Slope Erosion Research Articles

Bio-cementation for tidal erosion resistance improvement of foreshore slopes based on microbially induced magnesium and calcium precipitation

In most coastal and estuarine areas, tides easily cause surface erosion and even slope failure, resulting in severe land losses, deterioration of coastal infrastructure, and increased floods. The bio-cementation technique has been previously demonstrated to effectively improve the erosion resistance of slopes. Seawater contains magnesium ions (Mg2+) with a higher concentration than calcium ions (Ca2+); therefore, Mg2+ and Ca2+ were used together for bio-cementation in this study at various Mg2+/Ca2+ ratios as the microbially induced magnesium and calcium precipitation (MIMCP) treatment. Slope angles, surface strengths, precipitation contents, major phases, and microscopic characteristics of precipitation were used to evaluate the treatment effects. Results showed that the MIMCP treatment markedly enhanced the erosion resistance of slopes. Decreased Mg2+/Ca2+ ratios resulted in a smaller change in angles and fewer soil losses, especially the Mg2+ concentration below 0.2 M. The decreased Mg2+/Ca2+ ratio achieved increased precipitation contents, which contributed to better erosion resistance and higher surface strengths. Additionally, the production of aragonite would benefit from elevated Mg2+ concentrations and a higher Ca2+ concentration led to more nesquehonite in magnesium precipitation crystals. The slopes with an initial angle of 53° had worse erosion resistance than the slopes with an initial angle of 35°, but the Mg2+/Ca2+ ratios of 0.2:0.8, 0.1:0.9, and 0:1.0 were effective for both slope stabilization and erosion mitigation to a great extent. The results are of great significance for the application of MIMCP to improve erosion resistance of foreshore slopes and the MIMCP technique has promising application potential in marine engineering.

Taxonomic and Feeding Trait-Based Analysis of Macroinvertebrates in the Antisana River Basin (Ecuadorian Andean Region).

High-elevation tropical streams are under increasing threat from human activities and climate change. Specifically, Ecuadorian Andean streams require priority actions such as bioassessment (e.g., biodiversity and functional ecology of macroinvertebrates) in order to generate adequate environmental management policies. Therefore, we investigated the distribution and composition of the macroinvertebrate taxa and their functional feeding groups in relation to the environmental variables in the Antisana river basin (Andean-Ecuadorian Region). We sampled macroinvertebrates from 15 locations to assess ecological conditions (ECs), expressed as the Biological Monitoring Working Party Colombia (BMWP-Col) classes, the Andean Biotic Index (ABI) and the Andean-Amazon Biotic Index (AAMBI). Results indicate that dissolved oxygen saturation, elevation, nutrient concentration and conductivity contributed significantly to the composition of the taxa and functional feeding groups (FFGs). Taxa diversity and FFGs were more abundant in the best EC sites. Shredders (SH) were, overall, dominant and abundant at sites with medium-high ECs. Scrapers constituted the second most prevalent assemblage, exerting dominance at moderate ecological conditions (high altitude and high oxygen saturation). Collector-gathers (CGs) are less sensitive to contamination than the previous two groups but were equally abundant at medium-high EC sites. Collector-filterers (CFs) and parasites (PAs) were less abundant, although the presence of the former was slightly related to better environmental conditions. Predators (PRs) were almost absent throughout the study, but they were collected from poor EC sites. CGs, PAs and PRs showed more tolerance to the presence of human disturbances (e.g., hydraulic constructions or slope erosion). The BMWP-Col index seems to be the best fit for this ecosystem, showing a significant difference in FFG between the index classes, compared to the other indices evaluated. The results of this investigation may be regarded as a fundamental starting point and used in future bioassessment work in other similar ecosystems, particularly high-altitude tropical Ecuadorian streams.

