Effects of hydrophobicity on splash erosion of model soil particles by a single water drop impact

Raindrop impact can be a major contributor to particle mobilization for soils and other granular materials. In previous work, water repellent soils, comprised of hydrophobic particles, have been shown to exhibit greater splash erosion losses under multiple drop impact. However, the underlying principle differences in splash behavior between hydrophobic and hydrophilic granular surfaces have not been studied to date. In this study the effects of particle hydrophobicity on splash behaviour by a single water drop impact were examined using high‐speed videography. Water drops (4 mm in diameter) were dropped on beds of hydrophilic and hydrophobic glass beads (sieved range: 350–400 µm), serving as model soil particles. The drop velocity on impact was 2.67 m s^‐1, which corresponds to ~30% of the terminal velocity of a raindrop of similar size. The resulting impact behaviour was measured in terms of the trajectories of particles ejected from the beds and their final resting positions. The response to the impacting water drop was significantly different between hydrophilic and hydrophobic particles in terms of the distance distribution, the median distance travelled by the particles and number of ejected particles. The greater ejection distances of hydrophobic particles were mainly the result of the higher initial velocities rather than differences in ejecting angles. The higher and longer ejection trajectories for hydrophobic particles, compared with hydrophilic particles, indicate that particle hydrophobicity affects splash erosion from the initial stage of rainfall erosion before a water layer may be formed by accumulating drops. The ~10% increase in average splash distance for hydrophobic particles compared with hydrophilic particles suggests that particle hydrophobicity can result in greater net erosion rate, which would be amplified on sloping surfaces, for example, by ridges in ploughed agricultural soils or hillslopes following vegetation loss by clearing or wildfire. Copyright © 2012 John Wiley & Sons, Ltd.     

A physically-based model of the dispersion of splash droplets ejected from a water drop impact

A model has been developed which predicts the dispersion of splash droplets produced by the impact of a water drop on a sloping soil surface. Experimental results of the ejection velocities and ejection angles of the splash droplets are generalized to a planar slope and the resulting splash distances are calculated taking into account the effects of air resistance. The predictions are presented in terms of the numbers of splash droplets from the impact point to surrounding squares arranged in a grid on the slope. The model explains many experimentally observed features of raindrop splash in terms of the mechanics of the processes involved and can make predictions of the effects of slope, wind, raindrop size, and soil properties on droplet dispersion. The component of the raindrop velocity parallel to the surface of the slope is identified as the main factor determining the degree and the direction of the asymmetry in the splash droplet dispersion. By combining the model with a theory of the entrapment of soil in the splash droplets it is possible to extend it to predict the dispersion of soil particles by raindrop impact, which is the basis of a model of soil erosion by rainsplash.     

A model of the redistribution of disaggregated soil particles by rainsplash

A model of the dispersion of splash droplets from a single raindrop impact on a sloping soil surface is combined with a theory of the entrainment of mineral particles from a disaggregated mixture in splash droplets to obtain a model of the dispersion of such particles by a raindrop impact. Stochastic modelling techniques extend this further to a model of the spatial redistribution of soil on a plot after a period of rainfall. Since the model is probabilistic and physically based it enables the incorporation of further advances in the understanding of splash erosion at all stages and can simulate the effect of the stochastic nature of rainfall and soil properties on the process. Several different situations are simulated. These include the movement of marked soil particles from point sources and the spatial patterns of erosion on a sloping plot. The model can also simulate the differential erosion of different soil particle size fractions.     

Effects of physical soil crusts on infiltration and splash erosion in three typical Chinese soils

Physical soil crusts likely have significant effects on infiltration and soil erosion, however, little is known on whether the effects of the crusts change during a rainfall event. Further, there is a lack of discussions on the differences among the crusting effects of different soil types. The objectives of this study are as follows： （i） to study the effects of soil crusts on infiltration, runoff, and splash erosion using three typical soils in China, （ii） to distinguish the different effects on hydrology and erosion of the three soils and discuss the primary reasons for these differences, and （iii） to understand the variations in real soil shear strength of the three soils during rainfall events and mathematically model the effects of the crusts on soil erosion. This study showed that the soil crusts delayed the onset of infiltration by 5 to 15 min and reduced the total amount of infiltration by 42.9 to 53.4% during rainfall events. For a purple soil and a loess soil, the initial crust increased the runoff by 2.8% and 3.4%, respectively, and reduced the splash erosion by 3.1% and 8.9%, respectively. For a black soil, the soil crust increased the runoff by 42.9% and unexpectedly increased the splash erosion by 95.2%. In general, the effects of crusts on the purple and loess soils were similar and negligible, but the effects were significant for the black soil. The soil shear strength decreased dynamically and gradually during the rainfall events, and the values of crusted soils were higher than those of incrusted soils, especially during the early stage of the rainfall. Mathematical models were developed to describe the effects of soil crusts on the splash erosion for the three soils as follows： purple soil, Fc= 0.002t- 0.384 ; black soil, Fc. =-0.022t ＋ 3.060 ; and loess soil, Fc = 0.233 In t- 1.239 . Combined with the equation Rc= Fc （Ruc - 1）, the splash erosion of the crusted soil can be predicted over time.     

