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Experimental study of point bar erosion on a sand-bed sharp bend under sediment deficit conditions

Wang, Junzhou, Chen, Li, Zhang, Wei, Chen, Fan
Sedimentary geology 2019 v.385 pp. 15-25
hydrodynamics, laboratory experimentation, rivers, sediment transport, sediments, shear stress, Yangtze River
Dam operation modifies downstream flow and river sediment regimes, resulting in convex point bar erosion and concave pool deposition along sand-bed meandering rivers, with different erosion patterns and consequent chute cutoff processes. The underlying mechanisms are not thoroughly understood. In this study, based on Chibakou Bend in the Jingjiang Reach of the Yangtze River, laboratory experiments were conducted to investigate the dynamic interaction between flow and sediment in a sand-bed sharp bend. Flow structure is measured at different discharges and morphological changes are compared under conditions of different flow discharges and sediment influxes. The results indicate that with increasing discharge, hydrodynamic parameters on the point bar such as flow velocity, boundary shear stress and sediment-transport capacity, increase and finally exceed those in the concave pool. A prominent increase in sediment deficit (S⁎-S) on the point bar due to the reduction in sediment influx is the main reason for erosion of point bars in meandering rivers after impoundment. During high discharge, hydrodynamic parameters of the point bar exceed those of the concave pool in the upper part of the sharp bend and decrease dramatically in the lower part, so that partial chute cutoff may proceed in the upper part of the sharp bend.