Dunedin sink holes grow bigger
Wednesday 29 May 2013 11:45 a.m.
Four new sink holes have opened up on a popular Dunedin waterfront, as the cost of repairing the already severely damaged walkway balloons into the hundreds of thousands of dollars.
The St Clair Esplanade has been eroding since last Sunday, with huge holes swallowing seats in the public walkway, forcing police to cordon off the unsafe area.
- PHOTOS - Sink holes open in the waterfront
Dunedin City Council transportation operations manager Graeme Hamilton says the new holes are evidence of an erosion of the sea wall below, where strong waves have washed away around a metre of sand.
"The odd missing brick has opened out to the reality of what was beneath," he says. "If you look at those holes, they're actually a depression over about at least a metre each side. If you took a cross section through there, you'd see a cavern underneath the bricks."
Contractors have been rushing to block the sea wall from unusually high tides, which are continuing to erode the sand.
Work has been concreted on one particular weak sport – a surf club ramp leading to the ocean – and sheet steel piles have been added over the last few days to patch a gap that was letting water in.
That continued at low tide last night in snowy conditions, with workers pouring concrete to try and stop the tides.
Mr Hamilton says the area is expected to be closed for a number of weeks, with early cost estimates of the repair looking pricey.
"It won't be cheap. Before we finish it could be in the low hundreds of thousands," he says. "We just don't know. At the moment we're in full alert mode trying to get to the problem and then we'll try to think about the fix up."
The erosion is not a new problem according to the operations manager, as numerous sea walls have proven unable to hold up to the elements over the last century.
The first two walls, built in the 1880s, lasted only a few years while one built in 1913 had to be covered by the most recent version in 2004.
"It may be a case that under challenging circumstances over the years one has to do maintenance," Mr Hamilton says. "So if there's a hole or a mechanism for the water to get in under those extreme pressures, it finds a way in."
The newly cordoned-off walkway has proven to be a hot attraction for locals, who have been turning out in droves according to nearby Starfish Restaurant and Bar owner Kalena Dodds.
"All the parks have been taken from people taking a look," she says. "There's been heaps of people.
Mr Hamilton says some "absolutely bloody crazy" sightseers have even jumped the cordon to take a better photo.
"Those barricades and police cordons are there for a reason," he says. "That hole is probably three metres deep at least and they could be walking on a paver and just disappear from view."
Work to minimise the effect of the ocean is expected to continue at low tide today.