FLOOD09911

• County: Statewide
• Basin: Statewide
• Title: Culvert Design
• Date: 8/1/2000
• Prepared By: Ayres Associates
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Lesson 2

Basic Hydraulics - Participant Workbook

2. Supercritical

Supercritical flow occurs when the depth of flow, velocity, and orientation
of flow is dependent upon factors from the point in question to upstream.
The flow usually has a high velocity and may be described as rapid,
shooting, and torrential.

Supercritical flow can also be defined as the condition when normal depth
is less than critical depth.

2.7 WEIR AND ORIFICE FLOW

WEIRS

. TYPICALLY A NOTCH OF REGULAR
SHAPE

. WEIR CREST IS THE EDGE OR SURFACE
OVER WHICH WATER FLOWS

2.14 Weirs

2.15 Wier Diagrams

A. A weir is typically a notch of regular shape (rectangular, square, or triangular)
with a free surface.

. the edge or surface over which water flows is called the crest
. a weir with a crest where the water springs free of the crest at the
upstream side is called a sharp-crested weir
. if water does not spring free and the crest length is short, the weir is called
a not sharp-crested weir, round edge weir, or suppressed weir
. if the weir has a horizontal or sloping crest sufficiently long in the direction
of flow that the flow distribution is hydrostatic it is called a broad-crested
weir
. the discharge across a weir (sharp-crested or broad-crested) is:

Q = CD L H3I2

2-9

where:

Q
CD
L
H

=

=

Discharge (cfs)
Coefficient of discharge for weirs
Flow length along the weir (It)
Depth of flow above the weir crest (It),
Typically measured a distance 2.5H upstream
of the weir

=

=

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