Rainfall-induced consolidation and sealing effects on soil erodibility during concentrated runoff for loess-derived topsoils

Flume experiments simulating concentrated runoff were carried out on remolded silt loam soil samples (0.36 x 0.09 x 0.09 m(3)) to measure the effect of rainfall-induced soil consolidation and soil surface sealing on soil erosion by concentrated now for loess-derived soils and to establish a relationship between soil erodibility and soil bulk density. Soil consolidation and sealing were simulated by successive simulated rainfall events (0-600 mm of cumulative rainfall) alternated by periods of drying. Soil detachment measurements were repeated for four different soil moisture contents (0.04, 0.14, 0.20 and 0.31 g g(-1)). Whereas no effect of soil consolidation and sealing is observed for critical flow shear stress (tau(cr)), soil erodibility (Kc) decreases exponentially with increasing cumulative rainfall depth. The erosion-reducing effect of soil consolidation and sealing decreases with a decreasing soil moisture content prior to erosion due to slaking effects occurring during rapid wetting of the dry topsoil. After about 100 mm of rainfall, Kc attains its minimum value for all moisture conditions, corresponding to a reduction of about 70% compared with the initial Kc value for the moist soil samples and only a 10% reduction for the driest soil samples. The relationship estimating relative Kc values from soil moisture content and cumulative rainfall depth predicts Kc values measured on a gradually consolidating cropland field in the Belgian Loess Belt reasonably well (MEF = 0.54). Kc is also shown to decrease linearly with increasing soil bulk density for all moisture treatments, suggesting that the compaction of thalwegs where concentrated flow erosion often occurs might be an alternative soil erosion control measure in addition to grassed waterways and double drilling. Copyright (C) 2007 John Wiley & Sons, Ltd.