Development Of Rill Erosion Research Articles

Characteristics and dynamic mechanism of rill erosion driven by extreme rainfall on karst plateau slopes, SW China

Driven by climate change and increased human activities, the frequency and intensity of extreme rainfall events are increasing, leading to increased risk of water erosion on slopes in karst rocky desertification (KRD) areas. However, the driving factors (rainfall intensity, slope gradient, and the degree of underground fissure pore), characteristics, and dynamic mechanisms of rill erosion on KRD slopes under extreme rainfall have received limited attention. A rainfall simulation experiment was performed to investigate the driving factors of rill erosion on KRD slopes under extreme rainfall events. The experiments were conducted using an erosion flume (4 m long, 1.5 m wide and 0.35 m deep) with five rainfall intensities (50, 105, 115, 125 and 145 mm·h−1), three-level slope gradients (5°, 15° and 25°), and three typical degrees of underground pore fissure (1 %, 3 % and 5 %). The results showed that extreme rainfall significantly stimulated the formation and development of rill erosion on KRD slopes. In particular, rainfall intensity and slope gradient significantly affected rill erosion (p < 0.05), whereas the degree of underground pore fissure did not have any distinct effect. Increasing rainfall intensity intensified rill erosion by significantly (p < 0.05) promoting the rill density, total rill surface area, and longest of rill length. With increasing slope gradient, the rill density, rill distribution density, and average rill depth significantly increased (p < 0.05). Moreover, extreme rainfall events exacerbated surface soil erosion by enhancing the hydrodynamic characteristics of slope runoff. Rill erosion was most sensitive to the shear stress of runoff, and rill density was found to be the most suitable rill index for describing surface soil erosion on the slope under extreme rainfall. The findings provide valuable insights into the characteristics and mechanisms of soil erosion in karst regions under future climate warming.

Effects of rock outcrops on runoff and erosion from karst slopes under simulated rainfall

AbstractRock outcrops play a crucial role in affecting hydrological and erosion processes on karst hillslopes. However, due to various difficulties in constructing runoff plots on field rocky slopes, previous studies used small metal flumes to simulate outcropped slopes, which greatly differed from the natural rock outcropped slopes. In this study, the effects of rock outcrops on runoff and erosion were studied on karst slopes with natural soil–rock conditions at a larger plot scale (10 m in length × 2.2 m in width, 25° in gradient). Simulated rainfall experiments were conducted on the four runoff plots with different rock outcrop coverages (0%, 5%, 13%, and 42%) under five rainfall intensities (30, 60, 90, 120, and 150 mm·h−1). The study indicated that the rock outcrops complexed the water erosion processes by playing multiple and opposite roles simultaneously. It positively influences water erosion by serving as impermeable surfaces, providing preferential flow paths, and offering flow barriers to hillslopes. Conversely, it can exacerbate erosion by causing increased runoff, concentrating flow paths, and thus intensifying erosion in specific areas. Besides, the effects of these roles varied with the coverage of rock outcrops and rainfall intensity. The main results showed that (i) limited rock outcrop coverage (5% and 13%) increased runoff and erosion, but the opposite was observed on the severe rocky slope (42%). Both “infiltration‐excess” and “saturation‐excess” mechanisms coexisted by turns on karst slopes during rainfall; the break of “saturation balance” tended to occur on the severe rock outcrop slope with abundant soil–rock interface and underground fissures. (ii) Rock outcrops greatly increased the spatial variability and uncertainty of hydrological and erosion processes on karst slopes. The rock outcrops resulted in a larger range of variation in flow velocity and a greater difference among the three slope positions; it also brought more spatial heterogeneity in the development of rill erosion. (iii) Rock outcrops tended to increase flow velocity, and intensify flow turbulence, stream power, and flow energy. The severe rock outcrops significantly reduced the soil erosion induced by the limited soil detachment. This study contributes to a deeper understanding of the mechanisms behind how rock outcrops influence runoff and erosion and provides insights for improving soil erosion prediction in karst regions.

