This discussion deals with some aspects of geological defects arising in soluble rocks and volcanic terrain. As either of these settings would require an entire session to cover them at all adequately the remarks are limited to chalk and acid volcanic rocks.
As the principal speaker has said, it is common practice to relate reservoir feasibility to rock type and condition and, on this basis, chalk sites have in the past been avoided as a matter of principle. In the U.K. there are no reservoirs in chalk to my knowledge, though one site is currently being investigated at Great Bradley in East Anglia. Much of this site is mantled by a blanket of boulder clay in places over 100 ft thick—the reason for its selection in the first place. In Cyprus, however, two reservoirs have been completed in the last five years in chalk valleys without the benefit of low permeability blankets. The dams are Polemidhia, 147 ft high, completed in 1965 and Yermassoyia, height 136 ft completed in 1968 (Fig. 1). Currently several other sites are being investigated, including one on the largest river in the country, the Kouris River, for which the proposed height of dam is 300 ft. For reservoirs in chalk, the main geological defect is not the occurrence of large karstic voids, for caves are rare or absent, but the presence of fissures which have been widened by solution. Groundwater conditions at sites generally fall in the main speaker's category 3 i.e. both the water