台灣地區地狹人稠,山坡地開發已日漸成為趨勢,過度開發山坡地,容易引發相當嚴重的崩塌、落石或土石流,本研究主要以土石流發生因子中的降雨因子來探討;以南投地區曾經發生過地震的溪流為標的,比較地震前與後的臨界降雨線的差異。 1998年瑞里大地震及1999年9月21日集集大地震,因地震後山坡地土石鬆軟,每當大雨來臨時更易發生山崩及土石流。本研究主要研究範圍為南投地區曾經發生過土石流的地區來取得降雨資料,將降雨資料分成地震前後之臨界降雨線,比較地震前後臨界降雨線的差別,讓往後的人可暸解當地震後土層鬆軟的地區如有降雨達到某一種程度需注意是否有引發土石流之可能性。 本研究利用費雪區別函數,並收集南投地區四個站的歷史雨量資料,以有效累積雨量Y及降雨延時X,藉此得出921地震前後之臨界降雨線;由歷史資料點得出921地震後南投地區臨界降雨線的改變,使得土石流發生的頻率增高。
Mass wasting disasters caused by over-development of slope lands has become one of major issues in Taiwan. Occurrence of landslides and debris flows has become more frequent after major earthquakes such as 1998 Ju-li and 1999 Chi-Chi. Rainfall is one of factors causing debris flow. This study is to find whether earthquake makes any difference of critical rainfall which causes debris flow, by comparing the pre-earthquake rainfall event with the post-earthquake rainfall event. The study area is focused on the Nan-tou district, Central Taiwan, where debris flows occurred frequently. Historical rainfall records were collected from four rain-gage stations. The plot of effective rainfall verse rainfall retention period was analyzed by the Fisher’s discrimination function to find the critical rainfall line. The result discloses that the slope of the critical rainfall line for the post-earthquake rainfall event is steeper than that for the pre-earthquake rainfall event. It confirms that the debris flow occurred more frequently after the 1999 Chi-Chi earthquake in that area.