Flooding in Urban Areas - 2D Modelling Approaches for Buildings and Fences

Flooding in urban areas presents a range of challenges to the modeller due to the complexity of the flow patterns and paths that occur. It is very difficult, if not at times impossible, to represent the myriad of flow behaviour that occurs as water flows down roads, through/under/over fences, and around/through houses. Additional complexity occurs due to fence collapses, debris blockages, and the displacement of cars and other obstructions. With continued advances in computer hardware and software, 2D solutions are increasingly being used for modelling overland flooding of urban areas. Whilst 1D hydrodynamic schemes readily model the underground pipe networks and manholes, they are generally inadequate for representing above surface flooding. When 2D schemes are linked with a 1D solution for the pipe network, they become a powerful modelling tool. One of the challenges for the modeller is how best to represent the roads, fences, houses and other features within the limitations and constraints he/she has to work with. 2D solutions are very computationally intensive and it is not always practical to utilise a mesh of very fine elements. This forces the modeller to make approximations when representing the urban domain to represent the fences, buildings, and other obstructions. Various approaches to modelling buildings and fences within a fixed 2D grid are presented, and their pros and cons discussed. The approaches would be of interest to 2D modellers and recipients of 2D urban flood modelling outputs. Real world and test model results using the TUFLOW software are presented.