Johnstone review following DCC Infrastructure Services meeting 26.4.16 #SouthDunedinFlood

Election Year. This post is offered in the public interest.

On and about 3 June 2015, South Dunedin was severely affected by stormwater flooding – the Council has since discussed why and how council-owned infrastructure failure occurred. The extent of stormwater damage to private property and the upheaval and distress for affected residents, property investors and businesses is undeniable. Council operationals refer to this as the “June 2015 Flood Event” in formal reports.

A public meeting coordinated by Dunedin South MP Clare Curran was held at South Dunedin on Monday, 7 March 2016. At the meeting the South Dunedin Action Group(SDAG) was formed. Group representatives headed by spokesman Ray Macleod have since met with the Mayor and council officials – the first meeting was held on Tuesday, 3 May 2016. A meeting with council staff has followed more recently.

Local media, the Otago Daily Times and Channel 39, are presently covering the anniversary and aftermath of the “flood event”. Noticeably, the city council has yet to formally apologise to all the many people affected by the lack of council-owned infrastructure maintenance and stewardship at South Dunedin during the rain event of June 2015.

Council ‘not liable for flood damage’ (ODT 27/11/15)
“The Dunedin City Council says it is not liable for private property damage caused by the South Dunedin flood, despite admitting problems with its pumping network prolonged the pain for residents …. The issue had been considered by the council’s lawyers and insurers, but the advice from both was the council was not liable, [council infrastructure and networks general manager] Mrs Stokes said.”

Otago Daily Times Published on Jun 4, 2015
Raw aerial video of Dunedin Flooding [Video courtesy One News]

DCC Reports and Responses:

● 30 November 2015 –Council
Agenda – Council – 30/11/2015 (PDF, 39.6 KB)
Report – Council – 30/11/2015 (PDF, 553.9 KB) ‘Infrastructure Performance During June 2015 Flood Event’ (McElhone)
Minutes – Council – 30/11/2015 (PDF, 121.8 KB) | Meeting Video

● 7 March 2016 –Letter, DCC Chief Executive [supplied by DCC]
Sue Bidrose to Neil Johnstone 7.3.16 (PDF, 653 KB)

● 20 April 2016 –DCC Media Release
Report on South Dunedin infrastructure performance during June 2015 flood released

● 26 April 2016 –Infrastructure Services Committee
Agenda – ISC – 26/04/2016 (PDF, 6.3 MB) [agenda and reports]
Item 5 Report, ‘South Dunedin Public Infrastructure Performance during June 2015 Flood Event Follow up’ (Stokes), pp 6-27
Minutes – ISC – 26/04/2016 (PDF, 123.0 KB) | Meeting Video

The following content from consulting engineer Neil Johnstone is provided for your information and convenience. However, the site owner cannot accept any liability for its accuracy or content. Visitors who rely on this information do so at their own risk.

Reviews previously published at this website:
● 8.3.16 Johnstone independent review of DCC report #SouthDunedinFlood
● 19.5.16 Johnstone review of 2nd DCC report #SouthDunedinFlood

█ Third Review | dated 31.5.16
[With minor formatting changes for the WordPress template only. -Eds]

A Follow-up Review subsequent to DCC Infrastructure Services Committee meeting 26 April 2016

By N.P. Johnstone, MIPENZ

DCC has produced 2 reports on infrastructure performance during the flooding that reportedly entered approximately 1000 houses and caused in excess of 100 million dollars of damage. I have previously produced 2 independent reviews that are highly critical of DCC’s Stormwater Infrastructure Report (November 2015) and its “follow up” (the “mudtank report”, April 2016).

I also attended DCC’s Infrastructure Services Committee meeting on April 26, and have sighted video recordings of that meeting, which were belatedly posted by DCC close to a month later. I have formed an opinion that DCC has not fully acknowledged its role in failing to prevent much of the flood damage, but (often unreasonably) blames external influences and alleged historical design deficiencies.

I had originally intended to present a blow by blow comment on proceedings of the meeting, but that has proved a bigger task than my time allows, and would probably prove as tedious as the meeting itself. I have preferred not to align statements with the individual staff or councillor that made them, but the reader can view the recording of the meeting at leisure. I can however, not resist the temptation to present the comments of one councillor who stated: I am heartened by how well staff have responded to the challenges…and we can be comforted, I think by the feeling that you are treating our assets like you would your own. South Dunedin residents who had their assets ruined might see things rather differently.

