Morphodynamic regime of gravel bed, single-thread meandering rivers

This work attempts to link theoretical and experimental findings on the issue of two-dimensional morphodynamic influence with field data from natural single-thread rivers. Theoretical and experimental work has shown that two-dimensional planform and bed deformation waves can propagate both upstream and downstream within single-thread meandering rivers. The existence of upstream influence is controlled by the value of channel aspect ratio with respect to a threshold that is determined by reach-averaged characteristics and by the evolutionary state of a given river section. We explore the predictions of a mechanistic meander simulation model based on the input of field data referring to more than 100 gravel bed rivers in order to quantify the regime of morphodynamic influence that can be expected in these streams. The analysis points out how the predicted morphodynamic regime of a given reach can be controlled by the bankfull aspect ratio and the Shields stress. Differences within the data set suggest an autogenic tendency of gravel bed rivers to behave superresonantly, while environmental factors like denser vegetation and reduced gravel supply tend to promote the subresonant regime. Moreover, the autogenic tendency of developing meanders to continuously modify their sinuosity and to consequently reduce the down-channel slope almost invariably promotes transition from the superresonant to the subresonant regime.