Quantification of red soil macropores affected by slope erosion and sediment using computed tomography

AbstractSoil structure is an important factor interacting with soil erosion and sediment processes. However, few studies have focused on the relationship between soil macroporosity and soil erosion across different terrains. The aim of this study was to quantify and compare soil properties and macroporosity characteristics in collapsing gully areas and to explore their impact on the formation and development of collapsing gullies. Soil cores were excavated at different positions of a typical collapsing gully and then scanned to analyze soil macropores. Soil properties and saturated hydraulic conductivity were also investigated. The results showed that the contents of sand, silt, and clay, the mean weight diameter of aggregates, and the infiltrate rates varied at different positions. The valley had the greatest macroporosity (1.09% ± 0.33%), the number (5919 ± 703), volume (1468 ± 194 mm3), and surface area (10.4 ± 2.6 m2) of macropores, as well as the mean volume (16.8 ± 7.4 mm3) of macropores >1 mm3, whereas these indices were lowest at the slope (0.15% ± 0.14%, 1189 ± 747, 266 ± 188 mm3, 1.7 ± 1.4 m2, and 10.6 ± 2.9 mm3, respectively). The macroporosity and the number of macropore decreased with increasing depth but were also influenced by the erosion and sediment processes. The processes of sediment and the roots of vegetation also influenced the orientation of the macropores. Macropore characteristics at different sites of the collapsing gullies affected the soil water infiltration and hydraulic conductivity and further affected the processes of water erosion and mass erosion.

Effect of microrelief features of tillage methods under different rainfall intensities on runoff and soil erosion in slopes

Tillage methods play a crucial role in controlling rainwater partitioning and soil erosion. This study utilized rainfall simulation experiments to investigate the impact of four tillage methods (manual digging (MD), manual hoeing (MH), traditional ploughing (TP), and ridged ploughing (RP)) on runoff and soil erosion at the plot scale. The smooth slope (SS) was used as a benchmark. Rainfall intensities of 30, 60, 90, and 120 mm h−1 were considered. The study revealed that tillage altered rainwater distribution into depression storage, infiltration, and runoff. Tillage reduces runoff and increases infiltration. The four tillage methods (30–73%) increased the proportion of rainwater converted to infiltration to varying degrees compared to the SS (22–53%). Microrelief features influenced the role of tillage methods in soil erosion. Surface roughness and depression storage accounted for 79% of the variation in sediment yield. The four tillage methods reduced runoff by 2.1–64.7% and sediment yield by 2.5–77.2%. Moreover, increased rainfall intensity weakens the ability of tillage to control soil erosion. When rainfall intensity increased to 120 mm h−1, there was no significant difference in runoff yield among RP, TP, MH, and SS. Therefore, assessing the effectiveness of tillage in reducing soil erosion should consider changes in rainfall intensity. Additionally, the cover management (C) factor of the RUSLE was used to assess the effects of different tillage methods on soil loss. Overall, the C factor values for tilled slopes are in the order MH > TP > RP > MD with a range of 0.23–0.97. As the surface roughness increases, the C factor tends to decrease, and the two are exponential functions (R2 = 0.86). These studies contribute to our understanding of how different tillage methods impact runoff and soil erosion in sloped farmland and provide guidance for selecting appropriate local manual tillage methods.

Experimental Research on Erosion Characteristics of Ecological Slopes under the Scouring of Non-Directional Inflow

Considering environmental sustainability, ecological embankments are often adopted in rivers, which benefit both the erosion resistance and the ecological balance of the bank. In this paper, the effectiveness of different types of dominant grass species in ecological slope protection and their impact mechanisms, as well as the impact of non-directional inflow on erosion characteristics, were investigated. Based on the principle of similarity theory in hydraulic modeling and the characteristics of flood erosion in riverbanks, a test model system for hydraulic ecological simulation was designed, including a vegetation bank slope and channels. Three types of dominant grass species were selected, and 12 series of erosion experiments were conducted in the grassed slope of the test model. Three types of root–soil composites and a reference plain soil were involved in the tests, and soil mechanical indicators such as shear strength were collected. Experimental results show that root–soil composite is a special elastic–plastic material, which provides additional cohesive force to the soil due to its root consolidation and reinforcement effects, Δc. The shear strength index reflecting soil cohesion was increased by 15% to 20%. The primary factor affecting slope erosion is the flushing velocity, and both the average erosion depth and the unit soil erosion loss present an exponential function with respect to this factor, while presenting a linear function with the angle of incoming flow. Compared with the plain soil slope, the ecological slope could decrease erosion significantly. The sand loss of the ecological slope is only 50~60% that of the plain soil slope as the flushing velocity is 3–4 m s−1. In vertical flushing, the sand loss in the plain soil slope is 1.73–2.43 times that of the ecological slope. This research might provide technical support for the anti-scourability design of the ecological embankment.

