Case study 2: CROATIAN CASE STUDY

For the Croatian case study, the impact of low probability, high consequence flood hazard scenarios were evaluated. The network vulnerability was assessed according to the potential for bridge scour, track inundation and track blockages due to rainfall-triggered landslides. A qualitative risk assessment was initially performed using the Objective Ranking Tool (ORT) method to demonstrate the use of such a methodology to determine the rail sections along the network where the risk was most substantial.

A quantitative risk assessment was subsequently demonstrated for the network. To consider extreme flood hazard scenarios, a statistical methodology was applied to historical rainfall and river discharge data to fit extreme value distributions and to extrapolate for high return periods. A linear hydrodynamic modelling approach was also adopted to calculate the propagation of the flood wave downstream over time and, therefore, to establish extreme water depth values at the downstream locations of interest. Fragility functions were developed for selected network elements to establish the potential for rail transport disruption due to bridge scour, track inundation and track blockages.

The overall consequences were assessed in both in terms of the direct restoration costs and durations for the network along with the potential disruption to freight and passenger rail transport. The results of the quantitative risk analysis demonstrated that the potential for damage due to bridge scour was the governing factor both in relation to the direct costs and also in terms of the potential for disruption to freight and passenger trains on the network.