Tsunami waves hitting natural kelp forests lose more of their power than those striking concrete walls. A GNS Science study led by Dr Jean Roger tested natural and artificial defences, with nature coming out ahead.
Simulations Highlight the Efficacy of Natural Systems
The modelling study compared a range of defences, including kelp forests, pōhutukawa trees, a restored estuary, a sea wall, and an artificial reef. Hybrid combinations involving multiple types of natural vegetation proved the most effective overall.
“The ecosystems, also known as bioshields, included kelp forest, pōhutukawa trees, a restored estuary, a sea wall, an artificial reef and a combination of vegetation types,” the research states. “Across the different scenarios the most effective decelerator of tsunami currents was a combination of natural ones.”
The computer models measured factors such as inundation extent, flow depth and speed, and areas of erosion or sediment deposition. The strongest natural defences slowed the tsunami waves enough to protect vulnerable areas more reliably than many built structures.
Infrastructure and Marine Protection Outcomes
One of the standout findings from the study was the protection of infrastructure, particularly bridges. The simulations showed a significant reduction in sediment transport around bridge piles which is a critical factor for structural stability.
“Sediment is important for stabilising piles that anchor bridges to the ground. Removing it weakens the structure and increases the risk of collapse,” the study noted.
In addition to infrastructure, natural bioshields helped curb coastal erosion and prevent sediment from smothering marine ecosystems. This not only protects the shoreline but also helps preserve water quality.
Dual Benefits for Coastal Resilience and Climate Adaptation
Dr Roger emphasised that bioshields provide more than just tsunami protection. They also help communities prepare for the effects of climate change.
“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,” she said.
Bioshields act as a buffer against sea-level rise, stronger storms, and more frequent cyclones, its expected that all threats that are expected to intensify in coming decades.
Pathway to Policy and Planning Integration
Kelp forests and other natural defences may soon play a bigger role in New Zealand’s coastal planning. GNS Science’s latest study urges collaboration with local governments and industry to integrate sustainable, site-specific solutions into long-term development.
“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,” Dr Roger said.
“We hope our research provides decision-makers with science-backed solutions for resilience planning and land-use decisions,” Dr Roger added.