impact of subsurface rock fragments on runoff and interrill soil loss from cultivated soils field and laboratory studies have indicated that rock fragments in the topsoil may have a large impact on soil properties soil quality hydraulic hydrological and erosion processes in most studies the investigated rock fragments still remain visible at the soil surface and only properties of these visible rock fragments are used for predicting runoff and soil loss however there are indications that rock fragments completely incorporated in the topsoil could also significantly influence the percolation and water distribution in stony soils and therefore also infiltration runoff and soil loss rates therefore in this study interrill laboratory experiments with simulated rainfall during 60 min were conducted to assess the influence of subsurface rock fragments incorporated in a disturbed silt loam soil at different depths below the soil surface i e 0 001 0 01 0 05 and 0 10 m on infiltration surface runoff and interrill erosion processes for small and large rock fragment sizes i e mean largest diameter equals 0 04 and 0 20 m respectively although only small differences in infiltration rate and runoff volume are observed between the soil without rock fragments control and the one with subsurface rock fragments considerable differences in total interrill soil loss are observed between the control treatment and both contrasting rock fragments sizes this is explained by a rapid increase in soil moisture in the areas above the rock fragments and

new results and a palaeomagnetic overview of the pontides in northern turkey summary palaeomagnetic results are reported from 16 sites within volcanic and volcano sedimentary rocks of cretaceous and eocene age from the central pontides in northern turkey the sampled area is bounded by the north anatolian fault naf to the south and the black sea to the north the palaeomagnetic data collected demonstrate the presence of both non rotated and anticlockwise rotated regions i declination directions including lower upper cretaceous and eocene sites do not indicate any significant rotations north of where the naf exhibits an arcuate shape ii 20 anticlockwise rotation was observed in the sinop peninsula the northernmost extremity of the central pontides iii in the west of the central pontides two sites with normal and reversed antipodal directions indicate a 20 anticlockwise rotation and iv another region lies to the east of the study area and shows a rotation in an anticlockwise sense of about 5 30 the upper cretaceous and eocene directions reported in this paper and other palaeomagnetic studies show that there is not much difference between the inclination values of the upper cretaceous i 40 1 95 7 2 and the eocene sites i 39 6 95 8 1 furthermore the values of the inclination available from both sedimentary and volcanic upper jurassic lower cretaceous formations are shallower than the upper cretaceous ones this suggests that the entire pontides have undergone a northward drift of over 2000 km since the upper jurassic

effect of embedded rock fragments on slope soil erosion during rainfall events under simulated laboratory conditions abstract quantifying the role of embedded rock fragments in soil water processes on a slope is crucial for the application of rock fragments in soil and water conservation practice in this study a laboratory runoff and erosion experiment was conducted in the soils embedded with rock fragments including five rock fragment contents rc of 0 0 1 0 2 0 3 and 0 4 kg kg 1 in a metal flume under three slopes 5 10 and 15 results showed that the mean steady infiltration rate in the soil without rock fragment null was lower than that in the soils containing rock fragments low rock fragment contents of 0 1 0 2 kg kg 1 and high rock fragment contents of 0 3 0 4 kg kg 1 labelled as low and high respectively as slope gradient 5 but was higher than the latter two soils as slope gradients 10 and 15 initial infiltration rate significantly increased with rc p

soil containing rock fragments effects on infiltration abstract infiltration is a very complex process rock fragments affect infiltration by their presence in the soil matrix and on the soil surface procedures for quantifying soil and surface rock fragments are reviewed within the soil the physical properties and hydraulic properties that affect infiltration are shown to be influenced by rock fragments physical properties discussed are bulk density porosity and water content hydraulic properties that affect infiltration are water retention saturated conductivity and unsaturated conductivity rock fragments on the soil surface have been reported to both increase or decrease infiltration rates and amounts

paleogeographic evidence on the jurassic tectonic history of the pontides new paleomagnetic data from the sakarya continent and eastern pontides the jurassic paleogeographic position of the pontides is not well studied because of insufficient paleomagnetic data for this reason a paleomagnetic study was carried out in order to constrain the paleolatitudinal drift of the turkish blocks during the jurassic period a total of 32 sites were sampled from volcanic and volcanoclastic rocks of the lower middle jurassic kelkit formation eastern pontides mudurnu formation sakarya continent and upper jurassic lower cretaceous ferhatkaya formation exposed around amasya region eastern pontides rock magnetic experiments demonstrate that the main ferromagnetic mineral is pseudo single domain titanomagnetite in these rocks paleomagnetic analysis revealed two main components of the natural remanent magnetization during stepwise thermal and alternating field demagnetization the first component is a low coercivity unblocking temperature component with a direction sometimes similar to that of the earth s present field or a viscous component the second component which is interpreted as the characteristic remanent magnetization chrm direction has low to high coercivity properties between 20 and 100 mt or unblocking temperatures between 300 and 580 c a positive fold test at the 95 level of confidence proved that the chrm of the sites is primary paleomagnetic directions calculated for the kelkit formation in the eastern pontides have a mean direction of d 334 8 i 49 7 95 7 1 after tilt correction a mean direction of d 332 2 i 48 5 95 14 6 was obtained from the volcanoclastic rocks of the mudurnu formation and d 324 3 i 43 3 95 9 5 was calculated for the upper jurassic lower cretaceous limestones ferhatkaya formation of the amasya region the jurassic rocks in the eastern pontides and mudurnu region are considered to represent products of the rifted neo tethys ocean while the upper jurassic lower cretaceous sediments in amasya are related to basin filling materials the data suggest that the kelkit formation was formed at 30 5 n paleolatitude and the equivalent mudurnu formation at 29 5 n paleolatitude the paleolatitude of the eastern pontides indicates that this rifting block was separated from eurasia by a marginal basin instead of being a part of eurasia the lower paleolatitude of the amasya region at 24 8 n in the upper jurassic to lower cretaceous clearly indicates southward drift of the turkish blocks during the jurassic to lower cretaceous period together with the motion of eurasia

