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Impact of different patterns of emitter clogging on hydraulic characteristics of microirrigation laterals.. Ghaemi, Ali Asghar 1998

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IMPACT OF DIFFERENT PATTERNS OF EMITTER CLOGGING ON HYDRAULIC CHARACTERISTICS OF MICROIRRIGATION LATERALS LAID ON FLAT AND SLOPED TERRAINS. By Ali Asghar Ghaemi B.Sc-, Jundi Shapour University, 1975 M.SC., Utah State University, 1987 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES INTERDISCIPLINARY PROGRAM (Chemical and Bio-Resource Engineering) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA March, 1998 © Ali Asghar Ghaemi, 1998 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) In presenting this thesis in partial fulfillment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Interdisciplinary Program The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1Z1 ABSTRACT A field experiment was conducted to evaluate the effects of different numbers and locations of clogged emitters on the hydraulics of a microirrigation system installed on flat and sloped terrains. The results obtained were compared with the theoretical results calculated using a computer program. The emitter flow variation, head loss, pressure variation, coefficient of uniformity, field emission uniformity, distribution uniformity, statistical uniformity of the emitter discharge, emitter statistical uniformity due to hydraulics, application efficiency, emitter discharge coefficient of variation, hydraulic design coefficient of variation, emitter discharge coefficient of variation due to hydraulics, and emitter performance coefficient of variation were evaluated. Five different slopes (0%, 3% and 7% up- and down-slopes) were used to examine eight different patterns (stage 1 to 8) of emitter clogging along the laterals. On the basis of the results obtained from this study, when 10% or more of total number of emitters are partially clogged, the uniformities (CU, EU', DU, and Us) are poor and unacceptable if the criteria suggested by ASAE EP458, and ASAE EP405.1 (1997) is applied. In case of flat terrain, the number and locations of clogged emitters were the major factors affecting the Hf, Hvar, qvar, Vqs, Vns, Vqn, and Vpj. The location of clogged emitters was not a significant factor affecting CU, EU', DU, and Us, but the number and degree of clogged emitters were the major factors effecting the uniformities in a microirrigation system. In case of slope terrain, the location of clogged emitters and the slope of lateral had significant impact on the Hvar, qvar, Vqn and Vns, but the latter had a higher impact than the former. It was found that the number and location of clogged emitters were the major factors affecting Hf, Vqs, Vpj, CU, EU', DU, and Us, but the former is more significant than the latter. No observed significant impact of lateral slopes on these parameters. In case of down-slopes in a no-clogged situation, the uniformities were higher (about 1-4%) than that in up-slope conditions. However, under the clogged situation there was no observed significant difference between the uniformities obtained from up- and down-slopes. In all different slopes studied, stages 4 and 5 (when 30% of total number of emitters are clogged and located at the first one-third section of lateral or randomly located along the lateral) were the worst situations of emitter clogging. ii A computer simulation program based on the solution of fundamental hydraulics relationship was constructed to simulate the effect of different patterns of clogged emitters on the hydraulics of a microirrigation system. The model predicts lateral flow rates with respect to the variation of individual emitter discharge due to pressure change within the lateral. Patterns similar to those of emitter clogging in the field experiment were used in the computer program. In all slopes and stages studied, the computed results did not deviate more than ±5% from the field observations. Based on field and synthetic data, the effects of different patterns of clogged emitters on reduction of crop yields (cotton yield in this study) were simulated and the farmer's loss was estimated. It was found that the reduction of crop yields was directly related to the number and degree of clogged emitters in different slopes. The effect of variation of air and water temperatures on hydraulic characteristics of emitters were examined. Results show that there were no significant differences in emitter flow rate along the lateral under various temperatures at the experimental site. The impact of lateral flushing on emitter flow rate was also investigated. It was found that although flushing the lateral improves the emitter flow rate, it can also create or increase the emitter clogging problem by introducing small suspended particles from the lateral flow into the emitter. The effects of injecting (using the venturi injector) water with different degrees of salinity on the emitter's hydraulic characteristics were studied. Two different cases were evaluated: (1) to maintain a constant value of electrical conductivity (EC) at the emitter's outlet and (2) a constant EC value of the injecting saline water was maintained and the EC variation at the emitter outlet. It was found that the turbulent flow at the venturi throat allows sufficient mixing of the liquid injection with the motive flow. Therefore, the mixed water of almost constant EC along the lateral was obtained over time. Results show that when the venturi was installed and the liquid was injected, the values of hydraulic parameters varied from those values obtained from a "no liquid injection" condition. The variation in hydraulics parameters is unavoidable unless the pressure at the venturi's outlet is adjusted to the same value as in the "no liquid injection" situation. iii Table of Contents Abstract ii List of Tables x List of Figures xiGlossary xvii Dedication xxiAcknowledgment xxii1 INTRODUCTION 1 1.1 Background1.2 Statement of the problem 6 1.3 Research objectives 8 2 LITERATURE REVIEW 10 2.1 Hydraulics of Microirrigation and Flow Variation 12.2 Hydraulic performance of the microirrigation system 13 2.2.1 Emitter flow equation 12.2.2 Turbulent flow in orifice emitters 16 2.2.3 Long-path emitters flow 16 2.2.4 Flow in multi-exit orifice emitters 17 2.3 Flow Regimes • L8 2.4 Head loss 19 2.5 Adjusted "F" factor 23 2.6 Variation of emitter flow rate 24 2.6.1 Dimensionless energy gradient line 22.6.2 Emitter manufacturer's variation 6 2.6.3 Temperature variations 28 2.7 Clogging in microirrigation system 31 2.7.1 Emitter clogging2.7.2 Causes of emitter clogging 31 2.7.3 Emitter clogging and hydraulics 4 iv 2.7.4 Prevention and reducing clogging 36 2.8 Water treatment and chlorination 38 2.9 Chemigation and fertigation 40 2.10 Microirrigation uniformity concepts 41 2.11 Microirrigation system evaluation 4 2.11.1 Emitter flow uniformity 42.11.2 Emitter flow variation caused by hydraulics 48 2.11.3 Coefficient of variations 49 2.11.3.1 Emitter flow coefficient of variation and statistical uniformity coefficient 50 2.11.3.2 Hydraulic variation 1 2.12 Emitter flow variation and crop response 54 3 SIMULATION MODEL 59 3.1 Microirrigation simulation model 53.2 Computer model description 60 3.3 Effect of different patterns of clogging on hydraulics of different length of lateral 66 4 MATERIALS AND METHODS 71 4.1 Description 74.2 Field measurements 6 4.2.1 Step 1 of the field experiment 74.2.2 Step 2 of the field experiment 80 4.2.3 Step 3 of the field experiment 3 4.2.3.1 inspection of the clogged emitters 85 4.2.3.2 Lateral flushing 87 4.2.3.3 Air and water temperature 84.2.3.4 Venturi injector 88 4.2.3.4.1 City water injection in naturally clogged condition 90 4.2.3.4.2 City water injection in no clogged condition 91 v 4.2.3.4.3 Saline water injection in no clogged condition....92 4.3 Impact of emitter clogging on crop yield and farmer benefit 94 5 RESULTS AND DISCUSSION 95 5.1 Introduction 95.2 Hydraulic characteristics of emitter 95 5.3 Manufacturer's coefficient of variation (CV) 97 5.4 Influence of energy gain or loss on pressure-compensating emitter 99 5.5 Simulation of emitter clogging 101 5.6 Relationship between dimensionless values of K%, C% and q% 106 5.7 Comparison of adjusted F factor 110 5.8 Field experiments 112 5.8.1 Step 1 hydraulic characteristics of lateral laid on flat terrain 112 5.8.1.1 Head loss (Hf) 116 5.8.1.2 Pressure variation (Hvar).... 121 5.8.1.3 Emitter flow variation (qvar) 125.8.1.4 Emitter discharge coefficient of variation ( Vqs) 127 5.8.1.5 Emitter discharge coefficient of variation due to hydraulic (v^) 127 5.8.1.6 Hydraulic design coefficient of variation (Vhs) 128 5.8.1.7 Emitter performance coefficient of variation (Vpj) 128 5.8.1.8 Coefficient of uniformity (CU) 130 5.8.1.9 Statistical uniformity (Us) 132 5.8.1.10 Distribution uniformity (DU) and application efficiency (Ea) 134 5.8.1.11 Field emission uniformity (EU') 136 5.8.1.12 Crop yield reduction due to emitter clogging 136 5.8.2 Step 2 hydraulic characteristics of lateral laid on slope terrain 140 5.8.2.1 Total head loss (Hj) 143 5.8.2.2 Pressure variation (Hvar) 149 5.8.2.3 Emitter flow variation (qvar) 152 vi 5.8.2.4 Coefficient of uniformity (CU) 152 5.8.2.5 Application efficiency (Ea) 155.8.2.6 Field emission uniformity (EV) 154 5.8.2.7 Distribution uniformity (DU) 155.8.2.8 Statistical Uniformity (Us) 157 5.8.2.9 Emitter statistical uniformity due to hydraulics (Us„) 159 5.8.2.10 Emitter discharge coefficient of variation due to hydraulic (Vqh) 159 5.8.2.11 Emitter discharge coefficient of variations (Vqs) 160 5.8.2.12 The hydraulic design coefficient of variation (Vf,s) 162 5.8.2.13 Emitter performance coefficient of variation (Vpj) 162 5.8.2.14 Crop yield reduction due to emitter clogging at different slopes 165 5.8.2.15 Relationship between random clogging and hydraulic parameters 170 5.8.3 Step 3 Hydraulic characteristics of lateral under naturally clogged emitters, venturi injector, and injection of saline water 179 5.8.3.1 Natural clogging and its relationship to CU. 179 5.8.3.2 Impact of lateral flushing on emitter flow rate 184 5.8.3.3 Effect of temperature on emitter flow rate 184 5.8.3.4 Comparison of hydraulic parameters under natural, artificial, and synthetic data of clogged emitters (flat terrain) 186 5.8.3.5 Selection of venturi injector , 189 5.8.3.5.1 Calibration of Mazzei 484 venturi injector 189 5.8.3.6 Hydraulics in lateral with venturi injector installed 191 5.8.3.7 Hydraulics of lateral with saline water inj ection 194 6 SUMMARY AND CONCLUSIONS 206.1 Summary 206.2 Conclusions 7 vii 6.3 Recommendations 209 Bibliography 212 Appendix A 223 viii List of Tables 2.1 Flow regime based on Reynolds number 19 2.2 Classification of manufacturer coefficient of variation recommended by ASAE, EP405 (1997) 28 2.3 Classification of water quality relative to its potential for emitter clogging 32 2.4 General criteria for an acceptable statistical uniformity (after Bralts, 1986) 51 2.5 The criteria for the emitter performance coefficient of variation by ASAE (1997) 53 2.6 Total emitter coefficient of variation (V-f) and deficit evapotranspiration 1-(ETave/ETm) when I/ETm is 1 and 5% of area is fully irrigated (adopted from sammis and Wu, 1985) 57 4.1 Number and location of clogged emitters at different stages along the lateral 80 5.1 Average discharge values of Hardi Turbo SC™ Plus, model DPJ04-A emitters, at different pressures (adopted from Hardi manufacturer's manual 96 5.2 Average emitter flow rate and pressure for sample test 98 5.3 Emitter discharge and pressure on flat and slope terrain affected by energy gain or loss 100 5.4 Effect of different types and amount of particles on pressure-compensating emitter (Hardi Turbo SC™ model DPJ04-A) flow rate 103 5.5 Values of K%, q%, and CJVo of 20 emitters along the lateral laid on flat terrain when 30% of the emitters are partially clogged and located at the one-third from the down stream end (field data) 107 5.6 Relationship between reduction in emitter flow rate q%, dimenssion reduction of emitter coefficient K%, and degree of clogging C% for different length of lateral syntheticdata) 110 5.7 Average emitter flow rate (l/h) along the laterals laid on flat terrain under different stages with clogged and no-clogged emitters 114 5.8 Flow rates at lateral inlet and head loss under different patterns of clogging 117 5.9 Values of hydraulic parameters under 8 different patterns of clogged emitters along the lateral (field results) 118 ix 5.10 Values of hydraulic parameters under 8 different patterns of clogged emitters along the lateral (computed results) 118 5.11 Coefficient of uniformity and statistical uniformity obtained from experimental and theoretical results for 20 m lateral laid on flat terrain 133 5.12 Yield production and value of cotton, United States, 1984-93 (adopted from Agric. Statis. US. Dept. of Agric, 1994) 138 5.13 Reduction in cotton yield (ton/area) under different number of clogged emitters randomly located along the lateral 138 5.14 Cotton yield reduction and money ($) lost in different areas under different patterns of clogging 141 5.15 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Field results: (3% down-slope) 145 5.16 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Theoretical results from synthetic data: (3% down-slope) 145 5.17 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Field results: (3% up-slope) 146 5.18 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Theoretical results from synthetic data: (3% up-slope) 146 5.19 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Field results: (7% down-slope) 147 5.20 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Theoretical results from synthetic data: (7% down-slope) 147 5.21 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Field results: (7% up-slope) 148 5.22 Values of hydraulic parameters under eight different patterns of clogged emitters along the lateral. Theoretical results from synthetic data: (7% up-slope) 148 5.23 Cotton yield reduction and money ($) lost in different areas under different patterns of clogging at 3% down-slope 166 5.24 Reduction in cotton yield (ton/area) under different number of clogged emitters randomly located along the lateral (3% down-slope) 166 x 5.25 Cotton yield reduction and money ($) lost in different areas under different patterns of clogging at 3% up-slope 167 5.26 Reduction in cotton yield (ton/area) under different number of clogged emitters randomly located along the lateral (3% up-slope) 167 5.27 Cotton yield reduction and money ($) lost in different areas under different patterns of clogging at 7% down-slope 168 5.28 Reduction in cotton yield (ton/area) under different number of clogged emitters randomly located along the lateral (7% down-slope) 168 5.29 Cotton yield reduction and money ($) lost in different areas under different patterns of clogging at 7% up-slope 169 5.30 Reduction in cotton yield (ton/area) under different number of clogged emitters randomly located along the lateral (7% up-slope) 169 5.31 Reduction or increment of head loss, pressure, and emitter flow variations due to emitter clogging at different slopes (field data) 171 5.32 Reduction or increment of head loss, pressure, and emitter flow variations due to emitter clogging at different slopes (synthetic data) 171 5.33 Reduction in CU, EU', and DU due to random number of clogged emitters along a lateral (field data) 175 5.34 Reduction in CU, EU', and DU due to random number of clogged emitters along a lateral (field data) 175.35 Degree of clogging (Q%) and coefficient of uniformity obtained from naturally and artificially clogged emitters along a 20 and 40 meter laterals (flat terrain) 181 5.36 Test of Mazzei 484 venturi injector under different pressure and motive flow (venturi inlet flow) 190 5.37 Effect of venturi injector, saline and city water injection on emitter flow rate, CU, EU', Ea, qvar, and Vqs in a 20 meters lateral laid on flat terrain 200 5.38 Effect of venturi injector, saline and city water injection on emitter flow rate, CU, EU', Ea, qvar, and Vqs in a 40 meters lateral laid on flat terrain 201 xi List of Figures 1.1 Basic components in a microirrigation system 4 2.1 Emitter discharge and pressure along the microirrigation lateral 15 3.1 Flowchart of the computer simulation model 62 3.2 Interpolation by coordinate method 66 3.3 Effect of number, location, and degree of clogged emitters on head loss 68 3.4 Effect of number, location, and degree of clogged emitters on pressure variation 68 3.5 Effect of number, location, and degree of clogged emitters on coefficient of uniformity 63.6 Effect of number, location, and degree of clogged emitters on field emission uniformity 8 3.7 Effect of number, location, and degree of clogged emitters on application efficiency 69 3.8 Effect of number, location, and degree of clogged emitters on manufacturer emission uniformity3.9 Effect of number, location, and degree of clogged emitters on emitter discharge coefficient of variation due to hydraulics 69 3.10 Effect of number, location, and degree of clogged emitters on hydraulic design coefficient of variation 63.11 Effect of number, location, and degree of clogged emitters on emitter performance coefficient of variation 70 3.12 Effect of number, location, and degree of clogged emitters on emitter discharge coefficient of variation4.1 The field experimental lay out (flat terrain) 72 4.2 Pressure compensating emitter, Hardi Turbo SC™ Puis 74.3 The field experimental lay out (slope terrain) 74 4.4 Venturi injector model Mazzei 484 and injection barrel 74.5 The field experimental lay out in step-1 (not to scale) 7 xii 4.6 Different patterns of emitter clogging along the lateral 81 4.7 Lateral A laid on 7% up-slope (not to scale) 82 4.8 Lateral B laid on 3% up-slope (not to scale)4.9 Lateral A laid on 7% down-slope in step-2 (not to scale) 84 4.10 Lateral B laid on 3% down-slope in step-2 (not to scale)4.11 Test of venturi injector lay out 89 5.1 Logarithm of the average emitter discharge and pressure to determine K and x for the pressure compensating emitter model DPLO-4, Hardi Turbo SC™ Plus 96 5.2 Comparison of emitter discharge on flat and slope terrain with manufacturer's emitter flow rate 100 5.3 Relationship between K%, q%, and Q% for 20 emitters along the lateral laid on flat terrain when 30% of total emitters are partially clogged and located at the last section (one third from down stream end) of lateral 107 5.4 Comparison of adjusted "F" factor (F, F, F , F ) for multi-outlet pipe 111 5.5 Variations of emitter discharge along the lateral due to emitter clogging, manufacturer and pressure variation 115 5.6 Relationship between discharge at leral inlet and total head loss under different patterns of clogged emitters 117 5.7 Head loss and pressure variation under different stages 119 5.8 Head loss and pressure per section along a lateral laid on flat terrain 120 5.9 Total head loss and i^per section under different patterns of emitter clogging (flat terrain) 122 5.10 Relationship between total head loss and energy drop ratio under different sections along lateral 123 5.11 Emitter flow and pressure variations along the lateral under different patterns of clogging 125 5.12 Relationship between Vqn and Hvar versus emitter flow variation (qvar) on flat terrain 126 5.13 Coefficient variations of Vqs, Vhs, Vqh, and Founder different stages 129 5.14 Variations of CU, Ea, DU, Us, and Ush under eight different stages 131 xiii 5.15 Relationship between CU and Us under different patterns of clogging for a lateral laid on flat terrain (experimental and theoretical results) 133 5.16 Relationship between Ea and Usn on a flat terrain 135 5.17 Cotton yield reduction at different areas when different number of clogged emitters are randomly located along the lateral 139 5.18 Cotton yield reduction and money lost in different areas under different patterns of emitter clogging along a lateral laid on flat terrain 142 5.19 Total head loss in different stages under different slopes 144 5.20 Total head loss and Hf per section along the lateral (7% down-slope) 144 5.21 Pressure variation in different stages under different slopes 150 5.22 Emitter discharge variation in different stages under different slopes 150 5.23 Coefficient of uniformity in different stages under different slopes 153 5.24 Application efficiency in different stages under different slopes 153 5.25 Field emission uniformity in different stages under different slopes 155 5.26 Distribution uniformity in different stages under different slopes 155 5.27 Statistical uniformity of emitter discharge in different stages under different slopes 158 5.28 Emitter statistical uniformity due to hydraulics in different stages under different slopes 155.29 Emitter discharge coefficient of variation due to hydraulics in different stages under different slopes 161 5.30 Emitter discharge coefficient of variation in different stages under different slopes 165.31 Hydraulic design coefficient of variation in different stages under different slopes. 163 5.32 Emitter performance coefficient of variation in different stages under different slopes 165.33 Impact of number and location of clogged emitters and slope of lateral on hydraulics of a microirrigation system 164 5.34 Relationship between head loss and pressure variation versus different number of clogged emitters randomly located along the lateral (field data) 173 xiv 5.35 Relationship between the reductions in head loss, pressure variation, and emitter flow variation versus different number of clogged emitters randomly located along the lateral 173 5.36 Relationship between number of clogged emitters (%) and reduction in coefficient of uniformity (Field data) 176 5.37 Relationship between number of clogged emitters (%) and reduction in coefficient of uniformity (Synthetic data) 176 5.38 Relationship between number of clogged emitters (%) and reduction in Emission Uniformity (Field data) 177 5.39 Relationship between number of clogged emitters (%) and reduction in Emission Uniformity (Synthetic data)) 177 5.40 Relationship between number of clogged emitters (%) and reduction in Distribution Uniformity (Field data) 178 5.41 Relationship between number of clogged emitters (%) and reduction in Distribution Uniformity (Synthetic data) 178 5.42 Emitter flow rate along a 20 m lateral laid on flat terrain under naturally, artificially, and synthetically emitter clogged conditions 180 5.43 Emitter flow rate along a 40 m lateral laid on flat terrain under naturally emitter clogged condition (before and after flushing) 180 5.44 Relationship between coefficient of uniformity (CU) and average degree of emitter clogging (Q) along the lateral 183 5.45 Effect of lateral flushing on emitter flow rate 185 5.46 Effect of air and water temperature on emitter flow rate along the laterals A&B laid on flat terrain 186 5.47 Comparison of hydraulic parameters in a microirrigation under artificial, synthetic, and natural clogged conditions (flat terrain) 188 5.48 Variations of emitter flow rate along a 20m (a) and 40m (b) laterals with and without liquid injection using city water and naturally clogged emitters 193 5.49 Variations of emitter flow rate and pressure along a 20m (a) and 40m (b) laterals with and without liquid injection using city water and no clogged emitters 195 xv 5.50 Variations of emitter flow rate along a 20m lateral with and without injection of different saline water under no clogged emitter condition 198 5.51 Variations of emitter flow rate along a 40m lateral with and without injection of different saline water under no clogged emitter condition 199 5.52 Impact of venturi injector with different inlet pressure and liquid injection on total emitter flow rate (T.E.F), CU, and Vqs in 20m and 40m laterals 203 xvi GLOSSARY Symbols Description a A fraction of the area receiving a full irrigation, % A Irrigation area, ha CH Pipe roughness coefficient C Proportion of emitter completely plugged c% percentage number of clogged emitter along the lateral cd degree of emitter clogging c Concentration of elemental nitrogen (N), kg// cq Emitter coefficient CU Christiansen Coefficient of Uniformity, % CUR Reduction in coefficient of uniformity, % cv Coefficient of variation d Flow cross section diameter, cm (in) D Inside diameter of pipe, mm (in) dm Flow cross section diameter of a multi-exit orifice emitter, cm (in) DU Distribution uniformity, % DUR Reduction in distribution uniformity, % Ea Application efficiency, % EC Electrical conductivity, dS/m (mmhos/cm) ECj Electrical conductivity of irrigation water, dS/m (mmhos/cm) ECL Electrical conductivity of injection liquid, dS/m (mmhos/cm) ECm Electrical conductivity of mixed water, dS/m (mmhos/cm) ET Evapotranspiration or crop water-consumption-use rate, mm/day (in/day) ETo Reference evapotranspiration, mm/day (in/day) ETave Mean evapotranspiration, mm/day (in/day) ETd Average evapotranspiration in the deficit area, mm/day (in/day) ETm Evapotranspiration of the crop under non-moisture stress condition, mm/day (in/day) xvii EU Design emission uniformity, % EU' Field emission uniformity, % EU'R Reduction in field emission uniformity, % f Dimensionless friction factor o F20 Friction coefficient for water at 20 C Fr Quantity of nutrient to be applied, kg/ha (lb/acre) FT Friction coefficient for a given water temperature F(n.) corrective function to account for the discharge through the outlets on the pipe (Adjustment correction factor) 2 2 g Acceleration due to gravity, m/s (ft/s ) G Ratio of the required irrigation depth (I) to satisfy ETm to the mean of irrigation depth H Pressure head in the lateral pipe, m or kPa (fit or psi) h Working pressure head at the emitter, m or kPa (ft or psi) Have Average pressure along the lateral, m or kPa (ft or psi) hf Head loss due to friction, m (ft) HF Total head loss along the lateral, m (ft) hf, Head loss at each section along the lateral, m (ft) Hj Pressure at the inlet of lateral, m or kPa (ft or psi) Hmin Minimum pressure along the lateral, m or kPa (ft or psi) H0 Total energy (pressure head) at the inlet, m or kPa (ft or psi) hvar Pressure variation, % I Irrigation depth, mm i Ratio of a given length or llh Id Average depth of irrigation in the deficit area, mm KH Conversion factor depending on selection units kc Crop coefficient K The constant of the proportionality that characterizes each emitter (emitter discharge coefficient) K% Percentage reduction of emitter coefficient xviii hi Fraction of K Yield response factor L Length of lateral, m (ft) / Length position along the lateral, m (ft) lc Length of the flow path in emitter, cm (in) m Flow exponent in the friction loss equation m Number of emitter exits n Exponent of the inside diameter N Number of outlets on the lateral n Number of emitter in the sample n. integer variable expressing the number of outlets on a given pipe Ns Number of section along the lateral OP Percentage of opening of the emitter cross section area, % Pi pressure at point 1 along a pipe, m or kPa (ft or psi) P2 pressure at point 2 along a pipe, m or kPa (ft or psi) q Emitter discharge rate, llh (gph) Q Total pipe flow, llh (gpm) q% percentage of reduction in emitter flow rate, % qa Average emitter discharge of all the emitters under consideration, llh (gpm) qave Average emitter flow rate, llh (gpm) qc Rate of injection of liquid fertilizer solution, llh (gpm) qi Discharge of an emitter, llh (gpm) Qi Lateral flow at ith section, llh (gpm) QL Flow at the inlet of lateral, llh (gpm) qm discharge of a multi-exit orifice, llh (gpm) qm Minimum emitter discharge computed with the minimum pressure, llh (gpm) qmax Maximum emitter flow rate, llh (gpm) qmin Minimum emitter flow rate, llh (gpm) qn Average of the lowest quarter of the emission flow rate, llh (gpm) qvar Emitter flow variation, % xix R'i Ratio of AH'i and AH Ri Friction drop ratio Se emitter spacing, m (ft) sh Standard deviation of the hydraulic pressure sq Standard deviation of the emitter discharge rate in the sample T Water temperature, C Ta Irrigation application time (set time), h TC% Total percentage of emitter clogging, % tr Ratio between set time and fertilizer time Us Statistical uniformity coefficient, % Ush Emitter statistical uniformity due to hydraulics, % V Average velocity of the flow, m/s (ft/s) vm Manufacturer's coefficient of variation Vhs Coefficient of variation due to hydraulics Vpf Emitter performance coefficient of variation vqh Emitter discharge coefficient of variation due to hydraulics Vqp Emitter discharge coefficient of variation including emitter plugging vqs Emitter flow coefficient of variation VT Total emitter coefficient of variation X Emitter discharge exponent Yave Average yield from the field, kg (lb) Ymax Maximum yield under non-moisture stress conditions, kg (lb) YR Reduction in cotton yield, kg (lb) I Mean irrigation depth, mm (in) q The mean emitter flow, llh (gpm) si Variance of the hydraulic pressures Aq Mean deviation of the emitter flow from the mean value, llh (gpm) Dynamic viscosity, kg/ms P Fluid density, kg/m3 (lb/ft3) XX V 2 2 Kinematics viscosity, m /s (ft /s) vT 0 2 2 Kinematics viscosity of water at T C, m /s (ft /s) V20 Kinematics viscosity of water temperature at 20 C, m /s (ft /s) Mpil Adjustment correction factor AH Total friction drop at the end of lateral line, m (ft) AH' Total energy gain or loss, m (ft) AH'i Energy gain or loss at /* location, m (ft) AH; Total friction drop at a given length ratio, m (ft) AL length between points 1 and 2 along the pipe, m (ft) Ap pressure drop, m or kPa (ft or psi) xxi To my wife Sara and our beloved Sally and Reza Acknowledgment I would have been unable to complete this study without the help of many individuals. In particular, I would like to express my deep appreciation for my major supervisor Dr. S. T. Chieng, who provided me with patient guidance, encouragement, and expert advice that motivated this study and its completion. His sustaining encouragement and support was a great incentive throughout my entire stay at UBC. I would also like to thank Dr. Douglas Golding, Dr. Denis Russell, and Dr. Anthony Lau for sitting on the supervisory committee, providing valuable suggestions and reviewing this dissertation. The ideas and recommendations from our discussions were an invaluable guide. I would like to acknowledge my gratitude to the government of the Islamic Republic of Iran for the financial support during these years. My deepest gratitude goes to my wife Sara, my daughter Sally, and my son Reza, for their endless patience, love and encouragement. I can not thank my family enough. I could never have finished without their backing. I wish this acknowledgment could compensate them for all the time I had to take from them to devote to my graduate program. Finally, my sincere appreciation is extended to the University of British Columbia and to the Canadian people. I will always remember friendly and beautiful British Columbia, the country and the people. Ali. A. Ghaemi xxiii Chapter 1. INTRODUCTION 1 Chapter 1 1. INTRODUCTION 1.1 Background: Water is one of the limiting natural resources affecting agricultural crop production. As the world's population increases, more efficient use of irrigation water is required to safeguard food supplies. The aim of irrigation is to provide adequate moisture to crops for the purpose of crop production, complementing natural rainfall. Irrigation systems can be broadly classified as being either gravity flow or pressurised. Gravity flow system are characterised by water flow in channels (furrow, border, contour, overland flow, etc.) across the field. Pressurised systems deliver water under pressure through pipes and release it from small orifices, tubes (spaghetti tube) or sprinkler nozzles. In many parts of the world, natural precipitation is not sufficient to provide adequate soil moisture for optimum crop growth. Inadequate rainfall limits plant growth and crop yields. Water conservation is very important due to high water prices and small allocated quotas in arid and semi-arid areas such as Africa, Saudi Arabia, Iran, etc.. Economical crop production in these areas is not possible without irrigation. Surface irrigation continues to be the predominant system in many countries due to historical knowledge and the low cost of implementation. The high cost associated with the pressurisation of irrigation water and operating energy use is also an important parameter in the design of pressure irrigation systems. Use of low volumes of water and low operating pressure can be achieved with a microirrigation system. However, to irrigate fields and orchards with fruit trees, there is evidence to support the claim that a microirrigation system is often a more efficient and advanced system than other irrigation methods (Dexroix and Malaval, 1985; Hanson et al., 1997). Microirrigation has resulted in considerable increases in water-use efficiency (yield per unit of water applied) over furrow and sprinkler irrigation (Hiller and Howell, 1973; Hanson et al., 1997). To obtain identical yields, microirrigation requires 50% less water than furrow irrigation (Singh et al., 1978). Microirrigation systems are presently being used successfully on a variety of row and tree crops. This type of system is not only applicable in the arid areas but is also useful in humid areas where supplemental water is needed during dry periods. A microirrigation system is one Chapter 1. INTRODUCTION 2 of the most suitable systems with high application efficiency for tree fruits, vegetables, berries, and vines in British Columbia, Canada (Chieng, 1993). Microirrigation systems are used for various crops and fruits, and are practical for areas with hilly topography, poor soil and water shortages. The term "microirrigation" is broadly used to refer to several methods of pressurised irrigation, such as subsurface trickle, surface trickle, drip, pulse, spray, bubbler, and micro-sprinkler. Microirrigation is considered a low pressure irrigation method. It is usually operated at a pressure of less than 103 kPa (15 psi). Microirrigation is described as the slow but frequent application of small quantities of water, which is accomplished by using small-diameter polyethylene or PVC pipe with devices called "emitters" or "applicators" at selected spacing intervals to deliver water on, above, or beneath the soil near the base of the plants (Howell and Hiller, 1974; Nakayama and Bucks, 1986; ASAE S526.1, 1997). The emitter is responsible for direct water discharge to the field. After leaving the emission device, water is distributed by its normal movement through the soil profile; therefore the area which can be wetted from each emitter along the lateral is limited by the horizontal water flow. Ideally, all emitters in a microirrigation system should deliver equal flow rate at irrigation events (Wu and Gitlin, 1973). The purpose of microirrigation is to apply water uniformly through the soil (Wu and Giltin, 1973; Wu, 1975). The application rate for pressurised systems is typically designed to be less than the ponded infiltration rate. In the case of uniformly spaced emitters, this would require that each emitter have the same rate of discharges even though pressure differences are unavoidable (Solomon and Keller, 1978). The uniformity of microirrigation system can be determined based on emitter flow variation along a lateral or sub-main (Bralts and Kenser, 1983; Wu, 1993). The application efficiency of the microirrigation system and the uniformity of emitter flow depends on the emitter flow variation along the lateral lines. Fertilizer or chemical may be applied directly into the microirrigation system by an injector. Ideally, all the emitters along the lateral should deliver the same amount of the liquid injection near the base of the crop. Non-uniformity of the chemical application caused by emitter flow variation along the lateral have a major impact on crop yield. The term "coefficient of variation" can be used to assess the uniformity of water and fertilizer application through the microirrigation sub-main Chapter 1. INTRODUCTION 3 unit (Hahn and Bralts, 1983). A microirrigation system consists of a control head (water supply, pump, pressure regulator, filter, flow meter, injector, etc.), a network of plastic pipes (usually polyethylene pipe such as main, sub-main, lateral) followed by the emitters. Figure 1.1 shows an example of the microirrigation system components. The pressure variation along the lateral line changes the emitter flow rate and hence water application uniformity. The pressure variation along a lateral is greatly affected by the combination of line slope and friction loss. In reality, unit to unit emitter discharge is variable. The emitter flow variation is affected by not only hydraulic design but also emitter manufacturer's variation, grouping of emitters, emitter characteristics, number and degree of clogged emitters through the lateral, friction loss along the line, topographic variation (slope), and temperature (Wu and Gitlin, 1981; Bralts et al, 1981; Keller and Bliesner, 1990; Wu, 1993). In considering uniformity of water application in microirrigation systems, Keller and Karmeli (1974) used basic hydraulics and manufacturer's variation to develop the emission uniformity concept. Wu and Gitlin (1974, 1975), Howell and Hiller (1974a, b), Mayer and Bucks (1972) developed lateral line design procedures based on the hydraulic energy gradient. Of all the factors affecting the uniformity of microirrigation systems the hydraulic design with an emitter flow variation of 10%-20% produces the least effect on the coefficient of variation(CV) or uniformity coefficient (CU). Wu (1997) showed the hydraulic design to be one of the minor factors in the evaluation of overall uniformity of a microirrigation system. In some instances, the microirrigation system was installed with little concern for basic engineering hydraulic principles and resulted in non-uniform emitter discharge throughout the irrigation plots. Over or under irrigation can result from non-uniformity (Bralts et al., 1981b). Among the factors affecting the uniformity of microirrigation system, the emitter clogging is one of the most significant, since it is associated with the operation and maintenance of microirrigation system. Wu (1997) reported that the clogging is the most significant factor, Chapter!. INTRODUCTION 4 i Chapter 1. INTRODUCTION 5 emitter spacing (grouping of emitters) is the second most significant, and that the hydraulic variation (qvar(H)) in a clogging situation is a less significant factor affecting the uniformity. It is known that emitter clogging is directly proportional to the irrigation water quality. However, knowing the exact factors that cause the emitter clogging is difficult because the various elements in the water can interact with each other and result in more clogging problems. Irrigation water should be carefully examined to assess any potential clogging problems. The stream of irrigation water carries organic particles such as algae and weed seeds as well as inorganic particles like sand, silt and clay. In some cases, particles may not adequately removed from the irrigation water by filtration treatment before it enters the pipe network. If lateral lines are not flushed regularly to remove the particles which pass through the filter, they may settle out of the water in the lateral. Bucks et al. (1979) classified the factors in irrigation water which cause emitter clogging in three groups: physical (suspended solid), chemical (interactions of the fertilizer with the dissolved chemicals in irrigation water can be precipitated ), and biological (bacteria and algae). Common causes of the emitter clogging are salt precipitation, microbial slime, insect lodging, and sediment bridging in the emitter passageway (Gilbert and Ford, 1986). Emitter clogging results in changes in the uniformity of emitter flow and lateral hydraulics (Keller and Karmeli, 1974; Bralts et al, 1982). Proper fertilisation and chemical treatment of irrigation water usually can reduce emitter clogging. The problem of major concern in emitter clogging is the change in discharge rates caused by partial to complete clogging of the emitters and how this affects water application through the field (Nakayama and Bucks, 1981). Several studies have related emitter clogging to hydraulics of the microirrigation system (Nakayama and Bucks 1981; Bralts et al, 1987; Solomon, 1985; and Hills et al., 1989). The effect of clogged emitters on the hydraulics of microirrigation is a challenging problem that has caused many operators to abandon their installations. Clogged emitters will not provide the plants with the proper amount of water and fertilizer. This affects the growth of plants and yield. One or two partially clogged emitters may not make changing the whole line economical. However, as the number of clogged emitters increases, the need to replace the line becomes more acute. Prediction of the number, degree, and location of clogged emitters along the lateral is almost impossible in practice. To date, there exists no guideline for Chapter 1. INTRODUCTION 6 the microirrigation users to determine when the clogged emitters or the lateral line should be replaced. Although many researchers have studied microirrigation uniformity, most of the assessments have been limited in scope and restricted either to a typical lateral (Wu and Gitlin, 1974 and Howell and Hiller, 1974) or to only a few of the factors known to affect microirrigation uniformity (Nakayama and Bucks, 1981). Bralts et al (1982) examined the emitter clogging and microirrigation lateral hydraulics. However, uniform or non-uniform clogging patterns along the lateral and their effect on hydraulics parameters were not considered. While many studies on the hydraulics of microirrigation laterals (Solomon, 1985) were made, little work has been done on the effects of emitter clogging. There exists no literature considering the effect of all the factors such as hydraulic design, manufacturer's variation, emitter clogging, emitter spacing, and temperature on emitter flow and uniformity in a microirrigation system. 1.2 Statement of the problem: In 1991, the International Commission on irrigation and Drainage (ICID) indicated that only 1,768,987 ha of 250 million ha of the total global irrigated area are irrigated by microirrigation systems. The majority of microirrigation was in the United States, where the area has expanded from 185,300 ha in 1981 to 606,000 ha in 1991. The area under microirrigation systems in Canada has expanded from 4,700 ha in 1981 to 6,149 ha in 1991 (Bucks, 1993). Total percent of areas under microirrigation are 3% in the United States, 48.7% in Israel, 7.8% in Australia and 0.65% in Canada. IRNCID (1993) indicated that 1.2% of irrigated land in Iran is under pressurised systems (micro and sprinkler irrigation). About half of the irrigated areas in the world (half of the 250 million ha) are in the arid and semi-arid regions. As the cost of water increases, there is heavier reliance on low-volume microirrigation systems. Land characteristics such as topography (slope) and soil texture (e.g. coarse) of the field orients farmers towards the use of microirrigation system. Microirrigation has been particularly successful in region with sandy soil and saline irrigation water (Goldberg and Shmueli, 1970; Goldberg et al., 1971). Also, there have been significant increases in the use of microirrigation in many countries such as Egypt, Mexico, Italy, India, Iran, Japan, France and Thailand (Bucks, 1993). The effects of Chapter 1. INTRODUCTION 7 clogged emitters on hydraulics of microirrigation systems are widespread problem that has caused many early users to abandon their installation. The problem with clogged emitters is that the plants that are to receive water and fertilizer do not receive the proper amounts. For example, if an emitter is 50 percent clogged, the plant at that location may only receive half the necessary water and the rest of emitters will receive too much water. Less water means less plant growth and crop production. If more water is delivered at one time than the soil in the plant root zone will hold, then that water will be lost to deep percolation. In the case of a completely clogged emitter, the plant will only have the water that was originally in the root zone available for growth. If fertilizer and other pesticides are delivered in the water, their distribution depends on the ability of the system to deliver the water uniformly. It is practically impossible to make emitters clog predictably. Salt and fertilizers that are completely soluble can not clog emitters. Emitters are only clogged by particulate matter such as silt, sand, clay, clumps of bacterial matter that grow in the water, or precipitates caused by interaction between the fertilizer and salts in the water. To avoid soil particle clogging, a screen or filter which is four to five times smaller than the opening in the emitter should be used in the microirrigation system. Emitters clog mostly because of bacterial bodies and by-products or dirty water. Growers/farmers who use microirrigation are often criticised for just about any choice of technology they use. Their decisions almost always stem from the bottom line of financial stability. They really need to know when the clogging is impairing their crops so badly that they should replace the lateral line. One clogged emitter would not make changing the whole line economical, but a number of clogged or partially clogged emitters would make changing the whole lateral worthwhile. The problem with the hydraulics of microirrigation is that when the emitter is clogged, the pressure and flow rate will vary throughout the lateral line. If the pressure in the lateral line is unbalanced, the crop production will vary along a lateral just due to the normal hydraulic pressure variation. The study of hydraulics of microirrigation with different numbers and Chapter 1. INTRODUCTION 8 patterns of emitter clogging along the lateral enables the microirrigation system users to predict how much clogging is acceptable and when a lateral will need to be replaced. When the emitter discharge rates and uniformity of the emitters along a lateral is determined, it is possible to predict what the effect on crop growth will be or how much production will be lost due to clogged or partially clogged emitters. It is also possible to estimate how much money in terms of water and fertilizer is wasted due to emitter clogging and variation of emitter flow rate along the lateral. In some developing countries in the arid region, there exists no experience of using microirrigation systems. Therefore, the study of effects of clogged emitters on the hydraulics of microirrigation will help the system users to estimate the degree of over- and under-irrigation based on hydraulics. 