DESIGN OF OFF TAKE CANAL

Total Ayacut under Left side Canal = 101.17 Ha

OR
= 250.00 Acres

Assuming the Duty for the Design of Canal = 62.00 Acres/Cusecs

Discharge Required (Qreq) = 250/80 4.03 Cusecs

Add Losses @ 25% = 4.03 x (25/100) = 1.01 Cusecs

Total Discharge Required (in Cusecs) = 5.04 Cusecs

or
Total Discharge Required (in Cumecs) = 0.14 Cumecs
Data Required :

1.) Co-efficient of rugosity (n) = 0.018 (Assumed as Un lined)

3.) Bed fall of canal (S) = 1 in 2000 (Assumed)

4.) Assuming the section

Bed width (B) = 0.75 m

Depth (FSD) = 0.30 m

Free Board = 0.30 m

3.15 m

0.60 m
Supply depth 0.3 m
Free Board 0.3 m

Bed width 0.75 m

Area of the Assumed Cross section(A) = (B + nd ) d

= (0.75+(1.5x0.3))x0.3 = 0.36 Sqm

Wetted Perimeter of the Section(P) = (B+nd√(n²+1)

= (0.75+2x0.3x(√1.5²+1) = 1.95 m

Hydraulic Mean Depth ( R ) = A/P

R = 0.36 / 1.95 = 0.185 m

Velocity (V) = 1/n x ( R )2/3 x (S)1/2

 1/n = (1/0.018) = 55.56

R⅔ = (0.185)⅔ = 0.325

S½ = (1/2000)½ = 0.022

V = (55.56x0.325x0.022) = 0.400 m/sec

Designed disharge (Qdes) = AxV

= (0.36x0.4) = 0.144 Cumecs

or
5.09 Cusecs
 HYDRAULIC PARTICULARS OF CANALS

S.No Description Unit Parent Cnal Off take Canal

U/s D/s U/s D/s

1 Ayacut Acres 250.00 250.00

2 Discharge (Required/Designed) Cumecs 24.63 0.140 0.14

0.00

3 Bed width m 14.20 0.75 0.75

4 Full Supply Depth m 1.98 0.30 0.30

5 Free board m 0.75 0.30 0.30

6 Side slopes (Inner) - 2:1 2:1 2:1

(Outer)

7 Bed fall - 10560 2000 2000

8 Velocity m/s 0.689 0.400 0.400

9 Value of 'n' - 0.019 0.018 0.018

10 Top width of banks L/R m

11 C.B.L. m 393.810 394.420 394.420

12 F.S.L. m 395.790 394.720 394.720

13 T.B.L. m 396.540 395.020 395.020

14 G.L. m 0.000
 DESIGN OF P I P E OFFTAKE

1 Fixation of Sill level of OT Sluice:

Parent Canal Discharge = 24.63 Cumecs

Offtake Canal Discharge = 0.14 Cumecs

% of offtake Discharge to Parent Canal Discharge

= (0.14/24.63)x100

= 0.57 %

Height of sill above the parent

Percentage of
canal Bed When FSD is of
Offtake Discharge
Parent canal is Remarks
to Parent Canal
Discharge Above 2.13 m to below
2.13 m 1.22 m 1.22 m
15% and Above 0.07 0.07 0.07
10% to 15% 0.15 0.07 0.07
5% to 10% 0.30 0.15 0.07 All the
2% to 5% 0.46 0.30 0.15 units are
1% to 2% 0.61 0.46 0.30 in metres
0.50% to 1% 0.76 0.61 0.46
Less than 0.50% 0.91 0.76 0.61

Height of sill above the parent canal CBL is 0.61 m as the FSD of Parent canal is in
between 1.22 m to 2.13 m and the percentage of discahrge is in between 5% to 10%

So the off take sill level = 393.81+0.61

= 394.420 m

2 Driving Head:

Considering 3/4 of the Supply of Parent canal

Full Discharge of Parent Canal = 24.63 Cumecs

Assuming depth of Flow as = 1.65 m (By trial and error)

Discharge (q) at 1/2 = (3/4)x24.63

= 18.47 Cumecs

Area of Section (A) = B + nd ) d

= (14.2+(2x1.65))x1.65

= 28.88 m²

Wetted Perimetre (P) = (B+nd√(n²+1)

