ion microprobe analysis of oxygen isotopes in garnets of complex chemistry abstract accurate ion microprobe analysis of oxygen isotope ratios in garnet is possible if appropriate standards are employed to correct for instrumental bias a component of which depends on the cation chemistry of the analyzed mineral in this study 26 garnet standards including 14 new standards that span the compositional range of pyrope almandine grossular spessartine and andradite were analyzed repeatedly by ion microprobe to develop a new method of correcting for instrumental bias in garnets all analyses were normalized to a single master garnet standard uwg 2 before bias from cation composition was considered bias due to cation composition in garnet was found to correlate with grossular content in pyralspite garnets and with andradite in ugrandite garnets bias is correlated with molar volume in garnets of all compositions in this study although this correlation is suitable as a correction scheme for bias a more accurate correction scheme based on the grossular and andradite compositions of garnet is proposed this method reproduces the bias of all but one standard to within a range of 0 4 an accuracy that is on the same order as the reproducibility 0 3 2 s d of the master garnet standard uwg 2 but that remains an independent source of error the new correction scheme is used to successfully reproduce laser fluorination analyses along a traverse of a polymetamorphic zoned skarn garnet from the adirondack mountains while previous analyses were at the mm scale the new data resolve a gradient of 18 o of 2 1 over 16 m if experimentally derived diffusion coefficients are correct these new results show that granulite facies metamorphism was significantly faster than previously assumed and the thermal peak was less than 5 myr

remobilization in the cratonic lithosphere recorded in polycrystalline diamond polycrystalline diamonds framesites from the venetia kimberlite in south africa contain silicate minerals whose isotopic and trace element characteristics document remobilization of older carbon and silicate components to form the framesites shortly before kimberlite eruption chemical variations within the garnets correlate with carbon isotopes in the diamonds indicating contemporaneous formation trace element radiogenic and stable isotope variations can be explained by the interaction of eclogites with a carbonatitic melt derived by remobilization of material that had been stored for a considerable time in the lithosphere these results indicate more recent formation of diamonds from older materials within the cratonic lithosphere

relations between rainfall runoff induced erosion and aeolian deposition at archaeological sites in a semi arid dam controlled river corridor process dynamics in fluvial based dryland environments are highly complex with fluvial aeolian and alluvial processes all contributing to landscape change when anthropogenic activities such as dam building affect fluvial processes the complexity in local response can be further increased by flood and sediment limiting flows understanding these complexities is key to predicting landscape behavior in drylands and has important scientific and management implications including for studies related to paleoclimatology landscape ecology evolution and archaeological site context and preservation here we use multi temporal lidar surveys local weather data and geomorphological observations to identify trends in site change throughout the 446 km long semi arid colorado river corridor in grand canyon arizona usa where archaeological site degradation related to the effects of upstream dam operation is a concern using several site case studies we show the range of landscape responses that might be expected from concomitant occurrence of dam controlled fluvial sand bar deposition aeolian sand transport and rainfall induced erosion empirical rainfall erosion threshold analyses coupled with a numerical rainfall runoff soil erosion model indicate that infiltration excess overland flow and gullying govern large scale centimeter to decimeter scale landscape changes but that aeolian deposition can in some cases mitigate gully erosion whereas threshold analyses identify the normalized rainfall intensity defined as the ratio of rainfall intensity to hydraulic conductivity as the primary factor governing hydrologic driven erosion assessment of false positives and false negatives in the dataset highlight topographic slope as the next most important parameter governing site response analysis of 4 years of high resolution four minute weather data and 75 years of low resolution daily climate records indicates that dryland erosion is dependent on short term storm driven rainfall intensity rather than cumulative rainfall and that erosion can occur outside of wet seasons and even wet years these results can apply to other similar semi arid landscapes where process complexity may not be fully understood copyright 2015 john wiley sons ltd

medalus soil erosion models for global change abstract two novel soil erosion models have been developed within the medalus projects their principal innovation lies in the explicit treatment of long term interactions with the vegetation and soil with implications for the way in which the surface flow and infiltration are described and distributed areally the models are primarily targeted on and validated against mediterranean landscapes for uncultivated conditions but the conceptual principles have wider application both models contain four inter related submodels for the atmosphere vegetation soil and surface subsystems for a series of points down the length of a hillslope flow strip or catena in the medalus model processes are represented in detail and the model is designed to simulate outputs of water and sediment from the single catena and the changes in this catena over time a simplified version of the catena model is now being incorporated into the medrush model in which subcatchments of 1 20 km 2 each represented by a family of catenas are combined using water and sediment routing algorithms to provide forecasts for catchments of up to 5000 km 2 the paper emphasises three novel aspects of the models first the long term interactions and their scope for forecasting erosional soil degradation second the way in which microtopography is treated within the models and third the nesting of catenas and subcatchments within large catchments in medrush