1.3 Research objectives: The aim of this research was to determine the effect of different patterns of emitter clogging on the hydraulics of microirrigation laterals. The effects of saline water injection on emitter flow variation and the hydraulics of lateral were also examined. The research objectives of this study were: 1- to quantify the flow uniformity and flow patterns along a lateral with different degrees and patterns of emitter clogging. 2- to simulate the pressure variations along a lateral with different number of clogged emitters and different clogging patterns and lateral slopes. Field experimental data will be collected to verify the simulated results. 3- to assess the location of the most severely clogged emitters along the lateral which have the highest impact on the coefficient of uniformity. Chapter 1. INTRODUCTION 9 4- to examine the effect of injecting different degrees of saline water (by using the venturi injector) on the emitter's hydraulic characteristics. 5- to investigate the change, over time, in injected fertilizer or chemical concentration along a lateral consisting of no-clogged and partially clogged emitters when the venturi injector is used. 6- to evaluate the hydraulics of a microirrigation lateral with a venturi injector installed. 7- to predict the economic effects of emitter clogging on crop production. 8- to construct a mathematical computer spreadsheet program to predict the effects of emitter clogging on the hydraulics of microirrigation systems and crop yield. Chapter 2. LITERATURE REVIEW 10 Chapter 2 2. LITERATURE REVIEW 2.1 Hydraulics of Microirrigation and Flow Variation: Microirrigation is a type of pressurised pipe network with a generally low operating pressure and application rate. The actual emitter discharge rate for typical field layouts varies considerably and is very sensitive to pressure variation, partial or complete emitter clogging, water quality variation, temperature variation, design emitter characteristics, emitter manufacture variation, friction head loss throughout the pipe distribution network, and topographic variation (slope). Therefore it is recommended that the system be monitored with time sequencing (Keller and Karmeli, 1974). The hydraulics of microirrigation has been fairly well established and documented by many researchers (Karmeli et al., 1985; Bralts et al., 1987). The flow condition in microirrigation lines (lateral or submain) is considered steady and spatially varied with decreasing discharge in the line. Among the factors affecting the microirrigation uniformity, the hydraulic design can be controlled by the engineers who design the system for a certain specified design criterion (Feng and Wu, 1990). Wu and Gitlin (1975) and Myers and Bucks (1972) derived the hydraulic energy gradient line for determining the emitter flow variations and uniformity along a lateral line. Howell and Hiller (1974) used the hydraulic energy gradient principle and developed lateral line design equations based upon specific uniformity criteria. Wu and Gitlin (1983) indicated that the microirrigation application efficiency can be estimated from the emitter flow variation caused by hydraulics alone or by the hydraulics and manufacturer's variation combined. The emitter flow variation or any non-uniformity of emitter flow results in an extra amount of irrigation to meet the crop water requirements. Wu (1975) and Wu and Irudayaraj (1989) developed a computer simulation program to determine all emitter flows within a submain unit with respect to energy gradient curve and changes of energy due to slope conditions. The shape of energy Chapter 2. LITERATURE REVIEW 11 gradient line will not be a straight line but a exponential curve. They also developed a simulation model which randomly selects the emitter flow samples for field evaluation purposes. The computer simulation model can also be used for determining the emitter flow through the lateral line caused by emitter manufacturer's variation or hydraulic design. Howell and Hiller (1974) presented a design equation for determining the length of microirrigation lateral to meet specific uniformity criteria. They also presented dimensionless graphs for trickle irrigation lateral design. Wu and Gitlin (1973) and Wu et. al. (1975) presented a dimensionless energy gradient line for drip irrigation lines. The dimmensionless energy gradient line can be used to determine energy drop along the line if total energy drop (head loss) at the end of the line is determined. When the pressure gradient line is estimated, then the uniform outflow can be achieved by using different sizes of emitter, different lengths of the lateral line or a combination of the length and diameter (size) of emitter, and different emitter spacing. Keller and Bliesner (1990) and Wu et al. (1986) reported that in a well designed microirrigation system, the emitter discharge variation along the lateral lines should not exceed 10%. For most normal emitters to achieve this range of discharge variation, the pressure variation along the laterals and manifold should not be more than 20%. The manufacturer's variation of emitter flow for microirrigation emitters is in a range of 2-20% (Solomon, 1979). The hydraulic variation in a microirrigation system will be less significant when an emitter with 10% or more manufacturer's variation is selected (Wu, 1997). If, for constant flow for each emitter, the pressure distribution is determined along a lateral line, the uniform irrigation can be achieved by using different sizes of emitters, different emitter spacing, and different lengths (Mayers and Bucks, 1972; Kenworthy, 1972; Wu et al, 1973). In a microirrigation system, the way that the water is distributed is one of the most important design aspects. One of the major design criteria is the minimization of emitter flow variation along a lateral or submain. The emitters are responsible for direct water delivery to the crop, and they play an important role in achieving high emission uniformity (Kimura, 1987). The discharge variation can be controlled by pressure variation along the line. Gillespier (1979) developed procedures to identify pressure profiles by land-slope and total friction drop at the end of the line. Howell and Hiller (1974) and Wu and Giltin (1973 and 1979) suggested that when the kinetic energy is considered to be negligible in microirrigation line, the pressure variation will be simply a linear combination of the friction drop and energy Chapter 2. LITERATURE REVIEW 12 gain or loss due to the slope. Wu et al. (1977) developed design charts based on hydraulic energy considerations and computer simulation. The chart allows a maximum of 20% variation in pressure in the submain. Microirrigation should be designed to minimize pressure variation so that the flow into all lateral lines and emitters will be nearly equal. Howell and Hiler (1974) developed a computer program to determine the lateral pressure loss and emitter flow ratio, emitter spacing and lateral slope. Wu and Gitlin (1979) developed various dimensionless design charts for lateral lines laid on non-uniform slopes. They suggested that if a relatively long lateral is laid on a non-uniform down-slope, a simple down-slope design can be used with variable pipe sizes. In case of a lateral with several sections, each section having a uniform slope, the pipe size for each section can be determined simply by the mean discharge and the slope. A method for designing microirrigation laterals on non-uniform slopes was developed using the finite element method (Kang et al., 1996). They reported that the diameter and length of a single lateral affects the uniformity of water application on sloped fields. The uniformity of water application is considerably decreased or increased if a small increment or reduction in lateral diameter or length of lateral occurs. They reported that it can not be said a priori that a shorter lateral or larger diameter will improve, or a longer lateral or smaller diameter reduce, uniformity of water application. They did not consider the effect of emitter clogging on uniformity in their hydraulic analysis. A personal computer is needed for this hydraulic analysis method; however, dimensionless design charts suggested by Wu and Gitlin (1979) are more practical for design of microirrigation laterals on non-uniform slopes. The energy gradient line approach, polyplot, and uniplot developed by Wu and Gitline (1979) and Wu (1985) are widely used to design microirrigation laterals on non-uniform slopes. A set of equations and graphs has been developed by Howell and Hiler (1974) to determine the length of a lateral with respect to desirable discharge uniformity and emitter spacing. Solomon and Keller (1978) derived an expression for the pressure head in a microirrigation lateral and through the pipe network. They provided the flow rate histograms which show the combined effects on emitter discharge variation, head losses and variation in emitter manufacture. They claimed that the emission uniformity can be improved about 2% by doubling the number of emitters. They reported that there is no practical analytical means for dealing with all factors affecting emitter discharge rate during system design. Nakayama et al. (1979) developed a method to show the water Chapter 2. LITERATURE REVIEW 13 application uniformity by microirrigation emitters based on the emitter's coefficient of variation. They compared the emitter flow uniformity by estimating the average flow rates for a specified subgroup of the entire emitter population. Myers and Bucks (1972) reported that the emitter flow variation can be reduced by water filtration, improved manufacturing processes, and management technique to avoid salt precipitation, but the major problem from the standpoint of the system design is the friction-induced pressure changes in the lateral pipe. Unless the system is designed to compensate for the pressure changes, emitter discharge will vary along the lateral line. 2.2 Hydraulic performance of the microirrigation system 2.2.1 Emitter flow equation: The emitter is responsible for emitting the water into the soil at the plant root zone. Kimura (1987) and Keller (1980) reported that most emission devices (drippers, bubblers, sprayers) commercially available regulate flow by dissipating energy through friction resistance. Microirrigation emitters vary in their design from the simple orifice type, long-path emitter to pressure-compensating devices. The emitter flow at any section along a lateral of a microirrigation system is controlled by the pressure in that section. Theoretically, the emitter outflow is a function of the square root of the pressure (Karmeli, 1977; Wu et al, 1979). The emitter's discharge characteristics are usually characterised by the relationship between discharge, pressure and an emitter discharge exponent. The equation for emitter flow that has been used by many researchers (Wu, and Gitlin, 1974; Karmeli, 1977; Howell and Hiler, 1974; Keller and Karmeli, 1974) can be expressed as: q = Khx (2.1) where: q = emitter discharge rate llh (gph) h = working pressure head at the emitter in m (psi) Chapter 2. LITERATURE REVIEW 14 K= the constant of proportionality that characterizes each emitter. The magnitude of K is a size or capacity parameter for an emitter since its value is equal to the emitter flow rate when h equals unity (Howell and Hiller, 1974; Braud and Soom, 1981). x = the emitter discharge exponent that is characterized by the flow regime. It is the measure of how sensitive the emitter discharge is to pressure. Solomon (1976) Karmeli (1977) and Wu (1974) suggested that K and x can be determined by measuring the slope of a log plot of pressure versus discharge. To determine the x, q at two different operating pressures should be known. If qi and q2 are emitter discharges at two operating pressures of hi and h2, then the x can be analytically determined as: log (SL) log 2. 2 The value of x depends on the type of flow regime. Karmeli (1977), Howell and Hiller (1972,1974), and Wu and Gitlin (1974) reported the following: x = 0.5 in fully turbulent flow (non-compensating orifice and nozzle emitters are always fully turbulent) x = 1.0 in laminar flow 0.5 < x < 1 for unstable flow regime x = 0.0 for fully pressure-compensating The lower the value of x, the less the discharge is affected by the pressure variation. Values of x in pressure-compensating emitters are normally near zero. With the value of x known, equation 2.1 can be used to determine K. Another common way to determine the x and K values is to perform a linear regression on the logarithms of the emitter flows and operating pressures. Equation 2.1 can be presented in logarithmic formula as: log(q) = x log(h) + log(K); this formula is the linear form of y = na + b, where y = log(q), n = x, a = log(h), and b = log(K). Chapter 2. LITERATURE REVIEW 15 The values of n and b can be reached from a linear regression of log(h) versus log(q). Since b = log (K), and k=10b, the equation 2.1 can be expressed as: b n -> -> q = lQ h 2.3 where « or x is determined from the linear regression and is a measure of the flow variation due to changes in pressure. The flow in a microirrigation lateral can be considered to be hydraulically steady, and spatially varied with lateral flow. In the other words, the total flow through the lateral changes, usually decreasing with respect to the length of lateral. Figure 2.1 shows the flow and pressure distribution along a lateral with equally spaced emitters along the line. h, hn-2 hn-1 h„ QL=( + emitter + qi q2 q3 q4 qn-2 qn-i qn Figure 2.1 Emitter discharge and pressure along the microirrigation lateral The emitter discharges are presented by q\ (/ =I,2,3,4,...n-2, n-1, n). Figure 2.1 shows that the inlet lateral flow (Qi) is the summation of all emitters' discharge along the line. QL can be estimated as follows: 2.4 Chapter 2. LITEM TURE REVIEW 16 where, Qi is the inlet lateral flow, q{ is the emitter discharge and /z, is the pressure at i section . There are different types of emitters used in a microirrigation system. The flow characteristics of emitters can be characterized by the relation between flow rate, pressure, and emitter discharge exponent, which is related to the flow regime. Karmeli (1977) defined several equations for determining flow rate in different type of emitters as follows: 2.2.2 Turbulent flow in orifice emitters: In this case water flows through an opening of small diameter, the flow regime is fully turbulent and most of the head loss takes place. The emitter discharge can be determined as: q = A.CqJ2g~H 2.5 where: A = the flow cross section area Cq = the emitter coefficient that accounts for areal and discharge effects and depends on the nozzle characteristics g = acceleration due to gravity H= pressure head in the lateral pipe at the emitter under consideration. As equation 2.5 shows in the turbulent flow discharge, q is the proportional to the square root of pressure. 2.2.3 Long-path emitters flow: In this case head loss will occur in the long-flow path and is directly proportional to the length of the flow path in the emitter. The flow can be estimated as follows: Chapter 2. LITERATURE REVIEW 17 H.g.d57T S.f.q2 2.6 where: lc = length of the flow path in the emitter g and H have the same definition as in equation 2.5 /= friction coefficient which is linearly dependent on the inverse of Reynolds number (f=64/Re, p = fluid density (kg/m ), p is the dynamic viscosity (kg/ms) v = kinematic viscosity (the ratio of viscosity to density) of the water which is equal to 1.0x10 m2/s at 20°C d = flow cross section diameter V= average velocity of the flow in the emitter q = emitter discharge. For the long-path laminar emitters' flow, the equation 2.6 can be modified as: Equation 2.7 shows that the discharge is directly proportional to H under the laminar flow condition. 2.2.4 Flow in multi-exit orifice emitters: There are two types of multi-exit emitter: a single orifice type supplies several outlet tubes, and the other type is twin-bore tubing. Most pressure head loss occurs in the inner orifice, and a small amount of head loss occurs in outlet tubes. Assuming a circular cross section, the discharge from the single-exit and multi-exit orifice emitter can be determined as follows: and i?e= pVD/p = Vd/v, since V= 4q/ju£, then Re=4q/vwd ) H.g2.d\n m.q.v 2.7 Chapter 2. LITERATURE REVIEW 18 d = m 2.8 where: dm = flow cross section diameter of a multi-exit orifice emitter m = number of emitter exits d = diameter of a single exit orifice emitter having the same discharge as one of the exits of the multi-exit emitter q = discharge of a single-exit orifice emitter qm = discharge of a multi-exit orifice emitter. 2.3 Flow Regime: The flow in the pipe can be characterized as a laminar, transition and turbulent flow depending on the magnitude of the external force, and density and the velocity of the flowing fluid (Papanastasiou, 1994). For a given flow rate, it turns out that the pressure drop, Ap, (assume Ap =P2-pi, where pi and p2 are the pressures at points 1 and 2 along a pipe) is directly proportional to AL length between points 1 and 2 along the pipe. By varying the flow rate and the pressure gradient (AplAL) along the pipe line, three distinct flow regimes ( laminar, transition, and turbulent) can be characterized. Sir Osborne Reynolds (1883 and 1901) correlated these flow regimes by means of a unique dimensionless number that incorporates the average fluid velocity ( V), its density (p) and viscosity (77), and the diameter (D) of the pipe. Reynolds number can be determined by the equation as given in section 2.2.3 (equation 2.6). Karmeli (1977) defined four flow regimes based on Reynolds number (A^) as described in Table 2.1. Chapter 2. LITERATURE REVIEW Table 2.1 Flow regimes based on Reynolds number. 19 Flow regimes Reynolds number Laminar flow 0<Re<2000 Unstable flow 2000 < R» < 4000 Partially turbulent flow 4000<Re<10,000 Fully turbulent flow 10000<Re 2.4 Head loss: Microirrigation laterals are mostly made of smooth materials (such pvc or polyethylene). Flow in lateral is generally assumed to be turbulent. Sometimes fully turbulent flow exists at the upstream end of the lateral and becomes laminar at the downstream reach where the velocity decreases to zero. If the microirrigation lateral is considered to be hydraulically smooth, any of several empirical equations can be used to calculate head loss due to friction (Bralts and Edwards, 1987). Usually, the designers are searching for simpler calculation methods that do not compromise accuracy. In a microirrigation system, either the Darcy-Weisbach or Hazen-Williams equation is generally used to compute the head loss of microirrigation pipes (Wu and Yue,1993; Bagarello et al, 1997). The Darcy-Weisbach equation is one of the more complex methods for calculating the head loss that are universally accepted (Watter and Keller, 1978; Pitts et a/.,1986; Hill et al, 1989; Hathoot et el. 1993; Reynolds et al, 1995; Bagarello et al, 1997). The Darcy-Weisbach equation is considered to be theoretical because of its derivation. This equation includes the friction factor, / which is a function of Reynolds number and the pipe roughness as follows (Bralts and Edward, 1987; Von Bermuth, 1990): hf=f rLV2> yD2g, 2.9 where: Chapter 2. LITEM TURE REVIEW 20 h/ = head loss due to friction (m) / = dimensionless friction factor L = length of pipe (m) V= average velocity of water in the pipe (m/s) D = diameter of the pipe (m) g = acceleration of gravity (9.807 m/s ). It is the calculation of the friction factor / that complicates the Darcy-Weisbach equation, because the friction factor cannot be conveniently expressed mathematically. There are theoretical methods for estimating the/ in these cases the solution is reached either by iteration or by reference to the Moody diagram. To estimate the/ empirical approaches are commonly used. Blasius (1913) proposed a simple equation for estimating / for very smooth pipes as:/= a.Reb, where / is the friction factor, Re is the Reynolds number and "a", and "6" are the empirically determined coefficients. However, the equation is valid for virtually any pipe size as long as the Reynolds number is limited to 105. In laminar flow or unstable (critical zones) flow when the Reynolds number is less than 4000, the Blusius equation will overestimate the friction factor by as much as a factor of five. If flow is assumed to be laminar,/can be estimated by: /= 64/Re. Practicing engineers do not like to use the Darcy-Weisbach equation and prefer simpler empirical equations which do not require calculation of the Reynolds number and reference to a table of viscosity values. Failure to correct for viscosity differences can cause significant error in results. In a microirrigation system, a widely used empirical equation for calculating the pipe friction loss is the Hazen-Williams formula (Howell and Hiller, 1974; Keller and karmeli, 1974; Wu and Gitlin, 1975 and 1977; Gillespie et al, 1979; Braud and Soom, 1981; Jepson, 1982; Bralts and Edward, 1987; Feng and Wu, 1990; Keller and Bliesner, 1990; Tajrishy and Hills, 1992; Wu and Yue, 1993) as expressed below: \ 1.852 hf=KH.L -4.87 2.10 Chapter 2. LITERATURE REVIEW 21 where: hf= head loss due to pipe friction (m) KH = conversion factor depending on selected units (1.212x 1010in this case) L = length of pipe (m) D = inside diameter of the pipe (mm) Q = total pipe flow (//s) CH = pipe roughness coefficient. The popularity of this equation is due to the simple calculation resulting from a single roughness coefficient factor for any pipe size or velocity. Equation 2.10 holds for a description of flow in any kind of pipe depending on the material as expressed by CH- However, the difficulty is that if accuracy is very important, a single Hazen-Williams factor (CH ) cannot be used for all range of flows or diameter (Haughes and Jepson, 1978). The value of the friction coefficient CH has a strong influence on the friction loss calculation. Many friction loss charts for smooth plastic pipe have been developed with a CH value of 150. Previous work (Keller and Karmeli, 1974) shows that for plastic pipe, CH — 150 is normally used. However, Hansen (1973) found that the laterals with emitters spaced at 1.52 m (5 ft) intervals had equivalent CH values between 98 and 136. Utah State Division of Health allows only CH =120 (Haughes and Jepson, 1978). Braud and Soom (1981) showed that the Blasius and Hazen-Williams equations are in good agreement at CH = 130. Hughes and Jepson (1978) reported that the CH factor of 150 recommended by most pvc pipe manufacturers is too high. They manipulated the Hazen-Williams equation into the form of the Darcy-Weisbach equation and then identified "f" as a function of CH. They measured coefficients averaging 133 which is closed to that predicted by superimposing Hazen-William's coefficients on the Moody diagram. They also reported that by the Moody diagram analysis, flow through PVC pipe at Reynolds numbers ranging from 10 to 104 requires CH of 130 to 140. In general practice, the CH value is assumed to be 140 for smooth polyethylene pipe (Sneed, 1973; Tajrishi and Hills, 1992). Howell and Barinas (1980) measured emitter friction loss in laterals and established a relationship between obstruction area and its friction effect. In the Hazen-Williams equation, the ability to adjust the friction factor CH for emitter presence is an advantage. Chapter 2. LITERATURE REVIEW 22 For a given pipe size and length, the total friction loss in a pipe consisting of a number of equally spaced outlets is less than in that of a constant flow and a single outlet (Scaloppi, 1988; Tajrishi and Hills, 1992). The concept of adjustment correction factor "F" has been developed by Christiansen (1942) to correct the friction loss calculated from the general formula that assumes that all of the water is carried to the end of the line. In this procedure, Christiansen assumed that all outlets along the lateral had equal spacing and discharges and that the total flow entering the pipe left through the line. Christiansen (1942) proposed a simple and fairly accurate solution for head loss in laterals with multiple outlets as: where: m = velocity exponent (m = 1 for laminar flow, and m - 1.852 for fully turbulent flow in the Hazen-Williams formula) n = exponent of the inside diameter F = adjustment correction factor. Equations 2.9, 2.10 or 2.11 are used to determine the flow friction loss in a lateral or manifold in a microirrigation system. The head loss in a microirrigation lateral with flow rates along its length is not linear but parabolic, with a steep slope at the beginning of the lateral and almost flattening toward the distal end. Keller and Karmeli (1974) reported that in a single lateral line for a wide range of emitter exponent and pressure losses, the average pressure head occurs at Z=0.39 (L = length of lateral). They also reported that approximately 77% of total lateral head loss occurs between L = 0.0 and L = 0.39, while 23% of head loss occurs between L = 0.39 and L = I. FK„L\ -(2m+n) 2.11 The losses through the lateral fittings and emitter connections are not included in those equations. Where there are only a few pipe fittings, the pressure loss across these fittings is Chapter 2. LITERATURE REVIEW 23 termed a minor loss. If there are a large number of fittings present in a microirrigation system, the minor losses can be an important consideration. In the present reseach, the friction loss due to a few pipe fittings is not considered. 2.5 Adjusted F factor: An adjusted F factor to compute pressure head loss in a multiple outlet pipe with equally spaced outlets has been derived by several researchers. The F factor introduced by Christiansen was derived by assuming that the first outlet is located one outlet spacing away from the lateral or manifold inlet (Jensen, 1980). The following approximation of adjusted "F" factor was presented by Christiansen (1942): _ 1 1 -Jm-\ F = + + 7- 2.12 m+l 2N 6N2 where N is the number of outlets on the lateral, and m is the velocity exponent (in Hazen-Williams formula m = 1.852). For JV>10 the last term of the equation 2.12 can be omitted. Jensen and Fratini (1957) modified the equation 2.12 to account for the first outlet being located one-half an outlet spacing from the supply line as follows: F = —+ \(N - If +(N-2)m +...+1" 2N-1 (2N-\)NmiK ' V ; 2.13 Utilizing the coefficient values from Jensen and Fratini (1957) in a nonlinear least squares correlation procedure yields the explicit function as follows (Gohering, 1976; Oron and Walker, 1981): F{no) = 0.63837/7/18916 + 0.3 5 9 2 9 2.14 Chapter 2. LITERATURE REVIEW 24 where n0 is an integer variable expressing the number of outlets on a given pipe. 2.6 Variation of emitter flow rate: The uniformity of emitter flow depends on the emitter flow variation, which is mainly affected by several factors as explained in previous sections.The main parameters affecting emitters flow variation are discussed below. 2.6.1 Dimensionless energy gradient line: In a microirrigation system the pressure variations in the lateral affect emitter flow rate. The pressure variation along the lateral can be determined by using the energy gradient line. Wu and Gitlin (1975) developed a procedure to determine the dimensionless energy gradient line. They assumed that all the emitters along the lateral line discharge the same flow. This approximation, which results in the energy gradient line in a curve of exponential type (not straight line), can be used to calculate the head loss directly at any point along the lateral. When a constant emitter flow rate along the lateral is assumed, the shape of the energy gradient line can be expressed dimensionlessly as the energy drop ratio (Rj) as follows: Rt=^L = \-(\-i)m+x 2.15 ' AH v ; Where Rt defines the shape of the energy gradient line and is expressed as a friction drop ratio, AH is the total friction drop at the end of lateral line (i.e., computed from equation 2.11), AHj is the total friction drop at a given length ratio(i), / is a ratio of a given length from the inlet / to the total length of lateral L (i=l/L), m a power coefficient of total discharge in the friction drop equation (when Hazen-Williams formula is used, m is 1.852), then the equation 2.15 can be expressed as: *,=i-(i-02J 2.16 Chapter 2. LITEMTURE REVIEW 25 The total pressure variation along a lateral in a microirrigation system can be expressed as a linear combination of the original pressure and the variation due to the energy slope and line(terrain) slope (Wu and Yue, 1993). Using the dimensionless energy gradient line concept and uniform slopes the pressure at any i location along the lateral line can be determined as follows (Wu and Gitlin, 1974; Wu et al., 1979; Bralts et al., 1987): hj = Ha - A//, + AH't 2.17 or ht =H0- RtAH± R\ AH' 2.18 where h\ is the pressure at any / location along the lateral, Ha is the total energy (pressure head) at the inlet and is specified as the operating pressure, AH is the total head loss due to friction at the end of lateral, AH' is the total energy gain or energy loss ("+" for down-slope and "-" for up-slope), R', is defined as the ratio of AH) and AH'(R', =AH't / AH'), where AH't is the energy gain or loss (for down-slope or up-slope situations) at the / location along the lateral. For uniform slopes, A", is the same as the length ratio, /. With respect to the general equation of emitter flow and considering energy gradient line formula, the emitter flow rate along the lateral at any / location (qi) is directly related to the pressure variation at the same / location along the lateral as follows: qi = K(Ho - RtAH± A". AH1)' 2.19 On uniform slopes, the term of R'jAH' can be changed to iAH' (Wu et al., 1986). Theoretically, flow rates of the pressure-compensating emitters should be independent of operating pressure (Madramootoo, 1988) and pressure variation along the lateral. Therefore, pressure-compensating emitters have an advantage, especially on sloped terrain. Chapter 2. LITERATURE REVIEW 26 2.6.2 Emitter manufacturer's variation: Manufacturing of an emission device must be precise because the emitter flow path is usually small, less than 2mm in diameter. Due to inconsistencies in the material used for manufacturing the emitter and the inability to hold constant pressure and temperature, it is difficult to manufacture two emitter flow passages that are exactly alike ( Solomon, 1979; Ozekici and Sneed, 1995). Small deviations in the critical dimensions of the emission devices would result in relatively large deviations in the emitter flow rates, although the absolute magnitude of the variation might be very small. In order to have a consistent flow rate, emitters must maintain the same physical characteristics over their lifetime. In manufacturing the pressure-compensating emitters, elastomeric material is used to achieve flushing action and pressure compensation, and these parts are very difficult to manufacture with consistent dimensions. It is generally assumed that the variations resulting from the manufacturing process are normally distributed about their mean value. The concept of manufacturer's variation of emitters was first developed by Keller and Karmeli (1974) and then researched by Solomon (1979). A number of researchers defined a parameter called the manufacturer's coefficient of variation, CV, as a statistical parameter used to identify the quality of a sample of new emitters (Solomon, 1979; Bralts et al, 1981; Wu, 1983; ASAE EP405.1, 1997). This parameter is used to evaluate the variation in discharge in a sample of new emitters when operated at a constant temperature and near the design operating pressure of the emitter. The value of CV can be calculated by measuring the discharge from a sample of new emitters at a fixed inlet pressure; however, it is usually available from the manufacture. The emitter manufacturer's coefficient of variation can be determined as follows (Keller, 1980; Wu, 1983; ASAE EP405.1, 1997): CV = ^- 2.20 where: CV= manufacturer's coefficient of variation Chapter 2. LITERATURE REVIEW 27 c[ave = average discharge of emitters in the sample (llh) Sq = standard deviation of the emitter discharge rate in the sample. qave and Sq can be determined as follows: 1 " 9 aye = ~S«'< 2.21 n-\ 2.22 where: q, = discharge of an emitter n = number of emitters in the sample. CV is one of the significant factors affecting the overall uniformity of the microirrigation system. Wu (1997) found that CF is one of the statistical terms which can be used to show the microirrigation system uniformity. Reasonable ranges of CV for evaluating the system uniformity vary from 0.05 or less to 0.15 or more. Numerous guidelines have been suggested for CV, but those recommended by ASAE EP405.1 (1997) shown in Table 2.2 are used for this research. Chapter 2. LITERATURE REVIEW 28 Table 2.2 Classification of manufacturer coefficient of variation recommended by ASAE, EP405.1 (1997) Classification Manufacturer's coefficient of variation <0.05 excellent 0.05 to 0.07 average 0.07 to 0.11 marginal 0.11 to 0.15 poor > 0.15 unacceptable 2.6.3 Temperature Variation: Microirrigation lines and emitters on the ground surface are subject to temperature changes which affect the hydraulics of microirrigation lines. The effect of temperature variation on emitter discharge variation occurs over a period of time with day-night, day-to-day, and seasonal weather changes, and through the lateral due to solar heating of black pvc or polyethylene pipe. As the water discharges through the lateral line, viscosity decreases and rate of heating increases. If the end-to-end of lateral line temperature variation due to solar heating is minimal, the seasonal temperature variation (i.e., spring and summer) can cause discharge variation from -20 to +10 percent (Parchomchuk, 1976). Karmeli (1977) showed that the Reynolds number, Re, is sensitive to water temperature variation due to change in water viscosity. The kinematic viscosity (v) of water changes with respect to the temperature. The kinematic viscosity of water for any temperature T with respect to the viscosity of water at 20 C as a base can be shown as follows (Assaf, K and S.A. Asaf, 1974): VT = V2Q (o.98)r~ 20 2>23 where V20 and VT are the kinematic viscosity of water at 20 C and T C water temperatures. Chapter 2. LITERATURE REVIEW 29 Keller and Bliesner (1990) found that the discharge from most long-path emitters depends on the water viscosity, which changes with temperature. They indicated for a long-path emitter the increase in discharge due to decreased water viscosity is roughly 1% for each 2°C increase in water temperature. For a tortuous-path emitter, the increase of discharge is roughly 1% for each 4°C increase in water temperature. Solomon (1985) reported that the flow rate from some emitters is sensitive to water temperature and the influence of water temperature on emitter flow rate is linear. Therefore the variation in water temperature through the subunit must be considered. Parchomchuk (1976) measured the effect of temperature variation on emitter flow rate for various types of emitter and found the effects of temperature to be less than theoretically predicted, but still significant. There is general agreement that the emitter flow rates should not vary more than ± 10% for uniform water application (Bucks and Myers, 1974; Wu and Gitlin, 1974; Keller and Karmeli, 1974). Water viscosity changes that are due to changing water temperature cause emitter flow variation greater than the maximum ±10% limit if the flow through the emitter is laminar (Parchomchuk, 1976). On the other hand, turbulent flow emitters are not affected by viscosity changes. Discharge variation at the temperature range +5°C — +60°C was reported 23 - 53% (Parchomchuk, 1975), while Keller and Karmeli (1974) expressed a list of theoretical discharge variation based on viscosity changes in the temperature range+5°C -+60°C as 2.8% per °C. The effect of water temperature on discharge variation can be decreased by creating turbulent flow or can be neglected when turbulent flow emitters are used. The microtube and spiral passage type of emitters are affected more by water temperature variation than orifice and vortex type emitters (Peng et al., 1986; Wu and Phene, 1984; WU, 1988; Parchumchuk, 1976). In a turbulent flow regime the effect of viscosity changes on emitter flow rate is insignificant [since v= 4q/(Rend) when Re has a high value, changes of v in turbulent flow can be ignored ]. Peng et al. (1986) derived several theoretical equations which showed that temperature differences ranging from ±20°C - ±50°C along the line causes only a 1% - 2% difference in relative friction loss at the middle section of the line. They reported that in a practical situation a temperature difference ranging from 10°C - 20°C will create only a 5%-6% difference in total friction at the end of the line. Zur and Tal (1981) measured the long-path emitter discharge Chapter 2. LITEM TURE REVIEW 30 along a lateral line exposed to solar radiation. They reported that with increasing distance from lateral inlet, the emitter discharge became less dependent on pressure distribution and more sensitive to the temperature distribution along the lateral and the discharge sensitivity to temperature. They found a linear relationship between the emitter discharge and temperate distribution along the lateral. They also reported that the sensitivity of emitter flow to temperature depends on the type of emitter (the labyrinth-type, for instance), the effect of temperature variation along the lateral on emitter discharge variation can be neglected. The following equations show the effects of temperature variation on the hydraulic of microirrigation lateral lines (Peng et al., 1986): FT = a f VD vv20(0.98)7'-2% 2.24 where: FT = friction coefficient for a given water temperature a and b = constant and dependent on the Reynolds number (the range of "a" is 0.0699-0.545 and "6" is between -0.133 and -0.315) V= mean velocity (m/s) D = inside diameter of pipe (m) 2 0 6 2 V20 = kinematics viscosity (m /s) of water temperature at 20 C which is 1.0x10" m /s T - water temperature in °C. The friction coefficient for water at 20 C (F20) can be determined as follows: 2.25 Chapter 2. LITERATURE REVIEW 31 It is suggested that shading or burying lateral lines will reduce the end-to-end lateral line temperature variation. Operating the system during the night will also completely eliminate the effect of solar heating. 2.7 Clogging in the microirrigation system 2.7.1 Emitter clogging: Emitter clogging is a major problem in the microirrigation system unless correct preventive measures are taken. Field evaluation of emitter clogging is a very difficult task. Partial clogging is just as bad as complete clogging, because both reduce application uniformity and alter the hydraulics of the entire system (Wu and Lau, 1991; Nakayama and Bucks, 1991). Partial clogging of emitters can be defined as the partial constriction of flow due to a decrease in emitter cross section area. A completely clogged emitter is a special case of clogged emitter where the emitter cross sectional area is zero (Bralts et ah, 1981). Award (1982) indicated that in polyethylene pipe line, as temperature is increased, the rate of chemical clogging will also be increased. The reason for this phenomena is that of some chemical action and reaction under temperature variation of water causes carbonate sedimentation (from soluble bicarbonate) in the lateral or emitter. Different factors cause emitter clogging in a microirrigation system. Clogging will affect the hydraulics of the microirrigation system and adversely affect the rate of water application. Following the cause of emitter clogging and its impact on the hydraulics of a microirrigation system are discussed. 2.7.2 Causes of emitter clogging: Knowing the exact factor that causes emitter clogging is difficult, because the various elements in the water can interact with each other and result in more clogging problems. The cause of emitter clogging varies from location to location. According to a lot of different research,aimed at solving the clogging problems in microirrigation system, emitter clogging is still the major problem in some arid and semi arid areas. The International Commission of Irrigation and Drainage have reported that the clogging results from physical, chemical, and biological factors. Bucks et al. (1979) classified the factors in irrigation water which cause emitter clogging into Chapter 2. LITEM TURE REVIEW 32 three groups: physical (suspended solids,), chemical (dissolves chemical in water which can be precipitated), and biological (bacteria and algae). Reservoir water contains a variety of phytoplankton and zooplankton which are developed during storage according to the specific conditions prevailing in the reservoir. Nakayama and Bucks (1991) and Bucks et al. (1979) have derived a water quality classification scheme relative to its potential for a microirrigation system as shown in Table 2.3. Table 2.3 Classification of water quality relative to its potential for emitter clogging Clogging factors Hazard Rating Minor Moderate Severe PHYSICAL (mg/l) Suspended solids <50 50-100 >100 CHEMICAL (mg/l) pH <7.0 7.0-8.00 >8.00 Dissolved solids <500 500-2000 >2000 Manganese <0.1 0.1-1.50 >1.50 Total iron <0.2 0.2-1.50 >1.50 Hydrogen sulphide <0.2 0.2- 2.0 >2.00 BIOLOGICAL (No./mT) Bacterial number <10000 10000-50000 >50000 Table 2.3 can be used as a guide for identifying potential clogging hazards as well as for selecting and designing water treatment systems. Emitter clogging is also related to emitter design and to the level of filtration treatment. Boman (1995) studied the effects of orifice size on emitter clogging rate. He reported that the clogging rates ranged from 1.6-34.4%, depending on the mechanisms used to disperse the water. Emitter designs which used enclosed caps to disperse water had the highest clogging rates. He also found that an inverse relationship was evident between the number of emitters clogged and Chapter 2. LITERATURE REVIEW 33 orifice area. Ravina et al. (1997) studied the control of clogging in microirrigation when the system utilised treated wastewater effluent stored in a surface reservoir. They reported that there are differences between and among emitters of various manufacturers, as to their sensitivity to clogging. They also found when the water is pumped from a depth where the dissolved sulphide concentration is high and the water is slightly oxygenated, the growth of sulphur bacteria is stimulated and a clogging biomass is formed. The most common causes of microirrigation emitter clogging are physical particles, chemical reactions in the water and biological growths such as bacteria and algae causing scale build-up (Pitts et al., 1990). Emitter clogging is usually caused by a combination of more than one of these factors. Gilbert et al. (1979) have reported in an experiment with Colorado River water on citrus trees that five of the eight emitter systems required sand and screen (200 mesh) filtration plus chemically conditioned water to prevent emitter clogging from physical suspensions. They explained that dominant cause of emitter clogging and flow reduction was physical particles, whereas biological and chemical factors were of secondary importance. Emitter clogging is affected more by physical factors if surface water (river or channel water) is the main source for irrigation. Emitter clogging may be caused by relatively large amounts of physical particles, which usually accumulate at the inlet of the emitter, or by instantaneous sedimentation of small particles through the emitter waterway. If ground water is used in a microirrigation system, the emitter clogging is usually caused by chemical components such as calcium, magnesium, and carbonate or sulphate (Gorgly, 1986). Salt or chemicals can precipitate in the emitters even after filtration if proper precautions are not taken. Waters relatively high in multivalent cation, pH and temperature are conducive to chemical precipitation. Hills et al. (1989) studied the chemical clogging effects of high calcium content water on drip irrigation uniformity. They evaluated the water qualities with electrical conductivity of 0.59, 1.12, and 2.02 ds/m by injecting the calcium, magnesium and bicarbonate ions into the water source. They found a reduction in submain flow rate over time. Emitter flow reduction was most dramatic for the water with high salt content and least for the water with the lowest salt content. Generally, emitter clogging begins with the emitter located at the far end of the lateral (Zeier and Hills, 1987; Ravina et al, 1992). Any carelessness in operating may cause a big problem in Chapter 2. LITERATURE REVIEW 34 microirrigation systems. Nakayama et al. (1991) have reported that either the large quantities of microscopic to sand-size plastic material which originate from the sawing of the pipes during the installation, or oil and grease particles which are leaked from the booster pump or other parts of microirrigation system cause emitter clogging. Biological activities are another factor that causes emitter clogging. The biological factors of emitter clogging are filaments, slimes, and microbial depositions such as iron, sulphur, and manganese (Bucks et al., 1979). Different types of organic components ( slimy material) are classified in four groups: compounds of iron, manganese compounds, sulphur compounds, and unspecific compounds (Ford, 1976). The timing of water sampling is important, especially when there are large fluctuations in water quality during the irrigation season. The quality of water may be good or poor at different times of the year (Bucks et al., 1979). The effects of fertilizer or other chemicals on the irrigation water may create clogging problems but can be tested by the operator by treating the water with the additive (Gilbert and Ford, 1986). Bucks et al. (1979) and Nakayama and Bucks (1991) suggested that chemical and physical analyses of the irrigation water should be made before a new microirrigation system is installed. If different water qualities are to be mixed, this mixture may require further evaluation as chemical and physical interactions may occur that can drastically change the quality of the resultant water. 