Roughness Decay Research Articles

Soil surface roughness decay under different topographic conditions

Soil surface roughness (RR) is one of the most significant factors influencing hydrological and erosion processes. It is most likely affected by topographic conditions, but this relationship has not been quantified. This study was conducted to detect the effects of topographic conditions on soil surface roughness decay after tillage and to determine the dominant mechanism affecting RR on the Loess Plateau. From June 10 to October 3, 2017, RR was measured using a handheld 3D scanner in six plots with different slope gradients and at three different slope positions along a 60 m plot. The results showed that soil surface roughness was significantly affected by slope gradient and position. RR increased exponentially with an increase in slope gradient (R2 = 0.97). The middle slope position exhibited the maximum RR, whereas the downslope position exhibited the minimum RR. Soil surface roughness decreased exponentially over time after tillage under different topographic conditions ranging from 0.91 to 4.50 mm. For the six plots with different slope gradients, rapid decreases in RR occurred from July 24 to Sept. 10, but for the three different slope positions, rapid decreases occurred from June 10 to July 24. RR declined exponentially with an increase in cumulative rainfall (266.4 mm, R2 = 0.88) and kinetic energy (38.9 MJ ha−1, R2 = 0.92). Cumulative kinetic energy was a better predictor of RR decay than cumulative rainfall at different slope positions. However, for plots with different slope gradients, RR decay after tillage was best estimated by slope gradient and cumulative rainfall (NSE = 0.95) or kinetic energy (NSE = 0.96). After tillage, the soil bulk density, crust thickness and soil cohesion increased significantly over time under different topographic conditions. RR decreased linearly with increasing bulk density, crust thickness, and cohesion. The breakdown of aggregates or clods was the dominant process leading to soil surface roughness decay in this study.

Long-term agricultural management effects on surface roughness and consolidation of soils

Soil surface characteristics affect soil–water interactions and are in turn influenced by a variety of soil properties. Likewise, the state and temporal change of soil surface roughness are major drivers for the interaction between soil and water.The use of different tillage tools such as plough or chisel directly affects soil roughness parameters. Moreover, soil roughness and soil consolidation after management may also be affected indirectly through the effect of different management practices on soil properties.This study examines the effects of two different long-term soil management experiments on soil roughness and the process of soil consolidation. At site Fuchsenbigl (FB), conventional tillage has been compared to reduced tillage since 1988. At site Ritzlhof (RH), three different methods of fertilization (green waste, mineral fertiliser, no fertiliser application) have been tested since 1991. We assumed that the different management practices had influenced soil properties – most likely organic carbon content – affecting soil roughness and soil consolidation.The photogrammetric method was applied to test these assumptions, and various soil surface roughness indices (random roughness, orientated roughness, limiting slope, limiting distance, tortuosity) successfully identified different initial roughness values.The limiting elevation difference index (Linden and van Doren, 1986) revealed significant differences between the sites FB 2012 (17mm) and RH 2012 (28mm) and between different years RH 2013 (22mm) after chiselling. We attributed the site distinction to the different soil textures and the temporal differences to the different water contents at time of management.The decay of roughness for all sites and treatments (n=276) parameterized by the RR Index followed the equation RR=94.6 e−0.001.We were also able to distinguish significant consolidation effects of different long-term treatments with respect to tillage intensity at site FB. The maximum consolidation for reduced tillage was 13.8mm compared to 16.8mm for conventional treatment. In contrast, no effects of different fertiliser application at site RH were observed. For all sites and treatments (n=35), soil consolidation (C in mm) due to precipitation (P in mm) followed the equation C=4.23×ln(1+P) with an r2 of 0.71.

