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

particle path characteristics at the large gravel bed river danube results from a tracer study and numerical modelling a tracer study performed on a 3 km long reach of the danube river in austria is presented forty artificial stones of three different sizes intermediate b axis 25 mm 40 mm 70 mm were produced and a coded radio acoustic transmitter was implanted the measurement system had to be improved to be applicable to large rivers with water depths up to 12 m the positions of the stones were observed approximately once a week depending on hydrology over a period of at least one year by radio tracking from a boat including a 15 year flood event transport paths and velocities as well as the incipient motion of bedload transport could be monitored for the first time on a large gravel bed river the particle paths were found to be mostly bankline parallel even though the stones passed a 30 river bend the median of the transverse particle displacement was found to be 4 of the longitudinal displacement calculations considering both transverse slope and transverse flow velocities showed transverse transport to be 6 6 of the longitudinal transport indicating that marginal lateral transport is mainly influenced by morphology a three dimensional 3d numerical model using a stochastic particle tracing approach was validated with the data indicating that the observed positions are well reproduced by the model within the observation period 74 of all stones passed the reach with more than 1000 detections particle transport could be characterized by a mean travel velocity of about 10 m per day variable for the different grain sizes single tracer stones were transported up to 1000 m during a single flood event size selective behaviour could be shown and the incipient motion of the large 70 mm gravel was detected at lower discharges than predicted by commonly used uniform bedload transport formulae copyright 2012 john wiley sons ltd

analytical expressions for transient specific yield and shallow water table drainage 1 new closed form expressions are introduced to capture the dependence of specific yield on time and depth to water table the expressions allow the user to convert observations of water table fluctuations to volumes of water released from storage in a shallow water table aquifer whereas a linear relationship between water table fluctuations and released volumes holds for a deep water table aquifer this relationship is nonlinear for shallow water table aquifers the dependence of specific yield on time stems from the slow drainage of soil water from pores above the water table the new expressions allow determination of transient specific yield and time to drain the soil water profile for a given water table fluctuation if the time step in a numerical groundwater model is longer than the time for limiting specific yield then a constant time independent specific yield can be justifiably adopted the new expressions are easy to use and require knowledge of soil hydraulic properties which are readily available from soil water retention data and surveys

the kinematics of movements along the insubric line and the emplacement of the ivrea zone schmid sm zingg a and handy m 1987 the kinematics of movements along the insubric line and the emplacement of the ivrea zone in h j zwart m martens i van der molen c w passchier c spiers and r l m vissers editors tectonic and structural processes on a macro meso and micro scale tecta a hys 135 47 66 the insubric line west of locamo is characterized by a 1 km thick greenschist facies mylonite belt east of locamo these mylonites are overprinted by a discrete brittle fault the mylonites are derived from basement units of the central alps sesia zone and the southern alps ivrea zone as well as from the permo mesozoic cover of the southern alps canavese sense of shear criteria indicate that the mylonites accomm ated backt s g followed by dextral strike slip motion mylonitization during backtbrusting was synchronous with backfolding of the central alpine nappes under higher metamorphic conditions a horizontal temperature gradient resulted from the rapid juxtaposition of the warm central alpine block against the cold southern alpine block mylonites formed during the later dextral strike slip event are related to large transcurrent displacements in the central alps deduced from regional kinematic considerations thus both mylo t ation events are contempor eous with deformation to the north and south of the insubric line insubric phase extensively modifying the pre insubric crustal configuration of the alps the insubric phase post dates the bergell intrusion 30 m y the emplacement of the geophysical ivrea body is a combined effect of vertical uplift due to e w directed crustal thinning during the early jurassic and underplating by continental crust associated with late cretaceous compression a deep crustal normal fault pogallo line subsequently rotated during tertiary alpine orogenesis separates deeper parts of the southern alpine crust ivrea zone from intermediate crustal levels strona ceneri zone the rigid ivrea body localir ed large strains within the insubric mylonite belt and is responsible for the present curvature of the insubric line in uetion

bar dynamics in a sandy braided river insights from sediment numerical simulations abstract bar dynamics in sandy braided rivers are keys to better understand the morphological processes of braided rivers and sediment distributions limited by insufficient quantitative information and satellite images that only show the larger scale morphology and do not reveal the sand bars in the deeper channels most previous studies have qualitatively assessed bar dynamics but the ways in which the hydraulic parameters of sandy braided rivers control bar dynamics remains poorly understood here we present sediment numerical simulations on sandy braided rivers to investigate the quantitative controls of river parameters on bar dynamics three bar dynamic forms downstream migration lateral variations and bar tail elongation are observed unit bars are prone to downstream migration following formation and the migration rate shows a deceasing trend during braided river evolution this gradually decreasing migration rate is proven to be strongly connected to the decreasing flow velocity of braided channels that confine bar growth the lateral variation in bar dynamics exhibits narrowing migration and widening of sectional morphologies we suggest that braided channel curvature dominantly controls lateral sediment transportation around the bar and thus results in several lateral variation forms of bars the bar tail elongation difference between the two sides of the bar is associated with bar asymmetry strong bar asymmetry can make apparent differences in bar tail elongation

spatial prediction of river channel topography by kriging topographic information is fundamental to geomorphic inquiry and spatial prediction of bed elevation from irregular survey data is an important component of many reach scale studies kriging is a geostatistical technique for obtaining these predictions along with measures of their reliability and this paper outlines a specialized framework intended for application to river channels our modular approach includes an algorithm for transforming the coordinates of data and prediction locations to a channel centered coordinate system several different methods of representing the trend component of topographic variation and search strategies that incorporate geomorphic information to determine which survey data are used to make a prediction at a specific location for example a relationship between curvature and the lateral position of maximum depth can be used to include cross sectional asymmetry in a two dimensional trend surface model and topographic breaklines can be used to restrict which data are retained in a local neighborhood around each prediction location using survey data from a restored gravel bed river we demonstrate how transformation to the channel centered coordinate system facilitates interpretation of the variogram a statistical model of reach scale spatial structure used in kriging and how the choice of a trend model affects the variogram of the residuals from that trend similarly we show how decomposing kriging predictions into their trend and residual components can yield useful information on channel morphology cross validation analyses involving different data configurations and kriging variants indicate that kriging is quite robust and that survey density is the primary control on the accuracy of bed elevation predictions the root mean square error of these predictions is directly proportional to the spacing between surveyed cross sections even in a reconfigured channel with a relatively simple morphology sophisticated methods of spatial prediction are no substitute for field data copyright 2007 john wiley sons ltd

