Call for Cantabs to think about future of water

Call for Cantabs to think about future of water

Canterbury would have much to gain from improving its water management practices but needs more information on how land use affects the water supply, Waterways Centre director Jenny Webster-Brown said during a recent talk at Lincoln University.

Almost three-quarters of New Zealand’s total water allocation comes from Canterbury, and current land and water use practices mean the future of the region’s water quality is far from certain, Dr Webster-Brown said.

“The region’s water management challenges have arisen for a unique combination of reasons. The main causes include a reliance on untreated groundwater for drinking, intense agriculture production and the fact that most of the population live in the lower catchments.”

Dr Webster-Brown said while a lot of water is used in irrigation on the plains, urban Christchurch residents go through around 400 litres of water each per day; one of the highest rates of city use in New Zealand or Australia.

“Irrigation takes have increased by 50 per cent per decade since 1960s, and are expected to double in the next 10 years,” she said. “Although it is unlikely that there will ever be insufficient water for drinking purposes in Canterbury, the quality of the water is likely to be a significant future concern.”

Dr Webster-Brown said the high nitrate levels in Canterbury groundwater are expected to increase further in the immediate future.

“The age of the groundwater carrying the nitrate is important,” she said. “Research by GNS has shown that nitrate in the groundwaters to the west of Christchurch is 30-to-60 years old and probably dates back to the increased application of fertiliser in the post-World War 2 era.

“We therefore have another 30-60 years’ worth of nitrate still to travel through the groundwater system, affecting drinking water supply and low land stream quality.”

It will be very difficult for more intensive irrigation and dairying to occur on the plains without the legacy of nitrate in groundwater increasing for future Cantabrians, Dr Webster-Brown said.

“In contrast to sewage bacteria contamination, which is already a problem periodically for many rural town water supplies, nitrate is soluble, making it very difficult to remove from drinking water using standard treatment techniques.

“The big questions are, what is the trajectory of increasing nitrate concentrations in the groundwater and what are our options for reducing its concentration in drinking water?” she said.

“If future irrigation water is taken from river water storage, instead of groundwater, will this improve or further degrade groundwater quality? Are there other economically viable options for agricultural growth in Canterbury, rather than focusing on dairy conversions?”

Dr Webster-Brown said we need a lot more information on alternative land-use scenarios and their effects on lowland water quality in order to manage the resource more effectively.

“We also need informed public debate and reasoned discussion about these issues.”

The Waterways Centre for Freshwater Management is a teaching and research facility that was created in 2009 by Lincoln University and the University of Canterbury.

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