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

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

evidence of subduction and crust mantle mixing from a single diamond abstract cathodoluminescence cl imaging of polished sections of a diamond from the guaniamo region of venezuela suggests a history of the diamond involving two periods of growth separated by a period of resorption and possibly brittle deformation in situ electron probe analysis of multiple eclogitic garnet inclusions reveals a correlation between garnet composition and location in the stone an early formed garnet in the diamond core has higher ca ca mg and lower mg mg fe values than later garnets associated with the second period of diamond growth this variation conforms to an extensive trend of variation in the suite of eclogitic garnets extracted from venezuelan diamonds the diamond is zoned in carbon isotope composition in situ secondary ion mass spectrometry sims data the core compositions 13c pdb corresponding to the first stage of growth average 17 7 the second period of growth is apparently in two sub sets of cl zones with mean values of 13 0 and 7 9 nitrogen contents of diamond are low 30 300 atomic ppm and do not correlate with carbon isotope composition oxygen isotope ratios of the garnet inclusions are elevated substantially above those expected for common mantle 18o vsmow of early garnet is approximately 10 5 and two late garnets average 8 8 the evolutionary trend of magnesium enrichment in garnet is unlikely to represent igneous fractionation the stable isotope data are consistent with diamond formation in subducted meta basic rocks that had interacted with sea water at low temperatures at or near the sea floor and contained a substantial biogenic carbon component during or following subduction diamonds continued to form in an evolving system that was progressively modified by interaction with mantle material

a general power equation for predicting bed load transport rates in gravel bed rivers 1 a variety of formulae has been developed to predict bed load transport in gravel bed rivers ranging from simple regressions to complex multiparameter formulations the ability to test these formulae across numerous field sites has until recently been hampered by a paucity of bed load transport data for gravel bed rivers we use 2104 bed load transport observations in 24 gravel bed rivers in idaho to assess the performance of eight different formulations of four bed load transport equations results show substantial differences in performance but no consistent relationship between formula performance and degree of calibration or complexity however formulae containing a transport threshold typically exhibit poor performance furthermore we find that the transport data are best described by a simple power function of discharge from this we propose a new bed load transport equation and identify channel and watershed characteristics that control the exponent and coefficient of the proposed power function we find that the exponent is principally a factor of supply related channel armoring transport capacity in excess of sediment supply whereas the coefficient is related to drainage area a surrogate for absolute sediment supply we evaluate the accuracy of the proposed power function at 17 independent test sites

anticorrelation between low δ13c of eclogitic diamonds and high δ18o of their coesite and garnet inclusions requires a subduction origin diamond is essentially impermeable and unreactive under many conditions and tiny mineral inclusions within natural diamonds can faithfully preserve information on the chemical and physical conditions during diamond growth the stable isotope ratios of carbon nitrogen oxygen and sulfur in diamonds and their mineral inclusions have been used to constrain models of diamond formation but interpretations of the data have differed dramatically the crux of the controversy lies in the interpretation of the carbon isotope ratios of eclogite suite diamonds which range well outside those expected for typical mantle materials such as peridotites basalts and carbonatites proposed explanations for these anomalous carbon isotope ratios include derivation from primordial mantle inhomogeneities fractionated mantle fl uids and subducted biogenic carbon working with samples from three continents we have analyzed the carbon isotope compositions of eclogite suite diamonds and the oxygen isotope composition of their mineral inclusions primarily by ion microprobe methods we have discovered a previously unrecognized remarkably consistent anticorrelation between these two isotopic systems in that virtually all diamonds with anomalously low carbon isotope ratios have silicate inclusions with anomalously high oxygen isotope ratios this is a fundamental observation that can only be explained by formation of eclogite suite diamonds through subduction of seafl oor altered basalt admixed with marine biogenic carbon into the fi eld of diamond stability

