Morphodynamic modelling of wave reworking of an alluvial delta and application of results in the standard reservoir modelling workflow - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 168

the grid cells in a reservoir model: physics-based
numerical modelling. Physics-based numerical
models apply basic hydrodynamic and sediment
transport algorithms to simulate delta formation and
the associated stratigraphic record.
Recent work on physics-based models clearly
shows their potential in reproducing essential
fluvio-deltaic processes as described from mod-
ern-day systems (e.g. Geleynse et al ., 2010;
Edmonds & Slingerland, 2010). Whilst most work
focuses on morphodynamics by sole river forc-
ing, Geleynse et al . (2011) have also shown that it
is possible to produce a detailed stratigraphic
record and include both wave and tide forcing
during delta progradation. However, so far, little
attention has been paid to reworking processes
following the formation of deltaic strata by wind-
generated surface gravity waves (hereafter abbre-
viated as 'waves'). Although numerical models
are able to produce realistic deltaic sediment
bodies, their preservation potential is deter-
mined by many other factors such as wave
reworking, subsidence, sea-level and sediment
supply. Here, we focus on the effects of wave
reworking following the formation of a fluvial-
dominated delta to the preservation potential of
deltaic stratigraphy.
Wave reworking is a key factor in the develop-
ment of present-day systems and ancient deltaic
reservoirs. Syvitski (2008) found that many deltas
become increasingly affected by waves due to
shoreline adjustment, water-extraction and hydro-
carbon extraction and Nicholls et al . (2008) state
that the impact of wave reworking on deltas will
increase due to the expected increase in frequency
and amplitude of waves and storm surges. As such,
a better understanding of the effects of wave rework-
ing on deltas is required. Surprisingly, few attempts
have been made to simultaneously model the mor-
phodynamic and stratigraphic development of
wave-influenced deltas (Geleynse et al ., 2011), in
part due to the limited accessibility of sufficient
computational power. However, the recent increas-
ing computational power of desktop computers
does allow for advanced physics-based numerical
models such as Delft3D (e.g. Lesser et al ., 2004) to
be run at time scales relevant to stratigraphic
modelling. Hence, qualitative concepts regarding
behaviour of retrograding deltas can be tested using
quantitative physics-based models.
The process-response shoreface model of
Storms (2003) and Storms & Hampson (2005) has
already shown that wave height regime and

sediment characteristics can be of equal signifi-
cance to stratal geometry of shallow-marine envi-
ronments as sea-level fluctuations and sediment
supply. In addition, it is widely recognised that
significant morphologic changes, particularly in
the shallow-marine regime, can be established
during low-magnitude, high-frequency events
as well as by high-magnitude, low-frequency
events, thus casting doubt on whether effective
representation of an 'event' is achieved in quan-
titative models (e.g. Storms, 2003; Swenson
et al ., 2005).

Goal and present numerical model scope

The work presented here continues along these
lines but shifts focus towards reworking of river-
derived sands and silts in deltas under wave
action. Schematised water and sediment flow
patterns in a river-dominated delta with charac-
teristic stratigraphy (Geleynse et al ., 2010) change
when subjected to quiet-weather short-crested
waves, in turn deforming delta morphology
and internal stratigraphy. Hence, we focus on
the transgressive part of the delta cycle
model (Scruton, 1960; Roberts, 1997) by applying
a physics-based numerical model (Delft3D) to
understand transgressive morphodynamics and
preservation potential under conditions of con-
stant high-frequency, low-amplitude wave forc-
ing due to wind action, without the complicating
effect of long-term sea-level fluctuations.

PREVIOUS WORK ON QUALITATIVE
AND QUANTITATIVE DELTA MODELS

Qualitative delta models

Several qualitative delta classification schemes
have been proposed throughout the past decades
(Nemec, 1990). Their inherent limitations and
practical implications were addressed in review
papers by various authors (Nemec, 1990; Reading
& Collison, 1996). The principles underlying these
schemes vary considerably; from the gross char-
acter of the feeder system (Holmes, 1965) to the
pattern of delta thickness distribution (Coleman
& Wright, 1975), tectono-physiographic setting
(Ethridge & Wescott, 1984), delta-front hydrologic
regime (Galloway, 1975), sediment characteristics
(Orton, 1988), delta-face slope (Corner et al ., 1990)
and main physiographic attributes (Postma, 1990).
The most commonly employed classification