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Council will make the call on future resilience of the Historic Reefton landfill

27 Mar 2023

Council will decide at this week's Council meeting about the repair work that is planned for the damaged Historic Reefton landfill rock wall.

In February 2022 the swollen Inangahua river damaged the rock wall of the Historic Reefton landfill and caused a significant amount of landfill material to be scattered downstream. This rubbish was collected and cleaned up in the months following the event.

The National Emergency Management Agency (NEMA) approved a total of $1,074,000+GST funding for the repair of the rock wall which will protect the Historic Landfill from future river inundations.

Council’s manger infrastructure delivery Eric de Boer says: “The NEMA funding is only for ‘like for like’ repair of the damaged section of the rock wall. It does not include any significant betterment or extension. This needs to be funded by council.”

The NEMA funding will only pay for the section of the rock wall directly damaged by the February floods. There is a 120m section of rock wall next to the flood damaged section that requires additional strengthening to ensure it is not eroded in future flood events.

Mr de Boer says: “Strengthening this part of the wall to withstand a 1 in a 50-year flood is expected to cost $250,000 excl GST.”

WSP Consulting Engineers (WSP) drafted a detailed plan outlining what repairs are required to make the Historic Reefton Landfill resilient to future floods. WSP undertook a full review of the site and surveyed the extend of the rubbish within the historic landfill.

Mr de Boer says: “WSP recommended option two and three, out of three options, as the most resilient choice.”

However, this recommendation does not consider costs. If we want to deliver a rock wall that is fit for the future for a price that council can shoulder, then option one is the recommended solution.

All three options require additional funding from council on top of the approved NEMA funding. For option two this would be $880,000 excl GST and for option three council had to pay an additional $975,000 excl GST.

If option one is approved, the existing wall will be strengthened at the bottom with an increase to the toe footprint and it will add an additional layer of rock over the remainder of the existing wall.

The rock wall height will remain suitable for a 1 in 50-year flood event, but the improvements will increase the wall‘s resilience to withstand such an event.

Option two takes into the account the effects of climate change and increases the toe size of the rock wall by another 1m, improving its resilience during higher peak flows. This construction of the toe size is best done at its first construction, in other words, it is difficult to retrospectively go back and upgrade this element if needed. This option also involves raising the rock wall height by an additional 0.5m. This would see the rock wall brace a 1 in 1,000 years flood. 

Option three incorporates all the elements of the previous options and increases the length of rock wall upstream and adds a rock groyne at the downstream end of the rock wall to help the direction of the river as it leaves the rock wall protection area. This would mean the rock wall could withstand a 1 in 1,000-year flood event.

If option one is signed off, council will fund the project out of a loan and increase its net debt by $250,000. Due to the timing of the recommendation the $250,000 was not included in the 2023-2024 Draft Annual Plan. This resolution would increase the total general rates by $15,268 per annum, which equals $2.32 including GST per ratepayer or an 0.1% increase for general rates.

Mr de Boer says: “If council chooses not to finance the additional work, the repair will proceed with only the NEMA funded part of the project; essentially only repairing what has been damaged and leave the remainder as it is. This risks future floods damaging and opening up the remaining rock wall.”


further information please contact:
Eric de Boer

Manager Infrastructure Delivery