on the connected porosity of mineral aggregates in crystalline rocks the 14 c pmma impregnation of rock samples and mineral staining methods provide the connected porosity map and the spatial distribution of mineral aggregates respectively combined image analysis of mineral and porosity maps allows quantification of the connected porosity distribution in rock forming mineral aggregates after the two maps have been superimposed numerically the 14 c pmma method provides an indication of the extent of pore connectivity for each pixel in the analyzed area which can be used to obtain the porosity distribution as a function of modal mineralogy when applied to undeformed and deformed kivetty granodiorite samples from finland the method allows for a detailed analysis of the rock porosity porosity distributions related to the undeformed rock are unimodal and approximately identical to each other on the other hand porosity distributions of the deformed granodiorite are multimodal and vary significantly constituent porosity sets of the deformed samples were albite crystals free of alkali feldspar patches and alkali feldspar phenocrysts average porosity 0 21 albite containing alkali feldspar patches 0 59 rapakivi albitic mantles 1 15 quartz 0 39 and mafic minerals 5 8 moreover the analysis indicates that the numerous micropores observed under sem within alkali feldspar phenocrysts and albite crystals free of alkali feldspar patches are unconnected in 3d

implications of bank failures and fluvial erosion for gully development field observations and modeling 1 gully erosion is most commonly triggered by fluvial erosion following natural and anthropogenic disturbances or as a response to changes in climate and tectonic forcing and base level drop field observations attribute the headward growth and widening of many gully systems to gravitational mass wasting processes of oversteepened sidewalls soil saturation groundwater sapping and tension crack development contribute to the instability recent landscape evolution models treat such mass failures as slope dependent continuous sediment transport processes sometimes conditioned on a slope threshold or with nonlinear dependence on slope gradient in this study we first present an explicit physically based theory for the stability analysis of gully heads and walls the theory is based on the force balance equation of an assumed planar failure geometry of a steep gully wall with a potential failure plane dipping into the incised gully bed and tension cracks developing behind the scarp face then we test the theory against field data collected in our field site in colorado and against other published data second the theory is implemented in a one dimensional hillslope profile development model and the three dimensional channel hillslope integrated landscape development child to study the effects of soil cohesion erosion thresholds and stochastic climate on the tempo of gully development and morphology preliminary results indicate that wider and shallower gullies develop and integrate forming wide valleys when soil cohesion is small as soil cohesion increases erosion slows down gullies become deeper with vertical walls and episodic mass failures occur differences in storm intensity duration characteristics and erosion thresholds are predicted to have a significant impact on gully development vertical gully walls develop rapidly and gullies enlarge by slab failures in a climate characterized by high intensity short duration storm pulses however under low intensity long duration storms gullies quickly stabilize and vertical walls are eliminated and rounded forming diffusion dominated hilltops erosion thresholds have a similar impact on the tempo of gully erosion but in the opposite direction lowering the erosion threshold enhances gully widening by slab failures gully walls stabilize when the erosion threshold is high due to a reduction in the erosion of the failure material on the toe of gully walls

threshold conditions for initiation of valley side gullies in the middle veld of swaziland abstract gullied and ungullied catchments in four areas of deeply weathered saprolite in the middle veld of swaziland can be successfully separated p

episodic late quaternary palaeogully erosion in northern kwazulu natal south africa abstract hillslope deposits in northern kwazulu natal south africa are incised by gullies dongas which expose sequences of buried palaeosols developed within a succession of discontinuity bounded colluvial sedimentary units infilled and buried palaeogully topography attests to at least four geomorphic cycles comprising gully cut and fill and palaeosol formation on hillslopes in the region during the past 135 ka past attempts at dating colluvial stratigraphic units were limited to radiocarbon dating of associated palaeosol organic matter and authigenic soil carbonates this study presents a preliminary set of infra red stimulated luminescence irsl age determinations pertaining to deposition of the succession of colluvial units infilling and burying palaeogullies at several sites of stratigraphic geochronological and palaeoenvironmental importance in the region interpretation of the irsl and 14 c dates in the context of cyclical hillslope processes suggests that past episodes of palaeogully erosion and infill were not synchronous and individual palaeosol landsurfaces were diachronous during the late pleistocene

