What stops underground lines filling with water during heavy rain?

king_walnut · 24 Jun 2019

I think I'm right in saying that most underground lines have their outer stations above ground, and then they head into tunnels under the ground passing through central London. So my question is - during super heavy periods of rain, what stops all the water flowing down into the tunnels? Os it just a case of fantastic drainage before it can get that far?

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Darandio · 24 Jun 2019

king_walnut said:
I think I'm right in saying that most underground lines have their outer stations above ground, and then they head into tunnels under the ground passing through central London. So my question is - during super heavy periods of rain, what stops all the water flowing down into the tunnels? Os it just a case of fantastic drainage before it can get that far?

Water pumps, something like 50 million litres are pumped out every day.

Elecman · 24 Jun 2019

Lots and lots of pumps in drainage sumps

TheSel · 24 Jun 2019

Darandio said:
Water pumps, something like 50 million litres are pumped out every day.

Elecman said:
Lots and lots of pumps in drainage sumps

Strictly speaking these pumps don't stop the water getting in (as in the original question) - they just get it out again as quickly as possible! :oops:

John Webb · 24 Jun 2019

The above-ground buildings are of course fitted with appropriate rainwater collection systems which discharge into the local ground drainage systems, and protect the station below ground from the rain. But if the road drainage system outside the station can't cope with the deluge, water can get into the station. This will usually result in the station being closed and lifts or escalators being turned off to isolated their electrics. A similar problem can arise if a large watermain should burst and overwhelm local drainage.
Water that does get into the underground station will then be pumped away as described above.

Highlandspring · 24 Jun 2019

The Glasgow Subway has flooded many times over the years, most famously after a very heavy storm on June 26th 1953 in one of the two sumps where the line passes under the Clyde. It's notable because the water was so deep that a council rowing boat was commandeered from Hogganfield Loch in the north of the city and rowed from Govan Cross to Merkland Street to inspect the tunnel lining.

Skie · 24 Jun 2019

Dont forget that normally tunnel approaches are going to be ballast anyway, so there's no water running alongside the track to run into the tunnel itself. Where it's a concrete bed on the approach and into the tunnel, not far inside the tunnel there will be extra drainage channels and sumps to handle the load.

How you handle water coming in through the walls is another matter, especially for sub-river tunnels. The Mersey railway tunnel pumps out enormous quantities of water via a pump house on each side of the river. The one on Mann Island pumps water to a nearby office block to help cool the building (and was intended to take excess heat from the Echo's printing presses to help warm the building in winter, but the modern presses they installed produced too little heat for that to work). Excess water is pumped into Canning Dock.

Elecman · 24 Jun 2019

The Liverpool Wirral loop line has several different pumping locations

edwin_m · 24 Jun 2019

Parts of the New York subway flooded during Superstorm Sandy, and 20-odd years back a 314 was soaked nearly up to roof level by an unexpected flood at Glasgow Central Low Level. So it happens occasionally. On some overseas metros you actually go up one step before going down the stairs into a station, which I believe is a precaution against relatively shallow surface water draining down the steps.

Bald Rick · 24 Jun 2019

Good design and engineering, basically.

Make sure your portal isn’t in an area at risk of flooding, and if it is, lift it up so that it is well above the 1:100 year maximum flood risk level + a further margin of error / safety.

AM9 · 24 Jun 2019

edwin_m said:
On some overseas metros you actually go up one step before going down the stairs into a station, which I believe is a precaution against relatively shallow surface water draining down the steps.

That's true on the MTR in Hong Kong which is relatively modern. The stations all have steps (2 I think) to the 'ticket hall' area. In the monsoon season, heavy rainfall on a scale that no European city endures regularly falls. There is effectively a flash flood where the street storm drains can't get the water away fast enough. The steps hold enough back until either the rain stops and the street drains catch up or the stations are fully closed with flood protection barriers.

