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What are the four basic types of estuaries?
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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).
The four basic types of estuaries, classified by the process and extent of mixing between fresh water and seawater, are as follows:12
- Salt wedge estuary: Dominated by river discharge with negligible tidal effects, this type features a distinct layer of fresh water floating atop a wedge-shaped layer of seawater, with very little mixing between the two.2
- Partially mixed (or slightly stratified) estuary: Characterized by increased tidal effects, this system experiences significant turbulence that causes prominent mixing of fresh and salt water, resulting in a less distinct boundary than that of a salt wedge estuary.12
- Vertically homogeneous (or vertically mixed) estuary: In these systems, tidal currents are strong enough to produce total mixing, eliminating the boundary between fresh and salt water so that salinity remains constant vertically.12
- Fjord (or highly stratified) estuary: Typically formed by glaciers, these deep, narrow fjords feature a submerged ridge or sill at the mouth that restricts water exchange, often resulting in a basin of undiluted seawater at the bottom.132