Original paper

Determining soil erosion and threshold friction velocity at different soil moisture conditions using a portable wind tunnel

Nourzadeh, Mehdi; Bahrami, Hossein Ali; Goossens, Dirk; Fryrear, Donald W.

Abstract

Measurements with a portable wind tunnel were performed to study the effect of surface soil moisture (upper 3 cm of the soil) on threshold friction velocity, horizontal sediment flux and airborne dust concentration above wind-eroding soils. Eleven soils near the city of Ahwaz, Iran were tested. Soils were generally silty and saline-calcareous, with low organic matter. As soil moisture increased threshold friction velocities increased, but airborne dust concentration and horizontal sediment transport decreased. Results also indicated that 3% (or 0.03 kg kg-1) surface moisture was the threshold at which dust concentration above the soils fell to zero. The increase of the threshold friction velocity with soil moisture followed a degressive trend, except for very dry soils ( 0.35% soil moisture) where the threshold friction velocity increased rapidly with soil moisture. Results also showed that the soil's median grain diameter, electric conductivity (as a measure for the salt content), pH, organic matter content, grain density and the proportion of CaCO3 in the soil do not affect the influence soil moisture has on threshold friction velocity, horizontal sediment flux and airborne dust concentration. The soil's silt and clay content (in this study represented by the PM75, or all particles < 75 μm), on the other hand, does have an effect as the rate of increase of threshold friction velocity with soil moisture, and the rate of decrease of dust concentration with soil moisture, are higher as the PM75 content increases. In general, increasing surface moisture is a very effective way for reducing the vulnerability of the Ahwaz soils to wind erosion.

Keywords

soil moisturesoil erodibilitythreshold friction velocitydust concentrationsediment flux