Temuka River gets early warning system

Temuka River catchment residents will be much safer in future flooding following success with a new hi-tech forecasting system.

The system was successfully trialled in the Temuka district during the May floods and has been commissioned for full installation this month by Environment Canterbury.

ECan's director of investigations, Ken Taylor, said yesterday fthat ECan was now able to predict the timing and quantity of flooding in the Temuka River with a good degree of confidence.

The MetService had given an early warning of heavy rain, which was entered into the flood forecast system – which predicted flood flows in the Temuka River nearly two days before they occurred.

The model had been developed by ECan staff in conjunction with an international consultancy group.

Mr Taylor said previously there had been no reliable way to predict the size and timing of floods after heavy rain in short foothill catchments such as the Temuka River. Results from the May 10 flood forecast were very encouraging.

Floods in Canterbury foothill catchments could occur within a few hours of heavy rainfall, not giving councils and Civil Defence enough time to provide adequate warnings, and putting local communities, stock and property at risk, he said.

The system provided an initial forecasted peak flow of 530 cubic metres per second for the May 10 flood, within 6 per cent of the actual figure of 564 cumecs. The peak was within half an hour of the time forecast.

Mr Taylor said the warning system used weather forecasts and real-time rainfall to provide a flood prediction against time.

"Getting a flood forecast wrong is always a major risk. If a flood is not forecast or turns out to be significantly worse than forecast, it can have serious impacts, including loss of life.

"However, if we are overly cautious and predict floods that do not occur people may not take future warnings seriously." The system is being installed at ECan's Timaru office and will run continuously from mid-August, providing engineering staff with automatic alarms of forecast events.

In 1945 the Orari River caused major flooding of the Temuka township. This prompted a large project from the 1960s to the 1980s by the then South Canterbury Catchment Board to improve the level of flood protection. Work included clearing river fairways of willows and building river training works.

A major flood in 1986, however, inundated the southern part of the town but the rest had been protected from floodwaters from the Orari and Waihi Rivers.

- © Fairfax NZ News

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