FLOOD06195

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Measurment of Peak Discharge at Culverts by Indirect Methods
• Date: 6/1/1968
• Prepared By: G.L. Bodhaine
• Floodplain - Doc Type: Educational/Technical/Reference Information

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MEASUREMENT OF PEAK DISCHARGE A T CULVERTS BY INDIRECT METHODS

By G. L. Bodhai""

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Abstract

This chapter classifies culvert flow into six types,
gives discharge equations based on continuity and
<'nergy equations, and describes procedures for meas-
uring peak discharges llsing culverts in the field. Di8.
charge coefficients for n variety of geometries and flow
t.ypes 1\n' given. Tl'll mmmph'51 detail stf>p-by-step
computation procedurc~.

Introduction

The peak discharge through culverts can be
determined from high-wuter marks that define
the headwater and tailwuter elevations. This
indirect method is used extensively to measure
flood discharges from small drainage areas.
The head-discharge characteristics of cul-
"erts have been studied in laboratory inves-
tigations by the U .S, Geological Survey, the
Bureau of Public Roads, and many universities.
The procedures given in this report are based

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Entrance loss

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(I)
Approach
section

(2)
Culvert
entrance

on the information obtained in these studies
and in field studies of the flow through culverts
at sites where the discharge was known,

Description of Culvert Flow

The placement of a roadway fill and culvert
in a stream channel causes an abrupt change
in the character of flow, This channel transition
results in rapidly varied flow in which aceelera-
tion rather than boundary friction plays the
primary role. The flow in the approach channel
to the culvert is usually tranquil and fairly
uniform. Within the culvert, however, the flow
may be tranquil, critical, or rapid if the culvert
is partly filled, or the culvert may flow full
under pressure.
The physical features associated with cul-
vert flow are illustrated in figure 1. They are
the approach channel cross section at a distance
equivalent to one opening width upstream from

Energy grade line
Top culvert

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Bottom culvert
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Culvert Ta iI water
outlet section

Figure 1.-Definition-sketch of culvert flow. Note.-The loss .of energy neat the entrance is related to the sudden
contraction and subsequent expansion of the lin stream within the culvert bane!.

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