a spectral approach for analyzing the rill structure over hillslopes part 1 development of stochastic theory abstract the rill structure over the soil surface plays an important role in determining the runoff and sediment loss from hillslopes the microtopography is often complicated and representation of the hillslope surface on a rill by rill basis is uneconomical and impractical a spectral approach combined with a stochastic theory is proposed for the rill profile the theory develops appropriate probability distribution laws for rill amplitudes and rill periods interrill areas under the assumption that the spectrum of the rill profile is narrow banded this study establishes a foundation for future studies dealing with parameter estimation and determining the global roughness and erodibility for runoff and sediment discharge predictions over hillslopes

an experimental study of rill erosion and morphology abstract rill erosion is recognized as an important process of water erosion on agricultural land the objectives of this study are to examine the effects of rainfall intensity on rill network development and to present some indicators for a quantitative description of rill morphology a soil pan 10 m long 3 m wide and 0 5 m deep and with an adjustable slope gradient from 0 to 30 was subjected to three successive rains under rainfall intensities of 50 and 100 mm h 1 the results showed that rainfall intensity significantly affected rill erosion especially in the active period of rill network development the magnitude of rill erosion was 28 5 and 33 1 kg m 2 and contributed 78 6 and 76 2 to the soil loss under rainfall intensities of 50 and 100 mm h 1 respectively the formation of rill network under the 50 mm h 1 intensity was more complex than that under the 100 mm h 1 intensity for the latter rill networks developed fast and then varied slightly the mean rill inclination angle mean rill density degree of rill dissection and mean rill tortuosity complexity cmean increased with the increase of rains under the same rainfall intensity the value was the optimal derivative morphological indicator to estimate rill erosion and morphology which was followed in descending order by mean cmean and

prediction of concentrated flow width in ephemeral gully channels empirical prediction equations of the form w d aq b have been reported for rills and rivers but not for ephemeral gullies in this study six experimental data sets are used to establish a relationship between channel width w m and flow discharge q m 3 s 1 for ephemeral gullies formed on cropland the resulting regression equation w d 2 51 q 0 412 r 2 d 0 72 n d 67 predicts observed channel width reasonably well owing to logistic limitations related to the respective experimental set ups only relatively small runoff discharges i e q 0 02 m 3 s 1 were covered using field data where measured ephemeral gully channel width was attributed to a calculated peak runoff discharge on sealed cropland the application field of the regression equation was extended towards larger discharges i e 5 10 4 m 3 s 1 q 0 1m 3 s 1 comparing w q relationships for concentrated flow channels revealed that the discharge exponent b varies from 0 3 for rills over 0 4 for gullies to 0 5 for rivers this shift in b may be the result of i differences in flow shear stress distribution over the wetted perimeter between rills gullies and rivers ii a decrease in probability of a channel formed in soil material with uniform erosion resistance from rills over gullies to rivers and iii a decrease in average surface slope from rills over gullies to rivers the proposed w q equation for ephemeral gullies is valid for sealed cropland with no significant change in erosion resistance with depth two examples illustrate limitations of the w q approach in a first example vertical erosion is hindered by a frozen subsoil the second example relates to a typical summer situation where the soil moisture profile of an agricultural field makes the top 0 02 m five times more erodible than the underlying soil material for both cases observed w values are larger than those predicted by the established channel width equation for concentrated flow on cropland for the frozen soils the equation w d 3 17 q 0 368 r 2 d 0 78 n d 617 was established but for the summer soils no equation could be established copyright 2002 john wiley sons ltd

experimental investigation of morphological characteristics of rill evolution on loess slope abstract the development of rill is the result of a complex interaction of soil properties with high spatial and temporal variability the rill morphology may act as a determinant as well as a stochastically driven process the description of their complex morphology requires geostatistics and nonlinear theories a study of the morphological characteristics of rill evolution was performed via indoor soil pan rainfall simulations experiments were run with loessial soil bulk density of 1 25 g cm 3 under a rainfall intensity of 90 mm h with a 20 slope gradient a detailed scan of the slope topographic analysis and statistical analyses were the main methods utilized in the study statistical analyses showed that characteristic parameters exhibited differences in the expression of the dynamic change of soil loss according to the comparison of quantitative methods we found that the fractal dimension can reflect the complexity of rill network but it is not able to reflect the dynamic changes of the erosion process perfectly in contrast geomorphologic comentropy is sensitive to the dynamic changes of soil erosion intensity and its variation can reflect the dynamic changes of erosion perfectly the topological parameters can reflect the degree of stability in the rill network structure but it is not suitable for reflecting the dynamic changes of erosion intensity the geomorphologic comentropy was evaluated as the most appropriate characterization parameter for the rill morphology description

