Ōtaki wastewater gravity main
We received $29.3 million from the Crown Fund to help improve water and transport systems in Ōtaki. This money will help us make big changes to the whole network, instead of doing one project at a time.
One project involves upgrading a major wastewater pipe in Ōtaki, to make the town’s wastewater system stronger and better for current and future homes. It'll also make the system work better by reducing the number of pump stations needed.
You can read more about this on our A blueprint for Ōtaki page.
Image: We’re laying 2.7 kilometres of new wastewater pipe along Aotaki Street and Mill Road to the Old State Highway 1. See larger image [JPG 489 KB].
Progress update September 2025
The final stage
The last stage of our wastewater upgrade involves crossing the Mill Road/old state highway roundabout and installing two new manholes on Rahui Road.
The manholes are very deep at this point, so it’ll take some time and a lot of careful planning to install them. Our crew will also rebuild the roundabout with new kerbs and road markings.
We expect to be working in this area until February, including a Christmas work break from 12 December to 5 January. Traffic arrangements, including detours, will change as the work progresses.
Expected stages but please note that dates might change
Stage 1: 26 September to 22 October, 3.5 weeks
Stage 1 tasks:
- Trench from Dunstan Street to across the roundabout
- Remove light from and demolish roundabout
- Install one manhole
- Install ducting for new streetlights
- Install new stormwater pipes at roundabout.
Stage 2: 22 October to 11 November, 3 weeks
Stage 2 tasks:
- Trench from roundabout along Rahui road
- Begin installation of pipe across roundabout and along Rahui Road
- Begin construction of new roundabout
- Complete installation of new stormwater pipes at roundabout.
Stage 3: 11 to 15 November, 4 days
Stage 3 tasks:
- Complete laying new pipe to new manhole on Rahui Road
- Reseal roundabout road surface.
Stage 4: 15 November to 12 December, 4 weeks
Stage 4 tasks:
• Install pipes to last manhole
• Begin building new kerb and channel and footpath at the roundabout
• Install new streetlights
• Begin backfilling wastewater trench and reinstate the road seal.
Stage 5: January 2026
Stage 5 tasks:
- Continue construction of new kerb and channel and footpath at the roundabout and installation of streetlights.
Stage 6: January/February 2026
- Rebuild kerbs on northwest corner of Mill Road
- Complete construction of footpaths and installation of streetlights.
Background
When there's a lot of rain, the Ōtaki wastewater network can flood and overflow. This happens because of:
- network infiltration – where groundwater gets into old underground wastewater pipes
- inflow – where stormwater pipes are connected to the sewer network.
We're finding and fixing these problems as part of our everyday work.
Some parts of the wastewater network are getting old and need to be replaced and upgraded to support growth.
What we're doing
This upgrade involves laying 2.7 kilometres of new wastewater pipes. The new pipe will start at Riverbank Road, go along Aotaki Street and Mill Road, and end at Old State Highway 1. The pipe will be 800 millimetres wide on Aotaki Street and 500 millimetres wide on Mill Road. In some places it will be buried up to three metres deep.
We started construction in August 2024 and expect it will take up to 14 months. To make sure we complete the work as soon as possible, we have crews working in up to three locations along the route at the same time.
Moving wastewater
There are two main ways to move wastewater:
1. Gravity wastewater system
This system uses gravity to move wastewater downhill. The pipes slope downward from the house to the main pipe in the street, and then the street mains slope down towards the treatment plant.
Because the pipes keep getting deeper as they go downhill, it can become very difficult to lay or repair them. When this happens, a pump station is built with an underground tank to collect the wastewater. Big pumps then push the wastewater out of the tank and up to the next section of shallower gravity main, where it continues its journey to the treatment plant.
Wastewater pipes are usually the deepest pipes underground. The average depth of a gravity main is 3 metres.
Rising main
Pumps push the wastewater uphill through the pipes.