= (14.2+2x1.65x(√2²+1)

= 21.58 m
 = A/P

R = 28.88 / 21.58

= 1.34 m

Velocity (V) = 1/n x ( R )2/3 x (S)1/2

1/n = (1/0.019)

= 52.63

R⅔ = (1.34)⅔

= 1.215

S½ = (1/10560)½

= 0.01

V = (52.63x1.215x0.01)

= 0.640 m/sec

Discharge (Q) = AXV

= 28.88 x 0.64

= 18.48 Cumecs

Hence the adopted FSD is OK

FSD @ 3/4 of Supply in Main canal = 1.65 m

There fore FSL @ 3/4 discharge in

Main Canal = 393.81 + 1.65

= 395.460 m

FSL in Off take canal = 394.720 m

Driving Head (h) = FSL of Main Canal - FSL of off take canal

= 395.46 - 394.72

(h) = 0.74 m

3 Calculation of Vent Way:

Discharge Through Vent (Qv) = 2.86 x A x √h

Discharge through vent (Qv) = 0.14 Cumecs

Driving head (h) at 1/2 of Qmain = 0.74 m

Therefore Area of Vent (A) = Qv / 2.86 x √h

 = 0.14/(2.86x√0.74)

= 0.0569 m²

Area of Pipe = 0.0569 m²

∏ x d² / 4 = 0.0569 m²

There fore dia of pipe required (d) = √(4x0.0569)/3.14

= 0.27 m
or Say
0.30 m dia pipe

There fore provide NP3 Class hume pipe of 0.30 m dia pipe for vent portion

Thickness of pipe as per table-3 of IS:458-2003 = 0.040 m

Cross sectional area of pipe = ∏ x d² / 4

= 0.071 m²

Velocity in the Pipe = .14/0.071

= 1.97 m/sec

But Allowable velocity through pipe = 3.00 m/sec

Hence it is OK

4 Scour Depth Calculations:

Scour Depth for Main canal

Discharge = 24.63 Cumecs

Bed Width of Canal = 14.20 m

Discharge per 'm' width of canal = 4.63/14.2

= 1.73 m²/sec

Normal scour depth ® = 1.35 x ( Q2 / f )1/3

Silt factor (f) = 1

= 1.35 x (1.73²/1)⅓

1.95 m

maximum scour depth (Rmax) = 1.50 x R

= 2.925 m

Scour level = FSL of Main canal - Rmax.

= 392.865 m
Scour Depth for off take canal

Discharge = 0.14 Cumecs

Bed Width of Canal = 0.75 m

Discharge per 'm' width of canal = 0.14/0.75

= 0.19 m²/sec

Normal scour depth ® = 1.35 x ( Q2 / f )1/3

Silt factor (f) = 1

= 1.35 x (0.19²/1)⅓

0.45 m

maximum scour depth (Rmax) = 1.50 x R

= 0.675 m

Scour level = FSL of off take canal - Rmax.

= 394.045 m
 DESIGN OF HEAD WALLS, WINGS AND RETURNS
DESIGN OF HEAD WALL (U/S)
unit wt of concrete = 2.40 t
unit wt of earth = 2.10 t
+ 396.540
W3

W4 W1

3.175
W2

0.30 1.800 0.600 0.30 + 393.365

2.400
W5 0.50
3.000 + 392.865

Taking moments about A (Stresses in concrete)

Force
Load Particulars L.A. Moment
V H
W1 0.600 x 3.175 x 2.400 4.572 2.100 9.601
W2 1.800 x 3.175 x 2.400 x 0.500 6.858 1.200 8.23
W3 1.800 x 3.175 x 2.100 x 0.500 6.001 0.600 3.600
Pv 0.0384 x 3.175 x 3.175 x 2.100 0.813 ---
Ph 0.1340 x 3.175 x 3.175 x 2.100 2.837 1.720 4.879
SV 18.244
SM 26.31

Lever arm = M/V = 26.3 / 18.24 = 1.4421455 m

Eccentricity = 1.4421 - 2.400 /2 = 0.242 m

Permissible 'e' = 2.40 /6 = 0.400 > 0.242 OK

Max. comp. Stress = 18.24 x ( 1 + 6 x 0.242 ) = 12.203207 t/sq.m.