the tectonic history of the nigde kirsehir massif and the taurides since the late mesozoic paleomagnetic evidence for two phase orogenic curvature in central anatolia the nigde kirsehir massif known also as the central anatolian block is bordered by the sutures of the neotethys ocean the massif suffered several deformation phases during and after the consumption of the surrounding oceans and the post collisional events of the continental pieces of anatolia in latest cretaceous to miocene previous paleomagnetic studies on the nigde kirsehir massif and its surroundings displayed either insufficient data or have claimed large rotations and or remagnetization in order to understand the tectonic history of the nigde kirsehir massif and its adjacent blocks we have sampled 147 different sites in the age range of upper jurassic to miocene from the nigde kirsehir massif throughout its w sw and e se boundaries and the central southeastern taurides the results display that except the limestones in central taurides all rocks examined carry a primary magnetization among these an important finding is that rotations between the massif and the central eastern taurides indicate an oroclinal bending with counterclockwise rotation of r 41 1 7 6 in the se and clockwise rotation of r 45 9 9 3 in the central taurides from upper cretaceous rocks with respect to the african reference direction paleomagnetic rotations in the se taurides are compatible with the vergent direction of the thrusts generated from consumption of the intra tauride ocean prior to post collisional convergence between taurides and the massif in the central taurides it has been shown that the clockwise rotation of 45 9 9 3 started in middle eocene because of a remagnetization in upper creataceous limestones the deformation was linked to the final closure of the southern neotethys and the collision between the african and eurasian plates in the nigde kirsehir massif counterclockwise rotation up to 25 5 7 3 is recognised during middle eocene and interpreted in terms of block rotation together with the taurides after the miocene a counterclockwise rotation of 16 8 3 9 along the eastern taurides shows that this area was mostly affected by the westward movement of anatolia despite the nigde kirsehir massif and its sw w area the central taurides which is recognised as stable with counterclockwise rotation less than 10

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

effects of rock fragments incorporated in the soil matrix on concentrated flow hydraulics and erosion rock fragments can act as a controlling factor for erosional rates and patterns in the landscape thus the objective of this study is to better understand the role that rock fragments incorporated into the soil matrix play in concentrated flow hydraulics and erosion laboratory flume experiments were conducted with soil material that was mixed with rock fragments rock fragment content ranged from 0 to 40 per cent by volume other treatments were slope 7 and 14 and flow discharge 5 7 and 11 4 l min 1 an increase in rock fragment content resulted in lower sediment yield and broader width of flow rock fragment cover at the soil surface i e surface armour increased with time in experiments with rock fragments flow energy was largely dissipated by rock fragment cover for more turbulent flow conditions when roughness elements were submerged in the flow hydraulic roughness was similar for different rock fragment contents in experiments with few or no rock fragments a narrow rill incised flow energy was dissipated by headcuts total sediment yield was much larger than for experiments with rock fragments in the soil adding just a small number of rock fragments in the soil matrix resulted in a significant reduction of sediment yield copyright 2007 john wiley sons ltd

jurassic cretaceous low paleolatitudes from the circum black sea region crimea and pontides due to true polar wander article in a recent study paleomagnetic and paleoenvironmental data from adria as part of the african plate suggest a trend toward much lower 15 latitudes from early jurassic to earliest cretaceous at the position of adria than suggested by the apparent polar wander apw paths the smoothing of existing apw paths has most likely caused this low latitude episode to be overlooked in this study we test if the low paleolatitudes in the jurassic to early cretaceous can also be found in eurasia i e crimea ukraine and the pontides turkey that are situated in the present day black sea region our eurasian data suggest the same low late jurassic to early cretaceous paleolatitudes as shown for africa the jurassic to lower cretaceous time span is characterized by tethys subduction between the african and eurasian continents and these subduction zones likely functioned as an anchor in the mantle therefore we regard it unlikely that both the african and eurasian plates moved by n1500 km south and subsequently north with respect to the mantle as suggested by the paleomagnetic results true polar wander tpw provides a mechanism that rotates the earth s crust and mantle with respect to its core and it was recently quantified the period from 195 135 ma early jurassic to earliest cretaceous is subject to clockwise tpw which could well explain our results we conclude that tpw rather than plate tectonics is the cause of low late jurassic to early cretaceous african and eurasian paleolatitudes in the eastern mediterranean area

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

illuminating wildfire erosion and deposition patterns with repeat terrestrial lidar erosion following a wildfire is much greater than background erosion in forests because of wildfire induced changes to soil erodibility and water infiltration while many previous studies have documented post wildfire erosion with point and small plot scale measurements the spatial distribution of post fire erosion patterns at the watershed scale remains largely unexplored in this study lidar surveys were collected periodically in a small first order drainage basin over a period of 2 years following a wildfire the study site was relatively steep with slopes ranging from 17 to 30 during the study period several different types of rain storms occurred on the site including low intensity frontal storms 2 4 mm h 1 and high intensity convective thunderstorms 79 mm h 1 these storms were the dominant drivers of erosion erosion resulting from dry ravel and debris flows was notably absent at the site successive lidar surveys were subtracted from one another to obtain digital maps of topographic change between surveys the results show an evolution in geomorphic response such that the erosional response after rain storms was strongly influenced by the previous erosional events and pre fire site morphology hillslope and channel roughness increased over time and the watershed armored as coarse cobbles and boulders were exposed the erosional response was spatially nonuniform shallow erosion from hillslopes 87 of the study area contributed 3 times more sediment volume than erosion from convergent areas 13 of the study area however the total normalized erosion depth volume area was highest in convergent areas from a detailed understanding of the spatial locations of erosion we made inferences regarding the processes driving erosion it appears that hillslope erosion is controlled by rain splash for detachment and overland flow for transport and quasi channelized erosion with the sites of highest erosion corresponding to locations with the lowest roughness by contrast in convergent areas we found erosion caused by overland flow soil erosion was locally interrupted by immobile objects such as boulders bedrock or tree trunks resulting in a patchy erosion network with increasing roughness over time

