Processes and mechanisms of dynamic channel adjustment to delta progradation: the case of the mouth channel of the Yellow River, China

Abstract

This paper analyses the processes and mechanisms of a three-stage channel adjustment over a cycle of the Yellow River mouth channel extension based on data comprising hydrologic measurements and channel geometric surveys. Rapid siltation in the mouth channel takes place in the young stage when the channel is being built by deposits and in the old stage when the channel cannot further adjust itself to keep sediment transport in equilibrium. It is disclosed that the bankfull width-depth ratio, bed material size and slope decrease in the young and mature stages but do not change in the old stage. The reduction of bankfull width-depth ratio and bed material size during the young and mature stages is found to be able to offset the effect of the slope reduction on sediment transport due to continuous mouth progradation. They reach their limits in old stage, and a constant slope is kept by unceasing sediment accumulation. The grain size composition of incoming sediment and the fining mechanism are responsible for the occurrence of lower limit of bed material size. The reason for the existence of a limit of bankfull cross-sectional shape is that the large flows can fully transport the sediment load they are carrying, and siltation in the channel in the old stage takes place mainly in the low flows. It is suggested that the bankfull discharge plays an important role in shaping the channel but that the entire channel form is the product of both the large and low flows plus the effects of interaction between them. Channel pattern change shows a process from a braided pattern in the young stage to a straight pattern in the mature and old stages, and the straight channel becomes gradually sinuous. The occurrence and transformation of the channel patterns are supported by two planform predictors, but are also facilitated by some other conditions.

River mouth bar formation, riverbed aggradation and channel migration in the modern Huanghe (Yellow) River delta, China

“…1; Wright et al, 1990;Qian et al, 1993;Shi and Zhang, 2003). The average sediment accumulation rate for 1976-1992 is about 1.2 m year À1 and the river mouth area has been an estuarine depocenter (Wang et al, 1992;Li et al, 1998b).…”

“…Although the active rivermouth bar is not large in size, it has a profound effect on the rapid growth of the Huanghe River delta (Li et al, 1998b). The rapid deposition on the river-mouth bar causes its seaward progradation that has been an important control on the upstream siltation in the lower channel of the Huanghe River, serving as a stimulus to the river channel migration (Qian et al, 1993;Shi and Zhang, 2003;Shi, 2005). Heavy sedimentation in the lower reaches of the river channel causes the riverbed to aggrade at a rate of several centimeters per year (Qian et al, 1993;Van Gelder et al, 1994;Xu and Cheng, 2002).…”

Causes for continuous siltation of the lower Yellow River

“…The delta is fan-shaped and is composed of juxtaposed lobes. Each lobe developed along a distributary channel, which survives for about 10 years on average (Shi and Zhang, 2003). The common apex of the lobes on the delta was located near Ninghai before 1934, but then shifted 30 km downstream to Yuwa.…”

Progradation of the Yellow (Huanghe) River delta in response to the implementation of a basin-scale water regulation program

“…Pang and Si, 1980;Wang and Liang, 2000;Ganti et al, 2014). Since the switch, a delta of about 6113 km 2 has formed in the northeast part of Shandong Province, with the delta's vertex moving downstream gradually from Lijin (Wright et al, 1990;Li et al, 1998;Shi and Zhang, 2003) (Fig. 1).…”