Geoscience Reference
In-Depth Information
rain/irrigation
Atmosphere
interception
transpiration
soil evaporation
runoff
Surface water
Unsaturated
zone
drainage/
infiltration
Saturated zone
drainage/
infiltration
groundwater flux
Deep groundwater
Figure 9.1
Scheme of water low processes in SWAP.
the ield scale very relevant. For broader management or policy studies, the catch-
ment or regional scale might be important. Up-scaling from ield to regional scale
can be accomplished by simulating the enclosed ields parallel, such as illustrated in
Chapter 8
.
Table 9.1
lists a number of typical studies with SWAP that appeared in scien-
tiic literature. Current developments with multidimensional physically based models
and integrated hydrological frameworks will further improve our analysis of water
and solute movement in soils. However, because of their lexibility, accessibility and
speed, the coming decade one-dimensional models as SWAP will be functional to
explore new low and transport concepts, to analyse laboratory and ield experiments,
to select viable hydrological management options, to perform regional studies within
geographical information systems and to illustrate atmosphere-vegetation-soil inter-
actions for education and extension.
In the next paragraphs we discuss speciic modelling features of SWAP. Subse-
quently we address soil water low, solute transport, heat low and crop growth.
9.1.2 Soil Water Flow
Combination of Darcy's law and the principle of mass conservation results in the
versatile Richards' equation for soil water low, as discussed in
Chapter 4
. To solve
Richards' equation numerically for arbitrary ield conditions, we need to know the
soil hydraulic functions
θ
(
h
) and
k
(
h
), the actual root water extraction rate and the
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