New South Wales Government
Water and Energy

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Water Management

Groundwater modelling

The Department of Water and Energy (DWE) uses computer-based models to better understand groundwater flow systems. They are the most sophisticated tools available for simulating aquifer behaviour, and for predicting the effects of groundwater use. They can tell us the volume of water flowing into an aquifer and where that water is coming from.

A groundwater model is a computer-based representation of the essential features of a natural hydrogeological system that uses the laws of science and mathematics. Its two key components are conceptualisation and the mathematical code. Conceptualisation is an idealised representation of the hydrogeology: aquifer dimensions, hydraulic characteristics, and the recharge and discharge processes within the system. The mathematical code is a set of equations which, subject to certain assumptions, quantifies the physical processes active in the aquifer system being modelled.

There are many computer programs which model groundwater systems. The Department has chosen to use the world’s most commonly used and accepted standard code, called MODFLOW, to assess sustainable levels of water extraction from regional aquifers.

A groundwater model which represents the groundwater system (aquifer) to an adequate level of detail can be used as a predictive scientific tool to quantify the impacts on the system of specified hydrological, pumping or irrigation stresses. Common applications of a regional scale groundwater model include:

• Evaluating recharge, discharge and aquifer storage processes (water resource assessment)
• Quantifying the sustainable yield (economically and environmentally sound allocation policies)
• Predicting the impact of alternative hydrological or development scenarios (to assist decision making)
• Risk based resource management (assessment of alternative policies).

The modelling process involves several stages such as conceptualisation, data collation, software selection, model design and model calibration against measured/observed data.  A sensitivity analysis is also undertaken to evaluate the influence of parameter uncertainty on model outputs. After the completion, models are expected to go through a process of peer review. Although this process consumes time and resources, it still remains the most effective way of ensuring model accuracy and robustness, hence acceptance by the broader community involved in water sharing.

A number of regional groundwater models of parts of NSW have been completed, or are in various stages of development. Areas chosen for numerical modelling are usually where the groundwater system is under stress from high levels of use or at risk in other ways such as from salinisation or contamination. For example, groundwater models were used to develop the water sharing plans for the large inland alluvial aquifer systems of NSW, as shown by this map (PDF 1MB).