Role of hydrophobic sand particle granularity on water droplet post-impact dynamics

This paper investigates, experimentally and theoretically, the effects of sand particle size and hydrophobicity of a water drop impacting horizontal and inclined surfaces within a context of post-wildfire mudflow precursors. Although previous research established that wildfires often turn hillslope surficial soil hydrophobic, little research shows how wildfire-altered soil surfaces affect raindrops' impact behavior. Specific findings point to a significant effect of sand type on the drop impact dynamics. After spreading, the drop gathers back more on finer than coarser hydrophobic sands due to the substrate air-entrapped grooves, as in the Cassie-Baxter model, leading to drop retraction, rebound, splash, and fragmentation into droplets. The results indicate that if the hillslope dominant median grain size is fine, alteration to hydrophobicity would multifold enhance drop downhill mobility. In contrast, coarse sand surfaces exhibit minimal effects on drop mobility after hydrophobization. In addition, the paper proposes a modified Tang et al. model for the maximum spread factor as a function of the median grain size and hydrophobicity. This research offers essential findings from the perspective of the previous limiting understanding that only drop infiltration prevents erosion in hydrophilic slopes.

Feasibility Assessment of a Magnetic Layer Detection Method for Field Applications

The lack of current data on the spatial distribution of soil erosion hinders the ability to predict soil erosion on slopes. To address this problem, we present a simple and sensitive soil erosion measurement method called the magnetic layer detection (MLD) method. This method can measure the changes in soil layer thickness (SLT) at a site featuring a pre-buried magnetic layer (ML) using the relationship between magnetic susceptibility and soil thickness, and then use this information to determine the erosion or accumulation at that point. To verify the adaptability and accuracy of this method, we designed three field tests. First, we conducted a simulated sediment siltation experiment using the erosion pin (EP) method as the control. This experiment demonstrated the accuracy of the MLD method for measuring SLT (Rad2 = 0.97, NSE = 88.14%, and RMSE = 1.17 mm). Next, a simulated rainfall experiment with the runoff plot (RP) method as a control was used to demonstrate the effectiveness of the MLD method under water erosion. The results demonstrated that this method can reliably estimate soil erosion on both bare plots (Rad2 = 0.83, NSE = 71.78%, and RMSE = 0.56 mm) and sparse grass plots (Rad2 = 0.90, NSE = 81.77%, and RMSE = 0.25 mm), with performance that is better than that of the traditional EP method. Finally, a soil scouring experiment, again with the RP method as a control, was designed to verify whether the MLD method could accurately measure the erosion of a slope after the soil was scoured by surface runoff. The MLD method could accurately measure the slope erosion (Rad2 = 0.91, NSE = 89.55%, and RMSE = 0.42 mm), with results superior to those of the traditional EP method. The MLD method’s results were similar to those from the laser scanner (LS) method, but more accurate and with less associated cost and data processing time. Therefore, the MLD method has potential as a reliable measurement method that can provide useful guidance for elucidating the spatial distribution of soil erosion and predicting slope soil erosion. This approach could be used to obtain raw data to quantify soil erosion on the Loess Plateau of China and beyond.

Earthworms reduce nutrient loss from loess soil slopes under simulated rain

Burrowing, feeding, and casting activities of earthworms affect nutrient cycling and hydrological processes that take place in sloping lands. However, the effects exerted by earthworms on nutrient losses associated with runoff and sediment during rain remains unclear, particularly in the Loess Plateau, where soil erosion and nutrient loss have led to severe environmental issues. In this study, our purpose was to quantify the effects exerted by the anecic earthworm species, Metaphire guillelmi, on nutrient loss via runoff and erosion in loess soil slopes. Six artificial grass slopes (mesocosms, 15°), comprising three with earthworms (100 individuals m−2) for 28 days, and three without earthworms, were subjected to simulated rain (90 mm h−1) for 60 min. Our results indicated that earthworms had (i) increased the content of NO3–-N from 8.1 to 151.8 mg kg−1 and OP from 51.0 to 71.8 mg kg−1, but decreased the content of OC from 6.6 to 5.2 g kg−1, TN from 0.76 to 0.62 g kg−1, TP from 0.73 to 0.68 g kg−1 and NH4+-N from 3.7 to 2.4 mg kg−1 at surface 2 cm soil; (ii) increased water-stable macroaggregates from 45.1 to 48.3% and soil saturated water conductivity from 0.07 to 0.28 mm min−1, and (iii) greatly reduced the cumulative runoff from 65.7 to 15.3 mm and sediment occurance from 0.44 to 0.16 kg m−2 on slopes. Consequently, earthworm activities decreased runoff-associated nutrients (decreased NH4+-N from 19.5 to 2.8 mg m−2, NO3–-N from 108.2 to 26.2 mg m−2, and SP from 2.2 to 0.1 mg m−2) loss by 75.8–96.2%, and sediment-bound nutrient (decreased OC from 2.4 to 0.8 g m−2, TN from 0.3 to 0.1 g m−2, TP from 0.3 to 0.1 g m−2) loss by 63.8–68.5%. Hierarchical partitioning and variation partitioning analyses showed that runoff and sediment yields and their interaction with the soil physical characteristics were the dominant pathways via which earthworms regulated nutrient loss during rainfall events. This study highlights the importance of soil fauna in regulating erosion and nutrient loss in the Loess Plateau, and indicates that these factors should be considered in future water and soil conservation management.

