Gravel barrier resilience in a changing climate (#gravelbeach)

含大量砾石的海滩和屏障系统，包括“纯”、“复合”和“混合砂砾”，在全球中高纬度地区很常见。这些地貌特征，在这里统称为“砾石屏障”，占英国暴露在海浪中的海岸线的20%。它们提供对海岸洪水和侵蚀的自然保护，并支持独特的生态系统。然而，我们预测它们地貌动力学的能力很大程度上来自对沙质海岸的研究，这在翻译上是有缺陷的。具体地说，我们对含沙砾石混合物的障碍物的形态动力学建模的了解和能力明显不足。沙和砾石沉积物迁移过程和形态响应的基本差异排除了沙质海岸模型直接应用于砾石障碍物的可能性。在混合砂砾系统中，一种粒级的存在通过选择性夹带和级联扰动影响另一种粒级的输运。因此，我们对砾石屏障行为的理解，特别是它们对海平面上升、风暴和与气候变异性有关的波浪条件变化的反应，主要是定性的。例如，我们了解到，向陆地的屏障迁移是由于风暴引起的洪水泛滥，但对迁移率的限制却知之甚少。虽然迁移可能会随着海平面的上升而增加，但不同的沉积物等级和容纳空间的影响尚不清楚。同样，优势波方向的变化通过海滩旋转和沉积物分选引起近岸和跨岸的反应。这反过来改变了海岸线的位置，并可能形成侵蚀热点，但缺乏针对不同气候变化情景强有力地预测这些过程的能力。砾石屏障在提供海岸保护方面具有重要作用。传统上，它们是通过沉积物循环和海滩滋养来维持的。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(#GRAVELBASH)旨在制定可靠、一致和适当的办法，利用这些自然特征并为其腾出空间，以便能够在全国范围内实行更可持续和更具适应性的管理做法。

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.