[1] Soil erosion and the associated nutrient fluxes can lead to severe degradation of surface waters. Given that both sediment transport and nutrient sorption are size selective, it is important to predict the particle size distribution (PSD) as well as the total amount of sediment being eroded. In this paper, a finite volume implementation of the Hairsine-Rose soil erosion model is used to simulate flume-scale experiments with detailed observations of soil erosion and sediment transport dynamics. The numerical implementation allows us to account for the effects of soil surface microtopography (measured using close range photogrammetry) on soil erosion. An in-depth discussion of the model parameters and the constraints is presented. The model reproduces the dynamics of sediment concentration and PSD well, although some discrepancies can be observed. The calibrated parameters are also consistent with independent data in the literature and physical reason. Spatial variations in the suspended and deposited sediment and an analysis of model sensitivity highlight the value of collecting distributed data for a more robust validation of the model and to enhance parametric determinacy. The related issues of spatial resolution and scale in erosion prediction are briefly discussed.
18The parameter consistency of the one-dimensional Hairsine-Rose (H-R) erosion model under 19 conditions of significant rainfall splash was examined. To account for the splash characteristic The observations taken during and after the experiment, as well as surface elevation data, 43 confirmed the noticeable impact of non-uniform flow on the erosion process.44
Rain splash soil erosion in the presence of rock fragments and different initial conditions was tested in laboratory flume experiments under controlled conditions. The aim of the experiments was to ascertain whether cumulative soil erosion is proportional to the area of soil exposed to raindrop detachment under the condition of constant and uniform precipitation. The surface area exposed to rain splash erosion was adjusted by placing rock fragments onto the surface of identically prepared soil in laboratory flumes. The laboratory results showed that the eroded cumulative mass depended on the cumulative runoff, and that soil erosion was proportional to the soil surface area exposed to raindrops, in situations where an initially dry, ploughed and smoothed soil surface were ensured. The results showed that this relationship was controlled to a smaller extent by the soil's initial moisture content, bulk density and soil surface characteristics.When the initial conditions were more complex, soil erosion was proportional to the area exposed only at steady state. Then, sediment concentrations during the first part of the erosion event were instead more sensitive to the initial state of the soil surface, whereas at steady state it was observed that the concentrations of eroded sediments were controlled mainly by the effective rainfall and area exposed to raindrops. Previously published field data on rain splash soil erosion were analyzed to ascertain whether the same behavior was evident under field conditions. For this case it was found that rain splash erosion is in general not proportional to the area exposed. In contrast to the controlled laboratory experiments, the field experiments were characterized by non-uniform initial surface roughness, surface soil aging and heterogeneous rock fragment size and spatial distribution. However, the presented laboratory results showed clearly that, for soils with negligible surface roughness, erosion depends on (i) the area of soil 3 exposed to rainfall and (ii) the cumulative runoff, and that it is only slightly dependent on other soil variables.Keywords: Soil erosion experiment, Area exposed, Flume experiment, Cumulative discharge, Cumulative eroded mass, Soil initial conditions. IntroductionOver several decades, attention has been given to the effect of the soil surface characteristics (such as surface roughness, crop residues, organic mulches, vegetation cover and rock fragment coverage) on runoff generation, infiltration and soil erosion rates Poesen et al., 1999;Li, 2003;Gyssels et al., 2006;Smets et al., 2008;Knapen et al., 2009;Guo et al., 2010;Zavala et al., 2010). Numerous studies have pointed out the role played by surface rock fragments on erosion as well as on the hydrological response of soils (such as infiltration rate, surface ponding, runoff generation) (Adams, 1966;Poesen et al., 1990Poesen et al., , 1998Poesen et al., , 1999 Parsons, 1991, 1994;Bunte and Poesen, 1994;Ingelmo et al., 1994;Poesen and Lavee, 1994;Torri et al., 1994;van Wesemael et al., 19...
[1] This paper presents a finite volume scheme for coupling the Saint-Venant equations with the multiparticle size class Hairsine-Rose soil erosion model. A well-balanced monotone upstream-centered schemes for conservation laws-Hancock (MUSCL-Hancock) method is proposed to minimize spurious waves in the solution arising from an imbalance between the flux gradient and the source terms in the momentum equation. Additional criteria for numerical stability when dealing with very shallow flows and wet/dry fronts are highlighted. Numerical tests show that the scheme performs well in terms of accuracy and robustness for both the water and sediment transport equations. The proposed scheme facilitates the application of the Hairsine-Rose model to complex scenarios of soil erosion with concurrent interacting erosion processes over a nonuniform topography.
