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

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

Investigation of Barrier Island Highway and Marsh Vulnerability to Bay-Side Flooding and Erosion

Coastal highways along narrow barrier islands are vulnerable to flooding due to ocean and bay-side events, which create hazardous travel conditions and may restrict access to surrounding communities. This study investigates the vulnerability of a segment of highway passing through the Pea Island National Wildlife Refuge in the Outer Banks, North Carolina, USA. Publicly available data, computational modeling, and field observations of shoreline change are synthesized to develop fragility models for roadway flooding and marsh conditions. At 99% significance, peak daily water levels and significant wave heights at nearby monitoring stations are determined as significant predictors of roadway closure due to flooding. Computational investigations of bay-side storms identify peak water levels and the buffer distance between the estuarine shoreline and the roadway as significant predictors of roadway transect flooding. To assess the vulnerability of the marsh in the buffer area, a classification scheme is proposed and used to evaluate marsh conditions due to long-term and episodic (storm) stressors. Marsh vulnerability is found to be predicted by the long-term erosion rate and distance from the shoreline to the 5 m depth contour of the nearby flood tidal channel. The results indicate the importance of erosion mitigation and marsh conservation to enhance the resilience of coastal transportation infrastructure

Investigation of Barrier Island Highway and Marsh Vulnerability to Bay-Side Flooding and Erosion

Coastal highways along narrow barrier islands are vulnerable to flooding due to ocean and bay-side events, which create hazardous travel conditions and may restrict access to surrounding communities. This study investigates the vulnerability of a segment of highway passing through the Pea Island National Wildlife Refuge in the Outer Banks, North Carolina, USA. Publicly available data, computational modeling, and field observations of shoreline change are synthesized to develop fragility models for roadway flooding and marsh conditions. At 99% significance, peak daily water levels and significant wave heights at nearby monitoring stations are determined as significant predictors of roadway closure due to flooding. Computational investigations of bay-side storms identify peak water levels and the buffer distance between the estuarine shoreline and the roadway as significant predictors of roadway transect flooding. To assess the vulnerability of the marsh in the buffer area, a classification scheme is proposed and used to evaluate marsh conditions due to long-term and episodic (storm) stressors. Marsh vulnerability is found to be predicted by the long-term erosion rate and distance from the shoreline to the 5 m depth contour of the nearby flood tidal channel. The results indicate the importance of erosion mitigation and marsh conservation to enhance the resilience of coastal transportation infrastructure

Extreme block and boulder transport along a cliffed coastline (Calicoan Island, Philippines) during Super Typhoon Haiyan

This paper presents data and analysis for block and boulder transport during Super Typhoon Haiyan along a 4.5 km long, low (5–12 m) cliffed coastline in Calicoan Island, Eastern Samar, Philippines. Wave runup exceeding 15.2 m elevation above mean sea level drove large limestone clasts, with volumes up to ~ 83 m3, up to ~ 280 m inland. A few very large clasts with volumes 65–132 m3 were not transported by the waves. When combined with recent transport reported in May et al. (2015), Cox et al. (2016), and other literature, it is becoming increasingly clear that the largest blocks transported by storms overlie much of the tsunami transport range, increasing the difficulty in attributing the transport source without additional evidence. Comparison of present results with a global database of storm boulder transport shows a mass-elevation envelope outside of which no transport is observed. Initiation of motion criteria were extended to include non-rectangular cross-sections, which significantly reduces inferred velocities, particularly for overturning motion. These new relations were applied to the largest observed sliding and overturning boulders while considering coefficient uncertainties, and resulting velocity uncertainty was large enough that direct inference of wave heights would be problematic. Estimates of initiation velocities for cliff-edge boulders computed using lifting/joint-bounded relations were unreasonably large when compared to those for sliding and overturning boulders, suggesting that processes other than Bernoulli lift forces dominated at cliff edges