What Is a Wetland Delineation?
A wetland delineation is the formal field survey that identifies and maps jurisdictional wetlands on a property — the boundary line between buildable land and regulated waters. Performed by a qualified wetland scientist using the Army Corps of Engineers methodology (vegetation, soils, hydrology), the delineation determines whether Section 404 permits apply and how much of the site is developable. Order it early: it can redraw the site plan.
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How delineation works
The scientist evaluates three parameters at sample points: hydrophytic vegetation (plants adapted to wet conditions), hydric soils (soils formed under saturation), and wetland hydrology (evidence of periodic inundation or saturation). All three must be present for a jurisdictional wetland (with limited exceptions). The result is a mapped boundary with flags in the field and a report the Corps reviews in a jurisdictional determination.
Why it matters for development
Impacts to jurisdictional wetlands need Section 404 permits — nationwide permits for small impacts (under 1/2 acre), individual permits for larger ones, with mitigation (restoring or creating wetlands elsewhere, often at ratios of 1.5:1 to 3:1) that can cost more than the land. The delineation tells the site designer where buildings, roads, and grading must avoid — or what the impact permitting will cost. A delineation done after site planning is how projects lose their preferred layout.
Timing and validity
Delineations are best done in the growing season when vegetation and hydrology indicators are visible; off-season delineations rely more heavily on soils. Corps jurisdictional determinations are typically valid for five years. If the site has any low areas, drainages, or historic wetland signatures on aerial photos, delineate before purchasing or entitling — the wetland boundary is the single biggest unknown in site feasibility.
The bottom line
A wetland delineation maps jurisdictional wetlands via vegetation, soils, and hydrology — order it before site planning. Impacts trigger 404 permits and costly mitigation; the boundary redraws developable area.
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