analysis of gully dimensions and sediment texture from southeast australia for catchment sediment budgeting abstract catchment scale sediment budgeting models are increasingly being used to target remediation works aimed at controlling erosion and improving water quality gully erosion is often a major sediment source and needs to be accounted for in such models in a manner consistent with the scale of analysis and available data using 130 measurements of gully cross sectional area and 45 measurements of gully wall sediment texture the variability in gully dimensions and particle size distribution for the lake burragorang catchment in australia is examined the distribution of gully cross sectional area measurements is log normally distributed and modelling indicates a representative value of 23 m 2 be used in catchment sediment budgeting applications the proportion of gully eroded sediment contributing to the bedload budget defined as particles 63 m diameter of a river link is approximately half though may be higher in igneous landscapes a continental scale spatially distributed subsoil texture dataset provided limited capacity to predict the finer scale spatial variation in the proportion of sediment contributing to bedload from gully erosion within the lake burragorang catchment

stages in the life of a magnetic grain sediment source discrimination particle size effects and spatial variability in the south african karoo mineral magnetic properties are commonly used to trace the sources of river and lake sediments with the aim of identifying areas of a catchment experiencing the high rates of soil loss in some areas however there is poor understanding of how magnetic properties are able to discriminate between potential sediment sources the basis for mineral magnetic source discrimination between topsoils and subsurface material over different rock parent materials was investigated in the south african karoo the effects of particle size soil development alteration and diagenesis processes on the source discrimination were investigated good discrimination up to 100 correct discrimination was found between the sedimentary sources soils and subsurface and dolerite soils due to much higher concentrations of magnetic minerals in the dolerite there was little evidence of alterations to magnetic properties in subsurface sediments resulting in only a small ability of properties to differentiate between surface and subsurface sources it was found that during the development of topsoils there was a loss of high coercivity weakly magnetic grains and an enrichment in small superparamagnetic and stable single domain grains particle size was strongly related to magnetic properties with almost all of the secondary superparamagnetic and stable single domain grains created during soil formation being concentrated in the 125 m fractions the small ability of sediment to discriminate between surface and subsurface sources was based upon the dissolution of primarily fd and arm carrying grains in the 32 m fractions and to a lesser extent the 63 32 m fraction as a result it was recommended that source tracing with the 32 m fraction of soils and sediment should be treated separately from the 63 32 m and larger particle size fractions the relationships between particle size and magnetic properties were fairly consistent in all soil samples in each source group raising the possibility that reliable correction factors could be developed for each source group

evaluation of different machine learning models for predicting and mapping the susceptibility of gully erosion abstract gully erosion constitutes a serious problem for land degradation in a wide range of environments the main objective of this research was to compare the performance of seven state of the art machine learning models svm with four kernel types bp ann rf and brt to model the occurrence of gully erosion in the kashkan poldokhtar watershed iran in the first step a gully inventory map consisting of 65 gully polygons was prepared through field surveys three different sample data sets s1 s2 and s3 including both positive and negative cells 70 for training and 30 for validation were randomly prepared to evaluate the robustness of the models to model the gully erosion susceptibility 12 geo environmental factors were selected as predictors finally the goodness of fit and prediction skill of the models were evaluated by different criteria including efficiency percent kappa coefficient and the area under the roc curves auc in terms of accuracy the rf rbf svm brt and p svm models performed excellently both in the degree of fitting and in predictive performance auc values well above 0 9 which resulted in accurate predictions therefore these models can be used in other gully erosion studies as they are capable of rapidly producing accurate and robust gully erosion susceptibility maps gesms for decision making and soil and water management practices furthermore it was found that performance of rf and rbf svm for modelling gully erosion occurrence is quite stable when the learning and validation samples are changed

alluvial terrace development and changing landscape connectivity in the great karoo south africa insights from the wilgerbosch river catchment sneeuberg dendritic channel networks in the wilgerbosch river catchment draining the south side of the sneeuberg south africa are deeply incised exposing terrace fills of varying thickness and extent channel long sections exhibit stepped profiles where resistant rock strata cross valley floors but are now partially or completely breached using a combination of aerial image analysis geomorphological mapping sedimentological investigations field logging grain size and magnetic susceptibility analyses and geochronology osl 14c this study demonstrates the patterns and controls on erosion and sedimentation and to a lesser extent the age structure of fills in two low order tributaries africanders kloof and wilgerbosch kloof and several reaches of the higher order wilgerbosch river a conceptual model of terrace development in relation to changing conditions of connectivity is presented valley headwaters are dominated by discontinuous palaeochannel and floodout sediments whilst in second to fourth order tributaries four sedimentologically and stratigraphically distinct terrace fills that exceed the scale and complexity of deposits on the northward side of the sneeuberg were identified and analysed the early part of this regional terrace succession highlights the importance of interactions between periglacial and fluvial activity on cut fill and pedogenesis around the time of the deglacial period terrace development is shown to have been a complex response to reconnection of the channel network with upland colluvial stores resulting in the valleys becoming choked with sediment this caused a rise in groundwater and formation of extensive calcretised rootmats on valley floors and slopes acting to blanket terraces 1 and 2 the thickness and longevity of this blanket is shown to restrict depth of incision in subsequent phases t3 t4 the deposits in these headwater valleys have until now been overlooked as a source of palaeoenvironmental information this study is the first to demonstrate the role and importance of changing connectivity in cut and fill phases that predate the late eighteenth century european incursion in the sneeuberg

