reach scale sediment transfers an evaluation of two morphological budgeting approaches this paper compares two approaches used to derive measures of annual sediment transfers within a 1 km long piedmont reach of the gravel bed river coquet in northumberland northern england the techniques utilize i channel planform and cross section surveys based on a theodolite electronic distance measurement edm survey of 21 monumented channel cross sections and channel and gravel bar margins and ii theodolite edm survey generating a series of x y z coordinates from which digital elevation models dems of the reach were constructed calculating the difference between dem surfaces provided a measure of volumetric change between surveys carried out during the spring of 1999 and 2000 the use of kriging in dem generation and differencing permits computation of estimate variances and confidence intervals for sediment transfer error analysis validating the dems using surveyed cross sections indicated a mean error between surveyed and dem generated cross sections of around twice the value of the d50 of the surface sediment in the reach comparison of sediment volumes derived from the two approaches suggests that compared with the dem method monumented cross sections underestimate the magnitude of volumetric changes that occur within the reach the cross section approach relies on a simplistic integration of the volumes whereas dem differencing provides an estimate at a resolution under the control of the analyst furthermore the cross section approach does not permit a reliable estimate of the uncertainty of the volumes calculated in addition the dem methodology based on the morphological unit scale provides an explicit identification of spatial patterns of erosion and deposition a feature that cross section based approaches may fail to include copyright 2003 john wiley sons ltd

laboratory experiments simulating the geomorphic response to tectonic uplift 1 we present the results of an experimental study of topography dynamics under conditions of constant precipitation and uplift rate the experiment is designed to develop a complete drainage network by the growth and propagation of erosion instabilities in response to tectonic perturbations the quantitative analysis of topographic evolution is made possible by using telemetric lasers that perform elevation measurements at an excellent level of precision we focus our study on the effect of initial surface organization and of uplift rate on both the transient dynamics and the steady state forms of topography we show that the transient phase is strongly dependent on the initial internally drained area which is found to decrease exponentially with time the topography always reaches a steady state whose mean elevation depends linearly on uplift rate with a strictly positive value when uplift is zero steady state surfaces are characterized by a well defined slope area power law with a constant exponent of 0 12 and an amplitude that depends linearly on uplift rate with a strictly positive value when uplift is zero these results are consistent with a stream power law erosion model that includes a nonnegligible threshold for particle detachment uncertainty regarding the sediment transport length is resolved by calibrating the transient dynamics with a surface process model reappraising published results on the linear dependency between mean elevation or relief and denudation rate we suggest that an erosion threshold is worth considering for large scale systems

developments in monitoring and modelling small scale river bed topography recent research in fluvial geomorphology has emphasized the spatially distributed feedbacks amongst river channel topography flow hydraulics and sediment transport although understanding of the behaviour of dynamic river channels has been increased markedly through detailed within channel process studies less attention has been given to the accurate monitoring and terrain modelling of river channel form using three dimensional measurements however such information is useful in two distinct senses firstly it is one of the necessary boundary conditions for a physically based deterministic modelling approach in which three dimensional topography and river discharge drive within channel flow hydraulics and ultimately spatial patterns of erosion and deposition and therefore channel change secondly research has shown that an alternative means of estimating the medium term bedload transport rate can be based upon monitoring spatial patterns of erosion and deposition within the river channel this paper presents a detailed assessment of the distributed monitoring and terrain modelling of river bed topography using a technique that combines rigorous analytical photogrammetry with rapid ground survey the availability of increasingly sophisticated terrain modelling packages developed for civil engineering application allows the representation of topographic information as a landform surface intercomparison of landform surfaces allows visualization and quantification of spatial patterns of erosion and deposition a detailed assessment is undertaken of the quality of the morphological information acquired this allow some general comments to be made concerning the use of more traditional methods to monitor and represent small scale river channel morphology

towards a protocol for laser scanning in fluvial geomorphology advances in spatial analytical software allow digital elevation models dems to be produced which accurately represent landform surface variability and offer an important opportunity to measure and monitor morphological change and sediment transfer across a variety of spatial scales many of the techniques presently employed aerial lidar edm theodolites gps photogrammetry suffer coverage or resolution limitations resulting in a trade off between spatial coverage and morphologic detail captured this issue is particularly important when rates of spatial and temporal change are considered for fluvial systems this paper describes the field and processing techniques required for oblique laser scanning to acquire 0 01 m resolution digital elevation data of an upland reach of the river wharfe in the uk the study site is variable with rapidly changing morphology diverse vegetation and the presence of water and these are evaluated with respect to laser data accuracy scan location frequency and distance are discussed with reference to survey accuracy and efficiency and a field protocol is proposed scan data cloud merging was achieved with a high degree of precision sub centimetre and positional data are shown to be very accurate for exposed surfaces vegetation and water decrease the accuracy as the laser pulse is often prevented from reaching the ground surface or is not returned copyright 2006 john wiley sons ltd

surface velocity and mass balance of ice streams d and e west antarctica over 75 000 surface velocity measurements are extracted from sequential satellite imagery of ice streams d and e to reveal a complex pattern of flow not apparent from previous measurements horizontal and vertical strain rates calculated from surface velocity indicate that the bed experiences larger basal shear where the surface of these ice streams is rougher ten airborne radar profiles and one surface based radar profile of ice thickness make possible the calculation of mass balance for longitudinal sections of each ice stream improved data collection methods increase data density substantially reducing random errors in velocity however systematic errors continue to limit the ability of the flux differencing technique used here to resolve local variations in mass balance nevertheless significant local variations in mass balance are revealed while overall ice streams d and e are in approximate equilibrium an earlier estimate of the net mass balance for ice stream d is improved

sediment removal during an extreme summer storm muskwa river northeastern british columbia extreme summer storms in northwestern canada can produce large changes in river channels and sediment loads in a short time these infrequent events cause effects downstream that persist over several years photogrammetric measurement was made of sediment removed during a 36 h storm flood in june 1977 on the muskwa river near its confluence with the fort nelson river the approximate volume of material removed was 1 398 000 m3 the sediment load added to the fort nelson river was between 2 3 and 2 4 million tonnes photogrammetric measurement techniques combined with field samples can provide adequate information on sediment removed during severe storms keywords erosion sediment photogrammetry storms floods

through water terrestrial laser scanning of gravel beds at the patch scale acquiring high resolution topographic data of natural gravel surfaces is technically demanding in locations where the bed is not exposed at low water stages often the most geomorphologically active surfaces are permanently submerged gravel beds are spatially variable and measurement of their detailed structure and particle sizes is essential for understanding the interaction of bed roughness with near bed flow hydraulics sediment entrainment transport and deposition processes as well as providing insights into the ecological responses to these processes this paper presents patch scale laboratory and field experiments to demonstrate that through water terrestrial laser scanning tls has the potential to provide high resolution digital elevation models of submerged gravel beds with enough detail to depict individual grains and small scale forms the resulting point cloud data requires correction for refraction before registration preliminary validation shows that patch scale tls through 200 mm of water introduces a mean error of less than 5 mm under ideal conditions point precision is not adversely affected by the water column the resulting dems can be embedded seamlessly within larger sub aerial reach scale surveys and can be acquired alongside flow measurements to examine the effects of three dimensional surface geometry on turbulent flow fields and their interaction with instream ecology dynamics copyright 2011 john wiley sons ltd

on the link between external forcings and slope instabilities in the piton de la fournaise summit crater reunion island we have analyzed the impact of different forcings such as rain and seismicity on slope instabilites on an active volcano for this we compiled a catalog of the locations and volumes of rockfalls in the piton de la fournaise crater using seismic records we validated it by comparing the locations and volumes to those deduced from photogrammetric data we analyzed 10 477 rockfalls spanning the period 2014 to 2016 this period corresponds to the renewal of volcanic activity after a 41 month rest our analysis reveals that renewed eruptive activity has unsettled the crater edges external forcings such as rain and seismicity are shown to potentially increase the number and the volume of rockfalls with a stronger impact on the volume preeruptive seismicity seems to be the main triggering factor for the largest volumes with a delay of one to several days rain alone does not seem to trigger especially large rockfalls we infer that repetitive vibrations from the many seismic events combined with the action of rain induce crack or slip growth in highly fractured or granular materials leading to the collapse of large volumes regarding their spatial distribution before an eruption the largest rockfalls seem to migrate toward the location of magma extrusion

drainage density slope angle and relative basin position in japanese bare lands from high resolution dems abstract relationships between drainage density and slope angle for three bare lands in japan were analyzed with special attention to channels at early erosion stages and channels in a badland type terrain two of the bare lands were caused by volcanic eruptions 1 or 30 40 years ago and the other one is a landslide scar formed more than 100 years ago raster digital elevation models dems with a 1 m resolution and ortho aerial photos were generated using digital photogrammetry to enable detailed stream net extraction and topographic analyses data for drainage density slope angle and relative height for 88 subwatersheds were obtained from the dems and derived stream nets the relationship between drainage density and slope angle for each subwatershed can be divided into two types downward sloping and convex upward although previous studies suggested that drainage density positively correlates with slope angle if overland flow is dominant this correlation seldom occurs in the study areas the two types of drainage density slope angle relationships correspond to differing channelization stages that reflect the extension and integration of existing channels as well as the formation of new low order streams in response to base level lowering the location of subwatersheds within each study area seems to play a major role in determining the stages of channel development and in turn the types of drainage density slope angle relationships

