Rill and interrill erosion on slopes in granite red soil quantified by using Sm and Eu as tracers: An indoor rainfall simulation study

Rainfall characteristics proven to trigger general erosive events (EE) and rill erosion events (RE) under reference experimental conditions of soil type, slope, and land use—previously established at a test site in central Italy—are applied as likely thresholds to characterize their spatiotemporal variability across Umbria using 24 years of semi-hourly data from 53 stations. Marked spatial patterns emerge, with mean EE frequencies per station ranging from 1.14 to 2.36 per month, while mean RE frequencies per station vary between 0.04 and 0.45 per season. No significant temporal trends are observed over the study period. Monthly and seasonal comparisons between EE and RE frequencies often deviate from the corresponding USLE R-factor dynamics, highlighting limitations of relying solely on this parameter. These findings are contextualized within common soil conservation practices—such as cover crops—to identify critical periods during which maintaining soil cover. For example, winter—when cover crops are typically present in Central Italian agroecosystems—is among the seasons with the highest EE frequency (4.45 yr−1), second only to autumn (6.47 yr−1). However, when focusing on REs, winter shows the lowest mean frequency (0.08 yr−1). In contrast, the mean RE frequency increases in summer (0.24 yr−1) and reaches its maximum in autumn (0.26 yr−1), when bare soil or poorly developed cover crops are common. Overall, results provide actionable insights for aligning protective measures with high-impact erosive event probabilities.

ABSTRACT Plant root‐induced variations in soil‐colloid electrochemical properties contribute to changes in rill flow detachment on the Loess Plateau. This field‐based study was conducted to examine the influence of various electrochemical properties of soil colloids caused by roots on rill flow detachment on the Loess Plateau, because this phenomenon has not gotten much attention. A total of 288 samples of undisturbed soil were collected from two soil layers (0–10 cm and 10–20 cm) across eight typical vegetation plots. The samples underwent scouring with six flow discharges (0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 L s −1 ) on a slope of 15°. The findings showed that plant roots had a marked influence on the electrochemical properties of soil colloids. The electrochemical properties of soil colloids for the respective 0–10 and 10–20 cm layers over the different sampling sites were soil surface electric field (1–22 × 10 8 and 4–23 × 10 8 V m −1 ), |surface potential|(94–160 and 114–162 mV), surface charge density (0.1–1.6 and 0.3–1.7 C m −2 ), specific surface area (17–201 and 14–89 m 2 g −1 ), surface charge number (7–13 and 6–10 cmol kg −1 ), and exchangeable sodium percentage (0.3%–0.6% and 0.5%–0.8%). These properties showed either a linear or exponential relationship with root length density (R 2 of 0.4 to 0.5; p < 0.01). Fine roots (0 < d ≤ 2 mm) played a prominent role in this process. Moreover, the electrochemical properties of soil colloids had marked effects on the rill detachment rate , with rates across the sampling sites ranging from 8 to 62 g m −2 s −1 in the 0–10 cm soil layer and from 29 to 59 g m −2 s −1 in the 10–20 cm soil layer, and showing either linear or exponential relationships with soil‐colloid electrochemical properties (R 2 of 0.5 to 0.6; p < 0.01). Soil specific surface area explained most of the variations in the rill detachment rate (46%). In conclusion, plant roots were found to alter soil‐colloid electrochemical properties by providing charge and ion‐binding sites, which in turn control rill flow detachment by regulating soil internal repulsive forces. Assessments of soil‐colloid electrochemical properties should therefore be a form part of strategies to prevent and control rill erosion.

