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Insight into marine science


Insight

Insight topics

Questions answered

Local topics

Schools & Careers

Tides

Observatory history

Useful links

Insight
Schools and careers
Insight topics
Tides
Questions answered
Observatory history
Useful links
Local topics





Apollo 8 photo of the Earth.

Tides
Tides are the alternating rise and fall of the surface of the seas and oceans. They are due mainly to the gravitational attraction (pull) of the moon and sun on the rotating earth. Two high and two low tides occur daily around Britain and, with average weather conditions, their movements can be predicted with considerable accuracy.

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Related links
Questions answered - includes questions and answers about tides.


The Doodson-Légé Tide Predicting Machine
Tides have been predicted at the Proudman Oceanographic Laboratory, Bidston Observatory, since 1924, firstly by hand and then by the early tide predicting machines.

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Online tidal predictions
As host to the National Tidal Facility online tidal predictions for standard browsers and for Wireless Application Protocol (WAP) phone versions can be obtained free of charge and for you to bookmark.

Related links
UK National Tidal & Sea Level Facility
POL online tidal predictions
UK Tide Gauge Network
Permanent Service for Mean Sea Level





The Qiantang Bore from the left bank.

Tidal river bores
In most tidal rivers the change from ebb to flood is a gradual process. The ebb current downstream slows, there is a period of slack water and then very slowly the flood tide starts flowing upstream. In a few rivers however, the behaviour is remarkably different. The onset of the flood tide is marked by a distinct and sometimes very vigorous wave - a bore.

The largest example of a river bore in the UK is the Severn Bore. Although large in UK terms it is dwarfed by the largest river bore in the world, found in China - The Qiantang Bore.

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Related links
Local bores to Merseyside


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