Tag Archives: DCC Infrastructure Services

Johnstone on ORC report : ‘The Natural Hazards of South Dunedin’ (July 2016)

The Natural Hazards of South Dunedin – July 2016 [read online]
Otago Regional Council
ISBN: 978-0-908324-35-4
Report writers:
Michael Goldsmith, ORC Natural Hazards Manager
Sharon Hornblow, ORC Natural Hazards Analyst
Reviewed by: Gavin Palmer, ORC Director Engineering, Hazards and Science
External review by: David Barrell, Simon Cox, GNS Science, Dunedin

Received from Neil Johnstone
Sun, 29 Aug 2016 at 8:17 p.m.

Message: Misinformation on the causes of the June 2015 South Dunedin flood have abounded since the event. As if the victimised residents haven’t suffered enough from others’ inactions (before and during the event), they are now being subjected to a hazards discovery process whose vigour appears to be exceeded only by its own recklessness. Following are a commentary of the hazards approach adopted by the Otago Regional Council (ORC), and a summary of my investigations into the flood event that I commenced after the publication of Dunedin City Council’s first flood report back in November 2015.

You can download Neil Johnstone’s report or read it below (formatted slightly differently to suit the WordPress template).




1. Introduction

There is some irony that DCC and ORC should be planning “drop in” sessions for residents in respect of South Dunedin hazard issues during September 2016, some 15 months after the major flood. The prime cause of flooding in June 2015 was DCC’s failure to maintain its infrastructure (not just mudtanks), and its failure to operate its pump stations to their intended capacities. The subsequent spread of misconceptions (i.e. groundwater levels, rainfall significance etc) surrounding the flood causes was at least partly due to inaccurate ORC analyses and reporting.

Repetitive and new doubtful information emanating from ORC via its latest report has been noted. Presentations and an over-simplistic video production have been observed. A footnote covering these observations is included at the end of this appraisal.

Long-delayed DCC reports on causes of the South Dunedin flooding have already been strongly criticised by the author. Specifically discredited are misrepresentations of sea level, groundwater and rainfall ranking. Accepted now by DCC as factors (somewhat grudgingly, and depending on the audience) are mudtank blockage and Portobello Road pump station failures (plural); still to be fully acknowledged are the failures at Musselburgh Pumping Station.

Attention is now turned to significant parts of hazard reports produced by the Otago Regional Council and utilised by DCC.

2. Coastal Otago Flood Event 3 June 2015 (ORC, published October 2015)

This report deals with a wider area than South Dunedin. It is apparent that ORC staff never visited the flooding areas of South Dunedin on 3 June, but took advantage of fine weather to take some water level readings the following day. The opportunity for useful progressive surface water level recording was thus lost. Levels were collected at some 150 points on 4 June. ORC’s main conclusion was that “localised variations in topography were probably the main driver of flood depth”. Or, put another way, water depth was deepest where the ground was lowest. This seems hardly surprising, and even trivial. No attempt was made to explain the photographic images presented of extensive ponding remaining well after the rains had ceased. The phenomena of blocked mudtanks and unutilised pumping capacity went seemingly unnoticed.

The report does usefully reference ORC’s four borehole recorders of groundwater, but makes the somewhat misleading assessment that groundwater levels were “elevated” prior to the rainstorm. This misinformation was seized upon by agencies such as DCC and the Office of the Parliamentary Commissioner for the Environment to highlight climate change impacts.

Having obtained the actual groundwater level data from ORC via the LGOIMA process, the author was able to reveal this “groundwater fallacy” in reviews from February 2016, but it was not until the publication of NZ Listener’s article (June 11-17, 2016) entitled ‘FLOOD FIASCO’ that ORC admitted that pre-flood groundwater levels were in fact “just a little bit above average”. ORC now seems intent on resurrecting this fallacy.

The ORC report fails to address the real and key issues of pumping station failures (Portobello Road and Musselburgh), or comparisons with much lesser flood impacts in the larger rainfall event of March 8/9 1968.

The report states that the 2015 24-hour rainfall was the largest since 1923. This was patently incorrect, but again was utilised by DCC to divert blame from their role in the disaster.

3. The Natural Hazards of South Dunedin (ORC, published July 2016)

The report states unambiguously in its Opening Summary that the major flooding of June 2015 was “a result of heavy rainfall, surface runoff, and a corresponding rise in groundwater”. By now, most people are aware that the causes of the flooding’s disastrous impact were failure to optimally operate pumping stations, failure to clear mudtanks, and failure to deploy staff to key areas during the event. Again, none of these factors is addressed in ORC’s report.

The report presents a table on its second page entitled “Factors Which Can Influence Flood Hazard”. Examples of exaggerated negativity include:

1. Heavy Rainfall:
– Many recorded instances of rainfall leading to surface flooding.
– Heavy rainfall events have occurred frequently over the last decade.

