Author(s): Shasha Han, Shan Zheng, Yunxing Shi
Linked Author(s): Shasha Han
Keywords: Yellow river delta, qingshuigou channel, geomorphologic adjustment, avulsion, human interruption
Abstract: Avulsion at the Yellow River delta (YRD) is very frequent due to the heavy sediment load and rapid channel aggradation. Nevertheless, the Qingshuigou channel has been maintained for about four decades, since an artificial avulsion in 1976. In this study, we comprehensively analyze the geomorphic adjustment of the channel during 1976-2014. Results showed that channel evolution processes may be divided into four phases: I (1976-1980) rapid aggradation, II (1980-1986) channel widening and enlargement, III (1986-1994) main channel aggradation and shrinkage, and IV (1994-2014) main channel incision and deepening. Fast aggradation caused the elevation of the channel bed and floodplain to generally rise by more than two meters in phase I. Channel slope decreased exponentially. A single-thread main channel is formed at about 1980. Channel evolution generally followed the sequences of �degradation�degradation and widening�aggradation and widening� in phase II during 1980-1986. Aggradation occurred at the main channel and its vicinity, forming an alluvial ridge in phase III. Steep transverse slope was formed and it generally increased in the downstream direction. Gradient advantage, defined as the ratio of transverse slope to longitudinal slope, was between 3 and 24 in 1994 and was generally greater than the critical value proposed by previous study. The normalized super elevation was also close to the critical value locally. Nevertheless, lack of overbank floods and constraint of lateral adjustment prohibit the occurrence of avulsion. Degradation in phase IV was mainly caused by anthropogenic influences including artificial avulsion at the most downstream reaches of Qingshuigou channel in 1996 and artificial floods created by water and sediment regulation since 2002. Despite of the increase of the lifespan of the recent lobe at the YRD, avulsion is inevitable in the evolution of the delta channel in the near future. Multiple criterions for avulsion should be adopted and used with caution
Year: 2017