Groundwater scenario of Chidambaram taluk, Cuddalore district, Tamilnadu

Chidambaram is the taluk headquarters, located at about 250 km south of Chennai on east coast road [ECR] in Cuddalore district of Tamilnadu. It is a coastal taluk having three panchayat unions, Keerapalayam, Melbhuvanagiri and Portonovo. Chidambaram is the most important pilgrim center of the country, and is blessed with the Lord Nataraja temple. The temple town is also known as Bhuloka Kailash and Lord Nataraja, a cosmic dancer, represent the ‘Aakash’ form which is one among the ‘Pancha Boothas’. 

Though this temple town is blessed with such historically important temple, the Nature has cursed Chidambaram area with brackish water, which is also one among the ‘Pancha Boothas’. The total aerial extent of this taluk is 649 square km and the most part of the taluk is confined between the rivers Vellar and Kollidam, which is a distributary of the river Cauvery. Some few lakhs years back the Kollidam river might have flown even north of Chidambaram town and might have receeded subsequently southwards to the present position. Due to this invasion, the entire area might have been changed as marshy lands and mangrove forests. The salinity of ground water may be attributable to the fluvio marine origin sediments, which might have been deposited during this paleo invasion by the river and due to the back water flow. Chidambaram is about 15 km west of sea shore and the mean sea level is 5.1 metres. Geologically this taluk is a sedimentary terrain and the eastern parts are covered by the quaternary unconsolidated formations of clay, black clay, soils, alluvium, silts, kankar and laterites of recent to sub recent age and the western parts by the tertiary formations of Mio-Pliocene age represented by litho units - sand stones, grits, clays with lignite seams and pebble beds.

Water occurs as surface [River, Lakes] and sub surface water. All the water contained in the pores, fratures and voids of sub surface is termed the ground water. Mostly ground water is derived from surface sources that is, rain fall. The ground water potential of an area depends on so many factors like physiography, topography, rainfall, geology and hydrogeology. Aquifer is a geological formation that can transmit significant quantities of water. Best examples are sand and alluvium. The transmitting capacity depends on the porosity and permeability of the formations. The aquifers are of two types. One is confined aquifer and the other one is unconfined aquifer. Groundwater occurs in all geological formations. Hydrogeologically the rocks can be classified as hard crystalline rocks and porous sedimentary rocks. The Chidambaram taluk comes under porous sedimentary formation type. Mother Nature does not provide ground water at the places of our choice. Based on the hydro geological conditions only the ground water occurs. The exploration of ground water by geophysical techniques is of two types. One is surface method and the other one is sub surface method. The common surface geophysical technique globally adopted is the electrical resistivity prospecting. By this method, only the sub surface geological formations can be delineated based on the electrical conductivity, where in the quality of ground water cannot be ascertained. In the sub surface method that is electrical well logging, the quality of formation water can be ascertained. The fresh and saline water zones and different potential aquifer zones can be identified and differentiated. The saline water zones have to be sealed while constructing the well. The success of tube well depends on the proper well construction and development. Thus electrical resistivity prospecting plays a vital role in the exploration.

The suitability of ground water for various purposes depends on the chemical quality. The basic chemical properties of water are controlled by its major chemical constituents. Ground water comes into contact with various minerals which are soluble in water to varying degrees. The dissolved minerals or solids determine the usefulness of water and the Total dissolved solids [TDS] is one of the governing parameter that determines suitability. Based on TDS, the water is classified as fresh water, brackish water, saline water and brine. For fresh water, the TDS is 0-1000 parts per million [PPM}. Various chemical parameters determine the standard for drinking water. According to the World Health Organization [WHO], the drinking water standard for TDS, is 500 to 1500 ppm. The ground water quality is poor and saline in most parts of Chidambaram town. In some pockets the shallow aquifer water is good and drinkable. Examples - Ammapettai and Vibeeshnapuram areas. But in most parts like Kanagasabainagar, Sivasakthinagar, S.R.Nagar and Mariayappanagar where even the shallow aquifer water is very poor and saline with rotten egg smell due to the presence of hydrogen sulphide [H2S]. The quality is poor in most parts of Portonovo, Keerapalayam and Kumarachi panchayat unions [Kattumannarkoil taluk]. Due to poor quality and salinity problems, the exploration of fresh water aquifers becomes difficult. In general the shallow well and tube well water is good in and around temple areas i.e., in the four main car streets. The TDS of a shallow tube well of depth 14 metres [domestic] in east car street is 993 ppm. But when the depth increases the quality deteriorates.

The ground water potential of Chidambaram taluk in general is good but the quality is the main constraint in major parts of the taluk. In the western parts of both Keerapalayam and Melbhuvanagiri unions, the quality of ground water is good. The quality of deep confined aquifers encountered at the depths of 160 to 180 metres below ground level, in and around Chidambaram town area, is fresh in nature, potable and suitable for irrigation and drinking purposes. The tube wells constructed after systematic explorations, at Kanagasabainagar, Mariyappanagar, Sakthinagar, Muthaiahnagar, Sri Chakra Avenue and Kadhirvelnagar in the depth range of 180 to 225 metres, have yielded 500 to 1000 liters per minute [lpm] of potable water. In Portonovo area, the scenario is entirely different. Only the shallow aquifers are good and that too wells sunk in sand dunes of coastal tracts. The very deep bore wells drilled [440 metres bgl] in Portonovo areas are saline. Hence the Portonovo area is not favorable to go in for deep bore wells in general. The deep tube wells constructed at Pinnathur, Thillaividangan and Arulmozhithevan of Portonovo union to the depths of 240, 220 & 120 metres respectively, have yielded copious fresh water for drinking water supply. The tube wells constructed at Keerapalayam and Pannappattu of Keerapalayam union to depths of 61 and 160 metres have yielded 270 & 670 lpm respectively. The TDS of Pannappattu tube well is 438 ppm. Keerapalayam is on the bank of the river Vellar and Pinnathur and Thillaividangan are on the down streams of Vellar. Shallow wells and tube wells are favorable in Ammapettai and Vibeeshnapuram areas to get fresh water for domestic purposes. Even in some parts of Ammapettai, due to excess iron content in shallow tube well water, there is a peculiar iron smell. Instead of sinking shallow tube wells, a smaller diameter ring wells may be sunk to over come this problem. In the ring wells, the water is directly exposed to the atmosphere and there by due to aerobic oxidation the iron smell goes off. Shallow wells and tube wells are not advisable in Mariyappanagar, Kanagasbainagar, Sivasakthinagar and S.R. Nagar areas even for domestic drinking purposes. Deep tube wells of depth 180 to 200 metres can be constructed after a systematic exploration.

Due to over extraction and exploitation of ground water, the water level gets declined resulting in the depletion. To protect it from such depletion artificial recharge methods may be followed not only to improve the potential, but also the quality as well. Suitable rain water harvesting structures may be constructed. In coastal areas heavy pumping is not advisable as it may influence sea water intrusion. During the last monsoon, Chidambaram recorded a heavy downpour of 22 cms [2007] and the major quantum of rain water might have been wasted and flown to the sea as run off. Proper storm water drains should be constructed to avoid flooding. The source of drinking water for Chidambaram municipality, Kanagasabainagar and Annamalainagar are the Vakramari lake, deep tube wells and infiltration wells sunk in the Kollidam river. These water sources should be protected from pollution and contamination. A check dam may be constructed across the river Kollidam in the upstream of the road bridge near Karuppur.

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