不同来源区洪水对黄河下游游荡河段河床横断面形态调整过程的影响

Impact of Flood Events from Different Source Areas on Channel Transects Adjustment at the Wandering-braided Reach of the Lower Yellow River

以黄河下游实测流量过程等水文资料为基础 ,从流域系统的角度出发 ,以洪水作为联系流域系统各子系统耦合关系的指标 ,揭示了不同来源区洪水对黄河下游游荡河段洪水前后河床横断面形态变化的不同影响及其原因。上少沙来源区洪水使河床形态变宽浅为主 ,变宽浅主要由于主槽淤积所造成 ;下少沙来源区洪水使河床宽深比以变窄深为主 ,主要由于主槽冲刷所造成 ;多沙粗沙来源区洪水造成河床宽深比减小 ,主要由于高含沙洪水淤滩刷槽所造成 ;多沙细沙来源区的洪水后宽深比变化不大 ,仅略减小 。

Based on the hydrological data from the Huayuankou station in the lower Yellow River, this paper reveals the different impacts of flood events from different source areas on the channel transverse cross section deformation of the wandering braided reach of the lower Yellow River by selecting the flood event as the indicator of coupling the water and sediment yield sub system in the upper and middle river basin and the sediment deposition sub system at the lower river reaches from the aspect of fluvial system. Flood events from different source areas have different characteristics of discharge, sediment concentration, suspended sediment diameter and duration time etc. that have different impacts on the channel fill scour behaviors and channel deformation modes. Flood events from the upper clear water producing area and the lower clear water producing area both have abundant runoff and low sediment concentration, but they have different impacts on channel deformation. Flood events from the upper clear water producing area generally have the sediment concentration just slightly larger than the carrying capacity, which makes the sediment slightly deposited in the main channel and thus cause the width to depth ratio slightly increase. Flood events from the lower clear water producing area generally have very small sediment concentration that the water have excessive energy to carry sediment, thus the main channel will be scoured that causes the width to depth ratio largely decreased. Flood events from the coarser sediment producing area and the fine sediment producing area both have large peak discharge and high sediment concentration, but they also have different impacts on channel deformation. Many of the flood events from the coarser sediment producing area are the hyper concentration flow that makes the sediment deposit heavily on the flood plain and scour in the main channel and thus cause the width to depth ratio decrease. Flood events from the fine sediment producing area may make the sediment deposited both in main channel and on flood plain and thus the width to depth ratio of the channel will not changed obviously.