HANDBOOKOF

TRICKLE IRRIGATION SYSTEMS

PART-I: TRICKLE IRRIGATION TECHNOLOGY,SYSTEM FEASIBILITY,

HYDRAULICS AND DESIGN

WATER RESOURCES RESEARCH INSTITUTENATIONAL AGRICULTURAL RESEARCH CENTRE

ISLAMABAD

Jannary, 1993

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CONTENTS

Chapter Particulars Page

I Trickle Irrigation Technology

II Feasibility of System in Pakistan

III Pipeline Hydraulics and Design Equations

IV Design of Trickle Irrigation Systems

V Appendices

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WHY DESIGN IS IMPRORTANT

Trickle irrigation systems require high initial investment and are energy intensivecompared to surface irrigation systems. These systems are also complex in operation toachieve uniform water application to meet crop water requirement.

The objectives of designing any trickle irrigation system suitable to the localenvironment and socio-economic conditions are to: a) apply water to meet peak crop waterrequirement; b) maintain application and uniformity efficiency at a desired level; c) energyand water efficient to keep initial and operation cost as low as possible; and d) simple inoperation and maintenance so that farmers can use these systems without extensive training.

The purpose of this handbook is to provide information about systems selection,advantages and disadvantages, feasibility of system in Pakistan, adaptation of technologypipe hydraulics and design equations, and system design. This information will helpagricultural and irrigation engineers to design appropriate systems considering farmersrequirements and farm layout. Some changes can be made, if desired, to meet farmersrequirement especially the prime mover and pumping systems, if these already exist with thefarmers. However, booster pumps can be used to enhance pressure if electricity is available.

At the end, I would like to acknowledge the contributions made by the engineers ofthe Water Resources Research Institute especially Mr. M. Yasin, Mr. P.M. Moshabbir, Mr.Asif Ali Bhatti and Munir Ahmad in the design, local manufacturing and testing of trickleirrigation components in Pakistan. I hope that the team members will continue further workto refine this handbook in future. The contributions made by Mr. Khalid Mahmood in typingthe manuscript are highly acknowledged. The readers and users are requested to providecomments and suggestions to improve this handbook.

Dr. Shahid AhmadDirectorWater Resources Research InstituteNational Agricultural Research CentrePark Road,Islamabad.

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I. TRICKLE IRRIGATION TECHNOLOGY

1.1 Introduction

Trickle irrigation is a system where water and fertilizer are applied directly toindividual plants, instead of irrigating the entire area with sprinkler and surface irrigationsystems. For orchards and other widely spaced crops, it is accomplished with small diameterlaterals running along each plant row. Emitters attached to the lateral supply water to eachplant to meet crop water requirement. In the case of row or truck crops, thin-wall tubings areavailable with small diameter orifices, spaced at regular intervals along a thin-wall hose.

With trickle irrigation, water may be provided to the crop on a low-tension, highfrequency basis, thereby creating a near optimal soil moisture environment. Because of thehigh irrigation frequencies, very high water use efficiencies are possible. Water useefficiency, as used in this handbook, is defined as the crop yield per unit of applied water.Research indicates that water use efficiency can be increased by 50 percent or more by usingtrickle irrigation as compared with surface irrigation systems.

There are a large number of considerations which must be taken into account in theselection of an irrigation system. These factors vary in importance from location to locationand crop to crop. Briefly stated, these considerations include the compatibility of the systemwith other agricultural operations, economic factors, topographic limitations, soil propertiesand agronomic influences.

1.2 Choosing a Trickle Irrigation System

With careful consideration of the factors outlined above and others as the particularscircumstance dictates, a right type of irrigation system can be selected. The array of availabletrickle irrigation system makes this method of irrigation compatible in almost any situation.For fields planted with trees, vines or other perennial crops of similar nature, permanentlylocated systems can operate effectively. Vegetables are best irrigated by a system whose partscan be moved away from the necessary cultural operations. Standard trickle irrigationsystems are not easily moved are, therefore, most compatible with trees and vines. It shouldbe noted, however, that trickle irrigation systems are widely used in row crops.

