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Estuarine water circulation is controlled by the inflow of rivers, the tides, rainfall and evaporation, the wind, and other oceanic events such as an upwelling, an eddy, and storms. Estuarine water circulation patterns are influenced by vertical mixing and stratification, and can affect residence time and exposure time. ==Residence time== The residence time of water is a key variable determining the health of an estuary, particularly from human-induced stresses. Rapid flushing ensures that there is insufficient time for sediment accumulation or dissolved oxygen depletion in the estuary; thus a well flushed estuary is intrinsically more robust than a poorly flushed estuary.〔Wolanski, E. (2007) "Estuarine Ecohydrology." Amsterdam, The Netherlands: Elsevier. ISBN 978-0-444-53066-0〕 Residence time also affects other parameters such as heavy metals, dissolved nutrients, suspended solids, and algal blooms that may affect the health of estuaries.〔Balls, B.W. (1994) "Nutrient inputs to estuaries from nine Scottish East Coast Rivers: influence of estuarine processes on inputs to the North Sea." Estuarine, Coastal, and Shelf Science, 39, 329-352.〕 A simple way to calculate residence time is using a simple classic estuary model, which can be useful for acquiring a conceptual understanding of an estuary, but is coarse in time and space. A classic estuary has the following components: 1) freshwater inflow with a discharge Qf and a salinity Sf (generally Sf = 0); 2) oceanic inflow with a discharge Qin and salinity So; and 3) outflow to the ocean with a discharge of Qout and a salinity S1. The inflow and outflow of water is equal because mass is conserved. Salt is also a conserved, therefore, the inflow and outflow fluxes of salinity are also equal. If groundwater inputs and evaporation are ignored, the continuity equation is: :''Qin So + Qf Sf = Qout S1'' The residence time T is the volume of water within the estuary (Vol) divided by the flow rate of the river:〔 :''T = (Vol/ Qf )(1 - S1/ So - Sf / So)'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Estuarine water circulation」の詳細全文を読む スポンサード リンク
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