FAQ
Find information based on frequently asked questions and answers.
Floods and cyclone Gabrielle
What is a 1 in 100-year flood?
A 1 in 100-year flood event is sometimes referred to as an event with a 1% Annual Exceedance Probability (AEP). This means that a flood of this magnitude will statistically occur once every 100 years, or that there is a 1% chance of an event of this magnitude occurring in any one year.
what size was cyclone gabrielle?
Water scientists estimate that during Cyclone Gabrielle, the Wairoa River flows were slightly less than that predicted for a 1 in 100-year flood event for the Wairoa River.
What caused the flooding in North Clyde during Cyclone Gabrielle?
The Wairoa River catchment (the area of land that flows to the river) is large.
Engineers and scientists believe that the flooding was primarily caused by the significant rainfall that fell across the catchment combined with the wet weather that occurred during the 2022- 2023 period.
The sudden onset of the flooding through North Clyde was due to the area acting as a secondary flow path of the river. With or without woody debris, North Clyde would still have flooded.
Engineers and scientists believe that the flooding was primarily caused by the significant rainfall that fell across the catchment combined with the wet weather that occurred during the 2022- 2023 period.
The sudden onset of the flooding through North Clyde was due to the area acting as a secondary flow path of the river. With or without woody debris, North Clyde would still have flooded.
When a flood mitigation solution is chosen, will it protect Wairoa from a Cyclone Gabrielle-level event?
The preferred flood mitigation solution will be designed to help protect Wairoa from a 1-in- 100-year flooding event. For Wairoa, Cyclone Gabrielle did not reach this level of flooding. It should be noted that with any flood scheme there is always a risk of a large event exceeding the level of mitigation, and no solution will provide absolute, foolproof flood protection.
floodways, spillways and stopbanks
What is a floodway?
A floodway, also called a spillway, is a channel constructed to take a portion of the river flow off the river to take pressure off the main river channel. The floodway then links back up with the river, which then takes the water out to sea.
Floodways are typically dry and are commonly used for grazing during normal river flow conditions, and only operate during flood events when the river is high enough to flow into them. Floodways also typically have stopbanks on one or both sides and sometimes include manually controlled flood gates and/or weir walls (spillways) to let the water enter into the floodway.
Floodways need to have roads crossing them, similar to a ford in a river.
Floodways are typically dry and are commonly used for grazing during normal river flow conditions, and only operate during flood events when the river is high enough to flow into them. Floodways also typically have stopbanks on one or both sides and sometimes include manually controlled flood gates and/or weir walls (spillways) to let the water enter into the floodway.
Floodways need to have roads crossing them, similar to a ford in a river.
What is a stopbank?
A stopbank is a specially designed and maintained mound of earth that helps to limit or prevent the spread of floodwater onto surrounding land. Also known as a levee, dyke, or flood bank, a stopbank is a constructed earthen barrier that runs parallel to a river or floodway to confine flows within the channel. Stopbanks typically need to be designed by specialist engineers and are constructed with appropriate soil.
What can be done with the land in a floodway?
The land in the floodway can still be grazed if adaptive stock fencing or cattle stops are used along the roads. Alternatively, the grass could be harvested and bailed. The floodways could potentially be used for community recreation or ecological habitat purposes. Buildings, structures, and large trees can’t be in a floodway.
How often will the floodway have water in it?
A floodway will be designed to only have water in it for large flood events, which will be very infrequent. With the floodway sill heights in the most technically preferred options of 1C and 1D, the floodway is predicted to have water in it statistically once every 10 to 15 years.
How will people cross the floodway in a flood?
It is envisaged that an early warning system will be in place and barrier arms will lower along the roads before the floodway entrance. Flashing lights would likely be installed along the sides of the floodway.
People will not be able to cross the floodway once the barrier arms are down, and lights are flashing. It it expected that the maximum duration the floodway would be unsafe to cross would be less than 24 - 28 hours.
People will not be able to cross the floodway once the barrier arms are down, and lights are flashing. It it expected that the maximum duration the floodway would be unsafe to cross would be less than 24 - 28 hours.
How will people evacuate if the floodway has water in it?
People will not be able to cross a floodway when it has water in it, or when the barrier arms are down, and lights are flashing. It is envisaged that an emergency management plan would be developed for the community with measures put in place to ensure people have access to safe shelter and supplies until the flood waters reside. This could include the use of community resilience hubs or emergency and resilience pods, like EPODs.
