Valves may keep city up if quake hits
A small plastic valve invented by the Japanese could keep Porirua’s residents flushing after a major earthquake.
The $ 400 valves are being installed in manholes in areas of Porirua which might see liquefaction in a large earthquake – if any part of the wastewater network is taken out, the whole system comes down.
‘‘The moment [manholes] pop out of the ground you’re done – with these valves you’re down but you’re not out,’’ Capacity Infrastructure Services engineer Des Scrimgeour said.
Four valves are put into the sides of the manholes – in a large earthquake the lid on the valves pops off, relieving the pressure and letting water in, which stops the pressure building up and ‘‘floating’’ up above the surface, putting them out of action.
The valves are being installed at 140 locations around the Porirua CBD and Titahi Bay, at a cost of about $3000 per manhole.
That’s value for money when you consider it can cost about $12,000 to fix a manhole once it’s popped up.
Japanese engineering corporation Nippon Hume invented the techonology and 30,000 manholes around Tokyo are now fitted with the valves – none of the manholes popped out in the 7.3 earthquake in 2012.
Porirua is the first to roll out the technology but Capacity, working with importer Hynds NZ, is hoping other cities in the region will see its benefits.
‘‘It’s just smart business to take an old network and try to rejig it to get it up to earthquake standards of today with prime technology,’’ said Scrimgeour.
‘‘Of 30,000 manholes [using the valves in Tokyo] not one has popped out of the ground, and that’s amazing.’’
Porirua mayor Nick Leggett said he was pleased Porirua was the first to be using the tech- nology and it backed the resilience work the council was doing.
‘‘It shows that a really cost effective, resilient investment in our network can save you money and time later on,’’ he said.