What is the usefulness of Ocean Tides?

Every 24 hours, the waters of the ocean rise and fall alternately. This alternate rise and fall in the sea level is known as ‘tide’. The rise of the sea level is called high tide or ‘flow’ and at its lowest point, it is called low tide or ‘ebb’. Tides are caused by the gravitational pull of the moon and to a lesser extent by the pull of the sun on the Earth.

As the moon resolves around the Earth, it exerts a certain amount of force on the Earth’s surface. The land surface, being solid, is not affected, but the ocean waters get drawn towards the moon. Simultaneously on the Earth’s surface facing away from the moon, water swells up away from the Earth. This happens due to the Earth’s rotation. At the same time, the other regions are having low tides.

Twice a day as the tides move up, seawater rushes into the mouths of rivers and the water level along the coast rises up. Twice a day the water recedes far back into the oceans. This happens to a greater extent on full moon (purnima) and new moon (amavasya) days when the sun is aligned with the moon. This is known as ‘Spring Tide’ when the high tide is higher than usual and the low tide is lower than usual.

Alternatively during the first and third quarters of the moon when the moon and the sun from a right angle, the high tide is lower than usual and the low tide is not as low as usual. This is called the ‘Neap Tide’.

Tides are useful in many ways:

I. Tides are a great help in navigation. During high tide when the water level rises, large ships can enter or leave the harbor safely. Diamond Harbor in West Bengal and Kandla in Gujurat are examples of such ports.

II. Tides help ships to travel up the mouth of the river. High tide increases the volume of water at the river ports to such an extent that large ships can sail in safely. They use the retreating tide to leave the port. Hooghly (Kolkata), London and New York are some of the important river ports of the world.

III. Rivers wear away and carry down a lot of soil and sand. These get deposited at the mouth of the rivers when they have lost their force. Tides wash away these deposits and help to keep the mouth of the river clear.

IV. Salt water freezes at a temperature lower than that of fresh water. In cold regions where as the rivers are often frozen in winter, the warmer seawater rushes in to keep the harbors free from freezing.

V. Tidal energy is largely being harnessed to produce electricity. Dams have been built, which get filled up during high tide and this water is used to produce hydroelectricity.