Typically, groundwater is flowing into the sea, direction results in a coastal area, salt water mass is under fresh water mass because fresh water is less density so it resembles the floating on the salt water mass.
Typically, the water will flow into the sea, resulting in coastal salt mass is the mass of fresh water because fresh water is less dense than it looks, mass floating on the water.
Groundwater flow direction usually have down towards the sea, resulting in a coastal estuarine under mass date ลน้ำ freshwater freshwater because less dense than the floating mass brine.