using lidar data to map gullies and headwater streams under forest canopy south carolina usa abstract the southeastern piedmont of the usa was severely gullied during the early 20th century a thick canopy established by reforestation in many areas now inhibits the identification or mapping of gullies by aerial photography or other conventional remote sensing methods an airborne laser scanning als or lidar mapping mission flown for the u s forest service in april 2004 acquired bare earth topographic data this paper tests the ability of the als topographic data to identify headwater channels and gullies for two branching gully systems in forested areas and to extract gully morphologic information comparisons are made with field traverses using differential gps and reference cross sections measured by leveling surveys at the gully network scale lidar data provide accurate maps the best available with robust detection of small gullies except where they are narrow or parallel and closely spaced errors in mapping channel location and network topological connectivity under forest canopy increase with attempts to identify smaller features such as large rills the ability of lidar data to map gullies and channels in a forested landscape should improve channel network maps and topological models at the gully reach scale attempts to use lidar data to extract gully cross section morphologic information under forest canopy were less successful due to systematic underestimation of gully depths and overestimation of gully top widths limited morphologic accuracy of the data set at this scale may be due to low bare earth point densities shadowing of gully bottoms and filtering of topographic discontinuities during post processing the als data used in this study are not suitable for detailed morphometric analysis or subtle change detection to monitor gullies or develop sediment budgets data collection may be improved by orienting flights over gullies and with increased point densities through improved scanner technology or better filtering and software capabilities to differentiate between vegetation and ground surfaces

on the spatial relationship between landslides and causative factors on lantau island hong kong abstract this paper presents a statistical approach to study the spatial relationship between landslides and their causative factors at the regional level the approach is based on digital databases and incorporates such methods as statistics spatial pattern analysis and interactive mapping firstly the authors propose an object oriented conceptual model for describing a landslide event and a combined database of landslides and environmental factors is constructed by integrating the various databases within such a conceptual framework the statistical histogram spatial overlay and dynamic mapping methods are linked together to interactively evaluate the spatial pattern of the relationship between landslides and their causative factors a case study of an extreme event in 1993 on lantau island indicates that rainfall intensity and the migration of the center of the rainstorm greatly influence the occurrence of landslides on lantau island a regional difference in the relationship between landslides and topography is identified most of the landslides in the middle and western parts of the island occurred on slopes with slope angles of 25 35 while in the eastern part the corresponding range is 30 35 overlaying landslide data with land cover reveals that a large number of landslides occurred in the bareland and shrub covered area and in the transition zones between different vegetation types the proposed approach can be used not only to analyze the general characteristics of such a relationship but also to depict its spatial distribution and variation thereby providing a sound basis for regional landslide prediction

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

characterizing the morphology of gully cross sections based on pca a case of yuanmou dry hot valley abstract a cross section of a gully gc is important not only for computing the volume and rate of erosion of the gully but also for understanding the relationship of the gullying process landforms land use and erosional features to effectively characterize the accurate morphology of gcs and to explain their statistical regularity this study proposes 26 morphological parameters for describing the cross sections of permanent gullies we surveyed 456 gcs with a laser distance meter located at the mouth middle and head of 152 gullies in the yuanmou dry hot valley of china mapped them with cass software and calculated the morphologic parameters based on principal component analysis pca the morphological characteristics can be notably expressed by four principal components and fewer parameters with heavier load information the first principal component pc reflected the dimensions of gcs with the key parameters of width depth and area of the cross section over 94 of the depth of the left side dl the top width wt and the area s were in the range of 0 12 m 3 27 m and 0 200 m2 respectively the second pc indicated the degree of the gully s asymmetry in terms of the parameter of asymmetry ratio of width there are 201 gcs of right deflection and 184 of left deflection the third pc expressed the degree of erosion in terms of erosiveness and shape there are 77 v shaped 25 u shaped and 354 intermediate shaped gullies the percentage of u shaped cross sections is noticeably higher at the gully head than at the gully mouth and middle the fourth pc reflects the erosional pattern difference the value of the width depth ratio was distributed and varied greatly within the range of 0 92 10 69 with an average value of 3 33 these key parameters differed at different locations and sites the shape of gcs differs at different stages of development weathering crusts soil properties and vegetation cover are important for controlling the morphology of gcs in the yuanmou dry hot valley this study will not only help to improve the content of gully morphology but will also contribute to understanding the controlling factors and evolution mechanism of gullies

