Culvert & Ditch Hydraulic Sizer
Calculate peak runoff discharge (Q = C·I·A / 360) and size pipe/box culverts and trapezoidal roadside ditches per Ethiopian Roads Administration (ERA) hydraulic specifications.
Report Metadata
Design Standard Manual Option
1. Hydrology (Rational Method)
2. Culvert Hydraulic Parameters
Hydraulic Performance Summary
HYDRAULIC SIZING & DRAINAGE DESIGN REPORT
Calculated via Rational Method & Manning Manning's Hydraulics Equations
| Project Name: | [Insert Project Title] | Date / Time: | 8/10/2026 |
| Station / Location: | Sta 14+350 Crossing | Design Standard: | ERA Drainage Manual 2013 |
| Designed By: | [Insert Engineer Name] | 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. Culvert Hydraulic Sizing Results
| Structure Type | Specified Dimension | Full Capacity | Velocity | HW/D Ratio |
|---|---|---|---|---|
| pipe Culvert | Ø900 mm Concrete Pipe Culvert | 2.217 m³/s | 2.55 m/s | 0.73 |
I hereby certify that the hydraulic calculations presented in this report have been performed in strict accordance with the Ethiopian Roads Administration (ERA) Drainage Design Manual 2013.
Hydraulic Engineering Guidance (ERA Drainage Manual)
1. Rational Method Limits
The Rational Method (Q = C·I·A / 360) is valid for small catchment areas A ≤ 80 hectares. For larger catchments, SCS Curve Number or unit hydrograph methods must be used.
2. Minimum Diameter
ERA mandates a minimum pipe culvert diameter of Ø900mm across major highways to facilitate manual cleaning and prevent debris blockage.
3. Velocity Control
Maintain channel velocities between 0.8 m/s (silting threshold) and 3.5 m/s (erosion threshold). Provide masonry/concrete lining if V > 1.5 m/s.
Culvert & Ditch Hydraulic Sizer Documentation
Technical specifications, mathematical formulas, and civil guidelines
1. Functional Purpose
The Culvert & Ditch Hydraulic Sizer calculates peak runoff discharges using the Rational Method (Q = C·I·A / 360) and sizes pipe/box cross-drainage culverts and roadside trapezoidal ditches according to the ERA Drainage Design Manual 2013.
It enforces hydraulic velocity constraints (0.8 m/s ≤ V ≤ 3.5 m/s) to prevent both sediment silting and severe outlet scour, checks headwater ratio limits (HW/D ≤ 1.2), and generates a clean, dark-lined printable hydraulic calculation report without color decorations for official engineering submittals.
2. Practical Workflow Instructions
- Input Hydrology: Select runoff coefficient (C) based on catchment terrain, rainfall intensity (I in mm/hr) for the design return period, and catchment area (A in hectares).
- Size Structure: Toggle between Pipe / Box Culvert and Trapezoidal Ditch mode. Adjust longitudinal slopes and Manning's roughness (n).
- Review Recommendations: Verify structure dimensions, flow velocities, headwater ratios, and recommended slope lining.
- Print / Export Report: Click Print Clean Report to export a black-bordered professional calculation sheet formatted for PDF printing.
3. Mathematical & Hydraulic Equations
Peak runoff discharge is computed via the Rational Method:
Culvert and open channel flow capacities are solved using Manning's Equation:
Where A is cross-sectional flow area (m²), R = A / P is hydraulic radius (m), S_0 is channel slope (m/m), and n is Manning's roughness coefficient.