Soil Erosion Processes Research Articles

Spatio-temporal variations of rainfall erosivity, correlation of climatic indices and influence on human activities in the Huaihe River Basin, China

Rainfall erosivity (RE) is an important factor in the soil erosion process, which cannot be altered by human intervention alone. The Huaihe River Basin (HRB) is a large agricultural watershed, suffering severe water erosion, investigating the spatio-temporal variation of RE is essential for local soil erosion prevention. The linear regression, Yue-Pilon method, and the Hurst exponent were used in analyzing the spatio-temporal variation within the HRB during 1960–2018. The slip correlation analysis and F-test were applied to obtain the correlation between climatic indices [the Arctic Oscillation (AO), the Southern Oscillation (SOI), the North Pacific Index (NPI), and the Niño 4SST index (SST)] and RE in the HRB. Results revealed that the annual average RE were 4280, 5061, 4068, 4886, and 4089 MJ mm hm−2 h−1 within the HRB, upper-HRB, middle-HRB, lower-HRB, and the Yishusi River Watershed, respectively. The annual average RE will increase within the upper-HRB and lower-HRB and decrease within the middle-HRB and the Yishusi River Watershed in the future. The seasonal average RE was ranked as summer > autumn = spring > winter in the HRB. The spatiotemporal difference was significant in the HRB, and different sub-regions exhibited a different trend in seasonal RE, except for the winter RE that increased significantly in all sub-regions (p < 0.05). The highest monthly RE occurred in July, with RE during May–September accounting for approximately 87% of the annual RE in the HRB. The AO and NPI had significant correlations with RE (p < 0.05) both on the annual and monthly scales with different lag times. The monthly AO, SOI, SST, and NPI were significantly correlated with RE in the long term with different lag times in different months (p < 0.05). These findings could provide potential predictive factors for RE prediction and help prevent soil erosion within the HRB.

Exploring the Relationship between Cover Crop Adoption and Soil Erosion Severity: A Case Study from the Simcoe Watershed, Ontario, Canada

Runoff from agricultural fields during the nongrowing season is a significant factor leading to phosphorous loading and diminishing water quality in Lake Simcoe, Ontario. Cover crops offer the potential to alleviate phosphorous loss during the nongrowing season by minimizing soil erosional processes and uptaking excess phosphorous; however, recent research suggests that its adoption remains relatively low. More concern lies with the lack of cover crop adoption on areas that are sensitive to soil erosion. This study intends to investigate the likelihood of agricultural productions located on erosive soils to adopt cover crops. Using satellite imagery in corroboration with the Universal Soil Loss Equation (USLE), this study reveals the frequency of cover crop production and associates soil loss sensitivity at a 30 m resolution from 2013 to 2018. Consistent with recent literature, this study reveals that a small portion (18%) of agricultural operations in the south Simcoe Watershed have incorporated cover crops over the past six years. Cover crops tend to be adopted at a low frequency in areas that have a low sensitivity to soil erosion. This study reveals that areas with higher soil erosion sensitivity are consistent with low-frequency adoption, indicating that these areas are less likely to adopt cover crops regularly. Promoting farm-scale benefits associated with cover crops should target areas in the south Simcoe Watershed that are prone to soil erosion to mitigate total phosphorus (TP) loading into Lake Simcoe.