influence of survey strategy and interpolation model on dem quality accurate characterisation of morphology is critical to many studies in the field of geomorphology particularly those dealing with changes over time digital elevation models dems are commonly used to represent morphology in three dimensions the quality of the dem is largely a function of the accuracy of individual survey points field survey strategy and the method of interpolation recommendations concerning field survey strategy and appropriate methods of interpolation are currently lacking furthermore the majority of studies to date consider error to be uniform across a surface this study quantifies survey strategy and interpolation error for a gravel bar on the river nent blagill cumbria uk five sampling strategies were compared i cross section ii bar outline only iii bar and chute outline iv bar and chute outline with spot heights and v aerial lidar equivalent derived from degraded terrestrial laser scan tls data digital elevation models were then produced using five different common interpolation algorithms each resultant dem was differentiated from a terrestrial laser scan of the gravel bar surface in order to define the spatial distribution of vertical and volumetric error overall triangulation with linear interpolation tin or point kriging appeared to provide the best interpolators for the bar surface lowest error on average was found for the simulated aerial lidar survey strategy regardless of interpolation technique however comparably low errors were also found for the bar chute spot sampling strategy when tins or point kriging was used as the interpolator the magnitude of the errors between survey strategy exceeded those found between interpolation technique for a specific survey strategy strong relationships between local surface topographic variation as defined by the standard deviation of vertical elevations in a 0 2 m diameter moving window and dem errors were also found with much greater errors found at slope breaks such as bank edges a series of curves are presented that demonstrate these relationships for each interpolation and survey strategy the simulated aerial lidar data set displayed the lowest errors across the flatter surfaces however sharp slope breaks are better modelled by the morphologically based survey strategy the curves presented have general application to spatially distributed data of river beds and may be applied to standard deviation grids to predict spatial error within a surface depending upon sampling strategy and interpolation algorithm

reducing elevation roundoff errors in digital elevation models abstract a smoothing algorithm is presented for the removal of roundoff error inherent in almost all digital elevation data elevation adjustments are kept within the tolerance of roundoff error so that the resulting terrain model is not over smoothed after smoothing the digital elevation model is more suitable for use with algorithms that seek to automatically delineate stream networks and basins of a watershed the algorithm is specifically intended for use with gridded data and is particularly effective when used with elevations originating from the 7 5 min quadrangles provided by the united states geological survey

studies of the grounding line location on ice streams d and e antarctica landsat thematic mapper tm images were used prior to the 1991 92 field season to infer the position of the grounding line at the mouths of ice streams d and e west antarctica our field plan for mass balance studies was based on this determination and thus the imagery played a central role in both the scientific and logistics planning a radar profile along the flow direction was made across the inferred grounding line at one location and ice thickness measurements together with surface surveying enable us to compare the hydrostatic surface and the actual topography to determine the point at which the ice becomes grounded the profile transits from floating to grounded ice at the same location as the grounding line inferred from the imagery changes in the radar echo strength also occur at this location giving further support to this interpretation tilt studies of the ice flexure caused by tidal variations at locations on either side of this grounding point give additional evidence that grounding is occurring close by the combination of these three measurements thus confirms the grounding line location derived from the satellite imagery and supports the use of this technique to determine grounding

the development of an automated correction procedure for digital photogrammetry for the study of wide shallow gravel bed rivers this paper develops an automated correction procedure for dealing with point errors associated with through water photogrammetry for application in the study of clear water shallow gravel bed rivers the procedure involves combining digital photogrammetry and image analysis techniques to i correct for the effects of refraction at an air water interface and ii eliminate and reinterpolate points where the bed has not been seen the correction procedure was applied to raw digital elevation models dems generated using digital photogrammetry from 1 3000 scale aerial photography of a small reach of the north ashburton river new zealand the accuracy of corrected and uncorrected dems is evaluated using an independent data set a measure of geomorphological usefulness as well as dem external reliability is obtained from calculations of water depth distributions and mean bed level results show that digital photogrammetry used in conjunction with image analysis techniques can successfully be used for extracting high resolution dems of gravel river beds in exposed areas errors are small and random tending to cancel out over large numbers of points where water is shallow and following correction point elevation errors are statistically no different from those for exposed zones in deeper water despite an improvement following application of the correction procedure elevation errors scale with water depth the geomorphological potential of photogrammetric survey of large gravel river beds is demonstrated by the ease and accuracy of calculations of water depth distribution important for the assessment of a river s ecological and recreational characteristics and mean bed level important for the calculation of reach scale sediment volumes copyright 2000 john wiley sons ltd

quantifying submerged fluvial topography using hyperspatial resolution uas imagery and structure from motion photogrammetry quantifying the topography of rivers and their associated bedforms has been a fundamental concern of fluvial geomorphology for decades such data acquired at high temporal and spatial resolutions are increasingly in demand for process oriented investigations of flow hydraulics sediment dynamics and in stream habitat in these riverine environments the most challenging region for topographic measurement is the wetted submerged channel generally dry bed topography and submerged bathymetry are measured using different methods and technology this adds to the costs logistical challenges and data processing requirements of comprehensive river surveys however some technologies are capable of measuring the submerged topography through water photogrammetry and bathymetric lidar are capable of reasonably accurate measurements of channel beds in clear water whilst the cost of bathymetric lidar remains high and its resolution relatively coarse the recent developments in photogrammetry using structure from motion sfm algorithms promise a fundamental shift in the accessibility of topographic data for a wide range of settings here we present results demonstrating the potential of so called sfm photogrammetry for quantifying both exposed and submerged fluvial topography at the mesohabitat scale we show that imagery acquired from a rotary winged unmanned aerial system uas can be processed in order to produce digital elevation models dems with hyperspatial resolutions c 0 02 m for two different river systems over channel lengths of 50 100 m errors in submerged areas range from 0 016 m to 0 089 m which can be reduced to between 0 008 m and 0 053 m with the application of a simple refraction correction this work therefore demonstrates the potential of uas platforms and sfm photogrammetry as a single technique for surveying fluvial topography at the mesoscale defined as lengths of channel from c 10 m to a few hundred metres this article is protected by copyright all rights reserved

west antarctic ice streams draining into the ross ice shelf configuration and mass balance extensive airborne radar soundings closely tied to accurately located ground stations made over a portion of the west antarctic inland ice sheet and the ross ice shelf have enabled us to map the boundaries of the ice streams and their flow bands on the ross ice shelf the surfaces of the active ice streams a and b are heavily crevassed but there are no visible crevasses on ice stream c however the existence of numerous crevasses at a depth of about 35 m implies that ice stream c ceased to be active about 250 years ago there is a complex zone at the head of ice stream b that suggests that ice stream b is currently widening and advancing toward the interior of the ice sheet the grounding lines between the inland ice and the ice shelf were mapped from the surface elevations using the requirement of hydrostatic balance and the character of the radar echoes the inland ice is more extensive than previously mapped and includes a large weakly grounded area downstream of ice streams a and b where the surface elevations are barely above hydrostatic equilibrium crary ice rise extends 70 km upstream of the previously mapped position to relate surface elevation data from satellite observations to sea level three geoidal models were tested we conclude that the gem 10c model is the best of the three for this section of antarctica a new map of surface elevation shows deep marginal troughs and longitudinal ridges along ice streams a and b but not on ice stream c whose surface contours show signs of stagnation ice stream c shows a strongly positive and ice stream b a significantly negative net balance rate ice streams a and d also show a significantly negative net flux whereas ice streams e and f do not the overall net balance of this part of the west antarctic inland ice is suggestively negative 23 15 km3 yr 1 from the measured flux into the ross ice shelf and previous measurements we calculate an average basal melt rate from beneath the ice shelf of 0 12 0 03 m yr 1

gravel transport and morphological change in braided sunwapta river alberta canada the relation between morphological change and patterns of variation in bedload transport rate in braided streams was observed by repeated daily topographic surveys over a 25 day study period in a 60 m reach of the proglacial sunwapta river alberta canada there are two major periods of morphological change each lasting several days and each involving the complete destruction and reconstruction of bar complexes bar complex destruction was caused by redirection of the flow and by downstream extension of the confluence scour zone upstream reconstruction involved accretion of unit bars on bar head flank and tail and in one case was initiated by disection of a large lobate unit bar high rates of sediment movement measured from net scour and fill of the cross sections coincided with these morphological changes sediment was supplied from both bed and bank erosion and patterns and distances of transfer were highly variable rates of transport estimated by matching upstream erosional volumes with downstream deposition were much greater than those estimated from either a step length approach or a sediment budget measurements of scour and fill and observations of morphological change indicate that step lengths virtual transport distances were typically 40 100m during a diurnal discharge cycle shorter step lengths occurred when transfer was confined to a single anabranch and longer steps involved channel changes at the scale of the entire reach sediment budgeting was used to describe the spatial patterns of sediment transport associated with the morphological changes and to estimate minimum daily reach averaged transport rates mean bedload transport rates correlate with discharge but with considerable scatter the largest deviations from the mean relation can be tied to phases of channel incision bank erosion scour hole migration bar deposition and channel filling apparently controlled by changes and fluctuations in sediment supply from upstream independent of discharge these are interpreted as field evidence of autopulses or macropulses in bedload transport previously observed only in laboratory models of braided streams

assessing the ability of airborne lidar to map river bathymetry airborne bathymetric lidar was collected for 220 river kilometers in the yakima and trinity river basins in the united states concomitant with the aerial data collection ground surveys of the river bed were performed in both basins we assess the quality of the bathymetric lidar survey from the perspective of its application toward creating accurate precise and complete streambed topography for numerical modeling and geomorphic assessment measurement error is evaluated with respect to ground surveys for magnitude and spatial variation analysis of variance statistics indicate that residuals from two independent ground surveys in similar locations do not come from the same population and that mean errors at different study locations also come from different populations systematic error indicates a consistent bias in the data and random error falls within values of expected precision

