Section 404 of the Clean Water Act: How Wetlands are Defined and Identified
"Wetlands are areas that are inundated or saturated by surface or
ground water at a frequency and duration sufficient to support, and that
under normal circumstances do support, a prevalence of vegetation typically
adapted for life in saturated soil conditions. Wetlands generally include
swamps, marshes, bogs, and similar areas."
-Definition of wetlands as used by the U.S. Army Corps of Engineers (Corps)
and the U.S. Environmental Protection Agency (EPA) since the 1970s for
regulatory purposes.
In more common language, wetlands are areas where the frequent and prolonged
presence of water at or near the soil surface drives the natural system
meaning the kind of soils that form, the plants that grow, and the fish
and/or wildlife communities that use the habitat. Swamps, marshes, and
bogs are well-recognized types of wetlands. However, many important specific
wetland types have drier or more variable water systems than those familiar
to the general public. Some examples of these are vernal pools (pools
that form in the spring rains but are dry at other times of the year),
playas (areas at the bottom of undrained desert basins that are sometimes
covered with water), and prairie potholes.
Characteristics of Wetlands
When the upper part of the soil is saturated with water at growing season
temperatures, soil organisms consume the oxygen in the soil and cause
conditions unsuitable for most plants. Such conditions also cause the
development of soil characteristics (such as color and texture) of so-called
"hydric soils." The plants that can grow in such conditions,
such as marsh grasses, are called "hydrophytes." Together, hydric
soils and hydrophytes give clues that a wetlands area is present.
The presence of water by ponding, flooding, or soil saturation is not
always a good indicator of wetlands. Except for wetlands flooded by ocean
tides, the amount of water present in wetlands fluctuates as a result
of rainfall patterns, snow melt, dry seasons and longer droughts.
Some of the most well-known wetlands, such as the Everglades and Mississippi
bottomland hardwood swamps, are often dry. In contrast, many upland areas
are very wet during and shortly after wet weather. Such natural fluctuations
must be considered when identifying areas subject to Federal wetlands
jurisdiction. Similarly, the effects of upstream dams, drainage ditches,
dikes, irrigation, and other modifications must also be considered.
Manual for Defining Wetlands
The EPA and the Corps use the 1987 Corps of Engineers Wetlands Delineation
Manual to define wetlands for the Clean Water Act Section 404 permit program.
Section 404 requires a permit from the Corps or authorized State for the
discharge of dredged or fill material into the waters of the United States,
including wetlands. The 1987 manual will remain in use pending review
of public comments on the 1991 proposed manual and the ongoing National
Academy of Sciences study of wetlands definition.
The 1987 manual organizes environmental characteristics of a potential
wetland into three categories: soils, vegetation, and hydrology. The manual
contains criteria for each category. With this approach, an area that
meets all three criteria is considered a wetland.
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