IMPERVIOUS SURFACE ANALYSIS FOR SELECT URBAN IMPAIRED WATERSHEDS IN MAINE

The Maine Non Point Source Education for Municipal Officials Program (NEMO) is part of the national NEMO network protecting natural resources in 31 states. NEMO educates decision-makers on the relationship between land use, natural resource protection and water quality. A major focus of the NEMO outreach program conveys the impacts of impervious surfaces (IS) on water quality. Here we present the results of IS buildout assessments from four watersheds in Maine conducted for the Maine Department of Environmental Protection as part of the impervious cover TMDL. We discuss data collection and creation, analysis methods and results. Data quality and availability varied by town and watershed, and we adapted our methods according to what was available. Towns with well developed GIS infrastructures (zoning and planning data) and complete cadastral data were easy to assess. Our methods also depended on the size of the watershed, smaller watersheds required greater positional accuracy and resolution. Large watersheds could be assessed using satellite-derived data (from MEGIS). Smaller watersheds required digitizing existing IS. We determined the average IS for each zoning type and, using potential buildout scenarios provided by each town, we predicted the watershed IS after future development. Where possible, we considered potential subdivisions, development proposals and other community-provided information (at times hand-drawn). Town cooperation and data availability heavily influence our assessments. The completed IS analysis was integrated into town presentations to educate municipal officials on the impacts of IS on water bodies and water quality, and methods of low impact development (LID) that can be used to mitigate impacts. The presentation includes the effects of extending the channel forming flow with traditional detention basin treatment of stormwater, examples of LID, and cost comparisons between traditional development and LID.