Geoscience Reference
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and currents, bed friction and sediment texture
on, for example, nearshore sediment transport.
Applied models, in contrast, set out to deliver
a quantitative prediction of nearshore sediment
transport or geomorphological response. Applied
models are deployed in a routine manner that
typically involves testing against a set of field data.
Differences between the predicted and observed
changes are then considered and coefficients are
applied to render the two as close as possible for
the historical data. This produces a 'calibrated'
or 'tuned' model that is then applied to design a
structure, to determine its environmental impacts,
or to predict future shoreline evolution.
There are several types of coastal applied
model in use. The most commonly used process
models in the USA for example are SBEACH
and GENESIS. Their formulation is public and
therefore can be subjected to public scrutiny
(and found wanting - Thieler et al. 2000). In
Europe, many of the applied coastal models are
proprietary software, developed and used in a
competitive environment by coastal engineer-
ing firms. The models are often sold and used by
other consultants. In this environment, where
the precise formulation of the models is not
public, such models (e.g. LITPACK, UNIBEST)
operate as black boxes. In nature the variability
between beaches and even within a single beach
is so great that the parameterizations on which
applied models are based are not transferable
between sites. This seldom contemplated fact
is somewhat masked by the calibration process,
which in fact involves the use of a constant
('fudge factor') to achieve agreement between
predicted and actual change. The 'calibrated'
model is then used to predict future scenarios.
Modelling is characterized by endless attempts
to compare model output with field data (Mulder
et al. 2001). This emphasizes on the one hand
the paucity of good field data sets, and on the
other the wide variety of model types. In spite of
efforts to test models against field data, model
refinement is fundamentally prevented by the
inability to resolve the spatial variability in
factors that control sediment transport and the
natural temporal variability in these factors.
Models themselves thus do not provide any
more reliable predictions of coastal behaviour
than other measures. This fact is not commonly
appreciated. Even in the comparatively simple
case of aeolian sediment transport, aeolian trans-
port modelling has had little success in predicting
actual transport rates at even short time-scales
(Sherman et al. 1998).
Modelling approaches are also used in longer-
term coastal evolution studies. Here, in spite of
a lack of scientific validation, the Bruun 'Rule'
model (see 8.7) is the most widely applied
approach in predicting coastal response to
sea-level rise. The shoreline translation model, a
two-dimensional model of coastal profile change
(Cowell et al. 1995), utilizes the Bruun approach
in maintaining a consistent nearshore profile as
the coastline responds to sea-level rise.
8.6.2.4 Composite approaches
Understanding the sedimentology of temperate
coasts is an imprecise science that is informed by
a range of potential data. Each dataset provides
only a piece of the necessary information for
correct interpretation and it is important that
this is considered in applied sedimentology. The
fullest understanding of coastal morphodynamic
behaviour is therefore likely to be achieved by
the compilation of data from a range of sources,
which when compared against each other for
consistency or opposing trends, enable descrip-
tion of coastal behaviour.
Understanding coastal sedimentology at time-
scales useful to humankind requires utilization of
a range of data of varying quality and covering
variable time periods. A composite approach
using historical, model and field observations
could provide the most comprehensive assess-
ment of coastal sedimentary behaviour. In
such studies 'order of magnitude' or qualitative
answers are sought that aid understanding of
the processes operative at varying time-scales.
Building on this type of composite approach,
a novel initiative in future shoreline prediction
has been undertaken in Great Britain. Termed
'Futurecoast' (Cooper & Jay 2002) this approach
uses a combination of geomorphological ex-
pert opinion (delimitation of cell boundaries),