DPWH · 25 Jun 2019

It's worth noting that there are broadly two types of tunnel. Tunnels through hills tend to have uphill approaches, and usually a summit within them so that water ingressing into the tunnel will naturally flow out. Tunnels under cities, particularly those that go under rivers, conversely tend to have a downhill approach and may be below the water table.

jamesst · 25 Jun 2019

Elecman said:
The Liverpool Wirral loop line has several different pumping locations

If you stand on the Wirral line platform (the lift end) of Liverpool Central you can both see and hear one of the pumping stations just before the platform in the tunnel. Used to lead to many concerns from passengers who weren't used to the noise that the tunnel and station was about to flood!!

Taunton · 25 Jun 2019

The tunnel at Chipping Sodbury, east of Bristol Parkway, has long had a flood problem, and some recent works there don't seem to have been a permanent solution. Part of the issue was the inability of local watercourses or public drainage to handle the periodic drainage extremes, it being suggested at one point by the river authority that a drain should be installed all the way from the tunnel to the River Severn (10 miles).

The Wirral loop in Liverpool has also been a recurring problem since being built in the 1970s, separately to the under-river section that has long been handled.

Embankment station on the Underground certainly has 4 steps up at the riverside entrance, presumably a flood prevention measure.

sharpley · 25 Jun 2019

From my days of working on the Jubilee Line extension I seem to recall there is a flood barrier installed in the Jubilee Line Canning Town portal, although not 100% sure of this. I did visit the building above the portal (that looks like a mini Thames flood barrier) a few times although I wasn't involved with anything like flood protection. Its location would make sense to have a barrier.

Taunton · 25 Jun 2019

There are different types of flooding. Tidal overtopping is behind the Jubilee Line structure at Canning Town, and an extreme case was the hurricane-driven tidal overtopping in New York some years ago. Separately there is surface rainwater/river flooding, there is groundwater penetration such as the Mersey Loop issues or Chipping Sodbury tunnel, which tends to be long term, and for sudden events which may be the most concerning there are breaches of major water supply pipes where the contents rapidly penetrate the system. Anyone remember the Euston station breach of about 20-30 years ago, which filled up the 4-storey underground car park there right up to the surface?

73001 · 25 Jun 2019

I think one of the problems with the Merseyrail system is that water used to be extracted from the rock around the system by various industrial users. As these closed down then the water table rose and caused progressively more problems over the years, requiring large quantities to be pumped out every day.

jopsuk · 25 Jun 2019

It is no longer Underground, but the Thames Tunnel, on the Overground's East London Line, is so leaky that the pumps have to run continuously.

DelW · 26 Jun 2019

I believe one of the biggest pumping operations is that at Severn Tunnel, which hit a freshwater spring late in the construction that has had to be pumped out ever since. Various flow figures are quoted, but 50 million litres per day seems to be commonly stated, which is the equivalent of the water supply to a good-sized town. When the spring was struck, tunnelling was halted during construction of substantial steam pumping stations, which continued in use until the 1960s, when they were replaced by electric pumps. Various industrial operations were built nearby to take advantage of the "free" water from the pumping, though I'm unsure whether any still do so.

DarloRich · 26 Jun 2019

DelW said:
I believe one of the biggest pumping operations is that at Severn Tunnel, which hit a freshwater spring late in the construction that has had to be pumped out ever since. Various flow figures are quoted, but 50 million litres per day seems to be commonly stated, which is the equivalent of the water supply to a good-sized town. When the spring was struck, tunnelling was halted during construction of substantial steam pumping stations, which continued in use until the 1960s, when they were replaced by electric pumps. Various industrial operations were built nearby to take advantage of the "free" water from the pumping, though I'm unsure whether any still do so.

there is an old article about this topic here: https://www.railnews.co.uk/news/2008/06/03-severn-valley-networkrail.html

68000 · 26 Jun 2019

edwin_m said:
and 20-odd years back a 314 was soaked nearly up to roof level by an unexpected flood at Glasgow Central Low Level.

Amazingly, 25 years ago this December!

http://www.hiddenglasgow.com/rail/flood1994/index.htm

What stops underground lines filling with water during heavy rain?

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