Can soil piping impact environment and society? Identifying new research gaps

AbstractSoil piping is a widespread, although often overlooked land degradation process. So far, subsurface soil erosion studies have been focused on the importance of soil piping in hydrological and geomorphological processes, and factors controlling piping processes. Nowadays, the environmental changes being caused by the Anthropocene have clearly demonstrated that society depends on soil more than ever before, so the traditional studies of soil erosion processes need to be redefined. In that sense, geomorphologists face to overcome new piping‐related problems. In this article we identify new possible areas of research: (i) soil pipes and pipe collapses (PCs) as natural hazards, (ii) role of soil piping in carbon cycle, (iii) soil pipes and PCs and their relationships with biodiversity, and (iv) piping‐affected areas as geodiversity sites. Only better recognition of natural hazards driven by soil piping, such as land subsidence and degradation, landslides, flooding and off‐site sediment effects may result in better prevention and control measures in piping‐affected areas. Moreover, in the context of Global Change the role of soil piping in carbon cycle should be raised. Land‐use and land‐cover changes, as well as climate change may affect piping dynamics in different morphoclimatic regions and soil loss due to piping may lead to carbon loss. Soil pipes and PCs are closely interlinked with biodiversity, both positively and negatively. Piping erosion may directly and indirectly destroy vegetation and animals, although in some cases piping erosion may create new habitats and provide favourable conditions for some species. However, soil piping is not only an environmental and societal problem, but it may also contribute to the world geodiversity, which is clearly observed in badland sites. Piping erosion may have a significant impact on environment and society, thus further research with new questions is essential to provide knowledge for sustainable development.

Spatial variation in sediment connectivity of small watershed along a regional transect on the Loess Plateau

Sediment connectivity likely varies greatly over space, which further affects the processes of hydrology, erosion and sediment delivery of watershed. Small watershed is the basic geomorphologic unit for soil and water conservation. Few studies have been performed to quantify the spatial variation in sediment connectivity of small watershed at regional transect. Six typical small watersheds distributed from south to north on the Loess Plateau were selected as a regional transect to investigate the spatial variation in sediment connectivity and its influencing factors. In this study, the widely utilized index of connectivity (IC) was used to investigate the spatial variation of sediment connectivity in small watersheds. The source-sink landscape index reflecting the source or sink effect of landscape pattern on soil erosion process was utilized to compute the weights for IC. The redundancy analysis (RDA) was applied to identify the main influencing factors contributing to the spatial variation in IC. The results showed that IC increased from south to north (ranged from −2.02 to 1.76). A significant positive spatial autocorrelation was detected in IC of small watershed on the Loess Plateau (p < 0.05). The relationships between IC and environmental factors differed between different small watersheds. The results of RDA showed that the contributions of different influencing factors varied along the tested transect. The relative contributions of climate factors and vegetation factors to IC declined whereas that of land surface factors raised with latitude. Vegetation and climate were the main factors controlling the spatial variation in IC. The results are helpful to understand the spatial heterogeneity of soil erosion and evaluate the conservation benefit of vegetation restoration in semi-arid region.

UAV-based vegetation monitoring for assessing the impact of soil loss in olive orchards in Brazil

Vegetation cover is one of the most critical factors in soil erosion processes. Notably, olive orchards have been cultivated in shallow and sloping soils, with low vegetation cover and increasing the soil exposure to raindrop impact. In the tropics, considerable care is required to adequately use cover crops to control water erosion in new frontiers of olive plantations. In this context, we proposed a new technique to correlate the cover-management factor (C-factor) with vegetation indices from images obtained by unmanned aerial vehicle (UAV) and evaluate soil erosion losses under natural rainfall. We studied the relationship between different cover indices (vegetation cover index, non-photosynthetic vegetation cover index, and total cover index) with the C-factor of the USLE/RUSLE. This study was carried out in standard erosion plots with different vegetation cover systems associated with olive cultivation. UAV images were classified by Random Forest algorithm, and soil losses were quantified by sampling after each erosive rainfall event. Results showed a good performance in UAV image classification: average user's accuracy of 94% for vegetation class and 91% for bare soil. The Total cover index presented a better performance in predicting soil loss and determining the C-factor for exponential model (R2 = 0.87). UAV-based imaging demonstrates promising potential in monitoring vegetation cover crops and their impact on soil erosion. Total cover index performs better in estimating C-factor and predicting soil loss. However, the result of response surface analysis suggested that the association between total cover index and rainfall erosivity using second-order model presented the best prediction (R2 = 0.98), positive correlation between rainfall erosivity and C-Factor, and negative correlation between C-factor and total cover index and rainfall erosivity.

