University of Canterbury PhD student Christina McCabe and Associate Professor Jonathan Tonkin. Photo: University of Canterbury
Researchers say New Zealand must change the way it manages river flooding risks, saying communities cannot continue to build ever bigger stop-banks indefinitely.
New research from the University of Canterbury and University of Otago published in journal Nature Water suggests giving rivers more room to grow will be better for protecting communities and improving their ecology.
Associate Professor Jonathan Tonkin of the University of Canterbury said the current method of building infrastructure to protect communities and people was not the answer.
"The conventional approach is to channelise rivers, narrow them down and constrain them in stop banks. It might be the logical response, but these approaches often exacerbate the long-term vulnerabilities and they transfer the risk elsewhere, like downstream.
"Do we continue to build bigger stop-banks to protect our towns and cities, or do we begin to give rivers back the space they need to roam on the landscape?"
Flooding was only expected to increase in future due to the effects of climate change, Tonkin said.
"Large floods are expected to increase in frequency with climate change, and the effects of such floods are exacerbated by the artificial confinement of floodplain river systems.
"Giving rivers room to move is being considered as an alternative to increasing fortification of existing flood infrastructure. Our research also shows that there are key co-benefits to ecosystems that have previously been overlooked."
A new approach could be a win-win for both people and biodiversity, allowing river flows to be slowed while also increasing nesting sites for rare bird species, such as banded dotterels and black-fronted terns.
"Healthy, free-flowing rivers provide significant contributions to people, from flood resilience to freshwater provision and recreation."
Tonkin pointed to the Hutt River as a prime example of a river needing a new approach, as the most dense active floodplain in New Zealand.
"There's already movement there to start to buy back land along the margins of the rivers and give it more space to move. Canterbury is another place where we have an overrepresentation of braided rivers in particular, and Environment Canterbury is also considering this need to give rivers more space to grow.
Lead author of the study, University of Canterbury PhD student Christina McCabe, said rivers left free to roam could support unique combinations of plants and animals, and traditional flood management had prioritised infrastructure and human safety over river ecosystems.
"Even exposed gravel, which is made possible in rivers that have the space to move, can be critical nesting sites for endangered birds. For instance, the banded dotterel travels long distances to nest on exposed braided-river gravels each spring.
"By considering the ecological benefits of dynamic rivers, decision-makers can implement solutions that enhance biodiversity, improve water quality, and build resilience to climate change."
Sign up for Ngā Pitopito Kōrero, a daily newsletter curated by our editors and delivered straight to your inbox every weekday.
