24-Hydrogeological Hydrogeophysical Hydrogeochemical studies in Sandur area, Bellary district Karnataka.

Abstract

Sandur is a chronically drought prone area in the underdeveloped Bellary district of Karnataka. Sandur schist belt chiefly consist of iron-formations and epidiorite surrounded by peninsular gneissic complex. Structurally it is a canoe-shaped doubly plunging synclinorium with many fault zones. The rocks are highly fractured and jointed and are exposed to intense weathering and climatic vicissitudes resulting in deep weathered zone which helps in the storage and movement of groundwater. Groundwater in the Sandur area occurs mainly under water table conditions. Electrical resistivity surveys were carried out to understand the subsurface hydrological conditions. The vertical electrical soundings (VES) conducted at selected points revealed typically 3-layered situations where the second layer is the thick weathered zone (10-30m) with low resistivity (10-105 ohm-m) and is interpreted as the saturated zone. It is found from resistivity survey as well as from field observation that the shallow dugwells and dug cum borewells are more successful than the deep tubewells. Few water samples collected from iron-formations and epidiorites were chemically analysed to test the quality of water and to establish the relationship between the chemistry of water and the major rock types. Chemical analysis of water samples from epidiorites show a high degree of concentration of ions compared to the waters from iron-formations. When total dissolved solids (TDS) are plotted against ratios of Na+K/Na+K+Ca and Cl/Cl+HCO3 in Gibbs variation diagram, is found that the quality of water is mainly controlled by the major litho units of the area. Since the chemical constituents are within the permissible limits, the waters of Sandur area is suitable for drinking, domestic and agricultural purposes.