How will I access the western end of Ruataniwha Road and Waihirere Road if there is a floodway?
As mentioned, people will not be able to cross a floodway when it has water in it. When there is no water, people will be able to use the road to cross the floodway similar to a ford in a river.
How can we ensure the integrity of the spillway?
Any flood mitigation solution, including a spillway, will be modelled extensively and designed to help protect Wairoa from a 1-in-100-year flooding event (noting that in Wairoa, Cyclone Gabrielle did not reach this level of flooding).
It should be noted that with any flood scheme there is always a risk of a large event exceeding the level of mitigation, and no solution will provide absolute, foolproof flood protection.
It should be noted that with any flood scheme there is always a risk of a large event exceeding the level of mitigation, and no solution will provide absolute, foolproof flood protection.
How will the spillway be managed?
Once constructed, the operational and asset management of any flood mitigation solution in Wairoa, including a spillway, will be the responsibility of the Hawke’s Bay Regional Council.
What will the regular maintenance be and who will do this?
Like all flood mitigation assets, annual maintenance will be required on an ongoing basis and could include site monitoring and maintenance such as fencing, weed control, mowing and possibly grass harvesting. As mentioned, this regular maintenance and ongoing management will be the responsibility of the Hawke’s Bay Regional Council.
A plan will also be developed for the operational phase of the spillway, in times that it will operate. This will include triggers for closing the roads that cross it and the clearing of debris and repairs after it has operated. This plan will be developed in conjunction with Wairoa District Council and the local community.
A plan will also be developed for the operational phase of the spillway, in times that it will operate. This will include triggers for closing the roads that cross it and the clearing of debris and repairs after it has operated. This plan will be developed in conjunction with Wairoa District Council and the local community.
What safety measures / risk management plan will be in place to mitigate these if not properly managed or if conditions become extreme?
The operational plan to be developed will contain a high health and safety component. As mentioned, this plan will be developed in conjunction with Wairoa District Council and the local community.
Can we also see a plan and picture of what the spillway will look like?
The is a ‘flyover’ animation (video) available on the Resources page of the Wairoa Flood Mitigation project here: wairoafloodproject.co.nz/resources. Please note, these animations are indicative only, noting that some refinements to both Options 1C and 1D have occurred since the animations were first developed.
Flood Mitigation Options
What other flood mitigation options have been considered?
As many as 18 flood mitigation options have been considered, some with further variations. These include stopbanks, floodways, dredging, bar structures and management, drain clearing, dams, reforestation, temporary flood barriers and house raising.
Why is dredging not being considered?
Dredging was previously considered as an option but has some significant limitations and is therefore no longer considered to be an option for reducing North Clyde flooding. The main limitations associated with dredging include the high likelihood that sediment would redeposit in the river after dredging has occurred therefore requiring ongoing dredging, the negative effects associated with disturbance of the river bed, including ecological impacts, and the extremely expensive costs associated with dredging, estimated to be $990 million in the immediate term, with a further $130 million per year in maintenance.
Why is house raising not being considered?
House raising was previously considered as an option too, but also has some significant limitations including the fact that not all properties can be raised, and there would still be damage to ground level assets and belongings, there would be no flood protection for marae, urupā, and local businesses, and there are very high costs associated with raising all of the affected buildings that can be raised. Additionally, the Government’s $70 million has been ring- fenced specifically for community scale flood mitigation and cannot be used to cover the costs of raising individual properties.
Why isn’t Wairoa River Bar management being considered?
The flood modelling indicates that the Bar does not influence flooding levels upstream of the State Highway 2 (SH2) bridge. This is because the river upstream of the bridge is is slightly higher than the sea and Bar levels. The Bar does, however, influence flood levels of the Wairoa township downstream of the SH2 bridge. It is worth noting that the Hawke’s Bay Regional Council is also expecting to have a new operational management plan for the Wairoa River Bar in place by November 2024.
Why is Kopu Road not being protected?
Following the June 2024 flooding event and Lawrence Yule’s appointment as Crown Manager in August, the scope of the Project has broadened to include potential flood mitigation options for Kopu Road.
Further work to determine the most technically viable solutions for Kopu Road is ongoing.
