A 1D–2D coupled numerical model is presented in this work. 1D and 2D models are formulated using a conservative upwind cell-centred finite volume scheme. The discretization is based on cross-sections for the 1D model and with triangular unstructured grid for the 2D model. The resulting element of discretization for the coupled model is analysed and two different coupling techniques based on mass conservation and mass and momentum conservation respectively are explored, considering both frontal and lateral configurations. The interaction with the boundaries in each model is highlighted and the necessity of using the appropriate strategy according to the flow regime is also justified. The coupled model is tested through academic test cases where the numerical results are compared with a fully 2D model as well as with experimental measurements in steady and unsteady scenarios. It is also applied to a real world configuration, where the flood wave propagation in the river bed is simulated by means of a 1D model and the inundation of the riverside is dealt with a 2D model. The computational gain is also analysed.