Geology Reference
In-Depth Information
14
Predicting Impacts of Land
Use and Climate Change on Erosion
and Sediment Yield in River Basins
using SHETRAN
J.C. BATHURST
School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, UK
14.1 Introduction
erosion are generally undesirable and are evident
both on-site (in the area of the erosion) and off-site
(distant from the erosion). On-site effects include
loss of soil fertility, loss of land itself (through
river bank erosion), and destruction of infrastruc-
ture and loss of life caused by landslides and debris
flows. Off-site impacts include reservoir sedi-
mentation, deterioration of aquatic habitat, and
increased frequency of flooding caused by river
sedimentation and clogging of water abstraction
plants. There is strong interest, therefore, in mini-
mizing the amount of accelerated erosion. This is
likely only to increase in the face of climate
change, with predictions variously of more intense
rainfall (increasing erosion potential) and longer
periods of drought (decreasing vegetation cover
and thence protection against erosion).
An important requirement in the development
of strategies for minimizing erosion is a frame-
work which integrates the many processes deter-
mining sediment yield in a river basin and which
can be used (a) to test our understanding of those
processes and their linkages, and (b) to predict
the impacts of proposed courses of action. Such a
framework can be provided by mathematical
modelling, the essence of which, in this context,
is the linking of on-site rates of erosion and soil
loss in a basin to the sediment yield at the basin
outlet. Field and laboratory studies are essential
for improving our understanding of the means
by which sediment yield is generated, for exam-
ple by identifying and quantifying individual
Erosion is a natural process that causes soil loss
and generates sediment yields from river basins
even in the absence of humans. Yields vary from
the very low in well-vegetated lowland catch-
ments such as in the UK (e.g. Walling & Webb,
1981), to the very high in areas of mountain build-
ing, glacial activity and volcanism (e.g. Griffiths,
1981; Lavigne, 2004). However, ever since humans
have modified the Earth's environment for their
own gain, erosion rates have risen above natural
levels, a phenomenon known as accelerated ero-
sion (e.g. Dunne & Leopold, 1978: 510; Vanacker
et al
., 2007; Wilkinson & McElroy, 2007). Some
well-documented examples include the impacts
of Viking farming activity in Sweden (e.g. Gaillard
et al
., 1991), widespread tree-felling to make way
for agricultural development by European settlers
in the US (e.g. Trimble, 1976) and New Zealand
(e.g. Glade, 2003), and hydraulic gold mining in
California (Gilbert, 1917, cited by, among others,
Trimble, 1995). As a result, human activity has
long been considered to be probably the greatest
single influence on the impact and balance of the
various erosion processes in a river basin (e.g.
Dunne & Leopold, 1978: 510; Simons
et al
., 1979;
Sundborg, 1983). The consequences of accelerated
