Assessments for seawall

The sink holes last Tuesday evening. Photo by Craig Baxter.
The sink holes last Tuesday evening. Photo by Craig Baxter.
A full assessment of the St Clair seawall is expected to start next week.

Advice will also be taken on providing a long-term solution to problems such as the one which caused a section of the Esplanade to be undermined.

While the integrity of the wall was believed to be still intact, the Dunedin City Council would have the entire seawall assessed as a precautionary measure, council roading maintenance engineer Peter Standring said yesterday.

The assessment would be carried out by contract engineers.

The first of several large holes appeared on Sunday behind the seawall in front of the St Clair Surf Life Saving Club and the South Coast Boardriders' Association, after heavy seas and high tides depleted the beach of sand, exposing the toe of the wall.

That allowed waves to flush behind the wall, washing out the backfill, causing the paving above to collapse.

The area from Forbury Rd to the north end of the wall is cordoned off and most access from the Esplanade to St Clair Beach is closed until further notice.

Tracked excavators have been on site since Monday, shifting rocks to protect the bottom of the seawall.

Vertical sheet steel piling is being installed in front of the seawall, on either side of the lifesaving club's ramp, along with cross-bracing under the ramp itself.

Mr Standring said contractors would backfill the area between the seawall piles and the sheet piles with concrete today and tomorrow.

He said much of the beach was at the lowest level staff had seen.

Because tides were so high, the waves had been hitting the sea wall without breaking, putting significant pressure on it. The situation was expected to improve after Tuesday's king tide.

However, it had highlighted the need for a long-term solution which worked with the natural environment, he said.

''This is a natural occurrence and we will be getting expert advice on how to best deal with these challenges in the future.''

He said some St Clair businesses and residents had reported heightened building vibrations this week.

That was ''more than likely'' happening because of the lack of backfill behind the wall at the northern end, which would normally dampen pounding waves.

He emphasised it was important for people to avoid the cordoned-off area while work continued.

There was public access to St Clair Beach via Middle Beach.

Updates on the project are available on the council's website.

-debbie.porteous@odt.co.nz

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