Determination of kinetic energy applied by center pivot sprinklers

The kinetic energy of discrete 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 seasonal runoff and erosion hazard. Size and velocity of drops from five common center pivot sprinklers were measured using a laser in the laboratory. The data were used to calculate kinetic energy transferred to the soil by each sprinkler on a center pivot irrigation system lateral with 2.5 m spacing between sprinklers. Specific power, which represents the rate that kinetic energy is transferred to the soil as a function of distance from a sprinkler and analogous to a sprinkler radial water application rate distribution, 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 characterization was found not to be correlated to actual kinetic energy transferred to the soil by the sprinklers. The results demonstrated that sprinklers with the smallest drop sizes do not necessarily transfer the least kinetic energy per unit depth of water applied. Conversely, sprinklers with the largest drop sizes do not necessarily transfer the greatest kinetic energy to the soil.