ABSTRACT
Flow in a stream or constructed channel is a function of many factors, including precipitation, overland ow, inter-ow, groundwater ow, and pumped inows and outows; the cross-sectional geometry and bed slope of the channel, the bed and side slope roughness; meandering, obstructions, and changes in shape; hydraulic control structures and impoundments; and sediment transport. Generally, ow in ditches, channels, streams, and large rivers is classi-ed as open channel flow because the water surface is open to the atmosphere. Open channel ow can occur in many ways. For example, it can be turbulent in steep, rocky areas or following severe storm events. Also, during severe storm events, there might be rapid changes in the depth and amount of ow. On other occasions, it can be tranquil, and it will be difcult to detect that the water is owing. Flow may be classied into many types (Figure 7.1), and a different mathematical equation is needed to describe each type. Flow in an open channel is steady if the ow depth does not change or is considered constant during the time interval under consideration. The ow is uniform if the ow depth is similar along a reach of the channel. Steady uniform open channel ow is often called the normal flow. In a natural channel, these conditions might only occur along reaches that are a few channel widths long or might never occur in some mountain streams. As we move from one feature, such as a rife, to another feature, such as a pool, we need to redene the cross section and perhaps switch calculation methods as the ow type changes. We see in Figure 7.1 that different types of ow are classied as subcritical, critical, or supercritical. We will learn in this chapter how to quantify and then apply knowledge of steady uniform ow. In Chapter 8, we will learn about some of the other ow conditions that might occur.