a palaeomagnetic approach to the origin of the black sea summary available palaeomagnetic data for the circum black sea region are reviewed with the object of evaluating the geodynamical evolution of the black sea jurassic data from the south of the stara planina forebalkan zone south of the moesian platform in bulgaria which was then part of the east european platform place the region at about 39 latitude while the pontides the northernmost tectonic unit of turkey were at a lower latitude 10 15 palaeomagnetic investigations on upper cretaceous magmatic rocks sampled in different parts of the srednogorie tectonic unit southern boundary of the stara planina forebalkan indicate that the region was at 39 palaeolatitude during the upper cretaceous while the pontides had moved northward to 23 palaeolatitude since early cretaceous time the great caucasus domain of the ussr was welded to eurasia by coniacian time and had a palaeolatitude of 36 calculated palaeopole positions for the above mentioned geological times for the pontides fit well with the african palaepoles but largely deviate from the eurasian ones taken together these observations indicate that the pontides were not part of eurasia instead they were separated from the east european platform by the early mesozoic tethys this conclusion does not favour the rifted back arc hypothesis for the formation of the black sea during cretaceous time as suggested by some researchers adamia et al 1977 hsii et al 1977 sengor yilmaz 1981

paleomagnetism and mesozoic cenozoic paleocontinental maps a method of making paleocontinental reconstructions based on ocean floor magnetic anomaly data and land based paleomagnetic data is briefly described and its limitations are assessed synthetic polar wander paths for the period 20 200 ma are presented for australia antarctica india africa eurasia north america and south america comparison is made with observed paths except for antarctica for which the data are too sparse there are no significant differences between observed and synthetic paths a plot of inclination anomaly against paleolatitude shows a large scatter that limits the precision of the paleogeographic grid on continental reassemblies the absence of any systematic trend to this scatter with time suggests that the field has had the same average behavior over the past 180 ma and that large scale expansion of the earth cannot have occurred in this period south america has undergone the least change in position relative to the poles in the past 160 ma

the 1964 prince william sound earthquake joint inversion of tsunami and geodetic data the 1964 prince william sound alaska earthquake mw 9 2 ruptured a large area beneath the continental margin of alaska from prince william sound to kodiak island a joint inversion of tsunami waveforms and geodetic data consisting of vertical displacements and horizontal vectors gives a detailed slip distribution two areas of high slip correspond to seismologically determined areas of high moment release the prince william sound asperity with average slip of 18 m and the kodiak asperity with average slip of 10 m the average slip on the fault is 8 6 m and the seismic moment is estimated as 6 3 1022 n m or over 75 of the seismic moment determined from long period surface waves

headcut retreat in a semiarid watershed in the southwestern united states since 1935 abstract headcuts are prominent features in the southwestern united states within the walnut gulch experimental watershed wgew survey data was available to quantify the retreat of the three most prominent headcuts in sub watershed 63 011 from 1935 to 2006 the headcuts serve as major sediment sources and were investigated to identify and understand factors controlling retreat rate in this watershed the data was incorporated and analyzed in a geographical information system gis the headcuts have retreated persistently since 1935 a power relationship was fitted by regression r 2 0 89 correlating the retreat rate with the product of contributing drainage area and areal precipitation for precipitation exceeding a threshold intensity i30 25 mm hr 1 this site specific relationship may not apply universally in other regions headcut retreat was not induced by external forcing the autocyclic behavior of headcut retreat was found typical for the southwestern united states the data did not allow timing or identification of initial causes for headcut retreat data suggests that all three headcuts will continue to retreat in the future even though the retreat rate of one headcut was severely inhibited by exhumation a layer of cemented material acting as local base level control most of the sediment eroded at the active headcut scarp was not transported very far indicating that headcutting in this area results in local reworking rather than removal of material from the watershed

effects of rock fragments on soil erosion by water at different spatial scales a review this paper reviews the various effects of rock fragments on soil erosion by water since these effects are scale dependent they are investigated at three different nested spatial scales the microplot 4 10 6 100m2 the mesoplot 10 2 102 m2 and the macroplot 101 104 m2 for each scale the corresponding process mechanisms are discussed particular attention is paid to the effects of rock fragment cover on the intensity of soil erosion processes at the mesoplot scale i e on interrill areas rock fragments at the soil surface can have negative as well as positive effects on sediment yield these ambivalent effects are conditioned by the type of fine earth porosity soil surface slope vertical position and size of rock fragments and by the occurrence of horseshoe vortex erosion at the microplot scale i e the soil surface area which is covered by a single rock fragment and at the macroplot scale i e upland areas where both interrill and rill erosion takes place rock fragments at the soil surface have a negative effect on sediment yield in these two scales rock fragments can thus be considered as natural soil surface stabilizers at the macroplot scale the mean decrease of relative interrill and rill sediment yield with rock fragment cover can be expressed by an exponential decay function the scatter of the data indicates that a given rock fragment cover can have different efficiencies in reducing interrill and rill sediment yield depending on the varying intensities of the hydrological and erosion subprocesses these findings have implications for erosion modelling and soil conservation