2.7.3 Emitter clogging and hydraulics: Emitter clogging will adversely affect the rate of water application and uniformity of water distribution, and will increase operating costs (Bucks and Nakayama, 1978). Bralts et al. (1982) found that due to emitter clogging, the total flow of lateral line will be decreased and thereby reduce the total friction in the lateral line. Reduction in friction along the lateral line results in a slightly higher pressure, or more flow from non-clogged emitter through the lateral. Regarding these hydraulic changes, a 20% rate of emitter clogging will not necessary correspond to a 20 percent reduction in lateral flow, but flow reduction should be less than 20 percent. The term "coefficient of variation" can be used to relate the effects of emitter clogging on the statistical uniformity and emitter clogging (Bralts et al., 1981). A statistical term called "emitter discharge coefficient of variation including emitter plugging" has been used by ASAE EP458 (1997) to calculate the effect of emitter plugging on the coefficient of variation. Chapter 2. LITERATURE REVIEW 35 Several methods have been used for describing the uniformity of water application in microirrigation, but as yet, none of these methods has isolated the effect of clogging (Nakayama and Bucks, 1981). Bralts et al. (1982) developed a theoretical equation to evaluate the effects of emitter clogging on drip irrigation for both single and dual chamber lateral line hydraulics, based on the assumption that the clogging is uniformly distributed along the lateral. For example, they reported that the percentage of total flow under 10% clogging situation can be calculated as: P0.i = q0Vqo = [0.9 nC (0.874 h0)05]/[nC (0.85 ho)05] = 0.913, where P09 is the percentage of total flow for 10% clogging. Their results indicated that 10% clogging will result in 91.3% total flow or only an 8.7% reduction of total flow. They made similar calculations for all other percentages of clogging and they showed the results of the calculations by several curves. They indicated that the relationship between clogging and flow rate was very close to a direct proportion for a single chamber lateral, whereas for dual chamber lateral lines, it was dependent on the design ratio of inner to outer orifices. The dual chamber is usually designed to have a ratio equal to 4 or 5 to 1. They claimed that when the inner and outer orifice are of equal size, the percentage of total flow is affected more by inner orifice clogging than by outer orifice. With different sizes of inner and outer orifices, the larger size of the outer orifice results in less change in total flow due to clogging. Emitter manufacturers attempt to meet the ideal characteristics such as accuracy, cost and feasibility to manufacture the emitter, but the characteristics are, to a certain degree, contradictory. A lower emitter flow rate requires smaller flow passages which clog easily. The benefits of pulse irrigation have been reported by Jackson and Kay (1987). They suggested that if pulse irrigation is used, emitter size can be increased, thus reducing clogging without diverse effects on soil water wetting patterns. On the other hand, a major factor limiting high-pulse discharge is surface water ponding. When the flow rate exceeds the local soil infiltration rate, ponding will spread rapidly and result in run-off losses and soil erosion. Hills and Ebaby (1990) studied the characteristics of six different types of self-cleaning emitters under clear water, but with organic or inorganic impurity conditions. They found that all emitters were relatively successful at self-cleaning when the water's impurities were inorganic. However, organic impurities resulted in gradual clogging through microbial growth (bacterial slimes) within the emitters. Chapter 2. LITERATURE REVIEW 36 Nakayama and Bucks (1981) developed a simulation model to evaluate the uniformity and the average water discharge rate of a microirrigation system with different degrees of emitter clogging. They introduced various combinations of clogging into the model, randomly selected the clogged emitter, and did not take into account partial clogging. They also reported that the simulation model did not consider the practical hydraulic implications of clogging. In a general way, the emitter clogging can lead to over-irrigation since the remaining, normally functioning emitters would be subjected to an increase in line pressure. Wu (1993) reported that the clogging can be decreased by reducing the emitter spacing when the spatial uniformity is under consideration. Bralts et al. (1982) predicted emitter clogging rates based on the lateral flow rate change. These predictions were based on the assumption that the clogging is uniformly distributed along the lateral line. Wu et al. (1991), confirmed that clogging is not based on a random process in which it may be distributed uniformly along the lateral line. Rather, more clogging is concentrated in the downstream quarters. 2.7.4 Prevention and reducing clogging: The prevention of clogging in drip systems begins with the proper design. Recommendations and guidelines for preventive maintenance, including water filtration, pipeline flushing, chemical treatment, and field inspection, have been presented by Bucks et al. (1979). In addition, proper procedures for the flushing and field inspection of a microirrigation system are essential. Gilbert et al. (1980) have reported that chemically conditioning the water with continuous acid provided further benefit to control emitter clogging. An experiment in Florida indicated that chlorinating successfully controls iron slime when iron concentrations were less than 3.5 mg/l and the pH below 6.5 (Nakayama and Bucks, 1986). It is important to keep debris from entering pipes and emitters before, during and after installation. Nakayama (1986) suggested that the municipal water which has been treated to remove suspended particles and bacteria is the ideal water for use in a microirrigation system. However, municipal water may be too expensive or not readily available for irrigation puprposes. An alternative source of water suitable for farm operation is water treated onsite to an acceptable level for the proper performance of microirrigation system. It is very rare that irrigation water does not need some Chapter 2. LITEM TURE REVIEW 37 sort of Alteration treatment. If the filter is utilized in a microirrigation system, the high quality of water may be maintained to prevent emitter clogging. However, complete removal of the suspended materials from the irrigation water for use in a microirrigation system is impractical (Nakayama, 1986; Zeier and Hills, 1987). Particles present in the irrigation water range in size from the submicrometer virus to the larger sand-size. The size of filter varies and depends on the water source and quality of water (Bruce, 1985). However, if the filters are the first line of defence in preventing clogging, they should be monitored and cleaned regularly. The microirrigation researchers and equipment manufacturers have chosen two approaches in order to reduce the emitter clogging. Emitter device developing is the first approach, which may require less or minimum maintenance (Wilson, 1972; Solomon, 1976,1979). The second approach is to focus attention on improving the quality of water before it reaches the emitters (McElhoe and Hilton 1974; Bucks et al, 1976). Many inventors and manufactures sold different types of emitter such as non-clogging or self-cleaning emitters which were supposed to solve the problem of emitter clogging but unfortunately did not adequately do so (Nakayama et al, 1991). The most important maintenance for microirrigation systems is preventative: there should be a regular routine of flushing all microirrigation lines whether they need it or not. The more frequent the flushing of the microirrigation system lines, the longer the system will provide trouble-free service. Most clogging factors can be found in open reservoirs and storage of waste-water effluent for use in microirrigation systems (Bucks et al., 1979; Gilbert et al, 1981; Nakayama and Bucks, 1991). Since the emitter clogging is caused by chemical, physical, and biological contaminants, filtration systems should also be flushed regularly to prevent orifice clogging and an excessive pressure loss through the filters. Jackson and Kay (1987) described the result of their laboratory study which showed the effects of pulsing flows on the reduction of clogging. They reported that an alternative approach to the clogging problem is to increase the emitters' waterway size. However, this may increase the emitter discharge, change the pattern of wetting in the soil, and cause surface water ponding, Chapter 2. LITEM TURE REVIEW 38 run-off and soil erosion. There is evidence to suggest, however, that an established soil wetting pattern can be maintained at the higher discharge rate if the flow is pulsed. Therefore, it is possible to increase the emitter size in order to reduce the clogging tendency. Emitter discharge variability may be periodically tested to identify the emitter clogging. The degree of emitter clogging can be used as an indirect measure for assessing the effectiveness of a microirrigation filtration system, and it can also be used as a measure of the effectiveness of preventative practices such as chemical water treatment. ASAE EP458 (1997) reported that in order to preventing emitter clogging, specific and detailed studies of the water quality and application of fertilizers or other chemicals should also precede the design. Neglecting to analyse the water and provide adequate treatments could result in the failure of the microirrigation system to function properly. 2.8 Water treatment and chlorination: Water quality is critical to microirrigation. Proper water treatment is the main approach to controling emitter clogging, and the type of treatment is based on the quality of irrigation water (Nakayama and Bucks, 1991). Presently, the major source for microirrigation is the water diverted from other traditional irrigation usage, such as waste water from cities and industries. In general, water with low amounts of suspended inorganic and organic particulate materials, dissolved chemical constituents (i.e. calcium carbonate, iron and manganese), and microbes that cause slime development, appears to create the least problems (Nakayama et al., 1987). Bruce (1985) reported that organic matter such as algae is not easily removed from the screen filter mesh because screen filters are used in systems where low amounts of organic matter are present in the water. For surface water supplies, total suspended solids may vary from 1 mg/l to 75 mg/l or more (Nakayama et al., 1978). Ayers (1975, 1977) suggested the four general problem areas of salinity, toxicity, permeability, and miscellaneous to evaluate the quality of water. Quality is difficult to evaluate except in terms related to specific use. Municipal water that is chlorinated for controlling disease-causing bacteria has the least problems, but treatment of agricultural water to this quality can be impractical and uneconomical (Bucks et al., 1979). Irrigation water with a high concentration of sulphide can Chapter 2. LITERATURE REVIEW 39 cause iron precipitation. The dissolved sulphide anion can also react with active chlorine when the water is chlorinated, and in this case, the effectiveness of chlorination is reduced. Consequently, the chlorination requirement of irrigation water including sulphide is higher than that of the typical non-sulphide irrigation water. When the soluble iron in irrigation water is high (>0.4 mg/l), the chlorination can cause large amounts of iron to precipitate. In this case, the chlorine injection should be made at a sufficient distance upstream from the filtration system to allow sufficient time for mixing and chemical reaction to take place before the iron flocculent reaches the filter to removal (Nakayama and Bucks, 1991). Gamble (1985) reported that adding hypochlorite into the wells with high soluble iron content can control the iron clogging in a microirrigation system. Bucks et al. (1979) suggested that when the pH of irrigation water is above 7.5 and water hardness (calcium or magnesium) is also high, the calcium or magnesium carbonate can be precipitated in the filter, tubing, or emitter. Adding acid to irrigation water will lower the pH and reduce chemical precipitation. They reported that the clogged emitters can be reclaimed by treating the system for about 24 hours with high chlorine and acid (100 mg/l of CI at a pH of 2). They found that by this treatment, the partially clogged emitter flow rates can be increased from 50% to approximately 90%—95% of design, and continuous 1 mg/l chlorine at a pH of 7 helped to maintain the system operation for several years. Gilbert et al. (1981) reported that in an experiment with Colorado River water on citrus trees under a microirrigation system, the emitter performance was best in a treatment with continuous acid. They claimed that the most efficient treatment for prevention of emitter clogging is continuous acid for pH control of carbonate formation and precipitation coupled with sand and screen filtration. Table 2.3 shows the water quality classification scheme relative to its potential for microirrigation system. Bucks et al. (1979) and Nakayama and Bucks (1991) suggested that chemical and physical analyses of the irrigation water should be made before a new microirrigation system is installed. They found that when different water qualities are mixed, this mixture may require further evaluation as chemical and physical interactions may occur that can drastically change the quality of the resultant water. In general, in a microirrigation system it is possible to use a lower quality of water which is generally considered unacceptable in a conventional irrigation method (Seifert et al., 1975). Bernstein and Francois (1973), in a study of comparison of different irrigation methods, used saline water with a salt concentration of 450 mg/l and 2450 mg/l (high salinity Chapter 2. LITERATURE REVIEW 40 water) in a trickle irrigation system. Similar work has been done by Singh et al. (1978) in which saline water at 3000 /jmhos/cm (^1920 mg/l) and 10000 fjmhos/cm («6400 mgA) was used for drip irrigation. 2.9 Chemigation and fertigation: Chemigation involves injecting a water soluble fertilizer, herbicide, insecticide, fungicide, or nematicide into the microirrigation system. Fertigation is the process of dissolving soluble fertilizer into the irrigation water and applying the solution to the microirrigation system. In arid and semi-arid regions, fertigation is necessary to supply sufficient fertilizer, especially nitrogen for fields irrigated with a microirrigation system (Keller and Bliesner, 1990). The criteria for fertilizer application in microirrigation have been developed by Rolston et al. (1986). They consider the solubility of the fertilizer and the interactions of the fertilizer with the dissolved components in the irrigation water. Many different liquid, liquid suspension, and dry fertilizer materials are applied to the irrigation water through the microirrigation system. There is a wide variety of soluble dry fertilizers containing N, P, and K for dissolution in the irrigation water through the system. There are some chemical problems related to the injection of various fertilizers into the irrigation water. For instance, ammonia injection causes a rise in pH and potential precipitation of both soluble calcium and magnesium which may result in coating the inside of the lateral pipe and, consequently, emitter clogging (Keller and Bliesner, 1990). Several kinds of ammonium phosphates are commonly used for both nitrogen and phosphorus in fertilizer (Pair et al, 1983). Ammonium sulphate (21-0-0), ammonium nitrate (34-0-0), ammonium phosphate sulphate (16-20-0), monoammonium phosphate (11-48-0), and diammonium phosphate (16-46-0) are widely used fertilizers (Van Der Gulik, 1987; Keller and Karmeli, 1975; Keller and Bliesner, 1990). The water quality must be considered before deciding to inject phosphorus fertilizer into the system. Phosphorus will be precipitated as dicalcium phosphorus in the pipe line and emitter flow passage if the irrigation water contains an appreciable amount of calcium. Emitter clogging can be overcome by injecting the phosphoric acid with an injection of either sulphuric or hydrochloric acid. The rate of injection Chapter 2. LITERATURE REVIEW 41 of liquid fertilizer into the irrigation water in the microirrigation system can be computed as follows (Keller and Bliesner, 1990): ac=-^- 2.26 C.tr.T where: qc = rate of injection of liquid fertilizer solution into the system in l/h Fr = quantity of nutrient to be applied (fertilizer application rate) per each irrigation cycle in kg/ha Ta = set time or irrigation application time in h A = irrigated area in ha tr = ratio between set time and fertilizing time C = concentration of actual nutrients in the liquid fertilizer kg/l. 2.10 Microirrigation uniformity concepts: Uniformity is a key factor in the evaluation of irrigation. It is nearly impossible for any irrigation system to supply the same amount of water to all plants within a field. A variety of terms have been developed to describe the irrigation uniformity. The uniformity of a microirrigation system is a quantitative measurement of the distribution of emitter discharge along a lateral line. Considerable work has been done regarding the uniformity in a microirrigation system. Karmeli and Keller (1974) described the emission uniformity based on the average low rate of the lowest quarter of all the emitter discharge. Solomon (1985) developed a simulation model for the study of trickle irrigation uniformity. Nakayama and Bucks (1981) developed a simulation model to evaluate the uniformity and the average water discharge rate of a trickle system with different degrees of clogging. Bralts et al. (1981) recommended that when emitter clogging is considered in a microirrigation system, the statistical uniformity coefficient is useful to determine the design of the emitter flow uniformity along the lateral lines. Chapter 2. LITERATURE REVIEW 42 In any irrigation system, the degree of uniformity is a consequence of the irrigation system itself and the soil variability. In a microirrigation system the variation is primarily due to uneven applications (Warrik, 1983). The factors that influence the uniformity of application from microirrigation systems include emitter factors and hydraulic system factors (Solomon, 1985). In microirrigation systems where applied water passes almost directly from the emitters into the soil, the uniformity of application depends entirely on the uniformity of the emitter flow throughout the system (On-Farm ICID, 1978). The emitter flow of a microirrigation system can be considered to have a normal distribution when it has a high uniformity (Wu and Gitlin, 1983; Bralts and Kesner, 1983; Solomon, 1985; Wu, 1988). Several uniformity definitions have been proposed and used to describe the uniformity of the system. A microirrigation system is designed based on the system uniformity and spatial uniformity. System uniformity shows the uniformity of emitter discharges with respect to the water pressure in the system, whereas spatial uniformity shows the amount of water application in the field. In general practice, emitter coefficient of variation (CV) is used to show the system uniformity and Christiansen coefficient of uniformity (CU) can be used to show the spatial uniformity (Wu, 1997). The CU has been most extensively used not only in microirrigation but also in the evaluation of sprinkler irrigation. Nakayama et al. (1979) reported the uniformity based on modification of Christiansen's definition used for sprinkler irrigation. Microirrigation does not apply water to the entire field surface. Reducing the wetting surface area minimizes soil evaporation. Soil surface run-off and drainage losses can be reduced under this condition. It is often assumed that all water applied from one or from a group of emitters is available to the corresponding plant (Bos and Nugteren, 1990). Microirrigation is typically designed with an application rate less than the infiltration rate, which can prevent run-off. Amir and Dag (1992) observed different uniformities of wetting pattern, width and depth of application rates by different types of emitters. Their experience indicated that a high application rate of water increases the uniformity of the wetting pattern and its width, and decreases the depth. On the other hand a high application rate, when it exceeds the soil water intake rate, will cause water ponding on the soil surface and, consequently, water run-off. Distribution uniformity and application efficiencies are also the two important terms which are Chapter 2. LITEM TURE REVIEW 43 considered in microirrigation system design (Wu and Gitlin, 1983; Bucks and Mayers, 1973; Nakayama and Bucks, 1986; Anoyji and Wu, 1994). The definition of distribution uniformity is based on how uniformly irrigation water can be distributed on irrigated land, whereas how well irrigation water is applied by microirrigation to the field can be determined by application efficiency. In microirrigation, the moisture distribution depends on the emitter spacing, water application rate, soil permeability, soil surface, evaporation rate, and crop distribution (Obbink, 1977 ). In many cases, crop yield may be directly related to the uniformity with which water is applied. Solomon (1985) describes the possible relationships between yields and different uniformity measures. In general, yield response to over-irrigation and under-irrigation is not linear (Clemmens, 1987). Linear relationship between cumulative evapotranspiration and yield have been reported (Sammis, 1981; Wu, 1988). Slight amounts of over- or under-irrigation have no significant impact on yields; however, large deficit or over-applications of water have a significant effect on crop yields. Application uniformity depends on the uniformity of emitter flow, which is a function of emitter characteristics including manufacturer's variation, temperature effect, emitter clogging, and the hydraulic design of the microirrigation system. Sammis and Wu (1985) studied the effect of the design and management parameters on cotton yield by applying different daily drip irrigation amounts, different application uniformity, and different sensitivity to moisture stress. In a microirrigation system the uniformity of dissolved fertilizer or chemicals when injected through the system is also important. The coefficient of variation can be used to assess the uniformity of water and fertilizer application through a microirrigation system. Hahn and Bralts (1983) studied the significance of differences in uniformity of water application and uniformity of fertilizer application in a trickle irrigation system. They also determined the relationship of injector type to the uniformity of fertilizer application in the trickle system. Any non-uniformity in emitter flow will require an extra application of water to compensate for the non-uniform distribution. Different methods have been used to describe the water application uniformity in the microirrigation system. Non-uniformity reduces application efficiency and may increase the deep percolation in areas which are over-irrigated. Solomon Chapter 2. LITERATURE REVIEW 44 and Keller (1978) reported that the emitter flow variations can significantly decrease the uniformity. Nakayama and Bucks (1981) have also found significant decreases in uniformity when only 1-5% of the emitters were completely clogged, even with 2-8 emitters per plant. Wu (1993) indicated that the emitter spacing is also a significant factor affecting spatial uniformity: a drop of 30%-40% uniformity coefficient was reported for an emitter spacing varying from 0.2—0.9 of the diameter of the wetting pattern. Wu (1997) suggested four commonly used parameters for evaluating microirrigation system uniformity, which are: Christiansen coefficient of variation (CU), emitter coefficient of variation CV, statistical uniformity coefficient (UCS), and emitter flow variation (qvar)-2.11 microirrigation system evaluation: Microirrigation design needs to be checked after installation and evaluated at least once a year (Bucks et al, 1982). The purposes of evaluating any irrigation system have been stated by Merriam etal. (1980) as: 1- to obtain information that will assist the engineers in designing the other system 2- to determine how effectively the irrigation system can be operated and if it can be improved 3- to determine the system efficiency as it is being used 4- to obtain information to enable comparison of various methods, systems, and operating procedures as a basis for economic decisions. The methods for evaluating the microirrigation system, the emitter flow uniformity, application efficiency, emitter flow variation caused by hydraulics, coefficient of variations, statistical uniformity coefficient, and hydraulic variations are discussed below. 2.11.1 Emitter flow uniformity and application efficiency: In a microirrigation system, the emitter flow uniformity depends on the variation of emitter flow rate along the lateral lines. The emitter flow variation is mainly affected by the manufacturing variation, hydraulic design, temperature and emitter clogging. If the effect of temperature on emitter discharge variation can be assumed to be negligible, the emitter flow variation will be Chapter 2. LITERATURE REVIEW 45 caused by clogging, manufacturing and hydraulic variation. The Christiansen coefficient of uniformity can be used to estimate the spatial uniformity in a microirrigation system (Yitaew and Warrik, 1980,1986; Nakayama and Bucks, 1979; Wu and Gitlin, 1974,1983; Keller and Bliesner,1990; WU, 1997): n = number of emitters qave or q = the mean emitter flow A q = mean deviation of the emitter flow from the mean value. According to equation 2.27 the uniformity of emitter flow rate will have an impact on the coefficient of uniformity (CU). In a microirrigation system, CU greater than 80-90% are considered; however, Wu (1974) has recommended CU^ 98% in a microirrigation system. Keller and Karmeli (1974, 1975) were the first to define an empirical design emission uniformity as a ratio of the minimum emitter discharge to the average discharge expressed as a percentage. They expressed the equations to determine the emission uniformity from design data or field test data. The design emission uniformity (EU) is the manufacturers discharge ratio, which is the average discharge of the low 1/4 to the average discharge of a test sample of the emitters operated at a reference pressure head. The average of the lowest 1/4 was selected as a practical value for the minimum discharge, as recommended by the Soil Conservation Service (1964) for the field evaluation of an irrigation system. Kimura (1987) reported that the term of low quarter is a consistent approach, since a single plugged emitter in a field would otherwise give an EU' of 0%. EU can be determined as (Keller and Karmeli, 2.27 where: CU= Christiansen Coefficient of Uniformity I qrqave I = absolute deviation of emitter flow from the mean 1975): Chapter 2. LITERATURE REVIEW 46 £(7 = 100 1- l.27v) q m 2.28 4e ) q, a where: v = manufacturer's coefficient of variation e = 1.0 or the number of emitter per plant qm = minimum emitter discharge computed with the minimum pressure using equation 2.1 in qa = average emitter discharge of all the emitters under consideration (l/h). There are several reasons for the importance of the estimation of field uniformity in a microirrigation system. From the engineer's standpoint, field uniformity is important in confirming whether a design was satisfactory; from the purchase's perspective in confirming product performance; and from the irrigator's point of view, in considering irrigation application efficiency and schedules (Bralts et al., 1987). The field test emission uniformity (EU') is expressed as a percentage of the average emitter flow rates from the lowest 1/4 of the field data to the average emitter flow rates of all the data. EU' evaluates the emission uniformity from all the emission points within the microirrigation system and is determined as follows (Keller and Karmeli, 1974,1975; Hill and Keller,1980; Keller and Bliesner, 1990): (l/h) £<7'=100 2.29 where EU' = field emission uniformity q„ = average of the lowest quarter of the emission flow rate from the field data (l/h) qa = average of all the emitters flow rate (l/h) Chapter 2. LITERATURE REVIEW 47 Keller and Karmeli (1974) suggested that the desirable emission uniformity should be 94% or more and should never be less than 90%. Bralts et al. (1987) found that the primary disadvantage of the field emission uniformity is its non-statistical basis, which makes a further breakdown of the components of emitter flow variation impossible. Distribution uniformity (DU) is the another term of uniformity which can be used in a microirrigation system. DU is a useful indicator of distribution problems (Clemmens and Solomon, 1997). A low DU indicates that excessive deep percolation losses will occur if adequate irrigation is supplied to all areas (On-Farm ICID, 1978; Burt et al., 1997). For lower quarter distribution uniformity, DU can be determined as (Keller and karmeli, 1974; Warrick, 1983; Hathoot <tfa/., 1993): 4 DU = - 2.30 nq Keller and Bliesner (1990) presented an empirical equation which shows the relationship between CU and DU as: DU = 100-1.59(100- CU) 2.31 where: DU= distribution uniformity qt = emitter discharge q = mean emitter dischage n = number of emitter. Chapter 2. LITERATURE REVIEW 48 Hill and Keller (1980) reported that since the EU' definition given by equation 2.29 is identical to the definition of distribution uniformity DU, it can be related to the coefficient of uniformity CU by: EU'=DU = \.6CU- 60 2.32 Application efficiency in a microirrigation system is related to pressure variation. Van Der Gulik (1987) and Keller and Bliesner (1990) reported an empirical equation for the efficiency of application as: Ea = \00\ f a \ (JJ \ "min | 100 n H„vp) 2.33 where: qmin = minimum emitter flow rate (l/h) computed from minimum pressure in the system qave= average emitter flow rate (l/h) for the average pressure Hmin = minimum pressure (m) Have = average pressure (m) x - emitter flow exponent. 2.11.2 Emitter flow variation caused by hydraulics: The emitter flow variation along a lateral line caused by hydraulics can be determined by emitter flow profiles. In uniform slope situations, the emitter profile is a smooth curve. However, all emitter flow along the lateral can be determined by equation 2.19, and the emitter flow variation can then be expressed by (Gillespi et al., 1979; Bucks et al., 1982; Wu andYue, 1993; Wu, 1997): Chapter 2. LITERATURE REVIEW 49 where qvar = emitter flow variation qmax and qmin are the maximum and minimum emitter discharge along the lateral respectively. Wu and Gitlin (1974,1975) recommended the general criteria for qvar values which are: 10% or less, desirable; 10 to 20%, acceptable; and greater than 20%, not acceptable. A major limitation of this procedure is that the qvar does not include the factors of emitter flow variation due to manufacturing or clogging which could be significant in the microirrigation lateral uniformity. Assuming the same expression, the pressure variation along the lateral can be determined as: h = ——— 2.35 in which hvar is the pressure variation along the lateral, hmax and hmin are the maximum and minimum pressure along the lateral respectively. With respect to equations 2.1, 2.34, and 2.35 the relationship between qvar and hvar can be expressed as: a =\-(\-h V 2.36 ^ var \ var / The relationship between hvar and qvar is dependent upon the type of emitter (Keller and Karmeli, 1974; Karmeli and Kellrer, 1975). Both qvar and hvar are used for hydraulic design only (WU and Yue, 1993; Wu, 1997). 2.11.3 Coefficient of variations: In addition to the emitter manufacturer's coefficient of variation (equation 2.20) which is used to describe the variation in emitter flow rate for a sample of new emitters, there are several statistical terms of coefficient of variation reported by researchers that can be used for evaluating a microirrigation system, as discussed below. Chapter 2. LITERATURE REVIEW 50 2.11.3.1 Emitter flow coefficient of variation and statistical uniformity coefficient: The emitter flow coefficient of variation Vqs is described as the standard deviation of emitter discharge Sq, divided by the mean emitter discharge q (ASAE, 1990; Bralts et al., 1987,1993). The emitter coefficient of variation can then be used to calculate the statistical uniformity Us. Bralts et al. (1981 a,b) recommended the use of the statistical uniformity coefficient Us for a microirrigation lateral line. Sammis and Wu (1985) reported that the application uniformity in a microirrigation system depends on hydraulic flow variation from the irrigation system. The hydraulic flow variation results from two major components: hydraulic pressure variation (the hydraulic components include the effect on flow of complete or partial emitter clogging) and emitter manufacturer's variation. Application uniformity of a microirrigation system can be quantified by the statistical uniformity coefficient, Us. Therefore, by using the statistical uniformity coefficient, most of the various factors such as lateral line friction, elevation differences, emitter manufacturer's variation, and emitter clogging are included in the final uniformity estimation. Emitter flow coefficient of variation VqS and its relationship with Us can be expressed as follows: V = qs (sq\ 2.37 */, = 100(1-^) = 100 V V qj 2.38 q = mean emitter dischage Us = statistical uniformity coefficient. One of the advantages of determining the statistical uniformity is to get information which assists in recognizing problem areas such as emitter performance and hydraulic variation. A graphical technique for field determination of statistical uniformity based on the time needed to fill a container (100 or 200 ml) rather than on the emitter flow rate was also presented by Chapter 2. LITERATURE REVIEW 51 Bralts (1986). The general criteria suggested by Bralts (1986) for an acceptable Us in a microirrigation system are given in Table 2.4 Table 2.4 General criteria for an acceptable statistical uniformity (after Bralts, 1986) Rating 90% or greater excellent 80% - 90% very good 70% - 80% fair 60% - 70% poor < 60% unacceptable An acceptable Us due to hydraulics depends on all of the various factors which affect uniformity. It is also suggested that in a microirrigation system, the value of Us due to hydraulics of 90% or better is recommended. Any system having a Us less than 90% requires a design change or replacement of existing emitters with the pressure-compensating type. Where the value of Us is less than 85% due to emitter performance, cleaning, replacing of clogged emitters, or placing an additional emitter per plant will improve the statistical uniformity. A statistical uniformity of 80% is the minimum acceptable value when fertilizer injection is used. 2.11.3.2 Hydraulic variation: Previous work shows that many researchers have used the term "hydraulic variation" to describe the variation in hydraulic pressures found along a microirrigation lateral line or submain. The statistical term "coefficient of variation due to hydraulics", Vhs, is used to quantify the variation in emitter pressures along a lateral line. However, from the engineering point of view, the variation of pressure due to hydraulics can be determined with the energy gradient line using equations 2.17, and 2.18 (Wu and Gitlin, 1983; Bralts et al., 1987). The Chapter 2. LITERATURE REVIEW 52 coefficient of variation due to hydraulics, Vhs, can be determined as follows (WU and Gitlin, 1983; Bralts etal, 1987; ASAE EP458, 1997): where: Vhs= coefficient of variation due to hydraulics Sh = standard deviation of the hydraulic pressures St, = variance of the hydraulic pressures Have= mean hydraulic pressure. If the emitter clogging and manufacturer's coefficient of variation are held constant, acocording to equation 2.39, the emitter flow variation due to hydraulics can be related to the hydraulic coefficient of variation as: where: Vqh = emitter flow coefficient of variation due to hydraulics x = emitter discharge exponent Vhs = coefficient of variation due to hydraulics. Using the value of Vqh, the emitter statistical uniformity due to hydraulics USh, can be determined as (ASAE EP458, 1997): 2.39 2.40 2.41 Chapter 2. LITERATURE REVIEW 53 The hydraulic and manufacturer's variations are the two most important factors affecting the uniformity of emitter flow along the lateral when the emitters are initially installed in a microirrigation system. However, other factors such as emitter wear and partial clogging will affect the performance of the emitters in the field over time. Emitter performance coefficient of variation (Vpf) is a statistical term and is a measure of emitter discharge variability due to emitter manufacturer's variation, hydraulic variation, water temperature, emitter wear, and emitter clogging. Emitter performance coefficient of variation, Vp/, can be determined as (ASAE EP458, 1997; Bralts et al., 1987; Bralts and Edwards, 1986): 2.42 where: Vp/= emitter performance coefficient of variation Vqs = emitter discharge coefficient of variation Vqh = emitter discharge coefficient of variation due to hydraulics. The criteria for emitter performance coefficient of variation recommended by ASAE EP458 (1997) are shown in Table 2.5. It is also recommended if the Vpf value is excessively high (greater than 0.2), emitter cleaning or replacement will improve the emitter performance coefficient of variation. Table 2.5 The criteria for the emitter performance coefficient of variation recommended by ASAE EP458 (1997) VPf Rating <0.05 excellent 0.05-0.1 very good 0.1-0.15 fair 0.15-0.2 poor >0.2 unacceptable Chapter 2. LITERATURE REVIEW 54 Another statistical term called emitter discharge coefficient of variation including emitter plugging (Vqp) was also reported by ASAE EP458 (1997). Vqp can be determined as: where: Vqp = emitter discharge coefficient of variation including emitter plugging C = proportion (decimal) of emitter completely plugged 1-C = proportional (decimal) of emitters openly flowing. The impact of different degree of partially clogged emitters along the lateral on Vqp is not considered in this equation. 