Britannica Sources used in this answer

Why does the salt wedge extend farther upriver during low river flows?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram showing four main types of estuaries: salt wedge, partially mixed, vertically homogeneous, and fjord. Each panel illustrates river and seawater mixing patterns, with arrows indicating the direction of saltwater and freshwater flow. — estuary Four main types of estuaries: (A) salt wedge estuary, (B) partially mixed estuary, (C) vertically homogeneous estuary, and (D) fjord (black arrows indicate salt water and white arrows fresh).

In a salt wedge estuary, the position of the salt wedge is determined by the balance between river discharge and the intrusion of seawater. Because river discharge acts to push seawater out of the estuary, the strength of the river flow directly influences how far the salt wedge can penetrate inland.

During periods of low river flow, the reduced volume and velocity of freshwater allow the denser seawater to push further upstream, causing the salt wedge to extend farther upriver. Conversely, during high-flow or flood conditions, the increased force of the river discharge pushes the wedge back toward the sea.12