Self-adjustment mechanism of bed structures under hydrology and sediment regimes

Abstract

Bed structures develop in many coarse gravel-bed rivers, and the distribution of bed structures is obviously impacted by the environment conditions, especially hydrology and sediment regimes. This study carried out field investigations in natural tributaries of the Yangtze River to study the sizes of bed structures, their distribution in the basin, as well as their connections with local hydrology and sediment regimes. A field experiment was also conducted to study the evolution and functions of bed structures. Results of both the investigations and experiment indicated that under the conditions of low bedload, the structure intensity is in a positive correlation with the unit-width stream power, which is consumed by bed structures when the river is in a dynamic equilibrium. If the structures are not able to dissipate the whole energy, the river status turns into disequilibrium and the riverbed would be eroded by excess energy, and the river system would move to a stable position on the structure-power equilibrium line. The fluvial morphology of coarse-grained riverbeds is controlled by this mechanism to some extent. Sometimes excess energy can be consumed by bedload transport even with insufficient structure intensity, thus a unified power consumption model including bedload is also discussed.