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less well sorted than deposits associated with
storms and may contain sequences deposited
during both landward and seaward return flows
(Nanayama et al. 2000).
It should be clear from the above discussion
that the three-dimensional changes that occur
in beach systems are multifarious in nature. The
processes that drive them (dynamics, sediment
supply and antecedent morphology) are diverse
in type and in the time-scales at which they oper-
ate. The very dynamism of these systems hinders
attribution of cause and effect and, as such, the
identification of process-response relationships
on beaches and barriers is difficult. Such rela-
tionships are perhaps most likely to be identified
at the short time-scale through instrumentation.
The difficulty lies in relating these observations
to longer time-scales because of the importance
of additional factors such as antecedent con-
ditions and sediment supply and periodicity of
episodic high-energy events. Relating site observa-
tions to other locations is equally fraught with
uncertainty because the particular constraints
on sediment movement and geomorphological
response are not conducive to full quantification.
The up-scaling of short term observations to
longer time-scales suffers similar constraints for
the same reasons, coupled with the non-linearity
of process-response mechanisms, unpredictability
(or impossibility of complete measurement) of
forcing mechanisms and morphodynamic feed-
back. By its very nature, investigation of the role
of sea-level change and climate change requires
a long-term approach.
In the pre-industrial era, coastal infrastructure
threatened by the sea was abandoned. Submerged
former landscapes and archaeological monuments
in the Middle East (Sivan et al. 2001) provide
evidence of this practice. This still happens in
some areas but the intensity of development and
its human value (both social and economic) has
prompted a range of engineering interventions
to defend infrastructure.
The problems posed by human intervention
arise partly from construction inside the active
profile of the coastal zone ( passive intervention )
- for example, failure to recognize that dunes
and/or the back-beach form an active part of
the system during storms. Long-term stability
during interstorm periods may give a false
impression of the coastal morphodynamic regime.
Consequent removal of foredunes and their
replacement with solid infrastructure renders
that infrastructure vulnerable to erosion during
storm conditions. Human alteration of sediment
movement ( active intervention ) occurs through
structures intended to alter wave and current
patterns and intercept sediment in transport (e.g.
groynes and jetties), and prevent sediment from
being eroded (e.g. seawalls). Additional, less
obvious impacts on sediment movement include
denudation or stabilization of dunes. Such actions
alter the natural sediment budget.
Human activities may also impede the ability
of the shoreline to adjust to rising sea-levels.
Developments built landward of the active coastal
sedimentary system eventually find themselves
within it, as a result of sea-level rise. Develop-
ment at the shoreline imposes restrictions on the
options available in response to rising sea-levels.
This type of anthropogenic constraint on the
boundaries of natural coastal systems poses a
major problem in coastal zone management and
is often stated as the 'erosion problem'. As noted
above, however, erosion is an entirely natural
part of the cycling of sediment along coasts. Only
the presence of human infrastructure renders it
a 'problem'.
There have been historical changes in human
use of the coastline (Nordstrom 2000). The first
impacts were probably vegetation destabiliza-
tion in coastal dunes. Prehistoric occupation of
8.5 PROCESSES AND IMPACTS OF ANTHROPOGENIC
ACTIVITIES
A range of human activities influence the natural
functioning of temperate coastal systems. Per-
haps the most pervasive impact results from
the legacy of development at the shoreline. This
impedes the ability of the coastline to respond
morphologically to natural forcing because
such responses may damage infrastructure. This
situation also influences contemporary manage-
ment approaches to the shoreline (see section 8.6).
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