Many hillside landslides and debris flows occurred by typhoon T ‚O‚S‚Q‚P in Miyagawa village ithe present Odai townj on September‚Q‚X, ‚Q‚O‚O‚S. These caused severe sediment]related disasters. In this study, several findings on the influence of precipitation, slope angle and forest practice on hillside landslides caused by typhoon T‚O‚S‚Q‚P were shown in Miyagawa]dam basin as followsF‚PjCorrelation between precipitation and collapsed area ratio was not clear. ‚QjAngle of collapsed slope in deforestation sites was ‚T|‚P‚O‹lower than those of non]forestation and reforestation sites. ‚RjCollapsed area in deforestation sites occupied ‚T‚V“ in total collapsed area. ‚SjMost of landslides were occurred since ‚P‚O to ‚Q‚O years after deforestation. ‚TjMore hillside landslides observed in larger deforestation area. ‚UjA prediction model of slope stability changes considering forest practice iKuroiwa and Hiramatsu, ‚Q‚O‚O‚Sj was applicable to Miyagawa]dam basin. As the result of this simulation, collapsed area is generally in proportion to collapsing possibility area ratio index iAPhritjj. ‚VjAngle of collapsed slope and APhritjand collapsed area ratio showed significant correlation.


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