豪雨と水害の研究 第2報

1969年南九州シラス地域の梅雨前線豪雨災害

抄録

From 28th of June to 8th July, 1969, very active Baiu front passing through the southern past of Kyushu, especially kagoshima prefecture, brought about extraordinarily heavy railfall, and disastrous floods, landslides, and agricultural calamities resulted. The author investigated from a point of calamity the relation of the distribution of landslidse to rainfall, landform and geology.
The results are summarized as follows:
(1) The Shirasu areas of the most frequent landslides nearly coincides with the area where the maximum 10min. rainfall exceeded 10-45mm, or hourly rainfall exceeded 30-50mm.
(2) The Shirasu areas where few landslides occurred in spite of hourly rainfall exceed 50mm has a landform composed mainly of gently slope.
(3) After intermittent rain which has continued from the morning of 28th of June, downpour started by midnight. At the time of maximum intensity more than 50mm or rainfall where recorded during one hour and a half. It was after this time that most of landslides occured.
(4) All the landslides are of a small-scale and only the weathered material 0.5-2.0 meters thick lying on the top has slided.
(5) Results of rainfall network analysis for June 30, 1969 storms seems to indicate direct correlations between the movements of severe storms and the surface topographical parameter distribution. These correlation were particular remarkable in the rain intensity and wind fields. There was also some evidence of correlation between the 10min. intensity of rainfall and number of landslides per Km².