In the steadily expanding world of the numerical models used for assessing groundwater, the effect of surface variables, directly correlated to groundwater recharge through the unsaturated zone, has been simulated with many different methods. Simple representations are preferred for computationally intensive uncertainty modelling, but physically realistic representations are required for accurate outputs. Finding a way to improve the representation of this correlation is of essential importance for the calculation of recharge, particularly where remote sensing data is used to improve recharge estimation. In this paper, a simplified approach to simulate the water flow through the vadose zone is linked to a groundwater model.
Specific attention is dedicated to the mechanism of evapotranspiration (ET), which is one of the most important variables in arid environments. Percolation, which eventually becomes recharge, is also extensively investigated.
It is expected that a vertical lumped approach can satisfactorily estimate the water flow through the unsaturated zone and, due to its intrinsic simplicity, will allow a straightforward calibration of parameters using, e.g., PET data that are available. A three-dimensional groundwater model is then combined with this vadose zone model, to obtain spatiotemporally distributed recharge values and water table levels.
The trade-off between the complexity and precision of such a model is examined via a test case in the Limestone-Coast and Murray-Basins in South-Australia. These areas are characterized by a heterogeneous interaction between vegetation and a generally shallow groundwater. The model is calibrated with data of potential and actual evapotranspiration, values of soil moisture, and a network of observation bores.
This paper is expected to provide a flexible model that can effectively be applied for data scarce regions where remote sensing is the only source of information, which is a useful tool for decision makers.