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Low-Head Hydropower Construction Impacts

Construction activities that may cause environmental impacts include ground clearing, grading, excavation, blasting, trenching, vehicular and pedestrian traffic, and drilling.

Typical activities during the construction of a low-head hydropower facility include ground clearing (removal of vegetative cover and trees in a forested region), grading, excavation, blasting, trenching, drilling, vehicular and pedestrian traffic, and construction and installation of facilities. Activities conducted at locations other than the facility site include excavation/blasting for construction materials (e.g., sands, gravels) if a borrow area on site is not available, and access road and transmission line construction. 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 construction activities.

Acoustics (Noise)

The primary sources of noise during construction would be equipment (e.g., rollers, bulldozers, diesel engines). Other sources of noise include vehicular traffic, tree felling, and blasting. Whether the noise levels exceed U.S. Environmental Protection Agency (EPA) guidelines or local ordinances would depend on the distance to the nearest residence. If near a residential area, noise levels from blasting and some equipment operation could exceed the EPA guidelines but would be intermittent and extend for only a limited time. Adverse impacts due to noise could occur if the site is located near a sensitive area, such as a park, wilderness, or other protected area. The primary impacts from noise would be localized disturbances to wildlife, recreationists, and residents.

Air Quality (including Global Climate Change and Carbon Footprint)

Emissions generated during the construction phase include vehicle emissions; diesel emissions from large construction equipment and generators; volatile organic compound (VOC) releases from storage and transfer of vehicle/equipment fuels; small amounts of carbon monoxide, nitrogen oxides, and particulates from blasting activities; and fugitive dust from many sources, such as disturbing and moving soils (clearing, grading, excavating, trenching, backfilling, dumping, and truck and equipment traffic), mixing concrete, storage of unvegetated soil piles, drilling, and pile driving.

As a state or local air agency permit is needed to control or mitigate these emissions; it is unlikely that these emissions would cause an exceedance of air quality standards or have an impact on climate change.

Cultural Resources

Direct impacts to cultural resources could occur from construction activities, and indirect impacts might be caused by soil erosion and increased accessibility to possible site locations. Potential impacts include:

  • Complete destruction of the resource if present in areas undergoing surface disturbance or excavation;
  • Degradation or destruction of near-surface cultural resources on- and off-site resulting from topographic or hydrological pattern changes, or from soil movement (removal, erosion, sedimentation). (Note: the accumulation of sediment could protect some localities by increasing the amount of protective cover);
  • Unauthorized removal of artifacts or vandalism to the site as a result of increases in human access to previously inaccessible areas, if significant cultural resources are present; and
  • Visual impacts resulting from vegetation clearing, increases in dust, and the presence of large-scale equipment, machinery, and vehicles (if the affected cultural resources have an associated landscape or other visual component that contributes to their significance, such as a sacred landscape or historic trail).

An archaeologist should be on-site during construction to assure that historic properties and resources are avoided.

Ecological Resources

Ecological resources that could be affected include vegetation, fish, and wildlife, and their habitats. Vegetation (including trees in a forested region) and topsoil would be removed in areas where facilities would be constructed, including associated access roads, parking areas, transmission lines, canals, pipelines, and other ancillary facilities. This would lead to a loss of wildlife habitat, reduction in plant diversity, potential for increased erosion, and potential for the introduction of invasive or noxious weeds. The recovery of vegetation following interim and final reclamation would vary by community (e.g., grasslands would recover before sagebrush or forest habitats) or the type of plant community desired. Indirect impacts to vegetation would include increased deposition of dust, spread of invasive and noxious weeds, and the increased potential for wildfires. Dust settling on vegetation may alter or limit a plant's ability to photosynthesize and/or reproduce. Although the potential for an increase in the spread of invasive and noxious weeds would occur during the construction phase due to increasing traffic and human activity, the potential impacts could be partially reduced by interim reclamation and implementation of mitigation measures.

Adverse impacts to wildlife could occur during construction from:

  • Erosion and runoff;
  • Fugitive dust;
  • Noise;
  • Introduction and spread of invasive vegetation;
  • Modification, fragmentation, and reduction of habitat;
  • Mortality of biota (i.e., death of plants and animals);
  • Exposure to contaminants; and
  • Interference with behavioral activities.

