Spatiotemporal data management of recurrent debris flow events using object-oriented data modelling

Abstract

This work is focused on the study of recurrent debris flow events on the north-facing mountain slope of the Bulgheria massif (Cilento Unesco Geopark, southern Italy). These phenomena pose a threat for at least two villages and infrastructures on the lower slope. The main morpho-structure of the mountain slope is strongly controlled by the tectonic overlapping in form of multiple thrust-folding of the Meso-Cenozoic limestone related to the inner margin of the Apennine Carbonate Platform over lower-middle Miocene marly-clay flysch and previously overthrusted basinal units ranging from upper Oligocene to lower Miocene. Therefore, the mountain slope is sculpted by erosional deep incided ravines and sub-structural interfluve cliffed slopes passing downslope to depositional piedmont by evident and abrupt knick-point. Channels along the slope are periodically filled both through rock fall deposits occurring on channel’s flanks and by soil creep and sheet wash phenomena at channel’s heads, which supply new material for future flows. Such relationship between infilling rock fall phenomena and debris flows represents an interesting case study of interaction among different and concurrent landslide types providing an optimal example of space-time evolving landslide system. Landslide classes have been stored and mapped using a previously proposed object-oriented and event-based model and producing in this way a multi-temporal database. Landslide objects have been grouped into landslide subclasses using the latest landslide classification available. In the next step, a hierarchical classification has been applied, introducing two levels of aggregation and one level of decomposition. Landslide complexes group landslide objects of the same class sharing spatial connection, defining rock fall complex objects and granular soil wet flow complex objects. Landslide systems group all the interacting landslides, regardless of their type. Landslide components describe the various portions of a single landslide object. Every stored object has its temporal attributes distinguishing between time points (events) and time intervals (time frames). The integration of complex spatial relations through topological analysis and temporal characterization of data allows to build a flexible database structure adaptable to several specific needs and different outputs, such as basic landslide maps or event maps, multi-temporal and frequency analyses, or the study of the interactions among different types of landslide hazards. In this framework, a neologism could be introduced in landslide studies, as landslide eventory mapping, as a challenge for future applications.