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標題: A study of relationship between the rainfall return period and the landslide site in a watershed
作者: Cheng-Yu Lin
Yuan-Jung Chen
Chao-Yuan Lin
關鍵字: Return period;Collapse scale;Spatial distribution of landslides;Near-riverbank;Off-riverbank;重現期距;崩塌規模;崩塌區位;近岸崩塌;離岸崩塌
Project: 水土保持學報, Volume 48, Issue 4, Page(s) 1863-1876.
Previous studies on the collapses indicated that the weak geology condition and extreme rainfall are the main reasons of landslide. However, it was unable to explain the neighboring non-failure site, which the similar geological condition. Frequency of landslide event is always inversely proportional to the landslide scale, and therefore return period and scale should be distinguished. In addition, landslides in the watershed could be categorized by the occurrence locations i.e. near-riverbank and off-riverbank landslide, which are not only caused different mechanism but also different landslide scale. Near-riverbank landslides are mainly affected by a stream, whereas off-riverbank landslides are usually influenced by rainfall intensity. Thus, the relationship between the collapse location characteristics and different rainfall return periods is relatively important to explore. Chen-You-Lan watershed was selected as the study area due to numerous landslides. The events of Typhoon Herb, Toraji and Morakot, which caused more serious disasters, were selected to estimate rainfall return period and extract the each newly collapses. According to the terrain and land use of landslide sites, the collapse sites can be classified as headstream, river, road and cultivation categories. In addition, the spatial distribution and trend relationships for the collapse site and the correspondent scale were also well discussed under the different return periods. The results showed that rainfall return period of the selected events is quite different although the rainfall intensity is similar. Typhoon Herb has the highest return period (100-yr) and caused the largest amount of collapse area and volume, which implies the noticeable factor for the collapse scale is rainfall return period. Over 60% of landslide sites, trigged by three typhoon events, were categorized as river landslide. Over 80% of the re-collapse area located at near-riverbank which was vulnerability to erode by stream and resulting in slope toe failure. In contrary, the headstream collapses are invulnerability to recurrence landslide since the deposited sediment could stabilized the slope toe.

過去研究對崩塌現象之發生,常歸咎於極端降雨及地質條件,卻未能解釋鄰近相似條件 之區位未發生災害之現象。崩塌發生頻率常與規模成反比,因此邊坡發生崩塌之機率及其規模 宜有區隔,集水區邊坡崩塌除立地條件不同外,主要可歸納為近岸及離岸崩塌,近岸崩塌主要 受逕流;離岸崩塌則受降雨強度所影響,不同區位不僅誘發的機制不同,規模大小也有所差異, 故集水區降雨重現期距與崩塌特性關係亟待探討。本研究以陳有蘭溪集水區為樣區,選取受災 較為嚴重之賀伯、桃芝及莫拉克等三場颱風事件,推估其降雨事件之重現期距及萃取新增崩塌 區位,另以地形及土地利用將崩塌發生區位分為源頭、河道、道路及農墾地等四類,針對集水 區於不同降雨重現期距下,探究崩塌區位與規模之空間分布及趨勢關係。結果顯示三場事件雖 單日降雨強度相近,重現期距卻以賀伯颱風之 100 年為最大,且崩塌面積及量體亦最大,可見 崩塌規模主要影響因子為降雨重現期距。三場事件中河道崩塌所佔比例最大,皆 60%以上,而 重複崩塌區位亦以近岸崩塌為主,重複崩塌面積達 80%,主因為河道邊坡本為水流易攻擊之區 位,一旦基腳被攻穿常造成淺層崩塌,而源頭區位則因崩落之土砂恰可穩定基腳,因此再次發 生崩塌機率不高。
Appears in Collections:第48卷 第04期

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