Comment: These conclusions do not appear to be supported by the report’s text, and are vague, factually challengeable and alarmist. Prior to 2015, no major flooding had occurred in South Dunedin since 1968, and even that was minor by comparison.

2. Sea Level:
– Groundwater level fluctuates (by up to 0.5m near the coast) on a twice-daily cycle in response to normal ocean tides.

Comment: All of South Dunedin is near the coast; most of the area does not experience such large fluctuations. This should have been made clear by the inclusion of groundwater data from all 4 ORC sites across the plain, not just from Kennedy Street.

3. Seismic:
– Large earthquakes could result in increased flood hazard on the South Dunedin plain, due to liquefaction-related land subsidence or direct, sudden, changes in land elevation relative to sea level.

Comment: All areas of NZ have some susceptibility to earthquake damage. Dunedin is amongst the areas at lowest risk; no incidences of even minor liquefaction have ever been reported in South Dunedin, and little or no clearly liquefiable materials have been identified (Refer GNS, 2014*). Continue reading


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

South Dunedin stormwater pipes —getting past the desktop ICMP

Dunedin City Council (website) on Stormwater:

Stormwater is rain or snow runoff that does not soak into the soil.
When an area is developed, stormwater generally increases due to runoff from impermeable surfaces (eg roofs, roads, carparks, or compacted soil). It flows naturally from higher to lower ground, and ultimately discharges into natural watercourses such as wetlands, creeks, rivers or the sea. Land development results in the creation of both private and public stormwater systems, which collect and transfer stormwater to lower ground more efficiently. The public stormwater system is a network of drains, gutters, pipes, mud tanks, detention ponds, stormwater reserves and other associated infrastructure.

At other threads (here and here), contributor JimmyJones has cited the South Dunedin Integrated Catchment Management Plan (ICMP) to draw attention to the actual or perceived state of the stormwater pipes at South Dunedin. He believes the type of pipeways and the deteriorating condition of the pipes contributed to the June 2015 South Dunedin “flood event”, and will require budgeted upgrade.

But is the South Dunedin ICMP correct about the underground pipes and their condition?

Largely, the ICMP was a desktop assessment carried out by consultants for the Dunedin 3 Waters Strategy. Namely, Opus International Consultants and URS New Zealand (now trading as Aecom) in association with Dunedin City Council.

South Dunedin ICMP – Integrated Catchment Management Plan
Sth Dunedin ICMP (PDF, 11.1 MB)
Sth Dunedin Mapbook (PDF, 12.0 MB)

Read more about the 11 ICMPs for Dunedin here.

DCC says ICMPs are used for planning and management of the stormwater system. For each stormwater management area, or catchment, issues are identified and prioritised, and solutions are identified and implemented. The ICMPs are mainly in the metropolitan Dunedin area (including Mosgiel and Port Chalmers). They inform investigation and planning decisions and help focus council priorities for future operational and capital works. Implementing the ICMPs is also a key requirement of DCC consents to discharge stormwater into the coastal marine area. Further information is available on the Stormwater monitoring page, see also the Stormwater responsibilities page.

The Pipes at South Dunedin
Local water and drainage experts familiar with the stormwater system say:

Sat, 18 Jun 2016 at 10:52 a.m.

The South Dunedin ICMP report has been read, it’s “ok”. But it’s also described as “…glossy and costly for the consultant(s). Basically, such reports tell the Council stuff they neither read nor understand, but would have mostly been trivial knowledge (where accurate)” to local experts familiar with the design and day-to-day workings of the stormwater system.

“You can believe any part of [the ICMP] or not. It’s a desktop study, which speculates on pipe condition. Robinson and Hendry have read it and obviously don’t agree. Pipes last for an eternity with limited maintenance (other than blockage removal) provided there isn’t ground movement or corrosion (these pipes are concrete).”

Listener, June 11-17 2016, pp22-29 (not yet available online):

[excerpt —click to enlarge]
Listener11-17 Jun 2016 pp26-27_0003

ODT 13.2.16
“Mr Hendry believed South Dunedin’s infrastructure, which he spent six years helping build as a surveyor in the 1960s, would have been good enough to prevent much of the damage had it been properly maintained. […] My view is that these people out here, a lot of them have got nothing. Now they have got a hell of lot less. It’s not fair on them. Nobody’s come out and said ‘we were wrong. Something wasn’t done right’.”

█ Come to the Public Meeting in South Dunedin on Monday evening, hosted by the South Dunedin Action Group.

