A simulation model for unified interrill erosion and rill erosion on hillslopes

A mathematical model was developed for simulating runoff generation and soil erosion on hillslopes. The model is comprised of three modules: one for overland flow, one for soil infiltration, and one for soil erosion including rill erosion and interrill erosion. Rainfall and slope characteristics affecting soil erosion on hillslopes were analysed. The model results show that the slope length and gradient, time distribution rainfall, and distribution of rills have varying influence on soil erosion. Erosion rate increases nonlinearly with increase in the slope length; a long slope length leads to more serious erosion. The effect of the slope gradient on soil erosion can be both positive and negative. Thus, there exists a critical slope gradient for soil erosion, which is about 45° for the rate of erosion at the end of the slope and about 25° for the accumulated erosion. Copyright © 2005 John Wiley & Sons, Ltd.     

Evaluation of an interrill soil erosion model using laboratory catchment data

Physically based soil erosion simulation models require input parameters of soil detachment and sediment transport owing to the action and interactions of both raindrops and overland flow. A simple interrill soil water transport model is applied to a laboratory catchment to investigate the application of raindrop detachment and transport in interrill areas explicitly. A controlled laboratory rainfall simulation study with slope length simulation by flow addition was used to assess the raindrop detachment and transport of detached soil by overland flow in interrill areas. Artificial rainfall of moderate to high intensity was used to simulate intense rain storms. However, experiments were restricted to conditions where rilling and channelling did not occur and where overland flow covered most of the surface. A simple equation with a rainfall intensity term for raindrop detachment, and a simple sediment transport equation with unit discharge and a slope term were found to be applicable to the situation where clear water is added at the upper end of a small plot to simulate increased slope length. The proposed generic relationships can be used to predict raindrop detachment and the sediment transport capacity of interrill flow and can therefore contribute to the development of physically‐based erosion models. Copyright © 1999 John Wiley & Sons, Ltd.     

Empirical relations for the sediment transport capacity of interrill flow

Experiments were carried out in order to measure the sediment transport capacity of interrill flow with and without rainfall and to relate the transport capacity to selected hydraulic parameters, such as effective stream power and shear velocity. Different sediments were used in order to study the effect of grain size. The proposed relationships show considerable variations with grain size and there is only a minor effect of rainfall on the transport capacity which also seems to be grain size dependent. The proposed relationships can be used to predict sediment transport capacity of interrill flow and can therefore contribute to the development of physically based erosion models.     

Erodibility of soil and organic matter: independence of organic matter resistance to interrill erosion

The enrichment of organic matter in interrill sediment is well documented; however, the respective roles of soil organic matter (SOM) and interrill erosion processes for the enrichment are unclear. In this study, organic matter content of sediment generated on two silts with almost identical textures, but different organic matter contents and aggregations, was tested. Artificial rainfall was applied to the soils in wet, dry and crusted initial conditions to determine the effects of soil moisture and rainfall and drying history on organic matter enrichment in interrill sediment. While erosional response of the soils varied significantly, organic matter enrichment of sediment was not sensitive to initial soil conditions. However, enrichment was higher on the silt with a lower organic matter content and lower interrill erodibility. The results show that enrichment of organic matter in interrill sediment is not directly related to either SOM content or soil interrill erodibility, but is dominated by interrill erosion processes. As a consequence of the complex interaction between soil, organic matter and interrill erosion processes, erodibility of organic matter should be treated as a separate variable in erosion models. Further research on aggregate breakdown, in particular the content and fate of the organic matter in the soil fragments, is required. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of the grain-for-green program on soil erosion in China

Severe soil erosion is a serious environmental problem in China.In 1999 the Chinese government implemented the Grain-for-Green Program (herein referred to as the Program),a well rounded program of ecol...     

