Raindrop Impact Research Articles

Evaluation of physical erosivity factor for interrill erosion on steep vegetated hillslopes

The process of interrill erosion is complex by interaction of raindrop impact and sheet flow. Their relative contribution to interrill erosion is difficult to be evaluated even on bare soil. This study presents the new erosivity factor to evaluate the interrill erosion on steep vegetated hillslope with the more relevant understanding of the physical processes. The effective energy, the erosivity factor, is defined as the sum of the effective kinetic energy of rainfall and effective potential energy of surface runoff based on the energy balance. The effective kinetic energy of rainfall is determined by the horizontal component for slope of kinetic energy deducting energies dissipated by structure of vegetation canopies and a litter layer. The effective potential energy of surface runoff is equal to potential energy of the available surface water following rain-mass allocations of interception and infiltration. The data from experimental field plots with various vegetation coverage after wildfire were used to verify the effective energy equation. On densely vegetated slopes sediment yield depended greatly on effective kinetic energy of rainfall, while they from hillslopes having sparse coverage were dominated by effective potential energy of surface runoff. The dissipated energy due to interrill erosion showed the highest correlation coefficient with the effective energy under various cover conditions. The kinetic energy of raindrops was greatly reduced by the litter layer and the potential energy of rainwater decreased predominantly due to infiltration. The ratio of effective potential energy of surface runoff to total effective energy was the highest at 71.2% in the plots with low vegetation coverage. The energy efficiency for interrill erosion increased with decreasing vegetation coverage and reached maximum 1.35% in extreme rainfall event under low vegetation coverage. The constant and exponent of power-law functions between the effective energy and the soil erosion work were strongly correlated with gravel ratio and litter coverage, respectively. The results indicate that the effective energy is useful erosivity factor to evaluate the interrill erosion occurred by the complicated interaction of rain splash and sheet flow on vegetated hillslopes.

Physicochemical Properties of an Alfisol under Fallow and Adjacent Forest Lands and their suitability for Cocoyam, Pigeon pea and Sweet potato Production in Nsukka, Southeastern Nigeria.

Forest land provides a wide range of ecosystem services such as reducing the impact of raindrops on the soil and maintenance of soil fertility, whereas fallowing is one method used in restoring the fertility status of degraded farmlands. This study evaluated the physicochemical properties of an Alfisol under fallow and adjacent forestland, and their suitability for cocoyam, pigeon pea, and sweet potato. The fallow plots were brought into cultivation in the year 1998 under the IITA-UNN long-term collaborative research. Soil samples were collected from 0-20 cm depth in triplicates using an auger and cylindrical core from the seven representative fallow plots previously grown to sole cassava from the year 1998–2003 and under fallow till the year 2016 as well as the adjacent forest land. The result obtained showed that the fallow land had higher fertility nutrients than the forest land in the year 2016. The fallow land gave the highest values of SOC, total nitrogen, percentage base saturation, total exchangeable bases (Ca2+, Mg2+, Na+, K+) and exchangeable acidity when compared with the forest land. Using the FAO’s principle of limiting conditions as guide, both fallow and forest soils are marginally suitable (S3) for cocoyam production but highly suitable (S1) for both pigeon pea and sweet potato production.

Experimental and modelling evidence of short-term effect of raindrop impact on hydraulic conductivity and overland flow intensity

Tropical montane areas of Southeast Asia are exposed to high-intensity rainfall during the monsoon period. This is particularly problematic in areas where soils on steep slopes are cultivated as it can lead to heavy runoff, high soil erosion, and water pollution. The objective of this paper is to analyse the effect of the impact of raindrops on the dynamics of runoff on such steep fields. Experiments under simulated rainfall were performed at the plot scale (1 m2) to quantify water export from the surface of upland agricultural soils during overland flow events. Four 1 m2 plots were divided in duplicated treatment groups: (a) control with no amendments, and (b) amended with pig manure. Each plot was divided into two 0.5 m2 rectangular subplots. One subplot was designated as a rain splash treatment; the other sub-plot was covered with a 2 mm grid size wire screen that was located 12 cm above the soil surface. The purpose of the screen was to break the raindrops into fine droplets and to reduce fall height in order to drastically reduce their kinetic energy. Runoff was measured for each sub-plot. The results show that raindrop impact drastically enhances runoff generation on both bare soils and on manure amended soils. When the impact of raindrops was limited by screening, runoff was higher on amended soils than on bare soils.The temporal evolution of runoff was correctly modelled using a soil hydraulic conductivity that exponentially decreases over time of exposure to rainfall. Both experimental and modelling results showed that droplet energy induces a rapid evolution of the hydraulic properties of the soil surface due to crusting, resulting in a reduction of hydraulic conductivity and a concomitant increase in runoff rate.