2.12 Emitter flow variation and crop response: A microirrigation system is often operated to satisfy the evapotranspiration (ET) requirement of the crop. In any irrigation operation, the application uniformity, depth of application, and crop sensitivity to moisture stress are among the factors affecting the average yield over the irrigated field. The average depth of application water in a microirrigation system is normally determined from the evapotranspiration requirements (ETm) of the crop under non-moisture stress conditions. In those parts of the field which are under moisture stress condition, the evapotranspiration decreases, resulting in an average evapotranspiration over the field (ET) of less than ETm (Sammis and WU, 1985). ETm can be determined from reference evapotranspiration (ET0) and an empirically derived crop coefficient (kc). Reference evapotranspiration can be estimated from daily meteorological data using Penman equation or any other methods given in Jensen et al. (1990). The relationship between ETm and ETQ can be determined as : 2.43 ET = kcxETQ 2.44 m Chapter 2. LITEM TURE REVIEW 55 Sammis and Wu (1985) reported that in cases where part of the field is fully irrigated, the ET can be determined as ET = ETm = kc x ETQ When a portion of the field is under deficit irrigation, then ETd>Id, where Id is the average depth of irrigation in the deficit area, and ETd is the average evapotranspiration in the deficit area. They also found the relationships between mean evapotranspiration, ETave, non-moisture stress evapotranspiration, ETm, and the fraction of area under fully and deficit irrigation as follows: ETave=ETma + ETd(l-a) 2.45 f EL.,.,} (l_ETd^ ave V1' ET) v ET) (1-a) 2.46 where: a = a fraction of the area receiving a full irrigation I-a = fraction of the area under deficit irrigation l-fETav/ETm) = mean relative deficit evapotranspiration in the total area. All of these parameters are the functions of application uniformity and the mean depth of application. In a microirrigation system, the application uniformity depends on hydraulic flow variation from the irrigation system. The total emitter coefficient of variation (VT) resulting from manufacturer's variation (CV) and the hydraulic design (Vf,s) can be determined as (Bralts et al., 1981): V,. = JVHS+CV 2.47 Sammis and Wu (1985) reported that for given values of VT, a dimensionless plot of EtJ I can be made. They found that when the mean irrigation depth ( 7) is equal to the daily ETm, 50% of the field is under deficit irrigation. As the /is increased relative to the ETm< or when Chapter 2. LITEM TURE REVIEW 56 ETm/ I <7, a smaller percentage of the area is deficit irrigated and ETave / ETm approaches 1 (« Etave = ETm). The mean relative deficit evapotranspiration over the total area (\-ETave/ETm) can be determined as (Wu and Gitlin, 1983; Sammis and Wu, 1985, Wu, 1995): x_ETave ET ^ C — 2.48 G where: C is the total deficit G = ratio of the required irrigation depth / to satisfy ETm to the mean of irrigation depth /. Walker (1979) presented an analysis of G for different VT and percentage of the area under deficit irrigation (PD) as: C _ 0.0032^233 2 49 G G Walker's analysis did not equate the C/G to l-iETayJETm) because G was assumed to be equal Xo I / I. Based on a table for a normal distribution presented by Hart and Reynolds, (1965) the mean relative deficit evaporation over the total area [l-(ETaVe/ET^)] can be computed for different 7/ ETm . The results are adapted and presented in Table 2.6 for different Vj. Table 2.6 shows, for instance, that when the irrigation amount is applied at the ETm rate ( / / ETm =1), an increase of VT by 10% causes a decrease in relative evapotranspiration of 4%. It was also reported when the Vr is small (VT < 10%) the relative deficit evapotranspiration is less than 4% for an irrigation amount equal to or greater than ETm rate ( F/ETm>l). Chapter 2. LITERATURE REVIEW 57 Table 2.6 Total emitter coefficient of variation (Vj) and deficit evapotranspiration 1-{ETave/ET„) when I/ETm is 1 and 50% of area is fully irrigated (adopted from Sammis and Wu, 1985). VT I/ETm Percent fully 1-iETaJETn) (%) irrigated (%) (%) 0 1 50 0 10 1 50 4 20 1 50 8 30 1 50 12 40 1 50 16 50 1 50 20 Sammis and Wu (1985) developed an equation to determine the reduction in yield caused by reduction in relative evapotranspiration as follows: ( Y \ j ave v or: Y ) max ' = K. l~-n YET V ,=l 2.50 Y =Y ave max 1-*,+ Kv-YET 2.51 where: Yave = average yield from the field Ymax = maximum yield under non-moisture stress conditions Chapter 2. LITERATURE REVIEW 58 Ky = yield response factor (Ky = 0.85 for cotton, consequently a 4% reduction in relative deficit evapotranspiration is equivalent to a 3.4% reduction in cotton yield) n = number of days in the growing season. When EET> SETm(i)i then Yave=Ymax, otherwise equation 2.51 can be used to estimate the average of the yield. Chapter 3. SIMULATION COMPUTER MODEL 59 Chapter 3 3. SIMULATION COMPUTER MODEL 3.1 Microirrigation simulation computer model: Many computer simulation models for designing, management and evaluation of microirrigation system were developed by researchers. For example, Howell and Hiler (1972) developed a computer solution method for determining lateral lengths for selected uniformities subject to emitter spacing and downstream pressure. Wu (1975) used the dynamic programming optimization to determine the optimal energy gradient lines to design the main line of drip irrigation. Bralts et al. (1993); Bralts and Segerlind (1985); Kang and Nishiyama (1996); and Kang et al. (1996) developed a finite element computer model to analyze the hydraulics of microirrigation laterals and submains. A simple computerized design method was used by Feng and Wu (1990) for a lateral and submain unit design. Most of the researchers adapted distinct computational approaches to deal with pipeline hydraulics. Feng (1989) used equations derived from the concept of energy gradient line to compute head loss. Anoyji and Wu (1987) used a statistical approach for drip lateral design. Gonzal and Hills (1986) developed a computer program using a step-by-step procedure based on the Darcy-Weisbach equation for the design of trickle irrigation laterals on non-uniform slopes. In most of the developed computer programs mentioned above, the average emitter flow rates along the lateral are assumed to be constant. Therefore, the discharge at the lateral inlet is simply determined by multiplying the number of emitters along the lateral by its constant average flow rate. In practice, the emitters along the lateral will never have equal or constant flow rate, due to manufacturer's variation, hydraulic variation, emitter clogging, and other factors affecting their discharges. The hydraulic spreadsheet simulation program described herein employs Hazen-Williams equation for computation of head loss at any section along a single lateral. The amount of flow at the inlet of the lateral is determined by summing up the flow rate of all the emitters along the lateral. Chapter 3. SIMULATION COMPUTER MODEL 60 3.2 Computer model description: A computer simulation program was constructed to determine the effects of number, location, and degree of clogged emitters on hydraulics in microirrigation laterals. This program was developed in Microsoft Excel (ver. 5 for Windows 95). This computer model was constructed to assist in the evaluation of microirrigation system uniformity and spatial uniformity by simulating emitter flows. A range of different patterns was used, including emitter clogging along the lateral, hydraulic variations, topography variations (slope), and manufacturer's variation. Each emitter flow for all emitters along a lateral was measured directly in the field, and the synthetic data were used to predict the hydraulics of microirrigation lateral and system uniformity. When using the synthetic data, manufacturer's variation (CV) was applied randomly to the emitters along the lateral. The reason for applying CV randomly to the emitters is to reproduces closely as possible the conditions of the field experiment. In reality, the emitter discharge from all the new emitters differs because of manufacturer's variation. In a sample of new emitters, some emitters may have the exact flow rate reported by the manufacturer, but the discharge from the rest may be higher or lower than the nominal flow rate. In practice, it is impossible to control the emitter's manufacturing variation and their locations along the lateral. Therefore, in the simulation model, the value of manufacturing variation is randomly applied to the emitters along the lateral. The emitter clogging was made by random selection along the lateral based on clogging patterns similar to those in the field experiment. Clogging was considered as "complete clogging," in which the emitter flow for the clogged emitter is zero. For the present research, partial clogging was considered as that in which the emitter flow was less than the initial emitter flow (3.78 l/h) reported by manufacturer. The simulations for emitter clogging, manufacturer's variation, and topographic variations were conducted to determine the worst situations of emitter clogging along the lateral. This analysis was based on emitter flow variations, system uniformity, spatial uniformity and the values of most of the hydraulics parameters in a microirrigation lateral. The program allows its user to simulate the effect of emitter clogging on the hydraulics of a single lateral consisting of 10, 20, 30, 40, 50, and 60 sections. The length of the lateral depends upon the emitter spacing and total number of Chapter 3. SIMULATION COMPUTER MODEL 61 sections along the lateral. Emitter spacing and total number of sections along the lateral are chosen by the user. Thus, the length of lateral can be determined as: L=NsxSe 3.1 where: L = length of lateral (m) Ns — number of sections along the lateral Se = emitter spacing (m). For instance the length of the lateral is selected as 90 m when desired sections and the emitter spacing along the lateral are assumed to be 60 and 1.5m respectively. The main objective of this program is to predict the effect of different numbers, locations and degrees of clogged emitters on the hydraulics of a microirrigation lateral. Figure 3.1 shows the schematic flowchart with the main steps used in the computerized hydraulics computation. This model requires only simple input data regarding basic information for microirrigation hydraulics consideration. The input data include emitter flow rate along the lateral (field data or synthetic data) in l/h, emitter discharge coefficient K, emitter exponent x, lateral inlet pressure P(psi), lateral diameter (m), lateral slope (%), emitter spacing Se (m), friction coefficient CH, and manufacturer's coefficient of variation CV. In an evaluation of a microirrigation system, the accuracy of the hydraulics computation is the basis of a successful estimation of real field conditions. Total flow at the inlet of lateral (Q[) is determined using equation 2.4 (previous chapter) by summing up the flow rate of all the emitters (obtained from field or synthetic data) along the lateral. The head loss at each section hf, along the lateral is estimated based on the input values of emitter flow rates along the lateral and using the Hazen-Williams equation (equation 2.10, Capter 3. SIMULATION COMPUTER MODEL Start Computer program : Field or Synthetic data evaluation ? 1 Field evaluation Set the length of lateral Synthetic data evaluation Select emitter spacing I Determine number of sections along the lateral Input emitter flow rate, lateral diameter, lateral-slope, operating pressure head, c, K, and x Select the patterns (No clog or Clog) If the emitter flow rate measured in the field No Input the value of Cvr yes Input the qi at each section along the lateral assume qi based on CVf Compute total Q at the inlet of lateral Compute head loss, Hf, at each section along the lateral Find total head loss at the end of lateral Find pressure at each section Yes Pressure and Hf computed by using experimental data ? No Calculate new q, affected by pressure at each section, from synthetic data Determie total Q at the inlet of the lateral J-Recalculate head loss at each section along the lateral • 1 Calculate total head loss at the end of lateral + Recalculate pressure at each section Determine H^, Hmi„, H,„., and dry dH * Compute q^ Vhs. ,Vqh, and U!h Sort qi Determine q„„„ qroi„, q.w | qi - q.vc I, v« , * lowest quarter compute Vpf No Compute CU, EU'.DU, and Ea One pattern only * yes Stop Figure 3.1 flowchart of the computer simulation model Chapter 3. SIMULATION COMPUTER MODEL 63 previous chapter). To calculate the head loss at each section (hf,), total lateral flow at the corresponding section (QJ is required. The following equation is employed in the model to determine the lateral flow at each section along the lateral: <2=<2L-I(<?,_,) 3.2 (=1 where: Qi = lateral flow at Ith section (l/h) QL = flow at the inlet of lateral (l/h) qj.\= emitter flow rate at section i-l. Based on g, determined in equation 3.2, the head loss at each section (hf,), is then determined by equation 2.10. The process is repeated for each downstream section with one emitter per section. The total head loss along the lateral (Hp) is determined by: where hf, is the head loss at each section along the lateral. The pressure (hi) at each section along the lateral is calculated when the HF was determined. The impact of lateral slope (up-or down-slopes) on hi is also considered. The new values of emitter flow rate (qj affected by pressure variation at each section is then calculated. Therefore, in the case of simulation with the synthetic data, if a constant value for an initial emitter flow rate (i.e. 3.78 l/h ) is chosen for all emitters along the lateral, the model will change the values to the more realistic values of emitter flow rate in the field. This is the result of considering the effect of pressure variation along the lateral and the impact of pressure gain or loss due to lateral slope on emitter flow rate. The following equations are used in the model to determine the h, and q{ at each section along the lateral: Chapter 3. SIMULATION COMPUTER MODEL 64 f I h,=H0- 1- 1--V L 2.852 3.4 qt=KHt -.-H-yr) x HF ± — (Z x slope) 3.5 where: //0 = pressure at the inlet of lateral in m I = length of pipe along lateral from the lateral inlet in m L = total length of lateral in m K = emitter constant x = emitter exponent. Since the inlet lateral flow is a function of emitter flow rate along the lateral, the effect of pressure variation on emitter flow rate is accounted for in the simulation program. In other words, once HF is calculated by the initial input of emitter flow rate, this value is used to determine the pressure at each section along the lateral. Then the emitter flow rate (qO at each section is computed by equation 3.5. Next, the total new head loss is computed with respect to the new emitter flow rate computed from equation 3.5. Therefore, an iterative procedure is employed to determine the emitter flow caused by pressure variations at each section along the lateral. The pressure losses due to friction are very small in microirrigation circuits in flat terrain [less than 2-3 psi (1.4-2.1m) per 2-3 hundred feet (60-100m) of lateral length], whereas a 2-3 m rise in elevation along the lateral could double the pressure loss. Since the emitters operate at low pressure [usually 10-15 psi (7-10.5m) ], pressure loss or gain by elevation can cause significant variations in the emitter discharge along the lateral. The simulation allows users to evaluate the hydraulics of microirrigation laterals laid on flat or any type of uniform slopes (down-slope or up-slope) terrain. Eight different patterns (or stages) of emitter clogging along the lateral were simulated as follows: Chapter 3. SIMULATION COMPUTER MODEL 65 Stage 1 - no-clogged emitter through the lateral. Stage 2 - 30% of total number of emitters with different degrees of clogging are located at the last section (one-third from the downstream end) of the lateral. Stage 3 - same as stage 2, except the location of the clogged emitters is in the middle one-third section of the lateral. Stage 4 - same as stage 2, except the location of the clogged emitters is in the first one-third section of the lateral. Stage 5 - same as stage 2, except the clogged emitters are randomly located along the line. Stages 6, 7 and 8 - 20%), 10% and 5% of the total number of emitters are partially clogged and randomly located along the lateral. In order to calculate the hydraulic parameters under different patterns of clogging, equations number 2.20-2.22, 2.27, 2.29, 2.31, 2.33, 2.35-2.41, and 2.51 were employed in the simulation program. In addition, the relationships between these parameters are also plotted on the worksheet for each stage and can be easily compared to each other. The hydraulic model also accounts for the total emitter coefficient of variation (VT) and deficit evapotranspiration [1- (ETave/ETm)] detailed in chapter 2, to determine the impact of different patterns of emitter clogging on crop yield (cotton yield, see 2.51) for different areas. The reason for choosing the cotton yield was based on the availability of several parameters required for the crop yield analysis from previous studies reported by Sammis and Wu (1985). Therefore, the computer model incorporates the data adopted from Sammis and Wu (1985) by means of an interpolation procedure to determine VT when clogging occurs in different patterns along the lateral. The interpolation procedure is used to determine the exact value of deficit evapotranspiration on the Y axis (in this study, Y values deficit evapotranspiration) corresponding to the value of VT on X axis (in this study, X values emitter coefficient of variation) by the following equation and figure 3.2: BC/AC = BE/DE or: (y2-yi)/(x2-x,) = (y2-Y)/(x2-X) or: Chapter 3. SIMULATION COMPUTER MODEL 66 where: y2-yi = BC X2-x; = AC y2-Y=BE x2-X=DE yi and ^2 = values corresponding to the deficit evapotranspiration [ 1-(ETave/ETm)~\ xi and X2 = values related to the total coefficient of variation (Vj) as indicated in Figure 3.2 3.3 Effect of different patterns of clogging on hydraulics of different lengths of lateral: Six different lengths of laterals of 10, 20, 30, 40, 50, and 60m, all 15 mm in diameter were selected to simulate the effect of eight different patterns of emitter clogging on hydraulic characteristics of microirrigation laterals laid on flat terrain. The values of emitter hydraulic characteristics, lateral inlet pressure, emitter spacing, nominal emitter flow rate and emitter manufacturer's variation were selected to be similar to those values used in the experimental Chapter 3. SIMULATION COMPUTER MODEL 67 set-up which will be explained in the following chapter. The eight different patterns of emitter clogging described in previous section were used for each length of lateral. The manufacturer's variation (CV) of 0.0193 was applied randomly to the emitters along the lateral. The value of 0.0193 was determined from a sample test of emitters which is detailed in chapter 5. Clogging was considered to be "complete clogging," in which the emitter flow for the clogged emitter is zero. Partial clogging considers the condition in which the emitter flow rate was less than the minimum emitter discharge after the manufacturer's variation was applied to the emitters along the lateral. The computer simulation was used to assess if there are significant differences in the hydraulic characteristics of different lengths of lateral affected by clogging. Then, based on the results obtained from the simulation program, the appropriate length of lateral for the experimental set-up was selected. Head loss, emitter flow variation, coefficient of uniformity, application efficiency, distribution uniformity, statistical uniformity, emitter coefficient of variation, hydraulic design coefficient of variation, emitter discharge coefficient of variation due to hydraulics, and emitter performance coefficient of variation were evaluated. Results presented in Tables A.3.1 to A.3.16 in appendix A show that the hydraulic characteristics of different lengths of laterals have similar trend under eight different patterns of emitter clogging. Figures 3.3 to 3.12 show the relationship between all aforementioned hydraulic parameters and the different lengths of lateral under eight different stages of emitter clogging. Based on these theoretical analyses, the 20m lateral was considered to be the appropriate length for the field experiment. Chapter 3. SIMULATION COMPUTER MODEL 68 0 ii O Q °, Q _i S LU' U U U r,co mnoooy - - - of c£ cc £ «\» .\« .\° «\« ** ** ?T-' o o o o o o ox : co co co CO co c*j in cn c CU _1 I 1—1—I CMOOM-OCDCMOO-fO COCMCNCNT-T-OOO ooooooooo (LU) JH ssoi peaH o CD 0 i CO (D T3 "D c CD c o "co o o GO LJ* CO CD o XJ E ad CD c x: o on o (0 CD I 111 itte 1 co E CD co TJ 0 CD £- CO CO CO LL clo o CD O LO o _ o CO o CM CO c CD OLOOLOOLOOLOO ocj)Cj)cocor--r-cDco (%)no 'Ajjiujojiun jo juapiyaoo O CO Q £ a: a* w 0 o n CM 1 i 3 a o o . . CO CO LT) ra 5? Q. ° ^ a: n **' o o o Z CO T-o CD CD i_ CO 0 T3 "O c E CO u. o cf g "(0 o o o , . c s ." 0 0 'o mb effii o c o o on o CO 0 0 •4—> LU ^—' • m E 0 co T3 0 0 & CO 13 CO CO o LL o Chapter 3. SIMULATION COMPUTER MODEL 69 Q Q u: u <_> o n o o Q y ^ a: of a: 9-.Nf J\° S-? °J o o o o o co co co CM T— m , it O CO o in o o CO o CN c CD CN in oo m in m a> co a> CO (n3)^!UJJ0j!un uoissiLug nue|/\| o 0 0 O) 0 ••= •a E •D o c s CD c - ZJ c •S | CD CO o co Og -D =J II o co CD »— a> LU E oo aj <*> T3 CM CU I- O) 5. °> ra o LL o Q °. Q rnroCOCOOOOy O CM o oo CO CN o ,— T— o o o o o O o o o o o o o o o cl ci d d (siyO'JBAjo-jjsoo uBjsspjpAH T3 a> ra ra o o **-o ra ro <" ^ "D JD s ° CD o c CD O ro it O CD o o ~ o 0 = .o .2> t cu § "° *I ° 0 .£ 1 B !t T3 LU >. i O c ^- o CO CO 0J CD 3 £ •2> E LL CD L_I i i I i—i—i i—i i— o CO o m o o co o CN sz -t-» cn c cu o o d o 00 CO CN o o a> a) o> o> cri cri CO cri cri o> 05 CO CO (B3)Aou8!oyjg uorjeonddv CD 2? ra CD TD E ^ CD g c .Q> o o !t 8 a o c — g CD CD .Q O E =5. ^ a. C= CD °° O CO £ J. LU ±5 • E <*? -a CD 0 b- ra 2, °> ra o Lu o c 0) IIIH _i i • -i • o CO CO CN o o o o O o o o o o O o o o o o O o d d d d d d (i|bA)o!|nejpAL] 0} anpjBA jcvyaoo'ipsjp jamwg CO u "5 ro -o % 0 p ra J~ g>2 o § o ^ 0 .2 ra ro °> is "O <D CD 2 d g •So CD tfc O CD 0 o O 1 & O XI ^ <— O 0 LU i cn co 0 E 0 c o CO 0 - E ^ 0 Chapter 3. SIMULATION COMPUTER MODEL 70 CL ro > o ifci CD O O CU O c CO £ o t 0) CL I— 0) E LU 0.50 0.40 0.30 0.20 0.10 0.00 -•—No Clog 30%,1/3M,DC -0-30%,R,DC H— 10%,R,DC -•-30%,1/3L,DC -O-30%,1/3F,DC -A-20%,R,DC 5%.R,DC 10 20 30 40 Length (m) 50 60 Figure 3.11- Effect of number, location, and degree of clogged emitterson emitter performance coefficient of variation. Figure 3.12- Effect of number, location, and degree of Clogged emitters on emitter discharge coefficient of variation . Chapter 4. MATERIALS AND METHODS 71 Chapter 4 4. MATERIALS AND METHODS 4.1 Description: In May of 1995, a microirrigation system was constructed at the Plant Science Research Field (near S.W. Marine Drive) of the University of British Columbia. The average slope of the field experiment was 3.25% in the north-south and less than 1% in the west-east direction. A 20m rectangular wood frame, 60 cm in height, lm in width, was made to support two suspended lateral lines horizontally above the ground surface. Figure 4.1 shows the experimental layout (flat terrain). Two 20m polyethylene laterals (A and B) of 15 mm inside diameter were used. The laterals were spaced lm apart and connected to the wood frame at 60 cm above the ground. Each lateral was divided into 20 sections. Pressure-compensating emitters (DPJ04-A, Hardi Turbo SC™ Plus) with a nominal emitter flow rate of 3.78 l/h, manufacture coefficient of variation (CV) of 0.0193 and emitter flow exponent (x) of 0.075 were used (Figure 4.2). Calculation of values of CVand x is detailed in chapter 5. The pressure at the inlet of lateral was kept at a recommended pressure of 105 kPa (15 psi) using a pressure regulator. The emitters were inserted on-line in the polyethylene lateral. Emitters were spaced 1 m apart along the laterals. A 20 mm polyethylene hose as a main line carried the clean water (drinking water) into the system. A polyethylene manifold 15 mm in diameter was used to carry the water from the main line to the laterals. The average pressure of the city water supply was 420 kPa (60 psi). A pressure regulator and a pressure gauge were installed at the manifold inlet. Two valves were also installed in the manifold after pressure regulator and close to each lateral inlet. Four pressure gauges were also installed for monitoring and measuring the pressure, one pressure gauge at the inlet and the other at the end of each lateral. In addition, one portable pressure gauge was connected to a 3 cm piece of metal pipe ( 3mm outside diameter) and used to measure the pressure at each emitter location along the lateral. The ends of the laterals were closed by a plug. Eight different patterns (as described in chapter 3) of emitter clogging were used. The partially and completely clogged emitters were artificially made by introducing some fine sand (as will be discussed later) into the emitter through the emitter barb. In May 1996, another rectangular wood frame, 1 m in height was constructed and placed on the top of the Chapter 4. MA TERIALS AND METHODS 72 Chapter 4. MATERIALS AND METHODS 73 previous set-up. Therefore, the experimental set-up consisted of two frames (Figure 4.3), one at the bottom and the other at the top. Two 20m polyethylene laterals 15 mm in diameter were connected under the 20m piece of straight bar and were laid along the top frame. The system consisted of four laterals, two laterals laid on flat terrain at the bottom frame and the others laid on the sloped terrain at the top frame. Four different slopes (3% up-slope, 3% down-slope, 7% up-slope, and 7% down-slope) were tested. The slope of lateral could be changed by moving the 20m (wood) bar upward or downward to achieve the desired slope. The pressure regulator, pressure gauges and the manifold were disconnected from the previous set-up and connected to the new laterals laid on the slope terrain. The former laterals (laid on the flat terrain at the bottom frame) were connected to the manifold by a lm piece of polyethylene pipe 15mm in diameter. Patterns of emitter clogging similar to those in flat terrain were used for sloped terrain. Then the effect of number, degree and the location of clogged emitters along the lateral laid on sloped terrain on hydraulics of microirrigation system were determined. The laterals on flat terrain were also operated whenever the laterals on slope terrain were running. In May 1997, the emitters along the laterals (A and B) located in the bottom frame were examined. The cap of each individual emitter was removed in order to inspect the inside of the emitter to see if natural clogging occurred. The number, degree, and the type of clog particles were determined. Then the effect of naturally clogged emitters on coefficient of uniformity (CU) was measured and a least-square regression equation was determined (as detailed in chapter 5). In May 1997, the laterals laid on slope terrain were disconnected from the top wood frame and the new laterals were installed. Two 20m, 15mm diameter polyethylene laterals were installed on the top frame with zero slope. A venturi injector (model Mazzei 484, 3/4", the smallest commercial size available in the market) with 68 l/h (18 gph) injection capacity was chosen for injecting the saline water into the lateral. A barrel of 180 liters capacity was used as an injection tank. The city water was carried into the injection tank by a piece of polyethylene pipe connected to the main line. The venturi injector was installed right after the pressure regulator and gauge in the manifold (Figure 4.4). The impact of the venturi injector and the injection of the saline and the city water on the variation of emitter flow rate along the laterals (consisting of naturally clogged and no-clogged emitters) and their effect on C hapter 4 MA TERIAIS A.XD METHODS 74 Figure 4 4 Venturi injector model \la//ei 4X4 and injection barrel Chapter 4. MATERIALS AND METHODS 75 hydraulic characteristics of microirrigation laterals were determined. The length of lateral was increased to 40m, and a similar test as on the 20m lateral was done on the 40m. The effects of the venturi injector and saline water injection on hydraulic characteristics of laterals consisting of new emitters were investigated. Table salt was used to prepare the saline water with different levels of electrical conductivity (EC). Three different tests were conducted to examine the impact of injecting different degrees of saline water (using the venturi injector) on the emitter's hydraulic characteristics: (1) - In the first test, 20m and 40m laterals consisting of new emitters, the venturi injector, and the city water (EC = 0.022 mmhos/cm ) were used. The effect of the venturi injector and the injection of city water on emitter flow rate and the system uniformity was examined. (2) - The second test was done in order to maintain a constant value of electrical conductivity (EC) at the emitter's outlet. EC values of 1.5 and 3.0 mmhos/cm were maintained. (3) - The third test was similar to the second, but a constant EC value of the injected saline water was maintained and the EC variation at the emitter outlets was investigated. The system was run under different phases of venturi injector operation. Different phases were applied in three runs at each test. Each run was repeated once and the average measurements were taken. The flow of each individual emitter at each section along the lateral was collected in each run for 30 minutes. Then emitter flow rates along the lateral were determined. The impact of emitter flow variation on the hydraulic characteristics of the microirrigation were investigated. The impact of air and water temperatures on emitter flow rates along the lateral (consisting of naturally clogged emitters) and their effects on the hydraulic characteristics of the lateral were also examined. Chapter 4. MATERIALS AND METHODS 76 4.2 Field Measurements: The microirrigation system was operated and field data were collected in three distinct steps: 1. The first step was done on flat terrain from May to September 1995. 2. The second step was done on sloped terrain from May to September 1996. 3. The third step was done on flat terrain under the venturi injector and injection of saline water from May to October 1997. 4.2.1 Step 1 of Field Experiment: Experimental system was constructed during May to July of 1995 and the first step of the research experiment started in August, 1995. Figure 4.5 shows the field experiment in step 1. The first step of the experiment was done on a flat terrain to determine the effect of number, location, and degree of clogged emitters on the hydraulics of the microirrigation system. Two 15 mm inside diameter polyethylene laterals (A and B) of 20m length were used. The laterals were spaced lm apart and laid under the top side of wood frame 60 cm above the ground surface. The laterals were connected flush with the wood frame, with zero slope (flat). Each lateral was divided in 20 sections. The pressure compensating emitter model DPJ04-A, Hardi Turbo-SC™ Plus, was used for this experiment (Figure 4.2). The emitters were inserted on-line in the polyethylene laterals. Each lateral consisted of 20 emitters, one emitter per section along the lateral. Before operating the system in the field, the emitter flow rates were measured and compared with the manufacturer data. 50% of the emitters from a total of 40 emitters were randomly selected in order to test the emitter manufacturer's coefficient of variation (variation in emitter flow rate). A piece of 1 meter polyethylene pipe was used and a 15 psi pressure regulator and a pressure gauge were installed at the inlet of this pipe. The end of the pipe was plugged. Then, Chapter 4. MATERIALS AND METHODS 77 Figure 4.5 The field experiment layout in step-1 (not to scale) Chapter 4. MATERIALS AND METHODS 78 emitter number 1 was inserted on-line 50 cm from the inlet of this pipe. The system was run for 2 hours, then the emitter flow was collected in a container for three different duration times (3 minutes, 15 minutes, and 1 hour ). This test was done for all 20 emitters six times at the same duration intervals. In spite of installing a pressure regulator to fix the pressure inlet at 15 psi, the pressure gauge showed a pressure variation of 15 to 15.5 psi during the tests. The standard deviation of the emitter flow rate and the average emitter flow rate were computed, and the emitter manufacturer's coefficient of variation CV were then determined. In order to determine the emitter's hydraulic characteristics, the emitter flow rate and pressure data given by the Hardi Turf Irrigation Products Catalogue (1995) were used. The flow rate versus pressure curve can be fitted into an emitter flow formula. Based on these data, the values of x and K (in equation 2.1) were found by the least-square regression analysis of the natural logarithm of flow rate against the natural logarithm of pressure (detail given in Chapter 5). The x and K values of 0.0757 and 3.147 were obtained respectively. The emitter flow equation for this type of pressure-compensating emitter was established as follows: q = 3.\47h00151 4.1 where q is the emitter flow rate in l/h and h is the pressure in (m). The first emitter was spaced lm from the lateral inlet. The laterals were connected to a 15mm inside diameter polyethylene manifold. Water was carried to the manifold from a 16mm inside diameter hose connected to the city's water main. Four pressure gauges were installed and used to measure the pressures at the inlet and end of each lateral. The pressure at the inlet of the lateral was kept at the recommended of 105 kPa (15 psi) by using a pressure regulator. Due to pressure variation in the city's water main, the inlet pressure varied between 15 psi and 16.8 psi. Different patterns of emitter clogging along the lateral in 8 different stages were examined as follows: Stage 1: desired situation with no-clogged emitter along the lateral A. The system was operated Chapter 4. MATERIALS AND METHODS 79 under this condition and the emitter flow rates along the lateral were measured. In order to ensure that the pressure and temperature had reached equilibrium, the system was running for 1.5 to 2 hours before data collection. Then, the emitter flow rate from each individual emitter was directly measured by using a stopwatch, bucket, and a graduated cylinder. The volume of water from each individual emitter was collected for 30 minutes and emitter flow rate was determined. The average pressure at the inlet and at the end of lateral were also recorded. This test was repeated four times (four runs) and the average emitter flow rate was determined. The system under the conditions of stage 1 was continuously operated for one and half months, 3 hours per day, in order to investigate if any emitter clogging occurred along the lateral. Stages 2 to 8 were done on lateral B. In these stages, several partially or fully clogged emitters (artificially clogged emitters) were inserted at different locations along the lateral B. Fully or partially clogged emitters were manufactured by introducing very small amounts of fine sand (lOOmesh <D< AOmesh and 40mesh <D< lAmesh, where D is the diameter of a sieve through which sand was screened) into the emitter from the emitter inlet. Uniform clogging could not be achieved because of the characteristics of elastomeric disk placed on the top of the spiral path of the emitter. For the present experiments different numbers and degrees of emitter clogging were made and used in stages 2 to 8 as follows: Stage 2: 30% of the total number of emitters were partially clogged and located at the last section (one-third from the downstream end) of the lateral. This stage was assigned as 30%, 1/3L, DC (30%, Last 1/3 of lateral, Different degree of Clogging). Stages 3 and 4 : same as stage 2 except the partially clogged emitters were located in the middle and first one-third sections of the lateral respectively. These stages were assigned as 30%-l/3M-DC and 30%-l/3F-DC. Stage 5 : same as stage 2 except the clogged emitters were randomly located along the lateral. Stages 6, 7 and 8 : at these stages 20%, 10% and 5% respectively of the total number of emitters Chapter 4. MATERIALS AND METHODS 80 were partially clogged and randomly located along the lateral. Each emitter along the lateral was known by a number assigned to its location. The number of partially clogged emitters and their locations are shown in table 4.1. Table 4.1 Number and location of clogged emitters at different stages along the lateral. Stage # Clogged emitters # Location Stage- 1 No clogging Stage-2 15,16,17,18,19,20 1/3 from downstream end Stage-3 7,8,9,10,11,12 1/3 middle of lateral Stage-4 1,2,3,4,5,6 1/3 first of lateral Stage- 5 1,3,5,9,11,16 randomly Stage-6 3,6,8,12 randomly Stage-7 4,13 randomly Stage-8 16 randomly Similar patterns of emitter clogging as in step 1 were simulated with the synthetic data by the computer spreadsheet program (explained in chapter 3). Figure 4.6 shows different patterns (stages 1 to 8) of emitter clogging along the lateral. 4.2.2 Step 2 of the field experiment: Step 2 was done at the same location as step 1. The effects of emitter clogging on the hydraulics of microirrigation laterals laid on a uniform sloped terrain were investigated. To achieve the different slopes for step 2, a wood frame of 20m length and lm in height was constructed. This frame was placed on the top of the frame constructed for step 1. Therefore, the total height of the frame was 1.6m in step 2. Four different uniform slopes of 3% and 7% (up- and down-slope) were chosen. Two 20m polyethylene laterals were connected to the two 20m straight bars. Two tests were done in step 2, tests A and B as described below: Test A- This part of the experiments consisted of two lateral lines laid on 3% and 7% uniform up-slopes. Lateral A was laid on a 7% up-slope in one side of the frame. Lateral B was also placed on a 3% up-slope on the other side of the frame. Figures 4.7 and 4.8 show the laterals A and B laid on 7% and 3% up-slopes respectively. The difference in elevation between the fronts and ends of lateral A and lateral B were 1.4 and 0.6m respectively. The impact of partially clogged emitters on the hydraulics of laterals laid on 3% and 7% up-slopes Chapter 4. MATERIALS AND METHODS Qo Stage-1 Stage-2 Stage-3 Stage-4 Stage-5 Stage-6 Stage-7 Stage-8 iQo 9 Q< ® Q2 9 Q *3 © qi q2 q3 a a, Qn_i o • • • Qn-1 <f Qn § qn-2 qn-i qn No Clogged Emitters 30%, 1/3L, Diff.Clogging 30%, 1/3M, Diff.Clogging ff 30%, 1/3F, Diff.Clogging -4- 1 30%, Randomly, Diff.Clogging 20%, Randomly, Diff.Clogging 10%, Randomly, Diff.Clogging 5%, Randomly, Diff.Clogging 1/ Figure 4.6 Different patterns of emitter clogging along the lateral Chapter 4. MATERIALS AND METHODS 82 20 meter in Figure 4.7 Lateral A laid on 7% up-slope (not to scale) 20 meter Lateral in Step-2 in Figure 4.8 Lateral B laid on 3% Up-slope (not to scale) Chapter 4. MATERIALS AND METHODS 83 were investigated. Test A consisted of eight different stages similar to those reported in step 1. Similar patterns of emitter clogging as in test A were simulated with synthetic data by the computer program. Test B- This experiment also consisted of two 20m laterals laid on 3% and 7% uniform down-slope. Lateral A was installed on a 7% down-slope on one side and lateral B on a 3% down-slope on the other side of the frame. The difference in elevation between the front and the end of lateral was same as in test A. Figures 4.9 and 4.10 show the laterals laid on 3% and 7% down-slopes. Similar patterns of emitter clogging as explained in step 1 were done in eight different stages. The volume of emitter flow was measured along the laterals A and B at each stage four times, for 30 minutes duration each. The average individual emitter flow rate along the lateral was then determined. The impact on the hydraulics of the microirrigation system of clogged emitters along the laterals laid on sloped terrain was then determined. 4.2.3 - Step 3 of the field experiment: The last part of the field experiment was done from May to September of 1997. The effects of naturally clogged emitters, no-clogged emitters, the venturi injector, and injection of saline water on the hydraulics of microirrigation laterals laid on flat terrain were investigated. The following tests were done in this step: 1- Inspection of the system to determine the number, degree, and the formation of naturally clogged emitters along the 20m laterals (laterals A and B) laid on flat terrain and installed in June 1995. 2- Determination of the hydraulic parameters of 20m and 40m laterals consisting of naturally clogged emitters laid on flat terrain. The results obtained from the naturally clogged emitters were compared with the results obtained from the artificial clogging and the synthetic data in Chapter 4 MA TERIALS AND METHODS 84 Figure 4.10 Lateral B laid on 3% down-slope in step-2 (not to scale) Chapter 4. MATERIALS AND METHODS 85 1995. 3- Comparison of the emitters flow rate along the laterals (laid on flat terrain) before and after flushing the laterals under naturally clogged conditions. 4- Investigation of the impact of air and water temperature on the flow rate of naturally clogged emitters (on flat terrain). 5- Test of the venturi injector (Mazzei Venturi Injector model 484) with city water in order to determine the pressure differences between the inlet and outlet of venturi needed to creates a vacuum at the throat of the venturi injector. This vacuum is the suction for injecting the liquid fertilizer or chemical (saline water in this research) into the microirrigation system. 6- Investigation of the impact of the installation of the venturi in the microirrigation system on the hydraulic parameters of laterals laid on flat terrain. 7- Installation of the new 20m and 40m polyethylene laterals with the new pressure-compensating emitters (same type of emitters as in previous steps) laid on flat terrain. The venturi injector was also installed in order to determine the impact of saline water injection on the hydraulics of microirrigation laterals under the no-clogged condition. 8- Injection of different degrees of saline water as a nutrient liquid by the venturi injector through the 20m and 40m laterals. The flow rate and electrical conductivity (EC) of each emitter flow were measured in order to determine how uniformly the nutrient (saline water) was distributed along the lateral. 4.2.3.1 Inspection of the clogged emitters: The microirrigation system consisting of four 20m laterals (A and B on flat and sloped terrain) were installed in the field from June 1995 to summer 1997. The system was run three hours a day, four days a week from August to September 1995 and from May to September 1996. The system did not operate from October 1996 to May 1997. Since laterals A and B were operated several times from 1995 to 1996, some emitter clogging was expected to occur along the laterals. In May 1997, each emitter along laterals A and B was carefully opened to reveal the formation and degree of clogging. Different types of particles were found in several emitters along laterals A and B. The number, degree, and the nature of the clogging formations were investigated. In order to determine the number of clogged emitters, the Chapter 4. MATERIALS AND METHODS 86 system was operated for 30 minutes in May 1997. Then the emitter flow rates along laterals A and B were measured. It was assumed that every emitter along laterals A and B with a flow rate less than the minimum emitter flow rate measured in June 1995 was partially clogged. Then, the number of partially clogged emitters along the laterals was determined. The caps of partially clogged emitters randomly located along the laterals were removed and the insides of the emitters were inspected. The caps were then closed and the system was run for 30 minutes [Keller and Bliesner (1990) suggested that a minimum velocity of 0.3 m/s is necessary to adequately flush fine particles from the lateral if the lateral hoses of the system are flushed for about one hour. The velocity of water was about 5.7m/s in this study ]. It was confirmed that the clogged particles were still there; they were not removed from the emitter. The clogging was mostly from slime, insect feathers, and in some cases, very small particles of fine sand. The system with the naturally clogged emitters was run, and the volume of water delivered by each emitter along the lateral was measured for 30 minutes. This run was repeated three times and the average of each individual emitter flow rate along the 20m laterals was determined. In order to extend the length of lateral to 40m, the laterals A and B were joined and extended by a lm piece of polyethylene pipe. Similar runs were done on 40m lateral and the average of emitter flow rate along the lateral was determined. The variations of emitter flow rate along the lateral were then plotted. The degree of clogging (C//o) of the naturally clogged emitters was estimated using the equation of linear relationship between the degree of clogging and the reduction of emitter flow rate obtained from the field experiment data in 1995 (detail given in chapter 5). The degree of clogging of the artificially clogged emitters in step 1 were also estimated by the same equation. Then, the total degree of clogging (TC%) along the laterals was measured by adding all the degrees (Ca%) of clogged emitters along the lateral. The average degree of clogging was calculated as: Ave.Q% =TC%/n where, n is the number of emitters along the lateral. A linear relationship between Q% and coefficient of uniformity (CU) was found in such a way that the values of CU under naturally and artificially clogged emitters were measured. Chapter 4. MATERIALS AND METHODS 87 Then the values of CU versus average Cd% obtained from the naturally and artificially clogged emitters was plotted and a least-square regression was determined. In addition, a similar calculation to the one mentioned above was done to determine CU and CJVo using synthetic data. Different numbers of clogged emitters (0%,10%, 20%.... to 100% of the total number of emitters) and different percentages of clogging were simulated along the 20m lateral. CU and Q were then measured and plotted, and a least-square regression was determined. A general relationship between CU and C//o was found by combining all values of CU and C//o obtained from natural, artificial, and synthetic data. The hydraulic parameters {Hf, CU, EU, Hvar, qvar, Vqs, Vhs, Vpf, and Vqh) of microirrigation laterals obtained from the no-clogged, naturally clogged, artificially clogged, and synthetically clogged conditions were compared to each other. 4.2.3.2 Lateral flushing: The effect of lateral flushing on the naturally clogged emitter's flow rate was also examined. In order to flush the lateral, the pressure gauge and the hose plug from the end of lateral was removed and the system was run for 30 minutes. Then the end of lateral was plugged and the system was run for one hour. The volume of water delivered from each emitter along the lateral was measured in 30 minutes and the emitter's flow rates were determined. This test was done for both 20m and 40m lateral lengths and each run was repeated twice. The variations of emitter flow rate along the lateral before and after flushing were determined and compared to each other. 4.2.3.3 Air and water temperature : It is suspected that temperature may have an impact on the emitter flow rate and hydraulics of laterals in microirrigation systems. The impact of air and irrigation water temperature at the experiment site on emitter flow rate was examined. Different water and air temperatures could be achieved under different weather conditions such as cloudy, sunny, immediately after sunset, and immediately after sunrise in July, 1997 on different days. The microirrigation system consisting of naturally clogged emitters was run under various air and Chapter 4. MATERIALS AND METHODS 88 water temperatures (high and low temperatures) on different days. The volume of water delivered from each emitter along the lateral was measured and the emitter flow rate was determined. In all cases, the pressure at the inlet and end of the lateral was checked and recorded. The variations of emitter flow rate under different temperatures versus sections along the lateral were measured, plotted and compared to each other. 