Wetland Delineation
1 Purpose
This SOP describes the field and office procedures for conducting a wetland delineation using the three-parameter approach established by the US Army Corps of Engineers (USACE). A jurisdictional wetland must exhibit all three criteria simultaneously: hydrophytic vegetation, hydric soils, and wetland hydrology (US Army Corps of Engineers, 1987). Delineation establishes the boundary between jurisdictional wetlands (and other waters of the US) and upland areas, which is a prerequisite for regulatory compliance under Section 404 of the Clean Water Act.
Wetland delineation at EA Program sites supports baseline characterization, impact assessment, restoration planning, and student training in applied environmental science.
2 Scope
- Applies to: Freshwater palustrine wetlands (marshes, swamps, riparian wetlands, vernal pools, seeps) at EA Program field sites in the Arid West region of California. This SOP follows the USACE Arid West Regional Supplement (US Army Corps of Engineers, 2010), which supersedes the 1987 Manual for all delineations in this region.
- Does not apply to: Tidal or estuarine wetlands (require separate tidal methods); riverine waters regulated solely as ordinary high water mark (OHWM) features; non-USACE state-level wetland determinations under California law (e.g., Porter-Cologne Act), which may apply different criteria.
- Location: All EA Program wetland field sites
3 Responsibilities
| Role | Responsibility |
|---|---|
| PI / Field Lead | Approve delineation design; coordinate permits and landowner access |
| Trained Personnel | Conduct three-parameter assessment per this SOP |
| New Students | Complete training before independent plot assessment |
4 Definitions
- Dominant species: A species contributing 50% or more of the relative frequency or relative cover within a stratum; used in the 50/20 rule for hydrophytic vegetation determination.
- Facultative (FAC): A wetland indicator status category applied to plant species that occur in both wetland and upland habitats with roughly equal frequency (34–66% occurrence in wetlands); neither confirms nor denies wetland conditions when dominant.
- Facultative upland (FACU): Plants that usually occur in uplands (67–99% upland occurrence) but are occasionally found in wetlands; their dominance is evidence against hydrophytic vegetation.
- Facultative wetland (FACW): Plants that usually occur in wetlands (67–99% wetland occurrence); their dominance is strong evidence for hydrophytic vegetation.
- Hydric soil: A soil that formed under conditions of saturation, flooding, or ponding long enough to develop anaerobic conditions in the upper part; identified by USACE hydric soil field indicators (e.g., depleted matrix, redox concentrations, sulfidic odor); a required criterion for wetland delineation (US Army Corps of Engineers, 1987).
- Hydrophytic vegetation: Plant community dominated (by the 50/20 rule) by species with a wetland indicator status of OBL, FACW, or FAC; a required criterion for wetland delineation.
- Obligate wetland (OBL): Plant species that occur almost always (> 99% of the time) in wetlands; their dominance is the strongest evidence for hydrophytic vegetation.
- Ordinary high water mark (OHWM): The line on the shore established by the fluctuations of water leaving physical characteristics such as a clear natural line impressed on the bank, shelving, destruction of terrestrial vegetation, or presence of litter and debris; used to define the lateral extent of jurisdictional waters.
- Problem area: A site where one or more of the three wetland criteria are not clearly met or where atypical conditions (drought, altered hydrology, recent disturbance) complicate standard application of the three-parameter approach; requires additional documentation and may require a USACE district determination.
- Sample plot (data point): A defined area (typically 5 m radius for vegetation; a single soil pit for soils; a 10 m radius for hydrology indicators) within which all three wetland criteria are assessed together.
- Upland: An area that does not meet one or more of the three required wetland criteria; not subject to Section 404 jurisdiction.
- Wetland boundary: The line on the landscape separating areas that meet all three wetland criteria from areas that do not; the primary product of a wetland delineation.
- Wetland indicator status (WIS): A USACE classification of plant species by their probability of occurrence in wetlands: OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), UPL (upland). Current designations are maintained by the USACE National Wetland Plant List (NWPL).
