Tsunami versus Infragravity Surge: Comparison of the Physical Character of Extreme Runup

Recent observations of energetic infragravity (IG) flooding events, such as those in the Philippines during Typhoon Haiyan, suggest that IG surges may approach the coast as breaking bores with periods of minutes: a very tsunami-like characteristic. Energetic IG waves have been observed in various locations around the world and have led to loss of lives and damages to property. In this study, a comparison of overland flow characteristics between tsunamis and energetic IG wave events is presented. In general, whenever the tsunamis and energetic IG waves have similar runup, tsunamis tend to generate greater flow depths and longer flood durations than IG. However, flow velocities and Froude number are larger for IG primarily due to bore-bore capture. This study provides a statistical and physical discriminant between tsunami and IG, such that in areas exposed to both, a proper interpretation of overland transport, deposition, and damage is possible.