Soil erosion transport through multiple rainfall events in the presence of stone cover: Laboratory flume experiments and analysis with the Hairsine-Rose model

, ,
2011
Poster talk

Abstract

Soil erosion is a major environmental problem that can lead to loss of fertility and degradation of agricultural fields. In order to develop efficient strategies to mitigate the impact of precipitation and reduce the erosion rate, a process-based understanding of the mechanisms that govern sediment transport and delivery is necessary. Soil state and physical properties prior to a precipitation event can affect significantly the erosion rate. Among the most important soil variables are moisture content, compaction and infiltration capacity. Additionally, the presence of stones on the topsoil surface retards the overland flow discharge, reduces runoff generation as well as the sediment delivery and prevents the development of a surface seal, which in turn maintains the infiltration rate. The aim of this study was to examine in detail the effect of surface stones, soil compaction and sealing for a sequence of rainfall events on soil erosion. Experiments were conducted using the EPFL erosion flume, which was divided into two identical flumes (one with stone and one without). The experiment involved four rainfall events with the precipitation rates: 28, 74, 74 and 28 mm h-1. After each 2-h event, the soil was allowed to air dry for 22 h. The total sediment concentration, the concentration of seven sediment size classes and the flow discharge were measured during each event at the outlet of each flume. Experimental results were analyzed using the Hairsine and Rose (H-R) soil erosion model. Results showed that (i) within each precipitation event, the proportion of each size class for the bare/stone-covered flume pairs at steady state were similar, whereas the initial response differed significantly; (ii) in all cases the effluent was enriched in finer particles relative to the original soil; and (iii) the effluent sediment composition was different from that of the original soil, and there was no clear trend towards the parent soil sediment size composition with time. The H-R model was able to reproduce well the events with high precipitation rate (events 2 and 3) with the same parameter set, while the match was less satisfactory for the low precipitation events. A possible explanation for this is that the initial soil compaction/sealing/development of the deposited layer combined to yield a surface that eroded similarly for identical rainfall conditions. Changes in the precipitation rate modifies the soil surface (the deposited layer in particular) and thus the erosion rates. Model application further suggested that over the course of the rainfall events, the contribution of the original soil to the eroded sediment decreased gradually, while that of the deposited layer increased.

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, ,
2011
Poster talk

Abstract

Official source

About this result

Related concepts (21)

Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life of plants and soil organisms. Some scientific definition

Soil erosion is the denudation or wearing away of the upper layer of soil. It is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water,

An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effe

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Related publications (76)

Related publications

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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.

2012

Laboratory flume experiments to study the influence of initial conditions and rock fragment cover on soil erosion dynamics

David Andrew Barry, Alessandro Brovelli, Seifeddine Jomaa

The influence of the initial soil surface characteristics and rock fragment coverage on precipitation-driven soil erosion was investigated through laboratory experiments on a 6-m × 1-m soil parcel with mild slope. A sequence of four experiments, consisting of 2-h precipitation followed by 22 h of air drying, was conducted. The precipitation rates used were 28, 74, 74 and 28 mm h-1. 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 (named H7-E1). Experiments were designed such that for H7-E1 steady state concentrations were obtained at the end of the erosive event only for the finer sediments. Results suggest that steady state concentrations were mainly controlled by the rainfall intensity. The sediment yields during the transient phase at the beginning of each erosive event were instead sensitive to the initial soil condition, in particular to whether steady-state was reached in the previous event. 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 the stationary behaviour was not reached, the subsequent event produced effluent concentrations that increased gradually to steady state. Steady state concentrations were achieved faster in the presence of stones on the soil surface compared with bare soil condition. The suitability of the Hairsine and Rose model to analyse the sediment concentration of the individual size classes was evaluated. The model could not predict in detail the erosion yields when topsoil was heavily modified by rainfall (H7-E1 and H7-E2), while a satisfactory comparison was observed for the last two experiments (H7-E3 and H7-E4), in which the soil was less modified by raindrop impact. Model application indicates that the contribution of the original soil to the eroded sediment decreased gradually during the sequence of experiments, while that of the deposited layer increased.

2012

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The parameter consistency of the one-dimensional Hairsine-Rose (H-R) erosion model under conditions of significant rainfall splash was examined. To account for the splash characteristic length scale and its interaction with the transverse erosion width, experiments were carried out using erosion flumes of the same length (6 m), but different widths, with sediment concentrations measured at the flume exits. Total sediment concentration and the concentration of seven size fractions (< 2, 2-20, 20-50, 50-100, 100-315, 315-1000 and > 1000 µm) were measured at high rainfall intensity (60 mm/h) and with a gentle slope (2.2%). The conditions employed ensured that erosion was predominantly precipitation-driven. The experimental results showed that raindrop splash affected particularly the sediment breakthrough from the wider flumes (flumes 1 and 2, 1- and 0.5-m wide, respectively). However, the raindrop splash effect was less significant in observed sediment concentrations from the narrower flumes (flumes 3 and 4, both 0.25-m wide). For these flumes, the detached sediment was affected by the transversal width of the flume in that an amount of detached sediment adhered to the barriers instead of being removed in the overland flow. The one-dimensional H-R model was fitted to the experimental results and good agreement was found, in particular for the finer size classes. The data for the coarser grain sizes were more scattered, suggesting sediment motion by mechanisms other than as a suspension in the overland flow (e.g., rolling along the soil surface). The optimized parameters indicated that the shield layers (where the shield consists of redeposited eroded sediment) of the wider flumes (1 and 2) developed within 5-10 min from the start of the experiment, whereas in the narrower flumes (3 and 4) they never fully developed. The optimized detachment rates were consistent with previous findings, but the estimated thickness of the deposited layer was too small to provide complete protection of the original soil against raindrop detachment, indicating that the shield was not uniform. The experimental design allowed us to investigate directly the effect of flow non-uniformity on soil erosion by inclusion of an offset drainage point in flume 4. The observations taken during and after the experiment, as well as surface elevation data, confirmed the noticeable impact of non-uniform flow on the erosion process.

2010

Laboratory flume experiments to study the influence of initial conditions and rock fragment cover on soil erosion dynamics

David Andrew Barry, Alessandro Brovelli, Seifeddine Jomaa

2012

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2012

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2010