5 Safety and Hazards
- Physical: Unstable substrates (soft muck, quicksand-like conditions in saturated soils); risk of sinking, tripping on submerged debris, or falling. Standing water may conceal holes and channels.
- Biological: Mosquitoes (disease vectors including West Nile virus), ticks (Lyme disease, RMSF), venomous snakes, poison oak/ivy (Toxicodendron spp.), stinging nettles, and waterborne pathogens. Avoid direct skin contact with standing water.
- Environmental: Heat stress in summer; hypothermia in winter and spring. Wetlands offer little shade in open marsh environments.
5.1 Required PPE
5.2 Emergency Procedures
Work in pairs at minimum. If a team member becomes stuck in soft substrate, distribute weight on a board, backpack, or rope and pull laterally rather than vertically. Refer to SOP-F001 Field Safety.
6 Equipment and Materials
| Item | Notes |
|---|---|
| USACE 1987 Wetland Delineation Manual | Required reference; bring to field |
| USACE Arid West Regional Supplement (2010) | Required for all CA Arid West delineations |
| Munsell Soil Color Charts (moist) | See SOP-F405 |
| Soil auger or push probe (60 cm minimum) | For reading soil profile to 50 cm depth |
| Tile spade or sharpshooter spade | For opening soil pit |
| 30 cm metric ruler | Depth to WTHS and horizon thickness |
| Flagging tape (two colors: wetland, upland) | For marking boundary and sample plots |
| GPS unit or smartphone with mapping app | See SOP-F006 |
| 50 m fiberglass measuring tape | Transect layout |
| Plant identification keys (regional) | Jepson Manual for California |
| National Wetland Plant List (NWPL) | Current WIS designations (usace.army.mil) |
| Hydric Soils Field Indicators guide | USDA NRCS Field Indicators of Hydric Soils |
| Wetland delineation field data sheets | See Appendix A |
| Clipboard, mechanical pencils, waterproof paper | Rite in the Rain recommended |
| Camera (waterproof or in dry bag) | Photo-document each sample plot |
| Compass | Transect bearings |
| 10x hand lens | Plant identification |
7 Estimated Time
| Task | Time (2-person crew) |
|---|---|
| Office pre-work (maps, records, NWPL lookup) | 2–4 hours |
| Site reconnaissance walk | 30–60 minutes |
| Sample plot assessment (per plot) | 15–30 minutes |
| Boundary flagging and GPS waypoints | 1–2 hours per 100 m boundary |
| Field data compilation | 30–60 minutes |
| Office post-work (report, map, data entry) | 4–8 hours |
8 Procedure
8.1 Step 1: Pre-Field Office Work
Before entering the field, complete the following:
Obtain and review available information:
- USFWS National Wetlands Inventory (NWI) maps (fws.gov/wetlands)
- USDA Web Soil Survey (websoilsurvey.nrcs.usda.gov) – note mapped hydric soils and map unit descriptions
- USGS topographic maps (7.5-minute quadrangles)
- Aerial/satellite imagery (Google Earth historical layers) – look for inundation signatures, dark organic soils, and characteristic vegetation patterns
- NOAA precipitation records for the region to assess whether current year is a drought, normal, or wet year (relevant to atypical situation determinations)
Generate a base map at a scale appropriate for the site (1:2,400 for small sites; 1:4,800 for large sites). Include NWI polygons, soil map unit boundaries, topographic contours, and property boundaries.
Look up current wetland indicator status (WIS) for all plant species expected at the site on the USACE National Wetland Plant List (plants.usace.army.mil).
Identify the appropriate USACE district and confirm whether a preliminary jurisdictional determination (PJD) or approved jurisdictional determination (AJD) is ultimately required.
8.2 Step 2: Site Reconnaissance
On arrival at the field site, conduct a reconnaissance walk before placing any sample plots:
- Walk the entire site perimeter and any internal drainages or basins to develop a mental model of landscape position, drainage patterns, and vegetation transitions.
- Identify probable wetland areas (standing or ponded water, dark organic soils visible at surface, wet-adapted vegetation) and probable upland areas (well-drained soils, upland vegetation).