4.2.3.4 Venturi Injector: The maximum amount of lateral inflow was determined based on the total number of emitters along the lateral and their nominal emitter flow rate. Different values of pressures [i.e. 70 kPa to 420 kPa (10 psi to 60 psi)] in upstream and downstream were chosen in order to determine the size of venturi injector for the experiment. The diameter of the venturi throat (d) was calculated based on the maximum required flow, the diameter of the lateral, and the pressure at the upstream and downstream. Then, the minimum and maximum values of venturi throat diameter were found. The venturi injector (model Mazzei 484 ,3/4", the smallest commercial size available on the market) with 68 l/h (18 gph) injection capacity was selected for the experiment. The venturi injector was tested before installation under different pressures in up- and downstream. Figures 4.11a,b,c show the test of the venturi injector's lay out. A pressure regulator and two pressure gauges were used to test the venturi injector under different inlet and outlet pressures. The city's water was used in the test. This test was done in order to determine the amount of pressure difference required between the inlet and outlet of the venturi injector at the experiment site. The amount of liquid flow (injected liquid through the throat) under different motive flows (venturi inlet flow) and inlet and outlet pressure was compared to the values reported by the manufacturer. The minimum amount of motive flow was about 600 l/h («3 gpm) when the pressures at the venturi inlet and outlet were 168 and 105 kPa (24 and 15 psi) respectively. This amount of inflow and pressure difference between the venturi inlet and outlet create a vacuum at the venturi throat to inject the liquid. The effects of injecting water of different degrees of the salinity (by using the venturi injector) on the emitter's hydraulic characteristics were examined (detail is given in chapter 5). In addition, the hydraulic parameters (i.e. CU, EU', qvar, Vqs) when the venturi Chapter 4. MA TERIALS AND METHOD 89 Pressure Regulator Valve Main . Pipe | City Water 60 psi—k 15Psi Motive Flow (-a) Valve Main pipe 1 City Water I 60 psi (-b) Main Pipe City I water 1 Valve I I 60psi Pipe D • Venturi Injector L3 0 psi Liquid flow Pressure Regulator Venturi Injector IK • Venturi Injector Pressure Regulator li I Pipe C Lateral B H 1 1 1 '15 psi t Lateral A Figure 4.11 Test of venturi injector lay out Chapter 4. MATERIALS AND METHODS 90 injector was installed were measured and a comparison was made to the parameters that existed without the injector. The venturi injector was installed in the system and used in different tests as follows: 4.2.3.4.1. City water injection in naturally clogged condition: Two 20m laterals (A and B) consisting of naturally clogged emitters were used for this experiment. The venturi injector was connected to the manifold right after the pressure regulator and before the lateral inlet. Two pressure gauges were also installed, one right after the venturi outlet close to the inlet of lateral A, and the second at the end of lateral A. The end of lateral was connected to a pressure gauge, a valve and a piece (5 m) of polyethylene pipe. Therefore, the amount of motive flow (venturi inlet flow) could be adjusted by gradually opening or closing the valve at the end of the lateral. Increasing the lateral flow (at a fixed length and number of emitters) can be simulated with longer lengths of lateral. This test was done on 20m lateral A and city water was used as an injection liquid. A 180 liter barrel was used as an injection tank. The system was run in three different phases. In the first run, the throat of the venturi injector was shut off and the city water was delivered to the system from the main line. The pressure regulator was adjusted to 175 kPa (25 psi) and the inlet lateral pressure was also adjusted to 105 kPa (15 psi) by controlling the amount of motive flow by adjusting a valve at the end of lateral A. Therefore, the pressure difference between the inlet and outlet of the venturi was adjusted to 10 psi (25 psi at the venturi inlet and 15 psi at the venturi outlet). In order to ensure that the pressure and temperature had attained equilibrium the system was running for one hour before data collection. Then, the emitter flow rate from each individual emitter was directly measured by using a stopwatch, bucket, and graduated cylinder. The volume of water from each individual emitter was collected twice for 30 minutes each time. Then the average emitter flow rate was obtained. The amount of flow rate from the pipe connected at the end of lateral was also measured. In the second run the suction pipe of venturi was opened and put into the injection barrel (180 liter). The venturi outlet pressure (lateral inlet pressure) was dropped to 84-87 kPa (12-12.5 psi) immediately. Under this condition, the water was delivered to the system from the main pipe and the injection barrel. In order to ensure that the pressure and temperature had attained Chapter 4. MATERIALS AND METHODS 91 equilibrium, the system was running for 30 minutes before data collection. Then the volume of water delivered from each emitter was measured for 30 minutes. The volume of liquid suction from the barrel and the flow rate at the end of the lateral (the flow from the additional piece of polyethylene pipe) were also measured at the end of 30 minutes. In the third run, the pressure at the inlet of lateral was adjusted to 105 kPa (15 psi) by adjusting pressure regulator and increasing the pressure at the venturi inlet to 34 psi. Then, as in the second run, the volume of water delivered by each emitter and the volume of liquid injection from the barrel were measured for 30 minutes. The flow rate at the end of the lateral from the connected pipe was also measured. The length of lateral was extended to 40m by joining the two 20m laterals. The same test as with the 20m lateral was done with the 40m. In all cases, the pressure at the beginning and the end of lateral was checked by a pressure gauge and recorded. In the case of the 40m lateral, the pressure at the middle was also checked. The hydraulic parameters were determined in the three runs and evaluated. The variation of emitter flow rates obtained from the three different runs versus sections along the laterals were then plotted. 4.2.3.4.2 City water injection in no-clogged condition: Two 20m new polyethylene laterals (laterals A and B ) with lm emitter spacing (similar to the description in step 1) were installed on flat terrain. Two tests were carried out. The first test was done without the venturi injector and the second test was done when the venturi injector was installed in the manifold before lateral inlet. Lateral A was used for the first test. Two pressure gauges were connected, one at the lateral inlet and the other at the end of lateral. In order to ensure that the pressure and temperature had attained equilibrium, the system was run for 1 hour before data collection. Then, the emitter flow rate from each individual emitter was directly measured. The average emitter flow rate was obtained from four measurements (replications). The pressure inlet of each individual emitter along the lateral was also measured by a pressure gauge. The length of lateral was extended to 40m with one emitter spacing. Similar measurements as for the 20m lateral were done for the 40m lateral. The hydraulic parameters were measured and then plotted for both 20m and 40m laterals. Chapter 4. MATERIALS AND METHODS 92 In the second test, the venturi injector was installed in the manifold right after the pressure regulator. A barrel of 180 liter capacity was used for storing the liquid (city water in this case). The system was run under three different pressures at the venturi and the lateral inlet (25 and 15 psi, 25 and 12 psi , and 34 and 15 psi pressures at the venturi and lateral inlet respectively). The volume of water from all emitters along the lateral was collected for 30 minutes. The average emitter flow rate was obtained from two measurements (replications). Three different runs were done similar to those described in the previous section. 4.2.3.4.3 Saline water injection in no-clogged condition: Similar tests as reported in the previous sections were done with an injection of saline water. Saline water represented the nutrient (fertilizer) injected into the microirrigation system. The electrical conductivity (EC) of water was measured as a degree of salinity. The EC of city water for this experiment was 0.022 mmhos/cm. To make the saline water, different types of salt could be used to increase the salinity of the water. Table salt (Windsor salt, iodized) was chosen for this experiment as it is cheap and easy to get. The saline water with different EC was artificially made by adding the amount of salt to the known volume of city water. Two different cases for injection of saline water through the microirrigation system were considered as: (1) -Ideal case (2) - Conventional case In the ideal case, the aim was to maintain a constant value of electrical conductivity (EC) at the emitter's outlet. EC values of 1.5 and 3 mmhos/cm were maintained. Therefore, it was assumed that saline water with a constant and known value of EC is expected to be delivered from all emitters along the lateral. This case can be simulated in a field condition when a fixed concentration of chemical liquid (fertilizer and pesticide) is required to be delivered from the emitters in a microirrigation system. To provide saline water as an injection liquid in an ideal case, the amount of salt per liter of city water was determined based on the percentages of liquid flow and motive flow. In this case, high saline water with an EC of 13 Chapter 4 MATERIALS AND METHODS 93 to 15 mmhos/cm and 27.5 mrnhos/cm was used as an injection liquid, and the city water with an EC equal to 0.022 mmhos/cm was used as the motive flow (detail is given in Chapter 5). A conductivity meter model CDM3 Radiometer/Copenhagen was used to measure the electrical conductivity of high saline water. In the conventional case, a constant EC value for the injecting saline water was maintained, and the EC variation at the emitter outlets was investigated. In this case it was assumed that two different kinds of irrigation water with different EC's are going to be applied in a microirrigation system. Therefore, the conventional case was set-up in order to investigate how venturi injector and pressure variations (venturi and lateral inlet pressures) affect the EC of the injected liquid along the lateral (or EC of the mixed water delivered by the emitters). In this case two different saline water with EC of 1.5 and 3 mrnhos/cm were used as the liquid injection and the city water as the motive flow.The conventional case can also be simulated with the real conditions in the field when two different sources of irrigation water (such as sea water of high salinity and well or river water of low salinity) are available to irrigate the crops. In both cases, the saline water was stored in a barrel so that it could be injected through the microirrigation system. In both cases, the EC pf mixed water was dependent upon the portion of liquid flow and its EC (ECL) and the portion of motive flow and its EC (EC,). Three runs similar to those indicated in the previous section were considered in each case. In both cases, each run was repeated and the average emitter flow rate along the laterals was determined. The electrical conductivity of mixed water delivered from each individual emitter along the 20m and 40m laterals was also measured. A portable conductivity pDS meter model EP11/pH, M6/pH was used to measure the EC of mixed water along the lateral. In all runs, the pressure at the venturi inlet, lateral inlet and end of lateral were checked and recorded. The variations in emitter flow rate along the laterals obtained from the three runs were measured and then plotted. In addition, the impact of the venturi injector being installed, venturi inlet pressure in three different runs, and the different injection liquids on total emitter flow rates and the hydraulic parameters of laterals were measured and then plotted. In Chapter 4. MATERIALS AND METHODS 94 both cases, the air and water temperatures at the experiment site were also recorded. 4.3 Impact of emitter clogging on crop yield and farmer benefit: The effects of different patterns of clogged emitters on the hydraulics of laterals and their impact on reduction in cotton yield (the reason for selecting cotton was discussed in chapter 3) and farmer's loss per unit area were simulated. The computer simulation model determines the value of the total emitter's coefficient of variation (VT) by means of interpolating the data (using table 2.6) as explained in chapter 3. This is to account for relative deficit evapotranspiration (1- ETave/ETm) when clogging occurs. The cotton yield under the no-clogged condition and reduction in yield under different numbers of partially clogged emitters were determined by using equation 2.51. The average of cotton yield harvested per acre and the average marketing price were adopted from the data in the Agricultural Statistics United States, Department of Agriculture (1994). Relationship between the yield reduction and farmer's loss versus different areas were plotted. Relationship between the yield reduction and number of clogged emitters were also plotted and a least-square regression was determined for each area. Chapter 5. RESULTS AND DISCUSSION 95 Chapter 5 5. Results and Discussion 5.1 Introduction: The following sections describe and compare the field experimental measured and predicted values of hydraulics parameters of microirrigation laterals affected by different patterns of emitter clogging along the lateral. First, the hydraulic characteristics of the pressure-compensating emitter model DPJ04-A, Hardi Turbo SC™ Plus, and the emitter manufacturer's coefficient of variation (CV) are determined. Then the test of emitter clogging simulated in the experimental set-up by modifying the Hardi Turbo SC™ emitter in different ways is presented. Next, a relationship between the percentage or degree of clogging, reduction in emitter flow rate and K (emitter coefficient that accounts for areal and discharge effects) is presented. Then, the results obtained from the field experiments are discussed and compared with the theoretical results obtained from computer model with synthetic data. The theoretical results consist of two parts. The first part includes the impact of different patterns of emitter clogging along the different lengths of laterals (10-60 m) on the hydraulics of microirrigation. In the second part, the effect of similar patterns and degrees of emitter clogging as in the field experiment on the hydraulics of a 20m lateral is presented. 5.2 Hydraulic characteristics of emitter: The pressure-compensating emitters are characterized by a very low value of emitter discharge exponent JC. The values of K (emitter coefficient that accounts for areal and discharge effect) and x (emitter exponent) in emitter flow equation (equation 2.1) were estimated to determine the discharge rate for the Hardi Turbo SC™ Plus emitter. A least-square regression analysis based on the logarithm of pressure and discharge of the emitter yielded: x = 0.0757 and K = 3.147 (Figure 5.1). Table 5.1 shows the emitter flow rates operated under different pressures from which the regression analysis was determined. The emitter discharge coefficient K accounts for conversion factors to balance both sides of equation 2.1. The slope of the regression line in Figure 5.1 is the emitter discharge exponent x, which is the measure of the change in emitter flow rate with variations in operating Chapter 5. RESULTS AND DISCUSSION Table 5. 1 Average discharge values of Hardi Turbo SC™' Plus, model DPJ04-A emitters, at different pressures (adopted from Hardi manufacturer's manual). Emitter Pressure(P) Pressure(P) Flow (q) Log(P) Log(q) # (psi) (M) (L/h) (M) (L/h) 1 5 3.52 3.14 0.55 0.50 2 7 4.93 3.60 0.69 0.56 3 10 7.04 3.94 0.85 0.60 4 15 10.56 3.86 1.02 0.59 5 20 14.08 3.94 1.15 0.60 6 25 17.60 4.01 1.25 0.60 7 30 21.12 4.05 1.32 0.61 8 35 24.64 4.05 1.39 0.61 9 40 28.16 4.01 1.45 0.60 10 45 31.68 3.97 1.50 0.60 11 50 35.20 3.90 1.55 0.59 O 0.7 r 0.65 ; 0.6 F 0.55 0.5 0.45 0.4 0.35 F 0.3 0.4 0.6 q = 3.147(h) 0.0757 -i I i i i i L. 0.8 1 log ,P (m) 1.2 1.4 1.6 Figure 5.1 Logarithm of the average emitter discharge and pressure to determine K and x for the pressure compensating emitter model DPJ04-A, Hardi Turbo SCTM Plus. Chapter 5. RESULTS AND DISCUSSION 97 pressure. Based on equation 2.1 and Figure 5.1, the emitter flow equation for this type of pressure-compensating emitter is found to be: According to Karmeli (1977); Kimura (1978); Keller and Karmeli (1975) and Von Bernuth and Solomon (1986), the values of x normally fall between 0.0 and 1.0. The larger the value of x, the more sensitive the emission device flow rate is to a change in pressure. In fully turbulent flow* = 0.5 and in a laminar flow, x = 1. For non-compensating orifice and nozzel emitters, x would be 0.5, and for fully compensating emitters x = 0. When x is equal to 1.0, a change in pressure will be matched by a proportional (equal percentage) change in flow rate (laminar flow). A value of x = 0 means no flow variation with pressure. Values of x greater than 1.0 or less than 0.0 are possible when the elastomeric parts are used in the flow passages. The value of the discharge exponent x (0.0757) obtained from the least-square regression analysis indicates the fully turbulent flow regime for this type (Hardi Turbo SC™) of pressure-compensating emitter. However, it is expected that the emitter flow rates of pressure-compensating emitters should be independent of operating pressure, but our field experiments (to be discussed later) indicate that the discharge from the pressure-compensating emitters may not be constant if a variation in operating pressure occurs. 5.3 Manufacturer's coefficient of variation (CV): The emitters' flow paths are very small and the performance of an emission device is strongly influenced by the quality and consistency with which the devices are manufactured. The manufacturer's coefficient of variation (CV) is a function of the emitter type and the quality control exercised during the manufacturing process. A sample of 20 emitters from total of 40 emitters were randomly chosen to determine the emitter manufacturer's coefficient of variation for the first step of this research. Table 5.2 shows the average emitter flow rate and pressure for this sample. The coefficient of variation was computed by dividing the standard deviation of discharges by the average of emitter flow rate at specific pressure level (equation 2.20). In spite of installing the pressure regulator, it was still difficult to achieve the Chapter 5. RESULTS AND DISCUSSION 98 Table 5.2 Average emitter flow rate and pressure for sample test. Emitters Average Pressure (psi) Average Pressure (kPa) Average Flow Rates(l /h) 1 15.0 105.0 3.94 2 15.2 106.4 3.79 3 15.0 105.0 3.90 4 15.5 108.5 3.90 5 15.1 105.7 3.75 6 15.2 106.4 3.87 7 15.0 105.0 3.90 8 15.3 107.1 3.75 9 15.2 106.4 3.90 10 15.0 105.0 3.78 11 15.1 105.7 3.95 12 15.3 107.1 3.79 13 15.2 106.4 3.90 14 15.3 107.1 3.78 15 15.0 105.0 3.85 16 15.1 105.7 3.90 17 15.5 108.5 3.78 18 15.4 107.8 3.70 19 15.0 105.0 3.75 20 15.2 106.4 3.85 Standard deviation = 0.074 Average emitter flow rate =3.83 CV = 0.0193 Chapter 5. RESULTS AND DISCUSSION 99 constant pressure for this experiment due to the fluctuation of pressure in the city water pipe line. Therefore, the pressure could only be adjusted to 15-15.5 psi by a pressure regulator under the experiment conditions. The calculated value of 0.019 (Table 5.2) for this type of emitter is classified as excellent by the ASAE EP405.1 (1997). Therefore, the computed CV indicates an acceptable quality control during the manufacturing process. 5.4 Influence of energy gain or loss on pressure-compensating emitter: Theoretically, discharge from the pressure-compensating emitters should be independent of operating pressure or energy gain or loss due to slope when the pressures fall within the manufacturer's recommendation. Emitter manufacturers have claimed that the pressure-compensating emitters offer an advantage, especially on sloped terrain. In order to get a reliable measurment of pressure compensation by the Hardi Turbo SC™ emitter, 5 emitters (# 1,6, 10, 15, and 20) under no-clogged conditions were randomly selected along the lateral line laid on flat terrain (experimental set-up described in previous chapter). The system was operated under the 15 psi (average) inlet pressure. Discharge of the relevant emitters were measured two times and average values were determined. Next, this lateral was changed to 3% and then 7% up-slopes conisting of the same number and locations of emitters along the lateral as on flat terrain. Similar measurements were carried out. Table 5.3 shows the average values of pressure and discharge of emitters along the lateral on flat terrain, up-slope at 3% and 7% and down-slope at 3% and 7%. A comparison of discharge variations on flat, up- and down-slopes with manufacturer emitter discharge is shown in Figure 5.2. Table 5.3 and Figure 5.2 indicate that none of the 5 emitters tested under different slopes were even close to the manufacturer's claim. The average deviations in emitter flow (when compared to the manufacturer data) were ± 5.9%, ±3.47% and ±4.51% in flat terrain, and 3% and 7% up-slope respectively. Results show that the emitter flow rates in the case of down-slope terrains were less than the manufacturer's emitter discharge. The average emitter flow variation in 3% and 7% down-slopes were 6.64% and 5.12% respectively. Based on these results, it is concluded that the pressure-compensating emitter may not produce a constant and uniform emitter flow rate along the lateral under pressure variations (i.e. energy gain or loss) caused by sloped terrain. Chapter 5. RESULTS AND DISCUSSION Table 5.3 Emitter discharge and pressure on flat, and sloped terrain affected by energy gain or loss Emitter Flat Terrain -3% (up-slope) -7% (up-slope) 3% (down-slope) 7% (down-slope) # P q P q P q P q P q (psi) (l/h) (psi) (l/h) (psi) (l/h) (psi) (l/h) (psi) (l/h) 1 13.97 3.73 14.95 3.67 14.90 3.64 15.05 3.52 15.10 3.81 6 13.80 3.97 . 14.70 3.74 14.40 4.11 15.30 3.60 15.60 3.57 10 13.67 3.53 14.50 3.94 14.00 3.70 15.50 3.49 16.00 3.62 15 13.50 3.85 14.25 3.93 13.50 4.02 15.75 3.62 16.50 3.61 20 13.33 3.67 14.00 3.84 13.00 4.04 16.00 3.77 17.00 3.76 4.20 4.10 4.00 3.90 £ *_ 3.80 =5 o LL 3.70 CD E LU 3.60 Manufacture -0% slope - * - - 3% slope - - H 7% slope - -* - +3% slope - - +7% slope Manufacturer L; 3%up"slope \ •' / \ \ / + \ ; 7% down £lope / 3.50 I- y 3% aown slope 3.40 ^ 30 |" " " * | | |" * * * * * | | j i n i n 11 i • | • • • • 11 • j i • j n j i 13 13.4 13.8 14.2 14.6 15 15.4 15.8 16.2 16.6 17 17.4 Pressure (psi) Figure 5.2 Comparison of emitter discharge on flat and sloped terrain with manufacturer's emitter flow rate Chapter 5. RESULTS AND DISCUSSION 101 5.5 Simulation of emitter clogging: Partially or completely clogged emitters were artificially made for this research to be placed at different locations along the lateral. Partial clogging may be simulated by installing smaller emitters, and a plug would simulate complete clogging. Many researchers have used a smaller size of emitter to obtain the uniform emitter clogging of their prediction. The problem with this type of simulation is that the hydraulic path-way of the smaller size of emitters may not have the same hydraulic characteristics as the larger size emitters. The other problem with using smaller sized emitters for partial clogging is that it creates uniform partial clogging along the lateral. In practice, this uniform clogging rarely occurrs. A perfectly uniform partially-clogged emitter in a microirrigation system rarely happens in the field due to different types of particles and chemical reactions which cause the clogging. In a microirrigation system, non-uniform clogging often occurs due to the settling of different particles or salt precipitation caused by the interaction of chemical elements with liquid fertilizer or pesticide applied through the system. Therefore, to achieve a more realistic clogging situation, the emitter clogging was simulated by modifying the Hardi Turbo SC™ (nominal emitter flow rate 3.78 l/h) in different ways as follows: A- Removing the emitter cap and randomly plugging several holes of the pressure regulator in the emitter with epoxy glue. B- Gluing the perimeter of the elastomeric disk of the emitter with epoxy. C- Inserting 4-10g coarse sand (40mesh<D<14mesh) on the top of elastomeric disk. D- Introducing 4-15g fine sand (100mesh<D<40mesh) from the inlet barb into the emitter. Table 5.4 shows different types of emitter clogging by epoxy or by introducing sand into the emitter. The volume of water delivered from each clogged emitter under 15 psi- pressure was collected 2-4 times and the average emitter discharge was determined as shown in Table 5.4. Data shows that different types and degrees of clogging resulted in different out-comes from Chapter 5. RESULTS AND DISCUSSION 102 the emitters. It was found that introducing the same amount of particles but at different locations of particles inside the emitter caused different impacts on emitter flow rate. The emitter flow rate was lower than the nominal flow rate in most cases. However, in some cases, the emitter flow rate was higher when the same amount and size of sand was inserted into the emitter under the elastomeric disk. Adding very small particles (fine texture) of sand into the emitter on the top of the elastomeric disk could decrease the emitter discharge. The variation of emitter flow rate was dependent upon the location of particles that settled inside the emitter inlet. Table 5.4 shows that the same amount of fine sand decreased the emitter flow rate from 3.78 //h to 2.63 l/h for test #19 (introducing sand on the top of the elastomeric disk) or increased the emitter flow rate from 3.78 to 5.59 l/h for test #22 (introducing sand under the elastomeric disk). When coarse and medium textured sand was put into emitters #17 and #18, the emitter flow rate decreased from 3.78 to 3.35 and 1.69 llh respectively. Results show that there was an almost 90% chance of lowering the emitter discharge by inserting sand or epoxy into the emitter on the top of elastomeric disk. There was an uncontrolled variable of emitter clogging for this type of pressure-compensating emitter. The variation of flow rate of clogged emitter was dependent upon the amount of clog particles and the nature of the clogging inside the emitter. An emitter having a discharge less than the nominal emitter flow rate (<3.78 l/h) was assumed as the partial clogged emitter in this research. Several partially clogged emitters were artificially made by introducing sand into emitter and measuring the emitter discharge. It was practically impossible to achieve a pre determined degree of emitter clogging. Therefore, different degrees of emitter clogging were made and used in different stages as explained in the previous chapter. Chapter 5. RESULTS AND DISCUSSION 103 Table 5.4 Effect of different types and amount of particles on pressure-compensating emitter (Hardi Turbo SC™ model DPJ04-A) flow rate. Test No. Type of clogging Time Volume of water (cc) q (l/hr) 1 7 holes from 15 pressure regulator holes were clogged by epoxy glue.(50% clog) 13' 26'8" 13'37" 250 cc 250 cc 250 cc 1.115 1.1 1.108 AVE.=1.11 2 3 holes from 15 pressure regulator holes at the middle were clogged by epoxy glue (20% clogging) 5* 57" 5' 58" 5' 58" 250 250 250 2.52 2.51 2.51 AVE.= 2.51 3 Same test as test No. 2 but the clogged location was different. Three clogged holes (by epoxy glue) were selected at the middle part of the 15 pressure regulator holes. 16' 12* 250 250 0.94 1.25 AVE.=1.09 4 50% of the single outlet hole was clogged by epoxy glue. 3' 05' 3' 06" 3"03" 250 254 250 4.86 4.58 4.91 AVE.= 4.78 5 1 hole (the last hole ) from 15 pressure regulator holes was clogged by epoxy glue. 12*50" 13' 14" 250 250 1.168 1.13 AVE.=1.15 6 Same test as test No. 5, but the last hole include outlet were partially clogged. 17' 26" 35' 02" 100 200 0.34 AVE.=0.34 7 4 holes from the end part of 15 pressure regulator holes were clogged by epoxy glue. 180* 0.00 0 AVE.=0.0 8 3 holes (include inlet ) from 15 pressure regulator holes were clogged by epoxy glue. 16' 14" 15'30" 250 250 0.92 0.97 AVE.=0.95 9 All holes except inlet and outlet holes were clogged by epoxy glue. 23' 28" 42' 130 250 0.33 0.36 AVE.=0.35 Chapter 5. RESULTS AND DISCUSSION 104 Continue (Table 5.4) 10 Perimeter of the elastomeric disk was completely clogged by epoxy glue(except the inlet hole) 4' 40" 4' 44" 4' 45" 3' 45" 250 250 250 250 3.21 3.17 3.16 3.88 AVE.=3.18 11 3 holes at the last part (include out-let) from 15 pressure regulator holes were clogged by epoxy glue. 10' 8.5" 10' 8.5" 250 250 1.47 1.47 AVE.=1.47 12 Sand was put into the central hole ( a few particles of sand into the outlet) under the elastomeric disk. 3'38.5" 3'38" 250 250 4.11 4.12 AVE.=4.11 13 Same test as No. 12 but more sand was put into the central hole (under elastomeric disk). 2' 13" 2' 13" 250 250 6.7 6.7 AVE.= 6.7 14 The mixed texture of sand was put around the top of elastomeric disk. 4' 13.5" 5' 6" 250 308 3.55 3.62 AVE.=3.58 15 Sand under the elastomeric disk into the pressure regulator holes. 2' 30" 5' 04" 250 500 6 5.92 AVE.=5.96 16 Same test as test No. 15 but the amount of sand was different. 1*4.5" 0' 56" 1'0" 1*2" 1*45" 250 250 250 250 250 13.95 16.07 15.0 14.51 13.95 AVE.=14.68 17 Coarse texture sand was introduced into the emitter from the inlet barb (not removing the cap). 4' 25" 4*31.5" 4- 29» 250 250 250 3.39 3.31 3.34 AVE.=3.35 18 Medium texture sand was introduced into the emitter from the inlet barb(not removing the cap). 8' 34" 3' 32" 3'33" 3'38" 250 100 100 100 1.75 1.69 1.69 1.65 AVE.=1.69 19 Fine texture was introduced into the emitter from the inlet barb (not removing the cap) 5'38" 5' 44" 5' 43.5" 250 250 250 2.66 2.62 2.62 AVE.=2.63 Chapter 5. RESULTS AND DISCUSSION 105 Continue (Table 5.4) 20 A small amount of sand was put on the top of elastomeric disk from the inlet (not removing the cap) 5' 54" 5* 16" 2* 50" 250 250 115 2.54 2.84 2.43 AVE.=2.52 21 Removed the cap, then a grains of medium textured sand was put on the top of elastomeric disk (test 21,22, 23, and 24 were done with three emitters installed to a piece of polyethylene pipe, 10 cm apart from each other) 7 53" 8* 05" 3' 18" 250 250 100 1.9 1.85 1.82 AVE.=1.86 22 Removed the cap, fine texture of sand was put under the elastomeric disk 1* 08" 2* 35" 2' 38" 100 250 250 5.29 5.8 5.7 AVE.-5.59 23 Removed the cap, mixed texture of sand was put on the elastomeric disk 12' 9' 9" 9' 22" 318 250 250 1.59 1.63 1.6 AVE =1.61 24 Removed the elastomeric disk from emitter, no sand or particles inside the emitter. This emitter was inserted to the one meter polyethylene pipe close to in emitters that had been clogged. The pressure was decreased from 15 psi to 12.5 psi. 0' 12" 0' 12" 0' 12.5" 250 250 250 75 75 75 AVE.=75 25 0.22 gram coarse sand (40 mesh < D < 14 mesh) was put on the top of elastomeric disk by removing cap. 4' 29.5" 4'31" 4' 30" 250 250 250 3.34 3.34 3.33 AVE = 3.33 26 0.22 gram coarse sand was put on the top of elastomeric disk as same as test No. 27, but the system was operated for 8 hours, then the emitter flow rate was measured. 6' 26" 6'31.5" 6' 34" 10' 15" 10' 29" 250 250 250 250 250 2.33 2.3 2.28 1.46 1.43 AVE.=1.96 27 0.22 gram coarse sand on the top of elastomeric disk (removed cap) same as test No. 27 and 28 5hr. 0.0 0.0 AVE.=0.0 28 0.15 gram fine sand ( 100 mesh < D < 40 mesh) was put on the elastomeric disk from the inlet barb. 67 5'25.5" 5' 26" 3319 250 250 2.97 2.76 2.76 AVE.=2.86 29 0.15 gram fine sand ( 100 mesh < D < 40 mesh) was put under the elastomeric disk by removing the cap. 56' 30" 3' 46" 3* 40" 3' 48" 3915 250 250 250 4.15 3.98 4.09 3.94 AVE.=4.04 Chapter 5. RESULTS AND DISCUSSION 106 5.6 Relationship between dimensionless values of K%, Q%, and q%: Based on emitter flow rate and pressure at each section along the lateral (flat terrain) obtained from the field and synthetic data, the reduction of parameters K and q (expressed as K% and q%), and the degree of emitter clogging (Q%) for different patterns of emitter clogging were determined. Table 5.5 shows the values of emitter flow rate, pressure, K%, q%, and Cd% along a 20m lateral obtained from the field experiment. The relationship between K%, q%, and Cd% was plotted (Figure 5.3) and a least-square regression was performed. The K%, q%, and Cd% were determined as follows: There are two flow paths when water is flowing in the lateral of a microirrigation system. One is the path toward the downstream end inside the lateral, and the other is within the emitter. Theoretically, when the pressure-compensating emitters are used in a microirrigation system, the emitter flow rate is independent of operating pressure, if it falls within the pressure range recommended by the manufacturer. In the general equation of emitter discharge (equation 2.1), K is a constant of proportionality that characterizes each emitter and accounts for areal and discharge coefficients. According to the Hardi Manufacturer, the average emitter discharge from the Hardi Turbo SC™ is 3.78 l/h under the operating pressure range of 35 to 350 kPa (5 to 50 psi). Therefore, it can be assumed that the x value in Equation 5.1 for pressure variation along the lateral (within manufacturer's pressure range) is constant. The value was determined to be 0.0757. Equation 5.1 can be used to determine the .rv value as: r- q ^ ^0.0757 In this study, the K value of 3.147 was found for a no-clogged condition. Equation 5.2 shows that both q and h have an impact on K. Any reduction of q can lower the value of K. A lower value of K means a smaller cross-section area of emitter passageway in the emitter. Assuming that Cd% is the degree of clogging, then under a no-clogged condition, Cd% is zero, and the emitter flow rate should be 3.78 l/h (within manufacturer's pressure range) for the type of emitter used in this study. In equations 2.1 and 5.1, when x is constant, the parameters that Chapter 5. RESULTS AND DISCUSSION 107 Table 5.5 Values of K%, q%, and Cd% of 20 emitters along the lateral laid on flat terrain when 30% of the emitters are partially clogged and located at the one-third from the downstream end (Field data) Qi hi k, K% q% Cd% 3.64 10.56 3.045 3.24 3.70 3.24 3.43 10.56 2.870 8.82 9.26 8.82 3.50 10.56 2.928 6.96 7.41 6.96 3.60 10.56 3.012 4.30 4.76 4.30 3.69 10.56 3.087 1.90 2.38 1.90 3.65 10.56 3.054 2.97 3.44 2.97 3.71 10.55 3.104 1.37 1.85 1.37 3.48 10.55 2.911 7.49 7.94 7.49 3.68 10.55 3.079 2.17 2.65 2.17 3.76 10.55 3.146 0.04 0.53 0.04 3.52 10.55 2.945 6.42 6.88 6.42 3.71 10.55 3.104 1.37 1.85 1.37 3.40 10.55 2.845 9.61 10.05 9.61 3.63 10.55 3.037 3.50 3.97 3.50 2.49 10.55 2.083 33.80 34.13 33.80 2.63 10.55 2.200 30.08 30.42 30.08 0.30 10.55 0.251 92.02 92.06 92.02 1.49 10.55 1.247 60.39 60.58 60.39 1.23 10.55 1.029 67.30 67.46 67.30 0.00 10.55 0.000 100.00 100.00 100.00 Degree of clogging (Cd%) 0 10 20 30 40 50 60 70 80 90 100 Figure 5.3 Relationship between K%, q%, and Cd% for 20 emitters along the lateral laid on flat terrain when 30% of total emitters are partially clogged and located at the last section (one-third from downstream end) of lateral. Chapter 5. RESULTS AND DISCUSSION 108 will affect the emitter discharge q are K and h. Assume qt is an emitter flow rate from a "partially clogged" emitter located at zth section along the lateral (hence its value is less than the nominal flow rate q) and ht is the pressure at the corresponding section (i.e. fth section). Under this condition, the emitter coefficient kt can be determined as follows: 5.3 where kt is a fraction of K. The percentage reduction of emitter coefficient can then be determined as: where the K value was found 3.147 (as explained in section 5.1). In a no-clogged situation the percentage of clogging is zero ( or degree of clogging, Q%=0 ), and the emitter is fully opened (100% open), K has its maximum value (3.147). Based on equation 5.4, when there is no reduction in emitter coefficient (i.e. kt = K) K% is 0.0, and Cd% would be zero (no-clogged condition). Under a partially clogged condition, when the value of emitter coefficient decreases to kh the fraction of the passageway in the emitter that is clogged is Cf/o = K% and the fraction that is still operating (functioning) can be calculated by: <9p = (l-^%)l00 5.5 Where Op is the percentage or degree of opening (%). The dimensionless reduction of emitter flow rate from the nominal emitter flow rate can be determined as follows: ,K = I £311100 5.6 where q% is the dimensionless value of reduction in emitter flow rate. Chapter 5. RESULTS AND DISCUSSION 109 In order to obtain a relationship between K%, q%, and Cj%, the flow rates from 20 emitters along the 20m lateral (one emitter per section) laid on flat terrain were measured (see Chapter 4 for details). The pressure at each section along the lateral was determined by equation 2.18. The pressure at the inlet, middle; and end of the lateral was also measured with pressure gauges and was 15psi, 15psi, and 14.9psi respectively. These values were then compared with the computed values shown in Table 5.5. The values of K%, q%, and Cd% were computed by equations 5.4, 5.5, and 5.6 (Table 5.5) and were then plotted (Figure 5.3). The least-square regression analysis for the stage with 30% partially clogged emitters located at the last section (one-third from the downstream end) of the lateral was performed and the linear regression between q%, K%, and Cd% was found as follows: By assuming the conditions of the same field experiment, synthetic data were used in the simulation program for the case of 10, 20, 30, 40, 50, and 60m lengths of laterals. The manufacturer's coefficient of variation of 0.0193 (Table 5.2) was also applied to those emitters that were not clogged. Computed values for K%, q%, and Cd% for the same condition as described above are given in Table A.5.1 (Appendix A). The least-square regression equation for each length of lateral was determined as shown in Table 5.6. Results show that the relationship between K% and degree of clogging (Cd%) is independent of the length of lateral. However, the relationship between reduction of emitter flow rate (q%) and degree of clogging (Cd%) is dependent on the length of lateral. Table 5.6 shows that the intercept and slope values varied in all 6 linear equations for different lengths of lateral. However, these variations which are due to the insignificant differences in pressure variation along the laterals laid on the flat terrain, are not considered to be significant. Table 5.6 shows that the percentage of reduction in emitter flow rate is directly related to the degree of q% = 0.4868 + 0.995\Cd% 5.7 and K% 5.8 Chapter 5. RESULTS AND DISCUSSION 110 clogging. It is found that the rate of reduction in emitter discharge is slightly higher than the rate of degree of emitter clogging. For example, 30% of emitter clogging resulted in 30.19% and 30.22%) reductions of emitter flow rate for the emitters located on 20m and 60m lateral lengths respectively. Table 5.6 Relationship between reduction in emitter flow rate (q%) dimensionless reduction of emitter coefficient (K%), and degree of clogging (Cd%) for different length of laterals (synthetic data). Length of lateral (m) Regression equations 10 q% = 0.2732 + 0.9987Q K% = Cd% 20 q% = 0.2488 + 0.9983 Cd K% = Cd% 30 q% = 0.2473 + 0.9987 Cd K% = Cd% 40 q% = 0.2671 +0.9987 Cd K% = Cd% 50 q% = 0.2720 + 0.9980 Cd K% = Cd% 60 q% = 0.2720 + 0.9980 Cd K% = Cd% 5.7 Comparison of adjusted "F" factor: Computed value of adjusted "F" factor used in head loss equation suggested by Christiansen (1942), Jensen and Fratini (1957), Walker (1976) and Gohering (1976) when 1-200 outlets (emitters) were located along the lateral are given in Table A.5.2 (Appendix A). The value of "F" was computed based on assumptions that the first outlet was located 1 outlet spacing away from the lateral (equation 2.12) or the first outlet was located 1/2 an outlet spacing from the supply line (equations 2.13 and 2.14). Figure 5.4 shows a similar trend in the relationship between the values of "F" obtained from these equations and the number of outlets. Results show that when the number of outlets were less than 20, the "F" values obtained from Jensen, Walker, and Gohering did not deviate more than 4% from "F" values computed by the Christiansen equation. As the number of outlets increased along the lateral, "F" values obtained from all three equations closely approach to each other. Therefore, to determine "F", where either the first outlet is located one outlet or a half outlet spacing from the lateral inlet, one of the aforementioned equations can be used and applied to the Christiansen head Chapter 5. RESULTS AND DISCUSSION o o a T3 0) GO < F' Jensen F" Walker F'" Gohering 50 100 150 Number of outlet (emitter) 200 Figure 5.4 Comparison of adjusted "F" factor (F.F'.F.F'") for multi-outlet pipe Chapter 5. RESULTS AND DISCUSSION 112 loss equation. In this study, as the first emitter was located one spacing away from the lateral inlet, the Christiansen equation was used to calculate "F". Table A.5.2 shows the value of "F" is equal to one when there is one outlet along the lateral. Therefore, in determining the head loss (hf) at each section consisting of one emitter per section along a lateral, both the Hazen William equation ( equation 2.10) and the Christiansen equation (equation 2.11) will yield the same result. 5.8 Field experiments 5.8.1 Step 1, hydraulic characteristics of lateral laid on flat terrain: Step 1 of the field experiment was conducted to evaluate the effects of different patterns of emitter clogging (different number, degree, and location of clogged emitters) on the hydraulic characteristics of a microirrigation lateral laid on a flat terrain (Figure 4.1). The results obtained were compared to those simulated with the computer program. Head loss (Hf), pressure variation (Hvar), emitter flow variation (qvar), emitter discharge coefficient of variation (Vqs), emitter discharge coefficient of variation due to hydraulics (Vqh), hydraulic design coefficient of variation (Vhs), and emitter performance coefficient of variation (Vpf) were evaluated. To estimate the uniformity through the microirrigation system, the impact of different patterns of clogging on coefficient of uniformity (CU), field emission uniformity (EU') ^distribution uniformity (DU), application efficiency (Ea), statistical uniformity of emitter discharge (Us), and emitter statistical uniformity due to hydraulic (USh) were also evaluated. In addition, by using the field and synthetic data, the impact of clogging on reduction of cotton yield was simulated and the farmer's money loss caused by emitter clogging along the lateral in a microirrigation system were estimated for different areas. Equations number 5.1, 2.4, 2.10, 2.15, 2.18, 2.19, 2.27, 2.29, 2.31, 2.33, 2.35, 2.36, 2.37, 2.38, 2.39, 2.40, 2.41, 2.42, and 2.51 were used to calculate the above parameters. Two 20m, 15mm inside diameter polyethylene laterals (laterals A and B) were used for this step of the field experiments. Twenty pressure-compensating emitters with a nominal emitter flow rate of 3.78 l/h were inserted on-line along each lateral. The first emitter was located Chapter 5. RESULTS AND DISCUSSION 113 lm away from the lateral inlet. A 105 kPa (15 psi) pressure regulator was installed at the inlet of the laterals to keep the pressure at the manufacturer's recommended level. The emitter flow variation along the laterals was measured under eight different patterns of clogging (stages 1 to 8) as explained in Chapter 4. The term "desired situation" (stage 1) was used to express an operating condition in the microirrigation system shown in Figure 4.1, with no emitter clogging and with the application of city water into the system. Lateral A was used in the first stage (no-clogged condition) and lateral B was used in the rest of the seven stages consisting of several partially clogged emitters. Different percentages and degrees of emitter clogging were applied in a lateral line of the microirrigation system. The number of partially clogged emitters is expressed as the percentage of the total number of emitters along the lateral. The experimental set-up had 20 and 40 emitters per lateral. Therefore, a 30% partial clogging pattern means that 6 and 12 emitters respectively had been simulated to reduce their flow to lower than the nominal emitter flow rate. The individual emitter flow rates along the laterals were measured four times in each stage. The average emitter flow rates obtained from the field experiment are shown in Table 5.7 for all the eight stages. Although the constant and equal discharges from the no-clogged emitters were expected, as Table 5.7 shows, the emitter flow rates along the laterals were not the same at each section—even in stage 1 with the desired situation. The reasons for the variations in emitter flow rates in all of stages are the emitter manufacturer's variation and pressure variations along the lateral. Figure 5.5 shows how the manufacturer and pressure variations along the lateral have an impact on the discharge of emitters. The microirrigation system was operating within the pressure (15 psi) recommended by the manufacturer, but the emitter discharge along the lateral varied between 3.4 and 3.97 l/h. Non-overlapping curves in Figure 5.5 also indicate the variation of discharge from no- clogged emitters along the lateral in different stages. For example, the first 6 emitters in stages 2 and 3 (no-clogged emitters) which should have delivered the same flow rate show different values of discharge, as shown in Table 5.7. It is found that any clogged emitters along the lateral have significant impact on the flow rate of the rest of the no-clogged emitters along the line. However, it is practically impossible to predict the exact nature of clogging and its actual impact on the rest of the emitters in the system. Chapter 5. RESULTS AND DISCUSSION 114 Table 5.7 Average emitter flow rate (l/h) along the laterals laid on flat terrain under different stages with clogged and no-clogged emitters* Emitter # Stage-1 Q d/h) Stage-2 q(l/h) Stage- 3 Q 0/h) Stage-4 Qd/h) Stage- 5 q(l/h) Stage- 6 q(l/h) Stage- 7 Stage- 8 q 0/h) q (l/h) 1 3.73 3.64 3.83 1.71 1.99 3.78 3.61 3.65 2 3.55 3.43 3.48 2.58 3.46 3.47 3.38 3.43 3 3.74 3.50 3.89 2.11 1.72 1.92 3.46 3.56 4. 