geometry of the rivera cocos subduction zone inferred from local seismicity the rivera microplate and the cocos plate are subducting beneath the north american plate to obtain new insights into the subduction geometry we located earthquakes recorded by seismic stations deployed during the mapping the rivera subduction zone experiment from january 2006 to june 2007 we implemented standard procedures for earthquake location and we also manually corrected phase detections and picks to increase accuracy of the earthquake catalog we located about 2100 earthquakes within the 2 0 5 3 m l magnitude range the average location error is 0 8 km horizontally and 1 0 km vertically and the origin time has a mean error of 0 2 s we observed crustal seismicity over the subducted rivera microplate at no depth greater than 25 km on the other hand seismicity over the subducted cocos plate is present to depths of 40 km the rivera plate shows a gently subduction angle near the trench then dives more steeply into the mantle at an angle of 34 in the north and 37 in the south near the colima graben the distance between the inflection and the trench gradually increases from 40 km in the north of the study area to 60 km in the south near the colima rift cr the cocos plate has a slightly curved subducted slab with oblique geometry dipping toward the cr ranging in dip from 18 in the south to 30 in the north

geomorphological palaeoenvironments of the sneeuberg range great karoo south africa sedimentary sequences within headwater valleys on the landward side of the great escarpment of south africa are elucidated and their significance as indicators of environmental change is assessed this study focuses on the sneeuberg range the most prominent mountain range in the semi arid central great karoo valley fills of a hitherto unrecognised complexity and of a greater age than any previously recorded in the central great karoo are reported three phases of deposition spanning the late pleistocene up to the present are documented from sites where gully erosion has incised the valley fills the earliest depositional phase is represented by deeply weathered calcretised gravel deposits which probably were emplaced by debris flow and fluvial processes in the form of a fan these deposits subsequently were buried by finer grained largely unconsolidated sediment with much of this emplacement occurring during the holocene there is evidence for phases of landscape stability and instability within this facies finally sheetwash has removed fine grained sediments from valley flanks and has deposited it either on valley bottoms or in presently active gullies this process appears to be ongoing and is the subject of current investigation the sedimentary deposits are interpreted as representing a wide range of palaeoenvironmental conditions that have prevailed within the central great karoo since the penultimate glaciation copyright 2003 john wiley sons ltd

controlling factors of the size and location of large gully systems a regression based exploration using reconstructed pre erosion topography abstract the role of different factors potentially affecting the size and location of large gully systems is explored in two tributary basins of the tagus river s portugal the hillslopes of these basins corresponding to tertiary sedimentary formations are affected by hundreds of large gully systems varying in extent from somewhat 2 to 3 ha a study set of 90 gully systems were vectorized from aerial ortophotos and analysed in relation to a set of potential control variables obtained by reconstructing the pre erosion topography multiple linear regression and logistic regression were combined in order to investigate controls over the general morphometry of these landforms area perimeter and sinuosity and their location in the respective basins results indicate that gully systems initiated as bank gullies in response to an incision by the drainage network in both basins and then evolved as a function of upslope contributing area developing progressively more sinuous outlines as a result of headcut bifurcation pre erosion topographic form was shown to have only a marginal effect with results suggesting gully systems have grown essentially through mass movements in headcuts and sidewalls influenced by subsurface water

bedrock incised gully erosion phenomena on round island mauritius abstract round island is a 219 ha volcanic island that lies 22 km north of mauritius reaching almost 300 m in altitude the small island has steep slopes thin soils and a rocky coast that dips steeply into the sea in the past the island has been subjected to human influence through the introduction of alien species including goats rabbits and plants severely degrading the floral and faunal ecology since being declared a nature reserve in 1957 the rehabilitation of the island has received international praise however extensive erosion remains problematic unusually the island exhibits gully forms that extend deeply into the tuff bedrock a modified version of the southern african regional commission for the conservation and utilisation of the soil sarccus erosion classification system was used to describe two such bedrock incised gully networks camp and big gully based on morphometric parameters and erosion severity rock hardness was also assessed to determine lithological controls on bedrock incised erosion features the gullies have their starting points on the mid upslope regions as rills these increase in width and depth downslope to a very severe bedrock gully erosion classification and an exit at sea level the predominant rock type on round island is tuff which is a relatively weak volcanic rock as indicated by low mean schmidt hammer r values implying higher expected bedrock erosion rates during periods of intense rainfall the bedrock incised gullies act as transport channels for sediment which is ultimately lost to sea rehabilitation efforts entail planting of indigenous species and mechanical soil traps on the slopes which has been effective although localised natural re vegetation has been occurring in the gully channels particularly in the mid sections of the gullies the most appropriate steps toward rehabilitation should thus focus on the wide scale establishment of vegetation as it would appear that due to the extensive nature of gullies on round island and its steep topography erosion is a natural phenomenon that is sensitive to human influence

