Rill Erosion Research Articles

Experimental determination of sediment transport capacity of rill flow over sandified loess slope

Rill erosion is affected by the sand particle content in soil, especially in the wind and water erosion transition region of the Loess Plateau. The sediment transport capacity (STC) is a key parameter in rill erosion research, assessing the impact of aeolian sand intrusion on the STC of rill flow is of importance for a better understanding of rill erosion. This study aimed to assess the effect of aeolian sand intrusion on the STC on sandified loess slopes, with typical slopes and flow discharges, using a flume system which consisting of a sediment-feeding and a sediment-supply/settlement flume. The sediment feeding flume was jointed by 10° higher than that of the sediment measurement flume section. Three flow discharges (2, 4, and 8 L min−1) and four slope gradients (5°, 10°, 15°, and 25°) were used to represent the natural hydrological conditions under three intrusion rates (SIR) of aeolian sands (10%, 20%, and 50%). The results show that STC increased with slope gradient and flow discharge, and the relationship between the STC and the SIR was significantly affected by the slope gradient; the STCs decreased with the SIR on a slope of 5° but increased with the SIR on steep slopes of 15°–25°, implying a significant impact of slope gradient on the relationship between SIR and STC. The SIR of 50% resulted in the highest sediment concentration nearly 1200 kg m−3 on slopes of 25°. On sandified loess slopes of 10%, 20%, and 50% SIR, the STC were about 30%, 46%, and 57% higher than on loess slopes, indicating an increased erosion rate by sand particle intrusion into loess soil. These results highlight the impact of sand intrusion on STC of rill flow and provide deeper insights into the soil loss process on the sandified loess slope.

Soil Erosion, Sediment Yield, and Runoff Modeling of the Megech Watershed Using the GeoWEPP Model

Modeling soil erosion, sediment yield, and runoff are crucial for managing reservoir capacity, water quality, and watershed soil productivity. However, the monitoring and modeling of soil erosion and sedimentation rates in developing countries such as Ethiopia is not well practiced; thus, the reservoir capacity is diminishing at faster rates. In this study, the soil erosion, sediment yield, and runoff in the Megech watershed, Upper Blue Nile Basin, Ethiopia were modeled using the physically-based geospatial interface, the Water Erosion Prediction Project (GeoWEPP). The GoWEPP model was calibrated and validated at the Angereb sub-watershed and simulated to representative sites to capture the spatiotemporal variability of soil erosion and sediment yield of the Megech watershed. The model parameter sensitivity analysis showed that the hydraulic conductivity (Ke) for all soil types was found to be the dominant parameter for runoff simulation, while rill erodibility (Kr), hydraulic conductivity (Ke), critical shear stress (τc), and inter rill erodibility (Ki) were found to be sensitive for sediment yield and soil loss simulation. The model calibration (2000–2002) and validation (2003–2004) results showed the capability of the GeoWEPP model; with R2 and NSE values, respectively, of 0.94 and 0.94 for calibration; and 0.75 and 0.65 for validation. In general, the results show that the sediment yield in the study watershed varied between 10.3 t/ha/year to 54.8 t/ha/year, with a weighted mean value of 28.57 t/ha/year. The GeoWEPP model resulted in higher sediment value over that of the design sediment yield in the study basin, suggesting the implementation of the best watershed management practices to reduce the rates of watershed sediment yield. Moreover, the mean soil loss rate for the Angerb sub-watershed was found to be 32.69 t/ha/year.

