Controlling and Managing Saltwater Intrusion

Controlling and Managing Saltwater Intrusion

One key to controlling saltwater intrusion is to maintain the proper balance between water being pumped from an aquifer and the amount of water recharging it.  Constant monitoring of the salt-water interface is necessary in determining the proper management technique.  In the past, many communities who came across a saltwater intrusion problem simply set up new production wells further inland.  This only complicated the issue.

Since then, various methods have been employed to help alleviate the concerns of saltwater intrusion.  Efforts towards the promotion of water conservation, and restricting withdrawals from coastal aquifers have been the focus in many areas.  Using alternative freshwater sources has also been encouraged.  Ocean water desalination plants are showing up in coastal regions around the world.

Where there are no other options for fresh water, efforts to maintain groundwater levels by ponding surface water and stormwater runoff, or using river water to recharge the groundwater table have been successfully implemented.  Aquifer Storage and Recovery (ASR) systems can help restore aquifers that have experienced long-term declines in water levels due to over-pumping.

Deep recharge well creates groundwater ridge.

Other methods to control saltwater intrusion, such as using deep recharge wells, have also been successful.   These wells create a high potentiometric surface, which allows for the pumping of groundwater below sea level landward of a groundwater ridge created. In some instances, barrier wells have been set up near the shore to pump out salt water and recharge a fresh water gradient toward the sea.

In all of these cases, hydrologic studies and water quality monitoring are essential to help better understand the movement and interaction of fresh water and salt water in the subsurface, and determine the best method to manage saltwater intrusion.  Potentiometric surface mapping of an aquifer can provide important information determining the direction of groundwater flow within a confined aquifer.  Plotting water level elevations on a map and contouring the results determines this.  The contoured surface is known as the potentiometric surface, which is actually a map of the hydraulic head in the aquifer.

Monitoring well networks allow continuous observation of the saltwater interface, after management strategies have been put in place.  This provides early warnings of saltwater intrusion and tracks the effectiveness of the strategy.  Overall, proper groundwater monitoring techniques and groundwater management, combined with groundwater conservation are needed to keep saltwater intrusion under control, and ensure fresh water supplies are sustained for future generations.