Related Posts and Comments:
17.6.16 So we’re going to play it this way #SouthDunedinFlood
● 16.6.16 Public Meeting: South Dunedin Action Group #AllWelcome
10.6.16 “Civic administration” reacts to hard hitting Listener article
● 6.6.16 Listener June 11-17 2016 : Revisiting distress and mismanagement
● 4.6.16 Johnstone review … DCC Infrastructure Services meeting 26.4.16
3.6.16 DCC —godsakes, how did it get to this? #flood #property damage
● 19.5.16 Johnstone review of 2nd DCC report #SouthDunedinFlood
29.4.16 Vandervis emails batch 2 #Dunedin #infrastructure #flood #mudtanks
27.4.16 Vandervis emails batch 1 #Dunedin #infrastructure #flood #mudtanks
27.4.16 DCC meeting and apology NOT Enough— #SouthDunedinFlood
20.4.16 DCC Politics : Release of Infrastructure Report #SouthDunedinFlood
14.4.16 South Dunedin flood risk boosters #ClimateChangeCrap #PissOffPCE
31.3.16 DCC: Infrastructure report 2 pending —Mudtanks & stormwater…
● 8.3.16 Johnstone independent review of DCC report #SouthDunedinFlood
2.3.16 DCC compels extensions on LGOIMA requests #SouthDunedinFlood
26.2.16 Mudtanks and drains + Notice of Public Meeting #SouthDunedinFlood
21.2.16 DCC infrastructure … report (30.11.15) subject to ‘internal review’ only
● 13.2.16 South Dunedin Flood (3 June 2015): Bruce Hendry via ODT
4.2.16 2GP commissioner appears to tell Council outcome… #hazardzones
4.2.16 Level responses to Dunedin mayor’s hippo soup #Jun2015flood
30.1.16 DCC Rates: LOCAL CONTEXT not Stats —Delta and Hippopotamuses
● 25.1.16 DCC: South Dunedin Integrated Catchment Management Plan (ICMP)
19.1.16 Listener 23.1.16 (letter): South Dunedin #Jun2015flood
16.1.16 NZ Listener 16.1.16 (letter): South Dunedin #Jun2015flood
14.1.16 ‘Quaking!’ Dark day$ and tide$ to come #Dunedin #Jun2015flood
10.1.16 Infrastructure ‘open to facile misinterpretation’…. or local ignore
5.1.16 Hammered from all sides #fixit [dunedinflood Jun2015]
24.12.15 Site notice: posts removed
● 3.11.15 South Dunedin Flood | Correspondence & Debriefing Notes released by DCC today #LGOIMA

Kerr, Elizabeth LGOIMA Correspondence Hendry and Williams 2015
Kerr, Elizabeth LGOIMA Flood Debrief Notes 2015

█ For more, enter the terms *flood*, *sea level rise*, *stormwater*, *hazard*, *johnstone*, *hendry*, *south dunedin action group*, *debriefing notes* or *listener* in the search box at right.

Posted by Elizabeth Kerr

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


Filed under Business, Climate change, Construction, Democracy, Design, District Plan, Dunedin, Economics, Education, Events, Finance, Geography, Health, Heritage, Housing, Infrastructure, Media, Name, New Zealand, Ombudsman, People, Pet projects, Politics, Project management, Property, Proposed 2GP, Public interest, Resource management, Site, South Dunedin, Town planning, Transportation, Travesty, Urban design, What stadium

So we’re going to play it this way #SouthDunedinFlood

ODT 17.6.16 (page 10) —[click to enlarge]

ODT 17.6.16 Letter to editor Johnstone p10


1. The claim of “factual errors” is surely able to be substantiated or thrown out by a suitably qualified (named) EXTERNAL peer reviewer acceptable to DCC and engineer Neil Johnstone. The ‘matter of degree’ (serious ?) is a matter for the peer reviewer to comment on. As are issues of professional competencies —which only an independent and transparent peer reviewer with nationally recognised engineering expertise can deal to. Not an in-house operational.

2. Neil Johnstone has issued three reviews, two of these deal to DCC’s formal reports on the June 2015 South Dunedin “flood event”, dated 30 Nov 2015 and 26 Apr 2016 respectively; and the third deals to comments (video recorded by Ch39 and published at DCC’s Youtube channel) during the DCC Infrastructure Services Committee meeting held on 26 April 2016. The reviews are published at this website – enter the term *johnstone* in the search box at right.

3. Neil Johnstone has requested that factual errors noted by DCC be made discoverable. DCC appears to be side-stepping qualification and quantification of its verbal assertions every which way.

4. It is highly likely that no expert external peer reviews exist or they would have been made public by now. More than a year after the “flood event”, we wait.

5. A peer review(s) is not something to hide. Why is DCC doing secret squirrel when challenged to substantiate its earlier comments (publicly stated on more than one occasion, recorded by mainstream media – for example, by Mayor Cull and Transportation’s Ian McCabe, who later resigned) – that external peer reviews of its formal reports did happen. After the fact is a little squiffy, if DCC is writing them now.

