Modification of alluvial channels in western tennessee has created increased energy conditions along main stems and tributaries and initiated longitudinal channel adjustment. Changes in bed level are functions of the magnitude and extent of the imposed disturbance andthe location of the adjusting reach in the fluvial network. Streambed degradation is described by simple power equations. Computed exponents define the magnitude of downcutting with time and decrease nonlinearly with distance upstream from the area of maximum disturbance(amd). Aggradation begins immediately in reaches downstream of the amd and in upstream reaches after overadjustment by the degradation process. Aggradation rates increase linearly with distance downstream from the amd and can be estimated from local degradation rates. Channel widening by mass wasting follows degradation and continues through aggradational phases. Piping in the loess-derived bank materials enhances bank failure rates by internally destabilizing the bank. Development of the bank profile is defined in terms of three dynamicand observable surfaces: (a) vertical face (70 to 90 degrees), (b) upper bank (25 to 50 degrees), and (c) slough line (20 to 25 degrees). The slough line develops through additional flattening by low-angle slides and fluvial reworking and is the initial site at which riparian vegetation and stable bank conditions are reestablished. A six-step, semiquantitative model of channel evolution in disturbed channels was developed by quantifying bed level trends and recognizing qualitative stages of bank slope development. This paper appeared in transportation research record no. 1151, hydraulic erosion. For covering abstract see irrd no 818454.
Abstract