laboratory experiments simulating the geomorphic response to tectonic uplift 1 we present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate the experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations the quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision we focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography we show that the transient phase is strongly dependent on the initial internally drained area which is found to decrease exponentially with time the topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero steady state surfaces are characterized by a well defined slope area power law with a constant exponent of 0 12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero these results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model reappraising published results on the linear dependency between mean elevation or relief and denudation rate we suggest that an erosion threshold is worth considering for large scale systems

alluvial fan deposition along a rift depocentre border from the neuquen basin argentina the interaction between hangingwall block rotation and alluvial deposition is examined from late triassic early jurassic successions exposed along the catan lil half graben border fault system in the neuquen basin argentina analysis of transport and depositional processes clast composition and rock body geometry allowed the identification of three distinctive fan shaped alluvial units the contrasting lithologic nature of the basement igneous metamorphic and syn rift fill volcanic and volcanic derived permits detailed studies of clast provenance the origin of each alluvial system footwall vs hangingwall derived can thus be verified a simple method was implemented to establish the geometry of each alluvial unit by comparing the stereographic projection of its bedding to that of an idealised fan shaped body results show that the three alluvial systems occupied the same relative location in the rift depocentre unit 1 is interpreted as an alluvial fan orientated transverse to the depocentre border fault system and fed from the footwall non cohesive debris flow deposition was the dominant process in this environment unit 2 is interpreted as a mainly hangingwall fed alluvial fan parallel to the depocentre border fault system and shows an upward decrease in footwall derived clasts hyperconcentrated flow was the principal transport process unit 3 represents a fan delta parallel to the depocentre border fault system its components are completely hangingwall derived and hyperconcentrated flow deposition was the dominant process differences in grain size composition transport directions and fan body geometry are proved to be directly linked to variations in ground tilting induced by the direction of hangingwall block rotation in an endorheic rift depocentre

misrepresentation of hydro erosional processes in rainfall simulations using disturbed soil samples abstract interrill erosion is a primary soil erosion process which consists of soil detachment by raindrop impact and particle transport by shallow flow interill erosion affects other soil erosion sub processes e g water infiltration sealing crusting and rill initiation interrill erosion has been widely studied in laboratories and the use of a sieved soil i e disturbed soil has become a standard method in laboratory experiments the aims of our study are to evaluate the hydro erosional response of undisturbed and disturbed soils in a laboratory experiment and to quantify the extent to which hydraulic variables change during a rainstorm we used a splash pan of 0 3 m width 0 45 m length and 0 1 m depth a rainfall simulation of 58 mm h 1 lasting for 30 min was conducted on seven replicates of undisturbed and disturbed soils during the experiment several hydro physical parameters were measured including splashed sediment mean particle size runoff water infiltration and soil moisture we conclude that use of disturbed soil samples results in overestimation of interrill processes of the nine assessed parameters four displayed greater responses in the undisturbed soil infiltration topsoil shear strength mean particle size of eroded particles and soil moisture in the disturbed soil five assessed parameters displayed greater responses wash sediment final runoff coefficient runoff splash and sediment yield therefore contextual soil properties are most suitable for understanding soil erosion as well as for defining soil erodibility

effects of sediment load on hydraulics of overland flow on steep slopes eroded sediment may have significant effects on the hydraulics of overland flow but few studies have been performed to quantify these effects on steep slopes this study investigated the potential effects of sediment load on reynolds number froude number flow depth mean velocity darcy weisbach friction coefficient shear stress stream power and unit stream power of overland flow in a sand glued hydraulic flume under a wide range of hydraulic conditions and sediment loads slope gradients were varied from 8 7 to 34 2 unit flow rates from 0 66 to 5 26 10 3 m2 s 1 and sediment loads from 0 to 6 95 kg m 1 s 1 both reynolds number re and froude number fr decreased as sediment load increased implying a decrease in flow turbulence this inverse relationship should be considered in modeling soil erosion processes flow depth increased as sediment load increased with a mean value of 1 227 mm caused by an increase in volume of sediment laden flow contribution 62 4 and a decrease in mean flow velocity contribution 37 6 the mean flow velocity decreased by up to 0 071 m s 1 as sediment load increased the darcy weisbach friction coefficient f increased with sediment load showing that the total energy consumption increased with sediment load the effects of sediment load on f depended on flow discharge as flow discharge increased the influence of sediment load on f decreased due to increased flow depth and reduced relative roughness flow shear stress and stream power increased with sediment load on average by 80 5 and 60 2 respectively however unit stream power decreased by an average of 11 1 as sediment load increased further studies are needed to extend and apply the insights obtained under these controlled conditions to real world overland flow conditions copyright 2010 john wiley sons ltd

flow resistance equation for rills in this paper a new flow resistance equation for rill flow was deduced applying dimensional analysis and self similarity theory at first the incomplete self similarity hypothesis was used for establishing the flow velocity distribution whose integration gives the theoretical expression of the darcy weisbach friction factor then the deduced theoretical resistance equation was tested by some measurements of flow velocity water depth cross section area wetted perimeter and bed slope carried out in 106 reaches of some rills modelled on an experimental plot a relationship between the velocity profile the channel slope and the flow froude number was also established the analysis showed that the darcy weisbach friction factor can be accurately estimated by the proposed theoretical approach based on a power velocity profile

channel width flow discharge relationships for rills and gullies abstract research conducted during the first half of the last century has shown that a strong power relationship exists between channel width and total flow discharge in streams recent studies have shown that this power relationship can be theoretically derived for bankfull discharge in channels the relationship has been extended empirically to rills and gullies revealing that the discharge exponent for rills and gullies is significantly smaller than that for rivers however water flow in rills and gullies is only rarely bankfull indicating that the theoretical explanation for the power relationship found for rivers does not apply to rills and gullies in order to investigate the width discharge relationships for rills and gullies a new method is proposed based on field measurements of widths of concentrated flow erosion channels both upstream and downstream of channel junctions although the method only allows the determination of the exponent of the power relationship it is easy and inexpensive to apply a total of 322 rill and gully channel junctions with various soils and land use types were investigated in belgium italy and spain the obtained data confirmed the existence of the power relationship for rills and gullies with the exponent varying from 0 43 for small rills about 3 cm in width to 0 5 for gullies about 50 to 100 cm in width the data did not allow deciding whether the exponent varies consistently with channel width or in a step wise fashion the exponent values obtained in this study are larger than those reported in previous studies but this may result from differences in the definition of the discharge that eroded the channel to its current width

