Wednesday 6 September, 2023
Tairāwhiti’s stopbanks are the unsung, unseen heroes of our region, says Gisborne District Council’s Regional River Manager Joss Ruifrok.
“They’re big and they’re in the background. You don’t see them.
“And when they do their job well, you don’t know about it.”
Last week Council considered the Crown’s cyclone recovery support package which included $64 million to go towards flood resilience improvements across Tairāwhiti.
Gisborne District Council must contribute 10 per cent towards flood protection projects to cement this Government funding, and the estimated $7million from Council will be allocated in Council’s 2024-2027 three-year plan.
If Council accepts the Crown offer it means $71m of additional funding will be used to accelerate the delivery of existing flood protection scheme upgrades (like the Waipaoa Stopbank Upgrade Project).
It will also enable staff to investigate, consider options, or construct flood resilience improvements in places like Te Karaka, Uawa and Tokomaru Bay over the next five years.
Stopbank projects have been busily increasing resilience for our region against the future impacts of climate change.
The Waipaoa stopbanks saved the city during Cyclone Gabrielle.
It’s estimated up to 1.5m of water would have flowed across Ormond township if the floodbanks weren’t there.
Council has resumed stopbank construction work to upgrade the Waipaoa River Flood Control Scheme.
The work involves significant earthworks to upgrade the stopbank on the western side of the Waipaoa River, downstream of the Waipaoa Bridge near the Manutuke Township.
Local contractors Earthwork Solutions Limited is carrying out the works. Construction will continue upstream towards Patutahi Township and the Whakaahu Stream until June 2024 (weather permitting).
The stopbank improvements are designed to cater for a 100-year rain event, accounting for climate change out to 2090.
“The existing stopbank is being raised and widened to provide for climate change effects and to improve flood resilience,” says Joss.
The scheme is comprised of 64km of stopbanks and is one of Council’s most valuable assets. It protects approximately 10,000 hectares of fertile floodplain land and has increased the amount of land being used for high-yield horticulture.
Approximately 32km of stopbanks has have been successfully upgraded since construction started in February 2019.
Council apologises for any inconvenience this work may cause to residents and road users in the area.
Background
The Waipaoa Flood Control Climate Change Resilience project had been humming along for about four years until around January 10 this year. That’s when “everything happened”.
Stopped in its tracks by Cyclone Hale on January 10, work started again in early February only to be halted again when Cyclone Gabrielle struck in the middle of that month. In May, work got back underway until June arrived with unrelenting rain and the third state of emergency this year.
However, the stop-and-start nature of the work due to extreme weather only reiterates just how crucial any stopbank project is.
The Waipaoa project will increase the level of flood protection of the Waipaoa River to cater to a 100-year heavy rain event, accounting for climate change until 2090.
Cyclone Gabrielle showed heartbreakingly the areas that need funding fast.
Funding is being secured urgently for the Te Karaka community, severely impacted after the Waipaoa River topped the stopbanks there.
Those stopbanks had been built post-Bola to 300mm above the peak levels of the 1988 cyclone.
But even that wasn’t enough to protect Te Karaka from Cyclone Gabrielle.
The high-intensity rain, the changing face of our riverbeds over decades, and climate change are all contributing factors.
In the background, Joss is ensuring the plans and designs for Te Karaka’s stopbank project are ready to go for when funding is confirmed.
If anyone has video footage of the Cyclone Gabrielle event, in particular, the volumes of stopbank overtopping that occurred between Te Karaka and the Kaitaratahi Bridge areas, please email us as these will help with the design and planning for the stopbanks.
The Waipaoa Stopbank Project
The Waipaoa Stopbank project was initially put forward for budget allocation in the 2015 Long Term Plan (LTP).
It’s about building stopbanks higher (up to 1.8metres in some places) and widening them to 4metres on top.
This project is building on top of the original Waipaoa Flood Control Scheme designed after the 1948 floods and constructed between 1953 and 1969.
Funding for this resilience project was confirmed after community engagement found 61 per cent of people felt it should be a priority.
Work got underway in 2019 and it’s expected to be finished by 2029.
It’s a huge project. The 10,000 hectares on the Poverty Bay Flats are fertile because of this significant waterway yet they also need protection from the river during heavy rain.
The impacts of sediment and silt destroy crops, affect businesses, jobs and the source of vegetables for our whole country.
The Waipaoa River winds its way south from its headwaters north of Whatatutu Township to the Waipaoa River mouth into the Pacific Ocean down the end of Centennial Marine Drive.
