Droplet Kinetic Energy from Center-Pivot Sprinklers

Authors: King, Bradley - Brad; Bjorneberg, David - Dave

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: 9/15/2010
Publication Date: 12/5/2010
Citation: King, B.A., Bjorneberg, D.L. 2010. Droplet Kinetic Energy from Center-Pivot Sprinklers. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE), December 5-8, 2010, Phoenix, AZ. Paper No. IRR10-8726. p. 1-11.

Interpretive Summary:

Technical Abstract: The kinetic energy of discrete water drops impacting a bare soil surface is generally observed to lead to a drastic reduction in water infiltration rate due to soil surface seal formation. Under center-pivot sprinkler irrigation, kinetic energy transferred to the soil prior to crop canopy development can have a substantial effect on seasonal runoff and soil erosion. In the design of center-pivot irrigation systems, selection of sprinklers with minimum applied kinetic energy could potentially minimize the seasonal runoff and erosion hazard. The size and velocity of drops from common rotating spray-plate sprinklers center-pivot sprinklers with flow rates of approximately 40 and 20 L/ min were measured using a laser in the laboratory. The data were used to evaluate two approaches to characterize the kinetic energy transferred to the soil by rotating spray-plate sprinklers on a center-pivot irrigation system lateral with 3 m spacing between sprinklers. Specific power represents the rate at which kinetic energy per unit area is transferred to the soil as a function of distance from a sprinkler and is analogous to a sprinkler radial water application rate distribution. Specific power was used to estimate actual kinetic energy transferred to the soil by overlapping specific power profiles of sprinklers equally spaced along a center-pivot lateral. Kinetic energy of irrigation sprinklers has traditionally been characterized using area-weighted kinetic energy per unit drop volume. This method heavily favors the largest drops, which travel the farthest from the sprinkler and have the largest kinetic energy and does not account for the volume of water applied by each drop size. Sprinkler kinetic energy per unit volume of sprinkler discharge was not well correlated to actual kinetic energy transferred to the soil by the sprinklers.