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at 5.30p.m. and for subsequent written discussion SYNOPSIS The Paper mentions several recent failures of dams and the resultant damage by flooding. The causes of different types of failure are reviewed and brief histories given of the examples chosen. The effects of reservoirs on the balance of nature are mentioned, the design of dams is considered and suggestions advanced for the protection of persons and property. The question of insurance against damage is raised. The author concludes that every dam which impounds water presents a potential danger and the risk of sudden disaster is for ever inescapable. INTRODUC~ON DURING 1961 the following were added to the list of recorded dam disasters: The failure of a dam in the Babii Yar gorge of the Ukraine as the result of overtopping due to high winds. The flood released inundated the lowerlying parts of the city of Kiev. The failure of the Panshet dam near Poona in India during the monsoon rains, and the consequential destruction of the Khadekvasla dam a few miles downstream. The failure of the Hyokiri dam 125 miles south of Se01 in South Korea as the result of torrential rains. F~D S DUE TO NATURAL DAMS 2. Out of 265 floods recorded in the Rhone Valley in Switzerlandno fewer than a tenth were caused by the breaching of glacial barriers. Lake Maeryelen which lies adjacent to the Aletsch glacier has been the cause of periodic disasters, the most recent occurring in 1913 when 7800 acre-ft of water were suddenly released.The unusual phenomena associated with such disasters had been observed by Alpine herdsmen from very early times and they had noticed that on occasion the ice barrier would lift and suddenly release the water stored in the lake. A more recent example of such natural disasters occurred in 1934 when theTrans-Andean Railway was breached near Mendoza in the Argentine. Investigations showed that the Nevado glacier had blocked the valley of the Rio Plonio and had created a temporary lake of 46 800 acre-ft. At its peak the flood 47

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