new technique for measuring water depth in rill channels abstract water erosion is one of the most important soil degradation processes and rill erosion contribution to total soil loss is usually dominant as compared to interrill erosion rill erosion modelling requires that rill flow has to be adequately modelled flow depths in rills are typically of the order of millimeters to several centimeters and bed topography characterized by steep slope values significantly affects flow hydraulics in this paper a new technique for measuring the water depth inside a rill channel is proposed and the effects on flow resistance estimate are examined this technique couples an accurate ground survey of the rill channel obtained by close range photogrammetry with the survey of the water tracks inside the channel the comparison between the water depth measurements carried out by a micro hydrometer local technique and those obtained by the water tracks volumetric technique demonstrated that the data pairs are characterized by a wide scattering respect to the line of perfect agreement furthermore the hydraulic radius values obtained by the proposed volumetric technique are always greater than those corresponding to the local technique the developed analysis showed that the volumetric technique is affected by the adopted cross section spacing even if reliable results can be also obtained using a distance interval which is equal to ten times the best investigated reference condition which corresponds to the minimum tested distance interval having the same order of magnitude of the mean 3d dtm resolution using of the volumetric measurement technique for the water depth improved the agreement between the measured darcy weisbach friction factor values and those calculated by the theoretical flow resistance law based on a power velocity profile finally a constant scale factor equal to 0 8257 was proposed to convert the function of the power velocity profile obtained by local measurements into that corresponding to the volumetric technique

field experiments on the transport of rock fragments by animal trampling on scree slopes qualitative observations in an area with steep scree slopes in turkey suggested that trampling by goats and sheep may contribute significantly to the downslope movement of rock fragments in these environments therefore a series of field experiments was set up to determine the rate of rock fragment transport caused by trampling the experimental results allowed the calculation of a unit displacement distance from each trampling experiment which may then be used to extrapolate the measured transport rates over longer time periods and larger areas although such extrapolations should be interpreted with great caution the results demonstrate that trampling contributes significantly to rock fragment transport in such environments as calculated yearly displacement distances are equal to or higher than those reported in the literature for other geomorphic processes the observed travel distance distributions are not well described by a negative exponential distribution trampling causes a weak downslope sorting the coarsest clasts move farther but has a significant effect on vertical sorting and is one of the factors which can explain the layered structure of the scree slopes in the area

suitability of lidar point density and derived landform curvature maps for channel network extraction this study uses landform curvature as an approach for channel network extraction we considered a study area located in the eastern italian alps where a high quality set of lidar data was available and where channel heads and related channel network were mapped in the field in the analysis we derived 1 m dtms from different ground lidar point densities and we used different smoothing factors for the landscape curvature calculation in order to test the suitability of the lidar point density and the derived curvature maps for the recognition of channel network this methodology is based on threshold values of the curvature calculated as multiples 1 3 times of the standard deviation of the curvature our analyses suggested that i the window size for curvature calculations has to be a function of the size of the features to be detected ii a coarse ground lidar point density could be as useful as a finer one for the recognition of main channel network features and iii rougher curvature maps are not optimal as they do not explore a sufficient range at which features occur while smoother curvature maps overcome this problem and are more appropriate for the extraction of surveyed channels copyright 2010 john wiley sons ltd

a method for measuring erosive flow velocity with simulated rill abstract the water flow velocity along an eroding rill is of interests for understanding rill erosion hydrodynamics soil erosion makes the measurement of flow velocity highly variable in this paper a new method is suggested to simulate rills so as to make controllable and efficient measurements of erosive velocity of rill flow a series of comparative flume experiments were conducted to verify the method by measuring the shallow water flow velocity along both the simulated and real rills by using a computerized electrolyte tracer method the experiments involved three flow rates 12 24 and 48 l min and three slope gradients 5 10 and 15 five sensors were used to trace the solute transport processes at 30 60 90 120 and 150 cm from the location where the salt solute was injected into the water flow flow velocities under simulated rill and real conditions were computed by fitting the measured solute transport processes with its analytic solution the results showed that under different flow rates and slope gradients velocities along the simulated rill agreed very well with those along the real rill this demonstrates that the simulated rill well simulates the real rill this method will help further study of the hydrodynamics in eroding rill