effects of rock fragment cover on hydrological response and soil loss from regosols in a semi humid environment in south west china abstract controlling soil hydrological processes and combating soil erosion on agricultural fields are high priorities for crop production and ecological environments in this research the effect of land application of rock fragments on surface runoff subsurface runoff infiltration and soil loss on regosols had been investigated under field conditions using a portable rainfall simulator experimental twin plot two subplot with 1 m wide by 2 m long 32 slope with different rock fragment covers ranging from 0 40 were exposed to three rainfall intensities low 57 2 mm h 1 medium 91 3 mm h 1 and high 122 5 mm h 1 fifteen treatments were conducted in the experiments in duplicates surface runoff subsurface runoff soil moisture and sediment were measured results show that surface rock fragment cover retarded surface runoff increased infiltration and subsurface runoff and diminished sediment concentration and soil loss the final infiltration rates which increased with increasing rock fragment covers were 16 5 42 7 mm h 1 at low intensity 19 7 50 8 mm h 1 at medium intensity and 23 8 56 4 mm h 1 at high intensity compared with bare soils surface runoff rates were reduced to 24 51 and 64 in soils with 40 rock fragment cover at low medium and high intensity rainfall respectively subsurface runoff volume was significantly higher and time to start subsurface runoff was shorter as surface rock fragment cover increased compared with bare soils subsurface runoff coefficients increased to 3 5 3 3 and 2 9 times in soils with 40 rock fragment cover at low medium and high intensity respectively sediment concentrations increased from 9 8 g l 1 for 40 rock fragment cover under high intensity rainfall to 51 5 g l 1 for bare soils with rain falling at high intensity the erosion rate was 15 g m 2 min 1 for bare soils under low intensity the relationship between rock fragment cover and soil loss ratio can be expressed by an exponential function with a high degree of reliability regardless of rainfall intensities overall results indicate the surface rock fragments can be influential in shaping hydrological processes and soil loss from sloping farmland

on the combined effects of vertical shear and zonal electric field patterns on nonlinear equatorial spread f evolution in order to understand observations of modulated irregularities in a localized region on the bottomside of the equatorial ionosphere without the presence of vertically rising large scale plume events an investigation is carried out by means of a nonlinear numerical simulation model using different background ionospheric conditions the investigation revealed that the development of long wavelength 200 km perturbations can only be confined to the bottomside of the ionosphere in a localized region with the combined effects of shear in the zonal plasma drift and a nighttime westward electric field the variabilities in the occurrence characteristic are shown to depend on the variabilities in the prereversal enhancement in the zonal electric field further the resurgence of a plume event at a later time as seen by the jicamarca radar is explained on the basis of confined preseeded structures subject to a fresh instability source first evidence is presented that a source of fresh instability may actually be a wind and or a temperature disturbance launched hours earlier by a small substorm

gps phase fluctuations in the equatorial region during the miseta 1994 campaign in this paper we present the first coordinated use of global positioning system gps multisite and multisatellite observations with ground based radar and optical diagnostics to investigate equatorial irregularity patterns thirty second samples of total electron content tec obtained from gps phase differences between 1 2 and 1 6 ghz signals are used to study phase fluctuations at several stations comparisons were made with various types of ground measurements during the multi instrument studies of the equatorial thermosphere aeronomy miseta period depletions of 6300a airglow emission from arequipa peru correlated with phase fluctuations recorded at the same site phase fluctuations at arequipa occurred at the times when the jicamarca radar backscatter returns from plumes were noted but were also seen on other nights when there were no radar returns from plumes levels of phase fluctuations noted at arequipa varied considerably on nights when only thin layers of irregularities were observed by the jicamarca radar differences of ionospheric conditions between the two sites separated by only 5 5 geographic longitude may account for the different behavior patterns of irregularities noted similar differences in the general behavior pattern of phase fluctuations were shown when data from arequipa and fortaleza brazil were compared these stations 33 apart but at the same dip latitude had different patterns for some days during a magnetic storm a very high altitude plume was observed by the radar and by phase fluctuations noted at santiago at 18 dip latitude this correlation of high plume altitude during some periods of magnetic activity was validated by additional examples of phase fluctuations from three other magnetic storms in the solar minimum years of 1994 and 1995

rock fragments in top soils significance and processes this introductory paper reviews various aspects of rock fragments in top soils such information is required for various reasons and in particular for predicting the impact of climatic or landuse changes on the response of these soils particular attention is paid to the definition and measurement of rock fragment content in top soils the density of soils containing rock fragments the spatial distribution and movement of rock fragments in top soils the effects of rock fragments on some key hydrological processes thermal properties of top soils physical soil degradation soil erosion and soil productivity

