Home 1. Update Wetland Maps

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 United States wetlands available and serves as a primary source of wetland mapping data for the country. However, the NWI does have a number of data limitations that suggest an update may be beneficial before it is used in subsequent steps of the WARPT:

  • As of 2010, digital NWI maps are available for approximately 61% of the country; much of the data are over 20 years old (Tiner, 2009).
  • Federal funding has typically only allowed for an average of less than two percent of the national wetlands map to be completed each year (Awl et al., 2009; Tiner, 2009).
  • In addition, the NWI typically does not include wetlands smaller than one to three acres, ephemeral wetlands, farmed wetlands, and certain wetland types that are difficult to interpret from aerial photos.

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:

  • How old are the data? Has there been much recent development activity since the maps were created?
  • What is the resolution of the data or minimum mapping unit
  • Are there known issues or inaccuracies with the data?

To determine the status of wetland mapping in your area, check with the following sources:

  • Your local planning or natural resources department may have developed a wetlands map, or have included wetlands as part of a local land use/land cover layer.
  • Association of State Wetland Managers Wetland Mapping highlights the latest state-level wetland mapping efforts and State Wetland Programs provides information and links for individual states to determine the status of state wetland maps.
  • To determine whether digital NWI maps are available, refer to  Regional Wetlands Coordinators.  At the main NWI page, you can download digital data, order hard copy maps, and obtain metadata that describes when the maps were created for your region and identifies the minimum mapping unit.
  • Natural Resources Conservation Service (NRCS) Wetland Determinations (aka “Swampbuster” maps) were used to determine compliance with swampbuster provisions in the 1985 Farm Bill and are available as paper maps only for individual sites. However, many of these wetlands are isolated and small (<1 ac), which are easily missed on NWI and other wide-scale maps or imagery.  They may be useful to supplement your NWI by digitizing the wetland boundaries. Contact your local or regional NRCS office to access these maps.
  • If the wetland maps available from the above sources are outdated or there has been a lot of recent development activity in your community, the U.S. Army Corps of Engineers (USACE) Section 404 Permit Wetland Determinations may be useful to identify wetlands for which some type of permitted impact or mitigation has been authorized   You can request this information from your USACE district office.

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
(540) 231-8825

St. Mary's University of Minnesota
Department of Resource Analysis
360 Vila Street #7
Winona, MN 55987
(507) 457-8712

Atkins North America
1616 East Millbrook Road
Suite 310
Raleigh, NC 27609
(919) 431-5276

Contact your U.S. FWS Regional Wetland Coordinator for other possible contractors.

Some additional partners for wetland mapping include:

Table 1.1. Wetland Mapping Methods

Method

Description

Limitations

Resources

“Heads-Up” method of wetland delineation

Digitize wetlands directly from digital imagery

Requires image analysts experienced in the identification and classification of wetlands

Dahl et al.(2009)

Manual stereoscopic interpretation

Stereoscopic viewing of aerial photos to interpret them in three dimensions and delineate wetlands

Requires photo interpreters who can see in stereo and have an understanding of surface water hydrology and wetland ecology

USFWS (1995)

Addition of “potential wetlands” to existing wetland maps

Use wetland indicator layers to identify areas with high likelihood of wetland presence

Requires field confirmation of wetland presence and boundaries

Munoz et al. (2009)

Ralph Tiner

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 Wisconsin has used the former method to develop a map of ‘potential wetlands’ (Figure 1.1).   The Munoz et al. (2009) method may be most useful in regions with a known abundance of isolated wetland types that are insufficiently mapped.  However, the method may need to be adapted for the isolated wetland types in your region.  This analysis can be done with in-house GIS staff in conjunction with a wetland consultant, or may be contracted out if GIS capabilities are not available within your jurisdiction.  If the results are to be incorporated into local wetland maps and assigned wetland functions, field verification of all ‘potential wetlands’ is needed to confirm that they exist.

Figure 1.1. Map of wetlands (shown in orange) and potential wetlands (shown in pink) for Verona, Wisconsin (source: http://dnr.wi.gov/wetlands/mapping.html)

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.

