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Technical Aspects of Wetland Identification and Delineation

A creek flowing through an emergent wetland area
Environment, Great Lakes, and Energy

Technical Aspects of Wetland Identification and Delineation

The majority of the remaining wetlands in Michigan formed when the last glaciers retreated thousands of years ago. For a wetland to develop over time, the presence of water (the hydrology) is necessary as a saturated zone near the soil surface during a significant portion of the growing season. The timing, frequency, and amount of soil saturation each year influences the specific type of vegetation that can grow in an area and the type of chemical, biological, and physical processes that occur in the soil.

Michigan's Wetland Protection Statute and Rules (i.e., Part 303) require the use of the technical wetland delineation standards set forth in the United States Army Corps (USACE) of Engineers 1987 Wetland Delineation Manual (i.e., ’87 Manual), and especially the two modern, regional supplements, when identifying wetland boundaries. 

Wetland Delineation Method

The ‘87 Manual pertains generally to wetland delineation throughout the nation, and is now applicable primarily to portions of the nation that do not yet have modern regional supplements available.  Within Michigan, the ’87 Manual has been effectively replaced by the modernized contents of two important regional supplements.  The Midwest Regional Supplement is a comprehensive, stand-alone wetland delineation manual that is applicable to a portion of Southeast Michigan (portions of Hillsdale, Lenawee, Washtenaw, Livingston, Wayne, and Oakland Counties).  The Northcentral and Northeast Regional Supplement is a comprehensive, stand-alone wetland delineation manual that covers the remainder of Michigan.

As described in the applicable USACE documents, identification of wetlands using the federal delineation method primarily involves the determination of three factors:

1. predominance of wetland vegetation

2. hydric soils (i.e., distinct soil types that form only in wetlands)

3. distinct hydrology that occurs within the upper portion of the soil profile

USACE wetland delineation manuals

Hydrophytic Vegetation

Technical knowledge of the plant species typically found within a region is essential for accurately delineating wetlands. Wetland plants have specialized adaptations and responses that allow them to survive, grow, and reproduce with their roots in standing water or within saturated soils for a significant portion of the growing season.  Conversely, many plants cannot survive in saturated conditions and are commonly referred to as “upland” plants.  The National Wetland Plant List provides information about how often a plant species occurs in wetlands.  Because of the need to identify plant species for accurate wetland delineation, it is typically necessary that wetland identification occur during the growing season.
Three examples of wetland plants

Hydric soil

A hydric soil is a soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic (i.e., very little available oxygen) conditions. This lack of oxygen in the soil leads to the formation of certain observable characteristics in wetland soils, such as a thick surface layer of dark organic matter and/or the presence of redoximorphic features (i.e., locations of chemical concentration and depletion of iron and other elements) within the upper portion of the soil profile.  Field Indicators of Hydric Soils in the United States is an important reference document that describes hydric soil indicators approved by the Natural Resources Conservation Service (NRCS) and the National Technical Committee for Hydric Soils (NTCHS) for use in identifying, delineating, and verifying hydric soils in the field.
Profile of wetland soils

For highly disturbed sites, as described in the USACE Regional Supplements and other technical publications, the use of mapped hydric soil data from the NRCS and mapping data derived from modern remote sensing (e.g., aerial photography, LIDAR topographic data) can be extremely important when trying to ascertain where wetland boundaries were located on site prior to any major disturbance.

Resources

Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Northcentral and Northeast Region

Regional Supplement to the Corps of Engineers Wetland Delineation Manual: Midwest Region

The National Wetland Plant List

Field Indicators of Hydric Soils in the United States

Are there wetlands on my site? [link to Wetland Identification and Mapping]

Finding a Wetland Consultant

State and Federal Wetland Regulations