Geography Reference
In-Depth Information
and navigation hazard (Nordstrom 1994), with this
figure reaching close to 100 per cent in some
localities (e.g. the coastline of Belgium). The
profound implications of these engineering
structures for coastal processes and erosion are
discussed below.
This chapter takes the view that dealing with
coastal erosion requires an assessment of its
position in the wider scheme of coastal dynamics
(erosion is just one component of a sedimentary
budget for any coastline) and that only by
understanding, and allowing for, changing coastal
position will truly sustainable coastal
management be achieved. This review, limited by
space, concentrates upon problems on sandy and
muddy coastlines in the developed world (Plate
8.1); however, the pressures generated by coastal
erosion in developing countries are enormous.
Thus, for example, in Bangladesh a huge and
rapidly growing, poor, rural population must
contend, not only with a tectonically active,
highly mobile floodplain coast, subject to both
major riverine floods and catastrophic storm
surges, but also the environmental problems
resulting from the construction of hard-
engineered flood defence lines imposed by
external agencies (e.g. Brammer 1993). The
diverse coastal problems faced by developing
countries are well covered by Nicholls and
Leatherman (1995).
Box 8.1
Coastal classification and coastal
erosion
Coastal dynamics, including erosion, are controlled at
the large scale by two sets of factors, one historical (in
the broadest sense) and one contemporary. In the first,
coastal type is controlled by plate tectonic setting, and
this provides a broad emergence/submergence
categorisation. This in turn is overlain by more immediate
historical factors, particularly the nature of sea level
change over the last 10,000 years of the postglacial
transgression. Site-specific variations in sea level in this
period have resulted from the varying contribution of
regional isostatic (affecting the movement of land
surfaces) and global eustatic (affecting the volume of the
oceans) factors to sea level change. Thus the different
sea level histories of, for example, Australia, where
present sea level was reached 6000 years ago, and
Arctic Canada, where sea levels have been falling since
the start of the deglaciation, are a component in
explaining shoreline morphology. This historical
backdrop is then worked upon by current global
variations in wave energy, tidal regime and, for vegetated
coastal ecosystems, biogeographic patterns and
processes. In 1952, Valentin brought these factors
together in an elegant coastal classification scheme. In
Valentin's diagram, the
y
axis represents the historical
and the
x
axis the contemporary components. Varying
combinations of these two factors give coastal advance
or retreat. The solid line running through the centre of
the diagram from top left to bottom right separates all
retreating coastlines (bottom left) from all advancing
ones (top right).
Plate 8.1
A developed coast: Waikiki, Honolulu, Hawaiian
Islands. How does one devise a sustainable coastal
management strategy for such a coastline?
(photograph:
T.Spencer).
