Two analytical block models to estimate the maximum velocity reached by granular flows are proposed. The first one models the speed evolution of coarse-grained materials flows (e.g. debris flows, avalanches); it is based on the power balance of a granular mass sliding along planar surface, written by taking into account the volume of the debris mass, an assigned interstitial pressure, the energy dissipation due to (i) grain inelastic collisions ('granular temperature' within a basal 'shear layer'); (ii) friction along sliding surface; (iii) fragmentation of grains. The second model allows to simulate the speed evolution of fine-grained materials flows (e.g. mudflows, quick clays) by taking into account the dissipation of the excess pore water pressure due to consolidation phenomena. Finally, the comparison between the results obtained through the proposed models and field and laboratory measures is carried out.