The Rangitāiki Floodway is a multi-stage project designed to take pressure off the Rangitāiki River in a flood event, by diverting some of its flow, via a Spillway, into near-by farmland between stopbanks (known as the Floodway) and out the Rangitāiki River mouth at Thornton.

The Bay of Plenty’s most frequent natural hazard is flooding. As we have seen throughout history, the results of a significant flood event can be catastrophic to the lives and livelihoods of those in flood-affected areas.

The Rangitāiki River has a long history of flooding. Between the 1960s and 1980s, the Rangitāiki Floodway was created by the Bay of Plenty Catchments Commission to provide flood protection to the community in and around Edgecumbe.

Over time, the level of flood protection that the Floodway offers has decreased, for reasons such as ground settlement. As technology has advanced, we can also better predict what future flood events may look like and how our flood defences need to be constructed.

In 2009, Bay of Plenty Regional Council was granted resource consent to increase the amount of water that could be diverted into the Floodway (190 cubic metres per second) and upgrade the existing Spillway to better control how the water gets into the Floodway. Upgrades to the Floodway have been ongoing since then.

By diverting the consented amount of water during a flood event, in a controlled manner, through the Floodway, we can reduce the flood levels in the Rangitāiki River upstream of Edgecumbe, reducing pressure on the river near populated areas before it can cause disruption.

stage 6b and 6c
Construction to raise the bank heights (March 2022).

Construction to upgrade the Floodway began in 2011 and will be complete in 2023. To date, there have been seven stages of the project, each stage with its own engineering considerations.

Upgrades that have been undertaken on the Floodway include:

  • Sections of the existing Floodway channel have been widened.
  • Stopbanks have been reconstructed to raise the bank heights.
  • Culverts have been upgraded to support the new stopbank design.
  • Greater seepage control beneath the ground has been installed.
  • A new bifurcation cut was made at Thornton Hall Road. This allows water from the Floodway to exit into the Rangitāiki River mouth at two places, instead of one.
  • A road bridge was created over the new Floodway exit and a wetland was established between the two exits as an ideal spot for inanga spawning.

The swing gates at McCracken and McLeans Road are the final defences to be constructed. In a flood event, the swing gates act as a barrier to close the roads and maintain the same stopbank height of the Floodway, to convey the water out to sea.

The Floodway (and Spillway) will form part of a network of protection along the Rangitāiki River. This includes the Rangitāiki Floodwalls and future work along the lower catchment. In a flood event, these defences will work together to help protect communities along the awa, by managing the increased water levels and reducing pressure on other flood defences.

Crown Infrastructure Funding

Bay of Plenty Regional Council received funding for Stage 6 of the Floodway and the Spillway from Central Government’s Crown Infrastructure Funding for this project as part of the Climate Resilience Programme ($10.275M). This funding was granted as part of the Covid-19 Response and Recovery Fund, and was one of six projects Bay of Plenty Regional Council received funding for

The purpose of the Spillway is to alleviate pressure on the Rangitāiki River during large flood events by diverting floodwater away from the main river upstream of the Edgecumbe township and into the Floodway.

When the river reaches a certain level, the Spillway allows water to pass over a section of lowered stopbank (fixed crest weir) and into an area of paddock near Hydro Road. This water is then channelled into the Floodway and out to the Rangitāiki River mouth.

The Spillway is designed based on what the predicted river level could be at the Spillway during operation and the level determines how much flow will go over the Spillway. The Rangitāiki Spillway is designed with contingency gates, which provides ‘back up’ if required flows are not met, giving reassurance that pressure can be taken off the Rangitāiki River and the flood defences down stream of Edgecumbe.

diagram

In October 2022, we publicly notified the variation to the resource consent application, for the construction and operation of the Spillway (located at 266 Hydro Road, Edgecumbe).

While consent was first granted in 2009, we reapplied for consent as the design and operation of the Spillway had changed in 2020, to have greater certainty of its operation.

