Bioshields Could Help Slow Tsunami Flow

New GNS Science research suggests natural ecosystems such as kelp forests can slow the flow speed of tsunamis. Curbing flow speed can reduce the harmful impacts of strong tsunami currents such as coastal erosion, damage to infrastructure like bridges, and sediment transport that can smother marine environments and affect water quality.

Lead researcher and GNS Tsunami Scientist Jean Roger said the study findings are expected to help local governments, planners, environmental agencies and infrastructure managers make informed decisions about natural environment management and natural hazard solutions.

“We hope our research provides decision-makers with science-backed solutions for resilience planning and land-use decisions,” Dr Roger says.

The GNS research looked at both natural and manmade tsunami defences applied to the Napier coast using computer simulated models. The models mimicked the resistant forces of each ecosystem and compared the maximum inundation extent, flow depth and speed, and where areas may have been eroded and sediments deposited.

The ecosystems, also known as bioshields, included kelp forest, Pohutukawa trees, a restored estuary, a sea wall, an artificial reef and a combination of vegetation types. Across the different scenarios the most effective decelerator of tsunami currents was a combination of natural ones.

Notably, the modelled scenario showed a significant reduction in sediment transport around bridge infrastructure. Sediment is important for stabilising piles that anchor bridges to the ground. Removing it weakens the structure and increases the risk of collapse.

Dr Roger says an added co-benefit of bioshields is that they can also reduce coastal erosion from climate change impacts such sea-level rise and more frequent and intense cyclones and storms.

“It’s a win-win situation. Nature-based solutions not only improve our ecosystems, they also help protect us from the impacts of natural and climate-change induced hazards in a cost-effective and sustainable way,” Dr Roger said.

“Following on from this research we hope to work closely with government and industry stakeholders to come up with the most effective tailored nature-based solutions for individual areas and circumstances.”

Notes

• The research was funded by the MBIE Hazard and Risk Management Strategic Science Investment Fund.

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