Effects of different wind directions on soil erosion and nitrogen loss processes under simulated wind-driven rain

“Wind-driven rain” is the main form of natural rainfall. Wind affects runoff, soil, and nutrient loss processes on slopes by changing rainfall characteristics. Wind direction is one of the main factors affecting the falling trajectory of raindrops, raindrop splash angle, and direction of the rainfall erosivity force. However, existing research on soil displacement and nitrogen loss driven by different wind directions and rainfall is still lacking. Based on a simulated wind-driven rain experiment, this study explored the influence of different wind directions (leeward, windward, and crosswind) on runoff, sediment yield, and nitrogen loss on slopes. The results showed that wind direction had a significant influence on runoff, sediment yield, and nitrogen loss in both runoff and sediment. The influence of wind direction on the slope runoff and sediment yield rates was leeward > crosswind > windless > windward. Compared with windless rainfall, the average runoff rate and sediment yield rate under leeward rainfall and crosswind rainfall increased by 6.17%–11.56% and 37.75%–41.58%, and 1.80%–2.40% and 13.31%–18.12%, respectively, while under windward rainfall, they decreased by 5.13%–7.38% and 7.86%–13.02%, respectively. Hydrodynamic parameters are physical parameters that characterize the process of sand-bearing shallow flow acting on surface soil particles. The mean flow velocity and unit stream power affected by the wind direction were ranked: leeward > windless > crosswind > windward. The mean flow velocity and unit stream power under leeward conditions were both 1.31 times those under windless conditions, indicating that leeward wind strengthened the erosion effect of the slope flow on the soil. The mean flow velocity and unit stream power caused by different wind directions may be the main reasons for soil erosion processes. The average nitrogen loss rate in runoff was ranked: windward > crosswind > windless > leeward. The law of nitrogen loss rate in the sediment is consistent with the regularity of the sediment yield rate in all wind directions, which increased respectively by 60.18%–163.86% and 19.39%–69.57% under leeward and crosswind conditions, respectively, and decreased by 10.23%–25.15% under windward conditions when compared to windless treatment. Therefore, when the intensity of wind-driven rain is constant, the impact of wind direction on slope runoff, sediment yield, and nitrogen loss is uncertain and may be either positive or negative. The angle between the raindrop movement direction and the runoff flow direction on the slope changes owing to the influence of different wind directions. This leads to changes in the slope infiltration rate, hydrological characteristics, and soil crusting process, and is one of the main reasons for the difference in soil erosion and nutrient loss rates.

Measurement of Water Soil Erosion at Sparacia Experimental Area (Southern Italy): A Summary of More than Twenty Years of Scientific Activity

The main purpose of this article is to give a general idea of the scientific activity that was carried out starting from the 2000s on the basis of the data collected in the plots installed at the Sparacia experimental station for soil erosion measurement in Sicily, South Italy. The paper includes a presentation of the experimental site, a description of the methods and procedures for measuring soil erosion processes both available in the literature and applied at the Sparacia station (sediment sampling and water level reading in the storage tanks for total erosion measurements; profilometer, and Structure from Motion technique for rill erosion measurements), and the main results obtained in the monitoring period in the experimental site. The latter concern the effects of plot size and steepness on soil loss, the measurement variability, the frequency analysis of soil loss, the rill erosion characterization, and the comparison between rill and interrill erosion rates. Each of these topics is addressed with multi-temporal analyses performed with increasing size of the available database, which allowed to draw robust conclusions. Soil loss did not vary appreciably with plot length in contrast with the assumption made in the USLE/RUSLE. The variability of the measurements of soil loss, runoff volume, and sediment concentration at the event scale in replicated plots decreased as the mean measured value increased. The normalized event soil loss was distributed according to a two-component distribution. A power relationship between rill volumes and lengths was established. The measurements also confirmed the morphological similarity between the channels of the rills and ephemeral gullies described by a power dimensionless relationship. Rill erodibility of the sampled clay soil varied over time, maintaining relatively low values. Finally, rill erosion was dominant relative to interrill erosion, and a more efficient sediment transport system through the rill network occurred as plot steepness increased.