The 2009 design utilised a reinforced earth stopbank (fixed crest weir) and an inflatable rubber dam (a rubber, cylinder-shaped balloon that can be inflated and deflated to control the water flow into the Floodway).

Since obtaining the 2009 consent, we determined that the consented Spillway design would not be the most suitable or reliable option (more on this below).

We went back to the community with an updated design (lower fixed crest weir with contingency gates) in 2020 and 2023, and through this process it was confirmed that this design was the preferred approach. As a result, changes to the resource consent were made to reflect the updated design.

After community consultation in 2020, a detailed design phase began.

During this phase, river modelling and ground investigations identified key risks that needed to be addressed. These risks were seepage and erodibility (sour) of these structures when the Spillway is in operation, as well as creating certainty that the Spillway achieves required flows.

Based on this, a detailed design was developed to address the above issues.

Because of these design changes (and a few other factors), the estimated cost to upgrade the Rangitāiki Spillway increased to $7.8M since consulting with the community in 2020 (the initial estimate was $2.8M).

Why has the cost increased?

  • The design option that was presented in 2020 proposed that the fixed crest weir would be finished in reinforced grass. This is now a 114m concrete capped section, with erosion protection (such as riprap) up and down stream of the weir. The concrete cap ensures the weir can handle river flows during operation and maintains its dimensions. It also needs less maintenance than reinforced grass.
  • Other design requirements, such as the need for installing sheet piles around the structures, sub-structure drainage and additional paddock contouring, are all required to manage risk during operation.
  • Since the 2020 estimate, high inflation, rising interest rates, Covid-19 and high labour costs have led to price hikes across all sectors (including construction).

The cost increase will be passed on to Rangitāiki-Tarawera ratepayers via targeted ratepayers over the next 20 years. There will also be a small increase in general rates.

Consultation was held with the community in April 2023 about the cost increase. We presented two options for feedback: Construct the Spillway design as planned, or only construct the fixed crest weir.

While the latter was a cheaper option ($3.8M), there would be no contingency ‘back up’ and the community would be without reassurance of its operation.

The majority of community consulted supported the full design option, and this was approved at Council in May 2023.

Frequently asked questions

The new, proposed Spillway design will ‘activate’ at a lower river level (a more frequent flood event).

However, the volume of water sitting in the Floodway during a smaller event will be less – for example, there may be localised ponding or increased water levels in Reid Central Canal only (amount of water subject to size of flood event).

Through the detail design process, a lot of effort has gone into setting the fixed crest weir at an optimal level, based on predicted river levels, to ensure the Spillway’s operation during a flood event.

Unfortunately, there will always be some uncertainties which cannot be eliminated, i.e. there will always be an element of uncertainty as to how the Rangitāiki River will ‘behave’ during a flood event.

As an example, if the river level was 100mm lower than predicted, this could account for an approximate 9% flow reduction. While this may not seem like much, it would be a significant in a flood event and highlights the importance of having contingency ‘back up’.

This is why having the contingency gates provides ‘back up’, by allowing controlled flow into the Floodway. 

Prior to reaching Te Teko, the Rangitāiki River passes through Lake Aniwaniwa, then into Matahina Dam. Both used for hydroelectric power generation.

For Matahina Dam, the role of dam management is to lower the lake level before a flood peak so that, at peak flows, the outflow from the dam can be kept significantly lower than the inflow for as long as possible that is consistent with the safety of the dam.

stage 6
Stage 6b and 6c.

Project updates

5 months ago

Leaning on local labour for flood protection builds in the Bay

When taking on a project, Managing Director of Romanes Construction, Paul Romanes, always looks to employ locals to be part of his crew.

2023-07-18 - Leaning on local labour for flood protection builds in the Bay

When taking on a project, Managing Director of Romanes Construction, Paul Romanes, always looks to employ locals to be part of his crew.

“It’s an important part of our business model. It always has a positive flow-on effect – from the large crew we hire, there are stand-outs, and those people tend to become part of our regular crew for project after project. They’re also more likely to hire other locals for their own projects.”