Factors contributing to rill erosion of forest roads in a mountainous watershed

Forest roads are a major source of and transport pathway for eroded sediments in mountainous watersheds. When rills develop on these roads' surfaces, they amplify sediment erosion. Best management practices can decrease sediment erosion, but in order to efficiently implement these practices it is necessary to determine which factors have the most influence on rill development on forest roads. Despite this need, there is scarce literature on rill development on forest roads. To fill this gap in knowledge, based on field survey and multivariate statistical methods including redundancy analysis (RDA) and variation partitioning analysis (VPA), we investigated unpaved forest roads in the Xiangchagou watershed in China and quantified the extent to which various factors influenced rill formation. Specifically, we studied how rill erosion intensity (REI) and rill morphological characteristics (like rill length, mean width and depth, density, and severity of fragmentation) varied along the slope of a forest road. We also introduced the concept of a road's hydrological constituents (its upslope catchment, surface, and cutslopes), and determined how much each constituent contributed to REI. We found that REI and morphological characteristics decreased moving from the upper portion of road segment downward, implying that rills developed more intensely uphill. Additionally, REI increased exponentially with rill width, density, and severity of fragmentation, and increase linearly with length and depth. Conversely, REI decreased exponentially with rill width-depth ratio. These relationships suggest that the morphological characteristics of rills could be used to predict the REI of a given road segment. Finally, we found that the road characteristics that best predicted rill formation included catchment area, cutslope area, and gravel bareness. Correspondingly, the upslope catchment, cutslopes, and road surface contributed 11.56%, 30.83%, and 8.23% of the variation in REI and morphological characteristics. The interaction between upslope catchment and road surface explained 19.89% of the variation. These results suggest that when best management practices are implemented to decrease erosion caused by forest roads in mountainous watersheds, they should integrate these hydrological constituents of a road.

The Influence of Short-Term Heavy Rainfall on Hydraulic Characteristics and Rill Formation in the Yuanmou Dry-Hot Valley.

Rill erosion is one of the major environmental problems in the world; it is an important factor with regard to land degradation and has a serious impact on production and daily life in the region. The widely distributed Yuanmou group stratum promotes the development of rill erosion, whereby the strong time-concentrated rainfall and the alternating arid-humid climate prepare the ground for the development of rills in soils. Therefore, a study of the processes of slope rill erosion was carried out, and a gravel-soil slope in the Yuanmou dry-hot valley was chosen to simulate short-term heavy rainfall (25 mm/h) (No. 1 plot) and moderate rainfall (15 mm/h) (No. 2 plot), to study the erosion processes of soil and the dynamic characteristics of runoff involved in erosion. The study results showed that the width of runoff was significantly different between the two plots, while the depth of runoff was not significantly different. During the rill formation process, the width of the two plots first decreased and then increased with increasing washout duration, while its depth did not change significantly. Flow was the key factor in determining the hydraulic characteristics of runoff, and it had a significant or extremely significant positive correlation with hydraulic characteristics parameters, except in the case of Fr (Froude number) (r = 0.039). The total sediment content (CS) of plot No. 1 (0.158 g/cm3) was significantly different from that of plot No. 2 (0.153 g/cm3), and both CSs in the two plots decreased with increasing washout duration. The CS had an extremely significant negative correlation with τ (runoff shear force) (r = -0.863 **) and DW-f (Darcy-Weisbach drag coefficient) (r = -0.863 **) and a significant negative correlation with Re (Reynolds number) (r = -0.735 *) in the short-term heavy rainfall experiment, while the CS had a significant positive correlation with V (velocity) (r = 0.814 *), R (hydraulic radius) (r = 0.811 *) and P (unit stream power) (r = 0.811 *) in the moderate rainfall experiment. The results of this study will help guide further examination of the processes involved in the dynamic mechanisms of rill erosion on slopes under short-term heavy rainfall conditions.

Comparison of three land evaluation systems in capability assessment of soils of coastal plains sand in Southeastern Nigeria

