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leads to localized erosion and accretion that is
dependent on the ambient wave conditions and
the antecedent morphology. Such a coast may
exhibit spatially variable patterns of erosion and
accretion that are to some extent envisaged in
the coastal cell model of May & Tanner (1973).
Long-term sediment scarcity may be manifest in
barriers retreating, such that back-barrier sedi-
ments (e.g. lagoonal muds) are exposed on the
beachface (Fig. 8.13).
Migration of tidal inlets may take place under
sediment abundance, which promotes longshore
extension of up-drift barriers, or under sediment
scarcity, as sediment is reworked to accommod-
ate changing wave energy. The migration of inlets
causes reworking of the associated tidal deltas
(Reddering 1983). A suite of models of barrier
planform change has been presented (Carter
et al. 1987; Carter & Orford 1993). Although
based on gravel barriers, a number of the changes
envisaged are evident on sand barriers, where
the higher degree of dynamism makes changes
less readily attributable to a particular forcing
factor. Cooper & Navas (2004) measured plan-
form changes in a headland-embayment system
over more than 100 years, and attributed them
to natural variations in bathymetry caused by
sediment accumulation on the sea-bed. These,
in turn, altered the pattern of waves approach-
ing the shore, and changed the longshore drift
directions at the coast.
levels than normal. Thus, sediments in dunes
and back-beach areas are exposed to the effects
of waves and currents.
The importance of storms on boulder and
gravel beaches has already been inferred, as
they produce conditions necessary for sedi-
ment transport. In comparison, the importance
of storms on sand beaches is more difficult to
isolate from the effects of other processes. One
important consequence of storms on barriers
is the occurrence of overwash, which moves
sediment landward of the active beach profile,
effectively removing it from the system until the
barrier migrates landward and it then re-enters
the system. Storms, which have been difficult
to monitor because of the high energy levels
involved, have recently been identified as pro-
ducing orders of magnitude differences in long-
shore transport rates and even change in the
nature of processes operating compared with
lower energy conditions (Miller 1999). Storms,
too, lead to enhanced energy levels in the surf
zone. This has been associated with the enhanced
likelihood of infragravity waves and nearshore
circulations, which give rise to rhythmic shore-
line topography (Komar 1998).
Storms have also been important in raising
wave energy levels such that they can overcome
tidal currents and close inlets. The Kosi Lagoon
in South Africa closed as a result of a tropical
cyclone that temporarily enabled wave energy
and wave-sediment transport processes to over-
come the tidal currents generated by a massive
tidal prism (Cooper et al. 1999). The ebb-delta
was thus mobilized and reworked landward
to seal the former inlet. Without human inter-
vention the system was unlikely to have ever
reopened. Storms have also been responsible for
formation of new inlets in barrier island chains
through erosive overwashing, which has lowered
barriers to the extent that tidal flow is initiated
through low points (Fig. 8.14).
Large-volume, near instantaneous sand trans-
port during storms has been responsible for major
changes in beach erosion and accretion rates at
tidal inlets, with storms interpreted as the major
determinants of tidal inlet behaviour at decadal
time-scales (Case Study 8.1). Similarly, Orford
8.4.3 Response to storms and tsunami
Storms have been cited as the most important
sedimentary forces on temperate coasts. This
is intuitively believable because of the high-
magnitude processes that operate during storms
and the potential for dynamic thresholds to be
exceeded that may dominate coastal behaviour
at the historical time-scale. Their location out-
side the tropics does expose temperate coasts to
the impact of cyclonic weather systems, as well
as to hurricanes that originate in the tropics but
which make occasional landfall in temperate
zones (Fig. 8.1). Storms produce large waves and
elevated water levels (surge). Thus wave energy
is not only increased but it operates at higher