When it comes to the benefits of a local team, Paul says there are many: “Local employees know the area, they know the people and know good suppliers. They also have a real pride in their place; we’ll often hear of them popping down the road to the work site, making sure it is tidy and that the equipment isn’t getting destroyed in the elements.”

The construction company has partnered with Bay of Plenty Regional Council on both the construction of the Kaituna Mole and the final stage of the Rangitāiki Floodway – two jobs which aligned well to Paul’s company ethos.

Both projects are part of the Climate Resilience Programme, a joint initiative between Kānoa (the Regional Economic Development and Investment Unit), regional councils and the community focused on developing and upgrading vital river management and flood protection schemes in Aotearoa.

These two projects attracted Kānoa funding for their ability to support new and existing local employment opportunities, and help grow local sectors impacted by Covid-19, for a more productive, sustainable, resilient regional economy.  

The final stage of the Floodway is the installation of two sets of swing gates across two roads (McCracken and McLean) near Edgecumbe. To construct the gates, it involves cutting into the road to create a new concrete pad. They then set up two concrete walls at each site for the gates to attach to (the steel gates were made off-site by Page Macrae and were brought in when the concrete work was done).

The design of this swing gate system is unique to New Zealand – while stoplogs and sliding gates are commonplace, hinged gates across a road are the first of their kind.

In a flood event, these swing gates will act as a barrier on the road, keeping cars from entering a flood zone, and maintain the stopbank height of the Floodway, creating a channel that will help send water out to the Rangitāiki River mouth.

Sub-contractor Tim Walters (Te Arawa) has worked with Paul on both Kaituna and Rangitāiki River projects, along with his brothers, Justin and Tom, cousin Kaia and neighbour TK. The Maketū local had been working in Australia on form work construction and returned home to New Zealand in 2018. He met Paul when he was recruiting local iwi to be involved in the Kaituna Mole construction.

“We had about six of us from Maketū get involved, all with different levels of experience, which was good as we could help build up the younger fellas.

“Being from Maketū it was a project I wanted to be part of, so I could go down there with my son and tell him, ‘Yeah, I built this’.”

When Paul secured the contract for the Rangitāiki job, he gave Tim a call to come and carry on working together. While it’s 40 minutes away from Tim’s home, it’s like another home to him, as his partner and her whānau have strong connections to the area.

“Her grandfather was Bill Kerrison, the ‘kaitiaki of tuna’ in the East, so although this is a different site, the Bay of Plenty is a small community where everyone knows everyone.

“For me and the other guys working on the site, it feels special to be part of these kinds of projects when you know what the purpose of it is – to help protect the people. We really enjoy it.”

Tim says there are plenty of advantages when it comes to locals working on local projects, particularly the pride that is put into them.

“Bringing in people who know the area, who know the people, is important. It gives the community peace of mind about who is working in their backyard as they know they will respect the place that they are working in.

“It’s also a great way to get the word out what’s happening, and encourage other locals to get involved and employed on these jobs.”

Paul says he is really enjoying the Rangitāiki project and he’s got a great team around him.

“Our crew have gelled together really well and we really enjoy working with Regional Council. The boys (Jordan and Peter) are straight-up when it comes to supporting local business and we’ve built a really good relationship.”

Bay of Plenty Regional Council received $10.28M for the Rangitāiki Floodway and Spillway, and $1.63M for the Kaituna Mole from Kānoa.


Tim Walters and Harry Thomson from Romanes Construction at the McCracken Road swing gate site. 

swing gate
7 months ago

Council approves construction of proposed Rangitāiki Spillway design

Bay of Plenty Regional Council Councillors have approved increase in budget for the construction of the Rangitāiki Spillway, following overwhelming support from the community.

In an event, the Spillway enables water from the Rangitāiki River to pass over a fixed crest weir (lowered, concrete-covered stopbank) and into the Floodway. This will help divert water away from the Rangitāiki River and reduce the risk of significant flood damage to both rural and urban areas.

Read more.