Physically-based distributed modelling of the hydrology and soil erosion under changes in landuse and climate of a humid tropical river basin

The effects of landuse/landcover (LULC) and climate change on hydrology and soil erosion processes are of major concern, especially in the humid tropics. In this study, an evaluation of these changes is performed in a humid tropical catchment (Vamanapuram river basin, India) using a physically based distributed model, SHETRAN. The past landuse maps and climate data from six fine resolution NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) are used to force the SHETRAN model. A comparison of the change in the rate of soil erosion and hydrological responses during the future climate scenarios (near: 2021–2050 and far: 2071–2100) with respect to the historical period (1980–2005) is conducted.The isolated effects of landuse, climate variability and the combined effect caused change in streamflow (1.1%, 7.9%, 9.0% respectively) and sediment load (−10.4%, 1.7%, −10.5% respectively) in the past. An ensemble mean of general circulation model (GCM) projections showed that mean temperature and average annual precipitation under representative concentration pathway RCP 4.5 (8.5) scenarios for near and far futures increased from the historic period by 0.51 °C (1.6 °C), 0.6 °C (3.2 °C) and by 9% (6%), 15% (22.8%), respectively. Under RCP4.5(8.5), the average annual streamflow increased gradually from the near to far future, by 3.2% (−1.8%) and 13.6 % (22.1%) whereas, the projected sediment load a showed change of −21.05% (−26.63%) in near future while far future indicated change by −11% (4%). The SHETRAN model has been found to be effective in evaluating climate change impacts on hydrology and sediment yield and is useful for future river basin management.

Determination of the intensity of erosion processes by the Smith method of the Olenty river basin of the West Kazakhstan region

The article takes an actual topic for the present and carried out work to determine the intensity of erosion processes using the Smith method of the Olenty River basin of the West Kazakhstan region. The purpose of this work was to determine the process of soil erosion in the Olenty River basin for various types of land use. To determine soil flushing, the following were used: erosion potential of sediments, soil type, mechanical composition, slope steepness, vegetation, types of plowing, erosion forecast model, universal soil loss equation and the ArcGIS 10.4 program. The southern part of the river basin has a soil flushing rate from 0 to 0.06 t/ha per year. These lands are mainly used for pastures and small areas of territory for haymaking, located in most cases on chestnut soils and small salt marshes, the mechanical composition is mainly dominated by heavy loam. This territory occupies about 40% of the entire river basin. The central and northern parts have different indicators and range from the lowest to the highest. The highest rate of soil flushing is 1.57 – 5.96 t/ha per year are arable lands located mainly on chestnut soils, having a mechanical composition dominated by medium and heavy loam, and arable lands with the highest rate are characterized by a territory with high rainfall and a steeper slope. These indicators of soil flushing from 0.45 to 1.57 t/ha per year also belong to arable land, but unlike the previous class, these arable lands are located in most cases on soils that are mechanically related to medium loam. According to the results of the study, the highest rate of soil flushing falls on arable land, the average is about 1.50 t/ha per year, which corresponds to the “acceptable level of loss”. Key words: erosion processes, river basin, WKO, GIS, soil.

The Impact of Using Different Doses of Biomass Ash on Some Physical Properties of Podzolic Soil under the Cultivation of Winter Oilseed Rape.

This two-year study was focused on the effect of the application of different biomass ash doses on selected soil physical properties, i.e., soil moisture (SM), bulk density (BD), penetration resistance (PR), and soil stability in water measured by the content of readily dispersible clay (RDC), following control and mineral NPK fertilization in the cultivation of winter oilseed rape (Brassica napus L. var. napus). A one-factor field experiment conducted on podzolic soil (control, NPK, 100, 200, 300, 400, 500 kg K2O·ha−1) showed that the use of biomass combustion ash significantly improved soil moisture at all depths and variants, and especially at a depth of 30–35 cm in the 500 kg·ha−1 variant, i.e., by 2.99% v/v, compared to NPK. In turn, the moisture content in the 30–35 cm layer increased by 3.19% v/v in all variants in both years compared to the control. In 2020 and 2021, bulk density in the 0–5 cm layer treated with a dose of 500 kg·ha−1 exhibited a positive 0.15 and 0.12 Mg·m−3 decrease, respectively, compared to the control. In both years, the BD values in the 30–35 cm layer were reduced by 0.14 and 0.16 Mg·m−3 compared to the control. The PR values decreased in the treatments with doses of 300, 400, and 500 kg·ha−1, especially in 2021. The RDC content was found to decline in both years, i.e., 2020 and 2021, upon the application of even the lowest dose (100 kg·ha−1) in all the analysed layers. The reduction in the RDC content, especially in the 0–5 cm layer, is very important for soil structure stability and to protect the soil environment. This layer is most susceptible to crusting, which results in poor aeration and weak plant emergence during drought and/or periods of excessive moisture. It may also increase surface runoff and intensify soil erosion processes.

