碩士 / 國立中央大學 / 水文與海洋科學研究所 / 99 / The annual yield of terrestrial sediment in the estuaries around Taiwan is dominated by fluvial discharge in extreme rainfall events. The transportation of terrestrial suspended sediment in the middle of Taiwan Strait is effected by tidal current, considering that the tidal range reachs 4-5 m while the current speed up to 1.5 m/s. The present study emphasize on the tidal effects on suspended sediment transport in Taiwan Strait.
Four field surveys, including a typhoon case in the summers from 2008 to 2010 at Cho-Shui estuary were carried out. For the suspended sediment concentration (SSC) measurement, we discuss the validity of using acoustic echo intensity to infer the SSC. The associated accuracy is influenced by suspended sediment particle size and instrument parameters. In present study we establish the relationship of acoustic echo intensity with the optical back-dispersion turbidity to reduce the uncertainty of the estimation of SSC.
We found that the Nonlinear Weibull distribution can be adopted to describe the probability distribution of suspended sediment particle size. It is found that the Weibull shape parameter is inversely proportional whilist the Weibull scale parameter is proportional to SSC. These results illustrate that the SSC feature high correlation to suspended sediment particle size distribution.
Concerning to the tidal effects, resuspension by strong tidal current dominated the SSC in the estuary. The SSC at the bottom boundary layer increases with the current speed, moreover it increases more rapidly than in the sub-surface layer. Hence it contributes to the stratification strengthened in the estuary. As a result, when current speed reaches 0.8 m/s, the stratification effect damps the turburlence intensity, and reduce shear stress in bottom boundary layer, which limits the resuspension.
This study also show a significant difference between normal condition and extreme events: In normal condition, temporal and spatial distribution of the SSC is dominated by the resuspension incluced by tidal current, with a phase lag of 80 minutes. In the Cho-Shui estuary, when the resuspension dominates, suspended sediment with grain size greater than 16 μm increases. In extreme events, the tidal sea-levels is responsible for the SSC temporal and spatial distribution, the estuary SSC increase rapidly by the low slack tide induced sediment discharge.
| Identifer | oai:union.ndltd.org:TW/099NCU05761010 |
| Date | January 2011 |
| Creators | Yu-Fan Zheng, 鄭宇凡 |
| Contributors | Hwa Chien, 錢樺 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 271 |
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