All of this analysis allows the authors to produce a range of predictions based on future sea level rises, to assess their potential impact on the railway. They make alarming reading. A rise in sea levels of 0.05m-0.07m by 2020 could lead to the number of DLRs doubling to 16-19 per year; by 2060 a sea level rise of 0.27m-0.39m could lead to DLRs increasing to between 46 and 63; and by 2100 a rise of 0.55m-0.81m could lead to between 84 and 120 DLRs each year.
In detail, by 2020 - just four years away - the authors suggest that speed restrictions will be imposed ten times per year, that Down line closures will happen 8.4 times per year, and complete closures every two years.
By 2060 those figures increase further, with complete closures of the route predicted twice per year and in 2100 3.6 times per year. By the turn of the century, the number of average DLRs could increase by 1,170%.
So, by 2040, if the medium-range predictions are correct, there could be some sort of service restriction on the railway at Dawlish on up to 10% of days. In the worst-case scenario envisaged, given that the worst weather happens in winter, a third of days in that time could be hit by restrictions.
The impact of Network Rail’s sea defence plans inevitably cannot be forecast. However, the authors suggest that while lengthy closures (such as that in 2014) could reduce, by the end of the century “multiple breaches, undermining and subsidence of the track with extensive damage to footpaths and offshore breakwaters can probably be expected”.
The conclusion is damning: “By 2060, with high-impact events occurring on average twice a year, the extent to which the railway would
be able to maintain a credible service has to be brought into question. Indeed, even by 2040 there are likely to be serious issues in relation to its reliability.”
The authors add: “An increase in the number of overtopping events and associated service restrictions very much beyond current norms can be expected in future decades.”
The coastal railway through Dawlish is already among the most expensive to maintain in the country for Network Rail, costing around £800,000 per year for the short section between Dawlish and Teignmouth. Then there’s an average £5m every three or four years, to deal with one-off events such as landslips.
The authors admit that it is a “rather rudimentary approach”, but by multiplying the reported average annual cost of maintenance by the estimated increase in days with DLRs they estimate that at today’s prices maintenance will cost between £5.8m and £7.6m per year by 2040.
Furthermore, these costs take no account of the compensation paid by Network Rail to train operators when the railway is disrupted or closed. The authors estimate average annual compensation paid to train operators between 1997 and 2009 to have been £270,000 per year. Should the number of DLRs increase to the high sea level rise scenario, this could increase to £1.1m per year at current prices in 2040.
The costs don’t end there. Network Rail estimates the repair costs of the February 2014 storms to have been £50m, and that works to protect and improve the current alignment could cost between £398m and £659m over 20 years. “Running trains in Devon will cost the railway industry (and ultimately the Government) even in a ‘do nothing’ scenario rather more in the future than it has in the past.”
The wider costs to the region of the two-month closure in 2014 are rather harder to quantify, and the authors suggest that the economic effects of transport disruption such as this “are not well understood and will not necessarily be captured especially successfully by variations of conventional appraisal processes”.
An alternative approach to deciding between infrastructure schemes is that rather than deciding between doing nothing, protecting the existing route or re-opening/building, an alternative might be to determine which interventions are most likely to achieve the stated aims of transport policy.
Applied to Dawlish, the authors suggest that the question might shift from “How much does it cost when the line is closed” to “How can we best ensure that as far as possible this does not happen again.” They point out that in Italy, two billion euros worth of engineering works have been completed along the Adriatic coast to reduce the vulnerability of passenger and freight travel to sea level rises and coastal storms.
In a sense, Network Rail may be somewhat in the role of King Canute in trying to hold back the tide (although that king did so to prove to his courtiers that in fact he could not). If the authors are correct, even if Network Rail significantly strengthens the Sea Wall, “it is reasonable to expect ongoing disruption because of continuing periodic overtopping of the sea defences. Whatever the policy response, there looks set to be a significant cost increase, possibly running into the billions of pounds, associated with running trains through Devon in the future.”
The ramifications of this study are clear: there is real merit in conducting similar investigations on other vulnerable stretches of railway line both in the UK and abroad.
This remarkable work, based largely on evidence and existing trends, shows that a co-ordinated and coherent approach to addressing the vulnerabilities of coastal transport infrastructure is likely to be required. Given that the impact of sea level rises on the railway at Dawlish (and by extension other locations around the country) could be noticeably worse by the end of the decade, there is no time to lose.
The full study is available at http://www.sciencedirect.com/science/article/pii/S0966692315002197
- This feature was published in RAIL 792 on January 20 2016