Combined infragravity wave and sea‐swell runup over fringing reefs by super typhoon Haiyan

Abstract

Super typhoon Haiyan struck the Philippines on 8 November 2013, marking one of the strongest typhoons at landfall in recorded history. Extreme storm waves attacked the Pacific coast of Eastern Samar where the violent typhoon first made landfall. Our field survey confirmed that storm overwash heights of 6–14 m above mean sea level were distributed along the southeastern coast and extensive inundation occurred in some coastal villages in spite of natural protection by wide fringing reefs. A wave model based on Boussinesq‐type equations is constructed to simulate wave transformation over shallow fringing reefs and validated against existing laboratory data. Wave propagation and runup on the Eastern Samar coast are then reproduced using offshore boundary conditions based on a wave hindcast. The model results suggest that extreme waves on the shore are characterized as a superposition of the infragravity wave and sea‐swell components. The balance of the two components is strongly affected by the reef width and beach slope through wave breaking, frictional dissipation, reef‐flat resonances, and resonant runup amplification. Therefore, flood characteristics significantly differ from site to site due to a large variation of the two topographic parameters on the hilly coast. Strong coupling of infragravity waves and sea swells produces extreme runup on steep beaches fronted by narrow reefs, whereas the infragravity waves become dominant over wide reefs and they evolve into bores on steep beaches.

Post-Disaster Survey of Storm Surge and Waves Along the Coast of Batanes, the Philippines, Caused by Super Typhoon Meranti/Ferdie

“…7, the correlation between W and c of all the obtained data is relatively weak while Shimozono et al [2015] shows clear negative correlation between W and c observed along the east of coast of Eastern Samar. According to Shimozono et al [2015], negative correlation between W and c is mainly because wider reef dissipates more wave energies through wave breaking and bottom frictions.…”

“…Both coasts of Batanes and Eastern Samar are fronted by a coral fringing reef, facing the deep Pacific Ocean and were dominantly affected by severe storm waves [Shimozono et al, 2015;Tajima et al, 2016]. Both Meranti and Haiyan migrated toward the WWN direction while the track of Meranti was about 6-8 • north from that of Haiyan as shown in Fig.…”

Block and boulder transport in Eastern Samar (Philippines) during Supertyphoon Haiyan

“…Supported by post-typhoon survey reports (Bricker et al, 2014;Tajima et al, 2014), recent wave models (Roeber and Bricker, 2015;Shimozono et al, 2015), eyewitness accounts, and video footage (Mas et al, 2015;Bricker and Roeber, 2015), our findings suggest that a variety of hydrodynamic processes related to TC landfall must be considered when interpreting boulder deposits along coasts. These processes may include, in addition to incident (potentially very high) gravity waves and (or on top of) pressure-and wind-driven storm surge, meteo-tsunamis or seiches (Mori et al, 2014), as well as infragravity waves with periods of up to several minutes.…”

“…A Haiyan-related meteo-tsunami can be excluded due to a lack of bathymetric conditions with suitable resonance properties. Most recently, based on models simulating wave transformation over shallow fringing reefs using Boussinesq-type equations, Shimozono et al (2015) and Roeber and Bricker (2015) confirmed that the extreme run-ups and the bore-like flooding pattern in Eastern Samar must be explained by strong coupling of sea swells and infragravity waves with periods of > 1 min, which may have experienced excitation by resonances with the fringing reef (cf. Péquignet et al, 2009).…”

“…Hence, it experienced maximum wind speeds with the highest modelpredicted waves of up to 19 m, but only a limited wind-driven surge during Haiyan (Bricker et al 2014). Field indicators document inundation levels of up to 6 m onshore flow depth, nearly 11 m run-ups above local event tide level, and inundation distances of up to 800 m depending on onshore topography (Quinto et al, 2014;Tajima et al 2014;Shimozono et al, 2015).…”