the october 9 1995 colima jalisco mexico earthquake mw8 an aftershock study and a comparison of this earthquake with those of 1932 data from portable seismographs and a permanent local network called resco are used to locate the aftershocks of the october 9 1995 colima jalisco earthquake mw 8 0 the maximum dimension of the aftershock area which is rectangular in shape is 170 km 70 km our study shows that the mainshock nucleated 24 km south of manzanillo near the foreshock of october 6 1995 mw 5 8 and propagated 130 km to the nw and 40 km to se the aftershock area lies offshore and is oriented parallel to the coast the observed subsidence of the coast is a consequence of this offshore rupture area the aftershocks reach unusually close to the trench within 20 km this may be due to lack of sediments with high pore pressure at shallow depth there are some similarities between this earthquake and the two great earthquakes of 1932 3 june ms 8 1 18 june ms 7 8 which occurred in this region in both cases the aftershocks were located offshore and the coastline subsided the sum of seismic moments and the rupture lengths of the 1932 events 1 8 1021 n m and 280 km respectively however were greater than the 1995 earthquake also a comparison of seismograms of 1932 and 1995 earthquakes show great differences it seems that the 1995 event is not a repeat of either june 3 or june 18 1932 earthquakes

sediment tracing and environmental history for two small catchments karoo uplands south africa abstract as part of an investigation of land degradation in the south african karoo three types of fine sediment signatures radionuclides mineral magnetism and sediment geochemistry were used to trace the origins of fine particulate sediment accumulating in two reservoirs that were constructed around the mid 1930s both reservoirs are fed by gullies that are known to have been in existence before their construction robust chronologies were derived from the 137 cs profiles in the reservoir sediments from aerial photographic records and from an analysis of extreme storm events that have left stratigraphic markers in the reservoir sediments extreme daily rainfalls have become more frequent in the last 30 years but sediment accumulation rates in the two reservoirs differ significantly one reservoir has high sediment accumulation rates between 1958 and 1964 that correlates with an expansion in the area of cereal cultivation the second catchment has no cultivated land but sedimentation rates in the reservoir declined after 1941 when livestock grazing densities decreased by a factor of around three despite the increase in the frequency of high magnitude daily rainfalls after 1970 sediment availability as controlled by land use appears to be the most important limit on changes in sedimentation rates differences in lithology and land use provided an opportunity to evaluate the number of sources that could successfully be discriminated in each catchment at different timescales 137 cs and unsupported 210 pb can be used to trace sources of actively transported or very recently deposited sediment and to discriminate sources of reservoir sediments between topsoils cultivated and uncultivated and subsoils or gully sidewalls lack of current 137 cs inputs means that it will become less useful as a future discriminator of topsoil subsoil sources because it only has a half life of ca 30 years and will eventually be undetectable the potential for unsupported 210 pb to provide an alternative method for discriminating these sources is demonstrated using principal component and discriminant function analysis and the three groups of sediment fingerprint signatures it was possible to discriminate doleritic soils from other potential sources in the catchments including valley fill and soils underlying vegetation that had been recently burned as part of the rangeland management system results suggest that fire was an important contributor to destabilising soil which was subsequently delivered to the reservoir during high magnitude rainfalls it is concluded that 1 changes in the extent of cereal cultivation and livestock grazing density are most closely related to temporal changes in sedimentation rates in each of the two reservoirs 2 temporal changes in the magnitude and frequency of extreme daily rainfalls do not correlate with reconstructed patterns of sediment accumulation through time 3 the gully systems provide connectivity between the dominant hillslope sources and the reservoirs but have not contributed significantly to the sediment deposited in either reservoir and 4 there is no evidence to suggest that sources of sediment accumulating in the reservoirs have changed significantly over the last ca 70 years

long term studies of land degradation in the sneeuberg uplands eastern karoo south africa a synthesis for the past 15 yr the sneeuberg uplands in the eastern karoo south africa have been a focus for research on land degradation by the above authors and other colleagues earlier work in the karoo emphasised vegetation change whereas we concentrate on physical changes to the landscape at the small catchment scale e g bare degraded areas badlands and gully donga systems analysis of sedimentation in farm dams allows for reconstruction of environmental histories using 210pb 137cs geochemical and mineral magnetic properties of the sediments erosion rates on badlands are monitored using arrays of erosion pins sediment source tracing within small catchments points to the importance of hillslope sources and the relative erosional inactivity of gully systems sediment supply from hillslope and colluvial sources is maintained by high rates of weathering on mudstones and sandstones current degradation should be viewed in the context of a c 200 yr history of overgrazing by european style stock farming and limited areas of former cultivation in the valleys grazing pressures are now much reduced but the loss of soils and vegetation suggests that landscape recovery will require several decades additional drivers of past degradation are likely to have been periods of drought and fire natural and managed and a gradual increase in both rainfall intensity and the frequency of extreme rainfall events the future of the degraded sneeuberg landscape will depend on future farming practices desirable options include more sustainable livestock practices adoption of wildlife farming and other more benign regimes involving mixes of agriculture tourism and wildlife protection together with landscape rehabilitation measures

