HYD-33

Culvert inlet-control orifice

Q = Cd A √(2 g (H − y/2)). Inlet-control orifice when the barrel is unsubmerged at the outlet.

Reading speed

CulvertsFHWA inlet control

Governing equation

Q=C_d A\sqrt{2g(H-y/2)}

where

C_d: Inlet Cd (—)
A: Barrel area (m²)
H: Inlet head (m)
y: Inlet depth (m)
Q: Discharge (m³/s)

Lecture brief

Historical brief

Open-channel and pipe flow were written by Chezy, Manning, Darcy and Weisbach in the nineteenth century, then Bakhmeteff and Bélanger on the hydraulic jump. The sheets compute conveyance, head loss and gradually varied profiles. This sheet (HYD-33 — Culvert inlet-control orifice) is the form associated with FHWA inlet control. Working symbols: $C_d$ , $A$ , $H$ , $y$ $\rightarrow$ $Q$ . FHWA inlet-control: the barrel can carry more than the inlet will admit. Head H is measured from the invert.

Purpose

Purpose: compute

Q

from

C_d

A

H

y

in Hydraulics via

Q=C_d A\sqrt{2g(H-y/2)}

Q = Cd A √(2 g (H − y/2)). Inlet-control orifice when the barrel is unsubmerged at the outlet. Use it when a real hydraulics question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

C_d = 0.620\,\mathrm{—}

A = 0.800\,\mathrm{m^{2}}

H = 1.400\,\mathrm{m}

y = 0.800\,\mathrm{m}

, the governing relation

Q=C_d A\sqrt{2g(H-y/2)}

yields

Q = 2.197\,\mathrm{m^{3}/s}

. A pipe through an embankment, an inlet head, a Q. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Inlet Cd C_d0.62 —Barrel area A0.8 m²Inlet head H1.4 mInlet depth y0.8 m

Outputs

Discharge Q2.197 m³/s

Reading speed

Watch on YouTube

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Narration of this film

A pipe through an embankment, an inlet head, a Q.

FHWA inlet-control: the barrel can carry more than the inlet will admit. Head H is measured from the invert.

Reading speed

Watch on YouTube