CE404 09 Aqueduct

Hydraulic Structures –Design of Aqueduct

May 30, 2011

Flow rate Bed width Depth of water Full supply level Side slopes Manning n for concrete

= 30 cumec = 20 m = 1.5 m = 251.50 m = 1½ :1 = 0.016

High flood discharge High flood level High flood depth General ground level

= 250 cumec = 247.50 m = 2.5 m = 251.00 m

Lacey’s regime wetted perimeter

Pw  4.83 Q  4.83 250  76.37 m Let the clear span between piers be 8 m and the pier thickness be 1.5 m. Provide 8 bays of 8 m each = 64.0 m 7 piers of 1.5 m each = 10.5 m Waterway between abutments (Bed width of canal)

= 74.5 m

Bed width of canal = 20 m Let the canal to be flumed to 10 m. Provide 2:1 splay in contraction and 3:1 in expansion. Length of contraction transition  Length of expansion transition 

20  10  2  10 m 2

20  10  3  15 m 2

In the transitions, the side slopes of the section will be warped from 1½ : 1 to vertical. 1

Hydraulic Structures –Design of Aqueduct

May 30, 2011

At section - Area of section   B  1.5D  D

  20  1.5 1.5 1.5  33.375 m 2 Velocity V  

Q 30   0.899 m s A 33.375

0.8992  0.041 m Velocity head  2  9.81 R.L. of bed (given) R.L. of water surface R.L. of T.E.L.

= 250 m = 250+1.5= 251.5 m = 251.5+0.041= 251.541 m

At section -

30  2m s 10 1.5 22  0.204 m Velocity head  2  9.81 Loss of head in expansion from section (3)-(3) to sec (4)-(4) 0.3  22  0.8992   0.049 m  19.62 Velocity 

R.L. of T.E.L. R.L. of water surface R.L. of bed

= 251.541+0.049= 251.59 m = 251.59-0.204= 251.386 m = 251.386-1.5+0.041= 249.886 m Say 249.89 m

From section - to section -, area and velocity are constant A 15 R   1.154 m P 10  2 1.5 1 Velocity in the trough  R 2/3S 1/2 n 1 2/3 2.0  1.154  S 1/2 0.016 S  0.00084 Headloss due to friction in the trough  74.5  0.00084  0.063m At section - R.L. of T.E.L. R.L. of water surface R.L. of bed

= 251.59+0.063= 251.653 m = 251.653-0.204= 251.449 m = 251.449-1.5= 249.949 m Take 249.96 m

At section - 2

Hydraulic Structures –Design of Aqueduct

May 30, 2011

Loss of head in contraction transition from section - to sec - 0.2  22  0.8992   0.033 m  19.62 R.L. of T.E.L. R.L. of water surface R.L. of bed

= 251.653+0.033= 251.686 m = 251.686-0.041= 251.645 m = 251.645-1.5= 250.145 m Take 250.16 m

Figure 1: Bed levels, water surface elevations, and T.E.L. elevations at different sections of the structure. All dimensions are in meters. Drawing is NOT to scale.

a. Expansion transition Mitra’s formula is: Bc B f L Bx  L Bc   Bc  B f  x where Bf= 10 m, Bc= 20 m and L=15 m 20 10 15 3000 Bx   15  20   20  10  x 300  10x 3

Hydraulic Structures –Design of Aqueduct

May 30, 2011

For different values of x x (m) 0 3 6 9 12 15

Bx (m) 10.0 11.1 12.5 14.3 16.67 20.0

b. Contraction transition Bf= 10 m, Bc= 20 m and L=10 m 2000 Bx  200  10x x (m) 0 2 4 6 8 10

Bx (m) 10.0 11.1 12.5 14.3 16.67 20.0

To economize the construction cost of the road, the trough may be divided into two equal compartments each 4.8 m wide by providing an intermediate wall 0.4 m thick. The road shall be carried on the top of the left compartment. Check if the reduction of the waterway to 9.6 m instead of 10 m will do any change. Provide a freeboard of 0.75 m above the normal water depth of 1.5 m. so that, the slab should be 1.5+0.75= 2.25 m above bed level of trough. The trough body should be constructed in reinforced concrete. For full design details see Fig. 9.20.

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Hydraulic Structures –Design of Aqueduct

May 30, 2011

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