SUSTAINABLE GROUND WATER DEVELOPMENT IN FRACTURED HARD ROCK AQUIFERS IN INDIA

Development of a natural resource like ground water is a concerted activity towards its sustainable use for the benefit of mankind. The concept of sustainable use is quantitatively related to various factors like the volume of the existing resource, annual recharge or replenishment, benefit/cost ratio of the proposed use, and environmental impacts of the proposed use. From quality point of view sustainability is prevention of deterioration of quality of ground water beyond an acceptable limit, even after its prolonged use.

Fractured hard rock aquifers for the purpose of this paper, mean the non-carbonate, fractured rock aquifers in the terrain covered by crystalline basement complex and metamorphic rocks. Extensive, ancient volcanic rocks like basalts of western India (Deccan traps), which are more compact and impervious than recent volcanic effusions, are also included as a special case.

The most significant features of the hard rock aquifers are as follows: 1. A topographical basin or a sub-basin generally coincides with ground water basin. Thus, the flow of ground water across a prominent surface water divide is very rarely observed. 2. The depth of ground water occurrence, in useful quantities, is usually limited to a hundred metres or so. 3. The aquifer parameters like Storativity (S) and Transmissivity (T) often show erratic variations within small distances. 4. The saturated portion of the mantle of weathered rock or alluvium or laterite, overlying the hard fractured rock, often makes a significant contribution to the yield obtained from a dug well or bore well. 5. Only a modest quantity of ground water, in the range of one cu.m. to a hundred cu.m.or so per day, is available at one spot. Drawdown in a pumping dug well or bore well is often almost equal to the total saturated thickness of the aquifer.

In many developing countries, hard rock hydrogeologists have, therefore, an important role to play, by ensuring sustainable ground water development. For this purpose, a sub-basin is taken as a unit and ground water pumpage in relation to recharge is monitored. Recharge augmentation by artificial means and Pumpage control has to be adopted in many cases.