II-7-Assessment of Aquifer Vulnerability to Saltwater Intrusion using Modified Galdit Factors-A Case Study.

Abstract

The coastal aquifer of Odisha aligned in NE-SW direction for about 430 kilometers is confronted with typical problem of saltwater intrusion and salinization. Four types of aquifer disposition are mainly encountered i) fresh water zone overlying saline water zone ii) saline water zone overlying fresh water zone iii) alternate fresh and saline water zone and iv) saline water all through. Utilization of groundwater in the area is of greater significance since coastal belts are among the most densely populated human settlements and groundwater forms the major and sometimes the only source of potable water there. The study area; Basudevpur block, Bhadrakh district, Odisha is endowded with abundance of water resources and vast stretch of fertile land. The economy is agriculture based but its development is constrained due to proximity of the Bay of Bengal and salinity hazards. Its unplanned development has upset the hydro-chemical balance leading to seawater ingress. Thus the ground water development in the terrain requires a proper understanding of hydro-geological and hydro-chemical setup and management scenarios. GALDIT method has been used to assess the vulnerability of the study area to salt water intrusion using certain hydro-geological parameters. The paper deals with the determination of the water quality and to identify the areas affected by saltwater intrusion. An attempt has been made to use the remote sensing and GIS techniques for integration of spatial database. To map the saline affected areas, different hydrogeological parameters like hydraulic conductivity, aquifer types, distance to coast, water table above mean sea level are analyzed in a modified GALDIT model. Relationship of each layer to the ground water regime has been evaluated through detailed analysis of the individual parameters. These relationships are used for the development of an algorithm to be used in spatial multi-criteria evaluation (ILWIS, SMCE) decision model. Ground water potential zones and the areas demarcating the saline hazard areas have been identified based on integration of data and various themes. The map thus generated can be of vital importance for coastal hazard mapping agencies. The coastal tract has inherent salinity problem due to both natural and man-made causes and hence should be under strict surveillance for the over-all sustainable development of coastal areas. Necessary steps like artificial recharge and conjunctive use studies are to be taken up in the area in order to protect this aquifer system from the hazards of sea water intrusion and to devise means for the optimal utilization of the water resources. It is needed to construct wells along some transverse section of the coast with piezometer nest tapping different aquifers. Regular monitoring of water quality in the aquifers should be done where the quality deteriorates and where the fresh/saline water aquifers are in direct contact with the sea.