Trickle irrigation systems are high initial investment and energy intensive. But, at thesame time, these are labour, water and fertilizer efficient. No investment is involved in landlevelling, but usually there are maintenance requirements that can be more expensive thansurface8 irrigation systems. A major economic factor is the utility of the trickle systems inproviding a cost-effective means of fertilizer and pesticide applications.

The cost of trickle irrigation system is minimized when operated continuously duringthe critical demand period. Thus, these systems tend to favour conditions where available.Applications tend to be smaller than surface methods which not only minimize systemcapacity, but also reduces the consequence of shallow or badly stratified soils.

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1.3 Advantages

Under proper system management, little water is lost to deep percolation,consumption by weeds, or soil surface evaporation. Research results reported in the UnitedStates indicate that trickle irrigation increase cotton yield by more than 8 percent. Whileusing 24 percent less applied water as compared to surface irrigation. Trickle irrigation wasalso effective in controlling the return flow volume and in maintaining relatively low salinitylevels in the soil adjacent to the emitters.

In addition to reduced irrigation water requirements and minimization of return flows,trickle irrigation has other positive advantages which are as follows:

Ø The effective water control possible with trickle irrigation, water can be appliedvery efficiently. The portion of the soil with active roots needs to be irrigated, andsoil evaporation losses can be reduced to a minimum. The low rate of waterapplication reduces deep percolation losses.

Ø High temporal soil water level can be maintained with trickle systems. This resultsin a favourable response by most crops in increasing yield and quality.

Ø Trickle systems are generally permanent and have low labour requirements.

Ø Fertilizer can be applied through trickle irrigation systems using fertilizerinjectors. Effective control of water results in control over fertilizer application.However, the small amount of water lost through deep percolation results inminimum loss of fertilizer through leaching.

Ø The wetted surface is only a fraction of the total soil surface. Consequently, thereis a reduced potential for weed growth.

Ø The plant canopy is completely dry under trickle systems. It reduces fungusincidence and other pests which depend upon a moist environment.

Ø Matric and osmotic potential are additive. The maintenance of a low matricpotential is possible with trickle systems. This results in a lower overall potential,and hence a reduced stress under saline conditions. Therefore, some crops can begrown in areas which would otherwise be unsuitable with conventional systems.The upper limit of suitable water for furrow irrigation is about 0.75 dS per m,while for trickle irrigation, water as salty as 4 dS per m has been used. Water withas little as 3 milliequivalents per litre of sodium can be detrimental in sprinklersystems due to leaf burn.

Ø Experiments on crops like tomatoes, grapes and sugarbeets have resulted insignificantly earlier maturation attained with other irrigation systems.

Ø Soil surface crusting is a significant problem in some soils. This can preventemergency of plants, even if these have germinated properly. By maintaining aconstant high moisture content, soil surface crusting can be eliminated.

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Ø There is no loss at the edge of fields as can occur through wind drift of sprinklersystems or runoff from surface systems.

Ø Root penetration in some soils is minimal at low water contents, the high averagewater contents maintained with trickle systems alleviates this problem.

Ø Theoretically, water can be applied with trickle irrigation systems at rates equal tothe plant water use rate.

A wetted profile develops in the root zone beneath each emitter. The shape of theprofile is dependent on soil characteristics and is limited by horizontal flow constraints of thesoil. The surface area between plant rows is dry, receiving moisture only from rainfall.Trickle irrigation provides controlled irrigation for optimum yield for variety of crops.

1.4 Disadvantages

There are number of problems and disadvantages with trickle irrigation systems. Themost important one is that the small flows through emitters require small openings that havehistorically been plagued by clogging. With the smaller emitter orifices, more filtering andbiological controls are needed. Great advances have been made to rectify this problem but itwill always require the attention of the designer.

Point or strip wetting is not always an advantage even though water savings and weedcontrol are significant benefits. Salinity tends to accumulate a short distance from the emitterand can be transported into the root zone in case of heavy rainfall. In addition, the root zonetends to be smaller and more densely distributed. This can result in anchorage and aerationproblems for some crops. Interestingly, some of the predatory insects breed in the weedsaround a field and some evidence has been reported that trickle irrigation may causesomewhat higher pesticides demand. In windy areas, the dry regions between emitters canyield dust problem.

