What, Where, Why: Wetland Delineation

by | Dec 26, 2018 | Environmental, News, Thought Leadership, Water

What is a Wetland?
A wetland is an area where water covers a piece of land for varying periods of time near the soil surface. The prolonged existence of water determines the kind of soil that forms, the plants that cultivate in the area, and the types of fish and wildlife that use and thrive in the specific habitat that has been created. Some wetlands are often dry, and the amount of water present is dependent on weather, snow melt, and drought. Essentially, all wetlands are unique in their makeup and the way they look.

The 1987 Corps of Engineers Wetlands Delineation Manual and Regional Supplements has identified the characteristics of a potential wetland into three categories: vegetation, soil, and hydrology (water saturation). This is what differentiates a wetland from other types of bodies of water. Hydrology, climate, landscape shape (topology), and geology assist in determining how the soil develops and the type of plants and animals that can thrive in and on the soil. Wetlands can be home to a variety of life forms, including microbes, plants, insects, amphibians, reptiles, birds, fish, and mammals. Wetlands not only house lifeforms, but they also feed them. As foliage deteriorates in the water, it produces “detritus,” or small particles of organic material that feed many animals. This is just one example of the importance of a wetland.

What is Wetland Delineation?
Wetland delineation or a “wetland study” is a thorough report of a body of water and the land surrounding it on a site in order to determine if a wetland is present and to identify its boundary. Wetlands are protected by federal, state, and local laws and wetland delineation must be performed before any development or construction can be approved by the Army Corps of Engineers (Corps) and the Department of Natural Resources (DNR). Its identification and location are also important before the purchasing of land. Any wetland delineation looks at three criteria:

  • Vegetation: A prevalence of species that are considered wetland species in that particular region.
  • Hydrology: Saturated to the surface, or indicators they would be during a typical wet season.
  • Soils: Soils or soil morphology that indicates saturation in a typical wet season.


However, those factors only have to be present if the site is in a “normal” condition, that is, if it hasn’t been altered within the past five years. If it has or was significantly disturbed at any point in the past, an accurate delineation can be much more difficult, and these particular skills are even more critical.

Phases of the Delineation:
The delineation process is carried out in three phases: pre-field investigation, field data collection, and post-field analysis. The pre-field Investigation is a consultation of publicly available data sources to collect information regarding the site, including regional sales data, historical aerials and satellite photography, and wetland databases. The data collected and conclusions found are reported to Corps and the DNR for their consideration. The phases seem simple enough and easy to follow, but a delineation requires extensive knowledge of the three characteristics, multiple visits to a site, and many hours of time spent during these visits.

During the field data collection phase, a professional visits the site to access the condition of the soils, hydrology, vegetation of the land, and defining areas that meet the criteria of wetland designation. Mike Benham, PE, MS at McClure has surveyed many wetlands in the Iowa region for various projects.

In Action
In Bondurant, Iowa, Benham was commissioned to perform a delineation on a property consisting of 21.5 acres of undeveloped, inactive agricultural property that was home to two distinct bodies of water and was projected to experience construction and/or development, thus requiring a delineation. During the first phase of the delineation, the Pre-Field Investigation, Benham determined that the Property had been disturbed in late 2005 due to excavation and grading. The two bodies of water were the result of excavation or other construction on the land. Prior to the heavy disruption of the land, the site was part of a larger agricultural operation. Benham then visited the property and found that seasonal rainfall was low for the summertime, and only small amounts of precipitation had been recorded in the days leading to the delineation. Through Benham’s analysis and professional opinion, he concluded that hydraulic requirements were met near the surface of the wetlands during the post-field analysis. He later identified various distinct plant species used in the wetland determination and made pit excavations to identify the soil and hydrological conditions. Eventually, Benham determined that the two bodies of water and the excavated depression between them combined to make one continuous wetland area that was interestingly enough made up of two distinct plant communities, due to differing soil type.

Although the areas surveyed qualified as wetlands, the Corps has guidance on what waters to claim jurisdiction over, and whether or not the wetland is considered a Water of the United States. If a wetland is considered a water of the United States, it is subject to the requirements of the Clean Water Act, of which the main goal is to restore and maintain the integrity of the nation’s waters by eliminating the discharge of pollutants into the waters and to achieve water quality levels that are fishable and swimmable. A jurisdictional water is subject to federal control. Benham reported that the wetlands he identified generally do not fall into a jurisdictional category and therefore had the likeliness of meeting the definition of the waters of the United States.

Why is this necessary?
It’s important for any site to be reviewed to fully understand the environmental impacts, including wetland potential. As a general rule, any work which takes place in a waterway or wetland has to be permitted with the Corps, and possibly with other state or local agencies. Some sites may not necessarily look like a wetland but may actually be one because a statutory wetland does not require standing water, or even year-round saturation of the soils.

If you have questions about wetland potential on a site you’re developing contact Mike Benham at 515-964-1229 or mbenham@mecresults.com.