effects of land use changes on badland erosion in clayey drainage basins radicofani central italy abstract hillslopes of the radicofani area in the upper valley of the orcia river southern tuscany region italy consist mainly of early pliocene clayey sediments and are widely affected by frequent badland erosion reforestation with frugal conifers has been carried out in the area over the last 50 years the goal of the present study is to evaluate the impact of reforestation and land use change on erosion rates in nine small drainage basins through a multidisciplinary approach geological geomorphological hydrological and land use characteristics were analyzed by a diachronic confrontation between pre reforestation 1954 and post reforestation 2007 situations aerial photo interpretation and processing in gis allowed us to quantify changes in areas affected by badland erosion land use and variations in erosion rates moreover dendrometric data were gathered from 18 circular sample plots in forest stands of 40 years old this allowed us to evaluate both the adaptability of different forest species to the clayey substrate and reforestation fragmentation the differences between the pre and post reforestation situations led to increases in arable land and forest areas and considerable decreases in erosion rates and badland areas however no significant correlation between the erosion rates and the forest area emerged due to the excessive fragmentation of reforestation cores and relatively small reforested surfaces land reclamation seems to have played a more important role in reducing erosion in the clayey substrate the integrated method presented here is an important tool useful to understand the morphological dynamics of badlands in relation to forest vegetation and for land planning and management

banderas rift zone a plausible nw limit of the jalisco block 1 echo soundings recently made in bahia de banderas show that this region is a graben with steeply dipping walls and several basins it is the offshore continuation of the valle de banderas graben and of a branching rift rio ameca rift originating in the tepic zacoalco rift zone the general trend of the three structures is ene with some ne trending offsets and they have a total length of 150 km this banderas rift zone is proposed as the nw limit of the jalisco block the existence of this limit suggests that there is another platelet or block between the jalisco block and a portion of the rivera plate probably bounded by the tres marias escarpment the jalisco block and the north america plate

local gradient and between site variability of erosion rate on badlands in the karoo south africa site average values of local gradient defined as the steepest slope angle measured at a point are a powerful predictor of long term rates of soil loss as measured by erosion pins on the non channel floor portions of ten badland study sites in the karoo area of south africa local gradient may be easily measured using a smartphone clinometer the successful use of local gradient here is in strong contrast to the previous failure of other site specific attributes including other measures of gradient and relief to explain between site variation in erosion rate on these study sites each measurement of local gradient may be thought of as a sample of the site s microtopography microrelief is a strong determinant of the emergent patterns of inter channel overland flow and hence of the patterns of inter channel erosion by flow local gradient changes most rapidly during the initial stages of channel incision when channels are established local gradient changes more slowly leading to almost parallel retreat of channel sidewalls a sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long term erosion rate a greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas and a lesser share is contributed by measurements made on interfluves

theoretical constraints to gully erosion research time for a re evaluation of concepts and assumptions gullies are conceptualized in the literature as essentially fluvial forms with dimensional boundaries arbitrarily defined between rills and river channels this notion is incompatible with the existing variability of form and process as mass movements frequently exert a fundamental control on gully initiation and expansion to the point of features outgrowing their original contributing area the inability of a conceptual framework to incorporate existing observations inevitably constrains methodologies and research results in this commentary several examples of published results are contrasted with the prevailing assumption of an essentially fluvial nature with the purpose of encouraging discussion on the need for a revised conceptual framework in gully erosion research copyright 2011 john wiley sons ltd

geochronological position of badlands and geomorphological patterns in the guadix baza basin se spain abstract the guadix baza basin is one of a number of intramontane depressions located within the betic cordillera se spain where the geological and geomorphological evolution is controlled by tectonic activity the basin ceased to be closed after capture by the atlantic network when five main land systems developed late pleistocene geological evolution basically consisted of erosional modelling when badlands were deeply incised in highly erodible materials marls and silts three travertine platforms and several palaeolithic sites were used to determine that this main incision period fell within a 115 000 48 000 yr range there are few signs of geomorphological evolution of this basin in the last 48 000 yr based on these geomorphological data and soil development tectonic uplift of the basin probably played a secondary role in its evolution and climatic conditions in southern iberia in the 144 000 48 000 yr period were more humid and variable than later

210pb scavenging in the north atlantic and north pacific oceans the radionuclide210pb shows significant geographic variations in the extent of its removal from the open ocean water column this texture of scavenging is defined by mapping 1 the integrated deficiency of210pb in the water column relative to its supply from the atmosphere and from in situ decay of dissolved226ra and 2 inventories of excess210pb in deep sea sediments the ratio of210pb deficiency to its supply termed the scavenging effectiveness is 20 in the north equatorial pacific and 50 in the north atlantic this variation is related to the combined effects of uptake of210pb onto sinking particles and lateral transport of210pb to areas of more intense removal sediment inventories of excess210pb normalized to the210pb deficiency in the overlying water column permit evaluation of the relative importance of these effects in the north equatorial pacific virtually all of the210pb removed from the water column is present in the underlying sediments but in the mid latitude north atlantic the sediments comprise only about 50 of the210pb removed the deficiencies of210pb in the mid latitude north atlantic sediments south of 50 n are qualitatively offset by surpluses in high latitude sediments north of 50 n higher primary productivity and new production in the surface waters of the high latitude north atlantic and north equatorial pacific relative to the oligotrophic central north atlantic may account for the greater fluxes of210pb to bottom sediments in those areas

