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Transmission Wetlands and Riparian Zones

Wetlands and Riparian Zones
Present, Potentially Affected

The Clean Water Act(CWA) (33 U.S.C. 1251-1387) sets standards for the chemical, physical and biological properties of all bodies of water in the United States. It mandates a permitting system and is responsible for programs to mitigate the impacts of certain pollutants.

CWA Section 404 defines “discharge of dredged material" to narrow wetland drainage exemptions. Allowable actions that degrade or destroy wetlands include, “redeposit, of dredged material, including excavated material, into waters of the United States which is incidental to any activity, including mechanized land clearing, ditching, channelization, or other excavation.” While section 404 regulates discharge into wetlands and riparian zones, it does not regulate groundwater depletion or wetland loss.

Water quality standards (WQS) uphold wetland integrity through specific scientific guidelines and carry out (CWA) requirements. Wetland WQS’s include case-by-case narrative standards opposed to quantitative standards to account for geographic and geologic variability when comparing water flow rates.

https://www.epa.gov/wetlands/what-are-wetland-functions http://www.water.ncsu.edu/watershedss/info/wetlands/protect.html#404

Wetlands and Riparian Zones Impacts & Mitigation

Shallow water and abundant plants supply nutrients to, “microbes, plants, insects, amphibians, reptiles, birds, fish and mammals”, making wetlands a diverse ecosystem. Wetland habitats become ideal for bird nesting, breeding, and migration. Mitigation to these areas includes operational and construction methods to reduce impacts. Limiting wetland surface disturbance may have the biggest positive impact to these ecosystems. Wetland mitigation aims to repair natural wetland degradation from transmission line development activities.

When project impacts exceed the appropriate threshold established by the federal land managing agency, a compensation ratio is agreed upon. Section 404 of the CWA states three ways a developer can provide compensation for the impacted project area.

Typical mitigation measures include:


  • Infrastructure development is limited near wetlands, playas, riparian zones, 100-year floodplains and other surface waters. All exceptions are case-by-case.
  • Mark and identify wetland areas during construction to discourage unnecessary surface disturbance outside of the construction zone.
  • Improve existing seeps; springs and/or meadows access and install piping to maintain water flow from the wetland and riparian zones. Use pipe and rail fencing for the wetlands perimeter to discourage wildlife and unauthorized access. Fencing encourages riparian restoration. Install trough guzzlers to water wildlife and livestock. In dry months, monitor the trough’s water levels to ensure water presence.
  • To mitigate low spring flows, install a spring box and piping to direct water to a discharge point. In the event of excessive pumping, this mitigation measure will not revive dry groundwater supplies.
  • To mitigate soil impacts and decrease indigenous aquatic species impacts, place heavy equipment on mats when near wetlands and riparian zones.
  • In “exclusion zones”, build buffers between construction and riparian areas to decrease sediment intrusion. Avoid moving soil and limit activities to reflect a travel only zone.
  • Avoid constructing towers in riparian areas, as they do not provide a strong foundation and have large impacts on the habitat.
  • Manage dewatering activities including disposing drilling fluids and mud away from wetland or surface waters.
  • Dispose of excess concrete off-site.
  • Use high-visibility fencing to discourage parking or driving in sensitive areas.
  • Schedule the construction project phase in the dry season to minimize swampy conditions and water flow through exposed soils.
  • Store hazardous materials off-site or away from wetlands. This includes fueling stations.
  • Use “end hauling” methods if access roads are near riparian areas. This process includes making a slope cut and taking the displaced soil either off-site or to fill an area of lesser concern. This enables a buffer between sediment, vegetation, and water.

Birds and Vegetation

  • Avoid project development during nesting and breeding seasons, which is typically between February 1st and August 15th.
  • Avoid using heavy equipment and performing vegetation removal in wetlands to mitigate soil compaction, habitat destruction, and possible surface water alteration.


  • Recharge, rebuild, repair, or re-establish wetland and riparian functions.
  • These functions include enabling erosion and flood control, regulating groundwater levels and flow rates, protecting drinking water, acting as storm surge buffers, and replenishing soil nutrients.
  • Reseed impacted areas.
  • Expect three-five years of area monitoring and maintenance.

Compensation Types:

Mitigation bank

  • An off-site wetland is preserved, established, or restored by the utility company to offset the impacts the transmission line project has caused to a wetland or riparian zone.
  • “A mitigation bank sells compensatory mitigation credits to permittees whose obligation to provide compensatory mitigation is then transferred to the mitigation bank sponsor. The operation and use of a mitigation bank are governed by a mitigation banking instrument.”

In-lieu fee program

  • The project developer pays the federal land-managing agency to restore, establish or enhance a wetland.
  • “Similar to a mitigation bank, an in-lieu fee program sells compensatory mitigation credits to permittees whose obligation to provide compensatory mitigation is then transferred to the in-lieu program sponsor. However, the rules governing the operation and use of in-lieu fee programs are somewhat different from the rules governing operation and use of mitigation banks. An in-lieu fee program instrument governs the operation and use of an in-lieu fee program.”

Permittee-responsible mitigation

  • The project developer takes full responsibility to restore, establish, enhance, or preserve the wetland’s features.