Abstract:
The decay of roughness is an important factor governing surface processes such
as infiltration and soil erosion. Thus the decay of surface roughness under
different surface conditions was investigated and related to quantitative
amounts of soil loss, runoff and sediment concentration in a laboratory
experiment. Rainfall with an intensity of 128 mm/h was applied to a bare or
mulched surfaces of a sandy loam soil with known surface roughness at specified
time intervals. The decay of roughness as expressed by roughness ratio, in this
experiment, was better predicted when related to an exponential function of the
square root of cumulative kinetic energy of rainfall rather than with the
cumulative rainfall. The roughness decay equations in literature did not predict
breakdown under mulched surfaces accurately. Thus the exponent parameters of the
roughness decay equations were adjusted to reflect the reduced decay occurring
under mulched surfaces. In a bare soil, regression equations expressing the
dependent variables as a function of initial roughness index were significant,
but with low coefficients of determination, being 0.39 for soil loss, 0.12 for
runoff and 0.36 for sediment concentration. In addition to initial roughness
index, cumulative kinetic energy of rainfall was further included in the
regressions. This led to an increase in coefficients of determination, which was
0.81 for soil loss, 0.74 for runoff and 0.49 for sediment concentration. The
coefficients of determination (0.87 for soil loss, 0.85 for runoff and 0.51 for
sediment concentration) were further increased when the final roughness index
was included in addition to initial roughness index and cumulative kinetic
energy in the regressions. This work shows that soil loss and runoff could be
predicted from bare soil surface provided the initial roughness and the energy
of rainfall is known. However, field verifications of these relationships are
needed under different tillage tools and under natural rainfall. Copyright (C)
2002 John Wiley Sons, Ltd.
