PhD Thesis Emmanuel Obeng Bekoe - Cranfield University

• depths of each soil horizon
• Field Capacities (FC) and permanent wilting points (PWP)
• the porosities of the soil horizons
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• surface properties (e.g. crusting & cracking) which affect infiltration rate,
i.e. water entry rate into the soil
• the proportion of clay, sand and silt within the soil horizons, as they relate
to the redistribution rates of water and
• soil redistribution rates
The soil map (Annex B) of the area including the Densu Basin taken from Adu
and Asiama (1992) together with soil information derived from soil profiles within
the Densu basin and an adjacent basin (Ayensu) were used to generate the
depths of the various horizons, the textural classes and the vertical clay content
of the soils. Within the catchment of the Densu Basin, Adu and Asiama (1992)
depict eight soil series (Table 4.8) with their corresponding Food and Agriculture
Organization (FAO) soil classifications (FAO, 1988). Table 4.8 also shows the
percentage that each soil series occupies in the basin, with a description of the
soil texture and average depths of the A and B horizons.
To compute the field capacity (FC) and permanent wilting points (PWP),
porosity, and redistribution rates of the soils in this catchment pedo transfer
functions were used. As cautioned by De Vos et al. (2005), published pedo
transfer functions (PTF’s) show large differences in performance and should be
used with care when applied in environments other than the ones in which they
were calibrated. However, Nemes et al. (2001) did note that many simulation
models require water retention and hydraulic conductivity data which are difficult
and time consuming to measure. They noted that one way of overcoming this is
through the development of PTF’s from easily measured data. Pachepsky and
Rawls (1999) did note that PTF’s have been used in a wide range of studies,
Emmanuel Obeng Bekoe Phd Thesis Chapter 4 Data Availability, Model setup & Analysis