Irrigation New Zealand

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24th March 2017

The concern being expressed over the state of the Selwyn River shows just how far we’ve come as a community. It wasn’t that long ago when New Zealand’s fresh water resources were pillaged and plundered, used as waste chutes for the factories, industries and cities that developed around them.

That we have come so far as to be absolutely passionate about their care and consumed with concern for their future is commendable. But do we really have to be so dramatic about it?

When I hear people talking about the Selwyn being “in its death throes” and others talking about it “vomiting slime” onto its own stony banks, I really have to question where they’re getting their ‘facts’ from.

The Selwyn is running dry at Coes and Chamberlains Fords because Canterbury hasn’t had any decent winter rainfall for coming up three years. Any rainfall we do get is sucked down below the surface to recharge the groundwater aquifers; the river bed doesn’t get a look in. The slime is the result of shallow pools of water heating up and attracting insects – try it at home with the dog’s water bowl left in the sun for a couple of days. The river is not dying.

Nor has it been sucked dry by irrigation. There are full irrigation restrictions on all surface water takes from the lower Selwyn River. Many groundwater takes are on partial restriction and all deep groundwater takes have restrictions on their annual volumes. This has been the situation since November 2015. When you see irrigators working they will be using water sourced from winter storage, deep groundwater or large alpine rivers which currently have good flows.

And this is where the Central Plains Water Scheme (CPW) comes into play. ECan’s Plan Change 1 treats groundwater and surface water as a single body. It encourages people to move away from using deep groundwater at the top of the Plains by accessing surface water which is available through the Central Plains Water scheme. This keeps the groundwater in the system – data from 2016 shows that the amount of potentially ‘un-used’ groundwater [as a result of consent holders accessing CPW] was 2.5 cumecs.

The Selwyn is ephemeral – meaning it doesn’t flow above ground all of the time. Granted, this summer it has dried up in places it normally flows. But this has happened before. While no one talking to the media can remember the Selwyn ever being this bad, it has been this bad many, many times. Data doesn’t have a short or selective memory – it will tell you that the current situation in the Selwyn is similar to what it looked like in 2005/6, when the river recorded its lowest-ever flows and levels. It will also tell you that the river ran dry in the 1990s and in the 1960s. And well before data was officially collected, Ngāi Tahu ancestors described the river as waikirikiri, meaning ‘river of gravel or stones’ – it was dry way back then.

Before dairy cows; before irrigation – the river ran dry. It might not look pretty, and you might not be able to swim in it, but this is actually the natural state of things. The Selwyn isn’t dying. It isn’t dry because of dairy farmers or irrigators. It’s dry because nature is doing what nature sometimes does.

Hand-wringing and pointing the finger of blame won’t help the Selwyn. What it needs is a couple of wet winters, the assistance of the combined regulatory and community efforts and CPW.  And when all of these things happen, the change will be dramatic.

Graph shows an 18 metre deep monitoring well ECan has at Dunsandel, along the side of SH1 about 200 m from the river. Left side of the graph is meters below ground level.

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