Effect of organic matter on splash detachment and the processes involved

The influence of organic matter on splash detachment was investigated using soils with grass and peat treatments. The relationship between organic matter and aggregate stability to water disruption was positive for soils with grass treatment while it was negative for those with peat treatment. Organic matter from both treatments, however, reduced splash detachment by rainfall. Soils with grass did this by increasing aggregate stability while peat acted as a mulch on the soil surface. This implies that though organic matter always reduces splash detachment, different processes may be involved, depending on the form of the organic material. Because of the different processes involved, both negative and positive relationships between splash detachment and aggregate stability as reported in literature were obtained for the soils with grass and peat respectively.     

Surfactant and irrigation effects on wettable soils: runoff,erosion, and water retention responses

Surfactants are chemical compounds that can change the contact angle of a water drop on solid surfaces and are commonly used to increase infiltration into water repellent soil. Since production fields with water repellent soil often contain areas of wettable soil, surfactants applied to such fields worldwide will likely be applied to wettable soil, with unknown consequences for irrigation‐induced erosion, runoff, or soil water relations. We evaluated surfactant and simulated sprinkler irrigation effects on these responses for three wettable, Pacific Northwest soils, Latahco and Rad silt loams, and Quincy sand. Along with an untreated control, we studied three surfactants: an alkyl polyglycoside (APG) in solution at a concentration of 18 g active ingredient (AI) kg^?1, a block copolymer at 26 g kg^?1, and a blend of the two at 43 g kg^?1. From 2005 to 2009 in the laboratory, each surfactant was sprayed at a rate of 46·8 l ha^?1 onto each soil packed by tamping into 1·2‐ by 1·5‐m steel boxes. Thereafter, each treated soil was irrigated twice at 88 mm h^?1 with surfactant‐free well water. After each irrigation, runoff and sediment loss were measured and soil samples were collected. While measured properties differed among soils and irrigations, surfactants had no effect on runoff, sediment loss, splash loss, or tension infiltration, compared to the control. Across all soils, however, the APG increased volumetric water contents by about 3% (significant at p≤0·08) at matric potentials from 0 to ? 20 kPa compared to the control. With a decrease in the liquid–solid contact angle on treated soil surfaces, surfactant‐free water appeared able to enter, and be retained in pores with diameters ≥ 15 µm. All told, surfactants applied at economic rates to these wettable Pacific Northwest soils posed little risk of increasing either runoff or erosion or harming soil water relations. Moreover, by increasing water retention at high potentials, surfactants applied to wettable soils may allow water containing pesticides or other agricultural chemicals to better penetrate soil pores, thereby increasing the efficacy of the co‐applied materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Field studies of rainsplash erosion

Studies on sandy soils of the Cottenham Series in mid-Bedfordshire confirm in the field the relationships between splash erosion, rainfall energy and ground slope obtained in the laboratory experiments of other workers. Only 0·06 per cent of the rainfall energy contributes to splash erosion and rates are low, attaining a maximum of 0·082 kg m^?2 y^?1 on a slope of 11°. The major role of splash action is in the detachment of soil particles prior to their removal by overland flow.     

Response of soil aggregate disintegration to the different content of organic carbon and its fractions during splash erosion

Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar clay contents and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5 and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25 mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon. The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m⁻² mm⁻¹ and 12 m⁻² mm⁻¹. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.     

