Abstract
The over extraction of groundwater from the coastal aquifers, result in reduction of groundwater resource and lowering of water level. In general, the depletion of groundwater level enhances the landward migration of saltwater wedge. Pondicherry is one such region with recent alluvium as the major formation. Since the study area forms a part of the coastal aquifer system this behaves as a fragile ecosystem. The present study has been attempted to calculate the extraction of water and to estimate the amount of recharge into this alluvial aquifer by using groundwater level variations. The monthly water level fluctuation was observed during the study period (2000-2002) in eighteen locations. The maximum rise in groundwater level observed during 2000 was considered as the initial water level for the study and the subsequent decline in water level (draw down) was monitored monthly until the rising trend was noted. This indicates the fall in water level due to extraction. Later keeping the deepest draw down as the initial value increasing water level trend was studied until there was a notice of decline in groundwater level. This indicates as the rise in water level due to recharge. This method of observation carried out at a single location was adopted for all eighteen locations. The spatial representation of these data for eighteen locations were carried out by using GIS and the area occupied by different groundwater level contours were calculated and the amount of water withdrawn/re- charged was estimated. The maximum recharge was noted in the central and the northern part of the study area when compared to the other regions. Similarly, the maximum discharge was noted in the northern and the southern part of the study area during the study period.
Highlights
Groundwater is one of the most important and scarce commodity
In the simultaneous year (2001) the maximum drawdown level of groundwater is noted (DL). The difference between this two groundwater levels gives the discharge in region (IL~DL), using this phenomenon difference in water level was calculated for the different location in the study area
The above study facilitates to spatially identify the regions with high discharge and good recharge
Summary
Groundwater is one of the most important and scarce commodity. Groundwater exists in the geological formations through which it can penetrate, be transmitted and stored beneath the surface. When the rate of infiltration is sufficient and the rocks are saturated to an appreciable thickness, the groundwater becomes usable enough to yield useful supplies of water to wells, springs and stream. At present nearly 1/5th of all the water used in the world are obtained from the groundwater. Land use/ land cover pattern of Pondicherry and its surroundings were studied by using IRS 1C LISS III data [1]. The dependency of groundwater for the agricultural purpose has considerably increased in the recent past. About 80% of groundwater is used for agriculture. The quantification of the groundwater resources has become essential for water management. There are differebt methods for assessing the rate of recharge e.g., by using stable isotope, tra- cer techniques, groundwater modeling (thangarajan et al.) etc. Aquifer recharge studies using different isotopes for determination of infiltration capacities, permeability and in delineation of aquifer, inter connection were studied
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