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

a delineation of regional hydraulic conductivity based on water table fluctuation summary the estimation of regional hydraulic conductivity is essential for the sustainable development and efficient management of groundwater this paper presents a new physical method of estimating hydraulic conductivity based on the water level fluctuation model developed by park and parker park e parker j c 2008 a simple model for water table fluctuations in response to precipitation j hydrol 356 344 349 the developed procedure was validated by comparison with the hypothetical numerical model for a variety of hydraulic conductivities aquifer inclinations and the heterogeneities the model was found to be highly reliable when using water level data far from the hydraulic boundaries the results show that the monitoring data obtained over a range of relative distances of an observation location x to the flow domain w x w 0 2 avoided the boundary effects a correction factor was also proposed based on the deviation analysis of the calibrated k and f n ratio of recharge to precipitation divided by porosity the results from the basal inclinations and the heterogeneities cases suggest that the estimated hydraulic conductivity is representing regional property rather than the local one to confirm the validity of the proposed procedure it was applied to the coastal aquifer of jeju island korea the calibrated hydraulic conductivities were consistent with the results from previous studies these results show that the proposed method is an effective and economical means to estimate hydraulic conductivity of large supporting volumes of subsurface aquifers with the convenient use of recharge and groundwater level data

nappe geometry in the western swiss alps abstract detailed geological mapping during the last 20 years in the western swiss alps has shown clearly that most of the lower basement nappes are fold nappes possessing normal and inverted limbs moreover their cores are made of strongly deformed gneisses indicating that important ductile strain took place during the formation of the fold nappes it is therefore probably wrong to imagine deep basement nappes as rigid slices as often actually claimed especially when interpreting seismic profiles true brittle type thrust nappes involving basement rocks only occur in the internal and upper parts of the belt cover nappes on the contrary are in most parts of the alpine belt thrust sheets following more or less the rules of thin skinned tectonics many basement fold nappes lost part of their sedimentary cover during or just before their formation by decollement along ductile horizons the result is that many cover thrust nappes in the external part of the alps are directly related to their original basement fold nappes

effects of large floods on sediment transport and reach morphology in the cobble bed sainte marguerite river abstract sediment transport rates were estimated for two flood events on the cobble bed sainte marguerite river in the saguenay region canada morphologic methods were used to derive one set of estimates and a combination of the meyer peter and muller equation with a dimensionless sediment transport ratio after dietrich et al nature 340 1989 215 was used to derive another set of estimates both sets of estimates give consistent results for the first event which had a decade scale return period and for the second event which was the largest flood on record and had a century scale return period the transport occurring during the second event was an order of magnitude greater than that occurring during the first event despite this disparity in the transport intensity of the two events the channel morphology remained qualitatively similar the observed degree of channel stability is attributed to a change of channel pattern and the initiation of bed degradation following channel rectification in the 1960s

quantifying channel development and sediment transfer following chute cutoff in a wandering gravel bed river abstract three dimensional morphological adjustment in a chute cutoff breach alluvial channel is quantified using digital elevation model dem analysis for a ca 0 7 km reach of the river coquet northumberland uk following cutoff in january 1999 channel and bar topography was surveyed using a total station on five occasions between february 1999 and december 2000 analysis of planform change coupled with dem differencing elucidates channel and barform development following cutoff and enables quantification of sediment transfers associated with morphological adjustment within the reach this exercise indicates an initial phase of bed scour followed by a period characterised by extensive bank erosion and lateral channel migration where erosion including bed scour totalled some 15 000 m3 of sediment the channel in the post cutoff disequilibrium state is highly sensitive to relatively low magnitude floods and provision of accommodation space by bank erosion encouraged extensive lateral bar development bar development was further facilitated by infilling of channels abandoned by repeated within reach avulsion and large scale aggradation of sediment lobes deposited by higher magnitude floods calculations indicate that at least 6600 m3 of sediment was deposited on emerging bars within the reach over the survey period and 2300 m3 deposited within the channel sediment losses from the reach may have exceeded 6500 m3

results of nfp 20 seismic reflection profiling along the alpine section of the european geotraverse egt summary recent deep crustal seismic reflection profiling across the central alps of eastern and southern switzerland has provided a detailed image of this continental collision zone as part of the swiss national science project nfp 20 a series of reflection profiles was recorded during two phases along n s transects crossing the alpine edifice the eastern and southern profiles coincide with the alpine segment of the european geotraverse egt and in part with the earlier swiss geotraverse these data together with other geophysical and extensive geologic information form a unique and comprehensive volume of crustal information for this region of the alps on a larger scale the new reflection data also add to a growing set of profiles crossing the alpine fold belt which includes an additional traverse carried out by nfp 20 across the western swiss alps and the ecors crop profile across the western alps the initial results of the reflection data across the central alps outline a crustal framework involving northward indentation of the adriatic hinterland into the subducting european foreland this occurs beneath the collapsed oceanic basins of the penninic allochthon which is defined by its highly reflective crystalline nappes the present crustal thickness within the alpine collision zone has doubled to about 60 km by both vertical and horizontal displacements along an inferred complex detachment system controlled by the adriatic wedge the south plunging european foreland implies that portions of the thickened crust have been subducted into the upper mantle this general framework of flake tectonics is laterally consistent with the ecors crop results from the western alps however the western alps show a higher degree of crustal imbrication which may be related to the presence of the rigid ivrea body and an overall greater amount of crustal shortening compared to the central alps

