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 AT CULVERTS BY INDIRECT METHODS 47

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section and the culvert and at stages where
high-head flow is likely to occur.

Ratings with transition between flow types

For rectangular culverts a very pronounced
break in the computed rating curve occurs
between types 1 and 5 flows. This discharge
may vary as much as 35 percent between the
2 methods of computation at a headwater-
diameter ratio of 1.5. Because an instantaneous
reduction in discharge probably does not occur,
a gradual transition is expected between the
two types of flow. This is shown by the head-
discharge curves determined from the data of
various experiments.
Laboratory data show that an unstable con-
dition exists after the headwater-diameter

1

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ratio becomes 1.2 and before it reaches \,5
where flow usually becomes high-head. It is
recommended that the transition curve in
rating for types 1-5 flow be represented by a
straight line between the discharge computed
by low-head methods at a ratio of 1.2 and the
discharge computed by high-head methods at
a ratio of 1.5, Figure 27 is an example of a
rating curve for a box culvert where a transition
from type \ to type 5 flow occurs. This curve
is for a particular site, as are the other ex-
amples shown below. The rating curve for any
given site will reflect the unique features of
that site.
A curve for a rectangular culvert with a transi-
tion from type 2 to type 6 flow is shown in figure
28, where the limiting ratios are considered

50 100 150 200
DISCHARGE. IN CUBIC FEET PER SECOND

250

Figure 27.-Rating curve showing transition from type 1 to type S Row in a box culvert.