Having spent many years looking after railway infrastructure, I feel for industry colleagues who have been confronted with the effects of the extreme weather we’ve experienced in the last few months. Writes Chris Parker.
My own experience of this has been relatively mild this time, being confined to the frustration of having my narrowboat stuck on the Nottingham canal since before Christmas because the River Trent has been too high for safe navigation. Not a great hardship compared with the sufferings of thousands of people in the areas of the country where the worst weather effects have been seen!
I can only imagine what it has been like for colleagues in the rail industry this time. Robin Gisby has been doing a great job fronting Network Rail’s reports on Radio 4, and the internet and news reports in other formats have kept us all informed more generally about the effects of what is being said to be the worst weather for 250 years.
So what happens to the railways in the sort of conditions we have recently seen, what can be done to put right the damage, and perhaps more important, what might be done to mitigate the effects of similar events in the future? It seems accepted by most informed people that this kind of thing is likely to become much more common than in the past.
I don’t think I need to go into great details about the kinds of problems this sort of weather causes the railways. We’ve seen and heard plenty recently about trees on the line, speed restrictions, flooding and worse. So I will consider instead what happens in the aftermath.
Some things are not complicated; a tree across the line has to be cut up and loaded away. If overhead lines have been brought down or other infrastructure has been damaged by its fall, repairs are affected and the service can be restored. This process may not be easy to carry out, for example, because of the remoteness of the location or the shortage of staff and other resources, but the basics are otherwise pretty straightforward.
Shallow flooding of the line may seem even easier to deal with. The water goes away, whether naturally or with human assistance through pumping or other means. Unless the signalling or power supplies have been damaged, that’s it isn’t it? Restart the normal train service and away we go! Well, it may not be that simple. In track circuited areas there may be a problem with the circuits failing to resume normal operation due to contamination of the track and ballast by material left behind by the water. It’s fairly rare, in my experience, but it can happen and results in unpredictable track circuit failures that may require remedial actions. These may run from changing the rail pads and insulators to complete re-ballasting in the odd extreme case. Insulated joints might also need to be changed in some instances.
Re-ballasting may also be required if the water leaves behind a significant load of silt or clay deposits in the ballast. It would be unusual for it to be necessary immediately after flooding, but it is more likely that the life of the ballast will be shortened by the contamination. When ballast ceases to drain freely due to the blockage of the voids between the individual ballast particles, the resultant build up of water in the ballast and formation leads to “wet beds” and deteriorating track geometry which cannot be made good long term without renewal or cleaning of the ballast. These operations are disruptive and expensive, even when modern technology is used to good effect in their execution.
Deeper flooding of the line, even if relatively static, causes far greater problems. The issues will be much the same for the track engineer in all probability, but the signal, telecomms and power systems begin to be seriously involved too. Returning the line to traffic obviously takes longer and requires more money and resources once that happens.
When moving water is involved, then things can get really serious. Water movement affecting the track may take the form of swollen watercourses that become high enough to enter the railway and run along or across it, as at Cowley Bridge in 2011/12. It may take other forms too, such as the inflow of surface water from adjoining higher ground, or even the flow of flood-water trapped behind an embankment until it over-tops it and flows across the line. Finally, there is the sort of damage that we have recently seen from the sea, where tide and waves combine to invade and wreck the railway. The Cambrian Coast Line was severely damaged in this way recently and even more recently the Great Western main line around Dawlish.
The problems caused by moving water range from the washing out of ballast from a length of the line to the destruction of the underlying formation and even the complete removal of structures such as parts
of embankments or retaining walls. Clearly the track and its supporting structures are not the only things affected in such instances – if there are other infrastructure assets present, they too are likely to be damaged or destroyed. Dawlish Station is a recent example.
The restoration of this sort of damage is a major operation requiring a full scale project whose particulars will vary from site to site. Even the replacement of a few scores of metres of ballast on a relatively undamaged formation needs proper care and planning. Major damage such as that on the Cambrian or at Dawlish is serious heavy engineering needing proper surveying, design and construction skills and resources. It is not just a case of getting the railway back into use anyhow, proper diligence is required to consider how to do this in a manner that, if possible, eliminates or at least greatly reduces, the risk of re-occurrence.
Other infrastructure is at risk, of course. Overhead lines may blow down. Station canopies are vulnerable to heavy winds, and other buildings may be damaged – the collapse of part of a building in Holborn with fatal consequences recently is clear enough evidence of that, though not a railway structure this time.
Bridges and viaducts may be at risk from swollen rivers and water courses even when the water is not sufficiently high to directly affect the railway above. British Rail experienced this at Glan Rhyd on the Heart of Wales line in 1987. Four people died in a swollen river when an apparently sound bridge collapsed under a DMU because the foundations of one of its piers had been scoured away by flood-waters overnight. The weakened structure couldn’t bear the weight of the train, collapsing into the river and taking the train down with it.
A major project had to be set into being to investigate how this could have occurred without anyone becoming aware of such a risk, and to determine how to avoid further similar failures. This in turn led to the investigation of hundreds of BR bridges and structures over or near to watercourses to determine whether they were safe, safe if subjected to special precautions or in need of immediate strengthening or reconstruction.