the problem of the deep structure of the southern alps 3 d material balance considerations and regional consequences abstract the lombardic southern alps are a typical thin skinned frontal fold and thrust belt although this recent reassessment is widely accepted figures for shortening and schemes for transfer of shortening at their eastern end in the giudicarie vary exact section balancing is not feasible because of insufficient information but approximate shortening is on an order probably exceeding 100 km with about 80 100 km attributable to the middle to late miocene milan belt acceptance of this quantitative conclusion has farreaching consequences transfer of the milan belt shortening in the east follows the lateral edge of the allochthon which is sinistrally transpressive the giudicarie line with its sedimentary decollement zone the giudicarie belt the pre existing adamello intrusions and the jorio tonale line are part of the thrust masses and consequently allochthonous transfer of shortening across the insubric line into the tauern antiform and associated structures of neo alpine compression in the eastern alps resulted in the sinistral dissection of the insubric line at the giudicarie line superposition of this compression on pannonian stretching east of and transtensive motion at the brenner line west of the tauern produced a confusing structural pattern whose quantitative kinematics have not been worked out another sinistral probably compressive transfer zone is postulated at the western end of the milan belt retrodeformation leads simultaneously to both a straightening of the insubric line and the connection of the canavese line with the villalvernia varzi levanto line to define the boundary of the adriatic block at the beginning of neo alpine deformation

wildfire morphologic change and bed material transport at fishtrap creek british columbia abstract in 2003 a wildfire burned nearly two thirds of the fishtrap creek watershed including the forested floodplain annually repeated surveys of the stream channel combined with bed material tracer studies in 2006 and 2007 indicate that the channel has become unstable and that the bed material transport dynamics have changed since the fire using these data the morphologic changes have been quantified and event scale bed material transport rates have been estimated for four post fire freshets the immediate response of the channel during the 2005 and 2006 freshets was a progressive shift in channel morphology from a relatively featureless plane bed morphology devoid of significant sediment accumulations to a riffle pool morphology in which bars cover a significant proportion of the bed this transformation occurred in association with moderate bed material sediment transport rates and only minor bank erosion within the study reach extensive bank erosion occurred during the 2007 and 2008 freshets producing a dramatic change in channel morphology and increasing the local bed material transport rates by an order of magnitude post fire monitoring of streamflow and suspended sediment concentrations a surrogate for upstream sediment supply indicates that post fire increases are not detectable presented in eaton et al in press and our analysis demonstrates that major morphologic changes can occur following wildfire even when the common external drivers of stream discharge and sediment supply remain unchanged

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

the spatial and temporal patterns of aggradation in a temperate upland gravel bed river intensive field monitoring of a reach of upland gravel bed river illustrates the temporal and spatial variability of in channel sedimentation over the six year monitoring period the mean bed level in the channel has risen by 0 17 m with a maximum bed level rise of 0 5 m noted at one location over a five month winter period these rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2 6 times and overbank flow time increasing by 12 8 hours this work raises the profile of coarse sediment transfer in the design and operation of river management specifically engineering schemes it emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic exploration of the sediment supply and transfer system can explain patterns of channel sedimentation the complex spatial seasonal and annual variability in sediment supply and transfer raise uncertainties into the system s response to potential changes in climate and land use thus there is a demand for schemes that monitor coarse sediment transfer and channel response copyright 2009 john wiley sons ltd

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

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

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

contemporary geomorphological activity throughout the proglacial area of an alpine catchment abstract quantification of contemporary geomorphological activity is a fundamental prerequisite for predicting the effects of future earth surface process and landscape development changes however there is a lack of high resolution spatial and temporal data on geomorphological activity within alpine catchments which are especially sensitive to climate change human impacts and which are amongst the most dynamic landscapes on earth this study used data from repeated laser scanning to identify and quantify the distribution of contemporary sediment sources and the intensity of geomorphological activity within the lower part of a glaciated alpine catchment odenwinkelkees central austria spatially geomorphological activity was discriminated by substrate class activity decreased in both areal extent and intensity with distance from the glacier becoming progressively more restricted to the fluvially dominated valley floor temporally geomorphological activity was identified on annual seasonal weekly and daily timescales activity became more extensive with increasing study duration but more intense over shorter timescales thereby demonstrating the importance of temporary storage of sediment within the catchment the mean volume of material moved within the proglacial zone was 4400 m 3 yr 1 which suggests a net surface lowering of 34 mm yr 1 in this part of the catchment we extrapolate a minimum of 4 8 mm yr 1 net surface lowering across the whole catchment these surface lowering values are approximately twice those calculated elsewhere from contemporary measurements of suspended sediment flux and of rates calculated from the geological record perhaps because we measure total geomorphological activity within the catchment rather than overall efflux of material repeated geomorphological surveying therefore appears to mitigate the problems of hydrological studies underestimating sediment fluxes on decadal annual time scales further development of the approach outlined in this study will enable the quantification of geomorphological activity alpine terrain stability and persistence of landforms