Impact of rainfall pattern on interrill erosion process

The impact of rainfall pattern on the interrill erosion process is not fully understood despite its importance. Systematic rainfall simulation experiments involving various rainfall intensities, stages, intensity sequences, and surface cover conditions were conducted in this study to investigate their effects on the interrill erosion process. Five rainfall patterns designed with the same total kinetic energy/precipitation (increasing, decreasing, rising–falling, falling–rising and constant patterns) were randomly delivered to a pre‐wet clay loam soil surface at a 10° slope gradient. Significant differences in soil losses were observed among the different rainfall patterns and stages, but there was no obvious difference in runoff. Kinetic energy flux (KE_r) was a governing factor for interrill erosion, and constant rainfall pattern (CST) produced nine times greater soil loss than runs with no KE_r. Varied‐intensity patterns had a profound effect on raindrop‐induced sediment transport processes; path analysis results indicated that said effect was complex, interactive and intensity‐dependent. Low hydraulic parameter thresholds further indicated that KE_r was the dominant factor in detaching soil particles, while overland flow mainly contributed to transporting the pre‐detached particles. This study not only sheds light on the mechanism of interrill sediment transport capacity and detachability, but also may provide a useful database for developing event‐based interrill erosion prediction models. Copyright © 2017 John Wiley & Sons, Ltd.     

The use of small flumes for the determination of soil erodibility

The objective of this study was to examine the possibility of determining soil erodibility of loamy soils with small flumes. This was done by comparing the classification of soil erodibility obtained in the field with that obtained in the laboratory. Therefore twenty soils with a texture varying from silty loam to sandy loam were selected from the Leuven region. The erosion in the field was determined by measuring the volumetric evolution of the rill pattern. In the laboratory the soils were tested with a rainfall simulator and small flumes. The conclusion was that for loamy soils the flume experiments are a quick, simple, and reliable method for the determination of the relative soil erodibility.     

Size characteristics of sediment in interrill overland flow on a semiarid hillslope,Southern Arizona

This study examines the size characteristics of sediment removed from a semiarid hillslope by interrill overland flow. Rainfall simulation experiments were conducted on a runoff plot 18 m wide and 35 m long established on a piedmont hillslope in southern Arizona. The top of the plot coincided with the hillslope divide, and its outlet was located within a shallow rill. Samples of runoff were obtained from two cross-sections located in the interrill portion of the plot upslope of the rill and from a calibrated flume through which was directed interrill overland flow reaching the bottom of the plot. Analyses of sediment contained in these samples showed that sediment in interrill flow is finer than the matrix soil. The fineness of the interrill sediment compared to the matrix soil appears to be due to the inability of interrill overland flow to transport the coarser fraction of the sediment supplied to it by raindrop detachment. This finding implies that the rate of soil erosion in interrill areas is not. as is commonly supposed, limited by the rate at which raindrops can detach sediment but by the rate at which they detach sediment of a size that the overland flow is competent to transport. The relative fineness of sediment eroded from this hillslope is consistent with other evidence for the recent evolution of shrub-covered hillslopes in southern Arizona.     

Runoff and interrill erosion on sandy soils under cultivation in the western Paris basin: mechanisms and an attempt at measurement

Measurements made on different scales, such as rainfall simulations on 1 m² and 20 m² experimental plots and water sampling at the outlet of a watershed, enable the analysis of the mechanisms of pluvial erosion and therefore the importance of runoffs and soil losses in the hilly and sandy parts of the western Paris basin. Interrill erosion accounts for slow transfer of materials towards the lower part of plots and slopes. The overland flow caused by restructuring of the surface Tertiary and Cenomanian soils erodes some 150 to 200 kg ha^?1 during the month following sowing. Only a part of these deposits reach the river, which carries away less than 50 kg ha^?1 each month. Interrill erosion makes slopes still more uneven, fills in valley bottoms, and so paves the way to catastrophic erosion, which scoops out rises in the ground and colluvial deposits in the lower part of slopes and valley bottoms. Copyright © 2001 John Wiley & Sons, Ltd.     

