Design of Drip Irrigation Method

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Design of Drip Irrigation Method

Presentation · February 2017

DOI: 10.13140/RG.2.2.25797.29924

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A presentation

By

Dr Amresh Chandra Pandey

Scientist (Agril. Engg.)

Krishi Vigyan Kendra, Latehar Birsa Agricultural University

Ranchi Jharkhand

Email- [email protected] Mob. No. 9934183442

Design of

Drip Irrigation System

A typical layout of Drip Irrigation System

General information required to design a Drip Irrigation

System

Source of Irrigation water

Crops to be grown

Topographic conditions

Texture of soil

Climatic data

Layout of Drip System

Irrigation Water Requirement

Capacity of Drip System

Length of main

Length of sub-main

Length of lateral lines

Steps of Designing

Number of laterals and drippers

In Orchards and Vegetable crops

In close growing field crops

Number of fittings and accessories

Capacity of Main pipe

Capacity of Sub-main pipe

Capacity of Lateral pipes

Steps of Designing

Diameter of Lateral pipe

Diameter of Main pipe

Diameter of Sub-main pipe

Filters

Fertilizer applicators

Size of pumping unit

Total cost of drip system

Steps of Designing

Lay-out of drip system

Objective

Appropriate layout and components to

attain adequate and uniform distribution of water (and fertilizer) throughout the field to meet crop needs

Considerations

Economical

Operational

water quantity

water quality constraints

Lay-out of drip system

Generally, the main and sub-main pipes are laid across the slope and the laterals are

placed along the slope

In a small field, laterals may be allowed to take off directly from the main pipe

In large fields, it may be advisable to divide it into blocks. Each block may be provided with one Sub-main and a control valve. Lateral

pipes are connected with sub-mains

Middle Length

Corner-corner

Middle width

Irrigation water requirement

The irrigation water requirement of an area is based on following factors

Type of crop (crop coefficient)

Source of water

Weather data (Class A pan evaporation data)

Soil type

Area under cultivation

The monthly irrigation water requirement can be estimated on the basis of monthly pan

evaporation data and crop coefficient by using the following equation

Vm = Kc X Kp X Cc X Ep X A

where,

Vm = Monthly irrigation water requirement, L Kc = Crop coefficient

Cc = Canopy factor (Cc = 1.0, for closely spaced field crop, Cc = wetted area/plant area, for orchard and vegetables crop)

Kp = Pan evaporation factor (generally it is 0.8) Ep = Normal monthly pan evaporation, mm

A = Area to be irrigated, m²

Capacity of drip system

Factor affects the drip system capacity

Irrigation water requirement

Daily operating hours

Irrigation interval

Water application efficiency

Drip irrigation system is generally not recommended to operate for more than 1.5 - 2.0 hours at a stretch to avoid losses of water through leaching

Irrigation interval generally is not kept more than three days to avoid moisture stress to plants.

Equation to estimate Capacity of Drip System

where,

Q = Capacity of drip system, lph A = Total cultivated area, m

T = Irrigation interval, days

=Water application efficiency (in fraction)

t = Duration of each irrigation, h

) /( t T

CU A

Q     _a 



Discharge required per plant (Qp) can simply be estimated by dividing

the drip capacity (Q) by the number of plants (n) in the area

Qp = Q/n

Length of main, submain and lateral lines

Length of main, submain and lateral lines can be calculated with the help of length, width and total number of equal sized blocks in a field, as follows:

Length of main line = width of block (if number of block i.e. N

= 1, in small

fields)

Length of main, submain and lateral lines

Total length of main line (L_m) = (N_B-1) x width of block (if N_B>1)

Length of submain line (L_s) = width of block (B_w)

No submain if N_B = 1

Total length of submain = L_s X N_B

Length of lateral line (L_L)= Length of block (B_L)

Total length of lateral = L_L X N_B X N_R

Where, N_R = Number of plant row per block

Number of drippers and laterals

In orchard and vegetables crops

Drippers are installed close to each plant

Laterals are placed along each row of plant

Number of laterals is taken equal

to the number of plant rows

Number of laterals and drippers

N_LS = L_S÷ S

Where,

N_LS = Number of laterals per submain L_S = Length of sub main pipe, m

S = Spacing between two rows of laterals, m

In large fields total number of laterals is estimated by multiplying the laterals per submain and the number of submain used

