Dunedin: Erosion issues at St Clair and Ocean Beach

Received from Paul Pope
Fri, 25 Mar 2016 at 3:01 p.m.

█ Message: I filmed this short video the other day and spliced in some information on how the erosion at St Clair actually happens. I don’t often use video, but it looks very compelling. I put it into the Beginners Guide to Coastal Conservation on Facebook yesterday and it’s had more than 7000 views, so people are interested in what’s going on.

[view full screen]
Paul Pope Published on Mar 24, 2016
The Physics of Erosion
The erosion issues at St Clair Beach and the whole of Ocean Beach in Dunedin have become more and more serious in recent years. Understanding the reasons behind what people see at St Clair is very important. The community need to be able to make informed decisions about these damaging processes.

Related Posts and Comments:
● 11.9.15 RAPID dune erosion continues —Council doesn’t give a toss
● 19.8.15 Paul Pope’s strategic overview of coastal conservation #Dunedin
● 11.8.15 DCC’s unmanaged retreat for South Dunedin
● 22.7.15 DCC Long Term Plan 2015/16 – 2024/25
10.4.15 DCC: Natural Hazards
28.3.15 DCC Draft Long Term Plan 2015/16 to 2024/25 —Consultation Open
23.11.13 DCC: St Clair esplanade and seawall [public forum] 27 November
18.10.13 DCC: Final vote tally + St Clair boat ramp
18.8.13 South Dunedin and other low lying areas
26.5.13 [bad news] St Clair seawall #FAIL
10.9.12 John Wilson Ocean Drive … reminder to all of DCC incompetence
30.7.12 ORC on hazard risks and land use controls
28.11.11 St Clair seawall and beach access

█ For more, enter the term *coastal* in the search box at right.

Posted by Elizabeth Kerr


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17 responses to “Dunedin: Erosion issues at St Clair and Ocean Beach

  1. If the Sea Level rises, as would happen at present rate of glacial melt, do we go back to the drawing board, or build higher walls? Mr Wal D’Inn, Wallsend, Grey Valley.

    • Elizabeth

      Rather, Mr D’Inn, the Dunedin land mass is rising. Hang on to the plates. –Tilda

    • Gurglars

      brownestudy, the glaciers are melting. From personal observation they have retreated 100s of metres in the last fifty years.

      Just when does the sea level rise as a result?

      Does it require a trumpet fanfare?

      Or is the water accumulating in a deep hole somewhere, ready to escape and send sea levels back to Kurow where they have been before.

      If sea levels were rising just a teeny bit, surely it would fill the South Dunedin mudtanks.

      And if the ORC were really concerned about sealevel rise, would they seriously consider building new offices at the Dunedin wharf? Now that would be shortsighted.

      • Oh, I don’t know, someone told me the ice was melting. I didn’t expect a kind of Spanish Inquisition! But, I didnae mean the land glaciers. I meant the Polar Ice. It melts measurably. Whether it continues melting remains to be seen, and we’re really good at hanging around, doing nothing, waiting to see. If it does, the sea levels will rise. That’s oceanographic physics. If the melt slows, they won’t rise. Unless, as you say, there’s an maelstrom to take the ocean to the Centre of The Earth. I saw that film. The James Mason version, of course.

        • Calvin Oaten

          ‘brownestudy’, did I read you right? You didnae mean the land glaciers. You meant the Polar ice! Right? “If it does, the sea levels will rise That’s oceanographic physics.” Wrong!!! Study the physics again, when sea water (or fresh) freezes it expands – approximately 10% – and floats with the 10% above sea level. When it melts it simply reverts to its original volume. No sea level rise at all. Check it out. Pour yourself a whiskey, add two ice cubes, measure the level in the glass. Wait till the ice totally melts and then again measure the level. Unless you’ve drunk too many you will find the level unchanged.

        • Gurglars

          Now that’s an idea we haven’t tried yet brownestudy,

          The Dunedin Inquisition!

          If anyone lies, they are placed on the rack.
          If anyone uses tears to win the debate, they are excommunicated.
          Bearing false witness, brings on the tar and feathers.
          Suggesting climate change as the excuse for greater spending or as a panacea brings the sky falling down!

          (Yeh, I know that was chicken little, not the Spanish priests, but their response to those excuses would be disembowelling following ripping the arms off and cutting out the tongue and whilst an attractive option is probably illegal)

        • Calvin, what’s a man to do when a big Scientist makes the claim. It’s not my idea. Where does the sea go when it expands? Laphroaig doesna have ice.

        • The only problem with heretics having a little lie down (racked), is that, through the centuries, victims of torture were in the right. Joan of Arc threw a flaming brazier at me (in the stage play).

  2. Hype O'Thermia

    Very well done. I like video showing waves hitting the sea wall at an angle then bouncing back at the same-but-opposite angle which makes that point far better than words alone. Worth watching more than once, esp after a visit to St Clair to see how it’s looking on another day, then back to Paul Pope’s The Physics of Erosion to add depth to personal observations.
    In the absence of understanding dumb “solutions” will continue – or equally ruinous no action at all. As ratepayers we’re best to be informed so as to avoid money being thrown at further stupid schemes (this is not confined to St Clair) followed by more money to fix up mistakes.
    As for the point of work on St Clair, being informed will save us from being bullshitted that the sea is rising (so fast! Wow!!) and there’s no saving South Dunedin, it’s doomed, doomed [etc, rabbit on, mouth in downhill lane, brain in neutral].

