Project Future Proof

Started February 2024

Stage One will improve the flood defences from McAlister Street Pump Station to the Whakatāne iSite, and will be done in two parts to minimise disruption to the community. 

In areas where there are stopbanks (McAlister Street Pump Station to Yacht Club), we will be increasing the size (width and height) of the existing stopbank by filling it with more earth.

In areas where there are floodwalls (Yacht Club to iSite), we will be removing and replacing the existing floodwalls, and installing seepage control. This will involve driving large steel sheet piles into the ground to form a wall.

This wall will then be covered in pre-cast concrete panels, creating a floodwall that will range in height from 0.6m to a maximum height of 1.7m (this is for a 50m stretch next to the iSite).

A design and/or narrative will be etched into the concrete floodwall to enhance the look of the wall along the walkway. We are working alongside our partners to develop the design/narrative, and the final artwork is scheduled to be on the concrete panels by early 2025. 

Additional seepage control (including drains and pumps) will be installed. Any water that runs toward the roadside through the stopbank will be collected in the drains, then it will be pumped back into the river.

During the upgrade, we will improve pedestrian access onto the Warren Cole Walkway from the shopping area across the road and vehicle access into the Yacht Club car park. These changes are to make room for flood defence upgrades, while ensuring community continues to have access to the awa.

Scheduled to begin late 2024

Further stages are planned to upgrade flood defences along Quay Street through to the Muriwai Drive playground. In these areas, we know we need to improve seepage control and raise stopbanks, as part of our programme of work to address a changing climate.

We will share more information once the designs for these stages are ready.  

There are two main reasons:

The first is because we need to fix and improve areas where there is seepage. Seepage is when water passes through a stopbank when the river level is high. While controlled seepage is good for relieving pressure within the stopbanks, excessive, uncontrolled seepage can lead to stopbanks collapsing, putting people, property and livelihoods at risk.

The second reason is because these flood defences are not meeting their current level of service for a significant flood event. We have an agreed level of service with the community through our Long Term Plan, which means we have to provide flood protection that can withstand a flood event of a certain size and scale. In the case of Whakatāne CBD, the flood protection needs to be able to meet a 1% annual probability event through to 2040.

To achieve this level of service, the flood defences need to be upgraded to protect the town against the future impacts of a changing climate (such as increased rainfall and sea level rise).

We use several methods and data sources:

• Previous flood events, which we can use the learnings from to determine what might happen in the future.
• Modelling to predict what influence a changing climate might have, for example sea level rise and increased rainfall.

This is all analysed and recommendations are made. This is then peer reviewed before final heights are confirmed. This process is both common and best practice.

We then take this information and use a method called ‘back casting’, where we look as far as 100 years into the future and what flood protection might be required at that time, and then work backwards to make sure what we put in today fits in with that long term solution.

The modelling we have done at this point shows we don’t need to update the upstream stopbank sections this time as they are still meeting the level of service required.

To provide some context, the ‘spit fuse’ is a sand spit at the mouth of the Whakatāne River / Ōhinemataroa where it meets with the Piripai spit.

It is regularly lowered so that it can be better eroded by river flow, to provide an overflow path and increase the overall capacity at the river mouth. Regional Council’s Duty Flood Manager does monthly surveys and will report if it needs to be lowered, and Whakatāne District Council holds the resource consent to do this maintenance work on the spit.

In 2023, BOPRC and WDC jointly commissioned a review of 26 existing reports on the use of the spit fuse as a flood mitigation and response tool. The key findings from this report were that the effectiveness of the spit fuse decreases with increasing sea levels (due to climate change) and it will not provide the necessary flood protection in events where the sea conditions are extreme.

This means that while the spit fuse could be useful in small storm and flood events (where we don’t have high sea levels or storm surge), it does not provide effective flood protection in large scale events (which is what we are designing the flood protection in Whakatāne CBD to help withstand). 

The build-up of silt banks in the Whakatāne Harbour are mostly at a level below high tide level and all are below a level when storm surge occurs. This means that removal of the silt banks will just be replaced by water in the short term. This is what we call dead storage. Consequently, when we have a flood event that will extend through a high tide cycle, there is no advantage on whether there is a silt bank or water present.

In any case, during high river flows, the silt banks can be washed away. When there aren’t large flows, the silt builds back up, only to be washed away on the next cycle. This is why, when we look at our modelling (that considers the effects of floods over the years), the river profile hasn’t changed much since 1969.

No. Most of the flood defences we are upgrading will replace what is existing. Where we are creating new flood defences, we will be working closely with Whakatāne District Council and Te Runanga O Ngāti Awa to ensure the community can continue to have access.

We want to ensure that what we design not only functions well in the face of future floods, but is also a place that the community can continue to feel connected to the awa. 

During construction, the same level of flood protection will be maintained to what it is now. The contractor is only removing existing flood defences that can be reinstated quickly should a flood forecast predict high Whakatāne River levels.

However, it’s important to note that the CBD flood defences (stopbanks and floodwalls) do not currently meet the agreed level of service for flood protection. We have an agreed level of service with the community through our Long Term Plan, which means we must provide flood protection that can withstand a flood event of a certain size and scale. In the case of Whakatāne CBD, the flood protection needs to be able to meet a 1% Annual Exceedance Probability (AEP) event through to 2040.

The agreed level of service will not be achieved until all four stages of Project Future Proof have been completed.

As the climate changes, communities across New Zealand are adapting to meet the challenges of a rising sea level and more frequent, more significant rain events that may cause flooding.

One of the main issues facing communities around New Zealand is balancing the ability of ratepayers to pay for this work while keeping up with ongoing changes in our climate.

Over the coming years, there will be further conversations about how we manage this and at the heart of achieving this balance is regular community engagement, to look at different flood management options. Getting this right will help minimise and manage the risk to the community, their property and livelihoods.

The first two stages of Project Future Proof are budgeted at $11.2M across the next two financial years (1 July 2023 - 30 June 2024 and 1 July 2024 - 30 June 2025).

These costs will be covered predominately by targeted ratepayers in the Whakatāne-Tauranga Rivers Scheme (and a little bit by general rates as well). 

Costs associated with Stages Three and Four will be worked through with the community as part of a consultation process for the Long-Term Plan.

This project has attracted $3M from the New Zealand Government’s Kānoa – Regional Economic Development & Investment Unit Fund to help fund projects that support New Zealand’s economy after the Covid-19 pandemic.