evaporation from cultivated soils containing rock fragments abstract evaporation from bare soil surfaces represents an important water loss for agriculture in semi arid regions numerous efforts have been undertaken to modify the topsoil characteristics mulching tillage in order to create a thin dry topsoil that reduces evaporation however little attention was paid to the role of natural rock fragments in topsoils with respect to evaporation this paper presents the results of laboratory experiments simulating evaporation from initially wet and air dry soils containing a range of rock fragment contents and compares them to field conditions evaporation was stimulated by blowing fans at one high evaporative demand eo 7 7 9 2 mm day 1 time domain reflectometry tdr was used to investigate the relation between the water content of the topsoil and the actual evaporation rate for soils at field capacity initial fine earth water content decreases with rock fragment content and consequently evaporation rates decrease in the same order for air dry soils that received a limited amount of rain 10 and 20 mm an opposite behaviour was observed initial fine earth water content and evaporation rates increase with rock fragment content a strong positive sigmoidal relation between relative evaporation rate actual over open pan evaporation rates and fine earth water content in the centre of the wetted soil section was observed during the laboratory experiments except for the columns covered with a mulch there were no systematic differences in this relation between the treatments a rock fragment mulch reduces evaporation rate at a given soil water content significantly these trends explain the often ambivalent effects of rock fragments on evaporation rates in the field

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

sensitivity analysis of eurosem using monte carlo simulation ii the effect of rills and rock fragments a sensitivity analysis of the surface and catchment characteristics in the european soil erosion model eurosem was carried out with special emphasis on rills and rock fragment cover the analysis focused on the use of monte carlo simulation but was supplemented by a simple sensitivity analysis where input variables were increased and decreased by 10 the study showed that rock fragments have a significant effect upon the static output parameters of total runoff peak flow rate total soil loss and peak sediment discharge but with a high coefficient of variation the same applied to the average hydrographs and sedigraphs although the peak of the graphs was associated with a low coefficient of variation on average however the model was able to simulate the effect of rock fragment cover quite well the sensitivity analysis through the monte carlo simulation showed that the model is particularly sensitive to changes in parameters describing rills and the length of the plane when no rock fragments are simulated but that the model also is sensitive to changes in the fraction of non erodible material and interrill slope when rock fragments were embedded in the topsoil for rock fragments resting on the surface changes in parameter values did not affect model output significantly the simple sensitivity analysis supported the findings from the monte carlo simulation and illustrates the importance when choosing input parameters to describe both rills and rock fragment cover when modelling with eurosem

coupling mechanisms in double sandbar systems part 1 patterns and physical explanation crescentic sandbars and rip channels along wave dominated sandy beaches are relevant to understand localized beach and dune erosion during storms in recent years a paradigm shift from hydrodynamic template models to self organization mechanisms occurred to explain the formation of these rhythmic features in double sandbar systems both the inner and outer bar rip channels and crescentic planshapes are now believed to be free instabilities of the nearshore system arising through self organization mechanisms alone however the occasional occurrence of one or two inner bar rip channels within one outer bar crescent suggests a forced morphologically coupled origin here we use a nonlinear morphodynamic model to show that alongshore variability in outer bar depth and the relative importance of wave breaking versus wave focussing by refraction across the outer bar is crucial to the inner bar rip channel development the coupling patterns simulated by our model are similar to those observed in the field morphological coupling requires a template in the morphology outer bar geometry which through the positive feedback between flow sediment transport and the evolving morphology that is self organization enforces the development of coupling patterns we therefore introduce a novel mechanism that blurs the distinction between self organization and template mechanisms this mechanism may also be extended to explain the dynamics of other nearshore patterns such as beach cusps the impact of this novel mechanism on the alongshore variability of inner bar rip channels is investigated in the companion paper copyright 2010 john wiley and sons ltd

unsaturated hydraulic conductivity in limestone dolines influence of vegetation and rock fragments abstract vegetation and rock fragments have a profound impact on runoff generation in the dolines of the sierra de gador southeastern spain this study investigated the effect of vegetation and rock fragments on unsaturated hydraulic conductivity k h in three limestone dolines and examined whether variation in k h was consistent with differences in runoff from simulated rainfall tension infiltrometers were used to measure unsaturated hydraulic conductivity at three pressure heads h of 30 60 and 120 mm at 70 locations within the three dolines generally the trends of the k h were consistent with the simulated rainfall data and accounted for difference in runoff for the vegetated surfaces vegetation resulted in high infiltration with unsaturated hydraulic conductivities at 30 and 60 mm are significantly greater for the vegetated surface than for the rock fragment covered surface and bare soil surface rock fragments had no obvious effect on soil hydraulic conductivity as compared with bare soils the k h of the non crusted soil were 2 5 times higher than that of the crusted soil the k h decreased with increasing tensions k 60 and k 120 were only 8 4 and 0 89 respectively of k 30 for the vegetated surfaces and were about 30 and 8 7 respectively of k 30 for both rock fragment covered surfaces and bare soils suggesting that pores in the 0 5 to 1 mm diameter range dominate flow under unsaturated conditions there were significant differences in k h among the different topographic units of the dolines and k h tended to be higher in the upper position than in the lower position of the doline

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

millimeter scale microrelief affecting runoff yield over microbiotic crust in the negev desert abstract the negative effect of microrelief upon runoff yield explained by the increase in water storage and the slowdown in flow velocity is a known phenomenon however research concerning surface roughness hitherto focused on decimeter or centimeter scale microrelief owing to the heterogeneous character of many natural plots the effect of centimeter scale microrelief was mainly shown under controlled sprinkling experiments whereas no data was yet made available concerning the possible effect of a millimeter scale microrelief upon runoff yield under natural field conditions when runoff yield was measured over crusted i e surfaces covered by 1 3 mm of cyanobacterial crust and scalped 2 6 m 2 plots at the hallamish dune field negev desert israel during 5 winter seasons 1990 1995 no runoff was generated from the scalped plots during the first year following scalping while meagre quantities were received during the second year nevertheless during the third season and onward runoff yield at the scalped plots was consistently and significantly higher than that of the crusted control plots and this was so albeit the fact that the crust chlorophyll content of the scalped plots during the third season was as low as half the amount of the crusted plots these findings appeared to contradict previous findings that showed the existence of a positive linear relationship between the crust chlorophyll content and runoff yield the apparent contradiction was explained by the differences in the plot microrelief indicating that minute differences even of a millimeter scale may greatly affect runoff yield and thus may compensate for lower crust chlorophyll content surface smoothness which characterizes many of the arid zones may thus explain at least partially the high runoff yield obtained in deserts

rip spacing and persistence on an embayed beach 1 four years of daily time exposure images from an embayed beach were examined to study the spacing persistence and location preferences of rips in a natural rip channel system a total of 5271 rip channels was observed on 782 days occurrence statistics showed no evidence of the preferred location pattern associated with standing edge waves trapped in an embayed beach the histogram of rip spacing the primary diagnostic observable for most models was well modeled by a lognormal distribution mean spacing of 178 m however spacings were highly longshore variable time mean of the standard deviation longshore mean of rip spacing was 39 so they are of questionable merit as a diagnostic variable storm driven resets to the longshore uniform condition required by most models occurred only four times per year on average making rip generation models relevant to only a small fraction of the system behavior rip spacings after the 15 observed reset events were uncorrelated with bar crest distance the lifetime of the 324 individual rip channel trajectories averaged 45 6 days rips were equally mobile in both longshore directions but the coefficient of variation of rip migration rates was large even for high migration rates the mean migration rate was well correlated to a proxy for the longshore current r2 of 0 78 thus there is no significant evidence that the formation spacing and migration of rip channels on this beach can be explained by currently existing simple models moreover the alongshore uniform initial conditions assumed by these models are rare on palm beach making the models generally inapplicable