Determining and Modeling Dominant Processes of Interrill Soil Erosion

AbstractUnderstanding the dominant process of interrill soil erosion is imperative to better modeling interrill sediment delivery rates. The objectives are to (1) determine the limiting erosion process (detachment vs. transport) that controls interrill erosion under the study conditions, (2) quantify the effects of water and/or sediment influxes from upslope on downslope sediment transport and interrill erosion, and (3) evaluate the ability of commonly used hydraulic parameters for simulating interrill sediment delivery. Runoff, sediment delivery, and raindrop splash were simultaneously collected from two flumes (1.8 m × 0.5 m) and a 2.5‐cm slot between the flumes for three intensities of 60, 90, and 120 mm/hr at three slopes of 9%, 18%, and 27% under two cover treatments. Results showed that slot splash rates were consistently greater than flume wash rates, indicating that sediment transport capacity limited interrill sediment delivery under the study conditions. Soil detachment by raindrop impact was more influenced by surface water depth, while sediment transport capacity by flow velocity. The former played a bigger role in determining interill sediment delivery under detachment‐limited cases while the latter under transport‐limited conditions. Linear correlation coefficients between sediment delivery rates and hydraulic predictors were 0.545 for shear stress, 0.946 for stream power, 0.867 for unit stream power, and 0.948 for an empirical lumped model that includes a rainfall intensity term. Stream power and the empirical model were better predictors for interrill sediment delivery. However, their predictive abilities need to be assessed more rigorously at various impact levels of rainfall kinetic energy.

Estimating Soil Hydraulic Parameters Characterizing Rainwater Infiltration and Runoff Properties of Dryland Floodplains

The two-layered (0 - 50 and 50 - 250 mm) surface horizon hydraulic parameters of three dryland floodplain soil-types under aquafer water management in Postmasburg, Northern Cape Province of South Africa were estimated with HYDRUS-1D model. Time dependent water infiltration measurements at 30 and 230 mm depths from simulated rainfalls on undisturbed 1 m2 small plots with intensities of 1.61 (high), 0.52 (medium) and 0.27 (low) mm·min-1, were minimised using a two-step inversion. Firstly, separate optimisation of the van Genuchten-Mualem model parameters for the two surface-horizon layers and secondly, simultaneous optimisation for the joint two-layered horizon with first step optimal parameters entered as initial values. The model reproduced transient water-infiltration data very well with the Nash-Sutcliffe model efficiency coefficient (NSE) of 0.99 and overestimated runoff (NSE; 0.27 to 0.98). The upper surface horizon had highly optimised and variable parameters especially θs and Ks. Optimal Ks values from higher soil surface bulk-density (≥1.69 g·cm-3) were lower by at least one order of magnitude to double ring infiltrometers and water infiltration properties were different (P < 0.05) for the high rainstorm due to raindrop impact and surface crusting. Optimal α and n parameter values corresponded well with texture of the Addo (Greysols), Augrabies (Ferralsols) and Brandvlei (Cambisols) soil types. However, θs and Ksshowed greater sensitivity to model output and exerted greater influence on dryland floodplain water-infiltration and runoff characteristics. Increasing rainfall simulation period to attain near-surface saturated conditions and inclusion of surface ponding data in the inverse problem could considerable improve model prediction of hydro-physical parameters controlling surface-subsurface water distribution in fluvial environments.

