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Hydraulics Prof. B.S. Thandaveswara

Indian Institute of Technology Madras

21.2 Typical canal cross sections

Water enters the conveyance system through the intake structure located at the dam.

Depending on the topography of the terrain, this conveyance system may take the

shape of the tunnels, canals, flumes or pipes. Geological factors do influence the type of

the system to be adopted.

Some of the shapes of canals adopted are shown in following figures.

Original ground levelCanal in filling

Canal in cutting

Embankment

Original grand slope

Retaining wall

Part in cutting and in fillingOriginal ground level



braced type



Typical cross sections of Power canals

Covered duct R.C.Con piles when there island slide problem



Side slopes and other salient features

Width 'b' in

m

Length in km

Side slope

m : 1

Depth y (m)

Discharge Q (m /s)3

Average Velocity

(m/s)S0

Nangal - - 1.25 : 1 - 354 - - Sutlej - Beas link 9.45 11.8 1.5 : 1 6.26 255.0 2.1 1 / 6666

Lower Sileru 11.9 15.6 1.5 :1 3.97 127.4 0.665 -

Yamuna Hydel Stage I

11.0 - 1.5 : 1 - 200.0 - -

Hirakud 51.0 - 1 : 1 6.3 707 1.97 - Maximum permissible velocity (safe against erosion)

(1) Stenbergs formula

b

b

V = 4.43 2d in which V in m/s, d is the diameter of the particle in m

(2) Bogardi and Yens formula

4/9mV = 22.9 d -1

In which V is the velocity in cms-1, dm is the effective size of particle in cm, is the

specific gravity of the particle.

Minimum permissible velocity

1. Ludin suggested for preventing sedimentation (Minimum permissible velocity)

a. V = 0.3 in m s-1 in case of water containing silt.

b. V > (0.3 to 0.5) in m s-1 in case of water carrying fine sand.

2. Kennedy's formula for Minimum permissible velocity

0.64V = C y

In which V is in m/s, y is the depth of water in m, C is a coefficient between 0.54 and

0.70 depending on the size of the silt.

In general, a guideline is 0.6 m/s and a minimum water depth of 1.5 m.



1.524Stones of medium size

Rock fill1.524 m

300 mm sand layer300 mm thick smallstone layer

Channel in the hill at Hirakud Project

Stones of small sizeImpervious coreImpervious material

38.4 m

3.96 m1.524 m

4.572 m Jeepable road

1:3:6 lining

Recommended Manning N for different conditions The permissible rugosity coefficient N depending on the discharge capacity in soils

other than rock.

Q m3/s N 0.15 0.03

0.15 to 1.40 0.025 1.40 to 14.10 0.0225

> 14.10 0.02

0

00

00

0

0

Gangguillet and KutterNRV = (Chezy coefficient)

R D

1 0.00155N = 23 sn s

0.00155if D = 23 ns

1 0.0015523n s

C = 0.00155 n1 23

s R

+ + +

+ + +

+ + in which C is Chezy coefficient (MKS) in terms of Manning n.



Recommended Manning n for different conditions

Ashlar and well laid brick work 0.013Rough brick work, good stone work in fair order 0.015Rough brick work, good stone work in inferior condition 0.017Rubble masonry, coarse brick work and masonry 0.020Canals in earth above the average in order and regime 0.0225Canals and rivers in earth in tolerably good order and regime 0.025Canals and rivers in earth below the average in order and regime 0.0275Canals and rivers in bad order and regime 0.030Torrents encumbered with detruits 0.050

Safe velocities for different soils

Ordinary earth 0.5 to 1.0 m/s Firm gravel or clay 1.0 to 1.5 m/s Broken stone and light pitching 1.0 m/s Firm conglomerate 1.75 to 2.25 m/s Sound rock 3.5 m/s

Proportion of bed width to depth

2b 2 1 m 2my

1 bm is the side slope, equal to to 1, the 1.252 y

= +

=

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