runoff and sediment yield from topsoils with different porosity as affected by rock fragment cover and position abstract interrill runoff and sediment yield from a topsoil having essentially textural pores and from another with structural pores were measured in the laboratory under simulated rain to investigate the effects of cover and positions of rock fragments the results reveal that the relation between the cover of rock fragments and interrill runoff or sediment yield can be negative as well as positive porosity in the soil near rock fragments determines both the type of relation and the degree to which the positions of rock fragments affect this relation rock fragments increase runoff and sediment yield when well embedded in a surface seal i e a top layer with essentially textural pore spaces a negative relation occurs either where rock fragments are partly embedded in a top layer with structural porosity or where the rock fragments rest on the surface of a soil having either textural or structural pore spaces the time at which macropores at the soil surface close is crucial for then the effect of the cover of rock fragments on the generation of runoff switches from reduction to an increase since cover can have an ambivalent effect on the hydrological and erosion response descriptions of topsoils containing rock fragments should include the type of soil porosity as well as the positions of rock fragments

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

effects of soil surface components on soil hydrological behaviour in a dry mediterranean environment southern spain abstract various researchers have studied the spatial pattern of soil surface components such as vegetation rock fragments bare soil litter and surface crusts as a key factor of hydrological behaviour in mediterranean settings with heterogeneous patches of vegetation cover and strong human impact the studies indicate that there is a mosaic of patches that generate run off or infiltrate overland flow distributed in various ways along hillslopes few of these studies however have looked at areas underlain by metamorphic rocks such as phyllites or schists this study analysed the temporal and spatial variability of the effects of soil surface components on hydrological processes in a small dry mediterranean catchment underlain by metamorphic rocks a systematic sampling of multiple sites throughout a hydrological year was carried out we related the hydrological behaviour of soil surface components to 1 their position along the hillslope 2 the distance of existing vegetation tussocks from the line of run off 3 rainfall intensity and 4 the main physical chemical soil properties affecting infiltration processes statistical analysis was used to check the validity of the relationships the results show that soil surface components have highly variable effects in both space and time on soil hydrological behaviour these effects particularly depend on the location along the line of maximum slope and the intensity of preceding rainfall whose interaction defines soil hydrological status these results are similar to those for other mediterranean settings with different lithology in that the succession of contributing patches are hydrologically interconnected along a hillslope the variables used and the grouping of explanatory variables through principal component analyses were found to be suitable for discussing the spatial distribution of soil surface components in the hydrologically dynamic environment of the study area

the construction of a simple portable electromagnetic vibrator from commercially available components since its introduction in the late 1950s hydraulic vibrators have become the dominant source for land seismic surveys the hydraulic vibrators typically used for commer cial land seismic acquisition however are large costly to operate and expensive to purchase this inhibits their use for small scale and short duration surveys as well as vibroseis research in this paper we describe in detail the construction of a portable vibrator from commercially available components for a cost of less than us2 000 data shows that the vibrator is able to successfully transmit sweeps from 15 to 180 hz with different spectral contents the vibrator produces a stronger signal than a sledge hammer and we estimate its output to be around 1 kn the frequency content of the data was concentrated at lower frequencies 100 hz and the ground roll was far more energetic than that produced using a sledgehammer

analysis of soil surface component patterns affecting runoff generation an example of methods applied to mediterranean hillslopes in alicante spain abstract spatial patterns of soil surface components vegetation rock fragments crusts bedrock outcrops etc are a key factor determining hydrological functioning of hillslopes a methodological approach to analyse the patterns of soil surface components at a detailed scale is proposed in this paper the methods proposed are applied to two contrasting semi arid mediterranean hillslopes and the influence of soil surface component patterns on the runoff response of the slopes was analysed a soil surface components map was derived from a high resolution photo mosaic obtained in the field by means of a digital camera rainfall simulation experimental data were used to characterise the hydrological behaviour of areas with a specific pattern of soil surface components by means of the parameters of the horton equation plot runoff data were extrapolated at the hillslope scale based on the soil surface component maps and their hydrological characterisation the results show that in both slopes runoff generation is concentrated up and downslope with a water accepting area in the centre of both slopes disrupting the hydrological connectivity at the slope scale this reinfiltration patch at the centre of the slope is related to the type of soil surface component and its spatial pattern herbaceous vegetation and on top rock fragments increase the infiltration capacity of soils at the centre of the slope in contrast embedded rock fragments rock outcrops as well as crusted surfaces located in the upper and lower slopes favour runoff generation in these areas in addition a general pattern of water contribution areas downslope is apparent on both slopes the south facing slope shows a higher hydrological connectivity and more runoff 55 of the surface of the south facing slope produces runoff at the end of a 1 hour rainfall event and 17 3 of the surface is covered by a runoff depth between 0 5 and 1 mm while on the north facing slope only 38 of the surface produces runoff under the same conditions longitudinal connectivity of runoff is higher at the south facing slope where more runoff generating surfaces appear and where the vegetation pattern favours the connectivity of bare areas

soil hydraulic properties on the steep karst hillslopes in northwest guangxi china soil hydraulic properties such as soil infiltration rate and hydraulic conductivity are closely linked to runoff generation and infiltration processes but little is known about them on karst hillslopes the objectives of this paper were to investigate the change in soil stable infiltration rate q s and near saturated hydraulic conductivity k ns in different slope positions and to understand their relationship with rock fragment content and soil texture within the topsoil in subtropical karst regions of southwest china tension infiltrometers 20 cm in diameter were used to measure q s and k ns at pressure head of 20 mm on hillslopes 1 a disintegrated landslide failure and 2 an avalanche slope the change of q s and k ns was great and they mostly had a moderate variability with coefficient of variations cv between 0 1 and 1 0 in the different slope positions on average q s ranged from 0 43 to 4 25 mm min and k ns varied from 0 75 to 11 00 mm min these rates exceed those of most natural rainfall events confirming that overland flow is rare on karst hillslopes from bottom to top q s and k ns had a decrease increase decrease trend due to the presence of large rock outcrops 2 m in height on hillslope 1 but had an increasing trend on hillslope 2 with less complex landform they tended to increase with increase in total rock fragment content 5 250 mm within the topsoil as well as slope gradient on both hillslopes pearson correlation analysis suggested that higher coarse pebble 20 75 mm cobble 75 250 mm and sand 2 0 05 mm contents as well as total rock fragment content could significantly facilitate water infiltration into soils but higher clay 0 002 mm content could restrict water movement this result indicated that rock fragment sand and clay contents may remarkably affect water flow in the topsoil layers and should be considered in hydrological modeling on karst hillslopes in subtropical regions

a morphological stability analysis for a long straight barred coast a morphological stability analysis is carried out for a long straight coast with a longshore bar the situation with oblique wave incidence and a wave driven longshore current is considered the flow and sediment transport are described by a numerical modelling system the models comprise i a wave model with depth refraction shoaling and wave breaking ii a depth integrated model for wave driven currents and iii a sediment transport model for the bed load transport and the suspended load transport in combined waves and current the direction of the sediment transport is taken to be parallel to the depth integrated mean current velocity neglecting the effects of a bed slope and secondary currents an instability is found to develop around the bar crest the instability is periodic in the alongshore direction and tends to form rip channels and to steepen the offshore face of the bar between the rip channels the alongshore wave length of the most unstable perturbation is determined for different combinations of the wave conditions and the geometry of the profile