SfM-MVS Photogrammetry for Splash Erosion Monitoring under Natural Rainfall

An understanding of splash erosion is the basis to describe the impact of rain characteristics on soil disturbance. In typical splash cup experiments, splashed soil is collected, filtered, and weighed. As a way to collect additional data, our experiments have been supplemented by a photogrammetric approach. A total of three soils were tested across three sites, one in the Czech Republic and two in Austria, all equipped with rain gauges and disdrometers to measure rainfall parameters. The structure from motion multiview stereo (SfM-MVS) photogrammetric method was used to measure the raindrops impact on the soil surface. The images were processed using Agisoft PhotoScan, resulting in orthophotos and digital elevation models (DEMs) with a resolution of 0.1 mm/pix. The surface statistics included the mean surface height (whose standard deviation was used as a measure of surface roughness), slope, and other parameters. These parameters were evaluated depending on soil texture and rainfall parameters. The results show a linear correlation between consolidation and splash erosion with a coefficient of determination (R²) of approximately 0.65 for all three soils. When comparing the change in soil volume with rainfall parameters, the best correlation was found with the maximum 30-minintensity (I₃₀), resulting in R² values of 0.48 (soil A, silt loam, 26% clay), 0.59 (soil B, silt loam, 18% clay), and 0.68 (soil C, loamy sand, 12% clay). The initial increase in the sample volume for the lowest splashed mass corresponds with the increase in the clay content of each of the soils. Soil A swells the most. Soil B swells less. Soil C does not swell at all and consolidates the most. We derived the relationship between the photogrammetrically measured change in surface height and the splash erosion (measured by weight) by accounting for the effect of the clay content.     

Measuring sheet erosion using synthetic color‐contrast aggregates

The bulk of eroded soils measured at the outlets of plots, slopes and watersheds are suspended sediments, splash‐induced sheet erosion. It is depending on rainfall intensity and antecedent soil moisture contents and contributes to a significant proportion of soil loss that usually is ignored in soil erosion and sediment studies. A digital image processing method for tracing and measuring non‐suspended soil particles detached/transported by splash/runoff was therefore used in the present study. Accordingly, fine mineral pumice grains aggregated with white cement and coloured with yellow pigment powder, with the same size, shape and specific gravity as those of natural soil aggregates, called synthetic color‐contrast aggregates, were used as tracers for detecting soil particle movement. Subsequently, the amount of non‐suspended soil particles detached and moved downward the slope was inferred with the help of digital image processing techniques using MATLAB R2010B software (Mathworks, Natick, Massachusetts, USA). The present study was conducted under laboratory conditions with four simulated rainfall intensities between 30–90 mm h^‐1, five antecedent soil moisture contents between 12–44 % v v^‐1 and a slope of 30%, using sandy loam soils taken from a summer rangeland in the Alborz Mountains, Northern Iran. A range of total transported soil between 90.34 and 1360.93 g m^‐2 and net splash erosion between 36.82 and 295.78 g m^‐2were observed. The results also showed the sediment redeposition ratio ranging from 87.27% [sediment delivery ratio (SDR) = 12.73%] to 96.39% (SDR = 3.61%) in various antecedent soil moisture contents of rainfall intensity of 30 mm h^‐1 and from 80.55% (SDR = 19.45%) to 89.42% (SDR = 10.58%) in rainfall intensity of 90 mm h^‐1. Copyright © 2013 John Wiley & Sons, Ltd.     

A methodology to study rain splash and wash processes under natural rainfall

The complex interactions between rainfall‐driven erosion processes and rainfall characteristics, slope gradient, soil treatment and soil surface processes are not very well understood. A combination of experiments under natural rainfall and a consistent physical theory for their interpretation is needed to shed more light on the underlying processes. The present study demonstrates such a methodology. An experimental device employed earlier in laboratory studies was used to measure downslope rain splash and ‘splash‐creep’, lateral splash, upslope splash and rainfall‐driven runoff transport (wash) from a highly aggregated clay‐rich oxisol exposed to natural rainfall in West Java, Indonesia. Two series of measurements were made: the first with the soil surface at angles of 0°, 5°, 15° and 40°; and the second all at an angle of 5° but with different tillage and mulching treatments. A number of rainfall erosivity indices were calculated from rainfall intensity measurements and compared with measured transport components. Overall storm kinetic energy correlated reasonably well with sediment transport, but much better agreement was obtained when a threshold rainfall intensity (20 mm h^?1) was introduced. Rain splash transport measurements were interpreted using a recently developed theory relating detachment to sediment transport. Furthermore, a conceptually sound yet simple wash transport model is advanced that satisfactorily predicted observed washed sediment concentrations. The lack of replication precluded rigorous assessment of the effect of slope and soil treatment on erosion processes, but some general conclusions could still be drawn. The results stress the importance of experiments under conditions of natural rainfall. Copyright © 2002 John Wiley & Sons, Ltd.     

