Coastal dune dynamics in embayed settings with sea-level rise - Examples from the exposed and macrotidal north coast of SW England
Coastal dune dynamics in embayed settings with sea-level rise - Examples from the exposed and macrotidal north coast of SW England
复制标题
随着海平面上升，海湾环境中的沿海沙丘动态 - 英格兰西南部裸露和大潮汐北海岸的示例
DOI：
10.1016/j.margeo.2022.106853
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发表时间：
2022
期刊：
影响因子：
2.9
通讯作者：
Masselink G
中科院分区：
文献类型：
--
作者：
Masselink G
沿海沙丘系统是海岸防御的自然形式，但由于气候变化的影响，特别是海平面上升和潜在的暴风雨增加，预计将表现出更大的侵蚀率。这种情况在内湾沿岸环境中尤其如此，即没有来自沿岸来源的大量沉积物输入到海滩/沙丘系统。沙丘的发育与临海的海滩密切相关，但它们的时间动态往往是不同步的。因此，虽然海滩在短期到中期(事件-年代际)的时间尺度上通常是高度可变的，潜在地掩盖了较长期(十年-百年)海平面信号，但沙丘表现出低通滤波响应，其中可能包含海平面信号。在这项研究中，我们调查了25个沿英格兰西南部裸露和大潮的北岸被侵蚀的海岸沙丘系统的年代尺度、年际动态。然后，我们将观测到的行为与从简单参数模型中预测的行为进行比较，并预测未来由于海平面上升而导致的沙丘退缩速度。我们发现，几乎所有裸露的沙丘系统都表现出退缩，沙丘底部的区域平均退缩速率为0.5m/年−1。大部分退缩发生在少数特别活跃的冬季，发现沙丘退缩并不自动与沙丘体积变化联系在一起。许多后退的沙丘系统表现出所谓的“沙丘翻滚”，其特征是从沙丘表面清除沉积物，并在沙丘顶部沉积。观测到的沙丘退缩速度是使用简单的参数退缩模型预测的2-3倍，海平面上升迫使沙丘退缩。这表明撤退模型是不适当的，和/或海平面上升本身可能不足以解释观察到的撤退，这可能意味着冬季暴风雨的增加。推动沙丘撤退的一个关键因素被认为是海浪到达沙丘脚的小时数或沙丘脚抬高处存在的过剩助推能量。海平面上升和暴风雨的增强都将增加沙丘脚部暴露在高能波浪作用下的风险，预计这将加快沙丘在这些环境中的撤退速度。应用解释海平面上升速度加速的参数海岸线后退模型预测，到2100年沙丘后退约40米，后退范围相当大(20-75米)，这是由于模型选择和参数设置的不确定性造成的。简单地推算当前的沙丘退缩速度也会导致到2100年沙丘退缩约4000万米，但这种方法忽略了由于海平面上升速度的增加而导致的沙丘退缩速度的潜在加速。多年来海岸沙丘形态变化的分析与沙丘退缩模型的应用相结合，可以为海岸规划者和管理者提供对未来沙丘演变的有用见解。
Coastal dune systems are natural forms of coastal defence, but are expected to exhibit increased erosion rates due to climate change impacts, notably sea-level rise and, potentially, increased storminess. This is especially the case in embayed coastal settings, i.e., where there are no significant sediment inputs into the beach/dune system from longshore sources. Dune development is closely linked to that of beaches that lie seaward, but their temporal dynamics tend to be asynchronous. So, whereas beaches are generally highly variable over a short- to medium-term (event–decadal) time scales, potentially obscuring a longer-term (decadal–centennial) sea-level signal, dunes display a low-pass filtered response which may contain a sea-level signal.In this study, we investigate the decadal-scale, inter-annual dynamics of 25 embayed coastal dune systems along the exposed and macrotidal north coast of SW England. We then compare the observed behaviour with that hindcasted from simple parametric models and forecast future dune retreat rates due to sea-level rise. We show that practically all exposed dune systems show retreat with a regionally-averaged retreat rate of the dune foot of 0.5 m yr−1. The majority of retreat occurred over a small number of especially energetic winters and it was found that dune retreat is not automatically linked to dune volumetric change. Many of the retreating dune systems display so called ‘dune roll-over’, characterised by removal of sediment from the dune face and deposition at the dune top. Observed dune retreat rates were 2–3 times larger than predicted using simple parametric retreat models forced by sea-level rise. This suggests that the retreat models are inappropriate and/or that sea-level rise in itself may be insufficient to explain the observed retreat and that increased winter storminess may be implicated.A key factor in driving dune retreat is considered to be the number of hours that waves reach the dune foot or the excess runup energy present at the dune foot elevation. Both sea-level rise and enhanced storminess will increase exposure of the dune foot to energetic wave action and this is expected to accelerate dune retreat rates in these settings. Application of parametric shoreline retreat models that account for the acceleration in rate of sea-level rise predicts c. 40 m of dune retreat by 2100 with a considerable range in retreat (20–75 m), resulting from uncertainty in model choice and parameterisation. Simply extrapolating the current dune retreat rate also results in c. 40 m of dune retreat by 2100, but this approach ignores the potential acceleration in dune retreat rate due to an increase in the rate of sea-level rise.The combination of analysis of multi-annual coastal dune morphological change along with application of dune retreat models can provide useful insights into future dune evolution for coastal planners and managers.