Determine the difference in elevation between the edge of the runway and the culvert outlet and fill slope.
F2 = EL3  EL4
F2 = 607.00  599.62 = 7.38 ft
Determine the horizontal distance between the edge of the runway and the intersection of the culvert and
fill.
S2 = F2 x Y
S2 = 7.38 x 10 = 73.8 ft
Determine the actual slope of the culvert.
Determine the incremental elevation difference between the elevation of the upstream invert and the
invert of culvert at critical fill section.
0.005 ft/ft = 0.5 percent
F3 = S x S1
F3 = 62 x 0.005 = 0.31 ft
Determine the depth of critical fill section.
6.2 + .31 = 6.51'
Ft = F1 + F3
Ft = 6.2 + 0.31 = 6.51 ft. (Length of horizontal projection of the culvert.) The upstream invert elevation to
downstream invert elevation is
LIP = S1 + TW = S2 + 2 ft
LIP = 62 + 100 + 73.8 + 2 = 237.8 ft; (Round up to 238 ft)
NOTE: These computations depict the
cross section
and figure 511 summarizes the
calculations.
From these calculations, it has been determined that

(1) The actual length of the culvert is 235.8 feet. (2) A 2foot projection is added because there is to
be no downstream headwall. (3) The pipe must be rounded up to an even length of 238 feet. (4) This
gives a culvert length of 238 feet for a single pipe.
519
EN5465