Flow-measuring flumes are used to determine the discharge of a flume. Venturi flumes are specially shaped flumes with defined lateral contraction, sometimes also with a shaped bottom.
The constriction dams up the discharge. The backed-up water ensures that subcritical discharge occurs in the flume. The constriction is where acceleration from subcritical to supercritical discharge (including flow transition) takes place. Critical discharge is present at the narrowest cross-section. This results in a hydraulic jump in the expansion section of the Venturi flume.
The Venturi flume HM 161.51 consists mainly of two transparent side elements and a flat base plate. The transparent side elements allow to clearly observe the processes in the flume.