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Impact of different patterns of emitter clogging on hydraulic characteristics of microirrigation laterals laid on flat and sloped terrains

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Title: Impact of different patterns of emitter clogging on hydraulic characteristics of microirrigation laterals laid on flat and sloped terrains
Author: Ghaemi, Ali Asghar
Degree Doctor of Philosophy - PhD
Program Chemical and Biological Engineering
Copyright Date: 1998
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, Vhs, Vqh, and Vpf. 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, Vqh and Vhs, 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, Vpf, 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. 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. [Scientific formulae used in this abstract could not be reproduced.]
URI: http://hdl.handle.net/2429/8502
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]

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