CATCHMENT SOLUTIONS PROJECT - MAHARAKEKE & PŌRANGAHAU
SUMMARY
The Watch Our Water Maharakeke and Pōrangahau (WOWMAP) Catchment Group was one of three catchment groups engaged by Massey University as part of a Catchment Solutions Project.
This three-year project aimed to co-develop and demonstrate practical edge-of-field technologies to reduce contaminant losses from agricultural land to waterways. It also sought to inform the development of resources and educational materials that farmers can use well beyond the life of the project.
The project was funded by the Ministry for the Environment through the Essential Freshwater Fund, with additional support from the Hawke's Bay Regional Council.
Over the course of the project, TLC supported Massey and local farmers through five rounds of farm water testing, and supported them as they developed and trialed two innovative edge-of-field mitigation structures in the Maharakeke and Pōrangahau catchments.
WATER TESTING PROGRAMME
TLC supported the Massey Catchment Solutions team to deliver a comprehensive water testing programme to better understand nutrient loss flow pathways.
Sixteen landowners from across the catchments took part in five rounds of on-farm water testing. Samples were analysed for:
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Dissolved Inorganic Nitrogen (DIN)
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Dissolved Reactive Phosphorus (DRP)
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Sediment
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E. coli
Individual farm results remain confidential. However, key findings from the wider analysis can be shared.
Key Insights
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Long-term water quality data indicates improving DIN levels in the main streams.
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There is high spatial variability across sampling sites.
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Some local drains and streams recorded elevated concentrations of DIN, DRP and suspended sediments.
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Many hill country springs showed elevated nitrogen levels, highlighting the need for further sampling and investigation.
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Testing indicated potential positive effects from on-farm water systems and riparian management on water flows.
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Water in local streams is between 9 and 44 years old. This highlights the long lag times that can exist between land use practices and observable changes in water quality.
While the investigation of hill country springs sits beyond the formal remit of the Catchment Solutions project, both TLC and WOWMAP are particularly interested in understanding the elevated nitrogen levels in these springs and how downstream water systems and riparian management may be mitigating impacts.
EDGE-OF-FIELD MITIGATION
STRUCTURES
Water testing results, combined with site visits and workshops, helped identify two farms near Takapau as ideal sites to build and trial two innovative edge-of-field mitigation structures - the first of their kind in Hawke’s Bay.
The two structures are:
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A detainment bund to treat surface runoff
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A woodchip bioreactor to treat elevated nitrate levels in spring discharge
Detainment Bund
A detainment bund is a specialised sediment trap designed to temporarily detain stormwater runoff from pasture land. Low earth bunds are constructed across valley floors to briefly pond stormwater during high-intensity rainfall events. This slows water movement and reduces significant amounts of sediment, phosphorus and pathogens before water is released downstream. Water ponding is controlled via a flow structure and spillway to manage extreme runoff events. Importantly, pasture growth in the ponding area is not compromised due to the temporary nature of the storage.
In 2025, a detainment bund was constructed on Graham and Fiona Bayliss’ farm near Takapau. It was a while before there was sufficient rainfall to assess its performance.
Woodchip Bioreactor
A woodchip bioreactor is a novel edge-of-field practice designed to reduce nitrate losses from agricultural land. It works by diverting drainage or spring water through a pit filled with woodchips (a carbon source). Naturally occurring soil microorganisms use the carbon to break down nitrate in the water through biodegradation processes.
Woodchip bioreactors are relatively straightforward to construct, require low maintenance, and typically last 10–15 years before the woodchips need replacing.
In 2025, a woodchip bioreactor was installed on John and Cushla Williams’ farm to treat nitrate-rich spring water.
Massey will continue to monitor the effectiveness of these mitigation strategies in reducing contaminant losses, and we look forward to sharing the results in due course.
On the Massey University Catchment Solutions webpage you can take a tour of the woodchip bioreactor and detainment bund as well listen to farmer interviews about their experiences with this project. Head to www. catchmentsolutions.co.nz
WITH THANKS
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Watch Our Water Maharakeke and Pōrangahau Catchment Group (WOWMAP)
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Massey University Catchment Solutions Team including Associate Professor Ranvir Singh & Research Officer Fernando Avendano
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All the farmers who took part in the on-farm water testing programme
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Graham Bayliss and Fiona Greene
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John and Cushla Williams
FURTHER INFORMATION & CONTACT
To find out more about the Maharakeke and Pōrangahau sub-catchment, head to the Maharakeke & Pōrangahau sub-catchment page on this site.
To get in touch, please contact TLC Catchment Coordinator Kahlia Fryer:
Email: tukitukicoordinator@gmail.com
Phone: 027 3426071