atlantic water in the strait of sicily historical and recently acquired hydrographic and current meter data are used to study the behavior and the annual cycle of the surface layer of atlantic water aw within the sicilian channel section of the strait of sicily from january to march the surface layer isotherms and isohalines are much more steeply sloped toward the african coast the transition from winter to summer stratification occurs during the april to may period and by july both temperature and salinity isolines are quite horizontal the seasonal variations in temperature and salinity can be characterized by corresponding values of mean velocity mean kinetic energy and eddy kinetic energy during winter these values increased 2 3 times their summer values hydrographic and satellite data show that the stream of warmer and less saline aw enters the strait of sicily close to the tunisian coast south of cap bon the aw appears to decelerate forming meanders and detached parcels or small rings these structures are seen in satellite images more often during winter than summer when the aw current in the strait of sicily is more energetic

the cycle of instability stress release and fissure flow as controls on gully head retreat gully head and wall retreat has commonly been attributed to fluvial scour and head collapse as a result of soil saturation sapping or piping the empirical evidence to substantiate these conceptual models is sparse however and often contradictory this paper explores the hydrological and mechanical controls on gully head and wall stability by modelling the hydrology stability and elastic deformation of a marl gully complex in granada province south east spain the hydrological and slope stability simulations show that saturated conditions can be reached only where preferential fissure flow channels water from tension cracks into the base of the gully head and that vertical or subvertical heads will be stable unless saturation is achieved owing to the high unsaturated strengths of marl measured in this research failure in unsaturated conditions is possible only where the gully head wall is significantly undercut head retreat thus requires the formation of either a tension crack or an undercut hollow finite element stress analysis of eroding slopes reveals a build up of shear stress at the gully head base and a second stress anomaly just upslope of the head wall although tension cracks on gully heads have often been attributed to slope unloading this research provides strong evidence that the so called sapping hollow commonly found in the gully headwall base is also a function of stress release although further research is needed it seems possible that pop out failures in river channels may be caused by the same process the hydrological analysis shows that once a tension crack has developed throughflow velocity in the gully headwall will increase by an order of magnitude promoting piping and enlargement of this weakened area it is therefore possible to envisage a cycle of gully expansion in which erosion channel incision or human action unloads the slope below a gully head leading to stress patterns that account for the tension crack and a stress release hollow the tension crack promotes faster throughflow encouraging hollow enlargement and piping which undercut the gully head the tension crack permits the development of positive pore water pressures behind the gully head leading either to failure or contributing to toppling finally the debris may be eroded by fluvial action unloading a new section of slope and completing the cycle of gully head retreat copyright 2001 john wiley sons ltd

testing the water hypothesis quantitative morphological analysis of terrestrial and martian mid latitude gullies abstract although martian gullies resemble terrestrial counterparts two conflicting hypotheses exist for their formation still invoke fluvial processes on the one hand or lubricated co 2 flows on the other in this work we compared the quantitative morphology of terrestrial gullies known to have formed by liquid water and mid latitude martian gullies in the martian southern hemisphere we also compared these results with measurements of martian dry ravines adjacent to the gullies our results show a similarity between martian and terrestrial gully formation supporting the hypothesis that liquid water was involved in their erosion our results show dry ravines differ morphologically from gullies further suggesting fluidised flows as a likely origin of the latter variations in the relationships across various terrestrial and martian gullies indicate the significance of local environmental and geological conditions our work supports the idea that martian gullies may not have been formed by just one single process but may have evolved through a more complex interaction of processes and environment

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

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

assessment of shallow landslide susceptibility by means of multivariate statistical techniques several multivariate statistical analyses have been performed to identify the most influential geological and geomorphological parameters on shallow landsliding and to quantify their relative contribution a data set was first prepared including more than 30 attributes of 230 failed and unfailed slopes the performance of principal component analysis t test and one way test allowed a preliminary selection of the most significant variables which were used as input variables for the discriminant analysis the function obtained has classified successfully 88 5 per cent of the overall slope population and 95 6 per cent of the failed slopes slope gradient watershed area and land use appeared as the most powerful discriminant factors a landslide susceptibility map based on the scores of the discriminant function has been prepared for ensija range in the eastern pyrenees an index of relative landslide density shows that the results of the map are consistent copyright 2001 john wiley sons ltd language en

