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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. 

Inundation from storms like Hurricanes Katrina and Sandy, and the 2011 East Japan tsunami, have caused catastrophic damage to coastal communities. Prediction of surge, wave, and tsunami flow transformation over the built and natural environment is essential in determining survival and failure of near-coast structures. However, unlike earthquake and wind hazards, overland flow event loading and damage often vary strongly at a parcel scale in built-up coastal regions due to the influence of nearby structures and vegetation on hydrodynamic transformation. Additionally, overland flow hydrodynamics and loading are presently treated using a variety of simplified methods (e.g. bare earth method) which introduce significant uncertainty and/or bias. This study describes an extensive series of large-scale experiments to create a comprehensive dataset of detailed hydrodynamics and forces on an array of coastal structures (representing buildings of a community on a barrier island) subject to the variability of storm waves, surge, and tsunami, incorporating the effect of overland flow, 3D flow alteration due to near-structure shielding, vegetation, waterborne debris, and building damage.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EDLiEK6b64E