River flows low following settled dry weather and low rainfall

River flows in all Canterbury foothill rivers have been exceptionally low this Spring due to a long period of settled and dry weather starting in August and running into November.

“We’ve had enquiries from members of the public who have noticed the low flows in their local rivers, and are concerned about the effect this is having on water quality and ecosystem health,” said Tim Davie of Environment Canterbury.

“We noticed in September that many streams were beginning to display lower than usual flows.

“As a result in some areas we are already measuring flows more often so we can better track what is happening to our streams and rivers.”

In North Canterbury flows are lower-than-average. For example French Farm Stream on Banks Peninsula had the second-lowest monthly mean ever in September and October with a similar trend for Lyell Creek in Kaikoura.

“We are expecting a surface water deficit going into summer which is expected to be a dry period. We will continue to make additional river measurements.

“It is exceptional that in South Canterbury the Orari River – which flows from the foothills past Geraldine to the coast near Temuka – become unconnected across the plains during Spring.

The Orari recently was at a flow rate of 3.9 cubic metres per second (cumecs) at a monitoring site in the Orari Gorge, well below the average November mean flow of 9.3 cumecs. The lowest recorded flow for November was 2.95 cumecs in 1984.

The last substantial flood flow in the Orari was in early June, and floods provide much of the water which soaks into the plains and helps to keep the river connected between the coast and foothills.

Other South Canterbury rivers are showing similar low flows with the Hinds, Waihao, Orari and Otaio rivers dry where they cross State Highway 1.The Opuha lake level is 386.72 metres compared with a full level of 391.2 metres.

Flow rates in South Canterbury rivers

River

November mean flow

(cubic metres per second)

Mid-November flow

Cumecs

Orari River

9.3

3.9

Tengawai River at Cave

3.1

0.9

Temuka River at Manse Bridge

5.4

1.2

Pareora River at Huts

2.8

0.6

Waihao River at McCulloughs

1.9

0.4

Environmental effects of low flows and how that is managed

The low flows in Canterbury rivers will be having an effect on river health and ecosystems.

The provisions in plans - such as the Orari River Plan and the Land and Water Regional Plan - are designed to protect stream and ecosystem health by putting limits on the amount of water that can be taken from rivers and streams. What this means is when the flow in a particular river goes below a certain point, water takes for irrigation must stop.

Environment Canterbury’s response in a potential dry season such as this is to ensure that rivers flows are being accurately and adequately monitored and that water-use restrictions are put in place in time to protect rivers. Water users are also being reminded regularly of the need to use water as efficiently and effectively as possible.

For more information on river flows visit: http://ecan.govt.nz/services/online-services/monitoring/river-flows/pages/default.aspx