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Quarrying innovation protects and strengthens wetlands

A Kiwi quarry operator who engineered a wetland filtration system to prevent run-off in his quarry polluting an adjacent world heritage conservation site has received the Institute of Quarrying’s most prestigious award.

Baldwin’s Quarry, about 75km south of Central Auckland, is permitted to produce 500,000 tonnes per year. It is currently run by quarry manager Kerry Reilly, with eight staff and has an output of about 200,000 tonnes per year. A Waikato Regional Council discharge consent allows for up to 75m3 per second of treated quarry process water to be discharged into an unnamed tributary of the Whangamarino wetland.

The land was purchased by Kerry Reilly in late 1999 and he was granted consent to open a commercial aggregate quarry. The quarry was sold to Higgins Aggregates in 2011 and later to Winstone Aggregates in 2015. Despite the site being on-sold twice, Reilly has continued as quarry manager.

The land is steep and had little flat area for stockpiling or processing in the early stages. The challenge was to open up stockpile areas, haul roads, and processing areas. In particular, there was a requirement to mitigate the effects from any run-off to the stream which drains the large catchment area of the farm owned by Peter Buckley surrounding the quarry, through the operational quarry area and finally into the Whangamarino Heritage Wetland.

Driven by the need to move overburden, but with respect for the environment and neighbours, Reilly saw the opportunity to solve the initial construction challenges by the formation of a man-made wetland system on the Buckley Farm which would enable the treatment of any silt-bearing stormwater prior to it entering the Whangamarino Heritage Wetland (Figure 1).

Figure 1. Stages 1 and 2 of the approved wetlands plan set up by Kerry Reilly.

His experience told him that if the flow of water could be slowed it would enable use of natural methods of plant filtration and be a cost-effective, sustainable solution. It would also supplement the on-site settlement systems and silt ponds within the quarry itself.

Wetland centrepiece

The plan was developed from first observing the water flows during and after heavy rainfall. “I climbed the hill overlooking the Buckley farm and the Whangamarino swamp and came up with the master design,” Reilly said. “Instead of excavating ponds on the Buckley land, I decided it would be more beneficial to create the ponds by encapsulation, while also building roads and an observation island in the centre of the new wetland.”

This method had a number of benefits:

• It allowed the use of a larger volume of overburden and negated the need to excavate into the sensitive Wetland peat swamp.

• It simultaneously created a road network to enable access for machines to maintain the wetland in the future and for visitors to view the fish and birdlife

International Caernarfon Award winner Kerry Reilly.

Reilly designed an island as a centrepiece of the wetland which solved several challenges; it provided an ideal viewing area that overlooks the entire project and assists to create a larger pond network and longer water flow path which allows filtration of microscopic fines.

In the formative days of New Zealand, the local indigenous community (iwi) grew and harvested flax in the swamp. The flax was exported to Australia and manufactured into rope and hemp. Over-harvesting and disease killed off most of the flax and the Whangamarino then became overrun by willows, a non-native tree introduced by the early New Zealand settlers.

The creation of the new wetland within Baldwin’s Quarry has allowed for the clearing of the willows from the area. It has enabled unrestricted access for ducks, swans, fish, frogs and birds, all of which can be observed breeding in the wetland.

Whangamarino Wetland 

The Whangamarino Wetland encompasses about 7200ha. It is the second largest swamp/wetlands on the North Island, and was granted world heritage status in 1989. It stretches from the small township of Te Kauwhata in the south to Meremere in the north.

The Whangamarino Wetland is rich in mosses and 13 new species have been added to the list of New Zealand flora from this area. Lichens are also well represented. A number of threatened plants have been recorded within the wetland, including the water milfoil, the swamp helmet orchid and the club moss.

The birdlife includes the pūkeko, the bittern, the grey teal, the spotless crake, and the North Island fernbird. The pūkeko, essentially a bird of swampy ground, lagoons, reeds, rushes and swamps, is probably one of the most recognised native birds in New Zealand with its distinctive colourings and habit of feeding on the ground. It is found all over New Zealand. Commonly seen along marshy roadsides and low-lying open country, the bird’s range has increased with agricultural development. Unlike many other native birds, the pūkeko has adapted well to new habitats, such as grassed paddocks, croplands and even city parks, a necessity brought about by disappearing wetlands.

When severe weather events strike, the volume of sediment-laden stormwater run-off generated can be horrendous. Not allowing silt-laden run-off to enter directly to the Whangamarino wetland was of utmost priority in the development programme for Baldwin’s Quarry.

Creating a wetland was a low cost, low maintenance sustainable water treatment option. Its creation was enabled by the need for a stockpile area at Baldwin’s Quarry. This allowed removal of overburden to be done in a responsible manner with the Buckley dairy farming operation and quarry operator agreeing on joint benefits.

As described above, it was an opportunity to treat sediments, and allow clear water to drain to the Whangamarino Heritage Wetland.

The wetland’s island solved several challenges, including creating multiple ponds and a long water flow path, enabling greater pond retention times and promoting the filtration of microscopic fines through the vegetated wetland (Figure 2).

Figure 2. Stage 1 of the wetlands involved creating multiple ponds and a long water flow path.

Although work on the development of the wetlands project had been underway for nearly three years, the Waikato Regional Council had no hesitation in retrospectively approving a resource consent (May 2008). This was mainly due to the “full compliance” status issued at a previous audit of the discharge consent conditions in the permit issued for Reilly’s quarry operations.

