Morphological Processes Leading to Channel Avulsion, ice Jamming and Overflow on the Yellow River Delta

This paper is intended to address problems of avulsion, overflowing and ice jamming by analysis of evolving processes of longitudinal profiles, cross sections, and channel plan-form patterns of the strongly alluvial Yellow River estuary in order to determine when and where an channel avulsion, ice jamming and overbank flooding will take Place. On average for the past 140 years, the Yellow River estuarine course shifted approximately once every 15 years. The frequent course shifting discourages economic investment and development such that the delta economy lags behind those of many other large deltas, e. g. the Yangtze River Delta. Many research projects have been undertaken in the past decades to stabilize the estuarine courses relatively. The current investigation recognizes three morphological processes contributing to occurrences of channel avulsion, ice jamming and overbank flooding. The longitudinal profile of the estuary tends to evolve into a terrace-shaped profile while lateral floodplain slopes tend to change from those permitting easy return of overflow back to the channel to slopes permitting easy flow away from the channel. Meanwhile, the upper part of the estuarine course tends to change from a wandering to a meandering pattern while the lower part continues to wander seawards. When a terrace-shaped profile develops, the likelihood of overflowing, ice jamming, and channel avulsion becomes greater in the estuarine course. Linking river flow and sediment load to historical records of such events leads to the understanding that less sediment load will delay heavy sedimentation and development of a terrace-shaped profile. If a terrace-shaped profile appears, however, the increasing sinuosity of the estuarine course can be discouraged by controlling the flow and sediment load entering the estuary. Despite the lack of complete understanding of the relationships between sinuosity, river flow, and sediment load, there is consensus recognition that year-to-year decreases in flow will increase sinuosity. In addition, results show that dredging and man made small-scale shifting of the estuarine course should be executed when the terrace shaped profile is formed. Moreover, dredging and artificial channel shifting should be done in the topset of the terrace or somewhere downstream.