Does soil surface roughness increase or decrease water and particle transfers?

Most of prior research showed increasing soil roughness delayed runoff and reduced total runoff and sediment yields but failed to differentiate roughness effects on water runoff and on sediment production. This study was conducted to assess separately the effects of soil surface depressions on runoff initiation and water and particle fluxes. A 5-m long soil box, filled with a silt loam, was split into 0.6-m wide paired smooth vs. rough plots with manually formed depressions, and subjected to a sequence of 24 mm h(-1) simulated rainstorms at 5% slope. Eight experiments were conducted under different upstream inflows and subsurface regimes (drainage or seepage). Collected data include time to runoff initiation and fluxes of water and particles after an apparent steady state was reached. Depressions delayed the runoff initiation by storing water into puddles and enhancing infiltration. Once runoff reached an apparent steady state, surfaces with initial depressions produced 10% greater water flux than the initially smooth surfaces, regardless, the subsurface moisture regime. Roughness had no significant effect on steady-state particle flux and concentration. Our results indicate that the only assured soil and water conservation benefit from surface depressions is due to the delay in runoff initiation at the beginning of the rain event before the entire surface is contributing to runoff.