2.400 2.400

Min. Stress = 18.24 x ( 1 - 6 x 0.242 ) = 2.999836 t/sq.m.

2.400 2.400

Taking moments about B (Stresses on soil)

Force
Load Particulars L.A. Moment
V H
W1 0.600 x 3.175 x 2.400 4.572 2.400 10.9728
W2 1.800 x 3.175 x 2.400 x 0.50 6.858 1.500 10.287
W3 1.800 x 3.175 x 2.100 x 0.50 6.001 0.900 5.400675
W4 0.300 x 3.175 x 2.100 2.000 0.15 0.300
W5 3.000 x 0.500 x 2.400 3.600 1.5 5.4
Pv 0.0384 x 3.675 x 3.675 x 2.100 1.089 ---
Ph 0.134 x 3.675 x 3.675 x 2.100 3.800 1.92 7.297
Sv 24.120
SM 39.657475
Lever arm = M/V = 39.7 / 24.12 = 1.6441675 m

Eccentricity = 1.6442 - 3.000 /2 = 0.144 m

Permissible 'e' = 3.00 /6 = 0.500 > 0.253 HENCE OK

Max. comp. Stress = 24.12 x ( 1 + 6 x 0.144 ) = 10.358 t/sq.m.

3.000 3.000

Min. Stress = 28.51 x ( 1 - 6 x 0.253 ) = 4.623 t/sq.m.

2.700 2.700

DESIGN OF WING (D/S)

unit wt of concrete = 2.400 t

unit wt of earth = 2.100 t
+ 396.540
W3

W4 W1

1.995
W2

0.300 1.700 0.500 0.30 + 394.545

2.200
0.50
W5
2.800 + 394.045

Taking moments about A (Stresses in concrete)

Force
Load Particulars L.A. Moment
V H
W1 0.500 x 1.995 x 2.400 2.394 1.950 4.6683
W2 1.700 x 1.995 x 2.400 x 0.500 4.07 1.133 4.61244
W3 1.700 x 1.995 x 2.100 x 0.500 3.56 0.567 2.0179425
Pv 0.0384 x 1.995 x 1.995 x 2.100 0.32 ---
Ph 0.134 x 1.995 x 1.995 2.100 1.120 1.720 1.926
SV 10.346
SM 13.23

Lever arm = M/V = 13.2 / 10.35 = 1.278 m

Eccentricity = 1.2783 - 2.200 /2 = 0.178 m

Permissible 'e' = 2.20 /6 = 0.367 > 0.178 HENCE OK

Max. comp. Stress = 10.35 x ( 1 + 6 x 0.178 ) = 6.989 t/sq.m.

2.200 2.200

Min. Stress = 10.35 x ( 1 - 6 x 0.178 ) = 2.416 t/sq.m.

2.200 2.200

Taking moments about B (Stresses on soil)

 Force
Load Particulars L.A. Moment
V H
W1 0.500 x 1.995 x 2.400 2.394 2.250 5.39
W2 1.700 x 1.995 x 2.400 x 0.50 4.07 1.433 5.83
W3 1.700 x 1.995 x 2.100 x 0.50 3.56 0.867 3.09
W4 0.300 x 1.995 x 2.100 1.257 0.15 0.19
W5 2.800 x 0.500 x 2.400 3.360 1.4 4.70
Pv 0.0384 x 2.495 x 2.495 x 2.100 0.502 ---
Ph 0.134 x 2.495 x 2.495 2.100 1.752 1.92 3.363
Sv 15.144
SM 22.56

Lever arm = M/V = 22.6 / 15.14 = 1.49 m

Eccentricity = 1.4899 - 2.800 /2 = 0.090 m

Permissible 'e' = 2.80 /6 = 0.467 > 0.090 HENCE OK

Max. comp. Stress = 15.14 x ( 1 + 6 x 0.090 ) = 6.450 t/sq.m.

2.800 2.800

Min. Stress = 15.14 x ( 1 - 6 x 0.090 ) = 4.367 t/sq.m.

2.800 2.800