Working to reduce overflows

What is a wastewater (sewage) overflow?

A wastewater (sewage) 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

To help reduce overflows during wet weather, 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

We also carry out inspections and tests on the public wastewater and stormwater network and private drainage across Auckland. This is to find out where stormwater is entering the wastewater network. We inspect wastewater pipes, stormwater downpipes and gully traps in a variety of ways, including:

  • Smoke testing – harmless smoke, similar to what is used in discos and theatres, is used to pinpoint any places on a property where stormwater is entering our wastewater network or vice versa
  • Dye testing – non-toxic dye is poured down a specific drain so we can trace where the water ends up
  • CCTV camera inspections – a camera is inserted down the pipe to inspect internal conditions

Households that require a property inspection will be notified by a letter in the mail, confirming when the investigation will take place.

You can help prevent overflows by checking that your stormwater downpipes and gully traps are installed correctly, and landscaping and paved areas are draining into the stormwater network.

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 (sewage) 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 (sewage) 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.