Design drainage channels with confidence. Solve normal depth using flow, slope, roughness, and section geometry. Review charts, exports, and checks for smarter field decisions.
Use SI units. Discharge in m³/s, depth and widths in meters, and slope as m/m.
Rectangular: A = b y, P = b + 2y, T = b
Trapezoidal: A = y(b + zy), P = b + 2y√(1 + z²), T = b + 2zy
Triangular: A = zy², P = 2y√(1 + z²), T = 2zy
When normal depth is unknown, this file solves it iteratively using a bisection method until the calculated discharge matches the target discharge.
Pick rectangular, trapezoidal, or triangular. This changes the cross-section equations used for area, wetted perimeter, and top width.
Input design discharge, bed slope, and Manning n. These values drive the hydraulic capacity calculation.
Provide bottom width and side slope. For triangular channels, bottom width is ignored automatically.
Use normal depth mode to solve for required water depth. Use capacity mode to check an entered depth.
The result section shows depth, capacity, velocity, hydraulic radius, and Froude number for quick design review.
Use CSV for spreadsheets and PDF for site files, proposals, and construction checking records.
| Case | Section | Discharge (m³/s) | Slope | Manning n | Bottom Width (m) | Side Slope z | Approx. Depth (m) |
|---|---|---|---|---|---|---|---|
| Site Drain A | Rectangular | 1.20 | 0.0015 | 0.014 | 1.50 | 0.00 | 0.68 |
| Road Edge Drain | Trapezoidal | 2.50 | 0.0020 | 0.015 | 2.00 | 1.50 | 0.86 |
| Temporary Earth Cut | Triangular | 0.90 | 0.0040 | 0.022 | 0.00 | 1.00 | 0.77 |
These rows are illustrative examples for construction planning and checking.
It solves normal flow depth from Manning’s equation or checks the capacity of a channel at a depth you enter. It also reports velocity, hydraulic radius, top width, and flow regime.
The calculator supports rectangular, trapezoidal, and triangular open channels. These are common section shapes for site drains, lined channels, roadside ditches, and temporary earthworks.
Manning n is the roughness coefficient. Smoother channels have lower values, while rougher earth channels have higher values. Using the correct value is important for realistic depth and capacity estimates.
Freeboard adds a safety allowance above the hydraulic depth. Designers often include it to handle uncertainty, wave action, minor blockage, construction tolerances, and operational safety.
The Froude number indicates whether flow is subcritical, near critical, or supercritical. This helps you understand surface behavior, energy conditions, and whether transitions may require extra design attention.
Yes. The same hydraulic relationships apply to both. You mainly need to adjust Manning n, slope, and geometry to reflect the actual construction material and finished section.
A true triangular channel has no flat invert width. Its geometry is defined only by depth and side slope, so the bottom width field is not needed in that section type.
The exports use the same computed values shown on the page. Accuracy depends on the input quality, especially discharge estimates, slope, roughness, and whether the selected section matches site conditions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.