dam induced and natural channel changes in the saskatchewan river below the e b campbell dam canada abstract the e b campbell dam on the saskatchewan river east central saskatchewan was constructed in 1962 forming tobin lake 2 2 billion m3 capacity which today impounds most fluvial sediment and disrupts normal outflow patterns thirty five kilometers below the dam the river diverts into a 500 km2 belt of alluvial sediment initiated by an avulsion 140 years ago rejoining the parent channel 108 km from the dam effects of the dam on channel geomorphology including the historical channel reach i and the more recent avulsion affected channels were investigated by pre and post dam cross section surveys combined with grain size and bedload measurements twenty three sites were surveyed at least twice and 14 were resurveyed annually in 2003 2014 except 2007 during which significant floods occurred in 2005 2011 and 2013 all channel cross sections up to 81 km below the dam have coarsened and enlarged since closure resulting in excavation of 35 4 106 m3 of channel perimeter sediment since 1962 the most proximal segment is armored and has changed little in recent years since 2003 channel enlargement has been greatest in the 35 81 km segment between the avulsion site and the forks reaches ii iii manifested as widening and deepening enlargement rates were greatest during the three floods and the paucity of bedload has prevented degraded portions of the channel bed from replenishment following flooding budget calculations based on bedload measurements and channel cross section areas suggest that 30 years would be required to replace the sediment removed between 2003 and 2014 assuming all available bedload remains in the affected reach dam effects appear to be absent or uncertain beyond 81 km a multichanneled region of varied stages of activity reach iv recombining and eventually rejoining the parent saskatchewan river channel at km 108 reach v sediment evacuated from reaches i iii is sufficient to sustain modest aggradation in some distal portions of the avulsion belt including the mossy delta but little bedload is returned to the parent channel dam induced sediment starvation is speeding the rate at which a single dominant channel is evolving between the avulsion site and rejoined parent a process that will likely shift the patterns of flood inundation in the future

experiment on temporal variation of bed load transport in response to changes in sediment supply in streams a flume experiment was conducted to study channel adjustment to episodic sediment supply in mountain streams the bulk sediment used for the bed and feed included grain sizes 0 5 64 mm with geometric mean dg bulk of 5 7 mm water discharge was held constant for 40 h and 300 kg of sediment was supplied through a range of scenarios bed slope sediment storage sediment transport and bed surface texture responded to sediment supply during the first of seven runs bed slope decreased from 0 022 m m flume slope to 0 018 m m due to sediment starvation bed slope increased beginning in the second run as the bed aggraded due to preferential storage of grains 8 mm transport rate and bed surface particle size were significantly affected by magnitude frequency of sediment feed under constant feed transport rate increased gradually and dg surface ranged between 12 15 mm instead sediment pulses caused a pronounced increase in sediment transport rate and surface fining trends that were inverted as sediment evacuated at the run scale sediment transport and storage behaved as with constant feed if pulse relaxation time exceeded time between pulses the increase in transport rate and surface fining were proportional to pulse size after the 300 kg pulse transport rate reached 100 g m 1 s 1 and dg surface was 12 mm textural differences on the initial bed surface influenced the patterns of sediment transport channel adjustment was controlled by magnitude frequency of sediment feed and not by total feed this article is protected by copyright all rights reserved

stream power controls the braiding intensity of submarine channels similarly to rivers we use physical experiments to investigate the response of submarine braided channels driven by saline density currents to increasing inflow discharge and bed slope we find that similarly to braided rivers only a fraction of submarine braided networks have active sediment transport we then find similar response to imposed change between submarine and fluvial braided systems 1 both the active and total braiding intensities increase with increasing discharge and slope 2 the ratio of active braiding intensity to total braiding intensity is 0 5 in submarine braided systems regardless of discharge and slope and 3 the active braiding intensity scales linearly with dimensionless stream power thus braided submarine channels and braided rivers are similar in some important aspects of their behavior and responses to changes in stream power and bed slope in light of the scale independence of braided channel planform organization these results are likely to apply beyond experimental scales

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

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

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

observations of bedload movement bar development and sediment supply in the braided ohau river relative bedload transport rate and hydraulic parameters were measured on two occasions in a reach of the braided gravel bedded ohau river each reach contained a deep fast flowing chute leading to an area of diverging shallow flow which contained a middle bar the measurements are self consistent and indicate that where flow is concentrated in a deep chute shear stress is high but where flow diverges depth slope and shear stress decrease in the first survey the bed was scoured in the chute and sediment transport rates were high but where flow diverged sediment transport rate decreased it appears that deposition leads to bar growth bar growth in turn reduces slope and depth deposition is encouraged and the bar continues to grow vertically laterally and upstream in the second survey no sediment transport was observed despite hydraulic conditions very similar to the first survey the absence of sediment transport is attributed to the cessation of sediment supply to the river channel

the relation between particle path length distributions and channel morphology in gravel bed streams a synthesis abstract the path length downstream displacement over a given time period of individual bed particles in gravel bed rivers is central to morphological methods for measuring bed load transport rate and is also fundamental to understanding the bed load transport process and the development of channel morphology previous studies of particle movement using tracers report predominantly strongly positively skewed frequency distributions of path length with modes close to the point of entrainment however gravel bed rivers often have regularly spaced erosion scour pools and deposition channel bars sites that are several channel widths apart and it is reasonable to expect that particle path length would reflect this morphological scale at least during flows large enough to create and modify the morphology here we synthesize and re analyze results from published bed load tracing experiments in gravel bed rivers to identify the variety of possible path length distributions for differing channel morphology channel dimensions bed particle size and particle mobility i e flow magnitude and to look for occurrences of path length coinciding with the length scale of the morphology the results show that path length distributions may be positively skewed symmetrical and uni bi or multi modal and may include modes that coincide with known or expected pool bar spacing primary path length modes equivalent to possible pool bar spacing are more probable at higher non dimensional bed shear stress from which it is inferred that both particle mobility and channel morphology exert an influence on particle path lengths and that particle movement is unlikely to be stochastic except at relatively low particle mobility existing data are inadequate for more than a preliminary analysis of this problem consequently there is a need for new data collected explicitly and systematically to confirm these preliminary results isolate the effect of the several variables that influence the characteristics of path length frequency distributions and identify the conditions under which path length coincides with the length scale of the dominant morphology

