WIND EROSION - FIELD LENGTH

As the wind passes over eroding soil surfaces, the quantity of soil tr ansported by wind between the soil surface and 2 m above the surface i ncreases until the wind stream becomes saturated,The relationship betw een field length and the mass transported was used to test a transport model that has the form of a sigmoid curve, At the upwind portion of the field, the rate of increase in mass being transported is limited b y the emission rate from the soil surface, The mathematics of the sigm oid equation implies that when 63% of the maximum transport capacity o f the wind has been satisfied (field length at this point is called cr itical field length), the rate of increase in transport mass gradually decreases and approaches zero when the wind is saturated with soil pa rticles, From the instrumented field sites, a maximum transport rate o f 1231 kg/m width and average soil losses of 7.801 kg/m(2) were measur ed from a single event on a 2.6-ha field at Elkhart, Kansas, Critical field length varied from 31 to 129 m, depending on wind velocity and f ield conditions, Field mass transport data supports that a self-balanc ing mechanism of momentum extraction from the surface wind by accelera ting soil particles and the associated shear stress reduction will lim it the quantity of material that can be transported between the soil s urface and a height of 2 meters.