ABSTRACT

Rip currents can move unsuspecting swimmers offshore rapidly and represent a significant risk to beach users worldwide, including along the northern coast of Prince Edward Island (PEI), Canada. Although many rip currents are ephemeral and/or spatially variable in response to changes in the nearshore bar morphology and wave and tidal forcing, it is possible for rip channels to be geologically controlled and quasi-permanent in morphology, location, and flow. Several rip channels along the northern coast of PEI appear in the same location from year to year and correspond to elongated lakes, rivers, or swales behind the modern coastal dune system. Given their persistent location and alignment with back dune hydrology, ground-penetrating radar surveys were collected along Brackley and Cavendish Beaches in July 2019 to determine whether persistent rip channels are associated with now-buried river channels extending beneath the modern dunes and continuing offshore. Strong reflectors similar to V-shaped river valleys are present in alongshore transects at both beaches. These infilled valleys align with back-dune hydrology and persistent rip channels, suggesting modern rip channels are structurally controlled and maintained by antecedent geology. This link provides important guidance to beach access management and the distribution of lifesaving strategies along the affected beaches.

摘要

离岸流可以迅速将毫无戒心的游泳者带到海上，并对全球海滩使用者构成重大风险，包括加拿大爱德华王子岛 (PEI) 北部海岸。尽管许多离岸流是短暂的和/或空间可变的，以响应近岸坝形态和波浪和潮汐强迫的变化，但离岸河道有可能在形态、位置和流动方面受到地质控制和准永久性。爱德华王子岛北部海岸沿线的几个裂口通道每年都出现在同一位置，对应于现代海岸沙丘系统后面的细长湖泊、河流或洼地。鉴于它们的固定位置和与沙丘水文的一致性，2019 年 7 月沿布拉克利和卡文迪什海滩收集了探地雷达调查，以确定持久的裂口河道是否与现在掩埋在现代沙丘下方并继续离岸的河道有关。两个海滩的沿岸横断面都存在类似于 V 形河谷的强反射体。这些填充的山谷与沙丘后的水文和持久的裂口通道一致，这表明现代裂口通道在结构上受到先前地质的控制和维护。该链接为海滩通道管理和沿受影响海滩分配救生策略提供了重要指导。两个海滩的沿岸横断面都存在类似于 V 形河谷的强反射体。这些填充的山谷与沙丘后的水文和持久的裂口通道一致，这表明现代裂口通道在结构上受到先前地质的控制和维护。该链接为海滩通道管理和沿受影响海滩分配救生策略提供了重要指导。两个海滩的沿岸横断面都存在类似于 V 形河谷的强反射体。这些填充的山谷与沙丘后的水文和持久的裂口通道一致，这表明现代裂口通道在结构上受到先前地质的控制和维护。该链接为海滩通道管理和沿受影响海滩分配救生策略提供了重要指导。