This study presents an integrated assessment of geomorphological and hydrological risk in Romania’s Moldavian Plateau, combining manual inventories, high-resolution DEM/LiDAR, Corine LU/LC, geology–soils, Sentinel-2, and EGMS InSAR with HEC-RAS modeling and official 1% & 1%CC flood belts. The inventory maps 4,351 landslides, 3,343 gullies, 2,353 rill patches, and 17,681 sheet-erosion polygons – covering 28,900 ha (landslides), 4,661 ha (gullies), 21,500 ha (rill erosion), and 135,152 ha (sheet erosion), showing that areal processes dominate, while gullies and landslides mark acute instability nodes near settlement edges and infrastructure. Plateau-wide, the 1% AEP flood belt occupies 111,549 ha, expanding to 149,184 ha under the climate-corrected 1%CC scenario (+33.7%). Affected settlements increase from 398 to 451; intersected households from 10,514 to 14,112; and the estimated exposed population (excluding municipalities) from 27,350 to 36,700 (+34%). A HEC-RAS case study on the Suceava River (Mihoveni–Ițcani, Q2008 = 1,710 m³/s) indicates that levees shrink inundation footprints but raise depths and WSE (12.66→13.09 m; 285.93→286.86 m), highlighting trade-offs between footprint reduction and hydraulic load. The results support conservation agriculture on >8.5° slopes, grade-control and drainage where gullies approach settlements, targeted slope stabilization, and strict floodplain zoning paired with carefully engineered defenses.

Mechanistic insights into rill morphology and erosion processes on spoil heaps influenced by platform runoff

Variability in rill morphometry, surface runoff and erosion with soil conservation techniques (application of polyacrylamide and rice husk biochar and hydromulching) in deforested hillslopes under simulated rainfall

Impact of soil compaction on the rill erosion of Mollisol by waterflow: A comparative analysis before and after the seasonal freezing and thawing

Straw incorporation regulates rill erosion processes: Revealing multi-timescale hysteresis between runoff and sediment concentration in brown soil

Abstract Soil erosion, particularly when intensified by heavy precipitation, is a natural process and a persistent challenge in agricultural management. To date, this problem has been addressed using existing erosion models. However, these models often rely on simplified hydraulic approaches, whereas two-dimensional (2D) hydrodynamic numerical models are state-of-the-art for overland flow simulations. In this study, the combination of a 2D model and a soil erosion approach allowed for a more precise consideration of the hydraulics. The Govers approach was used with the 2D HydroAS model and evaluated using experimental plot data and naturally occurring field-scale erosion data, sourced from the literature. Results indicate that the combined model simulated sheet erosion and produced reasonable estimates for small rills using the Govers transport capacity approach. However, larger rills require calibration of this method. Additionally, the resolution of the digital elevation model (0.25 m) used as the basis for the simulation was of great importance to avoid overestimating smaller rills. Sensitivity analysis revealed that these smaller rills were particularly influenced by the input grain diameter and surface roughness. Comparisons with other erosion models underscore that incorporating an improved hydraulic approach and adapting the topography at each simulation time step enhances estimation of the spatial distribution and quantity of erosion of the rills. Knowledge about the occurrence and quantification of rill erosion can help planners develop geoecological solutions for flooding and erosion.

Preventing soil degradation caused by water erosion is essential for sustainable agriculture and long-term agroecological development. The objective of this study was to evaluate the effectiveness of an ethylene-vinyl acetate (EVA) polymer-based soil conditioner in mitigating soil erosion, a key driver of soil degradation. Laboratory experiments and simulations employing the Water Erosion Prediction Project (WEPP) model were conducted to assess soil erodibility parameters and sediment yield of two soil types from Okinawa, Japan. A key contribution of this work is the integration of these experimentally determined erodibility parameters into the WEPP model for robust validation. Interrill and rill erosion processes were analyzed under different soil conditioner application rates. Laboratory results showed that applying the soil conditioner reduced interrill erodibility by 59 to 99% and rill erodibility by 65 to 100%, while increasing critical shear stress and water infiltration rate. The effectiveness varied between the two soil types due to differences in particle-size distribution and inherent erodibility. The soil conditioner exhibited a more pronounced impact on rill erosion. WEPP simulations confirmed sediment yield reductions of 73% to 99%, primarily influenced by changes in rill erodibility and critical shear stress. While its practical application will be subject to various field conditions, our findings confirm the significant potential of this soil conditioner as a strategy for preserving topsoil resources.

