Coupling of lattice Boltzmann shallow water model with lattice Boltzmann free-surface model

•We present a novel scheme for the coupling of a lattice Boltzmann free-surface solver to a lattice Boltzmann shallow water solver. This is of interest for the simulation of multiscale systems in which a large part of the domain can be well approximated by the shallow water model, whereas higher accuracy is needed in a smaller part of the domain which is simulated with the free-surface model.•We study the accuracy and performance of the scheme. A quantitative validation of this type of coupling for the lattice Boltzmann method is novel, and opens the door to a range of large-scale simulations of canals and other hydrodynamic systems.•The presented model is efficient since the overhead of the coupling is kept small. It saves significant computational effort, in that the computational time of a coupled system simulation is essentially the time taken by the free-surface part of the domain.•We present test cases in order to evaluate the capacity of the coupling scheme to simulate flows dominated by current transmission as well as for flows dominated by wave transmission.