Serious accidents have frequently occurred due to avalanches on roads and railways until now. Accordingly, various anti-avalanche structures are installed at the slopes subjected to avalanches. However, it is impossible to completely protect roads and railways from the damage of avalanche only by anti-avalanche structures. When an avalanche has occurred, it is necessary to implement road traffic regulation, suspension of train operation and restoration work without delay. For this purpose, it is important to detect the occurrence of avalanche correctly and immediately transmitted the information to the administrators of roads and railways. The Authors had already developed a snow avalanche detecting device and verified its performance. Alarm transmitting and failure diagnostic functions were added to this device to develop a new snow avalanche alarming system. In order to confirm its availability, we carried out long-term field tests at a slope prone to avalanche, at Mitsumata in Niigata Prefecture, for two winter seasons, from January 2002 to April 2003. Consequently, this system correctly detected three avalanches, and the information on the occurrence of avalanches and their scales was successfully transmitted to remote places without delay. During the test period, no system failures due to snowfall or low temperature occurred to demonstrate that the system had excellent practicality.

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Snow environments were observed continuously for eleven years from 1988 to 1999 at a meteorological station located in the snowy mountains of Niigata prefecture. Observation data showed that annual mean precipitation was approximately 2, 990 mm, half of which appeared to be snowfall. Total annual precipitation was greatly influenced by the amount of snowfall, which fluctuated much more than that of rainfall. Although no remarkable upward trend in annual mean air temperature was observed, the annual range of air temperature trended to increase slightly. This region was covered with a thick snow accumulation of 360 cm in mean maximum depth for an average of 141 days per year. The water flow from snow accumulation increased in snowmelting periods and high intensity flows were recorded under rainy or foehn weather.

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