Water worries grow amid lax flood mitigation

Otago Daily Times

01-08-2025

South Dunedin is not the only area in the city with water worries. Mary Williams talks to residents in a North Dunedin suburb facing the threat of a catastrophic flood.
In March 1929, a grid of short, flat North East Valley streets, squeezed between North Rd and the Lindsay Creek, flooded up to a metre deep and one resident picked a trout out their garden, according to The Otago Witness.
For nearly 60 years, Roy and June Robertson have lived here. At the end of their Northumberland St garden, a concrete flood protection wall drops 4m to murky waters below.
It is hard to imagine a flood topping the wall, and the Robertsons don't worry about it, but flooding is a serious risk here.
A recent Otago Regional Council (ORC) report flags that the creek's Mt Cargill source can be a "mountain torrent". A flood with major consequences is "almost certain" and one with catastrophic consequences is "likely".
The risk is higher than tolerated elsewhere in New Zealand, the report says, yet flood protection proposals have, for decades, languished in council files.
Mr and Mrs Robertson are more concerned about river health. They saw a woman upending a bag of rubbish into the creek and Mrs Robertson chased her down the street.
A water quality monitoring site a little further downstream, where the the creek loops under North Rd at the bottom of Craigleith St, has been recording levels of E.coli among the worst in the country.
About 300m further downstream, the Dunedin City Council (DCC) has been adding to the pollutants — with ORC permission. DCC is allowed to discharge untreated wastewater, including the valley's sewage, into the Lindsay when the ageing pipe system overflows.
"That's shocking — disgraceful," Mr Robertson says.
It's one of six city locations where the council has been allowed to do it for eight years but increasing failure of council monitoring equipment has made it impossible to know how much pollution has been caused.
One thing is certain here: the 1929 flood was deemed a once-in-a-hundred-years event. It's about time for a repeat and the water will not be clean.
Serious flood risk
There are many water calamities that have happened, and could happen, across the city, most obviously in South Dunedin where the regional and city councils are engaging the community about flood risk due to rising sea levels.
Overflowing wastewater cannot be missed here; it travels in old pipes from the Kaikorai Valley then pours on to Surrey St sometimes — where an overflow pipe routed to the harbour fails to catch it all.
A resident-led action group is fighting to stop the outrage.
In Mosgiel, residents found they were living on an engineered spillway and banded together to fight for their property rights and for the Silver Stream to be dredged to give it more capacity.
The dredging has been promised.
However, in North East Valley, often called NEV, residents spoken to by the Otago Daily Times seemed variably worried and in the dark. Anna Samuel, who has three young children, says she moved into her Felix St home because she was told it would flood once in a hundred years and that didn't sound too bad, but after moving in she had water lapping at her steps.
"I now worry every time we get a rain warning. I would love to know there is a plan."
Jenny Wagner-Gorton, biodiversity co-ordinator at NEV's community organisation The Valley Project, said her group was organising an event about flood risk but would support council-led engagement that gave people "information needed ... everyone should have a basic expectation of a safe home".
The information is serious. The recent ORC report says that, in a rain storm, the creek's steep, upper reaches can suffer bank erosion, causing debris in the water. As the stream travels, and becomes confined by buildings, the debris — including any from landslips on the true right of the stream — can cause blockages and then flooding.
There is a pinch point, between Watts Rd and Felix St, where the old Palmers Quarry slopes to the creek and there is a capacity flow of about 30cum per second. The ORC estimates that this flow has a 79% probability of happening in a 10-year period and a 95% probability in a 20-year period.
Once exceeded, the stream will overtop its left bank and, depending on volume, inundate the small valley floor from Felix St to Allen St, possibly within two hours of rain starting.
The speed of a flood, combined with water depth and velocity, makes an emergency response plan challenging, the report says, creating "unsafe" conditions for people and rescue vehicles.
Planning and replanning
Work to prevent flooding in NEV has been limited and bank protection is controlled by various owners, including the DCC and private landowners.
In the 1970s, there was a plan to build concrete walls on either side of the creek between Selwyn St and Allen St. The wall on the true left was built, including the section at the end of the Robertsons' garden, but the wall on the right was not.
Decades passed. Then, between 2005 and 2011, the ORC developed a "concept design" for a $21.4m flood mitigation scheme for the Lindsay and the Leith. Various methods would be used, including raised banks and walls, and wider and deeper channels, and land was needed, which brings the story back to the Robertsons.
They have kept letters, sent by the ORC from 2005, indicating that their garden could be required and previous flood mitigation plans would not protect them. Their land was valued and while other land was bought by ORC, the Robertsons did not sell.
They say that living on a flood plain — previously an area of market gardens — means they can grow vegetables and they were loathe to relinquish land that delivered great garlic.
By 2011, the Leith flood protection was under way but the Lindsay work deferred. Cost and community opinion were cited.