thirty years of studies on badlands from physical to vegetational approaches a succinct review the scientific subjects addressed in the research into badlands since the publication of bryan and yair s book bryan r b and yair a editors 1982 badland geomorphology and piping geo books norwich 408 pp are briefly analysed with a steadily increasing number of papers per year attention to some aspects such as runoff generation piping and the role of lithology and soils varied whereas the percentage of studies on erosion rates increased steadily over time vegetation was not a subject of research in early papers as most of the papers dealing with vegetation were rather descriptive and published in local or limited diffusion media which contrasts with the present situation when about 40 of papers published in international journals about badlands address some aspect of vegetation however the growth in the attention paid to vegetation and erosion rates was not linked to any increase in papers dealing with badland reclamation badlands are now seen as a group of systems with some common features but diverse dynamics depending mainly on climatic and lithological drivers more attention should be paid in the future to investigating the evolution of these landforms over time mostly through modelling studies whereas emerging technologies foster detailed analyses that were not possible formerly although some badland areas determine on and off site environmental issues others are spots of landscape diversity that merit protection rather than reclamation

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

effects of the morphology of sediment transporting channels on the erosion and deposition of debris flows a series experiments are conducted to investigate the effects of streambed profile on the erosion and deposition of debris flows it is found that straight channel can increase the run out of debris flows by 10 25 compared to that of surfaces without channels and that travel distance was positively correlated with the hydraulic radius of the channel in addition the presence of straight channels caused the volume of debris flow deposition to become normally distributed with respect to travel distance in the case of curved channels increases in the sinuosity index resulted in significant blockage and obstruction in the deposition zone the maximum deposition volume for a channel with a comparatively low sinuosity index 1 05 was 50 of the minimum deposition volume for a straight channel furthermore the channel curvature affected not only the positions of deposition peaks along the travel distance but also the debris flow magnitudes in each unit interval 0 5 m this study demonstrates the effects of differences in channel morphology on the erosional and depositional processes of gully debris flows these findings are of significant importance for guiding debris flow risk assessment and for the restoration and reconstruction of downstream regions

an invasion percolation model of drainage network evolution stream networks evolve by headward growth and branching away from escarpments such as rift margins the structure of these networks and their topographic relief are known to be fractal1 3 but no model so far has been able to generate the observed scaling properties here i present a statistical model of network growth in which stream heads branch and propagate at a rate that depends only on the local strength of the substrate this model corresponds to the process of invasion percolation4 with the added requirement of self avoidance it is a self organized critical system5 with properties similar to those of standard percolation models6 a description based on self avoiding invasion percolation reproduces the known scaling behaviour of stream networks and may provide a valuable tool for delineation of drainage patterns from digital topographic data sets7 8

sediment erosion dynamics of a gullied debris slide a medium term record medium term post event sediment flux investigations are rare for headwater catchments and particularly sparse for gullied hillslope failures repeat field observation ground photography and cross section measurements of a debris slide scar at the wet swine gill headwater catchment 0 65 km2 in the english lake district uk provide evidence of erosion and deposition dynamics over the medium term 2002 2014 these data are compared to site topographic and meteorological conditions to evaluate potential process response linkages rill and gully erosion networks establish soon after the slide failure 1 february 2002 thereafter gully enlargement proceeds rapidly first by vertical downcutting prior to lateral expansion and gully wall angle decline changes in cross sectional width depth and area 2002 2013 are characterised by statistically significant p 0 05 negative exponential growth models r2 width 0 88 0 97 depth 0 71 0 86 area 0 87 0 93 gully walls were dominated by erosion but the gully bed was characterised by episodic sediment production storage and transfer often leading to temporary deposition specific erosion rates on the gully wall exceeded those on the adjacent slide scar by up to 764 maximum values wall 0 0084 scar 0 0011 m2 m 1 d 1 upslope contributing runoff area and slope gradient are generally important for erosion although linear regression analysis demonstrates weak or insignificant relationships between meteorological conditions and gully scar sediment flux a general conceptual model of slide scar evolution integrating gully growth and capture summarises activity at this site however transferability to locations with terrain characteristics land management practices and climate conditions different to those existing in the uk uplands remains to be tested this investigation adds to growing appreciation of the complexities of sediment dynamics in headwater catchments and provides clear evidence for the potential of early management intervention to counter detrimental post failure sediment erosion which at this site would have been most effective up to 3 4 years following gully initiation