  • Imagery should have a minimum resolution of 1 m
  • Wetland classification following Cowardin et al. (1979)
  • Topological verification (how point, line, and polygon features share coincident geometry)
  • Valid attribute coding for wetland habitat type
  • Metadata should conform to the most recent FGDC Content Standard for Digital Geospatial Metadata (CSDGM).

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).

Read more...

 

Resources for Updating Local Wetland Maps

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Digitize
The process of converting features on a paper map into digital format using a trace methodology, which results in the creation of a spatial dataset.
Ecotone

A transition area between two adjacent, but different plant communities.

Indirect Wetland Impacts
Impact to wetlands caused by inputs of stormwater and pollutants generated by land development or other activities within the wetland CDA.
Direct Wetland Impacts
Wetland loss or degradation resulting from activities that occur within wetlands, such as dredging, filling and draining.  Activities that cause direct impacts are largely regulated through the federal and state wetland permitting process.
Stormwater Treatment Practices

A structural or non-structural practice designed to temporarily store or treat stormwater runoff in order to mitigate flooding, reduce pollution, and provide other amenities (also called a Best Management Practice – BMP).

Hydrogeomorphic
Factors that influence how wetlands function, including geomorphic setting, water source, and hydrodynamics.
Hydrogeomorphic
Factors that influence how wetlands function, including geomorphic setting, water source, and hydrodynamics.
Sinks
A cell or set of spatially connected cells that cannot be assigned flow direction in a raster elevation dataset. This can occur when all neighboring cells are higher than the processing cell or when two cells flow into one another. Sinks can indicate areas where water is likely to pond, but can also be an error in the dataset.
Facultative Wetland Plants
Species that usually occur in wetlands (approximately 67% - 99% probability), but also occur in non-wetland areas (approximately 1% - 33% probability).
Obligate Wetland Plants
Species that occur almost always in wetlands under natural conditions (greater than 99% probability), but which may also occur rarely in non-wetlands (less than 1% probability).
Interferometric Synthetic Aperture Radar (IFSAR)
A radar technique that uses two or more synthetic aperture radar (SAR) images to generate surface elevation using differences in the phase of waves returning to the satellite or aircraft.
Interferometric Synthetic Aperture Radar (IFSAR)
A radar technique that uses two or more synthetic aperture radar (SAR) images to generate surface elevation using differences in the phase of waves returning to the satellite or aircraft.
Light Detection and Ranging (LiDAR)

A remote sensing technique that measures properties of pulsed laser light reflected from objects to determine their position, velocity, and other information.

Light Detection and Ranging (LiDAR)

A remote sensing technique that measures properties of pulsed laser light reflected from objects to determine their position, velocity, and other information.

Light Detection and Ranging (LiDAR)

A remote sensing technique that measures properties of pulsed laser light reflected from objects to determine their position, velocity, and other information.

Digital Elevation Model (DEM)
A digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals.
Digital Elevation Model (DEM)
A digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals.
Hyperspectral Data

Information collected and processed from across the electromagnetic spectrum. Spectral signatures (unique “fingerprint” left by specific objects) enable identification of materials that make up a scanned object.

Remote Sensing
Gathering and recording information about objects without actual contact through the use of such techniques as photography, infra-red imagery, and radar.
Hydrophytes
A plant that grows wholly or partially submerged in water.
Blackspots
Areas on aerial photos that show up as dark blue, dark grey, or black and are indicative of saturated soil conditions.
Stereoscopic
The ability to see three dimensionally by using two views of a single object from slightly different positions typically through the use of an optical aid known as a stereoscope.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Hydric Soils
Soils that are saturated, flooded, or ponded for a long enough period during the growing season to develop anaerobic conditions in the upper soil horizons.
Geographic Information Systems (GIS)

A system that integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information.

Geographic Information Systems (GIS)

A system that integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information.

Digitize
The process of converting features on a paper map into digital format using a trace methodology, which results in the creation of a spatial dataset.
Minimum Mapping Unit

The minimum size or dimensions for features to be mapped as lines or areas for a given map scale.