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Drip and Sprinkler designs
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Design & Scheduling
of
High Efficiency Irrigation Systems
(Drip & Sprinkler)
Designing Procedure
ET0 Maximum Evapotranspiration mm/ day From Table
Blenny Criddle Equation ETo = p (0.46 T mean + 8)
P = Mean daily percentage of annual daytime hours for different latitudes from Table
Evapotranspiration or Crop Water
Requirement
ET or CWR = Kc * ETo
ET = Evapotranspiration in mm/day
Kc = Crop Coefficient (Table)
ETo = Reference Evapotranspiration in mm/day (Table)
Peak daily consumptive use per day
PDCU mm/day = CWR * Canopy factor at maturityIrrigation System Efficiency
Canopy Factor = Canopy Area(p*p) (R*R)
Total No. of Plants = Area under system m2
(p*p) (R*R)
(p*p) = Plant to plant spacing m
(R*R) Row to Row spacing m
Number of Emitters require for each plant
This depends on the area of wetting (nearly 40% of total area) and radius of wetted area of single emitter.
The Number of emitters = A/R
Where
A = total area to be wetted.
r = radius of wetted area of single emitter
Hydrozones Area Divide in Equal Hydrozones
Equal Operating Time
Q = AV where V = 1.5 m/s A = Area of pipe
Importance
Reduce Cost by
1. Smaller Pump
2. Small Diameter Pipes
Block
Hydrozones under one Pump
Total no. of Emitters
T.E = No. of plants * no. of emitter per plant
Total flow rate of 1 zone = T.E of 1 zone * Emitter flow rate (lph)
Application rate = Flow of 1 zone mm/hr/day1 zone Area
Operating Time hrs = Peak Daily Consumptive Use
Application rate
Should be less than 12 hr per day of all zones
Max. depth of irrigation water that can be applied
Max. Depth mm = Drz * MAD * WHC
100
Drz = Depth of Root zone m
MAD = Management Allowed Deficit %
WHC = Water Holding Capacity mm/m
Max. irrigation interval
Max. Irrigation Interval days
= Max. Depth of Application of water mm
Peak Daily Consumptive Use mm/day
Total Drip line Length
Total drip line m = Area * No. of Drip lines per Row
Row Spacing
For all zones
No. of Plants = Plants of 1 zone * no. of zones
Drip line = Drip line of 1 zone * no. of zones
No. of Emitters = Emitters of 1 zone * no. of zones
Loop Around the Plant
Irrigation up to whole Canopy
Wetting Pattern
Storage Reservoir
Total Flow = Flow of 1 zone*Total no. of zones m3/ day
Irrigation Cycle Daily
Warabandi Days
Storage Capacity = Total flow * Warabandi m3
Safe Depth = 1.5 m
Area of Reservoir = Capacity
Depth
Select Length and find out Width of Reservoir
Head Loss Calculation
Hazen William Equation
Head Loss m/100m = K ( Q/C)1.85 * (D) - 4.87
K = Hazen William Constant = 1.21 * 1012
C = Pipe Friction constant
Q = Total Flow lps
D = Internal Diameter in mm
Total Head Loss m = Head Loss (m/100m) * Total Length
100
Repeat Procedure for all Lateral , Sub main line and Main Line.
Limitations
Lateral Head loss Should be =< 2m
Main line and Sub main Line m /100m =
Head loss gradient (Watter & Keller)
Head Loss m/100m = K * (Q)1.75
(D)4.75
K = 7.89 *10 7 (Constant)
Q = Flow in lps
D = Internal Diameter mm
Emitter Operating Pressure is 10 m
Fitting Losses
Fitting Losses are taken as 20 % of Pipe Network losses
Lateral Fitting Losses = 20% of Lateral Head Loss
Submain line Fitting Losses = 20% of Submain line Head Loss
Main line Fitting Losses = 20% of Main line Head Loss
Suction and Delivery line Fitting Losses = 20% of Suction and
Delivery line Head Loss
Other Losses
Head loss in
Filtration System = 8m
Fertigation System = 2m
Flow Meter = 1m
Field Fitting Losses = 2m
Miscellaneous Losses = 2m
Pumping Lift = At the Spot
Total Dynamic Head
(Pipe Network Losses = Lateral Sub main and Main line ) +
(Fitting Loses = 20% of Pipe Networks) + Field fitting losses
Head loss in filter + Head loss in fertigatin system + Pump lift +
Head loss in flow meter + Emitter operating Pressure (1bar) + Misc Head Losses
Total Dynamic Head = Sum of All Head losses
Pump hp Requirement
Pump hp = Q (lps) * Head (m)
75 * Ep * Em
Ep = Pump Efficiency
Em = Motor Efficiency
Irrigation Scheduling of Drip Irrigation System
Operating Time = Peak Daily Consumptive Use per day
Application Rate
For any month reading of ETo from table and Kc of Crop
Peak use = ETo * Kc & Application rate of Emitter mm /hr/day
Time to Open one zone Valve hrs = Peak Daily Use mm/day
in that month Application Rate mm/hr/day
Application rate of each Emitter
(E) = q/nt
Where
q = daily water requirement (mm)
n = number of emitters
t = time of operation (hour per day)
Difference between Drip & Sprinkler Irrigation Design
There are no Lateral in Sprinkler System
There Canopy factor is 1 because this system
is used in Field or Broadcasted Crops
There is no Plant to plant spacing and no Row to Row
spacing
There are Hydrants on which Sprinkler is Mounted
Design Difference
Peak Daily Use = ETo * Kc
Eirrg * (1-Lr )
Where Lr is Leaching Requirements
Lr = ECw5ECe - ECw
ECw = Quality of Irrigation Water dS/m
ECe = Estimated water quality of root zone
Sprinkler operating pressure is 4 bar = 40m
In Rain gun Sprinkler system no Filter is used
Spacing of Hydrants
spacing along lateral = 100% Overlap of Wetted Radius
Hence along lateral they are spaced at Wetted Radial Distance
Across the Lateral = 65% overlap of wetted Radius
Hence Sub main to Sub main line Distance is 65% of Wetted Diameter
Any Question