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Evaluation of parameters affecting emitter discharge of some low-head drip irrigation technologies in Kenya
Abstract
The use of low-head drip irrigation technology is a new development in Kenya due to the need to save water as a resource, among other advantages. However, during its adoption, high variations in emitter discharge occur on various drip tapes when water supply head of about 1.0m is adopted. The objective of this study was therefore to determine the effect of slope, lateral length and water supply head on emitter discharge of the most commonly used low head drip irrigation tapes under field conditions. Four tapes, sold as Chapin, Dream, T-tape, and Typhoon 25, were evaluated. Slopes were varied from 0% to 4%; lateral lengths varied from 5.0m to 20.0m; and water supply heads varied from 0.5m to 2.0m. The results showed that emitter discharges for Chapin were between 0.43 and 0.51 l/hr for 0-2% slopes with standard deviation of 0.05. Higher slopes resulted in increased flow variations as indicated by an emitter discharge of 0.53 l/hr at a standard deviation of 0.12 for the 4% slope. This would lead to low water distribution uniformity at higher slopes. Dream kit was also sensitive to change in slope. However, discharges from T-Tape and Typhoon 25 were less sensitive to change in slope and were suitable even for the 4% slope for 15 m laterals at a head of 1.0 m. Typhoon 25 system could also be adopted for longer laterals without affecting emitter discharges. Emitter discharge characteristic equations were also developed in which emitter discharge varied as the square -root of water supply head for T-tape (R2 of 97%) and Typhoon 25 (R2 of 98%) for 0% slope, indicating turbulent flow and less sensitivity to slopes. However, relationships for Chapin and Dream kit systems were nearly linear at R2 of 96% and 97%, respectively.
This indicated that emitter discharge tended towards laminar flow; the tapes were therefore quite sensitive to pressure differences within the respective systems.
Keywords: Low head drip irrigation technologies, data points, coefficient of variation, emitter discharge characteristics, and field conditions
Journal of Agriculture, Science & Technology Vol. 9 (1) 2007: pp. 28-43
