As the total runoff from subbasins reaches defined channels, the depth of water increases and the predominant flow regime begins to transition to open channel flow. At this point, open channel flow approximations are used to represent translation and attenuation effects as flood waves move downgradient. This section describes the models of channel flow that are included in the program; these are also known as routing models. Each of these models computes a downstream hydrograph, given an upstream hydrograph as a boundary condition. Each does so by solving the continuity and momentum equations. This chapter presents a brief review of the fundamental equations, simplifications, and solutions to alternative models. The routing models that are included are appropriate for many, but not all, flood runoff studies. The latter part of this chapter describes how to pick the proper model.