What Is a Wetlands Delineation?
A wetlands delineation is the field study identifying and mapping jurisdictional wetlands on a property — the boundaries that determine where the Clean Water Act (Section 404) and state regulations apply. A qualified wetland scientist examines vegetation, soils, and hydrology at sample points and flags the wetland edge. No delineation, no certainty: the mapped boundary drives the entire site design, permit strategy, and project feasibility.
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The three parameters
The Corps of Engineers manual requires all three: hydrophytic vegetation (plants adapted to wet conditions — identified by indicator status), hydric soils (soils formed under saturation — field indicators like redox features), and wetland hydrology (evidence of periodic inundation or saturation). A site meeting all three at a sample point is wetland; the boundary falls where any parameter drops out. The delineation report documents each sample point with data sheets.
Jurisdiction questions
Not every delineated wetland is federally jurisdictional — the 'waters of the United States' definition (post-Sackett, significantly narrowed) determines Corps jurisdiction; states often regulate more broadly (California, New York, and others protect wetlands the feds no longer reach). The approved jurisdictional determination (AJD) from the Corps confirms federal status — get it before designing around (or through) the wetlands.
Project implications
Avoidance first (design around the wetlands), then minimization, then compensatory mitigation for unavoidable impacts — the sequencing the Corps requires. Mitigation means purchasing credits from an approved mitigation bank ($50,000-$300,000+ per acre depending on region) or permittee-responsible mitigation. Nationwide permits cover minor impacts with streamlined review; individual permits for larger impacts take 12-24+ months. Delineate early — wetland surprises late in design are project-killers.
The bottom line
Wetlands delineations map the vegetation-soils-hydrology boundary driving Clean Water Act jurisdiction — delineate early, confirm with an AJD, and design around wetlands before considering mitigation credits.
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