Concern about possibly unconsented water take for irrigation in the Grey Valley is being investigated by the West Coast Regional Council.
Generic river water Photo: RNZ / Rebekah Parsons-King
Fish and Game had raised the matter after members had complained about low flows in the Grey River catchment last month, questioning the rate of water extraction.
Council consents and compliance manager Colin Helem said staff had visited one farm in the area but it was not clear if there had been any unauthorised water take or if the low flows were due to the extended dry weather.
"It's something we need to get on top of next summer," he said.
The West Coast has been fairly dry until recently with near record low river levels recorded from February to April.
A hydrology report this week noted the 'low-flow trend' from March had continued into early to mid-April, "with the majority of our monitored rivers reaching flows not seen for many years, and below their mean annual low flows".
"This trend would have continued were it not for the sporadic weather events that brought much needed rain to the West Coast," planning team leader Lillie Sadler said in a report.
The most notable rain events were on 20-21 April, when many of the rainfall monitoring sites in Westland received more than 20mm an hour and some up to 67.5mm.
"The Hokitika catchment recorded the most rainfall, with totals above 500mm at some of its alpine sites."
Downstream, the river rose rapidly to peak at the Hokitika Gorge at several hundred cubic metres below the highest flow on record.
"Fortunately, the northern branch of the catchment did not receive the same intensity of rainfall as the southern part," Sadler said.
Councillor Peter Ewen, who has recorded weather in the Rapahoe-Runanga area for 40 years, said the intensity of the 21 April rain event and the washover effect of the high flows in Coal Creek and the adjoining Seven Mile Creek catchment, had been "extraordinary".
He said it was the highest rainfall he had recorded for such a short period since 1981.
"It just shows you with coastal rain, the intensity there, to say nothing of what happens in the backcountry."
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