LIHI Certificate #202 - Lower Great Falls Project, New Hampshire and Maine

Lower Great Falls, NH/ME
Project Name Lower Great Falls
LIHI Certificate No.
 202
LIHI Certificate Term
 February 9, 2024 – February 8, 2034
Owner Green Mountain Power
State New Hampshire and Maine
Location River Mile 3.1 – Salmon Falls River.
Installed Capacity 1.28 MW
Average Annual Generation 3,917 MWh
Facility Type Run-of-river
FERC No. P-4451. License issued in 2023, expires 12/31/2062.

The Lower Great Falls Project is located on the Salmon Falls River in the states of New Hampshire and Maine. Most of the infrastructure associated with the Project, including the intake, penstock, and powerhouse, is located within the City of Somersworth, NH. The left abutment of the dam is in the Town of Berwick, ME.

The project dam is located at approximately river mile 3.1 and is the third dam on the mainstem of the Salmon Falls River. Downstream are the Rollinsford Project (LIHI #196) and the South Berwick Project (LIHI #195) The total drainage area at the Lower Great Falls dam is approximately 220 square miles, which is about 93.2% of the Salmon Falls drainage area (236 sq. mi.).

The project dam has been in place since 1825 and has a total length of 297 feet, consisting of a 50-foot-long left abutment, a 176-foot-long spillway section, and a 71-foot-long right abutment. The dam is a stone masonry and concrete gravity dam approximately 32 feet high and topped with 4-foot-high flashboards. The dam was rehabilitated in 1984 followed by rehabilitation of the spillway in 1991.

There is one low level outlet gate located in the left abutment which controls flow into a seven-foot-diameter, 40-foot-long bypass pipe. The gate is 8 feet wide by 8 feet high. A second inoperable outlet pipe that had previously been partially filled with concrete is present. In the Fall of 2022, the owner completed several FERC mandated dam safety repairs that included filling the remaining portion of the inoperable outlet pipe with concrete. The gate that is operable is opened when the impoundment level rises approximately 10 inches above the flashboards to avoid failure of the flashboards during high flow periods. The gate is operated manually by a hydraulic unit mounted to the gate structure that is run by a dedicated portable generator.

A small trash gate is located adjacent to the intake structure with a manually operated screw stem operator. The gate is typically used to sluice debris and is also opened when the impoundment level rises approximately 10 inches above the flashboards during high flow periods. The gate is inspected during flashboard repair activities but requires no routine maintenance other than regular lubrication of the gate operator mechanism.

The impoundment has a gross volume of 584 acre-feet with an approximate surface area of 40 acres at the normal pond elevation of 106.4 feet, NGVD 1929. Since the Project operates as a run-of-river facility, the useable storage volume is negligible.

The 40.5-foot-wide by 20-foot-high intake is a concrete structure with a wooden deck that includes four steel frame gates with a sloping steel trashrack at the upstream side of the wooden deck. Two pairs of gates control flow to each penstock. Each gate is 5 feet wide by 10.5 feet high and has a sill elevation of 92.0 feet.

The gates are hand operated with a chain hoist suspended from a monorail. These gates provide closure to two 8.5-foot-diameter penstocks and in turn each penstock bifurcates into two penstocks that convey water to the powerhouse. All the penstocks are buried and extend approximately 200-225 feet from the intake structure to the powerhouse.

The powerhouse is a 30-foot by 46-foot concrete and brick building with a wood frame superstructure. It  includes the 4 turbine/generators, controls, and station switchgear. Power is delivered directly to a 4.16 kV distribution line via a 260-foot-long underground transmission line that stretches to an Eversource Energy pole-mounted air break.

The Project tailrace is approximately 55 feet wide and 30 feet long. A 250-foot-long bypass reach extends between the dam and the tailrace. The bypass varies in width between approximately 90 feet at the downstream end to approximately 160 feet at the upstream end.

The project operates in a run-of-river mode utilizing a Programmable Logic Controller to monitor and control the elevation of the headpond. A minimum flow of 37 cfs is provided via two pipes at the base of the dam as well as through a cut out in the right side of the spillway. These measures help to protect aquatic habitat in the project reach and were developed in consultation with US Fish and Wildlife Service (USFWS), New Hampshire Department of Environmental Services (NHDES), New Hampshire Fish and Game Department (NHFG), Maine Department of Environmental Protection (MDEP), Maine Department of Inland Fisheries Wildlife (MDIFW), Maine Department of Marine Resources (MDMR), and National Marine Fisheries Service (NMFS).

Waters within the project reach are designated Class B in New Hampshire and Class C in Maine. In New Hampshire, Class B water bodies are considered acceptable for fishing, swimming, and other recreational purposes, and after treatment, as potential water supplies. In Maine, Class C water must ensure suitability for the designated uses of drinking water, fishing, agriculture, recreation, industrial processes, cooling water, hydroelectric power generation, navigation, and habitat for fish and other aquatic life. In New Hampshire, the Project impoundment is listed on the Clean Water Act section 303(d) list of impaired waters for pH. In Maine, the section of river in which the Project is located is listed on the 303(d) list for the following impairments: Escherichia coli, ammonia, eutrophication, dissolved oxygen, phosphorus, and biochemical oxygen demand. Long-term water quality monitoring is currently being undertaken by the project owner in consultation with NHDES and MDEP to ensure that the project is not adversely impacting waters in the project reach.