sediment yield from irregularly shaped gullies located on the fortuna lithologic formation in semi arid area of tunisia the fortuna geological formation dated from the late oligocene to early miocene is mainly composed of friable sandstone gully erosion on this substratum is developing complex shaped gullies where bank processes are as important as head advance by cutting and bed deepening by vertical incision for irregularly shaped gullies quantitative information on gully erosion rates as related to gully head extension are scarce because bank active sides take many forms presumably depending on topography climate and lithology our field cross section measurements of 4 gullies developed in the fortuna formation 2 located on a steep slope area 15 and the other two on a gentle slope 9 have shown that the geometry of these gullies is far from a conical gully shape these field measurements were used to calculate gully reaches geometry and volume variation no direct relationships between gully volume and length could be established for these gullies in the fortuna formation nevertheless since both gully top view area and maximum top width are increasing as the gully reach length increases relationships could be established between maximum top width and their equivalent width defined as the ratio between gully reach top view area and its length then gully volume length relationships could be established for each of the 5 maximum bank full widths studied on the two gentle and two steep slope gullies for any maximum top width the gully volume length relationship was found to be not unique but the volume is increasing linearly up to the 15 m and 45 m distance from the gully head and then logarithmically for steep and gentle slope gullies respectively the linear and logarithmic equations coefficients were also found to be a function of gully maximum top width these equations were then used to quantify gully sediment yields related to gully shape evolution for eight gullies tributaries of as sahsafa wadis for this purpose the top view areas and lengths of these eight gullies were digitized and monitored on rectified air photographs of 1962 1974 and 2000 using a geographic information system arc view half of these gullies were located in an area with a gentle slope gradient and the other half with steep slope gradient the average gullies length variation for the whole study period 1962 2000 were 11 74 and 10 32 whereas the average top view areas variation was 23 57 and 29 4 for gentle and steep slope gullies respectively gullies volume changes during the periods 1962 1974 and 1974 2000 were then derived from the variation of gullies length and top view areas photo measurements on these 8 tributaries using the relationships established from the four measured gullies on gentle slopes the average gully sediment yields during 1962 1974 and 1974 2000 periods were 3 98 and 2 28 m3 ha 1 year 1 respectively on steep slopes these values are 4 82 and 2 47 m3 ha 1 year 1

the history of human induced soil erosion geomorphic legacies early descriptions and research and the development of soil conservation a global synopsis abstract this paper presents a global synopsis about the geomorphic evidence of soil erosion in humid and semihumid areas since the beginning of agriculture historical documents starting from ancient records to data from the mid twentieth century and numerous literature reviews form an extensive assortment of examples that show how soil erosion has been perceived previously by scholars land surveyors farmers land owners researchers and policy makers examples have been selected from ancient greek and roman times and from central europe southern africa north america the chinese loess plateau australia new zealand and easter island furthermore a comprehensive collection on the development of soil erosion research and soil conservation has been provided with a particular focus on germany and the usa geomorphic evidence shows that most of the agriculturally used slopes in the old and new worlds had already been affected by soil erosion in earlier prehistoric times early descriptions of soil erosion are often very vague with regard to the roman times geomorphic evidence shows seemingly opposing results ranging from massive devastation to landscapes remaining stable for centuries unfortunately historical documentation is lacking in the following centuries historical records become more frequent and more precise and observations on extreme soil erosion events are prominent sometimes they can be clearly linked to geomorphic evidence in the field the advent of professional soil conservation took place in the late eighteenth century the first extensive essay on soil conservation known to the western world was published in germany in 1815 the rise of professional soil conservation occurred in the late nineteenth and early twentieth centuries soil remediation and flood prevention programs were initiated but the long term success of these actions remains controversial in recent years increasing interest is to recover any traditional knowledge of soil management in order to incorporate it into modern soil conservation strategies the study shows that local and regional variations in natural settings cultural traditions and socioeconomic conditions played a major role for the dynamics and the rates of soil erosion on a long term perspective geomorphic evidence and historical sources can often complement each other but there should be also an awareness of new pitfalls when using them together

measuring medium term sheet erosion in gullies from trees a case study using dendrogeomorphological analysis of exposed pine roots in central iberia the assessment of gully erosion poses a great challenge because of the complexity and connectivity of the geomorphic processes involved this study focuses on the quantification of sheet erosion rates in a set of slope gullies located on the northern piedmont of the guadarrama mountains spanish central system in order to delineate accurately the gully areas in which sheet erosion was predominant the hydrologic erosion response unit hru eru approach was used and a dendrogeomorphological analysis of exposed tree roots was carried out to quantify sheet erosion rates in one selected hru eru identification of the first year of exposure by erosion from anatomical criteria was therefore critical the 29 samples taken were prepared for anatomical analysis and cross dated anatomical analysis of the samples showed a reduction in the lumen area of earlywood tracheids following root exposure and also in most cases a slight increase in growth rings moreover at the end of the ring latewood tissue and visible annual borders were very clearly defined by several rows of thick walled tracheids a non parametric test was used on the findings derived from this qualitative analysis to objectify determination of the first year of exposure estimates of sheet erosion were obtained by dividing the height of eroded soil by the number of years that each root was exposed the mean value of soil erosion for the entire study site was then determined from statistical inference using this procedure a range of sheet erosion rates between 6 2 and 8 8 mm y 1 125 2 and 177 8 t ha 1 year 1 was obtained for the dominant hru eru of these gullies in central iberia these estimates of eroded soil thickness were adjusted based on the recent finding that root anatomical changes occur prior to their exposure by erosion

