conceptual formulations are used to generate salt export along the
drainage lines. The model is a component of a decision support
framework for exploring the impact of policy and programs on irrigation
futures over a 20 year time period.
Highly saline shallow groundwater fluctuations effect agricultural
productivity and stream water quality. Shallow watertable fluctuations
increase the potential of waterlogging and land salinisation. This is most
evident within irrigated areas of eastern and southern Australia where
records show that the groundwater table has risen markedly resulting in
an increase in land salinisation. Salinity is a significant cause of land
degradation in south-west Victoria. Currently 40,000 ha of land is
affected; resulting in annual losses of $4million to agricultural production.
In order to formulate effective long term farm
management practicesand options it is necessary to quantify the
dominant processes effecting watertable movement.
Fluctuations in the watertable are in response to unsaturated and
saturated physical processes that occur both on a local and regional
scale. Mathematical models havebeen developed to gain a better
understanding of the physical processes and to predict the catchment
response to changed land use practices. The mathematical models must
be capable of representing the spatial and temporal variability in climate,
soil, hydrogeology and vegetation at the appropriate scale.
Few mathematical models are currently available that purport to simulate
physical processes affecting water table fluctuations. To investigate
processes at a point scale the crop water use and solute transport model
called SWAGMAN Destiny has been developed by CSIRO. This model
is comparable to the one-dimensional eco-hydrological model WAVES
(CATCHWORD 1997). On a sub-catchment scale, SWAGSIM (also
developed by CSIRO) has been widely used. This model approximates
evaporative demand based on a modified Penman formulation and adopts
an analytical solution to estimate net recharge to a single layer
groundwater model (Prathapar et al .1995). The fully distributed
physically based catchment model Mike-SHE has been applied to irrigated
catchments with some success (Mudgway et al. 1997) butrequires
considerable data, computational resources and simulation time.
The objectives of the current project was to formulate and integrate a
simplified unsaturated module into the US Geological Survey three
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