seismic vibrator control and the downgoing p wave while the need for phase compensation is well established the best method to measure the seismic vibrator output is not phase control of the force exerted by a seismic vibrator upon the earth s surface ground force is shown to be useful in producing consistent downhole p wave signatures experimental results are presented which compare the downhole correlation wavelets produced by phase locking to ground force reaction mass acceleration and baseplate acceleration as changes in vibrator type sweep bandwidth drive level and coupling medium are made the empirical results support earlier theoretical work which predicts with suitable assumptions that ground force and far field particle displacement are in phase except for a time delay

discharge and suspended sediment patterns in a small mountainous watershed with widely distributed rock fragments summary understanding and quantifying sediment loads is important in watersheds with highly erodible materials which will eventually cause environmental and ecological problems within this context suspended sediment ss transport and its temporal dynamics were studied in a small mountainous watershed with sloping lands containing rock fragments in subtropical china soils containing rock fragments with many macro pores have a high permeability rate over a 7 year period the mean runoff coefficient of this watershed was 0 65 overall 30 flood events were monitored and accounted for 95 5 27 3 17 1 of the total ss load precipitation and total discharge respectively over a 5 year period the presence of rock fragments in soils can affect soil loss when comparing the soil loss in the studied watershed with that of other watersheds under similar climatic conditions rock fragments negatively affect soil loss however an extreme event occurred on 14 august 1990 and the sediment load exhibited a phenomenon called small deposits towards lump withdrawal which resulted in a soil loss of 20 499 t 4 6 times the mean yearly soil loss this event exhausted most of the ss s stored by the rock fragments on the slope and channel following this event the mean ss concentration ssc of the 11 events was 1 05 kg m 3 and the mean ssc of the 18 previous events was 1 75 kg m 3 twelve variables were separated using the classical hydrograph separation method partial least squares regression plsr was used to determine the highly co related variables of the discharge the results indicated that plsr could explain runoff well the relationship between discharge and ssc was highly scattered during 24 flood events three types of hysteresis loops were observed clockwise 17 events figure eight 3 events and complex 4 events

how good is the weighted sum estimate of the vibrator ground force vibroseis sources are the principal nonimpulsive sources used in land seismic exploration to achieve an improved image of the subsurface with higher accuracy and better resolution it is necessary to take the true ground force as the reference in calculating the cross correlation function with the far field data instead of using the theoretical reference signal the true ground force is defined as the total compressive force exerted by the earth upon the vibrator baseplate theoretically it can be calculated by integrating the compressive stress over the surface area that contacts the baseplate in practice it is very difficult to quantify the true ground force accurately as the vibrator shakes on highly variable surfaces such as desert sand dunes the vibrator will generate more harmonic distortion at the same time the baseplate will flex and rock this results in poor repeatability of source signatures this means that the true ground force varies from place to place and becomes impossible to determine

mechanisms governing incipient motion of ellipsoidal rock fragments in concentrated overland flow a modified shields criterion for incipient motion of ellipsoidal rock fragments in concentrated overland flow was previously defined based on laboratory data in order to apply this new criterion an estimate of the angle of repose for the considered rock fragment is needed therefore a set of laboratory experiments was conducted in order to develop an algorithm for this estimation the main result of these experiments shows that each rock fragment lying on a rill bed of a given roughness is characterized by a normally distributed set of angles of repose this distribution reflects the different local slopes that a rock fragment can experience the new criterion has been successfully validated for single rock fragments lying on an erodible rill bed application of this criterion to field conditions however did not explain all variation in the observed data in fact rock fragments having sizes larger than the predicted flow competence were removed during a moderate rainfall event a consideration of several mechanisms reveals that collisions between rock fragments seems likely to be a significant mechanism explaining the observed discrepancy

effects of rock fragment size and cover on overland flow hydraulics local turbulence and sediment yield on an erodible soil surface the interactions between overland flow hydraulics and sediment yield were studied in flume experiments on erodible soil surfaces covered by rock fragments the high erodibility of a non cohesive fine sediment d50 0 09mm permitted the effects of local turbulence and scour on sediment yield to be examined overland flow hydraulics and sediment yield were compared for experiments with pebble d50 1 5cm and cobble d50 8 6cm rock fragment covers cover percentages range from 0 to 99 per cent rock fragment size strongly affects the relations between flow hydraulics and rock fragment cover for pebbles spatially averaged hydraulic parameters flow velocity flow depth effective flow width unit discharge total shear stress darcy weisbach friction factor percentage grain friction and grain shear stress vary most rapidly within cover percentages at low covers power functions in contrast for cobbles these parameters vary most rapidly within cover percentages at high covers exponential functions as the type of the function that describes the relation between flow hydraulics and cover percentage can be deduced from the ratio of rock fragment height to flow depth the continuity equation can be employed to determine the actual coefficients of the functions provided the regression of one hydraulic parameter e g flow velocity with cover percentage is known and a good estimate exists for two values of another hydraulic variable for a low and a high cover percentage the variation of sediment yield with cover percentage is also strongly dependent on rock fragment size but neither the convex upward relation for pebbles nor the positive relation for cobbles can be solely attributed to the spatially averaged hydraulics of sheet flow rock fragments induce local turbulence that leads to scour hole development on the stoss side of the rock fragments while deposition commonly occurs in the wake this local scour and deposition substantially affects sediment yield however scour dimensions cannot be predicted by spatially averaged flow hydraulics an adjustment of existing scour formulas that predict scour around bridge piers is suggested sediment yield from non cohesive soils might then be estimated by a combination of sediment transport and scour formulas

the influence of hillslope gradient regolith texture stone size and stone position on the presence of a vesicular layer and related aspects of hillslope hydrologic processes a case study from the australian arid zone abstract a near surface layer of vesicles may be found in many dryland soils often below a stony desert pavement during and after rain the uppermost part of the regolith develops a surface seal trapping air which is compressed and which may also subsequently expand as a result of solar heating this results in the deformation of the soft regolith and the formation of a vesicular layer just below the surface the work reported here was undertaken to determine the influence of slope gradient regolith texture stone size and depth of stone embedment on the presence of a vesicular layer in arid australia this appears to be the first investigation of the role of topography in the formation of soil vesicularity the four factors listed typically vary systematically with position on a hillslope the data collected indicate that the development of a vesicular layer is inversely related to hillslope gradient and size of the stone positively related to the amount of silt and clay in the regolith and weakly related to the depth to which the stone is embedded field evidence indicates that the vesicular layer becomes much more extensive on the lower parts of hillslopes in the study area and thus so too must the choke on water penetration that such layers create the spatial distribution of vesicular layers thus constitutes a factor that has traditionally been overlooked in studies of dryland hillslope hydrology

rainwash experiments on the erodibility of loose sediments laboratory experiments using simulated rainfall splash boards and trays were conducted in order to obtain information on the erodibility of loose sediments as a time dependent phenomenon in all ten different sediments ranging from silt d50 24 m to coarse sand d50 593 m were studied the effect of three different initial states of the sediments namely the air dry state t1 the field capacity state t2 and the desiccated state t3 on the erodibility was also assessed variations in detachability during a rain erosion experiment can be explained by change in water content including liquefaction and the development of a water layer on the surface cohesion and granulometric composition of the top layer the coarsest sandy sediments almost always yielded the highest detachability when starting from an initial field capacity state t2 for the finer sediments the highest detachability was found for the homogeneous and not yet compacted initial air dry state t1 the effect of the initial desiccated state t3 on the detachability of the finer sediments was also a function of the rainfall duration the relationship between detachability and median grain size of the sediments was very similar to the relation between grain size and the susceptibility to runoff and wind erosion established by other investigators the highest detachability was found for a fine very well sorted sand with a median grain size of 96 m

