Several metres of a top tier of the three-tiered Oamaru stone wall near the intersection of Severn St and Douglas Tce failed about 4pm on Saturday, sending stone blocks tumbling on to the busy highway.
Waitaki Mayor Gary Kircher said the inspection identified the cause of the collapse as being weather-related, as opposed to a structural defect.
"Essentially, what they [council officers] are putting the cause down to, and it was thought the drainage might have been blocked, is the new soil and material . . . was very, very wet and the rain has been enough to thoroughly soak that soil and it has created a lot of weight behind that wall.
"The water's gone through there [the soil] and not enough has gone through to the drain and has pushed the wall forward,'' Mr Kircher said.
Up to a "cubic tonne'' of weight had result in the wall's failure.
In March, the Waitaki District Council spent $45,000 improving the wall's stability, removing leaning sections, re-establishing drainage and building a new stone wall.
Part of the newly-built section of the wall collapsed, along with an older section.
Council officers are now looking at options for rebuilding the collapsed section of the wall, and what materials would be suitable.
When the wall was originally built by the Oamaru Beautifying Society about 80 years ago, Oamaru stone was used.
The lower level was rebuilt about seven years ago using concrete with an Oamaru stone veneer, the same materials used in the most recent works.
Mr Kircher said the wall was not at risk of further collapse, and that it was difficult to determine what method would be used to repair it until all options were looked at more closely by council staff.
He dismissed speculation on social media the wall had collapsed due to poor workmanship when improvements were made in March, and was "disappointed'' with some of the comments that had circulated.
"Overall, the workmanship was good.
"The drainage was put in so it certainly wasn't the workmanship.
"It's a combination of factors and an unforeseen event has certainly been an issue there.''
The improvement work was carried out by The Stone Man and Steve McLeod Contracting.
- Oamaru Mail
