Report - - River Fleet CSO - London, 2013/14 | UK Draining Forum | 28DaysLater.co.uk

Report - River Fleet CSO - London, 2013/14


living in a cold world
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The River Fleet. The largest, and perhaps the most well known of London's buried rivers. I've wanted to see this for years, and first glimpsed upon the glistening bricks around two years ago. It was the first time I'd ventured underground since moving to London, and over the last few months we've spent numerous trips looking at lids, exploring the different sections and venturing up side pipes. It's the system that keeps on giving, and there's still more to see.

Here's a rough map of the Fleet watercourse, from one of its sources in Hampstead as it flows down through Camden, King's Cross, Farringdon, and enters the Thames underneath Blackfriars Bridge.

Also plotted are the 5 northern interceptor sewers which divert the bulk of the sewage across the city towards Abbey Mills and Beckton sewage works. The yellow line is the Fleet Storm Relief, which was built in the 1870's to help alleviate the flow down the main Combined Sewer Overflow (CSO). When the water level rises above a certain point along the CSO, the surplus flow is diverted via dropshafts into the relief tunnel below. This shadows the Fleet for the majority its route, and enters the same outfall chamber at the Thames.


Our journey starts underneath Kentish Town. The mile or so of watercourse from Hampstead Heath has been diverted, with the original tunnel blocked off with this brick wall. Trying to head upstream from here gives you the option of a 3ft RCP or a 4ft shrinking brick tunnel, neither of which attracted us.


This is taken from the wall, looking downstream. The tunnel off up the stairs to the left is an old side sewer that mostly looks disused. It curves around and heads NE, with a scurry of rats occupying it.


The main tunnel heads south where a heap of side branches join the flow. There were 2 or 3 junctions like this, with 3 foot side tunnels joining from either side. Each time one of them had been blocked up like you see below.


The mainline bends around and enters northern Camden Town, where the tunnel opens up to this larger size. This section seemed to be quite dated, and has started to crack and fracture.


Continuing downstream led us to this lovely little chamber, with the mainline coming in from the left, and two smaller channels joining to the right.


Creating this torrent for the SEWER STAIRCASE OF DOOM 2 (first is in the KSP) Although it looks much harder to traverse than it actually is. You just get really wet as it splashes you.


Below, looking back up.


Downstream from the tumbling bay are two overflow chambers to divert the excess flow down into the Fleet Storm Relief down the dropshaft at the back right hand side of the image.


The tunnel continues before shrinking into two separate 4 foot diameter pipes as it passes underneath Regent's Canal, in the same way the King's Scholar's Pond CSO does.

The development of the Regent's Canal area led to the section of river between Camden and King's Cross to be buried in the 1810's. By this point the entirety of the river downstream from Camden was underground, with the final earlier stages of the Fleet joining the subterranean in the 1870's after Bazalgette's interceptor sewer design had been implemented. The Fleet was now fully integrated into the London Main Drainage network.


As we flow downstream through Camden the tunnel snakes around slightly as local sewers and side pipes enter the mainline CSO.


We come across another overflow chamber, this time with a slightly newer screw-weir to divert more of the flow down to the Storm Relief if required. They would do this if they needed to work in the tunnel downstream and wanted to lower the flow.


A short trudge later and the pipe opens up into a larger chamber, with a weir board directing the flow down a staircase tumbling bay into the Mid Level Interceptor 2. I'd love to take a look down these interceptor tumbling bays, but they're designed to speed up the flow before channelling it down a narrower tunnel, getting it to Beckon sewage works as quickly as possible. Taking one wrong step and losing your footing would end in a pretty shitty death.


We then enter a section of dry tunnel, with sporadic side pipes punching more sewage into the pipe, gradually building up the flow. We pass more older bricked up connections.

The newest part of the network sits underneath King's Cross and St Pancras stations. The former brick construction has vanished as the tunnel was diverted around the foundations of the buildings above. This work was carried out during the 1980's development of King's Cross station.

A newer overflow and inspection chamber was added, with piles of weir boards ready to install. This would then stop the flow continuing downstream, allowing Thames Water or similar to carry out any remedial works in slightly drier conditions.


We soon rejoin the brick tunnel and further downstream we come across a now disused overflow chamber. The bricked up arches would have led into a weir chamber. Perhaps for the Storm Relief, but it's hard to work out exactly where it was.


A slightly newer Reinforced Concrete Pipe (RCP) enters the mainline tunnel through a large box section.


