DETERMINING INFLUENCES ON HEADWATER STREAM TRANSITIONS AND CLASSIFICATIONS IN ROCK ISLAND COUNTY, IL

Jurisdictional determinations of headwater streams under the Environmental Protection Agency’s Clean Water Act presently require extensive field work which make them labor intensive. While watershed parameters are regularly used to make discharge estimates for perennial rivers and streams, much less work has been done to extend this methodology upstream to the headwaters to identify the upstream extent of CWA jurisdiction (approximately at intermittent/ephemeral boundary). Furthermore, there is a need to better understand how headwater streams transition in different parts of the country and in different physical environments. Using the North Carolina Division of Water Quality’s “Methodology for Identification of Intermittent and Perennial Streams and Their Origins” and ArcGIS 10.1, this study sought to assess how GIS-derived channel slope, upstream average imperviousness, upstream average watershed slope, and watershed area within forested, urban, and agricultural environments affect the transition of headwater streams in Rock Island County, Illinois. Multiple linear regressions revealed that watershed area significantly influenced how streams transitioned across all subwatersheds that were part of this study (R²=.216). However, at the specific subwatershed sites, watershed area in the forested watershed (R²=.774), average upstream slope in the urban watershed (R²=.469), and average upstream slope and upstream average imperviousness in the agricultural watershed (R²=.886) were the variables found in this study that had an influence on how these headwater streams transitioned and were classified from ephemeral to intermittent to perennial. These results could be used to automate the process of making jurisdictional determinations of headwater streams based on the physical characteristics of the watershed and stream channel.