If the flow in the culvert is critical, what can be inferred about the Froude number?

• A. Less than 1
• B. Equal to 1
• C. Greater than 1
• D. Depends on slope

Answer: (B)

When the flow in a culvert is described as critical flow, it means that the flow is at a specific condition where the velocity of the flow is exactly equal to the wave celerity. At this point, the Froude number, which is a dimensionless quantity used to describe the flow regime, is equal to 1.

The Froude number is calculated using the formula:

[ \text{Froude Number} = \frac{V}{\sqrt{gD}} ]

where ( V ) is the flow velocity, ( g ) is the acceleration due to gravity, and ( D ) is the hydraulic depth of the flow. When the Froude number is equal to 1, it indicates that the flow is neither subcritical (where the Froude number is less than 1) nor supercritical (where the Froude number is greater than 1).

In critical flow, any change in depth or velocity will result in a change in flow conditions. This behavior is crucial for the design and analysis of hydraulic structures, as critical flow conditions help in assessing the capacity and stability of the culvert.

The inference about the Froude number when the flow is critical is foundational