Strengthening work has been carried out to reinforce the tunnel, although I've not been able to work out exactly what for.


I really enjoyed this section of the tunnel because of the seemingly aged aesthetic of it. The bricks weren't immaculately in line, or as shiny and colourful as other sections. But the non-uniformed nature of it provided possibly my favourite image.


Spurring off up a side pipe is another overflow chamber into the Storm Relief below.


And a short wade away is a larger overflow chamber for the mainline. This is the largest weir section, and as it's quite a distance between interceptors allows high-level flow to be taken down to the storm relief.


The tunnel gets larger as the flow continues on until the Mount Pleasant area, where the Mid Level 1 interceptor takes everything away. The tunnel at this point is quite big, and drops into a slightly smaller tunnel the other side of the weir boards as it heads downstream towards Farringdon Road. This photo is looking back upstream, with the interceptor to the left.


As we approach Farringdon Road the tunnel swerves around the corner, with a tumbling bay taking it down to a slightly lower level.


The tunnel then continues to bend around, and passes next to Farringdon station. On a later trip we noticed tremor sensors mounted to the top of the ceiling to monitor any detrimental effect of the Crossrail works being carried on in the area. The Fleet doesn't run too deep in this area so I can only assume the Crossrail boring is happening below the tunnel.


The sections underneath the Holborn area towards Fleet Street were the earliest to be buried, back in the 1730's. This paved the way for Farringdon Road above, The lower stretch from Fleet Street to the Thames outfall being built over 30 years later in the 1760's.

The Holborn split. The tunnel is channelled off into two narrower courses as it runs down towards Ludgate Hill and Fleet Street. I've never really been too sure why it splits off, the only obvious sign on the road above is a public toilets that sits in the central reservation of the road, but the A201 above doesn't branch off until much further along.


This old map below shows the Fleet mainline running down the centre, with its' numerous side pipes and local sewers.


The channels meet back up just past Fleet Street and it opens up into a much larger horseshoe tunnel.


One night we ventured up one of the side pipes around into Ludgate Hill Sewer, and followed it upstream until it drops around St Paul's Cathedral and down into Paul's Wharf Sewer. The pipes weren't too hospitable, so I only got video footage and no photos. https://vimeo.com/105637049

Back to the Fleet. An interesting feature were these small "window" like arches in the side of the tunnel. There appeared to be a large iron storage tank the other side, but it was quite awkward to see.


Further downstream the flow is drawn away and down into the Low Level 2 interceptor. The metal bars either side of the tunnel allowing workers (and us) to safely navigate ourselves over the flow.


Metres downstream of the shot above is this motherfucker of a tunnel. It's a huge upside down horseshoe, segmented into 4 tunnels with large iron flaps at the end of them.


Looking back upstream from one of the higher tunnels.


A ladder to one side leads up into the upper workings of the sewer, with access to different sets of penstock mechanisms, allowing works to shutdown the flow to certain places.



There is a warren of tunnels leading off in each direction, with aged signs aiding you to the right location. These would have looked fantastic in pristine condition. There are numerous manhole access shafts to allow Thames Water to check on the outfall chamber at both high and low tide.


The entrance to the right here drops into the outfall chamber. Directly behind me is a ladder down to the Fleet Storm Relief.


Penstock mechanism for the chamber below that feeds into the Low Level 1 interceptor.


The outfall chamber. The four flaps to the rear of the photo are the 4 from the segmented chamber, and the two smaller ones on the left are the Fleet Storm Relief rejoining the CSO. As the Fleet is tidal this chamber fills up with Thames sludge. A mix of sewage, mud, silt and god knows what else. It was knee-deep when we were there, and wading through it was quite tough.


The final approach towards the Thames splits off under a 6 foot box section, and curves around before splashing out underneath Blackfriars bridge.

I've had to remove sa fair few images to fit in the 35 image allowance, to see the others head over to http://www.adeadendstreet.co.uk/2014/11/river-fleet-cso-london.html


28DL Full Member
28DL Full Member
Incredible stuff,pics and info. The amount of effort you've gone to is inspiring as are all the pics-only people who've tried to photograph underground know how hard it is...awesome report.


28DL Full Member
28DL Full Member
Very nice. The River Fleet featured in a recent episode of New Tricks on BBC1. Well worth a watch.


28DL Full Member
28DL Full Member
Nice photos mate, the brickwork in the Fleet is indeed amazing.

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