The solid-set structure of trickle irrigation systems along with filtration requirementsmake it a high cost technology. Applicable primarily to valuable row crops, orchards, andvineyards, trickle irrigation concepts are also finding wide acceptance in urban landscaping.

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II. FEASIBILITY OF SYSTEM IN PAKISTAN

2.1 Introduction

The initial capital cost of the standard trickle irrigation equipment is considered to beits limitation for large-scale adoption in Pakistan. Therefore, the high cost and economicconsideration limit its use to fruit trees and vegetables of high value grown in specific areas.These areas include the following.

Ø Areas of Balochistan province where the value of water is high and high valuecrops are grown.

Ø Green belt around urban centres where high value vegetables and fruits are grown.

Ø Undulated sandy lands in the Thal, Thar and Cholistan deserts which areunderlined with groundwater of reasonable quality.

Ø Sandy and undulating riverine areas.

Ø Un-commanded sandy high areas within Indus basin which require hugeinvestments for surface irrigation.

Ø Fringe areas or where water is either saline or extremely scarce.

Ø Northern Areas and Pothwar plateau where high value crops are grown on slopyterraces with very coarse-textured soils.

The inefficiency of surface irrigation, probably 20 percent or less on sandy roughlands is well known. Thus the attractiveness of highly controlled trickle irrigation is obviouswhich has the potential to increase efficiency to 85 percent or more. Further, the use of trickleirrigation which utilizes pipe to convey the water directly to the plants makes thedevelopment of the most sandy lands and rough topography practical even with relativelysaline water. Thus, existing water supplies can be greatly extended and a totally new class oflands becomes available for irrigation and development by application of trickle irrigationtechnology. There is little question as to the technical feasibility of trickle irrigation systemswhich have already been substantiated on extensive installation throughout the world. Thequestion we face in Pakistan is whether such systems or special adaptations are sociologicallyand economically practicable at present.

The cost of the system depends mainly on the spacing of laterals. For fruit trees, thetrickle system is even more economical than sprinkler irrigation, whereas, for closely spacedvegetables sprinkler system is more feasible. The cost of the unit and the net return from thecrop should be compared before a decision is made on installing trickle irrigation system. Themain item of expenditure is the lateral lines; however, the wider the row spacing the lesserthe initial cost.

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Crops like grapes, almond, apples, papayas, guava, citrus, coconut and other fruittrees can be grown well on trickle irrigation system whereas high value vegetables can becultivated by using sprinkler irrigation system.

2.2. State of Trickle Irrigation in Pakistan

Trickle irrigation is being introduced in Pakistan. The most significant effort is theincorporation of 500 ha of trickle irrigation in the next three years, planned by theGovernment of Balochistan and financed by the Asian Development Bank (ADB).

Additional trickle irrigation installations include the FAO supported Deciduous FruitDevelopment Centre, Sariab, Quetta; five demonstration plots installed by AgriculturalDevelopment Bank of Pakistan (ADBP); a coconut farm in Uthal, and several small-scalesystems installed in the green belt areas of urban centres. Some demonstration plots are alsoinstalled in different parts of the country.

According to an estimate, there are over 300 ha under trickle irrigation in Pakistanwhich cover deciduous fruits and forest plants. The area will increase significantly during thenext few year. Especially the development and indignization of trickle irrigation technologyby PARC in collaboration with Griffon Industrial Corporation will help to extend thistechnology in Pakistan.

2.3. Adaptation of Trickle Irrigation Technology

The conventional trickle irrigation system provides optimum soil-water regimes whenproperly designed, installed and managed, and requires a minimum of labour. However, atthe beginning, the pressure compensating emitters would have to be imported. But, sooner,these would be manufactured in Pakistan. PARC in collaboration with Griffon IndustrialCorporation have developed low-density polyethylene (LDPE) tubings with carbon and UVstabilizers, spiral emitters, microtubings, connections and filters. The quality of theseproducts is similar to ASTM standards as tested by Plastic Technology Centre, Karachi. Theestimated material cost of locally manufactured standard trickle irrigation system in Pakistanwill not be more than Rs. 25,000 per ha, excluding the cost of pump and electric motor.Efforts are underway to reduce this cost further and brig it to a level of Rs. 15,000 per hawithin 1-2 years period.

