Struggling stopbank rebuild set to start

An underestimation of historical damage on Wairau River stop banks, turning a repair into a complete rebuild of flood prevention infrastructure, is getting underway.

Groundwork on Marlborough’s “most important public river works in the past 30 years” after a presentation on October 1 to give Spring Creek locals up to date information on the ongoing efforts, and nationally provided funding getting ever closer.

The Lower Wairau Flood Capacity Upgrade Programme on the most at-risk stop banks along the Lower Wairau has been underway since 2021; with the Peninsula Road stop bank at Spring Creek reprioritised following the August 2022 flood.

Reconstruction and upgrade of this flood protection asset is now budgeted at $22.5m with significant contingency funding included given the project’s risk profile, but with Central Government partnering with Council due to the risk to State Highway 1 and rail lines.

MDC Rivers and Drainage Engineering Manager Andy White say concentrated efforts on the stop bank is a focus of life and death for many Marlburians.

“Once we started examining the repairs required, we quickly realised there are incredibly pressing issues, from the size of lateral spread cracks and cavities from the 2016 earthquake to the depth of the undercutting beneath sections of the stop bank.

“Initial measurements showed the riverbed to be scouring at the toe of the stop to a depth of 4.5m; after the June 2025 flood event it’s 7m. That extent and rate of undercutting, combined with future climate scenarios, and extensive lateral spread, completely changed our approach – we couldn’t just fill the gaps in, it’s not just a repair.”

While the stop banks require a complete structural overhaul, Andy says no time frame changes are needed.

“We remain committed with our co-investment partners at Central Government to delivering the project by the end of June 2027 as promised to the community”.

“People have been pissed off and understandably so, but the danger of a full failure is catastrophic which makes this so urgent - a stop bank failure at this location during a flood event like June 27, 2025, would send a two-metre wave of water and debris through the Eastern half of the township.

“Recent flood events have been closely examined by Council Rivers’ engineers to evaluate the stopbanks performance and ensure that the replacement stopbank is designed to be resilient in the face of climate change, accommodating significantly higher flows of the Wairau.”

The June event saw surface flooding at the rear of the Peninsula Road stopbank due to an extremely high groundwater table, and the backing up of water from White’s Drain which occurs when the Wairau is in full flood – so the rebuild incorporates upgraded culverts and pipework to accommodate a potential future pump station at Gouland Road, subject to future funding and Council approval.

As an interim measure, Council is currently purchasing a new mobile pump and an updated response plan of similar rain events that could affect Spring Creek.

This year’s construction work will be mostly done underwater depths of up to 8metres – “which makes any project even more complex”. By Autumn 2026 the riverbed will be stabilised preventing any further undermining of the existing stopbank.

“The programme is ambitious, but the project team is committed to achieving this key milestone by the end of April, providing the community with additional reassurance going into the winter.”

To achieve this, the team have already constructed a large staging area to receive rock and fill material from Council’s Pukaka Quarry – the quarry being a major development project in anticipation of major river works expected.

Construction of the haul road down to the waterline is programmed to commence in November, a key milestone that will carry the near 100,000 tonnes of rock and 160,000m3 of fill to the worksite over the next couple of years.

“To futureproof this stop bank for future climate scenarios we couldn’t simply raise it the required metre and a half, that height requires building out into the channel.
“But to alleviate the pressure on the stop bank itself from high velocity water continuing to scour material off that stop bank, we’re widening the river channel on the inside bank removing deposited material. We’ve been transparent with the community throughout the project, in that we couldn’t do this in a single season as locals want it done correctly, so we will go into next winter with a refined Emergency Management Plan especially for the region.

“November 2026 to April 2027 will see the stop bank fully reconstructed, and a series of untreated timber groynes and plantings to further protect the works, with June 2027 the target for completion”.

Andy says that conscious planning with finances, residents, iwi, proven contractors, and central government –- has seen a community-wide effort in ensuring the future success of these works.

“Preparation work as well has brought Council’s Pukaka Quarry back online, we have the first year’s material ready for transport to our riverside staging point to start building the access road, and due to being close to delivery site we’re saving immense transport costs.

“But concerns from residents on Peninsula Road have been taken into consideration, so they’ll maintain access throughout, while we’re also working out of white baiting season”.

Yet, Andy and the MDC Rivers team’s battle with Marlborough’s rivers continues.

“For Marlborough, this is the first rivers project to fully incorporate consideration for future climate scenarios, whilst we fully evaluate what future 1 in 100-year floods look like alongside the ageing infrastructure we rely upon to keep us safe and prosperous”.