Mitigation of Flood Risks with the Aid of the Critical Points Method

Concentrated surface run-off caused by torrential rain leads to the transport of sediments from soil erosion processes within catchment areas of critical points, which represents a basic component of flood risks. Clear identification of such critical points offers a basis for a suitable new strategy of threat mitigation, via both organizational and structural measures in catchment areas. Critical points are determined in places where generated paths of concentrated surface run-off cross given boundaries of built-up areas. The threshold values for the catchment area of a critical point were derived on the basis of hydrological calculations, field research, and the evaluation of hundreds of specific manifestations of damage in built-up areas for particular critical profiles. The characteristics were determined as follows: contributing area between 0.3 and 10 km2, average slope more than 3.5%, and percentage of arable land more than 40%. Indicator F was determined for the distribution of the territory of the Czech Republic according to the risk of flooding. Knowledge of the existence of critical points enables the implementation of preventive measures, the evaluation of flood risk associated with the transport of sediment due to erosion processes, and the improvement of management measures in respective catchment areas, even before an event occurs. The proposed procedure outputs shall be reflected in spatial planning documentation, land consolidation, and catchment area management plans. Incorporation of critical points into open-access public web-maps can help with assessing the semi-quantitative expression of risk to built-up areas arising from the threat of local flooding.

A Review on the Possibilities and Challenges of Today’s Soil and Soil Surface Assessment Techniques in the Context of Process-Based Soil Erosion Models

To investigate relevant processes as well as to predict the possible impact of soil erosion, many soil erosion modelling tools have been developed. The most productive development of process-based models took place at the end of the 20th century. Since then, the methods available to observe and measure soil erosion features as well as methods to inter- and extrapolate such data have undergone rapid development, e.g., photogrammetry, light detection and ranging (LiDAR) and sediment tracing are now readily available methods, which can be applied by a broader community with lower effort. This review takes 13 process-based soil erosion models and different assessment techniques into account. It shows where and how such methods were already implemented in soil erosion modelling approaches. Several areas were found in which the models miss the capability to fully implement the information, which can be drawn from the now-available observation and data preparation methods. So far, most process-based models are not capable of implementing cross-scale erosional processes and can only in parts profit from the available resolution on a temporal and spatial scale. We conclude that the models’ process description, adaptability to scale, parameterization, and calibration need further development. The main challenge is to enhance the models, so they are able to simulate soil erosion processes as complex as they need to be. Thanks to the progress made in data acquisition techniques, achieving this aim is closer than ever, if models are able to reap the benefit.

A high-resolution physical modelling approach to assess runoff and soil erosion in vineyards under different soil managements

