Analysis of the potential effects of dam break flooding using a GIS-tool for risk assessment in mountain regions - An exploratory study on an hypothetical event: the Val Canaria flood.

Pozzoni, Maurizio and Baruffini, Mirko and Marzocchi, Roberto (2011) Analysis of the potential effects of dam break flooding using a GIS-tool for risk assessment in mountain regions - An exploratory study on an hypothetical event: the Val Canaria flood. In: Proceedings of the VIII Forum Italiano di Scienze della Terra VIII Forum Italiano di Scienze della Terra, 19-23 settembre 2011, Torino.

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Abstract

Several percent of the Canton Ticino (Southern Switzerland) is prone to slope instability. The climate of southern Switzerland favors slope failure. In particular, landslides and accelerated creep are commonly triggered by major storms associated with warm humid air flowing from southwest towards the Alps. These storms can be particularly severe in the Ticino region. The storms of 1993 and 2000 caused extensive flooding, triggered debris flows and landslides, and induced higher rates of creep in some existing large landslides. Some of these landslides are located near Airolo in the upper Leventina valley (Val Canaria). They consist of failed rock masses on both sides of the valley with a total volume of about 80 million m3. The area is historically known for its instability (Seno and Thüring, 2006). In particular, the channel of the Canaria stream at the slope’s toe is filled with unvegetated landslide debris. A natural dam could form after a landslide event with a possible subsequent disastrous failure and destructive consequences on the important traffic lines passing in the Leventina valley. This scenario, although characterized by a very low probability of occurrence, is nevertheless possible and could have effects that would certainly be devastating for a big part of the Swiss economic system. A damaged infrastructure would cause serious material damage that would require extraordinary repairs or restorations. The services inactivity, as a result of a malfunction, would generate important financial losses and problems in essential services supply in the region (Maggi R. et al, 2009). All these elements justify a risk analysis of this region. With a Geographical Information System adapted to run with a tool developed to manage risk analysis, it is possible to survey the data in time and space, obtaining an important system for managing natural risks. The aim is to join and organize the various data currently available to carry out a qualitative and semi-quantitative analysis giving an overview of the risk (BUWAL, 1999). In this work we present few scenarios of flooding in the upper Leventina valley that are obtained applying two different 2D computational model: (i) FLO-2D, a hydraulic model distributed by FLO-2D Software Inc and (ii) a numerical GIS embedded model appositely implemented for dam break flooding (Marzocchi & Cannata, 2011). Evaluation of the models was performed by comparing simulation results against each other and finally a risk analysis is performed using a specific tool appositely developed in a GIS (Baruffini, 2010). The outcomes can provide an answer to the questions: “what can happen?” and “how achieve maximum safety with a minimum of effort?” or, depending on the desired depth, they can represent also input to start an increasing order of analytical analysis (i.e a cost-benefit analysis or so on).

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