Mapping seepage in the tailrace channel, Bhama-Askhed dam: a case study

The Bhama-Askhed irrigation dam, with a side spillway, is located on the Bhama river, Maharashtra, India where the bedrock is chlorophacitic porphyritic basalt. During the monsoon of 2005, thirteen reinforced concrete panels in the tailrace channel area were raised and displaced, exposing the underlying rock. Continuous oozing of water was observed in the tailrace channel at RD 83 m. Nuclear logging and tracer studies were conducted in boreholes drilled 6 m below the foundation level, to identify weak and porous zones and ascertain the seepage path. The nuclear logging identified weak zones at about 34 m depth corresponding to a red breccia zone. The tracer studies established the interconnection between the red breccia in the dam foundation and the oozing water at RD 83 m in the tailrace channel. The studies assisted in the determination of suitable remedial measures for the treatment of the red breccia zone and the recommendation of proper drainage holes in the tailrace channel area to release uplift pressures.