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

a gis based approach for gully erosion susceptibility modelling using bivariate statistics methods in the ourika watershed morocco gully erosion is an important environmental issue with severe impacts this study aimed to characterize gully erosion susceptibility and assess the capability of information value infval and frequency ratio fr models for its spatial prediction in ourika watershed of the high atlas region of morocco these two bivariate statistical methods have been used for gully erosion susceptibility mapping by comparing each data layer of causative factor to the existing gully distribution weights to the gully causative factors are assigned based on gully density gullies have been mapped through field surveys and google earth high resolution images lithofacies land use slope gradient length slope aspect stream power index topographical wetness index and plan curvature were considered predisposing factors to gullying the digitized gullies were randomly split into two parts sixty five percent 65 of the mapped gullies were randomly selected as training set to build gully susceptibility models while the remaining 35 cases were used as validation set for the models validation the results showed that barren and sparse vegetation lands and slope gradient above 50 were very susceptible to gully erosion the roc curve was used for testing the accuracy of the mentioned models the analysis confirms that the fr model auc 80 61 shows a better accuracy than infval model auc 52 07 the performance of the gully erosion susceptibility map constructed by fr model is greater than that of the map produced by infval model the findings proved that gis based bivariate statistical methods such as frequency ratio model could be successfully applied in gully susceptibility mapping in morocco mountainous regions and in other similar environments the produced susceptibility map represents a useful tool for sustainable planning conservation and protection of land from gully processes

spatial analysis of factors controlling the presence of closed depressions and gullies under forest application of rare event logistic regression abstract although numerous studies have reported on past geomorphic change it is a common difficulty to identify the relative role of driving human or climatic forces to that end the possibilities of rare events logistic regression are explored in a 1300 hectare large ancient forest in central belgium here 43 permanent gullies and 71 closed depressions were observed that were probably caused by an anthropogenically induced land use change in the past this human origin was confirmed for a limited number of case study areas by recent geomorphic research with dating and soil profile analysis the objective of this study is to analyze the factors controlling the position of all gullies and closed depressions in the study area and investigate their mutual relation this will indicate whether or not the results obtained for the small case study areas can be extrapolated to the rest of the geomorphic features found in the whole study area the obtained logistic regression models show that both anthropogenic and physical factors are important in the spatial distribution of both geomorphic features for the prediction of the occurrence of closed depressions anthropogenic factors are most important however the probability of finding a depression is larger close to reported prehistoric and roman archaeological sites on well developed undisturbed luvisols and on northeast to southeast facing slopes the local slope gradient of the soil surface is the most important factor in the multivariate model for predicting the presence of the permanent gullies the occurrence probability of permanent gullies is also larger on northeast to southeast facing slopes the anthropogenic factor expressed by the distance to the closed depressions is significant as a univariate model this suggests that a critical slope gradient is a prerequisite for gully incision but gully formation still needs to be triggered by a human induced land use change it can therefore be concluded that both the gullies and the closed depressions in the meerdaal forest are related to past human activity either directly through mining of loess or indirectly through runoff production on cropland this study also showed the potential of rare events logistic regression for analyzing the spatial pattern of geomorphological features in relation to environmental factors

extreme crustal oxygen isotope signatures preserved in coesite in diamond the anomalously high and low oxygen isotope values observed in eclogite xenoliths from the upper mantle beneath cratons have been interpreted as indicating that the parent rock of the eclogites experienced alteration on the ancient sea floor1 recognition of this genetic lineage has provided the foundation for a model of the evolution of the continents whereby imbricated slabs of oceanic lithosphere underpin and promote stabilization of early cratons2 early crustal growth is thought to have been enhanced by the addition of slab derived magmas leaving an eclogite residuum in the upper mantle beneath the cratons3 but the oxygen isotope anomalies observed in eclogite xenoliths are small relative to those in altered ocean floor basalt and intermediate stage subduction zone eclogites and this has hindered acceptance of the hypothesis that the eclogite xenoliths represent subducted and metamorphosed ocean floor basalts we present here the oxygen isotope composition of eclogitic mineral inclusions analysed in situ in diamonds using an ion microprobe secondary ion mass spectrometer the oxygen isotope values of coesite a polymorph of sio2 inclusions are substantially higher than previously reported for xenoliths from the subcratonic mantle but are typical of subduction zone meta basalts and accordingly provide strong support for the link between altered ocean floor basalts and mantle eclogite xenoliths

