Several approaches have been proposed previously to describe the global (mean) flow behavior of debris flows. Comparison of theoretical and observed flow resistance indicates that resistance laws similar to those used for turbulent water flows in rough channels can be applied to granular type debris flows. This finding is also in agreement with results from previous studies simulating unsteady debris flow waves by means of numerical models. A similar conclusion is drawn from experimental data on granular debris flow surges with a wide range of overall solid concentrations. For these flows, the flow resistance increases with increasing concentratiOn. For higher concentrated granular debris flows, the flow resistance may also be predicted by a dilatant grain shearing approach. This approach may also be suitable for the front part of more diluted granular debris flows where local concentrations can be rather high.