Effects of a Macro-Roughness Element on Tsunami Wave Amplification, Pressures, and Loads: Physical Model and Comparison to Japanese and US Design Equations

Tori Tomiczek,Adi Prasetyo,Nobuhito Mori,Tomohiro Yasuda,Andrew Kennedy

doi:10.1142/s0578563417500048

Tori Tomiczek, Adi Prasetyo + Show 3 more

Open Access

https://doi.org/10.1142/s0578563417500048

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Abstract

Experiments were conducted at a 1:20 length scale in a large tsunami flume to measure wave evolution and pressures on and around structural elements. The water surface profiles of waves propagating across a bare beach were compared with those recorded in front of an onshore obstacle representing an urban macro-roughness element. The addition of a structure significantly changed the water surface profile for broken waves: the water surface amplification in the presence of a macro-roughness element reached seven times the bare-earth water surface elevation. Estimated pressures from design equations were calculated using recommended inputs and compared with pressures recorded by gauges installed on the structural elements. Design equations showed good agreement for non-breaking wave pressures but underestimated peak pressures for breaking waves. Likewise, force integrations of measured pressures on the experimental specimen indicated that design equations may underestimate loads due to waves that break offshore and propagate across a beach as a turbulent bore. The time-integrated pressure impulse was shown to be less sensitive to wave characteristics than the peak recorded pressures. Time-averaged loading curves were also developed for different average periods.

Highlights

Tsunamis pose significant threats to coastal communities worldwide: recent tsunamis that have caused major damage in coastal regions include the IndianOcean Tsunami (2004), the South Pacific Tsunami (2009), and the Tohoku Earthquake Tsunami (2011)
The control, bare-earth time series in Fig. 4 indicates that the wave propagated past both locations with a very low water surface elevation ηbe ; visual observation and video analysis of the trial confirmed that the wave broke near the crest of the slope and propagated along the flat beach as a turbulent bore with a high propagation speed
Trials with the obstacle positioned at both distances L2 and L3 showed wave amplification due to wave-structure interaction; the wave gauge in front of the obstacle positioned further inland recorded a larger amplification despite having a lower peak water surface elevation when the wave propagated across the no-obstacle topography

Summary

Introduction

Ocean Tsunami (2004), the South Pacific Tsunami (2009), and the Tohoku Earthquake Tsunami (2011). The 29 September 2009 South Pacific Tsunami and the 27 February 2010 Chilean Tsunami caused substantial damage and loss of life in local villages [see Reese et al, 2011; Mas et al, 2012]. Earthquake Tsunami caused severe damage to over 400,000 homes and catastrophic loss of life along the east coast of Japan [see Mimura et al, 2011; Mori et al, 2011; Udo et al, 2012; Suppasri et al, 2013]. To ensure the safety and vitality of coastal communities, local and national governments across the globe must evaluate their tsunami response and preparedness plans to adequately protect citizens and defend structures from damage, especially from beyond-design basis events

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