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[MIS13-P05] Summary of distribution characteristics of sand/boulder tsunami and storm deposits using dimensionless numbers
Extreme tsunami and storm waves sometimes form sand deposit and transport boulder over land. These kinds of deposits can be utilized for estimating inundation zones and recurrence intervals of extreme waves in modern, historic, and prehistoric times. However, the distribution of these deposits is extremely complex and subject to various factors such as the size of the waves, topography, and bathymetry. We use numerical computations to identify the key factors affecting the distribution of sand deposits and boulders formed by both waves. We conducted numerical computations of sand sediment transport and boulder transport based on tsunami and storm waves over an idealized topography with variable input wave conditions for identification of the key parameters.
Then, we derived the distribution distance of the deposits from both tsunamis and storm waves. We used a multiple regression analysis based on the stepwise method to identify the influence of each factor on the three key parameters above. As a result, the overall topography slope has the most significant impact on the inland distribution distance of the transported tsunami and storm sand deposits. The parameters that mainly control the sediment deposit volume over land under tsunami and storm wave conditions are the grain size and wave height, respectively. In case of boulders, roughness and topographic slope significantly controls their maximum inland extent rather than the offshore wave height.
We also summarized the numerical results by using the Iribarren number. We then compared the calculated dimensionless distribution of sandy deposit and coastal boulders with observed records. The computed values fall in the range of the observed dimensionless distributions of both deposits, implying that our computations are realistic and reasonably accurate. The dimensionless distribution of sand deposits and boulders transported by tsunami and storm deposits can be expressed using the Iribarren number. However, in the case of coastal boulders, the relation between Iribarren number and dimensionless distribution distance is not as strongly pronounced as for sand deposits.
The identification of the origin of sand deposits and coastal boulders can provide a broader view on the recurrence of inundation scenarios and therein contribute to future efforts in coastal risk assessments.
Then, we derived the distribution distance of the deposits from both tsunamis and storm waves. We used a multiple regression analysis based on the stepwise method to identify the influence of each factor on the three key parameters above. As a result, the overall topography slope has the most significant impact on the inland distribution distance of the transported tsunami and storm sand deposits. The parameters that mainly control the sediment deposit volume over land under tsunami and storm wave conditions are the grain size and wave height, respectively. In case of boulders, roughness and topographic slope significantly controls their maximum inland extent rather than the offshore wave height.
We also summarized the numerical results by using the Iribarren number. We then compared the calculated dimensionless distribution of sandy deposit and coastal boulders with observed records. The computed values fall in the range of the observed dimensionless distributions of both deposits, implying that our computations are realistic and reasonably accurate. The dimensionless distribution of sand deposits and boulders transported by tsunami and storm deposits can be expressed using the Iribarren number. However, in the case of coastal boulders, the relation between Iribarren number and dimensionless distribution distance is not as strongly pronounced as for sand deposits.
The identification of the origin of sand deposits and coastal boulders can provide a broader view on the recurrence of inundation scenarios and therein contribute to future efforts in coastal risk assessments.