Erosion detection and monitoring in quick clay areas by repeat UAV-borne LiDAR surveys: Two case studies from Norway

Recent examples of catastrophic quick clay landslides in Norway have demonstrated that the risks posed by quick clay can be partly mitigated through systematic erosion monitoring schemes. Monitoring can be carried out by comparing multi-temporal digital elevation models generated from airborne LiDAR datasets. However, aircraft-based LiDAR campaigns are expensive, and surveys are typically conducted only every few years. In contrast, Uncrewed Aerial Vehicles (UAVs) equipped with LiDAR sensors offer a cost-effective alternative for frequent monitoring of surface conditions in localized areas. This paper presents a comparison of repeated UAV-borne LiDAR measurements used to detect and monitor erosion in quick clay areas, with close-range photogrammetry used as ground truthing. Results from two case studies in southeastern Norway demonstrate that UAV-borne LiDAR measurements can be conducted with increased spatial resolution (on the centimetre scale) and at a higher frequency than aircraft-based LiDAR measurements. The method enables more rapid detection of potential erosion or other terrain changes that could threaten the stability of slopes in high-risk areas. The paper also demonstrates how rapid analyses of repeated, topographic survey data can serve as an early warning tool for critical erosion in areas with quick clay. Such tools will help transition from today’s infrequently updated static hazard maps to a more dynamic hazard management approach.