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A computational case study is presented of the flooding in urban Jiujiang due to the Yangtze River dike break in August 1998. A shallow water hydrodynamic model was deployed based on the weighted average flux -- total variation diminishing (WAF-TVD) finite volume algorithm. A series of numerical modelling was conducted to identify the influences of the mesh resolution and model parameterisation on the flood propagation. Three mesh resolutions (2, 5 and 10 m) were used, and spatially distributed roughness was specified based on land-use classification. Due to the highly irregular topography and densely distributed buildings, the flood propagation is largely hindered. The numerical results show that an area of merely 6 km² was inundated at 6 h following the dike break with a discharge of 400 m3/s. Mesh resolution and roughness parameterisation have considerable effects on the flood propagation, whereas the impact of turbulent eddy viscosity is negligible. A coarser mesh could result in a larger inundation area (10%), and a lumped roughness may produce an appreciable overestimation of the inundation area in the initial period of the flood propagation. This observation highlights the significance of mesh resolution and also physically meaningful estimation of the roughness for urban flood modelling. [ABSTRACT FROM AUTHOR]