LiDAR for rapid geomorphological assessment in relict periglacial landsystems

The construction of the A21 Sevenoaks bypass in Kent is a seminal case study in engineering geology. In 1965 during the earthworks for the road, major slope failures occurred presenting a significant setback to the programme. No slope stability issues were foreseen before the groundworks commenced. Post-failure forensic investigations revealed multiple shear surfaces within lobe-like landforms that dissected the original route alignment. At that time, these landforms were not recognized, and their problematic nature not fully understood. Similarly, the Maidstone district has long been described as an area of relict periglacial landforms, specifically cambering and associated gulls, and valley bulge. This chapter presents key case studies, which detail the nature of the relict periglacial landsystem that gave rise to the encountered geohazards and demonstrates the advances in ground model assessment offered by airborne LiDAR (Light Detection and Ranging; laser scanning) datasets for engineering geomorphology. High-resolution digital elevation models derived from the LiDAR imagery (that became available for the first time in 2019) can be utilized to interpret and visualize the on-ground geomorphology. The available LiDAR imagery is described, and examples of their use presented from these classic case study sites.