Land evaluation systems vary in approach and have not always produced good results outside regions where they were originally conceived. To test the extent of their agreement, Land Capability Classification (LCC), Fertility Capability Classification (FCC), and Suitability Rating were combined in physically evaluating soils of Coastal plains sand, Imo State, Nigeria, using data from 20 pedons. With respect to LCC, soils of inland valleys were limited mainly by wetness, which had 2 out of 6 profiles of the unit classified beyond the arable. The well-drained upland soils, all of which fell within the arable classes, were subject to sheet and rill erosion. By standards of FCC, soils were limited by ‘g’ - water logging; e - low ability to retain nutrients; i - potential fe - toxicity; k - low nutrient capital reserves. Based on suitability rating, soils potentials for agriculture varied from poor to good. Results of LCC and FCC correlated significantly (r = 0.771), but none of these correlated with suitability ratings of the soils. Use of the international systems should be augmented with further soil tests some of which may be got from other comparable systems so as to capture other locally important environmental details. Subjecting factors identified by FCC to suitability rating improved evaluation procedure. Land use in the location did not strictly consider the capability of the land. Cultivating rice to the wet soils or draining them, contour cultivation on slopes, adequate fertilization of soils are recommendations to improve land management.

Mapping rill soil erosion in agricultural fields with UAV‐borne remote sensing data

AbstractSoil erosion by water is a main form of land degradation worldwide. The problem has been addressed, among others, in the United Nations Sustainability Goals. However, for mitigation of erosion consequences and adequate management of affected areas, reliable information on the magnitude and spatial patterns of erosion is needed. Although such need is often addressed by erosion modelling, precise erosion monitoring is necessary for the calibration and validation of erosion models and to study erosion patterns in landscapes. Conventional methods for quantification of rill erosion are based on labour‐intensive field measurements. In contrast, remote sensing techniques promise fast, non‐invasive, systematic and larger‐scale surveying. Thus, the main objective of this study was to develop and evaluate automated and transferable methodologies for mapping the spatial extent of erosion rills from a single acquisition of remote sensing data. Data collected by an uncrewed aerial vehicle was used to deliver a highly detailed digital elevation model (DEM) of the analysed area. Rills were classified by two methods with different settings. One approach was based on a series of decision rules applied on DEM‐derived geomorphological terrain attributes. The second approach utilized the random forest machine learning algorithm. The methods were tested on three agricultural fields representing different erosion patterns and vegetation covers. Our study showed that the proposed methods can ensure recognition of rills with accuracies between 80 and 90% depending on rill characteristics. In some cases, however, the methods were sensitive to very small rill incisions and to similar geometry of rills to other features. Additionally, their performance was influenced by the vegetation structure and cover. Besides these challenges, the introduced approach was capable of mapping rills fully automatically at the field scale and can, therefore, support a fast and flexible assessment of erosion magnitudes.

Flow-driven soil erosion processes in a calcareous semiarid soil: Rill length and flow rate impacts

Understanding the dynamic mechanisms of rill erosion is vital for accurately modeling of soil erosion. In this research, rill erosion was experimentally studied using different rill lengths. A flume, 11 m long and 0.2 m wide adjusted to 3% slope, was used for constructing rectangular rills of 0.05 m width and six different lengths (1 to 12 m). The experiments were carried out on a clayey calcareous soil from a semiarid region under two flow rates of QL = 0.025 and QH = 0.045 L s−1. Temporal sediment concentrations (C) were measured at the rill outlet for 40 min and the sediment size distribution (PSD) was recorded twice during each test. The common decreasing trend of C was affected by both flow rate and rill length. The formation of head-cuts along the bed of long rills was an important erosion process affecting C and PSD. The compiled data were used to determine the exponential models' parameters of both C and soil detachment rate based on the steady, unsteady, and event-average values. While, the equilibrium sediment transport occurred by increasing rill length beyond 7 m under QL, the tested rills under QH were not sufficiently long for the flow to reach its maximum transport capacity at the gentle slope used and for the calcareous soil tested. Based on the sediment PSD, the selective transport of coarse particles was evidenced. Selectivity transport was affected by rill length reached its maximum at the rill length of 7 m.The findings provides better understanding of rill erosion processes for calcareous soils on gentle slopes in semiarid regions. Further research is needed for better understanding of the rill erosion processes on short gentle slopes to provide experimentally supports for the existing theoretical concepts of rill erosion models.

