Effects of gravel mulch on aeolian transport: a field wind tunnel simulation

The shape, size and coverage of gravels have significant impacts on aeolian sand transport. This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation. The tested gravel coverage increased from 5% to 80%, with a progressive increment of 5%. The gravels used in the experiments have three sizes in diameter. Wind velocities were measured using 10 sand-proof pitot-static probes, and mean velocity fields were obtained and discussed. The results showed that mean velocity fields obtained over different gravel mulches were similar. The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces. The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly. According to the present study, the optimal gravel coverage was found to be around 30% or 40%. Threshold velocity linearly increased with gravel coverage. Sand transport rate first increased with height above the wind tunnel floor (Hf), reaching a peak at some midpoint, and then decreased.