comparison of hydrodynamic parameters for predicting soil and water loss on simulation landslide deposit slope in wenchuan earthquake area china hydrodynamic parameters should be identified firstly for predicting soil and water loss with specific issues and objectives the laboratory simulation scouring experiments were conducted with different gravel contents flow discharges and slopes based on the field investigation which achieved the most suitable parameter for predicting soil and water loss on simulation landslide deposit slope in wenchuan earthquake area china the results showed that the gravel content of 25 always was the threshold that controlled the flow shear stress and stream power increased or decreased under different flow discharges the unit stream power up and unit flow energy e both decreased when gravel contents increased the ratio of manning coefficient to flow depth n h was higher in fine sediments with gravels than that without gravels the flow discharge had the consistent effects on hydrodynamics which was ordered as 4 8 12 l min 1 the was the most suitable parameter for predicting soil and water loss by considering the degree of reliability even though the also had significant positive power function with soil and water loss the n h could describe the hydrodynamics and soil and water loss and be the alternative parameter for predicting soil and water loss the results provide useful information for soil and water loss prediction in landslide deposits

transporting capacity of overland flow on plane and on irregular beds in this paper the transporting capacity of thin flows in the laminar and transitional flow regime is studied experiments were carried out on irregular as well as on plane beds using two totally different set ups the results of these two types of experiment were convergent in both cases sediment concentration was clearly related to grain shear velocity and unit stream power expressed as the product of mean velocity and slope yang 1973 the data agreed with those of kramer and meyer 1969 for a sandy bed the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface for laminar and transitional flows both the unit stream power and the shear velocity are related in the same way to slope and unit discharge the unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow however before a sediment transport equation for thin flows can be developed more information is needed about the influence of the flow regime and grain size and density

a long flume study of the dynamic factors affecting the resistance of a loamy soil to concentrated flow erosion experiments were carried out in a 20 m long flume to assess the variation of the runoff erosion resistance of a loamy soil as a function of initial moisture content and compaction the results of seven experimental runs show that the runoff erosion resistance of a loamy material is extremely sensitive to variations in initial moisture content and to a somewhat lesser extent in bulk density the very low resistance to runoff erosion of initially dry material is explained by structural changes which take place at the time of wetting slaking and microfissuration cause a considerable decrease of the soil s shear strength and therefore of its resistance to runoff erosion a first analysis shows that during a given rainfall event initially dry soils may well show significantly more erosion than initially wet soils despite the increase of infiltration with decreasing initial moisture content

interaction between bed roughness and flow hydraulics in eroding rills govers 1992 showed that the flow velocity in rills eroding loose nonlayered materials could be predicted from knowledge of discharge only without significant slope or soil effect the objective of this paper is to investigate to what extent the observed slope independence of flow velocity in eroding rills can be explained by the interaction between rill bed roughness and flow hydraulics in a laboratory study two situations were compared 1 rills which can freely erode a uniform soil layer and 2 rills with a fixed bed geometry during the experiments rill discharge and flow velocity were recorded after each experiment a detailed topographic survey of the rill bed was carried out using a laser scanner from these data the main hydraulic variables mean values of flow depth wetted perimeter and hydraulic radius were estimated the experiments confirmed the slope independence of rill flow velocities on mobile beds when the bed is fixed the flow velocity in rills is clearly slope dependent the slope independence of flow velocity on mobile beds is due to a feedback between rill bed morphology and flow conditions the roughness amplitude which was assessed from the standard deviation of corrected height values and the frequency of macroroughness elements which was assessed by counting the number of peaks per unit length in a previously simplified longitudinal profiles both increase and tend to counteract the effect of the increase in slope gradient on rill flow velocity the final rill flow velocity appears to be characterized by a constant average froude number

hydrological response and soil detachment rate from dip anti dip slopes as a function of rock strata dip in karst valley revealed by rainfall simulations rock dip angle plays a significant role in surface hydraulic characteristics and leads to different spatial distribution of water and soil loss in karst trough valleys in this study the rock dip angle effect on the hydraulic characteristics and soil detachment rate on dip anti dip slopes was explored via rainfall simulations and a steel experimental flume the rainfall intensities ranged from 30 to 90 mm h and the rock dip angles varied from 10 to 60 the results revealed that i surface runoff on the dip slope was higher than that on the anti dip slope whereas underground runoff presented opposite results the 30 rock dip angle presented the critical flow velocity for the anti dip slope and the flow velocity reduced as the rock dip angle of the dip slope increased ii laminar water flow occurred on the dip anti dip slope re was 500 in all cases for the anti dip slope the re value reduced by 3 53 89 79 the fr value reduced by 34 13 73 04 and the f value increased by 61 07 93 78 compared with that of the dip slope iii a linear function model can describe the relationship between the soil detachment rate and hydrodynamic parameters w and e it was found that w was the best of the hydrodynamic parameters to describe the soil detachment rate these results could provide valuable information for establishing a national scale empirical soil erosion model for karst trough valley

field investigation of rill and ephemeral gully erosion in the sparacia experimental area south italy abstract this paper reports the results of a field investigation aiming at characterizing the morphology and hydraulics of both rills and ephemeral gullies egs monitored at sparacia experimental area sicily italy the comparison between rill and interrill erosion measurements showed that sediment delivery processes occurred in some erosive events and that the rill erosion rate was dominant in many cases the measurements were used for testing both the empirical relationships between the channel rill egs and gully length and its eroded volume and among the morphological variables length width depth and volume describing the channelized process finally the rill and egs hydraulic geometry was modelled by three well known power equations relating the discharge with the mean flow velocity with the flow depth and with the width of each channel segment respectively the rill measurements also showed that the flow velocity was affected by the rill segment slope while the flow depth and width were controlled by the plot slope therefore three equations taking into account these slope effects were proposed to estimate the hydraulic characteristics of the rills monitored at the sparacia area