Evolution of nanoscale roughness in Cu/SiO2 and Cu/Ta interfaces

Synchrotron x-ray scattering was used to study the evolution of interface roughness with annealing for a series of Cu thin films. The films were encapsulated in SiO2 or Ta/SiO2 and prepared by sputter deposition. Specular x-ray reflectivity was used to determine the root mean square roughness for both the upper and the lower Cu/SiO2 (or Cu/Ta) interfaces. The lateral roughness was studied by diffuse x-ray reflectivity. Annealing the films at 600 °C resulted in a smoothing of only the upper interface for the Cu/SiO2 samples, while the lower Cu/SiO2 interfaces and both interfaces for the Ta encapsulated films did not evolve significantly. This difference in kinetics is consistent with the lower diffusivity expected of Cu in a Cu/Ta interface (compared to a Cu/SiO2 interface) and the mechanical rigidity of the lower Cu/SiO2 interface. As a function of roughness wavelength, the upper Cu/SiO2 interfaces exhibited a roughness decay with annealing that was only 12.5% of that expected for classical capillarity driven smoothening of a free surface.

Significance of soil erosion on soil surface roughness decay after tillage operations

Soil surface roughness (SSR) indicates a soil's susceptibility to wind and water erosion and it is strongly related to field management practices. Several methods have been developed to capture and evaluate SSR under specific field and climate conditions. Based on previously developed techniques, the shadow analysis method has been shown to be a suitable technique for characterising SSR in the field when used in arid and semi-arid regions of Spain. This is because of the climate and soil conditions that prevail during the spring and summer in the semiarid regions of Spain. However, the method has not yet been used in whole climate and edaphic conditions and still needs further development. Therefore, the goal of this study was to assess the SSR decay of a sandy clay loam soil after fall tillage operations using the shadow analysis method. The experiment was performed in the field in eight controlled 1 m 2 plots of a Technosol ( FAO, 2006). The project was designed to evaluate the validity of the method for further measuring SSR decay and to overcome potential problems associated with the method. The data were collected from the beginning of the fall of 2009, after tillage operations, through the spring of 2010, when the fields were tilled again. Half of the experimental plots were covered and used as controls. The remainder of the plots was uncovered to evaluate SSR decay mainly associated with water erosion. The average SSR was similar for the two subsets at the beginning of the experiment with 68% and 70%, respectively. The SSR after the experimental trial showed marked differences between the covered (45%) and uncovered plots (20%) after 53.2 mm of rainfall. The parameters demonstrated that the method can be used to study the influence of wind and water erosion on SSR decay at field conditions throughout the year. The shadow analysis technique has the advantages of being non-disturbing, easy to handle and less time consuming than other classical techniques. However, the method presents some limitations and further research must be conducted to adjust for utilisation in the field.

Degradation of the soil surface roughness by rainfall in two loess soils

The soil surface roughness is one of the main factors affecting wind erosion. Little is known about the influence of rains on the degradation rate of the soil surface roughness in different tillage systems and soil types. The purpose of this paper was to evaluate the dynamics of the oriented (Kr) and the random (Crr) soil surface roughness as affected by three tillage tools: a disk tandem (DT), a lister-bedder (LB) and a drill-hoe (DH), and two rain amounts (7 and 28 mm), in two soil types (an Entic Haplustoll and a Typic Ustipsamment). Measured Kr and Crr decay rates were compared with the predicted data, according to the equations provided by the Revised Wind Erosion Equation (RWEQ). Results indicated that initial Kr values were different in each tillage tool in both soils (LB > DH > DT, p < 0.05), while Crr values were mostly similar. The degradation rate of Kr (ORR) was in general higher in the Ustipsamment than in the Haplustoll and in DT than in DH and LB, in both soils. The degradation rate of Crr (RRR) was affected by the soil type (mostly higher in the Ustipsamment than in the Haplustoll) but not by tillage. Increasing rains degraded Kr and Crr at higher rates in both soils, but Kr degraded relatively less when its initial values were higher (LB < DH < DT). RWEQ equations underestimated the soil surface roughness decay in both studied soils, between 60 and 72% for RRR and between 90 and 97% for ORR. The accumulated rain amounts (CUMR) and rain energy (CUMEI) allowed a good prediction of the relative degradation of the oriented roughness. The relative Kr variation as a function of the initial Kr value varied potential negatively and were different for each soil and rain amounts. These equations may allow the calculation of the degradation rate of the oriented roughness as affected by certain rain amounts and the initial Kr. In view of these results it must be further investigated if a unique equation can be developed for predicting soil surface degradation for different soils and rain amounts.

