36
assumptions were: (1) The physical properties of the soil are
homogeneous and isotropic; (2) The physical and chemical properties of
the soil are constant in time; and (3) The hydraulic conductivity and
soil pressure potential are single-valued functions of water content.
One-Dimensional Model
Equation (6) was used to describe the one-dimensional movement and
extraction of water. Finite difference methods were used to solve the
water potential based flow equation. The model used an implicit finite
difference technique with explicit linearization of the soil parameters.
The finite difference form of equation (3) was written as
k
k+1 k
(h h )
k i i
k+1 k+1 k k+1 k+1
K (h h ) K (h-h)
i+1/2 i+1 i i-1/2 i i-1
At
Az
where
i-1/2
AZ
K
i-1/2
K
i+1/2
+ K
i-1
(16)
(17)
and
i+1/2
i+1
(18)
The subscript i refers to distance and the superscript k refers to time.
To apply this equation to soil profiles, the soil was divided into a