Soil and dryland salinity are two problems degrading the environment of Australia. Saline intrusion occurs on the coast and at evapo-concentrated waterbodies. Mine dewatering may enhance the propagation of salinity in the groundwater environment. The environmental impacts and the future water quality from the abstraction bores are often simulated by numerical models.
Water quality predictions are extremely sensitive to the initial salinity distribution. Statistical analysis relying on the simulations of traditional advective-dispersive transport models is often not practical due to long processing times.
A simplified approach to forecast the water quality of a well field is presented with one steady-state groundwater age simulation. The method relies on mapping an initial concentration to the travel times using a post-processing algorithm. The method was repeated for as many times as the number of generated initial concentration fields necessary to build a statistically significant population of realisations without the burden of additional simulations. This reduced the required computation by two orders of magnitude in our example.
The method equivalent to an advective water quality transport model that ignores dispersion. This can be both an advantage or drawback, depending on the situation. Where dispersion effects are dominating, the calculation above mentioned will fail by overestimating peak concentrations. In the case of large-scale models or low-dispersive situations, however, this method can effectively reduce unwanted numerical dispersion and therefore improve the modelling results.
In this work, we present a simple model set up using a 2D vertical cross section with abstraction on the right and a constant head on the left. The model was implemented using traditional transient transport modelling and the steady-state groundwater age simulation. Model results from the transport model and the groundwater age approach are compared for different values of dispersivity and initial salinity.