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

variation of rock fragment cover and size along semiarid hillslopes a case study from southeast spain abstract the spatial variation of rock fragment cover rc and rock fragment size rs along semiarid hillslopes and transects in the mediterranean is largely controlled by hillslope gradient total rock fragment cover rc 5 mm often increases in a convex upward curve with hillslope gradient while the d50 of the surface rock fragments 5 mm increases linearly with hillslope gradient on south facing slopes rc 5 mm is slightly higher than on north facing slopes lithology controls the size distribution of the stone pavement rather than its cover percentage spatial variation of rock fragment cover reflects spatial variation in past erosion and deposition rates hillslope sections that are steep south facing or have been abandoned a long time ago have undergone intense interrill and rill erosion and thus have high rock fragment covers tillage erosion leads to high rock fragment covers on convex hillslopes in intensively cultivated areas thus using information on hillslope gradient aspect lithology and landuse we have been able to describe the spatial variation of rock fragment cover and size along semiarid hillslopes in southeast spain such information is crucial for understanding and modelling the spatial variation of the hydrological and erosion response of semiarid hillslopes under environmental change especially in semiarid environments of the mediterranean where vegetation cover is predicted to decrease due to climatic or landuse changes and rock fragments at the surface become the only soil surface stabilisers

research on soil detachment rate and hydrodynamic parameters of dip anti dip slope in simulated karst trough valley bedding dip has an important influence on soil detachment and flow hydrodynamics in a karst trough valley the laboratory rainfall simulation was conducted with three bedding dips bare slope dip slope and anti dip slope under three rainfall intensities 30 60 90 mm h 1 the characteristics of soil detachment and hydrodynamic parameters were assessed including water flow shear stress stream power unit stream power and unit flow energy the significant effects of bedding dips and rainfall intensities and their interactions on soil detachment and hydrodynamic parameters were examined the results showed that 1 the soil detachment rate decreased with increasing rainfall duration and the soil detachment rate in 30 bedding dip of dip slope was much larger than those in bare slope and anti dip slope in most rainfall intensities 2 the 60 bedding dip of dip slope was the threshold that controlled the stream power unit stream power and unit flow energy increased or decreased under different rainfall intensities and 3 the soil detachment rate had extremely significant positive power relationships with water flow shear stress stream power unit stream power and unit flow energy meanwhile the stream power was the most suitable parameter for predicting soil detachment in a karst trough valley slope therefore these results could provide useful information for soil erosion prediction in a karst trough valley

macroscale surface roughness and frictional resistance in overland flow the hydraulics of overland flow on rough granular surfaces can be modelled and evaluated using the inundation ratio rather than the flow reynolds number as the primary dimensionless group determining the flow behaviour the inundation ratio describes the average degree of submergence of the surface roughness and is used to distinguish three flow regimes representing partially inundated marginally inundated and well inundated surfaces a heuristic physical model for the flow hydraulics in each regime demonstrates that the three states of flow are characterized by very different functional dependencies of frictional resistance on the scaled depth of flow at partial inundation flow resistance is associated with the drag force derived from individual roughness and therefore increases with depth and percentage cover at marginal inundation the size of the roughness elements relative to the depth of flow controls the degree of vertical mixing in the flow so that frictional resistance tends to decrease very rapidly with increasing depth of flow well inundated flows are described using rough turbulent flow hydraulics previously developed for open channel flows these flows exhibit a much more gradual decrease in frictional resistance with increasing depth than that observed during marginal inundation a data set compiled from previously published studies of overland flow hydraulics is used to assess the functional dependence of frictional resistance on inundation ratio over a wide range of flow conditions the data confirm the non monotonic dependence predicted by the model and support the differentiation of three flow regimes based on the inundation ratio although the percentage cover and the surface slope may be of importance in addition to the inundation ratio in the partially and marginally inundated regimes the reynolds number appears to be of significance only in describing well inundated flows at low to moderate reynolds numbers as these latter conditions are quite rare in natural environments the inundation ratio rather than the reynolds number should be used as the primary dimensionless group when evaluating the hydraulics of overland flow on rough surfaces 1997 by john wiley sons ltd

neutral temperature anomaly in the equatorial thermosphere a source of vertical winds data obtained from the wats wind and temperature spectrometer instrument on de 2 dynamics explorer during high solar activity show new evidence for the presence of vertical winds of a significant magnitude in the equatorial thermosphere they reveal a latitudinal structure that can be related to the recently discovered phenomena of the equatorial temperature and wind anomaly etwa in the local evening hours the vertical winds usually are downward around the dip equator and collocated with the temperature minimum of etwa in general they are upward at about 24 dip latitude away from the dip equator and are collocated with the etwa temperature crests the magnitude of the vertical winds is in the 10 40 m s range it is proposed that the temperature and pressure ridges formed by the excess ion drag on the zonal winds around the two crests and ordered by the relatively lower ion drag at the trough of the well known equatorial ionization anomaly eia drive a new wind system in the meridional plane and that the measured vertical winds form part of this wind system

jurassic cretaceous paleomagnetism and paleogeography of the pontides turkey published paleomagnetic data from the pontides indicate anomalously low jurassic and early cretaceous paleolatitudes compatible with the southern neo tethyan african continental margin and significantly different from paleolatitudes predicted for the northern eurasian neo tethyan margin we present a new set of paleomagnetic data from 50 late cretaceous sites mainly from the western pontides and from the eastern pontides and 11 early jurassic sites mainly from the eastern pontides fold tests indicate that the characteristic magnetization components predate eocene folding late cretaceous site mean declinations are northerly in the eastern pontides and rotated to the west by a few tens of degrees in the western pontides late cretaceous site mean declinations are affected by local clockwise rotation in one sampling region close to the north anatolian fault the mean late cretaceous inclinations and resulting paleolatitudes are 41 1 23 5 n and 43 7 25 5 n for the western and eastern pontides respectively for the eastern pontides the early jurassic liassic mean inclination is 60 5 yielding a paleolatitude of 41 4 n considerably further north than previous paleolatitude estimates for the eastern pontides at this time the paleolatitude estimates for the western and eastern pontides are consistent with these units being close to the eurasian continental margin during liassic and late cretaceous time

