Page 119 - Soil Degradation, Conservation and Remediation

4.4 Factors Affecting Wind Erosion 107

forward. The rippling of wind-blown sand has been attributed to unevenness in
surface creep flow (Bagnold 1941). Surface creep constitutes 7–25 % of total transport
(Bagnold 1941; Chepil 1945; Horikawa and Shen 1960). Creep appears nearly passive
in the erosion process, but creep-sized aggregates may abrade into the size range
of saltation and suspension and, thus, shift modes of transport. Creep aggregates
seldom move far from their points of origin.

4.3.4 Abrasion

The percentage of erodible soil (<1,000 pm) in the surface layer is highly correlated
with the mass of soil removable from that surface in wind tunnel tests (Chepil 1958).
On long, erosion-susceptible fields, the total amount of soil that can be lost is usually
several times the amount of erodible material initially present at the surface. Thus,
resistance to abrasive breakdown of surface aggregates is important in wind erosion.
The abrasion susceptibility of soil can be defined as the mass of material abraded
from target aggregates per unit mass of impacting abrader (Lyles 1988).

4.3.5 Sorting

Unless surface-layer aggregates or particles are homogeneous in physical properties
(size, shape, density), which is highly unlikely in agricultural soils, sorting will
occur during erosion. Sorting here refers to the selective removal during erosion
of aggregates or particles because various sizes move at different mass flow rates.
The sorting process over time removes the finer, nutrient-enriched materials, leaving
behind those that are coarser and less fertile (Lyles 1988).

4.4 Factors Affecting Wind Erosion

Several factors of wind erosion have been included in the wind erosion equation
(WEQ), which is an erosion model designed to predict long-term average annual soil
losses from a field having specific characteristics. The equation is shown as
E = (
f IKCLV)

where
E = estimated average annual soil loss expressed in tons per acre per year
I = soil erodibility index
K = soil ridge roughness factor