Rumford Falls Hydroelectric Project - Upper Falls and Powerhouse

Knowledge is (Hydro)Power for Fish Natural Resources

Understanding Fish Issues in FERC Relicensing

Water is one of our most precious — and versatile — resources. Yet there are constant challenges and debate over how water is allocated for its many uses by humans and the environment. One important intersection of water’s competing uses is the generation of electricity using hydropower. In the United States, there are an estimated 1,500 hydropower plants that generated approximately 291 billion megawatt hours in 2020, or enough energy to power roughly 26.5 million homes for one year. Whereas hydropower provides the U.S. with an essential source of carbon-free renewable energy, its use of water can impact resources such as fish habitat and migratory fish. In the U.S., hydropower facilities under the jurisdiction of the Federal Energy Regulatory Commission are relicensed every 30 to 50 years using a robust public process that analyzes, evaluates and balances the developmental (energy generation and flood protection) and non-developmental (aquatic and terrestrial habitats) resources related to the hydropower plant. Our hydropower experts have supported the FERC relicensing of hundreds of hydropower plants and have helped the industry navigate the delicate balance between optimizing valuable hydropower resources and preserving natural environmental resources. At the forefront of these efforts is the need to support the balancing of hydropower with the rivers and aquatic habitats that are home to America’s fisheries.

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The Relicensing Process

FERC regulates the hydropower industry, including the relicensing process, under authority from the Federal Power Act. In 1986, Congress amended the FPA through the Electric Consumers Protection Act. This landmark legislation requires FERC to give equal consideration to both power and non-power resources when issuing a new hydropower license. ECPA, in conjunction with subsequent court rulings, established the hydropower relicensing process we know today.

The formal relicensing process begins about five years prior to expiration of the existing license — when the licensee files a Notice of Intent and Pre-Application Document. The PAD provides agency personnel and interested stakeholders with existing, relevant and reasonably available information regarding the hydropower plant and the surrounding assets that include environmental, cultural and recreational resources. Although these filings are the first formal step of FERC’s relicensing process, our teams begin working with our clients well in advance of this initial milestone. Essential to this process is developing clear goals and objectives for the relicensing and defining a successful outcome for the proceeding. There is no benefit to undertaking a multiyear relicensing process that, in turn, does not result in a viable project that logistically and fiscally supports an owner’s long-term success.

The PAD also identifies data gaps that need to be addressed during the proceeding. This information is required to help define structural and operational modifications to the hydropower plant following issuance of the new license. These information needs are often addressed through resource-specific studies and by determining a nexus or connection between plant operations and effects on a resource. Performing resource studies in support of obtaining the new license is a critical phase of relicensing. The study plan design and implementation phase can account for 40 to 60 percent of the overall cost of relicensing and typically involves consultation with agencies (state fish and wildlife, federal land managers, etc.), Native American tribes and nongovernmental organizations (e.g., Trout Unlimited, American Rivers, American Whitewater). We develop aquatic studies in collaboration with agency staff while keeping an “owner’s perspective” throughout the process.

After addressing the information needs and performing necessary studies, relicensing focuses on the development of the License Application, which by statute must be filed with FERC at least two years prior to expiration of the existing license. The License Application includes protection, mitigation and enhancement measures that the licensee proposes to implement over the term of the new license. In some relicensing cases, the licensee chooses to develop and negotiate these PM&Es with various stakeholders ahead of filing the License Application. We provide critical support during this phase by helping our clients negotiate reasonable PM&E measures — considering capital and operational costs, generation impacts and resource benefits. Given that negotiated PM&Es will be required for the term of the new license (30 to 50 years), negotiating reasonable measures is essential to a successful relicensing. Once FERC and the resource agencies complete their respective environmental analyses (an environmental assessment or environmental impact statement for FERC) and the State issues a Section 401 Water Quality Certificate, FERC issues the new license. The license grants our clients the right to operate the hydropower plant consistent with the terms of the new license. Given the site-specific expertise developed over the course of a relicensing, we often continue supporting our clients with the implementation and compliance of the new license. This support is often in the form of regulatory, environmental and engineering services.