MODELING OF INTERRILL EROSION IN THE LOESS PLATEAU OF CHINA

IINTRODUCTIONTheinterrillerosiononafieldplotisaffectedbythekineticenergyoftherainfall,wind,topographyfactors,propertiesofsoilandthecanopy.Theinterrillerosionoccursasthefirstdropimpactsthehillslopes.Theinterrillerosionoccursinallkindsofrainfallandtheamountofthesplasherosion,whichisthemainpartofinterrillerosion,canaccountforagreatpanofthetotalerosionamountinaheavystorm(Baner1990,Glymph1957,QianandWan1986,Zhou1981).Therefore,itisveryimportanttorevealthemechanismtoestimatetheamountofinterri…     

Effects of grass contour hedgerow systems on controlling soil erosion in red soil hilly areas,Southeast China

Soil erosion by water is a well-recognized serious environmental problem in the world.While contour hedgerow systems are an effective method for soil water conservation,there are a few studies on its effect in the red soil hilly areas in Southeast China.With a fixed field experiment,we constructed a runoff plot at hilly area in Zhuji County,Zhejiang province,to evaluate the effect of the grass hedgerows in soil water conservation,and to determine the optimized hedgerow patterns.Hemerocallis citrine(HC)and Ophiopogon japonicas(OJ) were selected to build the hedgerows in patterns of one row and two rows.The REE method was used to trace the source of the sediment for a better understanding of the characteristic and mechanism of erosion with hedgerows control.Our results showed that(1) hedgerows reduced erosion and surface runoff by 31.99-67.22%and 15.44-45.11%,respectively;(2) hedgerows delayed the development of rills;(3) hedgerows reduced the soil nutrients loss;(4) hedgerows reshaped the soil physical properties,especially in increasing > 0.25 mm water-stable aggregates.Taken together,our results suggest that two-row OJ is the optimized contour hedgerow pattern in the experiment condition,and downward sloping land should have the highest priority to take measures for soil water conservation.This research comprehensively studied the effects and mechanism of contour hedgerows in controlling soil and water loss in red soil hilly areas,Southeast China,so that the practice of soil and water conservation can be implemented more effectively in these areas.     

The soil erosion bridge: A device for micro-profiling soil surfaces

The soil erosion bridge is a simple, robust, cheap, lightweight device comprising a bar which, when mounted on two stakes, provides a stable datum for micro-profiling the soil surface beneath. Its main advantage over similar devices is the unique combination of mounting clamps, which allow for variation in the distance and angle with respect to the vertical of the mounting stakes without loss of accuracy. The design, installation and measurement procedures are described. Applications and limitations are discussed.     

A stochastic distributed model of soil erosion by overland flow

A model has been built to simulate runoff and erosion on slopes of varying form with soil of varying hydraulic conductivity, porosity, storage capacity, and particle size distribution. The model is based on known physical laws and takes into account spatially dependent random variation in the initial conditions of the soil. The rainfall is similarly both random and autocorrelated in space. Detailed results show how runoff is generated as a result of slow conductivity and high water table, how this leads to erosion, the degradation of the land surface, the capture of flow lines, and the development of networks of rills. The last accords well with results from laboratory experiments. Changing the initial conditions produces results that accord with intuition and reality.     

Time-dependency of runoff velocity and erosion the effect of the initial soil moisture profile

The paper reports on experiments carried out to evaluate the effect of the initial soil moisture profile on temporal variations in runoff erosion rate. The moisture profile was varied by applying infrared heating to the soil sample surface over various time periods, while runoff erosivity was varied by varying the slope of the flume. The experiment confirms that dry loamy soils are very erodible: on a slope length of only 4.3 m long sediment concentrations are near transporting capacity in case of a dry soil sample. It appears that temporal variations in sediment concentrations can be well simulated using a simple relationship between runoff erosion resistance and initial soil moisture content, thereby implicitly assuming that the effect of initial moisture content is persistent over the whole duration of the experiment. The implications of these findings with respect to the modelling of sediment output from larger catchments and the design of experiments on rill erodibility are discussed. The experiments also show that, under the present circumstances, mean velocities in the rills appear to be independent of slope. This finding may be of importance with respect to overland flow routing and deterministic erosion modelling.     

Loess erosion change modeling during heavy rainfall

A typical gully sub-basin with a complex geomorphological form is used to do a model test of gravity erosion of loess by considering the sequence of slopes in a prototype gully creating a sequence of underlying surface forms in the upper reaches. The results show that the runoff from heavy rainfall is the main external force for the erosion of loess, and also is an important influencing factor to stimulate and intensify the development of gravity erosion. The soil structure and the height of the...     

