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| − | {{revision}} | + | {{Definition|title=Tide |
| | + | |definition= The periodic rise and fall in the level of the water in oceans and seas as a result of gravitational attraction of the sun and moon and the rotation of the earth.<ref> CIRIA (1996). ''Beach management manual'', CIRIA Report 153.</ref>.}} |
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| − | Tides are the longest of oceanic waves. So long, that we often only observe them as a rise and fall of sea level over a period of several hours. However, a good understanding of tides and tide generated currents is important for all areas of [[ICZM]]. Together with waves, tides play an extremely important part in coastal processes, geomorphology, flood risk, species zonation and water quality.
| + | A more general definition from a geophysical viewpoint is |
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| − | The aim of this article is to present a broad overview of tides, for the generalist, with links to more specific articles for those who are interested.
| + | {{Definition|title=Tide (more general) |
| | + | |definition= A tide is a distortion in the shape of a body induced by the gravitational pull of another nearby object.<ref> Morrison & Owen (1996). "The Planetary System", Addison-Wesley. </ref>.}} |
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| − | == Introduction ==
| + | The term 'tide' in the Coastal Wiki refers to the first definition. |
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| − | It is worth mentioning two definitions of tides. Within coastal science, tides are often taken to be:
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| + | ==Notes== |
| − | Definition|title=Tide
| + | The tide (more precisely, the '''astronomical tide''') is the large-scale water motion generated by the rotation of the earth in combination with the varying gravitational influence on the ocean of celestial bodies, especially the moon and the sun. These phenomena cause predictable and regular oscillations in the water level, which are referred to as the tide. The astronomical tide at a specific location can be predicted and is published in Tidal Tables. |
| − | |definition= The periodic rise and fall in the level of the water in oceans and seas; the result of gravitational attraction of the sun and moon.<ref> CIRIA (1996). ''Beach management manual''. CIRIA Report 153.</ref>.}}
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| − | However, we should never lose sight of the astronomical perspective:
| + | The term 'tide' is sometimes used for the combined effect of astronomical tide and wind-driven set-up or set-down of the sea level (including [[#Storm surge|storm surges]]). |
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| − | {{
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| − | Definition|title=Tide (more general)
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| − | |definition= A tide is a distortion in the shape of one body induced by the gravitational pull of another nearby object.<ref> Morrison & Owen (1996). "The Planetary System".</ref>.}}
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| − | The tides of our planet display extremely complex behaviour. For example, in the Mediterranean, the [[tidal range]] is very small (<1m), whereas in the Bay of Fundy, Canada, the shape of the bay augments the [[tidal range]] to over 15m. In Europe, the biggest tides can be found in the Severn estuary (~12m) in the UK and near Mont Saint Michel, in France. Tides in many parts of the world (eg. English Channel) can be described as semi-diurnal (occurring twice a day), while some tides are purely diurnal (once a day) as evident in parts of the Mediterranean. [[Tidal resonance]] can produce strange behaviour, for example, on the south coast of the UK, Southampton Water famously exhibits two high waters, approximately 30mins apart.
| + | ==Related articles== |
| | + | :[[Ocean and shelf tides]] |
| | + | :[[Tidal motion in shelf seas]] |
| | + | :[[Coriolis acceleration]] |
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| − | The importance of tides in the coastal zone is often in the currents they generate, which can reach speeds of up to ?????m/s (Severn estuary). The rising tide is usually referred to as the flood, whereas the falling tide is called the ebb. The [[tidal currents]] of the ebb and flood play a major part in shaping our coasts, transporting large volumes of [[sediment]] and moulding [[estuarine|estuary]] environments.
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| − | In contrast to the majority of coastal processes, the tides can be predicted with very good accuracy, for as much as 200 years into the future. However, there is sometimes a difference between the observed and predicted tide, due to weather induced effects such as the [[storm surge]].
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| − | == Theory of tides ==
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| − | Sir Isaac Newton (1642-1727) was the first to suggest that the planets produced the tides on earth, through their mutual gravitational pull. Astronomical tides are those tidal movements which are governed by the planets. The tide-generating forces can be precisely calculated through the motion of the planets ([[the equilibrium theory of tides]]), and the response of the oceans to these forces is modified by the effects of topography ([[the dynamical theory of tides]]) and by the transient effect of passing weather patterns ([[storm surge]]s).
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| − | ==Introduction to the equilibrium theory==
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| − | The Earth and the Moon revolve around each other (around a common centre of mass) with a [[period]] of 27.3 days.
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| − | The tidal range is largest just after a full or new moon.
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| − | The magnitude of the Sun’s tide producing force is about 0.46 that of the Moon, because, although enormously greater in mass than the Moon, the Sun is some 360 times further from the Earth. <ref???> The solar tide has a semi-diurnal period of 12 hours.
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| − | ==Introduction to the dynamical theory of tides==
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| − | Kelvin wave
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| − | Cotidal and corange lines. Figure
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| − | Amphidromic point
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| − | ==Terminology==
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| − | Admiralty charts provide useful information on the bathymetry of a coastal area, as well as tidal range and frequency.
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| − | ODN / Ordnance Datum Newlyn
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| − | Admiralty Chart
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| − | CD / Chart Datum
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| − | HAT
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| − | LAT
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| − | MHWS
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| − | MHWN
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| − | MLWS
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| − | MLWN
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| − | ==The frequency of tides==
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| − | - Spring neap cycle
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| − | - Nodal? cycle
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| − | semi-diurnal
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| − | diurnal
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| − | ==Tidal measurement==
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| − | Tide gauge
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| − | Data sets
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| − | ==Tidal prediction==
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| − | Since we can predict the movement of the planets to extremely good accuracy, we can use this to predict the tides.
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| − | -harmonic analysis
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| − | Tidal constituents
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| − | ==Tidal currents==
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| − | Tidally generated bedforms
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| − | tide dominated coasts
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| − | ==Tides in estuaries==
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| − | estuary evolution
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| − | estuary hydrodynamics
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| − | stratified estuaries
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| − | partially-mixed estuaries
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| − | well-mixed estuaries
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| − | halocline
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| − | salt-wedge estuaries
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| − | coriolis force
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| − | flood-dominant estuaries
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| − | ebb-dominant estuaries
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| − | bar-built estuaries
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| − | drowned river valleys
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| − | rias
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| − | fjiords
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| − | Tidally generated bedforms
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| − | intertidal
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| − | ==Related topics==
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| − | Tidal power
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| − | Internal tides
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| − | Navigation
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| − | Intertidal and biology
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| − | tidal bore
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| − | The equilibrium theory of tides
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| − | Tide producing forces vary directly with the mass of the attracting body, but are inversely propoertional to the cube of its distance from Earth.
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| − | The dynamical theory of tides
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| − | ==See also==
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| − | Definitions related to tides are: [[tidal current]], [[tidal flat]], [[tidal wave]], [[astronomical tide]], [[highest astronomical tide]] (HAT), [[lowest astronomical tide]] (LAT), [[mean high water springs]] (MHWS), [[mean high water neaps]] (MHWN), [[mean high water]] (MHW), [[mean low water]] (MLW).
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| − | For more definitions of coastal terms and a sketch, see [[Definitions of coastal terms]].
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| − | An article related to tides is: [[waves]].
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| | ==References== | | ==References== |
| | <references/> | | <references/> |
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| − | Article by
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| − | |AuthorID=18394
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| − | |AuthorFullName=Somerville, Tracy
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| − | |AuthorName=Tracy}}
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| − | [[Category:Help]]
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