Geology Reference
In-Depth Information
1
Introduction
R.P.C. MORGAN
National Soil Resources Institute, Cranfield University, Cranfield, Bedfordshire, UK
The movement of sediment and associated pollut-
ants over the landscape and into water bodies is of
increasing concern with respect to pollution con-
trol, prevention of muddy floods and general envi-
ronmental protection. This concern exists whether
the sediment is derived from farmland, road
banks, construction sites, recreation areas or other
sources. In today's environment it is often consid-
ered of equal or even greater importance than the
effects of loss of soil on-site, with its implications
for declining agricultural productivity, loss of bio-
diversity and decreased amenity and landscape val-
ues. With the expected changes in climate over
coming decades, there is a need to predict how
environmental problems associated with sediment
are likely to be affected so that appropriate man-
agement systems can be put in place.
Whilst it is possible to instrument a few indi-
vidual farms and catchments in order to obtain
the data to evaluate the current situation and pro-
pose best management practices, it is not feasible
to study every location on the Earth's surface in
detail. Instead, evaluation and predictive tools
need to be applied to assess current problems,
predict future trends and provide a scientific base
for policy and management decisions. Erosion
models can fulfil this function provided that they
are robust and used correctly. Despite, or maybe
even because of, the vast amount of research over
the last 30 years or more on erosion modelling,
potential model-users are confronted with a
multiplicity of models from which to choose,
often with little guidance on which might be the
best for particular circumstances or the steps
required to apply a selected model to a given situ-
ation. Many models have been tested for only a
limited range of conditions of climate, soils and
land use, and little information is available to
enable a user to assess in advance how well a
model might perform under different conditions.
Models range from empirical to physically- or
process-based, and vary considerably in their
complexity and the amount of data input required.
Very little guidance is available on how accurate
that data input has to be, or what effect different
levels of accuracy can have on the accuracy of the
model output. Further, sediment problems can
exist at scales that range from a farmer's field or a
small construction site to the effects of sediment
transport and deposition in small and large catch-
ments. Somewhat limited information exists on
the range of scales over which different models
can operate successfully, leaving the user uncer-
tain on whether a particular model is the most
appropriate for a given scale. In the worst case, as
a result of a lack of clear guidance, the user may
choose a totally inappropriate model.
Users can obtain a list of the leading soil ero-
sion models from the Internet site http://soil
erosion.net/doc/models_menu.html. Links are pro-
vided to other sites associated specifically with
each model from which the software can be
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