emergence and erosion a model for rill initiation and development soil erosion by overland flow resulting from infiltration excess rainfall generates rill networks on hillslope areas the way in which these networks emerge and develop suggests that hillslope erosion functions as a self organizing dynamic system based upon this argument a model for soil erosion rillgrow 1 has been developed this operates at the spatial scale of raindrops and microtopography in this paper the second generation of the model rillgrow 2 is described and applied to four different soil surfaces results suggest that even at this early stage in its development rillgrow 2 is capable of replicating the success of the earlier model and in some cases of extending them the success of both models suggests that this self organizing view of rill generation may capture some fundamental aspects of the operation of real erosional systems copyright 2000 john wiley sons ltd

hydraulic conditions for rill incision under simulated rainfall a laboratory experiment a series of controlled laboratory experiments were conducted in order to obtain precise data on the hydraulic and sediment transport conditions during rill formation tests were carried out using a crusting prone binary mixed soil in a 15 m long flume at an average slope of 0 087 under simulated rainfall rainfall intensities varied from 30 35 mm h 1 and developed about 70 per cent of the kinetic energy of natural rainfall of similar intensity runoff and sediment discharge measured at the downstream weir were strongly influenced by rill forming processes essentially rill incision reduced runoff discharge as a result of increased percolation in rill channels but increased sediment discharge secondary entrainment processes such as bank collapse also increased sediment discharge at the weir knickpoint bifurcation and colluvial deposition however decreased sediment discharge rills always developed through the formation of a knickpoint the critical condition for knickpoint initiation was the development of supercritical flow and waves which mould and incise the bed prior smoothing of the soil surface by entrainment and redistribution of sediment facilitated supercritical flow statistical analysis showed that hydraulic and sediment transport conditions differed significantly in rilled and unrilled flows the relationship between sediment discharge rill erosion and flow hydraulics was found to be nonlinear conforming to a standard power function in the form y axb rills were also associated with significantly increased sediment transport capacities however rill initiation was not clearly defined by any specific hydraulic threshold instead rilled and unrilled flows were separated by zones of transition within which both types of flow occur

soil erodibility and processes of water erosion on hillslope abstract the importance of the inherent resistance of soil to erosional processes or soil erodibility is generally recognized in hillslope and fluvial geomorphology but the full implications of the dynamic soil properties that affect erodibility are seldom considered in canada a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility this paper aims to place this work in an international framework of research on water erosion processes and to identify critical emerging research questions it focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales essential for event based soil erosion prediction results show that many components of erosional response such as partitioning between rill and interrill or surface and subsurface processes threshold hydraulic conditions for rill incision rill network configuration and hillslope sediment delivery are strongly affected by spatially variable and temporally dynamic soil properties this agrees with other recent studies but contrasts markedly with long held concepts of soil credibility as an essentially constant property for any soil type properties that determine erodibility such as soil aggregation and shear strength are strongly affected by climatic factors such as rainfall distribution and frost action and show systematic seasonal variation they can also change significantly over much shorter time scales with subtle variations in soil water conditions organic composition microbiological activity age hardening and the structural effect of applied stresses property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and therefore both short and long term hillslope erosional response similar property changes linked to climatic conditions may also significantly influence the stability and resilience of plant species and vegetation systems full understanding of such changes is essential if current event based soil erosion models such as wepp and eurosem are to attain their full potential predictive precision the complexity of the interacting processes involved may however ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics

mineralogical and geochemical signature of mine waste contamination tresillian river fal estuary cornwall uk the mineralized district of sw england was one of the world s greatest mining areas with mining commencing in the bronze age peaking in the 1850s to 1890s but still continuing to the present day consequently it is not surprising that mining has had a major impact on the environmental geochemistry of sw england in this study the mineralogical and geochemical signature of mine waste contamination within the fal estuary at tresillian cornwall has been examined a pulse of mine waste contamination is recognized at approximately 50 cm below present day sediment surface sn as cu pb and zn are all enriched within this contaminated interval with up to 1800 mg kg 1 sn 290 mg kg 1 as 508 mg kg 1 pb 2210 mg kg 1 zn and 1380 mg kg 1 cu within this interval the dominant minerals present include chalcopyrite arsenopyrite pyrite cassiterite fe ti oxides ilmenite and rutile wolframite sphalerite baryte zircon monazite tourmaline and xenotime in addition man made slag products commonly occur the exact timing of the release of mine waste into the estuary is poorly constrained but probably occurred during or immediately following the peak in mining activity in the nearby camborne redruth district which was between 1853 and 1893 the mine waste may have entered the estuary either via the tresillian river and its tributaries or via calenick creek and the truro river and or the carnon river which flows into rostronguet creek

measuring rill erosion by laser scanning abstract this paper reports the results of a field investigation on the rill morphology and the corresponding soil loss using a terrestrial laser scanner tls at the masse experimental station umbria central italy laser scanning is a survey method that allows determining the three dimensional position of a large number of points point cloud through the measurement of angles azimuth and zenith and distances for this paper five scans were made of some rills which formed during particularly erosive rain in the plots of the masse station the point cloud was first interpolated by the natural neighbor method to create a discrete 0 02 m 0 02 m square cell grid digital elevation model dem used for mapping the flow network the same cloud was also used to generate a continuous modeling of the surface by the triangulated irregular network model tin to quantify the total eroded volume and the morphological characteristics of the rill formations three methods were applied to the dem for detecting the channel network the slope method horn 1981 wood 1996 the constant drop method described by broscoe 1959 and the method of landform curvature tarolli et al 2012 the comparison has shown a good agreement between the three methods but broscoe s method seems to be more accurate for rill recognition the morphological characteristics of the rill formations derived by the tin model i e length width depth and volume were compared with the corresponding characteristics obtained manually using a profilometer the analysis showed a good agreement between the width at the top measured by the two methods a general overestimation of the maximum depth and of the cross section areas and an underestimation of the rill length when the manual method is used lastly the comparison between the volumes obtained by the tls survey and by the manual method showed that the total volume calculated by the manual measurements overestimates that evaluated by the tls with a good agreement between these variables

the value of a physically based model versus an empirical approach in the prediction of ephemeral gully erosion for loess derived soils abstract a data set on soil losses and controlling factors for 58 ephemeral gullies has been collected in the belgian loess belt from march 1997 to march 1999 of the observed ephemeral gullies 32 developed at the end of winter or in early spring winter gullies and 26 ephemeral gullies developed during summer summer gullies the assessed data have been used to test the physically based ephemeral gully erosion model egem and to compare its performance with the value of simple topographical and morphological indices in the prediction of ephemeral gully erosion analysis shows that egem is not capable of predicting ephemeral gully cross sections well although conditions for input parameter assessment were ideal some parameters such as channel erodibility critical flow shear stress and local rainfall depth showed great uncertainty rather than revealing egem s inability of predicting ephemeral gully erosion this analysis stresses the problematic nature of physically based models since they often require input parameters that are not available or can hardly be obtained with respect to the value of simple topographical and morphological indices in predicting ephemeral gully erosion this study shows that for winter gullies and summer gullies respectively over 80 and about 75 of the variation in ephemeral gully volume can be explained when ephemeral gully length is known moreover when previously collected data for ephemeral gullies in two mediterranean study areas and the data for summer gullies formed in the belgian loess belt are pooled it appears that one single length l volume v relation exists v 0 048 l 1 29 r 2 0 91 these findings imply that predicting ephemeral gully length is a valuable alternative for the prediction of ephemeral gully volume a simple procedure to predict ephemeral gully length based on topographical thresholds is presented here secondly the empirical length volume relation can also be used to convert ephemeral gully length data extracted from aerial photos into ephemeral gully volumes