3.78 3.60 3.70 2.47 3.76 3.78 2.14 3.75 5 3.62 3.69 3.48 0.55 0.26 3.58 3.46 3.52 6 3.97 3.65 3.72 0.86 3.73 1.03 3.51 3.60 7 3.91 3.71 1.74 3.66 3.66 3.69 3.59 3.65 8 3.69 3.48 0.05 3.46 3.92 3.19 3.77 3.89 9 3.42 3.68 1.67 3.68 1.32 3.64 3.54 3.60 10 3.52 3.76 2.49 3.77 3.49 3.52 3.39 3.46 11 3.74 3.52 2.22 3.50 1.17 3.72 3.58 3.62 12 3.55 3.71 2.17 3.74 3.42 0.92 3.37 3.43 13 3.50 3.40 3.42 3.40 3.37 3.40 0.33 3.60 14 3.83 3.63 3.65 3.63 3.61 3.66 3.51 3.56 15 3.85 2.49 3.56 3.80 3.59 3.63 3.45 3.48 16 3.54 2.63 3.46 3.42 2.24 3.54 3.44 1.85 17 3.48 0.30 3.54 3.55 3.53 3.52 3.44 3.42 18 3.40 1.49 3.62 3.64 3.57 3.57 3.50 3.54 19 3.73 1.23 3.64 3.62 3.64 3.61 3.54 3.59 20 3.67 0.00 3.72 3.80 3.66 3.70 3.56 3.63 lateral inh 73.22 58.54 61.05 60.95 * Stage-1: no-clogged emitters * Stage- 2 to 8: partially or fully clogged emitters 59.11 64.87 65.57 69.83 Chapter 5. RESULTS AND DISCUSSION 115 No Clog 30%,1/3L,DC 30%,1/3M,DC 30%,1/3F,DC 30%,R,DC 20%,R,D10%,R,DC —I— 5%,R,DC nominal flow rate Figure 5.5 Variations of emitter discharge along the lateral due to emitter clogging, manufacturer and pressure variations. Chapter 5. RESULTS AND DISCUSSION 116 5.8.1.1 Total head loss (Hf): Total head loss along the lateral was directly related to the amount of flow at the lateral inlet. Table 5.8 shows the values of head loss (Hf) and the lateral inlet discharge. The highest head loss was found under no-clogged conditions (stage 1). The minimum head loss was obtained in stage 2, when 30% of emitters are partially clogged and located at the last one-third section of the lateral. Figure 5.6 shows the variations in head loss and the flow at the lateral inlet under different patterns of emitter clogging. As number of clogged emitters along the lateral increased, the amount of flow at the lateral inlet and, consequently, the total head loss will decrease. Tables 5.8 and 5.9 show the values of head loss increased from 0.0073m in stage 2 (30% clogging) to 0.0119m in stage 8 (5% clogging) and 0.0132m in stage 1 (no-clogged). Similar results as in the field experiment were obtained from computer simulation of the synthetic data (Table 5.10). Figure 5.7 shows the total head loss and pressure variations under different stages consisting of different percentages of clogged emitters. The variations in Hf'm. stages 2 to 8 were due to the different locations and degrees of clogged emitters. As shown in Table 5.8 and Figures 5.6 and 5.7, as the clogged emitters occurred closer to the lateral inlet, the total Hf approached that of the no-clogged condition. It was found that if the clogged emitters were located at the first one-third section of the lateral, they had no significant impact on the emitter flow rate from the rest of the emitters along the lateral. Figures 5.6 and 5.7 also show that stages 2 to 5 with 30% of emitter clogging at different locations, the same manufacturer's variation, and almost the same lateral inlet discharge have different impacts on head loss. The pressure was almost constant at each section along the lateral laid on flat terrain in each stage. Figure 5.8 show that there are no significant differences between pressure in each section under different stages. Table A.5.3 and A.5.4 (Appendix A ) show the values of head loss and pressure per section, and energy drop ratio and total pressure drop per section obtained from the experimental set-up. Results show that the location and the degree of clogged emitters were the major factors affecting Hf along the lateral on flat terrain. This is because the different locations of clogged emitters cause different pressure variations along the lateral, which have different effects on head loss (Figure 5.7). As shown in Table 5.8, there were no significant differences in /^obtained from stages 4, 6, and 8 with 30%, 20% and 5% clogged emitters. Results show that the number of partially clogged emitters had less effect on Hf than location and degree of Chapter 5. RESULTS AND DISCUSSION Table 5.8 Flow rates at lateral inlet and head loss under different patterns of clogging Stage # Inlet lateral QL (l/h) Head loss H',(m) 1 73.22 0.0132 2 58.54 0.0073 3 61.05 0.0095 4 60.95 0.0113 5 59.11 0.0098 6 64.87 0.0110 7 65.57 0.0108 8 69.83 0.0119 CD 2> CO _£Z O 0) "ro L— CD CD 80 -r 70 -\ 60-\ 50 -I 40 -I 30 -\ 20 -I 10 -\ 0 +-.0 + + • lateral discharge • Head loss —I 1 3 4 5 Stage T 0.020 4- 0.015 + 0.010 4- 0.005 8 Figure 5.6 Relationship between discharge at lateral inlet and total head loss under different patterns of clogged emitters. Chapter 5. RESULTS AND DISCUSSION 3 CO CD i_ CD co i CD TO CD -C D) C o 03 CO E CD "O CD CD D) O O CO c 1_ CD • CO Q. 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T— CM oo LO LO j sS CO CD LO ^— CO CM CO Q CO CO CD CD ai CD fn oi LO CO LO LO r- 00 CD CO CO co 00 CO LO LO r-~ CD CM LU oo LO ai cb T— CO CD CD CO •<J- •<t CO CO 00 00 LO co CD •c— CM ^ CN o CD CO CD CD ,—. h~ CO rr\ oo r-~ 1^-CO CD \J1 CD CD cn CD CO CD LU o> 05 CD CD CO CO CO CO CD CO CD CO CO cb ai ai ai CD CD CO CO CO CO CO CO CO CD ~p CD CD co oo CO O CO CO CM CM CO d CD d CD CD co 00 00 CD o LO CN CD LO oo 00 1_ o LO 00 00 00 00 CO ^— o o o o o o o > o o o o o o o o d d d d d d d d CD CD CD CM CM co ITI V- CM LO CO CD T— LO CD CO CO T— CD T— T— X O o o o T-d d d d d d d d CO o oo co m o CO X CD o o CM CM — (— CO o CM o T— CM CM CO T— o ^— T— T— T— o o o o o o O O O 1- d d d d d d d d 0) O) CO -1—< No CM CO LO CD 00 V) Chapter 5. RESULTS AND DISCUSSION 119 Stage Figure 5.7 Head loss and pressure variation under different stages Chapter 5. RESULTS AND DISCUSSION 120 0.002 0.0015 4-g 0.001 0.0005 4-—•— No Clog (Hf/sec.) »-* 30%,1/3F,DC • 10%,R,DC 30%,1/3L,DC 30%,R,DC 5%,R,DC -30%,1/3L,DC -30%,R,DC -5%,R,DC -30%,.1/3M,DC • 20%,R,DC * 30%,1/3M,DC H 20%,R,DC • • • No Clog (Hi/sec.) • • -30%,1/3F,DC - — 10%,R,DC T 10.57 10 12 14 16 18 20 Section Figure 5.8 Head loss and pressure per section along a lateral laid on flat terrain. Chapter 5. RESULTS AND DISCUSSION 121 clogged emitters. Similar results as in the field experiment were found for ///•from the computer simulation program. Figure 5.7 compares the observed (field) results and predicted results (from simulation) of Hf whitin different patterns of clogging. Figure 5.9 shows the relationship between the cumulative Hf and head loss per section along the lateral. The total Hf at each section was rapidly increased at the first OAL of lateral and was almost constant at the last 0.6L of lateral. These results closely agreed with those reported by Keller and Karmeli (1974). Figure 5.9 also shows that the increment of total head loss at each section decreased from inlet to the end of lateral and is almost zero at the last section of lateral. This is due to the reduction of flow in the lateral along the line toward the downstream end. 5.8.1.2 Pressure variation (Hvar): The pressure variation Hvar shows the variation between maximum and minimum pressures along a lateral. The largest pressure variation (0.12%) was found in stage 1, and the lowest (0.069%) occurred in stage 2. Figure 5.7 shows that pressure variations follow a similar trend to head loss whitin different patterns of clogging. In the case of 30% clogging in stages 2, 3, 4, and 5, the higher pressure variation was obtained when clogging occured near the lateral inlet (stage 4) and the minimum Hvar was observed when the clogging occurred at the lateral downstream end (stage 2). Therefore, the location of clogged emitters had an impact on pressure variation along the lateral. The average pressure variation in stages 2, 3, 4, and 5 was 0.089%, where, the values of Hvar were 0.10%, 0.10%, and 0.12% in stages 6, 7, and 8 respectively. Results show that as the number and degree of clogged emitters along the lateral decreased, the pressure variation increased. Figure 5.10 shows that the energy drop ratio in all 8 different stages studied have a similar trend. 5.8.1.3 Emitter flow variation ( qvar): The variation of emitter flow rate was evaluated in each stage by using equation 2.36. Under a no-clogged condition the emitter discharges along the lateral were not equal to each other. Most of the emitters along the lateral had higher or lower discharges than the nominal emitter flow rate in stage 1. Figure 5.5 shows that the maximum and minimum emitter discharge in the no-clogged condition (3.97 and 3.4 llh) were obtained from emitters number 6 and 18 respectively. Chapter 5. RESULTS AND DISCUSSION No Clog (Total Hf) 30%,1/3F,DC —I 10%,R,DC • O- - 30%,1/3L,DC - X- - 30%,R,DC - +- - 5%,R,DC 30%,1/3L,DC 30%,R,DC 5%,R,DC • - •• • 30%,1/3M,DC - - X- - 20%,R,DC 30%,1/3M,DC • - +- - 20%,R,DC • - — - No Clog (Hf per section) - A- - 30%,1/3F,DC - O- - 10%,R,DC -r 0.0020 0.0015 4- 0.0010 4- 0.0005 I i iOi"iyri0i-i*l*Lf c<p«^ 0.0000 8 10 12 Section 14 16 18 20 Figure 5.9 Total head loss and Hf per section under different patterns of emitter clogging (flat terrain). Chapter 5. RESULTS AND DISCUSSION No Clog -• 30%,R,DC No Clog • -X • • 30%,R,DC • •• - 30%,1/3L,DC 20%,R,DC 30%,1/3L,DC • * • • 20%,R,DC 30%,1/3M,DC - 10%,R,DC -30%,1/3M,DC - 10%,R,DC 30%,1/3F,DC 5%,R,DC 30%,1/3F,DC • + - - 5%,R,DC 11 13 15 17 19 0.03 0) c E o 0.03 + 0.02 4-0.02 « 0.01 4-0.01 0.00 jfTT^^-*'—* * * 1.0 :-0.9 :- 0.8 :- 0.7 :• 0.6 i- 0.5 -r-.ZLT-"-r£- 0.4 :- 0.2 + 0.1 0.0 10 11 12 13 14 15 16 17 18 19 20 Section Figure 5.10 Relationship between total head loss and energy drop ratio under different sections along lateral. Chapter 5. RESULTS AND DISCUSSION 124 The major reason for these variations is the emitter manufacturer coefficient of variation (CV). Wu and Gitlin (1974) reported that a microirrigation system can be designed hydraulically to maintain emitter flow uniformity within 10% or 20% emitter flow variations. The emitter flow variation (qvar) caused by hydraulics was found to be 0.0101 (or about 1%) in stage 1, which is in the acceptable ranges according to Wu and Gitlin (1974) and Bralts et al. (1987) (The value of qvar less than 10% for a well-designed system and greater than 20% is not acceptable). The relationship between the observed and predicted qvar and pressure variations along the lateral are shown in Figure 5.11. It was found that the qvar was indirectly related to the number of clogged emitters. On the other hand, as the number of clogged emitters along the lateral increased, the value of qvar decreased. The reason is that the reduction in lateral flow due to clogged emitters reduces the pressure variation and resulted lower qvar. The qvar is changed whenever the pressure changes along the lateral. Therefore, qvar is used in a microirrigation system for hydraulic design evaluation. Figure 5.12 shows the relationship between gwand Hvar resulting from the field and synthetic data in different stages A linear relationship was found as: Hvar = 13.198 qvar + 0.00005 with R = 0.99999 for a lateral laid on flat terrain under different patterns of emitter clogging. At least two factors can result in this high correlation: one is the use of pressure-compensating emitter, and the second is that there was no significant pressure variation along the lateral laid on flat terrain. This close relationship verified that qvar is one useful parameter which can be used for evaluating the hydraulic design of a microirrigation system. Figure 5.11 shows that qvar varied in stages 2 to 5. These stages consisted of 30% clogged emitters along the lateral at different locations. It was found that the location of clogged emitters has an impact on qvar. For example, Tables 5.8 and 5.9 show that the total lateral flow in stages 3 (61.05 l/h) was higher than in stage 4 (60.95 l/h ) but the values of Hvar and qvar in stage 3 were less than stage 4. The qvar according to these stages were 0.0061 and 0.0081. This means higher lateral flow in stage 3 resulted in a lower value of Hvar and qvar- The major factor in this reduction was the location of clogged emitters. Chapter 5. RESULTS AND DISCUSSION 125 Figure 5.11 Emitter flow and pressure variations along the lateral under different patterns of clogging. Chapter 5. RESULTS AND DISCUSSION 126 Figure 5.12 Relationship between Vqhl and Hvar versus emitter flow variation(qvar) in flat terrain. Chapter 5. RESULTS AND DISCUSSION 127 5.8.1.4 Emitter discharge coefficient of variation (Vqs): The emitter discharge coefficient of variation (Vqs) is the statistical term used to describe the variation in emitter flow rate in a microirrigation system for a given set of operating conditions.Tables 5.9 and 5.10 show the values of Vqs obtained from the field and synthetic data respectively. The maximum and minimum Vqs were found in stages 2 and 1 respectively. The emitter discharge coefficients of variation were 0.04 and 0.01 in stage 1 resulting from the field and computer simulation respectively. This means that there is no significant difference in emitter flow rate under this stage. The values of Vqs increased as the number of clogged emitters along the lateral increased. Figure 5.13 shows the relationship between coefficients of variation versus different patterns of emitter clogging. Emitter discharge coefficient of variation, Vqs is directly related to the degree and number of clogged emitters. Therefore, the more clogged emitters along the lateral, the higher the values of Vqs. Results show that the values of Vqs were 0.4, 0.32, 0.32, and 0.35 in stages 2, 3, 4, and 5 consisting of 30% emitter clogging, whereas its values were 0.04, and 0.1 in stages 1 and 8 with no-clogged and 5% clog conditions respectively. It is evident that the fewer the clogged emitters (higher lateral flow), the smaller the coefficient of variation of emitter flow in a microirrigation system. Results also show that the location of clogged emitters along the lateral has a different impact on the emitter discharge coefficient of variation (Figure 5.13 and Table 5.9). For example, 30% clogging in stage 2 resulted in 0.398 of Vqs and 58.54 l/h in lateral flow (Table 5.8), whereas they were 0.356 and 59.11 l/h in stage 5 respectively. It is found that in spite of an existing lateral flow in stage 2 lower than in 5, the Vqs was higher in stage 2. 5.8.1.5 Emitter discharge coefficient of variation due to hydraulic (Vqh): The maximum (2.9xl0~5) emitter discharge coefficient of variation due to hydraulic (Vqh) was found in stages 1 and the minimum (1.6xl0"5) in stages 2 in both experimental and simulation results. The values of Vqh were 2.1xl0"5, 2.5xl0"5, and 2.1xl0"5, in stages 3, 4, and 5. Results indicated that although location of clogged emitters have an impact on Vqh, the number of clogged emitters is a major factor affecting F^.The higher the number of clogged emitters along the lateral, the lower the values of Vgh. The smallest value of Vqh was found in stage 2, consisting of 30% clogged emitters with the highest value of emitter discharge coefficient of Chapter 5. RESULTS AND DISCUSSION 128 variation (Vqs). This is because the 30% clogged emitters in the last one-third section of lateral reduced the lateral flow and decreased the pressure along the lateral. Figure 5.13 shows the inverse relationship between Vqs and emitter discharge coefficient of variation due to hydraulic, Vqf,. It also shows that the Vqh is slightly changed under all eight stages. This is due to the very small variations of pressure along the lateral laid on flat terrain. 5.8.1.6 Hydraulic design coefficient of variation (Vhs): The Vf,s is a statistical term used to describe the variation in hydraulic pressure in a lateral or throughout the microirrigation system. It is found that there were no significant differences in hydraulic design coefficient of variation at different stages under the flat terrain condition. However, as the number of clogged emitters along the lateral decreased, the value of VhS increased. Figure 5.13 shows that Vhs has a trend similar to the emitter discharge variations due to hydraulic (Vqh ). The maximum value of Vhs (3.8 x 10"4) was obtained in stage 1 and the minimum value (2.2 x 10"4 ) occurred in stage 2. Table 5.9 shows that the values of Vhs varied within the stages 2, 3, 4, and 5 when the 30% clogged emitters were located at different parts along the lateral. The differences of Vhs in stage 1 and 2 with 0% and 30% clogging was 1.7 x 10"4. The values of Vhs also differed up to 1.2 x 10"4 in stages 2 to 5 consisting of 30%> clogged emitters. Higher values of hydraulic variations were found in stages 6 to 8 than in stages 2 to 5. The reason was the lower number of clogged emitters in stages 6 to 8 resulted the higher discharge and pressure variation along the lateral. Results show that the number, degree and location of clogged emitters along the lateral affect Vhs, but the former have a higher impact than the latter. 5.8.1.7 Emitter performance coefficient of variation (VPJ): The values of emitter performance coefficient of variation obtained from field and synthetic data are presented in Tables 5.9 and 5.10. The values of Inversus different stages were plotted as shown in Figure 5.13. In stage 1, the value of Fp/was 0.04 and it was considered to be acceptable according to the ASAE criteria (ASAE EP458, 1997). In stages 2 to 5 where 30% of total number of emitters were partially clogged, Vp/ was greater than 20%. The Chapter 5. RESULTS AND DISCUSSION Figure 5.13 Coefficients of variation of Vqs, Vhs, Vqh, and Vpf in different stages studied. Chapter 5. RESULTS AND DISCUSSION 130 highest value (0.40) of Vpj was found in stage 2. Different values of Vpf were found under stages 2 to 5 (0.40, 0.32, 0.32, and 0.36 respectively). According to the ASAE EP458 (1997) a value of Vpf greater than 20% is unacceptable. In stage 8, when 5% of total number of emitters were partially clogged, the Vpj decreased to 0.11 which is fair for the microirrigation system. Figure 5.13 shows that I^/has a similar trend to Vqs at different stages. Results show that very small variations of Vqh along the lateral have no significant impact on Vpj. It is found that the number of clogged emitters has a higher impact on emitter performance coefficient of variation than the location of clogged emitters does. 5.8.1.8 Coefficient of Uniformity (CU): In general practice, the coefficient of uniformity (CU) is used for the evaluation of spatial uniformity in a microirrigation system. Under field conditions, the CU indicates the uniformity of water application to the soil resulting from the emitter water distribution and soil moisture overlapped by emitter spacing along the lateral. The CU was used to evaluate the application uniformity under the 8 different stages studied. As expected, CU was high (> 95%) under the no-clogged condition (Tables 5.9 and 5.10 ). The minimum CU were found in stages 2 and 5 (67.8% and 69.44% ) when 30% clogged emitters were located at the last one-third section or randomly located along the lateral. The values of CU were 73.87% and 73.73% in stages 3 and 4 respectively. In stages 6, 7, and 8 as the number of clogged emitters decreased, the values of CU increased as compared to stages 2 to 5. Figure 5.14 shows that the CU increased from 81.7% to 94.6% in stages 6 to 8. Results show that the number of clogged emitters along the lateral was the major factor affecting CU. Although the minimum value of CU was found in stage 2, there were no significant differences between the values of CU in stages 2 to 5. This means that different locations of clogged emitters along a lateral laid on flat terrain have no impact on CU. A CU of 95% or higher is expected for a well-designed microirrigation system. However, Wu (1974) has recommended a CU of 98% or higher. Results show that the coefficient of uniformity was low in stages 2 to 7 (CU were between 67% to 87%). The value of CU in stages 1 and 8 were 96.26% and 94.62% which indicates excellent and good uniformity throughout the microirrigation system. It is concluded that the number and degree of clogged emitters are the most important factors affecting CU. It is also found that the Chapter 5. RESULTS AND DISCUSSION 13 Figure 5.14 Variations of CU, Ea, DU, Us, and Ush under eight different stages. Chapter 5. RESULTS AND DISCUSSION 132 impact of the location of clogged emitter on CU was not significant for the lateral laid on flat terrain. 5.8.1.9 Statistical uniformity (Us): Statistical uniformity is used to estimate the uniformity of emitter flow rates throughout the system in similar way as for CU. The results show that both Us and CU have similar trends under all eight stages on a flat terrain (Figure 5.14). The maximum value of Us (>95%) was obtained under the no-clogged condition, and its value decreased as the number of clogged emitters along the lateral increased. Lowest Us occurred in stage 2 and 5 (60.1% and 64.3%). As with CU, the location of clogged emitters had no significant impact on Us. According to ASAE criteria (ASAE EP458, 1997) and Bralts and Edward (1986), the statistical uniformity of the emitter discharge was poor ( 60%-70%) in stages 2 to 5 and fair (70%-80%) in stages 6 and 7 (Table 5.9 and 5.10). The values of Us in stages 1 and 8 are 95.66% and 88.77%, which indicates excellent and good uniformity. Since the values of Us were low in the case of 30% clogging at different locations along the lateral, the clogged emitters should be replaced. If 10%-20% of emitters are partially clogged, the cleaning of clogged emitters will improve the statistical uniformity. Results show that the number, location, and degree of clogged emitters along the lateral all have an impact on Us, and Us is more sensitive to the number and degree of partially clogged emitters than to the location of clogged emitters. In all 8 patterns of clogging, the values of Us were about 9% lower than the values of coefficient of uniformity. The CU and Us obtained from experimental and theoretical analysis are summarised in Table 5.11. The CU versus Us were plotted (Figure 5.15) and a least-square analysis on the CU and Us yielded the following linear regression equation: CU = 14.017 + 0.S96Us 5.9 The statistical uniformity due to hydraulics (Ush ) was also analysed for different patterns of emitter clogging and presented in Tables 5.9 and 5.10. The small differences in the values of Ush obtained from experimental and theoretical analyses illustrated that the Ush was not affected by pressure variation along a lateral on a flat terrain. Figure 5.14 shows the values of Ush at Chapter 5. RESULTS AND DISCUSSION 133 Table 5.11 Coefficient of uniformity and statistical uniformity obtained from experimental and theoretical results for 20 m lateral laid on flat terrain. Stages Us(%) CU(%) 1 98.737 98.939 1 95.661 96.261 8 88.765 94.618 8 78.834 90.788 7 77.297 87.534 7 76.742 86.965 6 73.826 81.767 6 73.142 80.862 4 67.966 73.733 3 67.869 73.874 4 67.037 72.444 3 67.025 72.657 5 64.349 69.437 5 63.348 68.143 2 60.156 67.810 2 59.400 66.615 50 4^-"—'—1—1—I—'—'—'—'—I—1—'—'—'—I—'—1—'—>—I—'—1—>—1—I 50 60 70 80 90 100 Statistical uniformity (Us) Figure 5.15 Relationship between CU and Us under different patterns of clogging for a lateral laid on flat terrain (experimental and theoretical results). Chapter 5. RESULTS AND DISCUSSION 134 different stages. The flat line of this graph indicates that the Ush was almost constant and equal to 99.99% in all stages. It is indicated that the reason for low values of Us in stages 2 to 7 (mentioned above) was the combined impact of emitter clogging and emitter manufacturer's variations. 5.8.1.10 Distribution uniformity (DU) and application efficiency (Ea): The highest value of distribution uniformity was 94% under the no-clogged condition (Stage 1). It was decreased to 48%, 58%, 58%, and 51% in stages 2 to 5 respectively (Tables 5.9 and 5.10). The reason for the low value of DU in stage 2 is the higher degree of emitter clogging (see Table 5.8). Results indicated that there were no significant differences between values of DU when 30% of emitters were clogged and located at different parts along the lateral. Figure 5.14 shows that as the number of clogged emitters decreased, the DU increased. It was found that DU increased from 71% to 91% when the number of clogged emitters along the lateral decreased from 20% to 5% in stages 6 to 8 respectively. Results indicated that the number and degree of clogged emitters are the major factors affecting DU. The location of clogged emitter has little impact on distribution uniformity in a microirrigation system. The application efficiency (Ea) indicates how well the irrigation water is applied to the field. In other words, it reflects how efficiently a microirrigation system delivers water from its source to the field (or to soil near the crop root zone). The values of Ea in both experimental and theoretical results were greater than 99.9% for the eight different stages studied (Figure 5.14). Since the minimum and the average pressure along the lateral are considered in the application efficiency equation, the small pressure variations along the lateral line on a flat terrain have no significant impact on either emitter discharge or, consequently, on Ea under different patterns of clogging. Results obtained from the field and synthetic data presented in Table 5.9 and 5.10 show that there is a high correlation between Ea and Ush. Figure 5.16 shows the relationship between the Ea and USh for a lateral laid on flat terrain. A least-square regression line was fitted through the data point in Figure 5.16 and a linear equation was determined as follows: Chapter 5. RESULTS AND DISCUSSION 135 99.9988 -r 99.9984 4-99.9980 4-co LU >i O c a> £ 99.9976 + Q) C o I 99.9972 + cl Cl < 99.9968 Ea = Ush R2 = 0.9878 + + J • 1 1 + 99.9972 99.9974 99.9976 99.9978 99.9980 99.9982 99.9984 99.9986 Statistical uniformty due to hydraulics,USh (%) Figure 5.16 Relationship between Ea and USh on a flat terrain. Chapter 5. RESULTS AND DISCUSSION 136 Ea = Ush (R2 = 0.9878) 5.10 It should be noted that a high value of Ea does not necessarily mean a good distribution of water by the microirrigation system. 5.8.1.11 Field emission uniformity (JEW): The maximum value of field emission uniformity obtained from the field experiment was 94.62% in stage 1 under the no-clogged condition (Tables 5.9 and 5.10). In stages 2 and 5, EU' decreased to 37% and 43% respectively (Figure 5.14) and its values in stages 3 and 4 were 51.4% and 50.5% respectively. Figure 5.14 also shows that as the number of clogged emitters along the lateral decreases, the emission uniformity will increase. Figure 5.14 shows that the values of EU' in stages 2 to 5 consisting of 30% clogged emitters varied from one stage to the other. There are two factors which affect the emission uniformity in stages 2 to 5. One is the degree of emitter clogging and the other is the pressure variation. Both factors affect emitter discharge and hence the emission uniformity. However, it was found that the degree of clogging has a higher impact on EU' than the pressure variation along the lateral. When the total number of clogged emitters along the lateral decreased from 20% to 5% in stages 6 to 8, EU' increased from 64% to 89% respectively. Results indicated that the number, degree, and location of clogged emitters effected field emission uniformity. The number and degree of clogged emitters were the major factors, but the impact of the location of clogged emitters was not significant. 5.8.1.12 Crop yield reduction due to emitter clogging: Uniform application of water in agriculture has a major impact on crop production and net farm income. This part of study presents a rough estimation and the theoretical analyses of cotton yield based on the emitter coefficient of variations values obtained from different patterns of clogged emitters along the lateral in the experimental set-up. Cotton was selected as a sample crop because of the availability of several parameters required for the crop yield analysis from previous studies which were done by Sammis and Wu (1985). The effects of different patterns of emitter clogging on cotton yield and the loss caused to farmers were studied for different areas. The cotton yield reduction in percent was calculated using Equation Chapter 5. RESULTS AND DISCUSSION 137 2.51. This equation was applied both to results obtained from the field and synthetic data, and the results are given in Tables A.5.5 and A.6.6 (Appendix A). Results show that the minimum reduction of yield (1.475%) occurred in stage 1 (no-clogged ) and the maximum reduction (10.64%)) obtained in stage 5 consisting of 30% clogged emitters randomly located along the lateral. The reason for the reduction in yield in stage 1 was the emitter manufacturer's coefficient of variation. Results indicated that as the number and degree of clogged emitters increased, the reduction of cotton yield increased. There were no significant differences in yield reduction caused by different locations of clogged emitters along the lateral. Therefore, the number and degree of clogged emitters were the major factors affecting the cotton yield. According to the data reported by Agricultural Statistics US. Dept. of Agric. (1994), the average cotton yield of 0.7076 ton/hectare was determined from data in 1984 to 1993 (Table 5.12). The average value for cotton was also determined and estimated to be equal to US $1.3/kg (Table 5.12 ). Five different sized areas of 1 ha, 10 ha, 100 ha, 1000 ha, and 10,000 ha were selected in order to illustrate the reduction in cotton yield and money loss under different patterns of clogged emitters. Table 5.13 shows the reduction in cotton yield under different areas for stages 5, 6, 7, and 8 when the 30%), 20%, 10%, and 5% clogged emitters were randomly located along the lateral. The reason for selecting stages 5 to 8 was that these patterns can be encountered under real contitions. In the field conditions, there exists more chance of random clogging along the lateral. It is clearly shown that the larger the number of clogged emitters along the lateral, the higher the reduction in cotton yield. By assuming the constant conditions at different areas, the cotton yield and money loss caused by clogging are directly related to the size of planted area. Results show when there are just 5% clogged emitters along the lateral, the reduction of cotton yield is 0.027 ton/ha , whereas the reduction in cotton yield with 30% clogging is 0.085 ton/ha. If the cotton is planted in an area of 10,000 ha, the yield reductions increased to 270.29 ton and 857.7 ton under 5% and 30% clogging respectively (Table 5.13). Figure 5.17 shows the relationship between cotton yield reduction and the different number of clogged emitters randomly located along the lateral. It is shown that the reduction of cotton yield with 10% clogging is 0.054 (almost double the reduction with 5% clogging) and with 20% clogging is 0.062 ton/ha. The reason for the jumps in yield reduction under 10% clogging (Figure 5.17) is Chapter 5. RESULTS AND DISCUSSION 138 Table 5.12 Yield production and value of cotton, United States, 1984-93 (Adopted from Agric.Statis. US.Dept. of Agric, 199-Year Yield Yield Marketing Marketing lb/Acre Kg/ha US Cent/lb US $ /Kg 1984 600 672.50 58.9 1.30 1985 630 706.12 56.3 1.24 1986 552 618.70 52.4 1.16 1987 706 791.31 64.3 1.42 1988 619 693.79 56.6 1.25 1989 614 688.19 66.2 1.46 1990 634 710.61 67.1 1.48 1991 652 730.78 56.8 1.25 1992 700 784.58 54.9 1.21 1993 606 679.22 58.0 1.28 AVE 631.3 707.58 59.15 1.3040 *1 Acre= 0.4047hectare 1 Pound=0.4536 kg Table 5.13 Reduction in cotton yield (ton/Area)under different number of clogged emitters randomly located along the lateral. # of clogged Area(ha) Area(ha) Area(ha) Area(ha) Area(ha) emitters(%) 1 10 100 1000 10000 5 0.027 0.270 2.703 27.029 270.29 10 0.055 0.546 5.462 54.620 546.20 20 0.063 0.630 6.297 62.970 629.70 30 0.086 0.858 8.577 85.770 857.70 Chapter 5. RESULTS AND DISCUSSION Figure 5.17 cotton yield reduction at different areas when different number of clogged emitters are randomly located along the lateral. Chapter 5, RESULTS AND DISCUSSION 140 the higher degree of emitter clogging. A regression equation was performed in order to determine the yield reduction caused by emitter clogging. Based on experimental data, the reduction of cotton yield (YR) and percentage number of clogged emitters (C) randomly located along the lateral at any planted area (A) can be expressed by the regression equation as follows: 2 where YR is in Kg, C in percent, and A in hectares. The higher correlation (R = 0.93) between YR and C in polynomial rather than linear type of regression justifies the use of equation 5.11. Tables 5.14 and A.5.7 (Appendix A) summarise the reduction in cotton yield and farmer's money loss under eight different stages in different areas. Results show the minimum value of yield reduction in stage 1 (no-clogged) due to emitter manufacturer's coefficient of variation. The values of yield reduction in stage 1 were 0.01 and 104.38 tons in 1 ha and 10000 ha respectively. The amounts of money lost were $13.6 and $1361.7 in this stage for these areas. Table 5.14 also shows that the maximum money lost ($1,250,001.2) was obtained in stage 2 which consisted of 30% clogged emitters in a 10,000 ha planted area. Figure 5.18 shows the relationship between yield reduction and money lost in eight different stages of clogging resulting from the field. Figure 5.18 also shows that the effect of emitter clogging on yield reduction and money lost is more significant as the crop area becomes larger. There are no significant differences between the results obtained using the field and synthetic data. 5.8.2 Step 2, hydraulic characteristics of lateral laid on sloped terrain: In step 2 a similar field experiment as in step 1 was conducted to evaluate the effects of different patterns of clogged emitters along the lateral on hydraulics characteristics of laterals laid on sloped terrain. The impact of clogging on all hydraulic parameters described in previous sections was examined. Four 20m polyethylene laterals with 15 mm inside diameters were used. The laterals were laid on 3% and 7% uniform up-slopes and 3% and 7% down-slopes with equally spaced emitters (Se=\ meter). The sand was introduced into the emitter artificially. Eight different patterns (stages) of clogging as used in step 1 were tested at each slope. A total of 2560 (8stages x 4si0pes x 4repiiCates (runs) x 20flOw rates/run) emitter flow rates were 5.11 Chapter 5. RESULTS AND DISCUSSION 141 CD c CO CO CD CD -i—» c CD I _C -*—' 00 o CD c o E c CD c o o fi-a c o ° «• o O 42 LO C CD XI £ co ?E h- -o O CO 00 «> C S? °l S a] u » • c « <o CO m °l O CO >-U CO m 5? ° o 5 * ~ a> co u 3 " ~ c » c •o fl ti v co CM 3 OA co u 3 ,_ 2 2 c a> co r-~ o CM h~ O CM o d r-- cr> o r«~ co Oi o> LO o o> o -tf o o T-co o CM LO co LO •sr o m o d LO co o CO CO O CO odd co co 00 LO o co d d cci r- T-o r-~ d d o o co 00 m o o CD o CD CD CM CM P d CM CM CM o o CM CM in in ^ o o ® & ^ CM . CD CM CM CO CO N oo £ £ ^ IO ^ N LO LO CO CO ^ CO 00 o § cp O CO CO o o CD CD in m oo oo in in CD CD oo 00 co co o o O O i- *-* w CO CO (0 E 0> O CO 0)| —I i- cq Q. CO CO o « 'sI' Q. CO co N. i— <0 CD W C CO, q « o) Q. CO CM r; i: T-00 g W CN 00 00 (0 in CO C 0) q co o» -i i- n «/» CD £ Q. CO CO Tt (0 C 4), q co o> J L II Q. CO CO co 2. o co o>| S 3 CL CO CO ru -*-» QI CO C 0) O CO C)| 5> 8 Q. CO CO _ cu co o>| vy cij ^ Q. CO CO -c-CU CO CM ^ LO 1J co m co CD g CM ^~ r- ^-CM : CM CN k ^. tn LO co °o • -<r 2 ^[™ 3 S s °§§8p !§§§§ CM CM CM O ° o 0| o o r- CN ^ J*" I Chapter 5. RESULTS AND DISCUSSION 142 Chapter 5. RESULTS AND DISCUSSION 143 measured. Sample test data of emitter flow rate measurements at 7% down-slope are shown in Table A.5.8 (Appendix A.). The average emitter flow rate (l/h) and the lateral inlet flow (l/h) for different stages in 7% down-slope are also shown in Table A.5.9 (Appendix A). Similar calculations as explained in step 1 were done in order to determine the dimensionless values of emitter discharge, emitter discharge coefficient, and the percentage of clogging. Then the relationship between these values were plotted and the linear regression equations were determined for all different slopes (Table A.5.10 and Figure A.5.1). For example, a linear equation for stage 2 with a 7% down-slope was found and shown in Figure A.5.1. The impact of different patterns of clogging on hydraulics of lateral laid on four different slopes was examined. A comparable analysis of hydraulic parameters in a microirrigation lateral under different slopes reveals similar behaviour as in the flat terrain (step 1) as follows. 5.8.2.1 Total head loss (Hj): In all four slopes tested, the highest head loss was found in the desired condition (stage 1). The minimum head loss obtained in stage 2 when 30% of total number of emitters were partially clogged and located at the last one-third section of the lateral. The results obtained from stages 2 to 4 show that when the location of clogged emitters was closer to the inlet of lateral, the total /^approached that of the no-clogged condition. This is similar to those results obtained in step 1 on flat terrain. The results obtained in stages 2 to 5 show that when the same number of partially clogged emitters was located at different locations along the lateral, the value of /^varied from one stage to the other. Figure 5.19 shows the relationship between head loss obtained from the field and synthetic data versus different patterns of clogging in different slopes terrain. The minimum /^occurred at stage 2 for all different slopes. Head loss is a function of the lateral flow rate; i.e., as lateral flow increases Hf also increases. Results obtained from stages 5 to 8 show that head loss increased as the number of partially clogged emitters along the lateral decreased. The results show that the head loss in eight different stages in down-slope conditions were 7% to 15 % less than those in up-slope conditions. It is also found that the total amount of head loss at the end of lateral is slightly increased as the degree of slopes (down-slope or up-slope ) increased. Tables 5.15 to 5.22 show the values of head loss in different slopes and stages. Total head loss from the lateral inlet and the pressure Chapter 5. RESULTS AND DISCUSSION 144 0.014 T -No Clog (total Hf) -30%,1/3F,DC -10%,R,DC • 30%,1/3L,DC • 30%,R,DC • 5%,R,DC —Q—30%,1/3L,DC -X—30%,R,DC 5%,R,DC -X--30%,1/3M,DC - A -: 20%,R,DC - - -X • - • o • -30%,1/3M,DC -20%,R,DC • No Clog (Hf/Section)) • 30%.1/3F,DC • 10%,R,DC -r 0.002 Figure 5.20 Total head loss and Hf per section along the lateral (7% down-slope) Chapter 5. 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RESULTS AND DISCUSSION 149 drop at each section for all slopes were determined. Tables A.5.11 and A.5.12 (Appendix A) show the head loss and pressure drop at each section along the lateral laid on a 7% down-slope. Figure 5.19 shows that in stage 1, the values of H/were 0.0129m and 0.0136m at 3% and 7% down-slope respectively, while H/was 0.0143m and 0.0147m at 3% and 7% up-slopes respectively. It is found that Hj in stage 1 at down-slopes was 7% to 9% less than Hj in up-slope conditions. Similar trends were found for the rest of seven stages. Figure 5.20 shows that the variation of head loss per section was close to zero as the sections were closer to the end of lateral in each stage at a 7% down-slope. It is also shown that the head loss is almost zero at the last section of lateral in eight different stages. This was due to the very small flow at the last section. Figure 5.20 shows that the total head loss is rapidly increased at the first 40% length of the lateral and is almost constant at the last 60% of lateral length. Similar trends were observed for the other slopes. Results indicated that the total values of Hf in stage 4 at different slopes was almost same as total Hf in stages 7 and 8 (10% and 5% clogged emitters). On the other hand, total Hf'm stages 2, 3, and 5 (30% clogging) at 7% down-slope were 19% to 28%) and in up-slope 16% to 21% less than that in stage 4 (30% clogging). The lateral inlet flow presented in Table A.5.9 shows that the maximum QL (lateral inlet flow) was at stage 1 and resulted in maximum head loss. The Qi in stages 2, 3, 4, and 5 (consisting of 30% clogging at different locations) were 60.65, 59.27, 58.05, and 54.16 l/h respectively. Theoretically, the minimum head loss should have occurred at stage 5, which had the least lateral inlet flow. Results indicated that the minimum head loss was obtained in stage 2 with QL greater than stages 3, 4, and 5. It is clearly concluded that although having a different number and degree of clogged emitters has an significant impact on head loss, the location of clogged emitters is also one of the major factors affecting Hf. Similar results were found from theoretical data produced by the computer simulation program. 5.8.2.2 Pressure variation (Hvar): Results showed that the highest pressure variations occurred in stage 1 at 3% and 7% up-slopes. However, in the case of 3% and 7% down-slopes, the maximum Hvar values were found in stage 2. Figure 5.21 shows the relationship between Hvar versus different stages and slopes. The minimum Hvar were found in stage 1 at 3% and 7% down-slopes respectively, whereas the Chapter 5. RESULTS AND DISCUSSION 150 13.4 ;F 13.2 * 13.0 -j 12.8 -j 12.6 -: 12.4 -j 12.2 -12.0 -j 11.8 -: 11.6 it 11.4 -j 11.2 + 11.0 1 • * • —A-•O • -+-predict 7%d -observed 7%u predict 7%u -observed 7%d - Observed Flat Predict Flat - observed 3%d predict 3%d • observed 3%u predict 3% u 6.0 5.5 5.0 4.5 <D a. 4.0 % + 3.5 co 3.0 g 2.5 | 4 2.0 SP, Stage Figure 5.21 Pressure variation in different stages under different slopes 1.10 T 0.5 1.05 + CO o_ o w ;S 1.00 + re ^ 0.95 + -o- -0-• -X • —A-• o -—I— • + • * —£ —o- 0 • observed 7%d predict 7%d -observed 7%u predict 7%u • Observed Flat Predict Flat •observed 3%d predict 3%d • observed 3%u predict 3%u "¥• 0.4 O) o. o ui + 0.3 CO T3 C (0 + 0.2 ™ + 0.1 re > cr 0.90 stage Figure 5.22 Emitter discharge variation in different stages under different slopes Chapter 5. RESULTS AND DISCUSSION 151 minimum Hvar values were found in stage 3 and 5 at 7% and 3% up-slopes respectively (Figure 5.21). The maximum and minimum values of Hvar were found in different slopes as follows: -Minimum Hvar: 5.26% in 3% down-slope (stage 1) 11.6% in 7% down-slope (stage 1) 5.77% in 3% up-slope (stage 5) 13.35% in 7% up-slope (stage 3) -Maximum Hvar: 5.51 % in 3 % up-slope (stage 1) 13.39% in 7% up-slope (stage 1) 5.31% in 3% down-slope (stage 2) 11.64% in 7% down-slope (stage 2) According to the location and percentage of clogged emitters, the maximum and minimum pressure variations were inversely related to each other on up-slope and down-slope conditions. In other words when the Hvar was at a minimum on down-slope it was at a maximum on up-slope terrain. It was also found that Hvar on 7% up- or down-slopes were almost double the values of Hvar on 3% up or down-slope in eight different stages. This indicates that Hvar was directly related to the degree of lateral slope. Tables 5.15 to 5.22 show that as the number of clogged emitters along the lateral decreased in stages 2 to 8, the pressure variation also decreased in the down-slope conditions, but it increased in up-slope terrain. However, these variations were not significant. Tables 5.15 and 5.21 show that the value of Hvar in stage 4 was greater than in stage 6 on 3% and 7% down-slopes. In addition the Hvar was varied in stages 2 to 5 (30% clogged) at all different slopes. The location of clogged emitters also has an impact on Hvar along the lateral. Similar trends were found in the results obtained from synthetic data on down-slopes. Tables 5.15 to 5.22 show that although the variations of Hvar in different stages were not significant, the values of Hvar in all stages on up-slopes were about 13% higher than those values obtained from down-slopes. It was found that the slope of the lateral was a major factor affecting pressure variation in a microirrigation system, but number, degree, and location of clogged emitters have little impact on pressure variation along the lateral. Chapter 5. RESULTS AND DISCUSSION 152 5.8.2.3 Emitter flow variation (qvar)' The flow rate from the emitters along the lateral varied from the nominal emitter flow rate. It was found that emitter flow variation varied from one slope to the other, but the variations of Qvar were not significant at eight different stages (Figure 5.22). The highest and lowest emitter flow variations occurred in stages 1 and 5 in 3% up-slopes and in stages 1 and 3 in 7% up-slope conditions (Tables 5.17 and 5.19). In the case of down-slope conditions, the minimum and maximum qvar were found in stages 1 and 2 as shown in Figure 5.22. Results indicated that the location of clogged emitters has a higher impact than the numbers of clogged emitters on qvar. It was found that the emitter flow variation in all stages in up-slopes situations is greater than that in the down-slopes conditions. 