sand ramps as palaeoenvironmental archives integrating general principles and regional contexts through reanalysis of the klipkraal sands south africa abstract sand ramps occur on a continuum of topographically controlled landforms ranging from purely aeolian features climbing falling dunes to talus cones and alluvial fans sand ramps have been identified as potentially important palaeoenvironmental archives in dryland regions that possess relatively few quaternary proxy records their utility however requires not only good age control of depositional phases but clear identification of process regimes determined through morphological and sedimentological analyses with several recent studies indicating the complexities of palaeoenvironmental interpretations and the controls of ramp development bateman et al 2012 rowell et al 2018 klipkraal sands is a sand ramp on the north eastern margin of the semi arid karoo that has been important for inferences of the extent of southern african late quaternary aeolian activity thomas et al 2002 we reanalyse this feature in the light of both its significance and other recent studies that have inferred extensive southern african lgm aeolian activity telfer et al 2012 2014 new sedimentological data and twelve osl dates indicate the klipkraal sands formed episodically between 100 0 14 ka rather than accumulating rapidly while sedimentological data question the aeolian affinities of the bulk of the feature therefore klipkraal is reinterpreted as showing no particular affinity to the lgm with sediments locally sourced with a significant colluvial component only the upper historical sediments can be clearly interpreted as aeolian deposits a complex interplay of processes is suggested for which a meaningful palaeoenvironmental interpretation cannot be easily defined this implies that the local geomorphic processes and controls operating on sand ramps need to be established before they can be fully utilised as palaeoenvironmental archives with implications for their interpretation worldwide

evidence from field based studies of rates of soil erosion on degraded land in the central karoo south africa abstract degradation in sneeuberg region of the central karoo south africa is characterized by the development of badlands on the footslopes of upland areas and by gully systems in valley bottoms evidence from aerial photographs suggests that there has been a slight decrease in degraded areas between 1945 and 2002 although gully systems have increased in density if not in length field measurements were carried out using a grid pattern of erosion pins at ten sites over a three year period on interfluves within existing degraded areas erosion continues at an average rate of 5 6 mm yr 1 on channels footslopes and sidewalls erosion rates are 2 6 mm 4 7 mm and 16 7 mm respectively the overall figure masks the high degree of cut and fill experienced within degraded areas in channels approximately eight times as much sediment is being moved compared to the overall loss at the end of 3 years these figures indicate that the relief of most badland areas is decreasing erosion pin results are compared with losses from stones on pedestals and from the area around shrubs there is evidence that rainfall has increased in amount and intensity over the last century which would promote erosion on existing bare ground at the same time stock numbers have continued to decrease since a high point in the 1930s reducing grazing pressure this coupled with the fact that most available colluvial footslopes are already degraded may explain the overall decrease in the extent of degraded areas however monitoring results observational evidence and sedimentation in dams indicate that badlands remain active and an important source of sediment

how old are the gullies dongas of the sneeuberg uplands eastern karoo south africa abstract the sneeuberg uplands in the eastern karoo are wetter than lowland sites with 400 mm of rainfall for over 150 years until recently they have been overgrazed largely by sheep the landscape consists of badlands less degraded areas and networks of gullies occupying the valley floors and hillside depressions these gullies have been relatively stable since at least 1945 the age of the gullies is controversial but various authors have speculated that they result from european incursion from the late 18th century onwards reconsideration of the relationship between vlei wetland deposits in the valley bottoms and gullies suggest that the gullies must post date late holocene development of vlei conditions incision by gullies would have resulted in a drying out of wetlands which occurred later and allowed cultivation of many valley bottoms for wheat and fodder crops gullies may have developed from deliberate attempts to drain wetlands for agriculture they are also likely to have formed from wagon tracks and a changed hydrology resulting from overgrazing and vegetation degradation on valley bottoms and hillslopes in other parts of south africa it has been suggested that gullies result from climatic impacts including instability in the little ice age this study should be seen in the context of an on going global debate about the role of climate and human mismanagement of the natural landscape

long and short term evolution of several mediterranean denudation hot spots the role of rainfall variations and human impact abstract severe slope denudation is one of the most important environmental problems in the mediterranean region in particular badlands are widespread in central italy as a result of extensive clayey outcrops current climatic conditions and rapid quaternary uplift human activity may significantly affect the development and evolution of these denudation hot spots especially through changes in land use this work is focused on a badland site that has developed over the last 30 years on a gently sloping area of cropland in central italy the site named bargiano underwent cropland abandonment in 1980 and was selected to evaluate the effects of external forcing such as human impact and rainfall variations on the development of water erosion processes the remnants of the 1980 cropland surface and the present eroded surface were sampled using differential global positioning system techniques to perform a volumetric estimation of the eroded material and to calculate the average erosion rate for fairly large time spans the dgps survey was coupled with a 2 year monitoring with erosion pins in the region which permitted comparisons between long and short term average erosion rates in addition the analysis of the rainfall series recorded at the orvieto pluviometric station allowed us to assess and evaluate the role of critical rainfall events on denudation intensity finally a further comparison of the measured and estimated erosion rates from the bargiano site with the data recorded at other long lasting monitoring stations that are set up in certain key areas of central italy the tevere river and ombrone river basins revealed that the bargiano experimental hillslope experienced considerably higher erosion rates than were noted at the other sites our investigations demonstrated that cropland abandonment caused an increase in the erosion rate relative to what happened in natural areas characterized by similar physiographic conditions this finding is consistent with previously reported results for other badlands found in the mediterranean area moreover the results obtained suggest that after the abandonment of its cropland the bargiano site evolved in a cyclical manner that was driven by intrinsic thresholds to a greater extent than it was affected by external climatic changes

