Search

• The sediment transport capacity was developed for loessal slopes. • Two-dimensional erosion numerical model was developed for loessal slopes. • Erosion numerical model could accurately simulate slope runoff and sediment process. Simulated slope erosion sediment yield and its development process have great significance for quantitative evaluation of erosion and its sources. In this study, a loess slope erosion experiment was implemented indoors to establish a sediment transport capacity formula suitable for loess slope erosion. A two-dimensional slope erosion numerical model was developed with corrected sediment transport capacity formula, and the model was verified by a simulated indoor slope rainfall erosion experiment. The results showed that the corrected slope sediment transport capacity formula is suitable for loess slopes. The proposed two-dimensional slope erosion numerical model could simulate runoff and sediment processes in a relatively more accurate. The most severely eroded areas were the middle and lower parts on erosion spatial contribution based on the simulation erosion results. Good agreements between the simulated and observed results were found for erosion and its spatial distribution. The research results can further improve loessal slope erosion process simulation and prediction. [ABSTRACT FROM AUTHOR]

In this paper, we examine the effect of vegetation on soil erosion, runoff generation and sediment transport on saline rangeland hillslopes. Rainfall simulations were conducted at a fixed 114 mm/h intensity on 6 m × 2 m erosion plots with varying degrees of vegetation. Plots were grouped into three categories (L, M and H) based on their canopy cover (L: <5%, M: 5–19%, H: >19%) and selected to limit variations in slope across canopy cover groups. Runoff and sediment samples were combined with three dimensional (3D) reconstruction data used to monitor soil surface microtopographic changes. Runoff initiation was significantly delayed on the L plots but cumulative runoff after 20 min of rainfall simulation indicated a positive effect of vegetation on infiltration processes. Cumulative sediment after 20 min of rainfall was similar across vegetation cover categories. The 3D data suggest that vegetation reduced net sediment delivery from the plots by primarily increasing opportunities for deposition while marginally affecting gross soil erosion. Plots with H vegetation cover experienced lower 3D-estimated erosion volumes but average erosion depth on L plots was lower than that on plots with M and H vegetation covers. Lower runoff volumes on M and H plots may have been compensated by greater runoff erosivity on these plots as runoff was concentrated in a narrower inter-patch space compared to L plots. This study highlights the need for an increased integration between traditional runoff measurement techniques and 3D reconstruction methods. [ABSTRACT FROM AUTHOR]

• Effective sediment sizes were determined along a gradient of soil structural stability. • Sediment average size exhibited a unimodal variation with soil structural stability. • Suspension-saltation dominated sediment transport for low and high stable soils. • Suspension-saltation and rolling jointly dominated erosion for medium stable soils. • Soil structural stability determined rainfall intensity effect on sediment transport. Sediment transport patterns (suspension, saltation and rolling) not only depend on flow hydrodynamic characteristics, but also on sediment properties, both of which are largely influenced by soil structural stability. However, how sediment sizes and transport patterns response to original soils over a wide range of structural stability remains unclear. Herein, field plot rainfall simulation experiments on five soils along an increased gradient of structural stability were conducted at two rainfall intensities of 45 and 90 mm h−1 to investigate effective sediment size characteristics and associated transport patterns in sheet erosion. Differing from runoff and sediment yield, sediment sizes were most influenced by soil structural stability (F = 386.9) rather than rainfall intensity (F = 246.7, p < 0.001). Mean weight diameter of sediment (0.16–0.84 mm) and the proportion of coarse particles (>0.25 mm) exhibited a unimodal variation with increased soil structural stability. The effective sediment size distribution shifted from unimodal with the peak at < 0.10 mm for low and high stable soils to bimodal with two peaks at < 0.10 mm and 0.5–1 mm for medium stable soils. Correspondingly, suspension-saltation (>74 %) dominated sediment transport for low and high stable soils, which was determined by fine sized fragments from aggregate breakdown and small flow transport capacity, respectively; while both suspension-saltation (<0.10 mm) and rolling (>0.25 mm) jointly contributed to sediment transport for medium stable soils, which was controlled by the interaction between fragment size and flow transport capacity. Moreover, the positive effect of rainfall intensity on sediment sizes was more remarkable for the medium than for the low and high stable soils. A conceptual model of sediment transport mechanisms in response to soil structural stability is firstly proposed, which merits consideration in the future development of erosion modeling and soil conservation techniques. [ABSTRACT FROM AUTHOR]

• Demonstration of rise and fall of carbon discharge with time. • Demonstration of enrichment of sand in loose layer above soil. • Demonstration of no carbon enrichment is sediment at the steady state. Soil carbon losses from sheet and interrill erosion areas have an impact on the global carbon cycle. Sediment discharged in many experiments where artificial rainfall has been applied to sloping soil surfaces show greater proportions of carbon in the sediment than found in the cohesive soil source. In many cases, conclusions drawn from these experiments fail to recognise that the enrichment of carbon in the sediment discharge is a result of unsteady conditions that occur before the steady state develops. It is known that particles of sand of different sizes move at different rates when raindrop induced salation occurs with the result that initially the particle size distribution is finer than the source but tends towards that of the source as time progresses. The presence of carbon in aggregates influences the density of aggregates. Here a qualitative model of sediment transport of sand and coal particles by raindrop induced saltation is used to demonstrate time varying enrichment of coal resulting from the effect of carbon on particle settling velocity. The model also demonstrates how the layer of loose particles that develops on top of the cohesive soil surface influences the relative amounts of carbon and sand in the sediment discharges. The steady state is not achieved until the slowest moving particle detached at the farthest distance from the downslope boundary is discharged. That may not be achieved in many of the experiments reported in the literature. [ABSTRACT FROM AUTHOR]