relation between infiltration and stone cover on a semiarid hillslope southern arizona abstract a knowledge of the spatial distribution of infiltration rates is essential to the application of realistic distributed rainfall runoff models in semiarid areas one method of determining this distribution is to develop a predictive equation based on a readily observable surface property such as stone cover previous studies of the relation between infiltration and stone cover on shrub covered semiarid hillslopes have yielded both positive and negative correlations it is suggested that positive correlations result where infiltration measurements are confined to areas between large shrubs negative correlations on the other hand reflect pronounced shrub intershrub differences in infiltration and stone cover and are found where both shrub and intershrub areas are sampled in this study of a semiarid hillslope in southern arizona both shrub and intershrub areas are sampled and a negative correlation is obtained between infiltration and stone cover this correlation arises from the fact that under shrubs fine sediments have accumulated primarily as a result of differential splash whereas between shrubs such sediments have been selectively removed by a combination of rainsplash and overland flow leaving behind a gravel lag consequently infiltration rates are higher under shrubs than between them owing to the higher percentage of sand in the surface soil the larger quantity of organic matter both within the soil and on its surface and the greater digging and burrowing by animals in addition simulated rainfall experiments imply that shrubs with moderately dense canopies are more effective than adjacent surface gravels in dissipating the kinetic energy of raindrops and thereby reducing surface sealing and promoting infiltration inasmuch as the field site is typical of gentle shrub covered piedmont hillslopes over much of the sonoran desert inverse relations between infiltration rate and stone cover are probably characteristic of such hillslopes and may be used to predict the spatial distribution of infiltration rates for inclusion in rainfall runoff models

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

rocking the landscape chacma baboons papio ursinus as zoogeomorphic agents abstract animals sculpt landforms by physically altering the substrate many digging and burrowing animals are then considered zoogeomorphic agents while the significance of soil disturbing species is well established geomorphic impacts are rarely quantified for rock transporting species the chacma baboon papio ursinus a widespread and abundant primate throughout most of southern africa south of the zambezi may be a zoogeomorphic agent through its role in rock displacement while foraging we quantified baboon rock movement along belt transects placed across a catena in a semi arid karoo environment in south africa along each transect we the counted the number of moved rocks and recorded their dimensions mass and shape and related this to rock i e mass shape and landscape i e hillslope obstacles that hinder movement features to assess the drivers of the extent of rock transport baboon rock movement was found to be extensive ranging from 26 to 54 615 kg 10 967 2 2300 9 kg of rock material displaced per ha and year the distance of rock movement was influenced by rock size large rocks were displaced further and rock shape flat rocks were moved further followed by angular and rounded rocks furthermore slope influenced rock movement with rocks displaced greater distances on steeper slopes baboon rock movement brought about a loss in potential energy and a change in landscape entropy through the net downward movement of rocks we show that baboons play an important geomorphic role and probably serve as a keystone species as they are the only species in this environment to intentionally move rocks in this way because baboons are considered pests and are widely persecuted their role in zoogeomorphic processes are vulnerable to being lost

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

radiation from flexural vibrations of the baseplate and their effect on the accuracy of traveltime measurements we analyse the problem of radiation of seismic waves by a vibroseis source when the baseplate is subject to flexure a theoretical model is proposed to account for baseplate flexure generalizing the well known model of the vibroseis source of sallas and weber which was developed for a rigid plate using the model proposed we analyse the effect of flexure on the properties of seismic waves we show that the flexure does not contribute to the far field and mainly affects the readings of the reference accelerometer that is used to measure the force applied to the ground these readings generally become dependent on the location of the sensor on the plate for muddy and sandy soils the effect of flexure on baseplate acceleration measurements is nonetheless pronounced at the high end of the vibroseis frequency band only 100 hz and is negligible at all frequencies for stiffer soils the corresponding phase lags introduced by the flexural vibrations at high frequencies lead to errors in the traveltime measurements through the cross correlation function of up to 0 6 ms for muddy soils and less for denser soils we show the existence of an optimal position of the reference sensor on the baseplate and also propose a general method of eliminating the phase lag due to the baseplate flexure in acceleration measurements

a mechanism for the generation of wave driven rhythmic patterns in the surf zone the coupling between topographic irregularities and wave driven mean water motion in the surf zone is examined this coupling occurs because the topographic perturbations produce excess gradients in the wave radiation stress that cause a steady circulation this circulation in turn creates a sediment transport pattern that can reinforce the bottom disturbance and may thereby lead to the growth of large scale bed forms to investigate this coupling mechanism the linearized stability problem with an originally plane sloping beach and normal wave incidence is solved in two different cases first the breaking line is considered to be fixed and second the perturbations in water depth that produce a displacement of the breaker line are accounted for the first case shows that the basic topography can be unstable with respect to two different modes a giant cusp pattern with shore attached transverse bars that extend across the whole surf zone and a crescentic pattern with alternate shoals and pools at both sides of the breaking line showing a mirroring effect in the second case the varying breaker line may have a strong influence on the circulation this is clear for the giant cusp topography whose growth is totally inhibited in contrast the morphology and the growth of the crescentic pattern remains almost unchanged

erosion in mediterranean mountain landscapes during the last millennium a quantitative approach based on lake sediment sequences iberian range spain abstract land degradation and soil erosion are key environmental problems in mediterranean mountains characterized by both a long history of human occupation and strong seasonality of hydrological regimes experimental monitored catchments have identified main controlling factors on erosion dynamics but because of the short time span of the instrumental measurements they do not integrate the complete temporal and spatial variability of these environments to obtain some long term series of mediterranean landscape evolution we propose a novel strategy based on multi proxy analyses of lake sediments aimed to quantify sediment delivery and erosion dynamics karstic lakes in the iberian range central spain provide an opportunity to reconstruct the depositional evolution of the watersheds and to evaluate the response to both the variable anthropogenic impacts and climate forcings during the last 1000 years the most significant periods of increased sediment delivery 26 483 t km yr 1 in the iberian range sites took place during the 15th 16th and 18th 19th centuries as a result of large land use changes and land clearing positive synergies between increasing human population and more humid periods led to peaks in sediment deliver during some phases of the little ice age recent changes associated with the rural exodus and land abandonment during mid 20th century are more clearly shown in larger watersheds by decreased sediment delivery to the lakes due to the re vegetation of the landscape 6 200 t km yr 1 this new integrated approach based on long term lake sequences provides a longer perspective of erosion processes in mediterranean watersheds and validates the main factors identified in monitoring surveys land cover and surface formations erodibility in both settings lakes and experimental catchments most sediment delivery occurs during flooding events measured and reconstructed values show comparable large ranges underlying the punctuated nature of sediment dynamics in mediterranean landscapes at decadal and centennial scales

generation and nonlinear evolution of shore oblique transverse sand bars the coupling between topography waves and currents in the surf zone may self organize to produce the formation of shore transverse or shore oblique sand bars on an otherwise alongshore uniform beach in the absence of shore parallel bars this has been shown by previous studies of linear stability analysis but is now extended to the finite amplitude regime to this end a nonlinear model coupling wave transformation and breaking a shallow water equations solver sediment transport and bed updating is developed the sediment flux consists of a stirring factor multiplied by the depth averaged current plus a downslope correction it is found that the cross shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars either transverse or oblique to the shore in the latter case they can open an acute angle against the current up current oriented or with the current down current oriented at the initial stages of development both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude the former being somewhat stronger as bars keep on growing their finite amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs leading to a final saturated amplitude the overall shape of the saturated bars in plan view is similar to that of the small amplitude ones however the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger in the case of alongshore migrating bars the asymmetry of the longshore sections the lee being steeper than the stoss is well reproduced complex dynamics with merging and splitting of individual bars sometimes occur finally in the case of shore normal incidence the rip currents in the troughs between the bars are jet like while the onshore return flow is wider and weaker as is observed in nature

