Stilling well: a well separate from but adjacent to the primary
measuring device and interconnected by a small
duct to provide an ideal point of head measurement.
Subcritical flow: same as submerged flow.
Submerged flow: when the downstream level rises or the discharge
flow is so slow that it impedes the free flow of liquid
through the primary measuring device.
Ullage: the remaining spatial volume of a vessel
or the volume required to fill a vessel.
Weir: a dam with or without flow notch across an open
channel to produce a crest in the liquid upstream.
The head of the crest is proportional to the flow.
PL-443 10 – 3