Geology Reference
In-Depth Information
model to large areas requires not only that all
processes that are relevant over a larger spatial
scale are included in the model description. It is
also necessary to use appropriate scaling func-
tions; understanding how soil erosion rates depend
on slope length or unit contributing area over the
domain to be modelled is critical in this respect.
Misconceptions about soil erosion models do
not always lead to misapplications. Even if this is
not the case, however, misconceptions may have
important consequences as they may (mis)guide
scientific efforts. A particularly important mis-
conception is that increasing model quality will
be expressed in improved predictions of absolute
erosion rates at increasingly smaller temporal
scales. This will not happen as there is a funda-
mental upper limit to prediction accuracy, and it
appears that even the performance of older, sta-
tistically based models, such as the (R)USLE, is
close to this limit.
The latter does not imply, however, that
sophisticated, spatially distributed, process-based
models are useless. Rather, they are tools that
allow us to improve our understanding of how
erosion and deposition processes work at differ-
ent scales, allowing us to move away from the
plot to real landscapes. The development of such
models requires a continuous confrontation of
field and laboratory data with model predictions.
Temporally and spatially detailed data are neces-
sary to test thoroughly the last generation of ero-
sion models. Confrontation of model performance
with field or laboratory observations should be
designed in such a way that it allows assessment
of which of any competing model concepts is
'better' in terms of describing the data and why
this is the case. As the necessary field data or
laboratory data to do this are often not available,
there is a risk that efforts are uniquely directed
towards the improvement of model performance
through parameter optimization. By doing so, we
miss the opportunity that models give us to eval-
uate to what extent they are really capturing the
complex interplay between hydrology, erosion
and (size-selective) deposition that takes place in
real landscapes. Erosion models will also need
further development in order to make them suit-
able tools to answer scientifically and societally
relevant questions that even the most sophisti-
cated, present-day models cannot fully address,
such as erosion-soil interactions at different
scales and the size-selective transfer of sediment
and associated nutrients, pollutants and organic
matter through a landscape.
References
Alberts, E.E., Nearing, M.A., Weltz, M.A.,
et al
. (1995)
Soil component. In Flanagan, D.C. & Nearing, M.A.
(eds),
USDA - Water Erosion Prediction Project:
Hillslope profile and watershed model documenta-
tion
. NSERL Report No. 10. USDA-ARS National
Soil Erosion Laboratory, West Lafayette, Indiana,
pp. 7.1-7.46.
Baffaut, C., Nearing, M.A. & Govers, G. (1998) Statistical
distributions of soil loss from runoff plots and WEPP
model simulations.
Soil Science Society of America
Journal
62
: 756-63.
Bakker, M.M., Govers, G. & Rounsevell, M.D.A.
(2004) The crop productivity-erosion relationship:
an analysis based on experimental work.
Catena
57
:
55-76.
Bakker, M.M., Govers, G., Ewert, F.,
et al
. (2005)
Variability in regional wheat yields as a function of
climate, soil and economic variables: assessing the
risk of confounding.
Agriculture Ecosystems &
Environment
110
: 195-209.
Bathurst, J.C. & Lukey, B. (1998) Modelling badlands
erosion with SHETRAN at Draix, southeast France.
In Summer, W., Klaghofer, E. & Zhang, W. (eds),
Modelling Soil Erosion, Sediment Transport and
Closely Related Hydrological Processes
. IAHS
Publication 249, pp. 129-36.
Belyaev, V.R., Wallbrink, P.J., Golosov, V.N.,
et al
. (2005)
A comparison of methods for evaluating soil redistri-
bution in the severely eroded Stavropol region, south-
ern European Russia.
Geomorphology
65
: 173-93.
Beuselinck, L., Govers, G., Steegen, A.,
et al
. (1999)
Evaluation of the simple settling theory for predict-
ing sediment deposition by overland flow.
Earth
Surface Processes and Landforms
24
: 993-1007.
Beuselinck, L., Steegen, A., Govers, G.,
et al
. (2000)
Characteristics of sediment deposits formed by
intense rainfall events in small catchments in the
Belgian Loam Belt.
Geomorphology
32
: 69-82.
Beven, K. (2006) A manifesto for the equifinality thesis.
Journal of Hydrology
320
: 18-36.
