by Goutham Krishna
Tides are the long shallow-water waves generally found in the ocean and sea by the gravitational attraction of the moon, rotation of Earth and to a relatively lesser extent by the gravitational attraction of the sun. The imbalance between Earth’s centripetal force and the above-mentioned gravitational forces acting on Earth’s surface creates some residual forces in the Earth’s surface; the horizontal component of these residual forces pushes ocean water into two equal tidal bulges in the opposite sides of Earth. These bulges are accountable for the formation of tides.
The regular rise and fall of the ocean’s water are referred to as high and low tides. High tides happen when water covers most of the shore after rising to its highest level whereas the low tides are characterized by the retreat of water to its lowest level, moving away from the shore. The rotation of tidal bulges according to the change in the moon’s position is responsible for the phenomena of high and low tides. According to the occurrence of high and low tides on a lunar day, the tidal cycle can be divided into diurnal, semi-diurnal and mixed. A tidal cycle with two nearly equal high tides and low tides per lunar day is called a semi-diurnal tidal cycle, whereas a tidal cycle, one each high and low tides per day is called diurnal. A mixed tidal cycle is when two unequal high tides and low tides occur per lunar day.
India has a total coastline of 7516.6 km in total, with the mainland having 5422.6 km coastline. The Indian mainland can be divided into the east coast and west coast according to its geographical location, where the east coast is bounded on the east by the Bay of Bengal and the west coast is bounded on the west by the Arabian sea. Both east and west coasts of India experience two high tides and low tides per day, but the tidal cycle of the east coast is semi-diurnal whereas that of the west coast is mixed.
The forecasted schedule of high tides and low tides of Chennai coast, which belongs to the southeast coastal line of India is given below,
The role of tides in balancing and maintaining marine life and the ecosystem is pivotal. We can find numerous marine flora and fauna that are highly dependent on tides and tidal patterns for their survival. There are many fishes, which depend on the tides for their food. These fishes wait for the tides to wash smaller fishes into the sea or to pull them to the areas where food is abundant. The migratory and feeding patterns of many fishes are directly linked with the tides. Also, there are various seabirds that catch fish depending on the tides. Moreover, the phenomena of tidal pools; which are the isolated pockets of rocks and seawater found in the intertidal zones, can host diverse marine species and vegetation. But at low tide zones, these species are exposed to sunlight and predators at varying degrees.
Apart from these, tides are also important as they have the potential to become a regular energy generator in the near future. Tidal energy is naturally abundant and renewable and more importantly, is an emission-free energy source. Presently there are 8 operational tidal energy power stations in the world and many are under construction and planning. India is planning to build a tidal power station in the Gulf of Kutch and the project is now in its R&D (research and development) stage. Hence tides will be a trump card in the future, for building resilience against climate change and its after-effects.