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

paleomagnetism and the motion of large and small plates the focus of paleomagnetic research during past decades has varied greatly the first generation in paleomagnetism might be defined as beginning with the pioneering studies aimed at discovering whether the geomagnetic field has been a reliable reference frame for measuring and timing continental displacements an enormous effort followed in the form of individual paleomagnetic studies of cratonic rocks culminating with the construction of apw apparent polar wander paths for the continents which could be used to test paleogeographic reconstructions coupled with parallel research in marine geophysics and geology the refined apwp which result from this effort have helped to develop a reasonable first order history of cenozoic mesozoic paleogeography for the major plates

influence of rock fragment coverage on soil erosion and hydrological response laboratory flume experiments and modeling two laboratory flume experiments on the effect of surface rock fragments on precipitation driven soil erosion yields were carried out the total sediment concentration the concentration of seven individual size classes and the flow discharge were measured digital terrain models dtms were generated before and after one of the experiments the results revealed that the rock fragments protected the soils from raindrop detachment and retarded the overland flow therefore decreasing its sediment transport capacity rock fragments were found to affect selectively the different size classes in a manner that changed according to the time scale for short times the rock fragment coverage reduced erosion of the finer particles 100 m was unaffected at long times the rock fragment cover decreased the concentration of the individual size classes in proportion to effective rainfall intensity and the area exposed to raindrops an area based modification of the hairsine and rose h r soil erosion model was employed to analyze the experimental data the h r model predictions agreed well with the measured sediment concentrations when high rainfall intensity and low rock fragment cover were used predictions were instead less accurate with low rainfall intensity and high rock fragment cover the dtm results showed that the presence of rock fragments on the soil surface led to increased soil compaction perhaps due to higher soil moisture content from greater infiltration within the rock fragment covered flumes

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

can rock fragment cover maintain soil and water for saline sodic soil slopes under coastal reclamation abstract seeking a potential erosion control method for saline sodic soil slopes under coastal reclamation is essential we investigated the effect of rock fragment covers rc on the rainfall partitioning infiltration and runoff processes and the erosion processes for saline sodic slopes of 15 and 30 subjected to a 50 min simulated rainstorm with an intensity of 92 mm h 1 six rock fragment covers 0 10 20 40 60 and 80 were investigated soil was packed in 200 cm 100 cm 30 cm flumes divided into two to create two replicates for each treatment two sequential soil erosion events e1 followed by e2 were induced under two rainstorms that were 24 h apart results showed that in general rc had a positive effect on the runoff rate for both slopes a logarithmic relationship existed between the steady state infiltration rate and the rc for the gentler slopes an rc between 40 and 60 could protect the soil from erosion for e2 and e1 e2 events but did not do so for the e1 events alone for the steeper slopes the rc had no effect on soil losses for the e2 and e1 e2 events but increased the soil losses for the e1 events as the situation of rock fragment changed from situation 1 well embedded into the soil surface to situation 4 submerged in water the relationship between rc and soil loss became more complex and might change over time from a positive to a negative one the results suggested that the effect of rc on runoff and soil losses was influenced by the change of rock fragment situations over time during individual rainstorms the benefits of rc might be augmented by using them in combination with another protective measure

rock fragments and soil hydrological processes significance and progress abstract in this review we explore the significance of rock fragments in studies of soil hydrological processes because according to research the effects of rock fragments on soil hydrological processes are inconsistent positive negative rock fragments play a critical role in the biosphere as the primary filter for water and solutions containing contaminants and heavy metals rock fragments have a complex influence on soil hydrological processes e g soil erosion runoff generation water infiltration solute transport and water flow and are highly relevant in a typical system in the soil plant atmosphere continuum cracks related to rock fragments provide preferential flow paths through which pollutants are transported into groundwater in this paper the published literature is reviewed concentrating on rock fragments and their effects on soil hydrological processes systematic studies and examples illustrate the effects of rock fragments architecture i e coverage content size position spatial heterogeneity morphology weathering and topography on soil hydrological processes methods and models applied to evaluate the effects of rock fragments on soil hydrological processes are examined in detail we conclude that the relationship between rock fragments and soil hydrological processes is complicated and requires more international research efforts this review concludes with a discussion of perspectives on areas of research that can improve understanding of the effects of rock fragments on soil hydrological processes with insights and suggestions also being provided regarding potential research trends requirements and solutions

the condor equatorial spread f campaign overview and results of the large scale measurements during the condor campaign a number of instruments were set up in peru to support the rocket experiments in this series of papers we report on the results of the experiments designed to study the equatorial f region in this overview paper we summarize the main results as well as report upon the macroscopic developments of spread f as evidenced by data from backscatter radas from scintillation observations and from digital ionosonde meaurements in this latter regard we argue here that at least two factors other than the classical gravitational rayleigh taylor plasma instability process must operate to yield the longest scale horizontal organization of spread f structures the horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow although detailed comparison with theory seems to require shear frequencies a bit higher than observa tions indicate on the other hand the largest scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions using simultaneous rocket and radar data we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over jicamarca are primarily spatial structures advecting overhead the detailed rocket radar compari son verified several other earlier results and speculations particularly those made in the plumex experiments in particular companion papers discuss and extend some of the plumex results to include the role of anomalous diffusion labelle et al this issue in the theory of equatorial spread f and to shed light upon the shallow spectral form often observed in the intermediate scale regime labelle and kelley this issue

evidence of early cretaceous remagnetization in the crimean peninsula a palaeomagnetic study from mesozoic rocks in the crimean and western pontides conjugate margins of the western black sea