fluvial connectivity and climate a comparison of channel pattern and process in two climatically contrasting fluvial sedimentary systems in south africa abstract the aim of this research was to investigate the dynamics of valley formation sediment delivery and channel pattern in two climatically contrasting fluvial sedimentary systems in south africa each system comprised a network of headwater valley fills and floodplains underlain by sedimentary karoo supergroup rocks that are intersected by resistant dolerite dykes and sills the seekoei river floodplain and gordonville valley fill site in the great karoo however experience less than half the annual precipitation of the nsonge river floodplain and hlatikhulu valley fill in the kwazulu natal drakensberg foothills furthermore rainfall is more variable in the karoo despite climatic differences headwater valley fills were geomorphically similar in contrast floodplains in the two regions were vastly different even when the same downstream control a resistant dolerite intrusion crossing the drainage line was considered upstream of a dolerite dyke the nsonge river is highly sinuous and located in a wide floodplain that has been carved by lateral planation of the underlying bedrock in comparison the seekoei river located upstream of a dolerite sill is discontinuous and characterized by floodouts and avulsing distributaries that undergo periods of bedrock incision followed by infilling it is likely that this disparity is caused by the inability of infrequent unsustained flows to develop meanders and thus adjust the channel planform to changes in discharge sediment load and valley slope flow variability thus exercises a strong control on channel pattern and causes floodouts in headwater settings and the semi arid karoo floodplain as a result sediment transport in the seekoei river is likely to be episodic and net retention of sediment in the semi arid floodplain is greater than in the sub humid nsonge river floodplain where sediment depth is limited

morphodynamics of a gully and floodout system in the sneeuberg mountains of the semi arid karoo south africa implications for local landscape connectivity abstract the aim of this study was to investigate sedimentary processes in a discontinuous gully system and to establish how they impacted upon overland flow and erosion in the short term while also considering their impact on long term landscape connectivity this manuscript documents the effect that a series of discontinuous gullies located in the semi arid karoo south africa had on local valley morphology and landscape evolution the longitudinal and cross sectional morphology of two discontinuous gully systems were accurately surveyed in addition the sedimentology of eight cores was described and sediment particle size and percentage organics determined while the activity of the radioactive element 210 pb was measured in three of the cores in contrast to previous studies floodouts on the karoo gullies formed progressively downstream as avulsion occurred on the floodout more quickly than upstream backfilling 210 pb geochronology suggests that the most recent avulsion occurred following one of the wettest seasons on record where double the mean annual rainfall fell in just a few months a series of palaeo floodouts along the length of the gullies suggests that the process of gullying and depositional floodout formation is not restricted to the recent past and is a long term landscape process thus despite the lack of characteristic cut and fill features such as terraces the long term evolution of the karoo landscape may be related to episodic gullying in the short term palaeo and current floodouts alter the overland flow hydrology of the landscape and prevent the local formation of badlands by diverting overland flow away from gully thalwegs this results in the formation of amphitheatre type gullies with laterally eroded areas draining into narrow outlet channels incised into palaeo floodouts

factors related to gully erosion in woody encroachment in south eastern australia abstract gullies initiate when the equilibrium within a drainage line is upset by increased discharge or decreased soil resistance to detachment and transport of soil particles and is triggered and accelerated by human induced changes to vegetation cover woody encroachment is the increase in density cover extent and biomass of woody plants and can result in low ground cover which increases the potential of soil erosion this paper reports the relationships between gully erosion and site characteristics such as topography vegetation cover and road infrastructure in a 120 km study area of semi arid woodland subject to woody encroachment in south eastern australia this study characterised gully morphology and activity identified the factors related to gully volume and estimated the topographic thresholds for sub catchments subject to woody encroachment firstly relationships between gully volume activity topography vegetation cover and road infrastructure were explored secondly site characteristics of 32 sub catchments with and without gullies were compared finally the topographic thresholds for unstable and stable sub catchments with and without gullies respectively were estimated using the slope drainage area relationship s aa b all gullies were active and high gully volume was related to large sub catchments long gullies and short distances to roads stable sub catchments without gullies had gentler slopes higher foliage projective cover and ground cover than unstable sub catchments with gullies when data for sub catchments with and without gullies were combined the main factors related to gully volume were drainage area at the gully or stream heads and their local slope and ground cover the mean topographic threshold for gully development provided insights into the drainage area and slope conditions needed for gully development gully erosion in the study area is most likely the result of interactions among topography vegetation and human made structures roads in space and time the results of the study advance our understanding of gully erosion dynamics in areas of woody encroachment and can be used to identify areas susceptible to gullying