There is also an expert caucusing meeting involving technical experts, those with local lived experience and those with a cultural and/or historical perspective scheduled for early November, which will be looking at options to enhance the performance of the Wairoa Bar to minimise future risk of flooding to properties on the lower reaches of the Wairoa River.
Further work to determine the most technically viable solutions for Kopu Road is ongoing.
There is also an expert caucusing meeting involving technical experts, those with local lived experience and those with a cultural and/or historical perspective scheduled for early November, which will be looking at options to enhance the performance of the Wairoa Bar to minimise future risk of flooding to properties on the lower reaches of the Wairoa River.
Has a Wairoa River survey been done?
Hawke’s Bay Regional Council completed a river survey of the lower end of the Wairoa River after Cyclone Gabrielle in 2023, and a survey of the river up to Frasertown in August 2024.
Will there be another review of the two most technically viable flood mitigation solutions, or is there room to adjust the options based on feedback from affected residents?
Yes, there is room to adjust these options based on feedback – this is the reason we are engaging with both potentially impacted whānau, land and property owners and the wider community.
How do these proposed options integrate with other environmental or infrastructure improvements to minimise flooding risk?
While both Options 1C and 1D focus on providing more immediate flood mitigation solutions for Wairoa (once constructed), these options are only one part of a more holistic approach to overall flood plain management and would likely sit alongside other initiatives including the ongoing management of the Wairoa River Bar and the maintenance of existing water infrastructure across Wairoa.
Other environmental or infrastructure improvements may also be considered to assist with reducing the risk to flooding, however some of these may be longer-term solutions and may take some time before benefits are seen.
Other environmental or infrastructure improvements may also be considered to assist with reducing the risk to flooding, however some of these may be longer-term solutions and may take some time before benefits are seen.
How was community input considered in developing these options? Will there be additional consultations before the deadline?
Recognising that the people of Wairoa know the whenua (land) and awa (river) best, back in June 2023, a series of hui were held asking local people what they knew of the river and its patterns, what they saw and experienced during Cyclone Gabrielle, and what they thought might work best for the future.
From these kōrero, a long list of potential flood mitigation options was developed and further considered from an engineering perspective.
In October 2023, a Wairoa Flood Mitigations Scheme Stakeholder Group was established by the Tripartite partners, and included mana whenua and marae representatives, farmers, local businesses, and people whose homes and properties were impacted by Cyclone Gabrielle. You can find the Terms of Reference for this Stakeholder Group on the Wairoa Flood Project website.
Together, this Stakeholder Group worked with river engineers, other technical experts and mana whenua over an eight-month period to consider each potential option in more detail. The minutes of each of these Stakeholder Group meetings, as well as the various technical and engineering reports provided to the Group, can also be found on the Resources page of the Wairoa Flood Project website.
Some of the questions asked during this process included:
In October 2024, the Tripartite partners agreed to support the commencement of early engagement with mana whenua, including potentially impacted whānau and property owners, with this engagement covering both Options 1C and 1D and all other options that were previously considered.
From these kōrero, a long list of potential flood mitigation options was developed and further considered from an engineering perspective.
In October 2023, a Wairoa Flood Mitigations Scheme Stakeholder Group was established by the Tripartite partners, and included mana whenua and marae representatives, farmers, local businesses, and people whose homes and properties were impacted by Cyclone Gabrielle. You can find the Terms of Reference for this Stakeholder Group on the Wairoa Flood Project website.
Together, this Stakeholder Group worked with river engineers, other technical experts and mana whenua over an eight-month period to consider each potential option in more detail. The minutes of each of these Stakeholder Group meetings, as well as the various technical and engineering reports provided to the Group, can also be found on the Resources page of the Wairoa Flood Project website.
Some of the questions asked during this process included:
- What option/s will offer the community of Wairoa the best flood mitigation?
- What impacts will each option have – on people and their homes, land, businesses and livelihoods, as well as things like marae, urupā and cultural taonga?
- How much will each option cost?
- What matters most to our community?
In October 2024, the Tripartite partners agreed to support the commencement of early engagement with mana whenua, including potentially impacted whānau and property owners, with this engagement covering both Options 1C and 1D and all other options that were previously considered.
decision making and timelines
Is there a set date for when the flood mitigation option will be chosen?
