yc(m) H (m) Type Q (m^3 s^1 )
0.2 0.35 Free 0.336
0.4 0.70 Free 0.951
0.6 1.50 (1.2D) Submerged –
0.411 0.72 (1.2D) Just free 0.990
- For the orifice (equation (iii)),
H (m) Type Q (m^3 s^1 )y 0 (m) (equation (i) with S 0 1/100)*
0.72 Orifice 1.29 0.36
1.00 Orifice 1.66 0.44
2.00 Orifice? 2.58 0.61 (D)
1.95 Orifice 2.54 0.60
*Q9.23y 0 [1.2y 0 /(1.2 2 y 0 )]2/3
- For pipe flow (equation (iv) changes):
Q2.08(H 0.3)1/2forS 0 1/100.
H (m) Type Q (m^3 s^1 )y 0 (m) (equation (i))
1.95 ←Pipe flow ←2.67
2.00 ←Pipe flow ←2.71
3.00 ←Pipe flow ←3.42
Falling stages
3.00 ←Pipe flow ←3.42
2.00 ←Pipe flow ←2.71
1.95 ←Pipe flow ←2.67
1.74 ←Pipe flow ←2.50 ←0.60
1.74→ ←Orifice→ ←2.37
1.00 ←Orifice ←1.66
0.72 ←Orifice ←1.29
0.72 ←Just free ←0.99
0.70 ←Free ←0.951
0.35 ←Free ←0.336
Worked Example 10.5
The design flood with a 20-year return period is 15 m^3 s^1. Design the
culvert-type cross-drainage structure with a high embankment with the
following data: culvert length30 m; slope1.5%; available pipe barrel,
corrugated pipes in multiples of 250 mm diameter; Manning’s n0.024.
The barrel protrudes from the embankment with no end walls, with an
entry loss coefficient of 0.9. The maximum permissible head water level is
4 m above the invert with the barrel flowing full.
446 CROSS-DRAINAGE AND DROP STRUCTURES
