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thus stabilising the shoreface profile. One impor-
tant condition for this stabilising mechanism to
work is that sand is present in the system in order
to reduce or halt the retrogradation rate due to
wave-induced erosion. As mentioned by van Maren
(2005) for the Ba Lat delta in Vietnam, cross-shore
sediment transport may play a major role in the
formation of a new stage in delta development.
However, most delta formation models that include
wave influence mainly focus on longshore sediment
transport to reproduce characteristic deposition
patterns (Ashton & Giosan, 2007; Bhattacharya &
Giosan, 2003). This study shows that both trans-
port modes account for the morphodynamics of a
retrograding delta.
Fig. 6A and C shows both the subaereal (in green
colour) and subaqueous (in yellow to blue colours)
morphology. In time, the subaereal area of the delta
gradually reduces by shoreline retreat. Wave
induced sediment re-suspension combined with
wave and river induced currents generate a strong
morphological response with developing sand
ridges oriented perpendicular to the coastline.
Deflection of river plumes by wave action occurs in
nature, as reported via observations and our com-
putational modelling. At this stage, results from our
model experience may show some limitations in
morphological development which can be linked to
three factors: 1) Simulated sediment transport only
applies to subaqueous areas; no mechanism for sub-
areal sediment transport is included in the model,
although there is bank erosion that can erode higher
subareal areas, 2) the forcing (boundary conditions)
in these model experiments are constant, which
may exaggerate local morphological features or may
even produce unrealistic results and 3) there is a
high gradient in the forcing conditions from fully
fluvial to fully marine at the start of the simulations.
We also know that deposits of river plumes are
deflected into barriers and spits by (obliquely-
incident) windwaves and associated longshore cur-
rents. At this stage, barrier formation is probably
not well-simulated in Delft3D.
While the numerical experiments shown in this
paper are based on a fluvial delta that is subse-
quently reworked by waves after abandonment,
additional simulations were run to evaluate the
effects of waves during delta formation (Geleynse
et al
., 2011). These experiments showed that
wave-induced currents limit the settling of fines
in shallow water, which leads to a significant
reduction in delta plain area when compared to
the fluvial (no wave) case. In addition, there is a
reduction in the number of active channels, as
described in literature (e.g. Bhattacharya & Giosan,
2003). The present findings, based on explicit
descriptions of wave-related sediment transports,
are consistent with these results.
Partial preservation is something rarely addressed
in numerical simulation studies. From the experi-
ments shown in this paper it is clear that wave
reworking significantly affects reservoir properties.
Wave reworking leads to a change in sediment distri-
bution and associated facies when compared to
the initial undisturbed delta. In addition, the wave-
induced sorting mechanism results in cleaner sands
and improved reservoir properties. Also, reservoir
connectivity is improved by wave reworking because
the sandy shoreface that results from it connects the
different lobes of the delta.
Whilst physics-based simulation of sedimentary
systems is becoming more and more useful in reser-
voir modelling, it is still limited by calculation time.
Simulations like the ones described above take a
few days to finish. Applying such models to better
understand stacked parasequence sets is still unfea-
sible at the moment although numerical efficiency
is rapidly improving due to the use of adaptive grids
and parallel computations. Nevertheless, it remains
extremely challenging to take the next step: to con-
dition a physics-based numerical model to field
data. A common method for conditioning a numeri-
cal forward model to real-world data is inversion,
where each forward model realisation is compared
against the real-world data and evaluated based on
a number of criteria (e.g. Charvin
et al
., 2011, Miller
et al
., 2008). This approach, though successful,
generally takes many forward runs, ranging from
10
2
in the case of the approach of Miller
et al
. (2008)
to 10
4
in the case of the approach of Charvin
et al
.
(2011). Such conditioning by means of inversion is
not yet possible for delta simulations using Delft3D,
given the long computation times associated with
such inversion techniques. Nevertheless, physics-
based modelling is a very useful tool for reservoir
modelling when using the so-called 'Integrated
Process-Aided Reservoir Modelling' approach
(Miller
et al
., 2008), where geometric and statistical
information of sedimentary bodies are retrieved
from the simulations. Such synthetic information
complements real-world outcrop analogue data and
can be easily used when a reservoir model is built
based on statistical methods (Michael
et al
., 2010).
The advantage of physics-based modelling results
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