Abstract Tsunami induced Large Driftwood (TLD) can cause significant damage to a coastal environment. In a tsunami, TLD can become an additional impact and a drag force against a coastal structure. Modern research is now showing that hybrid-structures provide a more optimal solution against mitigating tsunami-related damages. Hybrid-structures involve structures like moats, embankments, and forests. This study considered the use of a dry moat and investigated the benefits of a hybrid-structure in controlling TLD’s damage potential. Through a laboratory-scale experiment, this paper elucidated the reduction potential of impact velocity and impact moment of a TLD. The experiment was conducted in a channel that generated a quasi-steady-flow, imitating a long period wave flow. As a result of the strong reflection of flow, generated within the moat structure of an embankment-moat design, this study observed the retention of TLD. Moreover, due to the turbulence and energy loss, the TLD after it had overtopped the hybrid-structure, had a lower impact velocity and impact moment. Changes to the upstream vegetation characteristic, for example, the ratio of trunk height to tree height, showed variation in the probability of retention. A trunk height to tree height ratio of 0.3 had a 71% probability of retention, while a TLD that had a trunk height to tree height ratio of 0.8 had a 42% probability of retention. Indicating the variation in the upstream tree’s characteristics influences the retention capability of an embankment-moat design. This same hybrid design, vegetation upstream of an embankment-moat design, also showed a rotation capability of TLD. The rotation of TLD against the streamlines can increase the role of trapping by a second vegetation patch, potentially further reducing the damage that can happen because of TLD. Therefore, the application of an embankment-moat design can be used to control the damage potential of TLD.

中文翻译：

---

混合结构在控制海啸引发的大型浮木中的作用

摘要 海啸引发的大型漂流木 (TLD) 会对沿海环境造成重大破坏。在海啸中，TLD 可以成为对沿海结构的额外影响和阻力。现代研究现在表明，混合结构提供了一种更理想的解决方案，可以减轻海啸相关的损害。混合结构涉及护城河、堤防和森林等结构。该研究考虑了干式护城河的使用，并调查了混合结构在控制 TLD 破坏潜力方面的好处。通过实验室规模的实验，本文阐明了 TLD 的冲击速度和冲击力矩的降低潜力。实验是在模拟长周期波流的通道中进行的，该通道产生准稳态流。由于流动的强烈反射，在堤防护城河设计的护城河结构内生成的 TLD，本研究观察到 TLD 的保留。此外，由于湍流和能量损失，TLD超过混合结构后，具有较低的冲击速度和冲击力矩。上游植被特征的变化，例如树干高度与树木高度的比率，显示了保留概率的变化。树干高度与树高之比为 0.3 的保留概率为 71%，而树干高度与树高之比为 0.8 的 TLD 保留概率为 42%。指示上游树木特征的变化会影响堤防护城河设计的保留能力。同样的混合设计，护城河设计上游的植被，也显示了 TLD 的旋转能力。TLD 相对于流线的旋转可以增加第二个植被斑块诱捕的作用，有可能进一步减少由于 TLD 可能发生的损害。因此，护城河设计的应用可用于控制 TLD 的潜在破坏。