Surfactant effects on the water‐stable aggregation of wettable soils from the continental USA

Surfactants may affect soil structure differently depending upon the soil or the quality of rainfall or irrigation water. This study examined whether the water‐stable aggregation of 11 wettable soils was affected by surfactants and the water in which the soils were sieved. The study also examined whether the wettable soils' water drop penetration time (WDPT) was affected by surfactants, water drop quality, and elapsed time since the surfactants were applied. Two nonionic surfactants and a surfactant‐free water control were sprayed (by misting) upon air‐dry soil, then WDPT was measured 1 and 72 h thereafter. Subsequently, this treated soil was slowly wetted with an aerosol to its water content at a matric potential of ?3 kPa, then immediately sieved for 600 s in water that contained either appreciable or few electrolytes. Water‐stable aggregation, quantified as mean weight diameter (MWD), varied widely among soils, ranging from 0.10 to 1.36 mm. The MWDs were affected (at p = 0.06) by surfactant treatments, depending upon the soil but not sieving water quality. Surfactants affected the MWD of an Adkins loamy sand and Feltham sand, two of the three coarsest‐textured soils. Although WDPTs never exceeded 5 s, depending upon the soil WDPTs were affected by surfactant treatments but not by water drop quality. After surfactant application, WDPTs generally decreased with time for three soils but increased with time for one soil. Findings suggested that surfactants interacted (1) with clay mineralogy to affect MWD and (2) with soluble calcium to affect WDPT for certain soils. Surfactant treatments but not water quality affected both MWD and WDPT for some but not all of 11 wettable, US soils. Published 2012. This article is a US Government work and is in the public domain in the USA.     

Fire‐induced changes in soil water repellency increased fingered flow and runoff rates following the 2004 Huelva wildfire

Water repellency (WR) from fire‐affected soils can affect infiltration processes and increase runoff rates. We investigated the effects of fire‐induced changes in soil WR and the related soil hydrological response after one of the largest wildfires in Spain in recent years. The vertical distribution of WR in soil profiles was studied under oak and pine forests and the wetting pattern was analysed after rainfall simulations (85 mm h^?1 during 60 min). After burning, the persistence of WR in soils under oaks increased in the upper 0–5 cm of soil in comparison with pre‐fire WR, but no significant changes were observed under pines. After a fire, WR was stronger and the thickness of the water‐repellent layer increased in soils under pines in the upper 0–16 cm of soil. The hydrophobic layer was thinner under oaks, where no strong to extremely water‐repellent samples were observed below 12 (in burnt soils) and 8 cm (in unburnt soils). Uniform wetting was observed through soil depth in burnt and unburnt soils under oaks, as a consequence of the prevailing matrix flux infiltration. Water was mostly stored in the upper few centimetres and soil became rapidly saturated, favouring a continuous rise in the runoff rate during the experiments. Moisture profiles under pines showed a heterogeneous wetting pattern, with highly irregular wetting fronts, as a result of wettable and water‐repellent three‐dimensional soil patches. In this case, runoff rates on burnt plots increased in relation to unburnt plots, but runoff generation reached a steady state after 25–30 min of simulated rainfall at an intensity of 85 mm h^?1. Rainfall water infiltrated over a small part of the ponded area, where the vertical pressure of the water column overcame the WR. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterization of rainfall generated by dripper‐type rainfall simulator using piezoelectric transducers and its impact on splash soil erosion