impact of terrain attributes parent material and soil types on gully erosion abstract gully erosion is a worldwide matter of concern because of the irreversible losses of fertile land which often have severe environmental economic and social consequences while most of the studies on the gullying process have investigated the involved mechanisms either overland flow incision seepage or piping erosion only few have been conducted on the controlling factors of gully wall retreat an important if not the dominant land degradation process and sediment source in river systems in a representative 4 4 km 2 degraded area of the drakensberg foothills south africa the main objective of this study was to evaluate the relationship between the rate of gully bank retreat gbr and parent material soil types and selected terrain attributes elevation specific drainage area mean slope gradient slope length factor stream power index compound topographic index and slope curvatures the survey of gully bank retreat was performed during an entire hydrological year from september 2007 to september 2008 using a network of pins n 440 from 110 pits both the gully contours and pin coordinates were determined using a gps with a 0 5 m horizontal accuracy n 20 120 the information on the parent material and the soil types was obtained from field observations complemented by laboratory analysis while terrain attributes were extracted from a 20 m dem generated from 5 m interval contour lines the average gbr value for the 6512 m of gully banks found in the area was 0 049 0 0013 m y 1 which considering bank height and soil bulk density corresponded to an erosion rate of 2 30 ton ha 1 y 1 there was no significant difference in gbr between sandstone and dolerite and between acrisols and luvisols despite a weak one to one correlation with the selected terrain attributes r gbr was the highest at hillslope inflexion points profile and plan slope curvatures close to zero in the vicinity of the head cuts and for drainage areas up to 500 m 2 as both situations experience a high removal rate of the soil material produced from the gully bank collapse and protecting gullies from laterally retreating these results could be used to digitally map the more active gully banks for the improved implementation of preventive measures of gully growth if high resolution dems are available there remained however a certain amount of unexplained variability in the data that further research studies on the mechanisms and associated factors of control of gbr could help to address

the use of slingram em38 data for topsoil and subsoil geoelectrical characterization with a bayesian inversion we use the bayesian method to invert a simple two layer pedological horizon 1 d with a topsoil and a subsoil of a surveyed site to be assessed we show how the bayesian method is well suited to the determination of topsoil subsoil features and can be used in particular as a tool for the analysis of parameters to be retrieved in terms of information content our approach is devoted mainly to the assessment of topsoil thickness and of topsoil and subsoil conductivities which are provided in terms of probability density functions we first summarize the methodology implemented with the geonics em38 mk2 conductivity meter and discuss the adaptation of field procedures and post processing methods to mitigate the effects of drift and bias we briefly review some non bayesian approaches and then develop the bayesian approach for the context of our geophysical survey highlighting its merits positivity constraints on thickness and conductivity are included in the form of log parameters a priori knowledge based on an objective choice made by the geophysicist is naturally included in the bayesian scheme we discuss the equivalence problem associated with the application of the slingram method to soil structure analysis the survey of a luvisol at the kwazulu natal south africa site of potshini is used to illustrate an ecological application of the slingram and bayesian methods used to define the geo electrical structure of the near surface soil these algorithms have demonstrated their usefulness in mapping the clay content of the bt horizon associated with the control of encroaching trees c 2013 elsevier b v all rights reserved

elastic wave velocities and permeability of cracked rocks abstract cracks play a major role in most rocks submitted to crustal conditions mechanically cracks make the rock much more compliant they also make it much easier for fluid to flow through any rock body relying on fracture mechanics and statistical physics we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks the main different schemes which can be used to derive the elastic effective moduli of a rock are presented it is shown from experimental results that an excellent approximation is the so called non interactive scheme the main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow at a larger scale macroscopic fluid flow takes place through the crack network above the percolation threshold two macroscopic fluid flow regimes can be distinguished the percolative regime close to the percolation threshold and the connected regime well above it experimental data on very different rock types show both of these behaviors

gully processes and gully dynamics this synthetic review of gully morphology and genesis focuses on incised semi permanent gully systems rather than on shallow ephemeral gullies it examines the conditions for gully formation a sharp step to initiate a headcut a sufficiently low effective bedload fraction to evacuate eroded material and the potential to maintain steep sidewalls usually dominated by mass movement processes gully formation is also favoured by an indurated surface layer which maintains steep sideslopes often with armouring material from the capping layer and a sharp headcut which does not diffuse away two different approaches towards the areal modelling of gully system development agree in treating the ratio of advective channel to diffusive sideslope processes as a key determinant of the morphology of a gully system as it evolves implications for gully prevention and remediation are briefly discussed copyright 2009 john wiley sons ltd

