One-dimensional modelling of channel evolution in an alluvial river with the effect of large-scale regulation engineering

Abstract

In an alluvial river, various kinds of river regulation engineering are usually constructed along the reach for the stability of channel regime and the safety of flood control, which greatly affects the process of channel evolution. Therefore, a one-dimensional (1D) morphodynamic model has been improved to simulate the fluvial processes influenced by large-scale river regulation works. In the refined model, each node of a cross-section was labeled using a specified point code representing the zones of floodplain and main-channel with or without regulation engineering, and sediment transport and bed deformation in different zones were treated separately. In the zones without regulation engineering, both bed deposition and bed erosion were permitted to occur; in the zones with regulation works, bed deposition was allowed, while bed erosion was not permitted to occur owing to the restriction of those engineering, unless there was a deposition layer newly formed over the previous simulation period. Then the improved model was calibrated and verified using field observations through the application to a 347-km-long alluvial channel located in the Middle Yangtze River in China. The results for the year 2016 show that the channel scour volume without the effect of river regulation works was 9% greater than the measured value (34.43 × 106 t), while the outcome considering this effect (35.81 × 106 t) was in closer agreement with the measurements. Moreover, the variation in channel geometry obtained from the improved model agreed better with the observed data. River regulation works would limit the channel incision, and it is likely to scour the other unprotected bed of a cross-section or the downstream cross-sections as the flow cannot carry enough sediment from the protected bed. Simulated results indicate that part of the main-channel zone at the Jing65 section was protected, but the riverbed continued to incise by about 0.68 m in the protected area when the effect of bed-protection works was not considered in the model, which was not in accord with the observed channel geometry. Therefore, this effect of large-scale river regulation works on channel evolution needs to be considered for a higher simulation accuracy.