Evolution of the soil surface roughness using geostatistical analysis

The objective of this work was to investigate the decay of initial surface roughness induced by simulated rainfall under different soil residue cover and to compare classical statistical indices with geostatistical parameters. A conventionally tilled loamy soil with low structure stability, thus prone to crusting was placed at 1 m² microplots. Each microplot received three successive rainfall events which bring about cumulative 25 mm, 50 mm and 75 mm at 65 mm h-1 intensity. Five treatments without replication were tested with different corn straw quantities (0, 1, 2, 3 and 4 Mg ha"1). Soil surface microrelief was measured at the initial stage and after each simulated rainfall event. Five treatments and four surface stages were monitored, resulting in 20 data sets. Point elevation data were taken at 0.03 m intervals using a pinmeter. Digital elevation models were generated and analysed using semivariograms. All data sets showed spatial dependence and spherical models were fitted to experimental semivariograms. A very significant relationship was found between the random roughness index, RR, and the sill of the semivariogram (C0+C1). All the treatments showed a clear trend to sill value reduction with increasing precipitation. However, roughness decay was lower in treatments with higher straw cover (3 and 4 Mg ha-1). Therefore, residue cover limited soil surface roughness decline. The control treatment, without straw, showed the lowest nugget effect (C0), which means the lowest spatial discontinuity of all treatments in this study. The range of spatial dependence (a) also showed a trend to decrease with increased cumulative rain, which was most apparent in treatments without or with relatively low straw cover (0, 1 and 2 Mg ha-1). The suitability of using sill variance and range for describing patterns of soil surface microrelief decline is discussed.

Quantification of tillage, plant cover, and cumulative rainfall effects on soil surface microrelief by statistical, geostatistical and fractal indices

Abstract. Changes in soil surface microrelief with cumulative rainfall under different tillage systems and crop cover conditions were investigated in southern Brazil. Surface cover was none (fallow) or the crop succession maize followed by oats. Tillage treatments were: 1) conventional tillage on bare soil (BS), 2) conventional tillage (CT), 3) minimum tillage (MT) and 4) no tillage (NT) under maize and oats. Measurements were taken with a manual relief meter on small rectangular grids of 0.234 and 0.156 m2, throughout growing season of maize and oats, respectively. Each data set consisted of 200 point height readings, the size of the smallest cells being 3×5 cm during maize and 2×5 cm during oats growth periods. Random Roughness (RR), Limiting Difference (LD), Limiting Slope (LS) and two fractal parameters, fractal dimension (D) and crossover length (l) were estimated from the measured microtopographic data sets. Indices describing the vertical component of soil roughness such as RR, LD and l generally decreased with cumulative rain in the BS treatment, left fallow, and in the CT and MT treatments under maize and oats canopy. However, these indices were not substantially affected by cumulative rain in the NT treatment, whose surface was protected with previous crop residues. Roughness decay from initial values was larger in the BS treatment than in CT and MT treatments. Moreover, roughness decay generally tended to be faster under maize than under oats. The RR and LD indices decreased quadratically, while the l index decreased exponentially in the tilled, BS, CT and MT treatments. Crossover length was sensitive to differences in soil roughness conditions allowing a description of microrelief decay due to rainfall in the tilled treatments, although better correlations between cumulative rainfall and the most commonly used indices RR and LD were obtained. At the studied scale, parameters l and D have been found to be useful in interpreting the configuration properties of the soil surface microrelief.

