SPRINKLER DROPLET EFFECTS ON INFILTRATION .2. LABORATORY STUDY

A companion paper by Chang and Hills, 1992, describes the stress distribution in a soil surface during water droplet impact according to a numerical simulation model. This project was undertaken to relate field data to the simulated stress values. In this paper, sprinkler droplet impact angle and surface water layer depth were studied in relation to a soil's infiltration rate. Droplet impact angles were monitored at different distances from the head of a conventional medium-size sprinkler. The test variables included nozzles with diameters of 3.2 mm (1/8 in.), 4.0 mm (5/32 in.), and 4.8 mm (3/16 in.), and operation pressures of 200 kPa, 300 kPa, and 400 kPa. The impact angles ranged from approximately 90-degrees near the nozzle to approximately 40-degrees near the wetted perimeter. Impact angles were not significantly affected by nozzle size; however, increase in pressure caused the angles near the wetted perimeter to increase. Infiltration tests were then conducted on three soil types with droplet impact angles of 90-degrees, 60-degrees, and 45-degrees. The basic infiltration rate for all soil types decreased in the following order of impact angle: no impact, 90-degrees, 45-degrees, and 60-degrees. These results correlate with the shear stresses predicted for those conditions by the simulation model.