Upslope inflow-driven variations in microtopography and size fractions effect on rill erosion in purple soil hillslopes

Upslope drainage area contributing inflow to downslope rill erosion can be affected by the dynamics of eroded sediment and soil surface microtopography. However, limited information has previously not recognized the variation of the sediment particles and microtopography on hillslopes where upslope inflow perpetually exists. A series of scouring flume experiments were performed on a 15° slope under upslope inflow rates (4, 6 and 8 L min−1) to investigate the inflow-driven microtopography and sediment particle-size distribution (PSD) during the rill erosion process. The results indicated that the surface elevation decay mostly occurred in the later stage of rill erosion. The spatial variability of microtopography increased gradually with increasing inflow rates, and obvious microtopography sharpness intensified with the development of rill erosion. The surface runoff under the 8 L min−1 inflow rate increased by 15.03 % and 90.14 % for 6 and 4 L min−1, respectively, and the sediment yield reached a maximum at the rill stabilization stage (RS). The overall particle-size distribution was mainly composed of silt-sized particles, accounting for approximately 40.97 %−50.15 % of the total eroded sediment. Considerable depletion of clay fractions occurred in the rill erosion process. High inflow rate significantly enhanced variation amplitude of critical hydrodynamic parameters (e.g., flow velocity, flow shear stress and Reynolds number). The spatial heterogeneity of microtopography was correlated with the coarser fraction of sediment PSD in rill erosion, suggesting that erosion processes were affected by the interaction between eroded sediment distribution and roughness. These findings highlight the importance of the PSD of eroded sediment and the development of soil surface structure for an in-depth understanding of the purple soil erosion mechanism at the hillslope scale.

Multi-temporal spatial modelling to assess runoff and sediment dynamics under different microtopographic patterns

Soil erosion is a multi-scale geographical interface process with high spatiotemporal variability. This study aimed to assess runoff and sediment dynamics under different microtopographic patterns based on wavelet analysis and SIMulated Water Erosion model (SIMWE). Three rainfall intensities of 1.0 mm min−1, 1.5 mm min−1, and 2.0 mm min−1, combined with three slope gradients of 10°, 15°, and 20°, were utilized to conduct rainfall simulations on three soil boxes measuring 4 m in length and 0.8 m in width. The soil boxes exhibited distinct microtopographic patterns, including smooth slope (CK), artificial digging (AD), and ridge tillage (RT). The results showed that the runoff and sediment reduction benefits of different tilled slopes decreased with an increase in both slope and rainfall intensity. The AD and RT slopes reduced runoff yields by 8.4% − 50.2% and 17.3% − 75.0% respectively compared to CK slope. Although sediment yields from AD and RT slopes were reduced by 4.2% − 51.6% and 1.8% − 53.0%, respectively, the sediment control benefits of AD and RT slopes were basically lost when the slope gradient increased to 20°. The rill erosion was the main source of soil erosion on different tilled slopes, accounting for 72% − 87% of the total soil loss. And the rates of both soil erosion and rill erosion exhibited a power function relationship with an increase in rainfall intensity and slope. The impact of slope gradient on soil erosion on the RT slope was greater than those on the CK and AD slopes. During the development of rill erosion, non-stationary and multi-scale periodic phenomena exist in the time series of runoff and sediment on different microreliefs. As surface microrelief increased, the fluctuations in runoff and sediment on tilled slopes intensified, resulting in a gradual shortening of the variation period. And this study verified the feasibility of the SIMWE model to simulate the runoff and sediment dynamics on microtopographic scale under a single rainfall event. The results can provide a theoretical basis for the scientific layout of soil and water conservation practices in sloping farmland and the construction of soil erosion model in purple soil area.

