Bankfull Geomorphic Relationships and Reference Reach Assessment of the Ridge and Valley Physiographic Province of East Tennessee

Waterways have been geomorphically altered or disturbed by development, mining, agriculture and other human activities for many years. Section 404 of the Clean Water Act determined that these impacts to our waterways must be mitigated for channel alterations. Stream restoration has been one method to mitigate for these impacts to our water resources. Stream restoration is considered to be a measurable improvement to the channel stability, water quality, habitat or overall function of a degraded stream system. Practices of stream restoration have changed in the last 10 to 20 years with the introduction of natural channel design methods. Natural channel design involves rebuilding a stream channel with the appropriate channel dimensions, slope, and planform to accommodate water and sediment inputs from its drainage basin without excessively aggrading or degrading. Dimensions of restored stream channels are based on a stage that is termed bankfull. The bankfull discharge is the flow that fills the channel just to the tops of its banks to the incipient point of flooding. Design dimensions used in natural channel design are based on bankfull stage and discharge because practitioners believe it is responsible for the average morphology of a stream channel. Practitioners of stream restoration use two tools to aid in the determination of these stable channel conditions: they are 1) regional channel geometry and discharge relations to drainage area (regional curves) and 2) reference reach derived dimensionless bankfull channel geometry ratios. These tools are developed for ecoregions that have similar climates, topography, geology, soils, hydrology and vegetation because these are also the features that dictate stream channel form. Regional curves and reference reach dimensionless ratios were developed for the Level III Ecoregion 67 Ridge and Valley, Tennessee. The regional power function equations of bankfull cross sectional area, width, mean depth, and discharge to drainage, and the dimensionless bankfull channel geometry ratios of reference reaches will help determine the bankfull channel dimensions used in natural channel design.