Hawke’s Bay Regional Council (HBRC) has completed a significant stopbank upgrade in Taradale as part of its Resilient River Community project.
Stopbanks are compacted earth banks built next to rivers to hold flood water in the berm and protect communities during flood events. The Taradale stopbank upgrade is to protect the local community during a 500-year Tūtaekurī flood event, as well as ensure less damage during an earthquake.
It is the first of several upgrades that will happen across the Heretaunga Plains with stopbank heights raised (up to 1m in certain places) and widths widened.
Regional Council Chair Hinewai Ormsby says expertly engineered stopbanks are critical in building community resilience to adapt to the increased magnitude and frequency of flood events due to climate change.
“Climate change will bring more intense flooding. Infrastructure investments like these are key in councils’ response to these increasing challenges. It’s fantastic to see the Taradale stop bank strengthened, with an increased height and weight.”
HBRC design engineer Andre Magdich explained to BayBuzz the work involved in upgrading a stopbank.
“First the stopbank’s condition has to be assessed. For this, two types of testing are completed, non-destructive and destructive.
“Non-destructive testing uses geophysical testing to determine shear wave velocities or speed of the sound for stopbank material. Sound travels faster in compacted material. We identified anomalies within the stopbank and performed destructive testing on those locations.
“Destructive testing then involved diggers opening part of the stopbank and material testing. The material was tested for compaction and permeability.” The stopbank is designed to prevent water from overtopping but also to stop or control water seeping through the stopbank during the flood event.
Hawke’s Bay has a long history of using stopbanks, and there have been trials to optimise stopbank width. The standard for a stopbank is 4m wide crest. This allows for pedestrian and cycle users but also maintenance and inspection vehicles.
“For the Taradale stopbank upgrade, we stripped back the topsoil and filled in the bank with appropriate material to widen and increase the height,” says Magdich.
“This stop bank is 2.5 km long and we increased the height by up to one metre. The slope went from 1:2m to 1:4m which gives the stopbank a wider toe and reinforces its ability to hold water when in flood.”
Overall the Taradale upgrade involved around 30,000m³ of new material placed on the stopbank.
Resilient River Communities is a joint initiative between the Government’s Kānoa – Regional Economic Development & Investment Unit, regional councils and unitary authorities over three years to promote vital flood protection projects to help reduce the impacts from heavy rainfall events. Kānoa is funding $12.8 million of this project, and the Regional Council is contributing an additional $7.2 million.
Further work to reinstate the berm in Taradale is planned for 2023 which will include native planting to encourage and enhance biodiversity. A car park will also allow the community better access to one of Hawke’s Bays most popular swimming spots along the Tūtaekurī.
Collaborating with iwi partners and local businesses has been key to this project, working closely with Ngāti Pārau who established Te Wai Mauri Limited. Te Wai Mauri Limited is a hapū led and owned business, established at Waiohiki Marae. The Regional Council will continue to work closely with Te Wai Mauri Limited on the planting programme in the Tūtaekurī berm area next winter.
Future planned stopbank upgrades a include at Moteo, Ngatarawa, Ōmarunui and East Clive.
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This is an excellent project, showing a very systematic, proactive approach that will improve resiliency. I see this as core Regional Council business, and an area that I am most happy for them to spend money on. It is great that the stop banks are improved before they are required – rather than after flooding, where there would be additional social and financial costs.
Thank you for doing this work, for the protection it offers to us residing off Guppy Road.