Niwa hydrologist Dr James Griffiths said there were many different "nature-based solutions" to consider, ranging from forested headwaters and corridors and the restoration of floodplain connectivity, through to landscape features that would help retain and detain water, such as natural, restored or constructed wetlands, as well as ponds and bio-retention swales which could store and treat stormwater runoff.
"While human-engineered structures such as dams, stopbanks, seawalls and stormwater drains are traditionally seen as the main water management interventions to reduce the impact of floods, there is great potential for ‘green infrastructure’ to boost flood protection and resilience.
"Using natural areas and nature-based solutions to catch, store and clean water could be a win-win scenario, delivering a range of co-benefits in addition to reducing flooding, including increasing biodiversity."
Dr Griffiths said New Zealand was capable of, and needed to be, at the forefront of developing new ways to respond to the risks of flooding.
"Two-thirds of New Zealanders live in areas prone to flooding, and flooding is our most frequent natural disaster, so as land use intensifies and the frequency and intensity of extreme rainfall events increase due to climate change, we need new approaches to preparing for, managing and responding to flooding."
He said Niwa researchers examined nature-based solutions from around the world and were now giving local authorities an overview of the wide range of options and the best ways to assess the benefits.
"Regional and district councils are undertaking feasibility studies on the use of nature-based solutions for flood mitigation, so our review of international studies will help with evidence-based decision-making."
Dr Griffiths said modelling could compare various flooding scenarios and predict the effectiveness of different options.
"A central question is, ‘how well will it perform in reducing flood peak, when the flood is at its highest?’
"Extreme rainfall events are a major challenge.
"They require efforts to be made right through the catchment, from the headwaters and middle reaches to the lowland flood plains, to increase infiltration and detention of water, so it impacts less further downstream in more populated areas."
While the main benefit was the reduction of flooding, nature-based solutions often delivered other advantages, such as improvements in water quality, ecosystem health, air quality, noise reduction and carbon storage, as well as positive outcomes for economic and social development.
Niwa has developed a preliminary road map to guide the evaluation and implementation of nature-based solutions and is collaborating with local authorities and other stakeholders so lessons can be learned and shared across New Zealand.
Regional and district councils will complete their feasibility studies by mid-2025 and these will help inform wider adoption of this approach into long-term planning.
