FLOOD04208

• County: Statewide
• Basin: Statewide
• Title: Hydraulic Charts for the Selection of Highway Culverts
• Date: 12/1/1965
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

Step 3: Find headwater depth for trial size cu1.vert.

a. Assuming INLET CONTROL

e

(2)

Using the trial size from step 2, find the headwater
depth HW by use of the appropriate inlet control nomo-
graph (Charts 1-7). Tailwater T'vl conditions are to be
neglected in this determination. HW in this case is

found by multiplying HW obtained from the nomographs
D
by the height of cu1.vert,D.
If HW is greater or less than allowable, try another
trial size until HW is acceptable for inlet control
before computing HW for outlet control.

.

(1)

.

b . Assuming OUTLET CONTROL

(1) APproximate the depth of tailwater T'vl, in feet, above
the invert at the outlet for the design flood condi-
tion in the outlet channel. (See general discussion
on tailwater, p. 5-11.)
(2) For tailwater TW elevation equal to or greater than
the top of the cu1.vert at the outlet set 110 equal
to T'vl and. find HW by the following equation (equation
3).

HW = H + ho - LSo

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where

HW = vertical distance in feet from cu1.vert
invert (flow liIle) at entrance to the
pool surface.
H = hea.c1 loss in feet as determined from the
appropriate nomograph (Charts 8-14)
110 = vertical distance in feet from cu1.vert
invert at outlet to the hydrau1.ic grade
line (In this case 110 equals T'vl, measured
in feet above the cu1. vert invert.)
So = slope o:f barrel in ft./ft.
L = cu1.vert length in ft.

(3) For tailwater 'l'W elevations less than the top of the
cu1.vert at the outlet, :find headwater HW by equation
3 as in b(2) above except that

ho = dc + D or T'vl, whichever is the greater.
2

.

where

dc = critical depth in :ft. (Charts 15 through
20) Note: de cannot exceed D
D = height o:f cu1.vert opening in ft.

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