Critical Depth Calculator
Calculate rectangular-channel critical depth and minimum specific energy at an entered discharge.
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Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Use the rectangular-channel Froude-one condition to minimize depth plus velocity head for a given discharge.
yc=(Q²/(g b²))^(1/3); critical specific energy=1.5yc
Worked example
Q=0.5 m³/s and b=1 m give critical depth about 0.294310966 m. The critical velocity equals √(g yc).
Assumptions and input details
Hydrostatic pressure, rectangular prismatic channel and kinetic-energy correction factor one. This is critical depth, not Manning normal depth or a prediction of the actual profile.
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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