Title page for etd-0213107-135633


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URN etd-0213107-135633
Author Yu-Cun Chen
Author's Email Address m925060001@student.nsysu.edu.tw
Statistics This thesis had been viewed 4685 times. Download 938 times.
Department Physical Oceanography
Year 2006
Semester 1
Degree Master
Type of Document
Language zh-TW.Big5 Chinese
Title Effect of currents and waves on ADCP echo intensity
Date of Defense 2006-12-27
Page Count 75
Keyword
  • echo intensity
  • Abstract In this study, bottom mounted ADCP and RCM 9 were deployed to collect time series data of current, turbidity and acoustic backscattered echo intensity (EI) in the estuarine environment near Love River and in the coastal waters of Howan. Our results indicate that in the torrential rain event, the Love River became very turbid with the flow speed exceeding 1.5 m/s. ADCP EI data also increase rapidly and correlate well with the turbidity data. Based on the empirical formula of Kim and Voulgaris (2003), the EI time series data of the first bin are converted into sediment suspension concentration (SSC), which compared reasonably well with those converted from the optical observations of turbidity. Therefore, ADCP EI data can be used as a good proxy of SSC. Velocity profiles measured by ADCP were also analyzed to obtain the friction velocity and roughness length according to the logarithmic relationship. The log layer height extended to almost full channel depth of 4 m during strong flows, the roughness lengths were about 10-3 m and the bottom shear stress reached 10 Pa. It is not surprising that bottom sediments are stirred under such a large shear stress.
    The sediment suspension due to current and wave action in the rather clear coastal waters of Howan is also investigated by means of ADCP EI data. In winters the observed current speed is stronger while the wave height is smaller (Hs<1 m). It is found that the near-bottom ADCP EI data have better correlation with the current magnitude but poorer correlation with surface waves. On the other hand, the ADCP EI data near the sea surface become more dependent on the surface waves. This is possible due to the bubbles entrained by breaking waves, especially under the condition of Hs>0.5 m. In summers the observed current speed is weaker while the wave height is generally higher. In one typhoon event the observed Hs even reached 4.5 m. The calculated maximum orbital velocity at the bottom and bed shear stress generated by surface waves are sufficient to mobilize sediment. The ADCP EI data of the whole water column (about 15 m) correlate nicely with the wave height but correlate poorly with current magnitude. In contrast to the results of the Love River, the near-bottom ADCP EI data show a weak correlation with the turbidity observation.
    Advisory Committee
  • none - chair
  • none - co-chair
  • none - co-chair
  • none - advisor
  • Files
  • etd-0213107-135633.pdf
  • indicate access worldwide
    Date of Submission 2007-02-13

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