Flow Parameters

Peak discharge for design storm
m
Elevation at culvert inlet
m
Elevation at culvert outlet

Site Conditions

m
Downstream water depth
m
Max upstream water depth
m
Elevation of roadway above culvert

Culvert Geometry

m
Diameter (round) or width (box)
m
Height (box/elliptical/arch)
m
%

Inlet/Outlet Configuration

Culvert inlet is below channel bottom

Hydraulic Parameters

Roughness coefficient (0.012-0.024 typical)
Head loss coefficient at inlet
Multiplier for conservative design

Design Options

Flow Capacity
--

Maximum flow capacity of current culvert

Headwater Depth
--

Upstream water depth for design flow

Control Type
--

Governing control condition

Design Status
--

Meets design requirements

Recommended Size
--

Optimal culvert dimensions for design flow

Performance Summary

Parameter Value Status
Flow Velocity -- --
Road Overtopping -- --
Tailwater Effect -- --
Safety Factor Applied -- --

Culvert Design Guide

Culverts operate under two primary flow conditions:

  • Inlet Control: Flow is controlled by culvert entrance conditions. Headwater depth is primarily a function of entrance geometry and flow rate.
  • Outlet Control: Flow is controlled by culvert barrel characteristics and tailwater conditions. Headwater depth depends on friction losses through the culvert.

The governing condition is the one that produces the higher headwater elevation for a given flow rate.

The Manning equation estimates flow velocity in open channels and culverts:

V = (1/n) * R2/3 * S1/2

Where:

  • V = Velocity (m/s)
  • n = Manning's roughness coefficient
  • R = Hydraulic radius (Area/Wetted Perimeter)
  • S = Slope of energy grade line

Key factors in culvert design:

  1. Design Storm: Select appropriate return period (typically 10-50 years for roadway culverts)
  2. Headwater Limits: Prevent upstream flooding and roadway overtopping
  3. Velocity Checks: Ensure flow velocity won't cause erosion (typically 2-6 m/s)
  4. Material Selection: Consider durability, hydraulics, and cost
  5. Inlet/Outlet Protection: Prevent erosion at culvert ends

Manning's Roughness Coefficients

Culvert Material n-value Range
Concrete 0.012 - 0.015
Corrugated Steel 0.021 - 0.030
HDPE 0.009 - 0.015
Corrugated Aluminum 0.022 - 0.027