Losses of soil, water, organic carbon and nutrients caused by water erosion in different crops and natural savannah in the northern Amazon

Currently in Brazil, the main form of erosion is caused by the impact of raindrops on the soil surface, triggering the process of water erosion and causing serious damage to agricultural areas. This study evaluated losses of soil, water, organic carbon and nutrients in different cultures, bare soil and savanna under natural rain. The experimental design was completely randomized with five treatments (bare soil - BS, cowpea bean - CB, Brachiaria brizantha - BB, corn - CO and natural savanna – SN) with three replications; The treatment of bare soil (BS), followed by the treatment cultivated with cowpea bean (CB) showed higher losses of soil, water, organic carbon and nutrients; The highest losses of soil, water, organic carbon and nutrients in the treatment of bare soil (BS) occurred during the period of greatest erosivity; but for treatments CB, BB and CO, the highest losses occurred during the establishment of the crop, in view of the lower soil cover. Soils cultivated with Brachiaria brizantha - BB, corn - CO and in the Natural Savana - SN area were more efficient in reducing soil and water losses during all months evaluated. Plant cover produced by the (SN) treatment and by the (BB) and (CO) treatments acted to reduce the harmful effects of erosion, minimizing losses of nutrients and organic carbon. The soil should be well protected during periods when rainfall presents the highest values of erosivity index.

The Role of Hydraulic Connectivity and Management on Soil Aggregate Size and Stability in the Clear Creek Watershed, Iowa

The role of tillage practices on soil aggregate properties has been mainly addressed at the pedon scale (i.e., soilscape scale) by treating landscape elements as disconnected. However, there is observed heterogeneity in aggregate properties along flowpaths, suggesting that landscape scale hydraulic processes are also important. This study examines this supposition using field, laboratory and modeling analysis to assess aggregate size and stability along flowpaths under different management conditions: (1) tillage-induced abrasion effects on aggregate size were evaluated with the dry mean weight diameter (DMWD); (2) raindrop impact effects were evaluated with small macroaggregate stability (SMAGGSTAB) using rainfall simulators; and (3) these aggregate proxies were studied in the context of connectivity through the excess bed shear stress (δ), quantified using a physically-based landscape model. DMWD and SMAGGSTAB decreased along the flowpaths for all managements, and a negative correspondence between the proxies and δ was observed. δ captured roughness effects on connectivity along the flowpaths: highest connectivity was noted for parallel-ridge-till flowpaths, where δ ranged from 0–8.2 Pa, and lowest connectivity for contour-ridge-till flowpaths, where δ ranged from 0–1.1 Pa. High tillage intensity likely led to an increase in aggregate susceptibility to hydraulic forcing, reflected in the higher gradients of aggregate size and stability trendlines with respect to δ. Finally, a linear relationship between DMWD and SMAGGSTAB was established.

Raindrop Size and Flow Depth Control Sediment Sorting in Shallow Flows on Steep Slopes

AbstractRaindrop size and flow depth interactions determine the energy available for erosion processes. A detailed laboratory study was conducted to investigate the influence of raindrop size on sediment sorting in shallow flows on steep slopes. Raindrops with sizes of 1.34, 2.45, and 4.04 mm were applied to three inflows (0.65, 1, and 2 L/min) with the same rainfall intensity (90 mm/hr). The De Brouckere mean diameter (D[4,3]) was enhanced with increases in the ratio between flow depth and raindrop size (h/d; p &lt; 0.05), indicating that more raindrop energy dissipated in deeper flows. Moreover, a greater proportion of energy was dissipated from small raindrops than from large ones with an increasing flow depth. Particles &gt;0.5 mm were slightly enriched by rolling under 1.34‐mm raindrop impact, whereas enrichment did not occur under 2.45‐ and 4.04‐mm raindrop impact, probably because the latter induced more severe aggregate disintegration, resulting in fewer coarse particles. The mean sediment concentrations under inflows of 0.65, 1, and 2 L/min were 101.65, 89.32, and 79.02 g/L, respectively. Shallow flows on steep slopes effectively carried detached particles; moreover, coarse particles could roll along the slopes, which was inconsistent with their behavior on gentle slopes. This study highlights the need to understand the influence of the interaction between raindrop size and flow depth on erosion processes associated with sediment size selectivity for better erosion modeling and water quality prediction.