why are there no clockwise rotations along the north anatolian fault zone mechanical analysis of lithospheric deformation associated with an intracontinental transform fault suggests that it should be associated with a pattern of vertical axis rotations governed by the length of the fault its displacement and the mechanical properties of the lithosphere paleomagnetic results from two transects across the north anatolian fault zone indicate that there have been no measurable clockwise rotations on a regional scale associated with neogene dextral strike slip motion along the fault the data come from two groups of volcanic rocks that have been dated by k ar whole rock geochronology and have yielded ages ranging from 45 3 3 1 m y to 41 8 1 3 m y eocene and 21 7 1 5 m y to 7 5 0 2 m y miocene the absence of clockwise rotations suggests one of the following explanations 1 in contrast to the assumptions underlying current mechanical analyses deformation in the upper crust may not directly reflect the flow in the lithosphere and is localized along a single fault trace 2 deformation is distributed but rotations have been prevented by the presence of elongate fault blocks subparallel to the trace of the main fault 3 displacement along the north anatolian fault may be too small or the rheologic properties of the lithosphere such that rotations about vertical axes cannot be resolved instead of the predicted clockwise rotations measured declinations show that there has been approximately 30 of anticlockwise rotation of both the eocene and miocene volcanic rocks this suggests that no significant rotation occurred between eocene and miocene times and that the anticlockwise rotation occurred either immediately before or concurrent with the plio pleistocene slip on the north anatolian fault

mining soil databases for landscape scale patterns in the abundance and size distribution of hillslope rock fragments landscape scale variation in rock fragments on soil mantled hillslopes is poorly understood despite the potential importance of rock fragments in soil weathering and coarse sediment supply to river networks we explored the utility of soil survey databases for data mining with the goals of identifying landscape scale patterns in the abundance and size distribution of rock fragments diameter d 2 mm and potential controls on grain size production we focus on data from three regions the hawaiian islands and the sierra nevada and cascade mountains where elevation transects span a range of environmental conditions we selected pedons from pits dug on hillslopes with active soil production and transport for the 27 pedons selected we constructed depth averaged grain size distributions and calculated the mass fraction of rock fragments frf and the median rock fragment grain size d50rf we also categorized as bimodal size distributions with a clear breakpoint between fine and coarse modes several strong patterns emerge from the data we find rock fragments in 85 of the pedons primarily in distinct coarse modes within bimodal size distributions values of frf and d50rf are strongly correlated although the best fit power law scaling between frf and d50rf differs between the warmer hawaiian and colder sierra nevada and cascade mountain sites we also find a regional contrast in the variation in frf with elevation frf declines with elevation in hawaii but increases in the mainland sites although this contrast could be an artifact of variable lithology precipitation may influence many patterns in the data lower mean annual precipitation correlates with higher frf dominantly bimodal distributions and surface enrichment in the vertical distribution of rock fragments these observations may be useful in refining models of coarse sediment supply to rivers and suggest opportunities for future work to test mechanistic hypotheses for rock fragment production on soil mantled hillslopes copyright 2011 john wiley sons ltd

effects of gravel on concentrated flow hydraulics and erosion in simulated landslide deposits abstract gravel has an important influence on concentrated flow hydraulics and soil and water loss we conducted a field investigation and a subsequent simulated scouring experiment with four gravel contents 0 25 33 3 50 and three inflow rates 4 8 12 l min under two steep slopes 67 5 72 7 we assessed the characteristics of concentrated flow hydraulics including flow velocity flow depth reynolds number re froude number fr darcy weisbach friction coefficient f and the rate of soil and water loss sw we observed significant effects of gravel and inflow rate on hydraulics and erosion as well as interactions between gravel and inflow rate the mean flow velocity reduced as the gravel content increased the changes in flow depth fluctuated with gravel content in the order 25 0 50 33 3 re was larger in 0 gravel than in 25 33 3 and 50 gravel fr was 1 in 0 gravel but was approximately equal to 1 in gravel containing soils values of f were lowest in 0 gravel the f values for gravel containing soils not only decreased as the gravel content increased but also had a significant relationship with the corresponding re values sw was maximal in 25 gravel content and gradually declined for gravel content beyond 25 sw had a significant logarithmic relationship with re the results have significant implications for predictions of soil and water loss steeply sloping gravel rich soils

a paleomagnetic study of the bilecik limestone jurassic northwestern anatolia abstract paleomagnetic analyses of samples collected from a 500 m thick jurassic section in the pontides reveal the presence of two components of remanent magnetization an unstable low temperature component which is removed during thermal demagnetization through 220 c and a dominant component which displays consistent directions through 650 curie point and irm studies indicate that goethite is responsible for the low temperature component whereas both magnetite and hematite contribute to the more stable component the pole position determined from the stable magnetization is located at 18 8 n 91 8 e 95 7 7 n 134 indicating that the section has undergone more than 90 clockwise rotation since the late jurassic ancillary geologic evidence particularly the orientation of jurassic facies belts is also consistent with a 90 clockwise rotation in this region of northwest anatolia the pole suggests that the section may also have migrated slightly northward although the age of these movements is currently unknow it is proposed that they are principally related to the closure of the neo tethys during the late cretaceous early tertiary some of the rotation may be related to the right lateral movement along the north anatolian transform fault which was initiated in the miocene

