DrainageCalculators

Compound Channel Calculator

Calculate flow in compound channels with multiple subsections using the divided channel method. Analyze main channel with floodplains, composite roughness, and velocity distribution.

What This Solves

Calculates flow in compound channels with a main channel and one or two floodplain sections using the divided channel method.

Best Used When

  • You are analyzing a natural stream with distinct main channel and overbank floodplain areas
  • You need to calculate the total conveyance and velocity distribution in a compound cross-section
  • You want to determine when flow begins to overtop the main channel banks into the floodplain

Do NOT Use When

Key Assumptions

  • The divided channel method (Chow) is used with separate conveyance calculations for each subsection
  • Each subsection has its own roughness coefficient and geometry
  • Shear stress at the interface between subsections is neglected
  • The channel is prismatic along the reach being analyzed
  • Water surface elevation is the same across all subsections at a given cross-section

Input Quality Notes

Roughness values for floodplain areas are highly variable and depend on vegetation, debris, and land use. Field reconnaissance is essential for selecting appropriate n values for overbank areas.

Division Method Reference

MethodDescriptionBest Used For
VerticalVertical lines from water surface to channel bottomMost common; main channel with floodplains
HorizontalHorizontal line at bankfull elevationWell-defined banks with distinct floodplain
BisectorBisector of angle between water surface and slopeChannels with gradual bank transitions

Input Parameters

Channel Parameters

ft/ft

Longitudinal slope of channel bed

Channel Subsections

sq ft
ft
ft
sq ft
ft
ft
sq ft
ft
ft

Ready to Calculate

Enter subsection parameters and click Calculate to analyze compound channel flow.

Disclaimer & Terms of Use

Educational Purpose: The calculations provided by DrainageCalculators.com are for informational and educational purposes only. While we strive for accuracy, these tools do not substitute for professional engineering judgment or designs stamped by a licensed Professional Engineer (PE) where required by law.

Professional Certification: Users are solely responsible for verifying all calculations, confirming compliance with local codes and regulations, and determining the appropriateness of any methodology for their specific application. Critical infrastructure and public safety projects require review and certification by a licensed Professional Engineer.

Limitation of Liability: DrainageCalculators.com, its owners, operators, and contributors assume no liability for damages or losses arising from the use of these calculators. By using this tool, you acknowledge that you have read, understood, and agreed to these terms.

This disclaimer applies to the Compound Channel Calculator calculator and all associated calculations.

PE Stamp Required: Many jurisdictions require drainage designs to be reviewed and stamped by a licensed Professional Engineer. Check your local requirements before using these calculations for construction or permit applications.

Professional Review: For projects requiring regulatory approval or where public safety is involved, have your calculations reviewed and stamped by a licensed Professional Engineer (PE).

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Last verified: February 2026

Disclaimer & Terms of Use

Educational Purpose: The calculations provided by DrainageCalculators.com are for informational and educational purposes only. While we strive for accuracy, these tools do not substitute for professional engineering judgment or designs stamped by a licensed Professional Engineer (PE) where required by law.

Professional Certification: Users are solely responsible for verifying all calculations, confirming compliance with local codes and regulations, and determining the appropriateness of any methodology for their specific application. Critical infrastructure and public safety projects require review and certification by a licensed Professional Engineer.

Limitation of Liability: DrainageCalculators.com, its owners, operators, and contributors assume no liability for damages or losses arising from the use of these calculators. By using this tool, you acknowledge that you have read, understood, and agreed to these terms.

PE Stamp Required: Many jurisdictions require drainage designs to be reviewed and stamped by a licensed Professional Engineer. Check your local requirements before using these calculations for construction or permit applications.