Determining the mechanism of the root effect on soil detachment under mixed modes of different plant species using flume simulation

Soil detachment is the separation and dislodgment of soil particles from a soil mass by the force of raindrops and flow, which is also the initial process of soil erosion. Plant roots have significant effects on the soil detachment rate (SDR). Current studies have mainly focused on root effects on the SDR under single species. Because it is difficult to identify the roots of different species in mixed-plant areas, few studies have evaluated the root effects on the SDR under mixed-plants. Natural, undisturbed soil samples containing roots were collected from four natural sampling plots with single plant types, and six natural sampling plots with mixed plant types. Bare soil was used as the control. The samples were subjected to flow scouring through indoor hydraulic flume experiments under six shear stresses (3.65, 7.28, 7.67, 8.59, 10.15, and 12.19 Pa). The results showed that the root reduction effect on the SDR under the mode of tap roots mixed with fibrous roots was 55.54 % weaker than that the mode of fibrous roots mixed with other fibrous roots. When fibrous roots were mixed with tap roots, the fibrous roots indirectly affected the SDR through soil mechanical properties, while the indirect path of the tap roots on the SDR was not unique. However, the indirect effect of roots on the SDR was weaker than the direct effect. The mixed roots affected the SDR mainly by rill erodibility, not critical shear stress. The variation in rill erodibility at the mixed root sites was similar to the SDR variation at those sites. The mode of grasses with fibrous roots mixed with other grasses with fibrous roots was considered as better for soil and water vegetation conservation.

Erosion Failure of Slope in a Dump with Ground Fissure under Heavy Rain

The dump, with the compact rock platform and high and steep loose slope that is formed during coal mining, is the most serious area of soil erosion in a surface coal mine. Ground fissures are a typical geological hazard in coal mining areas. However, the effect of ground fissures on soil erosion remains unclear. Rainfall experiments were conducted to determine the varying characteristics of wetting front, runoff and sediment production, and soil denudation rate, as well as the effects of ground fissures on these factors in a platform-slope system of a dump. Ground fissures could significantly enhance wetting front and soil erosion. Rill erosion was formed as the rainfall and runoff flushed the soil, which eventually developed into erosion gullies. Erosion failure modes with platform-slope systems in the dump could be divided into the surface erosion stage, fissure deformation stage, rill erosion stage, fissure collapse-rapid increase stage, and stable stage. Runoff power and flow shear stress had the greater influence on soil denudation rate, which indicated that erosion energy of concentrated flow had important influence on soil erosion. Moreover, shallow mudflow induced by rainfall was one of the forms of soil slope instability; it occurred in a short time with great soil erosion. Soil erosion in the dump with ground fissures was mainly shallow mudflow and rill erosion, resulting from the combined effect of hydraulic erosion and gravity erosion.

Calibration, validation, and evaluation of the Water Erosion Prediction Project (WEPP) model for hillslopes with natural runoff plot data

The Water Erosion Prediction Project (WEPP) model has been widely used for estimating runoff and soil loss. The evaluation of the latest version (version 2021.133) under a range of environmental conditions can provide confidence to its users. The objectives of this study were to evaluate the WEPP model for runoff and soil loss predictions using 1159 plot years of rainfall-runoff events data from field experimental plots with various climates, soils, topographies, and crops. WEPP runoff and soil loss predictions were compared to the observations before and after input parameter calibration. The results showed good predictions of runoff and soil loss were obtained with both the uncalibrated and calibrated WEPP model for all considered scales with Nash-Sutcliffe model efficiencies (NSE) over 0.4. The calibration of input baseline effective hydraulic conductivity (ke), baseline critical shear stress (τc), baseline rill erodibility (kr), and baseline interrill erodibility (ki) improved WEPP model performance with NSE values of 0.98 and 0.91 for average annual runoff and soil loss predictions, respectively. The WEPP model tended to underestimate the runoff and soil loss for large events with runoff over 100 mm and soil loss over 120 t/ha. Good event runoff and soil loss predictions (NSE ≥0.4) were obtained for the most common cropping/management systems considered, including corn, cotton, tilled fallow, and wheat after calibration. This study illustrates the most recent WEPP model's performance for runoff and soil loss predictions, and provides a comprehensive set of results.

