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dimensional finite difference groundwater flow model MODFLOW
(McDonald 1988).
The model presented in this paper is called SMILE (an acronym for
Simple Macropore Infiltration, Leakage and Evaporation) and it consists
of a spatially explicit model of saturated groundwater flow and a lumped
conceptual model of vertical unsaturated flow. The model concentrates
on the dominant processes that control recharge and salt load discharge
at the catchment scale. Model development of the unsaturated flow
processes proceeded from the simple to the more complex, where
additional complexity was only retained where it could be shown that it
yielded a significant improvement. While there are (arguably) a number
of physically-based models that have the potential to model the coupled
processes of interest, it was considered that there was not the data
available to validate model response at the required spatial and temporal
scales. The amount of calibration data available for this model application
is typical of many catchment investigations, and is representative of the
fundamental limitations imposed on physically-based models that has
been discussed by such authors as Klemes (1986) and Beven (1989).
The process of model development adopted here follows the suggestions
of Grayson and Nathan (1993), in which the model was developed for a
specific problem at a complexity commensurate with the available data.
The developed conceptual model simulates a well connectedsurface
water/groundwater system dominated by either matrix or macropore
flow. As such, the classical matrix flow approximations described by
the Richards Equation were not used. The simplified conceptual model
approximates one-dimensional vertical soil moisture movement which
recharges a three-dimensional finite difference groundwater model. The
vertical soil moisture model simulates soil infiltration, recharge to a
underlying groundwater system and evapotranspiration on a daily
timestep for each active cell within the model domain. Sub-surface
lateral flow within each soil column is not permitted. A detailed
description of the conceptual model is provided below.
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