GROUND WATER RESOURCES AND DEVELOPMENT POTENTIAL OF
RAMANATHAPURAM DISTRICT, TAMIL NADU

Ramanathapuram is one of the 12 coastal districts of Tamil Nadu spanning over an area of 4232 sq.km. It comprises seven taluks, which are sub-divided into 11 developmental blocks. Physiographically the entire district stretches out as at extensive plain forming a part of the vast coastal plain of Tamil Nadu. It forms a part of Vaigai and Gundar river basins and is drained by the rivers Vaigai, Gundar, Kottakarai and their distributaries. All the rivers are ephemeral in nature. Agriculture is the main stay of the rural populace and paddy, is cultivated extensively. Dry crops are also cultivated. The normal annual rainfall of the district is of the order of 827mm. The district is prone to droughts. The chief source of irrigation and drinking needs are tanks. There is no canal irrigation system. The net area irrigated is 68667ha., which is 34.47% of net area sown. The gross area irrigated in the district is 69625ha.

The district is underlain by the crystalline formations of Archaean age and porous sedimentary formations ranging in age from Mesozoic to Recent. Ground water occurs under phreatic, semi-confined and confined conditions. The depth to water level in dug wells varied from 1.32 to 13.13 m bgl during the pre-monsoon period (Aug.96) where as it ranged from 0.49 to 12.72 m bgl during post monsoon (January 97). The seasonal fluctuation of water table shows rise and fall. The rise varied from 0 to 4m and fall ranged from 0.10 to 4.56m.bgl.

Exploratory drilling by erstwhile ETO & CGWB has established the presence of fresh water aquifer at depth below 365m in upper Cretaceous formations. Five major aquifers exist in the district viz. Recent-Alluvium, Mio-Pliocene (Cuddalore formations), saline Cretaceous and weathered basement, saline shallow alluvial aquifers and deep fresh water aquifer.

The chemical quality of ground water of shallow aquifer is generally poor in major part of the district whereas in the West-north-western and northern parts and isolated pockets the quality is good. Brine concentration in the formation water of coastal areas of the district ranges up to 11.5⁰Be. However it decreases with depth and the deeper aquifer are not suitable for salt-based chemical industry. The chloride–bicarbonate ratio indicates insufficient flushing of aquifers. The total dynamic ground water resources and the utilisable ground water resources for irrigation (excluding saline area) in net terms are of the order of 0.02261 and 0.01729 m ha m/yr. respectively. Balance ground water potential available for development is of the order of 0.01781m ha m/yr.

The ultimate numbers of wells that can be constructed in the district works out to be 6778 at 65% of ground water development. The total electrical energy required is of the order of 19.97 MU. The stage of ground water development as on January 1997 was of the range between 0.01 and 15.49% and there are no over exploited or dark blocks in the district.