The right-hand side of the continuity equation, the sediment gradient across the control volume, compares the sediment inflow with the sediment outflow. Sediment inflow is simply the sediment entering the control volume from the upstream control volume(s) and any local sources (lateral sediment inflows). Computing the sediment leaving the control volume is more difficult, a measure of the sediment mass the water can move, which is a complex function of the hydrodynamics and sediment properties. Sediment transport capacity is a measure of the control volume competence to pass sediment, computing the maximum sediment it can transport by grain class.