Charlotte Wetland Database Development

Personnel: William Sweeney, Leslie Morrissey, The Rubenstein School of Environment and Natural Resources, The University of Vermont

Cooperators: Conservation Commission, Town of Charlotte, Vermont

Download the article that describes this project here.

Wetlands are an integral part of Vermont's dynamic landscape. In recent years, an improved understanding of the value of wetlands has led to efforts to preserve them in an effort to protect surface and groundwater quality, fish and wildlife habitat, recreational and economic uses, and aesthetics. Wetlands are also protected from development under federal and state jurisdiction. To meet the legal requirements for wetland protection, local municipalities must devise wetland plans. The Town of Charlotte is in the process of updating their Town Plan for the Year 2000. As part of that effort, the Conservation Commission has been charged with the task of identifying and assessing the location and areal extent of wetlands within the town's boundaries. University of Vermont researchers were funded to create an updated database of wetlands for the Town of Charlotte. Wetland database development summarized here was based on the use of GIS and remote sensing technologies.

Wetlands of Charlotte, Vermont
Charlotte Wetlands Map
Click here to view an enlarged image of the map (92 kb).

Approach

The wetland database developed for the Town of Charlotte was generated by photointerpreting 1:40,000 CIR aerial photographs. Wetland boundaries were drawn on acetate overlain on the CIR photos. Accuracy of the photointerpretation was evaluated by on-site inspections by members of the Charlotte Conservation Commission, the UVM team, and Karen Bates, a wetland ecologist from the State Wetlands Office. Aerial photos and acetate overlays (90 kb) were subsequently scanned and rectified to a map base. The scanned CIR photos with delineated wetland polygons were then screen digitized. Wetland attributes were added and ARC/INFO coverages generated. For map production purposes, the seventy-eight wetland types were summarized into eight distinct categories based on their Cowardin classifications. Database digitization and development for this project were conducted by Mr. William Sweeney, a graduate student, under the direction of Dr. Leslie Morrissey, School of Natural Resources, University of Vermont. For additional details of the processing and products generated as a part of this project, please refer to UVM's Summary Report.

Comparison with NWI

The Vermont Wetland Rules, Vermont's state wetland protection law, was passed in 1990 in an effort to preserve significant wetland ecosystems in Vermont. The law provided for the regulation of development and other destructive activities within and around significant wetlands. The primary means for identifying state regulatory wetlands was the delineation of inland wetlands on federal National Wetlands Inventory (NWI) maps. NWI-based maps, renamed the Vermont Significant Wetland Inventory (VSWI), were distributed to local municipalities and officials for regulatory purposes. In an effort to evaluate the effectiveness of the NWI maps in identifying Vermont wetlands, a comparison was conducted between the updated Charlotte wetland database and the existing NWI data. To see how the updated Charlotte wetland database boundaries differ from those shown on Vermont Significant Wetland Inventory (National Wetland Inventory) maps, click here (117 kb).

For the updated Charlotte wetland database project, seventy-eight different wetland types were coded according to the Cowardin Wetland Classification System (1979) and 1170 individual wetlands were delineated. For the same area within the town, the Vermont Significant Wetland Inventory identifies only 250 wetlands. Similarly, the total wetland acreage mapped in the updated Charlotte wetland database was 2544 acres, nearly twice the area (1391 acres) mapped by the NWI. A comparative histogram (52 kb) analysis of the distribution of wetland acreages between the two maps shows that the NWI omits many small wetlands (under 3 acres) which are reliably mapped by the updated Charlotte wetland database. Although the minimum mapping unit for the NWI is 3 acres, the NWI map for Charlotte also underestimates wetlands in the 3-10 acre size range. Wetlands larger than 10 acres in size are delineated reliably on both maps. Generally speaking, the minimum wetland mapping unit for the Charlotte map is less than 1 acre, while the minimum mapping unit for the National Wetlands Inventory is greater than 3 acres for northern New England. In addition to differences in numbers and areal extent, the positional accuracy of the revised Charlotte wetland boundaries are approximately +/- 20 feet, while the positional accuracy of the National Wetlands Inventory for northwest Vermont is as large as 500 meters in some locations. This further impacts the utility of NWI maps for local wetland planning and protection.

This project was funded by the Town of Charlotte Conservation Commission. The detailed digital database is available through the Town of Charlotte Planning Office and the Chittenden County Regional Planning Commission.


       Updated: 3 August 2007