ABSTRACT
This chapter introduces calculation procedures for discharge measurement structures. It focuses on a rational expression for discharge in terms of typical flow quantities and the geometry of the structure. The chapter presents the general one-dimensional flow equations, and a demonstration that critical flow can occur if either the cross-sectional area has a local minimum or the bottom geometry is characterized by a local maximum. It describes devices that involve gradually varied channel geometries, and shows that classical critical flow theory fits well with observations, and that discharges can be determined rationally. The chapter discusses weirs having rapidly varying geometry such as thin plate weirs, and explains the intermediate structures having moderately varied channel geometry such as broad-crested weirs and flumes of the Parshall type. It also discusses the WES-standard spillways often used on dams with high discharges, and miscellaneous discharge measurement structures.
