The Froude Number (Fr) is a dimensionless number used to describe flow conditions and is analogous to the Mach Number defining supersonic flight. If the Froude Number is less than one, flow conditions are described as subcritical. If the Froude Number is greater than one, flow conditions are described as supercritical. These conditions are identified on a scattergraph using an iso-Froude, as shown here. Flow conditions such as hydraulic jumps, sewer bores, and standing waves are readily identified by evaluating flow monitoring data with respect to iso-Froude lines.
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