Hydraulic Design of Highway Culverts - DOT On-Line Publications

English Units
INLET CONTROL:
AD
0.
5
Q / AD
= ( 487.
5)(
20)
0.
5
5,
500
= =
2,
180
0.
5
=
2.
52
2,
180
Based on Chart 51b, HW/D = 0.90, therefore:
HW = HWf
= ( 0.
90)(
20)
= 18 ft
= 220 + 18 = 238.
0 ft
EL hi
For the check flow:
Q / AD
0 . 5
=
3.
44
Based on Chart 51b, HW/D = 1.13, therefore:
HW = HWf
= ( 1.
13)(
20)
= 22.
6 ft
= 220 + 22.
6 = 242.
6 ft
EL hi
OUTLET CONTROL:
Backwater calculations will be necessary to check Outlet Control.
Backwater Calculations
From hydraulic tables for elliptical conduits (60):
for Q = 5,500 ft³/s, dc = 12.4 ft
for Q = 7,500 ft³/s, dc = 14.6 ft
Since TW > dc, start backwater calculations at TW depth.
Determine normal depths (dn) using hydraulic tables.
for Q = 5,500 ft³/s, n = 0.034 ;
dn = 13.1 ft
for Q = 7,500 ft³/s, n = 0.034 ;
dn = 16.7 ft
since dn > dc, flow is subcritical
since TW > dn, water surface has an M-1 profile
Plot Area and Hydraulic Radius vs. depth from data obtained from tables.
75