Tide

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.

The main patterns in the tides are

• the twice-daily variation
• the difference between the first and second tide of a day
• the spring–neap cycle
• the annual variation

Tide changes proceed via the following stages:-

• Sea level rises over several hours, covering the intertidal zone; Flood Tide.
• The water rises to its highest level, reaching high tide.
• Sea level falls over several hours, revealing the intertidal zone; Ebb tide.
• The water stops falling and reached to lower level, reaching low tide.

Tides produce oscillating currents known as tidal streams. The moment that the tidal current ceases is called slack water or slack tide. The tide then reverses direction and is said to be turning. 

Slack water usually occurs near high water and low water. But there are locations where the moments of slack tide differ significantly from those of high and low water.

Tides are commonly semi-diurnal (two high waters and two low waters each day), or diurnal (one tidal cycle per day). 

The two high waters on a given day are typically not the same height (the daily inequality); these are the higher high water and the lower high water in tide tables. 

Similarly, the two low waters each day are the higher low water and the lower low water. The daily inequality is not consistent and is generally small when the Moon is over the equator.

Neap Tide:-

A tide that occurs when the difference between high and low tide is least; the lowest level of high tide. Neap tide comes twice a month, in the first and third quarters of the moon. 

Neap tides occur when the Sun,  moon, and earth form a right angle and the gravitational pull of the sun counteracts the pull of the moon.

Spring Tide:- 

Spring tides occur when the Sun and moon are directly inline with the earth and their gravitational pulls reinforce  each other.

Either of the two tides that occur at or just after new moon and full moon when the tide-generating force of the sun acts in the same direction as that of the moon, reinforcing it and 

causing the greatest rise and fall in tidal level. The highest spring tides (equinoctial springs) occur at the equinoxes.

The Tidal Force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force exerted by one body on another is not constant across it; the nearest side is attracted more strongly than the farthest side. Thus, the tidal force is differential.

Energy Studies:-

Tidal power, also called tidal energy, is a form of hydro power that converts the energy of tides into useful forms of power, mainly electricity. Although not yet widely used, tidal power has potential for future electricity generation. 

Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. 

Tidal energy can be extracted by two means:-

1.  Inserting a water turbine into a tidal current, or
2.  Building ponds that release/admit water through a turbine

In the first case, the energy amount is entirely determined by the timing and tidal current magnitude. However, the best currents may be unavailable because the turbines would obstruct ships. 

In the second, the impoundment dams are expensive to construct, natural water cycles are completely disrupted, ship navigation is disrupted. However, with multiple ponds, power can be generated at chosen times. 

Environmental Studies:-

Intertidal Ecology is the study of inter-tidal ecosystems, where organisms live between the low and high water lines. 

At low water, the intertidal is exposed (or 'emersed') whereas at high water, the intertidal is underwater (or 'immersed'). 

Intertidal ecologists therefore study the interactions between intertidal organisms and their environment, as well as among the different species. The most important interactions may vary according to the type of intertidal community. The broadest classifications are based on substrates — rocky shore or soft bottom.