Landslide hazard and risk mapping at catchment scale in the Arno River basin |
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Authors: | F Catani N Casagli L Ermini G Righini G Menduni |
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Institution: | (1) Dipartimento di Scienze della Terra, Università di Firenze, Firenze, Italy;(2) Autorità di Bacino del Fiume Arno, Firenze, Italy |
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Abstract: | We present the methodologies adopted and the outcomes obtained in the analysis of landslide risk in the basin of the Arno
River (Central Italy) in the framework of a project sponsored by the Basin Authority of the Arno River, started in the year
2002 and completed at the beginning of 2005. In particular, a complete set of methods and applications for the assessment
of landslide susceptibility and risk are described and discussed.
A new landslide inventory of the whole area was realized, using conventional (aerial-photo interpretation and field surveys)
and non-conventional methods (e.g. remote sensing techniques such as DInSAR and PS-InSAR).
The great majority of the mapped mass movements are rotational slides (75%), solifluctions and other shallow slow movements
(17%) and flows (5%), while soil slips, and other rapid landslides, seem less frequent everywhere within the basin. The relationships
between landslide characteristics and environmental factors have been assessed through statistical analysis. As expected,
the results show a strong control of land cover, lithology and morphology on landslide occurrence. The landslide frequency-size
distribution shows a typical scaling behaviour already underlined in other landslide inventories worldwide. The assessment
of landslide hazard in terms of probability of occurrence in a given time, based for mapped landslides on direct and indirect
observations of the state of activity and recurrence time, has been extended to landslide-free areas through the application
of statistical methods implemented in an artificial neural network (ANN). Unique conditions units (UCU) were defined by the
map overlay of landslide preparatory factors (lithology, land cover, slope gradient, slope curvature and upslope contributing
area) and afterwards used to construct a series of model vectors for the training and test of the ANN. Various different ANNs
were selected throughout the basin, until each UCU was assigned a degree of membership to a susceptibility and a hazard class.
Model validation confirms that prediction results are very good, with an average percentage of correctly recognized mass movements
of about 85%. The analysis also revealed the existence of a large number of unmapped mass movements, thus contributing to
the completeness of the final inventory. Temporal hazard was estimated via the translation of state of activity in recurrence
time and hence probability of occurrence. The following intersection of hazard values with vulnerability and exposure figures,
obtained by reclassification of digital vector mapping at 1:10,000 scale, lead to the definition of risk values for each terrain
unit for different periods of time into the future. The final results of the research are now undergoing a process of integration
and implementation within land planning and risk prevention policies and practices at local and national level. |
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Keywords: | Landslide hazard and risk Catchment scale Artificial neural networks Arno River basin |
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