4. The Data Base

4.1. Physiography – General description

The proposed canal passes through the Adam’s Bridge and the Palk Bay. The structure and function of the Adam’s Bridge and the Palk Bay are influenced by the ocean dynamics of the Gulf of Mannar (which is an extension of the Indian Ocean (IO)) and the Bay of Bengal. Palk Bay, Adam’s Bridge and the GOM are bound in east and west by the Sri Lankan and Indian Peninsular land masses.

Adam’s Bridge is 31 km long with an average depth range of less than 5meters. It extends between the Rameshwaram and the Mannar islands. It is a formation of shallow ridge of Holocene conglomerate and sandstone mantled with islands (17 in number) and shoals of shifting sand, which is all resting upon Miocene limestone. (Cathcart, 2003). The average length of these islands is 0.8 km to 3 km. The total length of islands and shallows of this area is around 9km. The remaining 22 km stretch is open water.

Palk Bay has a width ranging from 57 km (Palk Strait) to 107 km (Thiruppalaikudi to Poonagari coast). Its length (from the midpoint of Adam’s Bridge to the mid point of Palk Strait) is around 150 km. It is very shallow and its depth varies between 3 to 15 meters. The bay is largely occupied by sand banks and shoals. It also has two major coral reef formations: one having a width ranging from 1-2 meters to 300 meters extending between Munakad and Thonithurai. This is around 5.5km long. The other reef formation is 25 to 30 km long with a width generally less than 200 meters. This extends between Thangachimadam and Agnitheertham (Rameshwaram). (Mahadevan and Nagappan Nair, 1969).                                          

Contrary to the sea beds of PB and AB, the sea beds of GOM in the south and the Bay of Bengal in the north east have a very deep throw. They fall steeply to depths of 1000 to 2000 meters within a matter of few kilometers from the Adam’s Bridge and the Palk Strait.

So, the ocean beds of PB and AB can be thought of as highly elevated (but submerged) dam like structures that separate the deep ocean beds of Indian Ocean (here GOM) and BOB.