The rainfall event of March 1968 was of the order of 10% greater than that of June 2015, on any comparison. This is incontrovertibly clear from readily available data, and thus demonstrates that the much greater flooding in the recent event should not have happened. DCC has consistently underestimated the significance of the 1968 rainfall.

DCC has misinterpreted ORC reporting that groundwater levels prior to the onset of rainfall were significantly elevated. DCC has extrapolated this error to claim that no infiltration of rainfall into the ground was possible, thereby explaining away the record surface flooding. ORC’s data is readily available, and demonstrates that groundwater levels only started to increase in concert with the June 3 rainfall, proving that infiltration was both significant and (probably) normal.

DCC, relying on superficial analyses of other agencies, have claimed that the 24-hour rainfall experienced in June 2015 was a 150-year event, then 100, then 60, then 100 again. The selection of 24-hour duration rainfalls is not entirely appropriate (being rather too long). Nevertheless, the March (or April) 1923 24-hour rainfall was much greater, the 1968 rainfall slightly higher (but ignored in analyses), and at least 2 others between the 1890s and late 1920s were similar, and possibly slightly lower. Analyses of shorter duration events would likely further reduce the assessed recurrence interval of the June flood. I believe it was a 30-year rainfall event at worst.

Increased impermeable areas have certainly increased runoff rates; based on DCC-supplied estimates of changes, I have estimated that these changes could have increased flood levels by up to 150mm. Ex-DCC engineers have expressed doubt as to the degree of landuse change. In any case, I would have expected additional stormwater infrastructure to have been installed to compensate.

The degree of blocked mudtanks across the catchment was underestimated by DCC, until the release of the mudtank report in April 2016. The extent of the mudtank issue was finally confirmed then, at no great surprise to South Dunedin residents. An unseemly blame game ensued, and may not be over. DCC then took the stance that the plethora of blocked mudtanks had no impact on the depth of flooding across South Dunedin, but may have prolonged the flooding. The claim defies reason, and in part relies on DCC’s adherence to the zero infiltration myth.

The partial blockage – and difficulties experienced in the clearing – of the screens at this pumping station has been well publicised, and may have added approximately 200mm to the depth of flooding. Less well publicised are the facts that no emergency staff visited the pump station until about noon on the day of the flood, and (apparently) only attended the station to attempt clearing the screens between visits to other locations during the latter part of the day. Equally poorly understood is that not all of the station’s pumps were operating throughout the flood event due to the manner in which pump cut-ins were programmed. No decision to override the pumps’ programming was made. No information on which pumps remained inoperative has been made available, so it is not possible to attribute the depth of flooding caused by the inability to clear screens, compared with that caused by poor pump management.

This pumping station has the ability to bypass the wastewater treatment plant and discharge sewage-contaminated stormwater directly to the ocean at Lawyers Head. The option was not taken in the June 2015 flood. By contrast, in the 1968 event the pumping option at Musselburgh was fully utilised to the extent that approximately 5m3/s was pumped to the ocean for a period of 24 hours. Such pumping would have proved effective as long as individual property gully traps were submerged by stormwater, and may have reduced flood depth by more than half a metre. It is not known (by me) whether a comparable benefit could be achieved under June 2015 conditions, but a very significant opportunity was apparently lost. No information on the Musselburgh station’s pumping operation in the June flood is included in either of DCC infrastructure performance reports.

DCC has relied heavily on the belief that the stormwater system can only handle rainfall intensities of 4.1mm/hr, and therefore regular flooding cannot be avoided. This is contrary to historic reality. The 4.1mm/hr limitation only applies if DCC’s assumption of zero infiltration applies. The assumption has no validity, and the existing infrastructure is far more capable than DCC is stating.

One of the main reasons for the extraordinary delay in the presentation of the “mudtank” report was that a robust external peer review was to be obtained. Reference to such peer review has surfaced occasionally since, but no review has been published. I have sought a copy of any such review – or even confirmation of its existence – from DCC. No such review has yet been confirmed to exist.