cluster growth modeling of plateau erosion the pattern of erosion of a plateau along an escarpment may be modeled using cluster growth techniques recently popularized in models of drainage network evolution if erosion on the scarp takes place in discrete events at rates subject to local substrate strength the whole range of behavior is described by a combination of three cluster growth mechanisms invasion percolation eden growth and diffusion limited aggregation dla these model the relative importance of preexisting substrate strength background weathering and seepage weathering and erosion respectively the rate of seepage processes is determined by the efflux of groundwater at the plateau margin which in turn is determined by the pressure field in the plateau aquifer if this process acted alone it would produce erosion patterns in the form of laplacian fractals with groundwater recharge from a distant source or poissonian fractals with groundwater recharge uniform over the plateau dla is used to mimic the laplacian or poissonian potential field and the corresponding seepage growth process the scaling structure of clusters grown by pure dla invasion percolation or eden growth is well known this study presents a model which combines all three growth mechanisms for the first time mixed growth processes create clusters with different scaling properties and morphologies over distinct length scale ranges and this is demonstrable in natural examples of plateau erosion

modelling suspended sediment concentration and load in a transport limited alluvial gully in northern queensland australia alluvial gullies are often formed in dispersible sodic soils along steep banks of incised river channels field data collected by shellberg et al earth surface processes and landforms 38 1765 1778 2013 from a gully outlet in northern australia showed little hysteresis between water discharge and fine 63 m suspended sediment indicating transport limited rather than source limited conditions the major source of the fine silt clay component was the sodic soils of upstream gully scarps and the coarser sand component was sourced locally from channel bed material in this companion paper at the same study site a new method was developed for combining the settling velocity characteristics of these two sediment source components to estimate the average settling velocity of the total suspended sediment this was compared to the analysis of limited sediment samples collected during flood conditions these settling velocity data were used in the steady state transport limit theory of hairsine and rose water resources research 28 237 243 245 250 1992 that successfully predicted field data of concentrations and loads at a cross section regardless of the complexity of transport limited upstream sources sheet erosion scalds rills gullies mass failure bank and bed erosion other disturbed areas the analysis required calibration of a key model parameter the fraction of total stream power f 0 025 that is effective in re entraining sediment practical recommendations are provided for the prediction of sediment loads from other alluvial gullies in the region with similar hydrogeomorphic conditions using average stream power efficiency factors for suspended silt clay fw 0 016 and sand fs 0 038 respectively but with no requirement for field data on sediment concentrations only basic field data on settling velocity characteristics from soil samples channel geometry measurements estimates of water velocity and discharge and associated error margins are needed for transport limit theory predictions of concentration and load this theory is simpler than that required in source limited situations copyright 2015 john wiley sons ltd

medium term gully headcut retreat rates in southeast spain determined from aerial photographs and ground measurements this paper deals with gully retreat rates at different time scales whereby the short term time scale may span a time interval of 1 5 years the medium term time scale a time interval of 5 50 years and the long term time scale a time interval of more than 50 years an analysis of high altitude aerial photographs in combination with ground measurements allowed us to quantify volumetric gully head retreat rates for 12 permanent gullies in southeast spain guadalentin and guadix study areas over a 40 43 year time interval medium term time scale this resulted in an average retreat rate ve of 17 4 m3 year 1 a power relationship between drainage basin area a and medium term volumetric gully head retreat rate ve 0 069a0 380 r2 0 51 n 21 was found by combining the gully head retreat rates obtained in this study with those obtained by a dendrochronological method the exponent b and the coefficient of determination r2 of the power relationships ve aab increases from the short term to the long term time scale expressing the increasing importance of drainage basin area in gully development with time considerable differences between gully head retreat rates measured at the short and medium term time scales at individual gullies showed the importance of land use changes and unsuccessful management practices on gully head retreat and the episodic nature of gully head retreat when piping and tension cracking are involved higher gully head retreat rates are obtained at the medium term time scale compared to the short term time scale but the differences are not significantly different at 10 the medium term methods tend to measure proportionally more high gully retreat rates but less extreme values compared to the short term method this is explained by a more equal distribution of extreme rainfall events both in space and time at a longer term time scale and hence a higher probability of measuring the average effect of both small and extreme rainfall events at each gully

