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Why does stronger river flow create a greater salinity gradient in an estuary?

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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).

Stronger river flow creates a greater salinity gradient in an estuary because it inhibits the mixing of fresh water and seawater.

In systems dominated by significant fluvial activity, the high volume of freshwater discharge acts as a barrier that restricts the landward penetration of seawater. Because the river flow prevents the two water types from blending effectively, the boundary between them remains distinct, resulting in a sharper, more pronounced transition in salinity levels between the riverine and marine environments. Conversely, in estuaries where river flow is weak, tidal forces generate more turbulence, which promotes greater mixing and reduces the salinity gradient.12