| Summary: | 碩士 === 國立成功大學 === 水利及海洋工程學系碩博士班 === 97 === 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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