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.

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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.

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

Received.
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).”

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

[excerpt —click to enlarge]

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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.

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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

Downloads:
● 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.

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Posted by Elizabeth Kerr

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

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

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

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whatifdunedin:

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.

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Posted by Elizabeth Kerr

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

Public Meeting: South Dunedin Action Group #AllWelcome

[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
https://www.facebook.com/SouthDunedinActionGroup/

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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]

█ 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.

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Posted by Elizabeth Kerr

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

“Civic administration” reacts to hard hitting Listener article

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

S o u t h • D u n e d i n • F l o o d

Truth and decency are owed to the flood affected people of South Dunedin.

Interpretations post flood and in the months since —appear without technical evidence, making false claim to Climate Change (the ‘end is nigh’ if only to avoid local government liability), in contradiction to data and analysis provided by local engineers, ORC, MetService and former council staff, amongst others.

6 June 2016
[post] Listener June 11-17 2016 : Revisiting distress and mismanagement #SouthDunedinFlood

‘Our leader’ is in a self-flagellating hole —prepared to say anything to attract votes in the October local body elections. Serious ? Genuine ?

We owe it to ourselves.
The Mayor of Dunedin should not get a third term.

‘Leadership’ has involved neglect of core council business – specifically, maintenance of key infrastructure network and services.

This has done too much damage: tens of millions of dollars of damage at South Dunedin. A massive hit sustained by constituents and insurers. Yet today ‘the administration’ rattles and unsettles the community it has comprehensively failed, with latest wanton burble at the opinion pages of the Otago Daily Times.

The Mayor should immediately resign his office at Dunedin City Council.

Bullshit from the Mayor and underlings is UNACCEPTABLE.
South Dunedin has a stormwater system that when properly maintained is well able to take rainstorms equivalent to that experienced a year ago.

Systems can always be improved but the current stormwater system is not all that old and has been designed with sufficient control mechanisms and stopgaps.

The Administration failed (for years) to deliver on budget, contracts, drain and mudtank maintenance; failed to check pump performance and screens at pumping stations during the June 2015 storm event; as staffing changed, failed to set in place procedures for weather events; failed to understand Civil Defence requirements for the most densely settled suburb of Dunedin; failed to adequately consider storm run-off from surrounding hill areas and the increase of impermeable surfaces as The Flat developed; failed to release stormwater to the ocean, etc etc……. but ultimately FAILED to put proper thought and planning to AVOIDANCE of Endangerment to the lives, health and livelihoods of thousands of South Dunedin residents.

Seriously. That’s the sort of ‘care and concern’ the gold-chained opinion-writer represents at ODT today. Further, there are Absolutely No Grounds to grease up the loophole backside of the technically inexpert Parliamentary Commissioner for the Environment.

The Listener article raises the issue of “mismanagement” during the rains of early June 2015. The liability rests at council doors.
That is a hammering public fact.

█ 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.

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Posted by Elizabeth Kerr

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

R E S O N A T E S
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.
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Posted by Elizabeth Kerr

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

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

Johnstone review following DCC Infrastructure Services meeting 26.4.16 #SouthDunedinFlood

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

B A C K G R O U N D
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]

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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

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WEBSITE DISCLAIMER
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]

SOUTH DUNEDIN FLOODING JUNE 2015
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.

1. THE FLOOD EVENT OF MARCH 8/9 1968
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.

2. PRE-EXISTING GROUNDWATER LEVELS
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.

3. RAINFALL SIGNIFICANCE
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.

4. LANDUSE CHANGES
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.

5. MUDTANK BLOCKAGE
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.

6. PORTOBELLO ROAD PUMPING STATION
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.

7. MUSSELBURGH PUMPING STATION
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.

8. INFRASTRUCTURE DESIGN LIMITATIONS
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.

9. EXTERNAL PEER REVIEW
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.

10. INFRASTRUCTURE SERVICES COMMITTEE MEETING
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

[ends]

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

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Posted by Elizabeth Kerr

Johnstone review of 2nd DCC report #SouthDunedinFlood

Updated post
Sat, 4 Jun 2016 at 4:11 p.m.

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DCC publications:

● 30 Nov 2015 (McElhone)
Infrastructure Performance During June 2015 Flood Event | Meeting Video

● 20 Apr 2016 (Media Release)
Report on South Dunedin infrastructure performance during June 2015 flood released

● 26 Apr 2016 Agenda (and reports) Infrastructure Services Committee
Item 5 (Stokes, pp 6-27) South Dunedin Public Infrastructure Performance during June 2015 Flood Event Follow up | Meeting Video

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WEBSITE DISCLAIMER
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.

