​​Thompson & Associates Wetland Services

1514 Menomonee Ave, South Milwaukee, WI 53172

Phone: 414.571.8383

Wetlands are determined by the presence of hydric soils (left), wetland plants (center), and evidence of water or hydrology (right).

What is Wetland Delineation?

Because wetlands are protected by various federal, state and local laws, the boundary of the protected wetland is important to determine before any development or construction is approved by various governmental agencies. In addition the location of wetlands is important to understand before land purchases as part of due diligence.

Wetlands are places with wetland soils, wetland plants and evidence of water or hydrology that create the wetland conditions.

To determine the wetland boundary, we choose a series of data points that are representative of the site. We dig a soil pit at each data point in sample wetland areas and sample upland areas. We compare the soils in each pit. Over many years, water causes chemical reactions that change the colors of the wetland soils as compared to the upland soils. We use a "Munsell" color chart that has various color chips to give the soil a specific color code and help us identify if the soils were formed with water present. Wetland soils may also be peat or muck, very spongy soils formed almost entirely of dead plants that have not decomposed over hundreds of years. Sometimes wetland soils can have distinct plant parts, buried snail shells and other relics from when the area was much wetter.

At these same points in the wetland and upland we inventory the vegetation, list each plant by species name, and determine if the plant is dominant or only a minor presence. Each plant is given a specific category depending on its ability to tolerate wetland conditions. For example, a cattail is in wetlands most of the time and is termed an obligate, while a dandelion plant is most of the time in uplands and is termed upland. There is a whole class of plants that could be in a wetland or upland equally and are termed facultative, a common facultative plant is the box elder tree. Wetlands typically have over 50% of the dominant plants at the data point ranging from facultative to obligate. Uplands would tend to be dominated by upland plants.

Finally we look for signs of hydrology or water. This is often difficult as wetlands may have visible water for only a week or two a year. We look for water in the soil pit, and then we look for evidence water left behind including water lines on tree trunks, drift lines created by flowing water (little piles of sticks against trees for example), water-stained leaves, or dried algae on the surface of the soil. Even more indirect evidence includes what plants are in the area, how the area sits on the landscape (in a depression or on top of a hill), and if the trees and shrubs looked stressed. A high water table will cause tree roots to grow very shallow and have thickened trunks and visible roots on the soil surface because the roots cannot go deep, as the water has removed oxygen from the soil.

The upland area is typically dominated by upland plants, has upland colored soils, and no evidence of water or wetland hydrology. Trees are healthy and don't look stressed by water. Between these two known points. . . the wetland and the upland. . . is the wetland boundary. We use flags to pinpoint the line, a transitional point where the wetland plants and soils drop off and the upland plants and soils take over. There is generally a rise in slope associated with this change in plants, soils and water. The more steeply sloped the site, the sharper the line. Very gradual slopes can have a more diffuse and difficult line to pinpoint.

The wetland delineation includes a staked line in the field and a wetland delineation report that details what is and is not wetland on the site. This report is typically sent to regulators at the U.S. Army Corps of Engineers and the Department of Natural Resources for their concurrence. The client also needs to have the flag locations surveyed and placed on any plans. A wetland line is generally valid for five years.

Alice Thompson, is an Assured Professional Wetland Delineator as determined by the Wisconsin Natural Resources since 2006. Delineations that she performs do not require DNR concurrence, and there will be no delay in using the results of her work in state waterway and wetland decisions. Complex or very challenging sites may still require local inspection by DNR staff.

Further details of this program are at: http://dnr.wi.gov/topic/wetlands/delineation.html