Bridget Freeman-Rock looks at the case for MAR: trialling managed aquifer recharge in Central Hawke’s Bay

The last two years have been tough for Will Foley, a Central Hawke’s Bay sheep and beef farmer. 

He’s had to “de-risk, to simplify” in a drying landscape. He’s now stopped farming over the mid-summer months altogether, destocking before Christmas and before the summer feed runs out. There’s more demand on water in the Ruataniwha catchment, less supply, and a trend of ever-less rain, which is “hugely worrying”. Anecdotally, there hasn’t been the usual snowfall on the Ruahine Ranges; springs are not running, streams are drying up. “It’s scary,” he says. 

Water supplying both Waipukurau and Waipawa townships comes from shallow wells beside rivers (effectively, surface water), while rural settlements like Ongaonga and Tikokino are on private bore supply, the bores often drying out now in summer. Yet CHB’s population is climbing, as property prices drive more people away from the main centres, with proposed large-scale housing developments in the cards. Questions of water infrastructure for domestic use and town supply have become critical.

There’s not great equity, when it comes to water takes (with the first in, first served basis of allocation in the days when water was ‘bottomless’, concentrating the now-capped resource in the hands of a few irrigators). Over the last 20 years, groundwater allocations for irrigation and industry (drawn from the deep, confined Salisbury aquifer) tripled from just over 9 million cubic metres per year in 2001 to 29 million m3/year, with allocation limits set at 28.5 million under Plan Change 6. 

Winter groundwater levels in that same period declined by 10-20cm annually (in the Forest Gate monitoring well, for example, groundwater levels have dropped 4 metres), a decline amplified by increasing groundwater takes over summer as conditions become drier and there’s less water in the landscape, which in turn further depletes the shallower systems. 

Climate change projections for Central Hawke’s Bay is for higher-intensity rain events followed by prolonged, drier drought periods, which will dramatically change the ability of its communities to manage water. Ecological habitats for native freshwater species like eel will be most vulnerable to the fluctuations. 

By slowing water down (capturing surface water in times of high flows and releasing it through the groundwater system), it’s hoped, managed aquifer recharge (MAR) – to be trialled in the Ongaonga area pending consent – will help mitigate against some of these extreme weather variations, while rebalancing an out-of-kilter system.

“It’s no silver bullet for the district’s water needs,” says Will, who is also a Hawke’s Bay Regional Councillor. But he hopes MAR will help on a localised scale to restore waterways (creeks, wetlands, springs), in combination with water efficiency and smarter, climate-change adaptative, land-use practices. 

Ruataniwha Basin

The CHB catchment is bounded in the west by the Ruahine Ranges and foothills, which provide the headwaters for both the Tukituki and Waipawa Rivers, and to the east by limestone hills on the coast, and includes 10 surface-water sub-catchments. The Ruataniwha Basin that sits beneath is effectively a closed groundwater system – hydrogeologist Clare Houlbrooke describes it as like a bath, with the two rivers that exit it as the plughole.

Within that basin are two aquifer zones: the shallow Young Gravels aquifer, which is fed by the Waipawa River and supplies baseflow to the springs and streams in the eastern side through the upwelling of groundwater flow, and the deeper Salisbury aquifer, which contains a more confined and older groundwater system (some of the water here is 150-200 years old). Pretty much all groundwater abstraction in the catchment is from the Salisbury. 

The proposed three-year MAR pilot will take water (about 170 litres per second) during peak flows from an infiltration gallery from within gravels below the Waipawa River, where it comes out near SH50. “The water here is beautiful,” says Clare, “relatively low sediment, low nutrient.” 

It will then be piped a couple of kilometres away to a site on private land (which will be made accessible and viewable to the public), where it will be channelled through a series of constructed wetlands and infiltration galleries (literally just a hole in the ground filled with sands and gravels), to settle out any sediments. About 100 L/s will be released into the shallow aquifers, while 70 L/s will be pumped some 70 metres down into the deeper aquifer through what’s termed an ASR (aquifer storage recovery) bore, half of which will be drawn back out in summer – or at least that’s the possibility being explored. 

ABOVE: The proposed trial for Managed Aquifer Recharge in Central Hawke’s Bay. Water will be captured from the Waipawa River, filtered through a series of constructed wetlands and basins, and stored in the underground aquifers. Graphics courtesy of HB Regional Council.