The municipality of Angra dos Reis, on Brazil’s Green Coast, is highly vulnerable to land degradation due to steep slopes, intense rainfall, and increasing human pressures. This study applied the United Nations Environment Program, Priority Actions Program Regional Activity Centre methodology, representing its novel application in a humid tropical coastal environment. This approach was integrated with multi-source remote sensing data, including Landsat images from 1985 and 2023, Airbus imagery (2024), and Esri’s World Imagery Basemap with Geographic Information System tools (ArcGIS, QGIS) to map erosion risk and prioritize areas for soil conservation. Results show that 88.17% of the area is stable, while 4.34% (35.3 km²) shows active sheet and rill erosion, especially near urban areas and steep terrains. A multi-criteria framework identified 24.63 km² of stable and 29.39 km² of unstable land as medium to high priority for intervention. Analysis of land use and cover change (1985–2023) revealed a significant urban expansion of 13.01 km², occurring concurrently with a 12.95 km² gain in forest cover. This seemingly contradictory trend highlights a fragmented development pattern where environmental gains in remote areas are offset by intense degradation in fragile, high-pressure zones. The study provides a replicable, data-driven model for assessing and prioritizing land degradation in similar vulnerable regions worldwide, offering a practical framework for municipal planning and disaster risk reduction efforts under Brazil’s Forest Code and urban master plans, with potential for funding implementation through national environmental funds.

Abstract Large‐scale photovoltaic (PV) panel installations may significantly affect local hydrological processes, especially in hilly and mountainous regions. However, there is large uncertainty in assessing the hydrological impacts of PV power stations, as the effects of PV panel arrays on overland flow and rill erosion processes in hillslopes have been overlooked. This study quantitatively investigated the interactions between overland flow, soil loss, and rill development influenced by a PV panel array through artificial rainfall experiments on a loess slope with bare surface. The dynamics of overland flow and soil erosion processes in the slope with a four‐panel PV array were compared to a control slope. In the experiments, it was observed that the rill development in the PV slope was largely inhibited. The experiment results demonstrated that, under varying rainfall intensities, the soil erosion mass and the peak erosion rates of the PV slope was 39.7%–64.1% and 38.0%–52.5% less than the control slope, respectively. The reason for this soil erosion mitigation might be that the PV panel array attenuated the impact of rainfall by blocking raindrops, and diminished the overland flow velocity as well as its concentrating movement into rills. These reduced the erosivity of overland flow and decreased soil particle detachment and movement in the slope, which ultimately inhibited rill development and erosion. These findings provide a quantitative basis for accurately assessing the early stage environmental impact of PV power stations, suggesting that large PV installations in arid and semi‐arid regions may reduce initial soil erosion.

Grass cover on karst slopes effectively reduces rill erosion due to concentrated flow

ABSTRACT Rill erosion is a major soil erosion process caused by water on extensive sloping farmlands and rangelands worldwide, leading to serious soil loss. To enhance comprehension of the correlation between soil erosion and rill erosion, a field laboratory study of soil erosion by rill formation under various natural conditions and tillage practices was implemented, which was conditions prevalent in the Loess Plateau of northwest China. The slope rills were graded following Strahler's stream ordering, and an analysis was conducted to examine the role of rill erosion in the erosion effect of surface roughness. The impacts of surface roughness on sediment yield and discharge volume exhibited similarities to those of rill erosion, where an increase in rainfall intensity and slope gradient converted inhibition into promotion. From the relationships among the amounts of water and soil conservation and rill erosion at all orders, it was found that second-order rill erosion was the optimum indicator of rill erosion when characterizing sediment yield and runoff. This study established the basis for a comprehensive understanding of the mechanism by which surface roughness influences soil erosion in the Loess Plateau.

