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changed rapidly. Considerable computational savings without appreciable
loss of accuracy was achieved using irregular grid sizes.
Perrens and Watson (1977) developed a two-dimensional numerical
model of water movement to analyze infiltration and redistribution.
They used an iterative alternating direction implicit technique to solve
the flow equation. Two soil types, a sand and a sandy loam, were
simulated. Nonuniform surface fluxes were applied along the horizontal
soil surface in a step type distribution pattern. They also
incorporated hysteresis of soil hydraulic characteristics into the model
to be used in the redistribution phase of the simulations.
Researchers have also utilized two-dimensional models to study soil
water movement from trickle irrigation systems. Brandt et al. (1971)
solved the flow equation in two dimensions to analyze infiltration
from a trickle source. They developed a plane flow model in cartesian
coordinates to analyze infiltration from a line source of closely spaced
emitters with overlapping wetting patterns. They also developed a
cylinderical flow model to analyze infiltration from a single emitter
when its wetting pattern is not affected by other emitters. Both models
were solved using noniterative ADI finite difference procedures with
Newton's iterative method. The results were compared to an analytical
solution of steady infiltration and a one-dimensional solution with good
results.
Armstrong and Wilson (1983) developed a model for moisture
distribution under a trickle source. They utilized the Continuous
System Modeling Program (CMSP) to simulate the soil moisture movement.
The model calculated the net flow rates into each grid. It then
calculated the change in water content by dividing the net flow rate