A major upgrade of the Waikato Regional Council’s most critical flood protection asset—the east and west foreshore stopbanks in the Hauraki Plains—has been completed, future-proofing the region against rising sea levels and increased flood risk.
Often compared to the Netherlands’ iconic dikes, the 15.5-kilometre-long stopbanks protect large swathes of low-lying land in the Hauraki District, where the sea sits higher than the land it borders.
“These stopbanks are like New Zealand’s version of the Dutch dikes,” said Waikato Regional Council Hauraki Zone Manager Karen Botting. “They’re holding back the sea every day.”
The $3.1 million upgrade, which received $1.92 million in co-funding from Kānoa – Regional Economic Development & Investment Unit through the Government’s COVID-19 Response and Recovery Fund, took four years to complete. The improvements included building a 6.5-metre-wide crest platform that allows the stopbanks to be raised further in future, if needed.
“They’re constructed like a pyramid with a wide base and a 3:1 slope, which provides structural strength,” Botting explained. “This design allows us to add height without needing to increase the footprint.”
Currently standing at 3.5 metres tall, the stopbanks exceed the 3-metre flood design height by an additional half metre of freeboard, meeting current climate resilience standards. The design enables them to be raised to 4 metres, preparing them for a potential sea level rise of up to half a metre.
“If you stood on the foreshore stopbanks, you’d see the land is actually lower than the sea. Without them, that land would be inundated daily,” said Botting.0.5 metres.
The stopbanks protect the largest area of productive farmland in the region, multiple towns, and critical infrastructure. Their protection zone reaches as far south as Morrinsville and spans three district council areas. They are also essential to safeguarding the national roading network connecting Hauraki and the Coromandel Peninsula with Hamilton, Tauranga and Auckland.
As part of the upgrade, the council also removed 170,000 cubic metres of suspended sediment from the Firth of Thames and the Piako and Waihou rivers. This sediment was captured in silt traps, dried, and used to raise the stopbanks—delivering environmental benefits and cost savings.
The sediment reuse helped avoid an estimated 10,000 truck and trailer movements, saving around $4 million in haulage costs and significantly reducing carbon emissions.
The stopbanks are routinely “topped up” due to natural land subsidence, making ongoing maintenance and future adaptability crucial for the sustainability of the Hauraki Plains in the face of climate change.
