DROUGHT IMPACT ON GROUND WATER REGIME

Abstract

For last few years many states in the country especially south western states have faced severe scarcity of water due to continuing drought conditions. Ground water is the main source of water supply in drought affected areas because of meagre surface water availability. Statistics recently compiled on the use of ground water and surface water show that in a number of states ground water is being over exploited in certain pockets resulting in continuous fall in water table. The situation is further aggrevated with continued drought conditions. With a view to study the effects of continuing drought conditions on ground water regime, analysis of rainfall and ground water level data recorded over last nine years for districts of Jamnagar and Rajkot in Gujarat state has been carried out. In each district 10 to 13 raingauge stations and 5 to 13 observation wells, uniformly distributed over the district, have been chosen for the purpose of data analysis. Average rainfall and average groundwater level were calculated using Thiessen Polygon Method. As a first step, the relation between annual rainfall and time was then developed using polynomial regression analysis. This relationship between annual rainfall and time has been used to correlate annual rainfall and pre and post monsoon ground water levels for each district by regression analysis. The applicability of these regression equations at 95% confi-dence level has been tested using F test. ii The analysis showed decreasing trend in groundwater levels which may be due to continuous increase of draft and decrease in rainfall recharge. The difference between computed and observed groundwater levels gives the effect of drought in terms of over and under exploitation of ground water. A sharp decrease in ground water levels have been observed in both the districts after year 1983 which may be attributed to over exploitation