“Technical qualifications and experience with stormwater infrastructure design and management” are not provided. Rhetorical.

Holes being dug, an epitaph.

█ For related posts and comments, enter the terms *flood*, *sea level rise*, *stormwater*, *hazard*, *johnstone*, *hendry*, *south dunedin action group*, *debriefing notes* or *listener* in the search box at right.

Posted by Elizabeth Kerr

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


Filed under Business, Climate change, Construction, Democracy, Design, District Plan, Dunedin, Economics, Events, Finance, Geography, Heritage, Hot air, Housing, Infrastructure, Media, Name, New Zealand, Ombudsman, ORC, People, Pet projects, Politics, Project management, Property, Proposed 2GP, Public interest, Resource management, Site, South Dunedin, Town planning, Transportation, Travesty, Urban design, What stadium

Public Meeting: South Dunedin Action Group #AllWelcome

SDAG Meeting Notice 20 Jun 2016 Nations Church 6pm[click to enlarge]

Date: Monday, 20 June 2016
Venue: Nations Church, 334 King Edward St, South Dunedin
Time: 6:00pm (1800 hours)

Facebook: South Dunedin Action Group

Message to Mayor David Cull

M E M O R Y • P R O B L E M S • C A N • H A P P E N • A T • A N Y • A G E
keep managed retreat and climate change out of local body politics

ODT 16.6.16 (page 12) —[click to enlarge]

ODT 16.6.16 Letters to editor Stedman Oaten p12

█ For related posts and comments, enter the terms *flood*, *sea level rise*, *stormwater*, *hazard*, *johnstone*, *hendry*, *south dunedin action group*, *debriefing notes* or *listener* in the search box at right.

Posted by Elizabeth Kerr

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


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

Listener June 11-17 2016 : Revisiting distress and mismanagement #SouthDunedinFlood

Listener 11-17 Jun 2016 p22 [20160606_154423] 3

Get the latest issue of New Zealand Listener (pp 22-29), more soon….

█ For related posts and comments, enter the terms *flood*, *sea level rise*, *stormwater*, *hazard*, *johnstone*, *hendry*, *south dunedin action group*, *debriefing notes* or *listener* in the search box at right.

Posted by Elizabeth Kerr

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

*Image: phoneshot at a diner by whatifdunedin [click to enlarge]


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

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

Mayor Cull won’t admit lack of maintenance #SouthDunedinFlood

Dave famous last words 1a

Mayor calls on government for help
39 Dunedin Television 20.11.15
A rising issue for seaside suburbs, a new report shows Dunedin is most at risk of suffering the negative effects of rising sea levels due to climate change. South Dunedin residents in particular are likely to experience flooding from rising ground water. Ch39 Link

Preparing New Zealand for rising seas: Certainty and Uncertainty
A report by the Parliamentary Commissioner for the Environment shows Dunedin is one of the most vulnerable areas in the country.

Related Posts and Comments:
● 3.11.15 South Dunedin Flood | Correspondence… released by DCC #LGOIMA
27.10.15 DCC: South Dunedin flood | higher learning for chief executive
16.8.15 June flood: Dunedin drop-in centre open 27 August
11.8.15 DCC’s unmanaged retreat for South Dunedin
22.7.15 DCC Long Term Plan 2015/16 – 2024/25
18.7.15 DCC Cycleways: SEEING RED, apology NOT accepted
14.7.15 DCC strategies needed like a hole in the head
12.6.15 Fairfax: DCC has no insurance cover for flood-damaged roads
● 5.6.15 WEATHER is not climate change; this is not the 100-year flood
4.6.15 Exchange makeover —or pumps and pipe renewals, um
3.6.15 Civil Defence response to Dunedin FLOODING
10.4.15 DCC: Natural Hazards
28.3.15 DCC Draft Long Term Plan 2015/16 to 2024/25 —Consultation Open
14.10.14 ORC: New strategic plan fosters Otago prosperity
12.9.14 ORC: City bus services, submissions
10.12.13 ORC restructures directorates
18.10.13 DCC: Final vote tally + St Clair boat ramp
18.8.13 South Dunedin and other low lying areas
26.2.13 DCC binge spending alert: Proposed South Dunedin cycle network
30.7.12 ORC on hazard risks and land use controls
7.6.12 Dunedin stormwater: more differences between ORC and DCC
25.11.11 South Dunedin and other flood zones

Posted by Elizabeth Kerr


Filed under Architecture, Business, Construction, Cycle network, DCC, Democracy, Design, Dunedin, Economics, Events, Geography, Heritage, Hot air, LGNZ, Media, Name, New Zealand, NZTA, OAG, Ombudsman, People, Politics, Project management, Property, Site, Tourism, Town planning, Transportation, Urban design, What stadium