Modeling Deltaic Lobe-Building Cycles and Channel
Avulsions for the Yellow River Delta, China
Andrew J. Moodie
1
, Jeffrey A. Nittrouer
1
, Hongbo Ma
1
, Brandee N. Carlson
1
,
Austin J. Chadwick
2
, Michael P. Lamb
2
, and Gary Parker
3,4
1
Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX, USA,
2
Division of
Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA,
3
Department of Civil and
Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, IL, USA,
4
Department of
Geology, University of Illinois at Urbana-Champaign, Champaign, IL, USA
Abstract
River deltas grow by repeating cycles of lobe development punctuated by channel avulsions,
so that over time, lobes amalgamate to produce a composite landform. Existing models have shown that
backwater hydrodynamics are important in avulsion dynamics, but the effect of lobe progradation on
avulsion frequency and location has yet to be explored. Herein, a quasi-2-D numerical model incorporating
channel avulsion and lobe development cycles is developed. The model is validated by the
well-constrained case of a prograding lobe on the Yellow River delta, China. It is determined that with lobe
progradation, avulsion frequency decreases, and avulsion length increases, relative to conditions where a
delta lobe does not prograde. Lobe progradation lowers the channel bed gradient, which results in channel
aggradation over the delta topset that is focused farther upstream, shifting the avulsion location upstream.
Furthermore, the frequency and location of channel avulsions are sensitive to the threshold in channel bed
superelevation that triggers an avulsion. For example, avulsions occur less frequently with a larger
superelevation threshold, resulting in greater lobe progradation and avulsions that occur farther upstream.
When the delta lobe length prior to avulsion is a moderate fraction of the backwater length (0.3–
0
.
5
L
b
), the
interplay between variable water discharge and lobe progradation together set the avulsion location, and a
model capturing both processes is necessary to predict avulsion timing and location. While this study is
validated by data from the Yellow River delta, the numerical framework is rooted in physical relationships
and can therefore be extended to other deltaic systems.
1. Introduction
The development of a fluvial-deltaic system over timescales of decades to millenia is characterized by
repeated lobe switching: a process whereby a primary distributary channel progrades basinward, building
a lobe until an avulsion causes the distributary channel to shift, generating a new lobe (Frazier, 1967). Over
time, lobes amalgamate and produce a delta that typically maintains an approximately radially symmetric
planform (Figure 1). Many large, lowland fluvial-deltaic systems require tens to thousands of years between
avulsions (Jerolmack & Mohrig, 2007). As a result, field studies of modern channel avulsions have identi-
fied, at most, only a few events (Assine, 2005; Brizga & Finlayson, 1990; Coleman, 1988; Donselaar et al.,
2013; Frazier, 1967; Jerolmack, 2009; Jones & Harper, 1998; McCarthy et al., 1992; Richards et al., 1993;
Smith et al., 1989; Törnqvist, 1994; Wells & Dorr, 1987; Xue, 1993; van Gelder et al., 1994). Insights into
deltaic lobe building have benefited from outcrop and experimental research, where multiple avulsions can
be examined (e.g., Hajek & Wolinsky, 2012; Mohrig et al., 2000). However, outcrop studies of avulsions are
subject to uncertainty around reconstructing relevant system characteristics, including river slope, regional
geography, and the timing of events (Lynds et al., 2014; Sheets et al., 2002). Experimental studies document
delta growth through many lobe-building cycles and are valuable because system boundary conditions are
controlled (Hoyal & Sheets, 2009; Kim et al., 2006; Kim & Jerolmack, 2008; Paola et al., 2009; Whipple et al.,
1998; Sheets et al., 2002; Reitz & Jerolmack, 2012; Ganti et al., 2016b; Ganti et al., 2016a). Additionally, phys-
ically based numerical models provide the opportunity to assess system responses to changing boundary
conditions over a range of spatiotemporal scales (Chadwick et al., 2019; Kim et al., 2009; Moran et al., 2017;
Parker, Paola, Whipple, & Mohrig, 1998; Parker, Paola, Whipple, Mohrig, Toro-Escobar, et al., 1998; Paola,
2000; Parker et al., 2008a, 2008b; Ratliff et al., 2018; Sun et al., 2002).
RESEARCH ARTICLE
10.1029/2019JF005220
Key Points:
• Patterns of Yellow River deltaic lobe
development are reproduced by a
quasi-2-D numerical model
• Avulsions are less frequent and occur
farther upstream when a delta lobe
progrades
• The Yellow River deltaic system
aggrades to 30% to 50% of bankfull
flow depth before avulsion
Supporting Information:
• Supporting Information S1
Correspondence to:
A. J. Moodie,
amoodie@rice.edu
Citation:
Moodie, A. J., Nittrouer, J. A., Ma, H.,
Carlson, B. N., Chadwick, A. J.,
Lamb, M. P., & Parker, G. (2019).
Modeling deltaic lobe-building
cycles and channel avulsions for the
Yellow River delta, China.
Journal
of Geophysical Research: Earth
Surface
,
124
, 2438
2462. https://doi.
org/10.1029/2019JF005220
Received 21 JUN 2019
Accepted 20 SEP 2019
Accepted article online 15 OCT 2019
©2019. American Geophysical Union.
All Rights Reserved.
MOODIE ET AL.
2438
–
Published online 6 NOV 2019