Assessing soil surface roughness decay during simulated rainfall by multifractal analysis

Abstract. Understanding and describing the spatial characteristics of soil surface microrelief are required for modelling overland flow and erosion. We employed the multifractal approach to characterize topographical point elevation data sets acquired by high resolution laser scanning for assessing the effect of simulated rainfall on microrelief decay. Three soil surfaces with different initial states or composition and rather smooth were prepared on microplots and subjected to successive events of simulated rainfall. Soil roughness was measured on a 2×2 mm2 grid, initially, i.e. before rain, and after each simulated storm, yielding a total of thirteen data sets for three rainfall sequences. The vertical microrelief component as described by the statistical index random roughness (RR) exhibited minor changes under rainfall in two out of three study cases, which was due to the imposed wet initial state constraining aggregate breakdown. The effect of cumulative rainfall on microrelief decay was also assessed by multifractal analysis performed with the box-count algorithm. Generalized dimension, Dq, spectra allowed characterization of the spatial variation of soil surface microrelief measured at the microplot scale. These Dq spectra were also sensitive to temporal changes in soil surface microrelief, so that in all the three study rain sequences, the initial soil surface and the surfaces disturbed by successive storms displayed great differences in their degree of multifractality. Therefore, Multifractal parameters best discriminate between successive soil stages under a given rain sequence. Decline of RR and multifractal parameters showed little or no association.

Analysis of surface roughness in relation to soil loss and runoff at high rainfall intensities

AbstractThe decay of roughness is an important factor governing surface processes such as infiltration and soil erosion. Thus the decay of surface roughness under different surface conditions was investigated and related to quantitative amounts of soil loss, runoff and sediment concentration in a laboratory experiment.Rainfall with an intensity of 128 mm/h was applied to a bare or mulched surfaces of a sandy loam soil with known surface roughness at specified time intervals. The decay of roughness as expressed by roughness ratio, in this experiment, was better predicted when related to an exponential function of the square root of cumulative kinetic energy of rainfall rather than with the cumulative rainfall. The roughness decay equations in literature did not predict breakdown under mulched surfaces accurately. Thus the exponent parameters of the roughness decay equations were adjusted to reflect the reduced decay occurring under mulched surfaces.In a bare soil, regression equations expressing the dependent variables as a function of initial roughness index were significant, but with low coefficients of determination, being 0·39 for soil loss, 0·12 for runoff and 0·36 for sediment concentration. In addition to initial roughness index, cumulative kinetic energy of rainfall was further included in the regressions. This led to an increase in coefficients of determination, which was 0·81 for soil loss, 0·74 for runoff and 0·49 for sediment concentration.The coefficients of determination (0·87 for soil loss, 0·85 for runoff and 0·51 for sediment concentration) were further increased when the final roughness index was included in addition to initial roughness index and cumulative kinetic energy in the regressions.This work shows that soil loss and runoff could be predicted from bare soil surface provided the initial roughness and the energy of rainfall is known. However, field verifications of these relationships are needed under different tillage tools and under natural rainfall. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Within-storm soil surface dynamics and erosive effects of rainstorms