Steep-slope viticulture is a common practice in the Mediterranean basin, and provides landscapes of considerable socio-economic value. However, these complex agricultural systems are intrinsically fragile. One of the main problems is soil erosion due to extreme rainfall events. This may cause a progressive reduction in soil fertility and the occurrence of instabilities and land degradation phenomena. To worsen this condition there is the increasing mechanisation of agricultural management causing soil compaction, and the pressure of climate change, with an intensification of extreme weather events. In this context, vineyard soil management plays a key role, as it can accelerate or mitigate overland flow and soil erosion phenomena. There are various techniques for quantifying these processes, often based on field measurements through prolonged data collection using experimental plots. However, the advent of new technologies in remote sensing opens new frontiers in the acquisition of high-resolution spatial data. Indeed, they could be used in runoff/erosion simulation models and integrated with site-specific data.The aim of this paper is to assess runoff and soil erosion processes in vineyard under four different soil managements. Specifically, four practices were tested: (1) Reference (inter-row managed with standard farm grass cover; RF); (2) Continuous Tillage (bare soil obtained by continuous mechanical weeding using roto-tiller; CT); Nectariferous (a mix of herbaceous species capable of attracting insects favouring inter-row biodiversity; NF); (4) Single Tillage (inter-row weeding once a year using roto-tiller; ST). The research proposes a modelling approach using a physically-based model (SIMWE) using samples of runoff and sediment as an assessment, collected with a low-cost methodology. In particular, a cost-effective approach easily replicable in different contexts (such as developing countries) is sought. In addition to cultivation specifics, areas of soil compacted by the passage of agricultural vehicles were also analysed using the connectivity index. In general, results show an interesting capacity of ST in mitigating soil erosion, as well as for NF. Furthermore, the negative role of wheel tracks as preferential pathways for surface runoff and sediment is highlighted. Finally, the work shows that CT aggravated soil erosion as compared to RF.

Soil erosion spatio-temporal exploration and Geodetection of driving factors using InVEST-sediment delivery ratio and Geodetector models in Dongsheng, China

Assessment of soil erosion processes and accurately identifying erosion drivers is crucial for effective control and conservation strategies. We introduced a new approach involving the integration of the SDR of the InVEST and Geodetector models to explore the spatio-temporal variability of erosion and investigate the key drivers contributing to soil erosion. The results revealed an average soil loss increase of 19 to 37 t ha−1 yr−1 in the watershed from 1990 to 2020, respectively. Cropland areas had the highest growth in soil loss from 26.53 in 1990 to 118.76 t ha−1 yr−1 in 2020. The Geodetector revealed that the key variables influencing erosion are vegetation, slope, precipitation, and aspect factors. The interaction of slope and aspect, slope and precipitation, had the strongest influence on erosion than other variables, with q values of 0.80 and 0.79, respectively. The approach of this study can be used in other regions characterized by severe soil erosion.

Estimating the Best Exponent and the Best Combination of the Exponent and Topographic Factor of the Modified Universal Soil Loss Equation under the Hydro-Climatic Conditions of Ethiopia

The effect of the topographic factor of the Modified Universal Soil Equation (MUSLE) on soil erosion and sediment yield is not clear. Except for the coefficient, soil erodibility, cover, and conservation practice factors of the MUSLE, an individual effect of the exponents and topographic factors of the MUSLE on soil erosion and sediment yield can be seen by applying the model at different watersheds. A primary objective of this paper is to estimate the best exponents and topographic factors of the MUSLE under the hydro-climatic conditions of Ethiopia. For the sake of the calibration procedure, the main factors of the MUSLE that directly affect the soil erosion process, such as cover, conservation practice, soil erodibility, and topographic factors, are estimated based on past experiences from the literature and comparative approaches, whereas the parameters that do not directly affect the erosion process or that have no direct physical meaning (i.e., coefficient a and exponent b) are estimated through calibration. We verified that the best exponent of the MUSLE is 1 irrespective of the topographic factor, which results in the maximum performance of the MUSLE (i.e., approximately 100%). The best exponent that corresponds to the best equation of the topographic factor is 0.57; in this case, the performance of the model is greater than or equal to 80% for all watersheds under our consideration. We expect the same for other watersheds of Ethiopia, while for other exponents and topographic factors, the performance of the model decreases. Therefore, for the conditions of Ethiopia, the original exponent of the MUSLE is changed from 0.56 to 0.57, and the best equations of the topographic factor are provided in this paper.

