No headwall will be constructed downstream. The following are known conditions:
Aircraft SR-71C. (Refer to table 5-1, page 5-9, and table 5-2, page 5-10.)
Culvert weight type = 9.
Q to be handled by culvert = 32 cfs.
Soil type is bare SC; therefore, the maximum allowable outlet velocity = 3.4 fps.
Pipe sizes available: 24-, 30-, 36-, and 42-inch CMP, 10 gauge.
Referring to figure 5-11, page 5-18, note that the following information is required before design can be
accomplished:
Horizontal length of one culvert, L.
Slope of culvert pipe needed to determine the flow characteristics of various pipe diameters (see table 5-3,
page 5-16) and Fc, which is a portion of the critical fill depth, Ft.
Critical fill depth, Ft, in order to determine if the cover over the pipe meets the requirements of table 5-2.
Solution:
STEP 1. Determine the runoff rate. Given for this example Q = 32 cfs.
STEP 2. Determine airfield culvert use.
STEP 3. Calculate the critical dimensions. Computations should be made in the following sequence (see figure
5-11).
Determine the difference in elevation between the edge of the runway and the culvert upstream invert.
F1= EL1 - EL2
F1 = 607.00 - 600.80 = 6.20 ft
Determine the horizontal distance between the culvert invert and the shoulder edge.
S1= F1 x X
S1 = 6.20 x 10 = 62 ft
5-17
EN5465
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