footwall uplift in an orogenic wedge the tauern window in the eastern alps of europe abstract in the tauern window tw the deepest structural units of the eastern alps are exposed in a 30 160 km antiform european basement and cover occur under nappes of oceanic penninic units and continental origin austroalpine nappes the tertiary structural history of the tw is related to a rapid uplift of 20 30 km since oligocene times structural mapping revealed 1 detachment and folding of the cover units and stacking of orthogneiss sheets 2 constrictional folding of the entire duplex with amplitudes and half wavelengths of several kilometres 3 backthrusting and backfolding along the northern margin of the tw and 4 displacement along steep dip divergent strike slip faults the strain history is complex and related to all these deformation phases the most uniform structural element is a stretching parallel to the long axis of the tw and its major fold axes strain did not contribute to tw uplift because ductile n s shortening was compensated by e w extension restoration of the tw shows that the exposed structures are not sufficient to explain the tw uplift by analogy with the engadine window and the western alps where seismic data are available a deep seated duplex is suspected the tw uplift is best explained in a dextral transpressive regime

morphological evolution and dynamics of a large sand braid bar jamuna river bangladesh the initiation and evolution of a kilometre scale sand braid bar was monitored during a 28 month survey period from 1993 to 1996 in one of the world s largest braided rivers the jamuna river bangladesh repeated bathymetric surveys through two monsoon flood seasons combined with bar top surveys during exposure of the bar at low flow provide the most detailed chronology of braid bar growth yet compiled for a large sand bed river during rising and peak flow of the 1994 monsoon flood a 1 5 km long 0 5 km wide 12 m high symmetrical mid channel bar was deposited in the centre of a major channel downstream of a zone of flow convergence and significant bank erosion initial deposition and growth of the bar core were probably caused by amalgamation of dunes that are present in the jamuna channels at all flow stages bar top aggradation continued through downstream migration of an accretionary dune front a 3 m high angle of repose slipface that was composed of amalgamated 0 5 to 1 m high dunes at waning and low flow the mid channel bar widened by up to 1 km through the lateral accretion of dunes onto the margins of the initial bar core a low velocity zone in the sheltered wake region of the bar tail led to the accumulation of substantial volumes of silts and clays during the rising and peak flows of the next monsoon flood the mid channel bar extended its bar tail by up to 1 5 km as one of the anabranches became dominant and flow was deflected across the bar tail accretion at the bar tail generated a lobate transverse bar front with a 10 m high angle of repose avalanche face emergence of several smaller bars along this depositional front produced an overall reach morphology that more closely resembled an alternate bar rather than several mid channel bars the conversion of a mid channel bar to an alternate bar is contrary to many previous descriptions of the braiding process

gravel transport in the braided waimakariri river mechanisms measurements and predictions abstract yields of grabel bed load in the braided lower waimakariri river in new zealand are investigated by several methods and for different timescales short term several months medium term several years and long term 1967 1983 short term estimates of gravel yield were made for five such periods in 1986 1987 by a morphological method bed morphology in a selected reach was mapped before and after flood events the gross volume of scour in that time period measured and a mean transport rate through the reach computed on the basis of the step distance of gravel movement from scour zones to areas of accretion the findings indicate that a considerable fraction of the annual gravel load is derived from scour of braid banks with the gravel being shunted downstream from one zone of temporary storage to another computation of bed load yields during the same period by the meyer peter and muller mpm equation revealed excellent agreement with the morphological estimate comparison of the mpm prediction based on flow duration data for 1967 1983 also showed excellent agreement with the long term rate assessed by stadia survey of cross sections in the reach of accumulation downstream of the study reach predictions using the mpm formula for the medium term however while acceptable showed greater differences from the surveyed rates evidence indicates that this is related to highly dynamic bed conditions in which the availability of more mobile finer grained gravel in the reach changes from year to year as slugs of such sediment move intermittently downstream thus while prediction of a short term yield based on bed conditions at the time of study and a long term yield based on temporal mean conditions as inferred from bed conditions averaged along the river are realistic goals the accurate prediction of successive short term or medium term yields seems to be impossible unless detailed analysis of bed conditions especially grain size is undertaken in each time period a major task

channel adjustment and a test of rational regime theory in a proglacial braided stream the upstream reach of the sunwapta river alberta provides a useful quasi experimental field case of channel adjustment in a proglacial stream historically the formation of a proglacial lake deprived the river of its coarse sediment supply for several decades and lead to a dramatic decrease in braiding intensity close to the lake while braiding intensity increased further downstream this response to the reduction of gravel input is consistent with previous experimental results subsequent construction activity and channelization close to the lake have contributed to the continuation of these temporal and spatial trends in channel pattern the current state of adjustment of the river morphology can be explained in the context of these historical changes using rational regime equations the study reach has no tributaries and bed material size decreases twofold along the reach while width and braiding intensity increase yet channel slope decreases by only 10 the absence of any significant change in discharge downstream along the reach allows testing of regime equations under conditions in which discharge is held constant the current downstream trends in slope and fluctuations in width are predicted reliably from rational regime equations but not by the existing empirical hydraulic geometry relations the rational equations incorporate the effect of grain size and slope on channel width and the effect of width and grain size on channel slope the regime equations are successful even though they were devised for single channel gravel streams the small 10 decrease in slope along the reach despite a halving of median grain size is attributed to the counteracting positive effect on slope of the downstream increase in braiding intensity and width the downstream increase in braiding intensity must be largely the result of decreasing grain size this confirms the influence of grain size on channel pattern thresholds and demonstrates using spatial transitions in channel pattern that channel pattern predictions based on stream power alone are inadequate