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

uas based remote sensing of fluvial change following an extreme flood event the effects of large floods on river morphology are variable and poorly understood in this study we apply multi temporal datasets collected with small unmanned aircraft systems uass to analyze three dimensional morphodynamic changes associated with an extreme flood event that occurred from 19 to 23 june 2013 on the elbow river alberta we documented reach scale spatial patterns of erosion and deposition using high resolution 4 5 cm pixel orthoimagery and digital elevation models dems produced from photogrammetry significant bank erosion and channel widening occurred with an average elevation change of 0 24 m the channel pattern was reorganized and overall elevation variation increased as the channel adjusted to full mobilization of most of the bed surface sediments to test the extent to which geomorphic changes can be predicted from initial conditions we compared shear stresses from a two dimensional hydrodynamic model of peak discharge to critical shear stresses for bed surface sediment sizes we found no relation between modeled normalized shear stresses and patterns of scour and fill confirming the complex nature of sediment mobilization and flux in high magnitude events however comparing modeled peak flows through the pre and post flood topography showed that the flood resulted in an adjustment that contributes to overall stability with lower percentages of bed area below thresholds for full mobility in the post flood geomorphic configuration overall this work highlights the potential of uas based remote sensing for measuring three dimensional changes in fluvial settings and provides a detailed analysis of potential relationships between flood forces and geomorphic change copyright 2015 john wiley sons ltd

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

response of the ha ha river to the flood of july 1996 in the saguenay region of quebec large scale avulsion in a glaciated valley modifications to valley form due to extreme flooding in the lower 34 km of the ha ha river were analyzed heavy regional precipitation in july 1996 triggered extreme runoff and the catastrophic drainage of ha ha lake producing discharges of 1100 m3 s 8 times the 100 year flood dominant valley modifications revealed by comparing preflood and postflood topographies derived photogrammetrically were related to two large scale avulsions in particular a deep retrogressive incision which bypassed the 30 m high perron falls exporting 6 106 m3 of glacial stratified drift from a 2 km section of valley and producing massive sedimentation in the reach downstream reconstructed maximum flow power values support the existence of a 300 w m2 threshold for major scouring of the alluvial valley bottom the evidence highlights the potential for massive scour and fill and reorganization of the long profile with potentially catastrophic effects on infrastructure during extreme floods in glaciated valley settings

spatial variability in river sediments and its link with river channel geometry 1 this study explores the link between spatial variability within fluvial sedimentary strata and river channel geometry this link is then used to determine the macrodispersion coefficients for solute transport in groundwater flow in river deposits in doing that we combine concepts from sedimentology geostatistics and the stochastic lagrangian theory of subsurface transport it is proposed to analyze the spatial variability of river sediments in terms of transition probabilities the transition probabilities can be determined from the averages and variances of the lengths of stratasets and their volumetric fractions using concepts developed by carle and fogg 1996 and ritzi 2000 strataset length scales are shown to correlate well with the geometry of the river channel and its bed forms and can be determined indirectly from aerial photogrammetry and more directly through surface ground penetrating radar surveys stratal dimensions can also be related using lagrangian transport analysis to macrodispersivity of subsurface transport this allows relationships between the geometry of river channels and subsurface transport parameters of associated fluvial deposits for demonstration the longitudinal macrodispersivity in a compound bar deposit in the gravelly braided sagavanirktok river was investigated

variability of basal melt beneath the pine island glacier ice shelf west antarctica observations from satellite and airborne platforms are combined with model calculations to infer the nature and efficiency of basal melting of the pine island glacier ice shelf west antarctica by ocean waters satellite imagery shows surface features that suggest ice shelf wide changes to the ocean s influence on the ice shelf as the grounding line retreated longitudinal profiles of ice surface and bottom elevations are analyzed to reveal a spatially dependent pattern of basal melt with an annual melt flux of 40 5 gt a 1 one profile captures a persistent set of surface waves that correlates with quasi annual variations of atmospheric forcing of amundsen sea circulation patterns establishing a direct connection between atmospheric variability and sub ice shelf melting ice surface troughs are hydrostatically compensated by ice bottom voids up to 150 m deep voids form dynamically at the grounding line triggered by enhanced melting when warmer than average water arrives subsequent enlargement of the voids is thermally inefficient 4 or less compared with an overall melting efficiency beneath the ice shelf of 22 residual warm water is believed to cause three persistent polynyas at the ice shelf front seen in landsat imagery landsat thermal imagery confirms the occurrence of warm water at the same locations

terrestrial structure from motion spatial error analysis of roughness and morphology structure from motion sfm photogrammetry is rapidly becoming a key tool for morphological characterisation and change detection of the earth surface this paper demonstrates the use of terrestrial structure from motion tsfm photogrammetry to acquire morphology and roughness data at the reach scale in an upland gravel bed river we quantify 1 spatially distributed error in tsfm derived digital elevation models dems and 2 identify differences in roughness populations acquired from tsfm photogrammetry versus tls we identify an association between local topographic variation and error in the tsfm dem on flatter surfaces e g bar and terrace surfaces the difference between the tsfm and tls dems are generally less than 0 1 m however in areas of high topographic variability 0 4 m such as berm or terrace edges differences between the tsfm and tls dems can be up to 1 m our results suggest that grain roughness estimates from the tsfm point cloud generate values twice those derived from the tls point cloud on coarse berm areas and up to four fold those derived from the tls point cloud over finer gravel bar surfaces this finding has implications when using sfm data to derive roughness metrics for hydrodynamic modelling despite the use of standard filtering procedures noise pertains in the sfm dem and the time required for its reduction might partially outweigh the survey efficiency using sfm therefore caution is needed when sfm surveys are employed for the assessment of surface roughness at a reach scale

effects of riparian vegetation on topographic change during a large flood event rio puerco new mexico usa 1 the spatial distribution of riparian vegetation can strongly influence the geomorphic evolution of dryland rivers during large floods we present the results of an airborne lidar differencing study that quantifies the topographic change that occurred along a 12 km reach of the lower rio puerco new mexico during an extreme event in 2006 extensive erosion of the channel banks took place immediately upstream of the study area where tamarisk and sandbar willow had been removed within the densely vegetated study reach we measure a net volumetric change of 578 050 490 000 m3 with 88 3 of the total aggradation occurring along the floodplain and channel and 76 7 of the erosion focusing on the vertical valley walls the sediment derived from the devegetated reach deposited within the first 3 6 km of the study area with depth decaying exponentially with distance downstream elsewhere floodplain sediments were primarily sourced from the erosion of valley walls superimposed on this pattern are the effects of vegetation and valley morphology on sediment transport sediment thickness is seen to be uniform among sandbar willows and highly variable within tamarisk groves these reach scale patterns of sedimentation observed in the lidar differencing likely reflect complex interactions of vegetation flow and sediment at the scale of patches to individual plants

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

close range digital photogrammetric analysis of experimental drainage basin evolution brasington james smart r m a 2003 close range digital photogrammetric analysis of experimental drainage basin evolution earth surface processes and landforms 28 3 pp 231 247 rae2008 special issue the generation of high quality topographic data for hydrology and geomorphology

monitoring channel responses to flood events of low to moderate magnitudes in a bedrock dominated river using morphological budgeting by terrestrial laser scanning abstract changes to channel morphology reflect geomorphic work by flood events of differing magnitude and frequency advances in remote sensing and digital terrain processing now allow for sophisticated analysis of spatial and temporal changes in erosion and deposition although the morphological budgeting approach using digital elevation models of difference has been widely applied to track volume estimation of changes to erosion and deposition over time appraisals of geomorphic effectiveness in high energy confined and partly confined channels are still lacking this study applied terrestrial laser scanning to monitor three reaches of the liwu river a bedrock dominated river in eastern taiwan from 2009 to 2012 to investigate channel responses to flood events of low to moderate magnitude and appraise their geomorphic effectiveness variability in geomorphic effectiveness reflected valley confinement and the composition configuration of geomorphic units on the channel bed annual low magnitude flood events reworked gravel and sand deposits creating local scour and fill

the timing and magnitude of coarse sediment transport events within an upland temperate gravel bed river this paper describes the application of a new instrument to continuously measure bedload transport an impact sensor to a 72 km2 test catchment in the yorkshire dales northern england data from a network of impact sensors are linked to repeat surveys of channel morphological response to get a better understanding of the conditions that lead to sediment generation and transfer results suggest certain areas of the catchment act as key sediment sources at the annual time scale with material being quickly delivered to the lower parts of the catchment along the steep bedrock channel sediment transfer within the tributaries occurs in significantly smaller magnitudes than within the main channel but it moves more frequently and at different times of the year with transfer rates being strongly conditioned by larger scale valley geomorphology the lower 5 6 km reach sees a significant reduction in gradient and a widening of the valley this permits significant accumulation within the channel which has persisted for many years this lower reach is very sensitive to changes in sediment supply and there is good agreement between changes in bedload transport data and the surveyed channel response these observations have major implications for how river management projects should be developed in upland environments especially those where large scale geomorphological controls have a major impact upon the sediment transfer process evidence suggests that where river management restricts lateral movement of the channel and transfer of sediment into floodplain storage changes in sediment supply can lead to areas of severe accumulation acceleration of bank erosion and exacerbated flood risk

