AN AUTOMATED LABORATORY RAINFALL SIMULATION SYSTEM WITH CONTROLLED RAINFALL INTENSITY, RAINDROP ENERGY AND SOIL DRAINAGE

We report on the construction and operation of a laboratory rainfall s imulator capable of producing rainfall of variable raindrop kinetic en ergy flux at the soil surface by varying raindrop size, drop height an d rainfall intensity. The simulator was designed to study breakdown of soil aggregates during simulated rainfall under conditions of variabl e soil and rainfall factors. During tests, eight soil samples, 104 mm in diameter and 50 mm deep were accommodated on drained beds with cont rolled suction at the base (drainage). Ponded water on the soil surfac e was removed by suction (runoff), preventing interaction between wate r on the surface and rain. Depth of rainfall, runoff and drainage were measured to within 0.5 mm, at 1 min intervals, by electronic sensors and the data stored in a computer. The soil samples were surrounded by a large drained bed covered with a thin layer of test soil which serv ed as an exchange bed, preventing splash loss of surface material from the sample during rainfall tests, These features enabled small quanti ties of soils to be tested under simulated held conditions (absence of pending, profile drainage, no net loss of surface soil) without the c omplex interactions between applied rain and the artifactual effects o f ponded surface water and excessively saturated soil often present in field and laboratory simulators with undrained target areas.