The Delany Wetland

An Amuri Basin Future Farming Project Pilot

A pilot programme is helping us determine if constructed wetlands could be implemented more widely in the Amuri Basin as an effective long-term solution to water quality issues. A four-year NIWA study has found that constructed wetlands can replicate natural systems to remove nitrate leaching from dairy farm pastures. Building on these findings, AIC’s pilot project aims to measure the impact of a wetland on water flowing into St Leonards Drain, a waterway with nitrogen concentrations five times the national standard. The trial is an important step in assessing the viability and effectiveness of wetland restoration in the Amuri Basin. Success will provide a template for future projects, enhancing our understanding of scalability, costs, perfomance, ecological values and biodiversity benefits.

At a Glance:

1.6 hectares of pasture restored

4,800 natives planted

60 samples tested per year

Five water monitoring sites

200mm average depth

Project Timeline

Sept 2023 >

Initial investigations and site selection
Feb 2024 >

Site establishment and earthworks
May 2024 >

Trees, flaxes and grasses planted
Aug 2024 >

First round of water testing
Sept 2024 >

Investigations into further wetland sites
Nov 2024 >

Site fully inundated with water

The Trial Site

Several potential sites with groundwater upwelling were considered, with the final selection based on replicability, low construction and maintenance costs, and suitable soil conditions. Approximately 1.6 hectares of pasture on Jerseyland Dairies in Culverden was eventually selected for the trial site. It has the ideal peaty soil layer over a clay base – the clay slows drainage, ensuring water stays in the wetland long enough for effective treatment. Proximity to two natural wetland features provides advantages for biodiversity and functionality.

Site History

The trial site is located on an operational dairy farm, adjacent to grazing paddocks and farm access tracks. Landowners Tim and Jo Delany explain they had already retired the surrounding natural wetland areas. Historical survey maps from the 1860s suggest that the site was part of a natural wetland, one of several drained during land development in the Basin in the early 1900s. The concept of a treatment wetland fits into the farm philosophy to restore biodiversity and natural function of the land.

The Design

Designed and built by Shane Dwyer of Dwyer Lewis Earthworks, with scientific oversight by Dr Peter Brown (PZB Civil and Environmental Engineering), Dr Lee Burbery (DairyNZ), and Brian Ellwood (Lowe Environmental), the trial has employed a ‘minimally constructed’ approach. The land was contoured into a serpentine system to reverse drainage and create conditions for slow water flow across the wetland, promoting maximum attenuation - allowing sediments to settle and contaminants to be removed through adhesion to vegetation and anaerobic decomposition.

Riparian Restoration

Totara and Kowhai trees, along with native flaxes, grasses and shrubs from Synlait Milk’s industrial nursery Whakapuāwai, were planted by Hurunui Natives with support from Te Rūnanga o Kaikōura. Seeds collected from an nearby wetland are being raised in Synlait’s nursery and will be reintroduced to the site in late 2025 to enhance nutrient uptake. A total of 4,800 specimens have been planted in and around the wetland. Water flow into the site has been temporarily reduced to allow the plants to take root and establish properly.

“It takes time for the soil to build up nitrate-breaking bacteria, but early results are promising, as indicated by the oily sheen of bacterial activity on the water surface.”

-Mike Hennessy, AIC’s Environmental Projects Lead

Monitoring

A full suite of water quality tests is conducted monthly at five monitoring sites across the wetland. The first round of sampling, completed in August 2024, revealed a substantial reduction in nitrate levels. While this initial result is promising, it's essential to base our conclusions on a robust set of statistically significant data. We look forward to sharing the wetland's performance as more data becomes available.

Enhancing Biodiversity

As the water levels rise, so too does the biodiversity. We’ve already enjoyed the lively chorus of frogs, witnessed native tuna (freshwater eel) swimming leisurely through the waters, and been treated to a stunning dawn chorus from the growing number of bird species calling the wetland home. It’s very pleasing to see the wetland flourishing and supporting diverse wildlife.

Play the video recorded by our wetland camera to hear the frogs!