Overfalls

Abstract

Overfalls allow to accurately determine discharge on the one hand, and may be used to submerge a channel on the other hand. This important control structure has a wide range of application, and many overfall shapes have been suggested until today. The purpose of this chapter is to introduce the main overfall types and to highlight their particular advantages. For sharp-crested overflow structures, the standard rectangular and triangular weirs are described. For discharge measurement, both accuracy and application limits are specified. In addition, general guidelines are presented regarding their installation in sewers or channels. The submerged weir flow is also described. For larger discharges, the overflow structure has to be sufficiently massive to satisfy static considerations. Particular attention is directed to the cylindrical weir and the broad-crested weir used for overflow depths of up to about 2 m.