Laserfiche WebLink
<br />~• CHAPTER III <br />STUDY METHODS <br />Field Measurements <br />Rainfall Simulation and Infiltration <br />A needle-drop-former rainfall simulator similar to those described <br />by Meeuwig (1973), Malekuti and Gifford (1978), and Arnold and Dollhopf <br />(1977) was used. The apparatus consisted of a 1.9 cm by one meter- <br />square plexiglass water chamber through which 1521 stainless steel tubes <br />were inserted to form raindrops. A flow meter regulated the amount of <br />water moving to the water chamber to maintain a constant rainfall appli- <br />cation rate of 7.6 cm/hr (3 injhr). The water chamber was suspended <br />~• two meters above the soil surface, and with a mean drop size diameter <br />of 2.5 mm (Gifford, 1979), the kinetic energy of the simulated rain was <br />about 49 percent of the kinetic energy of natural rainfall with the same <br />drop size distribution and intensity (Laws, 1941). <br />Runoff was collected in a container at the base of a trough in a <br />plot frame at five minute intervals during each rainfall application run. <br />The plot frame enclosed a surface area of 5000 square centimeters which <br />was considerably less than the area of water application, but error <br />in the estimation of infiltration due to lateral flow of water in the <br />soil was minimized. A windscreen was necessary during mast of the runs <br />but a certain amount of wind was let in between the water chamber and <br />the soil surface to allow the raindrops to fall somewhat randomly over <br />the soil surface. The difference between the amount of water applied <br />• to the area enclosed by the plot frame and the amount of runoff caught <br />' 17 <br /> <br />