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The Central Interceptor

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Central Interceptor (CI) is the name of a large wastewater tunnel that will make waterways in central Auckland cleaner. When the CI is built, it will reduce overflows into streams and the Waitematā Harbour during rain events and therefore help to create a better environment.

The need for a new wastewater tunnel

Auckland’s underground wastewater system is nearly 100 years old, and it was built when Auckland’s population was much smaller. Parts of it need replacing because there are often breaks or leaks.

Auckland also needs new tunnels and pipes because there are more and more people coming to live in the city. New homes are being built every day and all of them need to connect to the wastewater (and drinking water) systems.

Another problem Aucklanders face today is that when it rains hard the system cannot handle all the stormwater as well as all the wastewater that’s coming in. The only place for some of that mix to go is into nearby creeks and streams and then out to sea. People become aware of this when they can’t go swimming in a creek or at the beach – that’s not a nice thing to happen.

We all want to enjoy clean waterways and open spaces. Image: Watercare.

The longest wastewater tunnel in New Zealand

Watercare is always building new tunnels and pipes. One of these is the longest wastewater tunnel in New Zealand, called the Central Interceptor (CI). It has this name because it goes under central Auckland and it picks up, or ‘intercepts’ the mix of wastewater and stormwater before that can go into the waterways.

The CI will be nearly 15 kilometres long and 4.5 metres high (that’s as tall as a giraffe): it will be able to hold 200 million litres of water, which is the same as about 700 school swimming pools. Think of a litre of milk in your fridge: there are 300,000 of these in just one school pool.

The Central Interceptor will lie between 15 and 110 metres underground. It will run from Grey Lynn, under central Auckland and the Manukau Harbour, to the Māngere wastewater treatment plant. The tunnel will slope downhill, so it collects wastewater all along the way, taking it to Māngere to be cleaned up. It will have two link sewers and 16 shafts along the route for diverting flows and overflows from the existing wastewater network into the tunnel.

The Central Interceptor will lie between 15 and 110 metres underground. It will slope downhill and collect wastewater along the way to the Māngere wastewater treatment plant. Image: Watercare.

The Central Interceptor will be the longest wastewater tunnel in Aotearoa. Image: Watercare.

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Visit Watercare's Central Interceptor website - includes FAQs, key facts, and the latest videos.

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