volcanic winter and accelerated glaciation following the toba super eruption the eruption of toba in sumatra 73 500 years ago was the largest known explosive volcanic event in the late quaternary1 it could have lofted about 1015 g each of fine ash and sulphur gases to heights of 27 37 km creating dense stratospheric dust and aerosol clouds here we present model calculations that investigate the possible climatic effects of the volcanic cloud the increase in atmospheric opacity might have produced a volcanic winter 2 a brief pronounced regional and perhaps hemispheric cooling caused by the volcanic dust followed by a few years with maximum estimated annual hemispheric surface temperature decreases of 3 5 c the eruption occurred during the stage 5a 4 transition of the oxygen isotope record a time of rapid ice growth and falling sea level3 we suggest that the toba eruption may have greatly accelerated the shift to glacial conditions that was already underway by inducing perennial snow cover and increased sea ice extent at sensitive northern latitudes as the onset of climate change may have helped to trigger the eruption itself4 we propose that the toba event may exemplify a more general climate volcano feedback mechanism

remote sensing of glacier and ice sheet grounding lines a review abstract the precise positioning and long term monitoring of the grounding line forming the boundary between grounded and floating ice of marine ice sheets and tidewater glaciers is critical for assessing ice sheet glacier stability ice sheet glacier mass balance calculations and numerical ice modelling however mapping of the grounding line is a challenging task since it is a subglacial and transient feature remote sensing techniques do not map the grounding line directly but locate surface features in the grounding zone that serve as proxies for the true grounding line position the large variety of methods products and publications as well as an inconsistent use of terminology additionally complicate the topic we present the first detailed review of existing remote sensing techniques and data for grounding line mapping benefits and limitations of the different techniques and data sources are discussed and illustrated with examples we identify a present tradeoff between accuracy and both spatial coverage and temporal resolution of the derived grounding line products rather new methods like sentinel 1 sar synthetic aperture radar differential range offset tracking drot and pseudo crossover radar altimetry pcra offer the potential for recent measurements and to fill gaps in some areas nevertheless there is a high demand of new spaceborne radar sensors that provide time series of very short repeat pass data to enable regular grounding line monitoring with most accurate differential sar interferometry dinsar on a continental scale

lake sedimentation in the mackenzie delta nwt spatial variation in lake sedimentation within the mackenzie delta was documented and total lake sedimentation over the past 30 years was estimated by classifying via aerial photography the flooding characteristics of a complete transect of lakes about 2600 lakes across the upper subaerial delta plain then selecting representative samples of lakes 81 lakes from the transect and a random sample of lakes from a second transect 7 lakes across the lower subaerial plain for direct measurement of sedimentation rates the depth corresponding to the 1963 sediment layer was obtained from a sediment core from each of these lakes by sampling the core at frequent depth intervals to identify the peak in 137 cs caesium 137 content lake sediment bulk densities as obtained from the cores averaged 931 kg m 3 a value lower than reported in previous studies using mean bulk density above each 137 cs peak and the depth of the 137 cs peak mean lake sedimentation for different lake types varied between 1 19 kg m 2 yr and 5 34 kg m 2 yr with a decrease in sedimentation as lake sill elevation increased values for the lower delta transect averaged 1 36 kg m 2 yr by combining relationships between sedimentation and lake type with a classification of lake types total sedimentation across the upper delta transect is estimated as 8 2 mt yr and 0 8 mt yr for the lower delta these values are lower than previously reported primarily because they are derived from lower bulk density values of the total upper delta sedimentation 17 occurs in high closure lakes 53 in low closure lakes and 30 in no closure lakes lake sedimentation is higher in the middle channel segment of the upper delta transect 44 of total sedimentation across the transect than in the east channel 25 or peel channel 32 segments

cdw photogrammetry of low relief fluvial features accuracy and implications for reach scale sediment budgeting terrestrial photogrammetry enables rapid survey to be undertaken in the fluvial environment a crucial factor when assessing highly dynamic features in addition it permits the generation of terrain surfaces at a level of detail which given equal time constraints in the field far exceeds the detail permitted by conventional tacheometric survey this study details the levels of accuracy that can be achieved using the rolleimetric close range digital workstation cdw photogrammetric survey technique on a variety of low relief fluvial geomorphic features lateral point and mid channel bars ranging from 10 m 2 to 100 m 2 the cdw software processes image data from an array of photographs and establishes a set of three dimensional co ordinates for the photographed object the accuracies achieved across all bar surfaces were well within the resolution defined by the maximum size of the gravel on the bar surface mean errors were between 0 026 and 0 057 m the use of cdw photogrammetry does not require experienced personnel however care must be taken during the survey to minimize edge effects and to ensure that target density is sufficient to produce a terrain model that is accurate to within the limits of the surface sediment size guidance on target density as a function of terrain roughness is given to aid the user a methodology is suggested that will allow cdw to be incorporated into sediment budgeting techniques improving the level of achievable accuracy 1998 john wiley sons ltd

evaluating short term morphological changes in a gravel bed braided river using terrestrial laser scanner abstract braided rivers are dynamic and complex environments shaped by the balance of the flow and sediment regimes and by the influence of the riparian vegetation and disturbances such as floods in particular the balance between sediment supply and transport capacity can determine the morphological evolution of a river for instance aggrading and widening trends are distinctive of reaches where sediment supply is higher than transport capacity in contrast incising and narrowing tendencies are dominant the aim of the present study is to analyze the short term morphological dynamics and the processes of erosion and sediment deposition along a small reach of a relatively unimpacted gravel bed braided river tagliamento river northeast italy using a terrestrial laser scanner tls the study area is around 23 ha and has been surveyed before after two periods with relevant flood events two of which were higher than the bankfull level and occurred between september 2010 and september 2011 the very high point clouds density allowed us to derive three high resolution digital elevation models dems with 0 125 0 125 m pixel size scan data cloud merging was achieved with an overall high degree of accuracy and resolution subcentimeter topographic data were more accurate for exposed surfaces than those collected in wet areas a detailed net of dgps control points allowed us to verify the high quality of the dems derived from the surveys rmse of about 5 cm two dems of difference dod were computed revealing different and consistent episodes of erosion and deposition within the analyzed area and changes in morphology of channel and bars could also be detected such as bar edge accretion and bank erosion demonstrating a strong dynamicity of the tagliamento river moreover a very detailed estimation of the surface roughness in the study area has been carried out permitting a large scale analysis of the roughness values distribution the results of the analysis on the tls collected data show that along a river with a high natural character i e tagliamento river the dynamic processes are also common during low magnitude events

discharge and sediment supply controls on erosion and deposition in a dynamic alluvial channel research on dynamic alluvial channels has recognised the influence on river channel change of both discharge and sediment supply although it has proved difficult to measure the latter this paper presents the first accurate data from a dynamic alluvial channel that describe the interrelated effect on channel morphological change of both discharge and sediment supply variations over different timescales reliable information on the spatial patterns of erosion and deposition were obtained using combined photogrammetry and tacheometric survey of the meltwater stream of a glacierised catchment over a 5 week period over the full time period the morphological evidence suggested the passage of a wave of sediment counter intuitively the period of aggradation was associated with increasing diurnal peak and base flow discharge magnitude while degradation occurred during a period of steady peak diurnal discharge this suggests that the channel change was controlled by variation in upstream sediment supply over a shorter timescale information on diurnal changes in morphology reveals that although discharge was responsible for some aspects of channel change this was modified by the effects of upstream sediment supply consideration of the spatial patterns of erosion and deposition at the within reach scale reinforces this point with spatial aspects of morphological change being driven by discharge and sediment supply fluctuations but modified by spatial feedbacks associated with internal channel morphology the implications of these findings for fluvial geomorphology in general are considered

a new procedure for gridding elevation and stream line data with automatic removal of spurious pits abstract a morphological approach to the interpolation of regular grid digital elevation models dems from surface specific elevation data points and selected stream lines is described the approach has given rise to a computationally efficient interpolation procedure which couples the minimization of a terrain specific roughness penalty with an automatic drainage enforcement algorithm the drainage enforcement algorithm removes spurious sinks or pits yielding dems which may be used to advantage in hydrological process studies the drainage enforcement algorithm has also been found to significantly increase the accuracy of dems interpolated from sparse but well chosen surface specific elevation data moreover it facilitates the detection of errors in elevation data that would not be detected by more conventional statistical means and forms a sound physical basis for cartographic generalization

tracking landslide displacements by multi temporal dtms a combined aerial stereophotogrammetric and lidar approach in western belgium abstract the study of small and or slow reactivations of landslides requires describing their displacements over decades which may be done with accurate multi temporal digital terrain models dtms we applied aerial stereophotogrammetry to build the historical topographies of old deep seated landslides close to oudenaarde in the flemish ardennes west belgium at different dates three precise aerotriangulations 1996 1973 1952 were carried out after capturing the ground data manually from the stereomodels 2 m resolution dtms were interpolated by kriging with a final accuracy ranging between 45 cm and 65 cm another dtm was interpolated with an accuracy of 30 cm from airborne lidar data acquired in 2002 differential dtms were produced to identify vertical and horizontal ground displacements over the 1952 2002 period we describe here the kinematics of a particularly active landslide with a well documented recent activity until the first half of the 90 s little activity of the landslide was detected in february 1995 a reactivation event caused vertical displacements of up to 7 m along the main scarp and up to 4 m in the accumulation zone horizontal movements of 4 to 10 m are also inferred these topographic changes correspond to reactivated slip along the rotational basal shear surface in the same time the main scarp retreated by up to 20 m the reactivation favoured by several anthropogenic factors e g loading impeded drainage was triggered by intense rainfall between 1996 and 2002 the observed displacements correspond to limited scarp retreat 4 m and compaction of the slipped mass partly enhanced by artificial drainage

