Saltwater intrusion
Saltwater intrusion can naturally occur in coastal aquifers, owing to the hydraulic connection between groundwater and seawater.
Sea level rise caused by climate change also contributes to saltwater intrusion.
[4] The higher pressure and density of saltwater causes it to move into coastal aquifers in a wedge shape under the freshwater.
The saltwater and freshwater meet in a transition zone where mixing occurs through dispersion and diffusion.
Ordinarily the inland extent of the saltwater wedge is limited because fresh groundwater levels, or the height of the freshwater column, increases as land elevation gets higher.
Groundwater is the main source of drinking water in many coastal areas of the United States, and extraction has increased over time.
[5][6] Groundwater extraction can also lead to well contamination by causing upwelling, or upcoming, of saltwater from the depths of the aquifer.
[7] Under baseline conditions, a saltwater wedge extends inland, underneath the freshwater because of its higher density.
Some aquifers are predisposed towards this type of intrusion, such as the Lower Floridan aquifer: though a relatively impermeable rock or clay layer separates fresh groundwater from saltwater, isolated cracks breach the confining layer, promoting upward movement of saltwater.
Pumping of groundwater strengthens this effect by lowering the water table, reducing the downward push of freshwater.
Canals provide conduits for saltwater to be carried inland, as does the deepening of existing channels for navigation purposes.
Additionally, channel dredging in the surrounding wetlands to facilitate oil and gas drilling has caused land subsidence, further promoting inland saltwater movement.
Saltwater intrusion in southeast Florida has occurred largely as a result of drainage canals built between 1903 into the 1980s to drain the Everglades for agricultural and urban development.
There are many solutions developed to prevent or reduce the negative effects of Seawater intrusion.
[10] Many coastal communities around the United States are experiencing saltwater contamination of water supply wells, and this problem has been seen for decades.
[2][14] In some areas such as Washington State, intrusion only reaches portions of the aquifer, affecting only certain water supply wells.
Other aquifers have faced more widespread salinity contamination, significantly affecting groundwater supplies for the region.
[6] The first physical formulations of saltwater intrusion were made by Willem Badon-Ghijben [pt] in 1888 and 1889 as well as Alexander Herzberg [de] in 1901, thus called the Ghyben–Herzberg relation.
[15] They derived analytical solutions to approximate the intrusion behavior, which are based on a number of assumptions that do not hold in all field cases.
[17] As groundwater salinization becomes a relevant problem, more complex initiatives should be applied from local technical and engineering solutions to rules or regulatory instruments for whole aquifers or regions.
