Three dimensional physical modelling study on wave and current characteristics in coral reef coastal system
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摘要: 根据现场地形在港池中建立三维珊瑚礁−潟湖−裂口海岸定床整体物理模型，采用波高传感器、流速仪和表面流速测量系统分别测量了规则波作用下珊瑚礁海岸不同位置的波浪和流场特征。结果表明：礁坪上，波高在向岸方向逐渐减小，总减小幅度为86.7%，增水先增大后减小，沿礁坪下降幅度为65.9%，水流以向岸流为主，存在着先增大后减小的趋势；潟湖中，波高靠近裂口处较大，中部最大值约为两侧最小值的2.8倍，增水则靠近裂口处最小，相比两侧最大值下降了25.5%，水流主要为对称地指向裂口的沿岸流，流速从两侧到裂口先增大后减小；裂口中波高变化不大，增水在靠近潟湖处最大，为礁坪上增水的47.6%，水流主要为离岸流，流速同样是先增大后减小。量化分析了环流驱动力、辐射应力与波面压力梯度的空间变化规律，发现礁坪上向岸流变化是平均水位梯度和辐射应力相互作用的结果，在裂口中的离岸流驱动力主要为辐射应力，而潟湖中的沿岸流变化由平均水位梯度决定的。Abstract: Based on the on-site observation of the topography, a generalized three-dimensional physical model of coral reef-lagoon-channel system was established in the wave basin. Wave gauges, velocity meters, and surface velocity measurement system were used to analyze wave and current field characteristics at different locations under regular wave condition. The experimental results indicate that over the reef flat, the wave height gradually decreases by 86.7% cross-shore, and wave-induced setup first increases and then decreases by 65.9% along the reef. The mean current direction is mainly cross-shore, and there is a tendency of increasing first and then decreasing. In the lagoon, the wave height is larger near the channel, where wave-induced setup is the smallest. The maximum wave height is about 2.8 times of the minimum value, and the wave-induced setup is 25.5% lower than on both sides. The mean current is mainly a longshore one that points symmetrically to the rip channel. The velocity increases from the two sides to the rip channel first and then decreases. The wave height in the channel does not change much, and largest wave-induced setup is 47.6% than that on the reef. The mean current flows offshore, and increases first and then decreases. Using the results measured by the wave gauges, the spatial changes of the radiative stress and wave surface pressure gradient which drove the circulation were quantitatively analyzed. The current change on the reefs is the result of the interaction between wave surface pressure gradient and the radiant stress. The driving force of the offshore flow in the rip channel is mainly the radiant stress, while the change of the longshore current in the lagoon is determined by the pressure gradient of the mean water level.
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图 5 SVM系统与流速仪测量结果对比
Fig. 5 Comparison of measurement results between SVM system and current meter
图 6 两次重复实验波面和流速时间序列对比
Fig. 6 Time series comparison of two repeated wave surface and velocity
图 7 y = 8.7 m向岸剖面礁坪波高和平均水位分布
Fig. 7 Cross-reef variation of wave height and mean water level with y = 8.7 m
图 8 x=37 m潟湖沿岸剖面波高和平均水位分布
Fig. 8 Longshore variation of wave height and mean water level in the lagoon with x=37 m
图 9 y = 19.1 m裂口向岸剖面波高和平均水位分布
Fig. 9 Cross-shore variation of wave height and mean water level in the channel with y = 19.1 m
图 17 礁坪和潟湖中的波面压力梯度（
$F_x^{(1)}$ ）、辐射应力梯度（$F_x^{(2)}$ ）和总驱动力（$F_x^{(1)}$ +$F_x^{(2)}$ ）向岸变化Fig. 17 Cross-shore variation of the pressure gradient (
$F_x^{(1)}$ ), radiation stress gradient ($F_x^{(2)}$ ) and their joint forces ($F_x^{(1)}$ +$F_x^{(2)}$ ) on the reef -
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