Destructive tsunami-like wave generated by surf beat over a coral reef during Typhoon Haiyan.

Volker Roeber,Jeremy D Bricker

doi:10.1038/ncomms8854

Abstract

Storm surges cause coastal inundation due to setup of the water surface resulting from atmospheric pressure, surface winds and breaking waves. Here we show that during Typhoon Haiyan, the setup generated by breaking waves near the fringing-reef-protected town of Hernani, the Philippines, oscillated with the incidence of large and small wave groups, and steepened into a tsunami-like wave that caused extensive damage and casualties. Though fringing reefs usually protect coastal communities from moderate storms, they can exacerbate flooding during strong events with energetic waves. Typical for reef-type bathymetries, a very short wave-breaking zone over the steep reef face facilitates the freeing of infragravity-period fluctuations (surf beat) with little energy loss. Since coastal flood planning relies on phase-averaged wave modelling, infragravity surges are not being accounted for. This highlights the necessity for a policy change and the adoption of phase-resolving wave models for hazard assessment in regions with fringing reefs.

Highlights

Storm surges cause coastal inundation due to setup of the water surface resulting from atmospheric pressure, surface winds and breaking waves
The tsunami-like wave that struck the town during Typhoon Haiyan on 8 November 2013 (Fig. 2)[1] astonished both villagers and disaster managers, as the coast near Hernani is sheltered by a broad fringing coral reef, which was expected to serve as a reliable wave defence[2]
In the deep water offshore of Hernani, winddriven setup only grew to a few decimetres, similar in size to the setup caused by the barometric pressure drop[12]. This is in contrast to the situation of the area around Tacloban city (Fig. 1), which is located at the end of a shallow bay with a maximum water depth of 50 m

Summary

Introduction

Storm surges cause coastal inundation due to setup of the water surface resulting from atmospheric pressure, surface winds and breaking waves. In the deep water offshore of Hernani, winddriven setup only grew to a few decimetres, similar in size to the setup caused by the barometric pressure drop[12] This is in contrast to the situation of the area around Tacloban city (Fig. 1), which is located at the end of a shallow bay with a maximum water depth of 50 m. Storm surge and damage of the type seen in Tacloban was predicted with great accuracy[14], as similar wind-driven surges have been studied for decades, with some outstanding examples being Hurricane Katrina in the United States, the Bhola cyclone in Bangladesh and the Ise-Bay typhoon in Japan.

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Conclusion