificate #118 – Webster Pembroke Project, New Hampshire

Webster-Pembroke Project is located on River Mile 34 (of 36) on the Suncook River near Pembroke, New Hampshire. The project is located approximately one half mile upstream of the China Mill Dam and confluence of Suncook and Merrimack Rivers and approximately 16 miles downstream of the Pittsfield Mill Dam. The river runs for 35.7 miles, from the outlet of Crystal Lake in Gilmantown, New Hampshire through several small towns and rural areas to its confluence with the Merrimack in the town of Suncook. The river experienced heavy flooding in 2006, establishing a new route in several areas and resulting in the largest channel change in a New Hampshire river in systematic topographic mapping history. The flood also resulted in several safety changes, including the removal of several unoccupied dams on the river. The river is characterized by very high flow variations, from average lows of 3 CFS to record high of 13,000 CFS, with an average mean flow of 390 CFS. Fishing and kayaking (recreational, not whitewater,) are the two primary recreation uses of the Suncook River.

A series of active dam sites occur along the length of the Suncook River prior to its confluence with the Merrimack River. Although it is unclear exactly how many are active, their appears to be as many as 14 dam sites along the entire 36 miles of the river’s watershed, with the Webster-Pembroke facility being the second to last downstream prior to the confluence. Immediately downstream is the China Mill facility, a privately-owned 1.7 MW facility also located at a former mill site.

The Webster-Pembroke project technically consists of two dams, the Webster Dam as the primary impoundment and the Pembroke, a stone masonry dam located on the bypass section of the Suncook River receiving the minimum flow release and any spillage from the Webster Dam. The Pembroke Dam is located 1800 feet downstream of the Webster Dam, and the powerhouse is currently adjacent to the Pembroke Dam. The reservoir at Webster-Pembroke has a volume of 147 acre-feet, and a total surface area of 26 acres. Approximately 4.5 acres are occupied by non-reservoir facilities, including a 460 foot long, 8 foot diameter penstock and a powerhouse containing one horizontal Voith Kaplan turbine/generator that produces approximately 10 million kilowatt-hours of clean energy in a typical year.

Project Name Webster Pembroke
LIHI Certificate No. 118
LIHI Certificate Term February 23, 2020 - February 22, 2025
Owner Pembroke Hydro Associates Limited Partnership, a subsidiary of Eagle Creek Renewable Energy, LLC
State New Hampshire
Location Located at River Mile 34.25 on the Suncook River in New Hampshire.
Installed Capacity  2.6 MW
Average Annual Generation 10,100 MWh
Facility Type Run-of-river
FERC No. P-3185 exempt 1983

Partial removal of the Pembroke Dam is currently being proposed, as detailed in a letter provided by Kleinschmidt Associates:

“The reason for the partial removal is to sufficiently eliminate any hazard from dam failure or damage to adjacent property resulting from impounded levels during high flow events. The proposed partial removal addresses the upstream impact caused by the dam during the project design flood flow (100- year storm). Further, analyses has indicated that failure of the remaining portion of the dam under flood flow conditions would not have any significant downstream impact.” Any impact of flow from this removal process will be studied under the flow requirements study in the MOA to be conducted in 2015.

The Pembroke project consists of utilizing the total hydrostatic head available between the headwater of the Webster Dam, with 4 feet of flashboards (elevation 278 NGVD), and the tailwater of the Pembroke Dam (elevation 226 NGVD) which utilizes a gross head of about 52 feet. Flows are diverted through the existing Webster Canal, through a 460-foot-long, 8-foot diameter, 3/8” welded steel penstock to a full Kaplan Turbine rated at 2,600 MW, located in the old Pembroke Powerhouse which is immediately downstream of the Pembroke Dam.

The Pembroke project is operated as a run-of-river facility. Outflows from the project equal inflows on an instantaneous basis, and water levels above the dam are maintained at the crest of the dam and are not drawn down for the purposes of generating power. The Pembroke project consists of a stone masonry gravity dam, a 460-foot-long penstock, a powerhouse, one generation unit and appurtenant project equipment. The exemptee is required to maintain a minimum flow of 9 cfs or inflow, whichever is less at all times through the roughly 1,400-foot-long bypass.


Certification History

September 14, 2020: The decision to recertify the Webster-Pembroke Project became final after the close of the appeals period on September 5, 2020 with no appeals filed. The Certification term is from February 23, 2020 – February 22, 2025.

August 6, 2020:The Low Impact Hydropower Institute (LIHI) has preliminarily approved the Webster Pembroke Project (LIHI #118) for a new 5-year term of Low Impact Certification. The Certificate includes the following conditions:

Condition 1: The facility Owner shall provide the revised Operations and Flow Monitoring Plan and the amended or extended USFWS MOA within 90 days of finalization of each document with resource agencies. Any changes in operations or required fish passage measures shall be reported to LIHI in annual compliance submittals.

Condition 2: The facility Owner shall report to LIHI on the status and completion of the partial dam removal and mitigation measures under the SHPO MOA in annual compliance submittals until all work is completed and approved by the SHPO and FERC.

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 comments@lowimpacthydro.org with “Webster Pembroke Project” in the subject line, or by mail addressed to the Low Impact Hydropower Institute, 329 Massachusetts Ave, Suite 6, 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 September 5, 2020. The full application and reviewer’s report are available below. If no appeal requests are received and the decision becomes final, the Certification term for the Project will be February 23, 2020 through February 22, 2025.