When the slope of a bed,φb, is larger than the angle of repose,φR, the bed material will slide (avalanche) to form a new slope approximately equal to the angle of repose. The process of avalanching is simulated by enforcing|φb| ≤ φRwhile maintaining mass conservation between adjacent cells (Sánchez and Wu 2011a). Avalanching may occur between computational cells as well as within cells. The details of the avalanching algorithm in the following chapter.