the use of a landscape simulator in the validation of the siberia landscape evolution model transient landforms siberia is a physically based model for the geomorphic evolution of landforms it is essential that the siberia model be tested or validated against controlled landform development previous studies have demonstrated that siberia is able to simulate declining equilibrium landforms and in this paper we examine siberia s ability to simulate landforms as they evolve to their declining equilibrium form these landscapes are termed transient landforms landscapes generated by siberia were compared to those produced by a physical model experimental model landforms at stages of evolution comparison of the experimental landscapes with the simulated landscapes using total mass hypsometric curve width function cumulative area distribution and area slope demonstrate that siberia can simulate the experimental model landscape during development i e transient landscapes copyright 2002 john wiley sons ltd

advances in the continuous monitoring of erosion and deposition dynamics developments and applications of the new peep 3t system abstract in most episodic erosion and deposition systems knowledge of the timing of geomorphological change in relation to fluctuations in the driving forces is crucial to strong erosion process inference and model building validation and development a challenge for geomorphology however is that few studies have focused on geomorphological event structure timing magnitude frequency and duration of individual erosion and deposition events in relation to applied stresses because of the absence of key monitoring methodologies this paper therefore a presents full details of a new erosion and deposition measurement system peep 3t developed from the photo electronic erosion pin sensor in five key areas including the addition of nocturnal monitoring through the integration of the thermal consonance timing tct concept to produce a continuous sensing system b presents novel high resolution datasets from the redesigned peep 3t system for river bank system of the rivers nidd and wharfe northern england uk and c comments on their potential for wider application throughout geomorphology to address these key measurement challenges relative to manual methods of erosion and deposition quantification continuous peep 3t methodologies increase the temporal resolution of erosion deposition event detection by more than three orders of magnitude better than 1 second resolution if required and this facility can significantly enhance process inference results show that river banks are highly dynamic thermally and respond quickly to radiation inputs data on bank retreat timing fixed with peep 3t tct evidence confirmed that they were significantly delayed up to 55 h after flood peaks one event occurred 13 h after emergence from the flow this suggests that mass failure processes rather than fluid entrainment dominated the system it is also shown how by integrating turbidity instrumentation with tct ideas linkages between sediment supply and sediment flux can be forged at event timescales and a lack of sediment exhaustion was evident here five challenges for wider geomorphological process investigation are discussed this event based dynamics approach based on continuous monitoring methodologies appears to have considerable wider potential for stronger process inference and model testing and validation in many areas of geomorphology

methodological sensitivity of morphometric estimates of coarse fluvial sediment transport abstract the estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest the revival of the morphological method reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high precision high resolution topographic monitoring remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys however while photogrammetry presents the opportunity to acquire survey data over large areas data precision and accuracy particularly in the vertical dimension are lower than in traditional ground survey methods this paper presents results of recent research in which digital elevation models dems have been developed for a reach of a large braided gravel bed river in scotland using both digital photogrammetry and high resolution rtk gps ground surveys a statistical level of change detection is assessed by comparing surfaces with independent check points the methodological sensitivity of the annual channel sediment budget 1999 2000 to the threshold is presented results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing moderate precision dems of channel topography rmse 0 21 m the remaining errors imply significant limits on reliable change detection which lead to important information losses tests at a 95 confidence interval for change detection show that over 60 of channel deposition and 40 of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements this bias reflects the difficulty of detecting the topographic signature of widespread but shallow deposition on bar tops

reconstruction of subgrid scale topographic variability and its effect upon the spatial structure of three dimensional river flow a new approach to describing the associated topography at different scales in computational fluid dynamic applications to gravel bed rivers was developed surveyed topographic data were interpolated using geostatistical methods into different spatial discretizations and grain size data were used with fractal methods to reconstruct the microtopography at scales finer than the measurement subgrid scale the combination of both scales of topography was then used to construct the spatial discretization of a three dimensional finite volume computational fluid dynamics cfd scheme where the topography was included using a mass flux scaling approach the method was applied and tested on a 15 m stretch of solfatara creek wyoming united states using spatially distributed elevation and grain size data model runs were undertaken for each topography using a steady state solution this paper evaluates the impact of the model spatial discretization and additional reconstructed variability upon the spatial structure of predicted three dimensional flow the paper shows how microtopography modifies the spatial structure of predicted flow at scales finer than measurement scale in terms of variability whereas the characteristic scale of predicted flow is determined by the cfd scale changes in microtopography modify the predicted mean velocity value by 3 6 for a mesh resolution of 5 cm whereas a change in the computational scale modifies model results by 60 the paper also points out how the spatial variability of predicted velocities is determined by the topographic complexity at different scales of the input topographic model

an evaluation of the effectiveness of low cost uavs and structure from motion for geomorphic change detection abstract the measurement of topography and of topographic change is essential for the study of many geomorphic processes in recent years structure from motion sfm techniques applied to photographs taken by camera equipped unmanned aerial vehicles uavs has become a powerful new tool for the generation of high resolution topography the variety of available uav systems continues to increase rapidly but it is not clear whether increased uav sophistication translates into improved quality of the calculated topography to evaluate the lower end of the uav spectrum a simple low cost uav was deployed to calculate high resolution topography in the daan river gorge in western taiwan a site with a complicated 3d morphology and a wide range of surface types making it a challenging site for topographic measurement terrestrial lidar surveys were conducted in parallel with uav surveys in both june and november 2014 enabling an assessment of the reliability of the uav survey to detect geomorphic changes in the range of 30 cm to several meters a further uav survey was conducted in june 2015 in order to quantify changes resulting from the 2015 spring monsoon to evaluate the accuracy of the uav derived topography it was compared to terrestrial lidar data collected during the same survey period using the cloud to cloud comparison algorithm m3c2 the uav generated point clouds match the lidar point clouds well with rms errors of 30 40 cm however the accuracy of the sfm point clouds depends strongly on the characteristics of the surface being considered with vegetation water and small scale texture causing inaccuracies the lidar and sfm data yield similar maps of change from june to november 2014 with the same areas of geomorphic change detected by both methods the sfm generated change map for november 2014 to june 2015 indicates that the 2015 spring monsoon caused erosion throughout the gorge and highlights the importance of event driven erosion in the daan river the results suggest that even very basic uavs can yield data suitable for measuring geomorphic change on the scale of a channel reach

quantification of braided river channel change using archival digital image analysis historical archives of grey scale river channel imagery are extensive here we present and test a methodology to extract detailed quantitative topographic date from such imagery of sand bed rivers extracting elevation information from rivers is difficult as they are characterized by a low relative relief less than 4 m the area of interest may be spatially extensive e g active channel widths 500 m in large braided rivers the rate of change of surface elevation is generally low except in the vicinity of individual channel banks where the rate of change is very high there is the complication that comes from innundation and there may be an added complication caused by blockage of the field of view by vegetation here we couple archival photogrammetric techniques with image processing methods and test these for quantification of sand bed braided river dynamics illustrated for a 500 m wide 3 km long reach of the spouth sasketchewan river canada digitial photogrammetry was used to quantify dry areas and water edge elevations a methodology was then used to calibrate the special signature of inundated areas by combining established two media digital photogrammetric methods and image matching this allowed determination of detailed depth maps for inundated area and when combined with dry area data creation of depths detectable from sequential digital elevation models the result was a series of elevation models that demonstrate the potential for acquiring detailed and precise elevation data from any historical aerial imagery of rivers without needing associated calibration data provided that imagery is of the necessary scale to capture the features of interest we use these data to highlight several aspects of channel change on the south saskatchewan river including bar movement bank erosion and channel infilling

remote sensing of stream depths with hydraulically assisted bathymetry hab models this article introduces a technique for using a combination of remote sensing imagery and open channel flow principles to estimate depths for each pixel in an imaged river this technique which we term hydraulically assisted bathymetry hab uses a combination of local stream gage information on discharge image brightness data and manning based estimates of stream resistance to calculate water depth the hab technique does not require ground truth depth information at the time of flight hab can be accomplished with multispectral or hyperspectral data and therefore can be applied over entire watersheds using standard high spatial resolution satellite or aerial images hab also has the potential to be applied retroactively to historic imagery allowing researchers to map temporal changes in depth we present two versions of the technique hab 1 and hab 2 hab 1 is based primarily on the geometry discharge and velocity relationships of river channels manning s equation assuming average depth approximates the hydraulic radius the discharge equation and the assumption that the frequency distribution of depths within a cross section approximates that of a triangle are combined with discharge data from a local station width measurements from imagery and slope measurements from maps to estimate minimum average and maximum depths at a multiple cross sections these depths are assigned to pixels of maximum average and minimum brightness within the cross sections to develop a brightness depth relation to estimate depths throughout the remainder of the river hab 2 is similar to hab 1 in operation but the assumption that the distribution of depths approximates that of a triangle is replaced by an optical beer lambert law of light absorbance in this case the flow equations and the optical equations are used to iteratively scale the river pixel values until their depths produce a discharge that matches that of a nearby gage r 2 values for measured depths versus depths estimated by hab 1 and hab 2 are 0 51 and 0 77 respectively in the relatively simple brazos river texas r 2 values for hab 1 and hab 2 are 0 46 and 0 26 respectively in the lamar river a complex mountain river system in yellowstone national park although the r 2 values are moderate depth maps and crosssections derived from the hab techniques are consistent with typical stream geomorphology patterns and provide far greater

