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Low-Head Hydropower Operations and Maintenance Impacts

Operations activities that may cause environmental impacts include operation of the low-head hydropower facility, power generation, and associated maintenance activities.

Typical activities during the operation of a low-head hydropower facility include operation of the facility, power generation, and associated maintenance activities that would require vehicular access and heavy equipment operation when components are being replaced. Potential impacts from these activities are presented below, according to the type of affected resource.

The following potential impacts may result from low-head hydropower facility operation.

Acoustics (Noise)

Sources of noise during operations would be from the turbine, generator, and transformer. The powerhouse could be insulated to minimize noise from these sources. Another source of noise is corona from transmission lines. Vehicular traffic noise and noise from maintenance activities would be limited to weekly site visits.

Air Quality (including Global Climate Change and Carbon Footprint)

There are no direct air emissions from operating a hydroelectric facility. Minor volatile organic compound (VOC) emissions are possible during routine maintenance activities. Vehicular traffic will continue to produce small amounts of fugitive dust and tailpipe emissions during weekly maintenance activities. These emissions would not likely exceed air quality standards nor have any impact on climate change.

Carbon tied up in trees and plants is released when a reservoir is initially flooded and the vegetation rots. Plant matter settling on the reservoir's bottom decomposes without oxygen, resulting in the buildup of dissolved methane, which is released to the atmosphere. There is a rapid increase in greenhouse gas emissions shortly after flooding, followed by a return to normal values (10 years for carbon dioxide and 4 years for methane) measured in natural lakes and rivers. Greenhouse gas emissions from impoundments at hydropower plants are 1–10% of those produced by thermal energy plants. The lower values are for boreal reservoirs; the larger values for tropical reservoirs.

Cultural Resources

Impacts during the operational phase would be limited to unauthorized collection of artifacts, and visual impacts. The threat of unauthorized collection would be present once the access roads are constructed in the site evaluation or construction phase, making remote lands accessible to the public. Visual impacts resulting from the presence of low-head hydropower facilities and transmission lines could affect some cultural resources, such as sacred landscapes or historic trails.

Ecological Resources

During operation, adverse ecological effects could result from disturbance of wildlife by equipment noise; weekly site inspection and maintenance; exposure of biota to contaminants; and mortality of birds from colliding with the project facilities and/or electrocution by transmission lines. During operation, wildlife could still be affected by habitat fragmentation or the presence of barriers in fenced areas, canals or above-ground pipelines, utility rights-of-way (ROWs), and access roads. In addition, the presence of the hydropower project and its associated access roads and ROWs may increase human use of surrounding areas, which could, in turn, impact ecological resources in the surrounding areas through:

  • Introduction and spread of invasive vegetation;
  • Disturbance;
  • Mortality of wildlife from vehicles;
  • Increase in hunting (including poaching); and
  • Increased potential for fire.

The presence of a dam or weir would impose a physical barrier to fish migration. This could be mitigated by construction of a fish ladder or sluice. The impoundment would flood areas such as forests, sedge fens, shrub/scrub, and wetlands. Increases in water temperature from solar heating as a result of the creation of a 10–20-acre or less shallow impoundment would be small, since the retention time would be on the order of days. The shallowness would also prevent thermal stratification of the water. Passage of water through the penstock is not expected to affect water temperature. The water discharge structure or tailrace would be designed to prevent fish from entering. It would also be designed to prevent scouring and sedimentation downstream. Design of the low-head hydropower facility would have to provide for a minimum flow of water downstream of the plant. Impacts on downstream flora and fauna could occur, if the minimum flow is not calculated with those species in mind or is not maintained. If not properly managed, water quality degradation from vehicular traffic and machinery operation during maintenance (e.g., erosion and sedimentation) and wastewater disposal could occur and adversely impact ecological resources.

Environmental Justice

Possible environmental justice impacts during operation include the continued alteration of scenic quality in areas of traditional or cultural significance to minority or low-income populations and disruption of access to those areas. Noise impacts and health and safety impacts are also possible sources of disproportionate effect.