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

the role of vegetation on gully erosion stabilization at a severely degraded landscape a case study from calhoun experimental critical zone observatory abstract gully erosion was evidence of land degradation in the southern piedmont site of the calhoun critical zone observatory cczo during the cotton farming era understanding of the underlying gully erosion processes is essential to develop gully erosion models that could be useful in assessing the effectiveness of remedial and soil erosion control measures such as gully backfilling revegetation and terracing development and validation of process based gully erosion models is difficult because observations of the formation and progression of gullies are limited in this study analytic formulations of the two dominant gullying processes namely plunge pool erosion and slab failure are utilized to simulate the gullying processes in the 4 km2 holcombe s branch watershed in order to calibrate parameters of the gully erosion model gully features e g depth and area extracted from a high resolution lidar map are used after the calibration the gully model is able to delineate the spatial extent of gullies whose statistics are in close agreement with the gullies extracted from the lidar dem several simulations with the calibrated model are explored to evaluate the effectiveness of various gully remedial measures such as backfilling and revegetation the results show that in the short term the reshaping of the topographical surface by backfilling and compacting gullies is effective in slowing down the growth of gullies e g backfilling decreased the spatial extent of gullies by 21 46 and decreased the average depth of gullies by up to 9 revegetation however is a more effective approach to stabilizing gullies that would otherwise expand if no gully remedial measures are implemented analyses of our simulations show that the gully stabilization effect of revegetation varies over a wide range i e leading to 23 69 reduction of the spatial extent of gullies and up to 45 reduction in the depth of gullies depending on the selection of plant species and management practices

can bioengineering structures made of willow cuttings trap sediment in eroded marly gullies in a mediterranean mountainous climate abstract in the southern french alps high sediment yields from marly catchments cause socio economic and ecological problems downstream bioengineering structures made of willow cuttings could be used for efficient and sustainable sediment trapping in eroded gullies in order to decrease sediment yield at their outlets however little has been done to quantitatively assess the efficiency of such structures for trapping sediment or to improve their performance the objectives of this study were to analyze the ability of bioengineering structures to enhance vegetation development and sediment trapping in marly gullies in the southern french alps under a mountainous and mediterranean climate for five years after the restoration operations we monitored 101 bioengineering structures using willow salix cuttings including 55 brush layers on wooden sills bl and 46 brush layers with brush mats on wooden sills blm 1 2 m wide and 2 m long installed on the floors of eight experimental marly gullies the results showed that the ultimate survival of willow cuttings can be assessed after three years gully size and aspect appeared to be the most important factors influencing resprouting rates by avoiding south oriented gullies and those smaller than 1000 m 2 75 survival rates per structure may be achieved the results also showed that bl trapped 0 18 m 3 yr 1 of sediment per structure on average and blm 0 21 m 3 yr 1 but potential maximum values may reach 0 28 and 0 40 m 3 yr 1 over one year on bl and blm respectively therefore bioengineering structures made of willow cuttings can be used to trap significant quantities of sediment from the first year onwards and efficiently restore eroded marly gullies under a mediterranean mountainous climate it also provides design criteria to guide future restoration actions and future investigations in the southern french alps

importance of slope gradient and contributing area for optimal prediction of the initiation and trajectory of ephemeral gullies abstract ephemeral gully erosion rates are controlled by various factors out of which topography plays an important role this study investigates the possibility to predict the location of ephemeral gullies using two topographic attributes only i e local slope gradient s and upslope contributing area per unit length of contour a s an inverse relationship between s and a s in which the relative importance of the area exponent was varied was evaluated as to its performance in predicting the location of ephemeral gullies for three intensively cultivated catchments in the belgian loess belt this model is easily applicable as it only uses information on topography which can be derived from a digital elevation model and land use predicted locations of ephemeral gullies were confronted with the locations recorded over 5 years of field observations for all catchments a high relative area exponent relative to the slope exponent was required to yield good results the optimal relative area exponent ranged from 0 7 to 1 5 however the quality of the prediction did not vary significantly when changing the exponent within this range an average relative area exponent of ca 1 is appropriate for all three study areas and may therefore be proposed for similar areas under similar conditions a striking discrepancy was found between the high relative area exponent required to predict optimally the trajectory of the gullies and the low relative area exponent 0 2 required to identify the spots in the landscape where ephemeral gullies begin this indicates that spots in the landscape where gullies start are more controlled by slope gradient while the presence of concavities control the trajectory of the gullies until the slope gradient is too low and sediment deposition starts no relationship was found between the frequency of the occurrence of ephemeral gullies and the percentage of predicted gully pixels for each frequency class this indicates that frequently occurring gullies at the same location are not easier to predict than accidental gullies

