It is open channel type measuring devices that operates whit a small drop in head. The loss of head for free flow limit is only about 25%of that weir sand or silt in the flowing water does not affect its operation or accuracy .it allows accurate measurement even when partially submerged.
The walls of throat section are paroled and the floor is inclined downwards small flumes are made of sheet metal while large ones are made of concert .the size of flume is determined by width of its throat size ranges from 7.5m to several meters.
To determine discharge two scales Ha and Hb are provided at the upstream and down stream section of the flumes.
Width of throat
Free flow limit Hb/Ha
2.5 to 7.5 cm
15 to 22.5 cm
30 to 240 com
It is attempt to improve par shall flume by simplifying construction details .the flumes has flat bottom ,vertical walls and a zero length throat section .since it has flat non throat ,it was given the name “cutthroat “most advantage of this flume is economy. It can operate either as a free or submerged flow structure.