A “particularly concerning” landslip at Isis St in Oamaru was one of several which happened after heavy rains last month in spots where they had not been reported before.

The slip sits just half a metre from the road with stormwater runoff from Wye St and Queens Cres the likely cause.

Infrastructure manager Joshua Rendell told councillors this week that the nearby road had been reduced to one lane and depending on funding, “that may have to become permanent”.

The infrastructure “failings” during and after July’s floods were “quite different” to previous weather events, the assets and infrastructure committee heard.

“It was a more significant event this time around, or at least in a shorter space of time.”

More than 180mm of rain fell between July 5 and July 9 in Oamaru, with 18mm falling an hour at the peak on Monday, July 6.

There were a “number of slips” which were not in areas “where we normally experience slips”.

“The one at Isis St is particularly concerning.”

The slip was about 30m down the embankment in “quite steep terrain”.

Due to “low” traffic numbers on the road it would be up to the Waitaki District Council to decide whether to “restore services” given the “high cost”.

A slip also occurred in Ardgowan Rd between the road and a cycle path. The slip may also have undermined “rock armouring” protecting part of the embankment.

A family was evacuated from their house at the corner of Tay and Nith Sts when a landslip occurred at the back of the property, while there was also a minor slip at Glen St.

Numerous retaining walls — “already in somewhat poor condition” due to their age — had degraded “rapidly” as a result of the storm.

The upper tier of the retaining wall in Lune St collapsed on to the lower level following the heavy rains.

And while the initial collapse was “relatively minor”, a subsequent assessment revealed additional sections of the wall could collapse during similar events or even ones with less intense rainfall, a report prepared for Tuesday’s meeting stated.

The lane next to the retaining wall remains closed.

The wall is due to be fully replaced in the 2027/28 financial year, if the 2027/37 long-term plan is approved.

Officers were working on temporary solutions in the interim.

“I think what we’re seeing overall is some of the issues around investment in infrastructure coming home to roost,’’ Mr Rendell said. 

“Our infrastructure just wasn’t capable of handling the storm event, and certainly the volume that was experienced.”