Have you ever stopped to think why it is that the tide rushes up and down the beach twice a day causing inconvenience to all concerned? And it's not as if the tide comes in and goes out at set times of the day. It changes daily. In a predictable way, it is true, which is fortunate for those who work out our Tide Tables. The tide doesn't even rise and fall to set levels each day. It may expose a sand bank at low tide one week which couldn't be seen at low tide the week before.

 

The prediction of tides is vitally important for those working on the sea, fishermen, sea transport, ferry operators and so on. They need to know when there is maximum water available to access berths, cross the harbour, or to cast nets. And of course for those on holiday the tides make a great difference on how much beach is available on a given day, whether it is safe to go swimming and, for the more experienced, what type of wave will be best for watersport at a certain stage of the tide.

 

Tides are caused by the gravitational force of the moon and sun. The sea, being liquid, is pulled out towards the sun or the moon. The actual bulge of water occurs on the side of the planet exposed to the gravitational force, and on the opposite side of the planet. The earth spins around relative to the moon in 24 hours and 50 minutes, the lunar day. Consequently to fit in our 24 hour (solar) day, the tide time alters by 50 minutes per day at any given spot - or thereabouts, depending on the different coastal currents in operation. So if high tide at Eastoke one Wednesday is at 11 a.m., on the Thursday it will be at round about 11.50 a.m.

 

The reason we have a difference in the height of the tides, ranging from a series of relatively limited differences in tidal range between low and high water (known as neap tides), and very much greater differences, known as spring tides, is dependant upon the alignment of the sun and moon. When the sun and moon are directly in line with the earth, the combination of their gravitational pull creates a bigger bulge resulting in higher high and low tides. When the moon is in its first and last quarter, the sun and moon are pulling in different directions and the bulge and hence tidal range is less. There is therefore a 28 day cycle of spring and neap tides which are most pronounced at the equinoxes in March and September.

 

Because of this rhythmic cycle it is possible to predict with accuracy the times and heights of tides many years in advance. However there will always be local conditions, mainly due to the weather, which will change the predicted time and height. When the height of the tide is greater than predicted this is known as a 'surge' and it is these 'surges' which may cause flooding problems if they coincide with gales or heavy rain.