- Identify any obvious disturbances (ditching, filling, altered hydrology, grazing, invasive species) that could create problem areas.
- Note the approximate location of vegetation transitions, which are often close to the wetland boundary.
- Sketch a rough site map with probable wetland/upland zones and planned transect routes.
8.3 Step 3: Establish Transects and Sample Plots
Establish transects perpendicular to the suspected wetland boundary, spaced to adequately characterize the site. For EA Program sites, transects are typically spaced 25–50 m apart; closer spacing is used in complex or small-scale boundaries.
On each transect, place sample plots at:
- A clearly wetland location (well within the apparent wetland)
- A clearly upland location (well outside the apparent wetland)
- One or more locations straddling the suspected boundary
Flag each sample plot center with flagging tape and record GPS coordinates. Use a consistent color for wetland plots and a different color for upland plots.
Number all sample plots sequentially and record them on the base map.
8.4 Step 4: Assess Hydrophytic Vegetation
At each sample plot (approximately 5 m radius), assess vegetation in all strata present (tree, shrub/sapling, herb, woody vine):
List all plant species in each stratum. Identify to species level using regional keys (Jepson Manual for California).
Estimate percent areal cover for each species within each stratum to the nearest 5–10%.
For each species, record the current wetland indicator status (WIS) from the USACE NWPL for the Arid West region.
Determine dominant species in each stratum using the 50/20 rule:
- Rank species within each stratum by decreasing percent cover.
- Add species from highest to lowest cover until the cumulative cover total reaches 50% or more of the total stratum cover.
- Include one additional species if it contributes at least 20% of the total stratum cover.
- All species added in steps (b) and (c) are dominant species for that stratum.
Tally the number of dominant species that are OBL, FACW, or FAC (hydrophytic) and the number that are FACU or UPL (upland).
The hydrophytic vegetation criterion is met if more than 50% of the dominant species across all strata are OBL, FACW, or FAC.
In borderline cases where FAC species are dominant, apply the FAC-neutral test: exclude all FAC species and recalculate dominance using only OBL, FACW, FACU, and UPL species. If the remaining dominants are predominantly hydrophytic, the criterion is still met. The FAC-neutral test is described in the Arid West Regional Supplement (US Army Corps of Engineers, 2010).
8.5 Step 5: Assess Hydric Soils
At each sample plot, excavate a soil pit to at least 50 cm depth (or to the water table or bedrock, whichever is shallower):
Excavate with a sharpshooter spade. If the pit fills with water, record the depth to water table and excavate no deeper.
Describe the soil profile using the form in Appendix A:
Check for USDA NRCS Field Indicators of Hydric Soils (Version 8.2 or current). For the Western Mountains, Valleys, and Coast (WMVC) region, the most applicable indicators include:
Indicator Code Name Key Feature A1 Histosol Organic soil (Oi, Oe, or Oa horizon > 40 cm) A2 Histic epipedon Organic surface layer 20–40 cm A3 Black histic Black (10YR 2/1) organic layer >= 20 cm A11 Depleted below dark surface Dark A over low-chroma (chroma <= 2) matrix F2 Loamy gleyed matrix Gley hue matrix in loamy soils F3 Depleted matrix > 60% low-chroma (chroma <= 2) matrix F6 Redox dark surface Dark A over depleted or reduced matrix F8 Redox depressions Redox concentrations in depressions The hydric soil criterion is met if one or more applicable field indicators are present at the appropriate depth. For most indicators in the Arid West Supplement, this means within the upper 30 cm of the soil profile (US Army Corps of Engineers, 2010).
Soils in the Arid West may have low-chroma colors from parent material (e.g., some shales, volcanic tuffs) rather than from saturation. If in doubt, check for redox concentrations (bright orange/red Fe masses) as corroborating evidence, and note the soil series and parent material from Web Soil Survey.
8.6 Step 6: Assess Wetland Hydrology
At each sample plot, document evidence of wetland hydrology. The USACE defines wetland hydrology as saturation within 30 cm of the surface for a continuous period of at least 5% of the growing season (US Army Corps of Engineers, 1987, 2010).