step by step error assessment in braided river sediment budget using airborne lidar data abstract sequential airborne lidar surveys were used to reconstruct the sediment budget of a 7 km long braided river channel in southeastern france following a 14 year return period flood and to improve its accuracy step by step data processing involved i surface matching of the sequential point clouds ii spatially distributed propagation of uncertainty based on surface conditions of the channel and iii water depth subtraction from the digital elevation models based on water depths measured in the field the respective influence of each processing step on sediment budget computation was systematically documented this showed that surface matching and water depth subtraction both have a considerable effect on the net sediment budget although dem of difference thresholding based on uncertainty analysis on absolute elevation values had a smaller effect on the sediment budget this step is crucial for the production of a comprehensive map of channel deformations a large independent data set of rtk gps checkpoints was used to control the quality of the lidar altimetry the results showed that high density 7 9 points m 2 airborne lidar surveys can provide a very high level of detection of elevation changes on the exposed surfaces of the channel with a 95 confidence interval level of detection between 19 and 30 cm change detection from lidar data revealed that 54 of the pre flood active channel was reworked by the flood the braided channel pattern was highly disturbed by the flood owing to the occurrence of several channel avulsions

use of a landscape simulator in the validation of the siberia catchment evolution model declining equilibrium landforms this paper presents a study to test the ability of the current generation of landscape evolution models to correctly predict landscape form from measured erosion processes landscapes generated by the siberia landscape evolution model were compared to experimental model landscapes in declining equilibrium the model simulations were compared using geomorphologically and hydrologically significant parameters comparisons of the simulated landscapes with the experimental landscapes were carried out using the hypsometric curve width function cumulative area distribution and area slope relationship these comparisons demonstrate that siberia can correctly simulate the experimental model landscape at declining equilibrium the simulation showed sensitivity to the spatial distribution of the rainfall particularly with respect to hypsometry using the correct measured distribution of rainfall was necessary rather than using a spatially uniform rainfall distribution the results also highlighted the importance of digital terrain map dtm error in deriving geomorphic statistics the observed landform had a consistently larger width function than the simulation only when the simulations were corrupted with elevation errors with statistical properties of the errors in the experimental landscape dtm as measured by photogrammetry did the observed and simulated width functions match

quantification of bedform dynamics and bedload sediment flux in sandy braided rivers from airborne and satellite imagery images from specially commissioned aeroplane sorties manned aerial vehicle mav repeat unmanned aerial vehicle uav surveys and planet cubesat satellites are used to quantify dune and bar dynamics in the sandy braided south saskatchewan river canada structure from motion sfm techniques and application of a depth brightness model are used to produce a series of digital surface models dsms at low and near bankfull flows a number of technical and image processing challenges are described that arise from the application of sfm in dry and submerged environments a model for best practice is presented and analysis suggests a depth brightness model approach can represent the different scales of bedforms present in sandy braided rivers with low turbidity and shallow 2 m deep water the aerial imagery is used to quantify the spatial distribution of unit bar and dune migration rate in an 18 km reach and three 1 km long reaches respectively dune and unit bar migration rates are highly variable in response to local variations in planform morphology sediment transport rates for dunes and unit bars obtained by integrating migration rates from uav with the volume of sediment moved from dsms using mav imagery show near equivalence in sediment flux hence reach based sediment transport rate estimates can be derived from unit bar data alone moreover it is shown that reasonable estimates of sediment transport rate can be made using just unit bar migration rates as measured from 2d imagery including from satellite images so long as informed assumptions are made regarding average bar shape and height with recent availability of frequent repeat satellite imagery and the ease of undertaking repeat mav and uav surveys for the first time it may be possible to provide global estimates of bedload sediment flux for large or inaccessible low turbidity rivers that currently have sparse information on bedload sediment transport rates

the potential of 3d gully monitoring with gis using high resolution aerial photography and a digital photogrammetry system although gully erosion is generally considered a major process of land degradation its contribution to total soil loss by erosion has recently been a subject of much discussion the lack of adequate methods for the documentation and monitoring of gullies resulted in the shortage of quantitative data therefore a high resolution remote sensing system for aerial surveys by blimp or kite has been developed which meets spatial and temporal image resolutions required for short term gully monitoring the objective of this paper is to examine the potential of a method using non metric digital photogrammetry and gis for gully surface modelling and monitoring two bank gullies representing different morphological types of gullies v shaped and u shaped were chosen from a dataset of gully systems in semi arid spain the considerable relief energy and complex topography of the gullies in a natural vegetated landscape were found to be a challenge to digital photogrammetric techniques introducing errors which inhibit fully automated dem generation using a hybrid method combining stereomatching for mass point extraction with manual 3d editing and digitizing high resolution dems 5 and 7 5 cm pixel size were created for the study sites gis analysis of the dems for different monitoring periods 2 to 4 years allowed the computation of gully area and volume as well as their changes with an accuracy and detail sufficient to represent the geomorphological forms and processes involved furthermore the spatially continuous survey of the entire form offered the possibility of distinguishing different zones of activity both at the gully rim and within the gully interior identifying patterns of erosion and deposition which indicate the limited use of headcut retreat rates for the assessment of sediment production on a short term basis

integrating structure from motion photogrammetry into rock weathering field methodologies despite recent rapid advances in the field of structure from motion sfm photogrammetry the use of high resolution data to investigate small scale processes is a relatively underdeveloped field in particular rock weathering is rarely investigated using this suite of techniques this research uses a combination of traditional non destructive rock weathering measurement techniques rock surface hardness and sfm to map deterioration and loss of cohesion of the surface using 3 dimensional data the results are used to interpret weathering behaviour across two different lithologies present on the site namely shale and limestone this new approach is tested on seven sites in longyearbyen svalbard where active weathering of a rock surface was measured after 13 years of exposure to extreme temperature regimes and snow cover the surface loss was quantified with sfm and combined with rock surface hardness measurement distributions extrapolated in gis the combined results are used here to quantify the difference in response of both lithologies to these extreme temperatures this research demonstrates the potential for further integration of sfm in rock weathering research and other small scale geomorphological investigations in particular in difficult field conditions where portability of field equipment is paramount

effects of vertical resolution and map scale of digital elevation models on geomorphological parameters used in hydrology the advent of digital elevation models dems has made it possible to objectively extract calculate and store geomorphological parameters for hydrological modelling at several scales for a grid based dem the threshold area used to extract the channel network is analogous to the scale of the map produced in addition to the map scale the effects of the vertical resolution of the dem on some frequently used geomorphological parameters in hydrology are examined using high resolution dems of two natural and two artificial catchments the vertical resolution was varied between 1 cm and 1 m the most common vertical resolution of dems at a fixed map scale the mean absolute percentage error in the geomorphological parameters caused by a decrease in vertical resolution is within the range 0 5 for the medium sized catchments and 0 10 for the small catchments studied although it is true that a change in vertical resolution may cause a change in the individual pixel slope area and topographic index area slope particularly in low relief terrain their cumulative distributions do not show any significant change with the vertical resolution the shape of the normalized width function is not very sensitive to the vertical resolution and the map scale for small catchments order change may occur at different map scales for the different vertical resolution dems of the same catchment causing a significant change in order related parameters such as horton ratios it is suggested that the vertical resolution of the dem of a catchment be considered satisfactory for most hydrological applications if the ratio of the average drop per pixel and vertical resolution is greater than unity this ratio criterion could be used to define the minimum pixel area for reliable channel network definition for any given vertical resolution the minimum pixel area places a lower bound on the horizontal resolution with which a channel network can be extracted from a dem these results could potentially be used to assess the adequacy for hydrological purposes of existing and proposed digital elevation databases

dryland anabranching river morphodynamics rio capilla salar de uyuni bolivia the dryland anabranching river rio capilla is characterized by nonvegetated and vegetated reaches with prominent channel morphology to identify the morphodynamics of such dryland anabranching systems and their controls we investigated the rio capilla of the southern altiplano plateau using high resolution satellite imagery and field measurements comparison of high resolution satellite data reveals that erosion exceeds deposition for the main channel accompanied by changes in channel planform such as meander and channel morphology on site surveys combined with high precision gps and high resolution satellite imagery show that channels are characterized by shallowness and poor development of levees the study area of the rio capilla is divided into two zones of different slopes zone 1 with a high slope and zone 2 with a low slope zone 1 has a relatively straight main channel with few anabranches and grass covered banks that are stable despite the high gradient whereas zone 2 is typified by more anabranches with nonvegetated banks and the main channel experiences prominent bank accretion and erosion excavations show that point bar deposits are fine sand dominated in two reaches and that river banks primarily consist of silt and clay the limited vegetation cover and abundance of desiccation cracks and macropores make the river bank more erodible leading to pronounced lateral migration in this low gradient dryland river system shallow channels and poor development of levees in combination with in channel accretionary benches result in frequent overbank flooding which results in a high density of crevasse splays over unconsolidated river banks and accretionary benches connection of headcuts and crevasse channels together with lateral migration and chute channels and reactivation of partially abandoned meanders produces an anabranching pattern in such dryland river systems

landscape reorganization under changing climatic forcing results from an experimental landscape understanding how landscapes respond to climate dynamics in terms of macroscale average topographic features and microscale landform reorganization is of interest both for deciphering past climates from today s landscapes and for predicting future landscapes in view of recent climatic trends although several studies have addressed macro scale response only a few have focused on quantifying smaller scale basin reorganization to that goal a series of controlled laboratory experiments were conducted where a self organized complete drainage network emerged under constant precipitation and uplift dynamics once steady state was achieved the landscape was subjected to a fivefold increase in precipitation transient state throughout the evolution high resolution spatiotemporal topographic data in the form of digital elevation models were collected the steady state landscape was shown to possess three distinct geomorphic regimes unchannelized hillslopes debris dominated channels and fluvially dominated channels during transient state landscape reorganization was observed to be driven by hillslopes via accelerated erosion ridge lowering channel widening and reduction of basin relief as opposed to channel base level reduction quantitative metrics on which these conclusions were based included slope area curve correlation analysis of spatial and temporal elevation increments and wavelet spectral analysis of the evolving landscapes our results highlight that landscape reorganization in response to increased precipitation seems to follow an arrow of scale major elevation change initiates at the hillslope scale driving erosional regime change at intermediate scales and further cascading to geomorphic changes at the channel scale as time evolves

