MAINTAINING infrastructure to the required standard is the basis for ensuring the safety and continuity of rail services. Failure of a section of track or an infrastructure asset can result in potential fatalities, large repair costs, loss of service and reputational damage, leading to serious economic consequences. Climate change is already creating a surge in such events for the rail industry worldwide.

Rising global temperatures create new environmental conditions, such as rising sea levels, prolonged periods of drought and higher than usual precipitation. These factors have a direct impact on rail infrastructure. Increased precipitation can create flooding and lead to ground saturation, which can weaken embankments and slopes, creating the risk of landslides that can move the track from its alignment or block it with debris.

Periods of drought can cause drying, sinkage or cracking of underlying soils, leading to track misalignment or slope failures. A rise in sea level can increase the rate of coastal erosion, threatening railways built along the shoreline.

Traditional methods of monitoring infrastructure conditions under such scenarios include using track condition data to detect changes to the alignment, which can then be addressed by remedial work or further on-site surveys to determine the underlying causes of infrastructure deterioration.

But traditional methods might not easily identify some of the wider existing or developing spatial risks on or near the railway, such as signs of slope instability or ground movement. And given the major size of some networks, effective monitoring of climate change-related infrastructure risks can be a significant challenge.

Operating almost in real time, satellite-based movement assessment and monitoring provides an in-depth way for infrastructure managers to understand where the risks are actually located.

Analysis of data gathered by satellite radar enables highly accurate detection of movement that can point to existing or developing risks. These assessments can be delivered quickly and cost-effectively, enabling the rail industry to identify, monitor and quantify the risks posed by climate change.

Value Space has recently undertaken satellite-based analysis of ground conditions on sections of the 561.6km Lossan corridor in southern California, running from San Luis Obispo through Los Angeles to San Diego. It is the second-busiest inter-city passenger rail corridor in the United States, and also carries freight worth over $US 1bn every year.

Both passenger and freight services on sections of the corridor have been disrupted as a result of the more extreme weather patterns caused by climate change, particularly those sections where the railway was built along the coast. They have experienced ground movement caused by coastal erosion that has affected track alignment, as well as unexpected landslides blocking traffic and damaging infrastructure.

In September 2021 and in September 2022, two consecutive ground shifts took place on the shoreline at Cyprus Shore in San Clemente, between Los Angeles and San Diego, resulting in the track moving by as much as 381mm. After the September 2022 event, passenger services remained suspended for six months. Ground movement was attributed to coastal erosion which had worn away a counterbalance that allowed an ancient landslide to reactivate.

Figure 1: Analysis showing discrepancies in movement at the site of the landslip on the Lossan corridor. identified

The two events required emergency track stabilisation work costing a total of $US 21.7m. After the first shift, over 20,000 tonnes of large rocks and boulders were placed on the coastal side of the railway to counteract erosion and ground movement. More substantial works were carried out after the second ground movement event, with large metal anchors driven into the slope adjacent to the track to prevent the line from moving.

Satellite-based analysis for the period between January 2021 and September 2022 revealed two notable movement clusters with different directions on the section at Cyprus Shore. The larger cluster moved up to 20mm per year, and the smaller one up to 14mm per year. Analysis of detailed movement data showed that this section of the coast and the slope were moving throughout the period of analysis.

In August 2021, just before the first ground shift, there was developing movement instability. Movement stabilised after the first ground shift and initial emergency stabilisation work, but movement continued up until the second ground shift in September 2022. The differently moving clusters on the shore and slope beneath the railway point to the accumulation of stress that is typical of a developing ground slide or movement event. Further satellite-based analysis between January 2021 and January 2024 revealed that movement is still present in the area, with buildings above a slope next to the railway experiencing movement of up to 19mm a year.

Unusually high precipitation during the winters of 2022 and 2023 have caused an increase in landslide incidents in California. Railways have not been left untouched and several landslides have disrupted rail services in San Clemente, including a major event on April 27 2023 on the coastal slope below Casa Romantica cultural centre. Debris blocked the railway just below the slope and again after a second landslide in June that year. It cost $US 6m to clear the track and build a wall to protect the railway from further damage.

Value Space’s analysis of the landslide area for the period from October 9 2021 to April 26 2023 identified ground movement on the slope of up to 46mm per year that was distinctly different from adjacent areas. Analysis revealed that the area of the landslide started showing warning signs in November 2022. The sides of the marked area in Figure 1 (see above) are moving in opposite directions and the mid-section of the marked area stands out for the lack of stable satellite-measured readings. These signs indicate possible strong stress on the slope that are typical of a developing landslide. These findings would have led to a warning being issued well ahead of the landslide, had the area been under satellite-based monitoring.

The Lossan corridor has several longer sections along the coast that are already known or identified as being at risk from future weather and climate change-related incidents. The 2.72km section built on the Del Mar Bluffs north of San Diego has been of particular concern for a number of years, as the high sea cliffs here experience natural erosion resulting from earthquakes, rain, groundwater flows, breaking waves, and wind. The bluffs retreat naturally at an average rate of up to 152.4mm a year.

Eight surface slides on the bluffs have been reported in the area since summer 2018. Each time one takes place, rail traffic is stopped until inspection confirms that it is safe for operations to resume. Since 2003, the San Diego Association of Governments (Sandag) has completed several projects to stabilise the bluffs, with a new project due to begin this year at a cost of $US 78m.

Value Space has analysed movements in the Del Mar Bluffs area for the period from January 24 2021 to January 15 2024 (Figure 2). Satellite-based assessment of the area identified 17 different movement clusters on the track section, among them were six areas of significant movement.

Figure 2: Analysis of slope movements on the wider Del Mar Bluffs area.

Threats to service continuity on the Lossan corridor are not limited to the southern coastal sections at San Clemente and Del Mar Bluffs, however. Similar conditions exist on the northern part of the corridor. At a hearing of California Senate Transportation Subcommittee on Lossan Rail Corridor Resiliency last year, experts estimated the cost of stabilising these northern sections at $US 85m.

For the period from January 2021 to January 2024, Value Space analysed the 85km section between Santa Barbara and Vanderberg and the 45km section between Santa Barbara and Ventura with different areas of detected movement marked. These examples demonstrate that satellite-based movement assessments can be conducted on longer sections of railway to identify, monitor and quantify climate change risks on a network level.

With its highly accurate and up-to-date deformation detection capabilities, satellite-based monitoring and risk assessment is set to help the rail industry as it has already benefitted the insurance sector in understanding the risks to critical infrastructure posed by climate change. As infrastructure managers face increasing disruption and losses caused by more extreme weather patterns, they should seek to implement new tools to stay ahead of the curve and proactively manage the risks associated with climate change. Expect satellite-based technology to become standard practice.