evaluation of camel comprehensive areal model of earthquake induced landslides abstract a new comprehensive areal model of earthquake induced landslides camel has been developed to assist in planning decisions related to disaster risk reduction camel provides an integrated framework for modeling all types of earthquake induced landslides using fuzzy logic systems and geographic information systems camel is designed to facilitate quantitative and qualitative representation of terrain conditions and knowledge about these conditions on the likely areal concentration of each landslide type camel has been empirically evaluated with respect to disrupted landslides category i using a case study of the 1989 m 6 9 loma prieta ca earthquake in this case camel performs best in comparison to disrupted slides and falls in soil for disrupted rock fall and slides camel s performance was slightly poorer the model predicted a low occurrence of rock avalanches when none in fact occurred a similar comparison with the loma prieta case study was also conducted using a simplified newmark displacement model the area under the curve method of evaluation was used in order to draw comparisons between both models revealing improved performance with camel camel should not however be viewed as a strict alternative to newmark displacement models camel can be used to integrate newmark displacements with other previously incompatible types of knowledge

potential impacts of agricultural expansion and climate change on soil erosion in the eastern arc mountains of kenya the taita hills form the northernmost part of the eastern arc mountains of kenya and tanzania is one of the world s most important regions for biological conservation due to the expansion of agricultural activities during the last centuries currently only 1 of the original vegetation remains preserved in the taita hills these landscape changes together with potential increases in rainfall volumes caused by climate change offer a great risk for soil conservation the present research aims to evaluate how future changes in climate and land use can alter in time and space the variables inherent to a widely used soil erosion model and to assess the impacts of these changes for soil conservation a modelling framework was assembled by integrating a landscape dynamic model a soil erosion model and synthetic precipitation datasets generated through a monte carlo simulation the results indicate that if the current trends persist agricultural areas will occupy roughly 60 of the study area by 2030 although these land use changes will certainly increase soil erosion figures new croplands will likely take place predominantly in the lowlands which comprises areas with lower soil erosion potential by the year 2030 rainfall erosivity is likely to increase during april and november while a slight decrease tendency is observed during march and may an integrated assessment of these environmental changes performed using the modelling framework allows a clear distinction of priority regions for soil conservation policies during the next 20 years

the erosive growth of hillside gullies the rate of erosion of hillside gullies depends both on gully flow characteristics and the resistance offered by the gully soil profile to erosion this paper describes a method for quantifying a physically based resistance measure illustrated by application to a gully feeding sediment into the bremer river southeast queensland australia the dynamics of discharge down the gully during runoff events is the driver of erosion but this was unknown a new method is described whereby this unmeasured flow can be estimated using data on rainfall rate and river gauge monitoring the data collected on the gully was the increase in dimensions and volume and so soil loss over a two year period this information was obtained from a digital elevation model dem of the catchment derived from light detection and ranging lidar observations made at either end of the two year period the soil profile resistance characteristic evaluated is the energy required to erode a unit mass of soil from the gully walls a physically defined parameter j present in flow driven erosion theory which was adapted and applied to predict soil loss from the bremer river gully the value of j was evaluated by equating predicted to measured gully soil loss over the two year period using two alternative descriptions of gully cross section firstly a realistic gully shape description was used made possible by lidar data yielding j 405 5 j kg secondly in order to allow use of more widely available aerial photography for such studies the simplifying assumption of a semi circular gully shape was made yielding j 455 j kg allowing a error in estimated effective runoff rate for this ungauged gully the estimated j value would have an uncertainty of 1 7 using the actual gully geometry the assumptions made in estimating j are discussed and possible applications of this information listed