holocene floodplain formation in the southern cape region south africa abstract the sediments of holocene floodplain banks in several river catchments in the southern cape region south africa were sedimentologically investigated and radiometrically dated the study resulted in a differentiation into two sedimentation phases the sedimentation of the older phase starts directly above the bedrock or above coarse gravels these sediments are composed of 2 5 3 m of interbedded sand silt and clay in part they are stratified by organic horizons and inclusions the radiocarbon dating of numerous organic horizons as well as fossil wood shows that the sedimentation during the older phase occurred between 1215 and 875 years bp at the base and 670 and 15 years bp at the top of this sequence the sediments of the younger phase mainly consist of homogeneous fine sand and are at least 3 m thick stratigraphically above the sediments of the older deposition phase however the sediments of the younger layer can also comprise the entire holocene deposits situated above the current riverbed these sediments are mainly of modern age and are partly deposits of centennial flood events the context between the onset of sedimentation and the start of pastoral farming by settlers after ad 400 which has been archaeologically verified supports the hypothesis that the first sedimentation phase was set off or favoured by the degradation of the natural vegetation cover as a result of livestock farming later increased sedimentation as well as an increase in peak flows resulting from increased landscape degradation due to intensified pasture farming by the european settlers has to be assumed

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

gully head retreat rates in the semi arid highlands of northern ethiopia due to overgrazing and agricultural intensification gully erosion severely affects sub saharan countries however insufficient quantitative studies exist for this part of the world this paper presents data on gully head retreat rates in northern ethiopia and relates these rates to gully and environmental characteristics the monitoring of headcuts over one rainy season 2010 revealed that present day retreat rates are low with average annual linear rl areal ra and volumetric ve retreat rates of 0 34 m y 1 1 70 m2 y 1 and 5 2 m3 y 1 respectively these results express the positive effects of recent soil and water conservation practices on gully stabilization significantly higher values of rl up to 1 93 m y 1 occurred in the vertisol areas affected by soil piping when considering the medium to long time scale 1 47 years using archival terrestrial and aerial photographs headcut retreat rates proved to be significantly higher than those in the short term the averages for rl ra and ve are 3 8 m y 1 31 5 m2 y 1 and 47 7 m3 y 1 respectively retreat rates are up to 10 times higher after road construction for the medium to long term headcut retreat rates were positively related to the catchment area a a power relationship that best describes the relation between ve and a is ve 0 53 a0 31 r2 0 27 n 18 compared to other areas worldwide regressive erosion has been rapid in ethiopia as a result of the degraded and steep landscape combined with erosive rains and the occurrence of vertisols in vertisols headcut retreat is controlled by soil piping because no adequate techniques exist to control gully initiation and development in vertisols alternative techniques should be developed that deactivate soil pipes

a 13 year record of erosion on badland sites in the karoo south africa land degradation in south africa has been of concern for more than 100 years with both climate change and inappropriate land management overgrazing being proposed as primary drivers however there are few quantitative studies of degradation and in particular few of erosion by water badlands taken here to be the landform which results from extreme erosion have been notably neglected we report on 13 consecutive years of erosion pin measurements of badland erosion on 10 study sites in the sneeuberg uplands of the eastern karoo in south africa the study sites are on holocene colluvium which mantles footslopes they have been subject to overgrazing for at least 100 years c 1850 1950 currently they are lightly grazed by sheep the area receives about 500 mm rainfall per year the sites are remote with only informal farmer operated daily raingauges nearby the nearest subdaily raingauge is c 55 km distant also we report on an analysis of the erosion pin data which focuses on establishing the origins and context of the badlands including the relationship between study sites and adjacent valley bottom gully systems compare erosion rates on our study sites with rates determined by erosion pins on other badland sites and discuss the implications of these erosion rates for landscape development and off site impacts net erosion rates on the study sites are relatively high compared with global badland rates and range from 3 1 to 8 5 mm yr 1 which may be extrapolated to 53 to 145 t ha yr 1 using a measured bulk density of 1 7 g cm 3 however comparisons with badland sites elsewhere are difficult because of different measuring methodologies lithologies climate and dominant processes erosion rates on the study sites are strongly influenced by rainfall amounts and in particular by daily rainfall events which exceed 10 mm this is the threshold intensity at which runoff has been observed to commence on badlands of significance but of lesser influence is weathering mainly by wetting and drying this prepares bare surfaces for erosion however questions remain regarding the role of site characteristics and of processes at each site in determining between site differences in erosion rate crude extrapolation of current rates of erosion in conjunction with depths of incision into the badlands suggests that badland development started around 200 years ago probably as a response to the introduction of european style stock farming which resulted in overgrazing we assume but cannot quantify the additional influence of periods of drought and burning in the erosional history of the area intermittent connection of these badlands to valley bottom gullies and therefore to small farm dams and ultimately to large water storage reservoirs increases their impact on local water resources

