Variability in sandbank behaviour at decadal and annual time-scales and implications for adjacent beaches
Variability in sandbank behaviour at decadal and annual time-scales and implications for adjacent beaches
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十年和每年时间尺度沙洲行为的变化及其对邻近海滩的影响
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
J. Rees
中科院分区：
文献类型：
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作者：
T. Dolphin;Céline Vincent;C. Coughlan;J. Rees
沙洲是一种重要的沿海资源，无论是在沙洲上发生的活动（例如疏浚、海上风电场）还是沙洲对邻近海滩产生的直接和间接影响方面。由于沙洲占据较大的时空域，因此研究沙洲行为及其对其他沉积体（海滩和其他沙岸）影响的研究相对较少。历史港口附近的导航图可以生成用于沙洲分析的长数据集；然而，较大的时间间隔和数据差距使得很难区分趋势与周期、渐进行为与偶发行为。在本文中，我们收集了一个新的 182 年历史数据集，该数据集在数据密度和时间覆盖范围（即更少的间隙和更小的时间间隔）方面有了显着的改进，并允许对银行行为模式进行更详细的调查。沙洲在其运动、体积和高度方面表现出 70-80 年的周期性行为，并具有两种不同且相关的形态状态（三角洲和拉长）。年度测深表明，逐渐的河岸迁移对于两种形态来说都是常见的，但河岸重新配置（拉长？三角洲）在整个河岸范围内迅速发生（相对于周期周期），并且可以被认为是偶发的。假设从三角洲形态到细长形态的转变是由其他河岸形状或位置变化引起的上游形态-潮汐相互作用造成的。河岸高程、范围、与海岸的接近程度和形状的周期性对邻近海滩具有重要影响，因为沙洲特征的变化改变了波浪能的传输和沿岸分布（通过波浪能的折射和破碎耗散）。后者控制净沿岸沉积物输送，从而控制侵蚀/增生趋势。河岸与海滩的相互作用被证明是复杂的；高岸高程可以通过减少入射到海岸线的波浪能量来提供最大的海岸保护，但实际上与历史记录中最严重的侵蚀有关。为了进一步阐明岸滩关系，当前的现场和数值模拟工作研究了岸滩和海滩行为之间的直接（沉积物交换）和间接（折射、耗散）联系。
Sandbanks are an important coastal resource, both in terms of the activities that occur on them (e.g., dredging, offshore wind farms) as well as the direct and indirect effects they can have on adjacent beaches. Due to the large temporal and spatial domains that sandbanks occupy, there have been relatively few investigations that examine bank behaviour and impacts on other sedimentary bodies (beaches and other banks). Navigation charts near historical ports can yield long datasets for sandbank analysis; however large time intervals and gaps in the data make it difficult to distinguish trends from cycles and gradual from episodic behaviour. In this paper we assemble a new 182-year historical dataset that has significant improvements in data density and temporal coverage (i.e., fewer gaps and smaller time intervals) and permits a more detailed investigation of patterns in bank behaviour. The sandbank exhibits 70-80 year cyclical behaviour in its movement, volume and elevation and holds two distinct and associated morphological states (deltaic and elongate). Annual bathymetry shows gradual bank migration is common to both morphologies but bank reconfiguration (elongate?deltaic) occurs rapidly (relative to the cycle period), on a bank-wide scale and may be considered to be episodic. The switch from deltaic to elongate morphology is hypothesised to result from upstream morphology-tide interactions induced by changes in the shape or position of other banks. The cyclical nature of bank elevation, extent, proximity to shore and shape has important implications for adjacent beaches as variation in sandbank characteristics alters the transmission and alongshore distribution of wave energy (through refraction and dissipation of wave energy by breaking). The latter controls net longshore sediment transport and therefore erosion/accretion trends. Bank-beach interactions are shown to be complex; high bank elevations, which can provide the greatest coastal protection by reducing wave energy incident to the shoreline, are actually associated with the most severe erosion in the historical record. To further elucidate bank-beach relations, current field and numerical modelling efforts examine the direct (sediment exchange) and indirect (refraction, dissipation) linkages between bank and beach behaviour.