Pūrongo

Feature

Kobus van Zyl: Plumbing the depths of water sustainability

29 June 2021
University of Auckland Professor Kobus van Zyl is working to help municipalities save water by finding leaks.

In 2020, with Auckland in the grip of the worst drought in decades, it came out in the media that Auckland pipes are leaking 50 million litres of water a day. That’s more than the 30 million litres a day Aucklanders were saving through conservation measures such as short showers. It’s even more than the 40 million litres a day the entire city of Dunedin uses.

A year later, Auckland’s water supply dams are still only half full and water restrictions remain in place. With climate change predicted to make many areas drier, University of Auckland Professor Kobus van Zyl is working to help municipalities save water by finding leaks. 

Auckland’s water leakage rate is actually lower than that of other cities around Aotearoa New Zealand and the world, says Van Zyl, who is Watercare Chair in Infrastructure and a member of the Department of Civil and Environmental Engineering. However, performance is significantly better in Australia, where the long, severe Millennium drought forced the country to make massive infrastructure upgrades.

“To control leakage, we need a proper maintenance regime, which relies on having sufficient budgets. This requires increased water rates, which are unpopular with the public,” says Van Zyl. “Unfortunately, we have a system where we vote for people who say what we want to hear, which is not the best way to address serious but slow-burning problems like water leakage or climate change.”

Image
Kobus van Zyl
“We take drinking-quality water and use it to flush our loos. There are reasons we do that – it’s more expensive and risky to build a dual pipe network than to just purify all the water to a high standard – but really we should move to waterless toilet systems, flush less or use rainwater or grey water to flush our toilets.”

Kobus van Zyl

The problems with leaky pipes

Some might think leaky pipes aren’t a big deal, since the water will eventually return to underground aquifers. That process, however, can take thousands of years, says Van Zyl. Leaky pipes waste money and energy too, since have to we pump water to purification plants, purify it and then pump it out again. 

“We only have so much water available,” says Van Zyl. “We have a growing economy and population and we have to share water with the environment as well.”

Leaky pipes aren’t easy to detect because they’re buried underground. Most leaks are detected only when they become big enough to be noticed. Smaller leaks often aren’t noticed and run continuously for months or years.

Van Zyl became interested in water leakage two decades ago when he learned that water networks managers found leakage to be much more sensitive to pressure than theory predicted. He wanted to find out why.

Van Zyl investigated a range of factors that might contribute to the difference between theory and practice, including soils around the pipe, behaviour of pipe materials and location of leaks. He concluded the biggest reason for the difference between theory and practice is that pipe materials respond to pressure changes – higher water pressure tends to enlarge leaks.

By characterising the way different types and sizes of leaks respond to changes in pressure, Van Zyl was able to update theoretical models to allow more accurate modelling of leakage flows. 

From problem to solution

Van Zyl and some of his colleagues developed and patented a technique that involves isolating a pipe and using an external pump to pump water into it. If there’s no leak, no inflow of water is necessary to maintain the pressure. Simple.

If there is a leak, the more sophisticated work starts. By changing the pressure in steps, Van Zyl and his team can measure the relationship between pressure and the leakage rate. With the knowledge they have of the factors affecting this relationship, such as the size and type of the leak as well as the properties of the pipe, such as diameter, wall thickness and pipe material properties, they can identify the type, size and often location of the leak.

“Good maintenance practice requires that pipe network valves be ‘exercised’ once a year by fully closing and reopening them to ensure they operate properly,” says Van Zyl. “If you’re going to going to do that anyway, when you isolate the pipe, you might as well connect our device to a fire hydrant, press a button and test the condition of the pipe. If you do this every year, you can monitor how leaks develop. If a leak is really small, it may not be worth fixing. You always have a limited budget and you need to identify which pipes to spend your money on to get the most value.”

More water woes

Leaky pipes aren’t the only sustainability problem embedded in our water and wastewater systems. 

“The demand side is a huge part of it,” says Van Zyl. “For example, we take drinking-quality water and use it to flush our loos. There are reasons we do that – it’s more expensive and risky to build a dual pipe network than to just purify all the water to a high standard – but really we should move to waterless toilet systems, flush less or use rainwater or grey water to flush our toilets. We should also use rainwater or grey water to irrigate our lawns – or better yet, eliminate irrigation.”

Another big issue is eliminating sewage pipe failures and overflows, says Van Zyl. Sewer pipes fulfil a critical public health function by safely removing contaminated water to treatment plants. However, when their capacities are exceeded, sewage can spill into the environment. It eventually ends up in the sea, leading to no-swim advisories, with as many as 50 of Auckland’s beaches affected after a major rainfall.

water drop

“Sewage spills are mostly caused by a combination of reduced sewage capacity and increased flows through stormwater entering the system,” says Van Zyl. “Reduced sewer capacity is caused by many factors, including build-up of sediments, obstructions and plant root intrusions. Sewer systems are not designed for stormwater, and stormwater entering the system during rainfall events through illegitimate gutter connections or improper gully traps is probably the single biggest contributor to sewage overflows.”

Like water pipes, sewer pipes are difficult to monitor. Sometimes municipalities send mobile CCTV cameras into main sewer pipes, but this is a slow and expensive process.

With colleague Wei-Qin Zhuang, Van Zyl is now working on a distributed sensor system that will be able to identify where there are illegitimate stormwater connections and signs of sewer pipe deterioration. The two engineers believe they can make the system simple and cheap enough to operate to bring about a revolution in sewer condition assessment. UniServices is working with them to assess the market potential for the idea and link them with companies interested in investing in it.

“If we can pick up early on where problems are growing, we can fix them before they become catastrophic,” says Van Zyl.

Examining infrastructure holistically

As Watercare Chair in Infrastructure, Van Zyl is working with Associate Professor Kim Dirks to bring together people from a broad range of disciplines to address infrastructure-related problems.

“If we’re going to get to zero net carbon, we have to look at infrastructure holistically, not only from a technical point of view,” says Van Zyl. “We have to look at social, economic and health aspects too, because we’re going to need to make trade-offs and some of these are going to be tough.

“For example, some renewable energy projects have been prevented over the last decade due to environmental concerns. 

“Yes, there are legitimate concerns associated with building a dam or putting wind turbines in the natural landscape, but we need to consider the bigger picture. Not implementing these projects has meant we’ve ended up importing and burning coal from Indonesia. And the thing about big capital projects is that it often takes 20 years for a project to be planned and consented before it can be built. We don’t have that kind of time.

“Climate change is a bigger challenge than any we’ve ever faced. We need to be able to be able to compromise and make trade-offs because we can’t have everything. It’s just not possible.”

Want to connect with University researchers in sustainability and cleantech?
Contact Analeise Murahidy