Notwithstanding recent advances in hydrological modelling, flood simulations remain challenging since many processes must be simulated with high computational efficiency. This paper presents a novel geographic information system (GIS)-oriented platform 3DNet and the associated hydrologic model, with focus on the platform and model features that are relevant for flood simulations. The platform enables hydraulic structures to be incorporated in the hydrologic model, as well as water retention. A limiting capacity can be imposed on every river reach enabling estimation of flooding volume. Runoff is simulated within irregularly shaped units that can be aggregated providing spatial flexibility, i.e. model setup can vary from lumped to semi- and fully-distributed. The model contains many parameters with a physical connotation that can be inferred from catchment characteristics, and it enables simulations with minimum data requirements. All algorithms are implemented in C++ warranting fast computations, while the spatial flexibility can provide additional speed-up. The model is used for a reconstruction of a devastating flood in the Kolubara catchment in May 2014. Despite incomplete and uncertain observations, reasonable results across the catchment are obtained with the plausible parameter estimates. The results suggest that enclosure of the presented features in flood simulation tools would improve simulation accuracy and efficiency.