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Models Design of Drip Irrigation System

Crop = Mango ( 5m X 5m)
Area= 1 ha ( Assume square plot)
Pan evaporation = 8 mm/day
Pan coefficient = 0.7
Crop factor= 0.75
% wetted area= 60
Soil type= medium
Water source is well at the corner of the field ( well depth) = 10m
Assume pump efficiency 70% and motor efficiency = 80%

Solution:

i) Determination of Water Requirement ( WR):

WR= Crop area X PE X PC X KC X % wetted area
= 5m X 5m X 8 X0.7X 0.75 X 0.6
= 63 lit /day/ plant

ii) Selection of Dripper:

Selection 2 dripper of 8 lph capacity per plant

Total no of plants = Total area
__________
Plant area
= 10,000/ 5 X 5 = 400
No of drippers = 400 X 2 = 800

iii) Selection and Design of Lateral:

Flow rate of lateral =  No of dripper on lateral X Discharge of drippers per plant.

No of dripper on lateral = Length of Lateral
____________________________
Spacing between two drippers
= 50/5
= 10

Q of lateral = 10X 2 X8 = 160 lit/hr
Give the sub-main at the centre of the point
Length of lateral = 50 m
Diameter of lateral= 12 mm = 1.2 cm
Head loss in lateral ∆H= 1.526 X 104 X (Q/C) 1.852 X D -4.871 X LX F

Where, Q= Flow rate of lateral in m3 /hr
C= Hazen and William constant
D= Diameter of pipe in cm
L= Length of pipe in m
F= Outlet factor
∆H= 1.526 X 104 X (0.16/150) 1.852 X (1.2) -4.871 X 50 X 0.39
∆H= 0.38
∆ Head loss is less than 2 m , hence design is acceptable.

iv) Selection and Design of Sub-main: Select 40 mm Sub- main.

Select 40 mm mainline
Flow rate of mainline= Flow rate of Submain
Q= 6.4 m3 /hr
Diameter of mainline = 4cm
Diameter of mainline= 40mm=4cm.

Head loss in Mainline,

H= 1.526 X 104 X ( Q/C) 1.852 X D -4.871 X L X F
= 1.526 X 104 X  ( 6.4/150) 1.852 X (4) -4.871 X 100
So, H= 2.58m

Selection Pump:

Total discharge,
Q=6.4 m3 /hr
Q= 6400 lph

Q = 6400 lps
________ 1.77lps
60 X 60

Total head of pump = ( Suction head+ delivery head) + operating pressure of drip irrigation system+ filter loss + fitting loss + mainline loss + ventury loss + elevation difference

Suction head + delivery head = 10
Operating pressure= 1 kg /cm2 or 10m
Filter loss = 2m for sand filter + 2m for screen filter
= 4m
Ventury loss = 5m
Fitting loss= 2m
Main line loss= 2.58
Elevation difference = 2m

So, Total head of pump = 10+10+4 + 2 +2.58 +5+2
= 35.5 m
H.P of pump = Q ( lps) X H (m)
_______________
75 X 0.7 X 0.8

So, Pump efficiency and motor efficiency is given as 70% and 80% respectively.
HP= 1.49 hp

So, HP of Pump is 1.49 hp say 2 HP

vi) Irrigation Time:

Irrigation Time = Peak water requirement per plant
____________________________
Discharge of dripper per plant
= 63
_____= 3.9 ( say 4 hours)
2 X 8
So, Irrigation time required is 4 hrs.