The discharge of a sewer has to be determined often over a short period only. This can serve as design basis, and an accurate discharge measurement is required only later. In this chapter, the so-called mobile discharge measurement for rectangular, trapezoidal and circular profiles is introduced. Starting from the simplest configuration of a circular cylinder in a rectangular channel, the discharge-head curves, the modular limits, the submergence effect and practical questions are discussed for a number of designs. At optimal sites, the discharge can then be determined up to ±5% accuracy.
In addition, the thin-plate Venturi flume is presented that is proposed for larger channels or rectangular sewers of width up to 3 m, with an access by a standard manhole. Mobile discharge measurement with overflow structures is not recommended, because the mounting precision, the security and accuracy are demonstrated to be unsatisfactory.