Vembanad Lake - Geography and Hydrography

Geography and Hydrography

The Vembanad wetland system covers an area of over 2033.02 km² thereby making it the largest wetland system in India. Of this, an area of 398.12 km² is located below the MSL and a total of 763.23 km² area is located below 1 m MSL. The lake is bordered by Alappuzha, Kottayam, and Ernakulam districts. It lies at sea level, and is separated from the Arabian Sea by a narrow barrier island. Canals link the lake to other coastal lakes to the north and south. The lake surrounds the islands of Pathiramanal, Perumbalam and Pallippuram. The Vembanad Lake is approximately 14 kilometres wide at its widest point. The lake is a part of Vembanad-Kol wetland system which extends from Alappuzha in the south to Azheekkode in the north, making it by far, India's longest lake at just over 96.5 km in length. The lake is fed by 10 rivers flowing into it including the six major rivers of central Kerala namely the Achenkovil, Manimala, Meenachil, Muvattupuzha, Pamba and Periyar. The total area drained by the lake is 15,770 km², which accounts for 40% of the area of Kerala. Its annual surface runoff of 21,900 Mm accounts for almost 30% of the total surface water resource of the state.

The lake has become a major tourist location in the past few years thanks to its scenic beauty. The most popular location on the shores of the lake is the Kumarakom Tourist Village situated on the east coast of the lake. The Kumarakom Bird Sanctuary is located on the northern fringes of Kumarakom village. The Vembanad Wetland system was included in the list of wetlands of international importance, as defined by the Ramsar Convention for the conservation and sustainable utilization of wetlands in 2002. It is the largest of the three Ramsar Sites in the state of Kerala. Vembanad lake has been heavily reclaimed over the course of the past century with the water spread area reducing from 290.85 km² in 1917 to 227 km² in 1971 and 213.28 km² in 1990. In the same period almost 63.62 km of erstwhile water spread were reclaimed primarily for formation of polders and to enlarge the extent of the Wellington island of Cochin port. The lake faces a major ecological crisis and has reduced to 37 per cent of its original area, as a result of land reclamation.

A unique characteristic of the lake is the location of the 1252-meter-long Thanneermukkom salt water barrier. The Thanneermukkom salt water barrier was constructed as a part of the Kuttanad Development Scheme to prevent tidal action and intrusion of salt water into the Kuttanad low-lands. It is the largest mud regulator in India. This barrier essentially divides the lake into two parts - one with brackish water perennially and the other half with fresh water fed by the rivers draining in to the lake. This barrier has helped the farmers in Kuttanad by freeing the area of salinity and adding another crop in dry season. The Thanneermukkom barrier is located at one of the narrower parts of the Vembanad Lake. Only two-thirds of the original number of gates is opened in July to release flood flow. These gates remain closed mid-November. The main drawback of the structure has been the loss of opportunity for marine fish and prawns to migrate upstream and an increase in weed growth in the upstream and finally, severely restricted the natural flushing of pollutants. The Thanneermukkom bund has also created ecological problems, primarily, the rampant propagation of the Water Hyacinth in fresh water.