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Wetland Delineation. Wetland Delineation The process of identifying and mapping the upper boundary of a wetland for a particular purpose such as –wetland.

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Presentation on theme: "Wetland Delineation. Wetland Delineation The process of identifying and mapping the upper boundary of a wetland for a particular purpose such as –wetland."— Presentation transcript:

1 Wetland Delineation

2 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)

3 National Wetlands Inventory


5 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

6 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

7 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


9 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

10 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?

11 YES!

12 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.

13 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.

14 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

15 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


17 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

18 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

19 Identify Potential Wetland Areas Walk the site and verify (field check) the preliminary data.

20 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.)

21 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

22 Choose a potential wetland area to begin evaluation identify obvious wetland and non-wetland areas and locate the transition zone between them.

23 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.

24 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.

25 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


27 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

28 Primary Hydrology Indicators visual observation of inundation visual observation of soil saturation (top 12 in) watermarks drift lines sediment deposits drainage patterns within wetlands



31 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


33 Morphological Plant Adaptations buttressed tree trunks multiple trunks pneumatophores (knees) adventitious roots shallow roots hypertrophied lenticels aerenchymous tissue polymorphic leaves (many or unusual shapes)


35 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

36 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, soil material of any thickness rests on bedrock. Organic soils are saturated for long periods and are commonly called peats or mucks.

37 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.

38 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.

39 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.

40 Bright Mottles and/or Low Matrix Chroma 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

41 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


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