Project Future Proof

The first part of Project Future Proof is to upgrade stopbanks and floodwalls along the awa that have seepage issues.

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 seepage can lead to stopbanks collapsing, putting people, property and livelihoods at risk.

In conjunction with this seepage control work raising of the floodwall height will be necessary. This is based on increased flows in the awa due to climate change and predictions for sea level rise.

The second part of the project will be to raise the flood defences in the areas that do not have seepage issues.

Our team are also working with community groups and organisations to look at future flood protection options along the river to ensure it is suitable now and into the future.

This project supports the resilience of our river communities, by working to reduce the impacts of storm surges and heavy rainfall events that are endangering New Zealand communities, infrastructure and agricultural/horticultural economies as a result of climate change.
If protection measures are not replaced to withstand more frequent and potentially more intense weather events in the future, the impact on lives and livelihoods is likely to be significant.

Project Future Proof is budgeted for $11.2M across the next two years. To date we have been allocated $3M from the New Zealand Government’s Kānoa – Regional Economic Development & Investment Unit Fund to help fund projects that would support New Zealand’s economy after the Covid-19 pandemic.

As of mid-2023, we have completed an initial phase of surveying and testing the stopbanks and floodwalls to determine what needs to be done.

These investigations have helped our engineers to better understand the ground conditions and what options are possible. The data will determine what upgrades are required below the ground and will inform the upgrades needed for the flood structures.

We are scheduled to begin construction on Stage One by the end of 2023. This will focus on improving the stopbanks and floodwalls from McAllister St Pump Station through to the iSite. We are currently working with our partners to finalise construction plans.

More information will be released in the coming months ahead of construction beginning.

We have been working closely with Whakatāne District Council and Te Rūnanga o Ngāti Awa, and we will be engaging with the community on the proposed above-ground design options.

This is an opportunity to ensure the flood defences are suitable, while ensuring they aren’t stopping people from enjoying the mauri of the awa. 

We will share more information and seek public feedback on the project once we have the proposed designs ready for consultation. 

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. 

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.