A coarse-grid approach to representing building blockage effects in 2D urban flood modelling

The latest information and communications technology has enabled flood modelling in urban areas using high quality terrain data to simulate the detailed flow dynamics in local areas. However, the computational cost rises exponentially as the resolution goes finer. The advance of computing hardware is still a limiting factor for large-scale area or risk/uncertainty analysis modelling with fine resolution that describes the details of building features. Grid coarsening is the straightforward way to reduce the computing efforts for 2D flood modelling. The traditional approach to grid coarsening usually takes the average elevation of a fine grid as the new terrain model for the coarse grid. This approach often results in loss of information that introduces errors to modelling. In this study, the building features in coarse grids were abstracted using the building coverage ratio (BCR) and the conveyance reduction factor (CRF) parameters in a 2D model to simulate flooding in urban areas. The outcome of 2D case studies showed the proposed model can minimise the errors due to terrain averaging and provide a much better accuracy of modelling results at a marginally increased computing cost.