fossilization modes in the chengjiang lagerstatte cambrian of china testing the roles of organic preservation and diagenetic alteration in exceptional preservation abstract one important and poorly understood issue concerning the taphonomy of nonmineralizing organisms in cambrian burgess shale type deposits is the diagenetic pathways by which organisms have become exceptionally preserved scanning electron microscopy sem analyses of exceptionally preserved fossils from the lower cambrian chengjiang deposit of china demonstrate that nonmineralized tissue is preserved in a variety of ways and further suggest that there was some taxonomic control over the precipitation of authigenic minerals during early diagenesis organic preservation is limited to certain decay resistant structures such as heavily sclerotized spines on the claws of anomalocaridids labile organic tissues of nearly all nonmineralizing animals however are preserved by thin films of diagenetic minerals microstructural studies energy dispersive x ray edx analyses and elemental mapping of these minerals indicate that mineral films include apatite pyrite and fe rich aluminosilicates the results support the assumption that early diagenetic mineralization such as phosphatization and pyritization played a key role in the preservation of nonmineralized organisms pyritization seems to be the most important process by which nonmineralizing chengjiang organisms are preserved in exceptional condition precipitation of fe rich aluminosilicates which occurred following pyritization also played a role in the preservation of some chengjiang fossils phosphatization in the chengjiang lagerstatte was evidently rare and limited taxonomically or to animals having large masses of organic material

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

comparison of rill flow velocity regimes between developing and stationary rills abstract flow velocity is fundamental in calculating related parameters of physical soil erosion models it has been well known that rill flow velocity varies with developing rill form which complicates and impedes the development of soil erosion models in filed rainfall erosion frequently occurs with pre existing rills not damaged by tillage practices however the rill flow velocity in this case has received little attention in this study we investigated rill flow velocity regimes for both developing and stationary rills using 5 m length plots in the laboratory the experiments included two consecutive rainfalls which had similar runoff rate the first rainfall had an intensity of 90 mm h 1 which generated well developed rills the second had an intensity of 60 mm h 1 and did not damage the rills formed by the first rainfall the results show that for a developing rill rill flow velocity is higher in the lower slope than that in the upper slope and rill flow velocity in the lower slope fluctuates much more over time as a result of the variation of rill morphology following rill development with rill development the rill flow velocity of the lower slope decreased responding to the stabilizing rill channel and exhibited a similar trend to that in upper slope for a stationary rill the rill flow velocities at both sections varied little over time demonstrating that rill flow velocity is primarily influenced by rill morphology hence the results suggested that the strength of fluctuation in rill flow velocity could be used to characterize the instantaneous intensity of soil erosion and active level of rill development the channel of the stationary rill simply acted as transport pathways of sediment supplied by inter rill erosion the physical models of soil erosion should take into account the micro topography on land surface related to the antecedently formed rills

spatial variation of bed roughness in eroding rills and gullies when overland flow concentrates rill and gully channels can be formed if a series of thresholds are exceeded these thresholds are more or less explicitly linked to the erosion resistance of the topsoil moreover flow velocity and channel width depend on total flow discharge more recently also bed roughness in eroding channels has been attributed to the eroding effect of flow discharge while channel width was shown to be the result of the interplay between erosion resistance of the topsoil and flow discharge see channel junction approach torri et al 2006 which could be described by a modified leopold and maddock s relationship the objective of this paper is to investigate the spatial variability of channel bed roughness in rills and gullies using an approach based on these findings field data confirm the various aspects reported so far hence these were used to develop a new equation allowing one to predict bed roughness in eroding rill and gully channels each of the new aspects introduced into the channel width flow discharge equation by the channel junction approach is discussed and verified with new data the validity of this approach is tested against channel data from mars finally an equation predicting bed roughness and based on stream power is developed and compared with measured rill and gully bed roughness successfully confirming that 1 bed roughness if generated by concentrated flow increases with stream power 2 channel width local bed slope topsoil cohesion at saturation and grain size are all important factors controlling channel bed roughness and 3 these variables as well as soil characteristics all measurable in the field after a rill or gully forming event are sufficient to determine channel bed roughness therefore one may expect that bed roughness of an eroded channel and consequently hydraulic roughness or friction will generally increase with bed gradient erosion resistance of the soil and grain size following a logic which is best expressed by the final equations described in this paper

measuring rill erosion using structure from motion a plot experiment abstract in this paper the results of a plot experiment on rill erosion are reported the rill network manually incised on the soil and further shaped by a clear inflow discharge was surveyed using the three dimensional photo reconstruction 3d pr technique which allows to obtain a digital terrain model dtm by a large series of oblique images of the channel from consumer un calibrated and non metric cameras the three dimensional 3d dtm and the quasi tridimensional 2 5d model were generated by agisoft photoscan software for a single rill channel the reliability of the 3d image based ground measurements of morphological and hydraulic variables was positively tested by the corresponding measurements carried out on the rill gypsum cast moreover the morphological and hydraulic variables were measured at 11 transects of the plot by a profilometer p the 2 5d and 3d models using the 3d model as reference the analysis showed that the reliability of the measurements by p and 2 5d methods was comparable and the error was generally lower than 15 the rill measurements carried out by the three methods agreed with the available literature measurements and supported the applicability of both the empirical relationship between rill length and its eroded volume and the theoretical dimensionless relationship among the morphological variables describing the channelized erosion process the analysis also showed that the effect of the distance between two consecutive cross sections on the rill volume measurement by 3d model is negligible finally the shaping effect of different flow discharges on three straight rills incised into the plot was tested in particular three increasing flow discharges 0 15 0 35 and 0 5 l s 1 were used sequentially in two rills while the maximum discharge of the sequence 0 5 l s 1 was used into the third rill both the grain size distribution of the eroded sediment and the total amount of soil loss were affected by the discharge sequence

field measurement of the velocity of overland flow using dye tracing a new method of computing the mean velocity of overland flow using dye tracing is proposed in which a specified cross section is divided into zones of relatively uniform flow characteristics termed partial sections the mean surface velocity for each partial section is determined by timing the passage of injected dye and this figure is multiplied by 0 67 0 70 or 0 80 depending on whether the flow is laminar transitional or turbulent to give mean velocity the mean velocity for the entire cross section is calculated by multiplying the mean velocity of each partial section by its cross sectional area summing the products for all the partial sections and dividing by the total area of the cross section a field test shows that mean velocity derived in this manner differs from mean velocity derived by the discharge method i e by dividing discharge measured volumetrically by cross sectional area by an average of only 7 07 per cent thus the partial section technique appears to provide a reliable method of estimating mean velocity of overland flow