erosion in mediterranean landscapes changes and future challenges abstract intense erosion processes are widespread in the mediterranean region and include sheet wash erosion rilling gullying shallow landsliding and the development of large and active badlands in both subhumid and semi arid areas this review analyses the main environmental and human features related to soil erosion processes and the main factors that explain the extreme variability of factors influencing soil erosion particularly recent land use changes the importance of erosion in the mediterranean is related to the long history of human activity in a region characterized by low levels of annual precipitation the occurrence of intense rainstorms and long lasting droughts high evapotranspiration the presence of steep slopes and the occurrence of recent tectonic activity together with the recurrent use of fire overgrazing and farming these factors have resulted in a complex landscape in which intensification and abandonment wealth and poverty can co exist the changing conditions of national and international markets and the evolution of population pressure are now the main drivers explaining land use changes including farmland abandonment in mountain areas the expansion of some subsidized crops to marginal lands and the development of new terraces affected by landslides and intense soil erosion during extreme rainstorm events the occurrence of human related forest fires affecting thousands of hectares each year is a significant problem in both the northern and southern areas of the mediterranean basin here we highlight the rise of new scientific challenges in controlling the negative consequences of soil erosion in the mediterranean region 1 to reduce the effects and extent of forest fires and restructure the spatial organization of abandoned landscapes 2 to provide guidance for making the eu agricultural policy more adapted to the complexity and fragility of mediterranean environments 3 to develop field methods and models to improve the identification of runoff and sediment contributing areas 4 to contribute to the conservation of landscapes i e bench terraced fields having high cultural and productivity values 5 to improve knowledge of the hydrological and geomorphological functioning of badlands with the aim of reducing sediment yield and accessibility 6 to better understand the effect of climate change on soil erosion in the mediterranean region and 7 to improve quantitative information on long term soil erosion

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 thickness effect on hydrological and erosion characteristics under sloping lands a hydropedological perspective abstract soil thickness exerts a first order control on the hydrological processes of the hillslopes however from a hydropedological perspective the knowledge of soil thickness effect on hydrological and erosion characteristics under sloping lands is limited based on a comprehensive survey of an experimental watershed in the three gorges area of china five typical sloping land plots 2 m 1 m with different soil thickness were selected along a hillslope to investigate their hydrological processes and erosion response under three rainfall intensities 60 90 and 120 mm h 1 using a portable rainfall simulator the results can be summarized as follows 1 the surface flow coefficient was increased with increasing soil thickness especially under the event of 60 mm h 1 2 the subsurface flow of the 23 31 and 45 cm plots mainly took the form of preferential flow conversely the 59 and 76 cm plots mainly took the form of matrix flow 3 a prolonged low intensity rainfall is much more likely to facilitate deep percolation and subsurface flow than a short high intensity rainfall regardless of soil thickness 4 soil thickness and rock fragment cover were the most important factors than other soil properties in determining the hydrological and erosion behaviors thin soils showed higher infiltration capacity than thick soils due to their more distinct hydrological processes of subsurface flow and deep percolation rock fragment cover enhanced infiltration and served as a shield to protect the soil surface from detaching due to the synergies between thin soil thickness and high rock fragment cover thin soils displayed significantly lower erosion rates than thick soils in all rainfall events which increased from 211 g m 2 h 1 for the 23 cm plot with rainfall of 60 mm h 1 to 4220 g m 2 h 1 for the 76 cm plot with rainfall of 120 mm h 1 our study suggested that the emerging interdisciplinary field of hydropedology promotes synergistic integration of pedology e g watershed scale soil thickness investigation and soil profile description and hydrology e g rainfall simulation subsurface flow and deep percolation to enhance the holistic study of soil water interactions in the sloping lands with different soil thickness

characteristics of stone covers on the surface of basalt flows in arid northeast jordan variations in the stone covers on desert surfaces have implications for the operation of hydrological processes some recent attention has been given to the difficulties of identifying and quantifying relevant characteristics of stone covers investigation of how such characteristics vary in relation to geological and topographical controls are limited results are presented of a field study of the characteristics of stone covers on four lithologies in the late tertiary to quaternary basalt plateau of northeast jordan marked variations occur in clast dimensions and the characteristics of sorting between lithologies which are likely to affect hydrological response a more subtle control relating to slope conditions is superimposed on the lithological differences r and q mode factor analysis identifies groupings within the data which demonstrate the distinctiveness of different lithologies characteristics of the stone covers on sites affected by human occupation are markedly different from undisturbed sites on the same lithology

observations and conceptual modelling of morphological coupling in a double sandbar system nearshore sandbars located in 10 m water depth can contain remarkably periodic alongshore undulations in both cross shore position and depth in a double sandbar system the alongshore spacing of these morphological patterns in the inner sandbar may be identical to those in the outer sandbar although this morphological coupling has been observed previously its frequency and predominance remain unclear in this paper we use a 9 3 year dataset of daily low tide time exposure images from the double barred beach at surfers paradise gold coast australia to analyse the temporal and spatial characteristics of morphological coupling within a double sandbar system we distinguish five types of morphological coupling between the inner and outer sandbars of which four coincide with a downstate progression of the outer bar coupling is either in phase with a landward perturbation of the inner bar facing an outer bar horn or out of phase with a seaward perturbation of the inner bar facing an outer bar horn where the coupled inner bar features either consist of rip channels or predominantly perturbations of the low tide terrace cross correlation of the image derived inner and outer bar patterns shows coupling to be a common phenomenon in the double sandbar system studied here with coupling in 40 of the observations in contrast to previous observations of sandbar shoreline coupling at single barred beaches in phase coupling 85 of all coupled bar patterns predominates over out of phase coupling 15 based on our observations and bathymetries assimilated from the images for a restricted set of coupling events we hypothesize that the angle of offshore wave incidence wave height and depth variations along the outer sandbar determine the type of flow pattern cell circulations versus meandering currents above the inner bar and hence steer the type of coupling copyright 2012 john wiley sons ltd

shear wave reflection seismics as a valuable tool for near surface urban applications subsurface investigations in urban areas have to take sealed surfaces and densely built and populated areas into account the shear wave reflection seismic system developed at the leibniz institute for applied geophysics liag provides a solution for this acquisition technology problem using horizontally polarized shear waves sh waves and noninvasive source and receiver designs

surface sealing as influenced by slope angle and position of simulated stones in the top layer of loose sediments the influence of five different slope angles and two different positions of simulated stones in the top layer of a sandy and a silty sediment on surface sealing intensity is examined in the laboratory sealing intensity is assessed by studying changes of percolation rate through a sediment layer with simulated rainfall duration and by measuring cohesion of the 5 mm thick upper sediment layer a measure of seal strength by means of a torvane slope has a negative influence on sealing intensity for a constant per cent of simulated stone cover sealing intensity is lowest in the case of stones placed on the sediment surface compared to the case of stones pushed into the surface layer explanations for these findings are given and some implications are further discussed