Effects of Cyanobacterial Soil Crusts on Surface Roughness and Splash Erosion

AbstractSoil surface roughness (SSR) modifies interactions and feedback processes between terrestrial and atmospheric systems driven by both the abiotic and biotic components of soils. This paper compares SSR response to a low‐intensity multiday rainfall event for soils with and without early successional stage cyanobacteria‐dominated biological soil crusts (CBCs). A rainfall simulator was used to apply 2, 5, and 2 mm of rain separated by a 24‐hr period over 3 days at an intensity of 60 mm/hr. Changes in SSR were quantified using geostatistically derived indicators calculated from semivariogram analysis of high‐resolution laser scans. The CBCs were stronger and splash erosion substantially less than from the physical soil crusts. Prior to rainfall treatment, soils with CBCs had greater SSR than those without. The rainfall treatments caused the physical crusted soils to increase SSR and spatial patterning due to the translocation of particles, soil loss, and the development of raindrop impact craters. Rainfall caused swelling of cyanobacterial filaments but only a slight increase in SSR, and raindrop impact cratering and splash loss were low on the soils with CBCs. There is no relationship between random roughness and splash erosion, but an increase in splash loss was associated with an increase in topographic roughness and small‐scale spatial patterning. A comparison of this study with other research indicates that for rainfall events up to 100 mm, the effectiveness of CBCs in reducing soil loss is &gt;80% regardless of the rainfall amount and intensity, which highlights their importance for landscape stabilization.

Effects of rainfall patterns on runoff and rainfall-induced erosion

Rainfall-induced erosion involves the detachment of soil particles by raindrop impact and their transport by the combined action of the shallow surface runoff and raindrop impact. Although temporal variation in rainfall intensity (pattern) during natural rainstorms is a common phenomenon, the available information is inadequate to understand its effects on runoff and rainfall-induced erosion processes. To address this issue, four simulated rainfall patterns (constant, increasing, decreasing, and increasing - decreasing) with the same total kinetic energy were designed. Two soil types (sandy and sandy loam) were subjected to simulated rainfall using 15 cm × 30 cm long detachment trays under infiltration conditions. For each simulation, runoff and sediment concentration were sampled at regular intervals. No obvious difference was observed in runoff across the two soil types, but there were significant differences in soil losses among the different rainfall patterns and stages. For varying-intensity rainfall patterns, the dominant sediment transport mechanism was not only influenced by raindrop detachment but also was affected by raindrop-induced shallow flow transport. Moreover, the efficiency of equations that predict the interrill erosion rate increased when the integrated raindrop impact and surface runoff rate were applied. Although the processes of interrill erosion are complex, the findings in this study may provide useful insight for developing models that predict the effects of rainfall pattern on runoff and erosion.

Rainfall and inflow effects on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region

Erosion agents and patterns profoundly affect hillslope soil loss characteristics. However, few attempts have been made to analyze the effects of rainfall and inflow on soil erosion for hillslopes dominated by sheet erosion or rill erosion in the Chinese Mollisol region. The objective of this study was to discuss the erosive agent (rainfall or inflow), hillslope erosion pattern (sheet erosion or rill erosion) and slope gradient effects on runoff and soil losses. Two soil pans (2.0 m long, 0.5 m wide and 0.5 m deep) with 5° and 10° slopes were subjected to rainfall (0 and 70 mm h–1) and inflow (0 and 70 mm h–1) experiments. Three experimental combinations of rainfall intensity (RI) and inflow rate (IR) were tested using the same water supply of 70 mm by controlling the run time. A flat soil surface and a soil bed with a straight initial rill were prepared manually, and represented hillslopes dominated by sheet erosion and rill erosion, respectively. The results showed that soil losses had greater differences among treatments than total runoff. Soil losses decreased in the order of RI70+IR70 > RI70+IR0 > RI0+IR70. Additionally, soil losses for hillslopes dominated by rill erosion were 1.7–2.2 times greater at 5° and 2.5–6.9 times greater at 10° than those for hillslopes dominated by sheet erosion. The loss of <0.25 mm soil particles and aggregates varying from 47.72%–99.60% of the total soil loss played a dominant role in the sediment. Compared with sheet erosion hillslopes, rill erosion hillslopes selectively transported more microaggregates under a relatively stable rill development stage, but rills transported increasingly more macroaggregates under an active rill development stage. In conclusion, eliminating raindrop impact on relatively gentle hillslopes and preventing rill development on relatively steep hillslopes would be useful measures to decrease soil erosion and soil degradation in the Mollisol region of northeastern China.

