Among the former were DVC, Bhakra- Nangal, Tungbhadra and Hirakud of the pre- Plan vintage and Chambal,
Rihand, Koyna and Nagarjunasagar conceived in the planning era.
Last year, India's Borehole
Geophysics Research Laboratory has undertaken scientific deep drilling of the earth's crust in Koyna, Maharashtra and its
pilot borehole has now gone up to a depth of 2662m.