Center for Environmental Excellence by AASHTO CENTER HOME  
skip navigation
CEE by AASHTO Home | Compendium Home | Online Compendium Help | Recent Updates | Inquiries | FAQs | State DOT Links
About Best Practices | Comment on Best Practices | Suggest A Best Practice | Volunteer to Vet Best Practices
Printer Friendly Version Print This Page    
« Back to Chapter 3 | Go to Chapter 5 »
Chapter 4
Construction Practices for Environmental Stewardship
4.4. Construction in and around Drainage Areas and Streams, Wetlands, and Other Environmentally Sensitive Areas

Construction operations within existing drainageways and the construction of drainage structures (e.g. culverts, channels, and enclosed storm drain systems) increase the potential for erosion from a construction site. The major factors affecting erosion potential are the increasing velocities and concentrating of flows associated with construction of drainage structures and the exposure of erodible soil to frequent concentrated flow. The following list of items should be considered when constructing drainage features and operating within drainageways:

  • Minimize the disturbance of and access to existing waterways. Provide planned and protected stream crossings during construction activities.
  • When constructing cross drainage structures in existing waterways, provide a controlled diversion through the disturbed area as opposed to allowing uncontrolled flow through the construction area. This could be done by temporarily diverting the existing stream through a channel made from sandbag berms or even just protected with plastic sheathing. Divert the stream until the permanent structure is completed or partially completed (e.g. completing one barrel or a multi-barrel culvert installation and allowing the flow to cross through the partially completed portion.)
  • Appropriate coordination should be conducted in accordance with Section 404 of the Clean Water Act regarding the placement of fill material in the Waters of the U.S. (including wetlands).
  • Maximize the storage volume afforded in ditches, etc. for use as temporary sediment traps or ponds to contain sediment-laden runoff on the site.
  • Prevent sediment-laden runoff from entering the drainage system by installing controls at each storm drain inlet and culvert entrance.


4.4.1 Wetlands and Riparian Areas

Wetlands are defined as land that has the water table at, near, or above the land surface, or which is saturated for long enough periods to promote wetland or aquatic processes. Wetlands include bogs, fens, swamps, and marshes. Wetlands are valuable natural resources providing habitat for a variety of wildlife and plant species, both aquatic and terrestrial. Wetlands and riparian areas make up a small percentage of total land area in the United States, but are essential for maintaining water quality and quantity, ground water recharge, and dissipating stream energy. They also provide tremendous community benefits not only to fish and wildlife, but to people as well in the form of fisheries, and recreation, along with other uses. Due to their sensitivity, special attention is in order, including the general pre-contract and pre-construction practices for environmentally sensitive areas, which are outlined in the following section.

Stewardship practices particular to wetlands may include the following, taken from Nova Scotia Transportation & Public Works Environmental Protection Plan for highways. This list has the advantage of being able to be used as a construction specification, if desired: [N]

Travel on wetlands shall be avoided wherever practical. Access roads shall avoid all important wetlands where possible.Best Practice

Activities will be timed to coincide with low water or frozen conditions, where practical.Best Practice

Crossings will be restricted to a single location and will occur perpendicular to and at a narrow point on the wetland. Brush matting, swamp matting, ice bridges and floatation tires on vehicles shall be used when crossing as dictated by site conditions and the Project Engineer.Best Practice

Equipment shall be in good working order and free of leaks. No equipment maintenance including fueling shall be carried out within 30 m of a wetland.Best Practice

Excavation in wetlands should be carried out from a dry stable surface to minimize environmental impacts.Best Practice

Excavate only what is absolutely necessary to meet engineering requirements. Excavated material shall not be sidecast in the wetland unless permitted, or for beneficial environmental purposes.Best Practice

In wetlands associated with sensitive water crossings, grubbing shall be minimized by the placement of geogrid and geotextile prior to the placement of fill.Best Practice

Vegetation will be retained where possible to provide wildlife habitat. Best Practice

Where applicable, no work near wetlands will be scheduled during the wildlife's breeding season.

