With New Zealand’s two main economic sectors, farming and tourism, heavily reliant on access to clean water, the decline in quality is harming both agriculture and the 100% Pure New Zealand brand.

Origins of the problem

Much of the problem is caused by the rate of expansion in the country’s major cities. Auckland, especially, has witnessed huge growth in residential and commercial properties in recent years, but is still mostly served by a combined stormwater and sewer system built in the early 1900s; one designed for a much smaller city. While the central business district received an upgrade in the 1990s, with separate stormwater pipes being built, the inner suburbs still use a network more than 100 years old.

Engineering Solutions for New Zealand’s Sewage Problem The shortcomings of the system are becoming more and more evident, with raw sewage and stormwater overflowing into Auckland’s Waitematā Harbour from 41 different points around the city at least 12 times a year. The annual volume of the spills is estimated to be around 10,000 cubic meters, or the equivalent of four Olympic swimming pools. With an additional 800 new homes slated to be built in the immediate future, the pressures on the network are only going to increase.

It is a similar situation in Christchurch, made worse by the already overstretched system receiving heavy damage in the devastating 2011 earthquake. The cracked underground pipes have leaked some eight billion litres of untreated wastewater and raw sewage into the surrounding rivers since then, with experts suggesting it could continue for another 10 years even if the groundwork is brought back to pre-quake levels.

It all adds up to a big problem for New Zealand authorities. Already more than half of the rivers and one third of the country’s lakes have been deemed unhealthy and unsafe for swimming, and around two thirds of native freshwater fish species are at risk or threatened with extinction. There are currently more than 100 beaches, rivers and streams across the country with cautionary notices and many councils warn against entering the water for 48 hours after a rainfall. Health risks range from gastroenteritis and skin infections to Hepatitis A.

Looking forward

So what can be done? In Auckland, utility company Watercare is investing more than $1 billion in a ‘Central Interceptor’, a massive 5m-diameter, 13km-long pipeline to divert much of the city’s sewage and stormwater to their own regional treatment plant at Māngere. The project, due to start next year and be completed by 2026, expects to cut overflows by more than 80%. A further $300 million is earmarked to upgrade older sewers, plus an additional ‘Waterfront Interceptor’, a conveyance and storage tunnel costing $325 million, will be built and linked to the main Central pipe.

The treatment plant itself is also in the midst of a major modernisation. Already one of the biggest in Australasia, the $75 million renovation at Māngere is needed to cope with the extra volume of wastewater that will be brought by the Central Interceptor.

Once at the plant, the water is treated to separate the solid waste, or sludge, from the liquid. The sludge is then stabilised and turned into biosolids, while the liquid goes through two more processes—first, micro-organisms are used to eliminate the carbon and then ultraviolet lamps destroy the remaining bacteria and pathogens, before the water is emptied into Manukau Harbour.

It is an impressive engineering solution, and a huge amount of investment, being poured into New Zealand’s sewage problem, and one that authorities hope will see the beautiful waters surrounding the island return to their pristine state.

What other key areas of infrastructure in New Zealand need modernisation? Let us know in the comments box below. 

If you are interested in discussing any engineering roles available or any hiring requirements, please contact your nearest Cobalt office.

You may also be interested in: 

Autonomous Air Taxi Unveiled in New Zealand

In perspective: Peter Mahon