Abstract:
Glacial debris flows occupy a special place among other natural disasters in Kazakstan. They are connected with outbursts of the glacial lakes, which are more than 120 in Northern Tienshan area. At the second half of the XXth century a few tens of destructive glacial debris flows occurred and 10 events had catastrophic character. Preventive emptying of glacial lakes is widely used in practice for mitigation of debris-flow hazard. For the last 20 years such work was carried out on 14 lakes. That has allowed considerably to reduce their dangerous volumes and completely to exclude their outbreaks hereinafter. In 1985 the emptying of the largest glacial Bogatyr Lake with the volume more than 9 million m³ was accomplished. During the last years debris-flow hazard increased in the Malaya Almatinka River basin near Almaty City in the connection with the development of lake No. 6 at the M. Mametova Glacier. Its volume exceeded by summer 1997 200 thousand m³. Its outburst could have caused a greater disaster than the well-known debris flow in 1973 which was stopped by the Medeo Dam. A new Kazakstan technology is using with use a canvas screen and soft gate system without building mechanisms and machines allowed to carry out controllable emptying of more than 100 thousand m³ of water and to eliminate the debris-flow hazard for Almaty city.