HYDRAULICS_2 Design of Irrigation Systems by László Ormos

Total Head by Bernoulli’s Law where the relative elevation of the water; the pressure head of the water; the water velocity head.

Energy Head Loss in Pipes The energy loss (head loss) in pipes due to water flow (friction) is proportional to the length of pipe:, where J is the head loss in a pipe expressed by either % or ‰.

Energy Head Loss in Pipes The head loss due to friction is found out by the Hazen Williams expression: where J is the head loss expressed by ‰, Q is the flow rate expressed by m 3 /hr, vis the flow velocity by m/sec, Dis the diameter of pipe expressed by mm, Cis the smoothness of internal surface of pipe.

Energy Head Loss in Pipes The layout of an irrigation system is the following: The flow rate of pump at A is Q A =300m 3 /h at p A =6 bar pressure. The water flow rate out of B is Q B =200m 3 /h. What are pressures at the points B and C? L1=900m L2=200m D1=250mm D2=150mm A (h A =172m) B (h B =196m) C (h C =180m) QBQB QAQA

Energy Head Loss in Pipes For A-B: the head loss due to a friction for the D1=250mm pipe (C=130) and Q=300m 3 /h can be found out of tables or slide ruler. The hydraulic gradient is J=11‰. 1.The actual head loss due to a friction for L1=900m long pipe is: 2.The difference elevation between A to B is: 3.Water pressure at point B is:

Energy Head Loss in Pipes For B-C: the head loss due to a friction for the D2=150mm pipe (C=130) and Q=100m 3 /h can be found out of tables or slide ruler. The hydraulic gradient is J=18‰. 4.The actual head loss due to a friction for L2=200m long pipe is: 5.The difference elevation between B to C is: 6.The water pressure at point C is:

Energy Head Loss in Pipes The result can also be computed by Bernoulli’s law for B and C only as follows: 7.Water flow velocity in 250mm pipe is the following:

Energy Head Loss in Pipes 8.Water flow velocity in 150mm pipe is the following:

Energy Head Loss in Pipes 9.The difference head velocity is: 10.Water velocity heads are as follows:

Energy Head Loss in Pipes 11.Water pressure at point C is: (since the difference velocity head  h v has been too small it can be neglected)

Energy Head Loss in Pipes Given a 300 meters long pipe and its diameter is 250mm (C=130) which connects a cistern (A) at elevation of 30m to a booster (B) at a sea level, and from there to a cistern 2200m away at elevation of 180m. The booster pump generates 17bar pressure. What is the flow rate? A H A =30m L AB =300m C B(booster) H C =180m L BC =2200m

Energy Head Loss in Pipes 1.The water pressure just before the booster is as follows: 2.The water pressure just after the booster is as follows: 3.For B-C section

Energy Head Loss in Pipes 4.The total pipe length is 5.The head loss due to the friction is as follows: The water flow rate can be found out of tables or a slide ruler based on J=8[‰] and D=250[mm]. It is about 250[m 3 /h].

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