soil freeze thaw induced changes to a simulated rill potential impacts on soil erosion abstract flows in natural rills on hillslopes transport significantly more sediment down slope than overland flows which makes rills geomorphically significant landscape features the erosivity e g sediment transport capacity of the flows in rills is partially a function of the cross sectional geometry of the rill which determines flow velocity and depth conversely rill geometry is determined by flow erosivity and by soil processes that affect the erodibility and stability of soil along the rill thus complex feedbacks exist in the mechanics of rill erosion the objective of this study was to measure the effects of one of the soil processes that affect rill geometry soil freeze thaw ft cycling an unvegetated rectangular rill was subjected to two ft cycles each lasting several days in a controlled laboratory setting the ft cycling increased the water content and reduced the cohesion in the surface soil along the rill sufficiently to induce soil slumps and mud flows along the sidewalls of the rill these mass failures changed the rectangular rill to a triangular one which reduced the hydraulic radius of the rill by 32 using manning s equation it was estimated that this new geometry could reduce the velocity of the flow in this altered rill by about 25 the persistence of the new rill shape and thus that of the slower flow would depend on the complex interactions between flow velocity and the resistance of the slumped sediment to those flows that persistence was not investigated in this experiment these results can be used in parameterizing models of rill evolution that incorporate widening of rills by mass failures along the rill sidewalls

high resolution topography for understanding earth surface processes opportunities and challenges abstract in the last decade a range of new remote sensing techniques has led to a dramatic increase in terrain information providing new opportunities for a better understanding of earth surface processes based on geomorphic signatures technologies such as airborne and terrestrial lidar light detection and ranging to obtain high resolution topography have opened avenues for the analysis of landslides hillslope and channellization processes river morphology active tectonics volcanic landforms and anthropogenic signatures on topography this review provides an overview of the recent flourishing literature on high resolution topographic analyses underlining their opportunities and critical issues such as their limitations the goal is to provide answers to questions such as what kind of processes can be analyzed through high resolution topographic data and how to do it the review focuses on two different environments natural and engineered landscapes in both contexts high resolution topography offers opportunities to better understand geomorphic processes from topographic signatures particular attention is given to engineered landscapes in which the direct anthropic alteration of processes is significant the last part of the review discusses future challenges

permian triassic magnetostratigraphy new results from south china abstract continuous marine sediments of permian to triassic age are widely distributed over large areas in southern china they offer the potential for developing magnetostratigraphic columns to investigate the polarity status of the palaeomagnetic field three carbonate sections on the yangtze platform which represent mainly the upper permian but also parts of the lower triassic and possibly parts of the uppermost lower permian contain a long term main r n r n r polarity succession throughout the permian this signal is hidden under strong overprint magnetizations of variable origin and can be mostly obtained only from directional trends of the natural remanent magnetization during demagnetization rather than from clear stable end point directions the new chinese polarity sequences are in accord with magnetostratigraphic records from the former ussr and pakistan depending on stratigraphic assignment of the lithological formations studied either they include the boundary between the lower and upper permian and give evidence that the kiaman reversed polarity superchron had ended before the upper permian or the formations all belong stratigraphically to the upper permian with the oldest reversed interval to be correlated with the reversed zone in the midian stage of the palaeontologically well dated nammal section in pakistan this zone is preceded by at least one normal polarity zone at nammal so that the end of the kiaman superchron would not be observed in the new chinese sections

effects of rainfall and slope on runoff soil erosion and rill development an experimental study using two loess soils runoff generation and soil loss from slopes have been studied for decades but the relationships among runoff soil loss and rill development are still not well understood in this paper rainfall simulation experiments were conducted in two neighbouring plots scale 1m by 5m with four varying slopes 17 6 26 8 36 4 and 46 6 and two rainfall intensities 90 and 120mmh 1 using two loess soils data on rill development were extracted from the digital elevation models by means of photogrammetry the effects of rainfall intensity and slope gradient on runoff soil loss and rill development were different for the two soils the runoff and soil loss from the anthrosol surface were generally higher than those from the calcaric cambisol surface higher rainfall intensity produced less runoff and more sediment for almost each treatment with increasing slope gradient the values of cumulative runoff and soil loss peaked except for the treatments with 90mmh 1 rainfall on the slopes with anthrosol with rainfall duration runoff discharge decreased for anthrosol and increased for calcaric cambisol for almost all the treatments for both soils sediment concentration was very high at the onset of rainfall and decreased quickly almost all the sediment concentrations increased on the 17 6 and 26 8 slopes and peaked on the 36 4 and 46 6 slopes sediment concentrations were higher on the anthrosol slopes than on the calcaric cambisol slopes at 90mmh 1 rainfall intensity increasingly denser rills appeared on the anthrosol slope as the slope gradient increased while only steep slopes 36 4 and 46 6 developed rills for the calcaric cambisol soil the contributions of rill erosion ranged from 36 to 62 of the cumulative soil losses for anthrosol while the maximum contribution of rill erosion to the cumulative soil loss was only 37 9 for calcaric cambisol copyright c 2014 john wiley sons ltd

