It is increasingly feasible to develop multiple groundwater models with different conceptual assumptions, model structure and parameterisation, that are similarly well-calibrated in terms of hydrograph fitting, constraints imposed by expert knowledge and other measures. Such non-uniqueness is widely acknowledged in the groundwater industry but rarely explored in practice.
We present a case study from the Tatiara Prescribed Wells Area in South Australia, for which a small family of calibrated models have been developed. These collectively capture some of the uncertainty that we know exists within our model assumptions and are used to present a range of future projections of groundwater condition. These model assumptions commonly arise out of key decision points faced by the groundwater modeller. For example, what scaling factor should be applied to crop water requirements to provide estimates of historical groundwater extraction? The creation of a family of models (using a reasonable range of scaling factors) no longer narrows the model calibration and subsequent projections to those resulting from a single and uncertain model assumption.
If carefully presented, a multi-model approach such as this can engender a broader appreciation among stakeholders, water managers and policy makers of both the sources, and implications of uncertainty in hydrogeological models.