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This experimental project investigated the debris accumulation in front of structures during tsunamis (debris damming), which leads to an increase in the forces imposed by tsunami flow on structures. The study was conducted through the construction of a 1:20 geometric scale physical model. Tsunami-like waves were generated over an idealized slope and transported different shapes of multi-debris, representing shipping containers, over the flat test section to measure debris loadings on elevated column structures. The experiment optically measured the debris impact and damming process, along with the corresponding loads on the entire column structure using a Force Balance Plate and separately on an individual column in the front row using a load cell. This unique data set will help to understand the impact of various factors on debris-driven damming loads, including wave characteristics, specimen configurations, and debris shapes. This data will also help to develop and validate numerical models that predict the motion and dynamics of floating debris during extreme coastal events. This project is the outcome of “Collaborative Research: Experimental Quantification of Tsunami-driven Debris Damming on Structures” with collaborators from the University of Hawaii at Manoa, Louisiana State University, and Oregon State University. 

A 1:16 scaled physical model was constructed to investigate the effectiveness of a seawall, a submerged breakwater, and mangrove forests to mitigate overland flooding and forces on structures in an idealized urban coastal environment. The experiment was performed using tsunami-like waves at different water levels, wave amplitudes, and time scales to simulate long-wave dynamics. The baseline condition (no mitigation), seawall, submerged breakwater, and mangrove forest were tested individually, and the seawall and submerged breakwater were also tested in combination. Wave gauges, acoustic Doppler velocimeters, loadcells, and pressure gauges were used to measure wave elevations, velocities, forces, and pressures on coastal structures, respectively. The performance of these hard structures and mangroves was compared through their effects on wave elevation, particle velocity, and force reduction. Experimental results showed that each protecting structure reduced the horizontal wave forces and inland flow hydrodynamics in the low-water-level case, with a similar performance by the individual seawall, submerged breakwater, and four rows of mangroves. The combined configuration, when the seawall and submerged breakwater were installed simultaneously, caused the most significant maximum force percent reduction by approximately 50%, while mangrove forests arranged in eight rows resulted in a force reduction of 46% in the first building array. However, in the high-water-level cases, the impulsive force measured with the presence of the submerged breakwater was larger than in the baseline case; thus, the submerged breakwater may amplify the impulsive force on the vertical building rows for certain incident wave conditions. Generally, the combined hard structures induced the lowest force reduction factor measured in almost every building row compared to the seawall, submerged breakwater, and mangroves considered separately for all wave conditions and water levels. That means this multi-tiered configuration showed better performance than individual alternatives in reducing horizontal forces inland than the individual alternatives considered separately. 

A Computational Fluid Dynamic (CFD) model study of wave and structure interactions on an elevated residential building under various air gap and surge/wave conditions was performed using the olaFlow, an open-source program using the OpenFOAM (Open-source Fields Operation And Manipulation) platform. The numerical model results, including free surface elevation, wave velocity, and vertical pressures on the underside of the elevated structure, showed a good agreement with the measured time-series data from the 1:6 scale hydraulic experiment (Duncan et al., 2021). The numerical simulations were used to extend the physical model tests by computing the vertical distribution of the pressure and resulting wave-induced horizontal forces/pressures, which were not measured in the physical model studies. The simulated results indicate that the pattern of pressure distributions at the frontal face of the elevated structure was controlled by water depth and wavebreaking types (nonbreaking, breaking, and broken waves). The wave induced-vertical force on the elevated structure strongly depends on wave height and the air gap, which is a net elevation from the still water level to the bottom of the structure, but the horizontal force shows complicated patterns due to the varied surge levels (flow depth), wave heights and air gaps. The new dimensionless parameter, α′/h, comprised of the air gap, incident wave height, and flow depth, is introduced and utilized to predict the horizontal forces on the elevated structure. 

This study formulates the reduction effects of a sandy berm on irregular wave runup over a dune-berm coast. The numerical experiments by Park and Cox (2016) are closely re-examined to develop an empirical formula describing the variability of reduction effects of a sandy berm over a broad range of conditions. Based on a sequence of regression analyses, the reduction effects are expressed as a reduction factor in terms of normalized berm width, normalized surge level, and wave steepness in deep water. The comparison with the numerical experiments demonstrates that the regression formula can satisfactorily reproduce the variability of the reduction effects over the range of numerical experiments. The analysis of prediction uncertainty demonstrated that the derived formula reproduced the reduction effects observed in the numerical experiments with negligible bias and a 90% confidence interval of approximately ±20% relative error. In addition, conversion formulas between representative runup values based on different statistical definitions are derived to enable consistent comparisons between them. The proposed reduction formula is implemented into three empirical runup models that are applicable to the quick estimations of irregular wave runup on a dune-berm coast: the models by Park and Cox (2016), Stockdon et al. (2006), and Mase et al. (2013). Consistent comparisons were conducted among the empirical predictions and numerical experiments based on the statistical conversion formulas. Combined with the proposed reduction formula, all three models well reproduced the normalized 2% runup in the numerical experiments over a wide range of conditions. On the other hand, the uncertainty in the runup prediction appeared in different forms depending on the selected model. When the proposed reduction formula was implemented in the modified Park and Cox (2016) and modified Stockdon et al. (2006) models, the uncertainty was described by a log-normal distribution of the error ratio between the empirical predictions and numerical experiments. Quantitatively, these two models predicted 90% of the normalized runup on a dune within a range of relative error of less than approximately 20–30%. When the proposed reduction formula was combined with the model by Mase et al. (2013), the uncertainty followed a normal distribution of the residual error between the empirical predictions and numerical experiments. On the normalized runup, the model prediction indicated a small conservative bias (+0.05) and a root-mean-square error of 0.13. 

Overview report provides a summary of the datasets, including built-. natural-, and social-systems in Seaside, Oregon. Relevant references are also provided. Additional information is available in the README file in the correspondent dataset in DesignSafe. 

It presents an experimental study of tsunami-driven debris transport over the flat testbed. We utilize two types of debris elements, which have the same shape but different material (wood, HDPE) to create debris of different density. We considered variations in the grouping of debris (wood only, mixed wood and HDPE, and HDPE only), parameterized by the mean specific gravity (SGg). The final dislocations and local velocity of debris elements were optically measured and compared to flow velocity. The effects of obstacles on the passage of debris and the probability of collision to obstacles were examined and the process of debris-debris and debris-obstacle interactions from debris entrainment to final dislocation was studied. The curated data could be utilized to understand initial debris entrainment, and espeically utilized to verify/validate a numerical debris transportation model. This work highlights the importance of considering debris density in estimating the longitudinal distance and spreading angle. These variables were less dependent on the initial configuration of the debris field. Future studies should consider other aspects of the phenomena, including a better understanding of the potential impact by debris on obstacles, the role of the return flow in determining the debris trajectory, and investigations of the obstacles that more realistically reflect urban shorelines subjected to strong overland flow.