Update Local Wetland Maps
It is much easier to protect wetland resources when you have good maps of their locations and types. In addition, wetland maps provide “red flag” or up-front information or prioritization to inform local plan review and Clean Water Act Section 404 evaluations. Some states and local jurisdictions have a detailed and reasonably accurate wetlands mapping layer. However, many jurisdictions rely solely on the National Wetlands Inventory (NWI), maintained by the U.S. Fish and Wildlife Service (FWS). The NWI is the most comprehensive digital coverage of
Several options that are available for updating wetland maps include digitizing directly from digital imagery, manual stereoscopic interpretation, and using wetland indicator layers to identify potential wetlands.
Determine if an Update to your Local Wetland Maps is Necessary
Whether your community relies on the NWI for its wetlands mapping or has a state, regional or local wetland map, the following questions should be considered to determine if an update to these maps is necessary to help strengthen local wetland protection:
To determine the status of wetland mapping in your area, check with the following sources:
In general, if your wetland maps are more than 20 years old (10 if there has been a lot of recent development), has known inaccuracies, or is of a relatively small scale (e.g., smaller than 1:40,000), you should consider updating the maps. On the other hand, if your wetland maps include very small wetlands (e.g., less than 1 acre), as well as wetlands associated with intermittent and ephemeral streams, they are probably of sufficient detail to protect wetlands locally and you can continue on to:
Options for Updating Wetland Maps
Several options are available for updating local wetland maps (Table 1.1). The most accurate yet resource intensive methods include digitizing or photo-interpreting wetlands directly from digital imagery or high resolution aerial photos. To offset the associated costs, agencies and organizations may want to collaborate on a regional basis to acquire imagery (which has many uses besides wetland mapping) and/or mapping wetland resources. Potential partners may include: land trusts, non-profits, transportation and utility departments, universities, federal and state agencies, private consultants, and regional governing bodies. For additional information on identifying partners and building mapping coalitions, refer to Stetson (2009), Christie and Stetson (2009), and NACo (2007).
One option is to hire a government agency like the U.S. Fish and Wildlife Service (FWS), one of its mapping contractors, or a mapping company/organization with experience applying the Federal Geographic Data Committee's (FGDC) wetland mapping standard. The U.S. FWS may be interested in a wetland mapping project if it covers a relatively large geographic area and falls within one of their priority areas. Costs for these services vary with the type and density of wetlands in a geographic area, the recency of the NWI data, and the availability of digital data sources (e.g., land use/cover and soils).
Some of the wetland mapping contractors utilized by the U.S. FWS include:
Conservation Management Institute
Virginia Polytechnic Institute and State University
1900 Kraft Street
Blacksburg, VA 20160
St. Mary's University of Minnesota
Department of Resource Analysis
360 Vila Street #7
Winona, MN 55987
Atkins North America
1616 East Millbrook Road
Raleigh, NC 27609
Contact your U.S. FWS Regional Wetland Coordinator for other possible contractors.
Some additional partners for wetland mapping include:
A less intensive method of improving local wetland mapping is to use wetland indicator layers to identify potential wetlands using Geographic Information Systems (GIS). Ralph Tiner of the U.S. FWS has developed a method to identify potential wetlands based on hydric soils, while Munoz et al. (2009) describe such a method for identifying potential isolated wetlands. The State of
Whichever mapping method is used, you should be aware of the recently implemented Federal Geographic Data Committee (FGDC) wetland mapping standard. Compliance with these standards is required for all federal agencies and other organizations that use federal funds to map wetlands. However, states, local governments, and non-profit organizations are also encouraged to utilize the wetland mapping standard in an effort to contribute to the national wetland mapping effort being conducted by the U.S. FWS. An average of less than two percent of the national wetlands map is completed per year due to funding limitations. The mapping standard will allow diverse groups to produce wetlands mapping data that is compatible and consistent in quality so that it can be included in the NWI (Awl et al., 2009).
The basic FGDC wetland mapping standard requirements are listed below. For a more comprehensive list, refer to FGDC (2009). In addition, the U.S. FWS has created a companion document to the FGDC wetland mapping standard (Dahl et al., 2009) that describes the technical procedures and requirements for wetlands map data. It explains the appropriate application of wetland classification, wetland mapping process, and how to achieve the data quality requirements now required by the wetland mapping standard. The U.S. FWS, in conjunction with USGS, have developed customized GIS tools for performing data checks on wetland map data. These Attribution and Verification Tools are extensions to the ESRI ArcMap desktop software and have been designed to address geo-positional errors, digital anomalies, and logic checks for data included in the NWI. A Wetland Mapping training course is also available from the U.S. FWS for learning how to successfully submit standards-compliant wetlands geospatial data to the NWI.
For additional information on the process of contributing your data to the Wetlands Master Geodatabase, please visit http://www.fws.gov/wetlands/WetlandsLayer/ContributedData.html.
CASE STUDY - Wood County, Ohio
Wood County, Ohio is located in Northwestern Ohio, south of the City of Toledo. After the last glacier retreat 20,000 years ago, the majority of Wood County, Ohio (the County) was left as the Great Black Swamp (Figure 1.3). Over time the swamp was drained though aggressive ditching efforts to create rich and fertile agricultural land. Today, most of the County is in agricultural production with an extensive, well-maintained ditch network that drains to local waterways. Through a partnership with the Center for Watershed Protection, the County conducted an update of its local wetland map using a Geographic Information System (GIS).
Resources for Updating Local Wetland Maps