66. Hydropower Generation through Run of the River Schemes in Yamuna Valley, Uttaranchal Himalaya, India

The Yamuna river along with its numerous tributaries in Uttaranchal Himalaya constitute about 6000 MW of Hydel power potential hardly 10 per cent of which has been tapped so far. In a total stretch of about 62 km between Ichari in Tons valley and Khara power house in Yamuna valley through five run of the river schemes a total of 550 MW of hydropower is being generated by utilizing a gross available head of 240 m. The Chibbro underground power house of the Yamuna Hydel scheme stage-II part-I on river Tons is the first underground power house cavern constructed in Himalaya in the Indian Subcontinent under not very favourable rock conditions. The head race tunnel of Yamuna hydel scheme stage-II Part-II also posed challenging tunnelling conditions on account of intersection of two regional thrusts namely Krol thrust (MBF) and Nahan Thrust and their intra-thrust zone traversing for about 1 km length and experience of squeezing and flowing conditions with rock closures in the tunnel. The tunnel was successfully driven in this weak zone by trifurcating it into three tunnels of 4.8 m diameter size each. The syphon tunnel below the Tons river from Chibbro underground powerhouse is also a unique feature constructed in the project. The Khara hydel scheme was constructed across the fragile Siwalik rocks comprising sand rock, boulder conglomerate, siltstone and claystone with water charged horizons to give rise to flowing and squeezing conditions during tunnelling. The 12 km long power channel was constructed in a hostile terrain with numerous streams and unfavourable unstable patches causing landslides and instability problem of cut slopes along its banks resulting into delays in commissioning of the project. Two important tectonic features passing through the Khara Hydel scheme are (a) Yamuna Tear a major fault with a sinistrial sense of movement showing a huge 4 km horizontal shift of Siwalik rocks along this fault and (b) Foot Hill Thrust (FHT) encountered during the excavation of Khara Power house and bypass channel which shows deposits of Indo-Gangetic alluvium overridden by middle Siwaliks. Neotectonic activity along Yamuna Tear has been witnessed in the area indicated by cracks and displacement of tiles in the lining of power channel after two years of the commissioning of Khara project.