the statistics and kinematics of transverse sand bars on an open coast abstract ten years 1987 1996 of time exposure video images of the nearshore region at duck nc were used to study transverse sand bars bathymetric features of intermediate length scales 10 200 m oriented oblique or perpendicular to the shoreline these transverse sand bars extend seaward from both the shoreline trough transverse bars and the shore parallel sand bar offshore transverse bars transverse bars had not previously been observed in an energetic coastal environment such as that at duck and their dynamics and role in nearshore processes is unknown frequency of occurrence statistics and length scales of the transverse bars were calculated using the video images trough and offshore transverse bars appeared a mean of 39 and 73 days per year respectively the offshore bars were found to be much larger features than the trough bars with mean wavelengths alongshore spacing between consecutive crests of 79 and 172 m for trough and offshore bars respectively both the trough and offshore bars were found to persist for periods of days to months the alongshore movement of the bars was measured and compared to estimates of surf zone longshore currents which were calculated from wave height and wave angle data both sets of bars were observed to move at rates up to 40 m day at times both trough and offshore bars were observed shifting in the same direction as the current was flowing and at other times both sets of bars remained stationary even under relatively strong longshore currents trough bars were also observed moving against the current an hypothesis proposed by barcilon and lau 1973 j geophys res 78 15 2656 2664 that the transverse bars were created as a sea bed instability under longshore currents was tested by comparing the magnitude of estimated surf zone longshore currents with times of formation or presence of transverse bars there was no evidence to suggest that the bars were formed by this simple longshore current instability mechanism instead it is plausible that the combined effects of waves and currents may drive the formation of these features

self organization mechanisms for the formation of nearshore crescentic and transverse sand bars the formation and development of transverse and crescentic sand bars in the coastal marine environment has been investigated by means of a nonlinear numerical model based on the shallow water equations and on a simplified sediment transport parameterization by assuming normally approaching waves and a saturated surf zone rhythmic patterns develop from a planar slope where random perturbations of small amplitude have been superimposed two types of bedforms appear one is a crescentic bar pattern centred around the breakpoint and the other herein modelled for the first time is a transverse bar pattern the feedback mechanism related to the formation and development of the patterns can be explained by coupling the water and sediment conservation equations basically the waves stir up the sediment and keep it in suspension with a certain cross shore distribution of depth averaged concentration then a current flowing with against the gradient of sediment concentration produces erosion deposition it is shown that inside the surf zone these currents may occur due to the wave refraction and to the redistribution of wave breaking produced by the growing bedforms numerical simulations have been performed in order to understand the sensitivity of the pattern formation to the parameterization and to relate the hydro morphodynamic input conditions to which of the patterns develops it is suggested that crescentic bar growth would be favoured by high energy conditions and fine sediment while transverse bars would grow for milder waves and coarser sediment in intermediate conditions mixed patterns may occur

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

spatial patterns of soil water balance on intensively cultivated hillslopes in a semi arid environment the impact of rock fragments and soil thickness during past decades a diverse system of subsistence agriculture in south east spain annual rainfall of less than 300 mm has been overturned in favour of large scale plantations of almond trees without consideration for topography and related spatial patterns in soil hydrological properties the objective of this paper is to investigate the spatial pattern in soil physical properties induced by this cultivation system and to highlight its impacts on the water balance soil properties were recorded along hillslopes with shallow soils developed on slates and greywackes in the upper part of the guadalentin drainage basin murcia region frequent tillage of these almond plantations covering entire hillslopes has resulted in denudation by tillage erosion on the topographic convexities as well as transport of rock fragments and fine earth along the slopes these processes have created a systematic spatial pattern of soil thickness and rock fragment content shallow and stony soils on the topographic convexities and deep soils with a rock fragment mulch in the concavities at the foot of the slopes at the same time a negative relationship between rock fragment content and fine earth bulk density was observed the impact of this spatial pattern in soil properties on the water balance was evaluated using the pattern one dimensional hydrological and plant growth model the model simulates the water balance of soil profiles covering the observed variation in soil thickness stoniness and bulk density the model results indicate that the highest rates of infiltration evaporation and drainage as well as the lowest rates of overland flow are restricted to shallow soils on the hilltops in contrast the deeper soils in the valley bottoms produce a more stable moisture regime than shallower soils which tend to saturate and dry out quickly these model results are in agreement with the spatial patterns of almond productivity an asymptotic increase with soil thickness copyright c 2000 john wiley sons ltd

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

the spatial and temporal variability of sand bar morphology the spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years the data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology lippmann and holman 1989 the morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria the most frequently observed morphologies are the longshore periodic rhythmic bars observed in 68 of the data linear bars occur under highest wave conditions h s 1 78 m and are unstable mean residence time 2 days shore attached rhythmic bars are the most stable mean residence time 11 days and generally form 5 16 days following peak wave events non rhythmic three dimensional bars are very transient mean residence time 3 days eighty seven percent of transitions to lower bar types defined in text occurred one state at a time supporting our selection of the ordering of states and suggesting the suitability of a sequential morphology model transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states with more substantial changes in morphology resulting from larger wave increases this suggests that up state erosional transitions based on offshore bar migration are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance principal component analysis was used to decompose bar position into two dimensional linear and three dimensional longshore variable components cross shore linear bar position ranges 50 m about the 2 year mean 27 m standard deviation and dominates bar variability 74 6 three dimensional bar structure accounts for 14 of the variance 12 m standard deviation changes in incident wave height precede cross shore bar migration by less than 1 day changes in longshore variability are inversely correlated to changing wave conditions with bar morphology becoming linear rapidly during storms on time scales of less than 1 day evolution to significantly three dimensional structure typically occurs over 5 7 days following peak wave events

resistance to overland flow on desert hillslopes abstract this study examines the relation between the darcy weisbach friction factor f and the reynolds number re for overland flow on six runoff plots in semiarid southern arizona the surfaces of these plots are irregular and covered with stones as overland flow increases the stones and microtopographic protuberances which constitute the major roughness elements are progressively inundated thereby altering the flow resistance analyses of 14 cross sections reveal that the resulting f re relations have two basic shapes convex upward and negatively sloping these shapes bear little resemblance to the conventional f re relation for shallow flow over a plane bed whose shape is a function of the state of flow rather they are explained in terms of the simultaneous operation of two processes the first is the progressive inundation of roughness elements and increase in their wetted upstream projected area as discharge increases this process causes f to increase the second is the progressive increase in the depth of flow over already inundated parts of the bed as discharge increases this process causes f to decline whether the f re relation has a positive or a negative slope depends on whether the first or second process dominates and this depends on the configuration of the bed and level of discharge these findings have profound implications for the mathematical modeling of overland flow on desert hillslopes whether a model is based on the saint venant equations or makes use of the kinematic wave approximation it requires the specification of a relation between f and re or surrogates thereof and the computed hydrograph is very sensitive to the form of this relation hitherto the most widely used relation has been the conventional one for shallow flow over a plane bed however the present study suggests that this relation does not apply to desert hillslopes additional field and laboratory studies are needed to learn more of the behavior and controls of f re relations on such hillslopes so that models of overland flow can employ more realistic relations and better simulate runoff hydrographs

on the accuracy of the ground force estimated in vibroseis acquisition for a linear elastic earth the time derivative of the ground force is considered proportional to the far field wavelet under the assumption that the baseplate is stiff and the bending forces of the baseplate are negligible the ground force is also approximated by the sum of the accelerations of the baseplate and the reaction mass weighted by the respective masses combining these two assumptions the time derivative of the weighted sum is considered proportional to the far field wavelet this result often referred to as the far field wavelet assumption although convenient and most often employed is not always valid we explore its validity using the spectral harmonic ratios of recorded data which are used extensively in data filtering and analysis of vibratory data we show that the far field wavelet assumption fails particularly for harmonic components of even order more compact soil after repeated shots further invalidates this assumption non linear modelling of the ground under the vibrator point may provide a direction towards solving this discrepancy finally we describe a method for the estimation of the harmonic spectral ratios

