Wetland Classification and Delineation
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)
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
Mixed ocean water and freshwater runoff from land
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
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
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
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.
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)
Slopes and flats
2. Water source and its transport
Biotically important water conditions
Surface or near-surface flow
Overbank flow from stream channels
Direction and strength of flow within a wetland (an expression of the fluvial energy that drives a system).
Evaporation, replacement by rain or groundwater
Found in depressional wetlands
Channel or sheet flow
Found in riverine wetlands
Bi-directional surface or near surface
Tides or seiches.
Found in fringe wetlands
National Wetlands Inventory (NWI)
1987 Wetlands Delineation
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 1980s, 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]
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.
Histosols (organic soils) and soils in a few other groups, particularly aquic soils.
Determination of wetland hydrology depends on frequency, timing and duration of flooding or saturation.
(Inundation/saturation measured during growing season)
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.