Wildlife would be most affected by habitat reduction within the project site, access roads, canals, and pipeline and transmission rights-of-way. Wildlife within surrounding habitats might also be affected if the construction activity (and associated noise) disturbs normal behaviors, such as feeding and reproduction.

Construction of intake structures, dams, and weirs would significantly alter the river that would provide the water supply for the hydropower facility. These alterations could lead to habitat loss and/or degradation for aquatic species. Fish could be injured or killed during construction of the intake or dam through human or mechanical means or due to increased sedimentation downstream. These impacts could be minimized by timing construction during periods of low flow and by excluding fish from the work area.

Environmental Justice

If significant impacts occurred in any resource areas, and these impacts disproportionately affected minority or low-income populations, then there could be an environmental justice impact. Issues of potential concern during construction are noise, fugitive dust, and visual impacts from the construction site and possible impacts associated with the construction of new access roads and alterations to the river (e.g., impacts such as fish kills). Additional impacts include limitations on access to the area for tribal recreation, subsistence, and traditional activities.

Hazardous Materials and Waste Management

Solid and industrial waste would be generated during construction activities. The solid wastes would likely be nonhazardous and consist mostly of containers, packaging materials, and wastes from equipment assembly and construction crews. Industrial wastes would include minor amounts of fuels, spent vehicle and equipment fluids (e.g., lubricating oils, hydraulic fluids, battery electrolytes, glycol coolants), and spent solvents. Hazardous materials include compressed gases used for welding, cutting, brazing, etc., dielectric fluids, and oils. These materials would be transported off-site for disposal, but impacts could result if the wastes were not properly handled, and were released to the environment. No impacts are expected from proper handling of all wastes.

Human Health and Safety

Potential impacts to worker and public health and safety from low-head hydropower plant construction would be similar to those expected for any construction project involving earthmoving, large equipment, transportation of oversized materials, and construction and installation of industrial facilities. Most accidents in the construction industry result from overexertion, falls, or being struck by equipment. Construction-related illnesses could also result from exposure to spilled chemical substances. In addition, 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. All personnel involved with the construction would utilize appropriate safety equipment and would be properly trained in required Occupational Safety and Health Administration (OSHA) practices.

Land Use

Impacts to land use could occur during construction if there were conflicts with existing land use plans and community goals; conflicts with existing recreational, educational, religious, scientific, or other use areas; or conversion of the existing commercial land use for the area (e.g., agriculture, grazing, mineral extraction).

Existing land use during construction would be affected by intrusive impacts such as ground clearing, increased traffic, noise, fugitive dust, and human activity, as well as by changes in the visual landscape. In particular, these impacts could affect those seeking solitude or recreational opportunities in a relatively pristine landscape. Ranchers or farmers could be affected by loss of available grazing or crop lands, potential for the introduction of invasive and noxious plants that could affect livestock forage availability, and possible increases in livestock/vehicle collisions. An expanded access road system could increase the numbers of off-highway vehicle users, hunters, and others using the surrounding area for recreation.

The presence of the facility in or near a wilderness area would diminish the wilderness character in the project area.

Paleontological Resources

Impacts to paleontological resources could occur directly from the construction activities or indirectly from soil erosion and increased accessibility to fossil locations. Potential impacts include:

  • Complete destruction of the resource if present in areas undergoing surface disturbance or excavation;
  • Degradation or destruction of near-surface fossil resources on- and off-site caused by changes to topography, changes to hydrological patterns, and soil movement (e.g., removal, erosion, sedimentation). (Note: the accumulation of sediment could serve to protect some locations by increasing the amount of protective cover); and
  • Unauthorized removal of fossil resources or vandalism as a result of increased human access to previously inaccessible areas, if significant paleontological resources are present.


