Geoscience Reference
In-Depth Information
live in the coastal counties of the Atlantic and
Pacific coastlines and coastal population density
rose from 275 to 400 people per square kilometre
between 1960 and 1990 (Hinrichsen 1998).
human value system, politics and economics that
influence human responses to pressure (Pilkey
& Dixon 1996). In reality, the dynamics of
the coastline are unpredictable (storms occur
chaotically) and the coastal system is not well
understood (the complexities and feedbacks in a
coastal system are largely unresolved). Further-
more, sea-level, the plane at which coastal
dynamics operate, is changing on a global scale,
and global climate change may be altering the
frequency and intensity of storms. This is mani-
fest in many parts of the world as a propensity
toward coastal recession (Bird 1985). Added to
this is ongoing deliberate and accidental modifica-
tion of sedimentary processes through human
intervention.
8.2.1 Environmental sedimentology of
temperate coasts
The world's temperate coasts are among the
most densely populated and developed in the
world. As a consequence, large stretches of
temperate coastlines have been subject to inten-
sive anthropogenic modification with attendant
sedimentological impacts. In many cases these
involve direct impacts on the sediment volume
(e.g. dune removal, sand mining) or sedimentary
processes (e.g. jetty construction interfering
with longshore drift). In other instances, in-
direct influences result from, for example, the
armouring of coastal cliffs, which formerly
supplied sediment to adjacent beaches. In all
cases, human development of the coastline has
the potential to foreclose future management
options. Intensive infrastructural development
at the coast almost inevitably leads to the desire
to armour the shoreline in the face of coastal
erosion. Armouring fixes the shoreline position,
thus setting a human limit to the acceptable
extent of shoreline processes. This constrains
the ability of the beach system to operate natu-
rally and passes the fate of the beach into
the human decision-making sphere. This has
given rise to the study of 'developed coasts' as
a distinctive field of investigation (Nordstrom
2000). The distinction is somewhat blurred
as even remote, rural beaches often exhibit
significant human alteration and impact (Power
et al. 2000).
8.3
SEDIMENT SOURCES AND SEDIMENT
ACCUMULATION PROCESSES
8.3.1 Sources and characteristics of sediments
Temperate coastal environments receive sedi-
ment from various sources and inevitably
beach morphology is strongly influenced by
the nature and volume of available sediment
(Fig. 8.3). The main sources are rivers, the con-
tinental shelf, coastal erosion and redistribution
(see Chapter 1) and there are important regional
differences in the type of sediment supply. In the
western USA fluvial sediment supply is domin-
ant because of the steep hinterland gradient,
whereas on the eastern coast, continental shelf
sources predominate.
Fluvial sources are a key component of tem-
perate sediment supply, especially adjacent to
large rivers or rivers that drain steep hinter-
lands. Fluvial sediments may be reworked within
a delta complex, often to form barrier islands,
for example the Nile delta (Pilkey 2003). In
other instances, sediment is transported from
the river mouth to adjacent coastal depocentres
(Cooper et al. 1999). Fluvial sediment supply
is often episodic, particularly where a seasonal
discharge regime exists (see Chapter 3). Thus
coastal sediment supply may fluctuate between
periods of high fluvial supply followed by intervals
8.2.2 Overview of issues, processes and problems
There are many contemporary management
issues in the temperate coastal zone, most of
which involve conflicts between human utiliza-
tion and natural processes of change. Even in
an environment with predictable dynamics and
a fully understood coastal system, the issues
would still be difficult to resolve because of the