Many of the above topics were discussed to a greater or lesser level of detail at the Committee Meeting on April 26. From sitting through the majority of the meeting and viewing video coverage of it later, it became apparent that Councillors’ understanding of the June 2015 flood causes was generally weak, and that many of their questions directed to staff were inadequately or confusingly answered, if they were answered at all. These included:

10.1 Pre-existing Groundwater Levels
Selective reference was made to ORC report text, but no data was referenced. The data disproves the assertion of high groundwater and zero infiltration.

10.2 Mudtanks
According to staff, mudtank blockage didn’t increase flood levels, yet a raised vegetable patch could.

10.3 Portobello Road Pumping Station
No information on unused pump capacity or its impact on flood levels was given (or sought); and the final word on the subject was that the only issue at the station had been debris blockage, now fixed.

10.4 Musselburgh Pumping Station
In response to a question re pumping rates at this station, the reply was to the effect that “we have no data on this, is there a follow-up question?” There wasn’t a follow-up question on the subject, despite its fundamental importance.

10.5 Infrastructure Design Limitation
The existing infrastructure was repeatedly deemed to be inadequate on the basis that only 4.1mm/hr of rainfall could be accommodated, once pipe storage was exhausted. There was no proviso given that this determination required the impossible condition of zero infiltration of rainwater into the ground.

This review does not exhaust my concerns with the technical presented at the meeting, but I can conclude the following with confidence:

i. Maintenance prior to the flood was inadequate;
ii. Emergency management during the event was poor;
iii. DCC’s understanding and reporting of flood issues remains unconvincing, especially without the benefit of promised external peer review.

31 May 2016


█ For more, enter the terms *flood* and *south dunedin* in the search box at right.

Posted by Elizabeth Kerr


Filed under Business, DCC, Democracy, District Plan, Dunedin, Economics, Events, Finance, Geography, Heritage, Housing, Infrastructure, Media, Name, New Zealand, Ombudsman, People, Politics, Project management, Property, Proposed 2GP, Public interest, Resource management, Site, South Dunedin, Town planning, Transportation, Travesty, What stadium

12 responses to “Johnstone review following DCC Infrastructure Services meeting 26.4.16 #SouthDunedinFlood

  1. Elizabeth

    Sat, 4 Jun 2016

    The council yesterday disputed the conclusions Mr Johnstone had reached, saying they contained “serious factual errors”.

    ODT: Fighting for a ‘better deal’
    After dozens of hours writing reports on the causes of last year’s flood, semi-retired engineer Neil Johnstone has vowed to continue fighting for a “better deal” for South Dunedin. Mr Johnstone (65) was holidaying in eastern Turkey during the flood and was immediately concerned about how much damage the flood caused given how much rain there was. Since arriving home, he had used his experience to investigate the cause of floods to pick apart Dunedin City Council’s actions before and after the flood.


    “Worryingly, there was no commitment by the mayor and the councillors to the long-term future of the area which comprises 10,000 or more of its citizens and billions of dollars of its assets, including many key businesses, educational assets and industries.”

    ODT: Group fears withdrawal
    A group representing South Dunedin residents and businesses is calling for an assurance the area will not be abandoned, after last June’s floods raised questions about its infrastructure and future. South Dunedin Action Group spokesman Ray Macleod says many of the group’s questions remain unanswered and concern remains that a “strategic withdrawal” of the area is planned. The group met Dunedin Mayor Dave Cull in May and Dunedin City Council staff on Wednesday to seek answers about the cause of the floods, assurances measures were in place to prevent similar events in future, and an assurance about the future of the area.


    Other stories:
    ODT: Offer of house accepted
    ODT: Brought together by trials

  2. Elizabeth

    L I A B I L I T Y #SouthDunedinFlood

    If others have council or media references to “no” DCC liability for the Flood of 4 June 2015, by all means add them to this thread.

