U.S. Geological Survey, Santa Cruz, California, USA.
Washington Sea Grant, Port Angeles, Washington, USA.
Sci Rep. 2019 Sep 27;9(1):13968. doi: 10.1038/s41598-019-50387-7.
Coastal erosion outpaces land generation along many of the world's deltas and a significant percentage of shorelines, and human-caused alterations to coastal sediment budgets can be important drivers of this erosion. For sediment-starved and erosion-prone coasts, large-scale enhancement of sediment supply may be an important, but poorly understood, management option. Here we provide new topographic measurements that show patterns and trends of beach accretion following the restoration of sediment supply from a massive dam removal project. River sediment was initially deposited in intertidal-to-subtidal deltaic lobes, and this sediment was reworked by ocean waves into subaerial river mouth bars over time scales of several months. These river mouth bars welded to the shoreline and then initiated waves of sediment accretion along adjacent upcoast and downcoast beaches. Although the downcoast shoreline has a high wave-angle setting, the sedimentation waves straightened the downcoast shoreline rather than forming self-organized quasi-periodic instabilities, which suggests that simple coastal evolution theory did not hold under these conditions. Combined with other mega-nourishment projects, these findings provide new understanding of littoral responses to the restoration of sediment supplies.
沿海侵蚀的速度超过了世界上许多三角洲和很大一部分海岸线的土地生成速度，而人类对沿海沉积物收支的改变可能是这种侵蚀的重要驱动因素。对于沉积物匮乏和易受侵蚀的海岸，大规模增加沉积物供应可能是一种重要但了解甚少的管理选择。在这里，我们提供了新的地形测量结果，这些结果显示了在大规模大坝拆除项目恢复沉积物供应后海滩淤积的模式和趋势。河流沉积物最初沉积在潮间带到潮下三角洲叶瓣中，随着时间的推移，这些沉积物被海浪重新加工成陆上河口沙洲。这些河口沙洲与海岸线相连，然后在相邻的上游和下游海滩引发了一波沉积物淤积。尽管下游海岸线的波浪角度较高，但沉积物沉积波使下游海岸线变直，而不是形成自我组织的准周期性不稳定性，这表明在这些条件下，简单的海岸演化理论并不成立。结合其他大型营养物补充项目，这些发现为人们对恢复沉积物供应的滨岸响应提供了新的认识。