A map showing HDR's current and historic FERC relicensing efforts
HDR's current and historic FERC relicensing efforts

Aquatic Habitat Evaluations

Most hydropower owners are required to release a minimum baseflow of water downstream of their facilities for environmental benefits. The relicensing process provides agencies and stakeholders the opportunity to reevaluate the quantity and timing of these downstream releases. To better understand the environmental effects of varied flow regimes downstream of a hydropower plant, our teams perform detailed aquatic habitat evaluations using site-specific field data and various models from new or preexisting data. These models incorporate habitat variables such as substrate, water depth, water velocity and water temperature, along with the preferences of these variables by species expected to be present in the downstream river reach. Often, the analysis is broken down further by life stage and life history. HDR’s ability to develop and apply these robust models is due to the collaborative efforts of our fisheries, geomorphology and geospatial scientists and engineers.

One suite of studies was completed for the Merced Irrigation District’s Merced River Project in the Central Valley of California. The lower Merced River extends 52 miles from Merced ID’s Crocker-Huffman Diversion Dam to the river’s confluence with the San Joaquin River. Fall-run Chinook salmon are known to spawn mostly in the upper 20 miles of the lower Merced River, and the river contains potential habitat for Endangered Species Act-listed Central Valley steelhead.

To better understand how changes in flow and Merced ID’s project operations impact habitat availability for the various species and life stages, our staff completed both one- and two-dimensional habitat models for the lower Merced River. In support of the 1-D model, we established and collected data along 65 transects representative of the various aquatic habitats associated with the river. The combination of the transect data and model allowed us to extrapolate and apply the observed river conditions to the larger river reach. To further understand habitat conditions in the lower Merced River, we developed a 2-D model that incorporated data from the entire 20-mile “spawning reach” where each individual habitat unit was surveyed and evaluated. In total, millions of topographic data points were collected using a combination of aerial LIDAR, boat-based bathymetry and handheld surveying. To complete the model, we combined these data with hundreds of water depth and velocity measurements taken at three target flow rates. The model also incorporated substrate, vegetation and water temperature in order to evaluate habitat and flow suitability for species and life stages such as juvenile fall-run Chinook salmon.

The models gave Merced ID and the resource agencies a calibrated approach to evaluate base flow and operational scenarios in support of developing the License Application. In some instances, the models allowed Merced ID to demonstrate that higher seasonal flows were not always beneficial to the fish habitat of interest and paved the way for Merced ID to propose lower flows to better balance the flows in support of hydropower generation and environmental benefits. This was a critical success for Merced ID because any opportunity to conserve water or reallocate water for other beneficial uses such as agriculture or consumption, while still providing environmental benefits, is valuable and provides long-term sustainability to the aquatic system.

Model output of usable salmon habitat along the Merced River
Model output of usable salmon habitat along the Merced River.

Fish Populations

The aquatic communities and the fish species present in reservoirs formed by hydropower facilities, as well as the downstream river reaches, will dictate the scope of studies to be performed during a relicensing proceeding. Hydropower facilities with species listed under state or federal endangered species laws, or anadromous species, such as salmon, may require more robust evaluation. Our fisheries biologists perform species-specific and population-level fisheries studies throughout the United States and are well-versed with backpack and boat-based electrofishing, seining, gill netting and snorkeling to determine the presence of target species and the potential impact of hydropower operations on the species’ life cycle. Given that no two hydropower plants are identical, every methodology is customized to meet the study objectives and to address the data gap of the specific relicensing proceeding.

An example where our fisheries team performed a large-scale fisheries study was the joint relicensing of Pacific Gas and Electric’s Drum-Spaulding and Nevada Irrigation District’s Yuba-Bear Projects, considered one of the country’s most complicated relicensings due to the number of facilities, stream reaches and reservoirs. As part of the study, we sampled fish in 55 stream reaches and five reservoirs ranging in elevation from about 500 feet to almost 8,000 feet. Sampling consisted of electrofishing and snorkeling of stream reaches, and electrofishing and gill netting in reservoirs. Overall, approximately 4,500 individual fish were observed or captured from 15 species. Our staff performed field surveys, managed the field data and developed detailed analyses and reports. The results of this effort were essential to preparing the License Application and provided vital data and analysis used during negotiations of PM&E measures with resource agencies.

This large-scale study and corresponding data set was also used in conjunction with other studies related to water quality, water temperature, benthic macroinvertebrates and amphibians to better understand the overall aquatic community and help benefit the power and non-power resources through this robust relicensing proceeding.