Distribuição da precipitação e da erosividade mensal e anual na Flona Tapajós e seu entorno

A perda de solo por erosão hídrica é uma das principais causas do declínio da produtividade de sistemas agrícolas. Seus mecanismos envolvem os processos de desprendimento, arraste e deposição do material erodido por ação do impacto das gotas de chuva em uma superfície, principalmente com solo sem cobertura vegetal. O objetivo neste trabalho foi estimar o potencial erosivo das chuvas na Flona Tapajós e seu entorno para subsidiar a adoção de práticas conservacionistas de manejo do solo e da água nessa unidade de conservação de uso sustentável. Foram utilizados dados diários de precipitação pluvial referentes aos municípios de Belterra, Santarém e Rurópolis, obtidos nas bases do Instituto Nacional de Meteorologia (INMET) e Agencia Nacional de Águas (ANA). Fez-se a estimativa do potencial erosivo das chuvas para toda série de dados em cada localidade. Também, para efeito comparativo foram analisados os períodos contendo a mesma série histórica e realizadas análises exploratórias para extrair medidas de dispersão capazes de expressar efeitos decorrentes de processos erosivos, em anos com alta pluviosidade. O índice de anomalias da chuva também foi aplicado aos dados de totais anuais para identificar a ocorrência de anos extremamente chuvosos ou secos. Observa-se que os resultados de erosividade das chuvas apresentam oscilações semelhantes nos três municípios. Destaca-se o ano de 2008 foi o que apresentou o maior valor de erosividade nas três localidades, com 17.761, 20.785 e 17.567 MJ mm h1 ha-1 para os municípios de Belterra, Santarém e Rurópolis, respectivamente. Enquanto que os anos de 1992, 1988 e 2010 apresentaram as menores estimativas. Anos com maior potencial erosivo na área de estudo foram classificados como extremamente chuvosos, indicando a influência de eventos de La Niña no fator erosividade das chuvas. Por outro lado, anos classificados como de redução extrema de chuva os valores de erosividade estimados foram os menores das séries históricas analisadas, apontando a influência de mecanismo como o El Niño, na redução da precipitação e, consequentemente refletindo na redução do potencial erosivo das chuvas na Flona Tapajós e seu entorno.

Rain erosion resistance of injection moulded and compression moulded polybutylene terephthalate PBT

Offshore wind turbine rotor diameters still increase. Blade tip velocities are up to 110 m/s, giving rise to more severe raindrop impact conditions and related erosion of the wind turbine blades. In the current work droplet impingement erosion tests were performed for injection moulded and compression moulded polybutylene terephthalate PBT. The measured incubation periods were compared to an extended and improved fatigue based erosion model.The developed erosion test set-up was based on a high water pressure nozzle system spraying water drops at a stationary PBT surface. Model results with thermoplastic materials simulating heavy rain conditions with a droplet size of 1.8 mm and an impact velocity of 120 m/s are shown. Model results with PBT materials simulating the used test conditions are shown and compared with the measured incubation periods. Although a reasonable similarity between test results and model calculations for the injection moulded PBT was found, the absolute value of the incubation period predicted by the model for compression moulded PBT differed substantially. This probably resulted from the lower confidence level of the S-N curve for the compression moulded PBT. The droplet impingement measurements and model predictions both showed a substantially higher incubation period for injection moulded PBT compared to compression moulded PBT.

Influence of freeze-only and freezing-thawing cycles on splash erosion

Soil erosion is recognized as one of the most important types of land degradation in the world particularly in many developing countries like Iran. Water erosion is initiated by splash erosion triggered by raindrop impact. Understanding the process of splash erosion under freezing and thawing conditions is essential to unravel soil erosion mechanisms under temperate conditions leading to appropriate planning of soil and water conservation projects. The present study aimed to study the individual effects of freeze-only as well as freezing-thawing cycle on splash erosion in a loess soil from an erosion prone area in mountainous northern regions of Iran. The study was conducted under laboratory conditions using erosion plots. The erosion plots were subjected to freeze only and freeze-thawing treatments by simulating cold conditions using a large cooling compartment system specifically manufactured for this purpose. The splash erosion under a designed simulated rainfall (1.2 mm min−1 for 30 min) was then measured as upward, downward and net splash erosion in splash cups. The results showed that freeze only decreased the upward, downward and net splash erosion by 0.81 ± 0.43, 0.82 ± 0.29 and 0.85 ± 0.23% while freezing-thawing cycle decreased splash erosion to 0.93 ± 0.83, 0.61 ± 0.43 and 0.57 ± 0.36%. This may be attributed to temporary increase in soil strength and stability or surface sealing during freezing process leading to reduced splash erosion.

