The district is underlain predominantly by crystalline formations and alluvium is found along the courses of the river. Ground water occurs under phreatic conditions in weathered residuum and interconnected shallow fractures and under semi-confined to confined conditions in deeper fractures. The depth of weathering varies from 20-25 m bgl in Usilampatti, Sedapatti and Kottampatti area, while it varies from 30 to 40 m bgl in remaining parts of the district. The depth to water level in the district varies from 3.13 to 7.66 m bgl during pre-monsoon (May 2006) and 1.86 to 5.74 m bgl during post monsoon.
The prominent geomorphic units in the district are structural and denudated land forms such as structural and denudation hills, residual wells, linear ridges, uplands and barried pediments.
GROUND WATER QUALITY
Ground water in phreatic aquifer in general is colorless, odourless and alkaline in nature. The specific electrical conductance of ground water in phreatic zone during May 2006 varied between 632 -6520 μs/cm at 25°C and in major part of the state it is less than 2200 μs/cm.
It is observed that ground water is suitable for drinking and domestic uses in respect of all constituents except TH and NO3. It is found to be excess of permissible limit in 34% of sample analysed in respect of TH and in about 66% in respect of NO3. The high incidence of TH can be attributed to geogenic causes while NO3 excess may be due to either excess use of fertilisers or due to improper waste disposal.
In reference to irrigation suitability based on EC and Sodium Absorption Ratio (SAR), the ground water in phreatic zone may cause medium to very high salinity hazard and medium to high alkali hazard. Hence proper soil management practices are to be adopted when the ground water from phreatic aquifer is to be used for irrigation purposes. In case of deeper fractures, the ground water is suitable for domestic and irrigation purposes. However, the data of State Ground & Surface Water Resources Data Centres shows that ground water in Pulipatti, Chinnalatalai.
GROUND WATER QUANTITY
The estimation of dynamic ground water resources (as on 31.3.2004) have shown that out of 13 blocks in the district, 3 blocks have been categorized as over exploited and 2 blocks as critical. Dug wells are most common ground water abstraction structure with depth range of 10 – 20 m bgl. The yield of dug wells may vary between 45-135 lpm and can sustain for 4-6 hrs of pumping.
PRE-MONSOON WATER TABLE IN MADURAI
POST-MONSOON WATER TABLE IN MADURAI
WATER CONSERVATION AND ARTIFICIAL RECHARGE
The topography of Madirai district, in general, is suited for construction of various artificial recharge structures such as percolation ponds, check dams and sub-surface dykes. However, detailed studies are necessary to formulate a comprehensive scheme for artificial recharge of phreatic ground water in the district in view of the variations in the geomorphic setup and the complex hydrological and hydrogeological conditions.
The number and type of artificial recharge structures recommended for all the blocks in Madurai district. The exact locations of these structures, however, are to be decided on the basis of detailed field investigations. The implementation of the schemes may be taken up in phases, giving priority to blocks where the development of ground water resources is comparatively high.
GROUND WATER DEVELOPMENT POTENTIAL AND ARTIFICIAL RECHARGE PROSPECTS IN MADURAI
Madurai is located at 9.93°N 78.12°E. It has an average elevation of 101 meters. The city of Madurai lies on the flat and fertile plain of the river Vaigai which runs in the northwest-southeast direction through the city dividing it almost into two equal halves. The Sirumalai and Nagamalai hills lie to the north and west of Madurai.
The city has grown on the either side of the Vaigai river and lies at the low attitude and its about 100 M from mean sea level.
The land in and around Madurai is utilized largely for agricultural activity which is fostered by the Periyar Dam. Madurai lies southeast of the Eastern Ghats; the surrounding region occupies the plains of South India containing several mountain spurs. The soil type in central Madurai is predominantly clay loam, while red loam and black cotton types are widely prevalent in the outer fringes of the city. Paddy is the major crop, followed by pulses, millet, oil seed, cotton and sugarcane
Vaigai, a major ephemeral river originates in Western Ghats of Theni district flow in NW-SE direction, in the central part of the district. In addition, tributaries of Vaipar and Gundar drain in south-western part of the district, while the tributaries of Pambar drained in north eastern part. The general flow direction of the drainage is NW-SE.
CLIMATE AND RAINFALL
Madurai is hot and dry for eight months of the year. Cold winds are experienced during December to March as in the neighboring Dindigul. The hottest months are from March to July. The city experiences a moderate climate from August to October, tempered by heavy rain and thundershowers, and cool and climate from November to February. Fog and dew are rare and occur only during the winter season
Being equidistant from mountain and sea, it experiences similar monsoon pattern with Northeast monsoon and Southwest monsoon, with the former providing more rain during October to December. The average annual rainfall for the Madurai district at large is about 85.76 cm. Temperatures during summer reach a maximum of 40 °C and a minimum of 26.3 °C, though temperature over 42 °C is not uncommon.
Winter temperatures range between 29.6 °C and 18 °C. A study based on the data available with the Indian Meteorological Department on Madurai over a period of 62 years indicate rising trend in atmospheric temperature over Madurai city, attributed to urbanization, growth of vehicles and industrial activity. The maximum temperature of 42 °C for the decade of 2001- 2010 was recorded in 2004 and in 2010