The sea and the tide

One of the fascinations of the seaside is the ebb and flow of the tide. As it goes out it leaves miles of wet sand to explore, little rock pools full of fascinating life from tiny crabs to feathery sea-weed. It is a paradise for children to explore, to dig channels and collect shells and pebbles.

The tide can be treacherous so always watch children very carefully and make sure they are back long before the tide begins to flow in. Along some coasts it comes rushing back very fast and it is easy for a small child to be swept away. In the open sea the flow of the incoming tide can be as much as one meter high (about three feet) but in inland seas, like the Mediterranean and the Black Sea, the effect of the tide is so negligible as to be hardly visible.

Low tide and high tide occur approximately twice in every 24 hours — at intervals of 12 hours and 25 minutes. The highest tides are always at full moon and when the moon is new. During the other two weeks of the moon's cycle the difference between high and low tide is reduced.

This is because the rhythmic rising and falling of the sea is caused by the gravitational pull of both the sun and the moon. And at full moon and new moon the moon and the sun are in a direct line so there is the double pull of both sun and moon.

The oceans are kept down by the force of gravity on the earth which is many times greater than the pull of the moon. But the moon has enough "pulling power" to draw the water masses slightly towards her from the side of the earth which is facing in the direction of the moon. The same surge is caused in the water masses on the other side of the earth by the fact that in its orbit round the earth the moon pulls the earth slightly away from its orbit round the sun. This causes a centrifugal force making the waters surge on the other side of the earth to the moon. The wide beaches of Norfolk are a fine example of tidal flats, especially in the small sailing resort of Blakeney where you can walk for miles when the tide is out, fording small channels left by the sea. A few miles out, beyond Blakeney Point, is Seal Island. Boats can only reach the island at high tide, when they can negotiate the narrow channel which leads up to the waterfront of the small resort. At high tide the island is pretty well submerged, but you can see the seals swimming about and, if you are lucky, a baby seal sunning itself on the beach at Blakeney point which also houses a wild-fowl reserve.

Walking the flats is a fascinating pastime, but unless you know the area go with a local guide. You will learn a great deal about the small animals and plants which live there and you will avoid any dangerous channels. The strength of the wind is measured by the Beaufort scale, internationally accepted. This also evaluates the condition of the sea and the height of the waves in meters.