Boxing Day Tsunami: Here’s What We Have Learned in the 20 Years Since the Deadliest Natural Disaster in Modern History
In Japan, the idea that hard measures can protect against the loss of life has been discarded, with the view that large-scale tsunamis can overwhelm even the most robust defenses. For instance, in 2011, even a rubble breakwater followed by a five-meter-high wall could not protect the city of Watari. The tsunami covered half the city and hundreds of people died.
Tsunamis in the past decade or two have exposed vulnerabilities in existing protection strategies, with our field surveys showing breakwaters and other structures having suffered severe damage. While complete failure is expected in the face of extreme events, it’s crucial that certain critical infrastructure, such as power plants, are designed to withstand the biggest tsunamis. This requires further research into resilient engineering designs that may be able to partially fail but remain functional.
After the 2011 tsunami, Japanese engineers created two tsunami measurement levels. Level one tsunamis are more frequent, occurring perhaps once every century, but less dangerous.
Level two tsunamis are the big ones that any given bit of coastline might expect only once every thousand or so years: Indian Ocean 2004, Japan 2011. It is these tsunamis that critical infrastructure like power plants must prepare for. Nothing will entirely hold back a 2004-sized tsunami, but the goal is for structures to overflow without being destroyed. They should still be able to assist the evacuation process by reducing tsunami height and delaying the time it takes.
Despite evolving views on hard defenses, there remains value in building and planning coastal urban areas in more sustainable and responsible ways. In particular, critical infrastructure and densely populated areas in tsunami-threatened regions should be built on higher ground where possible.
Engineering advancements must also account for environmental consequences, including damage to ecosystems and disruption of natural coastal processes, with consideration given to nature-based solutions. Strengthening coral reefs with rock armor or heavy sandbags, and planting coastal forests as buffer zones may be a cheaper and more ecologically sensitive option than building high walls.
Climate Change and the Road Ahead
The progress is undeniable. However, tsunami and earthquake data still isn’t shared widely around the world, and local authorities and experts often don’t communicate the risk to residents of flood-prone communities. The passage of time can erode the memory of best practice when it comes to people’s disaster preparedness.
Added to that, rapid climate change is making sea levels rise and extreme weather, such as storms, more frequent. This doesn’t cause more tsunamis, but it can make them worse, and it does make “hard” defenses less sustainable in the long term.
While significant and urgent challenges remain, they are not insurmountable. By continuing to learn more about tsunamis and to prepare for the worst, we can minimize their impact and protect millions of lives.
Ravindra Jayaratne is Reader in Coastal Engineering, University of East London. Tomoya Shibayama is Emeritus Professor of Coastal Engineering, Waseda University. This article is published courtesy of The Conversation.