Record depth to surface water or saturated soil (standing water in the pit).
Check for primary hydrology indicators (in order of reliability):
Indicator Description Surface water Standing water present at time of visit High water table Water within 30 cm of surface in soil pit Saturation Saturated soil within 30 cm (water oozes when squeezed) Check for secondary hydrology indicators (two or more required when primary indicators are absent):
Indicator Description Water marks Staining on tree trunks or structures Sediment deposits Fresh mineral sediment on leaves or stems Drift lines Lines of debris deposited by receding water Waterlogged soils Confirmed by soil pit; no free water but saturated Water-stained leaves Grayish-brown discoloration of litter Oxidized rhizospheres Orange halos around living roots in grey matrix FAC-neutral plant communities Vegetation dominance by OBL/FACW species Crayfish burrows Chimney mounds indicating seasonal saturation For arid-region sites, pay particular attention to oxidized rhizospheres (a primary indicator in the Arid West Supplement) and drift/wrack lines along swales and basins.
The wetland hydrology criterion is met if at least one primary indicator is present, or at least two secondary indicators are present, at the time of visit; or if the site has documented evidence of seasonal or periodic inundation from well records or gauges (see SOP-F306).
At arid and semi-arid sites, surface water and high water tables may only be present during a brief seasonal window. When conducting delineations outside the wet season, rely on secondary indicators and, where available, water level logger data from monitoring wells. Document the date of the visit and regional precipitation conditions in all field data sheets. See SOP-F306 for long-term hydrology monitoring methods.
8.7 Step 7: Apply the Three-Parameter Test
At each sample plot, compile results from Steps 4–6:
Record whether each of the three criteria is met (yes/no) on the field data sheet (Appendix A).
A sample plot is classified as wetland if and only if all three criteria are met. If any criterion is absent, the plot is classified as upland (or a transitional/problem area if two of three are met).
If two of three criteria are met, flag the plot as a potential problem area and document the specific conditions. Common problem area types include:
- Recently disturbed wetlands (vegetation removed, soil disturbed)
- Drought-year assessments (hydrology not apparent)
- Altered hydrology (ditched, drained, or impounded areas)
- Atypical vegetation (recent burn, mowing, herbicide)
For problem areas, apply the appropriate USACE atypical situation procedures as described in the Regional Supplement (US Army Corps of Engineers, 2010).
8.8 Step 8: Flag and Map the Wetland Boundary
Between each pair of adjacent wetland and upland sample plots on a transect, locate the wetland boundary by walking perpendicular to the transect and reassessing the three criteria at intermediate points until the line of change is identified.
Flag the wetland boundary with a distinct color (use a third color different from the wetland and upland plot flags). Place flags every 5–10 m or at every change in direction.
Record GPS waypoints at each boundary flag using SOP-F006. Waypoint naming convention:
WB_[transect]-[sequence](e.g.,WB_T1-01).Photograph the boundary flags from multiple angles; include a scale bar (person or measuring tape) in at least one photo per transect.
Sketch the boundary on the field base map, noting all sample plot locations and transect lines.
8.9 Step 9: Field Quality Review
Before leaving the site, complete the following checks:
8.10 Step 10: Post-Field Office Work
Enter all field data into the project database within 48 hours per SOP-L803.
Import GPS waypoints and generate a georeferenced boundary map in GIS software (see SOP-L804).
Overlay the delineated boundary on aerial imagery, NWI maps, and soil survey maps to check for consistency; note and document any discrepancies.
Calculate wetland area (hectares) from the GIS boundary polygon.
Compile the delineation report with:
- Site description and location map
- Methods summary (reference to this SOP)
- Summary table of all sample plots and three-parameter results
- Wetland boundary map
- Photographs
- Conclusions regarding jurisdictional status
- Any problem areas and how they were addressed
Archive all raw field data sheets (scanned), GPS track files, GIS shapefiles, and the final report per project data management protocols.
