A typical New Zealand kelp forest. Photo: Supplied / GNS Science
New research from GNS Science reveals natural ecosystems, such as kelp forests, can slow down the speed of tsunamis in New Zealand.
The pilot study was carried out in Napier and looked at both natural and manmade tsunami defences along the coastline using computer simulated models. These 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. Researchers found the most effective one for slowing down tsunami currents was a combination of natural bioshields.
Lead researcher and GNS tsunami scientist Jean Roger told RNZ he had been wanting to do this study for years. He said that was because it can help coastal areas better understand what natural and artificial bioshields can be used to lessen the impact of tsunamis - which can damage infrastructure and smother natural environments in sediment.
"We found that this friction produced by ecosystems may be able to reduce the floor speed of the tsunami - which is something very important," he said.
Vegetation areas in Napier that were applied in the tsunami simulation. Photo: Supplied / GNS Science
The modelled scenario showed a significant reduction in sediment transport around bridge infrastructure, which can weaken the piles and increase the risk of collapse.
"We also did some sediment transport simulation to see what these ecosystems can provide in reducing sediment movement during an event. We found it will reduce it in some locations," said Roger.
The research is preliminary, so he said they need to do many more simulations to be sure that there is a large impact on the reduction of tsunami speed.
The researchers already knew that mangroves can reduce tsunami speed, but this is the first study to look at New Zealand ecosystems such as kelp forests and pohutakawa trees. Roger said these findings can benefit many coastal areas of New Zealand and should be considered by local councils.
"We hope that this research will provide decision makers, including councils and industries, with science-backed solutions for resilience planning and land use decisions to have more consideration of the benefits of coastal ecosystems in terms of coastal protection," he said.
While this study was based in Napier due to limited time and resource, Roger is keen to see it expanded further.
"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," he said.
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