short term bank gully retreat rates in mediterranean environments abstract in this study short term headcut retreat was monitored from 46 active bank gullies selected in the guadalentin and the guadix basin in southeast spain the measurements were carried out manually using an orthogonal reference system fixed by erosion pins around the gully heads between april 1997 and april 1999 with a 1 year interval the average volumetric retreat rate for all gullies was 4 0 m 3 year 1 corresponding with an average linear retreat rate of 0 1 m year 1 but more erosion took place during the first monitored year 1997 1998 compared to the second 1998 1999 an interplay of spatial variations in rainfall distribution and tension crack activity is assumed to be responsible for the important difference in annual headcut retreat compared to the small difference in annual rainfall amounts statistical analysis showed that the present drainage basin area a p was the most important topographical factor explaining average gully headcut retreat rate both in terms of annual eroded volume v e and annual linear retreat r l and expressed by the power relationships v e 0 04 a p 0 38 r 2 0 39 and r l 0 01 a p 0 23 r 2 0 39 the v e a p relationship was compared with the relationship between original drainage basin area a o and total eroded bank gully volume vol i e vol 1 71 a o 0 60 r 2 0 65 the importance of runoff generation from a drainage basin is shown by the positive correlation of linear headcut retreat and the runoff curve number cn representative for the conditions in the drainage basin high cn values tend to coincide with higher annual eroded volumes in the relationship between present drainage basin area a p and annual eroded volume v e but this effect was not observed in the relationship between original drainage basin area a o and total eroded bank gully volume vol stepwise multiple regression selected the relevant environmental parameters explaining annual eroded volume and linear retreat in both equations the present drainage basin area explained the largest part of the variation the cn was selected as another common parameter height of the headcut was the second most important variable explaining annual eroded volume indicating the role of energy transfers and undercutting at the headcut linear retreat was further explained by the average slope of the present drainage basin area representing the effect of decreasing transmission losses and increasing flow velocity with steeper catchment slopes and by the sand content decreasing the cohesion of the soil material promoting soil fall and headcut retreat spatial extrapolation of the measured volumetric retreat rate of 4 0 m 3 year 1 revealed that active bank gully heads contribute up to 6 of the sediment yearly filling up the puentes reservoir estimated gully ages i based on the ergodic principle and ii by linear extrapolation of actual gully retreat rates in the past range between 63 years and 1539 and between 64 and 1720 years respectively the high correlation between the gully ages estimated by the two methods is attributed to the fact that most gullies have not reached the evolutionary stage of significantly declining retreat rates since medium term gully retreat rates are more dependent on drainage basin area compared to the short term retreat rates obtained in this study the estimated gully ages represent maximum values assuming that present land use and climate conditions prevailed over the last two millennia

the role of sidewall processes in gully development some n s w examples little attention has been paid to the role of sidewall processes in gully development simple estimates of linear incision sidewall erosion ratios at two localities in new south wales australia suggest that sidewall erosion is responsible for more than half the gully volume studies at three localities where overland flow and throughflow are limited to only one sidewall indicate that these processes are responsible for 10 30 per cent of gully volume these observations have important implications for gully management

permeability of granular aggregate of soft gel application to the partially molten system abstract in the upper part of the earth there exists a region where the rock is partially molten the magmatic melt rises through the partially molten region as a form of permeable flow the timescale and efficiency of the melt migration are controlled by the permeability which is a function of the melt fraction and the distribution of the melt at the grain scale using gel as an analog of the solid phase of the partially molten system the permeability and the electrical conductivity were measured with deformation the gel deforms into a polyhedron due to its high deformability and the fluid phase exists at edge and corner regions the morphology of the mixture system is similar to that of the partially molten system controlled by the interfacial energy both of the permeability and the electrical conductivity obey power law functions of the liquid fraction the permeability is close to kozeny carman type permeability and the electrical conductivity obeys archie s law at higher liquid fraction about 10 to 30 they reduce drastically with reduction of the liquid fraction at lower liquid fraction about 2 to 10 these behaviors are considered to result from dispersion of pseudo dihedral angle the permeability in the upper mantle would behave like that of the gel fluid system because the dispersion of dihedral angle exists due to poly mineralic solid phase of the upper mantle and anisotropic interfacial energy also the permeability is found to be proportional to the square of the electrical conductivity this relation is useful to estimate the permeability at depth from the electrical conductivity measurement