In essence, the innovative adaptation of this form of irrigation involves the use ofportable hoses to supply water directly to small basis around each tree or near to each plant.The hoses can be systematically moved within the orchard to complete an irrigation everyfour days on sandy soils to further reduce the installation cost. The system could beredesigned for a longer irrigation intervals where soil conditions permit.

In these systems, the water will leave the tubewell, pass through a simple strainer orfilter, a fertilizer injection device, flow meters and through pipelines that feed the hoses. Thewater will only make exit from the system at and into the basins provided at each tree andthere will be no chance for losses except through poor distribution or over-irrigation of thebasins. If the labourers systematically move the hoses, the efficiency of the system will be inthe neighborhood of 90 percent.

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The modified hose-fed concept is particularly adaptable in Pakistan since it makes areasonable compromise between labour and resource inputs. These systems should provideoptimum water management on all types of soils for a variety of vegetables and fruitorchards. Furthermore, all of the components of these systems are now manufactured byGriffon Industrial Corporation using locally available resources and existing machinery. Thesystem need to be designed in a simplified way so that it can be understood and operated bythe farming community.

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III. PIPELINE HYDRAULICS AND DESIGN EQUATIONS

3.1. Introduction

Energy losses occur in the pipeline due to friction and elevation changes. The changein energy in the pipeline between two points, is described by the Bernoulli Equation.

V2 V2

Z1 + H1 + ------ = Z2 + H2 + ------- + hf (1) 2g 2g

in which

Z = elevation above an arbitrary datum, m; H = pressure head defined as the pressure divided by the specific weight of

water, m; V = velocity of flow, m/sec; g = gravitational constant, 9.818 m/sec2; and hf = friction8al head loss.

For constant flow conditions the equation (1) reduced to:

H1 = H2 + hf + (Z2 Z1) (2)

3.2. Basic System Hydraulics

The trickle irrigation system designer has two principal hydraulic problems: 1)evaluation of pipe flow without multiple outlets (mains, submains, and auxiliaries); and 2)evaluation of pipe flow with multiple outlets (laterals and manifolds). The basis for designwill be the selection of pipe sizes such that energy losses do not exceed prescribed lim8itsensuring that efficiencies and uniformities will be high.

3.2.1. Fundamental Flow Equations

The flow of water in pipes is always accompained by a loss of pressure head due tofriction. The magnitude of the loss depends on the interior roughness of the pipe walls, thediameter of the pipe, the viscosity of the water, and the flow velocity. These factors arelumped into fiction coefficients based on experimental data.

There are several common equations for computing headloss in pipelines. Probablythe most commonly used equation in irrigation calculations is the Hazen Williams formula:

K (Q/C)1.852

hf = ----------------- x L (3) D4.87

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in which,

K = 1.21 x 1010; Q = pipeline discharge, lps;

C = friction coefficient for continuous pipe sections, 120-140 for plasticmanifolds and laterals, 140-150 for main lines without discharging outlets8;

D = inside diameter, mm; L = pipeline length, m; and hf = frictional head loss, m.

The Hazen-Williams substantially under estimates friction losses when the Reynoldsnumber approaches the laminar range of values. A more correct equation is the Darcy-Weisbach:

L V2

Hf = f ------------ (4) D*2g8

where,

L = pipe length, m; D = pipe diameter, m; V = average flow velocity, m/sec; g = gravitational constant, 9.81 m/sec2; and f = frictional factor.

The friction coefficient, f, is determined as a function of the Reynolds number and therelative roughness of the pipe. The Reynolds number can be calculated using:

Re = 1.26 * 106 * (Q/D) (5)

in which;

Re = Reynolds number; Q = pipe discharge, lps; and D = inside pipe diameter, mm.

