Urban thirst

When Nature turns the tap off, urban water managers have their work cut out keeping ours turned on. In early 2013 they passed a stern test, but climate change and sustained urban growth are demanding new thinking, finds Colin Barkus.

When Nature turns the tap off, urban water managers have their work cut out keeping ours turned on. In early 2013 they passed a stern test, but climate change and sustained urban growth are demanding new thinking, finds Colin Barkus.

On 13 March this year – yet another breathless scorcher across most of the country – news headlines trumpeted that Wellington would run out of water in 20 days' time. Media devoured the story, relishing the irony of looming supply failure in a region renowned – often maligned – for its soggy climate.

"Actually," says Chris Laidlow, "it was serious, but we weren't close to running out. The '20 days' comment made by one of our councillors was reported a little out of context. If there'd been no other sources of water available, and given the demand at the time, our Te Marua storage lake would've lasted for about 20 days. It's Murphy's Law that, during one of the driest summers on record, the other storage lake was out of commission for a planned upgrade.

"But although river levels were dropping steadily, there was still water available, and we had the aquifer source. We could've sustained a limited supply indefinitely."

Nevertheless, Laidlow admits, the media frenzy did the region a big favour. "It galvanised public action and led to a big drop-off in demand – staving off more serious conservation measures until decent rain finally arrived."

Laidlow is General Manager, Water Supply, at the Greater Wellington Regional Council. He oversees the infrastructure that captures, stores and treats bulk water for the region and delivers it to city councils, who reticulate it to homes and businesses. It's Laidlow's job to balance inputs and outputs, and when inputs are meagre – as they were during the first 12 weeks of 2013 – reducing demand is paramount.

The Regional Council draws water from rivers fed by three surface catchments: the Tararua Range to the northeast of the city, and the Wainuiomata and Orongorongo hills to the east – and from an aquifer running under the Hutt Valley and into Wellington Harbour.

All up, the Wellington region actually received near average rainfall over summer (see graphic: How dry was it?). But it fell in just a few, isolated events. In mid-February, water shortage warning 'trigger' levels hadn't been reached, but with river flows declining, no rain in the 14-day forecast and only half the region's usual storage capacity available, Laidlow and his team knew they had to act. "We upped our media activity, raising the possibility of a water shortage and sprinkler ban."

During a normal summer, says Laidlow, the region receives rain at least every seven to ten days, "but this year the dry spells between rain events went on and on. River flow was declining, so we increased abstraction from the aquifer. But by the end of February it was also dropping away.

"We started thinking about what we'd need to do if the unusual weather continued for another three or four weeks. With two lakes available, there wouldn't have been a problem, but with reduced storage capacity we raised the possibility of rationing with our customers as a worst-case scenario. It's a serious step ... [and] very difficult to implement in local reticulation systems, so we agreed that additional demand controls were needed to preserve storage."

On 12 March, the Regional Council agreed with the city councils to ban all outdoor water use – the highest restriction ever imposed on the region's residents. The media and public sat up and took note.

Beyond reasonable drought

It was a similar story elsewhere across the parched North and upper-South islands.

Even before Wellingtonians were coming to grips with their extraordinary ban, residents in the far-north towns of Opononi, Omapere, Kaitaia, Rawene and Dargaville faced exceptional restrictions of their own. In Dargaville, the Kaipara District Council had drawn up the paperwork to extract water from the Kaihu River.

The Manawatu District Council trucked water from Feilding to supplement a struggling supply in Sanson.

Hamilton reached level three on a four-level restriction scale – putting garden hoses out of action for several weeks. Hamilton City Council ran a comprehensive public awareness campaign, including a 'dob in your neighbour' hotline during the hosing ban, but the situation worsened – prompting extraordinary measures. The city draws its water from the Waikato River and as the drought took hold, the river threatened to drop below the level of the intake pipe. The Council positioned a barge on the river, equipped with pumps ready to transfer water into the intake if necessary.

Mercifully, significant rain arrived in late March and continued throughout April, averting the need for costly contingencies like this in Hamilton, Wellington, the far north and across other affected areas.

Demanding future

All in all, Chris Laidlow is pleased with the way the Regional Council's management strategies stood the test and the public responded to restrictions. But, he concedes, "we were fortunate. Our awareness campaigns were helped by some keen interest from the media, and then Nature intervened just at the right time."

Analysis by NIWA suggests urban water managers may need to prepare for more – and more challenging – dry spells as our climate changes. Computer models indicate droughts are likely to become more frequent and more severe in eastern and northern parts of New Zealand. A drought in those regions with a one-in-20-year return period now, for example, may occur twice – even four times – as often by the end of this century.

In 2011, NIWA used its Urban Impacts Toolbox (a resource to help urban planners assess potential impacts of climate change) and the Regional Council's hydrological computer model (the Sustainable Yield Model, or SYM) to estimate how the Wellington region's water supply would cope with the combined effects of climate change and population growth. The study found that, by 2040, climate change could decrease available water by as much as five per cent, or 12 million litres per day, while population growth could inflate average demand by over two million litres per day during January and February – in a 'normal' year. Existing supply infrastructure would not cope.

Find out more about the Urban Impacts Toolbox

Chris Laidlow took action. "Building new infrastructure seems an obvious answer," he says, "but it's costly and time-consuming, so we're looking for other ways to extend supply."

His team is investigating the impacts of drawing more water from the Hutt aquifer. "If we can get a small increase without damaging the health of the aquifer or river, it could defer capital spend on new surface water sources," he says. "We're spending upfront to investigate, model, and put test bores down. It's indicating that our current operating levels are quite conservative."

But Laidlow acknowledges that augmenting supply is only part of the equation. And he's not alone.

