2026

IAH (NZ Chapter) Technical Meeting – Christchurch

Tuesday 21st April 2026

Presented by: Helen Rutter (Lincoln Agritech Ltd)

Nitrate state and trends: An assessment of historic data and the impact of a major irrigation scheme

Profile: Helen is a Senior Hydrogeologist at Lincoln Agritech Ltd. She has over 30 years’ experience in hydrogeological research and consultancy with an interest in groundwater and drinking water quality, shallow groundwater hazards, earthquake impacts on hydrogeological systems, hydrogeological aspects of ground source heat pump systems, and Canterbury Plains hydrogeology in general. She is a Chartered Geologist and a Senior Adjunct Fellow at the Waterways Centre at UC.

Abstract: In September 2025, ECan councillors declared a “Nitrate emergency” for the Canterbury region. This followed reporting that showed that across Canterbury, 36% of state-of-environment wells had nitrate concentrations greater than half MAV (5.65 mg/l) and over 60% of wells showed a very likely increasing or likely increasing trend. As reported by ECan, the gradual increase in irrigated land area and the associated rise in land use intensity since the 1990s, including a rise in the number of dairy farms, is believed to have resulted in increasing levels of nitrate leaching into groundwater.

Central Plains Water Ltd started in 2014–2017 and now provides water to 45,000 ha; of this, 25,000 ha represents new irrigation, where dryland was converted to irrigated land. The remaining 20,000 ha was land that was previously irrigated, mainly with groundwater. The consents to take water and discharge contaminants were highly contentious, and the outcome of the process was that CPWL have comprehensive monitoring requirements. Having been in operation for around 10 years, it is a useful time to assess the potential impacts of the scheme, and compare with what was predicted at the time of consenting.

The presentation explored some of the longer-term data and patterns that we see in terms of nitrate variability, explained a little about the CPW scheme, and outline the trends that we are observing now.

IAH (NZ Chapter) Technical Meeting – Christchurch

Tuesday 24th February 2026

Presented by: Carl Hanson (Environment Canterbury)

Late-Quaternary stratigraphy of the Christchurch Artesian System, coastal Canterbury Plains, New Zealand

Profile: Carl has 35 years’ experience as a groundwater scientist, more than 20 of those leading groundwater quality science at Environment Canterbury. He holds a Master of Science degree in geology from Dartmouth College, USA.

Abstract: The late-Quaternary stratigraphy of the Christchurch Artesian System (CAS), located along the coast of the northern Canterbury Plains, New Zealand, is formally extended. Six new formations – three interglacial formations and three glacial climate formations – are identified and described. The sequence is recognised in water well logs that extend to depths of up to 250 m, where the Pliocene-Pleistocene Kowai Formation unconformably underlies the sequence and marks the base of the CAS. The new formations underlie the Wainoni Gravel and correlate with international marine isotope stages (MIS) 11-16. The three new interglacial, coastal-marine, fine-sediment units do not extend further inland than the interglacial units in the overlying MIS 1-10 sequence. The three new glacial gravel units and gravel aquifers merge westwards into the continuous sequence of alluvial gravel, sand and silt sediments underlying the inland Canterbury Plains. West of the CAS, it is impossible to distinguish stratigraphic units in bore logs, and the middle- to upper-Quaternary sediments are undifferentiated gravel deposits. This improved stratigraphic knowledge of the sediments beneath Christchurch is important for the sustainable management of the CAS groundwater resource.