Assessment of Debris-Flow Hazards of Alluvial Fans

A strategy is presented for the assessment ofdebris-flow hazards on alluvial fans on the basis ofa case study carried out on the southern foot of astratovolcano named Mt. Yatsugatake. Transformation ofcommercial forests into a golf course was planned ata corner of the Kikkakezawa fan. The case studyinvolves an assessment of hazards due to debris flowsof different magnitudes and their recurrenceintervals. The environmental conditions for therecurrence of these debris flows are discussed as wellas the extent of the areas affected by them. In orderto generalize the case study, concepts of hazardpotential, hazard and risk for debris flows onalluvial fans are established. Accordingly, the hazardpotential is the possible hazards at any location onan alluvial fan in an indefinitely long time period,which can be assessed on the basis of hydrological andother geoscientific investigations. Hazards associatedwith a particular land use can be evaluated on thebasis of the hazard potential considering the locationand the time period associated with the land use. Riskcan be further assessed considering the life styles inthis land and the social conditions.