chronology and controls of donga gully formation in the upper blood river catchment kwazulu natal south africa evidence for a climatic driver of erosion dongas gullies and badland type terrain are found extensively across interior south africa but the controls on their formation remain contested establishing the timing of donga formation is essential for developing a clearer understanding of the relative importance of natural e g climatic and human e g overgrazing controls here we present optically stimulated luminescence osl ages for colluvial sediments exposed in the sidewalls of dongas and for tributary fan sediments deposited downslope of dongas in the upper blood river catchment eastern south africa the tributary fan ages enable the timing of donga formation to be established since fan sedimentation is a direct result of upslope donga erosion the osl ages indicate that net colluviation and intervening palaeosol formation occurred from prior to 22 ka until 1 6 ka from 0 89 ka to present there has been a shift to net erosion characterised by widespread donga formation and tributary fan sedimentation contemporary donga formation i

sediment budget for subalpine watersheds lake tahoe california usa abstract pinpointing erosional hot spots or sediment source areas within a watershed can be difficult because of the highly non linear and episodic nature of effective runoff and sediment transport continuous monitoring of stream networks can provide insight into sediment source areas not possible from routine sampling by capturing episodic events and integrating entire storm events this paper presents the results of a three year study of spring snowmelt runoff in watersheds of lake tahoe california usa using a network of nine nephelometric turbidometers we estimate that montane badlands comprising 1 2 of the ward creek watershed 25 km 2 contributed 10 39 of snowmelt derived suspended sediment load the badlands are comprised of poorly vegetated and deeply incised gullies formed in parent material of miocene volcanic mudflow breccia the larger 29 5 km 2 blackwood creek watershed also showed high relative erosion rates from volcanic terrain tributaries draining forested granitic and metasedimentary headwater regions had minimal sediment loads monitoring networks indicated that temporary main channel storage regulated release of fine sediment eroded from steep headwater slopes this lag between erosion and delivery may lead to underestimation of gully erosion contribution to sediment budgets

rapid and selective clast weathering on an alluvial fan eastern karoo south africa abstract a small alluvial fan formed on the surface of a dry infilled dam in january 2010 as a result of a high magnitude rainfall and flood event gravel and boulder size clasts in the fan comprised dolerite mudstones and fine grained sandstones within a month of formation some mudstone gravels had disintegrated due to weathering processes the fan was investigated four years later and the weathering of different lithologies was categorised and quantified almost half of the weathered clasts were completely weathered forming small heaps or spreads of particles

quantifying long term changes in gully networks and volumes in dryland environments the case of northern ethiopia abstract understanding historical and present gully development is essential when addressing the causes and consequences of land degradation especially in vulnerable dryland environments for northern ethiopia several studies exist on the severity of gully erosion yet few have quantified gully development in this study gully network and volume development were quantified over the period 1963 2010 for an area of 123 km2 representing the regional variability in environmental characteristics gully networks were mapped from small scale aerial photographs and high resolution satellite images for the latter visualizing google earth images in 3d proved to be very suitable to investigate gully erosion from the changes in networks and volumes over the period 1963 2010 the occurrence of one cut and fill cycle is apparent from a largely low dynamic gully system in the 1960s network expansion and increased erosion rates in the 1980s and 1990s caused the drainage density and volume to peak in 1994 the average gully density dtotal was then 2 52 km km 2 and the area specific gully volume va 60 103 m3 km 2 this coincides with soil losses by gully erosion slg of 17 6 t ha 1 y 1 over the period 1963 1994 by 2010 improved land management and the region wide implementation of soil and water conservation measures caused 25 of the gully network to stabilize resulting in a net infilling of the gully channels over the period 1994 2010 the study validates previous findings that land degradation by gullying was indeed severe in northern ethiopia in the second half of the 20th century but also shows that when proper land management is applied a gully can be transformed into a linear oasis which increases the resistance of gullies to further erosion

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

continental boundaries of the jalisco block and their influence in the pliocene quaternary kinematics of western mexico extensional faulting observed in southwestern mexico has been related to the incipient rifting of the jalisco block from the mexican mainland since the pliocene on the basis of new structural and geophysical data we propose that 1 the continental boundaries of the jalisco block are ancient structures reactivated since the pliocene at a low 1 mm yr rate of deformation and 2 pliocene quaternary extensional faulting at the edges of jalisco block is a basement controlled intraplate deformation related to plate boundary forces rather than to active continental rifting the jalisco block boundaries first developed in response to the uplift of the puerto vallarta batholith in pre neogene time and underwent a complex contractile deformation before the pliocene during pliocene quaternary times north northeast extension reactivated the northern boundary forming the tepic zacoalco rift whereas east southeast extension formed the northern colima rift south of the colima volcano active extension is found only west of the so called southern colima rift and partly reactivates old northeast trending basement faults the parallelism between the subducted rivera cocos plate boundary zone and the eastern neotectonic boundary of the jalisco block supports east southeastward motion of the southern mexican blocks induced by the differential motion and oblique subduction of the cocos and rivera plates on the other hand we envisage pliocene quaternary extension along the northern boundary as an upper plate response to the low convergence rate and the steep subduction angle of the rivera plate

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

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