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 potential use of digital image processing in geomorphology erosion of stony soils a case study summary techniques of digital image processing are now common place in remote sensing research this paper considers the potential use of some of these procedures on frame grabbed video images the example taken is that of the evolution of stone pavements and their implication for interrill erosion processes the results indicate a relationship between the total erosion loss and the rate of stone pavement areal cover in addition the paper shows how the technique could be of great assistance in the monitoring of many different types of environmental processes

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

hydric properties of some spanish soils in relation to their rock fragment content implications for runoff and vegetation abstract physical and hydric characteristics of the upper three horizons average depth of sampling 0 0 25 0 25 0 60 and 0 60 1 20 m of 92 soil profiles of spain grouped according to the geological nature of the rock fragments on the soil surface or in the soil profile were studied mathematical relations were developed to separate the contributions of the fine earth fraction and of the fraction above 2 mm indexes were obtained that relate gravitational water and available water in the fine earth fraction with the values from total soil a multiple comparison statistical study was performed for the mean values of 1 rock fragment content 2 organic matter content 3 silt plus clay content 4 gravimetric water content at different suction values the linear correlations of the gravitational and available water indexes with the rock fragment content by volume as independent variable were studied they showed positive or negative effects of the increase of rock fragment content on both indexes depending on their petrographical composition finally conclusions related tothe development of vegetation and to the production of runoff have been drawn when rock fragment content increases the results show positive effects for the development of vegetation and for the production of saturation overland flow

flow resistance in concentrated overland flow on rough slope surfaces field experiments have been done on simulated flows over different rough pre rill and rill bed surfaces the purpose of the experiments was to evaluate the hydraulic roughness properties of these bed surfaces conventional equations describing the relation of the resistance coefficient to the reynolds number for flow in closed conduits or open channels can also be applied to shallow flows provided the boundary values of the reynolds number which discriminate between the various flow regimes are adapted when the reynolds number is less than 100 the flow regime is laminar above this figure the flow is either transitional or turbulent depending on the roughness of the bed surface the degree of turbulence can be deduced from a morphological description of the pre rill and rill bed surface roughness

a mechanism for sandbar straightening by oblique wave incidence 1 breaker bars in the surf zone of sandy beaches generally evolve between straight bars parallel to the shore and meandering crescentic bars associated with intense dangerous currents flowing seaward through rip channels understanding the behavior of such systems is fundamental as they control the entire surf zone dynamics the shape of the coastline and the exchange of floating material with the shoreface although the mechanisms behind the meandering of an originally straight bar have been studied extensively a clear physical explanation on the crescentic bar straightening was missing recent field observations have highlighted that this morphological reset can be due to wave obliquity by using a two dimensional horizontal morphological model we show that the bar straightening by oblique waves occurs because the rip current is both weakened in intensity and shifted downdrift from the channel deepest section the technique employed is useful for the study of other types of bed forms

effects of redistribution processes on rock fragment variability within a vineyard topsoil in mediterranean france in mediterranean vineyard landscapes to understand soil cover evolution at the landscape scale via soil redistribution one must take into account soil and land use specificities soils are characterised by large quantities of rock fragments and affect hydrological and erosion processes that have widely been published in the literature vineyards require a persistent cultivation pattern and soil tillage operations can often affect vertical and lateral rock fragment distribution the aim of this study is to analyse rock fragment content and variability in the topsoil 0 15 cm of a mediterranean vineyard to determine whether rock fragment distribution 2 64 mm at a farm plot is influenced by soil type and or linked to environmental parameters furthermore relationships between observed rock fragment distribution tillage and water erosion processes are discussed the field survey was based on a stratified sampling strategy taking into account soil type cultivation patterns and farm plot topography the results suggest that the effect of cultivation in the row inter row system is more pronounced than the previously inferred topographic effect the long term vineyard cultivation pattern induces spatial segregation of redistribution processes with cumulative effects over several years that are responsible for rock fragment spatial variability in topsoil

soil erosion and hydrology of the western mediterranean badlands throughout rainfall simulation experiments a review abstract rainfall simulation experiments are widely used in geomorphological research in badland areas this technique contributed significantly to our understanding of badland geomorphology in the mediterranean belt due to the different types of simulated rainfall applied and the variable size of the plots a review of the state of the art is necessary this study confirmed that rainfall simulations are well suited to i analyse runoff infiltration processes and sediment detachment within badlands and ii to establish the factors determining the hydrological and erosion response at interrill scale in badland areas the hydrological response of badlands is characterized by rapid responses low to moderate infiltration rates ranging from close to 0 to 55 mm h 1 and high runoff coefficients i e 60 positive relationships are observed between antecedent soil moisture content and rainfall intensity on the one hand and runoff coefficients on the other sediment concentration and soil detachment rates are among the highest measured on the mediterranean region i e up to 84 8 g l 1 and 4722 4 g m 2 h 1 results show that rainfall intensity runoff coefficient and slope angle have a positive influence on sediment concentration and sediment detachment in the case of rock fragment cover its influence is variable according to the soil cover percentage rainfall simulations increase our understanding of the temporal and spatial variability of the soil erosion processes however rainfall simulation provides mostly qualitative rather than quantitative information because of the small plot size and the simulated rainfall characteristics due to facility for repeating experiments and recording a high quantity of data in short time however this method allows the comparison amongst different environments and soil conditions as the rainfall properties can be reproduced

can ash control infiltration rate after burning an example in burned calcareous and gypseous soils in the ebro basin ne spain abstract fire is a long established ecological factor that has shaped the life history hydrogeomorphological processes soil formation and landforms of mediterranean environments soil infiltration is one of the properties affected by fire as a consequence of litter and vegetation removal and heating of and changes to the biological chemical and physical soil properties in this context ash can play an important role in soil infiltration behavior and therefore affect sediment and runoff yield the aim of this work is to determine the effect of ash cover on infiltration rates a single ring infiltrometer was used immediately after a wildfire and before the first storm events to determine the soil infiltration rate a total of 24 infiltrations were made 2 soil types 2 treatments 6 replicates in each infiltration experiment the soil wetting front the bulk density and stoniness were also measured the results show that the final infiltration rate fc values are higher in calcareous soils than in gypseous soils the ash cover in calcareous burned soils only temporarily decreases the bulk density of topsoil and enhances infiltration

