Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/34034
標題: 泥流及土石流湧浪進入河道所引致之地形變化
GEOMORPHIC CHANGE INDUCED BY THE FLOW OF MUD AND DEBRIS SURGES INTO RIVER CHANNELS
作者: 彭思顯
Peng, Szu-Hsien
關鍵字: 堰塞湖;landslide-dammed lake;高含砂水流;交匯模式;Voronoï影像追蹤法;二層流體淺水流方程;賓漢流體;有限體積法;HLL型數值格式;hyperconcentrated flow;confluence mode;Voronoïimaging method;two-layer shallow water equations;Bingham fluid;finite volume method;HLL scheme
出版社: 水土保持學系
摘要: 
This study examines various ways in which flow slides and river currents interact, including blocking of rivers due to either accumulated debris or to the formation of landslide dams across the channel width. In other situations, local narrowing of a channel can occur due to partial invasion by a debris fan. At the outlets of debris flow gullies, thick deposits may be left for water currents to slowly transport downstream. The study is composed of three parts: (1) systematic field observations; (2) laboratory experiments; (3) computational simulations. The purpose of this work is to study this confluence behavior of a hyperconcentrated tributary inflowing the main river.
In the first part, it collects numerous previous studies and field investigations in order to study confluence modes of debris slides and river flows in Taiwan. A preliminary classification is established according to the basic concepts of sediment transport. We have analyzed several examples further and applied them to our catalogue to illustrate the classification method in detail. The confluence mechanism can be realized through this classification but it still needs more study, including of experimental research, as well as field investigation to better establish the classification framework.
In the second part, it uses digital image processing to survey the confluence behavior of a tributary with hyperconcentrated flow entering the main river. The experiment has two parts: in the first, digital terrain data were computed via coordinate transformation from profiles extracted by laserlines; in the second, velocity fields were obtained by using Vorono imaging method to analyze the images through low-pass and high-pass filters when trace-particles were added. The measurement approach is described and preliminary results are presented. Through the discussion of alluvial fan morphology, we can better understand the interaction of this mechanism.
Finally, we proposed a numerical scheme to simulate the confluence phenomenon by using two-layer shallow water equations. The rheology behavior of mudflow or debris flow was regarded as the Herschel and Bulkley or Bingham fluid. Thus the shear stress on rigid bed can be derived from the constitutive equation. The computational approach uses the HLL scheme as a basic building block, treats the bottom slope by lateralizing the momentum flux, then refines the scheme using the Strang splitting to deal with the frictional source term. This study successfully set up 1D and 2D two-layer shallow water computations on rigid bed. The numerical model can describe the variety of depths and velocities, including water and mud, when the hyperconcentrated tributary flows into the main river. The results in this study will be helpful for advanced research sequentially and design or plan of hydraulic engineering structures.

台灣地區山坡地及高山林地約佔全島面積四分之三,地勢可謂相當陡峻,因此大多數之河川呈現源短流急之特性,且雨量豐沛、地質脆弱,造成河川含砂量特別高。因此崩塌、土石流等山地災害頻傳,造成嚴重的生命財產損失,且崩塌土體及高含砂水流堵塞河道形成堰塞湖之事件也時有所聞。因此崩塌土體或高含砂水流挾帶大量泥砂入匯主河河道,對入匯口附近之水流形態造成影響,並進而引起當地河床突變,甚至於主河下游河段之河相亦可能發生改變。由於高含砂水流入匯主流所形成之交匯行為在台灣山區是十分常見的現象,但是因為其交匯機制牽涉到太多複雜之因素,致使相關文獻十分有限。
本研究分別由三個主軸,包括交匯型態之分類、室內水槽實驗及數值模擬等,對此課題進行探討。首先蒐集前人相關研究及配合現地調查,以基本之泥砂運移物理概念建立台灣地區河岸崩塌及高含砂支流與主河水流交匯模式之初步分類及型態描述。交匯型態主要可分為完全堵河與不完全堵河兩大類:其中完全堵河以崩塌造成的居多,可分為六種型態;而不完全堵河則包括崩塌與土石流支流入匯等情形,根據其相對於主河之作用強弱可分為四種類型。文中並舉出數個實例應用於此分類型態,包括土石流與主河交匯之例及河岸崩塌阻斷主河形成堰塞湖之例,以說明其交匯現象,增加對此機制更深一層之認識。
接著利用數位影像處理技術進行室內渠槽試驗,主要工作為探討高含砂支流入匯主河之交匯行為,其量測方法確實可行且已有初步成果。實驗量測主要可分為兩大部份:一是針對主支流交匯時流場之量測,係採用Voronoï影像追蹤法,於試驗區放置示踨球,將拍攝之交匯影像處理後取得流場分析;另一是使用雷射光筆投射於交匯後形成之泥砂堆積體,以擷取之各剖面經由座標轉換得出數位地形資料,所獲得之相關結果均可作為數值模擬之參考。
最後則利用二層流體之淺水流方程建立可模擬交匯現象之數值模式,以有限體積法之顯式均勻網格離散控制方程式,數值方法以HLL型數值格式為主要架構,利用lateralisation of momentum flux來處理坡度效應,最後再使用Strang splitting的方式計算含有摩擦力之源項部份。本研究已成功地建立一維及二維定床二層流體之數值模式,可模擬高含砂支流入匯主河時深度及流場之變化。冀望透過本研究能增進對此現象的了解,並可於未來進一步探討泥砂在主河水流中堆積或沖刷之過程及對河床變形之演變,作為日後研究的基礎或工程規劃設計上能有所幫助。
URI: http://hdl.handle.net/11455/34034
Appears in Collections:水土保持學系

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