Geomorphic change detection using LiDAR DTMs in two small basins of the Italian Alps

The description and quantification of landscape changes as modulated by geomorphic processes, at different spatial and temporal scales, constitute the core of modern geomorphic research. The high resolution and accuracy of currently available airborne digital terrain models (DTMs) allow the development of new methods for the quantitative monitoring of geomorphic changes. In this context, DTM of difference (DoD), which can be created by subtracting one elevation model from another, represents a convenient way to estimate volumetric changes across landscape components between successive topographic surveys. In this contribution we quantify the topographic variations associated with the activity of rapid geomorphic processes (e.g., debris slides and debris flows) in Gadria and Strimm catchments, two adjacent basins, covering a total area of 14.7 km2, in the Eastern Italian Alps. To this purpose we perform DoD on two LiDAR-derived DTMs (2 m resolution), acquired respectively in the summer of 2006 and 2011, applying a fuzzy logic-based method (Wheaton et al., 2010) which considers the uncertainty in the surface representation of the topographic data. Results indicate that shallow rapid failures and channelized processes such as debris flows and debris floods have been by far the dominant processes in both basins over the study period. In particular, we are able to track the effects of a debris-flow event (July 12th 2010) originating on the western slopes of Strimm basin and that has been estimated to transport 15,000 m3 of sediment down to the confluence with Gadria Creek. Not surprisingly, upland terrain characterized by subdued topography and dominated by slow periglacial processes does not exhibit any appreciable change. Reference: Wheaton J.M., Brasington J., Darby S. E., Shear D. A., 2010. Accounting for uncertainty in DTMs from repeat topographic surveys: improved sediment budges. Earth Surface Processes and Landforms, 35, 136- 156.