Lesson from the Thondaimannar scheme for creation of fresh water bodies.

Abstract

The Thondaimannar scheme was designed in 1943 to prevent the ingress of salt water from the sea into the lagoon by erecting a barrage with sluice gates and leach away periodically with rain water the salt from the blocked area of the lagoon so that ultimately this lagoon could become a fresh water system. This would help to recharge the adjacent aquifiers with fresh water thereby enhancing the quality of the ground water supply. The desalinated marginal lands were expected to provide new areas suitable for cultivation. Though the initial scheme was designed by Webb (1943), the one that was implemented in 1953 was a modified scheme. It was believed by the then planners that if the general possibility of transforming successfully the lagoon could be established the scheme could be an experimental forerunner to others.The water bodies involved in this scheme are the Vadamaradchi lagoon or Thondamannaru lagoon and the Upparu lagoon with a total of approximately forty square miles. Observations made over a period of over ten years from 1963 indicated physical, floral and faunal evidence of gradual desalination. However, by 1977 it was found that the scheme has failed primarily because of the malfunctioning of the barrage.A section of the population is opposed to the revival of the scheme, because they wish to restore its marine fishery by maintaining the original intergrity of the lagoon. However, data are presented to show that the loss in marine fisheries is negligible compared with the coastal fisheries production of the Northern Province. Further, if culturing of fish like Chanos chanos and fresh water prawn, Macrobrachium rosenburgii are undertaken in the vast areas of fresh water which becomes available, the production will more than compensate the loss in marine fisheries.The lessons from this innovation are valuable for planned revival of the Thondaimannar scheme and for planners of future schemes.