N_L = L_M ÷ S If N_B =1 N_L = N_LS x N_s if N_B >1 Where,

N_L= Total number of laterals

L_M = Length of main pipe, m

Numbers of plants per lateral are estimated by dividing the length

of lateral pipe by the spacing between two plants

N

= L

÷ P

Where,

N

=Number of plants per lateral L

=Length of lateral pipe, m

P

=Spacing between two plants, m

Number of drippers per plant is estimated as follow:

Q

= Q ÷ (N

x N

) N

= Q

÷ q

Where,

Q_P =Discharge required per Plant, lph Q = Drip Capacity lph

N_L= Total Number of laterals

N_PL = Number of Plants per lateral N_DP = Number of Drippers per plant q = Dripper discharge, lph

Total Number of Dripper required is estimated using the equations

N

= N

x N

N

= N

x N

N

= N

Χ N

Where,

N_DL = Number of drippers per lateral N_D = Total number of drippers

N_P = Total number of Plants N_L= Total Number of laterals

N_PL = Number of Plants per lateral N_DP = Number of Drippers per plant

In close growing field crops

In close growing field crops the whole area needs to be wetted

Drippers are used to act as a line source of water rather than a point source

In case of closely spaced field crops large number of drippers are required

Installation and operation of such a large number of drippers may pose problems

Therefore, emitting pipes or laterals with in built drippers placed at 30 to 40 cm along the lateral pipes better suit such a situation

In close growing field crops

In close growing crops, the spacing

between two drippers, laterals and

number of drippers per lateral are

estimated by taking into

consideration the movement of

water front with time in vertical and

horizontal direction in the soil

In close growing field crops

Spacing between two drippers and laterals in a closely spaced field crop were

estimated by using the relationship, allowing 20 % of overlapping of coverage’s of two

adjacent drippers^.

 

 ^{( 3 10}

^{) 2} 

9 .

0 q t

r     

   

Where,

r = Wetted radius, m

θ_i = Initial moisture content of soil, per cent θ_f = Final moisture content of soil, per cent

Type of soil Initial moisture content (%)

Final moisture content (%)

Sandy 6 13

Sandy loam 11 20

Loam 12 25

Silty loam 11 28

Clay loam 19 32

Clay 28 41

Range of available moisture content

in different soils

Emitter spacing is kept equal to twice the wetted radius

S

=2 X r

Where,

r = Wetted radius, m

S_E = Emitter spacing, m

Number of emitters per lateral may be estimated by dividing the length of lateral by the emitter spacing

Total number of emitters are then estimated by multiplying the emitters per lateral with number of lateral

N_EL =L ÷ S_E Q_L =N_EL X q Q_S = Q ÷ N_S N_LS = Q_S ÷ Q_L

N_L = Q ÷Q_L if N_B =1 N_L = N_LS X N_S if N_B > 1

Where,

N_EL = Number of emitters per lateral L = Length of Lateral, m

S_E = Emitters spacing, m q = Emitter discharge

Q = Drip Capacity or designed discharge N_LS = Number of Lateral per sub-main N_L = Total numbers of Laterals

Q_S = sub main discharge, lph Q_L = lateral discharge, lph

Number of fittings and accessories

Common PVC fittings are elbow, reducer, tee, straight connector, end cap and gate valve

Accessories for laterals includes gate valve,

tee, joiner, elbow, end caps and grommet takeoff etc

All these components are available in 4, 10, 12, 16 and 20 mm sizes

These takeouts/ starter and rubber grommet are used for taking out laterals lines from sub- main/main line

Number of fittings and accessories

Number of different fittings/accessories may be estimated as follows

1. Number of flush valves = N_s + 1 2. Number of elbow = 2N_s

3. Number of tees = N_s

4. Number of gate valves = N_s

5. Number of grommet assembly = N_l

6. Number of end caps = 1 (main size) + N_s (submain size) + N_l (lateral size)

Capacity of sub-main, lateral and main pipe

The capacity of each lateral pipe can be

estimated by multiplying the dripper discharge to number of drippers per lateral

 Capacity of sub main pipe can be estimated by multiplying the lateral capacity to number of laterals per submain

