Gravel barrier resilience in a changing climate (#gravelbeach)

含有大量砾石成分的海滩和屏障系统，包括“纯”、“复合”和“混合砾石”，在全球中高纬度地区很常见。这些地貌特征在本文中统称为“砾石屏障”，占英国受海浪影响海岸线的20%。它们为抵御海岸洪水和侵蚀提供了自然保护，并支持独特的生态系统。然而，我们预测它们形态动力学的大部分能力来自于对沙质海岸的研究，这在翻译上是有缺陷的。具体来说，我们对由砂砾混合物组成的屏障的形态动力学建模的理解和能力明显缺乏。砂石和砾石沉积物输运过程和形态响应的根本差异使砂质海岸模型无法直接应用于砾石屏障。在混合砂砾体系中，一种粒度的存在通过选择性夹带和级联扰动影响另一种粒度的输运。因此，我们对砾石屏障行为的理解主要是定性的，尤其是它们对海平面上升、风暴和与气候变化相关的波浪条件变化的反应。例如，我们知道，向陆地的屏障迁移是由风暴引起的冲过引起的，但对迁移速率的限制却知之甚少。虽然迁移可能随着海平面上升而增加，但不同沉积物等级和容纳空间的影响尚不清楚。同样，主要波浪方向的变化通过海滩旋转和沉积物分选引起沿岸和跨岸响应。这反过来又改变了海岸线的位置，并可能产生侵蚀热点，但是在不同的气候变化情景下对这些过程进行可靠预测的能力是缺乏的。砾石屏障在提供海岸保护方面具有重要作用。传统上，它们是通过沉积物回收和海滩营养来维持的。然而，有证据表明，其中一些做法对屏障的稳定性产生了负面影响，使其不可持续，特别是在海平面上升的情况下。因此，该项目（#砾石滩）旨在开发可靠、一致和适当的方法来处理这些自然特征，并为其腾出空间，以实现更具可持续性和适应性的国家规模管理实践。

Beach and barrier systems with a substantial gravel fraction, including 'pure', 'composite' and 'mixed sand-gravel', are common globally at mid to high latitudes. These geomorphological features, collectively referred to herein as 'gravel barriers', represent up to 20% of the wave-exposed coastline of Great Britain. They provide natural protection against coastal flooding and erosion, and support unique ecosystems. However, much of our ability to predict their morphodynamics comes from research on sandy coasts, which is flawed in translation. Specifically, our understanding and capability to model the morphodynamics of barriers comprising sand-gravel mixtures is significantly lacking.Fundamental differences in sand and gravel sediment transport processes and morphological response preclude direct application of sandy coastal models to gravel barriers. In mixed sand-gravel systems, the presence of one grain size fraction affects the transport of another through selective entrainment and cascading disturbances. Our understanding of gravel barrier behaviour, especially their response to sea-level rise, storms, and changes in wave conditions related to climate variability, is thus mainly qualitative. We understand, for example, that landward barrier migration occurs due to storm-induced overwash, but the constraints on the migration rate are poorly understood. Whilst migration is likely to increase with sea-level rise, the influence of different sediment grades and accommodation space is unclear. Likewise, changes in the predominant wave direction induce both alongshore and cross-shore response through beach rotation and sediment sorting. This, in turn, changes shoreline position and can create erosion hotspots, but the ability to robustly predict these processes for different climate change scenarios is deficient.Gravel barriers have an important role in providing coastal protection. Traditionally they have been maintained through sediment recycling and beach nourishment. However, evidence indicates that some of these practices negatively impact barrier stability making it unsustainable, particularly under rising sea levels. Thus, this project (#gravelbeach) aims to develop, reliable, consistent and appropriate approaches for working with, and making space for, these natural features, to enable more sustainable and adaptive national-scale management practices.