利用水深與地形共同測繪分析河川形貌動力學縮尺實驗之研究

Joint flow depth and surface topography mapping for small scale channel morphodynamics experiments

魏新容(Hsin-Jung Wei)

指導教授 ： 卡艾瑋

國立臺灣大學/工學院/土木工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101605

摘要

本論文主要研究目的為利用兩組小尺度水工模型試驗，探討不同供砂狀態對河川與地貌演化之影響，並透過影像分析的方式，進行水深分布與地形之重建。為獲得水深資訊，本研究發展出一套量測方式。將染劑溶入水中作為吸光材料，並以相機紀錄實驗過程。根據光的特性，光強度隨水深衰減，透過此一關係可進行影像亮度與水深資訊之轉換。經過驗證測試，此法之誤差值可控制在1毫米內。佐以雷射掃描技術，即可對水深與地貌進行共同測繪。最後就實驗結果加以討論，並與霧社水庫進行比較。
實驗結果顯示，供砂量之多寡明顯影響河川與地貌之演化。當上游供砂量較少時，河流的水深較深且窄，並呈現較穩定之狀態;當上游提供大量砂源時，河流之水深較淺且河幅較寬，並形成許多支流。其流路不穩定，隨時間快速擺盪。此外，在供砂量較高之狀態下，地貌之侵蝕與堆積作用亦較旺盛。兩組實驗中，河川下游出砂量與渠底坡度最終將趨於平衡。此些於水工模型中觀察到之現象皆與霧社水庫之河川與地貌演化相似。

關鍵字

水工模型實驗 ； 霧社水庫 ； 影像分析 ； 染料 ； 形貌學 ； 供砂量

並列摘要

In this thesis, two sets of small-scale laboratory experiments were carried out to investigate the effects of sediment supply on river morphodynamics. Flow depth and bed topography are reconstructed through the image processing technique. For the acquisition of flow depth distribution, we propose a measurement approach. A Colouring agent was added to the water as a light absorber, and the observation area was monitored by a camera throughout the experiment. The gray tones of the acquired images were converted into the depth maps according to the optical properties that the luminance intensity dissipates as water depth increases. The validation test shows that this measurement technique achieves an accuracy of sub-millimeter. Combined with the laser scanning method, the distribution of flow depth and surface topography were mapped jointly. Finally, the analysis results of experimental cases are discussed and compared with Wushe Reservoir.
The results show that the sediment supply significantly influences the river morphodynamics. A stable, deep and narrow channel is developed with low sediment influx, whereas the river fed by large amounts of sediment develops shallower but wider channels, separates into multiple tributaries and shifts frequently over time. In addition, erosion and deposition of bed topography are more intense as we provide more sediment influx. In both experimental cases, the sediment production at the outlet downstream and the channel bed slope consequently reach a plateau. The phenomena of river morphodynamics observed in laboratory experiments are very similar to those occurring in Wushe Reservoir.

並列關鍵字

laboratory experiment ； Wushe Reservoir ； image analysis ； dye ； morphology ； sediment supply

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