Saltwater Intrusion - Modeling

Modeling

Modeling of saltwater intrusion is considered difficult. Some typical difficulties that arise are:

• The possible presence of fissures and cracks and fractures in the aquifer, whose precise positions are unknown but which have great influence on the development of the saltwater intrusion

• The possible presence of small scale heterogeneities in the hydraulic properties of the aquifer, which are too small to be take into account by the model but which may also have great influence on the development of the saltwater intrusion

• The change of hydraulic properties by the saltwater intrusion. A mixture of saltwater and freshwater is often undersaturated with respect to calcium, triggering dissolution of calcium in the mixing zone and changing hydraulic properties.

• The process known as cation exchange, which slows the advance of a saltwater intrusion and also slows the retreat of a saltwater intrusion.

• The fact that saltwater intrusions are often not in equilibrium makes it harder to model. Aquifer dynamics tend to be slow and it takes the intrusion cone a long time to adapt to changes in pumping schemes, rainfall, etc. So the situation in the field can be significantly different from what would be expected based on the sea level, pumping scheme etc.

• For long-term models, the future climate change forms a large unknown. Model results often depend strongly on sea level and recharge rate. Both are expected to change in the future.