本研究主要以實驗的方式來觀測於不同初始泥水混合濃度條件下中的沉降過程。由初始泥水混合濃度估算出濃度的變化速度。除了運用在水庫上，本文亦希望了解整個沉降機制可以運用處理泥砂運動、解決海岸的流失以及港口淤泥等問題。
本文採用高嶺土做為本實驗泥質，於邊長0.8 cm的方形水槽，利用沒水式馬達調製出均勻的濃度環境下進行不同初始泥水混合濃度條件下的沉降實驗，運用ABS聲學儀器來量測沉降過程出現的泥水交界面的變化，估算出泥水交界面的速度，得到於低濃度時交界面的沉降速度會隨濃度增加而變快，直到濃度達到3000 mg/l其沉降速度會隨濃度增加而下降。本實驗於不同的位置設置六根濁度計用來量測垂直濃度剖面的變化，量測結果得到於濃度2000mg/l以下時交界面未出現，直到濃度條件為2000mg/l ~ 3000mg/l會出現較不明顯的交界面，濃度條件達3000mg/l以上時則會出現較明顯的泥水交界面，與ABS的結果相對應，故本文定義濃度條件達3000mg/l才會出現較明顯的泥水交界面。由濁度計所量測的垂直濃度剖面的結果運用質量守恆的概念計算出沉降速度。
根據ABS量測到的不連續交界面出現的時間及位置計算出最大梯度值得知在不同的初始濃度條件下整個空間的最大梯度分布會呈現不同的趨勢，依初始濃度條件分類可分成濃度為2000 mg/l ~ 2500 mg/l、2800 mg/l ~ 3500 mg/l、3500 mg/l ~ 5500 mg/l及5500 mg/l ~ 13000 mg/l共四種型態。

關鍵詞：高嶺土,沉降速度,泥水混合濃度,泥水交界面,濁度計

The experimental studies is focused research on the settling process with different suspended sediment concentration (SSC).Although settling velocity depends mainly on initial SSC. Settling behavior and distribution of concentration are also affected by the intensity of concentration gradient.
Kaolinite is used as bed material, which is typical cohesive sediment. The experiment is conducted in a square tank with length of 0.8 m, equipped with two smbmerged pumps. Six optical backscatter sensors (OBS) were used to monitor the change of suspended sediment concentration (SSC) at different levels. Time-averaged settling velocity was determined by depth-integrated mass balance equation from OBS. Additionally, acoustic backscatter system (ABS) was used to provide clear insight of interface, and the movement of interface will be used to determine fall speed. The result has shown that settling velocity increases with SSC in the enhanced settling velocity of SSC < 3000 mg/l and then decreases. From the result of OBS, interface didn’t appear in SSC < 2000 mg/l. The transition region ranges from 2000 mg/l ~ 3000 mg/l, and finally appear in SSC > 3000 mg/l. We define that when SSC is bigger than 3000 mg/l, there exist a interface. Furthermore, the similarlities of greatest concentration gradient distribution and the initial concentration are observed in our experiment.
KEYWORDS: cohesive sediment, suspended sediment concentration, settling velocity, concentration gradient, optical backscatter sensors, acoustic backscatter system

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