Geo-technical aspects in respect of civil structures for 800 MW Kol Dam project in South-West lower Himalayas have been brought out. The project is located in highest risk seismic zone of India. The project layout is governed by the consideration that Kol reservoir will be silted up and the river regime conditions formed 1n the reservoir in about 30 years. Leakage through Kol reservoir alignment of askew dam axis and ~ 100 m deep cut excavations in chute spillway both in terrace gravels and in rock have been highlighted.
Kol dam project is contemplated essentially as a hydro electric development on river Satluj in Himachal Pradesh State of India in South West Lower Himalayas. It is an immediate u/s development of Bhakra dam - a multipurpose project with 1164 MW power station. It envisages a 163 m high earth cum rockfill dam with central clay core having a crest length of 500 m between the abutments. A chute spillway to pass a probable maximum flood (P1W) of 16500 m3/s having a width of 108.5 m at the control structure and a chute length of 420 m has been incorporated on the left abutment. The river diversion during construction comprises 2–14 m dia and about 906 m long concrete lined horse shoe tunnels on the right bank together with a 60 m high u/s coffer dam as part of main dam and 25 m high d/s coffer dam to divert a 20g year retu~n period flood of 6500 m Is. A desilting arrangement has been planned in spillway approach channel for excluding all sediments down to 0.5 mm size. The power intake is located very· close to spillway crest on its right side i.e. river side. Four steel lined penstock tunnels 6.45 m in dia with total length as 1600 m take off from here and lead to 4-vertical axis Francis units of 200 MW each in a 800 MW surface power house on the left bank at toe of the dam. Maximum and minimum gross heads available by virtue of dam height for power generation are 140 m and 115 m corresponding to FRL 642 m and MDDL 624 m. The Kol dam reservoir with a gross storage capacity of 576 M m3 will have 206 M m3 of live storage in the first year of reservoir operation. Being a short life reservoir, it will get silted up to crest level of spillway and river regime conditions will be formed in the reservoir ·in about 30 years. Subsequently live storage available in post regime formation stage would be about 30 M m3 which is adequate for diurnal peaking operation purposes. The project will function as a peaking station and will feed into Northern Regional Grid of India. The project layout (as indicated in Fig-I) is controlled by three governing gonditions in post regime formation stage viz. power intake to be located very close to spillway crest so that it is always operative;
