Water Main fails - questions asked

Jul 28, 2009

A split in the same Fernhill water main that ruptured two weeks ago will require close scrutiny, Queenstown Lakes District Council infrastructure services general manager Mark Kunath said.

“Our contractors were alerted by a helpful resident calling the 24-hour Council service number at 1.50am, which coincided with an alarm indicating a drop in water levels at Fernhill reservoir and we were able to isolate the problem in time to maintain the second reservoir supply,” Mr Kunath said.

This meant that - whilst residents were asked to conserve water - supply was able to be maintained.

The same pipe, in the same location, ruptured 18 months ago and the supply also failed on July 14, causing a major water outage at Fernhill.

“Clearly this creates questions because these pipes, which normally have an 80 to 100-year life span, should not be failing at all,” Mr Kunath said.

Recent earthquakes may have contributed to today’s failure but Mr Kunath said the Council needed to rule out all considerations, including pressure loadings and also workmanship.

“The main pipes are effectively packed neatly into the ground to allow support. If the ground shifts or if the pipe is not correctly installed it can cause a small split of this nature in an otherwise healthy pipeline. We need to take a close look at what has happened and why,’ Mr Kunath said.

This morning’s failure sent a large quantity of water down a section of bank and onto the Fernhill Road.

“Something in the region of 700 cubic metres was released through the split. Fortunately this travelled down the road and did not cause damage to private property but has undermined a small area in front of the reservoir and left a trail of silt which went all the way to the One Mile Roundabout,” Mr Kunath said. As a precaution, geotechnical engineers visited the site today and would provide a report to Council in the next few days.

The release was more a small stream than a deluge. “You can see the nature of it from the way it has travelled down one side of the road in the gutter,” he said.

Reinstatement and pressure testing of the main was completed this afternoon, with normal water levels expected to be restored this evening.

“With three breaks in a 20-year pipeline in the last 18-months we need to take a very hard look at the integrity of this main to ensure this episode is not repeated and to give Fernhill residents some security in their supply”, Mr Kunath said.
A range of measures would now be investigated including ‘shut off’ valves at the reservoir to eliminate future significant water loss, he said.


For further information please contact Mark Kunath 03 441 0499.