We develop a full two-dimensional Coulomb-viscoplastic model and apply it for inclined channel flows of granular materials from initiation to deposition. The presented model includes the basic features and observed phenomena in dense granular flows like the exhibition of a yield strength and a non-zero slip velocity. A pressure-dependent yield strength is proposed to account for the frictional nature of granular materials. The yield strength can be related to the internal friction angle of the material and plays an important role, e.g., in deposition processes. The interaction of the flow with the solid boundary is modelled by a pressure and rate-dependent Coulomb-viscoplastic sliding law. We develop an innovative multiscale strategy to couple the full two-dimensional, non-depth-averaged model (N-DAM) with a one-dimensional, depth-averaged model (DAM). With the coupled model the computational complexity reduces dramatically by using DAM in regions with smooth changes of flow variables. In regions where depth-averaging becomes inaccurate, like in the initiation and deposition regions and particularly, when the flow hits an obstacle or a defence structure, N-DAM must be used, because in these regions the momentum transfer must be considered in all directions. The performance of the coupling is very high: The numerical results obtained by the coupled model deviate only slightly from the ones generated with the full two-dimensional model. This shows that the coupled model, which retains all the basic physics of the flow, is an attractive alternative to an expensive, full two-dimensional model. (C) 2013 Elsevier B.V. All rights reserved.