Fish Passage

The FERC relicensing process provides federal and state fishery management and resource agencies with the rare opportunity to require the installation of upstream and downstream fish passage at a hydropower facility. Although there may be opportunities during the term of the new license for an agency to pursue fish passage measures, the FPA and associated statutes and regulations provide the agencies with the defined process to require such measures during the course of the relicensing proceeding. Therefore, evaluating the need for fish passage, as well as the balancing of hydropower operations and fish passage, is a resource area of focus for many hydropower agencies.

Fish passage is very region specific. For example, our hydropower clients in the Northeast must consider upstream and downstream passage for American eel and alosines (e.g., shad and blueback herring) for all rivers that connect to the Atlantic Ocean and the St. Lawrence watershed. In addition, rivers in Maine are home to the ESA-listed Atlantic salmon, and various species of sturgeon and walleye are found in river systems throughout the country. Essential to a successful relicensing is the understanding of potential fish passage measures that may be required by the new license, as well as the costs to develop and operate the passage measures over the term of the new license. Our fisheries biologists and fishway design engineers routinely support hydropower agencies with developing the necessary information to understand the potential implications of fish passage to hydropower operations, and on the capital and operations and maintenance budgets related to implementing the new license.

Our fisheries biologists and fishway engineers are well versed in this design process, as well as the agency consultation that is required to develop an effective fish passage structure in a timely and efficient manner. Essential to a successful fish passage structure is the understanding and combining of fish biology and migratory movement, fishway hydraulics, structural design and the electrical and mechanical engineering required to integrate the fishway into the hydropower facility’s internal operations.

Recent fishway designs that we developed following the issuance of a new FERC license include two nature-like fishways that are operational in New York. In addition, we are currently supporting multiple agencies with the design and subsequent effectiveness testing of additional fishways that resulted from the FERC relicensing process.

Entrainment and Impingement

In addition to determining the composition, abundance and distribution of the fish community, and the need to provide passage for these species, relicensing agencies are often required to perform a field or desktop assessment of fish impingement or entrainment. Impingement occurs when a fish is held against or entrapped on the exterior intake structure screen or bar racks due to forces created by velocities at the intake. Entrainment occurs when the fish passes through the fish screens or bar racks and is withdrawn into the intake structure.

The potential for fish to become entrained or impinged at a hydroelectric facility is dependent on a variety of factors, such as fish life history, size and swimming ability, water quality, operating regimes, inflow, turbine configurations, intake structure dimensions and presence of a spillway or bypass channel. These factors are used to select comparable and representative studies from an existing entrainment database compiled by the Electric Power Research Institute (EPRI 1997).

The desktop entrainment study uses database entrainment results from studies performed at facilities comparable in design and operation to the current facility in order to estimate entrainment rates (monthly, seasonal, annual) for target species. Our experts estimate fish turbine entrainment or spillway passage mortality at hydroelectric dams using the U.S. Fish and Wildlife Service’s Turbine Blade Strike Assessment Model, which was released in 2018.

Our fish entrainment experts also design and implement field-based assessments of entrainment and impingement at cooling water intake structures for electric utility agencies across the U.S., including Duke Energy, Dominion Energy and Muscatine Power and Water, to support compliance with requirements of the Clean Water Act Section 316(b) Final Rule (CWA 2014). Fish and ichthyoplankton collections are processed and identified taxonomically at our biological laboratory in Nanuet, New York.


The FERC relicensing process is focused on balancing the power and non-power resources associated with a hydropower facility, as well as the interests of various stakeholders with the generation of carbon-free renewable energy. Our FERC regulatory specialists and fisheries staff collaborate with hydropower agencies to better define the aquatic communities and the potential impacts and benefits of hydropower operations on these resources. By developing and implementing site-specific and focused studies, we are able to help our hydropower clients successfully navigate the relicensing process by emphasizing the owner’s goals, while also developing effective and streamlined PM&E measures to address environmental interests and enhance the resources associated with the hydropower plant. As water availability continues to be a major issue in the U.S. and beyond, the ability to thoughtfully balance competing needs through regulatory processes like FERC relicensing will be invaluable.


Contact Chuck Vertucci at charles.vertucci [at] or at +1 (916) 679-8768, Jim Gibson at jim.gibson [at] or at +1 (315) 414-2202, Misty Huddleston at misty.huddleston [at] or at +1 (865) 556-9153 for more information.