Pohutukawa bio-shield on the coast of New Zealand as a tsunami mitigation strategy

Abstract

New Zealand is vulnerable to both far-field and near-field tsunamis. The Pohutukawa tree (Metrosideros excelsa), a native tree to New Zealand, is commonly found in the New Zealand coastal environment. This tree has strong roots that grow deep into the ground, as well as have a wide spreading branching system. It is considered that these characteristics would enable the Pohutukawa tree to act effectively as a bio-shield against tsunamis in New Zealand. However, there is no research to show its capability in reducing the hydrodynamic force of a tsunami. Field investigation of the Pohutukawa tree in Maraetai Beach, and the use of a one-dimensional depth-integrated shallow water numerical model, was conducted to assess the capability of a Pohutukawa bio-shield against a tsunami wave. A Pohutukawa bio-shield of 35 m width against a tsunami wave of height of 3.5 m at shoreline with wave period of 20 min reduced the hydrodynamic force of a tsunami directly behind the bio-shield by approximately 21%. This study, therefore, elucidates the capability of a Pohutukawa bio-shield as a tsunami mitigation strategy.

Keywords:

• Pohutukawa
• Metrosideros excelsa
• tsunami protection
• bio-shield
• tsunami modelling

Acknowledgement

We would like to thank Aaron and Zelma for their support in the field surveys, the reviewers for their comments and anonymous for their support in helping publish this work.

Disclosure statement

No potential conflict of interest was reported by the authors.