Rainfall erosivity represents the primary driver for particle detachment in splash soil erosion. Several raindrop erosivity indices have been developed in order to quantify the potential of rainfall to cause soil erosion. Different types of rainfall simulators have been used to relate rainfall characteristics to soil detachment. However, rainfall produced by different rainfall simulators has different characteristics, specifically different relationships between rainfall intensity and rainfall erosivity. For this reason, the effect of rainfall characteristics produced by a dripper‐type rainfall simulator on splash soil erosion (D_s) has been investigated. The simulated rainfall kinetic energy (KE) and drop size distribution (DSD) were measured using piezoelectric transducers, modified from the Vaisala RAINCAP^® rain sensor. The soil splash was evaluated under various simulated rainfall intensities ranging from 10 to 100 mm h^?1 using the splash‐cup method. The simulated rainfall intensity (I) and kinetic energy relationship (I–KE) was found to be different from natural rainfall. The simulated rainfall intensity and splash soil erosion relationship (I–D_s) also followed this same trend. The I–KE relationship was found to follow the natural rainfall trend until the rainfall intensity reached 30 mm h^?1 and above this limit the KE started to decrease. This emphasizes the importance of the I–KE relationship in determining the I‐D_s relationship, which can differ from one rainfall simulator to another. D_s was found to be highly correlated with KE (r = 0·85, P < 0·001), when data produced by the rainfall intensity ranged from 10 to 100 mm h^?1. However, when the threshold rainfall intensity (30 mm h^?1) was considered, the correlation coefficient further improved (r = 0·89, P = 0·001). Accordingly, to improve the soil splash estimation of simulated rainfall under various rainfall intensities the I–KE characterization relationship for rainfall simulators has to be taken into account. Copyright © 2010 John Wiley & Sons, Ltd.     

Screening of polymers on selected Hawaii soils for erosion reduction and particle settling

In recent years, high‐molecular‐weight anionic polyacrylamides (PAMs) have been tested on a variety of soils, primarily in temperate climates. However, little information is available regarding the effectiveness of PAM for preventing soil loss through runoff in tropical settings. Screening tests were performed using three negatively charged PAMs and one positively charged PAM on five Hawaii soils (two Oxisols, one Vertisol, and two Aridisols) to determine erosion loss, sediment settling, and aggregate stability. A laboratory‐scale rainfall simulator was used to apply erosive rainfall at intensities from 5 to 8·5 cm h^?1 at various PAM doses applied in both dry and solution forms. Soil detachment due to splash and runoff, as well as the runoff and percolate water volumes, were measured for initial and successive storms. The impact of PAM on particle settling and aggregate stability was also evaluated for selected soil‐treatment combinations. Among the PAMs, Superfloc A‐836 was most effective, and significantly reduced runoff and splash sediment loss for the Wahiawa Oxisol and Pakini Andisol at rates varying between 10 and 50 kg ha^?1. Reduced runoff and splash sediment loss were also noted for PAM Aerotil‐D when applied in solution form to the Wahiawa Oxisol. Significant reductions in soil loss were not noted for either the Lualualei Vertisol or the Holomua Oxisol. It is believed that the high montmorillonite content of the Lualualei Vertisol and the low cation‐exchange capacity of the Holomua Oxisol diminished the effectiveness of the various PAMs tested. The polymers were also found to enhance sediment settling of all soils and helped improve their aggregate stability. This screening study shows the potential use of PAM for tropical soils for applications such as infiltration enhancement, runoff reduction, and enhanced sedimentation of detention ponds. Copyright © 2005 John Wiley & Sons, Ltd.     

Modelling raindrop impact and splash erosion processes within a spatial cell: a stochastic approach

A new approach is proposed to simulate splash erosion on local soil surfaces. Without the effect of wind and other raindrops, the impact of free‐falling raindrops was considered as an independent event from the stochastic viewpoint. The erosivity of a single raindrop depending on its kinetic energy was computed by an empirical relationship in which the kinetic energy was expressed as a power function of the equivalent diameter of the raindrop. An empirical linear function combining the kinetic energy and soil shear strength was used to estimate the impacted amount of soil particles by a single raindrop. Considering an ideal local soil surface with size of 1 m × 1 m, the expected number of received free‐falling raindrops with different diameters per unit time was described by the combination of the raindrop size distribution function and the terminal velocity of raindrops. The total splash amount was seen as the sum of the impact amount by all raindrops in the rainfall event. The total splash amount per unit time was subdivided into three different components, including net splash amount, single impact amount and re‐detachment amount. The re‐detachment amount was obtained by a spatial geometric probability derived using the Poisson function in which overlapped impacted areas were considered. The net splash amount was defined as the mass of soil particles collected outside the splash dish. It was estimated by another spatial geometric probability in which the average splashed distance related to the median grain size of soil and effects of other impacted soil particles and other free‐falling raindrops were considered. Splash experiments in artificial rainfall were carried out to validate the availability and accuracy of the model. Our simulated results suggested that the net splash amount and re‐detachment amount were small parts of the total splash amount. Their proportions were 0·15% and 2·6%, respectively. The comparison of simulated data with measured data showed that this model could be applied to simulate the soil‐splash process successfully and needed information of the rainfall intensity and original soil properties including initial bulk intensity, water content, median grain size and some empirical constants related to the soil surface shear strength, the raindrop size distribution function and the average splashed distance. Copyright © 2007 John Wiley & Sons, Ltd.     