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

assessment of soil losses by ephemeral gully erosion using high altitude stereo aerial photographs the objective of this study is to explore in a critical way the potential of high altitude stereo aerial photographs for the assessment of ephemeral gully erosion rates on 28 may 1995 an intensive rainfall event 30 mm h 1 during 30 min return period 3 years occurred in central belgium ephemeral gullies formed within an area of 218 ha study area 1 were mapped and measured both in the field and by high altitude aerial photos taken at the same time comparison of these two methods shows that if only one of the two surveying techniques had been used only 75 per cent of the total ephemeral gully length would have been detected so that the combination of aerial and field data leads in fact to the best possible determination of total gully length within the selected area a correction factor c is proposed so that the results of an ephemeral gully erosion survey based on high altitude stereo aerial photos can be adjusted for the undetected gullies next a sequential series of high altitude stereo aerial photographs taken in six different years was analysed in order to determine ephemeral gully erosion rates in three selected study areas study areas 2 3 and 4 selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central belgium where intense soil erosion regularly occurs ephemeral gullies were mapped and their total length was measured from the aerial photos using a mean gully cross section of 0 2635 m2 determined in study area 1 the average eroded volume is 1 89 m3 ha 1 in six months for study area 1 0 86 m3 ha 1 in six months for area 2 1 44 m3 ha 1 in six months for area 3 and 2 37 m3 ha 1 in six months for area 4 according to the correction factor c these mean ephemeral gully erosion volumes have to be increased by 44 per cent the ephemeral gully erosion rates based on high altitude stereo aerial photos correspond well with the results of other surveys carried out in the belgian loess belt copyright 1999 john wiley sons ltd

modeling the effect of abrupt ocean circulation change on marine reservoir age abstract radiocarbon surface reservoir age is required for precise dating of marine organisms although often assumed constant changes in atmospheric radiocarbon content ocean circulation and ocean mixing imprint changes on this quantity the spatial and temporal variations of marine surface and bottom reservoir ages in response to a shutdown and subsequent recovery of atlantic meridional overturning circulation moc are analyzed using a cost efficient three dimensional ocean circulation model generally surface reservoir age changes are limited to the atlantic ocean with a reduction of about 100 yr after the moc shutdown followed by a slow increase and a peak at the time of moc resumption parameter sensitivity studies with respect to the roles of gas exchange diffusivity and north atlantic ice cover show that ice cover has the largest effect on the transient evolution of surface reservoir age during the shutdown our model results agree well with a recent reconstruction of surface reservoir age changes during the younger dryas when we reduce the rate of gas exchange in the model and include a parametrization of seasonal ice cover in the north atlantic

characteristics and controlling factors of bank gullies in two semi arid mediterranean environments abstract bank gullies are gullies that are formed due to a height drop caused by a terrace or a river bank which develop by headward retreat in erodible hillslopes this study aims i to investigate the morphology of actively eroding bank gullies i e geometrical characteristics resulting from past erosion and active erosion processes shaping the gully and ii to find relationships with environmental site characteristics such as topographical parameters material properties and climate the ultimate goal is to identify the most important controlling factors of past and present bank gully erosion fifty five active bank gullies formed in different lithologies by various erosion processes have been selected in the guadalentin basin and the surroundings of guadix southeast spain for each bank gully site geometrical and topographical parameters of both the channel and the drainage basin were measured erosion features indicating activity at the gully head such as tension cracks plunge pools undercutting fluting piping and rill or sheet erosion on sloping side walls were mapped and samples were taken from distinct lithological layers that were considered to influence the type and intensity of erosion processes a relationship could be shown between the presence of piping and fluting and a number of material characteristics including particle size distribution dispersion behaviour and electrical conductivity on the other hand lithology appeared not to be a differentiating factor on gully development in the long run as expressed by the total eroded volume v this parameter was most strongly related to the drainage basin area in which the entire bank gully had been formed a o explaining 66 of the variance the relationship is v 1 75 a o 0 59 no significant difference was found between regression lines through sub datasets of different soil textural classes finally multiple regression was used to include both topographical parameters and material characteristics in an explanatory and or predictive equation for the total eroded bank gully volume the results of the analyses using the entire dataset including the sites in the guadalentin as well as in the guadix area have been compared with the results for the separate study areas differences are not only related to topographical and lithological characteristics but may also be the consequence of a different climate in the two areas

