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

The Erode district is one of the 30 districts of Tamil Nadu with a geographical area of 8161.91 sq.km, the district is endowed with good forest wealth. The total population as per the 1991 census is 2,320,263 which is only 4.15% of the State’s population. The normal annual rainfall is 790 mm and the district falls in the rain-shadow region. The rainfall is meagre and erratic. The district forms part of the Cauvery basin and is drained by a network of rivers viz. the Cauvery, the Bhavani, the Noyil, the Amaravathi, the Palar and their tributaries. The drainage pattern is mostly controlled by the structural features. The important rivers flowing through the district have been fully exploited by means of several anicuts and dams built across them for irrigation purposes. The chief sources of irrigation are the canals and the wells, followed by the tanks and other sources. The Lower Bhavani Project constitutes the major canal irrigation system in the district. Out of the total geographical area, nearly 37% (2,97,779 ha) is the net area sown during 1997-98. The net area irrigated is 1,56,434 ha which is 52-53% of the net area sown. Of the net irrigated area, 58% is irrigated by canals, and 37.8% under well irrigation. It could thus be seen that there is every need to harness the ground water resources to the fullest extent in the district.

The major part of the district is underlain by the crystalline metamorphic rocks of Archaean age. Alluvial sediments comprising sands, silts and clays are seen along the major river courses and streams. The thickness of alluvial sediments ranges from 5 to 8 m The colluvium comprising fine to medium sands with lenses of clay and silt are seen in the valley fills at the foot hills and these colluvial deposits vary from 3 to 13 m in thickness. The district exhibits a polymetamorphic and multi-structural complexity, consisting of folds, faults and shears. Various structural features like lineaments and fractures occur in the district. Moyar-Bhavani and Noyil-Cauvery lineaments are the major structural features. The crystalline rocks are jointed and extensively weathered. The thickness of the weathered mantle varies from less than a metre to about 20 m.

By and large, the hydrogeological framework of the district is controlled by the distribution of rainfall, geological structure and morphological configuration. The rainfall and the return seepage from the canals, irrigation tanks and reservoirs are the important sources of ground water recharge. The faults, shears and the joints serve as conduits for recharge and promote the same. The occurrence and movement of ground water, the water-yielding capacity and the status of ground water development vary with respect to: i) areas underlain by the weathered formations and ii) areas underlain by the weathered/fractured formations and irrigated by the canal systems.

Ground water occurs under water table conditions in the weathered mantle of the crystalline rocks whereas in the fractured rock aquifers it occurs under semi-confined conditions. Conditions in the canal command areas are totally different due to heavy recharge from the canals during the flow periods. Also, the return flow seepage from the applied irrigation varies and the aquifers are more or less completely saturated during the canal flow period i.e. from August to January. During the canal flow periods, the depth to water level is almost near the surface. Presence of deep aquifers along the deep-seated fracture zones in the basement rocks has been established by exploration down to a depth of 200 m bgl.

CGWB has established 40 National Hydrograph Stations in Erode district to monitor the behaviour of water table and changes in the chemical quality of the shallow aquifers. In addition to this CGWB has constructed 30 purpose built observation wells with depth ranging from 31.0 to 91.70 m bgl under the World Bank-Aided Hydrology Project for monitoring purpose. The data collected on water level and quality has been utilised to have an idea on depth to water, water-table configuration, fluctuations in water levels, the chemical quality of the formation water and computation for dynamic ground water resources.

Ground water is the main source for rural water supply as well as for irrigation purposes. The quality of ground water from the phreatic aquifers in the canal command areas is good and can be used for domestic purposes whereas in other parts it is highly mineralised and found unsuitable for drinking purposes. The ground water is suitable for irrigation purposes. The quality of the shallow aquifers in and around the textile, bleaching and dyeing units, which use a wide variety of chemicals and dyes at Erode, Bhavani and Chennimalai and their environs are highly polluted due to the indiscriminate discharge of untreated effluents in the nearby low-lying lands and rivers and found unsuitable for all purposes.

The quality of the formation water from the deeper aquifers is uniformly good and found suitable for all purposes. Ground water in this district is developed to the maximum extent for irrigation by means of dug wells and dug-cum-bore wells and almost all the irrigation wells are fitted with centrifugal pumps energised by electric power. The balance of ground water potential available for further development is of the order of 143.45 MCM/yr. The stage of ground water development in the district as on January 1997 was of the order of 89%. The block-wise level of ground water development indicates that 6 out of 20 blocks are over-exploited and 3 blocks record withdrawals exceeding 85% of the utilisable recharge and in 9 blocks it is between 65 and 85%. As such, 9 blocks are in the advanced stage of development. Further development in the over-exploited and dark blocks has to be stopped to preserve the environment by introducing the appropriate ground water legislation and by simultaneously creating awareness amongst the users regarding the adverse effects of over-exploitation. In the areas falling under "Grey" category, the development should be carried out on scientific lines in a phased manner.

To ensure that the development of ground water does not cause an ecological imbalance, it is essential that the recharge of ground water be augmented by adopting techniques of rainwater harvesting, artificial recharge and water conservation.

A few recommendations are mentioned namely i) micro level studies in the canal command areas to explore the prospects of conjunctive use of surface and ground water resources, ii) pollution studies assess the extent of the damage caused by the untreated effluents from the industrial units in and around the industrial towns on the ground water quality and to evolve suitable preventative measures and iii) the participatory approach involving the farmers, NGOs and the government departments should be motivated and promoted for the better water management practices.

Keeping in view the increasing dependence on ground water resources, the future strategy for better prospects will have to be development-cum-management oriented which should include the aspects for conservation, protection and augmentation of ground water resources and better water use efficiency and pump efficiency.