50
Reddel and Simada (1970) utilized a Gauss elimination method for
the solution of a two-dimensional groundwater model. They used an
algorithm developed by Thurnau (1963) which operates only on the banded
part of the solution matrix. Computer storage is not required for the
matrix elements above or below the band. A minimum band width is
desirable and an appropriate choice of the grid numbering pattern can
reduce the total width of the band.
In this model of two-dimensional soil water movement and
extraction, a subroutine was written which used the BANDSOLVE algorithm
developed by Thurnau (1963) to solve the system of equations. A
subroutine was also written which solves equation (8) using an
alternating direction implicit method. The finite difference equations
for the ADI solution are presented in Appendix A.
Soil Water Extraction
A macroscopic soil water extraction term was used in this research.
The model used was based on actual field measurements reported in the
literature. Denmead and Shaw (1962) conducted experiments which
compared actual ET to potential ET of corn as a function of the
available soil water. Their study showed that under high potential ET
demands, the actual ET was considerably less than the potential rate
even though the available soil water was considered adequate. They also
observed that under low potential ET demands, the actual ET was equal to