    ODT 27 Nov 2015
    Infrastructure and networks general manager Ruth Stokes: “The issue had been considered by the council’s lawyers and insurers, but the advice from both was the council was not liable.” Link

    30 Nov 2015
    Mayor Cull cautioned councillors not to make statements that would cause liability to the Council

    ODT 8 Mar 2016
    Cr Andrew Whiley: In my opinion, the flood of June 3 was exacerbated by the poor maintenance of the mud tanks and the issues around the Portobello Rd pumping station. The mud tank report has yet to come to the council but any resident in the area will tell you there was an issue with maintenance. Link

    ODT 22 Apr 2016
    A report identifying failures in the lead-up to last June’s floods has highlighted the need for investment in South Dunedin infrastructure which could be worth hundreds of millions of dollars. Both Cr Andrew Whiley and the Insurance Council of New Zealand said the report showed investment was needed, with Cr Whiley saying successive councils had let South Dunedin down by putting off investment in the area. Link

    ODT 27 Apr 2016
    Council infrastructure and networks general manager Ruth Stokes started the meeting by apologising on behalf of the executive, saying staff and not councillors or the mayor, were responsible for the failings identified in the report. Link

    26 Apr 2016
    ICS meeting chairwoman Cr Kate Wilson cautioned councillors not to make statements that would cause liability to the Council

    RNZ News 26 Apr 2016
    Cr Lee Vandervis says the city council could face legal action based on emails showing it knew about problems with the city’s drainage tanks years before they flooded. Link

    RNZ Checkpoint 22 Apr 2016
    (listen from 08:04) John Campbell asks Mayor Cull: “Does the buck stop with Council at all for this?” The mayor replies: “Absolutely, we’re responsible for the stormwater system.” Audio Link

  3. Observer

    Government (local or central) denials and fabrications to protect those within at the cost of those being governed is a hallmark of third world corrupt countries.

    NZ is only perceived to have low corruption because Government has become good at it and citizens complacent about it.

    More Neil Johnstone’s are required to out government cover-ups.

  4. Hype O'Thermia

    “NZ is only perceived to have low corruption because Government has become good at it and citizens complacent about it” – and our media have been very polite (a polite term for it).

    Blogs and facebook have changed the scene. It’s no wonder the previously secure and unexamined in elected positions, and the squadrons of ‘crats and managers and consultants and spinners have taken to leaning heavily on those who make unflattering information available to one and all, using readily available digital media.

    Traditional media have to shape up. They’re already under threat of irrelevance. If they keep on being nicey-nice to Government and Councillors and council staff, tactfully omitting stories that come out anyway, they make themselves look pointless, not worth reading/watching, not worth advertising in.

    • Observer

      Yes Hype O’Thermia – media is a main cog in government corruption. Government rely on the media to ignore it and divert the truth.

      The Christchurch Press has gone as far as advising me that reporting corruption within local government is defamatory to those who are corrupt and refused to receive evidence of it.

      Of course when you give evidence of the corruption to the “leaders” in governance, as Neil Johnstone has, they too ignore it and divert the truth (save as a few such as Cr Vandervis).

  5. Calvin Oaten

    Having just read Rebecca Macfie’s excellent coverage of the June 2015 South Dunedin floods in the current ‘Listener’ it becomes patently obvious that the city council’s performance before, during and after the event was far short of that to be expected of that body.

    The lack of maintenance and attention to the cleaning of mudtanks [integral parts of the stormwater systems] and the inlet screens at the Portobello Pumping station cannot be disguised by ‘so called’ record rainfall, high groundwater nor Climate Change rising sea levels. This is all reiterated by the three experts in the system as installed. Bruce Hendry, former DCC surveyor/drainage specislist, vitally involved in the renewal of the system in the 1960s, Darrel Robinson, former DCC drainage specialist and Neil Johnstone, MIPENZ, former investigations engineer at Otago Regional Council which monitors ground water levels on a continuous basis. Then there is the unrrsolved anxiety for the victims and citizens of South Dunedin. Nothing the DCC has done or shown in their very belated report on the flood either accepts any shortfall, blame or displays contrition.

    One can ask why the reluctance of the DCC to ‘man up’ and say: “We cocked up here and now must in the interests of justice make amends.” No, the decision has been to procrastinate, to search desperately for excuses to hide behind, thus shedding the mantle of responsibility, leaving legions of distraught citizens to their own resources to recover.

