三角洲演進與輸砂量分布關係之研究

Abstract

本研究主要的研究目的是探討三角洲在不同的供砂情形下，如何堆積與對形貌改變之影響。分為兩個部分，第一部分是基於柯文韜博士在2016年所推導的三角洲前進方程式，附加考慮下游的泥沙通量，進而延伸此前進方程式，並已此為基礎，研發一套數值模型來模擬三維三角洲的動態演進過程，再利用三角洲形貌的解析解與實驗成果，對此數值模型進行驗證。第二部分是以現地調查作為啟發，現地調查是以位在台灣中部的霧社水庫作為研究案例，進行縱剖面的測量與無人飛行載具的航照測量，對獲取之現地資料進行觀察，並設計一套實驗，模擬水庫三角洲在定水位時與降低水位後的淤積情形，使用雷射掃描與追蹤粒子進行影像分析，最後將實驗成果與現地現象進行比較。 結果顯示，第一部分的數值模型得以成功模擬三角洲演進之過程，驗證出供砂分佈的多寡影響著三角洲前緣的形狀，此形狀再影響著三角洲在前基層的堆積分佈。第二部分的實驗模擬出霧社水庫現地之現象，包含在一段時間內發生的多變的河道網絡、三角洲演進、三角洲頂基層的形貌改變、水位下降後的沖刷現象等，實驗中，藉由粒子軌跡求得流速分佈，以流速大小代表供砂多寡並驗證其對三角洲淤積情況之影響，實驗的流速亦與現地流速比較得出河寬與流速之關係。

The purpose of the research is to investigate the delta progradation and the influence of morphology with different conditions of sediment supply. We divided into two sections. The first part is based on the theory for the curvature dependence of delta front progradation from Ke (2016). The theory is extended by considering the sediment bypass across the downstream boundary. Moreoever, a numerical model is developed to simulate the dynamic delta progradation in 3D. This numerical model is verified by the experimental results and the analytical solutions. The beginning of the second part is the field survey. Wushe Reservoir in central Taiwan is as our study case. We conducted the traverse survey and aerial photogrammetry by UAV to observe the phenomena in the field. To simulate the delta conditions in the reservoir, the experiment was designed and analyzed with the laser scanning and particle tracking. Finally, the experimental results are compared with the field data. In results, the numerical model in the first part can simulate the delta progradation. We verify that the sediment supply distribution influences the shape of shoreline, which affects the deposition on the delta foreset. The experiment in the second part can simulate the phenomena in Wushe Reservoir, including the various channel networks, delta progradation, change of morphology on the topset, and the erosion after water level falling. In the experiment, the flow velocity can be obtained by the particle paths. The velocity represents the amount of sediment supply and influences the deposition on delta. The velocity in the experiment is also compared with the velocity in the field to explore the relationship between the width of channel and the velocity.