Managed Aquifer Recharge

Climate change is projected to directly affect our groundwater levels. Less rain, longer, hotter summers and drought means less natural recharge of the aquifers occurs. This, paired with a growing demand for water, means at times we are consuming more freshwater than the environment naturally recharges.

Managed Aquifer Recharge, or MAR, is a set of physical tools that allow us to capture high-quality water from rivers and streams when flows are high, such as winter. We can then use it to purposefully recharge aquifers - complementing the natural recharge processes. Water is filtered using natural processes as much as possible, as well as using specific filtering methods, such as constructed wetlands and infiltration galleries, or ‘leaky ponds’.  

Groundwater replenishment schemes use MAR to proactively replenish groundwater storage, restoring catchment groundwater levels that have been drawn on during periods of peak demand, such as summer.

With the rising pressures of extreme droughts, and the uncertainty of climate change, ensuring that groundwater levels and the quality of freshwater stored in aquifers are appropriately managed is increasingly important.

Much of the worlds’ freshwater is found in groundwater aquifers.  Groundwater moves slowly through aquifers, at a snail’s pace compared to rivers and streams above.  Therefore, groundwater held in aquifers is termed as ‘storage’.

While we see the Waipawa and Tukituki rivers running above ground, there is a much larger water system underground being accessed by homes, industry and for irrigation – the Ruataniwha Aquifer.

The Ruataniwha groundwater system is within a large basin (covering nearly 800 km2) surrounded by the Ruahine Ranges to the west and limestone hills to the east with distinct shallow and deep aquifers within it. The basin’s gravels act like a reservoir, storing and filtering water from rainfall, rivers and streams, that replenish the aquifers with high-quality water. Due to the groundwater system’s individual elements scientists believe that it is likely to respond well to proactive recharge using MAR.  A trial aims to provide us further information and understanding.

Nature does a fantastic job of recharging aquifer systems, and we want to mimic nature and give it a hand at the same time. The basin’s gravel layers act like a reservoir storing and filtering water from rainfall, rivers and streams, that replenish the aquifers with high-quality water. 

For the MAR trial, we'll be diverting water from the Waipawa River during high flows and moving it through underground pipes to a recharge site. There, the water flows into a series of big leaky ponds where sediment settled from the water. The water then seeps down through the various layers of dirt and gravels into the shallow aquifer. 

We're also looking to replenish the deeper aquifer by using a pumping system, so it can be stored and recovered in summer.  Most of the water we access is from the deeper aquifer, so we are aiming to top up this supply and maintain a higher level in the aquifer during dryer months when demand peaks. 

Both the deep and shallow aquifers play an important role in protecting the environment, ensuring surrounding streams can continue to thrive during the dry months of summer.

This is a small-scale trial to monitor how MAR works in a localised environment – measuring the impacts and benefits so we can determine if MAR is a tool we can use in other locations and how to best apply it.

Water quality is a priority when designing the MAR recharge site and before the project even proceeds it must meet consenting conditions.

Water being diverted from the Waipawa River is filtered before it moves to the MAR site and is further filtered through a constructed wetland and the gravels as part of nature’s natural filtering processes.

During operation, a water-quality monitoring programme will be operating to ensure the filtering processes are working as expected and that only high-quality water is recharging the aquifer.

The diversion and storage of water using MAR is site specific.In this case, the project is seeking to divert up to approximately 3 million cubic metres of water a year through the natural river bed for use at the MAR trial site, of which most will be diverted during the wetter, winter months.   

Of the approximate 3 million cubic metres year available for recharge, more than 60% is targeted for the shallow aquifer system. This is for the sole purpose of increasing baseflows that support springs, wetlands and down-gradient tributary streams feeding the lower Waipawa River trial area.

Approximately 40% of the recharge is targeted on the deeper system, for the sole purpose of replenishing groundwater storage. This deeper aquifer provides groundwater supplies for a vast majority of the water users in this sub-catchment area.  

The trial will test how water recharged into the shallow aquifer will improve the environmental and cultural values of the trial area.  In addition to supporting the environment during summer, up to 60% of the water replenishing the deeper aquifer will be recovered for a productive use trial.  The remaining 40% is new stored water for the groundwater system.  Access to this newly stored groundwater is controlled by HBRC through allocation limits and the water permit process.

The key challenge to developing water security is the timing of water availability - relative to demands and/or needs. The MAR project diverts most of its water during the wetter, higher flow periods. 

Additional water recharge into aquifers during those periods helps to slow water down, utilising the natural storage features of the catchment.  This stored groundwater releases to spring-fed streams and rivers as baseflow through the drier, hotter summer months when ecological habitats and cultural values are under pressure. 

Climate change is impacting both ends of the hydrological processes in the catchment with higher, short duration winter peak flows coupled with more prolonged, lower summer flows which makes this kind of project important for our future water security.

The MAR site is located between Ongaonga and Tikokino on the Ruataniwha Plains. Water being diverted from the Waipawa River is filtered before it is delivered across farmland by an underground pipe to the MAR recharge site approximately 2.5km away. The MAR recharge site is approximately 40m wide and 300m long.

