Sally Letsinger, Sally L. Letsinger and
Indiana Department of Environmental Management (IDEM)
||The Indiana Department of Environmental Management, as Indiana's water-quality agency, uses reach indexing (the process of identifying and assigning unique identifiers and attributes to stream reaches) to link surface-water attribute information to detailed GIS data layers of streams. Prior to 2006, the Indiana Reach Index was at a scale of 1:200,000, which caused overly broad areas of the state to be listed as impaired waters because finer stream elements were not available.
||Conduct a pilot study to establish a methodology to update selected watersheds with high-resolution (1:24,000) stream segments from the National Hydrography Dataset (NHD).
||The tool for this task is the National Hydrography Dataset (NHD) Reach Indexing Tool, which is an interactive geographic information system (GIS) application that allows users to georeference surface-water data using the NHD.
||Geographic information system (GIS) data layers were updated for the following basins in Indiana:
Little Calumet/Galien, in the Great Lakes Basin;
Chicago, in the Upper Illinois Basin; Lower Ohio-Lower Pigeon, in the Lower Ohio-Salt River Basin; Highland-Pigeon, in the Lower Ohio-Salt River Basin; Blue-Sinking, in the Lower Ohio-Salt River Basin; Silver-Little Kentucky, in the Lower Ohio-Salt River Basin; and Upper White, in the White River Basin.
||The establishment of a methdology of incorporating high-resolution stream segments into the data layer used to track impaired waterbodies by IDEM will allow the regulatory agency to more accurately identify contaminated stream segments. The improved accuracy of impaired reach identification should allow IDEM to better assess the most contaminated streams, thereby allowing prioritization of resources to the areas of the state that need them most.