Simon Collins is the Herald’s education reporter.

Dirty water: Sewage overflows blight Auckland beaches 'every time it rains'

Experts warn we shouldn’t swim at any beach in the Auckland region after heavy rain. Simon Collins finds out why.

St Mary's Bay, a tiny sandy beach tucked in between the motorway and the Westhaven marina at the entrance to Auckland from the harbour bridge, has been reborn since a new boardwalk across the bay opened two years ago.

Kayakers and waka ama teams paddle in the bay. Children learn about water safety. Joggers, cyclists and tourists pound the boardwalk.

Three young Swedish tourists were down there on Wednesday, the day after arriving in New Zealand.

"We just walked down here," said Erik Strand, 21. "It looks nice to be close to the water, we wanted to take a swim. But we were not allowed."

Three young Swedish tourists went to the boardwalk at St Mary's Bay looking for a place to swim, but it is not allowed. Photo / Dean Purcell
Three young Swedish tourists went to the boardwalk at St Mary's Bay looking for a place to swim, but it is not allowed. Photo / Dean Purcell

Ladders hanging off a lower-level boardwalk at the city end of the bay, made for climbing in and out of the water, have small signs saying no swimming and no diving.

Look back landwards and you can see one reason why. A stormwater pipe discharges here - and in this part of Auckland there are no separate stormwater pipes. Rainwater simply flows into the sewers, and whenever we get more than 5mm of rain the sewers overflow and flush raw sewage into local streams or straight into the harbour.

Look landward from the new boardwalk at St Mary's Bay and you can see why swimming is banned. Photo / Dean Purcell
Look landward from the new boardwalk at St Mary's Bay and you can see why swimming is banned. Photo / Dean Purcell

Watercare says 16,000 households still rely on the old combined stormwater/sewer pipes, mainly in Auckland's inner-western suburbs from St Mary's Bay to Waterview but also in parts of Blockhouse Bay, Sandringham, Three Kings, Newmarket, Parnell, Remuera and Orakei (shown in pink on the map).

St Mary's Bay is one of 41 places, shown on the map from Blockhouse Bay around to Tamaki, where stormwater and raw sewage spills from these pipes at least 12 times a year in annual volumes of at least 10,000 cubic metres - equivalent to four Olympic swimming pools.

Most of these are among 50 places that spill more than 52 times a year - "most of which now spill every time it rains", as Watercare chief executive Raveen Jaduram said in an email to Auckland councillor Mike Lee last year.

At 65 Kelmarna Ave, which drains into Coxs Bay, the sewer overflowed 62 times in the year to last June.

An outfall at 65 Kelmarna Ave, which drains to Coxs Bay (above), overflowed 62 times in the year to June. Photo / Dean Purcell
An outfall at 65 Kelmarna Ave, which drains to Coxs Bay (above), overflowed 62 times in the year to June. Photo / Dean Purcell

In the Sandringham/St Lukes area draining to Meola Creek which enters the harbour at Western Springs, a 2012 study found overflow points at Haverstock Rd and Lyon Ave spilled more than 100 times a year "in the order of 1 million cubic metres" a year - three times the 300,000 cubic metres of wastewater treated across the Auckland region each day.

"During wet weather events of any size, there is currently a risk that substantial volumes and high concentrations of bacteria, as well as viruses, enter the receiving environment," the study found.

Cox's Bay and Meola Reef, an old lava flow jutting 2km into the harbour near the Meola Creek mouth, are among 10 places in Auckland where swimming is now permanently "not recommended" and officials have stopped monitoring water quality.

At St Marys Bay, where the water is still monitored, faecal bacteria exceeded the maximum safe level of 140 enterococci for every 100 ml of water twice last summer, once reaching 5500 enterococci/100 ml - 39 times the safe level.

This summer, St Marys Bay has been clean so far, but there have been two unsafe readings at Judges Bay next to the Parnell Baths, reaching 4900 enterococci/100 ml on November 2.

Environmental consultant Brett Stansfield says contamination can cause gastroenteritis and respiratory problems.

"In most cases the ill effects from exposure to contaminated water are minor and short-lived," he says. "However there is the potential for more serious diseases such as hepatitis A, giardiasis, cryptosporidiosis, campylobacteriosis and salmonellosis."

Pollutants entering the harbour are carried out by the tides, diluting the problem at its source but spreading the health risk to other beaches. For this reason, Auckland Council advises people across the whole region to "avoid swimming for up to 48 hours after heavy rain".

In Mike Lee's eyes, it's "a wilfully irresponsible approach".

"On the one hand we are talking about the sparkling Waitemata, the Hauraki Marine Park, the jewel in the crown," he says. "At the same time we are promoting the pollution of the harbour with human wastes."

The problem is not new. The combined stormwater/sewer system was built for what was then a much smaller city in the early 1900s. Lee says the old Auckland City Council hiked rates in the 1990s to build separate stormwater pipes, and completed this for the central business district, but never finished the job in the inner suburbs.

Instead, when Watercare took over the region's multiple sewerage systems with the creation of the Auckland Super City in 2010, it proposed a huge 4.5m to 5m-diameter, 13km-long pipe to divert all the stormwater and sewage from Western Springs westwards and then south to the regional treatment plant at Mangere.

