Unintended beach erosion, safety concerns and cost are some of the risks Dunedin City Council staff have identified in going ahead with any wooden groynes.
About nine much-photographed wooden poles at the beach are all that remains of a series of wooden groynes that were built in the early 20th century in an attempt to allay erosion.
Late last year, in a 12-2 vote, the council asked staff to assess the feasibility of reinstating the groyne structure, and how that would benefit the coast, including Kettle Park.
Cr Jules Radich advanced the motion — and in February he wrote in favour of the move in an opinion piece in the Otago Daily Times.
"Our famous St Clair poles are actually a sand-trap known as a groyne and they are the main reason the beach became so wide and their deterioration is why we now have so much erosion," he said in his
opinion piece.
"St Clair coastal erosion problems began 140 years ago as soon as the first seawall was constructed at the esplanade about 1880.
"The wall reflected the waves which then scoured away sand so that ever larger waves hit the wall with inevitable results."
In a report to be discussed at next week’s full council meeting, staff advise that reinstating the groyne could improve beach access at the Esplanade and the end of Forbury Rd, but a groyne could also speed up erosion elsewhere and could be installed, requiring maintenance, without any extended benefit.
"Conceptually, if a typical groyne was to protect Kettle Park it would need to be roughly 395m long, rather than 65m as proposed (if located in the existing location)," council coastal specialist Tom Simons-Smith wrote.
Realistically, a system of groynes would be needed to protect Kettle Park.
"Roughly seven groynes would be required . . . if built to the proposed specifications (e.g. timber groynes of 65m length), with the western-most groyne located in the proposed position (current poles)."
The reinstatement of the existing St Clair groyne would cost $150,000, and could cost up to $60,000 a year to maintain, he said.
Councillors will consider the matter on Tuesday.
The report recommends councillors stick with the status quo and consider groynes as part of the present work being done to develop a plan for managing the St Clair-St Kilda coastline. The plan is expected to be finalised in 2021.
Starting today, the council is hosting a series of public drop-in sessions at the South Coast Board Riders Club on the Esplanade as part of that work.
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Comments
Wow - One of the things that I really considered was an easy win and would not overly cost a great deal in the scheme of things, and yet again the Council doesn't want to listen, FB had a some really great posts on this a couple of months back. Time for Councillor Radich and Vandervis and others to pull the pin and to put the council dodgy deals out in the open so they are exposed.
Thank you for putting a question mark on your headline.
The meeting on Tuesday will be about the DCC staff report, not about repairing our iconic St Clair poles. That discussion will wait till after the community consultations and people have had an opportunity to voice their opinions.
The groynes at St Clair did a splendid job of protecting the esplanade for 100 years. A report entitled "The Shifting Sand of St Clair" can be accessed here: https://bit.ly/32GOce6
I urge anyone interested to read the report, attend a consultation and submit their thoughts. Restoration of the poles this summer for a 5yr trial is by far the most cost-effective and lowest risk action that Council could possibly take after two decades of continual erosion and huge expense.
I have posted the idea of AKMONS here many times......Please, Cr Radich, look into and research AKMONS. They have been used to great success in the New Plymouth breakwater, fortifying the harbour from Westerly ocean surges. Now consider the population of New Plymouth, and the amount of AKMONS that have been installed. Wellington, protecting the airport from the very roughest the Cook Strait could ever throw at the coastline. Indeed, they are used all around the world in very severe sea conditions to control erosion and diffuse sea action. The solutions that have been well and truly proven would be money better spent that contimuing with experiments. That old dump won't rest forever, nor will our coastline. The ravages of the sea are a different beast than in the past. Let's do this once, lets do this right. AKMONS. They are excellent at diffusing the brutal force of the waves. I have stood in the face of huge waves, right at the head of the New Plymouth breakwater AKMONS, and witnessed first hand the effectiveness. The effect they have is jaw droppingly effcient. The biggest and most powerful waves are almost instantaniously rendered powerless. Just a thought........
After you posted about akmons some time ago, I did take a look into them and I do agree that they are an effective device. Putting them against the wall would not be a great look and they would be difficult to climb over. They could be used for a seawall out from the saltwater pool to break the force of the southern ocean and protect the beach that way, however that concept was rejected when the esplanade was rebuilt in 2004.
Repairing the groyne would be way cheaper and the effect will be to build up sand till the poles mostly disappear, so that is worth trying first I reckon.
Did the staff at the DCC read all the material in your report Jules? There is some valuable insight to be gleaned from the work of past engineers and surveyors. If they didn't read or study it I would be asking some very hard questions about the quality of their work.
"The Shifting Sand of St Clair"
After reading this report fully, I would support the Groynes being reintroduced. There are some very compelling facts that I believe can't be ignored. However, for added insurance and longevity, I would still be placing a crop of AKMONS against the seawall esplanade, and place a crop of them between the Groyne poles. That way, not as many would be required, and they would help protect the poles.
With Cadbury buildings being demolished, I would be investigating crushing the old concrete into chips, repurposing steels where possible for reinforcing and recycling it into the new AKMONS using molds made from recycled plastics.
We're putting a lot of useful material into landfill.
Anyway, thankyou Cr Radich, an excellent read and very insightful.......