An improved cellular automata model for soil erosion in coastal areas based on discrete physical variables

AbstractSoil erosion is a major and costly environmental hazard worldwide. Obtaining a thorough understanding of the soil erosion process is essential for erosion control. The high erodibility of the saline‐sodic soil in coastal areas causes rills to develop rapidly and erosion patterns change substantially during the rainfall process. Understanding the temporal and spatial dynamics of the soil surface morphology is crucial for revealing the mechanism behind the severe soil erosion process, but simulating these dynamics with many existing empirical or physical models is difficult. Cellular automata (CA) provides a simple alternative approach with high computational efficiency for modelling the complex patterns of soil erosion evolution using local interactions rules. However, previously established CA models poorly simulated the lateral erosion. By dividing the runoff amount into a discrete variable of every constituent cell and considering the runoff flow velocity when calculating the flow direction, the CA model developed here, based on discrete physical variables (CADV), could simulate soil erosion rate dynamics and rill morphological development with low relative errors. The variations in the simulated sediment yield rates during rainfall events were consistent with the experimental measurements, and the relative errors of cumulative sediment yields between the simulated and measured values were lower than 5% from the 38th to 60th min (the end of rainfall event) during the rainfall. The morphological characteristics of slope erosion with relative errors in rill length, rill width, and rill depth were lower than 5% at specific times during rainfall events. Specifically, regarding the rill width parameter, the relative errors of the maximum and average rill widths were both lower than 5% when the rainfall event ended at the 60th min. The results show that the CADV is an appropriate tool for describing the soil erosion process and improving our understanding of the erosion process characteristics of saline‐sodic soil slopes in a coastal region of China.Highlights Cellular automata based on discrete variables (CADV) improves soil erosion simulation. CADV simulates soil loss and rill morphological development with low relative errors. CADV improves insight into the mechanism of soil erosion in coastal area. CADV provides a new approach to improve soil erosion modelling with cellular automata.

Effects of rock fragment coverage on soil erosion: Differ among rock fragment sizes?

The presence of rock fragments can change land cover and thus profoundly perturb soil erosion process. This study aimed to identify the effects of rock coverage on soil erosion, and how such effects were influenced by rock fragment sizes. A series of simulated rainfall experiments were applied to erosion plots with two initial soil moisture contents (dry run and wet run), under rock fragment coverage (15%, 30%, 45%, 60%) composed of eight different fragment sizes (0.7, 1.1, 3.0, 5.5, 12.0, 18.8, 26.4, 36.0 cm) from May to September in 2021. The results show that total runoff and sediment concentration increased with rock fragment size. When rock fragments with the sizes were less than 12.0 cm, the total runoff and sediment concentration were respectively 0.81–16.02% and 16.45–50.88% lower than the bare soil. Consequently, the soil loss decreased exponentially with rock fragment coverage. When rock fragment with the sizes were large than 12.0 cm, they decreased sediment concentration by 7.91–33.32% in the dry run, but increased the total runoff by 0.26–10.28% and sediment concentration by 9.33–82.91% in the wet run. As a result, the soil loss ratio firstly enhanced as rock fragment coverage up to 45% and then declined at the rock fragment coverage of 60%. Our findings demonstrate that the effects of rock fragment coverage on soil erosion are rock fragment size dependent. This can help to better parameterize the effects of rock fragment coverage in current soil erosion models, in turn providing guiding information for soil erosion control in stony regions.

Seismic modelling and observations of rainfall

Rainfall is a key driver of geomorphological processes ranging from impacting drops that lead to the small-scale dislodgement of soil particles to large-scale morphogenic floods and rainfall-induced hillslope processes. Although rainfall has been identified in seismic records, the associated power spectral density and its quantitative relation to the underlying physical processes have not yet been studied. Here, we analyze nearly 2 years of combined seismic and optical disdrometer measurements, where the latter enables the drop-based quantification of rainfall physical properties. Our measurements confirm the broadband observation of ground velocity power spectral density due to rainfall, allowing the seismic identification of rainfall at intensities as low as 1 mm/h. Seismic power, P, shows a power-law scaling with rainfall intensity, I, and kinetic energy, E: P∝I2.1 and P∝E1.6. The observed scaling relations are consistent between the three monitored sites although there are absolute differences in seismic power of about 1 order of magnitude, which are likely due to variability in landcover and subsurface seismic properties. With a physical model, we demonstrate that the observed power-law relations are set by an underlying linear relation between seismic power and rainfall impulse power, and that the associated exponent values of I and E are due to the covariance of the raindrop size distribution with the total number of drops. The largest raindrop fractions, whose relative contribution increases with rainfall intensity, dominate the seismic signal where, in our case, 90% of the seismic power is attributed to drops larger than 3 mm. Using our model, we estimate the contributing area of rainfall to seismic observations to be within a radial distance of ∼5–25 m. The spatially integrated nature of the seismic measurements and their sensitivity to large raindrops, which control the disaggregation and the mobilization of soil particles, make seismic records well-suited for the investigation of soil erosion processes. More generally, our work provides a basis for the temporally-resolved seismic quantification of rainfall that drives the dynamics of various hydro-geomorphological processes.

