Culvert & Ditch Hydraulic Sizer
Estimate peak runoff and screen full-barrel capacity or trapezoidal ditch normal depth.
Identify a candidate cross section and the site-specific checks it still needs.
- •ERA Drainage Design Manual 2013, Ch. 2 and §§5.7, 6.12.2, 7.12–7.13
- •Highway Drainage Engineers
- •Water Resources Engineers
Q = C I A / 360Q in m³/s, I in mm/h and A in ha.Q = A R^(2/3) S^(1/2) / nFlow area A in m², hydraulic radius R in m and slope S in m/m.Use these outputs for preliminary checks. They do not constitute official engineering approval. Verify the inputs, method and results against the project criteria before using them for design or construction.
Culvert & Ditch Hydraulic Sizer
Calculate peak runoff discharge (Q = C·I·A / 360) and size pipe/box culverts and trapezoidal roadside ditches referencing standard hydraulic and drainage design specifications.
Report Metadata
Preliminary screening using ERA Drainage Design Manual 2013. Inlet and outlet control, lining and freeboard require separate project checks.
1. Hydrology (Rational Method)
2. Culvert Hydraulic Parameters
Full-barrel uniform-flow screen
Candidate: Ø900 mm circular pipe
Estimated capacity: 2.217 m³/s
Discharge divided by capacity: 0.732
HYDRAULIC SIZING & DRAINAGE DESIGN REPORT
Reference Basis: Rational Method / Manning's Equation / Selected Hydraulic Criteria
| Project Name: | [Insert Project Title] | Date / Time: | |
| Station / Location: | Sta 14+350 Crossing | Design Standard: | ERA Drainage Manual 2013 |
| Designed By: | User-entered project information | Calculation Type: | Culvert Sizing |
1. Hydrologic Catchment & Peak Discharge
| Runoff Coeff (C) | Intensity (I - mm/hr) | Catchment Area (A - ha) | Design Peak Discharge (Q - m³/s) |
|---|---|---|---|
| 0.55 | 85 | 12.5 | 1.623 m³/s |
2. Preliminary Hydraulic Screen
Full-barrel uniform-flow candidate: Ø900 mm circular pipe. Capacity 2.217 m³/s. Discharge / capacity 0.732. Headwater and outlet performance require separate checks.
ENGINEERING VERIFICATION: Review and verify the result against project-specific data, governing specifications and professional engineering judgment before final use.
Hydraulic Engineering Guidance (ERA Drainage Manual)
1. Rational Method Limits
This screen uses Q = C·I·A / 360 for catchments below 50 hectares. Verify the assumptions and the rainfall intensity for the applicable storm and time of concentration.
2. Barrel Dimensions
Check clearance for inspection and maintenance, blockage risk, and minimum dimensions required for the project.
3. Velocity Control
Check sediment and erosion conditions, the lining, and the appropriate freeboard for the site.
Culvert & Ditch Hydraulic Sizer Documentation
Technical specifications, mathematical formulas, and civil guidelines
Estimate peak runoff for a catchment below 50 ha with Q = C I A / 360. Enter rainfall intensity I in mm/h and contributing area A in hectares. The runoff coefficient C and the rainfall intensity are project inputs. At C = 0.45, I = 85 mm/h and A = 25 ha, the estimate is 2.65625 m³/s.
The barrel screen compares that estimate with full-section Manning capacity. It shows the first candidate in the tool’s dimension list that meets the demand under the stated uniform-flow assumptions. A closed box uses the full perimeter. A demand-to-capacity ratio is dimensionless.
The ditch screen solves for steady, uniform flow in a trapezoid at a positive slope. It reports normal water depth, mean velocity and Froude number. The depth search is limited to 3 m. Use project-specific checks for erosion, lining and freeboard.
Use inlet and outlet control, tailwater, entrance and exit losses and the project’s design flood criteria to assess actual culvert performance. Source: ERA Drainage Design Manual 2013, Ch. 2, §5.7, §6.12.2 and §§7.12–7.13.
Developer of InfraDigital CAD
Read the tool-specific source, assumptions and limits before interpreting its output. These browser-based tools are provided as productivity aids for preliminary engineering and drafting checks. Project-specific independent verification and approval by a licensed Professional Engineer (PE / REng) is required before final design submission, drawing stamping, or construction implementation.
Author: Yonatan Abrham
InfraDigital CAD developer
Technical Integrity & Independent Verification: Use the tool for the stated calculation or workflow. Check the applicable edition, input assumptions and limits in the tool documentation.
The user remains solely responsible for verifying that all inputs, soil parameters, traffic projections, and geometry comply with project-specific statutory requirements and geotechnical investigations prior to final engineering approval or construction stakeout.