Published: 21st February 2014
Why does the railway get flooded?
Railways have a drainage system and these can become silted up and overwhelmed, especially by the vast quantities of rain we’ve had in the last two months. Curiously, the wrong sort of ploughing in fields can also create a flood if the furrows run vertically rather than transverse parallel with the railway.
If ploughed vertically the water runs down the furrow and on to the railway line bringing silt and other debris. This has also happened from roads where the Council/Highway Authority has not kept the road drainage in good condition and water cascades from a bridge over the railway and onto the line.
When water floods a railway line, it can dislodge the ballast which has several functions. It keeps the sleepers in place which in turn hold the rails in the right position and angle. For example on fast lines, the rail alignment line is tilted to allow trains to round a curve at speed and this different height of parallel rails, or cant as it is known, increases the permissible speed of the train and maintains passenger ride comfort.
So long as the floodwater is not more than a few inches above the top of the rail and standing still, trains can proceed at caution. If the water is flowing, then nothing can operate because the track formation may be destabilised or washed away, but hidden from sight. This shows another function of ballast, to provide good drainage for the track formation.
At Maidenhead where the slow lines were under water, Network Rail (NR) has raised these by 60mm providing a quick fix to recreate the ‘top and line’ of the track by giving it extra foundation in turn creating a stable base for the sleepers and rail. It will need to be consolidated sooner than later but at least allows trains to operate for now.
Where railways that are electrified with a third rail there are some serious aspects to be aware of when flooding occurs. The 3rd rail carries 750 volts DC current so if there is any flooding, trains will not run as the electricity has to be switched off for obvious reasons. These are the same as why there should not be any electric plug points in a bathroom as water and electricity at any voltage do not make good companions!
Railway signalling is based on power and data cables running between signalling cabinets, relay rooms and the actual signals. Flooding can obviously effect these as well as things called track circuits and Train Protection and Warning System (TPWS) grids in the centre of the tracks known as the ‘four foot’.
When signals fail, signalling has to be carried out manually by qualified people which is totally safe, but is not an efficient way of operating trains as they have to proceed on the individual signaler’s authority from what is known as block to block signalling section with each block controlled by a designated person.
NR is planning measures to improve flood resilience at Hinksey, just south of Oxford to be operational by next year. This is a well-known flood area but as the line gets busier and busier, the decision has been made to finally do something about it.
At Maidenhead, NR’s engineers raised one of the tracks by 60mm overnight using an engineering train called a tamper that crawled along a line at walking pace. This lifts up the rails and pushes more stones under the sleepers and relays the track at the new level.
This took the track out of the groundwater flood restoring the two main lines to increase the number of services operated through the Maidenhead area. This was needed as the water table had risen significantly through the chalk underneath the railway causing severe damage to the signalling equipment, despite sandbags being used.
NR has also reduced the number of temporary signals have been reduced on the slow lines, meaning trains do not have to stop as often passing through the affected area.
The Prime Minister has offered £61 million to help pay for the storm damage our railways and roads have suffered. This will help what they say will build ‘greater resilience into the railways of the south west’. This was announced at Prime Minister’s Questions on February 12 when David Cameron gave the go ahead for a £31 million scheme to deliver 10 rail resilience projects to help deal with flooding.
Cowley Bridge Junction (Just east of Exeter)
Hinksey (Just south of Oxford)
Whiteball Tunnel South (Near Taunton)
Athley – Cogload (east of Taunton)
Hele Bradninch (near Tiverton)
Flax Bourton (Near Bristol)
Patchway up Tunnel (Near Bristol)
Earthworks strengthening at Honiton and Crewkern
NR is also to install rainfall, river flow and groundwater monitoring around Cowley Bridge Junction and Chipping Sodbury.
Secretary of State for Transport Patrick McLoughlin said: We are facing exceptional weather conditions right now. We’re working with transport operators to make sure everything that can be done to reduce the impact of the storms and floods on our transport system and speed up recovery is being done. We’re also determined to boost the resilience of the transport network against future severe weather.
Network Rail has announced that the sea wall at Dawlish may take another two months to repair following further storm damage on February 16. This is due to the following 10 factors:
1. Work can only be carried out at low tide
2. The weather has to be right, no high winds or heavy rain
3. These conditions will allow the sea defences to be built up and allowed to set
4. They will also need to cut back the affected area to create a solid and stable boundary to work from.
5. The washed out area will need to be backfilled to the new section of shoreline
6. The track foundation has to be laid and is known as the formation
7. This has to be ballasted, sleepers and rails laid on top of this.
8. The track has then to be levelled to make sure the top and line are correct
9. Signalling systems need to be installed and tested including reinstatement of cables, track circuits and the trip wire warning system for possible cliff falls.
10. The weather improving!