Along its 80-kilometre journey out to sea, it passes through the townships of Te Karaka, Ormond and Patutahi. There are also significant tributaries that feed into it on the way.
Eastern side
The focus has been on upgrading the eastern city side first. The reasons for this included the important lifeline links like the airport and hospital being in this area.
The new Mahunga Floodgate is part of it at Ormond. It is the biggest concrete and steel construction we have in our region and sits behind the stopbanks in the Ormond township.
Despite the imposing structure being 8m high and made of 400 cubic metres of concrete and 100 tonnes of steel, you can only just see the tip of it as you drive through Ormond.
During heavy rain events the three huge floodgates close to stop Waipaoa River floodwaters flowing up the Mahunga Stream.
Huge milestone this Christmas
In all, 64 km of stopbanks and other pipes and infrastructure will protect our region during future flooding events.
A huge milestone is planned to be reached by Christmas 2023 with the completion of all the eastern side stopbank upgrades and earthworks from the ocean to Kaitaratahi Hill in Ormond.
This means the whole eastern city side of the Waipaoa Stopbank, which will mean the city and a large proportion of the Poverty Bay Flats, has extra security.
Western side – what’s coming up
The Waipaoa stopbanks near the Manutuke township on the Western side of our district have had around 6km of upgrades completed since October last year.
Over the next four years, work will move up the western side until this major project is completed.
The stopbanks new wide crests on top are also multi-purpose.
Trust Tairāwhiti has provided the money to create bike tracks on top of the stopbanks so you can bike from the Matawhero Bridge to the ocean on the Eastern side.
Joss says it creates a nice synergy between tourism, health and well-being and active recreation in our region.
There are suggestions about continuing this bike track on the Western side as well between Matawhero Bridge and Manutuke.
“It allows people to interact and see the different parts of our rivers and ocean as well as connecting our small townships and gets people off the State Highways.
“It’s moving the district forward.”
Joss says Council is full of smart engineering people who are reviewing design plans and ensuring that what gets built is robust, reliable and fit for purpose.
How stopbanks are built
The process to build a stopbank involves lots of people and some very big machines.
Joss says it’s been a long journey from the initial resource consent application to construction starting at the delivery phase, “which is where we are at the moment”.
The project is expected to be fully completed by 2029, possibly earlier.
“It’s huge in scale, varies in location and there’s some big technical components to it but in other ways, it’s quite straightforward when it comes to the compaction of dirt.”
Contracts were given to local companies, with Earthwork Solutions able to employ a whole team for this job. Currie Construction is also on board for the Mahunga floodgates.
This level of technical work upskills the capability of local contractors and the development of their staff.
First, the soil is tested and culverts are installed as the drainage component is crucial.
Then soil is removed from “borrow pits” beside the Waipaoa River, taken to the stopbanks and then densely compacted. The compaction process is key.
Work will get ripped up if compaction tests aren’t passed at various stages of the build and the next stage can’t be started until the right compaction levels are met.
These stopbanks need to be sturdy enough to contain a swollen river during a peak scenario. If there is one weak part – the whole thing fails.
Then there are the huge structural components with concrete and steel.
Council’s 4 Waters Construction Engineer Janine du Plessis is studying towards her civil engineering degree.
Being able to work on a project like this at the same time has been invaluable, she says.
“It’s taught me about construction. and when we get a good patch of weather we do so much in a week.”
Janine says the project was “pumping” before Christmas.
“We were getting so much achieved.
“The contractors are very efficient at what they do and the landowners have been great.
“Joss is a great boss and it all just works.”
Joss is a ‘Jack of all trades’. He’s been at Council for 17 years in four different roles. There were nine years managing stormwater for the city and rural townships.
Since the end of 2017, he’s been the senior project engineer for the Waipaoa upgrade.
Joss enjoys this work.
“It’s pretty fun, there’s a lot of responsibility because of the massive benefit it provides to the people, property and businesses.
“Stopbanks really are the unsung heroes protecting Tairawhiti.”
Janine agrees.
“It’ll be a nice feeling when it’s all done to know everyone is protected.”
Timeline
From September 2023 to June 2024, the sections completed include:
From October 2024 onwards
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Funding
In 2020, $7.5 million in funding came from Kanoa – a Government organisation that was formerly the Provincial Growth Fund.
This massively accelerated the delivery of this project and reduced the financial impact on ratepayers, says Joss.