Excavated wetland material shall be retained for placement in the median or along the ROW to improve seeding success. Material may be stored at locations specified by the Project Engineer or applied directly to designated areas to a minimum thickness of 100 mm (± 25 mm). Note that wetland material typically has a very high organic matter content that may require further mixing with inorganic soils prior to spreading.

Excavated material shall be replaced with approved fill material as soon as possible to minimize sloughing, over excavation and generation of sediment.Best Practice

The fill material shall be clean, coarse fill material with less than 10 percent fines to minimize the generation of sediment and to promote drainage.

Water control shall be maintained at all times. Water removed from the excavation shall be pumped to an approved sediment control measure (e.g., settling pond, adjacent vegetated area or filter bag). Best Practice

Ditches shall not drain directly to wetlands. Flows must be directed away from wetlands by take-off ditches for dissipation through adjacent vegetated areas.


4.4.2 Vegetation Protection
< back to top >

Protection of vegetation is a particularly important part of construction activities near or in streams, wetlands and environmentally sensitive areas. Consequently, environmental stewardship practices such as the following should be employed:

Avoid native vegetation removal and disturbance on streambanks unless absolutely necessary. Best Practice

Maintain a vegetated buffer strip between the work site and watercourse except at the actual crossing location.Best Practice

Mark large trees, where present, with colored and labeled flagging to ensure that the field crew understands what is to be cut and what is to remain and be protected from damage. Best Practice

Temporary barriers to protect existing trees, plants, and root zone should be provided, if necessary. Best Practice

Trees and other vegetation should not be removed, injured, or destroyed without prior written approval.

Ropes, cables, or fencing should not be fastened to trees.

Clear vegetation from unstable or erodible banks by hand instead of using heavy machinery.

Remove undesirable plant species such as nonnative and invasive species that might threaten the survival of targeted species.Best Practice

Retain as much understory brush and as many trees as feasible, emphasizing shade producing and bank stabilizing vegetation.

Minimize soil compaction by using equipment types such as wide track or rubber tired with a greater reach or that exerts less pressure per square inch on the ground, resulting in less overall area disturbed or less compaction of disturbed areas.Best Practice

Decompact disturbed soils where needed prior to revegetation.Best Practice

Heavy equipment may use various routes to reduce severe compaction in any one area.

Conversely, using fewer haul routes may result in less overall compaction.

After use, haul routes may be ripped or subsoiled to reduce compaction and promote infiltration.

If riparian vegetation is to be removed with chainsaws, consider using saws currently available that operate with vegetable-based bar oil.

Revegetate disturbed and decompacted areas with locally adapted native species that comprise a diverse community of woody and herbaceous species where practical and appropriate. Use of species that grow extensive root networks quickly should be emphasized. Sterile, non-native hybrids may be used for erosion control in the short term if planted in conjunction with native species.Best Practice

Allow at least four weeks of growing season when using seeding to stabilize erodible soils.


4.4.3 Fish & Wildlife Protection
< back to top >

Highway planning and design attempt to avoid all sensitive wildlife habitat, where possible. General protection measures that apply during construction may include the following specifications. Specific measures for wildlife should be discussed with your state Department of Natural Resources (DNR) for non-federally listed wildlife and with the U.S. Fish and Wildlife Service for wildlife listed as threatened or endangered under the Endangered Species Act. Typically, a DOT biologist or wildlife specialist can be consulted and take the lead in such matters. On construction sites, the following stipulations may be employed, or suggested for use in discussions with resource agency staff: [N]

DOT employees and Contractor employees and agents shall not interfere with wildlife and shall not carry firearms within the ROW.

Where important wildlife species are encountered impacts shall be minimized by avoiding noisy, disruptive activities during sensitive wildlife periods (e.g., March to June for Bald eagles) or as specified in permit conditions.Best Practice

All refuse shall be disposed of at an approved landfill facility. Refuse stored on site prior to removal shall be stored in closed containers.