effect of antecedent conditions and fixed rock fragment coverage on soil erosion dynamics through multiple rainfall events the effect of antecedent conditions and specific rock fragment coverage on precipitation driven soil erosion dynamics through multiple rainfall events was investigated using a pair of 6 m 1 m flumes with 2 2 slope four sequential experiments denoted e1 e2 e3 and e4 involved 2 h precipitation rates of 28 74 74 and 28 mm h 1 respectively and 22 h without rainfall were conducted in each experiment one flume was bare while the other had 40 rock fragment coverage the soil was hand cultivated and smoothed before the first event e1 only and left untouched subsequently sediment yields at the flume exit reached steady state conditions over time scales that increased with sediment size experiments were designed such that both steady and non steady effluent sediment yields were reached at the conclusion of e1 results from subsequent experiments showed that short time soil erosion was dependent on whether steady state erosion was achieved during the preceding event although consistent steady state effluent sediment yields were reached for each sediment size class steady state erosion rates were however dependent on the rainfall intensity and its duration if steady state sediment yields were reached for a particular size class that class s effluent sediment yield peaked rapidly in the next rainfall event the early peak was followed by a gradual decline to the steady state condition on the other hand for size classes in which steady state was not reached at the end of the rainfall event i e e1 in the following event e2 the sediment yields for those classes increased gradually to steady state i e the sharp peak was not observed the effect of rock fragment cover 40 on the soil surface was also found to be significant in terms of the time to reach steady state i e their presence reduced the time for steady conditions to be attained effluent sediment yields for the bare and rock fragment covered flumes e1 showed steady conditions were reached for the latter in contrast to the former we used the hairsine rose h r model to simulate the experimental data as it explicitly models soil particle size classes experiments e1 and e2 involved soil compaction by raindrops and in this case the model predictions were found to be unsatisfactory however compaction was effectively completed by the end of experiment e2 and the model provided reasonable predictions for experiments e3 and e4

paleomagnetic constraints on the tectonic evolution of the sakarya continent northwestern anatolia comment abstract thirteen sites were sampled in northwestern anatolia in order to gather paleomagnetic information concerning the tectonic evolution of this region through jurassic to early tertiary time an interval encompassing much of the history of the neo tethys in this area specifically information concerning the history and behaviour of a crustal block the sakarya continent was sought in order to place some constraints on geologic models that have been proposed for the region four jurassic sites are believed to exhibit early magnetization signatures that yield similar paleolatitudes for all sites these results when compared with paleolatitude information for eurasia suggest that sakarya lay in close proximity to the southern eurasian margin at least during the jurassic part of its history significantly different declinations from the same four sites are interpreted to reflect the deformation of sakarya when it docked with eurasia during the early tertiary these rotations are not attributed to motions of the north anatolian fault since results from three paleocene sites in the same area show no evidence of significant rotation with respect to eurasia

effects of rock fragment covers on erosion and transport of noncohesive sediment by shallow overland flow rock fragments on soil surfaces can have a variety of contrasting effects on the hydraulics of overland flow and soil erosion this makes modeling soil erosion difficult systematic studies are needed to assess the effects of rock fragments on the hydraulics of overland flow and to specifically relate these hydraulics to sediment yield therefore flume experiments were conducted in which overland flow was applied to a highly erodible sediment surface covered by various percentages of rock fragments high local turbulence was caused by horseshoe vortex erosion around individual rock fragments for a given discharge and slope the dimension of the scour was affected by the space between the rock fragments for low cover percentages the scour can develop undisturbed and sediment yield increases with percent of rock fragment cover up to about 20 sediment yield then declines as percent cover increases above 20 beyond a cover threshold value of 20 the larger opportunity for scour hole development is counteracted by limited inter rock fragment space that does not allow scour holes to develop to their full extent as sediment yield varies nonmonotonically with rock fragment cover percent sediment yield cannot be predicted by spatially averaged flow hydraulics

spatial distribution of surface rock fragments along catenas in semiarid arizona and nevada usa improved techniques for estimating soil erosion by water have shown that soil surface cover is a major component in the estimate of soil loss erosion prediction models require the user to input slope gradient and soil profile descriptions if equations expressing the relations between slope gradient soil profile rock fragment content and surface rock fragment cover were embedded in these models then direct user input could be reduced field measurements of slope gradient soil profile rock fragment content surface rock fragment cover and vegetation type and cover were made on 12 soil slope complexes on catenas in southeastern arizona usa correlation analysis showed that both slope gradient and soil profile rock fragment content were significantly p 0 01 correlated to surface rock fragment cover additional analysis indicated that the combined effects of slope gradient and soil profile rock content were better defined by a soil slope factor ssf two equations were developed to estimate surface rock fragment cover a logarithmic relation using slope gradient as the independent variable and a hyperbolic equation using the ssf as the independent variable these equations were used to estimate surface rock fragment cover from a soil slope complex in southern nevada the ssfrfc equation gave better estimates of the measured surface rock fragment cover these relations developed for catenas in southeastern arizona may be site specific but they do show that a relation exists for this semiarid area and suggest that similar relations may exist in areas with similar geology and climate such as parts of africa asia australia and south america development of simple relations describing important erosion processes will improve erosion estimates while simultaneously decreasing time and costs associated with using erosion prediction models

equatorial f region zonal plasma drifts we have examined in detail the f region plasma drifts measured at jicamarca peru during 1978 1981 a period of high solar activity and compared these drifts with jicamarca data taken during periods of lower activity as well as with other equatorial zonal neutral wind and plasma drift measurements the increase in solar activity causes larger nighttime eastward plasma drifts at jicamarca and delays the morning reversal time from eastward nighttime to westward daytime drifts the radar data seem to be in good agreement with nighttime neutral wind measurements made by the de 2 satellite but are systematically smaller than spaced receiver drifts measured with both the scintillation and the vhf polarimeter techniques for integration times of 20 30 min but perhaps not for shorter integrations the jicamarca zonal plasma drifts measured with both the incoherent scatter and the radar interferometer technique change little with altitude near the f region electron density peak and above however at nighttime below the f peak there is a clear shear in the zonal plasma drifts with decreasing eastward drifts below the f peak reversing to westward drifts at lower altitudes the nighttime profiles of the equatorial plasma drifts are in good agreement with the results from recent numerical models of the equatorial ionosphere

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