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Ecological Mitigation Measures

Mitigation measures to avoid or reduce ecological impacts from low-head hydropower development.

The following are examples of mitigation measures that could be applied to reduce ecological impacts of a project depending on site- and project-specific conditions. Impacts to ecological resources are related to the project activities (e.g., land disturbance, habitat destruction, erosion, changes in runoff patterns, and hydrological alterations), project emissions (e.g., fugitive dust, sediment runoff, air pollution releases, water releases), and resource use (e.g., water use). Many impacts can be reduced or avoided when taken into account during the siting and design phase.

Develop a final set of mitigation measures for the project in consultation with the appropriate federal resource management agencies and with stakeholders. Conduct these consultations as part of the project development process, preferably prior to final project siting and design.

Siting and Design Mitigation Measures

Siting and design considerations that mitigate impacts include:

  • Review existing information on species and habitats in the project area. Contact appropriate agencies early in the planning process to identify potentially sensitive ecological resources that may be present in the project area.
  • Conduct pre-disturbance surveys in order to locate site facilities away from important ecological resources (e.g., wetlands, important upland habitats, sensitive species populations).
  • Calculate minimum flow downstream of the low-head hydropower facility to minimize impacts to downstream flora and fauna.
  • Ensure protection of important resources by establishing protective buffers to exclude unintentional disturbance.
  • Use existing facilities and disturbed areas (e.g., access roads, graded areas) to the extent possible to minimize the amount of new disturbance. Configure new access roads and rights-of-way (ROWs) to avoid high-quality habitats and minimize habitat fragmentation.
  • Bury electrical supply lines in a manner that minimizes additional surface disturbance. Use overhead lines in cases where the burial of lines would result in further habitat disturbance.
  • Develop a site and ROW reclamation plan that addresses both interim and final reclamation requirements and that identifies vegetation, soil stabilization, and erosion reduction measures. Ensure that interim reclamation of disturbed areas is conducted as soon as possible following facility construction.
  • Develop a plan for control of noxious weeds and invasive plants that could occur as a result of new surface-disturbing activities at the site. The plan should address monitoring, weed identification, the manner in which weeds spread, and methods for treating infestations. Require the use of certified weed-free mulch. Prohibit the use of fill materials from areas with known invasive vegetation problems.
  • Develop a spill management plan.
  • Minimize the amount of land disturbance and develop and implement stringent erosion and dust control practices.
  • Minimize the number of stream crossings when locating access roads. When stream crossings cannot be avoided, use fill ramps rather than stream bank cutting. Design stream crossings to provide instream conditions that allow for and maintain movement and safe passage of fish.
  • Develop site fencing in conjunction with appropriate natural resource agencies to either allow or prevent site access by wildlife species.

General Mitigation Measures

General mitigation practices and principles that could apply to any or all phases of a low-head hydropower project include:

  • Educate workers regarding the occurrence of important resources in the area and the importance of their protection, including the appropriate regulatory requirements.
  • Schedule activities to avoid disturbance of resources during critical periods of the day (e.g., night) or year (e.g., periods of courtship, breeding, nesting, lambing, or calving).
  • Instruct employees, contractors, and site visitors to avoid harassment and disturbance of wildlife, especially during reproductive (e.g., courtship and nesting) seasons. Prohibit pets at the project site.
  • Establish buffer zones around raptor nests, bat roosts, and other biota and habitats of concern such as rare plants, if site studies show that proposed facilities would pose a significant risk to these species.
  • Reduce habitat disturbance by keeping vehicles on established access roads and by minimizing foot traffic in undisturbed areas.
  • Avoid the spread of invasive nonnative plants by keeping vehicles and equipment clean.
  • Reseed disturbed areas with native plants during interim and final reclamation. Undertake reclamation activities as early as possible on disturbed areas.
  • Regularly monitor the project site for invasive nonnative plant species establishment. Initiate control measures immediately upon evidence of invasive species introduction or spread.
  • Limit herbicide/pesticide use to nonpersistent, immobile herbicides/pesticides and apply only in accordance with label and application permit directions and stipulations for terrestrial and aquatic applications.
  • Apply erosion controls that comply with local, state, or federal standards. Apply practices such as jute netting, silt fences, and check dams near disturbed areas.
  • Use abatement techniques on unpaved, unvegetated surfaces to minimize fugitive dust.
  • Apply spill prevention practices and response actions in refueling and vehicle-use areas to minimize accidental contamination of habitats.
  • Address spills immediately per the appropriate spill management plan, and initiate soil cleanup and soil removal if needed.
  • Turn off all unnecessary lighting at night to avoid attracting migratory birds.
  • Require the use of certified weed-free mulch.
  • Prohibit the use of fill materials from areas with known invasive vegetation problems.
  • Implement stringent erosion and dust control practices.

Project Phase-Specific Mitigation Measures

Mitigation measures specific to a particular phase of a low-head hydropower project include:


  • Conduct blasting for raw materials only within specified times and at specified distances from sensitive wildlife or surface waters as specified by state, tribal, or federal agencies.
  • Maintain noise-reduction devices (e.g., mufflers) in good working order on vehicles and construction equipment.
  • Refuel in a designated fueling area that includes a temporary berm to limit the spread of any spill. Use drip pans during refueling to contain accidental releases and under fuel pump and valve mechanisms of any bulk fueling vehicles parked at the construction site.
  • Establish a controlled inspection and cleaning area to visually inspect arriving construction equipment in order to remove and collect noxious weed seeds that may be adhering to tires and other equipment surfaces.
  • Initiate interim site reclamation activities as soon as possible after construction activities are completed using weed-free native shrubs, grasses, and forbs.
  • Time construction of the intakes and dams to avoid periods of low flow.
  • Exclude the fish from the work area.


  • Report observations of potential wildlife problems, including wildlife mortality, to the appropriate wildlife agency.
  • Construct a fish ladder or sluice to minimize injury to fish.
  • Maintain minimum flow downstream of the low-head hydropower facility to ensure downstream flora and fauna are not adversely impacted

Decommissioning/Site Reclamation

  • Implement the site reclamation plan.
  • Review reclamation and weed control efforts periodically until it is determined that the site has been successfully reclaimed.