Impacts Of Cutoff On Flow Structure And Planform Evolution In A Conceptual Meandering Channel

Cutoffs across the neck of long meander bends improve the alignment of the river, reduce sinuosity, and shorten the river length, thus increasing the channel slope. Consequently, its planform evolution processes will be affected greatly. In the present paper, the impacts of cutoff on flow structure and planform evolution in a conceptual meandering channel are investigated by a 3-D morphodynamic model, which is developed using a 3-D flow and sediment transport module and a bank erosion module. The effects of meander cutoff on the upstream of the cutoff can be concluded as: 1) The water level slope is increased, resulting in velocity increased with water depth decreased; 2) The channel bed degradation is increased, and the increased magnitude is decreased from downstream to upstream; and 3) The processes of planform evolution with cutoff have been accelerated based on the meander evolutions without cutoff, and the increased magnitude of the lateral migration is decreased from downstream to upstream. The planform evolutions downstream of the cutoff are similar to that without cutoff, with channel widened, except for the transition segment between pilot channel of cutoff and the downstream meander bends. The differences between planform evolutions with and without cutoff in the transition segment depend on the scheme of cutoffs.