Author(s): Yiqi Wu; Simon Tait; Andrew Nichols
Keywords: SWMM; Hydraulic Performance Model; Railway Flood Risk; Asset Degradation; Resilience
Abstract: UK railway drainage systems are facing increasing flood risks due to climate change, long asset life and the large numbers of poorly understood drainage assets. Lack of hydraulic capacity in the existing drainage system can cause track flooding and severe obstruction to railway operation. It is in the asset manager’s interest to better understand and forecast the hydraulic performance of the current railway drainage system, and manage the system accordingly in order to cope with the increasing number of expected extreme rainfall events. Railway drainage assets are owned and managed by Network Rail (NR). Although the NR drainage system is required to be designed to stand rainfall events with certain return period following the company design standards, with climate change the original designed capacity may not be sufficient anymore. Also, since drainage assets normally have a long lifespan and a slow degradation process, their condition may not be fully understood or sufficiently monitored. The gradual declining in the drainage system serviceability could further exacerbate the flood risk imposed to the railway under extreme rainfall events. Hence it is critical to build a model that could analyse the existing drainage system’s hydraulic performance; as well as simulate the water carrying capacity with predicted asset degradation and forecast extreme weather events. In this study, a model is developed by integrating the Storm Water Management Model (SWMM) with a railway drainage asset degradation model. SWMM is comprised by a rainfall-runoff component that transforms rainfall into runoff through the catchment areas, and a routing module that transports the runoff through the railway drainage system. The degradation process of the drainage assets is simulated using a Markov Chain model based on the historical asset condition records. This new integrated model can provide an automated and dynamic simulation process to test the drainage system performance with randomly generated extreme rainfall events using various climate change forecast models. It can also simulate changes in weather conditions by changing the weather related input parameters such as temperature, evaporation and catchment infiltration rates. The degradation model is incorporated into SWMM by altering the drainage asset characteristics that reflect their condition such as roughness and pipe diameter. Combinations of possible climate and drainage condition changes can be tested to help examine the strength of the existing system and help predict whether it could withstand the future climate changes. The model could also help in the design stages to test the resilience of new drainage systems, and hence help mitigate future flood risks.