The continuity equation compares the transport capacity to the supply (i.e. inflowing sediment load) for each grain class for each time step. If the capacity exceeds the supply HEC-RAS computes a sediment deficit. If the supply exceeds capacity the model computes a sediment surplus. In general, the model converts surplus into deposition and deficit into erosion. However, HEC-RAS applies some physical constraints to the continuity equation, checking if computed deficit or surplus can actually erode or deposit. HEC-RAS models these constraints with three basic limiters: a temporal deposition limiter, a temporal erosion limiter, and the sorting and armoring algorithms that provide an additional constraint on erosion.