similarity between morphological characteristics of rills and ephemeral gullies in sicily italy this paper reports the results of a field investigation aimed to establish morphological similarity between rills and ephemeral gullies rill measurements were made on 14 plots having a surface area of 22 352 m2 located on a 14 9 slope and on a plot 6 0 m wide and 22 0 m long having a uniform 22 0 slope the plots are located on the experimental station for soil erosion measurements sparacia of the agricultural faculty of palermo university in sicily italy all plots are subjected to natural rainfall the measurements were made immediately following five events between november 2004 and december 2005 the ephemeral gully measurements were made on a cultivated area of about 120 ha located in central sicily which is representative of many soil crop conditions in the mediterranean basin the morphological similarity between rill and ephemeral gully was first tested then a power relationship between rill or gully volume and length theoretically deduced by dimensional analysis and self similarity theory was applied this power relationship needs a different scale factor for rill and gully measurements finally using two dimensionless groups representative of the channel morphology variables the analysis showed that a single relationship can be applied to rill and gully measurements copyright 2009 john wiley sons ltd

do deterministic sediment detachment and transport equations adequately represent the process interactions in eroding rills an experimental field study abstract this paper tackles two main questions by linking observations determination of hydraulic parameters and measurement of sediment transport with the formulae used in soil erosion models first do constant shear stress values in different rills with constant soil parameters result in the same soil detachment values secondly deterministic soil erosion models make the assumption that there is a relationship often further assumed to be linear between shear stress and soil detachment is this suitable for representing real erosion process combinations in natural rills following most process based deterministic soil erosion models derived hydraulic and erosion parameters should be similar however the results from the different experiments showed clear differences in sediment concentration transport rates and other measured as well as calculated values in contrast to our experimental results a model simulation would produce erosion parameters with low variations represented by the relative measurement error and the empirical variation coefficient this reveals the general problems of using process based deterministic models for erosion in shallow rills while soil erosion models simulate the processes resulting from the shear forces of flowing water on the soil surface other processes like side wall failure headcut retreat and plunge pool dynamics are not taken into account our results suggested that these other processes may contribute substantially to rill erosion processes the results of this study strongly suggested that the model concept of most physical based soil erosion models is inadequate for modeling rill erosion processes measured total rill erosion rates were the sum of erosion rates caused by a combination of different soil erosion processes with different spatial and temporal distribution this combination cannot be described by a single equation

morphometric and hydraulic geometry assessment of a gully in sw spain abstract gully erosion represents one of the most significant types of land degradation in the mediterranean areas giving place to important on and off site effects in this paper a second order gully located in sw spain is analyzed along the gully 28 cross sections were established and measured with a leica tcrm1102 laser total station approximately every 6 months from 2001 to 2007 the sections were located at variable distance placing them in areas where active erosion was evident in total 13 field measurements were carried out and the geometric characteristics of 28 cross sections were obtained morphometric analyses were carried out in both the main gully and a tributary reach by applying an empirical relationship between channel length and eroded volume morphometric variables of the gully sections were combined into two dimensionless groups and a morphological similarity between different linear erosion landforms rills ephemeral and permanent gullies was obtained then the coefficient of variation of the calculated volumes was used to compare the instability between the main gully and the tributary reach finally the hydraulic geometry of the gully was assessed by calibrating three empirical power equations which relate bankfull discharge with mean flow velocity cross sectional depth and width the hydraulic characterization of the main gully and the tributary reach was investigated for each field survey and a different behavior was detected the hydraulic analysis also demonstrated that higher values of discharge provide better predictions of flow velocity the size of the main and tributary gullies affects the discharge width relationship and that gully depth is the variable which can be predicted with the highest accuracy

hydrodynamic description for advective sediment transport processes and rill initiation a physically based model for advective sediment transport during rill initiation is developed based on 1 a short wavelength rescaling of the momentum balance equations for the surface water flux 2 a deforming coordinate system which characterizes local morphological changes of the surface during erosion and 3 a generalized transport function for the surface sediment flux which distinguishes the contributions of diffusive and advective transport a linear stability analysis of the coupled system indicates that an intrinsic minimum transverse length scale for rill initiation is forced by the cross slope pressure gradient in the surface water the wavelength of this initial rill spacing is dependent upon the relative significance of the advective component of sediment transport and the hydraulic efficiency of the surface water flux and is independent of the total length of the hillslope the hydrodynamic model presented can also be used to evaluate the nonlinear development of rills and rill networks subsequent to initiation

equation for high rate gully erosion abstract an approach to gully erosion is presented in this paper the approach is based on general equations derived from theoretical considerations the equations apply to a situation of intense erosion rate such as at peak discharge during the few critical rainstorms able to generate or to widen gullies equations linking gully widening to gully deepening are derived they do not depend on the way in which concentrated flow aggressiveness is estimated the equation expressing gully width depth relationship was successfully compared with data from the literature when runoff aggressiveness was estimated through unit stream power and bottom flow shear stress the width discharge relationships found were similar to those expected on the basis of previous studies e g leopold and maddock u s geol surv prof pap 252 1953 57 pp even if slope gradient explicitly appears in contrast with empirical evidence only threshold conditions for gullies indicate that flow shear stress for laminar flow conditions can explain the observed trends this astonishing result most probably indicates that gully initiation needs more complex contexts to be explained than the one here used based on a montgomery and dietrich 1994 landscape dissection and drainage area slope thresholds in m j kirkby ed process models and theoretical geomorphology wiley 221 246 approach a selection of the proposed equations have been arranged into a research model and an example of the outcome has been given for two situations typical of cropland in southern tuscany italy the results indicate that the spatial distribution of soil characteristics and of land use influences significantly gully generation and evolution this further confirms that gully morphological thresholds cannot be explained by simple approaches

