Wainuiomata water pipeline upgrade

Greater Wellington is replacing 300m of water supply pipeline along Wainuiomata’s Main Road to improve the security of our water supply in a major earthquake.

In 2003 a geotechnical report commissioned by Greater Wellington identified that the current water supply pipe is likely to fail in a major earthquake, as the site on Wainuiomata’s Main Road where the pipe crosses with Black Creek is prone to liquefaction (when solid ground becomes loose and take on a liquid quality due to strong shaking).

“The current pipe has served the community extremely well – it’s 125 years-old and is still supplying top grade water to our region’s four cities. However, the upgrade of the Black Creek section is critical for “future proofing” our water supply system and increasing the community’s resilience in a major earthquake,” says Murray Kennedy, General Manager of Greater Wellington’s Utilities and Services Group.

Work will begin in the first week of March and go for up to 10 weeks, taking place between 83 Main Road and the carpark behind Louise Bilderbeck hall (103 Main Road). Greater Wellington’s contractors will replace the 750mm diameter old pipe with a 900mm diameter fully-welded steel pipe that is more likely to withstand a major earthquake and is designed to hang like a snake if liquefaction occurs. The new pipe will serve not only as a replacement for the old pipe but also as a replacement for a parallel pipe that dates back to the 1920s, once it reaches the end of its life.

Traffic disruptions will be kept to a minimum but minor delays will occur. The contractor will maintain one lane of traffic each way along Main Road. The bus stops outside 90 Main Road and 93 Main Road will be relocated a short distance down the road for a short period of time. Access to all properties, driveways and footpaths will be maintained.

A small number of trees in Williams Jones Park are currently on top or near the pipeline and will need to be removed. Replacement trees will be planted away from the pipeline, in consultation with Hutt City Council.

Water supply to properties won’t be affected. The parallel pipe will be used to maintain water supply throughout the duration of the project.

The project is estimated to cost $850,000. Greater Wellington will continue to upgrade the Wainuiomata water supply pipeline, with replacements in less vulnerable areas over the next 10 years.


ENDS


Wainuiomata water pipeline upgrade – FAQs

Why is the pipeline being replaced?
In 2003 a geotechnical report commissioned by Greater Wellington identified that liquefaction after a major earthquake was likely to cause displacement around Black Creek in Wainuiomata. This has serious consequences for Greater Wellington’s water supply pipeline from Wainuiomata (which supplies water to Wainuiomata and to the four cities in our region). There is a section of a 125-year-old cast iron pipe that crosses Black Creek and its joints are likely to fail as a result of a major earthquake.

Why aren’t you replacing the whole pipeline from the Wainuiomata water treatment plant to the Wainuiomata tunnel?
The section we are replacing in this project is the most vulnerable. Other sections of the pipeline, in less vulnerable areas, will be replaced over the next ten years.

Is my water supply going to be disrupted?
No, your water supply will not be affected during the works – a parallel pipe will be used to maintain water supply.

If there are two pipes already in place, why don’t we just use the other pipe?
We’re “future-proofing”. The other pipe dates from the 1920s. The new, bigger pipe will be able to replace both pipes.

Will the work in the recreation field disrupt rugby games?
Yes. Some work will take place on a corner of the rugby fields in William Jones Park in early March – the contractor will reinstate the corner as soon as practical, reducing the time that the park is out of use.

Why are you removing trees?
Some trees in Williams Jones Park are currently on top or near the pipeline and will need to be removed. To compensate for the removal of the trees we will replant with totara trees – away from the pipeline.

Can we still use the carpark behind Louise Bilderbeck hall?
No – the contractor needs that space to store equipment. However, there is still parking available in front of the hall and on the street.

What happens to the old pipe?
Some sections of the pipe may be suitable for use as culverts on Greater Wellington land but this won’t be known until we can fully inspect the pipe. Sections of the pipe that are of no use to Greater Wellington will be sent to a scrap metal dealer for recycling.