COMPARISON OF GERMAN AND SWISS RAINFALL SIMULATORS - RAIN STRUCTURE AND KINETIC-ENERGY

The structure and the kinetic energy of the rains of eight rainfall simulators have been investigated. The data are compared to those registered during a thunder-shower at the research station of Mertesdorf near Trier/FRG. The results are summarized as follows: - The drop size distributions of the investigated rain are significantly different. The rainfall simulators Swanson, Bonn, Basel and Trier culminate in the 2 - 3 mm drop diameter class (approximately 40 %) and thus simulate best the drop size distribution of natural heavy rainfall. - The impact velocity of artificial raindrops depends on the water pressure within the rainfall simulator, the initial velocity of the raindrops and the fall height. A correction factor to match the kinetic energy of natural rainfall, which is based on the percentage of deviation from the terminal velocity, can be applied only to some extend. - With respect to various fall velocities of the artificial raindrops ali tested rainfall simulators except one yield a rainfall energy between 19 and 27 J/m2 per mm of rainfall. - The actual amount of precipitation measured at the end of the rainfall experiments sometimes differs significantly from the aimed value of 60 mm/h. Due to this variation, the total rainfall energy during the experiments accumulated to 9 - 15 MJ/ha. - This high variability depends on the used rainfall simulator. But it also demonstrates the importance of precipitation measurements on the plot during simulations in order to exactly calculate the rainfall energy.