Hazardous Materials and Waste Management

Very little waste would be generated during operation of the low-head hydropower facility. Any industrial wastes generated during routine operations and maintenance (dielectric fluids, cleaning agents, and solvents) would be put in containers, characterized and labeled, possibly stored briefly, and transported by a licensed hauler to an appropriate permitted off-site disposal facility as a standard practice. Materials collected from the intake and the trashrack would not be hazardous waste, but would also require disposal.

Impacts could result if these wastes were not properly handled and were released to the environment.

Human Health and Safety

Possible impacts to health and safety during operations include exposures to electromagnetic fields (EMF) and accidental worker injury or death during operation and maintenance activities. In addition, worker health and safety issues include working in potential weather extremes, and possible contact with natural hazards, such as uneven terrain and dangerous plants, animals, or insects. Risk to the public of accidental death or injury is unlikely, since the facilities would be fenced. However, access to the impoundment or tailrace would be a potential source for accidents.

Land Use

Land use impacts during the operation of the low-head hydropower facility would be an extension of those that occurred during the construction phase.

Paleontological Resources

Impacts during the operations phase would be limited to unauthorized collection of fossils. This threat is present once the access roads are constructed in the site evaluation or construction phases, making remote lands accessible to the public.


Direct impacts would include the creation of a few jobs for operation and maintenance workers and the associated income and taxes paid. Indirect impacts are those impacts that would occur as a result of the new economic development and would include things such as new jobs at businesses that support the workforce or that provide project materials, and associated income and taxes. The number of project personnel required during the operation and maintenance phase would be about an order of magnitude fewer than during construction. Therefore, socioeconomic impacts related directly to jobs would be minimal.

Soils and Geologic Resources

During operation, the soil and geologic conditions would stabilize with time. Soil erosion and soil compaction are both likely to continue to occur along access roads. Within the project footprint, soil erosion, surface runoff, and sedimentation of nearby water bodies will continue to occur during operation, but to a lesser degree than during the construction phase, and the impact is expected to be small once equilibrium is achieved.


No noticeable impacts to transportation are likely during operation. Low volumes of heavy- and medium-duty pickup trucks and personal vehicles are expected for routine maintenance and monitoring. Infrequent but routine shipments of component replacements during maintenance procedures are likely over the period of operation.

Visual Resources

Many of the visual impacts caused by construction will remain during operation. These include:

  • Ground disturbance and vegetation removal that could result in visual impacts that produce contrasts of color, form, texture, and line;
  • River modifications that would result in visual impacts from structures placed in or across the river. The creation of a head pond (impoundment) would change the visual appearance of the river at that location;
  • Road development (new roads or expansion of existing roads) and parking areas that could introduce strong visual contrasts in the landscape, depending on the route relative to surface contours, and the width, length, and surface treatment of the roads; and
  • Conspicuous but infrequent small-vehicle traffic for worker access during weekly maintenance that could produce visible activity and fugitive dust in dry soils.

Water Resources (Surface Water and Groundwater)

The amount of water required to operate the low-head hydropower facility is a function of the site-specific design and the minimum flow of water that must be maintained in the river at all times. Proper design should reasonably ensure that the minimum stream flow should be maintained for all but a few days per year, so that impacts on power generation capacity are minimal. As discussed in the Ecology Resources impact section, the low-head hydropower facility must be designed to provide for a minimum flow of water downstream of the plant to minimize impacts to downstream flora and fauna.

Impacts to water resources during the operation and maintenance phase would include possible degradation of water quality resulting from vehicular traffic and machinery operation during maintenance (e.g., erosion and sedimentation) and wastewater disposal. A sluice or low gate would be provided for an impoundment to allow bedload flushing.

If the facility includes an impoundment, there could be limited potential for flooding of surrounding areas depending upon the location of the impoundment, its design, and the magnitude of precipitation events.