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ESTUARY (from the Lat. aestuarium, a ...

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Originally appearing in Volume V09, Page 803 of the 1911 Encyclopedia Britannica.
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ESTUARY (from the See also:Lat. aestuarium, a See also:place reached by aestus, the See also:tide) , an See also:arm of the See also:sea narrowing inwards at the mouth of a See also:river where sea and fresh See also:water meet and are mixed, i.e. the tidal portion of a river's mouth. Structurally the estuary may represent the See also:long-continued See also:action of river erosion and tidal erosion confined to a narrow channel, most effective where most concentrated, or an estuary may be the drowned portion of the See also:lower See also:part of a river-valley. In a See also:map of See also:Britain showing sea-depths it will be observed that under the See also:Severn estuary the sea deepens in a number of steps descending by concentric V's that become blunter towards deep water until the last is a See also:mere indentation pointing towards the long narrow termination of the See also:present estuary. In this and in similar cases the progress of the estuary is indicated upon what is now the See also:continental shelf. The See also:chief See also:interest in estuarine conditions is the mingling of sea and fresh water. Where, as in the Severn and the See also:Thames, the fresh water meets the sea gradually the water is mixed, and there is very little See also:change in salinity at high tide. The fresh water flows over the See also:salt water and there is a continuous rapid change in salinity towards the sea, for the currents sweeping in and out mix the water constantly. Where the river brings down a See also:great quantity of fresh water in a narrow channel, the change of salinity at high and See also:low water is very marked. " When, however, the inlet is very large compared with the river, and there is no See also:bar at the opening, the estuarine See also:character is only shown at the upper end. In the See also:Firth of Forth, for example, the landward See also:half is an estuary, but in the seaward half the water has become more thoroughly mixed, the salinity is almost See also:uniform from See also:surface to bottom, and. increases very gradually towards the sea. The river-water meets the sea diffused uniformly through a deep See also:mass of water scarcely fresher than the sea itself, so that the two mix uniformly, and the sea becomes slightly freshened througtlout its whole See also:depth for many See also:miles from See also:land" (H. R.

See also:

Mill, See also:Realm of Nature, 1897).

End of Article: ESTUARY (from the Lat. aestuarium, a place reached by aestus, the tide)

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