A3. Effect of Antecedent Conditions on Soil Erosion Dynamics in a Laboratory Flume
Jomaa, S.; Barry, D.A.; Brovelli, A.; Heng, B.C.P.; Sander, G.C.; Parlange, J.-Y.
The effect of antecedent conditions on precipitation-driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6-m • 1-m flumes with 2.2% slope. Three experiments denoted H6, H7-E2 and H7-E3, involved the same precipitation rate of 74 mm h-1, but using the different initial conditions. In each experiment, one flume was bare while the other had 40% rock fragment coverage. The soil was hand cultivated and smoothed before the first event (H6) only. However, the initial bulk density and moisture content were increased before the two others events using different pre-wetting followed by 22h of air-drying. Sediment concentrations at the flume exit reach steady-state conditions over time scales that increase with sediment size, and experiments were designed such that both steady and non-steady effluent concentrations were reached in H7-E1. Results showed that short-time soil erosion was sensitive to whether steady-state erosion was achieved during the preceding event, although consistent steady-state effluent concentrations were reached for each sediment class. Steady state concentrations were, however, dependent on the rainfall intensity. If steady-state concentrations were reached for a particular size class, that class’s effluent concentration peaked rapidly in the next rainfall event, then declined gradually to its steady-state value. When steady concentrations were not reached, the subsequent event produced effluent concentrations that increased gradually to steady state. The results showed that the presence of rock fragments on the topsoil reduced the time needed to reach steady state compared with bare soil. Digital terrain models (DTMs) were generated before and after one of the experiments. The results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow, therefore decreasing its sediment transport capacity. The DTM results showed that the presence of rock fragments on the soil surface led to increased soil compaction, perhaps due to higher soil moisture content (from greater infiltration) within the rock fragment-covered flumes.
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