Oceanography

3.1.1.Tides -Introduction

Tides are produced by the attractions of the moon and sun on the waters of the ocean and are noticeable as a regular rise and fall of water. They occur in the ocean as progressive or standing long waves. Among all the oceanic long waves, tides are of maximum importance for people living near the sea shore and for those travelling the sea. Many activities like navigation shipping, reclamation of land from the sea, military operations, disposal of pollutants in coastal waters and fishing depend upon tides in the ocean. For safe navigation and shipping, it is necessary to know the tide levels and tidal currents at any moment for a particular harbor. Information about the water levels and about the currents is required for the construction of structures along the banks of tidal inlets, like drainage sluices for the removal of water from low-lying lands, dykes for the protection of the land against inundation and, jetties, wharves, piers, etc. For the design of these structures it is necessary to know the nature or extreme high tides and lowest water levels.

            The rise and fall of the tide is a contious phenomenon and varies from day to day and from place to place. Tides also differ in the character of the rise and fall. Tidal currents significantly increase the volume of the receiving waters at the outfall site; turbulence due to tide mixes the pollutants through the water column and the tidal current dramatically increases the rate at which pollutants diffuse horizontally, and in certain cases, tidal residuals can carry a pollutant away from the outfall site.

            Coastal fisheries are always influenced by tides. Some fish react to the tide in their biological cycle. Tides also influence the movement of intertidal organisms. Several fishing methods rely on tidal currents.