The field-based process of identifying and mapping wetland boundaries using three diagnostic criteria: hydric soils, hydrophytic vegetation, and wetland hydrology. Wetland delineation is required for regulatory compliance under the Clean Water Act.
Wetland delineation is the standardized technical procedure for identifying and marking the boundaries of wetlands for regulatory purposes, following the methodology established in the U.S. Army Corps of Engineers Wetland Delineation Manual (1987) and its ten regional supplements. The three-parameter approach requires that an area exhibit all three wetland indicators to be classified as a jurisdictional wetland: hydrophytic vegetation (plant species with a wetland indicator status of obligate, facultative-wet, or facultative, comprising more than 50% of the dominant species), hydric soils (soils that formed under saturated conditions showing characteristic morphological features such as gleying, mottling, or high organic content), and wetland hydrology (evidence that the area is inundated or saturated for a continuous period of at least 14 days during the growing season at a frequency of 50% of years or greater). Field delineation involves establishing data plots at representative locations, identifying plant species and calculating dominance, examining soil profiles using Munsell color charts, and documenting hydrological indicators. The delineated boundary is surveyed and mapped, then submitted to the U.S. Army Corps of Engineers for jurisdictional determination. Wetland delineation is a prerequisite for any development activity that may affect wetlands, as Section 404 of the Clean Water Act requires a permit for the discharge of dredged or fill material into waters of the United States, including most wetlands.