Report any nuisance wildlife to the Project Engineer or directly to the environmental specialist or the local DNR office.

The Contractor shall consult with the Regional Wildlife Biologist to determine appropriate measures for removing beaver dams and/or nuisance beavers.

Fish passage design practices are detailed in Chapter 3, Designing for Environmental Stewardship in Construction; however, the following practices are important to review and implement during construction:

  • Disturbance of the bed and banks should be limited to disturbance necessary to place the culvert, embankment protection and any required channel modification associated with the installation.Best Practice
  • The banks should be revegetated within one year with native or other approved woody plant species. Live stakes should be planted at a maximum interval of three feet (on center) and maintained as necessary to ensure 80 percent survival.
  • Approved structures should be constructed in the dry whenever possible.

Where significant live flow exists, isolation of the construction site from stream flow should be accomplished by techniques appropriate to local and site conditions such as jersey barriers, sheet piles, cofferdams, etc.Best Practice

Any wastewater from project activities and dewatering should be routed to an area outside the ordinary high water line in a location that will not drain directly into any stream channel, to allow settling of fine sediments and other contaminants prior to being discharged back into the subject stream.Best Practice

Use of species that grow extensive root networks quickly should be emphasized.

Sterile, non-native hybrids may be used for erosion control in the short term if planted in conjunction with native species.

If target species are likely to be present, fish clearing or salvage operations should be conducted by qualified personnel prior to construction. If these fish are listed as threatened or endangered under the federal or state Endangered Species Act, consult with FWS, NMFS, and/or state biologists to gain authorization for these activities. Care should be taken to ensure fish are not chased up under banks or logs that will be removed or dislocated by construction. Return any stranded fish to a suitable location in a nearby live stream by a method that does not require handling of the fish.Best Practice

If pumps are used to temporarily divert a stream to facilitate construction, an acceptable fish screen should be used to prevent entrainment or impingement of small fish.Best Practice

Migratory Birds, including Bald Eagles

Again, specific measures for wildlife should be discussed with your state Department of Natural Resources (DNR) for non-federally listed wildlife and with the U.S. Fish and Wildlife Service for wildlife listed as threatened or endangered under the Endangered Species Act. Typically, a DOT biologist or wildlife specialist can be consulted and take the lead in such matters. On construction sites, the following stipulations may be employed, or suggested for use in discussions with resource agency staff: [N]

No one shall disturb, move or destroy migratory bird nests. If a nest or young birds are encountered, the Contractor shall cease work in the immediate area of the nest and contact the environmental specialist and the Project Engineer.Best Practice

Should a bald eagle nest be identified, the following approach shall be followed: (note, such time stipulations and specific practices should be discussed with your DOT's environmental specialist, who can coordinate with the appropriate agencies)

  • Within 200 m of a nest, avoid activities that result in significant landscape changes.
  • Within 400 m of a nest, activity is permitted except during the most critical period, usually between March and mid-May.

Where bald eagle nests have been identified prior to construction:

  • Communication will be undertaken with the contractor to promote awareness of nest locations and protection requirements.Best Practice
  • Avoidance of noise disturbance in this area during the breeding period from March to June.
  • Blasting will be avoided adjacent to this habitat between March and June.
  • Setbacks from the area restricting machinery access will be established and clearly marked in the field
  • The amount of trees cleared in this area will be minimized.

Removal of Beaver Dams

As beavers are inclined to rebuild, beavers may need to be relocated if the intention is to permanently disassemble their dams. However, if a beaver dam must be removed, the following measures may be followed to safely remove the dam and minimize the impact of beaver dam removal on aquatic resources due to loss of pool/pond habitat and the discharge of excessive amounts of sediment and water.

Prior to proceeding with removal or modification of beaver dams and associated activities (e.g. dewatering, excavation, sediment removal, debris disposal, installation of water control structure or culvert guard, trapping, etc.), contact DOT environmental specialist for assistance and/or permit advice if watercourses or wetlands will be affected.

