GIS

Spatial Technologies-Using Geospatial Data to Restore Wetlands

1 Dec, 2006 By: James L. Sipes

Information from GIS helps map, evaluate and analyze wetlands.


Wetlands are important. They help regulate river flow, filter pollutants, absorb flooding overflow and provide homes to thousands of plants, animals and birds. Many people who live along the Gulf Coast believe that wetlands are important for different reasons. Last year the region was devastated by Hurricane Katrina, which caused billions of dollars in damage and displaced more than one million people. Many who live in the region discovered that wetlands could significantly reduce the impact of storm surges associated with hurricanes. According to the U.S. Fish and Wildlife Service, every 2.7 miles a hurricane travels across wetlands or marsh can reduce storm surge by 1 foot, so one way to make the Gulf Coast a little bit safer is to restore the region's wetlands.



Wetlands Data

There is no shortage of hydrological data. The USGS (U.S. Geological Survey) Seamless Data Distribution provides hydrography data such as ground water climate response, alluvial and glacial aquifers, hydrologic unit regions, principal aquifers, NHD streams, NHD streams and arsenic in ground water.

USGS provides hydrologic unit data originally collected as part of GIRAS (Geographic Information Retrieval and Analysis System). Geospatial One Stop, the National Geospatial Data Clearinghouse, the National Hydrography Dataset and NAWQA Digital Maps are just a few sources of water resource data.

The National Water Information System water data site provides access to water resources data collected at 1.5 million sites throughout the nation. This information includes real-time, surface water, groundwater, water quality and site inventory data. USGS also provides access to near real-time data as part of the National Streamflow Information Program, which oversees 7,300 streamgauges that monitor water flow. USGS's WaterWatch is an online map that tracks short-term flow changes in rivers and streams. The map depicts stream flow conditions as computed at USGS gauging stations

One of the major sources of wetland data is the U.S. Fish and Wildlife Service's NWI (National Wetlands Inventory). NWI digital data files are records of wetlands location and classification as defined by the USFWS. The NWI has more than 6,000 possible combinations of wetland coding nationwide. These include different categories for marine, estuarine, riverine, lacustrine and palustrine wetlands.

NWI data is produced from an analysis of NHAP (National High Altitude Photography) or NAPP (National Aerial Photography Program) aerial imagery, collateral data sources and fieldwork. Maps are produced at a nominal scale of 1:24,000. Delineated wetland boundaries are transferred manually from interpreted photos to USGS 7.5-minute topographic quadrangle maps and then labeled manually. These 7.5-minute quadrangle maps contain ground planimetric coordinates of wetlands point, line and area features and wetlands attributes.

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One of the primary sources for accessing NWI data is through the Wetlands Mapper, which identifies areas that have been mapped as part of the program. Users can toggle shaded relief, USGS DRGs (digital raster graphics), orthoquads, streams, roads and other data themes. Wetlands Mapper also provides links to other data sites and sources of wetland data, such as the National Map. The site provides geospatially referenced information about the status, extent, characteristics and functions of wetlands, riparian, deep water and related aquatic habitats.

Metadata for Wetlands Mapper data includes the date of the satellite imagery, type of imagery, date of map production, available formats for the data, intent of mapping, constraints and contributing data sources.

Planners can use the Wetlands Data Extraction Tool to download data viewed with Wetlands Mapper. Users can download a NWI wetland polygon, metadata that describes the wetland polygon and historic maps that might be useful for understanding landscape changes. The Wetlands Data Extraction Tool uses the USGS topographic quadrangle names for area selection and extraction. All data downloaded is georeferenced using NAD (North American Datum) 1983.

Features in Wetlands Mapper are stored as part of WMG (Wetlands Master Geodatabase), a national digital library that provides a layer of digital wetlands and deep water habitat. It includes links to hydrographic data in an effort to improve scientific research, strategic planning, resource management and tactical analysis for habitat conservation. The Wetlands Master Geodatabase contains available digital wetland and deep water map data, including around 27,000 wetland coverage maps combined to create a seamless ArcSDE geodatabase. The geodatabase also accommodates upland, riparian habitats and hydrogeomorphic coding of features within the data set. All data stored in WMG uses the Albers Equal-Area Conic Projection and NAD 83 datum, so it fits together smoothly.

As part of the NWI, the Fish and Wildlife Service also developed a standard for data that has been proposed as the National Standards for Wetlands Mapping. Expectations are that it will be adopted sometime in mid-2007.

Because Wetland Mapper meets the standards of the Open GIS Consortium, the data is available for use by other software developers. ArcIMS site administrators can connect to the new Wetlands Mapper servers and include wetlands into their own ArcIMS viewers as background layers.

The accuracy of wetland data from aerial and satellite imagery is based on the quality of the imagery, how the imagery is processed and the amount of cross-referenced data as well as ground truth verification. The majority of NWI data was developed with aerial images taken between 1971 and 1992, and this imagery was processed to delineate wetlands. In areas with minimal vegetative cover, such as open plains and prairies, the minimum size of wetlands being mapped is around 1 to 3 acres. In forested areas, the minimum size ranges from 1 to 3 acres, depending on wetland type and the quality of the aerial imagery. In areas with evergreen forests, wetlands had to be at least 3 acres or so in size to be mapped.

Data at the State Level

Many states are developing their own geospatial data for wetlands to augment the NWI data. In Oregon, the Oregon Geographic Information Council developed a statewide prototype wetland mapping framework. OWMS (Oregon Wetland Mapping Standard) is a collection of georeferenced features that depict wetlands within the state. It defines standards for data quality, including completeness, level of detail, positional accuracy and attribute accuracy. The format used is similar to that developed by the U.S. Fish and Wildlife Service for the NWI. This format provides a consistent structure for wetland data, and adoption of this standard will help improve compatibility of datasets.

The North Carolina DCM (Division of Coastal Management) has developed a wetlands conservation plan for improving wetlands protection and management in areas along the coast. One primary focus is to provide an accurate functional assessment of wetland significance. To help achieve this goal, DCM developed NC-CREWS (North Carolina Coastal Region Evaluation of Wetland Significance), a GIS-based functional assessment model used to evaluate the ecological significance of wetlands. It's intended to be used as a planning and decision support tool that helps planners, developers and managers define appropriate development or conservation practices to maintain and protect ecosystems.

NC-CREWS evaluates 39 separate functions such as water quality, wildlife habitat, water storage and bank stabilization. Some of the GIS layers used in NC-CREWS include DCM wetland type data, digital soils data, land use/land cover types, hydrography, watershed boundaries, endangered species occurrences, estuarine primary nursery areas, water quality classifications, unique natural ecosystem, wildlife habitat areas and fish spawning areas.

Advancing with Technology

As digital remote sensing technologies improve, so too will our ability to accurately delineate wetlands using digital imagery. Technologies such as LIDAR (light detection and ranging) and imaging spectrometers are used in remote sensing applications that create high-quality maps, and GPS-based surveys can delineate wetlands and produce and an even greater level of detail.

James L. Sipes is a senior associate with EDAW in Atlanta, Georgia, and the founding principal of Sand County Studios in Seattle, Washington. Reach him at jsipes@sandcountystudios.com.


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