Global warming is a phrase we’ve all become familiar with. However, it is perhaps a little difficult to understand how global warming can result in cold winters and floods, so perhaps ‘climate change’ is a better phrase. There is much debate over its causes. Are they part of the natural climate cycle; how much is due to man’s influence? However you choose to interpret the evidence, there is no denying that changes are taking place and they can cause major difficulties for everyone.
Running and maintaining a railway is a long-term undertaking so it’s only natural that Network Rail is considering what the effects of climate change may be on its operations. John Dora, Principal Engineer (Climate Change) is the man with the unenviable task of planning for this rather vague future. “As the climate changes, it is going to affect our weather,” John asserts. “That could put at risk the continuing safe operation of our railways and that is a risk we need to manage.”
One obvious example of how weather adversely affects the railway was the unseasonably-early heavy snow at the end of last year. Services were badly disrupted and the criticism levelled at Network Rail was not that it snowed – over which no railway company has any influence – but that the clear-up took too long and the continuing cold conditions made things worse. Sudden bad weather exposed weaknesses in planning and the availability of resources to cope with the problem. That is just the type of issue John is now investigating.
Enemy number one
It is alleged that the great Scottish engineer Thomas Telford once said “Water is every civil engineer’s greatest enemy”. It can certainly wreak havoc. John Dora calls on the experience he gained from 12 years with the Environment Agency to plan for the effects of too much water being in the wrong place at the wrong time. Network Rail, with funding from the Rail Safety & Standards Board, has commissioned the Meteorological Office to look at future climate forecasts and these studies will be used to determine what changes are needed.
Rainfall patterns over a 30-year period from 1971 to 2000 form the basis for part of that study. Using this historical data, maximum flows through drainage pipes and in culverts can be calculated for future decades, then an extra 20% is added. John is at pains to point out that this 20% is not just a ‘fiddle factor’ – it was determined by the Department for Environment, Food and Rural Affairs and other government agencies as a result of several detailed studies and hydraulic analyses of past trends, but he does accept that the result is a convenient round number!
Any installation that cannot cope with 20% more than current peak flows will need to be re-engineered at some time. New designs have to comply with the latest Drainage Systems Manual which has the 20% allowance built in. The railway is, in effect, its own indicator of where trouble might occur. In the 150 years since the bulk of the network was built, generations of engineers have improved the drainage of areas that flood regularly. So if drainage is present it is probably needed, and today’s engineers can look at the drainage provision to assess whether it will be adequate for future needs.
When the rains come
Flooding can also cause problems as was seen at Workington in November 2009. Bridges and other structures have to be able to withstand the power of water resulting from higher flow rates. The change in flow can also cause scour to undermine bridge piers quite quickly. This was demonstrated when a 20m section of Irish Rail’s 176m bridge over the Broadmeadow Estuary, between Malahide and Donabate, collapsed in August 2009. The Victorian masonry viaduct on the Dublin-Belfast main line was undermined when river flows changed due to damage to an upstream weir even though the bridge had been inspected and passed as safe only days before.
Network Rail has produced a handbook entitled Protecting structures from flooding. Scour protection is already in place on many bridges and water level markers can indicate when rivers are higher than normal, therefore posing a scour risk. In extreme floods a bridge can be closed to traffic then reopened after an underwater inspection, although currently it is rare for this to be necessary.
Sea spray
White-water flooding – when water splashes over sea defences – and high sea levels can also cause problems. Dawlish Sea Wall is the most obvious example of this in England. A 36-hour advance forecast of sea state and wind conditions helps engineers predict potential problems and these forecasts can be updated hourly if necessary. On average, the line at Dawlish is closed once every six years but, to mitigate problems with washout, the ballast is glued together to help prevent track damage during storms.
A similar advance warning system is in place on coastal railways in Scotland where comparable conditions exist. In Wales, the Conwy Valley line closes every five years on average when the ballast is washed away, however a recent protection project on the underlying earthworks means that these are not normally affected.
There is now a handy web-based design tool that shows where water concentrates close to the railway, and so where future problems could occur. This was developed by Network Rail in conjunction with JBA Consulting using methodologies developed for surface water flood risk for the Environment Agency.
However, water and snow aren’t the only problems that climate change is likely to cause. Increased temperatures at the height of summer can create difficulties too.
Heat expansion
Steel rail, which can be installed in continuous welded lengths of many miles, naturally expands and contracts with temperature. On installation, this Continuous Welded Rail is pre-tensioned so that it is stress free at a particular temperature. Below this, the rail will be in tension; above it and the rail goes into compression with the risk of buckling if temperatures, and compression stresses, get too high.
Currently, Network Rail track is set to a Stress Free Temperature (SFT) of 27C. The level of pre-tensioning is monitored and, when the SFT drops to 21C, it is time to retension the rail. At rail temperatures above 32C (5C above SFT), work cannot be carried out on the track as the risk of buckling is too high if the trackbed is disturbed.
With climate change, it is possible that the number of days when track temperatures exceed 32C will increase, especially in the south of England. So it may become prudent to move the SFT to 28C or higher, either nationally or regionally. This is another area monitored by the climate change team and it will be their recommendations that will be used to develop any new codes of practice.
Affordably resilient
There are other adverse results from increased temperatures. Overhead electrification wires may sag when it’s hot. Lineside cabinets and the equipment inside them can heat up. Ergonomically, trackside workers become less effective if the weather is too hot (or too cold). All of these factors need further study and an initial budget of £750,000 has been allocated for this type of research.
John Dora and his team do not work in isolation. Five weather experts from the Meteorological Office are currently assisting with future predictions. Discussions with the Office of Rail Regulation for the next and subsequent five-year control periods will help to produce an investment plan to ensure that the railway is ‘affordably resilient’, resisting the effects of climate change.
