Geology Reference
In-Depth Information
7
Misapplications and
Misconceptions of Erosion Models
G. GOVERS
Physical and Regional Geography Research Group, Department of Earth and Environmental Sciences,
Katholieke Universiteit Leuven, GEO-Institute, Celestijnenlaan, Heverlee, Belgium
7.1 Introduction
models continue to exist. We will take a some-
what provocative stance, not because we think
that most of the work that has been carried out
hitherto was substandard or ill-conceived, but
because we want to stimulate the discussion. It
should also be made clear that both issues have
been discussed before: Wischmeier (1976) has
already warned against the misuse of the USLE,
and since then several critical papers on soil ero-
sion model applications have been published
(Boardman, 2006; Jetten & Favis-Mortlock, 2006;
Jetten
et al
., 2003). Furthermore, critical consid-
erations on the use of spatial models in related
fields such as geomorphology and hydrology also
exist (e.g. Grayson
et al
., 1992). Here, we try to
provide the reader with a general overview of
model misconceptions and misapplications with
respect to soil erosion models: logically, some of
the material covered has already been discussed
in this earlier work. We also take a rather practi-
cal, empirical viewpoint. We thereby mostly
forego more philosophical/conceptual issues
related to spatial modelling in the Earth Sciences :
see Bras
et al
. (2003) for a more conceptual dis-
cussion of the issue.
Evidently, misapplication and misconceptions
about erosion models are strongly related. Mis-
applications of erosion models are, in principle,
always due to a misconception. On the other
hand, not all misconceptions necessarily lead to
misapplications. In this chapter we will first dis-
cuss misapplications: we will deal with what
might be called true misapplications: model
Soil erosion modelling has a long history. The
need for accurate soil loss prediction emerged in
the 1930s in the United States, after the Dust
Bowl. The first models, predecessors of the USLE
(Universal Soil Loss Equation), began to appear in
the 1940s (e.g. Zingg, 1940), and models have
been evolving ever since, albeit not continuously.
Erosion model development saw a major para-
digm shift from so-called statistical or empirical
models to so-called process-based models in the
1980s, mainly stimulated by seminal papers by
Foster and Meyer from 1972 onwards (Foster &
Meyer, 1972). Present-day process-based erosion
models such as WEPP (Nearing
et al
., 1989) and
PESERA (Kirkby
et al
., 2008) often are sophisti-
cated tools, describing erosion processes in great
detail. Some of them are now able to carry out
continuous simulations instead of event-based
simulations; others just provide long-term aver-
age estimates. One might therefore expect that,
by now, we have a clear view on what we may
achieve with soil erosion models and how we
should apply them. As the title of this chapter
suggests, this may not always be the case.
In this chapter we try to understand how and
why misconceptions about soil erosion models
might arise, and what kind of misapplications of
