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ELECTRICAL RESISTIVITY SURVEY ON THE LEFT BRANCH CANAL OF HIGH EMBANKMENT OF TUNGABHADRA DAM, MILES 69, 77 & 85, KARNATAKA STATE

ABSTRACT In order to investigate the presence of concealed cavities (locally known as Bongas), responsible for the seepage in the high embankments at miles 69,77 and 85 of left branch canal, Tungabhadra project, Karnataka State, Electrical Resistivity Profiling (ERP) and Imaging (ERI) were used. ERP was carried out in canal dry condition and both ERP and ERI were deployed at different locations (after due interpretation of the ERP studies) in canal filling condition. The geophysical investigations are carried out in April 2007 (canal dry condition) and November 2007 (canal filling condition). ERP was carried out using Schlumberger configuration with half electrode spacing (AB/2) of 10.0 m 15.0 m and 20.0 m. The ERI was carried out with Wenner & Schlumberger arrays with an inter-electrode spacing of 5.0 m. The locations, where relatively low resistivity values were observed during the canal empty condition and still lower values in canal filling conditions were attributed to the cavities. Thus the cavities/weak zones were delineated.