Estuary Classification
The hydrographic and morphologic characteristics of estuaries are very diverse, varying with changes in response to natural and non-natural phenomena as climate changes and human interference, and often show conflicting situations that make oceanographic
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Estuary Classification
The hydrographic and morphologic characteristics of estuaries are very diverse, varying with changes in response to natural and non-natural phenomena as climate changes and human interference, and often show conflicting situations that make oceanographic generalizations impossible. Until sixty years ago, studies of these environments interpreted such variations as local phenomena. Estuary classification criteria were developed with the aim of comparing different estuaries by categorizing them, using a database of their main characteristics. The known estuary classification schemes are based on salinity-stratification, river discharge, circulation and mixing and they allow the main characteristics an estuary’s circulation and mixing processes to be forecast. The first estuary classification was suggested by Stommel (1951), taking into account the main forces such as tides, fresh water discharge and wind. The estuaries in the USA, which are formed by the Raritan, Pamlico Sound and Mississippi rivers in the states of New Jersey, North Caroline and Lousianna have tide, wind and river discharge, as primary forcing, respectively. The remarkable characteristic of those estuaries is the vertical salinity stratification. The Raritan estuary, which is the shallowest, is forced by tides of moderate height and is almost vertically homogeneous. The Mississippi estuary, which is the deepest, is forced by micro-tides and is the most stratified due to the huge river discharge of the Mississippi river into the Gulf of Mexico characterized by microtides. However, in most estuaries, it is difficult to identify a single force that predominates the circulation and mixing processes. Estuaries forced by tides were the most studied type of estuary in the 1950s. They were characterised by tidal generate velocities which were more intense than velocities generated by river discharge. The most noticeable difference between the
© Springer Nature Singapore Pte Ltd. 2017 L. Bruner de Miranda et al., Fundamentals of Estuarine Physical Oceanography, Ocean Engineering & Oceanography 8, DOI 10.1007/978-981-10-3041-3_3
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3 Estuary Classification
three previously mentioned estuarine types is the vertical salinity stratification, the most extreme case being the vertically homogeneous Raritan river estuary, with a mean depth of only 3 m. One of the classical classification criteria was developed taking into account geomorphologic characteristics (Pritchard 1952a), which grouped estuaries into the following types: coastal plain (formed due to the river valleys flooding), fjord and bar built. The density (salinity) variations in estuaries that generate currents due to the mixing of the fresh and salt water, motivated Stommel (1953) to examine the physical characteristics of estuaries using the following examples: estuaries with negligible mixing (salt wedge), deep estuaries (such as fjords), and estuaries with moderate and intense mixing. These classification systems received improvements through the work of Pritchard (1955) and Came
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