The MAR trial is one of the Hawke's Bay Regional Council's Water Security projects, co-funded in partnership with Kānoa - Regional Economic Development & Investment Unit (formerly Provincial Development Unit).

Yes, and very successfully in places such as Spain, India, the United Kingdom, and Africa and throughout the United States. 

While a new method for New Zealand, MAR has been used extensively overseas for over 60 years in various capacities, developing over time with new techniques to improve water quality.

MAR has been proven internationally to be an effective and sustainable water management tool, and both Canterbury and Gisborne have successfully trialled and implemented MAR in priority catchments to support localised groundwater management.

After the success of Canterbury's Hinds MAR, the community is now rolling out a further 16 MAR sites to ensure they have plenty of quality freshwater throughout the year.  

In Hawke's Bay, most of the water we consume is from groundwater. MAR offers a way to give back to the system we take from and provides a means to manage the overall water balance.

MAR offers a low-energy water storage option, mimicking natural recharge processes to replenish our aquifers. Proactive groundwater replenishment helps to increase water levels and sustain baseflows to surrounding spring-fed streams, wetlands, and rivers.

We are running a three-year trial to test the effectiveness and concepts of MAR in Central Hawke’s Bay to determine whether it’s a viable storage option under the Regional Water Security Programme.

Hawke's Bay Regional Council has already put a number of interventions in place to control water usage, including capping the number of groundwater allocations and raising the river level flows for when takes cease. Based on our projections that still won’t be enough as the gap between demand and supply grows due to climate change.

Regional Council also works with city and district councils to encourage efficient water use. Alongside the objectives to supplement depleted waterways, the Regional Water Security Programme is investigating ways to further reduce demand for water.

MAR is just one solution the Regional Water Security Programme is investigating for water storage. The feasibility of above-ground storage for the Heretaunga Plains is also being investigated, as well as considering water conservation, alternative farming systems and land-use changes to increase supply and manage demand. The Regional Council has investigated above ground water storage options extensively in Central Hawke’s Bay and this continues to be an option explored within the community.

Our priority is ensuring the environment has the water it needs to thrive.

If the MAR trial performs as expected, it will be an additional and important tool in supporting our goal of ensuring Hawke's Bay has long-term, climate resilient and secure supplies of freshwater for all.

If the trial is successful, a network of MAR sites could be strategically located to operate as a groundwater replenishment scheme, helping us to manage the overall water balance in our catchments - supporting the environment and securing water for other uses in future.

By trialling MAR, we're not only seeking to hold the line for the environment in the face of climate change but also provide a viable option to store more freshwater to meet the increasing demands of growing populations and thriving industry and agriculture. 

As part of the consenting process, Regional Council is progressing the development of a Cultural Impact Assessment (CIA).  A CIA takes a Te Aō Māori (Māori world) view of the project to document cultural values, interests and associations mana whenua have in the area where the trial will occur. It also identifies any potential impacts the project may have and how mana whenua would like to see these managed.   

Additionally, plans are being put in place to develop a Cultural Health Monitoring programme should this be supported by mana whenua.  A Cultural Health Monitoring programme would operate alongside the groundwater monitoring and enrich our water quality and eco-system monitoring of nearby streams and habitats.

It's worth noting that, cultural monitoring at the Gisborne site observed no negative effects on the mauri of the aquifer at the end of the trial.

Hawke's Bay water security funding

https://www.growregions.govt.nz/media-centre/news/drive-to-improve-hawkes-bay-water-security-backed-by-pdu/

Canterbury's approach to water management.

https://www.ecan.govt.nz/your-region/your-environment/water/canterburys-approach-to-water-management/new-beginnings/

Article on the success of Hinds MAR, community investments, environmental benefits (nitrate/nitrogen reductions), and increase in MAR sites (17 from 1 in 2016).

https://www.odt.co.nz/rural-life/rural-life-other/rate-funding-hinds-aquifer-recharge-project

Managed Aquifer Recharge: An Overview of Issues and Options

https://link.springer.com/chapter/10.1007/978-3-319-23576-9_16

Te Mana o te Wai.

https://environment.govt.nz/assets/Publications/Files/essential-freshwater-te-mana-o-te-wai-factsheet.pdf

What the government is doing  about freshwater

https://environment.govt.nz/what-government-is-doing/areas-of-work/freshwater/

Managed Aquifer Recharge – A Potential Water Treatment Method in New Zealand?

https://www.waternz.org.nz/Attachment?Action=Download&Attachment_id=1279

CSIRO Managed Aquifer Recharge

https://research.csiro.au/mar/#:~:text=Welcome%20to%20Managed%20aquifer%20recharge&text=MAR%20offers%20numerous%20benefits%2C%20including,low%2Denergy%20water%20supply%20option

Hinds Canterbury Managed Aquifer Recharge (MAR) project

https://apps.canterburymaps.govt.nz/hindsMAR/

https://www.odt.co.nz/rural-life/rural-life-other/rate-funding-hinds-aquifer-recharge-project