Uncertainties in rainfall kinetic energy-intensity relations for soil erosion modelling

For bare soil conditions, the most important process driving and initiating splash and interrill erosion is the detachment of soil particles via raindrop impact. The kinetic energy of a rainfall event is controlled by the drop size and fall velocity distribution, which is often directly or indirectly implemented in erosion models. Therefore, numerous theoretical functions have been developed for the estimation of rainfall kinetic energy from available rainfall intensity measurements. The aim of this study is to assess differences inherent in a wide number of kinetic energy-rainfall intensity (KE-I) relations and their role in soil erosion modelling. Therefore, 32 KE-I relations are compared against measured rainfall energies based on optical distrometer measurements carried out at five stations of two substantially different rainfall regimes. These allow for continuous high-resolution (1-min) direct measurements of rainfall kinetic energies from a detailed spectrum of measured drop sizes and corresponding fall velocities. To quantify the effect of different KE-I relations on sediment delivery, we apply the erosion model WATEM/SEDEM in an experimental setup to four catchments of NE-Germany. The distrometer data shows substantial differences between measured and theoretical models of drop size and fall velocity distributions. For low intensities the number of small drops is overestimated by the Marshall and Palmer (1948; MP) drop size distribution, while for high intensities the proportion of large drops is overestimated by the MP distribution. The distrometer measurements show a considerable proportion of large drops falling at slower velocities than predicted by the Gunn and Kinzer (1949) terminal velocity model. For almost all rainfall events at all stations, the KE-I relations predicted higher cumulative kinetic energy sums compared to the direct measurements of the optical distrometers. The different KE-I relations show individual characteristics over the course of rainfall intensity levels. Our results indicate a high sensitivity (up to a range from 10 to 27 t ha−1) of the simulated sediment delivery related to different KE-I relations. Hence, the uncertainty associated with KE-I relations for soil erosion modelling is of critical importance.

Assessing the impacts of microtopography on soil erosion under simulated rainfall, using a multifractal approach

AbstractThis study aimed to investigate the changing characteristics of microrelief of purple soil and its erosional response during successive stages of water erosion, including splash erosion, sheet erosion, and rill erosion. Methods employed included a rainfall simulator and the use of a laser scanner to generate a digital elevation model. Three artificial tillage practices, including conventional tillage (CT), artificial digging (AD), and ridge tillage (RT), were used to simulate different microrelief patterns. Eighteen artificial rainfall experiments were conducted using three 2 × 1 m boxes with a rainfall intensity of 1.5 mm min−1 on a 15° slope. The results showed that the soil roughness (SR) index values for the tillage slopes were RT &gt; AD &gt; CT. The combined effects of detachment by raindrop impact and transport by run‐off decreased the SR index, whereas rill erosion increased the SR index during rainfall event. Microtopography and drainage networks have strong multifractal behaviours. The multifractal parameters of microtopography reflect the overall characteristics as well as the characteristics of the local soil surface. Within a certain range of threshold values, higher microrelief causes less soil erosion. However, when the parameters of spatial heterogeneity of microtopography exceed the threshold values, a higher degree of microrelief can increase soil erosion. These results help clarify the effect of microtopography on soil erosion and provide a theoretical foundation to guide future tillage practices on sloping farmland of purple soil.

Theoretical and testing investigation of wind–rain coupling loads on some typical bluff bodies

The article presents a mathematical theoretical framework and fitting parameters with aspects of joint probability distribution of wind and rain, separate wind and rain action, and coupled wind and rain effects on steady and unsteady forces acting on some typical bluff bodies. Gumbel and copula functions were first selected to describe the joint probability distribution of wind speed and rain intensity. Then, two models, a raindrop impact model and an equivalent air density model, were adopted to quantify the loading action considering only separate wind and rain action, and simplified coupled effects with superimposition of wind and rain show that it would be accurate enough to neglect separated rain influence in steady wind and rain loading conditions. Furthermore, wind tunnel testing has been carried out under coupled wind and rain conditions with the help of a high-precision raining simulation system in TJ-1 wind tunnel on various reduced-scale models with some typical cross sections, such as circular and rectangular, thin plate, and streamlined box, and their aerodynamic loading and wind–rain-induced performance have been systematically compared. It has thus been found that the coupling effects of wind and rain should not be neglected in steady and unsteady force models.

