Flow in Non-Erodible Open Channels

Abstract

Open channel flow or, more appropriately, free surface flow involves flow through a conduit with the liquid surface exposed to a constant pressure (atmosphere). Thus there can be open channel flow through a closed conduit (a pipe) provided the flow is not full bore. Full-bore closed conduit flow is referred to as pressure flow since pressure is the major controlling factor. In contrast, gravity and therefore conduit slope and elevation changes are important factors determining the nature of flow in an open channel. Nevertheless, all the fundamental principles of conservation of momentum, energy and mass (discussed in Chapter 2) are applicable to flow through open channels as they are to closed conduit pressure flows. Figure 4.1 shows the similarity of the energy concepts in both cases. It may be observed from the figure that depth (y) changes in an open channel follow the pattern of pressure (p) changes in a pipe. Comparison between pipe flow and open channel flow