More than 30 properties near the Mangarau Stream remain in Category 2C, the only Havelock North properties to be placed into a land category after Cyclone Gabrielle.
A report by Tonkin and Taylor investigating the stream’s flood infrastructure’s performance during the cyclone highlights the years of confusion over
But it will take months of further consultation before the much-needed upgrades can begin. For residents facing the threat of future disasters, they can’t come soon enough. James Pocock reports.
Michael Hannah and his family only recently moved back to their Joll Rd home, but what the flooding did during Cyclone Gabrielle is still written all over the backyard .
The inside of the pool has become an overgrown garden and the fence that used to separate the back of the property from the stream is gone, much of it washed away to somewhere unknown.
A jagged edge of concrete padding sticking out over the stream is all that remains of a shed that used to sit by the water’s edge before floodwater, which reached knee height inside the family home, took it.
A Tonkin and Taylor Mangarau Stream Report, prepared for Hawke’s Bay Regional Council and released publicly just before Christmas, notes the Mangarau Dam and stream course were managed by Hawke’s Bay Regional Council until they were transferred to HDC in 2003.
As part of the governance agreement, a memorandum of understanding concerning land ownership and responsibility was proposed, along with assessing levels of service of drainage assets, which was to be undertaken by HBRC,” the report said.
“It does not appear this work has been carried out, resulting in a misunderstanding of respective roles and responsibilities, particularly on private land.”
The report identifies legal and physical access to the stream, as well as a lack of understanding about HDC’s ability to access and undertake work on private land under drainage acts, as limiting factors to carrying out effective maintenance work.
The Tonkin and Taylor assessment showed the lower reaches of the stream did not have capacity for the original Mangarau dam design flow of 25.5 cubic metres per second (cumecs), with the most constricted section only having capacity for 12 cumecs.
At the height of the cyclone, 35 cumecs flowed through the Mangarau Stream.
An earlier Stantec report says that, without the dam, an additional 22 cumecs - or 22,000 litres of water - would have been rushing through the stream.
“Based on current assumptions, dam release flows in excess of about 25 cumecs will result in flooding even if mitigation works are implemented as currently anticipated,” the report’s conclusion states.
The report recommended HDC undertake a further high-level review of catchment planning and stormwater management.
It also recommended HDC and HBRC progress with community consultation to directly affected residents and get community feedback on the proposed solution.
Hannah pointed out that the lack of maintenance before the cyclone likely contributed to a fallen tree taking out a bridge over the stream, which blocked it and led to some of the worst flooding in his area during the cyclone.
“The whole stream [maintenance situation] is a bit weird around who owns what, so everyone put their head in the sand,” he said.
He believes the private landowners would encourage the council to start work rather than kick up any fuss about using their land as an accessway.
But he is concerned it could take months before any further action is taken by HDC to protect residents around the stream from flooding.
“Once it is cleared out and they reinforce the wall then we will feel a bit safer, but at the moment every time it rains the kids are panicking.”
A statement from council spokespeople across multiple teams in response to Hawke’s Bay Today queries said the clearing of the Mangarau Stream has been ongoing since the cyclone, along with the other four Havelock North streams.
“Council undertook physical inspections of the streams in the week post-Cyclone Gabrielle and has since worked with contractors to remove debris,” the statement said.
“Further work is planned where access is challenging, an example of which is a number of large trees in the upper reaches of the Mangarau Stream to be removed [February 2024].”
The statement said major work like stream widening will take longer as it requires funding and consultation with affected landowners and the community.
“Council and its project team are currently working on preparing a more thorough maintenance programme for the streams,” the statement said.
“This involves the procurement of a dedicated maintenance contractor to deliver a regular maintenance schedule. Alongside this will be improving access; understanding the cost of that and how it will be funded.”
It is expected it will take a minimum of three months for HDC to prepare a business case to access $10 million of Crown funding for upgrading dams and streams.
“Council is working on having this ready for submission to government (Crown Infrastructure Partners) by end June 2024, hopefully sooner,” the statement said.
Local artist Dr David Guerin lives down the street and, while the flooding narrowly missed his house, he had a metre of water through his studio which damaged 50 years of drawings and eight tonnes of books.
He said the flood had removed a natural barrier between his house and the water, and there was now a vertical drop where the bank of the stream was on his side, which was a cause for concern in the event of another flood.
He said his wife Shelley Hickson had informed HDC of the issue as it wasn’t outlined among the remediation tasks in the Tonkin and Taylor report.
He said “blaming was not helpful” as the cyclone was an extreme event, but he believed similar events were likely to happen again and he hoped there would be investment in resilience.
The cost of the preliminary and general stream works, according to Tonkin and Taylor’s report, will be about $4.3m, which includes the cost of creating accessways and retaining walls.
The Mangarau Dam was built in the late 1970s, after a flooding event in 1974 when 127 millimetres of rain fell in 12 hours.
During Cyclone Gabrielle 284mm of rain was recorded in the Mangarau Dam over 24 hours at the HDC’s gauge, with 237mm falling in a 12-hour peak.
James Pocock joined Hawke’s Bay Today in 2021 and writes breaking news and features, with a focus on environment, local government and post-cyclone issues in the region. He has a keen interest in finding the bigger picture in research and making it more accessible to audiences. He lives in Napier. james.pocock@nzme.co.nz
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