virtual rate and mean distance of travel of individual clasts in gravel bed channels travel distances in gravel bed rivers of tagged particles of various sizes are related to excess stream power estimated for peak discharge mean distance of movement irrespective of grain size is weakly correlated with stream power especially near the threshold of movement there may be several reasons for the weak correlation including variable effects of bed structure varying magnitudes of sediment mobilizing events and sampling problems grain size itself is of marginal significance the virtual rate of travel calculated using total time for which the flow is larger than that needed to initiate clast movement also bears a weak relation to the excess stream power over the period better results are obtained by relating the virtual rate of travel to the first peak of the flow event only this implies that the initial seeding of the tagged particles dominates the observations nonetheless an underlying general relation is indicated by the data which are derived from a wide range of flow regime types

channel morphology and bedload pulses in braided rivers a laboratory study bedload pulses in gravel bed rivers have been widely reported in recent years and attempts have been made to relate them to channel morphology bedload transport and channel morphology were measured in a small scale generic model of braided gravel bed streams two experiments are described in which braided channels developed in a 14 m 3 m sand tray total bedload output from the tray was weighed every 15 minutes stream bed geometry was surveyed every four hours pulses were observed in the bedload output time series and were qualitatively related to the channel morphology immediately upstream of the measuring section the bagnold 1980 bedload equation generally overpredicts measured bedload transport rates when applied to channels that were in equilibrium or aggrading underprediction occurred when applied to degrading channels aggradation was associated with channel multiplication and bar deposition channel pattern simplification occurred when degradation took place and bars emerged from the water flow development of phases of aggradation and degradation is dependent upon the three dimensional geometry of the stream beds spatial and temporal feedback loops can be identified enabling links between channel morphology and bedload transport rate to be directly identified

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

downstream effects of impounding a natural lake the snake river downstream from jackson lake dam wyoming usa a sediment mass balance constructed for a 16 km reach of the snake river downstream from jackson lake dam jld indicates that river regulation has reduced the magnitude of sediment mass balance deficit that would naturally exist in the absence of the dam the sediment budget was constructed from calibrated bed load transport relations which were used to model sediment flux into and through the study reach calibration of the transport relations was based on bed load transport data collected over a wide range of flows on the snake river and its two major tributaries within the study area in 2006 and 2007 comparison of actual flows with unregulated flows for the period since 1957 shows that operations of jld have reduced annual peak flows and increased late summer flows painted tracer stones placed at five locations during the 2005 spring flood demonstrate that despite the reduction in flood magnitudes common floods are capable of mobilizing the bed material the sediment mass balance demonstrates that more sediment exits the study reach than is being supplied by tributaries however the volume of sediment exported using estimated unregulated hydrology indicates that the magnitude of the deficit would be greater in the absence of jld calculations suggest that the snake river was not in equilibrium before construction of jld but was naturally in sediment deficit the conclusion that impoundment lessened a natural sediment deficit condition rather than causing sediment surplus could not have been predicted in the absence of sediment transport data and highlights the value of transport data and calculation of sediment mass balance in informing dam operations copyright 2011 john wiley sons ltd

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

the effects of survey frequency on estimates of scour and fill in a braided river model an erratum has been published for this article in earth surface processes and landforms 27 7 2002 795 estimates of scour and fill in rivers that are derived by differencing topographic surfaces are known to be negatively biased by local compensation of scour and fill between surveys but the magnitude of bias is not well known this study examines the effect of survey frequency on volumes of scour and fill over a period of active channel braiding in a small scale river model a 100 min high temporal resolution time series of digital elevation models is artificially coarsened by selectively removing models the resulting four overlapping time series have survey intervals of 10 min 20 min 50 min and 100 min cumulative scour and fill volumes for the 100 min period are compared between the four series it is concluded that the decay in measured volumes of scour and fill with increased survey interval can be described using inverse functions cumulative scour fill volumes are approximately 420 per cent greater over the study period for 10 min survey intervals than for a 100 min interval after the 100 min period of competent flow nearly 65 per cent of the channel area experienced significant compensation of scour and fill several compensation mechanisms were identified in association with braided channel kinetics including lateral channel migration the migration of bed forms and channel avulsion it is demonstrated that by negatively biasing scour fill and net estimates this error significantly affects morphological approaches to the estimation of bed load sediment transport copyright 2002 john wiley sons ltd

bedload transport processes in a braided gravel bed river model a 1 50 scale hydraulic model was designed based on froude number similarity and using hydrological and sediment data from a small braided gravel bed river the north branch of the ashburton river canterbury new zealand eighteen experiments were conducted seven using steady flows and eleven using unsteady flows the experiments were carried out in a 20 m 3 m tilting flume equipped with a continuous sediment feed and an automated data acquisition and control system in all experiments water at 30 c was used to reduce viscosity related scale effects analyses of the experimental data revealed that bedload transport rates in braided channels are highly variable with relative variability being inversely related to mean bedload transport rate variability was also found to be cyclic with short term variations being caused by the migration of bedforms bedload transport was found to be more efficient under steady flow than under unsteady flow and it was postulated that this is caused by a tendency for channel form to evolve towards a condition which maximizes bedload transport for the occurring flow average bedload transport rate was found to vary with channel form although insufficient measurements were made to define a relationship

