航空写真の判読による土石流の流走範囲の推定について(そのI)

Abstract

Rocky mudflow often occurs in the mountainous regions in our country by heavy rains, but manyproblems on mudflow have remained unsettled, for an example, the process of starting and stoppingof mudflow.Recently airphotographs of damaged district by mudilow have been taken for protection plann-ing.By the use of these photos starting and stopping point of mudflow can be found and the runoutextent of rocky mudflow can be estimated.Utilized airphotos are white and black pictures and the scale of photos are 1/6000, 1/8000 and1/10000.From airphotos of damaged districts at Amakusa. In Kumamoto, at Tsubeta in Niigata, Kumano and Owase city in Mie, starting and stopping points of mudflow were plotted on top-ographic maps.At the same time, flowing path of mudflow was devided into two parts, in the valley and fan.The starting point of mudflow was decided as a place where side erosion was cleary recognizedand stopping point was decided as a point where large stones stopped collectively.Runout distance of rocky mudflow estimated from above mentioned method ha-I no directrelation with the altitude of starting point, but there exists a relation between valley length andrunout distance at fan as shown in Fig. 6.And empirically the runout distance from fan head to stopping place seems to be 40% -60%of flowing down distance along valley.