THDC India Limited, Rishikesh, Uttarakhand, India
Online published on 11 November, 2021.
Vishnugad Pipalkoti Hydro Electric Project (VPHEP) is a run of the river scheme, located on river Alaknanda, spanning between Helong and Birahi Villages in Chamoli district of Uttarakhand, india. The Project envisages construction of 65m high Concrete Gravity Dam, three nos. underground Desilting Chambers of 390m length each, 13.4 km long Head Race Tunnel of 8.8m diameter, 3 km long Tail Race Tunnel of 8.8 m diameter etc.
During June 15 to 17, 2013, cloud bursts and heavy to very heavy rainfall hit higher reaches near to project. This unprecedented rainfall resulted in a sudden increase in water levels giving rise to flash flood in Alaknanda river basin, caused extensive river bed and toe erosion, landslides at various locations and huge transportation/deposition of sediments in downstream area. Flash flood had eroded the river bed profile significantly in dam area, affected the designed diversion arrangements -tackled by lowering of Inlet and Outlet levels & discharge capacity of Diversion Tunnel. Parallelly, this event led to some deposition at Power House area and caused steep rise in bed level. immense quantum of silt got deposited in power house exploratory drift, huge deposits of silt and muck was left by river at Tail Race Tunnel outlet area also. All of this was tackled by reviewing the layout and design of structures elaborately. This paper describes the impact of furious extreme flood event on the project planning and how in the middle of construction, this was tackled.