9 Quality Control
- A minimum of two observers must conduct the vegetation assessment at each sample plot; independent species lists must be reconciled before leaving the plot.
- Munsell color readings must be made by two observers and must agree within one value and one chroma step; discrepancies require a consensus re-read per SOP-F405.
- GPS boundary waypoints must be collected with horizontal accuracy < 3 m (WAAS-enabled or equivalent). Record DOP and fix type.
- At 10% of sample plots, return the following day and re-assess the hydrophytic vegetation criterion independently; dominant species lists must agree within 10 percentage points cover.
- Final delineation maps must be reviewed by the PI before submission to any regulatory agency or inclusion in project reports.
10 Data Management
- Raw field data sheets must be scanned and uploaded to the project folder within 48 hours of fieldwork.
- Enter tabular sample plot data into the project database using the standardized template in Appendix B.
- GPS tracks and waypoints must be exported and backed up immediately on return from the field.
- All GIS boundary files must be saved in both shapefile and GeoJSON formats and versioned in the project Git repository.
- Version-control all analysis scripts and report documents per SOP-L801.
11 References
13 Training Record
Before conducting wetland delineations independently, personnel must:
- Read this SOP, SOP-F001, SOP-F306, and SOP-F405 in full
- Review the USACE 1987 Manual and Arid West Regional Supplement (US Army Corps of Engineers, 1987, 2010)
- Complete at least one supervised delineation transect, including independent application of the 50/20 rule and hydric soil field indicators, with results reviewed by the PI
- Demonstrate Munsell color reading proficiency per SOP-F405 inter-observer calibration requirements
- Successfully enter and map a practice delineation dataset in GIS
- Be signed off by the PI or field lead
14 Appendix A: Field Data Sheet
Print double-sided on waterproof paper (Rite in the Rain). Complete one sheet per sample plot.
Site: ________________ Date: _________ Observers: ________________________
Plot ID: _____ Transect: _____ GPS (lat/lon): ________________
Landscape position: upland / footslope / toeslope / depression / flat / other: _______
14.1 A. Hydrophytic Vegetation
| Species | Stratum | % Cover | WIS |
|---|---|---|---|
50/20 Rule Tally: Dominants that are OBL/FACW/FAC: ___ / Total dominants: ___
Hydrophytic vegetation criterion met? YES / NO / Problem area
14.2 B. Hydric Soils
Depth to water table or bedrock: _____ cm
| Horizon | Depth (cm) | Munsell (moist) | Texture | Notes |
|---|---|---|---|---|
Hydric soil field indicator(s) present: ___________________
Hydric soil criterion met? YES / NO / Problem area
14.3 C. Wetland Hydrology
Primary indicators (check all present):
Secondary indicators (check all present):
Wetland hydrology criterion met? YES / NO / Problem area
14.4 D. Determination
All three criteria met? YES – WETLAND / NO – UPLAND / PROBLEM AREA
Notes / atypical situation documentation:
________________________________________________________________
15 Appendix B: Sample Plot Summary Table Template
Enter into data/raw/wetland_delineation_[site]_[date].csv:
plot_id,transect,lat,lon,veg_criterion,soil_criterion,hydro_criterion,
determination,dominant_species,hydric_indicator,primary_hydro_indicator,
notes,observers,dateColumn definitions are in the project data dictionary (data/metadata/wetland_delineation_datadictionary.csv).
16 Appendix C: Wetland Indicator Status Quick Reference
| Code | Category | Wetland Occurrence | Delineation Implication |
|---|---|---|---|
| OBL | Obligate wetland | > 99% | Strong evidence for hydrophytic veg |
| FACW | Facultative wetland | 67–99% | Evidence for hydrophytic veg |
| FAC | Facultative | 34–66% | Equivocal; apply FAC-neutral test |
| FACU | Facultative upland | 1–33% | Evidence against hydrophytic veg |
| UPL | Upland | < 1% | Strong evidence against hydrophytic veg |
Current WIS designations for the Arid West region are available at plants.usace.army.mil. Always use the regional list, not the national list, for California delineations.