Under water lake tapping is a Norwegian technique developed in that country mainly to tap the inland lakes located high up in the mountains below their normal levelsfor electricity generation and drinking water supply. This technique is used in sub-sea tunnels for oil and gas activities. In this technique, a shrft is sunk on the fringe of the lake/reservoir up to the bottom of the water conductor tunnel from which an in take tunnel is excavated underneath the lake to reach the lake bottom leaving a break-through rockplug which is finally blasted to connect the lake with the pre conceived water conductor system. The blast is designed in such a way that vibration produced in the adjoining roclc mass and the resultant hydro dynamic pressure built up in the system are kept at minimum acceptable levels, thus protecting the adjoining structures.
This technique has been usedfor the first time in India as well in Asian region on Koyna Hydroelectric Project Stage-IV. This paper is a case study describing the various aspects along with geotechnical aspects from investigations to actual execution of this technique on said project.This technique has opened a new avenue on several other projects involving improved utilization of water from the existing reservoirs.
