Changes in intra-city transport accessibility accompanying the occurrence of an urban flood

Flooding of the urban transport systems is becoming ever more common, and their ability to function under such conditions requires detailed research. The main objective of this study was to determine the changes (mainly in their spatial nature) of intra-urban transport accessibility of a large city (Lodz) when impacted by urban flooding. The study utilised a variety of data, including the Digital Terrain Model, the Topographic Object Database and the Road Transport Speed Model. These were employed to determine those areas where disruption to the transport system may occur under varying degrees of rainfall (15-minute rainfall with a 20% probability of occurrence and maximum daily totals – an empirical probability of approximately 1.4%). Next, the changes in potential accessibility due to the occurrence of flooding were determined for different scenarios (various depths of flood water). In order to identify the absolute and relative changes in potential accessibility following a flood in the different scenarios, its value in a “normal” situation had to be calculated for all journey lengths in question. The study revealed that there is no correlation between the location of flooded sections of the network and the spatial differentiation of drops in travel times (analysed topologically) or declines in potential accessibility (irrespective of how attractive the destination is).