3.3 Measurement of velocity and discharge Defination Velocity : This refers to how quickly the water is moving. [Measured in feet per second (ft/s).] Discharge : discharge refers to the water generated by the facility. It may be dewatering water, wash water, stormwater, or any combination of these. This term is comparable to “flow” which is used here in reference to receiving water flow. [Usually site discharge is measured in gallons per minute (gpm). Example Of Measurement Velocity Measurement with a Pitot Tube For pitot tube measurements and calculations, the reference plane is taken to be at the height of the pitot tube measurements, so the equation for stagnation pressure becomes: P stag = P + ½ ρV 2 , which can be rearranged to: V = (2ΔP/ρ) 1/2 Where ΔP = P stag – P. The pressure difference, Δp, (or P stag – P), can be measured directly w...