short term geomorphic analysis in a disturbed fluvial environment by fusion of lidar colour bathymetry and dgps surveys abstract objective estimating river s underwater bed elevations is a necessary but challenging task the objective of this study is to develop a revised approach to generate accurate and detailed digital terrain models dtms of a river reach by merging lidar data for the dry area with water depth indirectly derived from aerial imagery for wet areas methods this approach was applied along three sub reaches of the brenta river italy before and after two major flood events a regression model relating water depth and intensity of the three colour bands derived from aerial photos was implemented more than 2400 in channel depth calibration points were taken using a differential global positioning system dgps along a wide range of underwater bed forms results the resulting dtms closely matched the field surveyed bed surface and allowed to assess that a 10 year recurrence interval flood generated a predominance of erosion processes erosion dominated in the upper part of the study segment 104 082 m3 whereas a near equilibrium is featured on the lower reach 45 232 m3 the dtms allowed the detection of processes such as riffle pool downstream migration and the progressive scour of a pool located near a rip rap conclusion the presented approach provides an adequate topographical description of the river bed to explore channel adjustments due to flood events practice combining colour bathymetry and dgps surveys proved to represent a useful tool for many fluvial engineering ecology and management purposes implications the proposed approach represents a valuable tool for river topography description river management ecology and restoration purposes when bathymetric data are not available

creep buckling of ice shelves and the formation of pressure rollers pour mieux comprendre le phenomene des vagues de pression on etudie la stabilite des shelfs aux perturbations des champs moyens de contrainte et de vitesse de deformation l analyse des perturbations est basee sur la loi de fluage de glen on montre que si les vitesses de deformation sont suffisamment compressives on peut s attendre a voir apparaitre des ondulations les extensions laterales ont un effet stabilisateur et les vagues de pression ont plus de chance de se former lorsqu elles existent

a physical explanation for an observed area slope elevation relationship for catchments with declining relief a general relationship between the contributing area slope and mean elevation of catchments with relief declining after a tectonic uplift event is presented this relationship is based on the continuity equation for runoff and erosion processes in the catchment the key hypothesis underlying this relationship is that as a catchment declines the nondimensionalized catchment approaches a constant form this hypothesis is verified for computer simulated catchments the area slope elevation relationship covers several cases catchments declining toward a peneplain catchments declining from a high slope dynamic equilibrium resulting from a high rate of tectonic uplift to a low slope one resulting from a lower rate of tectonic uplift and catchments declining from an elevated initial condition as for example in the decline of a mine spoil heap a previously published relationship between slope and area for catchments in dynamic equilibrium and based on runoff and erosion physics is shown to be a special case of this general relationship the new area slope elevation relationship is compared with data from simulated catchments and a field catchment it is thus shown that for declining catchments the area slope elevation relationship is a good predictor of catchment form for catchments with declining relief it is argued that the slope area elevation relationship is sufficient with the planiform drainage pattern to completely define the elevation properties of the catchment such as for instance the hypsometric curve

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

results from a new model of river basin evolution this paper briefly describes a model of the erosional development of catchments and their channel networks the model differentiates between the dominant transport processes in hillslope and channels the development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms the growth of a river basin is qualitatively described the model concepts are used to study the basin during periods of growth transient periods as well as during dynamic equilibrium this leads to hypotheses about the relationship between slopes relief tectonic uplift erodability runoff and catchment area it is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation

internal and basal ice changes near the grounding line derived from radio echo sounding evidence of changing basal and internal ice properties near the grounding line was derived from airborne radio echo sounder observations of the ice sheet around the sor rondane mountains antarctica from the trailing figure of the bottom echo signal the roughness of the ice bottom near the grounding line was inferred results show that the specular components of scattering begin to appear on the ice shell side of the grounding line furthermore double trip echoes were observed with at strong scattering in the shelf area and their boundary of occurrence was very close to the grounding line this is evidence of interaction between ice and sea water at the bottom of the ice shelf we also examined the occurrence of internal layered echoes in most of the area around the mountains internal echoes were observed continuously but they were not found at or close to the ice shelf the boundary between the appearance and disappearance of internal layer echoes is distinct and occurs 20 30 km inland from the grounding line these results suggest that some major change may occur in the internal ice on the inland side of the grounding line

environmental impact of the 73 ka toba super eruption in south asia abstract the cooling effects of historic volcanic eruptions on world climate are well known but the impacts of even bigger prehistoric eruptions are still shrouded in mystery the eruption of toba volcano in northern sumatra some 73 000 years ago was the largest explosive eruption of the past two million years with a volcanic explosivity index of magnitude 8 but its impact on climate has been controversial in order to resolve this issue we have analysed pollen from a marine core in the bay of bengal with stratified toba ash and the carbon isotopic composition of soil carbonates directly above and below the ash in three sites on a 400 km transect across central india pollen evidence shows that the eruption was followed by initial cooling and prolonged desiccation reflected in a decline in tree cover in india and the adjacent region carbon isotopes show that c 3 forest was replaced by wooded to open c 4 grassland in central india our results demonstrate that the toba eruption caused climatic cooling and prolonged deforestation in south asia and challenge claims of minimal impact on tropical ecosystems and human populations

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

a physical explanation of an observed link area slope relationship an observed log log linear relationship between channel slope and contributing area is explained by the erosional physics that lead to catchment form it is postulated that tectonic uplift is in balance with the fluvial erosion down wasting that dominates catchment erosion and it is shown that this relationship results in the observed log log linear relationship at dynamic equilibrium in addition it has been observed that there are deviations from this log log linear relationship near the catchment divide with observed slopes being lower than those predicted from the relationship this is explained by noting that for small areas fluvial erosion effects are dominated by soil creep and rain splash modeled by diffusive physics the area at which this deviation from log log linearity occurs is that point on the hillslope at which diffusive physics like soil creep and rain splash begin to dominate fluvial erosion these predictions are confirmed by numerical simulations using a catchment evolution model

structure from motion photogrammetry a low cost effective tool for geoscience applications abstract high resolution topographic surveying is traditionally associated with high capital and logistical costs so that data acquisition is often passed on to specialist third party organisations the high costs of data collection are for many applications in the earth sciences exacerbated by the remoteness and inaccessibility of many field sites rendering cheaper more portable surveying platforms i e terrestrial laser scanning or gps impractical this paper outlines a revolutionary low cost user friendly photogrammetric technique for obtaining high resolution datasets at a range of scales termed structure from motion sfm traditional softcopy photogrammetric methods require the 3 d location and pose of the camera s or the 3 d location of ground control points to be known to facilitate scene triangulation and reconstruction in contrast the sfm method solves the camera pose and scene geometry simultaneously and automatically using a highly redundant bundle adjustment based on matching features in multiple overlapping offset images a comprehensive introduction to the technique is presented followed by an outline of the methods used to create high resolution digital elevation models dems from extensive photosets obtained using a consumer grade digital camera as an initial appraisal of the technique an sfm derived dem is compared directly with a similar model obtained using terrestrial laser scanning this intercomparison reveals that decimetre scale vertical accuracy can be achieved using sfm even for sites with complex topography and a range of land covers example applications of sfm are presented for three contrasting landforms across a range of scales including an exposed rocky coastal cliff a breached moraine dam complex and a glacially sculpted bedrock ridge the sfm technique represents a major advancement in the field of photogrammetry for geoscience applications our results and experiences indicate sfm is an inexpensive effective and flexible approach to capturing complex topography

photogrammetric monitoring of small streams under a riparian forest canopy the recent advent of digital photogrammetry has enabled the modeling and monitoring of river beds at relatively high spatial resolution 0 01 to 1 m through the extraction of digital elevation models dems the traditional approach to image capture has been to mount a metric camera to an aircraft although non metric cameras have been mounted to a variety of novel aerial platforms to acquire river based imagery e g helicopters radio controlled motorized vehicles tethered blimps and balloons however most of these techniques are designed to acquire imagery at flying heights above the riparian tree canopy in relatively narrow channels e g 20 m bankfull width streamside trees can obscure the channel and limit continuous photogrammetric data acquisition of both the channel bed and banks while still providing useful information regarding the riparian canopy and even spot elevations of the channel this paper presents a technique for the capture and analysis of close range photogrammetric data acquired from a vertically mounted non metric camera suspended 10 m above the channel bed by a unipod the camera is positioned under the riparian forest canopy so that the channel bed can be imaged without obstruction the system is portable and permits relatively rapid image acquisition over rough terrain and in dense forest the platform was used to generate dems with a nominal ground resolution of 0 03 m dems generated from this platform required post possessing to either adjust or eliminate erroneous cells introduced by the extraction process overhanging branches and by the effects of refraction at the air water interface for submerged portions of the channel bed the vertical precision in the post processed surface generally ranged from 0 01 to 0 1 m depending on the quality of triangulation and the characteristics of the surface being imaged copyright 2010 john wiley sons ltd