In 2013, a cheaper proposal, deemed less effective, was tabled. Flood water would be held upstream in a storage area, to be built in Chingford Park. The plan was also rejected for funding reasons.
Meanwhile, there has been patchy flooding and sandbag handouts, residents say, and the big one has got close. Since recording started in 1979, the stream reached its capacity in summer 1991, autumn 2006, and winter 2015.
Roll on to 2025, and there is a new, stretched out, plan for flood mitigation.
ORC's Infrastructure Strategy says options will be identified by 2027 with implementation of a $60m plan from 2028. Less than 6% of this — $3.5m — is allocated to be spent by 2035 with a promise to spend the rest after that and by 2054.
That is half a century after ORC started proposing solutions to the Robertsons and not the only council water headache in NEV.
Six overflow locations
The DCC's overflows of untreated wastewater into the Lindsay happens at a spot near Dunedin North Intermediate School (DNI) and is one of six locations where Dunedin City Council holds ORC consents to do this; three into streams and three into the harbour.
The other stream locations are along Kaikorai Stream: at Kaikorai Common, where locals love to stroll; and just above Kaikorai Valley College (KVC), known for its students' studies of the stream's limited ecology.
The harbour locations are at the mouth of the Waters of Leith near the yacht club and at Sawyers Bay. The DCC has said it informs shellfish company Southern Clams when wastewater is being discharged "so harvesting can cease".
The DCC also discharges overflowing untreated wastewater from the Portobello Rd pump station in South Dunedin.
Excepting the Portobello Rd consent, the other five consents were issued for the first time in January 2017, variably expiring in the 2030s and 2040s, requiring DCC to record and report overflow data and requiring an overflow stakeholders' meeting at a remarkably infrequent rate; once every five years.
An inaugural meeting, regarding the five consents, happened on November 16, 2021, only two months before DCC's deadline to hold it.
It is a perplexing fact that all five consents require KVC to be a stakeholder. None mention DNI. Neither school attended the 2021 meeting and it is unclear if they were invited.
KVC's science teacher Dr Simon McMillan said the college has been warned by the DCC about some overflow events but expressed surprise at being a stakeholder in overflow consents across the city. He thought the role was possibly "sleeping".
DNI's principal Heidi Hayward said the consents and their requirements were news to her.
Data difficulties
The 2021 meeting's minutes reveal that the DCC explained the problem but gave little data.
Overflows happen because rainwater infiltrates older wastewater pipes. The Kaikorai overflow aimed to "mitigate against wastewater flooding downstream".
As Surrey St residents in South Dunedin can attest, that still happens four years on.
The council also said it had been monitoring overflows since 2012 and overflows into the Lindsay Creek and Kaikorai Stream happened "more frequently" than at other locations which overflowed "around twice a year". No overflow frequency or volumes were provided.
The council then flagged that there were "often" monitoring failures due to ageing data loggers.
The ODT asked the DCC for more recent data about overflows. DCC's Three Waters group manager John McAndrew said the council couldn't answer by deadline.
The ODT then asked the ORC, which handed over data for a two-year period, ending July 2024. The DCC had reported 52 overflows across the five consented locations, releasing about 40,000cum of wastewater.
More than half, 30, were into Kaikorai Stream at the location near KVC and 13 went into the Lindsay. The worst overflows were at these locations, each more than 7000cum in a day.
ORC general manager for environmental delivery Joanna Gilroy said any overflow "can pose human health risks due to the presence of bacteria, viruses and other pathogens" and life in the river could also be lost.
The ODT circled back to the DCC, which then handed over a report listing 13 overflows in the year ending July 2024, releasing 3246cum of wastewater.
However, it explained there were now massive data gaps — due to the "deteriorated" loggers.
Data for overflows into the Lindsay Creek and at Kaikorai Common was lost or unreliable for most of the year and replacement loggers were planned.
DCC's Mr McAndrew said there was also "extensive" pipe renewal happening in North East Valley and Kaikorai Valley as part of the nine-year plan to spend $180m on wastewater network renewals, which should reduce overflows.
A DCC web page about overflows had been updated.
The page — if you know to look for it — talks about overflowing wastewater being "highly diluted" by stormwater and the waterways, and released in largely "inaccessible" locations.
It also links to a decade-old consultancy report that concludes, in desultory terms, that there is a "paucity of data" about overflow pollution but 'no doubt" that water suffers. Generally, the ecological value of Dunedin's waterways is "not particularly high".
Otago Fish & Game communications officer Bruce Quirey said there are still trout — University of Otago surveys show about 70 — in the Lindsay Creek's upper reaches at Bethunes Gully. It is an important spawning area.
Lower down, around Chingford Park, numbers are halved and, further down, where a man once found a trout in his garden, Mr Robertson says he doesn't see them.
Mr Quirey says an improved habitat would mean more fish. It "shouldn't come as a surprise" that the further streams flow through the city, and the more manipulated they are, the less healthy they are.
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