Report Released: Mapping Impervious Surfaces in the Lake Champlain Basin

The nature, extent, and distribution of impervious surfaces are important landscape factors affecting water quality and stormwater runoff volume. Accordingly, municipalities, planning agencies, state governments, and other entities are increasingly interested in monitoring these variables, their change over time, and their effect on natural resources. They are also interested in these variables at multiple scales, from regional landscapes to individual neighborhoods and ownership parcels. Effective monitoring thus requires periodic development of high resolution maps that are accurate at divergent scales, but until recently only moderate or coarse scale source datasets were available to map impervious surfaces across large geographic extents. Now, however, high resolution source datasets are commonly available and affordable, and improved mapping techniques permit analysis of multiple data sources simultaneously. This report describes high resolution mapping of impervious surfaces in the Lake Champlain Basin, covering portions of Vermont and New York (suitable imagery for Quebec could not be obtained). Using 1 meter aerial imagery and various thematic vector GIS datasets, two impervious classes were mapped: 1) Roads\Railroads; and 2) Other Impervious Surfaces. The latter category included parking lots, driveways, sidewalks, buildings, and quarries. As originally proposed, parking lots were to be assigned to its own class, but preliminary testing indicated that these features could not be reliably distinguished from driveways and buildings in the available source imagery. Natural impervious surfaces such as rock outcroppings and mountain summits were not mapped because they are permanent landscape features whose contribution to stormwater runoff is generally impractical to mitigate. The final map was considered current as of summer 2011 ground conditions.
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