Abstract Estimating the mean square error of a small area predictor under an informative sampling design is a challenging problem. Existing approaches rely on approximations that have not been justified theoretically. We provide rigorous support for a mean square error estimator that is applicable to an informative sample design. The procedure can be used in combination with predictors of general parameters that may be nonlinear functions of the model response variable. We also construct calibrated prediction intervals that rely less on normality than standard prediction intervals. We validate the proposed measures of uncertainty through simulation. We apply the methods to predict several functions of sheet and rill erosion for Iowa counties using data from a complex agricultural survey.

Abstract Flow velocity serves as a key hydraulic parameter in examining rill erosion on slopes. Analysing the characteristics of flow velocity changes and their influencing factors is critical for understanding the rill erosion process and hydrodynamic mechanisms. However, the understanding of the mechanism of flow velocity changes in gravel‐laden hyperconcentrated flows on steep slopes is still limited. In this study, different soil–gravel mixtures (with gravel mass contents ranging from 0% to 70% and gravel clast median diameters ranging from 0.08 to 2.95 mm) were used in indoor runoff scouring tests to examine the influence and mechanisms of gravel content on flow velocity under varying unit flow discharges (1.11–4.44 × 10−3 m2 s−1) and slopes (18–84%). These results indicate that a relatively high gravel content in the sediment significantly impedes the flow velocity. The structural equation model indicates that gravel content primarily reduces flow velocity by positively influencing settling velocity (path coefficient = 0.990, p < 0.001), which in turn exerts a suppressive effect on flow velocity (path coefficient between settling velocity and flow velocity = −0.295, p < 0.001). The contributions of flow discharge, slope and gravel content to flow velocity are 79.7%, 15.6% and 0.5%, respectively. The flow velocity prediction equation established on the basis of these three factors is not only highly accurate (NSE = 0.918) but also has easily obtainable parameters, making it the preferred equation for predicting the rill flow velocity. This study explored the mechanism of flow velocity changes in hyperconcentrated flows on steep slopes, enhancing the understanding of the relationship between sediment particles and the flow velocity, which aids in elucidating the erosion process in soil‐gravel mixtures.

ABSTRACTProgress in soil erosion mitigation necessitates integrated approaches, wherein modeling is validated by field observations and enriched with local knowledge. This study adopts such an integrated methodology to discern areas of severe erosion, understand its relationship with land use and management, and capture local communities' perspectives on erosion causes, indicators, and mitigation measures. The study was done in the 211 km2 Fota‐Gumara catchment, an erosion‐prone area in Northwest Ethiopia. Utilizing the land degradation surveillance framework, 150 plots were observed, and insights from 75 randomly selected farmers were synthesized. Catchment‐scale soil erosion susceptibility prediction employed an expert‐based, multi‐criteria evaluation model, validated against field observations. Findings revealed that 23.5% of the catchment was subjected to severe erosion, mainly by sheet and rill erosion on steep slopes under cropland or shrubland and valley bottoms with gullies. Local communities identified communal grazing land and cropland as vulnerable, attributing erosion to various causes, while they overlooked the erosion severity of shrubland and the heightened erosion susceptibility caused by conventional tillage. They perceived severe erosion in sandy‐textured soils and during the middle of the rainy season. Crop yield reduction, linked to soil fertility decline and gullies, emerged as a significant concern. Perceptions about soil erosion trends were different among male and female participants. A knowledge‐implementation gap in soil and water conservation practices, compounded by challenges like labor shortages, was identified. This underscores the need to bridge this divide for effective erosion control in the catchment. The presented holistic approach enhances the precision of soil erosion identification and contributes valuable insights for formulating effective mitigation strategies tailored to both environmental conditions and community needs.

