3.1 INTRODUCTION

By definition, an open channel is a flow conduit having a free surface: that is, a boundary exposed to the atmosphere. The free surface is essentially an interface between two fluids of different density. Open-channel flows are almost always turbulent, unaffected by surface tension, and the pressure distribution within the fluid is hydrostatic. Open channels include flows ranging from rivulets flowing across a field to gutters along residential streets and highways to partially filled closed conduits conveying waste water to irrigation and water supply canals to vital rivers.

In this chapter, the basic principles of open channel hydraulics are presented as an introduction to subsequent chapters dealing with design. By necessity, the material presented in this chapter is abbreviated an abstract of the fundamental concepts and approaches for a more detailed treatment, the reader is referred to any standard references or texts dealing with the subject: for example, Chow (1959), French (1985), Henderson (1966), or Chaudhry (1993)

As with any other endeavor, it is important that a common vocabulary be established and used:

Critical slope (S _c ):

A longitudinal slope such that uniform flow occurs in a critical state.

Flow area (A):

The flow area is the cross-sectional area of the flow taken normal to the direction of flow (Table 3.1).

Table 3.1: Channel Section Geometric Properties

Froude number

The Froude number is the dimensionless ratio of the inertial...