Rail Engineer explores Fulwell’s Blue Lagoons
Rail Engineer featured a story about the work Osborne are carrying out on behalf of Network Rail at Fulwell.
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What do we have to thank – or blame – King Henry the Eighth for? The Church of England? Some very ruined abbeys? The fashion for padded shoulders? Flooding and subsequent train delays on the Shepperton branch?
Yes, they’re all down to him.
Plenty has been written about the first two. The painter Holbein knew which side of his bread was buttered when he created the anatomical distortions, but there’s not been much coverage of Henry’s role in all the late arrivals of scores of commuters into Waterloo.
It has to be said that his was a minor role – even from one with such an apparently expansive torso – but by pushing forward a scheme to provide extra water for his Hampton Court Palace he effectively sealed the fate of one of the railways that was to be built in the nineteenth century.
The (then) new Longford river runs from the River Colne to Hampton Court, hugging the contours and passing round Hampton Hill. In 1864, the Thames Valley railway – subsequently renamed more mundanely the Shepperton Branch – had the problem of crossing the Longford river and yet still landing up at the right level to connect with the Kingston Loop that had been built just one year earlier.
The solution was to contain the river in an aqueduct over the new railway. The level of the river fixed the available gradient and so the railway dropped gently (very gently) down to Fulwell station and on to Strawberry Hill junction.
Collecting plenty of run-off water in its two cess drains, there came the problem of how to dispose of the water under the Kingston Loop before it was deposited in the Thames.
In the end, there was no happy solution. Water ran reasonably down from Hampton station and then, as there was almost no fall thereafter, for about 400 metres it tended to be stored. Another term, used in the trade, is to say that it flooded regularly from Fulwell tunnel and through Fulwell station.
Some floods have been dramatic. 2007, of course, was a case in point – but just about everywhere was flooded at that time. Fulwell’s flooding has been less about the dramatic and more about the mundane and irritating – the frequent interruptions of track circuits and thus signal failures.
The service on the branch is usually half- hourly, but is augmented with more trains in the morning peaks. These have to be threaded into an already intensive service either on the routes to London via New Malden or via the Windsor lines. A missed pathway to an allocated slot in a platform at Waterloo can lead to disruptions throughout the South West Network.
Something had to be done (again). This is a site that has been a problem for years. There are two restrictions to the free flow of water. One is the tunnel to the west of Fulwell station and the other is the station platform area.
The tunnel – more in name than reality – is a pair of parallel extended brick arches with limited clearances and no inverts. Probably built by the cut and cover method, they have no function other than to carry the railway under the A311 road.
Over the years, attempts have been made to renew/repair/improve the drainage through the tunnel. There are record drawings of work going back more than half a century. What was provided in the original build has been lost. Some of the schemes have gone ahead, some were aspirational and may never have happened or only happened in part.
Hector Kidds is the senior asset engineer in Network Rail’s geotechnical, drainage and weather management section. He relates that, towards the close of CP4, two approaches to the problem were being progressed.
Firstly, there were concerted efforts to discover how the drainage in the area was really meant to work using hydraulic modelling and to investigate what was actually in the ground.
The other approach looked at providing a temporary system of overpumping to try and reduce the inevitable train delays caused by track circuit failures. A new electrical supply was installed and connected to some small pumps that took water from catchpits upstream of the tunnel and pumped it through the flat area of drainage until it could be dropped into the drains at the far eastern end.
This has been effective and has held at bay the very worst of flooding and train disruption. It could only be considered temporary as there is quite an intensive maintenance regime in place to ensure that everything works and that the pumps kick in exactly when needed.
Network Rail’s framework contractor, Osborne, was commissioned to design and install a solution that addressed permanently all the drainage and train delay problems in the Fulwell area.
Working with design partner Arcadis, the scheme that was progressed involved providing large drains through the tunnel linked to a storage culvert under the Down line and a wet sump chamber on the Fulwell side of the tunnel. From there, the water passes though a pumping main to storage lagoons constructed on available ground at the Strawberry Hill junction triangle. Water from the lagoons is then released in a controlled fashion into the existing drains under the Kingston Loop.
“The philosophy behind this approach is that there is little point transferring all storm water straight to the discharge drains as there is not the capacity to cope with it all at once,” explains Hector. “In the end, we had to figure out how much water was coming into the system, how much could go out of the system and so calculate how much had to be held in temporary storage.”
There may be plenty of room for the lagoons and a construction compound at the Strawberry Hill triangle end of the site, but the same cannot be said of the tunnel end. Away from the railway boundary, everything is well and truly occupied. Thus the excavation works had to be serviced with engineering trains to take spoil away and to bring new materials in. Over the two-week closure period, five trains were used. Sump chambers were excavated for the new permanent pumps and the tracks within the tunnel were removed and the formation excavated for the 300mm diameter track drains.
“As soon as the track came out, the whole place looked like a canal as there was so much water lying there!”
The 400mm ductile iron pumping main, installed and tested by SES, was mounted on piles along the back of the Down platform running towards Stanley Road bridge. The main passes through a 600mm cored hole through the abutments and continues to the storage lagoons.
A new power supply was provided to the pump chambers from the local grid – this being the most cost effective method compared with taking a supply from the railway’s power network.
A two-week service disruption is not to be taken lightly, especially in the dense commuter land of the South East. Network Rail undertook a handshaking exercise with commuters along the line to explain why the work was necessary and the benefits that a reliable drainage system would bring.
“The approach went down well with some appreciating the problems with track circuits, but with many more understanding that flood water and 750V DC third rails just do not mix!”
The blockade has passed and the scheme is due to be complete in November 2016 with the final construction of the lagoons and downstream water management works.
In the meantime the existing temporary overpumping continues, but it now uses the much better upstream catchment chamber arrangements.
Henry VIII was also a song writer. One of his refrains starts with the line ‘Alack, alack, I know not what to do.’
It’s a good job, your Majesty, that our engineers knew exactly what to do…
Written by Grahame Taylor