土石流匯入主河道之堆積狀態及影響特性

Characteristics of Debris Fans Deposited in the Mainstream-Tributary Intersection and Their Impact on the Mainstream

蔡政廷(Cheng-ting Tsai)

指導教授 ： 林基源

朝陽科技大學/理工學院/營建工程系/碩士(2012年)

摘要

近年來全球極端氣候頻繁發生，天然災害規模擴大，複合型災害增加。2009年莫拉克颱風侵襲台灣，造成台灣中南部地區災情慘重，如小林村滅村及頭坑溪土石流等，均因山崩、土石流匯入主流形成堆積，土石擠壓主河道甚而造成堰塞湖，並因河道的束縮或隨著堰塞湖的流潰而對上、下游河岸產生嚴重影響。本研究以土石流渠槽試驗及FLO-2D二維數值模式，研究土石流在主支流不同交匯情況時，土石流扇狀堆積型態對主河道的影響。
土石流渠槽試驗共進行45組，包括三種交匯角度(30°、60°、90°)、三種支流坡度(13°、16°、19°)及五種體積濃度(0.45、0.50、0.55、0.60、0.65)，模擬並觀察支流發生土石流後匯入主流產生堆積，並經水流淘刷之過程，其堆積扇狀地上游、匯流口及下游面之變化情形。試驗結果依土石流扇狀堆積歸類劃分為支流淤積型、部分淤積型、完全淤積型、堰塞溢頂型等4種類型。而交匯角分別為30°、60°及90°時，擠壓率落在0~0.4、0.5~0.8及0.8~1之間；顯示交匯角度自30°增加到90°時，土石堆滿主河道機率有增加現象。堆積型態以支流坡度19°，體積濃度為0.45為例，交匯角30°寬厚比為23.7，交匯角60°寬厚比為21.2，交匯角90°寬厚比為16.8。顯示交匯角度愈大，交匯處堆積範圍縮小，堆積厚度變大，寬厚比則變小。尤其交匯角趨近於90°時，土石扇狀堆積堆滿主河道機率高，擠壓主河道之特性明顯，且堆積厚度大，最容易形成堰塞湖現象，對於匯流口及其對岸邊坡以及上下游兩岸之影響性也最高。
FLO-2D模式結合人為建置之水槽數值高程進行土石流模擬，分析結果與土石流渠槽試驗趨勢相同。藉由數值模擬觀測土石流在主支流交匯堆積與沖刷情形，包含土石流流動速度、堆積範圍、堆積厚度、主流之流速、流向及流況等。結果顯示土石流流速隨著支流流槽坡度的增加而增加，流速亦隨著土石流體積濃度的下降而增加。土石堆積擠壓主河道時，造成河道束縮，水流流速變快，在土石堆積前緣有沖刷情形。而FLO-2D雖可模擬土石流匯入主流之影響，但由於程式本身定床模式及較適合模擬泥流型土石流之限制，仍無法明確看出土石堰塞堆滿整個主河道，主流水流發生溢頂之情況。

關鍵字

土石流 ； 扇狀地 ； FLO-2D程式 ； 渠槽試驗 ； 極端氣候 ； 複合型災害 ； 莫拉克颱風

並列摘要

Due to the increasing extreme weather conditions in recent years, the frequency and magnitude of composite disasters are greatly increased. For example, in 2009, when Typhoon Morakot intruded Taiwan, there were severe disasters in both central and southern parts of Taiwan, including incidents as the whole village of Hsiaolin was wiped out, and occurrences of severe debris-flow disasters in Toukeng Creek. This study were completed through debris-flow flume experiments and a two dimensional numerical model FLO-2D. The flume experiments and FLO-2D simulation results were used to analyze the characteristics of debris fans deposited in the mainstream-tributary intersection.
Forty five sets of flume experiments, three intersection angle (30 °, 60 °, 90 °), three tributaries of the slope (13 °, 16 °, 19 °) and five volume concentration (0.45, 0.50, 0.55, 0.60, 0.65), were proceed in this research. According to the debris fans piling up in the mainstream-tributary intersection, four types of debris fans were classified as tributary deposited, part of mainstream deposited, completely mainstream deposited, and barrier-deposited and overflow.
The test results showed that the velocity of debris flow increased with the increase in the slope of tributary, also increased with the decline in the volume concentration. In general, when the angle of mainstream-tributary intersection increases, the debris flow squeeze the main river channel behavior becomes more obvious, the smaller deposition width, the larger deposition thick. In particular, the intersection angle of 90 °, most likely to form a short period of barrier lake, the impact to the upstream and downstream riversides is also the highest. Using the FLO-2D two-dimensional numerical model to simulate the flume experiments by the artificially building flume DEM, simulation results have similar trend with the flume experiment results.

並列關鍵字

debris flow ； debris fans ； flume experiments ； FLO-2D model ； Typhoon Morakot ； composite disasters ； extreme weather

參考文獻

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