Controls

This is a hydraulic term for a feature in a pipe or channel system that controls flows through the system, acting as a 'bottleneck'.

In open channel hydraulics, a control is some feature that obstructs flow to the extent that it produces subcritical flow upstream and supercritical flow downstream. Since additional energy is needed to force water through or over the control, the upstream water surface will rise and back-up. Often controls are used as flow measuring devices, since the flowrate can be  related to the upstream water level with reasonable accuracy.

Typical controls are brinks of waterfalls, weirs, flumes and sluice gates. Controls can change with the magnitude of flows and with possible backwater effects that can 'drown out' controls, so that water levels are then controlled by downstream water levels, influenced by downstream hydraulic structures and flow paths.'

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