Comparison of USACE Three-Factor Wetland Delineations to National Wetland Inventory Maps
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GENERAL WETLAND SCIENCE
Comparison of USACE Three-Factor Wetland Delineations to National Wetland Inventory Maps Edward Gage 1
&
David J. Cooper 1 & Robert Lichvar 2
Received: 6 May 2019 / Accepted: 2 October 2019 # Society of Wetland Scientists 2019
Abstract Wetlands are mapped across the USA for compliance with §404 of the Clean Water Act using field-collected data and protocols in the 1987 Federal Wetlands Delineation Manual (3-factor method). The National Wetlands Inventory (NWI) maps wetlands and deepwater habitats for management and policy-making using aerial image analysis with limited field verification. There have been few comparisons of maps other than for limited geographic areas or wetland types. We compared 3-factor wetland delineations to NWI maps for 1751 assessment areas (AA) in different regions. We did not assess the accuracy of either product, but instead compared mapped area and polygon count for existing data at sites, then aggregated results to broader scales and compared with ancillary data to identify factors correlated with map differences. In a subset of NWI polygons eliminating nonwetland Cowardin types, 74% of NWI polygons were mapped in common with 3-factor polygons. NWI identified greater area in 33% of AA and greater total area across all sites. Approximately 27% of AA had 3-factor but no NWI polygons, while 6.7% of AA had features mapped only by NWI. Multiple factors likely contributed to differences including polygon size and temporal mismatches between maps, suggesting caution be used when comparing products. Keywords Wetland regulation . Wetland mapping . Wetland delineation
Introduction Section 404 of the Clean Water Act (CWA), administered by the U.S. Army Corps of Engineers (USACE) and the U.S. Environmental Protection Agency (EPA), provides the framework for regulating wetlands in the U.S. at the federal level. Regulations and guidance documents define wetlands and provide procedures for their identification and delineation (Environmental Laboratory 1987). The U.S. Fish and Wildlife Service’s National Wetlands Inventory (NWI) has Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13157-019-01234-y) contains supplementary material, which is available to authorized users. * Edward Gage [email protected] Robert Lichvar [email protected] 1
Department of Forest and Rangeland Stewardship, Colorado State University, Fort Collins, CO, USA
2
Cold Regions Research and Engineering Laboratory, U.S. Army Engineer Research and Development Center, Hanover, NH, USA
created maps of wetlands and deepwater habitats for the entire U.S. that are widely used by managers, policy makers, and the public (Wilen and Bates 1995; Tiner 1997a; Dahl 2011; Dahl and Stedman 2013). While sharing a common focus on wetlands, these programs use different definitions and protocols and have distinct program histories and goals. The USACE Wetland Delineation Manual (Environmental Laboratory 1987) and subsequent regional supplements (USACE 2007, 2
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