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

gully erosion susceptibility assessment by means of gis based logistic regression a case of sicily italy article i nfo article history this research aims at characterizing susceptibility conditions to gully erosion by means of gis and multivariate statistical analysis the study area is a 9 5 km 2 river catchment in central northern sicily where agriculture ac tivities are limited by intense erosion by means of field surveys and interpretation of aerial images we prepared a digitalmap of thespatial distribution of 260 gulliesinthestudy area inaddition fromavailable thematicmaps a 5 m cell size digital elevation model and field checks we derived 27 environmental attributes that describe the variability of lithology land use topography and road position these attributes were selected for their potential influence on erosion processes while the dependent variable was given by presence or absence of gullies within two different types of mapping units 5 m grid cells and slope units average size 2 66 ha the functional re lationships between gully occurrence and the controlling factors were obtained from forward stepwise logistic regression to calculate the probability to host a gully for each mapping unit in order to train and test the predictive models three calibration and three validation subsets of both grid cells and slope units were randomly selected results of validation based on roc receiving operating characteristic curves attest for acceptable to excellent accuracies of the models showing better predictive skill and more stable performance of the susceptibility model based on grid cells

some factors controlling gully growth in fine grained sediments a model applied in southeast spain abstract gullies in the guadalentin catchment se spain are formed in a variety of lithologies ranging from schists to marls there are clear differences in valley and channel morphology between these two types gully erosion in schists produces large amounts of clastic material that restricts sediment transport leading to a relatively smooth transition from gullies to hillslopes and to broad alluvial valley bottoms with laterally migrating channels gullies in marls contain only limited gravels so gully extension leads to sharply incised gully heads a two dimensional model has been developed to investigate and simulate the distribution of gully heads in the guadalentin the model runs on a smooth initial surface with an added fractal perturbation without some perturbation of the initial surface or material properties symmetry prevents the formation of any channels fractal perturbation was used here to provide initial irregularities at all scales this paper explores the dependence of model response on the form of the sediment transport law initially sediment transport was considered to be transport limited and so depends on the relationship between wash and creep splash this was modified by i altering the exponents for gradient and area to conform with experimental results ii adding a critical tractive power for the initiation of rillwash iii including a more explicit treatment of mass movements iv including terms to reduce the dependence of the model on the computational grid size v providing a basis for explicitly integrating from individual storms to average long term behaviour and most critically vi introducing the effective bedload fraction ebf as a simplifying concept to allow for the selective transportation of eroded sediment this modification allows the model to represent removal of fines in marl rich catchments without the need to introduce a fully explicit travel distance formulation the steep gully heads and vertical side walls developed in marl catchments in the guadalentin basin are qualitatively well represented by the model preliminary tests showed that steep walled gullies are generated where the ebf falls to below about 0 5 if a tractive power threshold is also introduced gentler headcuts are produced selective transportation is thus seen as the critical determinant of steep headcuts in gully systems

headwater channel dynamics in semiarid rangelands colorado high plains usa incised ephemeral channels provide a window into the fluvial processes that help sculpt rangeland landscapes this paper presents observations of ephemeral channels and valley networks in the high plains of colorado usa with an eye toward painting a picture of the ingredients that must be included in mathematical models of landscape evolution in such environments channel incision in the study area is driven by summer thunderstorms which can with reasonable frequency 3 5 yr generate boundary shear stresses high enough to penetrate the highly resistant vegetation armor but only within erosional hot spots where hydraulic forces are amplified by channel constriction and locally steep gradients focusing of erosion at these hot spots which correspond to knickpoints and channel heads is amplified by the small areal footprint and short erosional reach of most convective storms upstream migration of knickpoints creates a pattern of short active channel reaches separated by unchanneled or weakly channeled fully vegetated stable reaches based on our observations we interpret the necessary and sufficient conditions leading to the observed channel forms and dynamics as 1 a resistant vegetation layer overlying an erodible substrate which sets up a conditional instability through which erosional perturbations can grow by positive feedback 2 high flow variability 3 moderate to high substrate cohesion and 4 a high volume fraction of fine grained erodible material concave upward valley long profiles are interpreted as a trade off between downstream increasing flood frequency and downstream decreasing flood effectiveness the observed process dynamics imply that long term rates of valley incision should be especially sensitive to climatic oscillations between episodes of drought and warm season convective rainfall