Development of rill erosion on bare sloping farmland under natural rainfall conditions

Rill erosion plays an important role in soil erosion, and studying this process can provide a basis for controlling soil loss on sloping farmland. The objectives of this study were to observe runoff and sediment transport processes during two continuous and two intermittent natural rainfall events and to monitor the changing morphological characteristics of rills within a standard runoff plot of bare soil (20 m length, 5 m width, and slope of 10°) at five successive observation times. We found that the processes of runoff and sediment transport presented a pattern with multiple peaks during continuous rainfall events and with a single or two peaks during intermittent rainfall events. The peak runoff and sediment yield rates exhibited a time-lag phenomenon of 1‒12 min compared with instantaneous rainfall intensity. Rills occurred as strip-shapes, V-shapes, and with a tree-branch-like distribution; their widths were mainly 5–20 cm and their depths 0–10 cm. Compared to our initial rill observation, the mean rill length, width, and depth increased by 227%, 26%, and 6%, respectively, after four subsequent rill observations over a period of almost one month. Side-wall collapse erosion was greater than downcutting erosion on the middle slope (section II; 6.67–13.34 m), while rill depth reached a minimum value on the lower slope (section III; 13.34–20 m). These findings help us to understand bare slope runoff and erosion mechanisms and provide a scientific basis for soil erosion modeling of sloping farmland.

An evaluation of erosion in cuesta relief: São Paulo State, Brazil

Cuestas are relief features whose evolution has traditionally been attributed to erosion processes. They are habitually studied in many regions of the world. In Brazil, however, studies of erosion processes in cuestas are uncommon, despite the presence of this type of relief in several parts of the country. The aim of this study was to identify relevant correlations between local geographical conditions and physical-hydrological properties of the soil, and to identify the prevailing factors in the development of rill erosion, ravines and gullies in cuestas. We analyze various physical properties of the soil, including grain size, resistance to penetration, permeability and infiltration rates. The geographic variable slope was also considered. The data variables were processed using geostatistical techniques (ordinary kriging) and statistics (factor analysis). The results show that data referring to grain size, soil resistance to penetration and infiltration present statistically significant differences and can be used to assess the spatial distribution of erosion landforms. Details of the behavior of clays and the transitions between the clayey and sandy sector also helped to understand the location of erosion landforms. The steep morphology of the cuestas, associated with the presence of lithologies of varying resistance, generates different soil types, even in small catchments. These differentiations contribute to the development of erosion features and generate gullies covering large areas and whose evolution is difficult to explain. Thus, the study of erosion in cuesta lands is necessary and should be expanded in Brazil. The methodology used in this study has the potential to be applied to other catchments, and can thus contribut to the study of erosion processes in cuestas.

Development of rill erosion and its simulation with cellular automata-rill model in Chinese Loess Plateau

ABSTRACT Rill erosion has serious impacts on arable soils in Chinese Loess Plateau. It is imperative to clarify the key processes of rill erosion to implement effective soil conservation practices. In this study, rill erosion on a 26.8% slope was evaluated using a Terrestrial Laser Scanner (TLS) and CA-Rill model under simulated rainfall. The results showed that (1) the TLS method and the CA-Rill model could effectively describe slope erosion processes, including the splash and sheet erosion, drop pits, intermittent rills, and rill network development stages; (2) compared with the traditional method, the average error of the CA-Rill model for estimating runoff and soil loss was 6.8% and 26.8%, respectively, the CA-Rill model could accurately simulate runoff processes, but poorly simulated sediment processes, especially in splash and sheet erosion stages; and (3) rill erosion evolved into the dominant erosion pattern after 30 min of rainfall, then rill morphological parameters – rill plane density, average rill depth, maximum rill length, and average rill width enlarged, and increased by more than 3.7, 1.8, 2.9, and 4.0 times by the end of rainfall. The methods used to estimate sediment yields and the variation of morphological parameters could provide reference for soil erosion monitoring and modelling.

