Though it happened almost 25 years ago, the dramatic collapse of Holbeck Hall Hotel in Scarborough, United Kingdom remains a pertinent reminder of just how unstable coastlines can be. In the weeks beforehand, cracks had been reported, but the subsequent landslide forced guests and staff to flee quickly before witnessing the entire building collapsing into the North Sea. Later, the British Geological Survey attributed this extraordinary event to a combination of heavy rainfall (140 mm in two months), drainage issues and water pressure.
Since 1993, lidar technology has vastly improved our ability to carry out surveys in vulnerable coastal regions. Less than 20 miles north of Scarborough, in the historic town of Whitby, in the county of North Yorkshire, teams from Durham University and 3D Laser Mapping have been gathering data along a 23 km stretch of coastline since 2013, in order to establish the extent of erosion, slope instability and landslide risk.
As well as being home to nearly 605,000 people, North Yorkshire is one of the most popular tourist destinations in the UK. The sheer number of hotels, restaurants, shops and historic attractions in Whitby means that a natural disaster could have a devastating impact on human life, infrastructure and the economy.
Of course, the challenges of working in coastal areas are well-known and this project was no exception. Much of the site, a mix of bare earth and heavily vegetated terrain, is inaccessible to survey teams working on foot because of major instability, including regular rockfalls and landslides.
The project, part of a Knowledge Transfer Partnership project funded by Innovate UK, aims to show how wave erosion at the base of the cliffs is undercutting the rock, resulting in land collapsing into the sea. Using a combination of airborne laser scanning, photography, terrestrial laser scanning, weather sensors and monitoring software, data is collected on a monthly and annual basis and then integrated to create highly detailed 3D models.
Given the challenging terrain and the fact that the area stretches 23 km along the coast, airborne surveys are conducted with the lightweight ROBIN +WINGS Mobile Mapping System from 3D Laser Mapping. This device was mounted onto a helicopter and, over a 10-month period, experts completed two surveys, creating a 3D map to show where changes had occurred.
Alongside the airborne device, Durham University chose the lidar-based SITEMONITOR LIVE solution, consisting of software and laser scanner, for regular and continuous data capture over 12 months. SITEMONITOR LIVE is a monitoring solution based on the use of a laser scanner and the software together. It allows for teams to manage the data generated from laser scanners across a whole site. This unique, scalable solution captures and manages 3D point-cloud data recorded with a scanner to provide real-time data and automated reports on volumes, berms and, for the Whitby project, slopes.
The laser scanner was configured to measure an important section of the cliff face at 60-minute intervals each day, with each scan sampling the cliff face at a resolution of 10 cm, generating more than two million points. With such vast quantities of data to process, the device was paired with automated analytical software that streams live information direct to the analysis team in Durham.
By monitoring small changes over time, geologists can alert engineers to remedial work that needs to be done to prevent a catastrophe. According to Dr Nick Rosser, from the university’s Department of Geography, SITEMONITOR LIVE enables them to measure small-scale movements and rockfalls with such high resolution and frequency that, “up until now would not have been possible”.
Using a bathymetric system, further environmental data was also captured to attempt a better understanding of the impact of higher sea levels and turbulent weather on coastal erosion. Until recently, research had relied on anecdotal evidence, suggesting a simple cause-andeffect between waves and erosion. Fresh data from this site indicates that erosion happens over a longer period of time than once thought and is often attributable to a range of factors, including freezing and thawing, temperature changes and friction from rising and falling tides.
Moisture in rocks, caused by water leaking from beneath, is one of the most common signs of unstable land, so laser scans show whether there has been an increase in this over time. Data from weather sensors is also used to show a link between rainfall and water in the rock face.
Each of the surveying methods is valuable in its own right, though they work best when combined. While terrestrial scanning generates high-resolution data, able to detect minute change, airborne surveys are lower resolution, but cover a much wider area in less time and can show long-term trends.
The Whitby project has become one of the world’s most pioneering coastal erosion programs, largely thanks to the depth and scope of the datasets. As work continues at the site, new techniques and methodologies are being developed– including algorithms to mine further information from time-series 3D scan data to show where land has become unstable.
Until this project got underway, the SITEMONITOR system had been used mainly in mining, but other industries are starting to see the benefits. By closely monitoring previously hard-to-reach areas in real-time, site managers are able to detect even small changes with greater speed and accuracy than before and, crucially, take appropriate action.