Working to reduce overflows

What is a wastewater overflow?

A wastewater overflow occurs when wastewater (sewage) spills out from gully traps, manholes, engineered overflow points or pump stations. It then flows into back yards or waterways and the sea.

Overflows are more common in wet weather, but they can happen at any time if caused by blockages. Learn more

What is the difference between stormwater and wastewater? 

Managing wet-weather overflows

We are:

  • expanding the wastewater network, for instance with the Central Interceptor
  • building storage tanks to hold excess flows that would overload the network during heavy rain. The tanks will slowly release the flow into the network.
  • inspecting the public wastewater network and private wastewater drains across Auckland to find out where stormwater is entering the wastewater network.

We are also working with Auckland Council to manage wastewater and stormwater in the long term.

Projects to reduce overflows

Central Interceptor

This wastewater pipeline will run from Western Springs to the Mangere Wastewater Treatment Plant.

The Central Interceptor is expected to reduce the annual overflow volume to the Waitemata and Manukau harbours by up to 80 per cent.
Learn more about this project

Franklin Road: separating wastewater and stormwater

Work is complete in Franklin Road and Collingwood Street in Ponsonby, with new wastewater pipes installed. The existing pipes are being used for stormwater. 

Building storage tanks

Wastewater storage tanks help to reduce frequency and volume of sewage spills into the environment.

Storage tanks are not continuously full. They are used in heavy rain to hold wastewater, then slowly release it back into the network. We have built tanks in Kohimarama and Henderson. Investment continues with tanks in Glen Eden and Fred Thomas Drive in Takapuna, and we are planning another for Sidmouth Street in Mairangi Bay.

Enhancing pump stations

We are replacing old wastewater pump stations across the network. The new designs incorporate storage tanks.

Hobson Bay Tunnel

In 2011, we completed a 3-kilometre tunnel that crosses Hobson Bay and connects to a new pump station in the Orakei Domain. The tunnel and pump station act as a storage tank to reduce overflows into the bay.