dye tracer technique for rill flows by velocity profile measurements abstract water flow on hillslope soil surface supplies energy which is required to detach soil particles to transport and deposit sediments therefore flow velocity is a key variable related to hillslope hydrodinamics of soil erosion processes among the different methods available for measuring velocity of shallow interrill and rill flow the trace technique is widely used trace technique is applied by adding a material salt magnetic material water isotope floating object and then measuring the speed of the material to travel a known distance from the injection point when flow velocity is measured using a dye tracing method the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor which was generally empirically deduced the main uncertainty of the dye tracing technique stands in the estimate of this correction factor which is the ratio between the mean flow velocity and the surface velocity the main goal of this paper is establishing a theoretical relationship for calculating the correction factor by using a power velocity profile at first the developed analysis demonstrated that the correction factor only depends on the exponent of the power velocity distribution eq 5 then this theoretical expression of the correction factor was applied using the velocity profiles measured by baiamonte and ferro for the condition of sediment free flow in motion on a rough bed and by coleman for a sediment laden flow moving on a smooth flume using the correction factor values calculated by the velocity measurements carried out for the sediment free flow in motion on a rough bed the relationship between the correction factor and roughness height was established in agreement with a previous study by ali et al for a sediment free flow the correction factor increases with roughness height finally the velocity profile measurements carried out for a sediment laden flow in motion on a smooth bed were used to state the effect of sediment load on the correction factor this last analysis allowed to conclude in agreement with li and abrahams and zhang et al that the correction factor decreases when the sediment load increases

soil erosion by surface water flow on a stony semiarid hillslope soil erosion on hillslopes occurs by processes of soil splash from raindrop impacts and sediment entrainment by surface water flows this study investigates the process of soil erosion by surface water flow on a stony soil in a semiarid environment a field experimental method was developed whereby erosion by concentrated flow could be measured in predefined flow areas without disturbing the soil surface the method allowed for measurements in this study of flow erosion at a much wider range of slopes 2 6 to 30 1 per cent and unit discharge rates 0 0007 to 0 007 m2 s 1 than have been previously feasible flow velocities were correlated to discharge and hydraulic radius but not to slope the lack of correlation between velocity and slope might have been due to the greater rock cover on the steeper slopes which caused the surface to be hydraulically rougher and thus counteract the expected effect of slope on flow velocity the detachment data illustrated limitations in applying a linear hydraulic shear stress model over the entire range of the data collected flow detachment rates were better correlated to a power function of either shear stress r2 0 51 or stream power r2 0 59 published in 1999 by john wiley sons ltd

using a thermal tracer to estimate overland and rill flow velocities flow velocity is a basic hydraulic property of surface flows and its precise calculation is necessary for process based hydrological models such as soil erosion and rill development models as well as for modelling sediment and solute transport by runoff this study presents a technique based on infrared thermography to visualize very shallow flows and allow a quantitative measurement of overland flow and rill flow velocities laboratory experiments were conducted to compare the traditional dye tracer technique with this new thermal tracer technique by injecting a combined tracer heated dye into shallow flowing surface water the leading edge tracer velocities estimated by means of infrared video and by the usual real imaging video were compared the results show that thermal tracers can be used to estimate both overland and rill flow velocities since measurements are similar to those resulting from using dye tracers the main advantage of using thermography was the higher visibility of the leading edge of the injected tracer compared with the real image videos copyright 2013 john wiley sons ltd

comment on rill erosion processes on steep colluvial deposit slope under heavy rainfall in flume experiments with artificial rain by f jiang et al abstract since rill flows are characterized by small water depths and steeply sloping channels the corresponding hydraulic conditions are very different to those which are typically found in channels of streams and rivers furthermore limited information is currently available on the effect of rainfall on flow resistance the objective of this comment was to investigate the applicability of a recently theoretically deduced rill flow resistance equation based on a power velocity profile using measurements carried out by jiang et al for both different slope steepness conditions and rainfall intensity the relationship between the velocity profile parameter the channel slope and the flow froude number was calibrated using the data by jiang et al the theoretical approach and the measurements carried out in the investigated conditions allowed to state that a the darcy weisbach friction factor can be accurately estimated using the proposed theoretical approach b the data were supportive of the slope independence hypothesis of rill velocity stated by govers and c the darcy weisbach friction factor varies with rainfall intensity

hydrodynamic characteristics of rill flow on steep slopes rill erosion is a dominant sediment source on sloping lands however the amount of soil loss from rills on steep slopes is vastly more than that on gentle slopes because of differences in rill shape and hydraulic patterns the aims of this paper are to determine the hydrodynamic characteristics of rills and the friction coefficients in steep slope conditions and to propose modifications of some hydraulic parameters used in soil loss prediction models a series of inflow experiments was conducted on loess slopes the results show that the geometric and hydraulic properties of rill on the steep loess slopes which are characterized by the mean width of cross sections mean velocity and mean depth of flow are related to discharge and slope gradient in power functions however the related exponents to discharge are 0 26 0 48 and 0 26 respectively which are different from the exponents derived in previous studies which were conducted on gentle slopes the manning roughness coefficient ranged from 0 035 to 0 071 with an average of 0 0536 and the darcy weisbach friction coefficients varied from 0 4 to 1 9 the roughness coefficients are closely related to the reynolds numbers and flow volumes however the correlations vary with slope gradient the roughness coefficients are directly proportional to the reynolds number and the flow volume on steep slopes in contrast with the roughness coefficients found on gentle slopes which decrease as the reynolds number and flow volume increase this difference is caused by the interactions among the hydraulics of the flow the shape of the rills and the sediment concentrations on steep slopes the results indicate that parameters used in models to predict rill erosion have to be modified according to slope gradient copyright 2015 john wiley sons ltd

assessing dye tracer technique for rill flow velocity measurements abstract rill erosion is considered one of the most important processes affecting soil because of the large amount of soil loss the rill network acts as sediment source and is able to transport both rill flow detached particles and those delivered from the interrill areas small flow depth in a rill and steep slope values of its bed affect significantly flow hydraulics when rill flow velocity is measured using a dye tracing method the mean velocity is calculated by multiplying the measured surface velocity of the leading edge of the tracer plume by a correction factor the main uncertainty of the dye tracing technique stands in the relationship between mean and surface flow velocity in this paper this relationship was firstly tested using the measured data pairs available from literature and then the influence of the adopted relationship on the estimate of the darcy weisbach friction factor was examined the developed analysis showed that the applied estimate criteria of the correction factor do not affect the estimate performances of the theoretical flow resistance equation finally a new flow resistance equation for rill flows which can be directly calibrated by surface velocity measurements was deduced the proposed procedure for estimating the friction factor was calibrated by rill data available from literature and was positively tested by the rill velocity measurements carried out in this investigation