  • The removal of the beaver dam or culvert should be limited to the debris in the structure. The original watercourse bed and bank material may not be removed or disturbed. Best Practice
  • Drainage of the ponds should, if possible, take place between June 1 and September 15, when water is at lower flow levels.Best Practice

Impounded water will be released over an extended period so as to minimize silt flushing from the impounded area and reduce channel erosion downstream due to the increased discharge and water velocities.

The pond can be drained by pumping down or siphoning to reduce potential for resuspension of sediment.

A good maximum allowable depth of water spilling over the structure at the drainage point is 10 cm (4 inches). The width of the opening should be no greater than the width of the watercourse downstream of the dam until the pond has been drained.

When dismantling beaver dams, the majority of the work should be performed using hand tools; remove only enough debris to start running the flow of water under controlled discharge.

If using machinery, only diesel powered cabled winches (not electrical) should be used to remove debris from dams and pipes.

All debris removed from the beaver dam will be placed at a location above the high water mark so as not to re-enter the stream.

If it is intended to remove accumulated sediment or organic material from a beaver pond area after a dam has been breached, this material should be allowed sufficient time to completely dry before it is removed. All appropriate permits for fill removal and working near a watercourse must be obtained for such a removal project.

In a location where it is impossible to eliminate dams, control the level of water by constructing and installing a temporary structure using water level control pipes.

For a small to medium sized culvert in locations where dams are totally dismantled, install culvert protectors which can be easily removed if the beaver rebuilds his dam.

In situations where a culvert must remain open to prevent road washouts during flood conditions, but a beaver pond is acceptable, a culvert guard can be constructed.

The excavation of sediment from the former pond site should be conducted in a manner to ensure that suspended sediment and organic matter do not re-enter the watercourse.

If possible, defer the removal of the nuisance beaver(s) until a beaver trapping season is in effect.


4.4.4 Stewardship Considerations to Avoid Watercourse Contamination
< back to top >

Prevent vehicle fuels and fluids from contaminating the watercourse.Best Practice

Refuel machinery at locations well removed from the watercourse (recommended minimum 100 m or 300 ft. separation)Best Practice

Wash and service vehicles and machinery at locations well removed from the watercourse.

Use bio-friendly hydraulic fluids in equipment operating in or adjacent to watercourse.

Store fuel, lubricants, hydraulic fluid and other potentially toxic materials at locations well removed from the watercourse.Best Practice

Isolate storage areas so that spilled fluids cannot enter the watercourse.Best Practice

Prepare a spill contingency plan.Best Practice

Ensure operators have spill clean-up supplies on site and are knowledgeable in their proper use and deployment.Best Practice

Report all spills. In the event of a spill, operators must immediately cease work, start clean-up, and notify the appropriate authorities.

Perform in-stream work in low flow conditions, to the maximum extent practicable.

Prevent any construction debris from falling into the stream channel. Any material that does fall into a stream during construction should be immediately removed in a manner that has minimal impact to the streambed and water quality.Best Practice

As appropriate, the construction should occur from the bank, or on a temporary pad underlain with filter fabric.Best Practice

Temporary fill must be removed in its entirety prior to close of work-window.Best Practice

Begin reclamation and site cleanup as soon as construction has been completed. Remove all waste material from the active floodplain as well as all temporary facilities and structures.Best Practice

Recontour, stabilize, and revegetate disturbed areas to suit original conditions; it is especially important to stabilize all slopes leading directly to the watercourse.Best Practice


4.4.5 State Resources and Fact Sheets for Stream Crossings
< back to top >

States have developed the following fact sheets outlining environmental stewardship practices with respect to stream crossings:

Ford Crossing, MD
Temporary Fording, NCDOT, p. 97
Utility Crossing, MD
Small Bridge Installation, MD
Temporary Access Bridge, MD
Temporary Access Bridge, NCDOT, p. 101
Temporary Stream Crossings, Caltrans
Temporary Piped Crossing, NCDOT, p. 99
Cofferdams , Alberta Transportation
Instream Silt Barriers , Alberta Transportation
Sensitive Area Isolation , Alberta Transportation