Effects of Hydraulic Erosion on the Spatial Redistribution Characteristics of Soil Aggregates and SOC on Pisha Sandstone Slope

Under the long-term effects of hydraulic erosion, soil particles and nutrients are continuously lost and enriched in the process of runoff and sediment movement, leading to a change in soil organic carbon (SOC) in different spatial positions on the slope, which is closely related to the carbon balance of the ecosystem. Therefore, the changes in slope erosion intensity and the spatial redistribution characteristics of soil aggregates and SOC under water erosion conditions were quantitatively analyzed by combining field runoff plots with three-dimensional (3D) laser scanning technology. The results showed that: (1) After rainfall, the slope erosion intensity successively declined from the upper to the lower parts of the slope, and the content of soil aggregates in each soil layer changed obviously. The loss of 1–2 mm soil aggregates was the largest in the sedimentary area of the 2–4 cm soil layer, at 0.38 g/kg. The concentration of 0.5–1 mm soil aggregates was the largest in the micro-erosion area of the 2–4 cm soil layer, at 0.36 g/kg. (2) After rainfall, the overall SOC on the slope showed a loss state in the 0–2 cm soil layer and an enrichment state in the 2–4 cm soil layer. Among them, the loss of SOC in the medium erosion area of the 0–1 cm soil layer was the largest, and its content decreased by 57.58%. The enrichment in the 2–4 cm soil layer was the maximum in the micro-eroded area, with a content increase of 79.23%. (3) Before and after rainfall, the SOC of each soil layer was positively correlated with small aggregates, and the correlation gradually tended to be negative with the increase in the particle size of soil aggregates, and the SOC showed a negative correlation with large aggregates (>2 mm).

Compound erosion effect of snowmelt, wind, and rainfall on sloping farmlands of Chinese typical Mollisol region.

Research on the processes and mechanisms of compound soil erosion by multiple forces can provide scientific guidance for precisely controlling cropland soil erosion. Based on the seasonal alternation of freezing-thawing, snowmelt, wind, and rainfall erosion forces on sloping farmlands under natural conditions from November to next October of each year, we used a set of indoor simulation experiments of multi-force superimpositions to analyze the compound soil erosion processes of snowmelt (1 and 2 L·min-1), wind (12 m·s-1), and rainfall (100 mm·h-1). We further discussed the erosion effects of multi-force superimpositions. The results showed that, under single snowmelt erosion, an increase in snowmelt flow had a greater effect on sloping snowmelt erosion intensity than that of sloping runoff rate. When sloping snowmelt flow increased from 1 L·min-1 to 2 L·min-1, sloping runoff rate and erosion intensity increased by 2.7 and 4.0 times, respectively. Under snowmelt-wind superimposition erosion, previous sloping snowmelt erosion inhibited late wind erosion occurrence. As sloping snowmelt flow increased from 1 L·min-1 to 2 L·min-1, the inhibiting action subsequently increased and wind erosion intensity caused by previous snowmelt reduced by more than 50%. Both wind erosion and snowmelt-wind superimposed erosion intensified late rainfall erosion. The early wind erosion increased rainfall erosion by 24.5%. The snowmelt-wind superimposed effect increased the later slope rainfall erosion by 132.8% and 465.4% under 1 and 2 L·min-1 snowmelt runoff rates, respectively. The compound soil erosion amount driven by multiple force superimposition was not the sum of the corresponding erosion amount caused by single erosion force, with promoting or inhibiting effects of erosion force superimposition. The erosion effect of snowmelt-wind superposition was negative, but that of wind-rainfall superposition and snowmelt-wind-rainfall superpositions were positive.

