HYDRAULICS_5

Design of Irrigation Systems

by

László Ormos

DESIGN OF MANIFOLD

The manifold is a pipe with multiple outlets to the inlets of lateral pipes. The size of plot, the flow rate and the number of shifts in a complete irrigation cycle should be taken into consideration.

An orchard is designed for irrigation with a solid set system. The manifold is laid in the center of the field. The whole plot is irrigated simultaneously.The flow rate of selected sprinklers is qs=0.11m3/h at a pressure hs=2bars. The space between the sprinklers along the laterals is es=6m. Space between laterals is eL=8m. What are the diameters of pipes if the local head loss in the manifold and laterals is 10%?

DESIGN OF MANIFOLD

The topography of field is the following:

B=

96m

manifold

late

ral

H=96m

DESIGN OF MANIFOLD

Design of lateral

1. The maximum allowable pressure head variation is:

2. The number of sprinklers on every laterals is as follows:

3. The length of lateral is:

4. The total outlet of a lateral is:

hh s

100

%20max

e

Bn

S

2

1 eenL

SSlat

nqQ S

mm 420100

%20

8

6

48

m

mmm 4536)18(

hm

hm 33

88.0811.0

DESIGN OF MANIFOLD

For 16mm PE lateral pipe

5. The hydraulic gradient when Q=0.88m3/h and J16=22%

6. The head loss in the lateral pipe (including 10% local head loss) and coefficient F6=0.38, is:

Since hf>h the pipe diameter has to be increased. 7. The hydraulic gradient if diameter is 20mm of PE which has

J20=6.5% by Q=0.88m3/h. is:

10016

16LJ

h lat

Fhh f 616, 1.1

10020

20LJ

h lat

mm9.9

100

45%22

mm 138.438.09.91.1

mm925.2

100

45%5.6

DESIGN OF MANIFOLD

8. The head loss in the lateral pipe (including 10% local head loss) and coefficient F8=0.38, is:

Since hf<h the pipe diameter is good.

9. The inlet pressure in the lateral is:

10. The water pressure by the last sprinkler on the lateral is:

Fhh f 620, 1.1

hhh fsu 20,4

3

hhh fuu 20,

mm 195.138.086.21.1

mmm 896.20195.14

320

mmm 701.19195.1896.20

DESIGN OF MANIFOLD

Design of manifold

11. The number of laterals is as follows:

12. The length of manifold is:

13. The total flow rate is as follows:

2e

HN

L

21

2e

eN

LL

Lman

QNQ LM

2428

96

m

m

mmm 924811

hm

hm 33

12.2188.024

DESIGN OF MANIFOLD

For 63mm PE manifold pipe14. The hydraulic gradient when Q=21.12m3/h and J63=7.2%

15. The head loss in the manifold (including 10% local head loss) and coefficient F24=0.371, is:

16. The pressure by the manifold inlet is:

17. The pressure by the inlet of last lateral is:

100

63

63LJ

h man

Fhh f 246363, 1.1

hhh fulum 63,4

3

hhh fumd 63,

mm624.6

100

92%2.7

mm 703.2371.0624.61.1

mmm 923.22703.24

3896.20

mmm 22.20703.2923.22

DESIGN OF MANIFOLD

18. The minimum pressure in the entire system at the last sprinkler on the last lateral is as follows:

19. The pressure difference between the first and last sprinkler is:

Since the pressure difference hf-l is lower than the allowable pressure head variation hmax, the system is good.

hhh fd 20,min

hhh umlf min

mmm 946.18274.122.20

mm 977.3946.18923.22

References

Azenkot, A.(1998):”Design Irrigation System”. Ministry of Agricul-ture Extension Service (Irrigation Field service), MASHAV Israel

Dr. Avidan, A.(1995):”Soil-Water-Plant Relationship”. Ministry of Agriculture Extension Service (Irrigation Field service), CINADCO,Ministry of Foreign Affairs, MASHAV, Israel

Sapir, E.-Dr. E. Yagev (1995):”Drip Irrigation”. Ministry of Agricul-ture and Rural Development, CINADCO, Ministry of Foreign Affairs, MASHAV, Israel

Sapir, E.-Dr. E. Yagev (2001):”Sprinkler Irrigation”. Ministry of -culture and Rural Development, CINADCO,Ministry of Foreign Affairs, MASHAV, Israel

Eng. Nathan, R. (2002):”Fertilization Combined with Irrigation (Fertigation)”. Ministry of Agriculture and Rural Development, CINADCO,Ministry of Foreign Affairs, MASHAV, Israel