deriving and evaluating hydraulics and detachment models of rill erosion for some calcareous soils abstract rill erosion plays an important role in the amount of soil detachment and the transport sediment load on hillslope quantification of the soil erosion requires a more precise understanding of the processes and development of rill erosion models the objective of this study was to derive and evaluate hydraulics and detachment models of rill erosion in calcareous soils of northwestern iran rill erosion experiments were carried out at 55 locations with three replications under field conditions at each point the rill plots were created with a 0 2 m width and 4 m length on agricultural soils the inflow rates were 4 12 20 and 30 l min 1 with varying slope from 4 to 25 5 the results indicated that all conditions of flow regimes including sub and super critical laminar and turbulent were observed in created rills by overland flow the mean flow velocity and rill depth have been described well by flow rate and slope gradient while rill width and flow depth have been explained well by flow rate the prediction detachment rate by rill flow based on stream power model by non linear regression yielded the best results r2 0 545 and rmse 0 00213 kg m 2 s 1 for all combinations of slope classes however there are no significant differences between prediction accuracy of linear and non linear models when individual slope classes were considered

dissipative analogies of step pool features from rills to mountain streams abstract in this paper the dissipative similarity of step pool units at different spatial scales ranging from rills to streams is analyzed this investigation benefits from the latest theoretical advances in open channel flow resistance high resolution topography from close range photogrammetry applied to rill erosion and the availability of published data from literature on step pool streams at first the integration of a power velocity distribution allowed to obtain a theoretically based expression of darcy weisbach friction factor in which function and exponent of the velocity profile are included then this theoretically deduced flow resistance relationship is calibrated and tested by flow measurements carried out in rill reaches where the step pool units occurred in particular the proposed function is calibrated using the measurements corresponding to 88 rill reaches shaped on a plot having a slope equal to 14 22 and 24 and the calibrated equation is also positively tested with measurements carried out in 48 rill reaches shaped on a 26 sloping plot for the rill flow the developed analysis stated that the friction factor is characterized by estimate errors which are less than or equal to 15 for 86 of cases and less than or equal to 10 for 70 of cases using measurements of flow velocity water depth width and bed slope measurements carried out in 109 reaches of step pool streams this investigation demonstrates that the theoretical flow resistance equation can be applicable to step pool streams carrying out a specific calibration of the function the comparison between the darcy weisbach friction factor values measured in streams and step pool rills demonstrates that in the stream features the friction factor values are on average higher than those related to rills with step pool sequences in conclusion the comparison between rills and streams with step pool units highlights that the same theoretical flow resistance equation can be applied even if a scale effect between the two features is detected

method for measuring velocity of shallow water flow for soil erosion with an electrolyte tracer abstract measurement of the velocity of shallow water flow on a hill slope is of great importance in soil erosion studies electrolyte tracers have been tried to estimate mean velocity of water flow with the velocity of the leading edge of the solute propagation multiplied with a somewhat arbitrary correction factor in this study an analytical solution of solute tracer transport was formulated to serve as the mathematical foundation for measuring shallow water flow velocity to estimate the flow velocity a procedure was advanced in the procedures the analytical solution is fitted with the measured propagation curve and given the the least square estimation of velocity a detailed mathematical description is outlined for this purpose experimental results are given to show the feasibility of the method including the analytical solution and the estimation procedures this study provides the theoretical foundation for measuring the velocity of shallow water flow and for studies of overland solute transport

measurement and modelling of high resolution flow velocity data under simulated rainfall on a low slope sandy soil the study presented here is focussed on the question of the hydraulic nature of the threshold that allows a rill to start a rainfall simulation experiment was carried out to produce high resolution flow velocity data the experiment employed a 10 m 4 m experimental plot with a 1 slope which had been previously eroded and had a small rill formed in the middle the experiment consisted of a 2 h 15 long rainfall at a constant intensity of 69 mm h 1 surface elevation was measured before rainfall at a horizontal resolution of 2 5 cm across and 5 cm along the slope direction during rainfall flow velocities were measured at 68 locations on the plot with the salt velocity gauge technology an automated miniaturized device based on the inverse modelling of the propagation of a salt plume the experiment led to the collection of flow velocity measurements which are novel in three ways i the small size of the measured section which was only 10 cm long and 1 cm wide ii the wide range of measured flow velocities which ranged from 0 006 m s 1 to 0 27 m s 1 and iii the large number of measured locations the flow velocity field was simulated with three models psem 2d solves the saint venant equations in 2d mahleran uses a 1d kinematic wave in the slope direction coupled with a 2d flow routing algorithm and rillgrow2 which involves an empirical runoff algorithm that is close in principle to the diffusion wave equation in 2d the darcy weisbach friction factor ff and the infiltration parameters were calibrated in all cases to investigate the capabilities of the different models to reproduce flow hydraulics compatible with the onset of rilling in a first set of numerical experiments ff was set uniform and calibration used only the hydrograph the comparison of simulated and observed flow velocity field showed that psem 2d was the most satisfying model at the cost of longer computational time mahleran gave surprisingly good results with regards to the simplicity of the model and its low computational needs however all models largely underestimated the highest velocity values located in the rill furthermore none of the models was able to simulate the reynolds re and froude fr numbers the next numerical experiment was done with psem 2d non uniform ff values were calibrated by fitting the simulated flow velocity field to the observed one the latter simulation produced realistic simulations of re and fr the hydraulic conditions at the transition from interrill flow to rill flow are discussed the results support the theory that supercritical flows are a necessary condition for a rill to emerge from a smooth surface