[1] Two laboratory flume experiments on the effect of surface rock fragments on precipitation-driven soil erosion yields were carried out. The total sediment concentration, the concentration of seven individual size classes, and the flow discharge were measured. 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. Rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale. For short times, the rock fragment coverage reduced erosion of the finer particles (<20 mm). For the midsize classes the protection decreased, while erosion of the larger size classes (>100 mm) was unaffected. At long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops. An area-based modification of the Hairsine and Rose (H-R) soil erosion model was employed to analyze the experimental data. The H-R model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used. Predictions were instead less accurate with low rainfall intensity and high rock fragment cover. 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.
Numerous models and risk assessments have been developed in order to estimate soil erosion from agricultural land, with some including estimates of nutrient and contaminant transfer. Many of these models have a slope term as a control over particle transfer, with increased transfer associated with increased slopes. This is based on data collected over a wide range of slopes and using relatively small soil fl umes and physical principals, i.e. the role of gravity in splash transport and fl ow. This study uses laboratory rainfall simulation on a large soil fl ume to investigate interrill soil erosion of a silt loam under a rainfall intensity of 47 mm h −1 on 3%, 6% and 9% slopes, which are representative of agricultural land in much of northwest Europe. The results show: (1) wide variation in runoff and sediment concentration data from replicate experiments, which indicates the complexities in interrill soil erosion processes; and (2) that at low slopes processes related to surface area connectivity, soil saturation, fl ow patterns and water depth may dominant over those related to gravity. Consequently, this questions the use of risk assessments and soil erosion models with a dominant slope term when assessing soil erosion from agricultural land at low slopes.
The effect of antecedent conditions and specific rock fragment coverage 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. Four sequential experiments -denoted E1, E2, E3 and E4, involved 2-h precipitation (rates of 28, 74, 74 and 28 mm h -1 , respectively) and 22 h without rainfall -were conducted. 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 (E1) only, and left untouched subsequently. Sediment yields at the flume exit reached steady-state conditions over time scales that increased with sediment size. Experiments were designed such that both steady and non-steady effluent sediment yields were reached at the conclusion of E1. Results from subsequent experiments showed that short-time soil erosion was dependent on whether steadystate erosion was achieved during the preceding event, although consistent steady-state effluent sediment yields were reached for each sediment size class. Steady-state erosion rates were, however, dependent on the rainfall intensity and its duration. If steady-state sediment yields were reached for a particular size class, that class's effluent sediment yield peaked rapidly in the next rainfall event. The early peak was followed by a gradual decline to the steady-state condition. On the other hand, for size classes in which steady state was not reached at the end of the rainfall event (i.e., E1), in the following event (E2), the sediment yields for those classes increased gradually to steady state, i.e., the sharp peak was not observed. The effect of rock fragment cover (40%) on the soil surface was also found to be significant in terms of the time to reach steady state, i.e., their presence reduced the time for steady conditions to be attained. Effluent sediment yields for the bare and rock fragment-covered flumes (E1) showed steady conditions were reached for the latter, in contrast to the former. We used the Hairsine-Rose (H-R) model to simulate the experimental data as it explicitly models soil particle size classes. Experiments E1 and E2 involved soil compaction by raindrops, and in this case the model predictions were found to be unsatisfactory. However, compaction was effectively completed by the end of experiment E2, and the model provided reasonable predictions for experiments E3 and E4.
Soil erosion due to rainfall and overland flow is a significant environmental problem. Studying the phenomenon requires accurate high‐resolution measurements of soil surface topography and morphology. Close range digital photogrammetry with an oblique convergent configuration is proposed in this paper as a useful technique for such measurements, in the context of a flume‐scale experimental study. The precision of the technique is assessed by comparing triangulation solutions and the resulting DEMs with varying tie point distributions and control point measurements, as well as by comparing DEMs extracted from different images of the same surface. Independent measurements were acquired using a terrestrial laser scanner for comparison with a DEM derived from photogrammetry. The results point to the need for a stronger geometric configuration to improve precision. They also suggest that the camera lens models were not fully adequate for the large object depths in this study. Nevertheless, the photogrammetric output can provide useful topographical information for soil erosion studies, provided limitations of the technique are duly considered.
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