The wetland’s resource consent conditions were very simple:

  To place quarry overburden and clean fill onto rural land to create a wetland area that drains into the Whangamarino Wetland.

  To manage noise, dust, landscape, rock spillage, and trimming of vegetation (to maintain sight distances along the road network).

  That the wetland construction plan be based on a two-stage operation: Stage 1 (shaded in blue) and Stage 2 (shown in green), as per Figure 1.

Wetland construction 

In Stage 1, quarry run-off is directed to the southern end of Pond 1 via a tree-lined stream across the Buckley dairy farm, while the surrounding pasture drains to Pond 3. Water in both ponds 1 and 3 are continuously filtered as it moves in a clockwise direction around the island.

Filtered water enters pond 4 via a rock culvert and discharges to the Whangamarino wetland as polished, clean water. The length of the watercourse is approximately 520m. To cater for the huge volumes of run-off generated in severe storm events, a section of the access road around Pond 2 was lowered to form a spillway, allowing excessive run-off to discharge directly to the Whangamarino Wetland without “blowing out” the bunds/roads.

Prior to the construction of Stage 2, the farmer pumped nitrate-laden dairy farm run-off collected in a table drain on the pasture-side of the levee directly to the Whangamarino Wetland. During Stage 2, construction of a new levee bund/access road on the southern side created a new Pond 1, allowing additional filtration and to lower the nitrate levels from pasture run-off. Pond 1 is about 400m in length.

In the completed wetland, Pond 1 collects run-off from both the Buckley farm and the quarry. The combined run-off enters Pond 2 via a rock-lined culvert, as described in Stage 1. Polished clean water enters the Whangamarino wetland via Ponds 4 and 5.

All ponds now feature prolific growth of grasses and sedges.

The wetland development commenced in 2005. For the road network around and within the pond complex, all roads were constructed on peat which requires pre-load to allow moisture to dissipate and the peat to settle and compress. Without the luxury of drilling and placing vertical wick-drains to speed up the removal of moisture from the peaty soils, the pre-load process had to be taken slowly. Construction in too short a period could have resulted in the roads rolling over into the surrounding peat like a piece of clay on top of a balloon.

The clearing of willows took several years. The Waikato Catchment Ecological Enhancement Trust (WCEET) sponsored the supply and planting of more than 15,000 native trees and shrubs to beautify and enrich the whole development. In addition, Kerry Reilly grew and planted hundreds of cabbage trees and flaxes obtained by harvesting seeds from existing plants already growing within the Whangamarino wetland.

The wetlands project garnered support and interest from many quarters. Dairy NZ realised the opportunity to demonstrate the quarry owner and farmer’s joint commitment to caring for the environment by facilitating in 2012 a field day at the wetland. The association hosted a large contingent of overseas guests, and local farming managers, together with district and regional council representatives.

Coaches were used to transport overseas visitors from the Dairy NZ conference to the wetland area on an educational site visit to promote the results of a farming owner working in conjunction with a quarrying company to achieve an outstanding new conservation habitat.

“It was encouraging to have the confidence of our neighbours,” Reilly said, “including the Waikato District Council and Environment Waikato for issuing the necessary consents to allow this project to proceed and the sponsorship of WCEET for its funding for the trees and shrubs.

“I am confident that this will help lead the way for other industries and farmers to co-operate and demonstrate that we can all work together to create a cleaner New Zealand.”


The reservoir in Baldwin’s Quarry acts as a safety net to receive run-off in heavy rainfall events. After sediments settle, clean water can be pumped away via the wetlands for further polishing.

Reilly said a survey conducted in December 2018 by market researcher Colmar Brunton found 82 per cent of New Zealanders want tougher rules to protect rivers and lakes from pollution and would support a move to introduce mandatory environmental standards for New Zealand’s waterways, even if it meant regulating intensive farming.

In 2014, the NZ Aggregate and Quarry Association received four nominations for the Mimico Environmental Award. Kerry Reilly received the gold award for Baldwin’s Quarry wetlands project.

In 2015, neighbouring farmers Peter and Judi Buckley received the Waikato River Authority Catchment Improvement Award.


The project has been a win/win for all concerned. Peter Buckley (who is a past chairman of the regional council) can demonstrate that farming discharge water can be naturally enhanced by Baldwin Quarry’s wetland. The quarry owner can sleep at night when the rain is pouring down, knowing the discharge water is not polluting the environment. The iwi and public can see that a solid commitment has been made to protect local waterways, and the fish and birds thrive in a clean healthy environment.

Reilly presented his paper – Baldwin’s Quarry, Construction of a Wetland – A Natural Solution –  at the Auckland branch meeting of the Institute of Quarrying New Zealand (IQNZ) on 19 March, 2019. It received high levels of interest, as evidenced by the large number of questions and feedback.

At the IQNZ’s joint annual general meeting with the NZ Aggregates and Quarries Association in Invercargill, on the South Island, in July 2019, Reilly received the Lyn Jordan Memorial Trophy for the best technical paper in New Zealand. His presentation also received the international Caernarfon Award, the annual international prize presented for the best paper at any worldwide Institute of Quarrying event that has contributed most to the technical, environmental or strategic advancement of the industry.

“By sharing the journey of this wetland project, I hope that others will be inspired to make a similar commitment to return our rivers and streams to clean waterways,” Reilly said. “The wetlands don’t have to be as large as the ones we’ve created. Building multiple smaller ones will work, we all just need to do our bit for an environment with clean water.”

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