Elucidation of the warning rainfall criteria against landslide disasters, taking the soil moisture content into consideration

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In mountainous forest areas, roads or railroads and local inhabitants sometime suffer from sediment related disasters along torrents. On this point of view, monitoring of the sediment runoff and analysis of its characteristic in a mountainous torrent have carried out, in order to set up the runoff criteria of sediment from the torrent and the local standard rainfall for warning and evacuation. The research is run on a torrent whose geology consists of Paleozoic metamorphic rocks (mainly schist) and whose vegetation consists of mainly Japanese cypress as well as in similar forest slopes in Nuevo Leon Mexico, Sulawesi Indonesia, around Kathmandu Nepal. Soil depth is approximately 50cm in average and permeability is k=10^<-2> 10^<-3> order. Rain, wind speed, soil moisture content, sediment discharge (periodical observation) were monitored and the sediment runoff characteristic obtained by the monitoring and the observation over 3 years.1) Theoretical Critical Standard of Sudden Sediment R … More unoff based on the Hirano's discharge theory or the Self Organized Criticality Assumption SOCThe soil moisture content along the torrent (riparian area) is not affected by antecedent rainfall according to the field observation, so is the sediment runoff from torrent bed or torrent sides which does not include the runoff triggered by landslides or slope failures.The accuracy of this method contemplated by detective ratio or critical success index with the present data is high (almost 100%).2) Theoretical Critical Standard based on the Elementary Catastrophe Theory (ETC)Providing that the Elementary Catastrophe Theory (ETC) can be applied to this critical line, the critical line is described by next equation adopting the wedge type catastrophe theory. However, it has the cross point with lateral axis i.e. Pd=0. It is impossible for rain to take this combination of the Pa and Pi. Therefore, the ETC is not suitable in this case.Since the sediment runoff from torrent bed or torrent sides (which does not include the runoff triggered by landslides or slope failures) is not affected by antecedent rainfall based on the field observation, formulas derived in this study is rather simple and handy than the other methods. Less