An experimental investigation of the erosion process and morphological characteristics of the tile-back type slope with non-uniform slopes based on a 3D reconstruction method

Tile-back type slopes comprise ephemeral gullies (EGs) and hillslopes; they are a unique and widely distributed micro-landform in the Loess Plateau region of China. Gully erosion from these landforms is a serious issue, but the micro-landform makes the erosion process and its estimation complex. Quantifying soil erosion processes and their distribution characteristics at different positions on tile-back type slopes will provide a clearer picture for ecological restoration to control further soil degradation. This study investigated the erosion process of tile-back type slope with non-uniform slopes using a 3D photo-reconstruction method during eight successive simulated rainfall events. The results showed that EG erosion began with a chain of intermittent headcuts. When the accumulated rainfall reached 76 mm, serious collapses dramatically increased the amount of sediment by 216% after the first rainfall (cumulative rainfall was about 15 mm). We quantified the sediment contribution of EG erosion (46.20%), rill erosion (35.62%), and inter-rill erosion (18.18%) to total soil loss. The erosion area of the steep slope section and extremely steep slope section accounted for 33.26% and 66.74% of the total erosion area, respectively. Moreover, sediment amounts significantly correlated with morphological parameters, particularly the amount of EG erosion and maximum gully depth, with a correlation coefficient of 0.98. Cumulative gully length and erosion area had the greatest effect on rill erosion, with a correlation coefficient of 0.97. These results provide insight into the qualitative and quantitative understanding of EG erosion process on Loess Plateau of China and an important reference for the rational arrangement of EG control measures.

A comparative experimental study of rill erosion on loess soil and clay loam soil based on a digital close-range photogrammetry technology

Accurately describing rill development is important for building physical process models of soil erosion. The objectives of this study were to investigate the evolution processes of rill erosion morphology, their impacts on runoff and sediment yield, and the relationship between flow hydraulic characteristics and rill erosion dynamic mechanisms on slopes of two soil types, namely, clay loam soil (CLS) and loess soil (LS), under two successive rainfall events at a rainfall intensity of 120 mm h−1. We used digital close range photogrammetry technology to obtain overhead images of two experimental soil bins (5 m long, 1 m wide and 0.5 m deep with a slope gradient of 20°) at 5-minute time intervals to monitor the dynamic processes of rill erosion. The results showed that rill erosion processes exhibited important impacts on sediment and runoff and its hydrodynamic characteristics. Compared with LS, runoff formed and rills developed earlier in the CLS slope. Soil with high clay content was more prone to form rills, but less susceptible to severe soil erosion than LS. Once rills began to develop in LS, soil loss increased and the morphology of rills changed rapidly, as did runoff rate. The flow velocity for the two soils decreased gradually with time and increased along the flow direction. The trend of Froude number (Fr) decreased with time, whereas the Darcy-Weisbach resistance coefficient (f) exhibited an opposite trend. The Reynolds number (Re) of LS increased first and then decreased, while Re of CLS decreased gradually with time. Sediment yield and runoff were positively correlated with f, but significantly negatively correlated with Fr. Moreover, Re was significantly negatively correlated with sediment yield, but not with runoff. These results are of great importance for soil loss prediction.

Quantifying the importance of different erosion processes and soil and water conservation measure collapses following an extreme rainstorm in the Chinese Loess Plateau

