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General Session 1: Physical oceanic processes: Dynamics and physical-biological-biogeochemical interactions |
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Measurement and analysis of mixing processes in estuaries and coastal zone
Tuesday 10th @ 1145-1200
Multi-function Hall
Hwa Chien* , Graduate Institute of Hydrological & Oceanic Sciences, National Central University, Taoyuan 320, Taiwan
Yao-Zhao Zhong, Graduate Institute of Hydrological & Oceanic Sciences, National Central University, Taoyuan 320, Taiwan
Hao-Yuan Cheng, Graduate Institute of Hydrological & Oceanic Sciences, National Central University, Taoyuan 320, Taiwan
Meng-Yu Lin, Department of Civil Engineering, Chung Yuan Christian University, Taoyuan 320, Taiwan
Presenter Email: hwa.chien.ucsd@gmail.com
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| The great amount of anthropogenic pollutants such as Nitrogen compound brought stresses to the vicinity of estuaries and coastal waters. It is difficult to evaluate the mixing processes, which dominate the fate of anthropogenic pollutants, because of its spatial heterogeneity and temporal non-stationary over the estuary domain. The aim of this paper is to develop a practical method and equipment for measuring hydrodynamic parameter over estuary and coastal area where dominated by integrated effects of tide, seabed terrain, wave breaking, river plume and so on. The diffusion of pollutants is essentially a Lagrangian process. This paper describes the development of the drifter array with temperature sensor and results from several field campaigns at the thermal outfall of nuclear power plant and Dan-shui estuary in 2016. The verification was carried out at the thermal outfall taking the water temperature measured by drifter as tracer. The Lagrangian dispersion coefficient, which was calculated using the trajectories and the statistic of the spacing between every three drifters, was compared with the dispersion coefficient in Lagrangian transformed 1-D diffusion equation which was evaluated by fitting the time decay curves of drifter measured water temperature. The comparison result showed a considerable match. The drifter array was then applied to the Dan-shui River which is the second largest river in Taiwan and its watershed population is over 800 million. The annual yield of DIN of Dan-shui watershed is 3800 kg-N km-2yr-1, which is 18 times greater than the global average. It is expected to cause serious eutrophication and seasonal aquatic hypoxia in Dan-shui estuary but actually not. During the experiments, CTD and water sampling were carried out simultaneously using R/V at 10 stations around the estuary. All these data were inter-compared to identify and explain the mixing in Dan-shui plume. In preliminary the temporal-spatial characteristics of dispersion coefficients were analyzed and found the near-field mixing zones are quite different in different tide. In-depth analysis is ongoing and will be shown soon. |
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