Then the value of f is determined as follows:

64 f = ------- for Re < 2100 (6) Re

f = 0.04 2100 < Re < 3000 (7)

0.32 f = --------- 3000 < Re < 105 (8)

Re0.25

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and 0.13 f = ----------- (9) Re0.172

Substitution of Eqns. 6, 7, 8 and 9 into (4) resulted into simplified expression.

Ai * Qmi * L Hf = ------------------------ (10) DPi

i Ai Pi R

1 4.1969 * 103 4.0 Re < 21002 3.3051 * 106 5.0 2100 < Re < 30003 7.8918 * 105 4.75 3000 < Re < 105

4 9.5896 * 105 4.828 105 < Re < 107

Hazen-William(C = 140) 1.283 * 106 4.852 105 < Re < 107

and

mi = Pi - 3 (11)

Friction losses are also induced in the pipelines due to fittings, bends, changes incross-sectional area, and entrances. These are generally evaluated as a function of velocityhead in the pipe as follows:

V2

hf = KF ------- (12) 2g

The values of KF are presented in Appendix-I.

3.2.2. Headloss in Pipes with Multiple, Equally Spaced Outlets

The flow of water in a pipe having multiple, equally spaced outlets will have less headloss than a similar pipe transmitting the entire flow over its length because the flow steadilydiminishes each time an outlet is passed. Computations start from the distal outlet.Christiansen developed the concept of a F factor which accounts for the effect of theoutlets. When the first outlet is one outlet spacing from the lateral or manifold inlet:

1 1 m-1 F = -------- + ------- + -------- (13) m + 1 2N 6N2

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in which

F = fraction of the head loss under constant discharge conditions expected with themultiple outlet case;

m = 1.85 for Hazren-Williams equation; m = 2.0 for the Darcy-Weisbach equation; and N = number of outlets along the pipe.

For situation where first outlet is only one-half the spacing from the inlet and.

2N 1 F = (---------) F - (--------) (14) 2N-1 2N-1

The pressure head loss in the pipe having multiple outlets is found by computing theheadloss using the inlet discharge and then multiplying this value by F of F .

3.2.3. Pressure Distribution Assuming Constant Outlet Flow

The flow conditions in lateral and manifold lines are generally steady and spatiallyvaried, with decreasing discharge along the line. The discharge at any point along the pipecan be expressed.

L QL = (N - ------)q (15) Ss

L = N. Ss (16)

q QL = ------ (L L ) (17) Ss

in which,

QL = pipe discharge at a particular point, lps; = distance measured from the inlet end, m;

Ss = emitter spacing, m;N = total number of emitters along the pipe; andq = emitter discharge, lps.

The pressure distribution in the lateral or manifold can be described in terms of thepressure at a distance L meter from the pipe inlet.

L HL = H1 RL hf + (Z1 Z2). ------ (18) L

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Where,

H1 = pressure at the inlet, m; Z1,Z2 = elevation at the pipe inlet and its distal end, respectively, m; RL = friction drop ratio; L = any point distance from inlet; and hf = total head loss in pipe.

and

aLPi-2

hf = ------------- (19) Pi-2

Ai (q/Ss)Pi-3

a = -------------------- (20) DPi

L-L RL = 1 [---------]Pi-2 (21) L

3.3. Friction Loss in Pipes with Multiple Diameters

It is often possible to design irrigation pipelines with two or more diameters in orderto achieve a desired head loss in the pipe network.

Consider a pipeline of length L consisting of two pipe diameters, DL and Ds,representing large and small pipes, respectively. Large pipe always at the upstream of thesmall pipe.