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

a method for dendrochronological assessment of medium term gully erosion rates abstract a method based on dendrochronology to estimate gully erosion rates was developed as an alternative of traditional methods for assessing medium term gully retreat rates such as field monitoring of headcuts or aerial photo interpretation of gully retreat the method makes use of trees or parts of a tree affected by gully erosion revealing information on the history of the erosion process by datable deviations of their normal growth pattern hence defined as datable objects these include roots exposed by erosion browsing scars made by ungulates on exposed roots or on above ground parts of fallen trees exposed and dead root ends root suckers stems branches and leading shoots of fallen trees and a sequence of trees within a gully the method is based on the differentiation between three main conditions depending on the relation between the dynamics of the datable object part of the tree and the development of the gully the first condition implies that the datable object was created before erosion of the gully volume to be dated e g exposed tree roots according to the second condition the datable object developed as an immediate consequence of the erosion event e g growth reactions of a fallen tree the third condition implies that the datable object was created some time after the erosion event took place e g trees colonising the gully bed each principle has consequences for the accuracy and the correct interpretation of the estimated erosion rate i e whether the true erosion rate is underestimated exact or overestimated in spite of methodological limitations and dendrochronological dating problems the method was successfully applied in southeast spain conservative estimations of gully head retreat rate resulted in an average medium term 3 46 years value of 6 m3 year 1 n 9 for gully sidewall processes the average minimum erosion rate per unit sidewall length amounted 0 1 m3 year 1 m 1 n 9 a strong correlation was found between the headcut retreat rate vm ortho m3 year 1 and the drainage basin area a m2 of the gullies expressed by vm ortho 0 02a0 57 r2 0 93 n 9 comparing the findings from this study with those obtained by short term headcut retreat monitoring suggests a high reliability of the estimated retreat rates supporting the applicability of the developed dendrochronological method

main types of soil mass failure and characteristics of their impact factors in the yuanmou valley china abstract gully erosion is a dominant process causing soil loss in the yuanmou valley of yunnan province china soil mass failure is a common process involved in gully development the development of the gully and the occurrence of mass failure are interdependent and mutually promotive but mass failure types have not been very well understood in this study we identify the main types of soil mass failure and the characteristics of their impact factors in the yuanmou valley a detailed field survey was conducted in may 2010 in a representative area of the studied region and selected soil parameters were measured in the field and laboratory results showed that there are four different soil mass failure types falling sliding exfoliating and toppling each having unique characteristics of geology topography soil and climate examination of these characteristics indicates that the occurrence of mass failure is controlled by four factors 1 the typical geological structure of the yuanmou group represented by alternating layers of sand and clay 2 the different terrain and landforms 3 the different gully development stages and 4 the particular soil properties under special weather conditions including a dry hot climate with distinct wet and dry seasons

doline probability map using logistic regression and gis technology in the central ebro basin spain in the surroundings of zaragoza karstification processes are especially intense in covered karst areas where fluvial terraces lie directly on tertiary evaporites since the beginning of quaternary these processes have lead to the development of collapse and subsidence dolines with a wide range of sizes which have significant economic impacts to reduce economic impact and increase safety a regional analysis of this phenomenon is needed for spatial management therefore a probability map of dolines was developed using logistic regression and geographic information system gis techniques this paper covers the selection of input data manipulation of data using the gis technology and the use of logistic regression to generate a doline probability map the primary variable in the doline development in this area is geomorphology represented by the location of endorheic areas and different terrace levels secondary variables are the presence of irrigation and the water table gradient

