Sediment deposition in cutoff meander bends and implications for effective management

Abstract

AbstractCutoff bends along modified, stabilized streams often constitute a valuable recreational, ecological, and aesthetic resource. However, their resource value rapidly declines as they fill with sediment, and new cutoff bends do not form to replace them in highly managed rivers.Data from repetitive hydrographic surveys of 20 cutoff bends along four rivers in the southeastern United States were examined using conceptual and analytical models in order to provide a more objective basis for bend management. Bend volume was found to be a log‐decay function of cumulative water discharge through the cutoff reach. Regression analyses were used to generate functions to predict the log‐decay constant. The log‐decay constant varied directly with master stream suspended bed‐material concentration and inversely with variables describing the geometry of the upstream entrance of the old bend. Management of cutoff bends should focus on sequencing construction activities and modification of the upstream bend entrance geometry to reduce the quantity of bed material diverted into the bend. Construction of blockage structures to top‐bank elevation in upstream entrances of cutoff bends is recommended for systems with average suspended bed‐material concentrations greater than about 50ppm. Blockage or modification of entrance geometry of longer bends preserves more aquatic habitat longer than similar levels of effort directed toward shorter bends. Maintenance of a hydraulic connection between the river and at least one end of the cutoff bend is recommended.