Froude Number & Flow Regime Calculator

Calculate Froude number and classify flow regime for open channels. Determine if flow is subcritical, critical, or supercritical. Includes wave celerity and specific energy calculations.

Input Parameters

Input Method

Choose how to specify flow conditions

Select calculation approach

Channel Configuration

Select channel shape

Cross-section geometry

ft

Depth of water in channel

Channel Geometry

Enter dimensions

ft

Width at channel bottom

Flow Specification

Enter velocity OR discharge

ft/s

Enter if known, or leave blank

cfs

Enter if velocity unknown

Note: If both are provided, velocity takes precedence.

Froude Number Overview

The Froude number is a dimensionless parameter representing the ratio of inertial forces to gravitational forces in open channel flow:

Fr = V / sqrt(g * Dh)

where:

  • V = flow velocity
  • g = gravitational acceleration
  • Dh = hydraulic depth = A / T

Flow Regime Classification

RegimeFr RangeCharacteristics
SubcriticalFr < 1Deep, slow flow; downstream control
CriticalFr = 1Unstable transition; minimum energy
SupercriticalFr > 1Shallow, fast flow; upstream control

Source: Chow (1959), Open-Channel Hydraulics.

For educational purposes only. Not a substitute for professional engineering judgment.

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