5.8.2.4 Coefficient of uniformity (CU): The highest CU was found in stage 1 at different slopes. The values of CU were 97.6%, 97.8%, 96.8% and 96.3% at 3% and 7% down-slopes and 3% and 7% up-slopes respectively (Tables 5.15 to 5.22). The values of CU in down-slopes were 0.8% to 1.5% greater than that those values in the up-slope conditions. Results show that the values of CU were between 55% to 78% in stages 2, 3, 4, and 5. The CU was lower as the degree of clogged emitters was higher (see Tables 5.15 to 5.22). Figure 5.23 shows that the lowest CU occurred in stage 5 at all different slopes except on the 3% down-slope where the minimum CU was found in stage 4. It was also found that the CU decreased as the clogged emitters were located closer to the first one-third section of the lateral. The number and degree of clogged emitters along the lateral were the major factors affecting CU. The slope and location of clogging have little impact on CU. 5.8.2.5 Application efficiency (Ea): Results indicated that the application efficiency was greater than 99% in all stages and slopes. Figure 5.24 shows that although application efficiency was almost constant under the eight different stages, the small variations of Ea were found in different slopes. One reason for the constant values of Ea in all different stages is the small pressure variations along the lateral Chapter 5. RESULTS AND DISCUSSION 153 50 -I 1 1 , 1 1 1 1 1 0 1 2 34 5 6 7 8 Stage Figure 5.23 Coefficient of uniformity in different stages under different slopes 99.51 i 99.5 99.49 99.48 -E 99.47 99.46 -f 99.45 4 99.44 f 99.43 1 -observed 7%d -predict 7%d • observed 7%u • predict 7%u - observed 3%d - predict 3%d - observed 3%u - predict 3%u - Observed Flat - Predict Flat Stage Figure 5.24 Application efficiency in different stages under different slopes Chapter 5. RESULTS AND DISCUSSION 154 at each slope. The values of Ea were 99.79% and 99.52%, in the 3% and 7% down-slopes and 99.77% and 99.44% in the 3% and 7% up-slopes respectively in all different stages (Tables 5.15 to 5.22). It was found that the highest Ea occurred in the 3% down-slope and the lowest in the 7% up-slope in all different stages. Results also show that the Ea obtained from down-slopes was 1%> greater than for up-slopes. The small differences between the values of Ea in up-slopes and down-slopes is not important for irrigation purposes. Therefore, the impact of slopes on application efficiency in a microirrigation lateral laid on sloped terrain is insignificant. 5.8.2.6 Field emission uniformity (EC): Similar trends as for CU were observed for EU'. The highest value of EU' was found in stage 1 at all slopes studied. Results show that EU' were 96.93% and 96.44% in stage 1 on 3% and 7% down-slopes and 95.2% and 94.03% in stage 1 on 3% and 7% up-slopes respectively. The values of EU' in stage 1 at down-slopes were greater than those obtained from the up-slope conditions up to a value of 2.5% (Tables 5.15 to 5.22). The lowest values of EU' were found as follows: Up-slope: 7% - 35.09% (stage 4) and 3% -20.0% (stage 5) Down-slope: 7% ~ 21.26% (stage 5) and 3% ~ 30.05% (stage 4) According to the criteria suggested by ASAE EP458 (1997) these values are within an unacceptable range (< 50%). It was found that the degree and number of clogged emitters (expressed in percentage of the total number of emitters along the line) are the important factors affecting EU'. Figure 5.25 shows that as the location of clogged emitters was closer to the first one-third section of the lateral, the EU' becomes lower. Results indicated that stage 5 in all four slopes represented the worst situation of emitter clogging affecting EU'. 5.8.2.7 Distribution uniformity (DU): Similar trends as for EU' were obtained for distribution uniformity. The highest values of distribution uniformity were found in stage 1 in different slopes and the lowest values were obtained mostly in stages 4 or 5 (30% clogging). Results show that DU was 96.23%) and 96.63% in stage 1 on 3% and 7% down-slopes and 95.01% and 94.24% in stage 1 on 3% and Chapter 5. RESULTS AND DISCUSSION 155 10 4 1 1 1 h 1 1 1 1 2 3 4 5 6 7 8 Stage Figure 5.25 Field emission uniformity in different stages under different slopes. 20 -I 1 H 1 1 1 1 1 1 2 3 4 5 6 7 8 . Stages Figure 5.26 Distribution uniformity in different stages under different slopes. Chapter 5. RESULTS AND DISCUSSION 156 7% up-slopes. It is found that DU in down-slope condition was about 1% to 2.5% greater than that in the up-slope. The minimum and maximum DU in different slopes were found as: Minimum DU: 40.3% in 3% down-slope (stage 4) 29.54% in 7% down-slope (stage 5) 34.18% in 3% up-slope (stage 5) 46.79%) in 7% up-slope (stage 5) Maximum DU: 96.23%) in 3% down-slope (stage 1) 96.63% in 7% down-slope (stage 1) 95.01% in 3% up-slope (stage 1) 94.24%) in 7% up-slope (stage 1) It is shown that the degree of slope has no significant effect on distribution uniformity. Figure 5.26 shows that the lowest values of DU occurred in stage 5 on 3% and 7% up-slopes, and 7% down-slope, and in stage 4 on 3% down-slope. Results also indicated that in the case of different locations of clogged emitters along the lateral, when the partially clogged emitters were located closer to the first one- third section of the lateral, the DU decreased in all different slopes. Stages 4 and 5 showed the worst stages of clogging patterns affecting DU. The number and degree of clogged emitters were the important factors affecting distribution uniformity. Results show that as the number of clogged emitters along the lateral decreased, the distribution uniformity increased. As presented in Tables 5.15 to 5.22, the values of DU were 58%, 63.18%>, 69.87%), and 64.54%) in stage 6 on 3%> and 7% down-slopes and 3% and 7% up-slopes respectively, and were 87.48%, 84.12%, 84.03%), and 87.97% in stage 8 on 3% and 7% down-slopes and 3% and 7% up-slopes respectively. When the number of clogged emitters along the lateral decreased from 20% to 5%, DU increased up to 16%> to 33%. It was also found that if the total number of clogged emitters increased from 5% to 30%, DU will decreased up to 64% at a 1% down-slope (Table 5.19). Results also show that when 30%) of the total number of emitters are partially clogged and located at different locations along the lateral, DU varied up to 103% within stages 2 to 5 in a 1% down-slope. It is concluded that the slope of lateral has little impact on DU, but the degree, number, and the location of clogged emitters along the lateral have a Chapter 5. RESULTS AND DISCUSSION 157 significant effect on distribution uniformity. The former has a higher impact on DU than the latter. 5.8.2.8 Statistical Uniformity (Us): The maximum and minimum values of Us were obtained in stage 1 and stages 4 or 5 respectively in all different slopes. Tables 5.15 to 5.22 show that the highest values of Us occurred in stage 1 at all different slopes. The minimum values were found in stage 4 at a 3% down-slope and 7% up-slope and in stage 5 at a 3% up-slope and 7% down-slope as follows: Minimum Us: 56.06% in 3% down-slope (stage 4) 50.30% in 7% down-slope (stage 5) 51.44% in 3% up-slope (stage 5) 58.88% in 7% up-slope (stage 4) Maximum Us: 97.16% in 3% down-slope (stage 1) 97.51% in 7% down-slope (stage 1) 96.34% in 3% up-slope (stage 1) 95.59 % in 7% up-slope (stage 1) Figure 5.27 shows that the statistical uniformity was decreased as the partially clogged emitters were located closer to the first one-third section of lateral. Results show that Us increases as the number of clogged emitters along the lateral decreases in all different slopes. The variations of Us in each stage at different slopes were not significant. According to the criteria for an acceptable statistical uniformity of the emitter discharge suggested by ASAE EP458 (1997) and Bralts and Edwards (1986), the values of Us were poor or unacceptable (60% to 80%) in stages 2 to 6 in all slopes (Us were less than 80%). It was found that although the location of clogged emitters and slope of lateral have an impact on Us, the number and degree of clogged emitters are the major factors affecting statistical uniformity in a microirrigation system. Chapter 5. RESULTS AND DISCUSSION 158 100.00 99.95 -: 99.90 -99.85 99.80 + 99.75 - j 99.70 + 99.65 1 1— -Observed Flat • — • Predict Flat —O—observed 3%d • -o- - • predict 3%d —I observed 3%u • H predict 3%u —9K—observed 7%d • X - • predict 7%d -A—observed 7%u • *• - • predict 7%u -X- -X--+-Stage Figure 5.28 Emitter statistical uniformity due to hydraulics in different stages under different slopes. Chapter 5. RESULTS AND DISCUSSION 159 The values of Us versus CU values under different patterns of clogged emitters at different slopes were plotted (Figures A.5.2 to A.5.5 in Appendix A.). The least-square regression line was fitted through the data points at each slope and the regression equations were found as follows: 1- For 3% and 7% up-slopes as: CU =17.576+0.8661(75 5.12 C7 = 15.2 + 0.8806(75 5.13 2- For 3% and 7% down-slopes as: CU = 11.809 + 0.92475 5.14 CU = 11.566 + 0.93675 5.15 Equations 5.12 to 5.15 show that the differences in CU estimated from the regression equation for different slopes are not significant. For example, the Us of 92% yields the CU of 96% to 97% at different slopes. 5.8.2.9 Emitter statistical uniformity due to hydraulics (Us/,): The emitter statistical uniformity due to hydraulics was almost constant in the eight different stages at different slopes (Tables 5.15 to 5.22). Figure 5.28 shows that the variations in Ush in different stages were less than 1% on all different slopes. These small variations come from the very small variations in emitter discharge coefficient of variation due to hydraulics, Vqh in all different stages. It was found that as the degree of slope increased, the Usu decreased. Figure 5.28 shows that highest Ush occurred on flat terrain, a lower value at 3% slopes and the lowest at 7% slopes. However, higher values of Ush were found in down-slopes rather than in up-slopes. 5.8.2.10 Emitter discharge coefficient of variation due to hydraulic (Vqh): The emitter coefficient of variation due to hydraulics, Vqh, were almost constant in all eight different stages at each slope but the values of Vqh vary from one slope to the other. The variations of Vqf, at different slopes were similar to those of Ush under different slopes but the Chapter 5. RESULTS AND DISCUSSION 160 trend was inverse. In other words, the Vqh in down-slopes was lower than in up-slopes. Also, Vqh decreased as the degree of slopes decreased. The highest value of Vqh was obtained in 7% slopes, the lower in 3% slopes, and the lowest was found on flat terrain. Figure 5.29 shows that the values of Vqh in eight different stages were almost constant, but it indicates that Vqh in up-slopes are 10% to 16% greater than those values occurring in down-slope terrain.This was due to the higher pressure variations in up-slopes than in down-slopes conditions. The values of Vqh were equal to 0.137% and 0.329% at 3% and 7% up-slopes and 0.124% and 0.283% at 3% and 7% down-slopes respectively (Tables 5.15 to 5.22). It was found that different locations, numbers, and degrees of clogged emitters had no major impact on Vqh, however, the former had a higher impact on Vqh than the latter. The slope of the lateral was the most important factor affecting Vqt,. 5.8.2.11 Emitter discharge coefficient of variations (Vqs): Figure 5.30 shows that the variation of Vqs in stages 5 to 8 was higher than that in stages 1 to 4 from down-slope to up-slope conditions. The minimum Vqs occurred in stage 1 and the maximum was found in stages 4 and 5 (Tables 5.15 to 5.22) as given below. Minimum Vqs: Vqs = 3.6% in 3% up-slope (stage 1) Vqs = 4.4%) in 7% up-slope (stage 1) V ' qs = 2.8%) in 3% down-slope (stage 1) V ' qs = 2.4% in 1% down-slope (stage 1) Maximum Vqs: V ' qs = 48.5% in 3% up-slope (stage 5) v ' qs = 41.0%) in 7% up-slope (stage 4) V = 43.9%o in 3% down-slope (stage 4) Vqs = 49.6% in 7% down-slope (stage 5) It was found that when 30% of the total number of emitters were clogged and located at the first one-third section of the lateral (or randomly located along the lateral), this represented the worst conditions for Vqs. It was also found that the degree, numbers, and locations of partially Chapter 5. RESULTS AND DISCUSSION 0.0035 -r , r-0.0030 --0.0025 - '-0.0020 --g 0.0015 + 0.0010 -f 0.0005 4-0.0000 • Observed Flat Predict Flat -0—observed 3%d O- - predict 3%d H observed 3%u +- • predict 3%u *—observed 7%d X- - predict 7%d A—observed 7%u A- • predict 7%u •+- -+-Stage Figure 5.29 Emitter discharge coefficient of variation due to hydraulics in different stages under different slopes. CO 0.52 0.42 + 0.32 + 0.22 + 0.12 4-0.02 Stage Figure 5.30 Emitter discharge coefficient of variation in different stages under different slopes. Chapter 5. RESULTS AND DISCUSSION 162 clogged emitters along the lateral have a larger impact on Vqs than the slope of lateral line. However, the Vqs at most of the stages in up-slopes were higher than in down-slopes. 5.8.2.12 The hydraulic design coefficient of variation (Vhs): Similar trends as for Vqh in different stages and slopes were found for Vhs- Figure 5.31 shows that Vhs were almost constant in different stages at different slopes. The values of Vhs in 3% and 7% up-slopes were 8.7% and 13.8% greater than those values obtained from 3% and 7% down-slopes respectively (Tables 5.15 to 5.22). Less than a 1% difference in the Vhs was found among the stages tested. Results indicate that the location of clogged emitters has a more significant impact on Vhs than the number and degree of clogged emitters. However, the slope of lateral was the major factor affecting Vhs-5.8.2.13 Emitter performance coefficient of variation: (Vpf): Similar trends as for Vqs were found for Vpf at different slopes. The lowest variations of Vpfwere 4%, 4%, 2%, and 3% in stage 1 at 3% and 7% up-slopes and down-slopes respectively (Tables 5.15 to 5.22). The highest Rvalues were 49% and 50% in stage 5 at 3% and 7% down-slope conditions. In case of an up-slope terrain, the maximum Vpj was 44% at 3% up-slope and 41% at 7% up-slope in stage 4. Figure 5.32 shows that in stages 2, 3, and 4 the Vpj increased on all different slopes when the clogged emitters were located closer to the first one-third section of the lateral. The values of Vpfin stages 2, 3, 6, 7, and 8 were less than those values in stages 4, and 5 on all different slopes. It was found that stages 4 and 5 were the worst stages (highest Vpf) affecting Vpf on sloped terrain. The number and location of clogged emitters were found to be the major factors affecting Vpfon all different slopes. Table A.5.13 (Appendix A) presents a sample of the results of the hydraulic parameters obtained from stage 2 at a 7% down-slope. Similar results to those shown in Table A.5.13 were found for all stages at different slopes. The summary of the impact of number and location of clogged emitters and slope of lateral on hydraulic parameters in a microirrigation system are shown in Figure 5.33. Chapter 5. RESULTS AND DISCUSSION 163 0.045 T 0.040 0.035 0.030 0.025 0.020 Observed Flat Predict Flat -o— observed 3%d • o - - predict 3%d —i—observed 3%u • + - - predict 3%u -»— observed 7%d • •* • • predict 7%d -*— observed 7%u - * - - predict 7%u 0.015 --0.010 --0.005 0.000 Stage Figure 5.31 Hydraulic design coefficient of variation in different stages under different slopes. 0.52 -r 0.42 0.32 0.22 0.12 0.02 $• Observed Flat Predict Flat —o— observed 3%d •••»•• predict 3%d —i— observed 3%u - - + - predict 3%u —*— observed 7%d - - * - - predict 7%d —*— observed 7%u - - * - - predict 7%u Stage Figure 5.32 Emitter performance coefficint of variation in different stages under different slopes. Chapter 5. RESULTS AND DISCUSSION 165 5.8.2.14 Crop yield reduction due to emitter clogging at different slopes: Similar analysis of cotton yield and farmer's loss (money lost) in different areas and with different patterns of emitter clogging as described in step 1 were done in step 2. Tables A.5.14 to A.5.21 (Appendix A) show the results of reduction in cotton yield under different patterns of partially clogged emitters compared with a no-clogged situation at 3% and 7% down and up-slopes. For example, results show that 5% and 30% clogged emitters can reduce cotton yield up to 5.8% and 15.4% respectively, compared with the no-clogged situation in 3% and 7% down-and up-slopes. Results indicated that as the number of clogged emitters increases, the cotton yield decreases. In addition, it was shown that different locations of clogged emitters along the lateral have an impact on cotton yield. The closer the clogged emitters to the first one-third section of lateral, the greater the rate of reduction in cotton yield. The minimum yield reduction (1.1% to 2.1% in 3% and 7% slopes) was obtained in stage 1 (desired situation) at all different slopes. The maximum yield reduction (13.5% to 16.9%) was estimated in stage 4 and 5 consisting of 30% clogged emitters for all different slopes. Similar trends were obtained from synthetic data in different slopes. The cotton yield reduction and money lost in different areas under different patterns of clogging are presented in Tables 5.23 to 5.30. For example, Table 5.24 shows that the cotton yield can be reduced from 10 kg/ha (O.Olton/ha) in a no-clogged condition up to 42.4 kg/ha (0.0424 ton per hectare) when 5% of the total numbers of emitters along the lateral are partially clogged in a 3%> down-slope. It is also shown that the yield can be decreased by up to 100 kg/ha (0.1 ton per hectare) if 30% of emitters are clogged and randomly located along the lateral laid on a 3% down-slope. The reason for the yield reduction was the variation in emitter flow caused by manufacturing, hydraulics, and emitter clogging along the lateral. The relationship between cotton yield reduction and money lost in different slopes and areas versus different number of clogged emitters was plotted and is shown in Figures A.5.6 to A.5.13 (Appendix A). The linear relationship between the reduction in cotton yield (YR) and percentage of clogged emitters (Q found at different slopes is expressed by regression equations as follows: Chapters. 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RESULTS AND DISCUSSION 170 - 3% down-slope: YR = (o.0146C3 - 0.8325C2 + 15.782C- 17.563)^4 5.16 - .3% up-slope : YR = (0.009C3 - 0.3254C2 + 4.6588C + 27.628)^ 5.17 - 7% down-slope : YR = (o.0105C3 - 0.4813C2 + 7.5483C+ 24.395^ 5.18 - 7% up-slope : YR =(0.001C3 - 0.0412C2 + 2.7106C+ 24.794)^ 5.19 where YR is the yield reduction in Kg and A is the area in ha. For example, 25% of clogged emitters along a lateral will reduce the cotton yield by about 81.6 and 84.8 kg/ha at 3%> up and down-slopes and 82.4 and 76.5 kg/ha at 7% up- and down-slopes (equations 5.16 to 5.19). Money lost per area due to emitter clogging can be interpreted as well as reduction in cotton yield in different slopes under different patterns of clogging. Based on the experimetal results and different factors affecting the hydraulic characteristics of lateral in different stages and slopes, it is found that stages 4 and 5 represented the worst conditions in all different slopes affecting cotton yield. Based on the field and synthetic data, the number and location of clogged emitters were the major factors affecting the cotton yield and money lost. The slopes of lateral have little impact on cotton yield under the conditions studied. 5.8.2.15 Relationship between random clogging and hydraulic parameters: In this section, the effects of different percentages of randomly clogged emitters at five different slopes on hydraulic parameters are discussed. The number of partially clogged emitters is expressed as the percentage of the total number of emitters (PN) along the lateral. Tables 5.31 and 5.32 show the values of Hf, Hvar, and qvar, in flat, 3%, and 7% up- and down-slopes under five different patterns of PN (0%>, 5%, 10%), 20%>, and 30%>) randomly located along the lateral. Results show that as the pressure variation increases, the emitter flow variation also increases. They also show that the pressure and emitter flow variations Chapter 5. RESULTS AND DISCUSSION 171 CO CO CO § 3 CO CU DS CU cr 5 5 cr — CO XM CO > CNI o CN t— oo CO CO CO T— OJ o OJ r-00 f- 00 r-. r-iri LO UO uo CO X=H »- £ X CD CO £-1 CO XH X aj 2 CO CD ^— T— O 00 00 00 o o O CO o O r- 00 r-CO CO CO CO CO CO T— T— h- OJ CO CM CN T— T— o o o o o d LO LO OJ O CN CO o d LO CT> LO r-O 1-CO CD CM CO T- CN CO CO OJ OJ LO f LO 00 CN CO CD CO co a> CO T-o o d d CO 1-o o> T- o o o d d I— CM CM T-UO UO d d uo uo d d CO CO 00 ,_ CD CM CM CN a> o o o o o o d d d d d •ST OJ CD OJ OJ o o o T— xr XT d d d UO OJ o UO T— o CD r- 00 a> a> CM CM CM CN LO LO LO iri OJ O O d d CM o as i- o o o d d LO r-00 h-O O O O d d OJ CM CM CM T- O OJ o o o o o d d o r-xr CM o o> T- O o o o o o 03 00 T- O o o d d o oo v- a> 1- o o o d d LO ° o o CN CO +.«> c QJ CO 3 E • 9>; o E ° b s< o o ?S ai a) or ~ i gj c g co o E Q o S o T3 a> CO c c 'Lt ° o at c ri T3 o T3 CO or CO i& c •? 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CM 00 00 oi S° S9 r- LO CM O XT CM oo 00 oo CD iri x— CN o o o T- CN CO in cu Q. o CO c £ -i—' CO O) c 'ay o> o o \ co E CD O a> T3 CO c o +-» ro i ro > o CD E CD "O c CO a> co CO a) CO co o ro c CD E £ o £Z g o T3 ^ CD ro ^ ro CN co .fJ iri a3 tu £ ™ ST ^-JCN JiSi00 00 --Joo X —Ico CO 5 ^ CO CO XH _ -*-* X CU X a3 CO > X ~H **— a> X CD 8 81 CO o CN o o ^— o CO 00 oo o o o r~- LO xr CD co CO CO CO CO CO T— T— CD CN CN CN T— T— O O o d d d i- CN CO CD OJ O O O CN CO CO CO O) O) O O) o o o o o CO CD OJ O T- co ->r cn O T- T- T-CO CO CO CO •<- LO co * CN CN T-o o o o d d d d CN CO CO T— T— o 00 LO uo uo ,—. d d d d c CN CN r-O) o CN O) o> o OJ CD Is- 00 r- r-iri iri uri uri •ST LO CN CN O O O O h- CO T- 03 i- O o o d d OJ OJ CN o 00 OJ o o o o T— XT d d d d LO CD OJ o CO ,—. CD CO CN CM OJ LO CD h- oo oo o— CN CM CN CN CN LO iri iri iri iri r- CM CM CM o o d d o o d d oo oo oo oo o o o o d d T- CO CD LO uo oo c-o o o o d d CN CM i- 03 1- 03 T- O o o o o o CO CM CM CM O O d d r- uo 1- O o o d d LO ° o o CM CO 6 £1 X IS1 .9 S1 t3 i2 3 o TO co or co S b O o c c li. CO — E ®. O o co > cr CD CO oo o OJ OJ O T— c\ O d o o a. CN T— var CM CD CD var CM cr d d d d o: CD r- CN •sr var O T— LO var CN X d d d d CO > cr CO I T- LO co OJ oo r— OOi-CM d d d d co r- CD o oo uo CN "? °> cd co OO OJ T- CN OJ 00 CD io co o r— T— co co d T- i- 1- CO CN r— oo Is— * CM CD CO CM CM CO r— d d d d m i- co N CO CN LO •!* CN CN CO r-d d d d CN 10 ° OJ Is- CN CD CD 00 O uri co T- CO CD oo o CO CN OJ xr g_ CN CO CO d d d d O CO CD CO T— 00 CN CN CO CO d d d d 00 LO — \— CD T— CO CM O f- CN CO d CO T— 1— X— CN CN 03 CN CO 00 O CN t- LO o xr r- oo CN CN LO T- T- CM CM m in N O T- O Of so CM CN iri xr i- T- CM CN LO LO r— o i- o o -<a- i-- oo CM CM iri t" i- T- CN ^ o o o *r— CN CO Chapter 5. RESULTS AND DISCUSSION 172 increased with the increase in the degree of slopes. In the down-slope case, the Hvar and qvar increased as PN increased. A reverse trend was found in up-slope conditions. The variation of Hf'm different slopes was mainly influenced by the number of clogged emitters. Although the values of Hf in up-slopes were greater than in down-slopes, the differences in Hf under each pattern of PN in up-slopes and down-slopes were not significant. The aim of this part of study was to find out how emitter clogging effects Hf, Hvar, and qvar at different slopes. It was also to find the relationships between the reduction in CU, EU', and DU and the different numbers of random clogged emitters along the lateral. To assess and evaluate this impact, based on values obtained for Hf, Hvar, and qvar, under no-clogged (0% clogging) and clogged situations at different slopes, the percentage of differences of these values were determined. When the values of Hf Hvar, and qvar under no-clogged condition were calculated, any reduction or increment of these values in clogged situations are related to emitter clogging when other factors such as manufacturer's variation, slopes and water temperature are similar to no-clogged situation. Tables 5.31 and 5.32 summarize the field and synthetic data of reduction (negative values) and increment (positive values) of Hf Hvar, and qvar at different slopes. These results show the variation of Hf, Hvar, and qvar in different PN when compared to those in the no-clogged situation. Figure 5.34 shows the relationship between the head loss, pressure variations and different patterns of PN. Figure 5.34 shows the maximum //^occurs under a no-clogged situation. The /^decreased as the number of clogged emitters increased along the lateral. Figure 5.35 shows the reduction of head loss (HfR), reduction or increment of pressure variation (Hvar(Rj)), and the reduction or increment of emitter flow variation (qvar(Ri)) under different PN. Figure 5.35 shows that the /^decreased from -8% in stage 8 (5% clogging) to -36% when the number of randomly clogged emitters was 30% (stage 5). Figure 5.35 also shows two different trends for Hvar(Rj) and qvar(Ri) in up-slope and down-slope conditions. In the down-slope case, the values of Hvar and qvar under randomly clogged conditions were greater than in the no-clogged situation. Both Hvar(m) and qvar(m) in down-slope conditions increased as the PN increased. However the values decreased as the PN increased in up-slope cases. The values of Hvar and qvar in up-slopes were greater than those values obtained from the down-slopes. Chapter 5. RESULTS AND DISCUSSION 0.020 T 0.015 =0.010 -f 0.005 0.000 0 10 15 20 25 30 co > X Hf(Flat) — Hf(3%D) X Hf(3%U) —I—Hf(7%D) —e—Hf(7%U) - * - Hvar(Flat) Hvar(3%D) ••o- Hvar(3%U) Hvar(7%D) --o-- Hvar(7%U) Number of Clogged Emitters Figure 5.34 Relationship between head loss and pressure variation versus different number of clogged emitters randomly located along the lateral (field data) —•—qvar3%D 0 5 10 15 20 25 30 _^_^var3o/oU —*—qvar7%D Number of clogged emitters (%) —e—qvar 7%u Figure 5.35 Relationship between the reductions in head loss, pressure and emitter flow variation versus different number of clogged emitters randomly located along the lateral (field data). Chapter 5. RESULTS AND DISCUSSION 174 Theoretically, the value of 100% for CU, DU, and EU' can be expected under the ideal condition. However, this ideal condition never occurs. Tables 5.33 and 5.34 show the reduction in coefficient of uniformity (CUR), reduction in field emission uniformity (EU'R), and reduction in distribution uniformity (DUR) due to the randomly clogged emitters. The reduction is defined in such a way that all values of CU, EU' and DU in randomly clogged conditions were compared to those values in no-clogged situations. Assuming that the values of CU under no-clogged and clogged conditions are X and X respectively, the reduction of CU (CUR) is determined as: CUR = [(X-X )/X|100. For example, the values of CU under no-clogged and 5% clogged conditions were 96.26% and 94.61% (Table 5.9) respectively on flat terrain. Based on above definition, the CUR under 5% clogging is determined equal to 1.71%. A similar calculation as defined for CUR was used for DUR and EU'R. Tables 5.33 and 5.34 show that in the no-clogged condition the reduction of CU, EU' and DU due to the clogging were zero at different slopes. All of these uniformities decreased as soon as the number of clogged emitters occurred along the lateral. Results also show that the uniformity in down-slopes was greater than in the up-slopes, but the rate of reduction of the uniformities due to clogging were higher in down-slopes than that in the up-slopes (Table 5.33). For example the values of CUR were 4.09% and 30.96% under 5% and 30% clogging situations in a 7% up-slope, and were 8.04% and 43.11% in a 7% down-slope. One of the reasons for this was the reduction in Hvar and qvar in up-slopes and increment in Hvar and qvar in down-slopes with respect to the increment in PN. The relationship between CUR, EU'R, and DUR obtained from field and synthetic data and the different random numbers of clogged emitters were plotted and least-regression equations were determined (Figures 5.36 to 5.41). Results indicated that when the number of partially clogged emitters is expressed as the percentage of the total number of emitters along the lateral, the following three findings are reached: (1) The coefficient of uniformity decreased by about 0.9 to 1.3 times the C% (percentage number of clogged emitters), (2) the reduction of the field emission uniformity varied by 1.7 to 2.4 times the C%, and (3) the reduction of distribution uniformity is about 1.5 to 2.1 times the C%. Chapter 5. RESULTS AND DISCUSSION 175 Table 5.33 Reduction in CU, EU', and DU due to random number of clogged emitters along a lateral (Field data). Field Data Reduction in coefficient of uniformity (CUR in %) #of 0% 3% 3% 7% 7% clogging Flat D-slope U-slope D-slope U-slope 0 0.00 0.00 0.00 0.00 0.00 5 1.71 5.64 5.15 8.04 4.09 10 9.07 15.63 9.45 13.84 8.62 20 15.06 24.63 16.32 21.49 19.38 30 27.87 35.02 39.50 43.11 30.96 Reduction in field emission uniformity (EU'R in %) 0 0.00 0.00 0.00 0.00 0.00 5 5.62 13.02 11.73 17.02 9.74 10 18.70 30.69 19.91 28.44 18.82 20 31.83 50.38 33.78 43.70 39.88 30 53.80 65.11 78.99 77.96 60.23 Reduction in distribution uniformity (DUR in %) 0 0.00 0.00 0.00 0.00 0.00 5 2.78 9.10 8.34 12.95 6.65 10 14.75 25.21 15.32 22.29 14.01 20 24.50 39.73 26.46 34.62 31.51 30 45.35 56.49 64.02 69.43 50.34 Table 5.34 Reduction in CU, EU', and DU due to random number of clogged emitters along a lateral (Synthetic data). Synthetic data same as field data Reduction in coefficient of uniformity (CU R in %) #of 0% 3% 3% 7% 7% clogging Flat D-slope U-slope D-slope U-slope 0 0.00 0.00 0.00 0.00 0.00 5 8.24 6.60 6.90 8.04 5.29 10 12.10 15.29 11.37 14.92 10.34 20 18.27 26.14 18.02 23.05 21.57 30 31.13 36.83 40.80 44.39 32.63 Reduction in field emission uniformity (EU'R in %) 0 0.00 0.00 0.00 0.00 0.00 5 14.42 11.83 12.32 14.10 9.83 10 21.50 26.87 20.31 26.24 18.68 20 35.27 50.13 34.83 44.30 41.64 30 57.62 67.00 79.97 78.39 62.00 Reduction in distribution uniformity (DUR in %) 0% 0.00 0.00 0.00 0.00 0.00 5 13.18 10.56 11.03 12.87 8.47 10 19.37 24.46 18.19 23.87 16.54 20 29.24 41.82 28.83 36.89 34.52 30 49.81 58.93 65.29 71.02 52.22 Chapter 5. RESULTS AND DISCUSSION 0 5 10 15 20 25 30 Number of Clogged emitters, C (%) Figure 5.36 Relationship between number of clogged emitters (%) and reduction in coefficient of uniformity (Field Data) Number of Clogged emitters, C (%) Figure 5.37 Relationship between number of clogged emitters (%) and reduction in coefficient of uniformity (Synthetic Data) Chapter 5. RESULTS AND DISCUSSION 177 Number of Clogged emitters, C (%) Figure 5.38 Relationship between number of clogged emitters (%) and reduction in Emission Uniformity (Field Data) Number of Clogged emitters, C (%) Figure 5.39 Relationship between number of clogged emitters (%) and reduction in Emission Uniformity (Synthetic Data) Chapter 5. RESULTS AND DISCUSSION 178 Number of Clogged emitters, C (%) Figure 5.40 Relationship between number of clogged emitters (%) and reduction in distribution uniformity (field data). DUK-O* = 1.53070 + 2.4193 R2 = 0.975 Number of Clogged emitters, C (%) Figure 5.41 Relationship between number of clogged emitters (%) and reduction in distribution uniformity (synthetic data). Chapter 5. RESULTS AND DISCUSSION 179 5.8.3 Step 3 hydraulic characteristics of lateral under naturally clogged emitters, venturi injector, and injection of saline water: In step 3 the field experiment was carried out to evaluate the effects of naturally clogged emitters (discussed in Chapter 4), the use of the venturi injector, and the injection of saline water (representing a nutrient liquid) on the hydraulics of microirrigation laterals (20m and 40m) laid on flat terrain.The following sections present the findings: 5.8.3.1 Natural clogging and its relationship to CU: The minimum and maximum emitter flow rates were found to be 3.4 l/h and 4.98 l/h under no-clogged condition on flat terrain. Based on a nominal emitter flow rate of 3.78 l/h reported by the manufacturer, the variations of -10% to +30% were observed in emitter discharge in a no-clogged situation. Tables A.5.22 to A.5.25 (Appendix A) show the average of emitter flow rates obtained from the measurements of four replications along the 20m and 40m laterals consisting of naturally clogged emitters. As shown in Figures 5.42 and 5.43, it was found that emitter numbers 2, 10, 13, and 17 along the 20 m lateral and numbers 1, 10, 13, 21, 24, and 28 along the 40m lateral were partially clogged. Results indicated that the naturally clogged emitters were randomly located along the lateral. These emitters were inspected and revealed some slime, insect feathers and some fine sand inside the emitters. Because of the irregular shape and structure of the waterpassage way of the pressure-compensating emitter, it was not possible to measure the cross section area of the emitter and relate the portion of clogged area to the degree of clogging. Therfore, equation 5.7 was used to estimate the percentage degree of emitter clogging. Table 5.35 shows the discharge and degree of clogging (Cd%) under naturally clogged emitters along the lateral. Similar computations as for step 1 were done for stages 5 and 6 (similar patterns as in natural clogging) with artificially clogged emitters in the 20m lateral. The degrees of clogging for artificially clogged emitters are shown in Table 5.35. The cumulative percentage of clogging or the total percentage of clogging (TC% ) for 20m and 40m laterals was determined by adding the degrees of clogged emitters along the lateral. The values of TC% obtained from natural clogging were 50.95% and 154.18% for 20m and 40m laterals respectively. Then, the average degree of clogging along the lateral was determined as: average Cd- TC%/«,where n er 5. RESULTS AND DISCUSSION Section Figure 5.42 Emitter flow rate along a 20m lateral laid on flat terrain under naturally, artificially, and synthetically emitter clogged conditions. - First Run No Flush -Second Run No Flush I 1 ' i •©- • First Run Flushing • x- • • Second Run Flushing Nominal Emitter Flow rate Min. Emitter Flow (no clog) —I—Ave.Emitter Flow (no clog) -i- -i- -t- 1-10 13 16 19 22 25 28 31 34 37 40 Sections Figure 5.43 Emitter flow rate along a 40m lateral laid on flat terrain under naturally emitter clogged condition (before and after flushing). Chapter 5. RESULTS AND DISCUSSION 1 ra CO 4-1 ra E o o —' aj <n £ m CO l£ E E 8 CO I'D C O) i. O 4) O ^ >. ™ 14-.2 c u O , ~ ~° S 3 D) a> C cu * D) O) SO ON ra O De O o *+~ o a> CD to s-'E o LU Li CD ft E c cu a 3 0-C ra SP o O O LU TJ i_ CU i_ CU O) CD .Q o> *s E o E 5 o LU —, r». i«- oo eo ~ CO Tt CO CN ,j T- fr o> co 5 o o> IO CM ~ T- CN co CO CJ) i- o CM O CD Oi fr CO fr CO CO O) CO CD O) CN CD CN N O) S N CO T-T- 1- O T- T-T- n u) en ^ ^2 •«- CN co fr m co m 2 o CO o CN o Q cc £ E cu TJ CD CO O) O O >• ra o SC < cn c ra v$ o O o b »4— o at c nl CO CO o So NO QN O E * I LU r? CD LU TJ CU i_ CD CO CU - oi s - I E ^ 14-o LU 00 00 CN cS «7 «Jr (ON 2 CN CO T-~ T- T- CN CO CN O fr CJ) CD CN CO CO CN LO IO fr IS- T- IS-CN CO CJ) CN O) O T- CJ) T— X— CO O CO CD 00 i- CN CO fr E E II " IS 3 |-S CO -C z < 2? 'ro O) O ll ^ ro 2 o Z < CU > ^ •4= C CO CD "P " 3 CL , E .E O CO » a * § IT. 2 CD CO 4-t ra — o ro O c >. '5>i ° o 'I » (£ 2 <D 5? •£ -S • £ I TJ S-' <D £ at 3= 51 u ±= co — « £ CJ) c _ o O O b o CO CO r* r* CD 00 CN CN CO 00 O O CO CO fr co T- co CO cu c cu 1 O) CO NO ON ra O 13 De of CI o co o oo o to 00 fr O) fr CN iri fr ai cd o CN T- LO CN CO fr IO CD 1— +-CU JO 1 * mi? CD LU TJ ^ CD i_ CU O) CD o Oi CN IS- CN CN CO CO T- fr O O CD O co co CO T~ fr T- CN CM E in CN CO fr LO CD 2 s ra CD at c o CO •o 2 co u o _>. E o TJ C 2 2 § E CO T> CO at at o o >. 2 3 co Z CO 2 O) CO TJ c 2 CO c CO 0S o O O b CO c D) NO CO ON O TJ o o T- IO T- IO O r CD O) CN CN Is* O T- CN CO LO fr CD fr O T- fr CO CN O LO CO 0) CU CO 1 * I LU r? cu t- oo oo co CO CO 1- CN CO CO CO CO CN O CO IN, LU TJ i- CD i_ CU O) CD D OI C E o E i " LU CN CO fr NO 3 «N oj CO CD O) „ =) =5 o " a •§ co t: z < E2 co ^ i^l CD CO 11 II en c S '5) o o O ° >, ^ |-S z < Chapter 5: RESULTS AND DISCUSSION 182 is the total number of emitters along the lateral. The coefficient of uniformity, CU, was also determined for the 20m and 40m laterals under naturally and artificially clogged emitters. Table 5.35 presents the values of CU, TC%, and the average degree of clogging obtained from natural and artificial clogged emitters. The relationships between CU and average C//o were plotted (Figure 5.44-a) and a regression equation was found as follows: CU = -1.4333C, + 96.383 5.20 A similar analysis was made on synthetic data using the computer simulation program. In the simulation, it was assumed that 10%, 20%, 30%, 40%, and 100% of the number of emitters along the lateral were partially clogged. Table A.5.26 (Appendix A) shows the values of CU and CJXo under different numbers and degrees of clogged emitters obtained from synthetic data. The relationships between CU and the average CJVo were then plotted (Figure 5.44-b) and a regression equation was found: The values of CU and the average Cf/o obtained from natural, artificial, and synthetic data of clogged emitters were then combined (Table A.5.27) and plotted (Figure 5.44-c). A regression equation from the combination of data was obtained as follows: The results of equation 5.22 are considered the most accurate, since a combination of data were used. CU can be estimated by using equation 5.22 if the average degree of clogging along the laterals is known. The equation accounts for any type of emitter clogging (uniform or non-uniform) along the lateral when evaluating CU. Equation 5.22 shows that the value of CU can be as high as 96.26%) if there are no-clogged emitters along the lateral (Cd =0). Equation 5.22 indicates that any degree of emitter clogging along the lateral will reduce the CU = -0.9\35Cd +87.509 5.21 CU = -1.0453Q + 96.26 5.22 Chapter 5. RESULTS AND DISCUSSION 183 50 1 4333Cd + 96.383 R2 = 0.9756 -CU and Cd (Naturally Artificially) - Linear (CU and Cd) 0 5 10 15 Average degree of clogging, Cd (%) CU and Cd obtained from natural and artificial clogging 20 100 90 80 70 60 50 40 30 20 10 0 CU = -0.9135Cd +87.509 R2 = 0.9538 -CUandCd - Linear (CU and Cd) (b) 10 20 30 40 50 60 70 80 90 100 Average degree of clogging, Cd (%) CU and Cd obtained from synthetic clogging CU = -1.045300 + 96.26 R2 = 0.9493 20 30 40 50 60 70 80 90 100 Average degree of clogging, Cd(%) CU and Cd obtained from natural, artificial, and synthetic clogging Figure 5.44 Relationship between coefficient of uniformity (CU) and average degree of emitter clogging (Cd) along the lateral Chapter 5. RESULTS AND DISCUSSION 184 CU of the system. The maximum value of Cd in equation 5.22 can be 92% which results almost 0%> coefficient of uniformity. 5.8.3.2 Impact of lateral flushing on emitter flow rate: The effects of lateral flushing on emitter flow rates along the 20m and 40m laterals with naturally clogged emitters were evaluated. The emitter flow rates were measured in four replications and the average of emitter discharges was determined. Tables A.5.28 to A.5.30 (Appendix A) show the emitter discharge at four runs and the average emitter flow rate after 30 minutes of lateral flushing. The plots of emitter discharges obtained before and after flushing the laterals (Tables A.5.22 to A.5.25), and the emitter number along the lateral are shown in Figure 5.45 a and b. Results show that 30 minutes of lateral flushing increased the flow rate for most of the emitters along the lateral. A few emitters such as emitters number 1 and 10 in lateral A, numbers 17 and 20 in lateral B, and numbers 1 and 21 in the 40m lateral had reduced discharges after flushing. Figures 5.45 a and b show that the flow from emitter number 1 decreased from 2.73 l/h to 0.45 l/h, number 18 from 6.41 l/h to 3.61 l/h, number 20 from 4.4 l/h to 1.78 l/h in the 20m lateral and emitter number 1 decreased from 2.79 l/h to 1.57 l/h in the 40m lateral. Other studies (see chapter 2) suggested that flushing of the lateral improved the emitter discharge. This study shows that both increase and decrease in emitter flow rates occurred after flushing. It should be noted that flushing the lateral improves the flow rate of most of the emitters along the lateral. 5.8.3.3 Effect of temperature on emitter flow rate The effects of air and water temperatures on the emitter flow rates along the lateral with naturally clogged emitters were investigated. The microirrigation system was operated at different temperatures and at different times. Different conditions including sunny and cloudy conditions, after sunset, and immediately after sunrise were chosen. Tables A.5.31 and A.5.32 show the average emitter discharges along the lateral A and B under the conditions. The maximum and minimum air temperatures were 21.8 C and 15.5 C during the study. The o o maximum and minimum water temperatures were 20.2 C and 14.7 C respectively. Water temperature varied along the lateral and increased as the water reached the downstream end Chapter 5. RESULTS AND DISCUSSION 1.50 1.00 0.50 0.00 - before flushing(Lat. A) - before flushing (Lat. B) after flushing (Lat. A) -x- - after flushing (Lat. B) + + -f-10 12 Section -+-14 -+-16 18 Emitter flow rates before and after flushing (20m lateral) 20 4 1 1 1 1 1 1 1 1 r 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 Section Emitter flow rates before and after flushing (40m lateral) Figure 5.45 Effect of lateral flushing on emitter flow rate Chapter 5. RESULTS AND DISCUSSION 186 of lateral. Tables A.5.31 and A.5.32 (Appendix A) show the water temperature at the first, middle, and last sections of lateral. The maximum variation of water temperature along the lateral was 2.5C (19C and 21.5°C at the first and last section of lateral) and was obtained on a sunny day (Table A.5.31). Figures 5.46-a and b show the relationship between emitter flow rate and emitter number along the laterals. Results indicated that the variation in temperature at the experiment site has no significant impact on emitter flow rate. Figure 5.46 shows that the emitter discharges vary slightly in different conditions. The slight variation of emitter flow rate may be caused by the small variation in the elastomeric disk displacement of the emitter after shutting off the system. Results show that the variation in emitter flow rate at different temperatures during the day (continuously operating the system) was negligible. This is because of less change in the elastomeric disk displacement of the emitter during continuous running. This study found that the variations of air and water temperature had no significant impact on the emitter flow rate. 5.8.3.4 Comparison of hydraulic parameters under natural, artificial, and synthetic data of clogged emitters (flat terrain): Table A.5.33 shows the values of hydraulic parameters obtained from natural, artificial (stage 5), and synthetic data (stage 5) of clogged emitters for the 20m lateral laid on flat terrain. The comparisons of coefficient of variations Vqs, Vhs, Vqh are shown in Figure 5.47-a, Hf'm Figure 5.47-b, CU and EU' in Figure 5.47-c, and qvar and Hvar in Figure 5.47-d. The values varied from one case to another, but similar trends in hydraulic variation were found among the natural, artificial and synthetic clogging. Table A.5.34 shows that although the degree of emitter clogging under naturally clogged conditions was less than the degree of emitter clogging in artificial and synthetic data, the Hvar were higher than qvar, CU greater than EU', and Vqs greater than Vqh under all conditions. The laterals flow rates were 73.66 l/h in laterals B under natural clogging and 59.09 l/h and 59.39 l/h under artificial and synthetic clogging. The value of CU was 90.43% under natural clogging, whereas it was 69.44% and 63.36% under artificial and synthetic clogging. The value of EU' was 89.66% under natural clogging, and 43.72% and 35.4% under artificial and synthetic clogging. The major reason for the differences in the value Chapter 5. RESULTS AND DISCUSSION 4.50 T 0.00 4—I 1 1-—I 1 1 1 1-—I 1 1 1 1 1 1 1 1 1 1 \ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Section b (lateral B) CD CO 52.00 o 1— .