Deep learning based slope erosion detection

Being increasingly present at the most diverse structure health monitoring (SHM) scenarios, many high-performance artificial intelligence techniques have been able to solve structural analysis problems. When it comes to image classification solutions, convolutional neural networks (CNNs) deliver the best results. This scenario encourages us to explore machine learning techniques, such as computer vision, and merge it with different technologies to achieve the best performance. This paper proposes a custom CNN architecture trained with slope erosion images that showed satisfactory results with an accuracy of 96.67%, enabling a precise and improved identification of instability indicators. These instabilities, when detected in advance, prevent disasters and enable proper maintenance to be carried out, given that its integrity directly affects structures built around and above it.

Using rare earth element tracers to investigate ridge slope erosion process in contour ridge system under extreme rainfall

Extreme rainfall is becoming more frequent and intense, which no doubt increases the risks and uncertainty of water erosion in widely-used contour ridge systems. Ridge slope erosion can increase the probability of contour failure occurrence and then induce contour ridge losing anti-erosion properties. However, there is little understanding of ridge slope erosive process controlled by contour ridge system responding to extreme rainfall. In this study, five rare earth elements were applied in different ridge segments and soil layers to monitor the successive development of ridge slope erosion process under extreme rainfall in contour ridge system. Simulated rainfall experiments at high rainfall intensity (100 mm h−1) lasting for 60 min were conducted in runoff plots with ridge tillage practices characterized by microtopography indices and ridge geometry indices. Results showed that three sub-processes were observed for ridge slope erosion, including inter-rill erosion, headward erosion, and rill erosion. Headward erosion mainly resulted from the break-point at ridge surface and sidewall collapse at ridge toe, and the pouring of ponding water in furrow greatly promoted rill development. Erosion rate was the largest during headward erosion process, and rill erosion contributed the most to eroded source. The dominated erosion process was transport-limited during inter-rill erosion process, and detachment-limited during headward and rill erosion processes. Sediment transport and deposition processes as well as their transformation occurred simultaneously after the development of headward erosion. Eroded sediment was mainly from the low part of ridge, which was transported by raindrop-impacted sheet flow or overflow. These findings provide better responding of agricultural tillage to global climate change and references for the development of physically-based erosion models.

Estimating sheet erosion on purple soil hillslope treated with polyacrylamide (PAM) in the Three Gorges Reservoir area

Study regionThe Three Gorges Reservoir area (TGR), China Study focusSoil erosion on purple soil hillslope and its negative effects are deleterious to the ecological environment of the TGR. Sheet erosion is the initial form of the slope erosion, which is notably impacted by land degradation, polyacrylamide (PAM) is commonly applied for soil and water conservation purpose, while the sheet erosion on purple soil hillslope treated with PAM remains unclear. New hydrological insights for the regionThe findings suggested that the sheet erosion and runoff rate increased as the rainfall intensity was increased and the slope gradient was decreased with increasing PAM application rate until reaching minimum values at 0.80 g m−2, and these quantities increased afterward. The single and combined impacts of the PAM application rate, rainfall intensity and slope gradient on erosion and runoff were significant. The slope gradient, rainfall intensity and PAM application rate also influenced the hydrodynamic parameters, and the stream power was the optimal parameter for describing the sheet erosion. An equation encompassing the rainfall intensity, slope gradient and PAM application rate was used for sheet erosion rate prediction with high accuracy relative to the stream power and PAM application rate. These results could be helpful to better understand sheet erosion on purple soil slopes treated with PAM and offer fundamental guidelines for soil and water conservation in the TGR.

A novel two-dimensional numerical model developed for slope soil erosion

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.