Direct impacts would include the temporary creation of a few new jobs for construction workers and the associated income and taxes generated by the hydropower project. Indirect impacts would occur as a result of the new economic development, and would include new jobs at businesses that support the expanded workforce or provide project materials, and associated income and taxes. Hydropower development activities could also potentially affect property values, either positively, from increased employment effects or negatively, from proximity to the facility along with any associated or perceived environmental effects (noise, visual, etc.).

Adverse impacts could occur if an in-migrant workforce, culturally different from the local indigenous group, is brought in during construction. This influx of migrant workers could strain the existing community infrastructure and social services.

Soils and Geologic Resources

Sands, gravels, and quarry stone would be excavated for constructing access roads; making concrete for foundations and ancillary structures; and improving ground surface for lay-down areas and crane staging areas.

Possible geological hazards (earthquakes, landslides) could be activated by excavation and blasting for raw materials, increasing slopes during site grading and construction of access roads, altering natural drainage patterns, and toe-cutting bases of slopes. Altering drainage patterns could also accelerate erosion and create slope instability.

Surface disturbance, heavy equipment traffic, and changes to surface runoff patterns could cause soil erosion and impacts to special soils (e.g., cryptobiotic soils). Impacts of soil erosion could include soil nutrient loss and reduced water quality in nearby surface water bodies. Proper erosion control would prevent silt mobilized by construction activities from reaching the river.

A reduction in bedload transport in the river would occur during the filling of an impoundment.


Short-term increases in the use of local roadways would occur during the construction period. Heavy equipment would likely remain at the site. Shipments of materials are unlikely to affect primary or secondary road networks significantly, but this would depend on location of the project site relative to material source. Oversized loads could cause temporary transportation disruptions, and could require some modifications to roads or bridges (such as fortifying bridges to accommodate the size or weight). Shipment weight might also affect the design of access roads for grade determinations and turning clearance requirements.

Visual Resources

Possible sources of visual impacts during construction include:

  • Ground disturbance and vegetation removal that produce contrasts of color, form, texture, and line. Such disturbances could occur as a result of excavation for foundations and ancillary structures; trenching to bury pipelines; grading and surfacing roads; clearing and leveling staging areas; stockpiling soil and spoils (if not removed); and soil scars and exposed slope faces resulting from excavation, leveling, and equipment movement. Invasive species could colonize disturbed and stockpiled soils and compacted areas.
  • River modifications from structures placed in or across the river;
  • The creation of a head pond or impoundment;
  • Road development (new roads or expansion of existing roads) and parking areas, depending on the route relative to surface contours, and the width, length, and surface treatment of the roads;
  • Conspicuous and frequent small-vehicle traffic for worker access and frequent large-equipment traffic (trucks, graders, excavators, and cranes) for road construction, site preparation, and construction of the facility that could produce visible activity and fugitive dust in dry soils;
  • Temporary presence of large equipment, producing emissions while operational and creating visible exhaust plumes; and
  • Support facilities and fencing associated with the construction work.

Water Resources (Surface Water and Groundwater)

Water Use

Water would be used for fugitive dust control when clearing vegetation and grading, and for unpaved road traffic; for making concrete for foundations, intake structures, dams and ancillary structures; and for consumptive use by the construction crew. Water would likely be obtained from the river, but could be trucked in from off-site. The quantity of water used would be small relative to water availability.

Water Quality

Water quality could be affected by:

  • Activities that cause soil erosion, including construction of the intake and dam, which could increase turbidity and suspended sediment transport;
  • Weathering of newly exposed soils, which could cause leaching and oxidation, thereby releasing chemicals into the water;
  • Discharges of waste or sanitary water; and
  • Untreated groundwater used to control dust could deposit dissolved salts on the surface, allowing the salts to enter surface water systems.

Flow Alteration

Surface flow in the river would be altered by construction of the intake system and more so by any dam or weir. If a dam or weir is required, a head pond (impoundment) of up to 20 acres would be formed upstream from the structure, which would normally be 10 ft high or less. Surface and groundwater flow systems could be affected by wastewater and stormwater discharges. Excavation activities and the extraction of geological materials could affect surface and groundwater flow. The interaction between surface water and groundwater could also be affected if the surface water and groundwater were hydrologically connected, potentially resulting in unwanted dewatering or recharging of water resources.