Tracing sediment movement in interrill overland flow on a semi-arid grassland hillslope using magnetic susceptibility

Experiments were undertaken to determine the feasibility of tracing sediment movement in interrill overland flow. Crushed magnetite was introduced as a source-line 10 cm wide by 8 m long on a runoff plot 18 m wide by 29 m long located in southern Arizona. Initial magnetic susceptibilities along this source line, and along three transects located 0·25, 2·95 and 5 m downslope of the source-line, were measured. Movement of the magnetite in response to three rainfall simulation experiments was monitored. During the first two experiments, overland flow discharge was sampled at miniature flumes located along two cross sections on the plot downslope of the source-line, and at a supercritical flume at the plot outlet. Magnetic susceptibilities along the source-line and transects were measured after all three experiments. Results show that the magnetite moves very early in the experiments and that it reaches one of the flumes 2 m downslope of the source-line in 3 min. Most of the tracer moves a very short distance: 29·7 per cent is deposited within 25 cm of the source-line and only 2·2 per cent is deposited 2·95 m away. The deposition rate appears to decrease exponentially away from the source-line. Very little magnetite is recorded in the flow through the miniature flumes: in general it makes up less than 1 per cent of the total sediment load. No temporal pattern in these percentages is observed. Magnetite appears to be an effective tracer of sediment movement in interrill overland flow, though its higher density than natural soil may affect its detachment and transport.     

Mechanics of interrill erosion with wind‐driven rain

The vector physics of wind‐driven rain (WDR) differs from that of wind‐free rain, and the interrill soil detachment equations in the Water Erosion Prediction Project (WEPP) model were not originally developed to deal with this phenomenon. This article provides an evaluation of the performance of the interrill component of the WEPP model for WDR events. The interrill delivery rates were measured in the wind tunnel facility of the International Center for Eremology (ICE), Ghent University, Belgium with an experimental setup to study different raindrop impact velocity vectors. Synchronized wind and rain simulations with wind velocities of 6, 10 and 14 m s^–1 were applied to a test surface placed on windward and leeward slopes of 7, 15 and 20%. Since both rainfall intensity and raindrop impact velocity varied greatly depending on differences in the horizontal wind velocity under WDRs, the resultant kinetic energy flux (KE_r, in J m^–2 s^–1) was initially used in place of the WEPP model intensity term in order to incorporate the effect of wind on impact velocity and frequency of raindrops. However, our results showed only minor improvement in the model predictions. For all research data, the model Coefficients of Determination (r²) were 0·63 and 0·71, when using the WEPP and the KE_r approaches, respectively. Alternately, integrating the angle of rain incidence into the model by vectorally partitioning normal kinetic energy flux (KE_rn, in J m^–2 s^–1) from the KE_r greatly improved the model's ability to estimate the interrill sediment delivery rates (r² = 0·91). This finding suggested that along with the fall trajectory of wind‐driven raindrops with a given frequency, raindrop velocity and direction at the point of impact onto the soil surface provided sufficient physical information to improve WEPP sediment delivery rate predictions under WDR. Copyright © 2012 John Wiley & Sons, Ltd.     

A conceptual model for determining soil erosion by water

Current estimates of rates of soil erosion by water derived from plots are incompatible with estimates of long‐term lowering of large drainage basins. Traditional arguments to reconcile these two disparate rates are ?awed. The ?ux of sediment leaving a speci?ed area cannot be converted to a yield simply by dividing by the area, because there is no simple relationship between ?ux and area. Here, we develop an approach to the determination of erosion rates that is based upon the entrainment rates and travel distances of individual particles. The limited available empirical data is consistent with the predictions of this approach. Parameterization of the equations to take account of such factors as gradient and sediment supply is required to proceed from the conceptual framework to quantitative measurements of erosion. However, our conceptual model solves the apparent paradox of the sediment delivery ratio, resolves recent discussion about the validity of erosion rates made using USLE erosion plots, and potentially can reconcile erosion rates with known lifespans of continents. Our results imply that previous estimates of soil erosion are fallacious. Copyright © 2004 John Wiley & Sons, Ltd.