• INS Sandhayak, the Indian Navy’s oldest hydrographic survey vessel, was decommissioned at the naval dockyard in Visakhapatnam on June 4 after serving the nation for 40 years.

• The ship was commissioned to the Indian Navy on February 26, 1981.

• INS Sandhayak, during her 40 years of illustrious service, undertook over 200 major hydrographic surveys in the Western and Eastern coasts of the Indian peninsula, the Andaman Sea and in neighbouring countries, including Sri Lanka, Myanmar and Bangladesh.

• The ship also took part in important operations like ‘Operation Pawan’ in Sri Lanka, 1987, ‘Rainbow for Humanitarian Assistance’ in the aftermath of the tsunami in 2004 and the maiden Indo-US HADR (humanitarian assistance and disaster relief) Exercise ‘Tiger-Triumph’ in 2019.

What is hydrography?

• Hydrography is the branch of applied sciences that deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the primary purpose of safety of navigation and in support of all other marine activities, including economic development, security and defence, scientific research and environmental protection.

• In addition to supporting safe and efficient navigation of ships, hydrography underpins almost every other activity associated with the sea, including:

• Resource exploitation (fishing, minerals)

• Environmental protection and management

• Maritime boundary delimitation

• National marine spatial data infrastructure

• Recreational boating

• Maritime defence and security

• Tsunami flood and inundation modelling

• Coastal zone management

• Tourism

• Marine science.

What is the significance of hydrographic survey?

• In the past, many artisanal shelters and fishing ports were built at convenient locations, with no particular attention paid to such environmental factors as wave heights, sudden changes in water depths, uncharted reefs, currents, tidal streams, seaweed and mobile beaches (sand drift).

• Many of the structures were subsequently expanded and, in countless cases around the world, many of the problems that used to be considered minor have now developed into major ones, with some shelters, for example, fouling up with seaweed or silting up (shelter mouth facing the wrong direction) or just being inaccessible in rough weather (reefs too close to entrance channel).

• A hydrographic survey, also known as a bathymetric survey, is therefore essential if the correct design decisions are to be made right from the project inception stage to ensure that the landing is easy to use and free of major maintenance problems under all conditions.

• Hydrographic surveys are required for a wide variety of purposes, ranging from simple reconnaissance (at project formulation, for instance) to payment for work carried out underwater, such as dredging or reclamation.

• The results from a hydrographic survey are normally plotted to produce a bathymetric contour map, which is a plan of the depth of the sea bed arranged in such a manner as to show lines of equal depth from the coastline.

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