rill erosion in natural and disturbed forests 1 measurements 1 rill erosion can be a large portion of the total erosion in disturbed forests but measurements of the runoff and erosion at the rill scale are uncommon simulated rill erosion experiments were conducted in two forested areas in the northwestern united states on slopes ranging from 18 to 79 we compared runoff rates runoff velocities and sediment flux rates from natural undisturbed forests and in forests either burned at low soil burn severity 10 months or 2 weeks post fire high soil burn severity or subject to skidding of felled logs the runoff rates and velocities in the natural sites 2 7 l min 1 and 0 016 m s 1 respectively were lower than those in all the disturbed sites 12 to 21 l min 1 and 0 19 to 0 31 m s 1 respectively except for the 10 month old low soil burn severity site where the velocity 0 073 m s 1 was indistinguishable from the natural sites the mean sediment flux rate in the natural sites also was very small 1 3 10 5 kg s 1 as compared to the rates in the disturbed areas 2 5 10 4 to 0 011 kg s 1 the hillslope gradient did not affect the runoff or sediment responses the sediment flux rates generally were greater in the initial stage of each inflow period than in the steady state condition but there was no corresponding transient effect in runoff rates rill erosion modeling implications based on these data are presented in part 2 of this study

terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics smith m w cox n j bracken l j 2011 terrestrial laser scanning soil surfaces a field methodology to examine soil surface roughness and overland flow hydraulics hydrological processes 25 6 842 860

relationship between discharge velocity and flow area for rills eroding loose non layered materials a relationship between discharge flow velocity and flow area in rills is established using data from four field and laboratory studies the proposed relationship is shown to predict successfully flow velocities measured in six other studies although slopes range from 0 035 to 0 45 and soil materials range from stony sands over silt loams to vertisols mean flow velocity can be well predicted from discharge alone thus there is no important influence of slope and or soil material characteristics on flow velocities in rills the proposed relationship may be used to improve performance of deterministic flow routing models when applied to rilled catchments furthermore it allows the calculation of unit stream power which has been shown to be related to the transporting capacity of overland flow in terms of slope and discharge

sediment transport capacity of sheet and rill flow application of unit stream power theory theoretical equations for calculating the unit stream power of both sheet and rill flow were developed and used to predict the sediment transport capacity of such flows independent data sets from three sources representing both finely aggregated clay soils and coarse textured nonaggregated soils sheet rill and composite sheet rill flow systems and a range of slopes were used to test the utility of the method the results were very good and demonstrated the simplicity and robustness of the method for shallow overland flow the best results were obtained when the critical unit stream power at incipient sediment motion was treated as a constant value that was independent of slope the results also suggest that a unique value of critical unit stream power for rill initiation exists that is independent of soil type for noncohesive loams or fine sands and finely aggregated clay soils the sediment transport capacity can be accurately predicted from a knowledge of the physical characteristics of the soil or bed material alone for aggregated clay soils this requires information on the aggregate size distribution and the effects of soil particle size differentiation as flow rates and unit stream powers increase with the transition from sheet to rill flow

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

rill hydraulics on a semiarid hillslope southern arizona seventy field experiments were conducted in seven rills located on a semiarid rangeland hillslope underlain by gravelly soils at walnut gulch arizona the rills which are characterized by wide shallow cross sections and gravel covered beds have mean at a station hydraulic geometry exponents of b 0 33 f 0 34 and m 0 33 although the differences between these values and typical values of b 0 30 f 0 40 and m 0 30 for cropland rills are not statistically significant they are thought to be real as cropland rills often have more rectangular cross sections and steeper sides than the rangeland rills under study for rills formed in silty loamy soils govers developed an empirical relation between mean flow velocity and discharge emphasizing the generality of this relation he suggested that it may be used as a simple means of routing runoff through rills he also noted that this relation appeared to be unaffected by either slope or soil materials the present data represent rills underlain by coarser and somewhat more varied gravel rich soils these data do not conform to govers relation and a multiple regression analysis reveals that slope and soil materials either directly or indirectly through bed roughness exert almost as much influence on flow velocity as does discharge three alternative methods are developed for predicting flow velocity in the rills under study all three methods give good results with the largest root mean square deviation being 3 115 cm s 1

effects of intensification of the indian summer monsoon on northern andaman sea sediments during the past 700 years recent studies have revealed an intensification of the indian summer monsoon ism over the past 700 years but its influence on the sediments in the northern andaman sea is unclear to examine this influence we used radiocarbon dated sediment core stmy6 acquired 100 km offshore in the northern andaman sea from the ayeyarwady river mouth and obtained a 700 year long record of the grain size distribution and geochemistry of the sedimentary sequence the ism influences precipitation surrounding the ayeyarwady river and thus the river water and sediment discharges to the northern andaman sea near the river mouth in the ayeyarwady river and the weathering intensity in the river catchment based on the system we propose that higher sedimentation rates and larger modal grain size the most abundant size in the grain size distribution of sediments and lower carbonate concentrations after about ad 1600 can be attributed to higher ism intensity profiles of total organic carbon toc content and carbon nitrogen c n ratios however did not show any trends after about ad 1600 which suggests that the ism has had little influence on these proxies at this site

hydrological responses on saline sodic soil slopes in a coastal reclamation area of china abstract evaluation of the effects of slope gradient and rainfall intensity on the hydrological responses on slopes can provide important information for soil and water conservation we conducted simulated rainfall experiments to study the hydrological response of a saline sodic soil on slopes with different gradients 6 11 22 and 35 and rainfall intensities 85 95 110 and 125 mm h 1 higher effective rainfall intensities significantly reduced the times to ponding and runoff while the infiltration coefficient did not always increase with increasing slope gradient it consistently increased with increasing rainfall intensity on slopes of 6 11 or 22 the mean flow velocities and stream power values tended to increase with increasing slope gradient but did not change consistently with changes in rainfall intensity hydraulic shear stress and its logarithm could predict sediment losses that were 1 h 1 however stream power and its logarithm were better predictors of a wider range of sediment losses from slopes with saline sodic soil these results suggest that existing hydrological and erosion models should be adjusted to take into account the effects of salinity and sodicity

sediment connectivity a framework for understanding sediment transfer at multiple scales a major challenge for geomorphologists is to scale up small magnitude processes to produce landscape form yet existing approaches have been found to be severely limited new ways to scale erosion and transfer of sediment are thus needed this paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales we propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment and movement of sediment between different zones within a catchment over hillslopes between hillslopes and channels and within channels using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity sediment travel distance when combined with an entrainment parameter reflecting the frequency magnitude response of the system maps onto these end members providing a coherent conceptual model for the upscaling of erosion predictions this conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape evolution models thus further research on the controls and dynamics of travel distances under different modes of transport is fundamental copyright 2014 john wiley sons ltd

