LOW 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 function
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 deviations
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, Ir, was related to the average intake opportunity
time, T, by the equation Ir = 48.6 + 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
