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Decadal shoreline erosion and recovery of beaches in modified and natural estuaries
Geomorphology ( IF 3.9 ) Pub Date : 2021-07-30 , DOI: 10.1016/j.geomorph.2021.107884
Thomas E. Fellowes 1, 2 , Ana Vila-Concejo 1, 2 , Shari L. Gallop 3, 4 , Ryan Schosberg 1, 2 , Vincent de Staercke 5, 6 , John L. Largier 7, 8
Affiliation  

Sandy beaches in estuaries and bays (BEBs) are common landforms on the coasts of many major cities. They exist under a wide range of settings and their morphology is controlled by their distance from the estuary/bay entrance, exposure to different types of waves (e.g., ocean swells vs locally generated wind waves), proximity to flood-tide delta/shoals, and anthropogenic interventions (e.g., dredging, groynes). Both swell waves propagating into estuaries/bays and locally generated wind waves can erode BEBs. However, more understanding of BEB storm erosion and recovery over decadal timescales is needed, as they typically respond slower than open coast beaches. Here we present decadal shoreline behaviours of nine BEBs from two estuarine systems in SE Australia are presented in this study, using 76 years of aerial imagery (1941–2017). We quantify and compare decadal behaviour between beaches, developing a new typology of BEBs based on shoreline evolution. We identify four decadal behaviours: prograding, quasi-stable, retreating and storm relict – and assess the influence of flood-tide deltas, river mouths, distance from the ocean entrance, and anthropogenic interventions. Swell-exposed BEBs near the entrance are quasi-stable and recover after storms at rates comparable with open coast beaches (<3 years). In contrast, BEBs further from the entrance and those with less swell exposure, have slower recovery timescales (3–15 years) and will only be quasi-stable if storms are sufficiently infrequent. Thus, long-term behaviour is controlled by storm return timescales. Prograding BEBs are typically far from the entrance, where fluvial and tidal processes dominate and erosion events due to wind waves are less pronounced. Whether BEBs recover (quasi-stable), partially recover between storms (retreating) or never recover (storm relict) relates to storm frequency, recovery rates and proximity to sediment sources and sinks (e.g., dredge sites, flood-tide deltas, tidal channels) and anthropogenic interventions. Findings will help to better understand and manage BEB shorelines in major cities.



中文翻译:

十年海岸线侵蚀和改造和自然河口海滩的恢复

河口和海湾 (BEB) 中的沙滩是许多主要城市海岸的常见地貌。它们存在于广泛的环境中,它们的形态受它们与河口/海湾入口的距离、暴露于不同类型的波浪(例如,海浪与当地产生的风浪)、与潮汐三角洲/浅滩的接近程度、和人为干预(例如,疏浚、挖泥船)。传播到河口/海湾的涌浪和本地产生的风浪都会侵蚀 BEB。然而,需要更多地了解 BEB 风暴侵蚀和十年时间尺度的恢复,因为它们的响应速度通常比开放的海岸海滩慢。在这里,我们使用 76 年的航拍图像(1941-2017)展示了来自澳大利亚东南部两个河口系统的九个 BEB 的十年海岸线行为。我们量化和比较海滩之间的年代际行为,开发基于海岸线演变的新 BEB 类型。我们确定了四个十年的行为:前移准稳定后退风暴残留——并评估潮汐三角洲、河口、距海洋入口的距离和人为干预的影响。入口附近膨胀的 BEB 是准稳定的,并且在风暴后恢复的速度与开放的海岸海滩相当(<3 年)。相比之下,离入口较远的 BEB 和那些膨胀暴露较少的 BEB 恢复时间较慢(3-15 年),并且只有在风暴足够少的情况下才会准稳定。因此,长期行为受风暴回归时间尺度控制。升级BEB 通常远离入口,那里的河流和潮汐过程占主导地位,风浪引起的侵蚀事件不太明显。BEB 是恢复(准稳定)、在风暴之间部分恢复(后退)还是永不恢复(风暴残余)与风暴频率、恢复率以及与沉积物源汇的接近程度(例如,疏浚点、潮汐三角洲、潮汐通道)有关) 和人为干预。调查结果将有助于更好地了解和管理主要城市的 BEB 海岸线。

更新日期:2021-08-07
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