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

particle path length distributions in meandering gravel bed streams results from physical models in gravel bed rivers with well de ned pool bar morphology the path length of transported bed particles must be at least during channel forming ows equal to the length scale of the morphology this is the basis for some methods for estimating bed material transport rates however previous data especially from eld tests are often strongly positively skewed with mean much shorter than the pool bar spacing one possible explanation is that positively skewed distributions occur only in channels lacking distinct pool bar topography or only at lower discharges in pool bar channels a series of ume experiments using uorescent tracers was used to measure path length distributions in low sinuosity meandering channels to assess the relation with channel morphology and ow conditions at channel forming ows 55 to 75 per cent of the tracer grains were deposited on the rst point bar downstream of the point of tracer input with 15 per cent passing beyond the rst bar path length distributions are symmetrical with mean equal to the pool bar spacing and can be described with a cauchy distribution in some cases there was a secondary mode close to the point of tracer introduction this bimodal distribution ts a combined gamma cauchy distribution only when discharge was reduced below the channel forming ow were frequency distributions unimodal and positively skewed with no relation to the pool bar spacing thus path length distributions become more symmetrical and mean path length increases to coincide with pool bar spacing as ow approaches channel forming conditions this is a substantial modi cation of existing models of particle transfer in gravel bed rivers copyright 2003 john wiley sons ltd

channel adjustments to historical disturbances along the lower brazos and sabine rivers south central usa historical channel adjustments are documented and discussed in context with anthropogenic disturbances along two meandering coastal plain rivers the lower brazos and sabine rivers in the south central united states hard copy streamflow measurement notes of the u s geological survey were utilized to render historical cross sections 1925 2007 at nine gauging stations which were complemented with repeat photographs and flood frequency analysis to assess trajectories of channel change and interpret causative mechanisms downstream and upstream propagating disturbances caused episodes of channel bed incision and aggradation at different locations for distinct time periods along both rivers incision associated with upstream dams is detected but channels are compensated downstream with sediment inputs from lateral channel migration and tributaries in one case temporary aggradation along the brazos river at waco was likely caused by a combination of dam construction and regional soil erosion channel bed incision on the lowermost brazos river is unrelated to dams but is associated with instream aggregate extraction possibly in conjunction with downstream channelization on the sabine river extensive aggradation during the 1930s might be associated with logging activities 1880s 1930s but whether the cause is pervasive regional scale hillslope erosion or local scale mill site activities is indeterminate following passage of this sediment the river generally recovered to pre disturbance conditions and has exhibited stability despite a mainstem reservoir translation of this sediment slug is attenuated by a transition to a flood prone distributary dominated system downstream of the holocene pleistocene terrace onlap position additional findings include cross channel hingepoints separating thalweg incision from simultaneous point bar or bank accretion at meander bends which indicates channel adjustment occurs along non cohesive beds in preference to cohesive or artificially reinforced banks also flood reduction has resulted in bankfull stages that are higher than levels associated with the post regulation 2 year return period finally vegetation encroachment along banks since the 1970s coupled with reduced flooding along the lower brazos river has promoted bank accretion deposits that when fully developed serve as morphologic indicators of the post regulation 1 to 2 year return period stage

decollement in the alpine system an overview decollement in the alpine system is implied in the nappe concept jura decollement originally proposed bybuxtorf 1907 is the latest addition north of the alps the rheology of evaporites shows easy feasibility of jura decollement which is required by material balance in eastern switzerland the front of the alpine foreland thrust belt in the molasse is a typical triangle structure tectonic wedge an important decollement structure also in other places and scales the helvetic nappes are flat and ramp structures similar to the jura but translated by greater amounts and deformed under larger overburden corresponding basement deformation was largely ductile basement lobes and lagged behind the penninic nappes are usually metamorphosed in various degrees except some cover nappes transported far into the foreland coordination between basement and displaced cover is uncertain the austroalpine cover nappes of switzerland and adjacent austria as a rule are only weakly metamorphosed and resemble the southern alps in both stratigraphy and its expression in tectonics the basement part of both are essentially upright slivers not more than five kilometers thick with a frontal ramp fold splitting apart of the sedimentary sequence particularly in the carnian with tectonic wedging is frequent in both domains extensional decollement occasionally accompanied by tectonic denudation and high cooling rates occurred during several episodes most notably during early jurassic rifting and between the compressional phases gosau oligocene early miocene episodes the main strike slip elements of the transpressive neoalps are the insubric fault system with its dextral riedel shears and the dextrally arranged brachyanticlines of the late alpine windows which again imply decollement

channel adjustments bedload transport and sediment sources in a gravel bed river brenta river italy this paper deals with the brenta river the alps italy a gravel bed river strongly affected by human impact the aims of this work are a to reconstruct the channel adjustments that have occurred during the last decades and b to analyse the present condition of the river in terms of bedload transport and sediment sources the study reach which is 23 km long was investigated using historical maps aerial photographs 12 monumented cross sections laser altimetry data and field survey bedload transport rates were estimated by a morphological approach which allows the construction of a sediment budget dramatic channel adjustments have occurred in response to an alteration of sediment fluxes caused by different human interventions gravel mining dams torrent control works major channel adjustments specifically incision up to 8 9 m and narrowing took place between the 1950s and the 1980s on the other hand widening has become the most important process and incision has continued only in the upper part of the study reach in more recent times about the last 20 25 years the estimate of bedload transport rates for the period 1984 1997 was carried out starting from the erosion and deposition volumes of the single sub reaches such an estimate has shown that a a high spatial variability of gravel transport rates exists from 0 up to 73 200 85 400 m3 year and b most of the bedload is supplied by local sources bank erosion is the main source of sediments for bedload transport and its contribution can be estimated as from 9 up to 20 times higher than the upstream contribution finally from a practical point of view results from this study should be taken into account in addressing maintenance sediment management and restoration along a dynamic and unstable river such as the brenta copyright 2007 john wiley sons ltd

