CHAPTER 2 - BASIC CONCEPTS RELATED TO FLOWING WATER AND MEASUREMENT

9. Thin Plate Weir Relationships

Most investigators derive the equation for sharp-crested rectangular weirs by mathematical integration of elemental orifice strips over the nappe (Bos, 1989). Each strip is considered an orifice with a different head on it. The resulting rectangular weir equation for theoretical discharge is:

(2-17)

A correction factor is needed to account for simplifications and assumptions.
Thus, a discharge coefficient, *C _{d}*, is added to obtain
actual discharge, expressed as:

(2-18)

This relationship is the basic weir equation and can be modified to
account for weir blade shape and approach velocity. However, *C _{d}*
must be determined by analysis and calibration tests. For standard weirs,