1
Journal of Geophysical Research: Earth Surface
Supporting Information for
Effect of Sea
-
level Change on River Avulsions and Stratigraphy
For an Experimental Lowland Delta
A.J.
Chadwick
1
, S. Steele
1
, J. Silvestre
1
, M.P. Lamb
1
1
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125
Contents of this file
Text S1
Figures S1 to S
4
Additional Supporting Information (Files
uploaded separately)
Caption for Table S1
Caption for
Movie S1
Introduction
This supplement provides
additional text explaining the propagation of
uncertainty in model input parameters (Text S
1
),
a
caption for the
data table
of
experimental results (Tabl
e S1),
a caption for the supplemental movie file (Movie S1),
supplemental figures showing
long
-
profile
progradation and back
-
filling during each sea
level condition in the experiment (Figs. S
1
-
S2
),
a
supplemental version of
Fig. 10 without
shaded
areas (Fig. S
3
),
a supplemental version of Fig. 12 with a logarithmic scale on the
y
-
axis (Fig. S
4
)
.
2
Text
S1.
Propagation of uncertainty in model input parameters
The model of Chadwick et al. (2020)
presented in Eq. (6)
accurately estimates
avulsion frequency in the CROF18 experiment within the expected uncertainty (Fig. 10b).
Uncertainty
in model predictions
arose from
variability in input parameters:
stochastic
variability in the avulsion threshold (
!
) and avulsion len
gth (
"
!
)
(Hajek and Wolinsky,
2012; Ganti et al., 2014; Chadwick and Lamb, 2021)
and
gradual
chang
es
in the basin
depth (
!
"
) as sea
-
level rose
and fell
(Carlson et al., 2018; Chadwick et al., 2020)
.
Uncertainty
in Eq.
(
6
)
was estimated
using the variance formula,
#
#
!
=
%
&
'
(
!
'!
#
$
)
%
+
&
'
(
!
'
"
!
#
&
!
)
%
+
&
'
(
!
'
!
"
#
$
"
)
%
(
S1
)
where
#
#!
is uncertainty in modeled avulsion frequency, and
#
$
,
#
&!
,
and
#
$
"
represent
the standard deviation in the
avulsion threshold
(
±
1
.
1
mm
)
, avulsion length
(
±
0
.
28
m
)
,
and
basin depth
(
±
2
cm
)
observed
across the entire
experiment
(Table S1)
.
The shaded
region of uncertainty shown in Fig. 10 represents
uncertainty of
±
#
#!
relative to the
mean prediction
8
#
!
, where the mean prediction was calculated using Eq. (6) with the
mean avulsion threshold (
2
.
3
mm
), mean avulsion length (
1
.
3
m
), and mean basin depth
(
4
.
9
cm
) observed across the experiment.
Table S1.
Data
table
showing results for each identified avulsion the CROF18
experiment
, including avulsion frequency (
(
!
),
sea
-
level rise rate (
<
),
basin depth (
!
"
), sea
level above basin floor,
avulsion length (
"
!
), and measured avulsion threshold (
!
).
Limited temporal resolution of
topographic
scan data
only allowed for quantification of
the avulsion threshold
for those avulsions where the trigger period
coincided with
scheduled scan time
within
±
1 min
.
During Phase E
the delta prograded across the
previously drowned
topset
surface
, and so the estimated b
asin
(
~
16
mm
)
was
significantly less than
the elevation of sea level above the basin floor.
The time of each
avulsion is indicated by the run time, as well as the corresponding experimental phase
(A
-
F)
, cycle
(1
-
300)
, and flow
(high or low)
.
Table
uploaded separately.
Movie S1
.
Timelapse video of the CROF18 experiment. Photographs were taken every 1
minute of run time,
each second of the video corresponds to approximately one hour of
run time (60 frames/sec).
3
Figure S1.
a) Photograph of the experimental delta during Phase A, overlain with
avulsion sites (yellow circles) and shorelines (gray lines) through time. Initia
l shoreline
(white dashed line) and final shoreline (white solid line) for the phase are also shown.
Numbers on avulsion sites indicate their chronological order. b) Long
-
profile
progradation and back
-
filling
of the main channel of the experimental delta d
uring
Phase A. Bed topography (black) is shown for the start (dashed line) and end (solid line)
of the phase, with synthetic stratigraphy shown in gray. Blue solid line shows end
-
of
-
phase levee
-
topography (in the basin section) and low flow water surface (
in the river
4
section
)
. Sea level is shown in a thin blue horizontal line. c
-
h)
S
ame as a and b, but for
experimental
P
hases B, C, and D.
Figure S
2
.
Same as Figure
S1
, but here shown for experimental
P
hases E and F.
5
Figure S3.
Same as Figure 10,
but here shown without shaded regions
.
Panels show
r
esults for dimensionless a) avulsion length, b) avulsion frequency, and c) avulsion
threshold as a function of dimensionless sea
-
level rise rate (Eq. 2). Yellow box plots are
CROF18 results for
Phases A
-
D, green box plots are CROF16 results (Ganti et al., 2016b),
and yellow diamonds are field data (Table 3).
Lines in
(a)
represent an avulsion length
that scales with the backwater length (solid blue) and an avulsion length at half the
backwater le
ngth (dashed blue).
Magenta line in (b)
shows
prediction from Eq. (6)
(Chadwick et al., 2020)
a
nd black dashed line shows upper limit of avulsion frequency
where all sediment is deposited on the lobe topset (Eq. 6 for D<0).
Lines
in (c)
represent
an avulsi
on threshold corresponding to aggradation of the channel by one channel
depth (solid line) and 10% of the channel depth (dashed line), which is the expected
range based on previous
(Ganti et al., 2014; Mohrig et al., 2000). Limited temporal
resolution of s
can data prohibits measurement of avulsion threshold for Phase D.
6
Figure S
4
.
Same as Figure 1
2
, but here shown
with a logarithmically scaled y
-
axis.
Panels
show b
ed thickness as a function of distance downstream (a) and dimensionless sea
-
level rise rate (b),
with
channel depth (black dashed line), grain size (black dotted line),
and avulsion threshold (gray line and shaded region corresponding to median and 25
-
75
p
ercentile range of all avulsions). Box plots show median (horizontal bar), mean (plus
sign), 25
-
75 percentile range (box), and 5
-
95 percentile range (whiskers). Yellow
horizontal box plot in (a) shows distribution of all avulsion sites, and gray labels sho
w
location of cross sections in Fig. 11b
-
d. Bold labels in (b) denote experimental phases A
-
F.