Sediment Size Effect on the Landward Coastal Structure Scour Prediction due to Tsunami

The existing predictive landward structure scour depth equation of Jayaratne et al. (2016) is able to foresee the scour depth induced by overflowing tsunami wave. The equation comprises several measurable parameters in the field such as dike height (Hd), inundation depth (h), and landward structural slope (𝜃). However, implementing the predictive depth equation urges careful attention due to simplification of the fitted coefficient (𝜆). This study explores the sediment size effect to the landward scour depth equation through laboratory investigation. Three different sediment sizes were tested and repeated three times during experiments to make total of nine test runs. Main scour feature of scour depth (Dₛ) is scrutinized to get an in-depth understanding of landward toe scour behavior in relation to median sediment size (D₅₀). In addition, we also show that in analyzing scour extent (length, Lₛ), sediment size effect cannot be easily omitted. This study found that in the range of non-cohesive sand samples in the range of D₅₀ = 0.30- 2.56 mm, Dₛ and Lₛ tend to be inversely proportional to the grain size. Therefore, we propose to revise the fitted coefficient (𝜆ₛ) to be a function of D₅₀ in applying existing scour depth predictive equation of Jayaratne et al. (2016). Regarding Lₛ, further work is required to explore the effect of sediment size on Lₛ.