ABSTRACTConstruction projects often involve intensive excavation and backfilling activities, resulting in the creation of spoil heaps. Rill erosion on spoil heaps poses a severe threat to the ecological security of construction sites and their surrounding areas. Previous studies largely concentrated on the spoil heaps rill erosion characteristics and the conservation benefits of vegetation measures, while the controlling mechanisms and efficiency of physical conservation structures to rill erosion are not clear. The objective of this study is to investigate the controlling mechanisms by characterizing rill erosion processes on physical structures‐treated spoil heaps. A series of artificial rainfalls was simulated on a 2 by 3 m artificial spoil heap plot under the intensities of 150 and 200 mm h−1, at the slope gradients of 20° and 30° with replications. Blocking wattles were simply made using soil bags as physical conservation structures and were deployed at the lower end of the plot. Results showed that: (1) blocking wattles reduced sediment yield up to 85%, and were more efficient in sediment reduction than in runoff reduction; (2) significant rills were found under 150 and 200 mm h−1 rainfalls, and rill density tended to increase with increasing slope gradient and rainfall intensity; (3) stream power was the best hydraulic parameter for predicting sediment yield rate at the bare plots; (4) blocking wattles decreased rill density and averaged rill depth by 45.9% and 31.5%, respectively, which was attributed to the decreasing stream power and runoff velocity. We therefore concluded that physical blocking structures reduced sediment yield on spoil heaps by directly trapping sediment and by mitigating rill development to indirectly abate further soil erosion and sediment transport. This latter effect is the novelty of this study. The present results would benefit the understanding of erosion processes on spoil heaps and promote conservation practices at construction sites.

Wildfires, whether natural or human-caused, significantly alter soil properties and increase soil erosion susceptibility, particularly through changes in rill detachment capacity (Dc). This study aimed to evaluate the influence of fire intensity on key soil properties and to recognize their relationships with Dc under controlled laboratory conditions. The research was conducted in the Darestan Forest, Guilan Province, northern Iran, a region characterized by a Mediterranean semi-arid climate. Soil samples were collected from three fire-affected conditions: unburned (NF), low-intensity fire (LF), and high-intensity fire (HF) zones. A total of 225 soil samples were analyzed using flume experiments at five slope gradients and five flow discharges, simulating rill erosion. Soil physical and chemical characteristics were measured, including hydraulic conductivity, organic carbon, sodium content, bulk density, and water repellency. The results showed that HF soils significantly exhibited higher rill detachment capacity (1.43 and 2.26 times the values compared to the LF and NF soils, respectively) and sodium content and lower organic carbon, hydraulic conductivity, and aggregate stability (p < 0.01). Strong correlations were found between Dc and various soil properties, particularly a negative relationship with organic carbon. The multiple linear equation had good accuracy (R2 > 0.78) in predicting rill detachment capacity. The findings of the current study show the significant impact of fire on soil degradation and rill erosion potential. The study advocates an urgent need for effective post-fire land management, erosion control, and the development of sustainable soil restoration strategies.

Abstract Quantifying sequences of events and materials involved in the growth and dispersal of post‐wildfire debris flows across entire mountain catchments and piedmont fans is rarely possible. However, understanding these processes facilitates assessing future flow magnitudes and recurrence risk. This study analyzed the evolution of debris flows generated by a rainstorm following near‐complete burning of vegetation in six mountain watersheds. The flows transported large volumes of boulders to downstream fans, devastating Montecito, California. With rainfall‐runoff modeling, lidar, photogrammetry, and field surveys, we quantified the hydrological and sedimentological components of the debris flows as they evolved from hillslope runoff to boulder‐rich fan deposits and ocean discharge. Runoff from burned soils drove larger amounts of rill erosion and slurry generation on shale hillslopes than on sandstones. Hillslope slurry mobilized ravel deposits and fine sediments stored in the channel network, mainly on shales. Channels draining sandstones mainly supplied the flows' boulder loads. One‐quarter of the mountain‐shed sediment escaped to the ocean, while all boulders settled on the fans. Flows confined to primary channels remained erosive across the fans except where channel gradients and dimensions decreased in response to fault‐related topography and where bridges trapped boulders, intensifying in‐channel and overbank deposition. Although the results derive from a single event, they illustrate how a sequence of processes and landscape conditions determine debris‐flow evolution across catchments and fans. Identifying debris‐flow components highlights useful measurement and modeling methods to improve prediction while highlighting current limits on understanding critical processes and transient antecedent conditions.