Comparison of German and Swiss Rainfall Simulators ‐ Accuracy of Measurement and Effect of Rainfall Sequence on Runoff and Soil Loss Rates

An important characteristic of the suitability of a specific rainfall simulator is the accuracy that can be obtained in measuring runoff rate, sediment concentration and soil loss rate. The accuracy of the different simulators currently in use in Germany and Switzerland was determined. The simulators differed greatly in the accuracy of sediment concentrations, runoff rates and soil loss rates they produced. Major sources of error were small plot sizes and wind drift. However, most of the simulators were suitable for erosion research (Average confidence interval: 30%). The time measurement of the runoff rates limits the accuracy of the best measuring method actually available. The smallest increment that can be measured during a run is one second. With high runoff rates, rounding to the next full second can cause the runoff rate to alternate by 10%. In erosion experiments, a sequence of rains is often applied on a plot to examine different soil conditions. Several sequences are in use. To facilitate comparison of the sediment concentration, runoff rates, and soil loss rates obtained with different sequences, it was concluded that the total rain duration should at least be 90 minutes and that the first run should last at least one hour. Therefore, a sequence is recommended that has a 1 h first run, a 0.25 h break and a 0.5 h second run. Sequences with a second and third run on the following day are disadvantageous in most cases.