Then

L = LL + Ls (22)

LL NL = ------- (23) Ss

Ls Ns = ------- (24) Ss

The procedure for calculating the head loss utilizes equations (4) and (14) as follows:

a) Calculate the head loss for the flow in the smaller pipe:

(hf)s = hf (Ds, Qs, Ls). F (Ns, m) (25)

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b) Calculate the head loss for the flow of the small pipe but in the large diameterpipes:

(hf) = hf (DL, Qs, Ls). F (Ns, m) (26)

c) Calculate the head loss for the inlet flow to the large pipe having a lengthequal to L:

(hf)L = hf (DL, Q, L). F (N, m) (27)

d) Then, the total pressure head loss is:

(hf)L = (hf)s - (hf) + (hf)L (28)

3.4. Trickle System Design Equation

Trickle system design is an interactive procedure in which successive adjustmentsmay be made to correct a deficiency that may show up in checking the designs. There will beseveral alternative designs that will satisfy the field criteria.

The capacity of the trickle system is based on the 10 day average peak demand. Ateach irrigation, the gross depth to apply is given as:

f. TAW Da = ------------- (29) Ea

Where,

Da = gross average water application, mm; f = allowable soil moisture depletion expressed as a fraction; TAW = total available soil moisture in the root zone, mm; Ea = application efficiency expressed as a fraction.

The frequency with which this depth must be applied is:

f. TAW Ii = ------------- (30) Et

in which

Ii = irrigation interval in days; and Et = design Et rate, mm/day.

For trickle irrigation systems, the discharge per unit area can be determined by:

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2.7778 * Da 2.7778 * Et Q1 = ------------------ = ----------------- (31) Ii * Td Ea * Td

Where

Q1 = system discharge per unit area, lps/ha; Da = grass average application, mm. and Td = number of hours per day the system operates.

The Kostiakov infiltration function is described as:

Z = a Tb (32)

Where

Z = cumulative infiltration, mm; T = hours since infiltration begins; and a,b = empirical functions

The total number of emitters in operation at one time, Ns, should be limited by:

QL Ns = -------- (33) qs

Where

QL = discharge of or lateral line, lps; Qs = emitter discharge, lps; and Ns = number of emitters.

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IV. DESIGN OF TRICKLE IRRIGATION SYSTEMS

4.1. Basic Considerations

The design procedures for trickle irrigation systems are similar to those of sprinklerirrigation systems discussed in the other handbook. The necessary agronomic, soil,water availability, hydraulic and climatic conditions must still be carefully evaluated.The design involves the following steps:

Ø Estimation of peak irrigation water requirements;Ø Selection of emitters or drippers or bubblers;Ø Selection and layout of subunits;Ø Lateral and manifold design;Ø Main, submain and auxiliary design; andØ Selection of pump and prime mover.

The standard trickle irrigation system layout is presented in Figure 1.

4.2. Optimization of Trickle Irrigation System Design

The elements of a trickle irrigation system present the designer-user with a series ofcompetitive demand which need to be balanced to achieve efficient and productiveapplication of water. This balance is generally developed on the basis of previous experienceand judgement of the designer and/or user. However, operation research methodologies areavailable to assist the engineer in systematically comparing alternative options to select thebest satisfying the selection design criteria.

4.2.1. Optimizing Criteria

Optimization is generally described as a process of maximization or minimization ofconcise numerical quantities which reflect the relative importance of the goals contained inalternative decisions. Goals do not yield the mathematical expressions for systematiccomparison of alternative options and therefore be expressed by a quantitative indicator. Themost commonly used indicators are the economic objective functions; namely, maximizationof net benefits or minimization of costs or both.

For irrigated agriculture in Pakistan or elsewhere, the principal objective is tomaximize net benefits, but in the context of design a more limited criteria of minimizing costis usually selected. This is because of the low investment capacity of small farmers especiallyin fragile environments.

4.2.2. Trade-off Design

The components of any irrigation system have competitive demands which requiretrade-off from traditional design procedures. An examination of some of these trade-offs willhelp to illustrate the optimizational problem.

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Uniformity of irrigation application influence the system design. For achieving highuniformity, each emitter discharge must have minimum variation from the average. Thisimplies that pressure throughout the system must be uniform. Since friction losses in pipenetwork are unavoidable, the desire to ensure nearly uniform pressure distribution requiresthat pipe diameters be relatively large and individual pipe lengths be shortened. Thus higheruniformities require higher costs which normally will be more than the benefits because ofincreased yields. In practice, the uniformity in trickle irrigation system design is maintainedarbitrarily limiting pressure variation to within 10% of the average design value, therebyeliminating the uniformity-yield considerations.

