UNIFORMITY OF LEPA IRRIGATION SYSTEMS WITH FURROW DROPS

Computer models for the movement and water delivery of low pressure center pivot and linear-move systems with furrow drops were used to compute water distribution uniformities. The models for small, 3-span, 170-m systems compared satisfactorily with field resuhs. The computed results for 396 m systems had lower uniformities than for the 170 m systems. Uniformities were lowest for furrow-check spacings of 0.5 m or less. As system speed increased, uniformities with short check spacings increased. At check spacings of 3 m or greater, speed had no effect with the center pivot but varied over a 10% range for the linear move. To obtain a uniformity coefficient of 0.8, check spacings needed to be at least 2 m. Uniformities were greatly improved if the alignment angles between spans, which controlled tower movements, were reduced from 0.7° to 0.4° or 0.25°. However, this caused more frequent movement of the center towers which requires more expensive equipment.