The influence of soil properties on the erodibility of Belgian loamy soils: A study based on rainfall simulation experiments

Twenty soils from the Leuven region were tested in the laboratory with a rainfall simulator. Their texture varied from loam to loamy sand. On the basis of the results obtained, they were classified as a function of the runoff and splash erodibility. For every soil, several properties were determined and tentatively used to explain the classifications based on the runoff and splash erodibility. Significant negative correlations were found between silt content, aggregate stability, C_5–10 index, water content at saturation, and cohesion on the one side and erodibility on the other; a positive correlation was found between sand content and erodibility.     

SPLASH TRANSPORT OF ORGANIC CARBON AND ASSOCIATED CONCENTRATION AND MASS ENRICHMENT RATIOS FOR AN OXISOL,HAWAII

Rainsplash is an important component of interrill erosion. To date, few studies have critically examined the linkages between aggregate entrainment by splash and associated nutrient flux. An Oxisol was used in laboratory rainfall experiments with two different antecedent moisture contents (AMC) and ten different rainfall energy flux densities (EFD). Splash and soil organic carbon (SOC) flux increased with increased EFD regardless of initial AMC. Aggregates were not transported in proportion to their content in the original soil matrix, those of 2000–4000 μm and <105 μm were found to be the most resistant to splash. Energy required to detach 1 gC varied from a median of 1870 J for the 2000–4000 μm fraction to 120 J for the 425–850 μm fraction. Temporal variation in cumulative splash flux and carbon flux for various combinations of AMC and EFD indicated distinct patterns. Under dry AMC, splash increased during 1 h duration storms and this was explained by increased aggregate breakdown by air-slaking, decreased soil strength and increased erodibility as soil moisture increased. Wet soil runs exhibited the opposite pattern of decreased flux with time, probably indicating a complex response to limited aggregate availability, increased seal development by raindrop compaction, and transient water layer effects in drop impact craters. The formulation of mass-based SOC enrichment ratios (ER) clearly indicated preferential detachment and transport of splashed aggregates between 250 and 2000 μm. A reliance of chemical transport models on concentration-based ER values can be misleading, because it is the balance between nutrient concentration and sediment quantity that is important for soil quality and non-point source modelling.     

Study of the importance of splash and wash on cultivated loamy soils of Hesbaye (Belgium)

During 1974 and 1975, measurements of splash and wash were carried out in the cultivated area, in a station installed on 6·5 per cent slope covered with a loess in which a grey-brown podzolic soil has developed. Splash has been measured using an apparatus prepared for this purpose and wash has been measured on plots of standard length (22·13m). The splash is some tens t/ha.year but the splash loss calculated using the results of the measurements of splash is only a few tens kg/ha.year. Splash is positively correlated with the erosion index of the rains and with the structural stability but negatively with the crop cover. As splash, wash is positively correlated with the erosion index of the rains and negatively with the crop cover, but unlike splash it is negatively correlated with structural stability. The mean value of the wash loss is a few t/ha.year but very important differences are observed from one plot to another with regard to the structural stability. However, on a given plot wash loss and splash are positively correlated because the particles of soil detached by splash are easily carried off by runoff, but the relation between wash loss and splash is very different from one plot to another because splash is positively and wash loss negatively correlated with the structural stability of soils.     

Downslope soil detachment–transport on steep slopes via rain splash

This study developed a one‐dimensional model of downslope rain splash transport based on field experiments and previous studies. The developed model considers soil detachment processes, ground cover, probability densities, and the effect of overland run‐off in preventing detachment. Field monitoring was conducted to observe precipitation run‐off, ground cover, and sediment production on steep hillslopes. Field‐observed data were used to develop the splash detachment rate equation, probability densities for splash transport, and the maximum splash transport distance. Observed and estimated splash transport showed overall agreement, with some differences for small storm events or events with relatively low intensity, probably caused by variation of overland run‐off depth and connectivity as well as differences in soil surface cohesion at various degrees of wetness. Our model can provide insights on the interactions among rainfall intensity, soil surface condition, soil wetness, and splash transport on forested hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.