Dynamics of rip currents associated with groynes — field measurements, modelling and implications for beach safety
Dynamics of rip currents associated with groynes — field measurements, modelling and implications for beach safety
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与防波堤相关的离岸流动力学——现场测量、建模和对海滩安全的影响
DOI：
10.1016/j.coastaleng.2015.09.013
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发表时间：
2016
影响因子：
4.4
通讯作者：
P. Russell
中科院分区：
文献类型：
--
作者：
T. Scott;M. Austin;G. Masselink;P. Russell
离岸流可能发生在沟滩和其他海岸结构（如防波堤和地质岬角）周围，这些结构为波浪引起的流场提供了边界，并对全世界的用水者构成威胁。海岸正常的砾岩是常见的沿漂流海岸。在北欧，这些通常是低能量，有限的环境，由当地产生的风浪主导。边界控制的裂口流的存在在文献中得到了支持，但很少有关于其存在和动力学的现场测量。这项研究为边界控制的离岸流动力学提供了新的定量科学理解。在英格兰南部海岸的博斯科姆比海滩进行了为期10天的实地实验，测量了一个不透水的土石滩周围的离岸流和近岸流体动力学。固定仪器（波浪、潮汐和流米）和gps漂移仪的观测证实，在一些斜波事件和漂移逆转期间，在一个沙坝结构周围存在危险的地形离岸流及其特征。最强的离岸导向撕裂速度可达1 m s - 1（平均10分钟）和2 m s - 1（瞬时），这是在沙坝的上升流侧测量到的，在那里，海湾内产生的岸流被偏转到离岸。这些强烈的裂口流是在相对较小的波高（Hs< 1 m）下测量的，并呈现出明显的沐浴危险。为了支持测量数据，研究人员使用了经过校准和验证的数值模型（XBeach），以探索在一系列砾岩配置和现场未观察到的波浪条件下，对撕裂行为的关键环境控制。主要结果是：1)上游偏转裂口流与波浪强迫作用下的滨岸冲力有较强的相关性；2)坡面坝长相对于冲浪带宽度强烈地控制着离岸流的范围，在相对坡面坝长（长/浪宽）为1.25以上，冲浪带出口显著增加；3)裂口流增加到相对沟距（间距/长度）约为4-6，在此之上，沿岸流充分发展。这些发现已被提炼成一些关键原则，这些原则与评估海滩上边界控制的撕裂危险有关。
Rip currents can occur around groynes and other coastal structures (e.g. breakwaters and geological headlands), which provide a boundary to the wave-induced flow field and present a hazard to water users worldwide. Shore-normal groynes are common along drift-aligned coasts. In northern Europe these are often low-energy, fetch-limited environments that are dominated by locally generated wind waves. The presence of boundary-controlled rip currents due to groynes is supported anecdotally in literature, but few field measurements of their presence and dynamics exist. This study provides new quantitative scientific understanding of the dynamics of boundary-controlled rip currents within this setting. A 10-day field experiment at Boscombe beach on the south coast of England measured rip currents and nearshore hydrodynamics around an impermeable groyne field. Observations from both fixed instruments (wave, tide and current metres) and GPS-drifters confirmed the presence and characteristics of hazardous topographic rip currents around a groyne structure during a number of oblique wave events and drift reversals. The strongest offshore-directed rip velocities of up to 1 m s− 1(10-min average) and 2 m s− 1(instantaneous) were measured on the updrift side of the groyne where the longshore current generated within the embayment was deflected offshore. These strong rip flows were measured under relatively small wave heights (Hs< 1 m) and presented a significant bathing hazard. A calibrated and validated numerical model (XBeach) was used, in support of measured data, to explore the key environmental controls on rip behaviour across a range of groyne configurations and wave conditions not observed in the field. Key outcomes were that: 1) upstream deflected rip flows were found to be strongly correlated to the alongshore thrust due to wave forcing; 2) the groyne length relative to surf zone width strongly controlled the offshore extent of rip flows, with a significant increase in surf zone exits above a relative groyne length (length/surf width) of 1.25; and 3) rip flows increase up to a relative groyne spacing (spacing/length) of around 4–6, above which alongshore currents are fully developed. These findings have been distilled into some key principals that are relevant to the assessment of boundary-controlled rip hazard on beaches.
影响因子：
2.3
作者：
Austin, Martin J.;Masselink, Gerd;Russell, Paul E.
通讯作者：
Russell, Paul E.
影响因子：
2.9
作者：
J. MacMahan;Jeff L. Brown;Jenna A. Brown;E. Thornton;A. Reniers;T. Stanton;M. Henriquez;E. Gallagher;J. Morrison;M. Austin;T. Scott;N. Sénéchal
通讯作者：
J. MacMahan;Jeff L. Brown;Jenna A. Brown;E. Thornton;A. Reniers;T. Stanton;M. Henriquez;E. Gallagher;J. Morrison;M. Austin;T. Scott;N. Sénéchal