Christchurch rivers lowest they've been in decades

Ilam Stream by the University of Canterbury has almost run dry.
IAIN MCGREGOR/FAIRFAX NZ

Ilam Stream by the University of Canterbury has almost run dry.

Christchurch's rivers are the lowest they've been in several decades, records show.

Several of the city's waterways dried up earlier this year, upsetting residents. Months later, some streams remain low and will likely dry up again next year if rain does not arrive.

Environment Canterbury's (ECan) Christchurch-West Melton zone committee met with the Christchurch City Council on Tuesday to give a monthly report on its work in greater Christchurch. 

Recordings from the headwaters of the Avon, Heathcote and Styx rivers showed they were at their lowest levels in 20 to 30 years, the committee said.  

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Tributaries such as the Waimairi and Wai-Iti streams near Fendalton dried up completely earlier this year. Water levels had dropped in the past, but not to the same extent.

The Christchurch-West Melton zone was one of the "luckier zones", the committee said, as most of the inflow into the aquifer north-west of the city came from the Waimakariri River. The rest came from rainfall recharge.

ECan surface water science manager Tim Davie said last month's rainfall levels were "well below" average in the city and groundwater was at a record low.

"To get the amount of groundwater recharge for streams not to dry up next summer we need a very wet late winter and spring."

Fish and Game North Canterbury manager Rod Cullinane said his organisation was concerned about the low water levels and did not believe low rainfall was the issue.

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"We are very much of the view that there's got to be some link between what we're seeing in the lack of water in the inner city streams and the irrigation draw off in inland Canterbury," he said.

"We do not accept ECan's reasoning that it is simply the result of a lack of rainfall."

Cullinane, who is running in ECan's election in October, said he wanted to know why the regional council did not take rainfall levels into account when granting water usage consents.

Climate changes had increased pressure on water supplies, but urbanisation and city water demand took the greatest toll on the city's waterways, University of Canterbury professor Bryan Jenkins said.

"The more we take out for the Christchurch water supply, the less that will be in the Avon, Heathcote and Styx rivers."

Jenkins said infrastructure such as roads and roofs prevented stormwater from infiltrating groundwater and recharging aquifers.

He suggested that for streams such as the Waimairi, local solutions could include changing the city's approach to drainage infrastructure.

Older infrastructure sent stormwater to surface water, preventing recharge of the waterways.   

He said caps or regulation on water usage needed to be put in place to decrease pressure on river headwaters.

"The drying reaches of the Waimairi and Wai-iti streams illustrate the complexity of our water resources and the need for both local and regional approaches to their management."

 - Stuff

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