CHAPTER 3 WETLAND DELINEATION

• Jurisdiction: United States

Wetland Issues in Resources Development
(Nov 1993)
CHAPTER 3
WETLAND DELINEATION
Lauranne P. Rink
Aquatic and Wetland Consultants, Inc.
Boulder, Colorado

TABLE OF CONTENTS

SYNOPSIS

1.0 Basic Wetland Delineation Criteria

1.1 Vegetation

1.2 Hydrology

1.2 Soils

1.4 Office Applications

1.5 Field Applications

1.6 Corps Verification of Delineations

2.0 History of Delineation Methodologies

2.1 Multiple Parameter Approach

2.2 1987 Corps of Engineers Manual

2.3 1989 Interagency Manual

2.4 1991 Federal Delineation Manual (Proposed)

2.5 Currently Accepted Methods

2.6 National Academy of Sciences Study

3.0 Proposed Delineator Certification Program

4.0 Wetland Classification Systems

5.0 Literature Cited

Appendix A: Wetland delineation data sheet.

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1.0 Basic Wetland Delineation Criteria

The U.S. Army Corps of Engineers (Corps) and U.S. Environmental Protection Agency (EPA) are responsible for making jurisdictional determinations of waters of the U.S. regulated under Section 404 of the Clean Water Act and Section 10 of the Rivers and Harbors Act of 1899. Under Section 404, the Secretary of the Army, acting through the Chief of Engineers, is authorized to issue permits for the discharge of dredged or fill material into waters of the U.S., including wetlands, with program oversight by EPA.

The regulatory definition for wetlands used by the Corps and EPA for administering the Section 404 permit program reads as follows:

"..those areas that are inundated or saturated by surface or groundwater 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."¹

This definition clearly emphasizes vegetation, hydrology and soils within the context of wetland environments. Section 404 also regulates other waters of the U.S. which include, by example, open water areas, mud flats, riffle/pool complexes, vegetated shallows, and other special aquatic sites. This paper intends to discuss wetlands only, while recognizing wetlands as just one subset of waters of the U.S. regulated through the federal program.

Subsections 1.1 through 1.5 describe the basic criteria which have been used over the years to identify wetlands subject to federal regulation. Section 2.0 follows with a discussion of the various methodologies which have been developed over time to guide wetland delineation practitioners, and how differences between the methodologies has affected the scope of the Corps jurisdiction over wetland areas.

1.1 Vegetation

Wetland vegetation is collectively referred to as hydrophytic vegetation using the simple term "hydrophytes" derived from the latin terminology for "water loving". Hydrophytes, due to morphological, physiological, and/or reproductive adaptations, have the ability to grow, effectively compete, reproduce, and/or persist in anaerobic substrate conditions. Anaerobic conditions occur when the substrate or soil is, at least periodically, deficient of oxygen due to excessive water content.

Hydrophytic vegetation can include trees, shrubs, forbs (non-woody herbs), aquatics, and

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grasses. Rocky Mountain regional examples include cottonwoods, willows, cattails, sedges, rushes, mints, arrowhead, cordgrass, and sloughgrass. Regional lists of wetland plant species have been assembled by several sources and are continuously updated (for example, Reed 1988).

In order to meet the vegetation criteria, wetlands should typically exhibit a dominance of hydrophytic vegetation based on percent areal coverage. Quantification of percent cover may be based on individual plant species or assemblages of species referred to as plant "community" types.

1.2 Hydrology

Permanent or periodic inundation of the soil or substrate that the plant roots inhabit is the driving force behind wetland formation. The duration and frequency of inundation necessary for wetland genesis and maintenance is highly variable and depends largely upon the soil type and its water holding and transport characteristics. Other influencing factors include stratigraphy, topography, and local plant cover. Hydrologic conditions within wetlands are wide ranging from permanent flooding or saturation to irregular saturation or flooding. All wetlands experience at least a temporary or seasonal abundance of water which may exist for as little as a few days out of the growing season. Water sources may include direct precipitation, overbank flooding, surface runoff from precipitation or snowmelt events, seeps and springs, or locally high groundwater tables.

Hydrology and its role in supporting wetlands is at best an inexact science and difficult to establish in the office or field due to annual, seasonal and daily fluctuations. Indicators of hydrology are heavily relied upon and include floodplain maps, U.S. Geological Survey (USGS) stream gaging data, and aerial photography, as well as field indicators of water marks, drift lines, drainage patterns, water-stained leaves, and morphological plant adaptations.

1.3 Soils

Wetland soils are grouped together and termed "hydric" soils. Hydric soils are defined as soils that are saturated, flooded, or ponded long enough during the growing season to develop anaerobic (absence of oxygen) conditions in the upper part (U.S.D.A. Soil Conservation Service 1987). These hydrologic conditions usually need to occur for a week or longer during the growing season when the soil temperatures are above the biological zero point of 41°F.

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Indications of a permanent or intermittent hydrology adequate to create hydric soil conditions can be observed through several characteristics found in the soil profile. Hydric...