Geoscience Reference
In-Depth Information
environmental assessment of specific engineer-
ing projects, and the other is the development
of management policies in response to environ-
mental change. These are outlined briefly below
and the techniques in use are described in the
following section. The design and impact assess-
ment of coastal infrastructure involves prediction
of coastal processes and sedimentary response
in the face of anthropogenic activities. Typical
considerations include the design of groynes
to interrupt longshore drift and the likely sedi-
mentary consequences of their installation at
relevant time-scales. In the face of actual or
potential coastal change four policy options are
commonly identified. These are as follows:
1
do nothing;
2
hold the existing line;
3
advance the line;
4
retreat.
The decision-making process related to coastal
management policy of this type varies in its
degree of formality and, depending on the local
resources and infrastructure at risk, the coast-
line will be defended or otherwise. The approach
has been formalized in the concept of shoreline
management plans (SMPs) in England and Wales,
whereby each section of the coast is subject to
a range of analyses designed to inform policy
choice. The 'do nothing' policy option is one in
which natural processes are left to operate free
of further human intervention. This option is
typically adopted where no coastal infrastruc-
ture is at risk and permits the coast to fluctuate
freely within current constraints.
In the 'hold the line' option, the loss of infra-
structure is considered to be unacceptable and
the coast must be defended. The Netherlands
decision to maintain the 1991 shoreline position
is an example of such policy at a national level
(De Ruig & Hillen 1997). This option is usually
associated with solid structures, although the
beach nourishment approach is becoming more
widespread. It is an unfortunate but unsurpris-
ing fact that most landowners prefer the 'defend'
option, particularly if the expense is borne by
others (Fig. 8.17b).
The 'advance' option is one in which a
deliberate decision is made to claim intertidal
or subtidal land and to defend this advanced
position. In practice this option is rarely taken
on the open coast and is confined mainly to areas
that are actively prograding, and where infra-
structural development follows the advancing
shoreline. An important consideration in this
policy is whether the progradation is likely to
be sustained.
The retreat option is one in which the inevit-
ability of shoreline retreat is identified and
accepted. Structures that are undermined or
collapse are not replaced, and might even be
deliberately removed, and human infrastruc-
ture is relocated landward (Fig. 8.17c). Statutes
that prevent seawall construction are usually
indicative of the adoption of a 'retreat' strategy
as in Maine or North Carolina (Pilkey et al.
1998). Selection of the retreat option is typic-
ally taken on economic grounds although it is
increasingly popular owing to the conservation
benefits of natural coastal systems. It is polit-
ically the most difficult option to pursue when
infrastructure is at risk.
8.6.2 Sedimentology in coastal zone management
Understanding the sedimentary dynamics of the
coastline is central to the adoption of manage-
ment policy and design of human infrastructure.
For the purposes of coastal management, the
time-scale of interest is typically in the range
of years to decades. A range of approaches are
available to the applied sedimentologist to develop
an understanding of the morphodynamics of tem-
perate coastlines, and more than one approach
may be necessary. The inability to upscale short-
term measurements to longer time-scales is a key
constraint on modern applied sedimentology.
This in part lies in the feedback relationships and
complexity of processes in the nearshore zone.
It should therefore be acknowledged at the
outset that it is impossible to quantify coastal
behaviour in a generic sense and that coastal
morphodynamics at meaningful time-scales will
always be expressed in qualitative terms. With
this caveat, three types of applied sedimento-
logical study typically inform coastal manage-
ment: field studies, historical geomorphological
