Spring and Neap Tide height over 6 hour period
Monthly Cycle for the River Tyne (sept 2001)
Tide height every hour on beach
Ok you've bought your tidetable from your tackle shop (some give them away free so shop around) and you want to know what the numbers mean. Every day we have 2 high tides and 2 low tides. In the tables the times are nearly always given in the 24 hour format. The tide height at that time is usually given in metres. From low to high takes roughly six hours. The difference in height between high and low water is called the tidal range. Spring tides give the greatest rise and fall, while neap tides produce the smallest.
| The tide does not rise at a constant rate but we experience slack water around high and low and tidal runs in between. As a guide it will rise 1/12 the tidal range the 1st hour an additional 1/6 the 2nd, a 1/4 the 3rd, a 1/4 the 4th, 1/6 the 5th and finally 1/12th. Hence the tidal runs are strongest during spring tides. Using this guide a useful tide chart can be produced to determine the height and strength of the tide at any given time. |
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| Both the gravitational pull of the sun and moon effect the tides. During the full moon and new moon the combined pull produces spring tides. Neap tides occur during the first and last quater. This is why many anglers use the moon as a guide to when to fish. Knowing the difference between spring and neap tides is important because some marks can only be reached during spring tides. At high water during neap tides the depth may be too shallow. |
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| Tides rise and fall vertically.and as they do the water flows over the beach. How far the tide comes in depends on the gradient of the beach. This is why on beaches with small gradients the tide often seems to go out for miles at low tide and comes in very fast. The best example of this is the causeway between Lindisfarne (Holy Island) and the mainland where it's guaranteed at least one idiot will lose his car every year. |
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The height given in the tidetable is always based on a specific local spot this varies around the country. Although it is spring/neap everywhere the tidal range for different locations can be considerable. This is why it is better to obtain a local tide table when going on holiday rather than relying on the add/subtract minutes guide found in most tide books.
Local tidetables are often displayed in tackle shops or around harbours.
Tide height can also be affected by wind direction, atmospheric pressure, siltation etc.
And finally a warning about internet tidetables and charts. It is surprising how many don't agree when you compare them. I suspect this is due to bad programing or using the add/subtract minutes method. Many people when plotting tide charts ignore the 1/12, 1/6, 1/4, 1/4, 1/6, 1/12 guide and just type in the days high and low waters into excel and let their computers plot the graph. This method is miles off and ignores both slack water and tidal run. If you want to make sure do it yourself. If buying or downloading tidal prediction software check it against a reliable tidetable.
Alternatively download this excel file which calculates the height at each hour from low to high or high to low and plots a graph. This is very useful in determining when different rock marks will become accessable as the tide falls. For example if you know that the water has to drop to 1.5 m before a mark is revealed by the ebbing tide the graph will tell you when this will be.
DOWNLOAD FREE TIDEPLOTTER EXCEL FILE...18kb