Tom Skerman, manager of HBRC’s Regional Water Security Programme, explains: “So, you’re building up the capacity over winter and spring, and then in the drier months, the water that’s sitting in the shallower aquifer effectively creates a mound that slowly discharges, supporting the nearby, lowland streams and springs. Hopefully you’ve increased the capacity of the deeper aquifer where most people access water, and we’re going to test to see how much we can pull out.”

What happens with the pilot’s extracted water is yet to be determined, but there’s opportunity to demonstrate future farming practice, whether that be something regenerative, says Will Foley, or trialling new climate-resilient crops. “People will need to see results; we will need to prove the concept.”

Supply and demand

HBRC’s water security programme was set up to guide decision-making around how to spend money that had been earmarked many moons ago for water storage on the Ngaruroro under the assumption the Ruataniwha dam would be completed, not ‘fall over’, and involves targeted investigations where the pressures are across the CHB and Heretaunga Plains. 

When the Provincial Growth Fund (now called Kānoa) came into play, HBRC made a comprehensive set of applications across four projects to speed up delivery, all of which were successful, including the 3D mapping project, which has been mapping the region’s aquifers, and the MAR pilot. 

“Our goal for the region is to have long-term, climate-resilient supplies of freshwater for all,” says Tom Skerman, “but it’s the ‘for all’ bit that’s the really challenging part. 

“With growing cities, growing industries, a drying climate and no more water to be allocated – the regional water security assessment and common sense tells us we’re a fully allocated system – we can safely say there’s going to be a gap between supply and demand at some stage in the future. The question becomes, how can you close the gap? And, what are your solutions on the supply side? 

“In the absence of solutions, it becomes really very tricky; then all your interventions come down to demand: water rationing, re-allocation, water-use prioritisation, etc. This pilot is essentially to look if MAR can be part of the supply solution.”

Groundwater Replenishment Scheme (GRS) is the term used to describe a network of MAR sites across a catchment, and in its design to capture, distribute, recharge and recover water would require systems-thinking conceptualisation. “The purposeful recharge of the groundwater supplies could help to mitigate, enhance and potentially lead to a more holistic and sustainable water management model,” the pre-feasibility assessment noted, though at this point a large-scale, joined-up GRS is not a focus of the MAR trial.

“There are two ways to store water: you can store water above ground in a bucket, or you can use the ground as a sponge to store water below. What aquifer recharge does is try and mimic nature. It deliberately takes high-flow water during winter and then returns that to the shallow or deeper aquifer.”

Tom Skerman is at pains to point out that MAR is not ‘dam by stealth’: 

“Aquifer recharge can never be an alternative to the Ruataniwha dam, which would have been absolutely, intergenerationally transformative (good or bad, depending on where you stand) for the whole community. If the MAR pilot shows promise, I am sure there will be a demand for it, but the nature of it being localised and networked, it probably lends itself to community groups applying it, with tailored rationale to their area and need. I can conceive of a number of models going forward.” 

And, theoretically, MAR could work in conjunction with other water storage approaches.

Restoring balance?

MAR is used around the world (in 1,300 or so locations), mainly as a filtering-type system, in places where there’s pressure on water resources. “It’s new to New Zealand but it’s not a new technique,” says Clare Houlbrooke, who attended an international MAR conference in Spain just before lockdown 2020, and shares multiple examples of where it’s been innovatively applied for years.

It is not without controversy, however. Research published in February this year on the Hinds-Ringatu plains, Canterbury, shows more efficient water-use for farming has reduced groundwater levels and increased groundwater contamination, backing international findings. The Hinds MAR scheme (which Clare has also worked on) is an attempt to address these consequences, and while ‘diluting polluting nitrates coming off farms’ was one of its aims, this wasn’t meant to replace on-farm management of nutrients – a point somewhat lost in media reports and on the chairman of the project himself.

Freshwater ecologist, Mike Joy, has been pretty damning about MAR, calling the technology a “public relations trick”, an attempt to “play God”, and environmentally risky. That view is similarly voiced by Ngāti Kahungunu’s director of environmental and natural sciences, Ngaio Tiuka. He argues that taking water from rivers and putting it underground is essentially “robbing Peter to pay Paul”, and benefits irrigators. 

Environmental concerns over MAR include the potential for surface-water contaminants to be introduced into pristine water (remember, some of the water in the Salisbury is 200 years old), and the downstream ecological effects (as yet unknown) of tinkering with the system. Philosophically, there’s concern that it’s a techno-industrial approach that treats water merely as a resource and not a taonga, and that it’s our relationship to water and the more-than human world that needs recharging.