the role of some site geochemical processes in the development and stabilisation of three badland sites in almeria southern spain samples of both surface and subsurface soils were collected on various surfaces in three badland areas of differing ages tabernas vera and mocatan in almeria province southern spain data were explored with the aim of identifying any diagnostic geochemical relationships between site ec ph sediment size and sar which might constitute typical signatures for site materials with some success data for the three sites are further used to explore the hypothesis that changes in site geochemistry through time are involved in badland stabilisation it was found that 1 the physico chemical properties of the three sites can be differentiated by the functional relationship between ec and sar and this may represent a useful tool in characterising sites where piping predominates 2 there is some equivocal evidence that sediment size distribution may play an additional role in site diagnosis and evolution and 3 surfaces appear to lose sodium over time the suggestion being that sodium is either progressively buffered by calcium during leaching or exchanges with hydrogen on the cation exchange sites under a vegetation cover since other research suggests that smectite can also relocate down the profile on some marl sites reducing hydraulic conductivity and suppressing pipes we argue that the surface at tabernas may be capable of long term autostabilisation in which piping intensity progressively reduces however this possibility really applies only to fine grained densely structured materials and evidence from the silty triassic rich unit in the mocatan basin suggests that without a high clay content piping may be expected to increase through time from this standpoint contemporary badland morphology at mocatan does not represent an early stage of the forms seen in vera and tabernas

spatial distribution of gully head activity and sediment supply along an ephemeral channel in a mediterranean environment abstract in this study we examined the factors that control the spatial distribution of bank gully heads along a reach of an ephemeral river rambla salada in an area threatened by desertification in southeast spain the activity of 458 gully heads was assessed in the field by pre defined criteria such as sharp edges presence of a plunge pool tension cracks recent deposited sediments flow marks and vegetation re growth the results showed that land use has a significant impact on bank gully head activity recent land use changes involving the extension of almond cultivation appears to intensify bank gully head activity also lithology has a clear impact on the bank gully extension it was further investigated whether the gully heads were important sediment sources that contributed to reservoir sedimentation the density of very active bank gully heads along the study reach was one per 17 m of channel length average annual retreat volumes were derived from measurements at 46 active gully heads 4 0 m3 y 1 by selecting all the channel sections in the catchment of the puentes reservoir with a similar pattern of bank gullies using aerial photographs an estimate of basin wide sediment production of bank gully heads was established it was estimated that the retreat of active bank gully heads alone in the 12 760 ha study area representing 12 of the total catchment area of the puentes reservoir produced 6 of the sediment filling up the reservoir considering that the sediment is also derived from other sources such as channel walls channel beds and hillslopes the overall conclusion is that bank gully expansion in southeast spain is a major point source of sediment and therefore a major process of land degradation

evaluation of a gully headcut retreat model using multitemporal aerial photographs and digital elevation models 1 a large fraction of soil erosion in temperate climate systems proceeds from gully headcut growth processes nevertheless headcut retreat is not well understood few erosion models include gully headcut growth processes and none of the existing headcut retreat models have been tested against long term retreat rate estimates in this work the headcut retreat resulting from plunge pool erosion in the channel hillslope integrated landscape development child model is calibrated and compared to long term evolution measurements of six gullies at the bardenas reales northeast spain the headcut retreat module of child was calibrated by adjusting the shape factor parameter to fit the observed retreat and volumetric soil loss of one gully during a 36 year period using reported and collected field data to parameterize the rest of the model to test the calibrated model estimates by child were compared to observations of headcut retreat from five other neighboring gullies the differences in volumetric soil loss rates between the simulations and observations were less than 0 05 m3 yr 1 on average with standard deviations smaller than 0 35 m3 yr 1 these results are the first evaluation of the headcut retreat module implemented in child with a field data set these results also show the usefulness of the model as a tool for simulating long term volumetric gully evolution due to plunge pool erosion

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

storms channel changes and a sediment budget for an urban suburban stream difficult run virginia usa abstract determining erosion and deposition rates in urban suburban settings and how these processes are affected by large storms is important to understanding geomorphic processes in these landscapes sediment yields in the suburban and urban upper difficult run are among the highest ever recorded in the chesapeake bay watershed ranging from 161 to 376 mg km2 y erosion and deposition of streambanks channel bed and bars and deposition of floodplains were monitored between 1 march 2010 and 18 january 2013 in upper difficult run virginia usa we documented the effects of two large storms tropical storm lee september 2011 a 100 year event and super storm sandy october 2012 a 5 year event on channel erosion and deposition variability in erosion and deposition rates for all geomorphic features temporally and spatially are important conclusions of this study tropical storm lee was an erosive event where erosion occurred on 82 of all streambanks and where 88 of streambanks that were aggrading before tropical storm lee became erosional statistical analysis indicated that drainage area explains linear changes cm y in eroding streambanks and that channel top width explains cross sectional area changes cm2 y in eroding streambanks and floodplain deposition mm y a quasi sediment budget constructed for the study period using the streambanks channel bed channel bars and floodplain measurements underestimated the measured suspended sediment load by 61 2130 mg y underestimation of the sediment load may be caused by measurement errors and to contributions from upland sediment sources which were not measured but estimated at 36 of the gross input of sediment eroding streambanks contributed 42 of the gross input of sediment and accounted for 70 of the measured suspended sediment load similar to other urban watersheds the large percentage of impervious area in difficult run and direct runoff of precipitation leads to increased streamflow and streambank erosion this study emphasizes the importance of streambanks in urban suburban sediment budgets but also suggests that other sediment sources such as upland sources which were not measured in this study can be an important source of sediment

