Rebuilding the wastewater network
Fixing the Christchurch's wastewater network is a key part of the infrastructure rebuild. Collecting, transporting and treating wastewater is vital for a healthy, functioning city.
Sometimes we have taken urgent short-term measures like pumping sewage into our waterways. These are a health hazard for you and your family.
Always check for current waterway and coastal water usage conditions and heed all warnings and restrictions on use.
Techniques we use
- Alternative new systems
- We may install, on a case-by-case, best-fit basis, some innovative new replacement systems at local levels. These are pressurised sewer systems (requiring tanks on private property, already installed as temporary systems in Avondale), vacuum sewer systems, and enhanced gravity sewer systems.
- Emergency pumping
- On occasions, we have to prevent wastewater building up in populated areas by pumping it into waterways for a short time. This dilutes the sewage and sends it out to sea. It is an emergency measure generally employed only after serious new damage has occurred, causing sewage to flow across the ground. We stop doing this when we have provided a temporary or permanent fix.
- Pipe bursting
- This allows us to restore pipes without digging a trench. Our workers pull a rod connected to a bursting (expander) head through damaged pipe. This disintegrates the old pipe, pushes it aside, and widens the space. A new replacement pipe is dragged through in the same motion just behind the bursting head.
- Raising pipes
- We raise pipes for two reasons. Most pipes run at downward pitches (gradients) and use gravity to help them flow. Some were vertically displaced and lost their fall, so the gradient has to be restored. The other reason is that many pipes were laid as much as 5 metres underground. This makes future maintenance difficult, so we take the opportunity to bring them closer to the surface.
- More pump stations
- Because we are raising the pipe network, we need to install more pump stations. We are also doing this to increase the pump station network's ability to withstand failures. More smaller pump stations will move us toward a more resilient pump station network.
- Bypass pumping
- When a small failure prevents a large part of the network from functioning, it's usually best to bypass that failure by pumping around it through a temporary diversion running from one manhole to the next.
- Better materials
- When presented with the opportunity, we replace infrastructure with a stronger alternative. In the case of pipes, we replace older materials with longer lasting and more robust polyethylene or PVC piping.
- Hand digging and hydro-excavation
- Sometimes we need to be extremely careful to avoid disruptions to other services using the same trench, and to avoid dangers like electrocution. In these cases, we can't use traditional excavating machinery, and have to hand dig or use hydro-excavators.
- Directional drilling machine
- A new drilling machine is allowing us to lay pipes much faster. We can weld longer pieces of pipe together and drag them along the old pipe alignment in a similar way to pipe bursting.
- Temporary wastewater systems
- We sometimes set up temporary local systems so that we don't have to pump wastewater into our waterways, or so that residents can have flushing toilets. They are temporary either because the affected pipes are within a red zone, or because we are planning permanent fixes on a larger scale. Our success stories include installing a temporary pressure sewer system in Avondale within the residential red zone, and installing a temporary wastewater pump station for some residents on Avonside Drive.