Asheville Ecological Services Field Office
Conserving the Nature of America





Recommendations for bridge and culvert design, construction, or improvements

These recommendations are meant to serve as a guide. Additional or alternative steps may be necessary depending on the situation, including species or habitat type present. Following these guidelines, though likely to expedite project review, is not a substitute for review of the project by a Service biologist.

Preventing direct water contamination – Water contamination can be one of the most damaging and difficult to control environmental impacts that can result from a project. In order to avoid these impacts, we recommend:

  • * Refueling construction equipment outside the 100 year floodplain or at least 200 feet from all water bodies (whichever distance is greater) and protecting the refueling area with secondary containment
  • * Storing hazardous materials, fuel, lubricating oils, or other chemicals outside the 100‑year floodplain or at least 200 feet from all water bodies (whichever distance is greater), at an upland site
  • * Inspecting and maintaining equipment daily to prevent the contamination of surface waters from leaking fuels, lubricants, hydraulic fluids, or other toxic materials
  • * Keeping equipment out of streams by operating from the banks in a fashion that minimizes disturbance to woody vegetation
  • Cleaning and checking equipment for leaks of hydraulic fluids, cooling system liquids, and fuel before fording any stream
  • * Wet concrete not contacting water entering or flowing in the river
  • * Not using fertilizers and pesticides near streams or wetlands
  • * The bridge design include provisions for the roadbed and deck drainage to flow through a vegetated buffer large enough to alleviate any potential effects from the runoff of storm water and pollutants
  • * Any bridge demolition occur at low flow

Protecting the flood plain and streamside forest -
Streamside forests provide travel corridors and habitat for wildlife and protect water quality by stabilizing stream banks and filtering storm‑water runoff. Development in the floodplain increases the potential for flooding adjacent properties and interferes with natural hydrological processes. Floodplain fill alters the volume of water the floodplain will hold, thus altering the extent of the floodplain.  This will:  (1) lead to a floodplain that contains property and facilities previously not in the floodplain, (2) cause flooding in new areas, and (3) have negative impacts on fish and wildlife resources. In order to protect these important and sensitive stream-side areas, we recommend:

  • * Limiting activities in the floodplain to those absolutely necessary for construction
  • * Maintaining riparian vegetation to the maximum extent possible, especially large trees
  • * If riparian areas are disturbed, revegetating them with native species as soon as possible
  • * Locating areas used for borrow or construction by‑products away from wetlands and out of the 100-year flood plain
  • * Using bridges for all permanent roadway crossings of streams and associated wetlands because they minimize impacts to aquatic resources, allow for the movement of aquatic organisms, and eliminate the need to fill and install culverts
  • * Designing the bridge to not alter the natural stream or the stream‑bank morphology or impede aquatic life passage.
  • * Designing the bridges and approaches to avoid any fill that will result in the damming or constriction of the channel or floodplain.
  • * Placing any piers or bents outside the bank‑full width of the streams.
  • * If spanning the floodplain is not feasible, installing culverts in the floodplain portion of the approaches in order to restore some of the hydrological functions of the floodplain and reduce high velocities of floodwaters within the affected areas.
  • * Using bottomless culverts if culverts are the only option, Bottomless culverts do not need to be buried, thereby minimizing adverse impacts to streams.
  • * Designing the culvert to allow for the passage of fish and other aquatic life
  • * Sizing the culvert ed to accommodate the movement of debris and bed material within a channel during a bank‑full event
  • * Maintaining sufficient water depth in the base‑flow barrel during low flows to accommodate fish movement
  • * Minimizing culvert length to the extent possible
  • * Installing alternating or notched baffles in a manner that mimics the existing stream pattern if culvert is longer than 40 linear feet

Preventing or minimizing erosion –
While soil forms the foundation of life on land, in water it becomes a pollutant, smothering aquatic insects, mussels, and other life; rendering fish spawning areas useless; and damaging sensitive tissues, like fish gills. It also increases drinking water treatment costs for downstream users. In order to minimize the amount of soil that enters a stream during the construction of a project, we recommend:

