Abstract While interactions between regular wave driven flooding and reefs have been widely studied due to climate change pressure, the effects of reefs on tsunami flooding have less been investigated. From studies of historical events, reefs can behave as buffers or as amplifiers of inundation, depending upon the location. Interactions between reefs and tsunamis have generally been analyzed with idealized models, and there have been only few studies of specific reefs and their characteristics. Using numerical NonLinear Shallow Water models, this study characterizes the influence of the Southeast Ishigaki Island reef during the 1771 tsunami that hit the Yaeyama Islands. In this work, we modified reef topography in silico and then, measured the impact of these changes using a new parameter, the Reef Impact Factor (RIF). First, a reference model was built, simulating the real event with an accurate reef representation and using run-up data to calibrate bottom friction. This calibration highlights the difficulty of representing reef friction with a homogeneous coefficient. Second, a model without a reef was compared to the reference model. The impact of reef removal varies considerably along the coastline and maximum wave heights at the shore were strongly affected, with a 12.5 % increase on average. Overall, this suggests a protective role of the reef along most of the coast. However, at local scale, channels that break the continuity of the front reef, increased wave heights by up to 40 % on the proximate coast, revealing their strong focusing influence. Finally, changes in tide level, which regulates reef depth, were investigated, showing a global positive correlation between sea level and maximum wave height at the coast. However, the impact of the reef depth appeared weak compared to the impact of incident wave parameters. This study contributes to a global effort to understand tsunami-reef interactions in a non-idealized framework, suggesting a Reef Impact Factor for inter-reef/study comparisons. Moreover, vulnerable and exposed coasts were identified at Ishigaki Island, which may help to improve inundation forecasting, resulting in more appropriate management of these vulnerable sections of the coast.

中文翻译：

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根据 1771 年明和海啸对珊瑚礁影响进行量化

摘要 虽然由于气候变化压力，规则波驱动洪水与珊瑚礁之间的相互作用已得到广泛研究，但珊瑚礁对海啸洪水的影响却鲜有研究。根据对历史事件的研究，珊瑚礁可以作为缓冲或淹没的放大器，具体取决于位置。珊瑚礁与海啸的相互作用一般采用理想化模型进行分析，对特定珊瑚礁及其特征的研究很少。本研究使用数值非线性浅水模型，描述了 1771 年袭击八重山群岛的海啸期间石垣岛东南部珊瑚礁的影响。在这项工作中，我们在计算机上修改了珊瑚礁地形，然后使用新参数珊瑚礁影响因子 (RIF) 测量了这些变化的影响。第一的，建立了一个参考模型，用准确的珊瑚礁表示模拟真实事件，并使用运行数据来校准底部摩擦力。这种校准突出了用均匀系数表示珊瑚礁摩擦的困难。其次，将没有珊瑚礁的模型与参考模型进行比较。珊瑚礁清除的影响沿海岸线变化很大，岸边的最大波高受到强烈影响，平均增加 12.5%。总的来说，这表明大部分海岸的珊瑚礁具有保护作用。然而，在局部尺度上，打破前礁连续性的通道使邻近海岸的波浪高度增加了 40%，显示出它们强烈的聚焦影响。最后，调查了调节珊瑚礁深度的潮位变化，显示海平面与海岸最大波高之间存在全球正相关关系。然而，与入射波参数的影响相比，珊瑚礁深度的影响显得微弱。这项研究有助于在非理想化框架中了解海啸-珊瑚礁相互作用的全球努力，为珊瑚礁间/研究比较提出了珊瑚礁影响因子。此外，在石垣岛确定了脆弱和暴露的海岸，这可能有助于改进洪水预报，从而对海岸的这些脆弱部分进行更适当的管理。建议珊瑚礁影响因子用于珊瑚礁间/研究比较。此外，在石垣岛确定了脆弱和暴露的海岸，这可能有助于改进洪水预报，从而对海岸的这些脆弱部分进行更适当的管理。建议珊瑚礁影响因子用于珊瑚礁间/研究比较。此外，在石垣岛确定了脆弱和暴露的海岸，这可能有助于改进洪水预报，从而对海岸的这些脆弱部分进行更适当的管理。