Channel variations of the different channel pattern reaches in the lower Yellow River from 1950 to 1999

摘要

The Yellow River is widely known as a "hanging river" due to its high sedimentation rate (the current channel bed is about 2.74 m higher than the overbank plains on average) in the lower reach. Understanding the variations in channel patterns and their influencing factors is crucial to regulate potential flooding risk in this critical region. Changes in discharge, suspended sediment delivery rate, median grain size, sedimentation rate, channel planform and cross-section, and channel width/depth ratio during 1950 -1999 from gauging stations in Huayuankou, Gaocun-Sunkou and Lijin that represent the braided, meandering and straight channel sections, respectively, were compared. During this period, frequent internal channel variations dominated in the braided channel section. The channel bed was continuously raised as a whole, but experienced strong erosion in certain times, mainly influenced by the operation and closure of the Sanmenxia Dam. The straight channel section was relatively stable due to restricted lateral migration by the solid artificial levees in both banks. Instead, channel aggradation was the dominant process and erosion only happened when channel avulsions occurred in the river mouth. The meandering channel section between the upstream braided and downstream straight channel sections was formed as a result of stream self-adjustment. Rapid lateral migrations were observed during this period, but the extent of the migration was restricted by artificial levees. Sediment aggradation on the channel bed and floodplain was apparent. Since 1970, the channel shrank remarkably in all sections due to the increased use of water resources and the decreased precipitation in the Yellow River basin. Recently, migration of the channel is limited, and the lower portion of the braided section seems to be a meandering channel.