水庫水位變動對於水庫淤積三角洲形貌變化：實驗與現地測量

Abstract

本論文利用野外現場資料以及實驗模型，討論水庫水位變化對水庫淤積三角洲形貌的影響。為了瞭解這層關係，我們選定了霧社水庫做為野外研究對象，台灣電力公司也提供我們關於霧社水庫淤積情況的淤積測量資料，並於我們兩次不同時間點的現地調查時給予協助；根據霧社水庫現場的資料，我們設計一個可調整水位高低的寬型三維水槽作為現地的水工模型，使用粗、細不同粒徑的沙子進行實驗，將實驗過程還有地形變化的發展，使用相機以及雷射掃描作記錄。從實驗及現地觀察得到三角洲上不同高度的河階，受河道遷移而退縮的河岸，及由不同粒徑大小的沉積物分層堆疊的堆積體的現象;另外受水位變化的影響，屬於三角洲頂積層部分會在水位上升時變成為前基層，反之亦然;當水位下降時三角洲頂積層會被河道沖蝕下切，砂土則被帶到下游形成了前基層,部分異重流造成的淤積，會由於河道偏向另一側時而被保留下來。當實驗可以達到非常近似於現地的現象時，我們可以在實驗時針對現象去做更完整、細部的觀察。

In this thesis, field measurements and laboratory experiments are performed to investigate the relationship between water level variations and delta morphodynamics. To understand this relationship, we selected Wushe Reservoir for a field case study. For this reservoir, subject to rapid sedimentation, Taiwan Power Company agreed to provide data and grant access for us to measure subaerial and subaqueous deltaic profiles at two different times. Based on the field data, we then conducted laboratory experiment with a wide flume, a changing water level, mixed coarse and fine sand, and a camera and laser system monitoring the experimental process and evolving morphology. Both in the field and in the experiments, we observed the formation of multiple terrace levels, banklines retreat due to migrating channels, and the deposition of interbedded coarse and fine layers. As the water level changes, subaqueous deposits become subaerial and vice versa. Moreover, some hyperpycnal deposits may be preserved within side terraces over at least one cycle of lake filling and emptying. During falling water stage, the river channel incises the topset bed and aliments a prograding subaqueous delta lobe. Unlike in the field, these processes can be monitored continuously in the laboratory experiments.