High and Low Tides off the Coasts of Europe

What Tides Are. People living near the coast can daily witness the advancing and receding of the water. This periodic and alternate rise and fall of the surface of the ocean and sea is called tides.

Fig.11 High tide. The high water-level makes it possible for ships to approach the shore.

the water rises, flooding the low-lying coasts. Low tides last a little over six hours, too, during which the water falls, leaving bare the coastal areas of the sea-floor (Figs. 11 and 12).
The tidal wave is especially high (16 to 18 metres) in gulfs which are open to the ocean, and in estuaries. In the open ocean and in in­land seas connected with the ocean by narrow straits, tides are so slight as to be unnoticeable. Off the European coasts of the U.S.S.R. the tides are highest in the northern part of the White Sea, reaching a height of 10 metres.
Tides are caused by the attraction of the Moon, and to a lesser degree, of the Sun.

Fig. 12. Low tide.
The water has receded from the shore, leaving bare the rocks and sand. The in­habitants are collecting seaweeds and small creatures left stranded by the sea. A ship is at anchor far from the coast.

The Sun is much larger than the Moon but, owing to the fact that it is so much farther from the Earth, its tide-raising effect is much weaker.
The Importance of Tides. Tides are a factor to be considered in shipping. Some harbours can be entered by ships during high tide only. The tidal wave, by raising the water-level in estuaries, makes it possible for ships to travel farther up rivers than would otherwise be the case. Thus, in Great Britain during high tides, ships can travel up the Thames as far as London, 64 kilometres from the sea. The rise and fall of tides deepen estuaries and help to keep them free from silt. In places where the tidal wave is exceptionally high (in the gulfs off the north-western coast of France, for instance) it is planned to construct big electric power-station, utilizing the tremendous power of the tides.