This study deals with the characteristics which make a rainstorm an event that can produce intense erosion and even trigger the formation of a badlands site. In order to keep the presentation closely linked to a real situation, a rainstorm which took place on an experimental farm equipped for soil erosion studies was selected. The effects of the erosive rainstorm, which fell on dry antecedent moisture conditions, are given in terms of total rill erosion and rill cross-section along the slope. Unfortunately, the data collected did not answer the basic question, i.e., what combination of factors makes a rainstorm critical? A set of rainfall simulation experiments was therefore carried out, in the field and in the laboratory, in order to evaluate the soil surface variations caused by the rainstorm. All the experiments were performed on dry antecedent soil moisture conditions. It was confirmed that the characteristics of the infiltration curve are modified considerably during such rain events. The saturated conductivity of the first thin top-layer is also modified and it can easily decrease by a factor of 10 due to drop impact forces. The runoff coefficient is also influenced by the raindrop impacting energy and it increases sharply with cumulate energy until a maximum value is reached. The surface micro-relief dynamics was also studied. It was very clearly shown that impacting drop kinetic energy is the rainfall characteristic which is linked to random roughness decay. Cumulative rainfall was not able to align all the data in a single trend. The effect of surface micro-relief decay on the rainstorm erosive power was examined using two equations, thus linking Manning's hydraulic roughness to random roughness. Using a simulated runoff over the field plots that were particularly eroded by the rainstorm, it was possible to observe that the runoff drag forces reached values of between 3 and 100 times the ones which would have been calculated if the random roughness had been constant during the same event. Many of the soil surface characteristics that are modified interact with one another and with erosion. Examining each of them in isolation cannot explain the drastic increase in erosivity of a rainstorm, as the latter is the result of the combined effects of all the surface modifications.

An interdisciplinary approach to the electrochemistry at solid electrodes

An interdisciplinary approach to the electrochemistry at solid electrodes is presented here taking into account new basic interpretations for either phase growth or phase disruption under conditions far from equilibrium. For this purpose imaging data derived from scanning tunneling microscopy (STM) and atomic force microscopy (AFM) at different scale lengths are extremely useful. This approach provides new insights into roughness development, roughness decay and reactivity at solid electrodes. The study of mobile interfaces by the sequential application of in situ STM data and an interpretation based on the dynamic scaling theory furnish a qualitative and a quantitative description of surface irregularities, and provide information about the interface evolution mechanism under steady and non-steady roughness regimes. Various examples of electrochemical interest are discussed on the basis of this interdisciplinary approach.

Effect of surface re-emission on the surface roughness of film growth in low pressure chemical vapor deposition

For films deposited by low pressure chemical vapor deposition (LPCVD) the effect of roughness in the underlying substrate on film microstructure is investigated by computer simulation. Previous workers have assumed a normal surface velocity related to the local surface curvature; however, transport in many LPCVD systems has been shown to be governed by surface re-emission of the deposition precursors with a single sticking coefficient. In this article, the dependence of film profile evolution on both the sticking coefficient of the precursors, as well as the wave number of the underlying roughness is demonstrated. All wave numbers are shown to grow in the small time regime, for all values of the sticking coefficient except zero. At longer times, the mechanism of cusp formation is shown to arrest this growth for small but finite values of the sticking coefficient. In the limit that the sticking coefficient approaches zero, a simple geometric model for profile evolution is developed to accurately predict both the time required for cusp formation, as well as the maximum rate of decay of roughness. All wave numbers grow for large values of the sticking coefficient, eventually leading to the formation of a columnar microstructure with voids. For the sticking coefficient equal to unity, small geometric perturbations on the starting surface are shown to grow into asymptotic columns. Pair interactions between adjacent, unequal perturbations are studied, and larger columns are found to ‘‘shadow’’ smaller columns. For low values of the sticking coefficient, these interactions result in slowing down the decay of surface roughness by an effective halving of the wave number. The conclusions obtained from simulating deposition on periodic, sinusoidal surfaces are shown to be useful in understanding deposition on statistically rough surfaces.

Effect of the solution composition and the applied potential on the kinetics of roughness relaxation at gold electrodes in slightly acid electrolytes

The roughness relaxation of thin columnar Au electrodeposits at constant potential and 25°C in 0.05 M NaF, 0.05 M KCl and 0.05 M K 2SO 4 has been studied. These measurements were taken in the −0.6 to 0.8 V (vs Hg/Hg 2SO 4 reference electrode) potential range. The kinetic data were obtained from the roughness factor decay over 5 × 10 4 s. The value of the surface diffusion coefficient D s of Au atoms was derived from the roughness decay law at constant potential and pH. At any potential, the value of D s increases in the order NaF < K 2SO 4 < KCl. This sequence correlates with the specific adsorption of anions on Au. In K 2SO 4 and NaF solutions, as the electroformation of AuOH species takes place, the effect of SO 4 2− and F − ions is no longer observed. In contrast, in 0.05 M KCl solution, the value of D s increases steadily as the applied potential is increased positively.

