A portable wind and rainfall simulator for in situ soil erosion measurements. (Special Issue: Experiments in earth surface process research.)

摘要

Laboratory research in wind tunnels with the capability of simulating rainfall highlighted the importance of considering the complex interactions between wind and rainfall in the analysis of soil erosion processes. In order to overcome the inherent limitations of laboratory research and to further investigate these interactions under comparable conditions in the field, a Portable Wind and Rainfall Simulator (PWRS) has been developed. The aim of this study was to specify the wind and rainfall characteristics of the PWRS and to evaluate if its simulation quality and reproducibility is adequate for comparative soil erosion studies in the field. Wind velocity measurements show that a pre-shaped logarithmic boundary layer with a thickness of about 0.2 m exists. The uniformity of airflow across the tunnel is acceptable within the lower 0.3 m of the tunnel with maximum standard deviations below 0.7 ms-1. Maximum variability of wind velocities between three consecutive repetitions of the measurements is lower than 15%. The spatial rainfall distribution for windless rain show rather poor uniformity (Christiansen Uniformity (CU) coefficient=60%), but very good reproducibility in-between five consecutive replications. About 90% of the test plot experiences a variability of rainfall below 5%. Simulated drop size distributions correspond very well with calculated Marshal-Palmer Distributions (MPD) of equal rainfall intensities (mean deviation of 2.1%). For wind-driven rain both above mentioned parameters clearly improve (CU=76%, mean deviation=1.7%). The mean rainfall intensities show also very low variability between the five replications with standard deviations of 0.31 mm h-1 for windless rain (mean intensity 96 mm h-1) and 0.69 mm h-1 for wind-driven rain (mean intensity 88 mm h-1). In conclusion, test results of the PWRS are very satisfactory, especially considering the physical constraints, which have to be taken into account to reach desired portability. The analysis presented in this study suggests in particular very good reproducibility of wind and rain conditions. The PWRS should therefore be a useful device for comparative in situ soil erosion measurements in the field and support the gathering of quantitative data on the relative importance of soil detachment rates between wind and water erosion, as well as windless and wind-driven rainfall.