    Why? Well for starters the problem is one of money. The city is carrying ‘consolidated’ debt of +$600million, due to reckless spending decisions by this and previous councils. I think back to when CEO Jim Harland was appointed and the city’s ‘core’ debt stood at $35million. Within ten years due to the Stadium, the Dunedin Town Hall Redevelopment, the Otago Settlers Museum and sundry other luxuries, the ‘core’ debt had ballooned to $360million. Substantial sums of additional debt have been incurred endeavouring to make the Stadium a stable financial venue. We now know that DCHL group has been less than frugal, wracking up huge deficits through poor commercial decisions, hence the total +$600million debt.

    All that indicates that nothing could be done in the way of upgrading strategic infrastructures without calling on the ratepayers for huge increases in rates. This mayor and council find that too difficult and would rather persevere on their ‘wastrel’ ways with BS like cycleways, sports funding and ‘trivia’ that demonstrates the overall shallowness of the occupants of the Civic Centre building. There is no better indication of this than Mayor Cull’s frequent overseas jaunting to China and other places, using citizens’ treasure in the vain hope of attracting substantial business to Dunedin. That very definitely is not the business of council, but rather that of the organisations best standing to benefit.

    It behoves the citizens come October to give the bulk of sitting councillors and Mayor Cull the ‘elbow’ out of here if there is to be any change for the better.

  6. Diane Yeldon

    Dunedin recent local government history in a nutshell: DCC debt going from $35 million to over $600 million in about 10 – 15 years. And without anything a city really needs, like a decent stormwater system or good public transport, to show for it.

    • Diane Yeldon

      And, Calvin, since you mentioned cycleways, it occurs to me that it has been suspiciously quiet on the central city one-way cycleway front. (I didn’t call it ‘proposed’ because I think it’s a done deal.)

      Are the movers and shakers behind this project cynical and manipulative enough to time the actual beginning of the work at the very beginning of a three year council term? So that it doesn’t become an election issue. And so that it can be completed or at least progressed to the point of no return before any council supporting it could be voted out?

      It ought to be an election issue. I believe an overwhelming proportion of Dunedinites don’t want it, that it will turn out to be a dog’s breakfast anyway and that even the few committed cyclists won’t like it either.

      It will cost a heap to maintain and even more to fix if it goes wrong and messes up the central city traffic flow. I would say ‘more money down the drain’, except that’s where the money should be going – in a constructive sense – on upgrading the water infrastructure faster so people aren’t washed out of their homes!

      • Elizabeth

        Absolutely! Was discussing this at coffee the other day. Unscrupulous sods – although there is more explicit language that fits.

      • Calvin Oaten

        Diane, your antennae are perfectly tuned to the cynicism of our ‘Great Leader’ and his acolytes. Face it, being winter and only four months away from the election what’s not to like about a small halt in proceedings?

        • Hype O'Thermia

          Winter is the wrong time to assess the popularity of cycling. Summer – lovely bike rides, cooling breeze through the helmet, virtuous perspiration joins with the rosy glow of virtue. Frost on the road, fingers blue with cold to lacking all sensation until the pain of returning blood flow when one gets indoors to the warmth.
          Winter is the time to be grumpy about slippery streets, invisible dark clad light-free cyclists appearing unlit out of increased hours of poor visibility.
          It’s not a good time for the majority to see more of their rates being spent on cycle lanes – not even if, for a change, the cycle lanes were to be intelligently planned so they worked without having to be removed (more expense of “islands” and kerb bunions built and removed and rebuilt, causing mini-dams along city blocks preventing water flowing and causing it to overflow into people’s driveways… no, this is a good time for procrastination and silence on whole cycling topic.

          Shhhh! When you have read this message please swallow your IT device.

  7. Elizabeth

    VALID Comment at ODT Online:

    Who are you going to trust?
    Submitted by tonznz on Mon, 06/06/2016 – 3:06pm.
    Who are you going to trust? A spokesperson from the DCC who has no engineering qualifications or someone who does and has many many hours reviewing the flood data.
    Hands up anyone who really believes that had the drainage network been maintained as it was intended the flood would have been as bad as the DCC maintains?
    If there are errors in Mr Johnstone’s analysis then I invite the DCC to produce the evidence. At the moment their response to his work has been arrogant and dismissive. [abridged]

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