influence of soil properties on the aggregation of some mediterranean soils and the use of aggregate size and stability as land degradation indicators abstract soil aggregation in relation to other soil properties was studied along a climatological transect in the southeast of spain three sites were selected along this transect ranging from semiarid to subhumid climatological conditions the aggregate size distribution the macro and microaggregate stability of the superficial soil horizon and their relations with other soil properties were analysed large aggregates 10 10 5 5 2 mm were present in highest proportions in the most arid of the studied areas these large aggregates were associated with high values of water stable microaggregates however they did not improve soil structure and are related to high bulk densities and low water retention aggregates 1 0 105 mm were positively correlated to medium fine very fine sand and silt fractions and to organic matter aggregates water stability of microaggregates showed a positive correlation with clay content while the stability of the macroaggregates depended on the organic matter content when the organic matter content was greater than 5 or 6 below that threshold the carbonate content was strongly correlated with aggregate stability a general conceptual scheme of associations between aggregate size distribution water stable microaggregation and textural characteristics for the area was developed the land use history affecting soil overlaps the pattern of climatological situations and has to be taken into account aggregate size distribution and stability can be used as indicator of soil degradation but not as a unique parameter

effects of land use changes in vegetation cover and sidewall erosion in a gully head of the penedes region northeast spain the present research addresses the effects of land use changes in the evolution of vegetation cover on gully erosion in the penedes region of northeast spain the contribution of vegetation cover to gully wall stabilization is also discussed the catchment area of the gully is 60 2 ha and is mainly composed of vineyards in this area large gullies have developed on tertiary marls and unconsolidated sandstones detailed aerial photographs 1 5000 and 1 7000 scale of three dates 1975 1995 and 2002 were ortho rectified to derive land use information in the catchment gully vegetation cover and height information to construct detailed digital elevation models land use and gully vegetation cover mapping of the most recent period was assisted by means of fieldwork and a photo interpretation key constructed to help map the older dates soil loss in the catchment was estimated for the 1975 and 2002 scenarios to determine the relations between land use changes to vegetation cover changes and gully sidewall erosion the revised universal soil loss equation was applied for that purpose sidewall mass movements were determined by subtraction of digital elevation models 1 m resolution of each period the results show important land use changes in the catchment due to field reorganization for the plantation of mechanized vineyards it increased soil loss from agricultural fields by 26 5 which influenced vegetation cover dynamics on gully walls with an important development of scrubland to forest and gully erosion with sidewall retreat at rates of 0 025 to 0 50 ha y 1 and mass movements at rates of 16 to 63 2 mg ha 1 y 1 these results indicate that vegetation cover on gully walls although suggesting an improvement with respect to wall protection against splash sheet and rill erosion did not affect sidewall retreat and mass movements copyright 2009 john wiley sons ltd

network modeling of the evolution of permeability and dilatancy in compact rock rock deformation and fluid transport are coupled together in many crustal settings nonhydrostatic stress can greatly affect pore structure and transport properties of a rock when a compact rock is stressed to failure dilatancy and permeability enhancement are generally observed whether the failure mode is brittle faulting or cataclastic flow laboratory data for the brittle faulting regime in westerly granite and for the cataclastic flow regime in carrara marble and synthetic halite are modeled dilatancy is simulated by incorporating an increasing number of stress induced microcracks with similar geometric attributes in a random network model thus enhancing permeability the microcracks are represented by sheet like conduits with crack length and aspect ratio distributions constrained by microstructural data before the onset of dilatancy a rock under overall compression has very low density of open cracks that occur in isolated clusters with relatively low connectivity nonhydrostatic loading induces damage in the form of extensile microcracks that gradually form a fully connected percolation network significant permeability increase of up to several orders of magnitude may occur in this percolative regime once the crack network is fully connected the accumulation of additional cracks is not as effective in enhancing permeability and our model predicts permeability and porosity changes to be linearly related in this fully connected regime after accounting for the existence of fine cracks that are below the microscope resolution our simulation results agree reasonably well with laboratory data