  3. Many thanks for putting this up. It’s been a mission of mine for some time to give people more information about coastal processes. There’s a large degree of uncertainty and in many cases a complete lack of understanding of exactly what is happening on the coast. It’s very important that we have an informed public, who can grasp some of the “very big” science involved at Ocean Beach Domain.

    Can I just say that in relation to “sea level rise” we should not confuse a lack of resilience in the coastline to this recent phenomenon. Dunedin’s historical record of coastal erosion is characterised by inundation, dune collapse, beach decline and the destruction of several sea walls. Local dune morphology has been irrevocably altered through exotic plants, sand mining, poor land use and ill-advised protection structures. These factors have exacerbated erosion events, they are not a consequence of modern climate change, but rather the lingering effects of uncontrolled human modification of dune and beach ecosystems.

    Ocean Beach is unable to sustain itself against storm events because of long term modification. That places it in an even more serious position in the face of predicted sea level rise. We should be urgently advocating for long term dune restoration and management into a healthy, viable and sustainable ecosystem, which will provide property protection and biodiversity services.

  4. Hype O'Thermia

    Let me repeat because it’s something we need to be alert to, next DCC genius comes up with a scheme: “These factors have exacerbated erosion events, they are not a consequence of modern climate change, but rather the lingering effects of uncontrolled human modification of dune and beach ecosystems.”
    We need action. What we don’t need is the cheapest nor the most expensive scheme, it’s well-planned action based on deep thorough understanding of the way sea and land interact *in that particular place* – and understanding of materials e.g. steel that’s fine for outdoor use in Central Otago is NOT okay right up close to salt water.

  5. Calvin Oaten

    brownestudy, Laphroiag doesna have ice. Correct. Where does the sea go when it expands? Depends where and what makes it expand. If it increases in temperature it would tend to expand, but then elsewhere on the planet it will almost certainly be cooling thus shrinking. That is the problem with this ‘Climate Change’ mania, it seems to presuppose that a one size fits all when in fact weather is chaotic and infinitely varied. You cannot put it in a bottle and say that is it. When you try, as IPCC has, via all the so called scientists are doing, to study any aspect, it immediately presets a definition, much like trying to put sixty cats into one paper bag at one moment. Just accept the fact that the weather is constantly changing, subject to all manner of influences, not least of which is the Sun and its varying activities. Please don’t have the effrontery to claim that man and CO2 release is the sole precursor to the catastrophic end predicted. That’s just egotistical. Look at recent history and you will see documented the cyclical warming and cooling periods. The fact that Earth is in a warming period, and has been since the turn of the 20th century would suggest no surprises in temperatures being on a rising trend. Just as certain is the fact that it will move back to a cooling phase when it is time. So, in answer to your question: it doesn’t go anywhere.

  6. Elizabeth

    “About 200m of sand sausages would be installed to protect the narrowest area of dunes” — 200m is Not Enough.

    See (12.4.16) ODT: Plea to hasten fixing of dunes and this comment (11.4.16) St Clair/Ocean Beach Domain Erosion : Bill Brown presented at the Public Forum today – his handout, scanned.

    █ DCC aims to finish sand sausage work by mid-June.

    Fri, 22 Apr 2016
    ODT: New sand sausages being made
    Measures to shore up coastal defences at Dunedin’s Ocean Beach are on track to start next month. Dunedin City Council parks and recreation group manager Richard Saunders said the council had called for tenders for the replacement of storm-damaged sand sausages and the successful contractor would be appointed soon. […] Final costs would not be known until the project had been completed.


    █ DCC budget for initial investigation of Dunedin coastlines ($75,000).

    Thu, 21 Apr 2016
    ODT: DCC has erosion ‘under observation’
    Coastal erosion along Taieri Mouth Rd has exposed part of the roadside, railing and a telecommunications cable, but is not a risk to road users, the Dunedin City Council says. Ten metres of the Taieri Mouth Rd bank, about 100m north of Dicksons Rd, had been eroded. […] The council has forecast $75,000 in the draft 2016-17 annual plan budget for an initial investigation of Dunedin coastlines threatened by erosion. If funding was approved, analysis would begin in July.

  7. Elizabeth

    Chair of the DCC infrastructure services committee Kate Wilson attempts to stave off informed public opinion, again….

    Fri, 17 Feb 2017
    ODT: Council urged to extend geotubes further 300m to the east
    The Dunedin City Council is being urged to do more to protect South Dunedin’s sand dunes from coastal erosion. St Clair resident Bill Brown, who has been petitioning the council on the issue since 2015, made the call at a public forum at the start of Monday’s infrastructure services and networks committee meeting. Mr Brown told the meeting the council should be congratulated for investing in new “geotubes” to protect sand dunes between St Clair and St Kilda beaches. However, the protection did not go far enough, as the tubes  extended only halfway along the dunes, he said. That left the dunes’ eastern face exposed, and more erosion could be expected over the coming months, he warned. Cont/

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