Geomorphic change detection in small Alpine basins using LiDAR DTMs

Morphological change evaluation of earth surface through time is an important task in environmental monitoring and risk management. Methods devoted to the assessment of geomorphic changes can be used to identify geomorphologically unstable areas, to quantify processes intensity, and to compute sediment budgets. Digital elevation models (DEMs) built from repeated topographic surveys can be used to produce DEM of Difference (DoD) maps and to estimate volumetric changes through time. Nowadays LiDAR technology can provide digital models representative of the bare earth surface (Digital Terrain Models – DTMs) at high spatial resolution and over great spatial extents contributing to the increase of accuracy of morphometric and volumetric measurement of varying surfaces. In this study, high-resolution DTMs derived from airborne LiDAR data acquired in different years (2006 and 2011) were used in order to characterize the sediment transport processes such as debris flows and bedload transport in a small Alpine basin. Two DTMs (2 m resolution) were derived for the Gadria-Strimm catchment (Vinschgau/Venosta valley, Autonomous Province of Bozen-Bolzano, Italy). These catchments, which cover a total area of 14.7 km2, have been chosen due to their contrasting morphology and because they feature different types and intensity of sediment transfer processes: the Gadria creek is characterized by frequent occurrence of debris flows (almost one debris flow per year), whereas the Strimm channel is essentially a bedload stream. A method based on fuzzy logic (Wheaton et al., 2010), which takes into account DTM uncertainties, was used to derive the DoD of the study area. The comparison between the 2006- 2011 DTMs permitted the analysis of the relationship between morphometric changes and the sediment transport dynamics at the basin scale over the 5 yr period. Besides, this approach proved useful to identify the relationship between erosion, deposition or no-change areas and geomorphometric parameters (e.g. slope, curvature, upslope area) relevant for sediment transport processes.