<p>Flood-induced inundation becomes frequent in low-lying coastal and riverine regions as a result of increase in storm surge and sea-level rise. An efficient and robust inundation assessment model is necessary for coastal flood management and inundation evacuation. Recently, a series of rapid flood inundation methods (RFIMs) were developed based on high-resolution digital elevation models (DEMs) and advanced geographic information system (GIS) technology. However, a shortage of hydrodynamic mechanisms has restricted application of the RFIM. This paper proposes a novel RFIM based on a combination of GIS and hydrodynamics for application in coastal and riverine regions. First, GIS-based algorithms are used to extract hydrodynamic parameters from the DEM. Specifically, this process includes extraction of the flow network and the bottom level cross-section on each flow segment, discretization of the main terrain into a triangulated irregular network (TIN) and division of the catchments. Next, a one-dimensional hydrodynamic network model is applied to calculate flood flow propagation in the complex network, including flood wave amplification and damping. Finally, a simple elevation-determined and domain-connected algorithm on the triangulated irregular network is implemented to obtain the extent of flood inundation. The results indicate that the proposed method can estimate a reasonable flooding extent with a good degree of agreement with that of the three-dimensional hydrodynamic model, while the runtime is significantly reduced by orders of magnitude.</p>