A wind tunnel study of the influence of pore water on aeolian sediment transport Original Research Article

Experiments conducted in a straight-line suction wind tunnel confirm numerous field observations of sand particles from an upwind source saltating over wet surfaces. Comparison of the mass transport rate on a wet surface (qw) with its dry surface equivalent (qd) yields a strong linear relationship (r2> 0·99) over a broad range in freestream velocity. Slope coefficients vary between 0·75 and 1·1. These results indicate that over short distances in the order of 5 m, the mass transport rate is minimally affected by the presence of pore water. However, the boundary-layer structure is substantially modified by grain saltation on a wet surface as compared to the dry condition. Inner region friction velocities associated with dry sand transport (u*d) generally exceed those for clean air (u*o), whileu*wfor mobile wet surfaces drops belowu*o. A model is proposed which relates the ratioqw/qdto several other dimensionless composite variables which address the aerodynamic drag on a wet surface relative to (1) that for an untreated surface and (2) capillary force magnitude. The product of these emulates the variation observed in the slope coefficients from the empirical regressions, thereby quantifying several of the underlying physical processes which govern transport in wet conditions.