A swift approach for identifying vulnerable linear transport infrastructures in areas prone to floods and erosion

Linear transport infrastructure, such as roads and bridges, is essential for the socio-economic development of industrialized countries, enabling the mobilization of people and goods. However, as these infrastructures extend over wide portions of territories, they are continuously exposed to adverse meteorological and hydrogeological events, including intense rainfall, floods, erosion, and landslides. These events can cause disruptions or malfunctions, leading to significant economic losses. In the last twenty years, floods have represented the natural disaster with the greatest socio-economic impact globally (EM-DAT; http://www.emdat.be/). It is also expected that the frequency and intensity of flood events will increase due to ongoing climate change, consequently escalating the expected impact. In addition to climate change, other factors contributing to increased flood risk include the expansion of urban areas and the extension of large networks of transport infrastructure over potentially flood-prone territories. In this context, studies on the evaluation and implementation of adequate mitigation systems that integrate aspects related to the intrinsic hazardousness of territories and those related to the exposure and vulnerability of elements at risk are of fundamental importance. The objective of this study is to identify portions of the hydrographic network prone to flood and erosion hazards where road infrastructures, such as bridges and/or viaducts, are located. As a test site, the Metropolitan City of Cagliari in southern Sardinia (Italy) has been chosen due to the occurrence of several coastal watersheds with high slope and short corrivation times. After a preliminary bibliographic research on methodological approaches developed in a similar context, the IDRAIM (Rinaldi et al., 2014) approach is applied with some simplifications to be compatible with datasets already available from public repositories (Sardegna Geoportale) and GIS analysis. The methodological approach includes i) the characterization of the physiographic context of the study area and the geomorphological conditions of the hydrographic network through the definition of specific indexes such as the Strahler stream order, confinement conditions, sinuosity index, average slope of homogeneous stream tracts, and average slope of sub-watersheds; ii) a census of stream tracts where bridges were damaged in past flood events and the identification, within the whole study area, of tracts characterized by similar geomorphological indexes; iii) multi-temporal satellite imagery analysis of potentially critical hydrographic network tracts for the identification of flood events and, therefore, the selection of vulnerable road crossings. The adopted methodology represents a useful and fast approach to identify, over wide portion of territories, critical tracts of the hydrographic network where flood and erosion vulnerable road crossings insist. Obtained results can provide the basis of knowledge for the implementation of further field analysis aimed at the detail characterization of infrastructure integrity and magnitude of floods and erosion events. Such information can be of valuable interest in the development of effective climate change adaptation strategies.