Present state of design rainfall intensities used for Sabo-related facilities

Abstract

Sabo-related facilities are planned and designed chiefly for peak sediment discharges and for the volume of sliding debris mass. Amounts of rainfall and river or slope (sub-) surface flow discharges do not always determine their plans and designs, despite their triggering impacts. Sediment production and landslide movement are less frequent events than floods or severe ground water flows. Sabo-related facilities are expected to be instrumental in river control as well as in hillside urban drainage systems, never to be of any harm. Harmonization is indispensable. Also, with the evolving climate change, extreme rainfall seems to happen more often than before. Basic rainfall intensities are set locally in different formats. In this paper, therefore, their present states are collected and shown nationwide in terms of both 24 hour rain and supplementary 60 min rain, which vary from one area to the others. In a worst area, current planned rainfall is 40% that of the estimation (1/100) suggested in this study. The result is expected to be a basis for further detailed studies, especially for risk assessment.