Testing morphodynamic controls on the location and frequency of river avulsions on fans versus deltas: Huanghe (Yellow River), China

Abstract

A mechanistic understanding of river avulsion location and frequency is needed to predict the growth of alluvial fans and deltas. The Huanghe, China, provides a rare opportunity to test emerging theories because its high sediment load produces regular avulsions at two distinct nodes. Where the river debouches from the Loess Plateau, avulsions occur at an abrupt decrease in bed slope and reoccur at a time interval (607 years) consistent with a channel-filling timescale set by the superelevation height of the levees. Downstream, natural deltaic avulsions reoccur at a timescale that is fast (7 years) compared to channel-filling timescale due to large stage-height variability during floods. Unlike the upstream node, deltaic avulsions cluster at a location influenced by backwater hydrodynamics and show evidence for episodic downstream migration in concert with progradation of the shoreline, providing new expectations for the interplay between avulsion location, frequency, shoreline rugosity, and delta morphology.

Avulsion cycles and their stratigraphic signature on an experimental backwater‐controlled delta

“…The experimental delta from Ganti et al [] that had persistent backwater hydrodynamics grew through deposition of multiple lobes that maintained a constant size, which scaled with the backwater length [ Ganti et al , ], similar to scaling relations for natural lowland deltas [ Jerolmack and Swenson , ; Ganti et al , ]. Further, they found that the avulsion locations translated seaward in step with shoreline progradation, consistent with the hypothesis presented in Ganti et al []. This was in contrast to the experimental delta without persistent backwater hydrodynamics, where avulsion nodes were fixed at the tank boundary and the delta grew in time to fill the basin, analogous to alluvial fans and fan‐deltas.…”

“…This idea is supported by numerical modeling of Chatanantavet et al [] and recent experiments [ Ganti et al , ] which showed that the variable floods in a backwater‐controlled coastal river can produce a locus of in‐channel deposition, and therefore a location of enhanced setup, that scales with the backwater length. Further, through analysis of a number of natural deltas, Ganti et al [] showed that threshold depth of channel sedimentation needed to induce an avulsion ( h * ) may be reduced in backwater‐dominated rivers with high flood variability. To our knowledge the path selection and abandonment processes have not been investigated in the context of backwater hydrodynamics, but an effect might be expected since backwater strongly influences water and sediment transport patterns in coastal rivers [ Lamb et al , ; Nittrouer et al , ].…”

Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements

“…On long time scales, rivers migrate by episodic, relatively abrupt changes in their course called avulsions 5 . Avulsions lead to diversion of river flow into new or abandoned channel pathways on floodplains 5–7 . They are stochastic events that typically occur at century to millennial timescales 8 .…”

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

“…They were separated in 1855 when a major switch occurred in the Yellow River's course, from the Huanghai Sea in Southeast China (south of the Shandong Peninsula) to the Bohai Sea in Northeast China (south of Tianjin) (e.g. 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.…”