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Pumping 24,000 flushes uphill: North New Brighton to Aranui

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One of the biggest parts of SCIRT’s work is repairing and rebuilding wastewater pump stations.  Two large, inter-connected pump stations in the east were recently “commissioned” which means fully tested, turned on and now operating.  
 
As well as being more earthquake-resilient, these big, efficient pumping stations will also help reduce overflows of wastewater into the Avon River/ Otakaro. They are two of 53 pump stations repaired or rebuilt by SCIRT since late 2011, representing 65% of the budget available to fix these large wastewater collection and pumping facilities.
 
SCIRT’s Fulton Hogan team has been working on the new Beach Road/ Ascot Reserve pump station and the Pages Road/ Bexley Reserve even bigger pump station for the past two years.
 
The Port Hills reflected on the concrete walls - good design from engineering, architect and landscape team
Pump stations are the ultimate utilitarian structure: they have a serious purpose which most of us just want to take for granted. SCIRT’s Iain Partington (seconded to SCIRT from Beca) led the engineering design team for the Ascot Reserve pump station; Murray Kerr, formerly of Beca, led the engineering team for the Pages Road pump station.
 
But as well as being functional, they can also add to the surrounding environment, just as the Victorian brick pump houses also did with their fancy brickwork on the corners and curved tile rooves in some places. These two structures are both designed to reflect the geography of the city with the external concrete designed to look like the Port Hills and wooden battens creating a rolling pattern around the Ascot Reserve structure, like hills and waves.
 
The landscape design was done by Chris Greenshields, of the Christchurch City Council, and the external architecture by Karen Sanderson.
 
The new wastewater pump stations on Ascot Reserve (top) and Pages Road with the vacuum wastewater station in construction next to it. These massive, earthquake-resilient structures were not built overnight.

How does it all work across the city?

More than 100 smaller pumping stations pump the wastewater (sewage plus laundry, bathroom and kitchen dirty water) around the city. Five large pumping stations then pump all the flow to the treatment plant at Bromley. 
 
In the earthquakes some of the city’s pump stations were very badly damaged, including one on Hulverstone Drive, Avondale, within the residential red zone, and the solid brick pump station on Pages Road, opposite Bexley Reserve. Both of these have been replaced on new sites by SCIRT’s Fulton Hogan team.  
 

Pages Road new pump station, Bexley Reserve

The old pump station on Pages Road, opposite Bexley Reserve, was severely damaged in the earthquakes. It was vital the Fulton Hogan team built a replacement pump station as quickly as possible. The damaged pump station was in a very fragile state, highly susceptible to more damage from future earthquakes.
 
As the pump station was such a critical part of the wastewater network, servicing about 24,000 properties, it was not possible to shut down the existing damaged station while the new pump station was built. As a result, a replacement pump station was constructed across the road on the Pages Road frontage of Bexley Reserve. The overpumping pipe was housed within a ramp crossing Pages Road for more than a year. This has now been removed.
 
Looking from the Pages Road pump station over the ramp on Pages Road towards Portchester Street. This photo was taken when the pipe was being rammed under Pages Road. 
 
Horsepower on Pages Road
Comprising a pump room, switch room, and generator, the main building in the Pages Road pump station houses four pumps, two in each wet well chamber and all of the mechanical parts of the pump station. Each of the pumps is about 180kW – similar to a slightly underpowered V8 engine per pump. This gives each one the capacity to pump about 940 litres of wastewater per second. The switch room houses all of the electrics, the 'brains' of the station.
 
Resilient structures
 

Before the building began, the ground was significantly “improved” or made stronger in the event of future earthquakes by injecting columns of grout/ concrete under the station site and around the surrounding area.  (See drawing of the columns.)

The pump station has an on-site generator which can run for three days if there is a power cut. 

The generator building is fireproof. It has a special link installed that, if burnt out, will stop the flow of fuel to the generator, isolating the fire to within the fireproof walls. 

The generator sits on special bearings, which enables it to withstand possible future earthquakes.

There are also two biofilters in the area around the pump station. These help to reduce any odours. Fans in the pump station suck the air to the biofilter. The air passes through the bark which absorbs odour. 

