ABSTRACT
Open channel flow is characterized by the existence of a free surface (the water surface). In contrast to pipe flow, this constitutes a boundary at which the pressure is atmospheric, and across which the shear forces are negligible. The longitudinal profile of the free surface defines the hydraulic gradient and determines the cross-sectional area of flow, as is shown in Figure 5.1. It also necessitates the introduction of an extra variable - the stage (see Fig. 5.l) - to define the position of the free surface at any point in the channel.
