Evaluation of a model for mapping intense pluvial runoff hazard using proxy data of runoff-related impacts. Application to the railway context

Abstract

Abstract. The IRIP method, for Indicator of intense pluvial runoff, in French, is a geomatics method which allows mapping the susceptibility of territory to surface runoff and that provides three maps of susceptibility to the generation, transfer and accumulation of runoff. It is based on the combination of binary maps that represent the impact of a given factor (favourable or not favourable) to runoff. These factors are summed up to provide susceptibility maps to runoff with levels ranging from 0 to 5. To be used for risk prevention, the quality and limitations of the produced maps must be assessed. However, runoff data are very scarce and not available everywhere in a territory. Proxy data of impacts related to runoff can provide information useful for the evaluation of the IRIP maps. However, both information cannot be compared directly and a specific methodology to compare susceptibility maps and proxy data must be proposed. This paper presents such a method that accounts for the hazard level, the vulnerability of the study area and possible mitigation actions taken to reduce the risk. The evaluation method is assessed using runoff-related impacts on railways as proxy data to compare with the maps. The evaluation is made on a 80 km railway line in Normandy (North of France), where a comprehensive database of runoff-related impacts on the railway has been gathered over the whole 20th century. The results show that the evaluation method is robust and relevant. The comparison with runoff-related impacts on the railway also shows that the susceptibility maps produced by the IRIP model provide relevant information related to runoff and that they can be used to design risk management strategies, as illustrated in the railway context.

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“…Depuis 2010, l'IRSTEA 1 développe un modèle de score pour cartographier les risques pouvant être liés au ruissellement intense (érosion, coulées de boue, dépôts) en utilisant la méthode IRIP 2 ©. L'évaluation de ces cartes est actuellement réalisée sur la base d'observations de terrain telles que les déclarations individuelles de catastrophes naturelles, de calamités agricoles ou encore les données d'incidents sur les réseaux linéaires (DDTM 3 , SNCF 4 ) (Lagadec et al, 2016 ;Braud et al, 2020). Cependant, ces données ou déclarations peuvent être le résultat d'autres phénomènes physiques et ne concernent pour l'essentiel que des zones à enjeux économiques (dommages aux biens, aux personnes).…”