Flash Flooding at London tube/train stations

[whole diary]

[infoman]

on Monday 12 july,various locations mainly in the South west london area,wimbledon.

As well as North East area of London, Watford to Euston.

[IndustryInsider]

One platform was shut at Paddington for a while yesterday evening when the drains were unable to cope with some very heavy rain.

[froome]

It seems obvious to say that, with climate change, the potential for flash flooding, particularly from summer thunderstorms, will only increase, quite possibly dramatically. Urban stations are those might likely to be at risk, and those in London especially so, given that the average temperature at these will be higher by a matter of degrees than other cities and towns.

I grew up in London and my local station as a child, Clock House, was once several feet under water (as was our garden which backed onto the railway, with the water lapping against the top step to the back door). That was in the late 50s or early 60s, and no doubt the potential is there for far worse now.

How robust are the drainage systems at urban stations? Is it assumed that water will mostly just drain through the ballast?

[stuving]

It seems obvious to say that, with climate change, the potential for flash flooding, particularly from summer thunderstorms, will only increase, quite possibly dramatically. Urban stations are those might likely to be at risk, and those in London especially so, given that the average temperature at these will be higher by a matter of degrees than other cities and towns.

I''m not sure that's so relevant. The main effect of warmer air is that it can hold more water vapour, which determines how much is available to become rain. So it's the temperature where the water is picked up, usually over the sea, that counts most. Any extra heat from the ground in cities might add power to thunderstorms, making them a bit more likely there, but as a smaller effect.

How robust are the drainage systems at urban stations? Is it assumed that water will mostly just drain through the ballast?

Railways have comprehensive drainage systems, but every drain has a capacity, and they are usually sized to meet (or not often fail to meet) flow rates found in the past. And, if its outfall is to a watercourse that itself flooded and now higher than the water to be drained away, that capacity is immaterial.

I'm sure a lot of us remember the one place locally that flooded that flooded first, often a road under a low railway bridge. These days there is probably a pump (or two) to prevent that happening, but that's only a viable solution for a few key points. For places only flooded in a very extreme event, the next event is likely to have a different pattern anyway.

[didcotdean]

There is often a maintenance issue revealed by flash flooding, as indeed is the case in roads.

Didcot Parkway station flooded twice in recent years from heavy rainfall in a brief period (2016 & 18).

Both had investigation reports by Oxfordshire CC as the Lead Local Flood Authority. The first was identified as a single cause where an outfall of Thames Water into a Network Rail ditch was obstructed as the latter had not been maintained. A fuller audit happened after the second which revealed a number of defects and blockages with the station drainage and downstream including one caused by wedged traffic cones that had entered a pipe via an open ditch.

Network Rail's records of the station drainage system were incomplete and had to be filled out by reference to plans in county and district council archives and investigations with cameras.

[broadgage]

It seems obvious to say that, with climate change, the potential for flash flooding, particularly from summer thunderstorms, will only increase, quite possibly dramatically. Urban stations are those might likely to be at risk, and those in London especially so, given that the average temperature at these will be higher by a matter of degrees than other cities and towns.

I grew up in London and my local station as a child, Clock House, was once several feet under water (as was our garden which backed onto the railway, with the water lapping against the top step to the back door). That was in the late 50s or early 60s, and no doubt the potential is there for far worse now.

How robust are the drainage systems at urban stations? Is it assumed that water will mostly just drain through the ballast?

Yes climate change is expected to increase the frequency and the severity of flooding, and increased flood risk should be taken into account for new or refurbished infrastructure.
The costs of major flood proofing throughout the network would be astronomical, but an incremental approach as part of other works should be considered.
Footbridges are better than subways for example.
Track side signalling equipment should be elevated on concrete plinths in high risk locations, and new installations should be elevated even in lower risk locations.
New bridges over rail lines should have extra clearance in order that the track may be later raised without altering the bridge.
Stations prone to flooding should have electrical equipment at high level.

London tends be to very warm due to the "urban heat island effect" but this does not increase the local flood risk. A warming climate increases evaporation from land and sea, and this extra moisture tends to fall as extra rain. The LOCAL temperature at the place where this extra rain falls is not relevant.
With the prevailing wind being from the west, much of the rain in the UK^▸ (United Kingdom) results from evaporation in the Atlantic, which is warmer than in the past.

[eightonedee]

It's not just urban stations.

At Goring there is a low point near the entrance to the car park, extending across Gatehampton Road that often fills after heavy rain. There is apparently meant to be a drain under the railway that is meant to carry the water away, and when the works were underway to electrify, extend the platforms and install the footbridge I was told that the drain would be cleared out to prevent this happening again (although I was also told that actually no-one knew precisely where this drain was!). The flooding still occurs!

[Electric train]

There is often a maintenance issue revealed by flash flooding, as indeed is the case in roads.

Didcot Parkway station flooded twice in recent years from heavy rainfall in a brief period (2016 & 18).

Both had investigation reports by Oxfordshire CC as the Lead Local Flood Authority. The first was identified as a single cause where an outfall of Thames Water into a Network Rail ditch was obstructed as the latter had not been maintained. A fuller audit happened after the second which revealed a number of defects and blockages with the station drainage and downstream including one caused by wedged traffic cones that had entered a pipe via an open ditch.

Network Rail's records of the station drainage system were incomplete and had to be filled out by reference to plans in county and district council archives and investigations with cameras.

Regards maintenance issues, the capability of the railway infrastructure to handle flooding is quite often compromised not by the poor railway maintenance or systems but failures in the adjacent infrastructure managed / maintained by others; with flood water overspilling into the railway systems.

I know from the Geotech team I work with historic records are only as good to the point where the NR^» (Network Rail - home page) current property boundary is, over the years the railway operators (the big 4, BR^▸ (British Rail(ways)), RT and NR) have disposed of land after which the rail operator has very little say in what happens on that land, hence drainage systems often get dug up, ditches filled in or not looked after etc