 Capacity of main line and control head can be estimated by multiplying the submain discharge to number of sub mains placed on it

Qm = Q_s x N_s

Diameter of lateral pipe

Lateral pipe is selected such that the head loss in lateral pipe is limited within 10 per cent of the operating pressure available at the head of the lateral

Expected head loss in different diameter pipes are estimated and that smallest diameter pipe is selected in which the head losses are within 10 per cent of the operating pressure

Lateral pipes having 10, 12, 16 and 20 mm internal diameter with wall thickness varying from 1 to 3 mm are used in drip irrigation system

First a smaller diameter lateral pipe should be selected to reduce the total cost of system and the friction losses are estimated by using Equation

and then elevation head is added to this. If the variation in total friction losses are found within 10 % of the operating pressure then selected diameter is accepted.

Where,

Q = Capacity of drip system, lps

h = Frictional loss in lateral pipe, m

F_d = Factor for multiple outlet (Based on number of outlets)

d = Diameter of lateral pipe, mm

 ^/ 

^{] /}

789000

[ Q N l F d

h  

 

Numbers of outlets in one lateral

Correction factor, Fd

1 1.00

2 0.63

4 0.48

6 0.43

8 0.41

12 0.39

16 0.38

20 0.37

>20 0.36

Correction factor (F) for friction

losses with multiple outlets

Diameter of Main and Sub-main

Selection of the diameter of main and sub-main pipes is done similar to the lateral pipes starting from the smallest size going towards the successively higher size pipes

If the variation in total head loss (friction losses + elevation head) in main and sub- main pipe are found within 10 % of the operating pressure of the system then selected diameter of sub-main and main pipes are accepted

Diameter of main and sub main

HDPE pipes of 65 mm diameter and more with a pressure rating of 2.5 to 6 kg/cm

are generally recommended for main pipe

Pipes with a diameter of 25 to 75

mm and with a pressure rating of

2.50 to 4.0 kg/cm

are used as the

sub main pipe

Filters – the must

Filter is an essential component of the drip system

Filters are used to minimize or prevent inflow of possible suspended material in the water to the pipe spacing and dripper network

The type of filter needed depends on

the water quality and the operating

pressure of the drip system

Filters – the must

There are four common types of filters namely, sand filter, screen filter, hydro-cyclone filter and disk filter

Each type of filter is effective for a

particular particle size and type of

suspended material, for a specific

flow rate, and has a particular

capacity for sediment collection

Fertilizer applicators

Fertilizer application through drip requires an additional device in the system

Allows simultaneous application of liquid fertilizers or granular fertilizers in aqueous solution

Select an appropriate fertigation system so that fertilizer injection can be achieved within a reasonable time without running the risk of over-watering

Fertigation methods

Three principal methods namely

1. Fertilizer tank (the by-pass system) 2. The venturi pump

3. The injection pump

Non-corrosive material should be used for the fertilizer containers and for the injection equipment

Size of pumping unit

Size of the pumping unit can be estimated based on the system capacity and the total head including friction losses, elevation head, suction head and efficiencies with the help of equation:

) 75

/(

)

( Q H

hp      

Where,

hp = Motor horse power, hp H = Total head loss, m

H = H_e + H_sm + H_m + H_s + H_e + H_o + H_f + H_a

H_L = Head loss in laterals, m = (head loss in one lateral X number of laterals)

H_sm = Head loss in submain, m = (head loss in one sub-main X number of submain)

H_m = head loss in main, m H_s = suction head, m

H_e = elevation head, m

H_o = operating pressure head, m

H_f = head loss in filters (2 m/filter), m

H_a = head loss in other fittings and accessories, m Q = Capacity of drip system, Lps

η_p =Pump efficiency (in fraction)

η_m =Motor efficiency (in fraction)

) 75

/(

)

(Q H _{p m}

hp ^{  } ^

Total cost of drip system

Total cost of the drip system can be estimated by the sum of the costs of its

different components and latest rate of component in the market or refer to the

catalog of said firm

THANKS

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