AbstractExtreme rainfall events can make disproportionally larger contributions than common rainfalls to soil erosion rates. Yet assessing the importance of different soil erosion processes during such events remains a critical challenge, especially due to a lack of field observations. Based on detailed field surveys and remote‐sensing analyses, we therefore provide erosion budgets for three representative catchments in the Chinese Loess Plateau, following an exceptional rainstorm event (July 26, 2017; estimated return period: 200 years). Our results show that the associated catchment‐scale erosion intensities were 2815 ± 529 t km‐2 for rill erosion, 787 ± 486 t km‐2 for gully erosion, 4433 ± 657 t km‐2 for landsliding and 3927 ± 1009 t km‐2 for the collapse of implemented soil and water conservation measures (SWCMs, specifically terraces and check‐dams). Hence, landslides (37 ± 4%) and SWCMs collapses (33 ± 4%) were the most important sediment sources, followed by rill (24 ± 3%) and gully erosion (7 ± 4%). The lower contribution of gully erosion likely results from earlier vegetation restoration efforts. Overall, our results indicate that successful erosion control during extreme events strongly depends on integrative and robust catchment management strategies. Specifically, the spatial intersecting of forestland and grassland can play a large role, with reforestation on problematic slopes being an important strategy limiting rill and gully erosion. Sufficient consideration should be given to the planning and maintenance of terraces and check‐dams. The latter should be constructed with good flood‐release facilities, meanwhile many small‐scale dams likely work better than a few large ones. Likewise, (unpaved) roads should receive attention as they can also be a significant runoff and sediment source.

Quantifying the sheet-rill erosion process along a saturated soil slope

The sheet and rill erosion process on a saturated soil slope is different from that on an unsaturated soil, resulting in different erosion masses. Nevertheless, few studies have investigated sheet erosion and rill erosion along a saturated soil slope. Quantifying and comparing erosion masses of sheet and rill erosion along a saturated soil slope are important to understanding soil erosion mechanisms and control soil loss. Based on indoor soil flume simulated rainfall experiments, the erosion process characteristics from sheet erosion to rill erosion were studied, and the erosion masses were measured under combined conditions of different rainfall intensities (30, 60, and 90 mm/h) and slope gradients (2°, 5°, 10°, 15°, and 20°). The fitting method of sheet erosion (FSM) and an analytical method of rill erosion (ARM) were utilized to determine the erosion mass in different erosion stages from sheet to rill erosion. The results showed that the FSM and ARM methods were applicable to estimate erosion masses during the erosion process from sheet to rill erosion. The relationship among the rainfall intensity, slope gradient and erosion mass in the sheet erosion and rill erosion states could be expressed by a power function. The erosion masses in the sheet and rill erosion states were more sensitive to the rainfall intensity than to the slope gradient. Furthermore, the erosion masses in the rill erosion state were approximately 2.31–5.42 times higher than those in the sheet erosion state under the combined conditions of three rainfall intensities (30, 60, 90 mm/h) and five slope gradients (2°, 5°, 10°, 15°, and 20°). Relatively higher slope gradients and rainfall intensities corresponded to greater amplitudes of the variation in erosion masses in the sheet and rill erosion states than those under relatively lower slope gradients and rainfall intensities. The results provide simplified and accurate experiments and methods for quantifying erosion masses in different erosion stages between sheet and rill erosion and clarifying the erosion process from sheet to rill erosion.

Response of rill erosion to rainfall types and maintenance on the Loess Plateau: Implications for road erosion control

Although road erosion represents a threat to regional environmental and ecological security, limited evidence exists regarding the relationship between road erosion, rainfall, and road maintenance. In this study, we investigated the effects of different rainfall types on rill erosion and the degree of rill dissection of roads involving petroleum transportation and agricultural production in the hilly and gully region on the Loess Plateau of China from 2019 to 2021. During this period, 30 natural rainfall events occurred that were classified into four rainfall types using K-means clustering analysis.The results indicated that road erosion caused by large amount of rainfall with high intensity (LH-R) was 4.31, 3.82, and 3.48 times higher than that with small amount of rainfall with high intensity (SH-R), small amount of rainfall with low intensity (SL-R), and large amount with low intensity (LL-R), respectively. This highlighted the devastating impact of the LH-R on road erosion (the most severe of all types), with an average erosion rate of 527.04 t ha−1. Road erosion caused by SL-R events (most frequent) during the rainy season also deserves attention because of its cumulative impact on rill erosion. Moreover, compared to bare runoff plots and sloping farmlands, unpaved roads experienced a greater erosion rate due to upslope drainage areas and frequent human disturbance. In addition, the drainage system mitigates road erosion under LH-R, thereby reducing the average erosion rate by 56.42 %. We also found that road rehabilitation impedes the development of rills and diminishes the rate of road erosion compared to road segments without road rehabilitation.Collectively, the effects of rainfall types and maintenance activities on road erosion were assessed. The findings indicate that strengthening water and land management of upslope drainage areas, complementing the drainage system of unpaved roads, maintaining appropriate maintenance activities, and promoting vegetation coverage on the downslope of roads mitigate the resistance of unpaved roads to LH-R.