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

large scale thin skinned thrusting in the southern alps kinematic models the tectonics of the southern alps are dominated by thrusting on extensive ramp flat systems and by folding some of which is ramp folding basement slivers are involved that frontally are not thicker than 5 km the most unequivocal section is that of the grigna mountains east of lake como for which kinematic modeling based on material balance considerations results in a shortening of 40 km it is separated from the grona section in the west and the valtorta section in the east by probably pre existing transverse zones that cut through the important decollement horizons and define blocks of different depths to basement local tectonics across these transverse zones change abruptly while over all shortening remains constant in particular both east and west of the grigna section basement ramp folds were wedged into the very incompetent raibl beds provoking back thrusting of the thick hauptdolomit and higher sediments with the substitution of the original cover of the frontal limb of the basement fold this new kinematic interpretation is compatible with the information facilitates the construction of balanced sections and is required for lateral constancy of shortening

prediction of discharge from water surface width in a braided river with implications for at a station hydraulic geometry 1 the total discharge of small braided rivers can be monitored nearly continuously using ground based orthorectified oblique images and a locally derived relationship between mean water surface width in a reach and total discharge with accuracy of the order of 10 the width discharge relationship is nearly linear over the normal range of summer flows measured in this proglacial stream the width discharge relation for a given location and channel configuration is transferable to adjacent reaches with different morphology with little loss in accuracy however the prospect of a more universal relation for braided rivers is remote because of differences in channel geometry and hydraulics between rivers the classical at a station hydraulic geometry exponent for width in this case is approximately 1 05 which is unique well above that observed in the few other braided rivers for which this has been derived and implies almost no change in mean velocity and depth with changing stage

measurements in a braided river chute and lobe 1 flow pattern sediment transport and channel change this paper and its companion ashworth et al this issue discuss measurements of channel change and associated flow and sediment transport processes in a representative chute and bar reach within a proglacial gravel bed river the sunwapta river in the canadian rockies during a week in which water discharge through the reach increased then decreased a sediment wave passed into and partly along the reach at first the chute aggraded then sediment was eroded from the chute and deposited in a prograding lobe to one side of the original bar head between two distributaries measurements of velocity shear stress and gravel transport rate revealed day to day changes in the divergent pattern of flow and sediment transport the off center location of the lobe reflected an initial asymmetry in the pattern of flow and sediment transport but as the lobe grew the flow and transport gradually switched away to the other distributary width averaged bed load transport rates do not agree well with average rates inferred from bar head deposition or from volumes and spatial patterns of scour and fill the indirect estimates are considered more reliable than those based on direct sampling for necessarily brief durations by the end of the study the new lobe had almost accreted onto the original bar head supporting the idea that most braid bars are of compound origin temporal and spatial patterns in grain size distributions of the bed bed load and deposited sediment are discussed in the companion paper

depositional character and preservation potential of coarse grained sediments deposited by flood events in hyper arid braided channels in the rift valley arava israel abstract four coarse grained braided channels undergoing rapid deposition in the hyper arid arava rift valley have been studied to determine the dynamics of strata deposition by monitored flood events and to ascertain the sedimentologic character of these event deposits the systems span granule sand to sandy gravel bed material having longitudinal bars with simultaneously increasing grains size slope and bed relief scour and fill were monitored along cross sections using scour chains and repeat surveys while event strata fill were described with reference to sediment calibre type of support grading thickness and location unlike many previous investigations of gravel sedimentology the source of information for this study involves not only stratigraphic description but also observation of the concomitant dynamics of the channel bed as expressed by the extent of event deposition the texture of the deposited sediment generally coarsens in sympathy with the surface bed texture of the studied channels the thickness of event deposited sediments increases as the magnitude of flow events increases the stratigraphic record is characterized by 1 sub parallel stratification 2 no grading 3 clast supported gravel infilled with sand granule matrices and 4 rapid sedimentation rates this character is hypothesized to mirror the elevated bedload fluxes in this hyper arid fluvial setting lacking densely vegetated banks the proximal braidplain of this arid environment often contains no extensive fine textured floodplain successions the depth of fill as well as the extent of strata obliteration increase with flood magnitude explaining the increased preservation potential of event strata with increase in flood magnitude it also explains why most event strata including large ones are only partially preserved

delineation of recharge rate from a hybrid water table fluctuation method 1 the concept of the hybrid water table fluctuation wtf method for recharge rate estimation was revisited to estimate the recharge rate a physically based wtf equation was established the concept of transient fillable porosity was proposed and computed with unsaturated hydraulics models the developed model is tested by applying to the water table fluctuation data from hongcheon korea in the applications the recharge and fillable porosity estimates were found to be most sensitive to nonlinearity in the unsaturated water content profile and permeability also the water table level drift which does not originate from precipitation serves as a major source of estimation error

unit bar architecture in a highly variable fluvial discharge regime examples from the burdekin river australia unit bars are relatively large bedforms that develop in rivers over a wide range of climatic regimes unit bars formed within the highly variable discharge burdekin river in queensland australia were examined over three field campaigns between 2015 and 2017 these bars had complex internal structures dominated by co sets of cross stratified and planar stratified sets the cross stratified sets tended to down climb the development of complex internal structures was primarily a result of three processes i superimposed bedforms reworking the unit bar avalanche face ii variable discharge triggering reactivation surfaces and iii changes in bar growth direction induced by stage change internal structures varied along the length and across the width of unit bars for the former down climbing cross stratified sets tended to pass into single planar cross stratified deposits at the downstream end of emergent bars such variation related to changes in fluvial conditions whilst bars were active a hierarchy of six categories of fluvial unsteadiness is proposed with these discussed in relation to their effects on unit bar and dune internal structure across deposit variation was caused by changes in superimposed bedform and bar character along bar crests such changes related to the three dimensionality of the channel and bar geometry when bars were active variation in internal structure is likely to be more pronounced in unit bar deposits than in smaller bedform for example dune deposits formed in the same river this is because smaller bedforms are more easily washed out or modified by changing discharge conditions and their smaller dimensions restrict the variation in flow conditions that occur over their width in regimes where unit bar deposits are well preserved their architectural variability is a potential aid to their identification this complex architecture also allows greater resolution in interpreting the conditions before and during bar initiation and development

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex