The application of numerical debris flow modelling for the generation of physical vulnerability curves

Abstract

Abstract. For a quantitative assessment of debris flow risk, it is essential to consider not only the hazardous process itself but also to perform an analysis of its consequences. This should include the estimation of the expected monetary losses as the product of the hazard with a given magnitude and the vulnerability of the elements exposed. A quantifiable integrated approach of both hazard and vulnerability is becoming a required practice in risk reduction management. This study aims at developing physical vulnerability curves for debris flows through the use of a dynamic run-out model. Dynamic run-out models for debris flows are able to calculate physical outputs (extension, depths, velocities, impact pressures) and to determine the zones where the elements at risk could suffer an impact. These results can then be applied to consequence analyses and risk calculations. On 13 July 2008, after more than two days of intense rainfall, several debris and mud flows were released in the central part of the Valtellina Valley (Lombardy Region, Northern Italy). One of the largest debris flows events occurred in a village called Selvetta. The debris flow event was reconstructed after extensive field work and interviews with local inhabitants and civil protection teams. The Selvetta event was modelled with the FLO-2D program, an Eulerian formulation with a finite differences numerical scheme that requires the specification of an input hydrograph. The internal stresses are isotropic and the basal shear stresses are calculated using a quadratic model. The behaviour and run-out of the flow was reconstructed. The significance of calculated values of the flow depth, velocity, and pressure were investigated in terms Correspondence to: B. Quan Luna (quanluna@itc.nl) of the resulting damage to the affected buildings. The physical damage was quantified for each affected structure within the context of physical vulnerability, which was calculated as the ratio between the monetary loss and the reconstruction value. Three different empirical vulnerability curves were obtained, which are functions of debris flow depth, impact pressure, and kinematic viscosity, respectively. A quantitative approach to estimate the vulnerability of an exposed element to a debris flow which can be independent of the temporal occurrence of the hazard event is presented.

Vulnerability curves vs. vulnerability indicators: application of an indicator-based methodology for debris-flow hazards

“…As far as debris flow is concerned, the first approaches for physical vulnerability assessment were qualitative (Fell and Hartford, 1997;Liu and Lei, 2003;Romang, 2004), including in some cases vulnerability matrices (Leone et al, 1995(Leone et al, , 1996Sterlacchini et al, 2007;Zanchetta et al, 2004) showing a descriptive relationship between the damage and intensity of the flow. However, recently the number of vulnerability curves for debris flows has considerably increased and several studies may be found in the literature Papathoma-Köhle et al, 2012;Quan Luna et al, 2011;Totschnig and Fuchs, 2013;Totschnig et al, 2011). Each vulnerability curve has been developed for a specific area, is based on a particular catastrophic event and expresses the intensity of the process in various ways.…”

“…13 buildings in Fuchs et al, 2007) or a larger number of buildings (1560 buildings in Lo et al, 2012). In some cases, due to lack of empirical data, information on the process had to be derived through modelling (Quan Luna et al, 2011;Rheinberger et al, 2013) that expressed the flow not only as debris height but also as velocity, viscosity or impact pressure. As far as the degree of loss is concerned, relevant information could be provided in some cases by the authorities.…”

Regional prioritisation of flood risk in mountainous areas

“…The relationship between impact intensity and degree of loss is commonly expressed in terms of a vulnerability curve or vulnerability function (Totschnig and Fuchs, 2013), although also semi-quantitative and qualitative methods exist (Totschnig and Fuchs, 2013;Fuchs et al, 2007;Jakob et al, 2012;Kappes et al, 2012). The intensity criteria of torrent (steep stream) processes, encompassing clear water, hyperconcentrated and debris flows, has been considered in terms of impact forces Quan Luna et al, 2011;Hu et al, 2012); deposit height (Mazzorana et al, 2012;Fuchs et al, , 2007Akbas et al, 2009;Totschnig et al, 2011;Lo et al, 2012;Papathoma-Köhle et al, 2012;Totschnig and Fuchs, 2013); kinematic viscosity (Quan Luna et al, 2011;Totschnig et al, 2011); flow depth (Jakob et al, 2013;Tsao et al, 2010;Totschnig and Fuchs, 2013); flow velocity times flow depth (Totschnig and Fuchs, 2013); and velocity squared times flow depth (Jakob et al, 2012). Different types of elements at risk will show different levels of damage given the same intensity of hazard (Jha et al, 2012;Albano et al, 2014;Liu et al, 2014), therefore vulnerability curves are developed for a particular type of exposed element (such as construction type, building dimensions or road access conditions).…”

Towards dynamics in flood risk assessment

“…residential buildings, see Papathoma-Köhle et al, 2011, for an overview). In particular, vulnerability functions for buildings impacted by debris flows (Fuchs et al, 2007b;Akbas et al, 2009;Quan Luna et al, 2011) and fluvial sediment transport (Totschnig et al, 2011) are limited. In most of these studies vulnerability was measured using an economic approach and derived from the quotient between the loss and the individual reinstatement value for each element at risk considered.…”