Geoscience Reference
In-Depth Information
beach morphology and behaviour. Differing clast
sizes influence packing, resistance to motion and
porosity, all of which affect beach morphology.
The accommodation space in which beaches
form is controlled by the antecedent coastal
geomorphology. Commonly beaches form in
embayments, but the geomorphology of the
shoreline is an important factor in their distribu-
tion. If too steeply dipping, sediment accumula-
tion may not break the water surface and no
beach will form. Sufficient wave energy to trans-
port available sediment sources is an obvious
requirement - insufficient energy will result in a
variety of unmodified terrestrial deposits rather
than beaches. The most important attribute of
the environments described here is their ability
to change morphology as energy levels change
and to seek equilibrium with environmental
conditions. This ability to accommodate change
renders them important buffers against high-
energy storm waves.
At a global scale, there is much variability in
wave energy levels (Fig. 8.1). Swell waves on
oceanic coasts are often fully refracted and arrive
parallel to the shoreline, whereas locally gener-
ated sea waves in sheltered environments may
arrive at an angle to the coast. Paradoxically,
these lower energy waves may be more efficient
in effecting net sediment transport through
longshore drift. Tidal range exerts a secondary
influence on beach morphology as it mediates
the vertical and horizontal area in which wave
energy is expended. Higher tidal range tends to
reduce the relative influence of waves on beach
geomorphology.
The defensive significance of such malleable
natural environments to human developments
at the coast has not been uniformly appreciated.
There has been much historical degradation of
beaches and dunes and in some localities this is
ongoing. The recreational and landscape attributes
of temperate coasts combine to draw increasing
numbers of humans to the coast. The consequent
infrastructural development is often poorly loc-
ated and impedes the ability of natural beach
systems to respond to changing conditions.
The environmental significance of temper-
ate coastal sedimentary environments can be
expressed or considered from several, often com-
peting, human perspectives (physical, ecological
and economic). In a
physical
sense, the environ-
ments provide a dynamic natural system capable
of responding to and absorbing high levels of
marine energy. These environments are often
regarded as hazardous to navigation. From
an
ecological
perspective, beaches have been
recognized, over the past 20 years in particular,
as important ecosystems (Brown & McLachlan
2002). The interstitial fauna and flora play a role
in the ecology and sedimentology of adjacent
inshore and dune ecosystems as do their distinc-
tive vegetation and related fauna.
The
economic
significance of beaches is evid-
ent in the extent of seafront development and
the vast numbers of visitors to resort beaches.
As a coastal defence against wave action, beaches
are also economic assets. Beaches too provide
access to the coast and they have also been
seen as ready sources of aggregate (Carter et al.
1991). The human values attached to beaches are
clearly not always compatible with each other
or with their ecological and physical value. The
nature of human pressure on beach and dune
environments changes with time (Nordstrom
2000). Much of this is technology-dependent.
For example, widespread kelp collection in the
north-west British Isles during the Napoleonic
wars for iodine extraction undoubtedly affected
the development of drift lines, so necessary for
dune development. Similarly, changes in farm-
ing practice have controlled the patterns of
small-scale sand removal from beaches in Ireland
(Carter et al. 1991).
Human pressure on the coast takes many forms
and the continuing migration to the coast is set
to increase those pressures. Cohen et al. (1997)
estimated that over 2 billion people (37% of
the global population) live within 100 km of a
coastline. Dramatic increases have been noted in
the temperate regions of the Mediterranean and
the USA ocean coasts. In the Mediterranean, the
coastal population was estimated at 146 million
in 1990 and the urban coastal population alone
is projected to rise to 176 million by 2025, with
an additional 350 million tourists (Hinrichsen
1998). In the USA, 55 - 60% of the population
