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