Resuspension of bottom sediment on Inner shelf - A case study of North-western coast of Taiwan;Resuspension of bottom sediment on Inner shelf - A case study of North-western coast of Taiwan

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题名:	Resuspension of bottom sediment on Inner shelf - A case study of North-western coast of Taiwan;Resuspension of bottom sediment on Inner shelf - A case study of North-western coast of Taiwan
作者:	黃英;Anh,Hoang
贡献者:	水文與海洋科學研究所
关键词:	Suspended sediment concentration;EMD method;Stokes drift.;Suspended sediment concentration;EMD method;Stokes drift.
日期:	2012-08-29
上传时间:	2012-09-11 18:26:15 (UTC+8)
出版者:	國立中央大學
摘要:	Factors that affect the resuspension of bottom sediment in the coastal zone of North-western coast of Taiwan were investigated. Field observations using ADCPs were carried out in 3 durations (Jan 14th – Feb 01st 2011; May 26th – June 21st 2011; and Feb 21st – April 13th 2012) to collect wave and current data. Besides, wind was recorded from anemometer equipped on the flux tower; hydrological data were recorded from CTD. Suspended sediment concentration (SSC) near bottom is estimated using ADCP echo intensity. SSC and current are decomposed into several components to elaborate the impact of currents components to SSC.The temporal variation of SSC is decomposed into several Intrinsic Mode Functions (IMFs) using Empirical Mode Decompositon (EMD). All the low-frequency IMFs are composed and referred as long-term SSC while all the high-frequency IMFs are composed and referred as short-term SSC. Observed current is decomposed into tidal current and non-tidal current using Harmonic Analysis. Stokes drift which represents for wave-induced current were estimated using Lentz’s formula or Ardhuin’s formula. Results from Ardhuin’s formula are adopted for following analysis. The non-Stokes residual current is then regarded as induced by wind. Inter-comparisons of the decomposed SSCs with tidal currents, wave-induced currents, non-Stokes residual currents were made. A high correlation is found between long-term SSC and wave while short-term SSC and tidal current are also in a good agreement. It is noted that, a semi-diurnal oscillation of water density is identified synchronized with the enhancement of SSC. These oscillations might owe to the fluctuation of river plume or the internal wave. During the rainfall, the sediment discharge from the creeks might be considerable. The fluctuation of fluvial water due to strong tide would induce the oscillation of water density at one fixed location. In the other hand, this water density oscillation is likely the internal wave oscillation which is quite possible in the inner shelf. So internal wave might also contribute to the resuspension but evidences of internal wave are weak. More observation is needed for further study to consolidate the presence of internal wave in this coastal region.Factors that affect the resuspension of bottom sediment in the coastal zone of North-western coast of Taiwan were investigated. Field observations using ADCPs were carried out in 3 durations (Jan 14th – Feb 01st 2011; May 26th – June 21st 2011; and Feb 21st – April 13th 2012) to collect wave and current data. Besides, wind was recorded from anemometer equipped on the flux tower; hydrological data were recorded from CTD. Suspended sediment concentration (SSC) near bottom is estimated using ADCP echo intensity. SSC and current are decomposed into several components to elaborate the impact of currents components to SSC.The temporal variation of SSC is decomposed into several Intrinsic Mode Functions (IMFs) using Empirical Mode Decompositon (EMD). All the low-frequency IMFs are composed and referred as long-term SSC while all the high-frequency IMFs are composed and referred as short-term SSC. Observed current is decomposed into tidal current and non-tidal current using Harmonic Analysis. Stokes drift which represents for wave-induced current were estimated using Lentz’s formula or Ardhuin’s formula. Results from Ardhuin’s formula are adopted for following analysis. The non-Stokes residual current is then regarded as induced by wind. Inter-comparisons of the decomposed SSCs with tidal currents, wave-induced currents, non-Stokes residual currents were made. A high correlation is found between long-term SSC and wave while short-term SSC and tidal current are also in a good agreement. It is noted that, a semi-diurnal oscillation of water density is identified synchronized with the enhancement of SSC. These oscillations might owe to the fluctuation of river plume or the internal wave. During the rainfall, the sediment discharge from the creeks might be considerable. The fluctuation of fluvial water due to strong tide would induce the oscillation of water density at one fixed location. In the other hand, this water density oscillation is likely the internal wave oscillation which is quite possible in the inner shelf. So internal wave might also contribute to the resuspension but evidences of internal wave are weak. More observation is needed for further study to consolidate the presence of internal wave in this coastal region.
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