Signalling and power supply assets may require attention, to move them out of harms way for example. This was done at Cowley Bridge, where signalling apparatus cases were raised above the level of likely future flooding. Doing this kind of thing won’t stop the flooding of the line itself, but it does reduce the time, money and resources necessary to restore it to traffic after the waters recede. At Cowley Bridge the second time around, it was definitely quicker and easier to get the line reopened because of the relocation of the vulnerable equipment after the first inundation.
Changing assets that cannot be moved to a type that is less vulnerable to water is another strategy, using axle-counters in place of track circuits being one example.
The foregoing is a quick view of some of the tactical issues. What about future strategies that might shift the railway totally out of the flood risk situation? A simple example would be the kind of works carried out to some bridges post-Glan Rhyd. There were many bridges (and some other structures) that could not be shown to be founded on sub-structures that were scour proof to a safe extent. Where reasonable investigatory techniques could not confirm the adequacy of the foundations, the foundations of such structures were typically strengthened by deepening them to take them below the level to which scouring might occur. This was done by various means, such as the installation of needle piles.
An alternative was the installation of a structural apron on the river bed under the bridge and for some distance up and down stream. This apron had the job of preventing the scouring away of the river bed in the vicinity of the bridge. It was not a usual choice though, as there are potential serious problems with that approach. The collapse of the Inverness railway viaduct demonstrated this, as that viaduct had an apron beneath it that failed, it is believed, due to works carried out by others downstream of the railway. The failure of the apron left the viaduct vulnerable to scour, and this was not detected in time to avoid its collapse.
Discrete problems such as scour prone bridges are relatively simple to deal with, what about long lengths of line that are at risk? The Brunel main line around Dawlish is one important example, but there are others all over the network. Long, deep cuttings like those at Merstham in Surrey are potentially seriously at risk, as has been shown by the landslip in the recent storms.
Tunnels and cuttings may be subject to flash flooding by surface water (or even burst water mains!), and as mentioned before, the adjoining topography means that the railway is liable to inundation by watercourses or flooded land. Embankments too may be at risk if deep flood-water builds up against them. This could cause problems due to the difference in the head of water between one side of the bank and the other, through wave action on the embankment slopes or by over-topping scouring away the track and structure.
The infrastructure owner must be forward thinking in planning for the likely increase in these flood related risks to their assets. In this country, that principally concerns Network Rail. As well as reacting to the damage recently done by repairing it in a suitable robust form, it needs to be examining its network in detail in the light of the increased potential for storm and flood damage to be expected if climate change continues as scientists are predicting.
A network-wide strategy is needed which covers the full range of issues. At its most basic, this would mean things like eliminating lineside trees that could fall onto the line or the OLE. That’s not as simple as it may appear, given that many such trees are not on the railway’s land nor in its ownership. However, let’s start with the easy stuff and get rid of those that Network Rail does have control of. It won’t be popular and may involve managing tree preservation orders and so on, but it needs doing so that we no longer need speed restrictions every time there is a gale forecast.
The Dawlish-type scenario is much more difficult. I am sure that my fellow engineers can design and construct better structures than the existing (or recently existing!) ones to support and protect the line along the Cornish and Devon coastline. I am sure that they could take into account the expected further increases in the height of the tides and surges to be faced in the future. Whether this would be cost effective for the whole of the length of ‘at risk’ railway is doubtful. I also imagine that, however good these structures may be, they will not provide an impregnable defence against the sea, and at some future time there would be further service disruption.
Dawlish cannot be the only place where such intractable problems may be foreseen, and strategies must be developed to manage each of them. There is already talk in the media of the possibility of reopening old alternative rail routes to the West Country, such as the line via Okehampton. That is one possible approach that would offer more benefits than just another way round when the sea gets rough. In normal times, it would additionally increase network capacity and provide a rail service to communities that lost it many years ago.
The restoration of former rail routes has been successful already, particularly in Scotland, so why not in a serious way in England and Wales too?
Finally, I have been concerned to see the current weather effects being used by some in the media to open up yet another front of attack on HS2. Why, they argue, spend all that money on a new railway when we can’t even keep the existing ones open when there is a bit of bad weather? Let’s have some of the cash to put right the existing network.
I have no time for such ideas. The existing network hasn’t the capacity to cope with demand when the weather is good and all is working perfectly. Perfecting its weather resistance will not alter the shortfall in capacity, just make that capacity more reliably available.
Our country needs to face up to the need to spend strategically on its infrastructure. To spend both to make existing long-lived infrastructure robust against climate change and to meet future demand changes and increases by providing new infrastructure. Those two are not alternatives, they are equal essentials that must both happen.
I was privileged to sit on a panel that assisted the Institution of Civil Engineers to draw up its responses to the public consultations on the Phase 1 and Phase 2 proposals for HS2. One of the Institution’s most important comments in both its response documents was the insistence that the country needs a proper transport strategy. One of the greatest difficulties in arguing coherently in favour of HS2 is the inability to show that it fits the country’s future transport needs because we do not have a transport strategy properly developed in response to a valid assessment of what those needs will be.
I go further, supporting far greater engineers than myself, people like Sir John Armitt. I say that there is a vital requirement in this country for a strategic plan for our infrastructure, not just our transport infrastructure. Which of our politicians has the guts to take up that requirement and do something positive and effective about it?