=§ 1.50 + LU 1.00 0.50 Air temp.=17.5c, W.temp.=16.1c(cloudy 10 AM) •Airtemp.=21.8c, W.temp.=20.2c (sunny 4 PM) • Air temp.=16c, W.temp.=14.3 (sunset 10PM) -Air temp.=15.5c, W.temp.=14.7c (sunrise 6 AM) •Air temp.=20.2c, W.temp.=20c (sunny 3 PM) 0.00 H h H h H 1 1 h H r- 4-3 4 5 6 7 8 9 10 11 Section 12 13 14 15 16 17 18 19 20 Figure 5.46 Effect of air and water temperature on emitter flow rate along the laterals A&B laid on flat terrain. Chapter 5. RESULTS AND DISCUSSION 188 Coefficient of variations for 20 m lateral 50 40 -E 30 20 -I—| 10 4 0 -a Hi j 0.05 \- 0.04 \- 0.03 |- 0.02 \- 0.01 4- o.oo x> O to — < Z O (0 — 03 Z O > TJ c (0 I Vqs (%) DVhs (%) 11 Vqh (%) 0.016 0.012 ; 0.008 0.004 0.000 Head loss (H() for 20 meter lateral -b a. ]Hf(m) q < 03 CO Z -IHvar 1 i • 1 1 i i - L O CO ro co z —-100 80 b 60 -t LU ca 40 | O 20 4 0 CU and EU' for 20m lateral -c o o TJ O 2 ^ 0_ *= CO co — < z o .« 4 00 z o • CU(%) gEU'(%) 0.15 §0.10 X 1 0.05 + 0.00 < 75 qvar and Hvar for 20m lateral o x> o 2 o. o lqvar(%) El Hvar (%) •3 ™ m CO —- LU Z O Figure 5.47 Comparison of hydraulic parameters in the microirrigation under artificially, synthetically, and naturally clogged conditions(flat terrain) Chapter 5. RESULTS AND DISCUSSION 189 of the specific hydraulic parameter under different conditions was the difference in degree of clogged emitters, which was the uncontrollable factor. 5.8.3.5 Selection of venturi injector: Based on the nominal emitter discharge, the maximum lateral inflow of 2.52 l/min was estimated for the field experiment. Different values of inlet and throat pressures for a venturi (explained in Chapter 4) were used to determine the optimum venturi throat diameter (d) for the experiment. Table A.5.35 (Appendix A) shows several estimated values of throat diameter based on the inlet and throat pressures for a 15 mm venturi inlet diameter. The minimum and maximum venturi throat diameters were found to be 0.141cm and 0.258 cm when the venturi inlet flow (motive flow) was 2.52 l/min. Table A.5.36 shows the values of minimum inlet flow (motive flow) for different pressures at the venturi inlet and throat. It was found that as the difference in inlet and throat pressures increased, more inlet flow (motive flow) was required to provide a vacuum (suction) condition for the venturi. Table A.5.36 also shows that the same amount of motive flow is required if the pressure differences under different inlet and throat pressures are equal. For example, when the inlet and throat pressure are 60 psi and 25 psi (35 psi difference in pressure) respectively, the required motive flow is 2.202 l/min. The same amount of motive flow is needed if the inlet and throat pressure are 50 psi and 15 psi (35 psi difference in pressure). Based on these results (Table A.5.36), the minimum venturi throat diameter of 0.141cm was chosen for this study. The smallest commercially available (for the irrigation industry) venturi injector was the Mazzei 484, 3/4" with an injection capacity of up to 1.13 l/min (li gph). 5.8.3.5.1 Calibration of Mazzei 484 venturi injector: In order to calibrate the venturi injector and determine the required pressure difference between the inlet and outlet of the venturi, three different tests as shown in Figure 4.11 (Chapter 4) were conducted at the field experiment. City water supply was used as the injection liquid for all three tests. In the first test (Figure 4.11-a), the motive flow was adjusted to 1.26 l/min (equal to the amount of lateral flow consisting of 20 emitters of nominal flow of 3.78 l/h) under the 15 psi and 0 psi inlet and outlet pressures respectively. No liquid suction was observed at the Chapter 5. RESULTS AND DISCUSSION Table 5.36 Test of Mazzei 484 venturi injector under different pressure and motive flow (venturi inlet flow). Test Pressure at Pressure at Motive Liquid venturi # venturi inlet venturi outlet flow suction out flow (psi) (psi) (l/min) (l/min) (l/min) 1 15 0 1.26 0.00 1.26 60 15 1.26 0.00 1.26 2 60 15 2.52 0.00 2.52 60 15 4.53 0.46 4.98 60 15 14.4 1.36 15.52 60 15 1.26 0.00 1.26 3 60 15 2.52 0.00 2.52 60 10 15.75 1.30 17.05 30 15 11.2 0.92 12.12 Chapter 5. RESULTS AND DISCUSSION 191 throat of the venturi. Table 5.36 shows the rate of liquid injection in l/min applied in different tests. The second test (Figure 4.11 -b) was done under 60 psi and 15 psi inlet and outlet pressures. The motive flows were adjusted to 1.26 l/min, 2.52 l/min, and 4.53 l/min which were the required flows in 1,2, and 4, 20m laterals consisting of 20 emitters. There was also no liquid suction observed under 1.26 l/min and 2.52 l/min of motive flow, but the rate of liquid suction was 0.46 l/min when the amount of motive flow was increased to 4.53 l/min. Finally, the third test was done in such a way that the venturi injector was connected to the microirrigation laterals (as shown in Figure 4.11-c) and inlet and outlet pressures were adjusted to 60 psi and 15 psi. Table 5.36 shows that no liquid suction was observed when the venturi was connected to the laterals having 1.26 and 2.52 l/min flow rate. When the motive flow increased to 15.75 l/min, the pressure fell to 10 psi. The rate of liquid suction was measured as 1.3 l/min under this operation. Then, the inlet and outlet adjusted to 30 and 15 psi (15 psi was the required lateral inlet pressure) and the rate of liquid flow was measured. Results indicated that the minimum required motive flow for the Mazzei injector 484 when it was connected to the microirrigation system at the experimental site was about 11.2 l/min under 15 psi lateral inlet pressure. This amount of motive flow for this study allows the venturi injector to inject the liquid (saline water, or liquid chemical) into the microirrigation system. The following tests were carried out to investigate the effects of liquid injection on hydraulics in microirrigation laterals. 5.8.3.6 Hydraulics in lateral with venturi injector installed: This test was done in order to find out whether the venturi injector has an impact on the emitter flow rate along the lateral and, if so, what its effect is on the uniformity. City water with an electrical conductivity (EC) of 0.022 (ds/m) was used. The test of hydraulics in laterals with a venturi injector installed was conducted on 20m and 40m laterals with naturally and no-clogged emitters. Tables A.5.37 and A.5.38 summarise the results obtained from three different runs of the microirrigation system on flat terrain. Table A.5.37 shows that in the first run (no liquid suction), the inlet lateral flow rate was adjusted to 745.9 l/h (12.4 l/min) and the pressures at the inlet and outlet of venturi were 25 psi and 15 psi respectively. The average pressure at the end of lateral was 12 psi. The reason for dropping the pressure to 12 psi was due to higher head loss Chapter 5. RESULTS AND DISCUSSION 192 resulted from increasing the lateral water flow in this test. Hydraulic parameters of CU, EU', Ea, qvar, and Vqs were 86.6%, 73.1%, 99.9%, 8.9x10"5, and 0.242% respectively. In the second run (injected liquid, pressure at the venturi outlet was not adjusted) the pressure at the venturi outlet dropped to 12 psi. Results in Table A.5.37 show that 96.4% of 792.98 l/h (13.2 l/min) of lateral inflow came from the main line of water supply and 3.56% from the liqiud injection tank (barrel). The values of CU, EU', Ea, qvar, and Vqs were 86.19%, 72.53%, 99.9%, 1.1 x 10"4, and 0.243%. In the third run, the pressure at the venturi outlet was increased to 15 psi (similar to the first run) by decreasing the lateral flow at the end of lateral. The CU, EU', Ea, qvar, and Vqs were 86.6%>, 73.2%), 8.9x10"5, and 0.242%. Results indicated that the values of hydraulic parameters obtained from the first and third runs were very similar. However, there were variations in the second run. Similar tests were done on 40m laterals. For the third run, it was found that increasing the pressure at the venturi outlet by decreasing the lateral flow was not a practical concern. Therefore, on the third run of 40m lateral, the pressure at the venturi outlet was increased from 12 psi to 15 psi by increasing the venturi inlet pressure from 25 psi to 34 psi. Table A.5.38 shows the results of hydraulic parameters for 40m lateral. Similar trends were found for 40m and 20m laterals in all three tests. Figures 5.48 a and b show the variation of emitter flow along the 20m and 40m laterals. It is shown that the emitter flow rates along the lateral in the first and third runs were similar, but varied in the second run. Table A.5.38 also shows the total emitter flow along the 40m laterals in three runs. In the second and third runs about 6.4%> of the total lateral flow was provided from the liquid suction and 93.4% from the main line of water supply. Total emitter flow rates were 137.2 l/h, 130.3 l/h, and 135.3 l/h at the first, second, and third run respectively. The emitter discharge coefficients of variation (Vqs) were 19.05%, 20.7%, and 19.6% in the first, second and third run respectively. Chapter 5. RESULTS AND DISCUSSION Figure 5.48 Variations of emitter flow rate along a 20m (a) and 40m (b) laterals with and without liquid injection using city water and naturally clogged emitters. Chapter 5. RESULTS AND DISCUSSION 194 Similar tests were done on the system with the no-clogged emitters along the lateral. First, the average emitter flow rate was measured when there was no venturi injector installed in the system. Then, three runs with venturi injector similar to those in the naturally clogged condition were applied to the system. Tables A.5.39 and A.5.40 show the average emitter flow rates along the 20m and 40m laterals under no-clogged condition with and without venturi. The pressure variations measured at each section along the 40m laterals are also shown in Table A.5.40. The average inlet lateral pressure was 15 psi (14.5 to 15.5 psi). The pressure along the lateral varied from 15.5 psi (maximum pressure) at the first section to 14.8 psi (minimum pressure) at the last section. An increase of inlet lateral flow was needed (in the case of the 20m and 40m lengths of laterals) in order to create suction at the venturi throat. Increasing the lateral flow resulted in higher head loss and lower pressure at the end of laterals. Tables A.5.39 and A.5.40 show that in the first run the pressure at the venturi inlet and outlet were 25 psi and 15.5 psi respectively. In the case of 40m lateral the pressure varied from 15.5 psi at the first section to 9.6 psi at the last section along the lateral. Figures 5.49 a and b show the emitter flow and pressure variations along the 20m and 40m laterals. Figure 5.49 shows that the pressures at each section along the lateral in second run were almost 2 psi less than those pressures in the first and third runs. It was also found that not only emitter flow rate but also the pressures along the lateral were almost overlapped in the first run, third run, and when operating the system without the venturi. The differences between the emitter flow rate in the second run and other runs were higher from mid-way up to the end of the laterals. The average differences in emitter discharge between the second run and the others were 0.06 l/h at the first half and 0.4 l/h at the second half part of the lateral. Tables A.5.40 shows that the total emitter flow was 156.4, 146.3, and 155.7 l/h, and the Vqs were 7.4x10"4, 7.8x10"4, and 7.4x10"4 in the first, second and third runs respectively. The hydraulic parameters in the first and third runs were found to be similar but differed from that the second run. 5.8.3.7 Hydraulics of lateral with saline water injection: Two different cases (ideal and conventional cases) were tested for injection of the saline water as a nutrient injection into the microirrigation system. This experiment was done in order to investigate how uniformly the nutrient injection is distributed along the lateral. In the ideal case, Chapter 5. RESULTS AND DISCUSSION 195 Figure 5. 49 Variation of emitter flow rate and pressure along a 20m (a) and 40m (b) laterals with and without liquid injection using city water and no clogged emitters. Chapter 5. RESULTS AND DISCUSSION 196 the saline water with a constant salt concentration (electrical conductivity, EC = 1.5 and 3 mrnhos/cm) was required from the emitters flow along the lateral. When the liquid nutrients are injected into the system, the flow in the lateral is the combination of a portion (%) of liquid injection and a portion of irrigation water (inflow) from the main line. Therefore, the EC of the mixed water delivered by the emitters is dependent upon the portion of liquid suction and the portion of inflow from the main line and their electrical conductivity. The injection water has an EC of 0.022 mmhos/cm. To obtain the mixed water (irrigation water and saline water) with EC of 3 mmhos/cm, saline water with higher EC than the irrigation water is provided. The amount of salt (g/l) required to make a saline water an injection liquid can be determined from the portion of liquid suction (%) and its electrical conductivity (ECL), and the portion of inflow (%) and its electrical conductivity (ECf). Based on different portions of motive and liquid flow, the values of the total amount of salt (g/l) that was needed in the irrigation water to make a saline water of ECL as an injection liquid were determined and summarised in Table A.5.41 (Appendix A). About 10 to 11 g/l and 22 g/l salt (table salt or sodium chloride) were required to use saline water as an injection liquid, resulting in the mixed water of ECm =1.5 and 3 mmhos/cm delivered by the emitters. Table A.5.41 gives an example of determining the amount of salt for an ideal case of mixed water of ECm equal to 3 mmhos/cm. Similar calculations as summarised in Table A.5.41 were done for ECm equal to 1.5 mmhos/cm. The ideal case was simulated similar to the real condition when the irrigation water is provided from two different sources of saline water and a constant value of ECm at the emitter is desired. In the conventional case, two different saline waters of EC equal to 1.5 and 3 mmhos/cm were prepared as the injection liquid. To provide the saline injection liquid of ECL - 1-5 and 3 mmhos/cm, 0.54 and 1.14 g/l of table salt were added into the irrigation water. These saline liquids were injected into the microirrigation system and mixed with irrigation water. Under both ideal and conventional cases, the average emitter flow rate and the electrical conductivity of the mixed water along the 20m and 40m laterals were measured. Three different runs similar to those explained in previous sections were done in each case. Tables A.5.42 to A.5.45 Chapter 5. RESULTS AND DISCUSSION 197 (Appendix A) summarised the average emitter flow rate obtained from injection of different saline water (ideal case) in three runs for 20m and 40m laterals. The hydraulic parameters were determined and given in Tables A.5.42 to A.5.45. Results show that about 6.5% of total lateral flow was provided from the liquid injection and 93.5% from the motive flow in the second and third runs for both the 20m and 40m laterals. These proportions of flows were slightly different in the second and third runs. The injection of saline water (as nutrient injection) with ECL of 27.5, 15 and 13.5 mmhos/cm resulted in mixed water with ECm of 3, 1.6 and 1.4 mmhos/cm. The ECm from the emitters along the 20m and 40m laterals were measured and are shown in Tables A.5.42 to A.5.45. It is found that ECm was constant along the laterals when the injection liquid with ECL of 27.5, 15 and 13.5 mmhos/cm was injected into the microirrigation system. Results indicated that the flow at the venturi throat was turbulent (Reynolds number greater than 10000). The turbulent condition mixed the liquid and motive flow sufficiently to give a mixed water with a constant ECm along the lateral. Tables A.5.46 to A.5.49 (Appendix A) show the results of the conventional case of the injected liquid. The ECm obtained from the mixed water released by the emitters along the laterals was constant over time and equal to 0.11 (when ECi was 1.5 mmhos/cm) and 0.2 (when ECL was 3 mmhos/cm) mmhos/cm respectively. The hydraulic parameters in the second run differed from those values obtained from the first and third runs. There were no significant differences between the values of hydraulic parameters in the first and third runs. Figures 5.50 a,b,c,d and 5.51 a,b,c,d show the emitter flow variation along the laterals with injection of different concentrations of saline water and without venturi injector under no-clogged condition for 20m and 40m laterals respectively. The straight line in the figures indicates the nominal emitter flow rate. It was found that the emitter flow along the lateral in the second run differed from that in the first and third runs. It also differed from the emitter flow rates when the venturi injector was not installed. The differences between emitter flow rates under different runs were greater from the middle part up to the end of the lateral and increased as the emitters were closer to the end of lateral. Tables 5.37 and 5.38 summarised the results obtained from the effect of the venturi injector and saline and city water injection on total emitter flow (T.E.F), CU, EU', Ea, qvar, and Vqs under seven different conditions and on three different runs for 20m and 40m laterals. The seven different conditions were: (1) natural clogging, water injection, (2) no-clogged (new emitters), water injection, (3) saline water Chapter 5. RESULTS AND DISCUSSION 198 Chapter 5. RESULTS AND DISCUSSION 199 OCOCDM-CNOOOCO^rCMO (L|/|) 9JBJ MOLJ J8MIUJ3 OOOCOM-CMOOOlD'*C\ip iri^^^^^cococo'co'co (i|/l) ajEj MOIJ janiuig o II o II o LU a a. •§••5 t? 11 CM eo g .E ccc°E 3 3 D ^ O cc cc cc s z IIIIIIIIIII o M-CM o o IOCOCDM"CM^J-COCDM"CMCO CO CO CO CO (l|/|)9JBJM0UJ9H!LU3 o LU CM II o LU o LU TO o LU o o o TJ c CO x: cu c -*—• jo o Om puc o CO 1 cn c itte o E CO cu cu TJ CU CO L OI 5 Bo o o 5^ i O CD c 1 E de cu c 14— ZJ o 1 c CD -4—' g co ro cu CO c > "co CO c LO 0) u. ffe O) TJ LL O moOCDTrCM^tOOCD^fCMCO u- co co co co (l|/|) 8}BJ M0|j J3H!LUg Chapter 5. RESULTS AND DISCUSSION 200 Table 5.37 Effect of venturi injector, saline and city water injection on emitter flow rate , CU, EU', Ea, qvar, and Vqs in a 20 meters lateral laid on flat terrain. RUN-1: venturi closed, no liquid injection Conditions Total emitter CU EU' Ea Vqs qvar flow (l/h) -•(%) (%) (%) (%) (%) City water, natural clogging 67.90 86.554 73.108 99.998 24.2123 8.9E-03 City water, new emitters 78.69 94.003 91.956 99.997 6.8083 1.1E-02 City water, ECL=13.5-15 75.85 94.285 92.604 99.997 6.6570 1 .OE-02 City water, ECL=27.5 76.13 94.018 92.332 99.997 6.7447 1 OE-02 City water, ECL=1.5 78.66 94.577 92.906 99.997 6.0523 1.1E-02 City water, ECL=3 78.53 94.624 92.625 99.997 6.1374 1.1E-02 City water, no Venturi installed 77.61 94.019 91.860 99.997 6.9764 1 OE-02 RUN-2:City water and saline water injection, no adjusted pressure Conditions Total emitter CU EU' Ea Vqs qvar flow (l/h) (%) (%) (%) (%) (%) Natural clogging, water injection 67.98 86.190 72.536 99.997 24.3070 1.1E-02 New emitters, water injection 76.49 95.998 94.481 99.996 5.1955 1.3E-02 Saline water injection, ECmix=1.5 73.44 95.301 94.092 99.997 5.4805 1.2E-02 Saline water injection, ECmix=3.0 74.30 95.046 93.285 99.997 5.7909 1 2E-02 Saline water injection, ECmix=0.11 77.50 95.161 93.161 99.997 5.6900 1.3E-02 Saline water injection, ECmix=0.2 76.82 95.829 94.038 99.997 5.1539 1.3E-02 No Venturi (No injection) 77.61 94.019 91.860 99.997 6.9764 1 .OE-02 RUN-3: City water and saline water injection, adjusted pressure Conditions Total emitter . CU EU' Ea Vqs qvar flow (l/h) (%) (%) (%) (%) (%) Natural clogging, water injection 67.67 86.648 73.297 99.998 24.2038 8.9E-03 New emitters, water injection 78.36 93.773 91.572 99.997 7.0976 1.1E-02 Saline water injection, ECmix=1.5 75.49 94.372 92.846 99.997 6.4402 9.9E-03 Saline water injection, ECmix=3.0 76.06 94.209 92.660 99.997 6.4598 1 .OE-02 Saline water injection, ECmix=0.11 78.47 94.651 93.029 99.997 6.0203 1.1E-02 Saline water injection, ECmix=0.2 78.51 94.573 92.778 99.997 6.1538 1.1E-02 No Venturi (No injection) 77.61 94.019 91.860 99.997 6.9764 1 .OE-04 Chapter 5. RESULTS AND DISCUSSION 201 Table 5.38 Effect of venturi injector, saline and city water injection on emitter flow rate , CU, EU', Ea, qvar, and Vqs in a 40 meters lateral laid on flat terrain. RUN-1: venturi closed, no liquid injection Conditions Total emitter CU EU' Ea Vqs qvar flow (l/h) (%) (%) (%) (%) (%) City water, natural clogging 137.23 89.394 78.787 99.984 19.0521 6.1E-02 City water, new emitters 156.42 94.162 92.111 99.980 7.4650 7.4E-02 City water, ECL=13.5-15 153.86 94.139 91.898 99.981 7.2352 7.3E-02 City water, ECL=27.5 152.40 94.239 92.310 99.981 7.2903 7.1E-02 City water, ECL=1.5 156.70 94.661 92.788 99.980 6.2372 7.5E-02 City water, ECL=3 154.23 94.786 92.693 99.981 6.4192 7.2E-02 City water, no Venturi installed 158.28 92.877 90.012 99.979 8.6960 7.8E-02 RUN-2:City water and saline water injection, no adjusted pressure Conditions Total emitter CU EU' Ea Vqs qvar flow (l/h) .(%) .(%) (%). (%). (%). Natural clogging, water injection 130.39 87.628 76.264 99.982 20.7621 6.6E-02 New emitters, water injection 146.31 93.452 90.821 99.979 7.9485 7.8E-02 Saline water injection, ECmix=1.5 148.55 94.228 92.134 99.978 7.4005 8.2E-02 Saline water injection, ECmix=3.0 147.62 94.504 92.397 99.978 7.0940 8.1E-02 Saline water injection, ECmix=0.11 152.16 95.141 92.908 99.977 5.9352 8.6E-02 Saline water injection, ECmix=0.2 147.03 94.395 91.600 99.979 6.8154 7.9E-02 No Venturi (No injection) 158.28 92.877 90.012 99.979 8.6960 7.8E-02 RUN-3: City water and saline water njection, adjusted pressu re Conditions Total emitter CU EU' Ea Vqs qvar flow (l/h) (%) (%) . (%) (%) (%) Natural clogging, water injection 135.36 88.470 76.954 . 99.984 19.6189 5.8E-02 New emitters, water injection 155.72 94.325 92.385 99.980 7.2797 7.4E-02 Saline water injection, ECmix=1.5 153.88 94.032 92.034 99.981 7.3948 7.3E-02 Saline water injection, ECmix=3.0 152.34 94.161 92.229 99.981 7.3711 7.2E-02 Saline water injection, ECmix=0.11 156.33 94.644 92.516 99.980 6.2489 7.5E-02 Saline water injection, ECmix=0.2 154.50 94.766 92.810 99.981 6.3199 7.3E-02 No Venturi (No injection) 158.28 92.877 90.012 99.979 8.6960 7.8E-02 Chapter 5. RESULTS AND DISCUSSION 202 injection, ECm = 1.5 mmhos/cm, (4) saline water injection, ECm = 3 mmhos/cm (5) saline water injection, ECm = 0.11 mmhos/cm, (6) saline water injection, ECm = 0.2 mmhos/cm, and (7) no venturi injector, no injection. Results show that the differences between the values of the total emitter flow, Vqs, and qmr in the second run with those values obtained from the first and third runs under the seven different conditions were significant. For example, the values of total emitter flow under condition (4) were 152.4 l/h, 147.62 l/h, and 152.34 l/h, in the first, second and third runs respectively for the 40m lateral. This means that there was about 5 l/h reduction in lateral flow in the second run for the 40m lateral. This amount of reduction is considerable if the growing season, size of cultivated area, and the number of hours of operating the microirrigation system are considered. On the other hand, there were less than 1% to 2% differences between the values of CU, and EU' under different conditions in three runs. For instance, the values of CU under condition (5) were 94.66%, 95.14%, and 94.64% in the first, second and third runs respectively for the 40m lateral. Figures 5.52 a,b,c,d show a comparison of the values of the hydraulic parameters under seven conditions. This clearly demonstrates that the venturi injector has an impact on the hydraulics in a microirrigation system. Chapter 5. RESULTS AND DISCUSSION 203 (uoipefui pinbn ON) jjniuaA ON 20=XIW03 'uoipafu; J91EM OU||BS U 0=X!LUQ3 uoipafm jajBM amies uoipafui JB)BM aui|BS 'uoipelui JOJBM aunes uojpafui jeieA 'sjauiiua cr > cr > tfl cr > uoipafui ^ JBJBM tiutOOap ' 1 ' 11 I 11 1 1 I IBjniBN O LO (%) sbA (uoipefui pinbi| ON) uniuaA ON uoipefui JGJBM 'Bu!66op IBJniBN cr > cr > UOIPafUl J3)BM > 'SJS11JUJ8 M3N DID CM (%) sbA (M/i)d'3'± PUB (%)no ooooooooooo (DlOtniMT-OCOflONlO (M/l)d31 PUB (%)nO c o c o o ^, c •g cr T3 c to CO 0) co CO CO Q- E 1 s *^ c c CO 2 E 5 > O CU LU > t CM CO -ri E CO co 3 TO 5> O Chapter 6 SUMMARY AND CONCLUSIONS 204 Chapter 6 SUMMARY AND CONCLUSIONS 6.1 Summary: A comprehensive study was undertaken to determine the effects on the hydraulics of a microirrigation system of different numbers, degrees and locations of clogged emitters along laterals laid on flat and sloped terrain. Results obtained from the field experiment were compared to the results predicted by a computer simulation program. The effects of air and water temperatures and lateral flushing on emitter flow rates were also investigated in the field. Finally, the impact of injecting saline water (as a nutrient) on the emitter's flow characteristics was examined. A computer spreadsheet program was constructed to simulate the effect of eight patterns of clogged emitters and five slopes on the hydraulics of the microirrigation system. The computer program was designed according to commonly used theoretical and empirical equations which determine the head loss, pressure and flow rate within a lateral. The program predicts lateral flow rates and variation of individual emitter discharges along the lateral due to pressure changes within the lateral line. The uniformities in a microirrigation system were estimated from the variation of emitter flow rates. The hydraulic parameters (Hf, Hvar, qvar, CU, EU', DU, Us, Vqs, Vhs, Vqh, Uh, and Vpj) were determined and presented in graphical form. The relationships between the hydraulic parameters under different patterns of clogging can be easily compared to each other by using the graphs. The program incorporates the data of coefficient of variation and deficit evapotranspiration adopted from the study made by Sammis and Wu (1985) to estimate the reduction of cotton yield due to emitter clogging. A field experiment was then conducted to study the effects of the same patterns of clogging and slopes on hydraulic characteristics of a microirrigation system installed on flat and sloped terrains. Five different slopes (0%, and 3% and 7% for both up- and down-slope) were used. The effect of emitter clogging on hydraulics parameters (similar parameters to those in simulation program) was evaluated. The results obtained from the field experiment were Chapter 6 SUMMARY AND CONCLUSIONS 205 compared to the theoretical values obtained from the computer simulation model output. In all slopes and stages studied, the computed results did not deviate more than ±5% from the field observations. Based on data obtained from the field and synthetic data, the effects of different patterns of clogged emitters on reduction of cotton yields were simulated, and the loss to the farmer was estimated. Under the no-clogged condition, the emitter discharge along the lateral varied from the nominal emitter flow rate in all five slopes studied. In the case offlat terrain, this variation is mainly due to the emitter manufacturer's coefficient of variation. In the case of sloped terrain, the pressure variation along the lateral was the major factor affecting emitter flow rate in addition to the manufacturer coefficient of variation. The behavior of the hydraulics on flat terrain was slightly different from that on sloped terrain. In the case of flat terrain, the number and location of clogged emitters had more impact on Hf, Hvar, qvar, Vhs, and Vqh than did the degree of clogging. The number and degree of clogging were the major factors affecting uniformities (CU, EU', DU, and Us). For the emitter discharge coefficient of variation, the number of clogged emitters had a higher impact than did the degree and location of clogged emitters. In the cases of sloped terrain, higher values of Hf, qvar, Vqh, Hvar, and Vhs were obtained in up-slopes than in the down-slopes in all eight stages. The slopes of laterals had a significant effect on Vqh, Hvar, and VhS, but had little impact on uniformities. While the maximum emitter flow variation (qvar) occurred in stage 1 in an up-slope, the minimum was found in stage 1 in a down-slope condition. Although the number, degree and location of clogged emitters affected the qvar, the last noted was found to have a higher impact than the other two. The number and location of clogged emitters had a significant impact on Vqs and Vpf, but the location of clogging had a greater effect than the number of clogged emitters. The highest values of Vqs and Vpf were found in stages 4 and 5 in different slopes. According to the ASAE EP458 (1997) criteria, the emitter performance coefficients of variation were too high to be accepted in all stages with clogged emitters. Chapter 6 SUMMARY AND CONCLUSIONS 206 On sloped terrain, both the number and location of clogged emitters were the major factors affecting uniformities, but the former had a higher impact than the latter. In the no-clogged situation, the uniformities in down-slopes were 1 to 4 % higher than that in the up-slope conditions. In the case of clogged conditions, the differences between the values of uniformities (CU, EU', DU, and Us) in up- and down-slopes depended upon the number and degree of clogged emitters. It was found that the uniformities were independent of the slopes of the laterals. For each slope there was a linear relationship between the uniformities and the percentage of the total number of partially clogged emitters along the lateral. The relationship between CU and average degree of emitter clogging (CJ) obtained from natural, artificial, and synthetic clogging data were plotted and a least-square regression equation was determined. The relationship between CU and Us under different slopes indicated that they were highly correlated. Therefore, either CU or Us can be used for evaluating the system. Both the field data and simulated results showed that stages 4 and 5 represented the worst emitter clogging patterns affecting the hydraulic parameters. Similar results for all aforementioned parameters were obtained from synthetic data generated by the computer simulation program in all stages and slopes. The economic effects of different patterns of emitter clogging on crop production were evaluated using the cotton crop as a paradigm. The reduction in yield and the farmer's money loss were highly dependent on the number and location of clogged emitters along the lateral. As the number of clogged emitters increased, the cotton yield decreased. The reduction of yield was independent of the type of lateral slopes (up- or down-slopes). Stages 4 and 5 were the worst stages of emitter clogging affecting the cotton yield. The effects of air and water temperatures on the hydraulic characteristics of the emitter were examined. It was found that there were no significant differences in emitter flow rate along the lateral under various temperatures at the experimental site. The impact of flushing the lateral on emitter flow rate was also investigated, and results indicated that the flushing Chapter 6 SUMMARY AND CONCLUSIONS 207 improves the emitter flow rate along the lateral. However, the flushing may also create an emitter clogging problem since the small, suspended particles from the lateral may be flushed into the emitter. The effect on emitter's hydraulic characteristics of injecting different degrees of saline water into the lateral were studied. Two cases were evaluated: (1) in which a constant value of electrical conductivity (EC) at the emitter's outlet was maintained and (2) in which a constant EC value of the injecting water was maintained. The turbulent flow at the injecting point (venturi throat) allows sufficient mixing of the injected liquid and motive flow. Therefore, a mixed water of almost constant ECm along the lateral was obtained over time. When the venturi was installed and the liquid was injected, the values of hydraulic parameters (emitter flow rate, emitter coefficient of variations, uniformity, etc.) varied from those values obtained without the injection. 6.2 Conclusions: The following conclusions can be drawn. The numbers correspond to objective numbers in chapter 1: 1- The emitter flow rate from pressure-compensating emitters and, consequently, the uniformities in a microirrigation system are highly dependent on the number, degree, and location of clogged emitters along the lateral. Pressure-compensating emitters do not produce constant and uniform discharge along the lateral. The average deviations of emitter flow rate on flat and sloped terrains from the nominal emitter flow rate were ± 5.9% in flat terrain, ±3.47% and ± 4.51% in 3% and 7% up-slopes, and -6.64% and -5.12% in 3% and 7% down-slopes. There were no significant differences in emitter flow rate along the lateral under various temperatures at the experimental site. 2- Synthetic data showed similar behavior to that of the field study for hydraulic parameters along the 10 to 60 meter laterals under all patterns of emitter clogging. Higher variations in Chapter 6 SUMMARY AND CONCLUSIONS 208 the hydraulic parameters were observed when the length of lateral was increased. The following results were obtained from the field experiment and the computer program: A- In the case of flat terrain, the number and location of partially clogged emitters were the major factors affecting pressure variation, head loss, and emitter coefficient of variations. The number and degree of clogged emitters had a major effect upon the uniformities. B- In the case of sloped terrain, the location of clogged emitters and the slope of laterals had a significant impact on pressure variation and emitter discharge coefficient of variation due to hydraulics. On sloped terrain the number of partially clogged emitters along the lateral had higher impact than the location of clogging on uniformities. The type of lateral slope (up- or down-slope) had no significant impact on uniformities. The differences observed between the values of unformities obtained from up and down-slopes were insignificant. 3- Stages 4 and 5 (when 30% of the total number of emitters along the lateral were partially clogged and located at the first one-third section or randomly located along the lateral) were the worst situations of emitter clogging. 4- Pressure drop occurred at the lateral inlet when fertilizer or chemical (in this study, saline water) was injected by the venturi injector. Changing the pressure at the lateral inlet caused variation in emitter flows and rate uniformities. 5- Turbulent flow at the venturi throat mixed the liquid injection and motive flow sufficiently to maintain a constant concentration of fertilizer or chemicals (in this study constant EC of saline water) at the emitter outlets over time. 6- When chemical is injected by the venturi injector into the lateral, variation of hydraulic parameters is unavoidable. In this case, variation of hydraulic parameters can be minimized if the pressure at the lateral inlet is adjusted to the amount of pressure in the no-liquid injection situation. 7- The reduction of crop (cotton in this study) yields was directly related to the number and degree of clogged emitters in different slopes. The highest yield reduction and farmer's money loss occurred when the partially clogged emitters were located at the first one-third section of the lateral or randomly located along the lateral (stages 4 and 5). Regression Chapter 6 SUMMARY AND CONCLUSIONS 209 equations indicate that as the number of partially clogged emitters along the lateral increased the cotton yield decreased. 8- A computer spreadsheet program (in MS Excel) was constructed and used to predict the effects of emitter clogging on the hydraulics of microirrigation system. In all eight stages of clogged conditions, the theoretical results obtained from the computer program did not deviate more than ±5% from the field results. From the point of view for future research numbers 1, 2, and 4 and from the point of view of applying these results numbers 2, 3, 5, and 6 are the most important. 6.3 Recommendations: The hydraulics of a microirrigation system under different patterns of clogging are very complicated, and it is practically impossible to make emitters clog predictably. The present study, the field evaluation of the hydraulics of a microirrigation system, is only a small step toward a better understanding and management of the emitter clogging problem. For extending this research, the following recommendations are made: 1- It is tedious work to measure individual emitter discharges manually with a stop watch, container and graduated cylinder. It would be desirable to utilize an electronic flow meter with a data logger to collect the data. 2- Theoretical results showed similar trends of hydraulic parameters of microirrigation system for 10 to 60 meter laterals under different patterns of emitter clogging. The length of lateral in this study was 20m. Field tests on laterals longer than 20m should be made to confirm this. 3- Only one type of pressure-compensating emitter was used in this study. More confidence could be gained in interpreting the hydraulic characteristics of pressure-compensating Chapter 6 SUMMARY AND CONCLUSIONS 210 emitters affected by clogging, if more pressure-compensating emitters with the same or with different nominal flow rates from different manufacturers were tested. 4- To obtain better evaluations and comparisons of the impact of different patterns of clogging on emitter flow rates, similar field experiments should be made with both pressure-and non-pressure-compensating emitters. Recommendations for the application of these results are as follows: 1 - Based on the results obtained from this research, and according to the criteria suggested by ASAE EP458 (1997) and ASAE EP405.1 (1997), when 10% or more of the total number of emitters are partially clogged, the uniformities (CU, EU', DU, and Us) are poor or unacceptable. To improve the uniformities, flushing the lateral or replacing the emitters is suggested. 2- Based on the finding of this research, when pressure compensating emitters are used, three among the thirteen parameters examined, CU or Us, EU', and Vp/, are the most important parameters for evaluating a microirrigation system. 3- Considering the cost of operating pressure and achieving similar values of uniformities in up- or down-slopes, the installation of microirrigation systems on down-slopes is suggested. 4- Although the flushing of laterals improves the flow rate from most emitters along the lateral, an inspection of emitters along the lateral is suggested because of possible emitter clogging after flushing. 5- When pressure-compensating emitters are used, adjustments (using a pressure regulator) should be made to compensate for the effect of different operating pressures (even within the pressure range recommended by the manufacture). 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Journal of the Irrig. and Drainage Engr. Div., ASCE, Vol. 101 (IR4) :321-326. WU, I. P. and C. J. Phene. 1984. Temperature effect on drip emitters and lateral lines. ASAE Paper No. 84-2628. Wu, L. P. 1975. Design of drip irrigation main lines. Journal of the Irrig. and Drainage Engr. Div., ASCE, Vol. (IR4) :265-278. Wu, I. P. 1997. An assessment of hydraulic design of micro-irrigation systems. Agricultural Water Management, No: 32. :275-284. Yitayew M. and A.W. Warrick. 1980. Trickle lateral hydraulics: design and examples. Journal of the Irrig. and Drainage Engr. Div., ASCE, Vol.114 (2) :289-300. Yitayew, M. and A.W. Warrik. 1986. Velocity head consideration for trickle laterals. Bibliography 222 Journal of the Irrig. and Drainage Engr. Div., ASCE, Vol. 113 (4) :611- 615. Zeier, K. R. and D. J. Hills. 1987. Trickle irrigation screen filter performance as affected by sand size and concentration. Trans, of the ASAE, Vol.30 (3) :735-739. Zur, B. and S. Tal. 1981. Emitter discharge sensitivity to pressure and temperature. ASCE, Journal of the Irrig. and Drainage Engr. Div., ASCE, Vol. 104 (IRI) :23-24. APPENDIX A. APPENDIX APPENDIX A. 224 co • OJ Oi CO -•—» C/) CD O) CO -I—' CO CD OJ O) CO » CO IO I CU O) ro CO fr • 0 D) CO CO co I CD CO CM • CD co -•—< CO 0 D) CO CO d) E LU CM CM CM CM CM CM 00 CD CD CD fr CD 00 CM o CM o CO CD CO CD CD CO CD -—- CD h~ CO oo CO CO CO h- CD h- CM h-CD CO CO co od co co CO co co co co co co CO co d co co co CO h~ CM CM CM CM CM CM CD 00 CO CD CO fr CD T— 00 CM o CM o CO CD •fr CO CD CO -—- CD CO CD 00 CD h~ CO CO CM CD 00 N-CD (///? CO CO CO o co co CO CO co co co co d CO co co co co CO co r~- CM CM CM CM CM CM CM 00 CD CO fr- 00 CO CM o CM CO CO CD fr- fr CD CO CO CD -—- CO CD h~ CO CM 1^ CD CO co CD h~ CO CD CO CO CM co CO d co o co CO co CO CO co CO co co co CO D" CM CM CM CM CM CM CM CM CM CM o CD 00 CO CO CD 00 co o o o CO CD -fr 00 CD CO CO CD -—- CD CO CD CO CM CO o CO CO CO CO CM CO co o CO co CO O CO d CO co co co "~ CO CO CO CO CX > CM CM CM CM o CM CM CD CO CD 00 CO 00 o CO i— CO CM o CM o CD CD -fr •fr CO -—- CO CO CD CM o CO r-- CO 00 CO ee h~ CO CM ^ O o o T— co co" co CO co co CO co co co co co CO CO CM CM CM CM CM CM CM CM CM o CM CM CM ^_ CO CO CD CD •fr CD T— CO 00 CO o co CO CD fr- fr CO CO co CD CD 1*--CO co CO CD CO CD CM o CD CD h- ee CO (//A? co co CO CO co CO CM ^ d d d co co co CO co CO co co CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM CM o CM 00 CO CD CD fr- CD T— CO CM o CM o CD CD T— CO CO 00 o CO -—~ CO I-- CO h-00 CD r< CO 1^. CO CO CO CO CD CM o CD (//ft CO co co co co CO CO co co CO CO CO co CO CM T~ d d d T~ r- CM CM CM CM CO co CD CO CD CD CO •fr CD CO CM o CM o CO CD •fr fr CO -—s CO CD 00 CO h- CO 00 h- CD 1^ ee h- r- CO CO co CO CO CO CO co CO CO co co co co co co CO co co co CO D" CM CO fr- in CD CO CD o CM co -fr in CO CO CD o CM APPENDIX A. 225 Table A.3.2 Effect of number, location, and degree of clogged emitters on head loss (Hf) in 10, 20, 30, 40, 50, and 60m length of laterals. Length Stage Stage Stage Stage Stage Stage Stage Stage (m) 1 2 3 4 5 6 7 8 10 0.0021 0.0012 0.0014 0.0018 0.0014 0.0016 0.0018 0.0017 20 0.0139 0.0073 0.0089 0.0116 0.0097 0.0112 0.0120 0.0123 30 0.0433 0.0253 0.0296 0.0379 0.0291 0.0341 0.0357 0.0405 40 0.0971 0.0586 0.0678 0.0847 0.0668 0.0737 0.0861 0.0922 50 0.1821 0.1022 0.1195 0.1562 0.1163 0.1445 0.1566 0.1647 60 0.3050 0.1696 0.1997 0.2609 0.1992 0.2326 0.2537 0.2814 Table A3.3 Effect of number, location, and degree of clogged emitters on pressure variation (Hvar) Length Stage Stage Stage Stage Stage Stage Stage Stage (m) 1 2 3 4 5 6 7 8 10 0.00020 0.00012 0.00014 0.00017 0.00013 0.00015 0.00017 0.00016 20 0.00132 0.00069 0.00084 0.00110 0.00092 0.00106 0.00114 0.00116 30 0.00410 0.00239 0.00280 0.00359 0.00276 0.00323 0.00338 0.00384 40 0.00920 0.00555 0.00642 0.00802 0.00633 0.00698 0.00816 0.00873 50 0.01724 0.00968 0.01132 0.01479 0.01102 0.01368 0.01483 0.01560 60 0.02888 0.01606 0.01891 0.02471 0.01886 0.02203 0.02403 0.02665 Table A.3.4 Effect of number, location, and degree of clogged emitters on emitter flow variation (qvar) Length Stage Stage Stage Stage Stage Stage Stage Stage (m) 1 2 3 4 5 6 7 8 10 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 0.00001 20 0.00010 0.00005 0.00006 0.00008 0.00007 0.00008 0.00009 0.00009 30 0.00031 0.00018 0.00021 0.00027 0.00021 0.00024 0.00026 0.00029 40 0.01145 0.00042 0.00049 0.00061 0.00048 0.00053 0.00062 0.00066 50 0.00132 0.00074 0.00086 0.00113 0.00084 0.00104 0.00113 0.00119 60 0.00222 0.00123 0.00144 0.00189 0.00144 0.00168 0.00184 0.00204 APPENDIX A. 226 Table A.3.5 Effect of number, location, and degree of clogged emitters on coefficient of uniformity (CU) Length (m) Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 Stage 7 Stage 8 10 98.81 70.72 70.71 70.56 70.61 78.54 85.68 85.67 20 98.94 63.37 63.38 63.34 63.36 76.11 83.68 90.79 30 99.00 69.98 69.99 69.94 69.96 78.61 85.55 93.59 40 99.05 72.30 72.25 72.28 72.23 77.49 87.86 94.34 50 99.03 68.05 68.03 68.05 68.01 79.71 86.20 91.38 60 99.07 67.42 67.41 67.45 67.41 77.12 86.20 93.61 Table A.3.6 Effect of number, location, and degree of clogged emitters on application efficiency (Ea) Length Stage Stage Stage Stage Stage Stage Stage Stage (m) 1 2 3 4 5 6 7 8 10 99.9996 99.9997 99.9997 99.9996 99.9997 99.9997 99.9996 99.9997 20 99.9973 99.9986 99.9983 99.9977 99.9981 99.9978 99.9977 99.9