Received: 18 May 2016 [full text]

An Independent Review of DCC Report : ‘South Dunedin Public Infrastructure Performance during June 2015 Flood Event Follow up’

By N. P. Johnstone, MIPENZ

1. This review complements my peer review of DCC’s first flood report, published in November 2015. This review assesses the content of the second report (described henceforth as “the report”) published in late April 2016, and contextual statements made elsewhere by DCC staff and elected members. The author of the report is Ms R. Stokes. The technical qualifications and relevant experience of the report’s author are not stated.

2. I consider that there is a need for such a review for reasons of historical accuracy and context, the identification of solutions (which can only be achieved be if the problem is understood and acknowledged) and – most importantly – to provide a considered assessment of what South Dunedin’s current flood risk really is, noting that two events (of which only the recent one caused major inundation) in five decades does not suggest a current flood risk much different from that existing in many other established New Zealand communities, despite some landuse changes. It is emphasised that the flood had nothing to do with climate change, nor therefore does this review. The failure to understand the issues may lead to inaction or to inappropriate and expensive actions.

3. This review may be criticised for being repetitive on some issues, but the repetition is at least partly driven by the number of times challengeable information on the flood event and its causes has been circulated by DCC. In many respects, the report under review could be seen as a concentration of such challengeable information. The report is solely based on my research, knowledge and experience; any errors are therefore mine, but hopefully, few.

4. This review has led to the following conclusions:
4.1 Council’s continued insistence that the June 2015 rainfall event was the largest since 1923 remains erroneous;
4.2 Pre-existing groundwater levels were unexceptional, and had no impact on the flooding, contrary to claims made in the report, previously and subsequently;
4.3 South Dunedin does not have a significant imminent exposure to stormwater flooding. This finding is based on the original design parameters, historical performance, an absence of groundwater issues, and provided existing infrastructure is properly maintained, monitored and operated;
4.4 Problems at the Portobello Road Pumping Station caused elevated flood levels and prolonged the period of inundation, but the report acknowledges only the latter;
4.5 Similarly, the now-admitted failures to ensure that mudtanks were properly maintained impacted adversely on flood levels attained in some locations at least, and prolonged the period of inundation in many areas;
4.6 Comparisons with the 1968 flood event can be instructive in assessing the impact of Council failures in 2015 in terms of water level, disruption and cost. The report fails to make such assessments.

5. My review of the first report, written by Ms L. McElhone, was driven by DCC claims that the prime causes of the flood were high sea and ground water levels, a 150-year, then a 100-year, then a 63-year (and incidentally and extraordinarily now again a 100-year*) rainfall event, and confirmed that Portobello Road pumping station issues added not less than 200mm to peak flood levels. That review also demonstrated that the rainfall event of March 1968 was demonstrably larger than that of June 2015, but caused much less damage, and that land use changes added up to 150mm to flood levels (based on DCC’s unconfirmed data on impermeable areas). Any consented landuse changes should, in my opinion, have been compensated for in past years with additional infrastructure to maintain drainage standards and South Dunedin’s protection standards.
(*Ms Stokes to John Campbell on Checkpoint, 21 April 2016).

6. Exaggerated assessments of both the historical significance of the 2015 rainfalls and groundwater levels, and the absence of mudtank information originally helped DCC promote its position of zero liability. The mudtank maintenance failures are at last largely revealed in the new report; significant mudtank maintenance issues were previously reported by Cr Lee Vandervis as early as 2014, but were seemingly largely ignored by DCC. Paragraph 37 of the report which reads: “Mudtank maintenance and performance in general has been the subject of focus for a number of years”, appears vague, and therefore requires elaboration. The statement, if accurate makes the failures more disturbing. There is still some unfortunate reliance on the groundwater myth (paragraphs 2 & 32), and to the underestimation of the 1968 event (paragraph 20). There appear to be newly-entrenched positions at DCC that the existing stormwater system is inadequate, presumably based on the report’s paragraphs 23-27, and reinforced in recent public statements from Ms Stokes and Mayor Cull, that the flood would have occurred (or that a serious flood would have occurred) even if the current system including the mudtanks had operated at optimum. This review strongly disputes such claims, and uses the well-documented event of March 1968 as a very useful “model” for key comparisons between a contained flood (1968) and a disaster (2015).

7. The general understanding was that DCC’s second review was to concentrate in detail on the performance of mudtanks, and was to be peer reviewed. Detailed reporting and peer review processes were understood to be the reason for the extraordinary delays in publication. In reality, only paragraphs 33-61 deal with mudtanks issues and no peer review is included. It is noted that Mayor Cull confirmed to John Campbell on Radio NZ’s Checkpoint programme (22 April 2016) that peer reviews of the report had been produced. The peer review(s) could usefully have been attached to the report; failing that, the report’s author should have explained their absence.