Synopsis The Geological Survey of India has done a comprehensive geological work from the reconnaissance stage to construction stage during the period from 1956 to 1977. The arduous geological conditions due to Lithological heterogeneity coupled with complex structures were not conducive for the 37.29 km long, 255 Cumecs capacity tunnel/channel. Some position of the tunnel had to negotiate very difficult flowing and squeezing conditions. Special tunneling techniques were adopted in crushed Kaolinised area and crushed granites and adequate drainage was provided with grouting.