sodicity effects on hydrological processes of sodic soil slopes under simulated rainfall soil salinization can occur in many regions of the world soil sodicity affects rainfall runoff relationships and related erosion processes considerably we investigated sodicity effects on infiltration runoff and erosion processes on sodic soil slopes for two soils from china under simulated rainfall five sodicity levels were established in a silt loam and a silty clay with clay contents of 8 5 and 46 0 respectively the soils packed in 50 cm 30 cm 15 cm flumes at two slope gradients 22 and 35 were exposed to 60 minutes of simulated rainfall deionized water at a constant intensity of 125 mm h 1 results showed that for both soils increasing soil sodicity had some significant effects on hydrological processes reducing the infiltration coefficient pr 0 69 p 0 05 moreover increasing sodicity significantly increased the reynolds number and the stream power pr 0 78 and 0 66 p 0 01 respectively of the runoff decreased manning roughness and darcy weisbach coefficient pr 0 52 and 0 52 p 0 05 respectively but did not significantly affect the mean flow velocity mean flow depth froude number and hydraulic shear stress stream power was shown to be the most sensitive hydraulic variable affecting sediment loss for both soils furthermore as sodicity increased the values of critical stream power decreased for both the silt loam r2 0 29 p 0 05 and the silty clay r2 0 49 p 0 05 the findings of this study were applied to a real situation and identified some negative effects that can occur with increasing sodicity levels this emphasized the importance of addressing the influences of soil sodicity in particularly high risk situations and when predicting soil and water losses

flume experimental evaluation of the effect of rill flow path tortuosity on rill roughness based on the manning strickler equation abstract numerous soil erosion models compute concentrated flow hydraulics based on the manning strickler equation v kst r2 3 i1 2 even though the range of the application on rill flow is unclear unconfined rill morphologies generate local friction effects and consequently spatially variable rill roughness which is in conflict with the assumptions of sectional uniform channel flow and constant channel roughness of the manning strickler equation the objective of this study is to evaluate the effect of rill morphology on roughness and hence to assess the manning strickler roughness coefficient kst by rill morphological data a laboratory experiment was set up to analyse rill hydraulics and roughness of i free developed rill fdr flows and ii straight constrained rill scr flows in the flume the flume experiment generated manning strickler roughness coefficients kst between 22 m1 3 s 1 and 44 m1 3 s 1 reflecting a potential area of the roughness parameter uncertainty it was found that fdr experiments generated significantly lower kst values compared to scr experiments because skin and local friction effects in the fdr experiments were more efficient reducing flow velocity probably due to higher energy dissipation rill flow path tortuosity tort was used to describe the rill morphology of the experiments and correlation statistics between tort and kst identified considerable explanatory capacity of rill flow path tortuosity on rill roughness the flume study demonstrated that a regression model between tort and kst can be used to assess local friction effects of unconfined rill morphologies and hence to reduce the area of uncertainty of the manning strickler roughness parameter

effects of freshly incorporated straw residue on rill erosion and hydraulics abstract rill hydraulics and hence flow detachment are modified by the presence of incorporated vegetation residue typically water flow in the rill is retarded due to the extra shear stress generated by the residue the main objective of this study was to develop an approach to predict soil detachment by rill flow in the presence of freshly incorporated vegetation residue that is compatible with our current understanding of rill hydraulics and requires no additional information on rill geometry laboratory experiments were carried out to collect a dataset on rill flow detachment on surfaces with incorporated straw that was compatible with existing dataset on bare soils gimenez and govers 2001 interaction between bed roughness and flow hydraulics in eroding rills water resources research vol 37 no 3 791 799 we found that effective unit length shear force e is well related to soil detachment when incorporated residue is present the determination of e is based on the recalculation of the wetted cross section area for a given flow velocity and slope a hypothetical wetted cross section area is estimated using empirical relationships defined for rills formed in bare soils this procedure was also successfully applied to data from former field experiments the procedure allows estimating erosion rates when flow characteristics velocity and hydraulic radius are known however the prediction of these flow characteristics remains uncertain

runoff erosion process on different underlying surfaces from disturbed soils in the three gorges reservoir area china abstract disturbed soil accumulation caused by all man made activities during the producing and constructing process of large scale projects is the main landform occurred artificial water and soil loss because of its different producing sources and soil rock ratios the underlying surfaces from disturbed soil accumulation often characterize a unique soil erosion process under same runoff scouring condition taking the ubiquitous purple soil deposits and yellow sand deposits associated with different soil rock ratio as examples the study aimed to explore the difference in both hydraulic properties and sediment yield characteristics on disturbed soils some field scouring experiments were conducted in chongqing china these results indicate that i runoff regime on all underlying surfaces from disturbed soils often manifest as turbulent and subcritical flow during runoff scouring process ii for rocky disturbed soils from purple soil sediment production rate shows continuously waving variations and the average sediment production rates are 0 28 11 65 33 69 73 00 and 177 37 g m 2 min respectively when flow discharge increase from 5 to 25 l min gradually the collapse on gully wall caused by its gravity from underlying surfaces is the important cause for the fluctuating variations of the sediment production rate iii the influencing degree of hydrodynamic parameters on sediment yield is in such order as q p v these study results could be used to control artificial erosion caused by production and construction projects and to provide some important parameters for soil and water loss predicting in the three gorges reservoir area of chongqing

distribution of depth of overland flow on desert hillslopes and its implications for modeling soil erosion abstract data collected during field experiments on hillslopes in southern arizona reveal that the depth of overland flow in interrill areas can be approximated by a negative exponential distribution soil erosion over the greater part of most hillslopes is equal to detachment capacity flow detachment in interrill areas is generally modeled using a du boys type equation in which shear stress is calculated using the mean depth of flow it is shown that using the mean depth rather than the distribution of depth can result in the severe underestimation of flow detachment insofar as the exponential density is characterized by a single parameter that is the reciprocal of the mean a knowledge of the mean depth is all that is needed to specify the distribution thus utilization of the depth distribution rather than the mean depth does not require any additional information yet it yields much more accurate estimates of flow detachment and hence soil erosion in interrill areas