patterns of rock fragment cover generated by tillage erosion abstract intensively cultivated areas in the upper part of the guadalentin catchment southeast spain show a systematic spatial pattern of surface rock fragment cover rc the objective of this paper is to quantify and to explain this spatial rock fragment cover pattern therefore a map of an intensively cultivated area of 5 km2 was digitised and for each pixel total topographic curvature was calculated next rock fragment cover was determined photographically at 35 sites with a range of total slope curvatures a linear relation between total curvature and rock fragment cover was found except for narrow concavities it was hypothesised that this pattern can be explained by a significant net downslope movement of rock fragments and fine earth by tillage the displacement distances of rock fragments by tillage with a duckfoot chisel were measured by monitoring the displacement of tracers painted rock fragments and aluminium cubes on 5 sites having different slopes the rare of tillage erosion for one tillage pass with a duckfoot chisel expressed by the diffusion constant k equals 282 kg m for up and downslope tillage and only 139 kg m for contour tillage nomograms indicate that mean denudation rates in almond groves due to tillage erosion 3 to 5 tillage passes per year can easily amount to 1 5 2 6 mm year for contour tillage and up to 3 6 5 9 mm year for up and downslope tillage for a field 50 m long and having a slope of 20 these figures are at least one order of magnitude larger than reported denudation rates caused by water erosion in similar environments hence tillage erosion contributes significantly to land degradation the downslope soil flux induced by tillage not only causes considerable denudation on topographic convexities hill tops and spurs and upper field boundaries but also an important sediment accumulation in topographic concavities hollows and valley bottoms and at lower field boundaries kinetic sieving i e the upward migration of rock fragments by the tines of the duckfoot chisel also concentrates the largest rock fragments in the topsoil in such a way that a rock fragment mulch develops in narrow valleys and at the foot of the slopes these results clearly indicate that tillage erosion is the main process responsible for the observed rock fragment cover pattern in the study area since the study area is representative for many parts of southern spain where almond groves have expanded since 1970 the results have a wider application they show to what extent intensive tillage of steep slopes has contributed to the increase in soil degradation to changes in hillslope morphology i e strong denudation of convexities development of lynchets and rapid infilling of narrow valley bottoms and to the development of rock fragment cover patterns which control the spatial variability of the hydrological and water erosion response within such landscapes

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

effects of agricultural practices on the hydrodynamics of a deep tilled hardened volcanic ash soil cangahua in ecuador abstract the rehabilitation of indurate pyroclastic formations of the ecuadorian sierra cangahua paves the way for the development of new agricultural areas the material derived from the fragmentation of the hardened volcanic ashes is strongly prone to pluvial erosion essentially because it has a fine silty sandy texture and because contains no organic matter and no clay minerals rainfall simulation was implemented before and after three cycles of cultivation to asses the evolution of soil structure and its susceptibility to erosion the cultivated plots were surface soil crusting occurred rapidly within the cultivated plots when compared to the recent tilled cangahua runoff and soil loss were generally higher on plots with lower structural stability and generally exhibited higher clay content in agreement with the structural stability measured in a laboratory organic matter inputs increase the soil porosity this condition had no effect on the structural stability of the soil resistance to crusting and therefore little impact on surface runoff and erosion the preferred option for land with these soils would be no tillage and a permanent soil cover pasture if they were to be utilised for agriculture

the hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface for a given cover level rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface for the same cover level rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer the effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by poesen 1986 i e runoff generated as rock flow or as horton overland flow can partly infiltrate into the unsealed soil surface under the rock fragments provided that they are not completely embedded in the top layer hence rock fragment position beside other rock fragment properties should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers a simple model based on the proportions of bare soil surface soil surface occupied by embedded rock fragments and soil surface covered with rock fragments resting on the soil surface describes the runoff coefficient data relatively well

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

conservation of soil moisture by different stone covers on alpine talus slopes lassen california abstract this study reports on the influence of stone covers with different clast sizes on the soil moisture of alpine talus slopes in lassen california fifteen four plot sets were sampled in the dry season july 1990 in sandy areas and in talus covered with pebbles cobbles or blocks between 2740 and 2775 m three depths 0 5 5 10 10 15 cm were sampled field moisture content increased gradually with depth in all soil profiles and also in plots covered by increasingly larger rocks surface soils in sand areas were very dry but under rocks had water contents 6 to 14 times greater differences among plots decreased with depth but subsoil samples in sand were still drier than those beneath any stone cover at similar depths blocks were most effective in conserving moisture water content below them was higher than even in deep 10 15 cm sand soils soil temperatures were recorded in sand and under blocks for an 11 day period minima were not significantly different but average maxima were 5 6 c lower under blocks than in sand which reached highs 4 4 c lower than the air differences in soil moisture among talus types are ascribed to lower evaporation losses under stones due to both disruption of capillarity by the coarse particles which prevented water flow to the talus surface and to their efficient reduction of maximum temperatures an irrigation experiment was conducted at 2110 m on a steep talus on the chaos crags from july 18 to aug 2 1993 four 100 75 cm plots with the same surface types than at lassen received 22 5 mm water moisture content was then periodically sampled watering produced similar water distributions among soil depths and talus types to those in lassen evaporation occurred quickly in bare soils due to high air and soil temperatures the sand surface was already dry 2 days after watering but stone covered plots remained moist until day 15 when soils under blocks still retained 77 97 of the water content percent by weight at the start of the test

un predictability in rip channel systems 1 predicting the development of rip channel systems on beaches is relevant for beach safety nearshore mixing and dispersion and has been puzzling researchers for decades field observations and computer simulations have focused on predicting the spacing and growth time of rip channels as a function of wave characteristics a satisfactory predictor of rip channel spacing and growth time has not yet been proposed here we show that the lack of predictability of rip channels is an inherent property of the system related to the high sensitivity to the bathymetry prior to pattern development sensitivity to the initial cross shore profile appears to be as important as sensitivity to wave height although we might be able to predict rip channel characteristics the information required by such predictors will need to account for the underlying bathymetry implications arising from this study are that other geomorphic patterns could display similar sensitivity

controls of infiltration runoff processes in mediterranean karst rangelands in se spain semiarid karst landscapes represent an important ecosystem surrounding the mediterranean basin for which little is known on runoff generation knowledge of the sources and patterns of variation in infiltration runoff processes and their controls is important for understanding and modelling the hydrological functions of such ecosystems the objectives of this paper are to determine the infiltration rates and their controls in a representative mountain karst area sierra de gador se spain at micro plots and to investigate the integrated response of rainfall on a typical hillslope rainfall simulations in micro plots and natural rainfall runoff monitoring on a hillslope were carried out complementarily we investigated the role of soil surface components vegetation rock outcrop fracture and soil crust topographic position antecedent soil moisture and rainfall characteristics in regulating infiltration runoff processes results of rainfall simulation revealed the importance of vegetation cover and the presence of rock fractures in promoting the infiltration in the limestone karst landscape while bare patches and rock outcrops acted as sources for runoff all plots with 50 vegetation cover had no runoff with up to 55mmh 1 of simulated rain in contrast nearly all bare plots had runoff under the same simulated rain with runoff coefficients ranging from 3 1 to 20 6 on dry soil surface conditions and from 2 0 to 65 4 on wet soil surfaces runoff coefficients amounted to 59 0 79 5 for rock outcrops without cracks but were drastically reduced by the presence of cracks the surfaces with rock fragments resting on the soil generally located in the middle of the slopes prevented more effectively the runoff generation than those surfaces where rock fragments were embedded in the top soil antecedent soil moisture had significant impact on runoff generation with wet soil having doubled runoff coefficient shortened time to runoff and increased runoff rate compared to the same but dry soil linear regressions indicated that the main controls for constant infiltration rate were the cover percentages of vegetation and litter plus rainfall intensity while the major controls for runoff coefficient were the bare soil and vegetation coverage plus rainfall intensity high infiltration rates measured at the micro plots agreed with low intra event runoff coefficients mostly below 1 observed under natural rainfalls at the hillslope runoff depth and coefficient at the hillslope was significantly correlated with rainfall depth maximum hourly rainfall intensity and antecedent precipitation over 20days ap20 during the 1 5 year monitoring period from sep 2003 to mar 2005 the overall infiltration was 41 of the total rainfall amount and the maximum infiltration rate was almost 94 of the largest single rainfall event the results from this study contribute to improved understanding of the magnitude and controls of the surface runoff in semiarid karst mountain areas 2011 elsevier b v