• Physically based 2D hydrodynamic and sediment transport model, CCHE2D. • High resolution mesh, topography photogrammetry, experimental landform evolution. • Watershed hydrology, raindrop soil detachment, displacement, erosion and transport. • Distributed solution, tilled watershed, cornfield tillage ridge and furrow morphology. • Simulated runoff, sediment transport, landform evolution; channel network analysis. Soil and gully erosion is a critical threat to sustainable agricultural land management and productivity. Soil erosion by rain splash, sheet runoff, and concentrated flow are complex problems conditioned by the combined interactions of soil physical properties, hydrology, human activity, landscape topography, and climate. Effective management of erosion processes driven by rainfall and surface runoff requires a combined effort of field observation, physical experimentation, and numerical simulation. A physically-based hydrodynamic numerical model, CCHE2D with updated raindrop erosion effects, is applied to simulate landscape evolution processes as a result of raindrop impact and overland flow. The numerical model simulates a thin layer of runoff and concentrated flow over complex terrains, and predicts sediment transport due to raindrop splash detachment, transport and soil surface erosions. Soil erosion and landform evolution simulations due to rainfall are presented for an experimental landscape and a tilled large scale agricultural field. Photogrammetric field data were collected using an unmanned aerial system (UAS) following planting and subsequent rainstorms. Numerical simulation results agreed well with the observed experimental soil surface topography, sediment yield, and drainage network developments. The simulated soil and gully erosion in the tilled field also agreed well with observations. This research successfully demonstrates how high resolution spatial and temporal topographic measurements in experimental and field landscapes can be simulated and interrogated by 2D physically-based hydrodynamic and morphodynamic models. The accurate predictions of tillage field and gully erosion process in agriculture watersheds with complex tillage conditions also indicated the usefulness of the model for studying soil and landscape degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Total volume and peak discharge are the most important drivers of sediment transport. • Antecedent moisture condition is correlated only with the initial discharge of floods. • Hysteresis loops between SSC and Q are analyzed with the hysteresis index (HI). • Negative HI are predominant indicating delayed SS transport and distant SS sources. • In the catchment soil erosion from hillslopes is the dominant process. This study aimed to evaluate the drivers of suspended sediment (SS) transport by analyzing the flood events recorded from July 2010 to June 2011 in the Celone River basin (Apulia, S-E Italy). High-resolution data of rainfall, streamflow (Q), and measurements of suspended sediment concentrations (SSC) were used to carry out the multivariate analysis. Among the initial 18 variables, the Principal Component Analysis revealed that total volume (m3), peak discharge (Qmax, m3/s), and the flood duration were the most important factors influencing SS transport. Total rainfall and total kinetic energy recorded in the gauging station located in the lowland were also important factors, whereas the same rainfall variables recorded in the remote mountainous area of the basin had a minor influence on SS transport. Antecedent moisture conditions were significantly correlated only with the initial discharge of the flood. Hysteresis loops between SSC and Q were analyzed for each flood event by using the hysteresis index (HI). Results showed that this catchment was dominated by anticlockwise loops (negative values of HI) representative of delayed SS transport and of distant SS source areas in terms of the gauging station. These results also suggested that soil erosion from hillslopes was the dominant process compared with channel and bank erosion and that there was no exhaustion of sediment availability in the basin. [ABSTRACT FROM AUTHOR]

Summary: This work presents three empirical models (MMFI, Morais Modification of Fournier Index; GJRM, Grimm–Jones–Rusco–Montanarella; REMDB, Diodato–Bellocchi Rainfall–Erosivity Model) where monthly-based climate data are used to estimate long-term (R)USLE (Universal Soil Loss Equation and its Revisions) rainfall erosivity factor (R m, MJmmh−1 ha−1 month−1). The objective was to evaluate two known models (MMFI and GJRM), and compare the results with the novel model REMDB meant for complex terrains. MMFI and GJRM are both based on the precipitation amount, whilst REMDB takes site latitude, elevation and precipitation seasonality also into account. The test area was the Italian region, where 30 stations (altitudes from about sea level up to 1270m, over the latitudinal range 36–46°North) with sufficient data to calculate R m according to USLE were available. The three models were evaluated against USLE rainfall erosivity over a validation data set of 14 stations, using a range of performance statistics. The REMDB estimates generally compared well with the USLE estimates according to different statistics. For REMDB, the relative root mean square error was, in average, 48.58% against 71.49% for MMFI and 66.55% for GJRM. The average modelling efficiency of REMDB was 0.51 against −0.02 (MMFI) and 0.13 (GJRM). REMDB was also superior in preventing biased errors in time, as quantified by the average pattern index versus months: 17.65MJmmh−1 ha−1 month−1, against 58.54MJmmh−1 ha−1 month−1 (MMFI) and 57.76MJmm h−1 ha−1 month−1 (GJRM). Of the two simplified models, the MMFI was the worst performer while the GJRM model performed similarly to the REMDB at two mid-altitude sites of Central Italy. [Copyright &y& Elsevier]