Historically, the Salmon Falls River was host to anadromous fish species including American shad, alewife, and blueback herring – potentially migrating as far upstream as Somersworth, New Hampshire (roughly a mile upstream of the project). However, the construction of dams started in 1847 which prevented the passage of such species. Resident species include black crappie, bluegill, bridle shiner, brook trout, brown bullhead, brown trout, common shiner, eastern silvery minnow, fallfish, golden shiner, largemouth bass, longnose dace, rainbow trout, rainbow smelt, redfin pickerel, smallmouth bass, white perch, yellow perch, and white sucker.  Currently, the downstream Rollinsford dam still prevents access for migratory species, though passage facilities are prescribed in that Project’s new license. Construction of fish passage facilities at that project, specifically for American eel, are slated for permanent operation in the spring of 2027. Further, an interim trap and truck transport program at the Rollinsford Project for river herring and American shad is planned for the beginning of 2025. This program will be operated in conjunction with the Town of Rollinsford, NH and USFWS. Upstream passage at Lower Great Falls  must be provided four years after passage is installed at Rollinsford.  Downstream passage facilities for anadromous fish and eel species must be provided at Lower Great Falls within 3 years of license issuance.

The project lands consist of roughly one acre comprised of forested uplands and a few areas of palustrine wetlands on the northern shoreline, while the southern shoreline is surrounded by developed land and some narrow strips of forested uplands. Otherwise, the surrounding lands are primarily developed, forested, or farmland. Run-of-river operations minimize impacts to the project shoreline.

Threatened or endangered species potentially present in the project vicinity include the northern long-eared bat, greater fringed-gentian, lopsided rush, northern beggar-ticks, northern blazing star, unpretentious yellow-seeded false pimpernel, small whorled pogonia, Georgia bulrush, spotted turtle, black racer, eastern elliptio, eastern floater, and triangle floater, redfin pickerel, bridle shiner, longnose dace, and Blanding’s turtle. Due to the small project area and restrictions on landscaping activities, the project is unlikely to adversely impact the listed species. However, due to the forthcoming construction activities related to fish passage, the project owner will engage with resource agencies in order to minimize and avoid any construction related impacts to listed species – northern long-eared bats and small whorled pogonia in particular.

Consultation with the Maine Historic Preservation Commission (MHPC) concluded that three archaeological sites in the Maine Area of Potential Affect (are eligible for listing on the National Register of Historic Places, including the remnants of a mid to late 19th century stone water tower, the remnants of a 19th century sawmill complex, and a Middle to Late Ceramic period site. Additionally, the Lower Great Falls dam includes foundations and industrial remains of a 19th century sawmill complex that was converted into an early hydroelectric plant in 1888. Structural remnants closest to the river are the most intact including the wheelhouse and southernmost stone wall foundation along the south side of the riverbank. The powerhouse foundation is perched on a ridge above the river with a steep slope down to the water and portions of the site are inaccessible due to safety concerns. The Maine SHPO is currently developing a “Mill Context” to include National Register eligibility standards.

Due to the project’s limited land area, no recreational resources exist on project property. However, recreational resources nearby include Riverwalk Park, a 10-acre area includes a parking area, river overlook, a trail that winds along the impoundment, and several shoreline locations providing access to the water for canoeists and kayakers, and several informal trails that allow access to the NH side of the river.

Compliance Status

The Certificate includes the following facility-specific conditions: 

Condition 1: In annual compliance submittals to LIHI, the facility Owner shall provide a copy of the future water quality monitoring required by the NHDES WQC and effectiveness review of the Water Quality Mitigation and Enhancement Plan required by the MDEP WQC. Agency comments on these filings and resolution of the comments shall also be provided.

Condition 2: In annual compliance submittals to LIHI, the facility Owner shall provide updates on the status of upstream and downstream fish passage activities including results of studies, plans, passage designs, construction of fishways, and effectiveness plans and monitoring studies.  Agency comments on these filings and resolution of the comments shall also be provided, until all passage measures are implemented and deemed sufficient by the resource agencies. This annual reporting shall also identify the status of the upstream fishway installation at the downstream Rollinsford Project, as it affects the schedule for upstream passage at this Project.

Condition 3: In annual compliance submittals to LIHI, the facility Owner shall summarize activities taken to protect impacts to the northern long-eared bat during eel and fish upstream and downstream passage construction.  The facility Owner shall also report on any ground-disturbing activity requiring surveys for the small whorled pogonia including results of such surveys as well as any additional requirements imposed by the USFWS if small whorled pogonia is found.

Condition 4: The facility owner shall notify LIHI within 60 days of submission of the updated Historic Properties Management Plan (HPMP) addressing previously identified deficiencies, and confirmation of final approval of HPMP. Until then, the annual compliance submittals to LIHI shall identify any activities that triggered the interim requirements.

2024: Annual reporting for the current Certificate has not yet taken effect.

Certification History

June 20, 2024: The Low Impact Hydropower Institute has issued a final decision on the certification of the Lower Great Falls Hydroelectric Project. The 10-year certification term is February 9, 2024 to February 8, 2034.

May 16, 2024: The Low Impact Hydropower Institute (LIHI) has preliminarily approved Low Impact Certification for the Lower Great Falls Hydroelectric Project, FERC# P-4451 (pending LIHI #202). The project is located on the Salmon Falls River in New Hampshire and Maine. 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 comments@lowimpacthydro.org with “Lower Great 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 June 16, 2024. If no appeal requests are received the certification terms will be February 9, 2024 through February 8, 2034.

February 12, 2024: The Low Impact Hydropower Institute has received a complete application for Low Impact Certification of the Lower Great 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 comments@lowimpacthydro.org with “Lower Great 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 April 12, 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.

2024 Certification Files

Key Documents