The impedance response of electrochemically roughened platinum electrodes. Surface modeling and roughness decay

The impedance response of electrochemically roughened Pt electrodes with roughness factors ranging from approximately 1.5 to 800 has been determined under experimental conditions involving a penetration depth of the ac signal exceeding the pore depth. Comparative data were obtained for smooth polycrystalline, preferred-oriented, and platinized Pt electrodes in the same solution. The roughness of the interface was modeled as asymmetric truncated conical pores on the electrode, i.e. a limiting approach to the brush-like structure derived from scanning tunneling microscopy imaging for this type of electrode. The impedance data were approximated with a finite transmission line equivalent circuit for a cylindrical pore. The time dependent change in the impedance response correlates with the kinetics of roughness decay resulting from independent measurements.

SOIL PROPERTIES EFFECT ON RANDOM ROUGHNESS DECAY BY RAINFALL

ABSTRACT Rainfall modifies random roughness (RR) at varying rates for different soils. Methods to estimate RR decay are needed for computer models which simulate physical processes occurring at or near the soil surface. The objective of this study was to estimate RR decay curves as a function of soil properties. Surface roughness has been reported for selected soils before and after simulated rainfall (5 to 80 mm on five soils, 35 to 300 mm on one soil) and before and after natural rainfall (7 to 350 mm on two soils). The soils represent a wide range of textural and physical properties. A modified exponential function was fit to normalized RR values (RR after rainfall/initial RR) using rainfall amount as an independent variable. The coefficients of this function were tiien approximated as a function of two soil properties: percentage organic carbon and percentage clay. Surface stability increased with greater amounts of organic carbon. Surface stability increased with clay content to about 31% and then decreased with greater amounts of clay. Random roughness decay curves may be estimated for specific soils by using the exponential function.

Stated monthly meeting, October 18, 1939

Soil surface characteristics affect soil–water interactions and are in turn influenced by a variety of soil properties. Likewise, the state and temporal change of soil surface roughness are major drivers for the interaction between soil and water.The use of different tillage tools such as plough or chisel directly affects soil roughness parameters. Moreover, soil roughness and soil consolidation after management may also be affected indirectly through the effect of different management practices on soil properties.This study examines the effects of two different long-term soil management experiments on soil roughness and the process of soil consolidation. At site Fuchsenbigl (FB), conventional tillage has been compared to reduced tillage since 1988. At site Ritzlhof (RH), three different methods of fertilization (green waste, mineral fertiliser, no fertiliser application) have been tested since 1991. We assumed that the different management practices had influenced soil properties – most likely organic carbon content – affecting soil roughness and soil consolidation.The photogrammetric method was applied to test these assumptions, and various soil surface roughness indices (random roughness, orientated roughness, limiting slope, limiting distance, tortuosity) successfully identified different initial roughness values.The limiting elevation difference index (Linden and van Doren, 1986) revealed significant differences between the sites FB 2012 (17 mm) and RH 2012 (28 mm) and between different years RH 2013 (22 mm) after chiselling. We attributed the site distinction to the different soil textures and the temporal differences to the different water contents at time of management.The decay of roughness for all sites and treatments (n = 276) parameterized by the RR Index followed the equation RR = 94.6 e−0.001.We were also able to distinguish significant consolidation effects of different long-term treatments with respect to tillage intensity at site FB. The maximum consolidation for reduced tillage was 13.8 mm compared to 16.8 mm for conventional treatment. In contrast, no effects of different fertiliser application at site RH were observed. For all sites and treatments (n = 35), soil consolidation (C in mm) due to precipitation (P in mm) followed the equation C = 4.23 × ln(1 + P) with an r2 of 0.71.