Strength and Mechanism of Granite Residual Soil Strengthened by Microbial-Induced Calcite Precipitation Technology

High rainfall environmental conditions can easily cause erosion or collapse of the granite residual soil slope. However, traditional slope reinforcement methods have drawbacks such as poor landscape effect, high energy consumption of raw materials, and environmental pollution. This study studied the application of microbial-induced calcite precipitation (MICP) in the reinforcement of granite residual soil. The consolidation effect of various methods was investigated, and the influence of cementing liquid concentration and pH value on consolidation under optimal curing conditions was explored. The results showed that the bacteria concentration reached OD600 = 3.0 and urease activity was 31.64 mM/min, which positively impact the production of calcium carbonate and the stability of crystal morphology. In addition, the soaking method was found to have the most effective consolidation effect on the surface soil samples, with the lowest disintegration rate. On the other hand, the peristaltic pump grouting method is the most effective in strengthening depth. This method resulted in a 513.65% increase in unconfined compressive strength (UCS), a 297.98% increase in cohesion, and a 101.75% increase in internal friction angle. This study also found that after seven rounds of grouting, the highest UCS was achieved in consolidated soil samples with a 0.5 mol/L cementing solution concentration, reaching 1.602 MPa. The UCS of soil samples increases as the pH value of the cementing fluid increases within the range of 6–8. As the pH value reaches 8–9, the strength increases and stabilizes gradually. These research findings can serve as an experimental basis for strengthening granite residual soil slopes and a guide for improving microbial geotechnical strengthening methods.

Laramide bulldozing of lithosphere beneath the Arizona transition zone, southwestern United States

Abstract The northwest-trending transition zone (TZ) in Arizona (southwestern United States) is an ~100-km-wide physiographic province that separates the relatively undeformed southwestern margin of the Colorado Plateau from the hyperextended Basin and Range province to the southwest. The TZ is widely depicted to have been a Late Cretaceous–Paleogene northeast-dipping erosional slope along which Proterozoic rocks were denuded but not significantly deformed. Our multi-method thermochronological study (biotite 40Ar/39Ar, zircon and apatite [U-Th-Sm]/He, and apatite fission track) of Proterozoic rocks in the Bradshaw Mountains of the west-central Arizona TZ reveals relatively rapid cooling (~10 °C/m.y.) from temperatures of >180 °C to <60 °C between ca. 70 and ca. 50 Ma. Given minimal ca. 70–50 Ma upper-crustal shortening in the TZ, we attribute cooling to exhumation driven by northeastward bulldozing of continental lower crust and mantle lithosphere beneath it by the Farallon flat slab. Bulldozing is consistent with contemporaneous (ca. 70–50 Ma) underplating and initial exhumation of Orocopia Schist to the southwest in western Arizona and Mesozoic garnet-clinopyroxenite xenoliths of possible Mojave batholith keel affinity in ca. 25 Ma TZ volcanic rocks.

Numerical simulation study on erosion collapse failure mechanism of cemented conglomerate accumulation

PurposeCemented conglomerate accumulation is a weak and heterogeneous medium that occurs in western China. It consists mainly of argillaceous cement that loses strength rapidly upon contact with water, leading to collapse instability failure. Its deformation failure mechanism is complex and poorly understood. In this paper, the erosion failure mechanism of cemented conglomerate accumulation is investigated.Design/methodology/approachThe collapse failure process after erosion of the slope foot for typical cemented conglomerate accumulation is studied based on field investigation using the particle discrete element method. And how the medium composition, slope angle and cementation degree influence the failure mode and process of the cemented conglomerate accumulation is examined.FindingsThe foot erosion of slope induces a tensile failure that typically manifests as “erosion at the foot of slope – tensile cracking at the back edge of slope top – integral collapse.” The collapse failure is more likely to occur when the cemented conglomerate accumulation has a higher rock content, a steeper slope angle or a weaker cementation degree.Originality/valueA model based on rigid blocks and disk particles to simulate the cemented conglomerate accumulation is developed. It shows that the hydraulic erosion at the foot of the slope resulted in a different failure mechanism than that of general slopes. The results can inform the stability management, disaster prevention and mitigation of similar slopes.

