Granular flows have been intensely studied in recent years, since they play an important role in the understanding of natural hazards (avalanches, submarine landslides,...) and industrial processes. The physical description of aerial granular flow models as well as other more complex models such as debris flows is a very active field of research.

Shallow depth-averaged models have been widely used in order to simulate such flows while having low computational effort. These models are mainly based on the pioneering work of Savage-Hutter, where the friction between the bottom and the granular material is modeled though a constant Coulomb friction coefficient. This friction term presents some challenges from the theoretical and computational point of view. Indeed, it is a multivalued operator that corresponds to the friction between the particles. This term makes the material to become steady in the case of zero velocity and slopes under a given threshold.

We shall overview different techniques to model and numerically solve granular flows in a shallow framework, specially focusing in the Coulomb friction term. We shall present several simple and complex models for avalanches as well as some well-balance numerical schemes adapted to them.