PhD Thesis Emmanuel Obeng Bekoe - Cranfield University

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area index (LAI) and Von Hoyningen-Huene (1983) equations have been
employed in ACRU to compute crop growth and interception losses (Schulze,
1995, Chapter 6).
Soil input decision support offers two levels of accuracy, depending on the data
available to the user; at the lower level, when soil information is very limited,
only soil texture and depth need be provided, with relevant hydrological soil
properties being estimated from default decision support tables developed for
soils from Southern Africa and from vertical percentages of clay content in the
soil profiles, while at the higher level, porosity, field capacity, wilting point and
drainage response rates, as well as textures and depth, are required.
ACRU makes use of a "cell"-type discretisation to subdivide the catchment,
where each cell may be regarded as a sub catchment of the main catchment.
Cell boundaries are defined by the user, using large scale orthophotos or
topographical maps. If the effect of land use changes on outflow from a
catchment is to be investigated, then the cell boundaries should be so defined
as to obtain a high degree of homogeneity of land use or vegetation type.
However, this may then often be achieved at the expense of, say, homogeneity
of soil type. Likewise, if the cell, or sub catchment, outlet is selected at a point
where hydrological information is required, e.g. at the inflow or outflow of a
reservoir, then this information is likely to be obtained at the expense of (say)
vegetation homogeneity, because in such a case the sub catchment boundary
would be defined uniquely by the selection of the location of the sub
catchment's outlet, irrespective of its soil and vegetation characteristics.
The ACRU agro-hydrological modelling system has been used extensively in
South Africa (Everson, 2001). Examples of its use include land use change in
Luvuhu catchment in South Africa (Jewitt et al., 2004) for the application of
Geographic Information Systems (GIS) in the analysis of nutrient loadings from
an agro-rural catchment in Southern Africa (Mtetwa et al., 2003); for climate
change studies in South Africa (New, 2002); water balance (Everson, 2001); for
Emmanuel Obeng Bekoe Phd Thesis Chapter 3 Catchment-Hydrol,& Model Selection