The Maryland Department of the Environment developed the following Temporary Instream Construction Measures and Guidance as part of its Waterway Construction Guidelines. Each fact sheet contains descriptions, effective uses and limitations, installation guidelines, and drawings. [N]

Ford Crossing
Utility Crossing
Culvert Installation
Multi-Cell Culverts
Depressed Culverts
Culvert Baffles
Small Bridge Installation
Temporary Access Bridge


4.4.6 Erosion Control in Environmentally Sensitive Areas
< back to top >

Erosion control receives particular attention in environmentally sensitive areas. Properly chosen, installed, and maintained sediment control measures can provide a significant degree of filtration for sediment-bearing runoff. For further detail on erosion control stewardship practice, see the section of this document on Erosion and Sedimentation Control, and the related section on Bioengineering, in Chapter 3, Designing for Environmental Stewardship in Construction & Maintenance:

Use environmentally sensitive bank and erosion control measures or bioengineered designs.Best Practice

Develop erosion and sediment control plans and install sediment control measures before starting work.Best Practice

Minimize the length of time that unstable erodible soils are exposed.Best Practice

Isolate the construction area from flowing water until project materials are installed and erosion protection is in place.Best Practice

Erosion control measures should be in place at all times during construction.

Do not start construction until all temporary control devices are in place downslope or downstream of project site.

Stockpile topsoil removed from the right-of-way outside of the active floodplain and use measures to prevent stockpile runoff from entering the watercourse. Use erosion controls to protect and stabilize stockpiles and exposed soils to prevent movement of materials.Best Practice

Direct runoff containing sediment away from the stream into a vegetated area.

Construct suitably sized settling ponds to precipitate suspended sediment before water is discharged into the watercourse. See Chapter 4.5 Erosion and Sediment Control for more information.Best Practice

Stabilize erodible soils as soon as practical by seeding, spreading mulch or installing erosion control blankets.Best Practice

Inspect erosion and sediment control measures regularly and make necessary repairs immediately after damage has been discovered.Best Practice

Maintain a supply of erosion control materials onsite, to facilitate a quick response to unanticipated storm events or emergencies.Best Practice

When needed, utilize instream grade control structures to control channel scour, sediment routing, and headwall cutting.

To divert flowing water away from in-stream or streambank construction activity, where equipment access is available, place jersey barrier wrapped in plastic and reinforced with woven geotextile gravel-filled bags to prevent seepage at base.Best Practice

To prevent the unintentional introduction of aquatic invasive animal species, such as zebra mussel, all water used for bridge washing shall be from the same stream or a public water supply source. See NYSDOT EPM Chapter 4.8.4- Invasive Species Control Practices for Maintenance and Construction: Best Practice

To divert flowing water away from in-stream or streambank construction activity, where equipment access is not available, erect a temporary dam using prefabricated steel frame covered with waterproof fabric material reinforced with woven geotextile gravel-filled bags along base to prevent seepage.

Whenever working in or near streams, wetlands, storm drains, or ditches; require vehicles and heavy equipment to carry a spill kit to contain and clean-up petroleum product spills. Spill kits contain absorbent materials, booms, culvert plugs and putty, etc. and prominently display the state spill report hotline phone number on the outside. Each kit is about the size of a small suitcase and costs about $75.00 depending on materials selected.Best Practice

Whenever working in or near streams, to prevent the unintentional introduction of invasive plant species through contaminated soil, all heavy construction equipment shall be cleaned to remove soil and plant parts from the bucket and tracks prior to arrival on-site. See USDA's ‘Vehicle Cleaning Technology for Controlling the Spread of Noxious Weeds and Invasive Species' and Chapter 4.1 of the NYSDOT Environmental Handbook for Transportation Operations.