In 2010, the Ministry for the Environment and the then Ministry of Consumer Affairs introduced the New Zealand Water Efficiency Labelling Scheme (WELS), which applies an efficiency rating label to new household products that use water. Consumers can compare, at point of sale, the water efficiency of different brands and models of washing machines, dishwashers, toilets, showers and taps – and choose accordingly.

Many local authorities offer a range of policies and guidelines for reducing water use in homes and businesses. They advocate a combination of good habits – turning off taps when brushing teeth, taking shorter showers, using dishwashers and washing machines only when full and establishing drought-tolerant gardens, for example – and one-off actions, like fitting low-flow shower heads and fixing leaks.

Leak-fixing campaigns by each of the Wellington region's city councils are partly responsible for a drop in demand experienced recently. Other factors, like more water-efficient household appliances and changes in consumer behaviour, have also had an impact.

Efficiency by design

Meanwhile, recent innovations in the design of urban water management systems have given authorities fundamentally new ways of thinking about meeting the supply challenge.

The idea of incorporating surface drainage infrastructure into urban design, variously known as Water-sensitive Urban Design (WSUD), Low-impact Urban Design and Development (LIUDD) and Low-impact Design (LID), has slowly gained ground over the last couple of decades. WSUD, the Australian term adopted in some New Zealand centres, emerged during the supply-crippling drought that gripped Melbourne for 10 years around the turn of the century.

"Historically, authorities sought to pipe untreated stormwater, along with wastewater, out of the city as quickly as possible to reduce flooding and to prevent outbreaks of disease," explains NIWA Urban Aquatic Scientist Dr Annette Semadeni-Davies. "WSUD is about managing and treating stormwater in situ, by diverting it into inner-city 'blue-green corridors' – park-like spaces in which carefully selected vegetation, detention systems and engineered soils are used to slow down and filter the stormwater.

"To all intents and purposes it looks like landscaping, but WSUD plays a vital flood management and water treatment role."

Rainwater harvesting and 'grey water' recycling are other key WSUD principles that, says Semadeni-Davies, "will become increasingly important as things get drier".

Rain butts and tanks to collect roof runoff are already widely used in rural New Zealand and are gaining popularity in urban areas. Rainwater, explains Semadeni-Davies, is "perfectly suitable for a range of non-potable purposes, including watering your garden, washing your car and even flushing your toilet. Recent studies in Australia suggest rainwater harvesting may save as much as 50 per cent of household water use."

Landcare Research can add weight to that claim. Landcare captures rainwater from the main roof of its new building in Auckland and uses it in flushing toilets and glasshouse irrigation systems. City water is used in laboratories, the kitchen, washbasins and showers, which feature low-flow fittings. The harvesting system meets about half the water needs of Landcare and other tenants in the building.

A new greenfields suburban development just north of Melbourne takes the idea several steps further. The Kalkallo Stormwater Harvesting and Reuse Project will collect stormwater from a 160-hectare area and treat it, on site, to a potable standard. Initially the water will feed into a recycled water network, but the goal is to purify it sufficiently to supplement domestic supply.

'Grey water' is what drains from your shower, washbasin, dishwasher and washing machine ('black water' is the nasty, unsanitary stuff). "Grey water is also suitable for many non-potable purposes," says Semadeni-Davies. "Alongside low-water-use appliances and toilets, water reuse is gaining popularity as a way of reducing demand on domestic supply and lessening the burden on sewer networks."

In Australia and Japan, some new residential developments are plumbed so that toilet cisterns receive only grey water. Grey water in-ground irrigation systems are also common overseas.

"Part of the challenge in New Zealand is to make the public and developers aware of options," adds Semadeni-Davies, "but that's slowly happening. Architects and urban engineers are now more commonly incorporating rainwater harvesting and grey water recycling considerations into their design guidelines for residential and commercial property.

"There are also important regulatory and cost issues for urban authorities to consider. Auckland Council recently undertook a study looking at impacts and implications if residents were required to install rain harvesting systems. The Kapiti Coast District Council is among others that have recently published rainwater and grey water codes of practice."

In the meantime, Chris Laidlow and his team at Greater Wellington Regional Council hope that Nature is a lot more cooperative next summer. He's in no doubt, however, about the salutary lesson delivered in 2013: "We have to extend our contingency planning out into the unknown."


Quenching the desert city

Phoenix, Arizona, receives 207 millimetres of rain annually, on average. That's about 60 per cent of the rain normally received by New Zealand's driest town, Alexandra, and less than one-fifth of the yearly watering received by Auckland, Hamilton or Wellington.

Greater Phoenix's 3.8 million residents receive water via the Central Arizona and Salt River projects – networks of canals hundreds of kilometres long that draw from the Salt, Verde and Colorado rivers. Supply is supplemented by groundwater and reclaimed water.

But as the city's population burgeons, the decades-old projects are struggling to meet demand.

The Arizona Department of Water Resources has a 100-year plan, updated every five years, to manage agricultural, residential and commercial needs. Public education is a significant component. Initiatives range from teaching homeowners how to capture and store rainwater and determine when gardens need irrigating, to fitting restaurant kitchens with high-pressure,

low-flow hoses. Phoenix led a nationwide 'fix a leak' campaign, which saw specialists helping homeowners curb the estimated 3.7 trillion litres of water wasted in the US each year.

The stakes, however, are high, and Phoenix needs a back-up plan. It comes in the form of a gift from Nature. Aquifers beneath the city hold immense reserves of water – largely untouched – that authorities are 'banking' for future emergency use.

In the meantime, conservation and prudent management are the pillars of a plan that aims to keep Arizona's desert city quenched for generations to come.