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SCREENING TO IDENTIFY AND PREVENT URBAN STORM WATER PROBLEMS: ESTIMATING IMPERVIOUS AREA ACCURATELY AND INEXPENSIVELY
Citation:
Bird, S L., J. Harrison, L R. Exum, S. W. Alberty, AND C. Perkins. SCREENING TO IDENTIFY AND PREVENT URBAN STORM WATER PROBLEMS: ESTIMATING IMPERVIOUS AREA ACCURATELY AND INEXPENSIVELY. 2002 National Water Quality Monitoring Council Conference, Madison, WI, May 20-23, 2002.
Impact/Purpose:
This research project sets out to design and conduct an assessment of the long-term ecological consequences of alternative watershed management choices. As the first project to be done at this scale using predictive ecological endpoints, we will seek to identify the appropriate components of such an analysis. We will use experience gained in the conduct of this analysis to identify key research and data needs for future analyses. We will extend this analysis beyond previous and ongoing studies in two ways: by incorporating biological endpoints, primarily properties of fish communities, and by introducing the concept of sustainability of ecological state under future scenarios contrasted with the present state of those same ecological resources. Requirements that are identified during the course of this study will permit the recommendation of specific capabilities that should be incorporated in a general modeling system currently under development to support environmental assessments. Finally, the analysis is intended to be of value for establishing environmental management choices that will be beneficial and those that would be detrimental to the sustainability of ecological resources. Specific objectives are listed below:
1. Develop watershed-based modeling systems to forecast the effectiveness of alternative management plans in meeting sediment-related, nutrient-related, pathogen-related, and toxics-related criteria and standards, and biologically-based criteria and standards; and
2. Develop and maintain a comprehensive technical support capability that directly links environmental TMDL exposure research activities and products for the EPA Office of Water, EPA Regional Offices, and the States to be used for implementation of policy, regulatory development, remediation, and enforcement needs.
Description:
Complete identification and eventual prevention of urban water quality problems pose significant monitoring, "smart growth" and water quality management challenges. Uncontrolled increase of impervious surface area (roads, buildings, and parking lots) causes detrimental hydrologic changes, stream channel erosion, habitat degradation and severe impairment of aquatic communities. Existing aerial photography (digital orthophoto quarter quadrangles - DOQQ's), sampled statistically using desktop GIS tools, was used to evaluate impervious area estimates based on readily available landscape data including: categorized land-cover data (National Land Cover Data - NLCD); block-level census data; and road networks. Models linking the photo interpretation and wide area estimation techniques provided: 1) cheap estimates of impervious cover with known accuracy at the watershed and sub-watershed scales; 2) a comprehensive state-wide ranking of Georgia waters likely impaired or threatened by urban storm water; and 3) characterization of change in imperviousness over time. Multiple data source estimation of imperviousness provides improved accuracy compared to the use of land-use/land- cover alone, especially for the 5-10% impervious range where prevention of storm water problems is critical. Estimated imperviousness change from 1993 to 1999 revealed 51 Georgia watersheds defined by 12-digit hydrological unit codes (HUCs) with substantial impervious area increases (class changes) during this short, 6-year period. For 1999, 92 HUCs were estimated to be more than 10% impervious with potentially detrimental aquatic impacts, and 137 in the 5 to 10% range with detrimental aquatic impacts likely with future growth unless preventive actions are taken. Similar analyses will be expanded to the 8 Southeastern states of EPA Region 4. These screening results can guide in-situ monitoring to confirm problems, aid listing of impaired waters under Section 303(d) of the Clean Water Act and total maximum daily load (TMDL) development, provide reliable scientific information to energize sound local planning and land-use decisions, and promote protection and restoration of urban streams.