Model part-full pipes for drainage and sewers projects. See geometry, friction, and discharge instantly today. Export results to reports, bids, and field logs fast.
| Units | Diameter | Depth | Slope S | Manning n | Area A | Rh | Q (Manning) |
|---|---|---|---|---|---|---|---|
| Metric | 0.600 m | 0.250 m | 0.004 | 0.013 | 0.0796 m² | 0.0926 m | 0.1640 m³/s |
| Metric | 1.000 m | 0.500 m | 0.002 | 0.015 | 0.3927 m² | 0.1667 m | 0.5336 m³/s |
| Imperial | 2.000 ft | 0.900 ft | 0.003 | 0.013 | 1.0901 ft² | 0.3380 ft | 6.1260 ft³/s |
R = D/2θ = 2·acos((R − y)/R)A = (R²/2)·(θ − sin θ)P = R·θRh = A/PT = 2·R·sin(θ/2)When slope and roughness are provided, discharge is estimated using Manning’s equation for uniform flow.
Q = (1/n)·A·Rh^(2/3)·S^(1/2)V = Q/AThis calculator supports storm sewers, sanitary lines, and industrial drains where pipes run partially full. It converts field measurements into hydraulic geometry, helping engineers compare alternatives quickly. Use it during preliminary sizing, CCTV condition assessments, and rehabilitation planning, where depth observations or level logger data are available. The geometry outputs also help estimate storage volume in low-slope reaches and check surcharge risk near junctions.
Small changes in depth can cause large changes in wetted area and conveyance. The tool accepts depth or percent-full, then computes the segment angle that defines the water section. Reporting depth as a ratio y/D improves consistency across diameters and simplifies comparison between sites. For operations teams, tracking y/D over time can reveal sediment buildup, infiltration, or pump control issues.
Friction losses depend strongly on wetted perimeter and hydraulic radius, not only area. As depth increases, perimeter grows, but hydraulic radius may rise or flatten depending on geometry. The computed top width helps evaluate free-surface behavior, surface velocity distribution, and debris transport potential. When combined with velocity, these values support checks for self-cleansing criteria and abrasion limits in slurries.
When slope and roughness are provided, discharge is estimated with Manning’s uniform-flow equation. Select roughness values that match material, joints, sediment, and aging. Keep slope as a dimensionless gradient, and confirm the assumption of steady, uniform conditions before relying on the flow result. If backwater, pressurization, or inlet control governs, consider hydraulic grade modeling and treat Manning Q as a screening estimate only.
Validate inputs against physical limits: depth cannot exceed diameter, and slopes should reflect surveyed grades. Compare “area vs full” and “Q vs full” to sanity-check whether partial flow is plausible. Exported CSV and PDF outputs support design notes, bid documentation, and construction records. For peer review, capture the selected unit system, roughness basis, and any safety factors applied to capacity.
It means the pipe conveys flow with a free water surface, so the cross-section is a circular segment rather than a full circle.
Use inside diameter for hydraulics, because the wetted area and perimeter are based on the space available for flow.
Enter slope as a positive, dimensionless gradient such as 0.004. That equals 0.4% grade and represents rise divided by run.
Select n based on material and condition. Smooth liners are lower, while corrugations, sediment, roots, and aging increase n.
Because area and hydraulic radius change differently with depth. Conveyance depends on A and Rh^(2/3), so capacity does not scale linearly.
Avoid it when the pipe is pressurized, affected by backwater, or controlled by inlets and outlets. In those cases, use energy-grade or dynamic modeling.
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.