秀姑巒溪河谷沖積扇之自然環境、土地利用及其土石災害

The Natural Environment, Land Use and Debris Hazard of Fluvial Fans in the Shiuguluan River Valley

陳紫娥(Zue-Er Chen)

《中華水土保持學報》 32卷1期 (2001/03) Pp. 17-27

https://doi.org/10.29417/JCSWC.200103_32(1).0003

摘要

秀姑巒溪河谷位於花東縱谷中段，谷口形成的沖積扇，屬於谷底沖積扇，有的形成中，亦有已因地殻抬升形成沖積扇階地以及河階地。研究結果發現，沖積扇階地安全性最高，而河谷扇多洪患，山溪扇多土石災害，重要的聚落集中於遠離洪水、土石影響之沖積扇階地，以及屬於土砂災害陰影區之發育中沖積扇扇緣。本河谷沖積扇材料來自易風化成黏土質之岩石，適植水稻田，而成爲東部著名的米鄉。河道偏扇緣者受災面較其位於扇央者廣，此因後者有較直而有效率之河道以疏解土石洪流之壓力；另沖積扇面上河道密集的攔砂壩，將土石攔阻於溪床上，土石淤高河床，與扇面高差逐漸降低，因此受河川的影響程度增加，是否適當應加考慮；其次河道彎曲而行，於攻擊坡處最易產生問題，考慮加強堤防工程或改變流路爲可行辦法。

關鍵字

沖積扇 ； 自然環境 ； 土地利用 ； 土石災害

並列摘要

Shiuguluan River valley is the middle part of the tectonic longitudinal valley of Eastern Taiwan. Topographic features observed in the field, such as the existence of ＂incomplete alluvial＂, ＂dissected fans＂ and ＂terraces＂, show that it is an area with stronger tectonic uplift than the other parts of the longitudinal valley. These terrains are physically safer in terms of flooding and debris flow, and thus have been well cultivated for agricultural produce and settlements. Two kinds of fluvial fans are identified in the valley concerned: one is of valley fan s and the other is of mountain fans. The former ones are larger in scale with flooding as its main hazard; the latter are smaller and are apt to debris flow, and thus have not been used for any purposes. Channels that run along the fan edge are easy to flood a wider area than those that run straight across the central part of the fans, because the latter are more efficient in releasing the flood pressure. Check dams built on the channels may have negative effects, because they upgrade the channel elevation and thus increase the probability of flooding the nearby areas. Another hazard related to the fluvial fan land use is the vigorous erosion taking place at the cut bank of the streams where stronger protection is needed to avoid unexpected hazards.

並列關鍵字

fluvial fans ； natural environment ； land use ； debris hazards

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