rill network development and sediment budgets threshold conditions for rill incision are well known but few studies have examined the effect of network geometry on water and sediment fluxes within an evolving rill system this paper reports the first in a series of studies designed to identify the influence of soil properties on rill network and confluence geometry and on water and sediment fluxes in rill systems the object of this study was to prepare detailed rill network water and sediment budgets identifying important sources and sinks simulated rainfall experiments were carried out on a canadian silt loam soil in a 7 1 m 2 4 m flume on a 5 slope rill networks of varying complexity developed which were ultimately constrained by flume boundaries sediment and water fluxes and hydraulic conditions were measured within networks and at a terminal weir networks evolved by initial knickpoint incision in the lower flume as flow shear velocities reached critical levels of 4 5 5 cm s 1 followed by headward migration and tributary development microtopography determined tributary location but the timing and intensity of development were controlled by the incision and migration rate of the main channel which changed local thalwegs and base levels raising shear velocities on side slopes above critical levels sediment discharge at the weir broadly reflected rill incision intensity and transport limited conditions but as active incision moved headward the linkage became attenuated and identification of discrete erosional incidents e g local bank collapse in the signal of the weir record became very difficult detailed water and sediment budgets showed much more complex patterns of localized incision and deposition within networks strongly influenced by local changes in thalweg and in water discharge due to seepage or return flow and by the effect of confluences on hydraulic conditions results indicate the value of detailed sediment budgets in interpreting weir water and sediment flux records and the necessity of linking such measurements for erosion plots and hillslope segments to rill network characterization experimental results are consistent with a simple model of rill system evolution based on channel incision headward migration and the critical shear velocities for rill initiation copyright 2000 john wiley sons ltd

rill erosion and morphological evolution a simulation model a mathematical model is advanced to simulate dynamically and spatially varied shallow water flow and soil detachment transport and deposition in rills the model mimics the dynamic process of rill evolution including variable rates of sediment redistribution along the bed and changes in local bed morphology the sediment source term in the model uses a point scale probabilistic relationship based on turbulent flow mechanics and a recently developed sediment transport relationship for rills based on stream power the interdependent feedback loops between channel bed morphology local flow hydraulics and local scour and deposition within the framework of the full hydrodynamic equations with inertial terms constitute a mathematical model with the capacity to represent spatial variability and temporal evolution of the rill finite elements were applied to numerically solve the hydrodynamic and sediment continuity equations a series of laboratory flume experiments were performed to evaluate the model initial bed slopes were 3 5 and 7 with step increases of water inflow rates of 7 6 11 4 and 15 2 l min 1 the soil material used in the flume was a kaolinitic sandy clay loam the rill model equations were solved for increasingly complex cases of spatial and temporal variabilities the model followed measured patterns of morphological changes as the rill evolved which suggests that the feedback loops in the model between erosion bed morphological changes and hydraulics were adequate to capture the essence of rill evolution

laboratory investigations of rill dynamics on soils of the loess plateau of china abstract we conducted a laboratory study on rill network evolution with detailed measurements under controlled experimental conditions the concepts of fractal geometry entropy and topology were used to quantify rill erosion intensity and morphology the objectives of this study are to reveal rill erosion processes and rill network development under different rainfall intensities and to present some indicators to provide a quantitative description of rill morphology a soil pan 5 m long 1 m wide and 0 6 m deep with slope gradient of 20 was subjected to three successive rainfall events under rainfall intensities of 66 94 and 127 mm h 1 the results showed that rainfall intensity played a major role in rill erosion the development of a rill network is most rapid under medium intensity rainfall rainfall intensity that is too weak or too strong is not conducive to rill development as rainfall duration increased under the same rainfall intensity the values of soil loss rill density geomorphologic comentropy and nodes increased rill network development was slow at the early stage but became more rapid at a later stage the results also indicated that the geomorphologic comentropy was the best basic morphological indicator of rill erosion and the number of rill nodes was the best derived morphological indicator of rill morphology which was followed in descending order by the fractal dimension rill density and bifurcation ratio