  • * Installing all erosion‑control measures prior to starting ground‑disturbing activities
  • * Frequently maintaining erosion-control measures
  • * Returning existing approaches to preconstruction contours upon completion of the project, and planting the area with native grasses and tree species.
  • * Planting temporary (e.g., rye, grain, wheat, millet) or permanent herbaceous material to help control erosion immediately following any ground‑disturbing activity (native annual small grains and herbs appropriate for the season are recommended.  Fescue‑based mixtures should be avoided)
  • * We recommend the development of a stream‑bank monitoring and maintenance program to promptly stabilize stream banks near the line crossings throughout the life of this project

Stormwater management
– Any development associated with new sewer lines will create more impervious surfaces (such as roofs, roads, and parking lots), which collect pathogens, metals, sediment, and chemical pollutants and without proper planning, quickly transmit them to streams, lakes and wetlands. In order to address these secondary impacts of the project, we recommend:

  • * Minimizing the amount of impervious surface area that will result from developments associated with this project
  • * Developing an adequate plan for the control and treatment of storm water for each development that occurs as a result of the new water system
  • * Implementing sufficient stormwater retention in each associated development to allow for the slow discharge of stormwater, attenuating the potential adverse effects of storm‑water surges: thermal spikes; and sediment, nutrient, and chemical discharges.
  • * The use of low‑impact‑development (LID) techniques to treat storm‑water runoff in the new service area. LID is a method of storm‑water management that allows for storm‑water and environmental controls to be incorporated into the landscape and infrastructure (i.e., green roofs, rain gardens, and grassed swales)

Protecting migratory birds -
The Migratory Bird Treaty Act (16 U.S.C. 703‑712) prohibits the taking, killing, possession, transportation, and importation of migratory birds (including the bald eagle), their eggs, parts, and nests, except when specifically authorized by the Department of the Interior.  To avoid impacts to migratory birds, we recommend:

  • * Conducting a visual inspection of the bridge and any other migratory bird nesting habitat within the project area during the migratory bird nesting season of March through September.  If migratory birds are discovered nesting in the project impact area, including on the existing bridge, impacting the nests should be avoided during the migratory bird nesting season (March through September).
  • * If birds are discovered nesting on the bridge during years prior to the proposed construction date, measures should be developed to discourage birds from establishing nests on the bridge by means that will not result in the take of the birds or eggs, or construction and demolition activities should be avoided during the nesting period.


  • * In most cases we prefer that a bridge be replaced in place by constructing the new bridge through staged construction or by detouring traffic to existing off‑site routes.


Note: Fish & Wildlife Service project planning and review is coordinated by the Asheville Field Office in the western half of North Carolina and by the Raleigh Field Office in the eastern half.

Map: Asheville and Raleigh Field Offices work areas. Credit: USFWS Link to Raleigh Field Office web site


The North Carolina Wildlife Resources Commission has developed a A Guidance Memorandum to Address and Mitigate Secondary and Cumulative Impacts to Aquatic and Terrestrial Wildlife Resources and Water Quality. The memorandum provides numerous recommendations to address the environmental impacts that may result from a project. We support this document and encourage you to use it.

Photo montage of biologists shocking for fish, a biologists studying a plant, and biologists recording mussel data. Photo credits: U.S. Fish & Wildlife Service



Project planning and review contacts:

Address for all:
160 Zillicoa St.
Asheville, NC 28801

Holland Youngman
Projects involving the North Carolina Department of Transportation or Federal Highway Administration

Lauren Wilson
Projects involving the North Carolina Department of Transportation or Federal Highway Administration

Rebekah Reid
cell - 828/782-0090
Project planning and review

Byron Hamstead
office - 828/258-3939, ext. 42225

cell - 828/337-2726
Projects involving the U.S. Army Corps of Engineers

Bryan Tompkins
office - 828/257-3939, ext.42240
cell - 828 450-7586
Projects involving the Federal Energy Regulatory Commission, Tennessee Valley Authority, or Natural Resources Conservation Service



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Last Updated: March 11, 2015