桃園海岸近岸流之數值模擬;Numerical simulation of nearshore current along Taoyuan coast

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Title:	桃園海岸近岸流之數值模擬;Numerical simulation of nearshore current along Taoyuan coast
Authors:	廖凱芹;Liew, Khai-Jing
Contributors:	水文與海洋科學研究所
Keywords:	近岸流;突堤效應;藻礁;nearshore current;forcing mechanism;jetty effect;algal reef
Date:	2018-01-24
Issue Date:	2018-04-13 10:50:16 (UTC+8)
Publisher:	國立中央大學
Abstract:	長久以來，科學家們都認為近岸流場對於物質傳輸過程扮演了重要的角色，而近岸流亦會受到地形、季侯風、潮汐和波浪的影響。在台灣海峽，前人對於此研究的著墨甚少。在另一方面，桃園海岸擁有全台最大的藻礁地形－觀新藻礁。因此，本研究希望（一）透過近岸數值模式(Delft3d)搭配現場觀測資料來探討桃園海岸，尤其是觀新藻礁區域的近岸流的時空變化，（二）探討結構物對近岸流的影響。本研究在夏季時期一共佈置了三臺聲學度普勒流速儀(ADCP)以進行為期四週對波浪及海流的觀測。在模式方面，經過仔細調整曼寧參數及碎波參數後，所使用的近岸數值模式亦成功重建研究區域之流場及水文型態。本研究結果發現，靠近結構物（觀新藻礁區域）的近岸流呈現向西北-北方流的現象。而在遠離結構物（非觀新藻礁區域），近岸流則持續性流向東北方。除此之外，模式分析結果顯示，由於結構物的關係，在觀新藻礁區漲潮時期會產生一逆時針渦流。由於該渦流的關係，觀新藻礁區域裡風場、潮流及波浪之間的交互作用也變得相對複雜。另一方面，在遠離結構物的區域，近岸流主要受到西南季侯風的影響而持續性流向東北方。整體而言，桃園海岸的近岸流特性在空間分佈上有顯著的分別。有別於以往的發現，本研究顯示風場在桃園海岸近岸流扮演了重要的角色。;Nearshore currents are important for material dispersion and sediment transport, yet, not well understood in Taiwan Strait where complicated forcing mechanisms such as influence from topography, tide, wind, waves, and large-scale current exist. This study was conducted along Taoyuan coast using both numerical model (Delft3d) and observational data. Three Acoustic Doppler Current Profilers (ADCPs) were deployed near-coast from June-July to investigate spatial variations of the current pattern. The model current was performed under different forcing conditions (with and without wind, tide, and wave) with various parameters to examine its sensitivity. Results suggested that the Manning coefficient and breaking index are the two most dominant factors affecting simulation performance for Flow-module and Wave-module respectively. Predicted water level and current velocity are in good agreement with field observations with averaged model skill up to 0.8. Based on the results, current pattern along Taoyuan coast displays remarkable spatial inhomogeneity. Current flow in a region far away from the structure was strongly influenced by wind forcing and always directed to northeastward during the Southwesterly monsoon period. Meanwhile, current flow at region close to the structure is primarily associated with wave forcing. In this region, an anti-clockwise eddy is generated due to the existence of coastal structure. The formation of eddy cause complex interaction of tide, wind and wave-driven current that occasionally offset each other. Further study is required in order to clarify the influence of eddy toward local hydrodynamic. This study is important that can enhance understanding of nearshore current pattern at algal reef region which can aid in future reef conservation.
Appears in Collections:	[Graduate Institute of Hydrological and Oceanic Sciences] Electronic Thesis & Dissertation

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