Effect of Rill Development on Slope Erosion and Sediment Yield Based on Stereophotogrammetry Technology

Rill erosion is an important kind of slope erosion and the main source of sediment. Through simulated rainfall tests, the morphological characteristics of rill were quantified by stereophotogrammetry technology, and the relationship between rill development and sediment yield was studied. The results show that there was a positive correlation between sediment yield and slope and rainfall intensities. With the increase in rainfall duration, sediment yield first increased sharply and then decreased gradually after reaching the peak value, until it reached dynamic stability. With the increase in rainfall intensity and slope, the length, width, and number of rills increased significantly, with a maximum length of 2.58 m and a maximum width and depth of 9.7 and 2.2 cm. The rill density (RD) increased from 16.67% to 62.65%; rill fragmentation degree (RFD) increased from 16.67% to 100.00%; rill complexity (RC) increased from 10.62% to 30.84%, and rill width–depth ratio (RWDR) decreased from 15.82% to 56.28% with the increase in slope from 6° to 15° and rainfall intensity from 2.0 to 3.0 mm/min. There was a good nonlinear relationship between sediment yield and RC and RWDR (R2 = 0.89, NSE = 0.85, n = 10). This study could provide help for the quantification research of rill erosion mechanisms and provide reference for the measurement and scale transformations of soil erosion at different scales.

Influence of topography on the asymmetry of rill cross-sections in the Yuanmou dry-hot valley

Rill erosion is one of the most common types of erosion, and the development conditions of the asymmetric characteristics of rill cross-sections are still relatively poorly understood. To explore the relationship between rill topography and rill cross-sectional asymmetry, we used the microtopographic profiler method to measure 712 groups of rill cross-sections in the Yuanmou dry-hot valley area. The results of correlation analysis and principal component analysis to investigate the topographical conditions of rill development show that: (1) asymmetry is the main feature in rill cross-sections; 53% of rill cross-sections are right-biased and 47% are left-biased. (2) There is an extremely significant positive correlation between the slope difference and the rill cross-section asymmetry ratio (p < 0.01); the asymmetry ratio increases as the slope difference on both sides (B) increases, and the directionality of the asymmetry ratio is affected by B. The difference between the catchment areas on both sides has a significant linear correlation with the asymmetry ratio of the width (r = 0.07, p < 0.05). (3) Seven topographic factors were divided into two types of principal components: the first represents the rill slope surface shape and the rill shape, and the second represents the difference between the two sides of the rill.

Land‐use change impacts on soil and vegetation attributes in the Kanshi River basin, Potohar Plateau, Pakistan

AbstractSoil erosion and land degradation have intensified recently, resulting from large‐scale land‐use and land cover (LULC) change, deforestation and farm mechanization. This phenomenon motivates the rationale for the assessment of such land‐use changes and their impacts on soil and vegetation in the Kanshi River basin using various remote sensing techniques between 1987–2019. The image classification enabled the identification of dry and highland zones. It was observed that around 17% of natural vegetation cover disappeared and was converted into agricultural land. Significant increase in extensive agricultural practices, population growth, settlement, and the brick industry have increased soil erosion and changed the landscape of the Kanshi region during 1987–2019. Further, we classify gully erosion, rill erosion, sprinkle erosion, and sheet erosion have all been found at rates of 43%, 27%, 9%, and 21%, respectively. Similarly, soil classes in 2019 were doubled, with Sambrial association (1%), Rajar complex (36%), Dhulian association (15%), Gullied (15%), Missa complex, Rough mountainous (2%) and Rough broken (17%), compared to four classes in 1987: Gullied, Missa complex, rough broken land, and Torrent bed land. Whereas in 1987, four types of soils were observed. The recorded soil series had a limited water holding capacity and were well drained. Soil erosion is a natural and inevitable phenomenon; however, its intensity can be reduced by appropriate water resource management in this basin.

