ON THE EFFICIENCY OF VERTICAL ARRAY AEOLIAN FIELD TRAPS

The efficiency of three vertical array field traps for measuring the d istribution of aeolian mass transport with height was compared with me asurements with an isokinetic trap. The vertical traps seem to work ad equately (efficiency > 80%) at heights greater than approximate to 15 mm above the bed. Closer to the bed, however, the open array trap catc hes about 70%, the two continuous arrays only about 50%. Because most of the transport takes place close to the surface, the overall efficie ncy of the field traps ranges from 50 to 70%. Based on these wind tunn el tests, we have developed a low single-compartment wedge-shaped trap , its shape, in combination with flow straighteners at the entrance, m inimizes stagnation effects, so that the efficiency is approximate to 80%. Our data indicate that with the wedge trap used in combination wi th the vertical array Aberdeen trap, we can sample mass transport in t he held during periods with unidirectional winds with an overall effic iency of the order of 80%.