Cablegation: III. Field Assessment of Performance

Abstract

ABSTRACT FLOW rates into and out of furrows were monitored as a cablegation system irrigated a field. The resulting data were used to calculate furrow intake rates as a func-tion of time. The initial supply rates to the furrows were within ± 13 percent of the designed flow rates. Seventy-eight percent of the variation was associated with devia-tions of the pipe elevation from the design grade. The computer model of this system predicts that deviations in flow rates resulting from elevation deviations will decrease as grade becomes steeper than the 0.28 percent used in this study. Seventy-three percent of the water applied to the field infiltrated. Intake opportunity times averaged 11.0 h at the top end and 8.3 h at the bottom. The furrow intake rate, I„ was related to the average intake opportunity time, T, by the equation I, = 48.6 4- 214/T. From these data it can be calculated that water applications at the bottom of the field averaged 84 percent of the application at the top end. Runoff rate was relatively constant and total runoff was only about half of that which would have occurred under fixed set surface irrigation. Variability of furrow infiltration rates was high and 10 percent reduction in furrow supply rates would have resulted in water not reaching the ends of some furrows. In general, the cablegation system provides more uniform water application than is normally achieved with other surface irrigation systems. The automatic cutback in supply reduces runoff and the runoff is more easily reused because of its steady flow.