Soil internal forces contribute more than raindrop impact force to rainfall splash erosion

Soil internal forces, including electrostatic, hydration and van der Waals, play critical roles in aggregate stability, erosion, and other processes related to soil and water. However, the extent to which soil internal forces influence splash erosion during rainfall remains unclear. In the present study, we used cationic-saturated soil samples to quantitatively separate the effects of soil internal and raindrop impact forces (external) on splash erosion through simulated rainfall experiments. An electrolyte solution was employed as rainfall material to represent the combined effects of soil internal and external forces on splash erosion. Ethanol was used to simulate the sole effect of soil external force on splash erosion. The soil splash erosion rate increased with increasing rainfall kinetic energy in experiments with electrolyte solution and ethanol and was also greatly influenced by soil internal forces. Moreover, the soil splash erosion rate increased first (from 1 to 10−2 mol L−1) then leveled off (from 10−2 to 10−4 mol L−1) with decreasing electrolyte concentration in the bulk solution. This finding was in agreement with the theoretical analysis of soil internal forces. The contribution rate of soil internal forces on splash erosion was >65% at a low electrolyte concentration (<10−2 mol L−1) and only 3%–25% at an electrolyte concentration of 1 mol L−1. Even though the electrolyte concentration of the soil bulk solution reached 10−1 mol L−1, the contribution rate of soil internal forces to splash erosion was >50%. Hence, soil internal forces exerted higher contribution to rainfall splash erosion than raindrop impact force under most field conditions. This work provides new understanding of the mechanism of soil splash erosion and establishes the possibility of controlling splash erosion by jointly regulating the soil internal and external forces.

Peculiarities of Using Biomass for Oil-Contaminated Soils Remediation in the Far North Regions

The rainfall-runoff events and erosion process usually begins with raindrop impact on bare or nearly bare soils with the resulting splash causing the soil particles to become detached and subsequently, overland flow transports these particles towards down slope. During the past decades, the understanding of soil splash mechanisms by raindrops and their erosivity have been actively investigated. Many significant studies and models are performed to investigate the process of raindrop-induced erosion and sediment transport in shallow waters which differ in terms of their effecting factors.

Interrill erodibility in relation to aggregate size class in a semi-arid soil under simulated rainfalls

Interrill erodibility can be affected by soil aggregates, especially by those aggregate size classes that are dominant in the soil. In the Water erosion Prediction Project (WEPP) model, interrill soil erodibility (Ki) is estimated using very fine sand content. Despite that some studies have indicated an effect of aggregate stability on the Ki, information on the relationship between the aggregate size class and Ki and factors controlling it, particularly in semi-arid region is limited. This study was conducted to determine the variation of Ki for different aggregate size classes under various rainfall intensities and evaluation of the WEPP model in estimating the Ki for different aggregate fractions. Five aggregate size classes (0.25–2, 2–4.75, 4.75–5.6, 5.6–9.75 mm, and 9.75–12.7 mm) were separated from a sandy clay loam soil sampled in an agricultural land and put in laboratory flumes of 100 cm × 50 cm. The flumes were placed on a 9% slope and exposed to ten sequential rainfall simulations varying from 10 to 60 mm h−1 for 30 min. The Ki of each aggregate size classes was determined using the interrill sediment delivery rate and compared this with the values estimated using WEPP. All physicochemical properties were also determined in the aggregate size classes. Organic matter content in the aggregate size classes was very low (0.65–0.73%) and didn't show strong relationships with the aggregate stability and hydraulic conductivity, whereas clay was major factor controlling determining these properties for the different aggregate fractions. Significant differences were found among the aggregate size classes in clay content (P < 0.05), aggregate stability measured using both wet-sieving method (P < 0.05) and water drop test method P < 0.05, saturated hydraulic conductivity (Ks), and measured Ki (P < 0.05). The measured Ki was about 34 and 90 times bigger than the estimated Ki for the fine aggregates and coarse aggregates, respectively. The fine aggregates showed higher susceptibility to interrill detachment with increasing rainfall intensity as compared with the coarse aggregates. Significant decrease was observed in the measured Ki with increasing the aggregate size which was associated with increases in clay content, aggregate stability and Ks. The stability of aggregates against raindrop impact (CND) was an important indicator describing the effect of aggregate size on the interrill erodibility in semi-arid soils. Therefore, this indicator can be taken into account as a soil structure measure to develop a proper equation for estimating interrill erodibility (Ki) for agricultural lands. The minimum use of tillage practices is essential to prevent aggregate breakdown and control interrill erosion in semi-arid regions.