Experimental research on sediment transport processes affected by frozen layer and stone content

Rill erosion on frozen-stony slope in high-altitude or high-latitude areas commonly undergo freeze–thaw cycle, which is significantly influenced by partially thawed soil with rock fragment. This research aims to investigate the influences of thawed soil depth (TSD) and rock fragment content (RFC) on rill erosion and quantifying the mathematical relationships among them. The laboratory experiment is conducted to evaluate the influences of TSD (1, 2, 5, and 10 cm) and RFC (0%, 10%, 20%, and 50%) on sediment delivery processes by concentrated meltwater flow under three slope gradients of 5°, 10°, and 15°, and three flow rates of 1, 2, and 4 L min−1 at nine rill lengths from 0.5 m to 8.0 m. Five runoff samples are obtained from each experiment run and used to calculate sediment concentration (SC). The SC increases linearly and then exponentially with rill length to approximate the extremum and fits well with piecewise functions. Restrictive effect of TSD and RFC on sediment supply is evident during linear stage induced by shallow TSD, which keeps a long distance under shallow TSD and low RFC to collect sufficient sediment for exponential period. However, TSD and RFC impacts become apparent during the exponential period and lead to higher sediment yield with RFC of 10% and 20% than that on totally thawed soil without rock fragment. In this research, the positive effect on sediment yield increases with RFC increases from 10% to 20%, which may need to be eliminated for efficiency in erosion control. In contrast to low RFC, the protection impact of rock fragment always exerts with RFC of 50%. The experimental data and the functional relationship can provide the basic knowledge for evaluating the model parameters such as soil detachment rate and erodibility of rill erosion on frozen-stony slope.

Relationship between soil erodibility by concentrated flow and shear strength of a Haplic Acrisol with a cationic polyelectrolyte

To clarify the relationship between rill erodibility in an excess shear stress model for concentrated flow erosion and soil particle–particle interactions, we examined the rill erodibility and aggregation-dispersion behavior of Shimajiri Maaji soil, classified as a Haplic Acrisol, with different amounts of cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC). The effect of particle–particle interaction on rill erodibility was determined by performing shear strength measurements and rill erosion experiments as a function of the PDADMAC dose without changing other soil conditions. Moreover, the mechanisms of particle–particle interactions were examined by comparing the electrophoretic mobility (EPM) with the transmission of the supernatant of the soil suspension and soil shear strength. The EPM and transmission showed that the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction governed the aggregation-dispersion behavior. At the same time, the shear strength monotonically increased with increasing PDADMAC dose, even when charge reversal and electric double layer (EDL) repulsion occurred. This result suggests that the shear strength is sensitive not only to the EDL interaction but also to the interactions, the so-called non-DLVO forces, such as bridging interaction. The difference between transmission and shear strength should be due to the difference in the characteristic length because the transmission is attributed to the collision/approaching process between particles, whereas the shear strength is attributed to the broken/retracting process of particle–particle contact. Rill erodibility decreased with increasing shear strength. Furthermore, our quantitative analysis demonstrated that rill erodibility can be represented by a linear function of shear strength. These results clearly show that a high attractive force between soil particles results in low rill erodibility. The strong particle–particle attraction protects soil particles from peeling off by increasing the shear stress of the flowing water. Our study suggests that shear strength measurement can be used to quickly estimate the effect of soil conditioners on rill erodibility in the field.