Wetland Delineation

2.  Wetland Delineation Methodology

The wetland consultant will use methods described in the 1987 Corps of Engineers Wetland Manual. Additionally, the Corps of Engineers has Supplemental Guidance for wetland delineations in specific regions of the country.  The Corps of Engineers method to delineate wetland areas has three components, summarized on the Wetland Determination Data Form.   A wetland identification focuses on hydric soil, hydrology, and wetland vegetation, as described in numbers 3, 4, and 5, below.

3. Hydric Soil

• • USDA NRCS Soil Survey – classifies soils as hydric or non-hydric as determined by satellite imagery and as depicted on soil survey maps.  According to wetland delineation guidance, hydric soils have 13 consecutive days of saturation or 7 days of inundation during the growing season in most years. Many hydric soils have a landform component required for hydric status. On-site wetland survey results are used to determine wetland areas rather than the USDA NRCS Soil Survey data.

• Field Soil Classification – determines whether the soil is hydric using hydric soil indicators such as redox dark surface, depleted matrix, or 2 cm muck.

4. Hydrology

• • Surface inundation rule – an area is considered to have wetland hydrology if it is inundated or saturated to the surface for a consecutive number of days for more than 12.5 percent of the growing season.

• Evidence of inundation – wetland hydrology is assessed on site by wetland hydrology indicators such as saturation, hydrogen sulfide odor, watermarks, water-stained leaves, or algal mats.

5. Wetland Vegetation

• Dominance test – an area is considered to have wetland vegetation if it passes the Dominance or Prevalence Test.  Wetland vegetation is dominant if more than 50 percent of dominant species are obligate, facultative wetland, or facultative species.  Wetland species status can be found on the National Wetland Plant List.

6. Reporting

A wetland delineation report identifying the type and acreage of wetland areas will be prepared by the wetland consultant and is a required attachment to a Section 404 Permit, if applicable.  The wetland report must include a narrative of the regional and local hydrology, soils, and vegetation; include GIS-based maps including regional National Wetland Inventory maps, wetland sample locations, and completed Corps of Engineers Wetland Delineation Forms for each sample location.  Wetlands are commonly delineated by wetland sample locations within the wetlands, upland sample locations outside the wetlands, and boundary sample locations defining the edge of the wetlands.

7. Requesting A Jurisdictional Determination

A wetland delineation differs from a jurisdictional determination.  A wetland delineation is the field wetland survey completed by the consultant that uses Corps of Engineers Wetland Delineation Guidance to determine the boundaries and areas within a study area that, in the opinion of the consultant, meet Corps of Engineers definition of “wetlands” as defined in the Wetland Delineation Manual.  A Jurisdictional Determination, on the other hand, is a request, generally made by a consultant on behalf of and authorized by the property owner, to the local Corps of Engineers Regulatory Office, to make an official agency determination if wetlands identified by the consultant are under the jurisdiction of the Clean Water Act as administered by the US Corps of Engineers.  Wetlands under Corps of Engineers jurisdiction are considered “Waters of the US” under Section 404 of the Clean Water Act and must be permitted prior to impact.

Although a wetland consultant can give you an opinion of whether the wetlands on your property meet the definition of wetlands, only the Corps of Engineers can determine whether the wetlands are jurisdictional Waters of the US (WOUS).  It is generally recommended that owners who contract wetland delineations on their property also authorize their consultant to request a jurisdictional determination following the wetland delineation to confirm results.

8. Avoidance or Permitting – The Corps of Engineers under the Clean Water Act excerpts jurisdiction over wetlands that have a functional contribution to “Waters Of the US” (WOUS) or “Traditional Navigable Waterways” (TNWs).  These include wetlands directly or indirectly connected to ephemeral and perennial streams under Corps of Engineers jurisdiction.  

Projects that impact these WOUS jurisdictional resources wetlands must have a permit to impact the wetlands.  Disturbing most wetlands is unlawful unless permitted by the agencies with jurisdiction over the wetland resource. Disturbing includes cutting vegetation, disturbing soil, or changing the wetland hydrology.  Agencies at the state and federal level may both have jurisdiction of a wetland area.

• • 404 Permit – The Corps of Engineers Section 404 Permit Process is explained in a previous blog.  A 404 Permit Application is required for submittal to a local Corps District, such as the New Orleans District,  Memphis District, or Nashville District,

• 401 Water Quality Certification – State water quality agencies differ in their compliance requirements for protected wetland resources.  Some states defer to the US Corps of Engineers to determine the jurisdiction of the wetland resource while others, such as Tennessee, have their own “Waters of the State” rules for wetland areas.  Check with your consultant to obtain state jurisdictional determination requirements in your state. Either way, state water control agencies are offered a review of Section 404 Permits by the US Corps of Engineers.  State agency review and approval are a Section 401 Water Quality Certification.

9. Wetland Construction

If a permit is issued for impacting wetlands, once your permit is approved it will require you to perform standard wetland construction techniques within the wetland delineated area.  The methods are listed in the approved Corps of Engineers Nationwide Permit and state 401 Water Quality Certification.  Common conditions of Nationwide Permits include:

• • Segregating soil – segregate the topsoil from the subsoil during excavation so that topsoil is replaced in the restoration phase;

• • Utilizing mats – equipment mats to reduce the compressive footprint of excavators during construction within defined wetland areas;

• • Flagging boundaries – wetland boundaries must be clearly marked or flagged so that construction crews in the field may avoid impact;

• • Filtering discharge – Any discharge from dewatering must meet the local erosion and control or other NPDES permit requirements;

• • Preserving topography – restoration includes returning the surface to grade following pipeline installation;

• • Crossing streams – clay trench plugs are  required 200-feet apart during the crossing of streams or floodplains to prevent a french drain effect; and

• Restoring cover – restoring vegetation within wetland areas is project specific; some requiring native seeding while others requiring no seeding so natural wetland plants can revegetate.
• No non-biodegradable nylon-filament-type erosion and sediment control mesh is allowed

10. Wetland Monitoring

Once construction is completed, wetland monitoring may be required if previously undisturbed areas were crossed that contained wetlands.  Wetland monitoring is usually required for two years by the US Corps of Engineers to provide documentation that wetland conditions returned to pre-construction status or recommend corrective actions if they have not.