some physical and chemical properties of sediments exposed in a gully donga in northern kwazulu natal south africa and their relationship to the erodibility of the colluvial layers abstract gullies locally termed dongas are a characteristic feature of the landscape in central kwazulu natal and are highly associated with widespread stratified colluvial sediments and the buried palaeosols that have formed in this material research objectives were to find out which sediment property or properties contribute most to the vulnerability of the colluvium to gully erosion to study the erosion susceptibility of the sequence of buried stratigraphic layers and palaeosols and to improve understanding of the relationship between erosion susceptibility of the colluvial layers and palaeosols and their disposition in the landscape materials from several colluvial layers and palaeosols exposed in the donga sidewall of the dabekazi donga 13 km north of nqutu in central kwazulu natal were subjected to chemical and mineralogical analyses several dispersion and erodibility tests and were characterized physically exchangeable sodium percentages esp ranged from 0 to 23 and the dispersivity and erodibility tests revealed a range of dispersion potential and erodibility across the sequence of colluvial layers and palaeosols however a poor correlation was found between the results of different dispersion tests as well as between dispersion tests and dispersion related properties dispersion tests showed significant correlation with silt content an erodibility test using a flume showed very strong correlation with electrical conductivity ec and sodium adsorption ratio sar of the saturated paste extract and esp values the plasticity index ranged from 0 to 0 23 and estimated hydraulic conductivities ranged from 33 to 0 7 m day high correlation with esp and ec suggests that dispersion plays an important role in the erodibility of the materials under conditions of short duration turbulent water flow however colluvium in which deep gullying occurs is not necessarily strongly sodic also the degree of erodibility of the materials differs depending on the test used illustrating the complexity of the interactions that govern dispersion and erosion the erodibility of the colluvial layers and palaeosols from the dabekazi donga and properties with relevance to dispersion differ considerably down the profile indicating that geomorphic threshold conditions and position in the landscape with respect to surface runoff hydrology also codetermine donga erosion hydraulic conductivity estimates of the investigated materials are relatively high and do not differ sufficiently to enable lateral subsurface flow through and piping of these materials to be the main causes of donga formation

quality assessment of a satellite altimetry data product in the nordic barents and kara seas 1 satellite altimetry provides high quality sea surface height data that have been successfully used to study the variability of sea level and surface geostrophic circulation at different spatial and temporal scales however the high latitude regions have traditionally been avoided due to the persistent sea ice cover most of the validation studies have focused on the areas below the polar circles in this paper we examine the quality and performance of a gridded satellite altimetry product in the nordic barents and kara seas the altimetric sea level in coastal areas is validated using available tide gauge records we show that at most locations in the nordic seas the altimetry and tide gauge measurements are in a good agreement in terms of the root mean square differences and the amplitudes and phases of the seasonal cycle the agreement deteriorates in the shallow areas of the barents and kara seas subject to the seasonal presence of sea ice and where the altimetry data are contaminated by the residual aliasing of unresolved high frequency signals the comparison of linear trends at the locations of tide gauges reveals discrepancies that need to be taken into account when interpreting long term changes of sea level in the region away from the coast the altimetry data are compared to drifter trajectories corrected for ekman currents the drifter trajectories are found consistent with the mesoscale variability of the altimetric sea level this study provides the first comprehensive validation of a gridded satellite altimetry data product in the high latitude seas

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

development of badlands and gullies in the sneeuberg great karoo south africa abstract the study aims to examine the origin and development of land degradation with particular emphasis on badland and gully systems in the sneeuberg uplands of the great karoo this is an area of semiarid extensive stock farming where land degradation in the form of rill and gully erosion has accompanied the replacement of grassland by shrub vegetation species diversity has declined and ground cover has been reduced leading to a positive feedback loop which exacerbates the degradation many foot slopes developed in shales clays and colluvium have extensive incipient badland development with closely spaced gullying up to 1 5 m deep in valley bottom and valley side depression locations gullies up to 8 m deep have developed usually cut to bedrock through valley fills of mainly holocene colluvium both badlands and gullies appear to have developed since european settlement and to be part of the same hydrological system with extensive areas of bare ground badlands feeding water to incising gullies experiments using simulated rainfall throw some light on current processes badland areas are active under high frequency low magnitude rainfall events major gullies are likely to be the result of occasional high magnitude events but these have not been observed overgrazing in the past is the most likely cause of the degradation

stochastic components in the gully erosion modelling abstract the great complexity of the geo mechanical structural and electro chemical forces in soil as well as of initial and boundary conditions in the equations of hydrodynamics leads to a necessity of spatial temporal averaging of deterministic equations related to soil behaviour the stochastic terms which appear in the equations after averaging procedures must be incorporated into the modelling of erosion features in this study a new method of estimating detachment rate was used in stochastic gully erosion modelling it is based on estimation of the probability of excess of driving forces above resistance forces in the interaction of water flow and structured soil knowledge of the probability density functions for the flow and soil main characteristics as flow velocity soil cohesion aggregate size and others makes it possible to calculate theoretically the rate of cohesive soil erosion for any combination of these stochastic variables the proposed theory allows explicit explanation of relationships between detachment rate and flow soil characteristics detachment rate increases with flow velocity more rapidly for soil with higher cohesion and larger aggregates this theory also shows great difference in type of soil erosion for relatively high and relatively low flow velocities and explains rather high errors in calculating of soil erosion rate even with detailed models