What is saline water intrusion??

Question

What is saline water intrusion??

Answer 1

It means that salty water is moving into volumes that were previously occupied by fresh water.  

One example of this is the intrusion of salt water from San Francisco Bay into the aquifer in the East Bay.  As fresh water has been withdrawn from wells above the aquifer, salt water from the bay has moved into the spaces vacated by the fresh water. This is being treated by capturing rfresh unoff water in abandoned quarries so that it can percolate down into the aquifer.

Another example is the intrusion of salt water eastward from San Francisco Bay up the delta towards Sacramento.  One cause is the diversion for agriculture of fresh water from the rivers that feed into San Francisco Bay.  This problem will be exacerbated by rising sea level caused by global warming.