Geophysical study for saline water intrusion in a coastal alluvial terrain

摘要

Geophysical investigations comprising electrical resistivity and shallow seismic refraction methods have been employed in the alluvial coastal belt of Digha, in the Eastern India for environmental study, to investigate the nature and status of subsurface saline water contamination. Geophysical surveys have delineated different subsurface geological formations such as dune sand, top sandy soil, saline sand and saline clay on the basis of their characteristic resistivity and velocity signatures. It is also inferred from geophysical interpretation that the thickness of the near-surface saline zone decreases inland away from the shore. Fortunately for Digha, clay layers present at different subsurface levels, which have probable extensions under the sea, have acted as barriers against any large-scale saline water intrusion at depth, even though pockets of saline/brackish zones have been interpreted in the subsurface. Clay formations are predominant up to a depth of about 60 m in the area below which an aquifer zone has been demarcated. A few locales that are already saline or are vulnerable for saline water intrusion have been identified at different depth levels and these zones should be avoided for ground water development. Further, several comparatively safe zones where ground water can be effectively exploited, have been delineated in the area. It has been observed that geophysical methods are highly useful in the environmental study for assessing saline water intrusion in alluvial terrain even in the presence of thick clay formations. (C) 2001 Published by Elsevier Science B.V. [References: 15]