Infoscience

Poster

Soil erosion dynamics through multiple rainfall events

The dynamics of soil erosion during repeated rainfall events was studied, in particular focusing on the effect of initial soil characteristics and surface shielding by rock fragments. A sequence of four 2-h erosive events (named H7- E1, E2, and E3, respectively) separated by 22 h of air drying was performed using a 6-m long laboratory rainfall simulator and erosion flume. A loamy soil was used in all experiments. The surface was hand cultivated before the first event. Rainfall intensities of 28, 74, 74 and 28 mm h-1 were considered. The erosion flume was divided into two identical 1-m wide sections, one of which was covered with rock fragments. Results showed that steady-state behavior is mainly controlled by the rainfall intensity. Soil initial conditions, in particular whether steady state was reached during the previous event, control the sediment yields during the initial transient phase of the erosive event. If quasi-steady behavior was reached for a particular sediment size class, that class’s effluent concentration peaked rapidly in the next rainfall event, then declined gradually to its steady-state value. In contrast, if the sediment concentrations were still varying at the end of a rainfall event, the subsequent event produced effluent concentrations that increased gradually to steady state. The surface rock fragments reduced the time needed to achieve the steady state, compared to bare soil conditions. The Hairsine and Rose erosion model was adopted to analyze the measured sediment delivery. A satisfactory comparison was observed for the two experiments in which the soil was only slightly modified by raindrop impact (H7-E3 and H7-E4). On the contrary, the model could not predict accurately the erosion yields of the first two rainfall events (H7-E1 and H7-E2), during which the soil surface was heavily compacted and a surface seal developed. Furthermore, the model could not reproduce in detail the sediment concentrations of the individual size classes, when partially steady conditions were obtained during the event.

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