experimental study on soil erosion prediction model of loess slope based on rill morphology abstract rill erosion frequently occurs in agriculturally disturbed dry areas despite many research efforts over recent decades the characteristics of rill erosion and its intrinsic mechanisms remain unclear the objectives of this study were to investigate the impacts of rill morphology evolution on rill erosion processes a soil pan 5 m long 1 m wide and 0 6 m deep and with an adjustable slope gradient of 0 30 was subjected to rainfall simulation experiments under three intensities of representative erosive rainfall 66 94 and 127 mm h 1 the rill morphology evolution exhibited significant nonlinear change regulation and the stronger the rainfall intensity the clearer the nonlinear feature the equation between rill morphological characteristics with geomorphological comentropy and bifurcation ratio was generated which indicated that the contribution rate of geomorphological comentropy to sediment yield was 80 and the contribution rate of bifurcation ratio was 20 for the experimental treatments a soil erosion model was constructed with and without rill development and the coefficient to describe the influence of rill development on slope erosion was obtained the rill erosion coefficient was embedded into an existing soil erosion model for steep slopes as a result when rill erosion occurred on the slope the contribution of the rill morphology to the rill erosion was fully realized by the model verification indicated that the accuracy of the model was significantly improved in previous studies the accuracy of slope water erosion prediction model was low because the evolution process of slope topography was not considered our results solve the spatial variability problem in the slope erosion prediction model and improve the simulation accuracy of the soil erosion prediction model on a loess slope

measurements of rill and gully erosion in sicily this article reports the results of a field investigation aimed to characterize the morphology of both rills monitored at sparacia experimental area and two ephemeral gullies egs located in the tremamargi basin sicily italy at first the available literature data together with the measurements carried out in this investigation were used to show that the eg length is a key parameter for the estimation of the eroded volume then the comparison among the pairs length and volume corresponding to measured rills egs and gullies showed that the exponent of the power relationship is independent of the channelized erosion type rill eg and gully while a different scale factor has to be used for each erosion process finally a single relationship applicable to all channelized erosion processes was deduced applying the dimensional analysis and the self similarity theory copyright 2011 john wiley sons ltd

detachment and transportation of loose sediments by raindrop splash summary laboratory experiments on sediments ejected by splash consisted of two parts quantities ejected and mean projected distances were measured since the splash tray was 100 cm long and 20 cm wide and since both measurements were made on a receiving screen of one square metre it was obvious that only part of the translocated sediment was caught it was subject to serious doubt that the measured distances were representative for all sediment translocated if it is stated that the ejected sediment is distributed according to an exponential function around any point of impact located on the tray and if by definition tray and rainfall are perfectly homogeneous the ratio of the true to the measured distance and the ratio of the caught to the translocated sediment are only a function of the exponent of the real function the apparent distance being also a function of this exponent is thus the only factor needed to solve the two questions hence all empirical data were transformed into true data

concentrated flow erosion rates as affected by rock fragment cover and initial soil moisture content abstract concentrated flow experiments using a small hydraulic flume and a constant flow discharge and bed slope have been conducted in order to investigate the effects of rock fragment cover rc on sediment yield for an initially wet and an initially air dry loamy topsoil the experimental results indicate that rc reduces concentrated flow erosion rates e in an exponential way i e e e brc which is similar to previously reported relations for other water erosion processes such as interrill erosion and sheet rill erosion measured on runoff plots the decay rate b of this exponential relationship increased throughout the experiments because of scour hole development and bed armouring the concentrated flow erosion rates and b values also depend on the initial moisture content of the topsoil depending on rc mean concentrated flow erosion rates were 20 to 65 less on initially wet compared to initially air dry topsoils the mean value for b was 0 032 for the initially wet but only 0 017 for the initially air dry topsoil indicating that a rock fragment cover is less efficient in reducing concentrated flow erosion rates when the topsoil is initially air dry than when it is initially wet the results help explain the data scatter in reported relationships between rc and interrill rill erosion rates they also indicate that a given surface rock fragment cover will offer more protection to wet topsoils than to dry topsoils which are very common in mediterranean environments event based water erosion models should incorporate effects of antecedent soil moisture content as well as those of rc on concentrated flow erosion rates