9 months ago

Community session to be held in Edgecumbe to discuss the Rangitāiki Spillway

Bay of Plenty Regional Council is holding a community session in Edgecumbe to discuss the Rangitāiki Spillway project.

2023-03-31 - Community session to be held in Edgecumbe to discuss the Rangitāiki Spillway

Bay of Plenty Regional Council is holding a community session in Edgecumbe to discuss the Rangitāiki Spillway project.

The Spillway needs to be upgraded as it is part of the Rangitāiki Floodway, a key piece of flood defence infrastructure to help protect the community in a flood event.

In an event, the Floodway and Spillway upgrades will help divert water away from the Rangitāiki River. This helps reduce the risk of significant flood damage to both rural and urban areas (for example, the economic damage of the 2017 event was estimated to be $95M).

Engineering Manager Mark Townsend says since Regional Council last consulted with the community on the project in 2020, the estimated cost to upgrade the Spillway has increased.

The purpose of the community session is to have a conversation about why that is, how it will affect ratepayers and what the options are in a challenging economic climate.

“High inflation, rising interest rates, Covid-19 and high labour costs have led to price hikes across all sector, including construction.”

He adds that during the detail design phase of the project, river modelling and ground investigations identified key risks that needed to be addressed.

“These risks were seepage and erodibility (scour) of the structures when the Spillway is in operation, as well as a need to create certainty that the Spillway would achieve the required flows into the Floodway.

“Since meeting with the community in 2020, the Spillway has been designed to address these issues, better manage water flows over the Spillway and give the community reassurance that it will perform as required. These design changes include additional concrete work, sheet piling around the structure for seepage control, drainage and paddock contouring.”

The current estimate to construct the revised design in its entirety is $7.8M (less $2.1M of central government funding), a $5M increase from the original estimate ($2.8M). The increased costs will be passed on to ratepayers via targeted rates.

The community session is being held on Saturday 15 April from 10.30am to 12.30pm at the Edgecumbe War Memorial Hall (corner of Kauri Street and Main Street), Edgecumbe.

If you wish to attend, please RSVP (for catering purposes) to engineering@boprc.govt.nz

spillway diagram
12 months ago

Construction update: Disruption on McCracken and McLean Roads

Bay of Plenty Regional Council will begin construction for the final stage of the Rangitāiki Floodway from Monday 1 May 2023.

2022-12-15 - Construction update: Disruption on McCracken and McLean Roads

Bay of Plenty Regional Council will begin construction for the final stage of the Rangitāiki Floodway from Monday 1 May 2023.

The Rangitāiki Floodway is a key piece of flood defence infrastructure to help protect the lives and livelihoods of the community.

In a flood event, the Rangitāiki Floodway is designed to take pressure off the Rangitāiki River by diverting some of its flow (via a Spillway) into near-by farmland between stopbanks and out the Rangitāiki River mouth at Thornton.

diagram of swingate

What’s happening?

The construction process involves installing swing gates (heavy duty steel flood barriers) at two sites along the Rangitāiki Floodway:

  • Site one: Two sets on McCracken Road (located between Hydro Road and Western Drain Road, Edgecumbe)
    map

  • Site two: Two sets on McLean Road (located between East Bank Road and Western Drain Road, Edgecumbe).
    map

When the Floodway is activated, these swing gates will have two functions: They will act as a barrier on the road, keeping the community from entering a flood zone, and maintain the stopbank height of the Floodway, creating a channel that helps send water out to the Rangitāiki River mouth.

When not in use, the gates are locked open, allowing uninterrupted traffic flow.

How might this impact you?

Construction is due to begin from Monday 1 May 2023 and each site is expected to take approximately seven weeks.

During construction, road closures will be in place around the swing gate site and there will be no through traffic. Residents will be able to access their homes, however detours will be in place to travel to and from McLean and McCracken Roads.

We will keep you updated on construction and road closures via this project page.

If you have any questions or concerns, please contact Project Lead Niroy Sumeran on engineering@boprc.govt.nz or 0800 884 880.

Thank you for your patience during this time.

swing gate diagram
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