Geology Reference
In-Depth Information
address these problems in the context of tropical
steepland cropping systems was provided by fund-
ing from the Australian Centre for International
Agricultural Research (ACIAR), in collaboration
with a range of institutions in southeast Asia.
Two successive collaborative projects were funded
in 1985 and 1992, with three general aims cover-
ing a number of related soil conservation con-
cerns (Coughlan & Rose, 1997a), which included:
●
testing a range of locally-applicable technolo-
gies to reduce soil-loss rates to some acceptable
level, such as less than 10 t ha
−1
y
−1
;
●
quantifying hydrological and sediment trans-
port processes with a view to matching soil con-
servation technologies to dominant processes at
different sites;
●
developing methodologies to predict runoff,
soil and nutrient losses, and the consequences of
these losses in terms of soil productivity.
These soil conservation concerns were deemed to
be sufficiently serious by authorities and institu-
tions in Malaysia, Thailand, the Philippines and
Australia that they agreed to provide substantial
staff and funding support for the projects, supple-
mented by ACIAR support for staff, design and
technical input, and training in soil erosion proc-
esses and research methods.
In the collaborating countries, a substantial frac-
tion of the cultivated area commonly remained bare
during crop growth. Thus it was decided that the
layout of field experiments would in all cases
include a bare soil treatment, sustained during the
cropping season by hand-weeding. The results
obtained from the bare soil treatment plots then
provided a base from which any improvement
resulting from a soil conservation measure employed
on other plots could be judged. Because of its recog-
nised importance to soil erosion, the runoff rate was
a measurement incorporated into the experimen-
tal methodology of the ACIAR-supported multi-
country experiments. A special issue of
Soil
Technology
(Rose, 1995) and chapters in Coughlan
and Rose (1997a) describe the methodologies and
some of the outputs from these projects.
The GUEST program can be used even if data
on runoff rates are not available. For example,
prior to the development of GUEST, long-term
soil erosion plots had been established in a wide
range of countries based on the methodology set
out for the USLE. Measurement associated with
these USLE plots included rainfall rate, but not
runoff rate − a factor recognised in GUEST to be
of great importance to erosion. Because of their
historical significance, it was decided to apply
the GUEST framework of soil erosion analysis to
data from 11 USLE sites in the international
network known as the ASIALAND Management
of Sloping Lands project, co-ordinated by IBSRAM
(the International Board for Soil Research and
Management). For this to be accomplished, meth-
ods were developed to infer runoff rates from the
USLE-recorded measurements of total runoff and
rainfall rate, as described by Yu (1997), Yu
et al
.
(1998, 1999), and Yu and Rose (1999).
The well-documented program WEPP (Water
Erosion Prediction Project) uses a range of infor-
mation which was readily available in the US, but
it was not available for the range of countries
involved in the multi-country projects referred to.
Whilst this precluded the use of WEPP in these
projects, there were other more theoretical objec-
tions to the use of WEPP, for example, the manner
in which the consequences of the size or settling
velocity distribution of soil was dealt with, and in
its lack of recognition of the role of a deposited
layer. Also, instead of using shear stress as adopted
in WEPP, advantages (as shown by Nearing
et al
.,
1997) were seen in using stream power. In GUEST
an effective fraction of stream power is assumed
to overcome the cohesion of the original soil in
entrainment, and to raise saltating sediment into
the water layer against its immersed weight.
Despite such differences in conceptual approach,
since both conserve mass of sediment and water,
there are some similarities in mathematical form
between WEPP and approaches expressed in
GUEST in steady-state situations (Yu, 2003).
11.2
Short History of the Development
of GUEST
A precursor to the development of GUEST was
recognition of the utility of the concept of stream
power in describing erosion dominated by over-
land flow (Rose
et al
., 1983a,b). This approach