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

development of gullies and sediment production in the black soil region of northeastern china abstract gully erosion is an important environmental hazard in the black soil region of northeastern china it is a primary sediment source in the region which needs appropriate soil conservation practices gully incision in rolling hills typical of this region was monitored using real time kinematic gps to assess the rates of gully development and the resultant sediment production from 2002 to 2005 gully heads in the study area retreated between 15 4 and 33 5 m giving an average retreat rate of 8 4 m yr 1 field measurements showed that total sediment production due to gully erosion during the three years ranged between 257 and 1854 m3 yr 1 which is equivalent to 326 to 2355 t yr 1 with gully head retreat accounting for 0 to 21 7 4 4 in average the sediment delivery ratio was especially high during the summer rainy season 56 in average sediment production by ephemeral gullies and permanent gullies was 1 5 times greater than that from surface erosion gully heads retreated faster in the spring freeze thaw period than in the summer the stage of gully development could be identified based on short term changes in the gully erosion rate

a sapping erosion susceptibility model for the southern cantabrian range north spain abstract a susceptibility model of sapping related depressions has been produced by analysing the statistical relationship between the location of depressions and topographical variables sapping erosion plays an important role in the growth of gullies developed over poorly consolidated quartzite conglomerates in the northern sector of the duero tertiary basin the cantabrian mountain range of spain gullies topsoil subsidence depressions related to sapping processes and shallow slides have been identified over sandy soils in an area of 37 km 2 this area underwent major changes in land use during the 20th century leading to the expansion of gully erosion processes on the surface depressions of several meters in diameter caused by internal erosion related to sapping processes can be identified using the topographical location of these topsoil depressions and several topographical variables 14 discriminate functions were derived to provide information about the influence of topography on the development of sapping erosion processes the functions have accuracy levels varying from 56 to 81 the most accurate function was regionalized by means of a geographical information system and was used to complete a land classification method which is based on the mahalanobis distance to the multivariate average centroid of a sapping erosion form group the classification of this model allows the identification of areas with different relative probabilities of sapping processes and the resultant growth of gullies

modelling the occurrence of gullies in rangelands of southwest spain gully erosion has been recognized as an important soil degradation process in rangelands of southwest spain in this paper a relatively new data mining technique called multivariate adaptive regression splines mars was applied to construct a model capable of predicting the location of gullies a large database was used to support the model composed of a target variable presence or absence of gullies and 36 independent variables related to topography lithology soils rainfall land use and vegetation cover the performance of the model was evaluated using the receiver operating characteristic roc curve for five external datasets the model had high predictive power with values for the area under the roc curve of the external validation datasets varying from 0 75 to 0 98 1 0 being perfect prediction the most important variables explaining the spatial distribution of gullies were lithology and soil type finally the model was compiled and implemented into a geographical information system to obtain maps of susceptible areas for gully erosion these maps show that approximately 7 of the study area presents favourable conditions for the development of gullies the results demonstrate that mars constitutes a valuable model in geomorphic research and could also be a useful tool for assessing the impacts of changing climate and land use on gully erosion copyright 2009 john wiley sons ltd

comparison of gully erosion estimates using airborne and ground based lidar on santa cruz island california abstract gully erosion removes comparatively large volumes of soil from small areas it is often difficult to quantify the loss of soil because the footprint of individual gullies is too small to be captured by most generally available digital elevation models dems such as the usgs national elevation dataset airborne lidar light detection and ranging has the potential to provide the required data density but an even newer class of ground based sensors may provide better local resolution at lower cost in this study we compared digital elevation models produced by airborne and ground based lidar systems with ground based geomorphic and geodetic survey data to determine their utility in quantifying volumetric soil loss due to gully erosion in a heavily degraded watershed 7 55 10 2 km 2 on southwestern santa cruz island in southern california volumetric estimates of the eroded sediment were produced by comparing the lidar derived dems of the gully system to a modeled pre erosion surface average point densities were significantly higher for the ground based lidar system and provided more detailed information however its limited scanning footprint and side looking orientation presented serious challenges in collecting continuous data from deeply incised gullies making the airborne system preferable for this type of investigation and likely for most applications where heavy topographic shadowing is prevalent

