A quantitative vulnerability function for fluvial sediment transport

Abstract

In quantitative risk assessment, risk is expressed as a function of hazard, elements at risk exposed, and vulnerability. Vulnerability is defined as the expected degree of loss for an element at risk as a consequence of a certain event, following a natural-scientific approach combined with economic methods of loss appraisal. The resulting value ranges from 0 (no damage) to 1 (complete destruction). With respect to torrent processes, i.e., fluvial sediment transport, this concept of vulnerability-though widely acknowledgeddid not result in sound quantitative relationships between process intensities and associated degrees of loss so far, even if considerable loss occurred during recent years. To close this gap and establish this relationship, data from three well-documented torrent events in the Austrian Alps were used to derive a quantitative vulnerability function applicable to residential buildings located on torrent fans. The method applied followed a spatially explicit empirical approach within a GIS environment and was based on process intensities, the spatial characteristics of elements at risk, and average reconstruction values on a local scale. Additionally, loss data were collected from responsible administrative bodies and analysed on an object level. The results suggest a modified Weibull distribution to fit best to the observed damage pattern if intensity is quantified in absolute values, and a modified Frechet distribution if intensity is quantified relatively in relation to the individual building height. Additionally, uncertainties resulting from such an empirical approach were studied; in relation to the data quality a 90% confidence band was found to represent the data range appropriately. The vulnerability relationship obtained allows for an enhanced quantification of torrent risk, but also for an inclusion in comprehensive vulnerability models including physical, social, economic, and institutional vulnerability. As a result, vulnerability to mountain hazards might decrease in the future.

Adaptability and transferability of flood loss functions in residential areas

“…Therefore, ancillary information with a higher resolution, such as land use data, are commonly applied to transfer the aggregated (municipal) values to a higher spatial resolution . Object-based studies, on the other hand, evaluate each element at risk by assigning average economic values to buildings using the volume and type of building (e.g., Keiler et al, 2006;Fuchs et al, 2007) or the building size and number of storeys (e.g., Totschnig et al, 2011;Totschnig and Fuchs, 2013). In this study, we rely on a land use map of 2006 for attributing aggregated asset values to residential areas.…”

“…Even if the general consideration of flow velocity in flood damage modeling on buildings cannot be necessarily recommended , the dynamic load of flooding seems to be fundamental for the damage pattern on buildings particularly for mountainous regions like the European Alps (e.g., Totschnig and Fuchs, 2013). In case of torrent processes, such as fluvial sediment transport (e.g., Totschnig et al, 2011) or debris flows (e.g., Fuchs et al, 2007), debris actions, such as the deposition of the accumulated sediment material, influence the relation on building losses remarkably (Totschnig and Fuchs, 2013).…”

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.…”

“…7) are still missing. However, first estimates can be obtained by re-analysing the datasets used by Fuchs et al (2007b) and Totschnig et al (2011). In fact, knowing the duration of the analysed events, different trial values for a i can be tested until the calculated final vulnerability comes sufficiently close to the vulnerability assessed with the functional approaches of Eqs.…”

Mountain hazards: reducing vulnerability by adapted building design

“…Recently, promising approaches for a quantification of vulnerability have been made by Wilhelm (1997), Borter (1999), Barbolini et al (2004) and Keiler et al (2006) with respect to avalanches and rock fall processes, respectively. However, sound suggestions for landslides and torrent processes are still largely unavailable, even if these processes caused major losses in the Alps in the recent years (Fuchs et al 2007a;Fuchs 2009;Totschnig et al 2011). Although such empirical relationships become increasingly important in determining the vulnerability of structural elements at risk, the results only mirror the average expected systems behavior (expected destruction due to impacting forces) for a specific setting, e.g., the entire area of a torrent fan presumably affected by a defined 1 in 150 year event.…”