Quantifying the contributions of soil surface microtopography and sediment concentration to rill erosion

Soil surface microtopography plays a significant role in rill erosion. In addition, upslope inflow has a large effect on downslope soil erosion processes. Experiments including four different upslope filling areas (0 m2, 0.15 m2, 0.30 m2, and 0.45 m2) with a upslope inflow rate (6 L min−1) were conducted in two 1 m × 2 m boxes on a 15° slope to examine the effects of microtopography and sediment concentration on rill erosion processes. The upslope filling areas were used to simulate different areas of earthen dike terraces. The results showed that the minimum values of soil surface elevation increased from −120 mm to −110 mm as the upslope filling area increased. The values of the simple fractal dimension (f(α)max), the singular index span (Δα) and the difference of multifractal spectrum (Δf(α)) reached minimum values in the 0.45 m2 upslope filling area. With the development of rill erosion, the soil surface microtopography tended to sharpen, and the relative elevation changed greatly. The runoff and soil loss associated with rill erosion gradually decreased as the upslope filling area increased. We identified the temporal evolution of rill erosion using Morlet wavelet analysis. The main period of temporal fluctuation of rill erosion was 28 min under different upslope filling areas. Multi-scale periods of temporal fluctuation of rill erosion emerged with the increase in upslope filling area. The Δα significantly affected the runoff and soil loss. The proportional contributions of Δα to the runoff and sediment yield were 80.95% and 77.34%, respectively. While the contributions of sediment concentration to runoff and sediment yield were 17.05% and 20.66%, respectively. The findings are important significance for better understanding rill erosion mechanisms of purple soil.

Micro-topographic assessment of rill morphology highlights the shortcomings of current protective measures in loess landscapes

Due to urban expansion and the rapid development of infrastructure in the loess area of China, artificial earth-fill embankments and excavated slopes are increasingly widespread in recent years. Erosion is typical in such loess slopes; however, quantitative statistical analyses of various counter-measures that affects rill erosion are still lacking. Here, we quantified rill morphology and rill erosion development in two newly constructed slopes with different engineering protection measures. We used high-resolution digital surface models (DSMs) acquired using an Unmanned Aerial Vehicle (UAV) to analyze the case areas during two-time periods. Our results from centimeter accuracy differential DSMs demonstrated that rapid rill erosion is prevalent in the study area, expressed as rill density varying between 2.03 km−2 and 8.81 km−2 at different slope surfaces (viz., erosion protected slopes [EPS], landslide protected slopes [LPS], and unprotected slopes [US]). The slope gradient responsible for rill erosion of the EPS, LPS and US are obviously different, and such information is essential for planning preventive measures in each slope type. At the EPS, the severity of erosion is maximum at the top of the ridges, whereas the gap between reinforced concrete lattice and loess deposits are of serious concern at the LPS. The current engineering measures employed in the study area are thus found ineffective for protection against rill erosion. We therefore propose an improved design by implementing an intercepting drain to the existing design for preventing further erosion.

Effect of conservation structures on curbing rill erosion in micro-watersheds, northwest Ethiopia

Accelerated soil erosion by water is a critical problem in Ethiopia, where population is rapidly growing and extensive farming systems are very common with no or less preventive measures. The study aimed to evaluate effects of conservation structures (terraces) in reducing the magnitude of rill erosion by using rill survey technique at cultivated field scales in relation to crop type and location in hill slope direction of the fields in the Beribere micro-watershed (catchment), northwest Ethiopia. The study assessed factors accelerating rill erosion in the micro-watershed. Rill erosion in the terraced fields was reduced by 53.5% as compared to the non-terraced control fields. In the terraced areas, terracing damage is the main contributing factor to soil loss due to rills. In the non-terraced fields, entering of high erosive runoff from uphill areas and damage of drainage ditches were observed as the principal accelerating factors for initiation and development of rill erosion, whereas these processes had insignificant effect on rill erosion in the terraced fields. Moreover, rill erosion shows spatial differences in terms of crop covers and location in hill slope direction of the study site. Hence, there should be adequate criteria for effective communication between farmers and extension staff to design site-specific erosion control practices for addressing the problem. The study verifies that rill surveying is a significant method to pragmatic assessment of the effectiveness of terracing practices in controlling soil erosion by water.