COMPARISON OF MODELS DESCRIBING THE VERTICAL-DISTRIBUTION OF WIND-ERODED SEDIMENT

For the study of field wind erosion, detailed observations of wind-blo wn sediment transport in the field are needed. The objective of this s tudy was to determine the best method to quantify the mass of wind-blo wn material moving past a fixed point during four storms. Twenty-one M odified Wilson and Cooke (MWAC) sediment catchers were installed in a pearl millet [Pennisetum glaucum (L.) R. Br.] field in the Sahelian zo ne of Niger, on a sandy, siliceous, isohyperthermic Psammentic Paleust alf. Each catcher trapped materials at seven heights between 0.05 and 1.00 m. The vertical profiles of measured horizontal mass fluxes were described by two different models, a three-parameter power function an d a five-parameter combined model, which is a combination of an expone ntial function and a pow er function. For all four storms, both models described accurately the mass fluxes between 0.05 and 0.26 m, but fit ted mass fluxes at 0.50, 0.75, and 1.00 m deviated from measured fluxe s. Deviations were 21.1, 45.2, and 60.6% for the power function and 12 .4, 18.5, and 38.0% for the combined model. Mass transport rates were calculated by integrating the mass Bur profiles across height. The dif ferences in calculated mass transport rates were small, but because of the better fit, the combined model was preferred. Correcting for the trapping efficiency of the MWAC catchers (0.49) and multiplying by the storm duration resulted in total mass transport values, which are equ al to the mass of soil passing a strip of 1-m width perpendicular to t he mean wind direction. The average mass transport, values were 102.7, 15.5, 31.8, and 149.8 kg m(-1), respectively, for the four storms.