崩塌為集水區帶來大量泥砂，也是河川重要的土砂的來源。過去雖然有學者研究其河道發展，然而，如何量化輸送到下游的崩塌產生土砂量仍然是一個挑戰。本研究致力於量化受水流侵蝕的崩塌體的形貌變化和河川演化機制。我們使用去藕合二維模型來研究它的崩塌地貌受河川侵蝕演化過程。
本研究在水理方面，選用淺水波方程式來模擬水流流況。同時,利用流場求出河川輸砂率,在輸砂方面,則使用Exner方程式來計算泥沙傳輸質量的守恆，進而看出河川形貌的演化。此外，兩個方程都是以水平二維基礎以可侵蝕的河岸及沒有二次流假設下，選取的非線性項的控制方程，然而，解析方法無法解決此問題。因此，本研究採用有限體積法進行數值模擬。初步由流場結果發現，侵蝕最嚴重的區域為崩塌的下緣處，最為可能會發生二次崩塌的地方，而在進一步的河川演化過程，可以發現在本研究之假設條件下，結果發現於攻擊岸下游處為淤積處，主要控制原因為流場分布，原有的崩積體也由半圓形變得接近半橢圓,總體來說,河川的發展愈來愈趨近趨近於曲流。

Landslides produce enormous volumes of sediment in mountainous watersheds. However, quantifying landslide-derived sediment transported downstream remains a challenge. This study makes an effort in determining the amount of landslide-derived sediment that eroded by the water and the ratio of sediment yield of this problem. We try to use a decoupled two-dimensional model to investigate the evolution of landslide aggregation influenced by the channel flow.
In terms of the hydrodynamics model, we choose the shallow water equations to simulate the flow condition. Meanwhile, the flow field is used to determine the sediment transport rate of the river. In the aspect of sediment transport, the Exner equation is used to estimate the conservation of sediment transport and investigate channel evolution. Besides, both of the two equations under a horizontal 2D straight, non-erodible banks, and no secondary flow channel can be derived as our governing equation which has the nonlinear terms, and the analytical method may not work to solve the two equations under the 2D condition. As a result, this study adopts the finite volume method to proceed with this work. According to the preliminary results of the flow field, it is found that the most severely eroded area is at the lower edge of the landslides aggregation, and the place where the second collapse is most likely to occur. In the process of further river evolution, it can be found that under our assumptions, the results suggest that the deposition is in the downstream part of the attack shore and channel evolution is dominated by the flow field distribution. Also, the original landslides aggregation transforms a semi-elliptical into a semi-circle. In summary, the river develops the meandering stream gradually.

誌謝 i
中文摘要 ii
ABSTRACT iii
CONTENTS v
LIST OF FIGURES ix
LIST OF TABLES xiii
NOTATION xiv
Chapter 1 Introduction 1
1.1 Problem Statement 1
1.2 Research Objectives 2
1.3 Overview of thesis 3
Chapter 2 Literature Review 5
2.1 River morphodynamics 5
2.2 2D Shallow water equations 8
2.3 Sediment transport 11
Chapter 3 Methodology 15
3.1 Hydrodynamics model 15
3.1.1 Governing equations 16
3.1.2 Numerical scheme 17
3.1.3 The HLL Riemann solver 20
3.1.4 Source terms 23
3.1.5 Dry and wet fronts 23
3.1.6 Runge-Kutta time discretization 24
3.1.7 Initial and boundary conditions 25
3.2 Morphodynamics model 27
3.2.1 Sediment aggregation 27
3.2.2 Sediment transport 28
3.3 Model establishment 30
3.4 Model Validations 31
3.4.1 Linearized model: 2D tidal-wave problem 31
3.4.2 1D open-channel flow over a hump on basement 36
3.4.3 1D dam-break flow with a triangular hump located on the downstream channel. 38
Chapter 4 Case Study 42
4.1 Hydrodynamics simulations - steady flow 42
4.2 Sediment simulations – steady flow 58
Chapter 5 Conclusions and Recommendation 68
5.1 Conclusions 68
5.2 Recommendations 70
REFERENCES 71

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