An arrested salt wedge estuary is one of four principal types of estuaries as distinguished by prevailing flow conditions.
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This is a type in which there is a relatively stationary interface between an underlying stable salt wedge of sea water and an overlying strong flow of fresh river discharge to the sea. As a result the salinity stratification is extremely strong with an underlying layer of marine saline water, and a surface layer of brackish water. In this regard the salinity stratification most closely resembles that of a fjord, compared to the other two types of estuaries: drowned river valleys and deltaic estuaries.
The quantitative measure of salinity differential of the upper (freshwater efflux to the sea) and lower (marine influx to land) typically ranges from two to ten parts per thousand of salinity.
Types of Estuary
A general definition of an estuary is a semienclosed and coastal body of water with free communication to the ocean; and, within which ocean water is diluted by freshwater derived from land. (e.g., Cameron and Pritchard). Based upon water column stratification or salinity vertical structure, estuaries can
be classified (Valle-levinson) as:
- salt wedge
- strongly stratified
- weakly stratified
- vertically mixed
Examples of arrested salt wedge estuary
A classic example of an arrested salt wedge estuary is the mouth of the Columbia River separating Oregon and Washington in the northwest USA. The powerful discharge of the Columbia overwhelms the ability of the freshwater discharge to mix completely. The explorers Lewis and Clark were the first to document the powerful flow of the Columbia mouth, when their rafts were hopelessly unmaneuverable and they required rescue by Native Americans, who were familiar with the navigation techniques required in this fast moving surface flow estuary.
- Cameron, W. M. and D. W. Pritchard. 1963. Estuaries. In M. N. Hill (editor): The Sea vol. 2, John Wiley and Sons, New York, 306 - 324.
- Clinton J. Dawes. 1998. Marine botany. John Wiley and Sons. 480 pages
- Valle-levinson, A. 2010. Definition and classification of estuaries, In Contemporary Issues in Estuarine Physics, Edited by A. Valle-Levinson. Cambridge University Press. ISBN:9780521899673
- Physical Oceanography Index