Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy, macro-tidal beach
Role of wave forcing, storms and NAO in outer bar dynamics on a high-energy, macro-tidal beach
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DOI：
10.1016/j.geomorph.2014.07.025
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发表时间：
2014-12-01
期刊：
影响因子：
3.9
通讯作者：
Russell, Paul
中科院分区：
文献类型：
--
作者：
Masselink, Gerd;Austin, Martin;Russell, Paul
利用长期（多年）的潮间形态和近海水深测量数据，研究了高能潮海滩外拦门沙的动力学。利用15年的时间序列的阿格斯视频图像，五个不同的外部酒吧类型被确定为：大撕裂，沿岸，新月形，新月形连接和焊接。最常见的分类是新月形附着，外沙洲振荡与内沙洲振荡异相，这与该地点的海岸正常波方法相同。外坝的典型振幅为0.5-1米，沿岸波长为600米。外部酒吧形态的变化与测量和模拟近岸波数据。然而，外沙洲形态的变化时间尺度（每月到每年）比波高和周期的每日到每周变化要长得多。能量波作用的持续时间延长，需要带来一个上州酒吧过渡到沿岸或巨型撕裂状态，酒吧然后保持逮捕了大量的时间，需要几个月的低波条件，以诱导下状态过渡到焊接通过新月形。这种缓慢的形态反应的解释是延长松弛时间归因于大潮差在研究现场的外酒吧形态是活跃的潮汐周期的一部分（几个小时左右的低潮）。外部酒吧的配置和位置是相关的：更多的上州（下州）酒吧类型与更多的离岸（岸上）酒吧的位置。去趋势外酒吧的位置显着相关的强迫项的基础上波功率和不平衡的无量纲下降速度与离岸（岸上）酒吧迁移时发生的波条件更（少）精力充沛的前提条件。在16年的监测中，有14年在冬季的某个时候达到了北部端元（沿岸或巨型裂口）;在2005/2006年和2010/2011年冬季，外坝仍然附着在低潮海岸线上。这两个冬天，不完整的北部周期，其特点是最低的冬季波条件和负冬季北大西洋涛动（NAO）指数，这表明冬季NAO与海滩状态和近岸酒吧配置。(C)2014爱思唯尔有限公司版权所有。
Outer sand bar dynamics on a high-energy macro-tidal beach were investigated using long-term (multi-year) field datasets of intertidal morphology and offshore bathymetry. Utilising a 15-year time-series of Argus video images, five distinct outer bar types were identified: Mega Rip, Longshore, Crescentic, Crescentic Attached and Welded. The most common classification was Crescentic Attached, with the outer bar oscillations being out of phase with the inner bar oscillations, as would be expected for the shore-normal wave approach at this site. The outer bar had a typical amplitude of 0.5-1 m and a longshore wavelength of 600 m. Changes in outer bar morphology were related to measured and modelled nearshore wave data. However, the outer bar morphology changed over a much longer timescale (monthly-to-annual) than the daily-to-weekly variations in wave height and period. An extended duration of energetic wave action was required to bring about an upstate bar transition to the Longshore or Mega Rip state, where the bar then remained arrested for a significant amount of time, requiring several months of low wave conditions to induce a down state transition through Crescentic to Welded. This slow morphological response is explained by extended relaxation times attributed to the large tidal range at the study site where the outer bar morphology is only active for part of the tidal cycle (several hours around low tide). The configuration and position of the outer bar were related: the more upstate (downstate) bar types being associated with a more offshore (onshore) bar position. The detrended outer bar position was significantly related to a forcing term based on wave power and disequilibrium of the dimensionless fall velocity with offshore (onshore) bar migration occurring when wave conditions were more (less) energetic that the antecedent conditions. The upstate end-member (Longshore or Mega Rip) was attained sometime during the winter months for 14 out of the 16 years of monitoring; the outer bar remained attached to the low tide shoreline over the winter 2005/2006 and 2010/2011. These two winters, with incomplete upstate cycles, were characterised by the lowest winter wave conditions and negative winter North Atlantic Oscillation (NAO) indices, suggesting that the winter NAO is correlated with both beach state and nearshore bar configuration. (C) 2014 Elsevier B.V. All rights reserved.