assessment of sidewall erosion in large gullies using multi temporal dems and logistic regression analysis although in the last decades gully erosion has been a thriving research field few studies have specifically addressed the contribution and location of sidewall erosion processes in gullies in this paper sidewall erosion in some large gullies in a mediterranean area anoia penedes ne spain is mapped and assessed for two time intervals 1975 1995 and 1995 2002 using detailed digital elevation models derived from aerial photographs at a scale of 1 5000 to 1 7000 logistic regression analysis is applied to compute the probability of occurrence of gully sidewall erosion from terrain variables the results confirm the complex nature of sidewall processes whose intensity is most probably related to rainfall characteristics prolonged wet soil conditions in the period 1995 2002 together with the large and high intensity rainfall of an extreme event occurred on 10th june 2000 help to explain the different sediment production rates 16 0 4 mg ha 1 year 1 in 1975 1995 and 83 6 3 mg ha 1 year 1 in 1995 2002 the logistic regression analysis revealed that gully wall slope angle was the main factor controlling gully sidewall failure in gully walls with high slope angles tension crack development is the main process promoting wall collapse the application of the logistic regression model showed a high overall accuracy 87 but over 50 of commission and omission errors for the class of interest sidewall erosion in agreement with the variance explained by the model

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

geomorphic change detection using historic maps and dem differencing the temporal dimension of geospatial analysis abstract the ability to develop spatially distributed models of topographic change is presenting new capabilities in geomorphic research high resolution maps of elevation change indicate locations processes and rates of geomorphic change and provide a means of calibrating temporal simulation models methods of geomorphic change detection gcd based on gridded models may be applied to a wide range of time periods by utilizing cartometric remote sensing or ground based topographic survey data to measure volumetric change advantages and limitations of historical dem reconstruction methods are reviewed with a focus on coupling them with subsequent dems to construct dems of difference dod which can be created by subtracting one elevation model from another to map erosion deposition and volumetric change the period of dod analysis can be extended to several decades if accurate historical dems can be generated by extracting topographic data from historical data and selecting areas where geomorphic change has been substantial the challenge is to recognize and minimize uncertainties in data that are particularly elusive with early topographic data this paper reviews potential sources of error in digitized topographic maps and dems although the paper is primarily a review of methods three brief examples are presented at the end to demonstrate gcd using dods constructed from data extending over periods ranging from 70 to 90 years

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis

experimental study on the development of collapse of overhanging layers of gully in yuanmou valley china the collapse of overhanging layers of the heads and sidewalls of gullies accelerates gully development thus the development features of the collapse of overhanging layers must be understood in this study the process of collapse of overhanging layers in man made soil bodies containing different soil layers was investigated by flow scouring experiments a soil body composed of a lower sandy layer and an upper layer of clay soil was evaluated and a field soil profile was modelled in a test tank with an open side the results revealed that the occurrence of the collapse of overhanging layers could be attributed to the development of a scour hole in the open side the greater the flow rate the lower the proportion of on wall runoff on wall runoff played a more important role in the development of scour holes than off wall runoff the shape of scour holes formed under different flow conditions was similar also the scour hole is not apparently related to the flow rate implicating that the collapse is more dependent on rainfall runoff time rather than rainfall runoff intensity in the studied region this is substantially different from other soil erosion types that are closely related to rainfall intensity moreover the maximum length s l and height s h of the scour holes increased gradually with accumulated flow and scouring time in addition the height of the hanging soil body h d gradually decreased and a linear relationship between sl and hd was observed h d 0 359 s l 117 3 r 2 0 861 p 0 003 after the seventh scour test the scour hole triggered the collapse of the upper clay layer the cantilever model was modified to predict the stability of the overhanging soil body it provided a satisfactory explanation of the static balance of the weight of the soil as well as the tensile strength after the seventh scour test the measured and predicted threshold values of h d s l and t c were nearly equal and a stable balance state was attained however when a 10 cm tension crack appeared in the overhanging soil body a stable balance state was obtained during the sixth scour test c 2013 elsevier b v all rights reserved