There is a meeting on Wednesday, 5 February 2025 where the Tripartite partners – WDC, HBRC and Tātau Tātau o te Wairoa Trust – are expected to make a recommendation on their preferred flood mitigation option.
This recommendation will then be considered by HBRC at a formal decision-making meeting on Thursday, 13 February 2025. It is at this point that we expect to be able to notify home and landowners and the people of Wairoa of the confirmed preferred flood mitigation option.
These dates are important for ensuring we can meet the Government’s mid-March 2025 deadline for a preferred flood mitigation solution, and a business case based on that preferred solution.
This recommendation will then be considered by HBRC at a formal decision-making meeting on Thursday, 13 February 2025. It is at this point that we expect to be able to notify home and landowners and the people of Wairoa of the confirmed preferred flood mitigation option.
These dates are important for ensuring we can meet the Government’s mid-March 2025 deadline for a preferred flood mitigation solution, and a business case based on that preferred solution.
Who is paying for the flood protection?
Central Government has committed to providing $70 million of funding which has already been ring-fenced for community scale flood protection for Wairoa.
It is important to note that the Government requires a confirmed preferred flood mitigation option, and a business case based on that preferred option, by 31 March 2025. If this deadline is not met, the $70 million of Government funding could be withdrawn and there will be no flood mitigation for Wairoa.
It is important to note that the Government requires a confirmed preferred flood mitigation option, and a business case based on that preferred option, by 31 March 2025. If this deadline is not met, the $70 million of Government funding could be withdrawn and there will be no flood mitigation for Wairoa.
How will people who are confirmed as being impacted, be compensated?
There will be compensation entitlements for properties that are confirmed as being impacted by any final flood mitigation solution. These entitlements may vary depending on the actual impacts to each property and the levels of land access required and are being discussed with whānau and property owners in more detail now that the land access and compensation framework has been finalised and agreed.
Can I still own my land, even if it’s part of a floodway?
Where land access is required for a preferred flood mitigation solution, whānau will be able to retain ownership of their land if this is their preference.
What levels of compensation can confirmed impacted property owners expect to receive?
If HBRC required full access to a one-hectare property without a house, the indicative levels of compensation for that bare land would be around $75,000 to $100,000. Under the Public Works Act, there are additional entitlements that HBRC would be required to pay on top of this amount, and the owners’ fair and reasonable valuation and legal costs would also be reimbursed.
Further to this, if there is only partial access required and HBRC damages the part of a property that its owners are keeping, HBRC will also pay to remediate any damage caused – this can include things like reinstating fencing or repairing a driveway. Remediation is determined on a property-by-property basis.
The project has made it clear that it will be seeking easements or leases to secure access to land. There is no intention to acquire ownership of land unless this is the owner’s preference. Additionally, the project has made it clear that it will not be alienating Māori from their whenua. The Māori Land Court and Te Tumu Paeroa Māori Trustee continue to work closely with the project team to support whenua Māori owners through this process.
Further to this, if there is only partial access required and HBRC damages the part of a property that its owners are keeping, HBRC will also pay to remediate any damage caused – this can include things like reinstating fencing or repairing a driveway. Remediation is determined on a property-by-property basis.
The project has made it clear that it will be seeking easements or leases to secure access to land. There is no intention to acquire ownership of land unless this is the owner’s preference. Additionally, the project has made it clear that it will not be alienating Māori from their whenua. The Māori Land Court and Te Tumu Paeroa Māori Trustee continue to work closely with the project team to support whenua Māori owners through this process.
I’VE GOT SOME MORE QUESTIONS – HOW DO I ASK THEM?
Construction
How will people get access to their homes and land during construction?
If a floodway like option 1C or 1D is confirmed as the preferred option, access to peoples’ houses and land on the other side of a floodway will be maintained throughout the construction of that option.
If a floodway is excavated, how will groundwater be managed?
An excavated floodway will have drains in it to lower the ground water and direct this ground water to the river. These drains would be similar to the drains currently in the North Clyde paddocks.
When is construction expected to start?
Provided the above deadlines can be met, Government funding is confirmed, and consents and land access are secured, flood mitigation construction works are expected to commence in the summer 2025-2026 construction period.
When is construction expected to be completed?
Works are expected to take two summer construction seasons to be completed. Provided construction commences as expected in the summer 2025-2026 construction period, this would mean works are expected to be completed by the end of the 2026-2027 construction season.