The Super City's first 10-year plan in 2012 earmarked $797 million to complete the pipe by the end of that plan in 2022.

By the time of the second long-term plan in 2015 the cost of what is now called the "Central Interceptor" had risen to $966 million, with completion by 2025.

The new plan also allocated $299 million to upgrade older sewers linking into the new pipe, plus $325 million for a "Waterfront Interceptor" to finally connect the area from St Mary's Bay to Western Springs into the Central Interceptor. But both these items were - and still are - budgeted to be built after the Central Interceptor, in the period 2026-2035.

This week Watercare said construction of the Central Interceptor would now start in 2019 with completion in 2026.

It said the Central Interceptor would cut wet-weather overflows from the old combined stormwater/sewer system by 80 per cent, implying a reduction from 2.2 million cubic metres a year now to about 440,000 cubic metres by 2026.

But even after completing the linking sewer upgrades and Waterfront Interceptor, Watercare still expects wet weather overflows of 190,000 cubic metres a year by 2035.

It says 99 per cent of the material that spills into the harbour in wet weather today is stormwater (rainwater) washing off roads and buildings. Only 1 per cent is sewage ("wastewater"), and most of this is from facilities such as showers and washing machines so only 0.2 per cent of the total overflow is from toilets.

Overflows

Watercare infrastructure planning manager David Blow says new developments in the combined stormwater/sewer area are not allowed to increase stormwater runoff above its current level on each site.

In practice, that usually means developers must install tanks under new buildings to collect rainwater for at least the start of a heavy downpour, so that by the time the tanks overflow the water level in the nearest sewers may have dropped.

If we were to do sewer separation in St Marys Bay, the amount of community disruption would be massive. Every one of those roads would have to be dug up.
Craig McIlroy Healthy Waters

However sewage can't be held back, so a perverse effect of restraining stormwater runoff is that the concentration of sewage in the total overflow will increase from 1 per cent at present to 1.4 per cent of a much-reduced overflow volume by 2035.

In the short term until the new interceptors are built, even though new housing cannot increase stormwater runoff, each extra home will add to the baseload of sewage in the combined pipes.

Both Auckland Council and the Government are actively promoting more intensive housing in the inner suburbs to ease the city's desperate housing shortage. Twelve "special housing areas" (SHAs) in the combined stormwater/sewer network provide for just over 800 new homes in the next three years, and for up to 1000 homes eventually in just one of these, the Great North Rd Strategic Area.

Adding in other new housing outside the SHAs, intensification could easily add something like 1000 to 2000 new homes to the 16,000 now served by the combined network, increasing the sewage baseload by 6 to 12 per cent, before the new interceptors are commissioned.

However, because sewage is such a small proportion of total overflows, Watercare modelling in Herne Bay found extra housing would increase local short-term overflows to Cox's Bay and the harbour by less than 1 per cent.

The council's Healthy Waters general manager, Craig Mcilroy, says even the maximum region-wide population growth permitted by the new unitary plan "is not a show-stopper in terms of the adverse effect [on water]".

"In Cox's Bay we have a significant water quality issue," he says. "It's bad already, and future growth will not have a significant impact on this situation."

The adverse effect of more housing will be offset by short-term improvements planned before the new interceptors kick in.

We are talking about the sparkling Waitemata, the Hauraki Marine Park, the jewel in the crown. At the same time we are promoting the pollution of the harbour with human wastes.
Mike Lee Auckland councillor

Work has already started around Franklin Rd on a separate stormwater and wastewater system for 76 existing homes in Freemans Bay. Further targeted separation projects in Newmarket, Waterview and Okahu Bay are planned over the next five years to take a further 600 properties out of the old combined system.

But Mcilroy says it is more cost-effective to upgrade combined stormwater/sewer pipes in other areas that will feed into the new interceptors than to build separate stormwater pipes everywhere.

"If we were to separate all of those pink areas [on the map] it would cost an additional $1.5 billion, on top of the $1.7 billion [already budgeted for the new interceptors and associated upgrades]," he says.

"If we were to do sewer separation in St Mary's Bay, the amount of community disruption would be massive. Every one of those roads would have to be dug up, and the pipes are often at the back of the properties.

"Wholesale comprehensive separation doesn't make economic sense or social sense."

Instead, in St Marys Bay, he favours a $30 million plan to divert the combined sewer overflows to the Watercare network in Pt Erin Park and in extreme events release the overflows to an existing outfall near the Curran St harbour bridge on-ramp.

St Marys Bay

"This will both reduce the volume of overflows and disperse them more quickly and safely," he says.

That pipe could be built in three to four years and could eventually form the start of the Waterfront Interceptor programme.

"These are interim measures, but we are trying to be practical and innovative by developing projects that form part of a long-term solution and avoid future costly re-work," Mcilroy says.

In 2008, the old Auckland City Council adopted a target to "eliminate combined sewer overflows by 2021".

Nine years on, not only will that target date not be met, but the new Super City appears to have abandoned the basic principle of eliminating overflows.

- NZ Herald

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