Deep dive into the Taranaki Street Rising Main works

We’ve spoken to Taranaki Street Rising Main Project Manager Dave Philipson, of G. P. Friel Ltd, to find out more about the works. 

What is a rising main and why do we need it? 

Most of our current wastewater network is comprised of pipes that fall under gravity to the lower part of the city. A rising main aims to get the waste to rise from the bottom of the city to the top. So we put it under pressure and force it up. 

The rising main that we’re building on Taranaki Street will be used to send waste to the main interceptor tunnel, which carries wastewater to the Moa Point treatment plant. It will be connected to the existing rising main network and help continue service if other mains need to be replaced in the future. If a problem arises, such as a burst pipe, this system will be able to pick up the load and pump it via an alternative route to the interceptor. 

The new rising main network will also cater for growth in the city by allowing us to move more waste.

What will the next few months look like with this work?

New technology is being used to reduce disruption. The team are using a new piece of kit called an ‘ Auger Boring Rig’, which is the latest in ‘guided trenchless’ technology that uses a smart front steering system to horizontally drill and fit new pipe. Using this kit means a massive 4,300 tonnes of waste will not be hauled by big trucks to the landfill, which reduces noise, dust and disruption! 

What would happen if this work didn’t go ahead?

We generally design things to last for 100 years and the existing system was built in the 1930s, so the old network is reaching the end of its life. We can already see this with major bursts, like on the main in Victoria Street, which has had several recent bursts, and Featherston Street which burst during the Rugby World Cup. All these pipes need to be renewed. 

If we don’t do this work, we are likely to see more bursts that will result in waste being discharged to the harbour. And we will not be able to build more residential properties in the city.

What is the history of the area?

In the late 1800s, Wellington city was growing but there wasn’t a wastewater network. It wasn’t until 1872 when the NZ Public Health Act banned cesspits and required cities to have sewerage systems. 

At the time, local leaders were opposed to the cost and decided that night soil collections and surface drainage were more effective and cheaper. However, the growing population of 20,000 ended up having poor sanitation, with typhoid fever and cholera. After 77 deaths, Wellington City Council appointed a Drainage Commission. 

This commission recommended a sewerage scheme.

Six years later after much tunnelling, Wellington had its first ‘wastewater system’ – a network of pipes in residential areas around the harbour and a large pipe called ‘the interceptor’ taking the city’s flows to an outfall at the South Coast, near Moa Point.

Find out more about the Taranaki Rising Main on the Wellington Water website.