But Clare insists the intention for CHB is restoring balance, as well as water storage, and any freshwater pumped into the groundwater system (at this stage, a relatively small slug) will be stringently tested; it’s a completely different scenario to Canterbury, under a unique set of conditions. 

When water is introduced into the groundwater system, it dissipates out into a bubble. “For it to mix, be naturalised (i.e. more like the ambient groundwater),” she explains, “it has to move through the groundwater system, which happens very slowly – in the space of months, from what we’ve seen in Gisborne – but how long is something we’ll be watching closely in this pilot.

“The pilot is about demonstrating what’s possible at this point and how that system’s responding. It will allow us to understand the whole system better; to understand some of those other connections (the interlink between surface water and groundwater), while also taking the community along on the journey.”

Unintended consequences

So, what about unforeseen implications when considering ki uta ki tai (the connectivity of water from the mountains to the sea)? Is there a risk we mess up the whole aquifer? I am reminded of the fact that the historic solution to flooding on the Heretaunga Plains (building channels and stop-banks to contain rivers) has exacerbated the increasingly gnarly issue of sediments flushing out into the ocean; while ‘reclaiming’ land for urban development and agriculture led Hawke’s Bay to lose 98% of its vital wetlands, which hold and filter water in the landscape.

An even more pertinent example is the open stockwater races (which carried water from streams and rivers to farms), once prevalent across the Ruataniwha catchment, but closed 2001-2004 due to concerns about potential discharge contamination and due to their overall ‘inefficiency’. 

Ironically, it was this very inefficiency that helped buoy baseflows to streams and rivers in the eastern part of the catchment, as water leaked from the races into the shallow gravel aquifer beneath the plains in what scientist Clare Houlbrooke terms “incidental recharge”, and which irrigation ‘efficiency’ effectively put a stop to, to the ecosystem’s detriment. 

By way of answer, Tom hands me Elizabeth Kolbert’s latest book, Under a White Sky, about “people trying to solve problems created by people trying to solve problems”. The book explores what’s at stake if we don’t intervene in an unfolding human-made disaster (climate breakdown) – she asks, is that even an option? – along with the accompanying, paradoxical risk of unintended, uncontrolled-for consequences. 

Like the book’s engineers, scientists and ‘atmospheric entrepreneurs’, Tom believes we don’t have much choice but to try: “We face some stark facts. There is not going to be more water; we’ve reached the limits of what the environment is going to give us naturally.”

Worse, according to NIWA’s (2018) hydrological projections, Hawke’s Bay rivers will be among the most affected by climate change in New Zealand, with the Tukituki River and the Wairau in Gisborne topping their list of most vulnerable waterways. 

Under HBRC’s Regional Water Security Programme there will be a series of water projects aimed at ‘water security’, of which the MAR pilot is but one. For Tom, the programme’s “a climate-change adaptation programme – there’s no question of that”. It’s not a mitigation piece of work, it’s not to improve water quality (there are plans and regulations in place for that), it’s about protecting baseline flows and ensuring we have water in the first place, he says, and that’s going to require interventions. 

Tom concedes that environmental groups like Forest & Bird are highly sceptical of interventions, but believes it’s unrealistic to just focus on cutting demand, and the regional council has to cater to a broader community of needs. 

He assures me there will be seven monitoring bores, a heap of science applied at every juncture (“We’re going to test the bejesus out of it”), along with the principles of Te Mana o Te Wai. The latter being the newest iteration of the National Freshwater Policy, which is about lifting standards of care for freshwater in step with Māori values, under a hierarchy of obligations in which the environment comes first, followed by human health and wellbeing. 

The team is currently in process of engaging with local hāpu and iwi and, if mana whenua are willing, will be setting up a “strong” cultural monitoring programme alongside. 

“It is a trial, it is about monitoring, we’re not just standing this up.” 

He would like sceptics to keep an open mind. “Let’s give it a chance and see what the environmental benefits are, because there are good reasons for doing MAR, not least providing more consistent flows to water bodies that are struggling,” including four nearby wetland systems close to the proposed site. 

He cites former HBRC chair Rex Graham’s talking point on water security earlier this year, “All levers will have to be pulled”. MAR is not looking to be the techno-fix to Central Hawke’s Bay’s looming water crisis. But is touted as just one lever, or one possible – ‘if we’re lucky’ – solution, amongst others. 

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