measurement of gravel bed topography evaluation study applying statistical roughness analysis abstractin this two part study experiments are conducted to evaluate available topography measurement techniques for gravel beds in a laboratory flume and to study their suitability for statistical roughness analysis the available instruments for this study include 1 an acoustic bed profiler 2 a hand held laser scanner and 3 two digital consumer cameras forming a stereophotogrammetric system and are employed to obtain digital elevation models dems of water worked gravel beds in the first part of the study the three measurement techniques are reviewed and their feasibilities for future grain scale roughness work assessed based on the obtained elevation datasets water worked gravel bed topographies are measured with all three available measurement techniques the analysis of the dems concentrates on using probability distribution functions pdfs and second order structure functions of bed elevations roughness coefficients are determined and used as a benchmark for comparison of the three

changes in the west antarctic ice sheet the portion of the west antarctic ice sheet that flows into the ross sea is thinning in some places and thickening in others these changes are not caused by any current climatic change but by the combination of a delayed response to the end of the last global glacial cycle and an internal instability the near future impact of the ice sheet on global sea level is largely due to processes internal to the movement of the ice sheet and not so much to the threat of a possible greenhouse warming thus the near term future of the ice sheet is already determined however too little of the ice sheet has been surveyed to predict its overall future behavior

can dem time series produced by uav be used to quantify diffuse erosion in an agricultural watershed abstract erosion and deposition modelling should rely on field data currently these data are seldom available at large spatial scales and or at high spatial resolution in addition conventional erosion monitoring approaches are labour intensive and costly this calls for the development of new approaches for field erosion data acquisition as a result of rapid technological developments and low cost unmanned aerial vehicles uav have recently become an attractive means of generating high resolution digital elevation models dems the use of uav to observe and quantify gully erosion is now widely established however in some agro pedological contexts soil erosion results from multiple processes including sheet and rill erosion tillage erosion and erosion due to harvest of root crops these diffuse erosion processes often represent a particular challenge because of the limited elevation changes they induce in this study we propose to assess the reliability and development perspectives of uav to locate and quantify erosion and deposition in a context of an agricultural watershed with silt loam soils and a smooth relief erosion and deposition rates derived from high resolution dem time series are compared to field measurements the uav technique demonstrates a high level of flexibility and can be used for instance after a major erosive event it delivers a very high resolution dem pixel size 6 cm which allows us to compute high resolution runoff pathways this could enable us to precisely locate runoff management practices such as fascines furthermore the dems can be used diachronically to extract elevation differences before and after a strongly erosive rainfall and be validated by field measurements while the analysis for this study was carried out over 2 years we observed a tendency along the slope from erosion to deposition erosion and deposition patterns detected at the watershed scale are also promising nevertheless further development in the processing workflow of uav data is required in order to make this technique accurate and robust enough for detecting sediment movements in an agricultural watershed affected by diffuse erosion this area of investigation holds much potential as the images processing is relatively new and expanding

a statistic for testing the elevation characteristics of landscape simulation models there is an urgent need to test recently constructed conceptual models of landscape evolution and geomorphology against field data many statistics that have commonly been used such as strahler statistics are poorly suited to this testing being unable to potentially falsify the models when applied in controlled conditions the relations between these statistics and catchment mass movement processes are in many cases indirect moreover they are sensitive to unknowable inputs e g initial conditions one of the main differences among the competing landscape evolution models is their representation of mass movement and erosion processes so that statistics that are directly linked to these processes or their geomorphic signature are needed this paper examines the use of a log log linear relation between catchment area slope and elevation this relation has been previously derived quantitatively from the catchment erosion and hydrologic processes for dynamic and declining geomorphic equilibria using a catchment evolution model this paper shows that the relation is robust against deviations from the assumptions of spatial and temporal homogeneity of erosion climate and tectonic uplift made in its derivation the sensitivity of the geomorphology to time varying tectonic uplift and climate and spatially variable soil erodability is examined it is thus asserted that the relation between area slope and elevation is suitable for testing of models against field data where spatial and temporal homogeneity of erosion climate and tectonic uplift are only approximately true in the case of variable soil erodability planar drainage patterns exhibit self organization with the high elevation regions of the catchment having low soil erodability consequently a downstream increasing erodability of the soil material consistent with a downstream fining type of behavior is observed it is further argued that the equilibria relation is fundamental and uniquely defines the elevation form of catchments so that all other elevation statistics are derived from it

volumetric analysis and hydrologic characterization of a modern debris flow near yucca mountain nevada abstract on july 21 or 22 1984 debris flows triggered by rainfall occurred on the southern hillslope of jake ridge about 6 km east of the crest of yucca mountain nevada rain gages near jake ridge recorded 65 mm and 69 mm on july 21 and 20 mm and 17 mm on july 22 rates of rainfall intensity ranged up to 73 mm h on the twenty first and 15 mm h on the twenty second digital elevation models with 2 0 m grid node spacing measured from pre storm and post storm aerial stereo photographs were used to map hillslope erosion and the downslope distribution of debris volumetric calculations indicate that about 7040 m 3 of debris was redistributed on the 49 132 m 2 hillslope study area during the two day storm period about 4580 m 3 65 of the eroded sediment was deposited within the study area and the remaining 35 was deposited outside the study area in a short tributary to fortymile wash and in the wash itself the maximum and mean depths of erosion in the study area were about 1 8 m and 5 cm respectively the mean depths of erosion on the upper and middle hillslope were 27 cm and 4 cm respectively the mean depth of deposition on the lower hillslope was 16 cm analysis of the values of cumulative precipitation in the context of the precipitation frequency atlas of the national oceanic and atmospheric administration indicates that precipitation from the main storm on july 21 was more than double that expected on average once during a 100 year period the relations of precipitation intensity duration developed from data recorded at a nearby precipitation gage indicate a storm interval of 500 years or greater the amount of erosion caused by such a storm is primarily dependent on three variables storm intensity development of the drainage network on the hillslope and the amount of available colluvium additionally the erosive ability of successive storms of equal intensity will decrease because such storms would tend to progressively isolate and reduce the amount of colluvium available the preservation of pleistocene deposits on hillslopes of yucca mountain in general indicates that erosional events that strip 5 of the available hillslope colluvium must be quite rare we conclude that the recurrence interval of an erosional event comparable to the july 1984 event is probably much longer than 500 years

simulation of braided channel topology and topography a computer code bcs was developed to simulate the three dimensional topographical expression of braided channel systems the model uses a random walk approach to simulate channel braiding and incorporates the hydraulic geometry of stream channels to assign width depth and velocity to each channel segment input parameters are directly related to observable geometric characteristics of a braided system such as channel system width depth and sinuosity thirty one measures of the degree or type of braiding were taken from the literature and used as calibration targets for the model all targets were matched for a portion of the ohau river new zealand this simulation technique can be used to assess quantitatively the distribution of channels with their associated hydraulic properties and visualize topographic surfaces associated with braided channel systems this information provides a foundation for probabilistic multiple realizations geometric simulation of three dimensional distribution of braided stream sediments 39 refs 4 figs 3 tabs

creating and coupling a high resolution dtm with a 1 d hydraulic model in a gis for scenario based assessment of avulsion hazard in a gravel bed river abstract in this paper we explore the development and assimilation of a high resolution topographic surface with a one dimensional hydraulic model for investigation of avulsion hazard potential on a gravel bed river a detailed channel and floodplain digital terrain model dtm is created to define the geometry parameter required by the 1d hydraulic model hec ras the ability to extract dense and optimally located cross sections is presented as a means to optimize hec ras performance a number of flood scenarios are then run in hec ras to determine the inundation potential of modeled events the post processed output of which facilitates calculation of spatially explicit shear stress and level of geomorphic work specific stream power per unit bed area for each of these further enhancing this scenario based approach the dtm is modified to simulate a large woody debris lwd jam and active channel sediment aggradation to assess impact on innundation and under previously modeled flow conditions the high resolution dtm facilitates overlay and evaluation of modeled scenario results in a spatially explicit context containing considerable detail of hydrogeomorphic and other features influencing hydraulics bars secondary and scour channels levees this offers advantages for i assessing the avulsion hazard potential and spatial distribution of other hydrologic and fluvial geomorphic processes and ii exploration of the potential impacts of specific management strategies on the channel including river restoration activities

volume estimation of the 1998 flank collapse at casita volcano nicaragua a comparison of photogrammetric and conventional techniques in october 1998 a precipitation triggered flank collapse occurred at casita volcano nicaragua leading to a devastating lahar in this paper the failure volume was calculated using a range of methods several pre and post failure digital elevation models dems were created based on photogrammetric cartometric and surveying data the wide range in resulting volumes prompted an assessment of the accuracies and potential problems associated with each of the datasets and techniques used the best estimate for the failure volume is 1 6 106 m3 it is based on a vegetation corrected pre failure dem generated using automated digital photogrammetry and a post failure surface based on a field survey carried out with a total station the volume figure is approximately an order of magnitude higher than values reported in previous publications all of which are based solely on field estimates this demonstrates that values reported in the literature if they are not based on rigorous quantitative analysis must be regarded with caution copyright 2002 john wiley sons ltd

the production of digital elevation models for experimental model landscapes automated digital photogrammetry was used to produce digital elevation models of experimental model landscapes under controlled laboratory conditions as part of a series of rainfall erosion experiments looking at the evolution of landforms in response to erosion the method allowed the elevations of the experimental landscapes to be studied in great detail on a regular grid digital terrain map with relatively very little effort digital photogrammetry produced elevation data at a resolution of 6 mm with a standard deviation of 2 0 mm over an experimental catchment relief of approximately 200 mm this resolution is considerably better than that achievable by conventional manual photogrammetry the density of grid points was sufficiently high that small scale details such as knickpoints developing in channels were represented the method can facilitate the study of both experimental and natural landscapes in great detail copyright 2001 john wiley sons ltd