豐丘土石流災害之探討

A Study on the Debris-Flow Disasters at Feng-Chiou

游繁結(Fan-Chieh Yu) ； 陳重光(Chung-Kuang Chen)

《中華水土保持學報》 18卷1期 (1987/05) Pp. 76-92

https://doi.org/10.29417/JCSWC.198705_18(1).0008

摘要

台灣之土石流災害雖然嚴重，但有關土石流發生之個案研究極少，本文因掌握到南投縣信義鄉豐丘於民國75年8月間所發生之土石流災害的前後地形資料，乃擬對該區之土石流發生原因加以探討，並預測其未來之發展，以爲治理工作之參考。而主要調査工作包括地形測量、土砂採樣分析、粒徑分析、比重與孔隙率測定、及雨量資料分析等，並根據理論公式推估其發生之特性，所得結果如下述：1.該區土砂災害之發生係因上游段大面積崩塌，其所產生之土砂堆積於溪床上，在日降雨量達200〜300 mm時，以土石流之方式流出。2.民國75年8月之土石流，當土砂流出谷口後，即以8〜10 m/min之速度推進，且流出之總土砂量約爲3 x 10^5 m^3，重達4.9 x 10^5 ton，造成下游廣大之受災面。3.現有之攔砂埧可有效攔阻土砂流下，改變局部溪床之縱向坡度，對土石流之發生有抑制之功效，但集水區上游段之土砂生產，若無法有效抑制，該地仍有土石流流下之虞。4.為預防上游崩塌土砂之生產及土石流之發生，該地區在現有攔砂埧之上游仍有作一系列攔砂埧之必要，以有效防止該溪谷之土石流災害發生。5.依該地土砂之特性，土石流之臨界坡度約爲16°，此一標準可作爲攔砂埧安定坡度設計之參考。

並列摘要

The debris-flow disasters frequently occurred on the slope land of Taiwan, but there're few studies on it. This paper had gotten the geomorphological informations before and after the disaster that occurred at Feng-Chiou on August, 1986, so we tried to study on the mechanism of the occurrence of debris-flow, and to predict what it will be. The major items of investigation including geomorphological surveying, soil samples analysis, grain-size analysis, specific gravity and porosity measuring, rainfall data, and so on. And according to the theoretical formula, the characteristics of debris-flow occurrence were studed. The results were obtained as follows: 1. The disaster was caused by the form of debris-flow, when the rainfall intensity was as large as 200-300mm/day. 2. After the debris-flow passed through the valley, it flowed at the velocity of 8-10 m/min, and at a volume of 3x10^5 m^3 of sediments, which produced a large disastrous area in the downstream. 3. A check-dam was built on this valley to save sediments. But as the check-dam is full of sediments and the landslides continually proceed in the upstream of watershed, the debris-flow will occure again in future. 4. For controlling the landslides and preventing from the occurrence of debris-flow, a series of check-dam should be built in order to stabilize this valley. 5. According to the characteristics of deposited sediments, the critical slope of the debris-flow occurring was estimated about 16°. This value may be applied to design the equilibrium slope of check-dam.