When does saltwater typically intrude into freshwater aquifers?

Saltwater typically intrudes into freshwater aquifers primarily when groundwater is extracted heavily. This phenomenon occurs because excessive pumping of freshwater can lead to a decrease in the hydraulic pressure within the aquifer. As a result, the natural balance between the saltwater and freshwater interface can be disrupted, allowing saltwater from nearby bodies of saltwater, such as oceans or estuaries, to move inland and mix with the freshwater.

The intrusion of saltwater into aquifers is a significant concern, especially in coastal areas where freshwater supplies are in close proximity to saline environments. When groundwater extraction reduces the freshwater pressure, the denser saltwater can seep into the aquifer, leading to contamination of the freshwater resource. Thus, sustainable groundwater management practices are essential to prevent such occurrences and ensure the long-term viability of freshwater supplies.

In contrast, heavy rainfall events can temporarily recharge aquifers and increase freshwater levels, which helps to maintain the pressure needed to prevent saltwater intrusion. Similarly, when groundwater levels are high, this often indicates a balanced system that can ward off intrusion. Seasonal factors, such as winter months, do not have a direct impact on the processes driving saltwater intrusion when compared to heavy groundwater extraction.