Tides

An Introduction to tides...

THE tide is an important part of diving as if you do not get the tide times correct you could be in trouble!

Tides are the regular rising and falling the ocean's and sea's surface caused by changes in gravitational forces external to the Earth.   This  rhythmic movement of the rise and fall of the surface (or water level) must be calculated before setting off on a day out.   It is coursed by the changing gravitational field of the Moon which push and pulls the Earth's surfaces,  while the secondary gravitational field of the Sun course the same effect.  

The gravitational fields pushes and pulls the seas and oceans.  This effect moves the water on the Earths surface around creating a bulge of water that creates the high tide and the low tide.    

To find out the time and water levels of different tides, you can use tide tables for your area.   Tide heights are never the same from one location to another.    The period of high water level is known as high tide and the period of low water level is known as low tide, but tide times do not include all meteorological effects and geological effects, so check the weather.

Tide Terms

High Tide = High tide is the time of high water.   High tides occur when the gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon.

Low tide   = Same as low water.   The minimum height reached by a falling tide.   The low tide is due to the periodic tidal forces and the effects of meteorological, hydrological, and/or oceanographic conditions.

Flood Tide = A none technical term used for rising tide or flood current. In technical language flood refers to current. The portion of the tidal cycle between low water and the following high water.

Spring Tide = The tide with the most variation in water level, occurring during new moons and full moons. This is the time of the highest high tide and the lowest low tide. The opposite of a neap tide.

Neap Tide = This is an especially low tide that occurs when the angle between the direction of the Moon and the direction of the Sun is 90°.

Ebb Tide =  This is a tide that lowers the water surface of an ocean or the sea and moves the shoreline farther seaward.

Diurnal Tide = This is a daily tide that happens only once a lunar day (intervals of 24 to 27 hours).   It is coursed by tidal variations in sea level, which increase with lunar or solar declination north and south of the equator. When added to semidiurnal tides they can cause a diurnal inequality. 

Storm Tide =  This is can be a deadly combination of a storm surge, the normal astronomical tide, and wave setup.   If the storm surge arrives at the same time as the high tide, the potential risk of flooding  can be great.   An additional threat at this time could come from the presence of very high waves that can course severe danger to the coast and the people living along the coast as well as shipping in inshore waters or moored up.   Not a good idea to go out for a dive if you hear this on the forecast, get your serf board!

Things to do before setting off.

WHEN going out to sea check to make shore you apply the correct tidal difference (add or subtract) for the area you are going into.   

EXAMPLE to calculate High Water Aberdovey 30 April 2003

1. High Water Liverpool 03:24hrs

2. Add hour for BST 04:24

3. Subtract 3:00 hours.

4. 04:24 -3hrs=01:24hrs

Note:- that the above is only intended as a guide and is not authorative. Miscalculating tides can be dangerous in certain circumstances, if in any doubt check local experts before departing.

Remember

Predictions of tide heights DO NOT include meteorological effects, like Storm Tides!   Often the heights use these as abbreviations to say high water and low water.   HW = high water & LW = low water.

Link to tide times URL = www.nbi.ac.uk/ntslf/tides/

Added note...   What is a red tide?

A Red Tide is not the same as a tide tide, but we thought we would add it anyway.  We will stress that this term has no connection with astronomical tides   This is a term this is applied to toxic algal blooms.     It is caused by several genera of dinoflagellates (Gymnodinium and Gonyaulax) that turn the sea red in colour and are frequently associated with a deterioration in water quality.   The colour occurs as a result of the reaction of a red pigment, peridinin, to light during photosynthesis by the algal.  These toxic algal blooms pose a serious threat to marine life and are potentially harmful to humans.

Design Copyright © Patrick Trollope 2006.