Beach Rotation at Two Adjacent Headland-Enclosed Beaches
Beach Rotation at Two Adjacent Headland-Enclosed Beaches
复制标题
两个相邻岬角封闭海滩的海滩轮换
DOI：
10.2112/si65-354.1
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发表时间：
2016
影响因子：
0.8
通讯作者：
Iain T. MacDonald
中科院分区：
文献类型：
--
作者：
K. Bryan;R. Foster;Iain T. MacDonald
[摘要]布赖恩，K.R.福斯特，R，麦克唐纳，I. 2013。在两个毗邻围海滩的泳滩旋转时，当波浪气候导致沙粒优先在泳滩的一端积聚时，围海滩就会发生海岸线旋转。过去的研究表明，这些旋转事件可能会随着波浪气候的季节性变化而发生。在这里，我们研究了新西兰两个相邻海滩3年的海岸线变化，这两个海滩暴露在相同的波浪气候和潮汐条件下，但具有不同的形态动力学分类。泰尔瓦海滩长约1.2公里，由中细沙组成。波阿努伊海滩长约3公里，其特点是坡度较低，沙粒尺寸较细。这种纹理上的差异是由波阿努伊海滩靠近泰鲁瓦河口入口处造成的。在2002年至2004年期间，两个泳滩均设有视频监测站，每小时平均收集15分钟的视频片段。利用红蓝光比检测海岸线，识别水沙边界。通过将回归线拟合到岸线位置的沿岸系列来量化旋转。结果表明，在风暴事件中，这两个海滩的增加和侵蚀量相当。然而，旋转特征却大不相同，在较短的Tairua海滩旋转的幅度远大于Pauanui。Pauanui的反应是在整个数据集上进行缓慢的旋转，而不是在Tairua海滩发生的更基于事件的旋转。此外，在大部分数据集中，两个海滩在相反的方向上旋转。建立了一个SWAN模型，以了解引起两个地点之间旋转差异的波诱导过程。模型网格是通过对场地的多波束调查生成的。该模型以平稳模式建立，在整个数据集期间每3小时提供一个解决方案。结果表明，沿岸波能通量在很大程度上受Shoe岛和Slipper岛两个近海岛屿的存在控制，造成了Pauanui海滩北端和Tairua海滩南端的阴影。这反过来解释了在两个海滩上观察到的旋转模式的差异。这些结果表明，近海地形对旋转的控制比整体变化对入射角变化驱动的沿岸波能通量的控制更强。
ABSTRACT Bryan, K.R. Foster, R., and MacDonald, I. 2013., Beach Rotation at Two Adjacent Headland-Enclosed Beaches Shoreline rotation occurs on headland-enclosed beaches when the wave climate causes sand to accumulate preferentially on one end of the beach. Past research has shown that these rotation events can occur in response to seasonal variations in the wave climate. Here we investigate 3 years of shoreline variations on two adjacent beaches in New Zealand that are exposed to the same wave climate and tidal conditions, but with different morphodynamic classification. Tairua Beach is approximately 1.2 km long, and is composed of medium-fine sand. Pauanui Beach is approximately 3 km long, and is characterised by lower slopes and finer sand grain sizes. The textural differences are caused by the proximity of Pauanui Beach to the entrance of Tairua Estuary. Both beaches are overlooked by video monitoring stations which collect 15-minute averages of video footage every hour between 2002 and 2004. Shorelines were detected by using the ratio of red to blue light to identify the water-sand boundary. Rotation was quantified by fitting a regression line to the alongshore series of shoreline locations. Results showed that both beaches accreted and eroded by comparable amounts during storm events. However, the rotation characteristics were quite different, with the magnitude of rotation being far greater at the shorter Tairua Beach than at Pauanui. Pauanui responded with a slow rotation over the whole dataset rather than the more event-based rotation that occurred at Tairua Beach. In addition, the two beaches rotated in opposite directions during most of the dataset. A SWAN model was set up to understand the wave induced processes that caused the differences in rotation between the two sites. The model grid was generated from a multibeam survey of the site. The model was set up in a stationary mode providing a solution every 3 hours over the entire duration of the dataset. Results showed that the alongshore wave energy flux was largely controlled by the presence of two offshore islands, Shoe and Slipper island, which caused shadowing of the north end of Pauanui Beach and the south end of Tairua Beach. This in turn accounts for the observed differences in the rotation pattern at the two beaches. These results show that the offshore topography was a stronger control on rotation than overall changes to the alongshore wave energy flux driven by incidence angle changes alone.