Transcript Wetland Delineation

Wetland Delineation
Wetland Delineation
• The process of identifying and
mapping the upper boundary of a
wetland for a particular purpose
such as
– wetland regulation
– inventory
– assessment
– management
(National Wetlands Inventory is too
coarse at a scale of1:24,000)
National Wetlands Inventory
Guidelines to determine and delineate wetlands use three features as defined
in Section 404 (b) (1) of the Clean Water Act:
1. hydrophytic vegetation
2. hydric soils
3. wetland hydrology
Basic Approach to Delineation
• Wetlands exhibit all three essential
characteristics:
– hydrophytic vegetation
– hydric soils
– wetland hydrology
• Identified in the field by looking for
“indicators” of these characteristics as
specified in the manual
Basic Approach to Delineation
• systematically explore the site noting
potential wetland areas
• confirm by detailed sampling of vegetation,
soils, and hydrology at representative
sampling points.
• determine boundaries by additional
sampling along the wetness gradient
Wetland Delineation
Section 404 of the Clean Water Act
Definition of Wetlands:
Those 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
What are ‘Normal Circumstances’?
• By definition, under normal circumstances
wetlands support a prevalence of
vegetation adapted for life in saturated soil
conditions.
• But what if the vegetation on a wetland
has been cleared? What if the land now
supports an agricultural crop? Is it still a
wetland?
YES!
What are Normal Circumstances?
• The Army Corps of Engineers (Corps) manual
states that normal circumstances are dictated by
soils and hydrology regardless of whether the
vegetation has been altered or removed.
• Presence of a crop or cropping history is not the
normal circumstance because all three
characteristics would have been present if
natural vegetation had not been removed.
What are Normal Circumstances?
‘Normal circumstances’ can change
– A permanent change (e.g., construction of a
highway) done under permit, or that did not
require a permit, may become the new normal
circumstances for the site.
– E.g., wetlands formed when a river is
dammed may be regulated even if not present
historically, and even if they have not yet had
time to develop indicators of all three wetland
characteristics.
Delineation Methods
• Offsite: insufficient time for comprehensive
evaluation, but enough information is available.
(For non-critical areas)
• Routine Small Areas: < 5 acres with
homogenous vegetation and distinct boundary
• Routine Large Areas: > 5 acres with
heterogeneous vegetation and/or non-distinct
boundary.
• Comprehensive: When litigation is expected
Step 1: Off-site information review:
– Locate the site and develop a base map
– Estimate the size of the site
– Summarize available information about the site
Step 2: On-site Preliminary Reconnaissance
– Identify potential wetland sites
– Determine if normal circumstances exist
– Evaluate hydrologic and vegetative patterns
– Determine whether further evaluation is needed
On-site Preliminary Reconnaissance
What you’ll need
• Base map with site located on the map
• Data report form
• State wetland plant list
• State hydric soils county list
• Soil survey
• Soil auger
• Munsell color charts
• Plant ID keys
• GPS
Identify Potential Wetland Areas
• Walk the site
and verify (field
check) the
preliminary
data.
Determine if normal circumstances exist
Identify human-induced impacts that may
have affected:
– alteration or removal of vegetation
– removal of original soil
– significant alteration of soil profile (tilling)
– fill material
– hydrology has been altered (e.g.,
channelizations, water diversions, tiles, etc.)
Evaluate hydrological and
vegetative patterns on the site
• locate indicators of hydrology (e.g.,
streams, rivers, ponds, seeps, standing
water)
• describe diversity of plant communities
• note all wetland and non-wetland areas
• estimate wetland boundaries
Choose a potential wetland area to
begin evaluation
• identify obvious wetland and non-wetland
areas and locate the transition zone
between them.
Point Determination Method
• determine whether a predominance of
wetland vegetation exists
• determine whether visual evidence of
wetland hydrology is present
• determine whether hydric soils are present
• if starting point does not have indicators of
hydrology, repeat at other points along the
transition zone.
Does a predominance of wetland
vegetation exist at the site?
• determine the dominant
vegetation in each strata
(overstory, shrub, understory) by
visual estimate or sampling
using the 50/20 dominance rule
(greater than 50 percent of the
plants must be fac, fac-wet, or
obl species)
• rank total species abundance
and use all species that exceed
a cumulative 50% abundance,
plus all other species with >20%
for each stratum.
Vegetation Strata
• Tree (overstory): woody plants > 3 in dbh
• Sapling/shrub (shrub): woody plants 3 ft
tall but < 3 in dbh
• Herb (understory): all non-woody plants
and woody plants <3 ft tall
• Woody Vine: woody climbing plants < 3 ft
tall
Point Determination Method
• determine whether
visual evidence of
wetland hydrology is
present
• one primary indicator
or two secondary
indicators must be
present to conclude
that wetland hydrology
exists
Primary Hydrology Indicators
• visual observation of
inundation
• visual observation of
soil saturation (top 12
in)
• watermarks
• drift lines
• sediment deposits
• drainage patterns
within wetlands
Secondary Hydrology Indicators
• oxidized rhizospheres associated with
living roots in the upper 12 in of soil
• water stained leaves
• local soil survey hydrology data for
identified soils
• FAC-neutral test (redo plant test without
FAC plants)
• bare soil areas
• morphological plant adaptations
Morphological Plant Adaptations
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buttressed tree trunks
multiple trunks
pneumatophores (knees)
adventitious roots
shallow roots
hypertrophied lenticels
aerenchymous tissue
polymorphic leaves (many or unusual shapes)
Determine whether hydric soils are present
Indicators:
• organic soils (histosols)
• histic epipedon
• sulfidic material
• aquic or periaquic moisture regime
• reducing soil conditions (ferrous iron test)
• soil gleying
• mottles
• soil appearing on hydric soils list
• Iron and manganese concretions
Organic Soil (Histosol)
A soil is organic when
1. more than 50-% (by volume)
of the upper 32 in of soil is
composed of organic soil
matter; or,
2. organic soil material of any
thickness rests on bedrock.
Organic soils are saturated for
long periods and are
commonly called peats or
mucks.
Histic Epipedon
• an 8-16 inch layer at or near the surface of
a mineral hydric soil that is saturated with
water for 30 or more consecutive days in
most years and contains a minimum of 20
percent organic matter when no clay is
present, or a minimum of 30 percent
organic matter when clay content is 60%
or greater.
Sulfidic Material
When mineral soils emit an odor of rotten
eggs, hydrogen sulfide is present. Such
odors are only detected in waterlogged
soils that are permanently saturated and
have sulfidic material within a few
centimeters of the soil surface. These are
only produced in a reducing environment.
Soil Gleying
• under anaerobic
conditions, iron is reduced
producing bluish,
greenish, or grayish
colors.
• gleyed soils immediately
below the surface layer
are an indication of
saturation and/or
inundation for long
periods, and are
considered to be wetland
soils.
Bright Mottles and/or Low Matrix Chroma
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indicate a fluctuating water table
mineral hydric soils usually have one of
the following color features in the horizon
immediately below the A-horizon or 10
inches (whichever is shallower):
1. matrix chroma of 2 or less in mottled soils, or
2. matrix chroma of 1 or less in unmottled soils
Sandy Soils
• not all indicators
listed previously can
be applied in sandy
soil, especially color
• addition properties
may be used
– high OM in the
surface horizon
– streaking of
subsurface horizons
by OM
– organic pans
http://forest.mtu.edu/classes/fw4220/wetlands/Delineation(06).pdf