Wetland Classification and Delineation

 

Classification

 

 

–Circular 39

–Cowardin (USFWS)

–Hydrogeomorphic (HGM)

 

 

•Circular 39, USFWS

• 

–Developed in 1956

–Twenty types of wetlands

•Under four main categories (inland fresh, inland saline, coastal fresh, coastal saline)

•In each category, wetlands arranged according to increasing depth or inundation frequency

–Assessed value of wetlands as wildlife habitat (primarily for ducks)

 

Cowardin system (USFWS)

 

•Systems

–Marine

–Riverine

–Lacustrine

–Palustrine

–Estuarine

 

•Marine system

–Open ocean along the coast

–Salinity > 30 ppt

–Outer limit: continental shelf

–Inner limit: high tide line or emergent vegetation, or edge of estuarine system

 

•Estuarine system

–Mixed ocean water and freshwater runoff from land

–Limits: Normal salinities between 0.5 and 30 ppt

•But estuaries may become hypersaline after long periods of evaporation, or totally fresh during events like hurricanes.

–Limits: Edge of emergent vegetation.

–Limits: Line across the mouth of a river, bay or sound.

–Includes both estuaries and lagoons

–Includes subtidal and intertidal vegetation

 

 

•Riverine system

–Wetlands and deepwater habitat within a channel

–Excluding  wetlands dominated by emergent vegetation

–Excluding habitats with ocean-derived salts in excess of 0.5 ppt

–Water is usually flowing

 

•Lacustrine system

–Is situated in a depression

–Lacks emergents with greater than 30% cover

–Total area exceeds 8 ha (20 ac)

•or, water depth in deepest part exceeds 2 m at low water

–Ocean-derived salinity less than 0.5 ppt

 

•Palustrine system

–Everything else

–Includes all non-tidal wetlands dominated by emergents, and all such wetlands occurring in tidal areas where salinity from ocean-derived salts is less than 0.5 ppt.

–Also includes areas lacking emergents, but

•Area less than 8 ha, shallower than 2 m, ocean-derives salts less than 0.5 ppt

 

 

•Further description is possible through the use of subclasses, dominance types and modifiers.

•Hierarchy

–System

•Subsystem

–Class

»Subclass

»Special modifiers

 

 

Common wetland designations

–PEM  palustrine emergent

–PSS  palustrine scrub-shrub

–PFO  palustrine forested

 

 

Hydrogeomorphic Classification (HGM), Brinson

 

•1. Geomorphic setting (topographic location within the surrounding landscape)

–Depressional wetlands

–Riverine wetlands

–Peatlands

–Fringe wetlands

–Slopes and flats

 

 

•2. Water source and its transport

–Biotically important water conditions

•Depth

•Flood duration

•Flow velocity

•Water source

–Water sources

•Precipitation

•Groundwater discharge

•Surface or near-surface flow

–Tides

–Overbank flow from stream channels

–Interflow

–Overland flow

 

 

•3. Hydrodynamics

–Direction and strength of flow within a wetland (an expression of the fluvial energy that drives a system).

 

•Vertical fluctuation

–Evaporation, replacement by rain or groundwater

–Found in depressional wetlands

•Unidirectional flow

–Channel or sheet flow

–Found in riverine wetlands

•Bi-directional surface or near surface

–Tides or seiches.

–Found in fringe wetlands

 

 

 

•Delineation

 

–National Wetlands Inventory (NWI)

–1987 Wetlands Delineation Manual (US Army COE)

 

•National Wetlands Inventory

 

–Used Cowardin Classification

–Overlaid onto USGS quad maps

–Black and white, and then later, color infrared aerial photography used to create maps

•Manual image interpretation

•Some ground truthing

–About 90% of lower 48 states complete

 

•For regulatory purposes, NWI maps are too coarse

–They do not approach the <1 meter accuracy needed.

–They understate the extent of wetlands.

–SCS hydric soils maps overstate the extent of wetlands.

 

•Requirement for Section 404 dredge and fill permits drove the standardization of wetland delineation methods.

–After very political wrangling in the 1980’s, the 1987 Wetlands Delineation manual was settled upon as mutually acceptable.

 

1987 Wetlands Delineation Manual

 

•1987 Manual differs from Cowardin classification in two principle ways:

–1.  Not all Cowardin wetlands are included.

–2.  It requires all three wetland indicators to be present: vegetation, soils and hydrology.

•The Cowardin (USFWS) method requires only one to be present to indicate wetlands.

 

•Section 404 Definition of wetlands:

–“those areas that are inundated or saturated by surface or ground water [hydrology] at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation [vegetation] typically adapted for life in saturated soil conditions [soil]”

 

•Vegetation

–OBL  Obligate wetland plants

–FACW  Facultative wetland plants

–FAC  Facultative plants

–FACU  Facultative upland plants

–UPL  Obligate upland plants

 

–To be a wetland, more than 50% of the dominant species must be OBL, FACW or FAC.

 

•Hydric Soils

–Histosols (organic soils) and soils in a few other groups, particularly aquic soils.

–Additional indicators:

•Low permeability

•Low chroma

•Mottles

•Concretions

 

•Wetland hydrology

–Determination of wetland hydrology depends on frequency, timing and duration of flooding or saturation.

•(Inundation/saturation measured during growing season)

 

 

•Delineation process

–Routine delineation begins with gathering and synthesis of available information

•USGS maps, NWI maps, plant surveys, soil surveys, gage data, environmental impact statements, remote data, applicant designs and plans.

•On-site evaluation done when available data are inadequate.