Whenever working in or near streams, to prevent the unintentional introduction of invasive plant species, when restoring disturbed areas, do not use hay mulch. Use mulch from straw, wood fiber or paper.Best Practice

To protect sensitive aquatic habitats, when removing small stands of invasive Japanese knotweed or phragmites, cut the stems by hand and inject herbicide into basil stem with hand syringe. Cut plant stems should be composted or disposed by burial or landfilling. See NYSDOT EPM Chapter 4.8.4- Invasive Species Control Practices for Maintenance and Construction:

Bridges scheduled for rehabilitation or removal should be inspected for bird nesting activity prior to commencing any washing, painting, rehabilitation or construction activity. If the nest(s) is determined to be occupied, avoid disturbing, damaging or removing the nest until the young are fledged (leave the nest.) At no time should large nests of hawks, falcons or eagles be destroyed, as these species return to the same nest site year after year and reuse the same nest. Methods of preventing migratory bird nest construction, such as the use of tarpaulins installed before the beginning of nesting activity, should be considered in order to avoid construction or contract delays. If this method is used, tarps must be secured tightly so as to prevent entry into the underside of the bridge, and must not have any gaps, holes, or tears that would allow entry.Best Practice

To reduce potential flood damage to culvert and roadways due to beaver activities, installing bypass pipes (Water Level Control Devices, a.k.a. ‘WLCD's') through existing beaver dams and deep water fencing offer potential solutions. If persistent damage continues, trapping may be required in conjunction with the above mentioned practices. See Appendix S: Beaver Damage of the NYSDOT Guidance for the Adirondack Park: Best Practice

Driving live stakes deep into saturated soil in stream bank stabilization material (i.e.: riprap armor) increases the survivability and root development of the live stake vegetation, further stabilizing the slope in conjunction with mechanical means. Providing a spud hole, driving stake with a soft-blow hammer and cleanly trimming off top portion of the stake will increase the live stake survival.Best Practice

Removing/ treating priority invasives and noxious species prior to stream access construction will reduce fragments entering water and aid in reducing the spread of invasives downstream.Best Practice

Where other practices are not appropriate, careful planning should be considered in the placement of filtration bags used to treat turbid water, in regards to ease of disposal and minimizing risk of impacts from accidental breakage. The filtration bags could either be placed in a location where they can be buried in place when full or they can be placed within a harness or on a platform, dump truck, flatbed trailer, etc. that can be easily picked up later without puncturing the bag. Filtration bags shouldn't be placed in/near stream channels where a bag failure would discharge lots of sediment.Best Practice

With more efficient equipment, agencies and contractors face a greater risk of causing inadvertent environmental damage. Work practice training for streams and wetlands is a high priority. It consumes time and funding, yet such costs are reasonable compared to time and funding consumed if an agency violates mandates. The New York State Department of Transportation has a corps of Equipment Operator Instructors who instruct equipment users on proper operation and may address environmental considerations while working near streams. The Department partners with regulatory agencies, universities, environmental groups and nationally known experts (i.e.: Dave Derrick for stream restoration) for instruction on minimizing environmental impacts to wetlands and streams - - and enhancing such resources.Best Practice

< back to top >
Continue to Section 4.5 »
Table of Contents
Chapter 4
Construction Practices for Environmental Stewardship
4.1 General Construction Site Stewardship Practices
4.2 Work Area
4.3 Construction Involving Historic Properties and/or Other Cultural Resources
4.4 Construction in and around Drainage Areas and Streams, Wetlands, and Other Environmentally Sensitive Areas
4.5 Erosion and Sedimentation Control
4.6 Vehicle Fluid, Fuel, and Washwater Control
4.7 Air Quality Control Practices
4.8 Noise Minimization
4.9 Materials Storage, Collection and Spill Prevention on Construction Sites
4.10 Vegetation Management in Construction
4.11 Soil Management in Construction
4.12 Establishing Vegetation at Construction Sites
Lists: Examples | Tables | Figures
Website Problems Report content errors and/or website problems
PDF Document Download Adobe Acrobat Reader