Investigating the stability of contour ridge system using rare earth element tracers under natural rainfall in the rocky mountain areas of Northern China

Erratic and intensively erosive natural rainfall is becoming more frequent with the intensification of global climate warming, increasing uncertainty and unpredictable risks of the stability of contour ridge system. However, little attention has been paid to the in situ quantitative evaluation of contour ridge stability under natural rainfall. When water ponds in furrows, contour ridges tend to breach, inducing contour failure followed by ephemeral gully erosion, which greatly affects the stability of contour ridge system. To track sediment sources during ridge slope erosion, contour failure, and ephemeral gully erosion stages, ten rare earth element (REE) tracers were applied in three soil layers (total 0.3 m in depth) at four slope positions in-situ runoff plots under five rainfall levels. Runoff plots were conducted with contour ridgess for sweet potatoes (SP) and peanuts (PT). The stability of contour ridges was gradually weakened when erosion form shifted from ridge slope erosion to contour failure and then to ephemeral gully erosion. Ridge slope erosion controlled contour ridge stability, with contribution of 76.28–80.49 % to the total sediment yield. Sediment yield occupied 40.99 % of the total after contour failure appearing and 55.80 % after ephemeral gully formation. The lower-middle slope was the most fragile area for contour ridge system. Rainstorm (with precipitation 50–100 mm in 24 h) played a destructive role in weakening contour ridge stability, which generated the largest runoff (36.81–39.25 % to the total) and sediment yield (46.75–57.84 % to the total). Rainstorm made the greatest contribution to the occurrence of ridge slope erosion (51.64–59.99 %), contour failure (38.07–40.91 %), and ephemeral gully erosion (24.32–30.53 %). When using REE oxides to determine contour ridge stability, the tagging depth above 0.2 m and the uniform binding of oxides with < 0.05 mm particles should be considered. Thus, some modifications to lower the likelihood of ridge failures under rainstorm conditions may be effective to enhance the stability of contour ridge system.

Formation of new erosion-deposition patterns after farmland conversion: The major role of topography

The “Grain for Green” project has a profound impact on the allochthonous process of erosion sediment stripping and transportation, which in turn interferes with the distribution of erosion patterns. Therefore, understanding the changes in erosion patterns after farmland conversion and the factors controlling the new patterns of erosion distribution are essential for understanding the mechanism of slope erosion. Accordingly, this study investigated the formation of new erosion patterns and their control factors after farmland conversion by field sampling combined with nuclear tracing (137Cs) techniques, considering the “Grain for Green” project on the Loess Plateau as the study focus. We found that the implementation of the “Grain for Green” project can significantly reduce soil erosion intensity and create a new erosion-sediment source-sink pattern on the slope. The conversion of farmland to grassland can effectively store soil organic carbon as well as more environmentally sensitive active organic carbon, and the sorting effect on sediment particles is more obvious. Meanwhile, using stepwise regression, we found that the key limiting factor affecting the erosion intensity of farmland is the topography; the response of topographic factors to erosion is much higher than the physicochemical properties of the soil itself. By quantified the direct and interactive contributions to erosion intensity, we find that the direct contributions of silt and relief amplitude were 0.48 and 0.46 in farmland, while slope (0.16), Roughness (0.20) and Relief amplitude (0.33) in grassland, respectively. The interactive contributions were 0.06 and 0.30 in farmland and grassland. The conversion of farmland to grassland results in an increase in the factors that resist erosion and the factors interact more closely with each other to limit the occurrence of soil erosion. Our study provides scientific support for a deeper understanding of the slope erosion mechanism.

Mapping bedrock topography: a seismic refraction survey and landscape analysis in the Laramie Range, Wyoming

Physical, chemical, and biological processes create and maintain the critical zone (CZ). In weathered and crystalline rocks, these processes occur over 10–100 s of meters and transform bedrock into soil. The CZ provides pore space and flow paths for groundwater, supplies nutrients for ecosystems, and provides the foundation for life. Vegetation in the aboveground CZ depends on these components and actively mediates Earth system processes like evapotranspiration, nutrient and water cycling, and hill slope erosion. Therefore, the vertical and lateral extent of the CZ can provide insight into the important chemical and physical processes that link life on the surface with geology 10–100 s meters below. In this study, we present 3.9 km of seismic refraction data in a weathered and crystalline granite in the Laramie Range, Wyoming. The refraction data were collected to investigate two ridges with clear contrasts in vegetation and slope. Given the large contrasts in slope, aspect, and vegetation cover, we expected large differences in CZ structure. However, our results suggest no significant differences in large-scale (&amp;gt;10 s of m) CZ structure as a function of slope or aspect. Our data appears to suggest a relationship between LiDAR-derived canopy height and depth to fractured bedrock where the tallest trees are located over regions with the shallowest depth to fractured bedrock. After separating our data by the presence or lack of vegetation, higher P-wave velocities under vegetation is likely a result of higher saturation.