Stream Channel Stability and Channel Evolution in a Rapidly Urbanizing, Ridge-and-Valley Watershed, Beaver Creek, Knox County, Tennessee

In Tennessee, sedimentation is among the leading causes of stream impairment. Excessive loads of alluvium are detrimental to the ecological health and human use of these resources. Sediments in streams have many sources, but there is evidence that stream bank erosion is a major contributing factor. Development and urbanization in a stream’s watershed will have impacts on the concentration of stream sediment because the increase in the area covered by impervious surfaces, which reduces initial abstraction and retention times. This, in turn will increase the peak storm water discharge and sediment carrying capacity. If the stream channel cannot accommodate these flows, the form of its bed and banks will begin to adjust. These adjustments are described by the Channel Evolution Model developed by the USDA National Sedimentation Laboratory. The channel response will proceed through 6 stages, moving from a premodified condition through periods of degradation and periods of aggradation until a new, stable channel form is attained. Theoretically, it would be possible to use an evaluation of the stage of channel evolution at several sites along a disturbed stream to predict the response of the entire stream network. However, this can only happen in streams in which there are no controls on the ability of a channel to adjust freely. If this pattern were to hold true in the case of a rapidly developing watershed and could be detected by a relatively fast and easy assessment scheme, it would ease the difficulty of determining where to focus stream bank stabilization projects. In an effort to determine whether or not this was the case, a semi-quantitative Rapid Geomorphic Assessment, introduced by Andrew Simon, was used to evaluate