 

Ascot Reserve pump station

This pump station was built on Ascot Reserve, corner Frosts and Beach Roads, North New Brighton, to replace the very badly earthquake-damaged pump station on Hulverstone Drive in Avonside.  SCIRT and Council engineers decided to move the pump station out of the river-side red zone to a more resilient location.
 
Ascot Reserve station pumps all of the wastewater from about 18,000 properties in north-east Christchurch  - Kainga, Brooklands, Spencerville, Parklands, Burwood, Waimairi Beach and Belfast - through the pipeline to the large new pump station in Bexley Reserve, Pages Road. From there it gets pumped on to the Wastewater Treatment Plant.
 
Building the Ascot Reserve pump station 
Wastewater in
Ascot Reserve pump station had to be connected up to the existing wastewater network as it was a whole new site on the north side of the Avon. To do this a large manhole (access point) was built and installed in the middle of the Frosts, Mairehau and Beach Roads intersection. New pipes run from this manhole down into the pump station on the reserve.
 
Wastewater out
Ascot Reserve station pumps wastewater through a  pressure main pipe (ie pumped under pressure, not flowing using gravity), Pressure Main 128, installed by Fulton Hogan in 2013/14, which runs down Bower Ave and under the Avon River/ Otakaro.
 
How these pump stations were constructed
A lot of work needs to be undertaken below ground level before the actual buildings can be constructed. 
 
First the soil needs to be stabilised and the whole ground area made stronger before large trenches are dug. Long sheet piles, interlocking sheets that form a temporary wall, were installed. This made it safe to excavate the deep trenches. Then to ensure the work area in the trenches wasn’t flooded with groundwater, dewatering wells and pumps were installed to lower the groundwater levels around the work site. 
 
Once the trench was safe, dry work began on the wet well chambers. Pages Road pump station has two wet well chambers, large rooms below the ground level where the wastewater is stored. The wet wells were constructed insitu (on site) out of steel and concrete. Following the wet wells, the floor is poured allowing work to begin above ground. The steel frames for the building and large pre-cast concrete wall panels popped up in no time and work then began to install the large pumps and associated machinery as well as all of the electrical equipment. 
 
Both pump stations are now commissioned. This means they are successfully pumping wastewater to the treatment plant, making the wastewater service for 24,000 households secure. 
 
 
The badly damaged Hulverstone Drive, Avondale, wastewater pump station, now surrounded by red zone. It has been replaced by the new station on Ascot Reserve across the river in North New Brighton - Beach Road/ Frosts Road.
 
Ascot Reserve pump station takes shape. Ground stabilisation was the first important step.
 
The dewatering tank.
 
This engineer's drawing shows the placement of ground columns deep into the soil which strengthen the ground underneath and around these pump stations.
 
Sheet piles in place, construction starts.
 
 
 
 
 
Pages Road Pump Station 136 over the past two years.
 
 
The pipe connection under Pages Road.
 
 
 
 
 
 

The third part of the Fulton Hogan pump station trio – Wigram Skies

The first of Fulton Hogan’s brand new pump stations to be commissioned was not a replacement for a broken station, but a completely new one designed to service new demand in the city’s south-west, particularly after the quakes. The Wigram Road Pump Station 105 services 14,000 homes and businesses and began pumping a year ago in 2014.
 
The one-way system along Birmingham Drive in 2013 was driven by the need to connect the big new pipe servicing the station along Matipo St, Wrights Road, Birmingham Drive and finally through the dog park and across the motorway to Wigram Road.
 
The pump station services the new Wigram Skies/ Ngai Tahu subdivision in Christchurch’s south west. It also collects wastewater flow from a Halswell pump station to service a new development in Halswell West and another pump station on Halswell Road. 
 
Like the other new pump stations, it is designed to be more resilient in earthquakes. If a repair is required this can be done within a few weeks, minimising the disruption to wastewater networks. The station has been designed to accommodate population increases in the south-west, the new areas of population growth.
 
Gavin Hutchison, of Beca, led the SCIRT engineering design team for this project.
 
Key features of the building and site include:

•   The concrete panels are textured to reflect and link with the Port Hills and Banks Peninsula area, visible to the south.

•    All storm or rain water on site goes into a garden area for filtering before it discharges into the storm water system, thanks to thoughtful, sustainability-minded landscape design from Chris Greenshields.

•    Planted areas are designed to screen and soften the site while adding to the environment in this area. 

 
 
Published: 09 June 2015