There is also a competition between the costs of pumping and the cost of pipe. If thepipe diameters are reduced the head loss in subunits will increase and must be compensatedwith higher energy. Similarly the pumping energy can be reduced by increasing pipediameters. The optimum level will be achieved by minimizing the sum of both pipe andenergy costs. The other tradeoffs include labour versus automation. This is again related withthe system cost and the farmers preferences. The systematic procedure for optimizationrequires a mathematical expression of relationship between the optimizing criterion(minimum costs) and the decision variables (pipe lengths and energy costs). Consideringsocio-economic situation of the farming community in Pakistan, both the decision variablesare important. However, in practice, there are flat electricity rates based on horsepower of theelectric motor. Therefore minimizing energy cost will be an important objective functionbecause electricity is not easily available and farmers are now preferring diesel-operatedpumping systems. Furthermore, optimization of design must be given due emphasisconsidering the operating cost of the system in terms of unit irrigation cost. This will alsorequire clear understanding of the design objectives by the engineers involved in this process.

4.3. Special Design Considerations

For trickle irrigation design, there are some special points which must be consideredin the design process taking into account the socio-economic and technological framework ofthe farming community. These are:

Ø For young orchards, it is easy to design the system because roots follow thewetting pattern based on the emitters type and soil characteristics. The plantsrooting pattern is tuned towards the wet soil.

Ø For matured orchards which are presently irrigated using surface irrigation, thedesigning process requires knowledge of the rooting pattern and plants sensitivitytowards partial water uptake through limited rooting system. This might requiresome special modification in the system considering the best possible points toirrigate without considerable reduction in yield and quality. For fruit plants grownin round basins, there is a possibility to use modified hosefed irrigation systemand provide water through pipeline using small tube openings or bubblers. Thepurpose is to use the concepts of trickle irrigation and design cost-effective systemconsidering farmers preferences and site-specific conditions.

Ø For steep slopes, the land development and reclamation costs are high. Therefore,trickle irrigation for fruit/forest plants provides and alternate option for farmingand resource conservation. Designing for such system will be complex

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considering the elevation differences. The objective will be to provide waterduring dry spells and low uniformity levels might be acceptable considering theminimization of cost. The placement of mains, submains and manifold willrequire special attention and laterals must be planned with minimum elevationdifferences.

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Appendix-I. Values of the coefficient, KF, for various fittings.

Nominal Diameter, mmFitting or Valve 76.2 101.6 127 152.4 177.8 203.2 254

Beds:

Return flanged 0.33 0.30 0.29 0.28 0.27 0.25 0.24Return screwed 0.80 0.70

Elbows:

Regular Flanged 90° 0.34 0.31 0.30 0.28 0.27 0.26 0.25Long radius flanged 90° 0.25 0.22 0.20 0.18 0.17 0.15 0.14Long radius flanged 45° 0.19 0.18 0.18 0.17 0.117 0.17 0.16Regular screwed 90° 0.80 0.70Long radius screwed 90° 0.30 0.23Regular screwed 45° 0.30 0.28

Tees:

Flanged line flow 0.16 0.14 0.13 0.12 0.11 0.10 0.09Flanged branch flow 0.73 0.68 0.65 0.60 0.58 0.56 0.52Screwed line flow 0.90 0.90Screwed branch line 1.20 1.10

Valves:

Globe flanged 7.00 6.30 6.00 5.80 5.70 5.60 5.50Globe screwed 6.00 5.70Gate flanged 0.21 0.16 0.13 0.11 0.09 0.075 0.06Gate screwed 0.14 0.12Swing check flanged 2.00 2.00 2.00 2.00 2.00 2.00 2.00Swing check screwed 2.10 2.00Angle flanged 2.20 2.10 2.00 2.00 2.00 2.00 2.00Angle screwed 1.30 1.00Foot 0.80 0.80 0.80 0.80 0.80 0.80 0.80

Strainers-basket type 1.25 1.05 0.95 0.85 0.80 0.75 0.67