Geomorphic Evolutionary Influence Of Deltas On Groundwater A Case Study In Godavari Delta, Andhra Pradesh

摘要

Andhra Pradesh has a coastline of 974 km. encompassing Godavari, Krishna and Pennar Deltas. The deltaic coast is the receptacle of vast pile of sediments with several marine transgressions and regressions during Quarternary period, resulting in fluvial, fluvio-marine and marine deposits. The Godavari Delia between Vasishta and Gautami distributaries in East Godavari district, characterised by complex hydrogeo-chemical conditions, presents typical deltaic environment. Four major strand lines were identified indicating the progradation of delta. Some of the existing drains were believed to represent palaeo-channels of Godavari River. The presence of major neo-tectonic fault trending ENE-WSW parallel to the coast separates marine/fluvial landforms. Study of lithological logs indicates the vertical variation of sediments owing to different depositional environments. The aggregate thickness of granular zones ranges between 3 and 109 m down to explored depth of exploratory wells. In general fresh water is limited to palaeo-channels and beach ridges while the brackish/ saline water occurs at deeper depth in all geomorphic units. The chemical quality of groundwater varies both spatially and depth-wise and is governed by geomorphic evolution of delta. A study of ionic ratios of groundwater indicates the mixing of sea water with fresh water. The distribution of sub-surface facies, genesis of salinity, distribution of fresh/saline zones and hydrochemical aspects of groundwater are discussed.