Many farmers who are part of the the Central Plains Water run-of-river irrigation scheme have stopped using their groundwater wells
Canterbury’s Central Plains Water Trust chairman Denis O’Rourke said although the Rakaia River-based scheme had only been going for one year, the volume of groundwater abstraction had reduced and this would be good news for aquifers.
The scheme was touted to provide multi-million dollar benefits to the region as well as ecological improvements.
There were 152 consented groundwater bores in the scheme area allowing abstraction of 97,207,658 cubic metres a year but 70 per cent of the groundwater water allocation was not used last year thanks to the irrigation scheme, he said.
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The amount unused was the equivalent to two Wellington Harbours, O’Rourke said.
However the CPW farmers were not surrendering their groundwater permits and were probably holding onto them as insurance against adverse conditions, he said.
The CPW sustainability report said dairy and various combinations of dairy and beef grazing accounted for a significant component of overall land use.
“Because no water was taken from the Rakaia River during mid to low flow periods, the take of water for the scheme had no effect on the natural character of the river nor on its ecology,” O’Rourke said.
He predicted the effect of leaching nitrates and phosphorous into the ground water will reduce in future years because of the expected rise in the water table which would also reduce pollution of Te Waihora/Lake Ellesmere on the coast, one of New Zealand’s most degraded lakes.
“It is likely to take up to 30 years before the water in the system will be fully flushed away, and up to 70 years before the full positive effects are seen in Te Waihora,” O’Rourke said.
However O’Rourke’s positive report was disputed by freshwater ecologist at Massey University Mike Joy.
Joy said the notion the scheme would improve Te Waihora/Lake Ellesmere was completely speculative without any evidence.
Joy said the overall ecology of the Rakaia River depended on its high flows and it was “rubbish” to claim the natural character of the river was unaffected by taking water at higher levels.
The amount of groundwater unused showed the incredible amount of water used by the scheme, and confirmed how over-allocated the groundwater was, Joy said.
The Rakaia River alpine water being used by CPW would have gone into the aquifers, Joy said.
One area O’Rourke and Joy agreed on was the over-allocation of ground water.
O’Rourke, who is a member of Parliament, referred to a recent media release from his NZ First leader Winston Peters who referred to trading of water permits in Canterbury as a scandal.
The HydroTrader water permit exchange web site shows about 60 groundwater permits available for trade, although technical director Warwick Pascoe said the regional plan forbade CPW shareholders from transferring them.
Pascoe expected that CPW farmers would retain their groundwater permits as a back up but it was likely in future years when they came up for renewal the regional council, Environment Canterbury, might require them to be surrendered.