Assessing the effect of land use changes on sediment connectivity for landslides runout characterization

Persichillo M.G., Crema S., Bordoni M., Meisina C., Cavalli M, 2017, Assessing the effect of land use changes on sediment connectivity for landslides runout characterization, 12 Convegno GIT - Geology and Information Technology, Gavorrano (GR), 12-14/06/2017,

The study of a landslide runout (i.e., the distance traveled by sediment detached by a landslide) is fundamental for a comprehensive understanding of the risk associated with landslide occurrence since sediment mobilized from landslides can often reach downstream areas causing extensive damages. The spatial characterization of sediment dynamics through geomorphic systems (i.e., sediment connectivity) is a key property to define sediment transfer paths. Sediment connectivity is mainly controlled by the morphological complexity of the catchment and the spatial organization of vegetation. In particular, vegetation plays an important role on sediment connectivity, since it influences surface roughness and local sediment retention capacity. Moreover, vegetation changes due to land use and management practice modifications can introduce major changes in sediment delivery dynamics, leading to important effects on earth surface processes, especially in relation to slope instability phenomena. Within this framework, the aim of this work is to evaluate how vegetation characteristics and its modifications over time can affect sediment connectivity in response to shallow landslides occurrence. A GIS-based index of connectivity (IC) was computed for a hilly catchment located in the northern Apennines in Italy. This area was characterized by a high degree of land abandonment, leading to important landscape modifications over the last 60 years. Moreover, the studied catchment was highly affected by shallow landslide phenomena, mainly triggered by an intense rainfall event in 2009. Land use changes characterizing the study area in the last 60 years were integrated into IC computation. The Overland Flow Manning's n Roughness Values was used in order to represent the impedance to water and sediment fluxes related to each land use class. This parameter was integrated into a revised version of IC weighting factor (W). In particular, both a linear e non-linear relationship for the Manning's n based W was computed. This allowed integrating the hydraulic efficiency of overland runoff flow in the analysis framework. Finally, the results of IC implementing the revised W, based on land use change dynamics, was integrated into a data-driven model to evaluate the probability that the sediments produced by instability phenomena could reach downstream areas. In particular, this analysis allowed identifying those areas in which the mobilized sediment could damage the road network blocking traffic, isolating villages and stopping activities.

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