Earthworm (Metaphire guillelmi) activities increase the risk of soil erosion – a simulation experiment

AbstractEarthworms exert a great impact on soil physical and chemical properties through feeding, burrowing, and casting activities. These activities can further affect soil erosion processes. However, we have insufficient knowledge on the effects of earthworm activities on soil erosion. In this study, we quantified the effects of earthworm activities on soil water distribution, runoff rate, and soil erosion rate under three slope gradients (5°, 10°, and 15°) through a laboratory‐simulated rainfall experiment. The uniform rainfall intensity (80 mm h−1) was set, and the rainfall duration after runoff generation was set to 60 min. Results showed that earthworm increased soil water infiltration and soil water storage (SWS). The increments in SWS were 41.2, 24.0, and 34.9 mm, respectively, in the tanks with earthworms at the slope gradients of 5°, 10°, and 15°, which were 93%, 51%, and 70% higher than the values of the control plots (21.3, 15.9, and 20.5 mm). Compared with the control plots, earthworm activities reduced the runoff rate at slope gradients of 5°, 10°, and 15° by 70%, 13%, and 39%, respectively; and increased soil erosion rate at slope gradients of 10° and 15° by 42% and 46%, respectively. Through their feeding, burrowing, and casting activities, earthworm increased soil water infiltration, reduced surface runoff, and increased soil erosion. This study provides insights into the effects of soil animals on soil erosion processes, and these data could then be incorporated into existing soil erosion simulation models or provide a basis for new models.

A coupled hydro-mechanical model for subsurface erosion with analyses of soil piping and void formation

A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model treats the soil as a two-phase porous medium composed of a solid phase and a liquid phase, and accounts for its elasto-plastic deformation behaviour caused by frictional sliding and granular compaction. The kinetic law characterizing the erosion process is assumed to have a similar form as the type of threshold law typically used in interfacial erosion models. The numerical implementation of the coupled hydro-mechanical model is based on an incremental-iterative, staggered update scheme. A one-dimensional poro-elastic benchmark problem is used to study the basic features of the hydro-mechanical erosion model and validate its numerical implementation. This problem is further used to reveal the interplay between soil erosion and soil consolidation processes that occur under transient hydro-mechanical conditions, thereby identifying characteristic time scales of these processes for a sandy material. Subsequently, two practical case studies are considered that relate to a sewer system embedded in a sandy soil structure. The first case study treats soil piping caused by suffusion near a sewer system subjected to natural ground water flow, and the second case study considers the formation of a suffosion erosion void under strong ground water flow near a defect sewer pipe. The effects on the erosion profile and the soil deformation behaviour by plasticity phenomena are elucidated by comparing the computational results to those obtained by modelling the constitutive behaviour of the granular material as elastic. The results of this comparison study point out the importance of including an advanced elasto-plastic soil model in the numerical simulation of erosion-driven ground surface deformations and the consequent failure behaviour. The numerical analyses further illustrate that the model realistically predicts the size, location, and characteristic time scale of the generated soil piping and void erosion profiles. Hence, the modelling results may support the early detection of in-situ subsurface erosion phenomena from recorded ground surface deformations. Additionally, the computed erosion profiles may serve as input for a detailed analysis of the local, residual bearing capacity and stress redistribution of buried concrete pipe systems.