大甲溪流域土石流發生時警戒指標值建立之研究－以敏督利颱風為例

The Study on the Creation of Alarm Index Value Upon the Occurrence of Debris Flow in Dajia River Basin-Example from Mindulle Typhoon

楊宏宇(Horng-Yu Yang) ； 許菁倩(Ching-Chien Hsu) ； 楊修毅(Hsiu-Yi Yang) ； 王怡君(Yi-Chun Wang)

《中華技術學院學報》 38期 (2008/06) Pp. 127-143

https://doi.org/10.7095/JCIT.200806.0127

摘要

台灣山坡地占總面積73.3%，為東西兩岸狹長平原，地理環境特殊，是生態環境敏感地區，由於山勢陡峭、降雨豐富且集中（全年平均雨量高達2,500mm），河流短促，地層鬆軟，加上山脈地質脆弱易斷裂且地震頻繁，充分構成土石流的有利條件。此環境地形影響，各河川形成上、下游兩段截然不同的流況，上游段地勢陡峻，水流湍急；下游段衝出山谷流入平地後，河幅突增，地勢平緩，水流轉為蜿蜒曲折，流路不定；山區地質多不穩定，土壤淺薄，天然條件不佳且地震頻繁，山區易發生山崩及地滑，伴隨產生大量的土石堆積於河床，遇豪大雨時泥沙則隨山洪急瀉而下，形成土石流並造成下游水質渾濁，河床逐漸升高，造成沿岸高度發展地區嚴重災害；更因人口急遽增加及工商業高度成長，山坡地過度開發使用，環境嚴重遭受破壞因而失去平衡。
而台灣再經歷了民國89年九二一集集大地震後，造成中部地區苗栗縣、台中縣、南投縣、彰化縣、雲林縣、嘉義縣等山區發生大量的土石崩落，且地震也使得原本脆弱的地質更加惡化，鬆散的土石更提供危險溪流豐富的材料來源，以提高土石流發生的頻率。民國90年桃芝颱風夾帶著豪大雨來襲，亦造成中部重建區及花蓮地區嚴重的土石流災情，共造成103人死亡、111人失蹤、189人受傷，民眾的生命財產安全遭受到嚴重的損失。因此，如何發展出土石流預警系統，並提高預警的精準度，能適時提供有效的訊息，讓民眾有充裕的逃生時間，儼然已成為當前土石流災害防治工作的重要課題。

關鍵字

降雨驅動指標 ； 地文潛勢指標

並列摘要

As for potential debris flow torrents, whether the debris flow will occur or not depends on local hydrologic and geologic conditions. The previous researches studied the critical hydrologic condition (critical rainfall condition) for the occurrence of debris flow, which lacked the consideration of geologic condition. So, this paper utilizes the product of rainfall density and effective accumulated rainfall amount as the rainfall driven index of debris flow. But the critical rainfall driven index of debris flow depends on the change of geologic condition. Due to the geologic condition of debris flow is much complicated, this paper will create the potential geologic index of debris flow, which includes several geologic factors. Then the relationship between potential geologic index and rainfall driven index will be analyzed, and the comprehensive rainfall-geologic alarm index of debris flow (abbreviated as rainfall-geologic index of debris flow) will be created.
The subjects of this paper are the potential rivers in Dajia River Basin, Taichung County. At first, collect various possible geologic factors which might influence the occurrence of debris flow, and apply the statistical analysis method to screen out 5 major geologic factors which will influence the occurrence of debris flow. The fuzzy statistics is used to create the quantitative geologic index Ni for 5 geologic factors, respectively. Then the profile analysis method is used to evaluate the weight ai of each geologic index, and the linear addition method is used to create the potential geologic index of debris flow GI. Finally, the product of the rainfall driven index RI and the potential geologic index GI is used as the comprehensive rainfall-geologic alarm index of debris flow RGI (rainfall-geologic index of debris flow).

並列關鍵字

Rainfall driven index ； Potential geologic index