Comparison of the results of a small-plot and a large-plot rainfall simulator – Effects of land use and land cover on surface runoff in Alpine catchments

Abstract

Many surveys with differently sized rainfall simulators have been conducted in the past to study runoff and erosion processes on the plot scale. Concerning the understanding of runoff processes on the slope scale, comparative studies have shown that sprinkling devices with large plot sizes (≥40m2) produce more representative results than small-plot rainfall simulators (4m2 and less). Nevertheless, the latter ones are frequently used due to their portability and the reduced effort and water demand compared to large-plot simulations. In this study the results of torrential rain (100mm h−1) experiments using a small (1m2) dripper device and a large (40–80m2) spray device are compared regarding to identify site characteristics which allow estimating the representativeness of surface runoff coefficients measured with a small-plot rainfall simulator. We conducted 39 small-plot (1m2) and 14 large-plot (40–80m2) rainfall simulations at eight selected experimental sites in the Eastern Alps with differing land cover, land use, intensity of grazing and antecedent soil moisture content. At sites with intensive grazing, due to topsoil compaction and the shortened flow path, the small-plot device delivered significantly higher runoff coefficients than the large-plot device. At mainly mowed grassland sites with at most a short grazing period in autumn both sprinkling devices showed similar results or even lower runoff coefficients compared with the results of the large-plot simulator. The measured surface runoff coefficients strongly depended on antecedent soil moisture content and grazing intensity.