HUMAN INFLUENCES ON CHANNEL-MIGRATION RATES: TWO EXAMPLES FROM CENTRAL INDIANA

An assessment of channel - migration rates in 42 Indiana stream reaches was conducted by Robinson (2013) as part of the Indiana Fluvial Hazard Mitigation Program. He determined that 65 percent of the stream systems had migration rates of greater than 1 ft/yr, and 75 percent of the sites were migrating at less than 10 ft/ yr. The distribution of the streams migrating at rates greater than 10 ft/yr was not evenly distributed, with most of the more mobile streams located in the west-central and east-central parts of the state. Robinson noted that many of the actively migrating channels had been identified as former glacial sluiceways by Thornbury (1950). The continuing threat to infrastructure from channels migrating at rates greater than 10 ft/yr is significant enough that work has continued trying to determine why some stream channels are so mobile. While early work suggested a correlation between highly mobile streams and broad outwash valleys, that observation did not identify a process for the increased mobility. More recent work is suggesting that within the context of the modern climate the boundary conditions in the outwash valleys are sensitive to disturbance, and that many of the most mobile stream reaches are trying to achieve stability following a disturbance, or in many cases - multiple disturbances, often of human origin. In this presentation, we will consider case studies from two of the most mobile streams in central Indiana, White Lick Creek, and the West Fork of the White River. Continued work is needed to determine the role that climate change is playing in accelerating the mobility of these already highly mobile streams; and whether these more mobile streams are precursors of more widespread channel instability.