bed material transport estimated from the virtual velocity of sediment this study evaluates the possibility of determining bed material transport using the virtual rate of travel of individual particles dimensions of the active layer of the streambed and porosity and density of streambed material magnetically tagged stones and scour indicators were employed in carnation creek british columbia to quantify transport rates observations cover flows up to 36 m3 s 1 0 081 transport rates ranging from 0 090 to 9 7 kg s 1 0 12 13 2 m3 h 1 display a relatively sensitive trend with maximum stream power as expected error analysis indicates that uncertainty in virtual velocity covers the majority of sample variance an evaluation of the two measurement techniques used to delineate active layer dimensions magnetically tagged stones and scour indicators indicates that they yield comparable depths widths and transport rates over the range of flows observed issues for further study are discussed 1998 john wiley sons ltd

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

a mixing layer theory for flow resistance in shallow streams 1 a variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics when the water depth h is much larger than the characteristic roughness height ks roughness formulations such as manning s n and the friction factor f can be explicitly related to the momentum roughness height zo in the log law formulation for turbulent boundary layers thereby unifying roughness definitions for a given surface however when h is comparable to or even smaller than ks the log law need not be valid using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer a model for the flow resistance in shallow flows is developed the key model parameter is the characteristic length scale describing the depth of the kelvin helmholtz wave instability it is shown that the new theory originally developed for canopy turbulence recovers much of the earlier roughness results for flume experiments and shallow gravel streams this study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization the broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types

fission track analysis unravels the denudation history of the bonar range in the footwall of the alpine fault south island new zealand we apply fission track thermochronology to shed new light on the tectonic history of zealandia during late cretaceous continental extension and the onset of late tertiary mountain building in the southern alps of new zealand the southern alps are one of the fastest erosionally exhuming mountain belts on earth exhumation of the bonar range in westland just to the northwest of the alpine fault is orders of magnitude slower we report apatite and zircon fission track ages from samples that were collected along an ene wsw profile across the central bonar range parallel to the tectonic transport direction of a prominent ductile fabric in the basement gneiss zircon fission track zft ages show a large spread from 121 9 12 1 ma to 74 9 7 2 ma 1 errors the youngest zft ages of 78 to 75 ma occur at low elevations on either side of the bonar range and become older towards the top of the range thereby showing a symmetric pattern parallel to the ene trending profile across the range age elevation relationships suggest an exhumation rate of 50 100 m ma 1 we relate the zft ages to slow erosion of a tectonically inactive spot in the late cretaceous magmatic arc of zealandia therefore the first main significance of the paper is that it demonstrates that not all of 110 90 ma zealandia was necessarily participating in extreme core complex related extension but that there were enclaves of lithosphere that underwent slow erosion the apatite fission track aft ages range from 11 1 1 9 ma to 5 3 1 0 ma and age elevation relationships suggest an exhumation rate of c 200 m ma 1 we relate the aft ages to the inception of transpressive motion across the alpine fault and modest exhumation in its footwall in late miocene times if so the second significant point of this paper is that transpressive motion across the alpine fault was already under way by c 11 ma

a hybrid method for size characterization of coarse subsurface fluvial sediments this paper introduces and evaluates a novel method for ascertaining the grain size distribution of subsurface sediments that involves profoundly less sampling effort than standard methods it is based on hybrid sampling principles previously applied to the construction of synthetic surface grain size distributions the method is developed from an empirical demonstration of the approximate similarity of surface and subsurface grain size distributions when compared over a common range of sizes subsurface hybrid models are found to provide good facsimiles of grain size distributions de ned using standard criteria and to yield distribution percentiles with millimetre accuracy the technique is presented as an expedient alternative to standard methods for large perennial gravel bed rivers as this is a new technique prudent application is advised in lieu of further investigation copyright 2004 john wiley sons ltd

sediment generation and delivery from large historic landslides in the southern alps new zealand abstract there is much variability of sediment yield in mountain river systems because it is influenced by both periodic e g snowmelt monsoonal circulation and episodic high intensity rainstorms earthquakes controls in the southern alps of new zealand landslides are dominant mechanisms of conveying large amounts of debris to river channels this paper attempts to quantify catastrophic modes of sediment delivery by presenting three recent examples of large landslides on the western slopes of the southern alps a combination of ground surveys dem based volume calculations and air photo interpretation attributes immediate postfailure sediment yields in excess of 70 000 t km 2 a 1 in the short term such landslide derived sediment pulses pose significant hazards to downstream settlements and infrastructure on alluvial fans where they cause massive aggradation increased flooding frequency and large scale channel avulsion in addition to intramontane valley floor obliteration or channel metamorphosis these geomorphic impacts may thus occur far beyond the initial locations of slope failure these catastrophic off site effects involve apparent net sediment delivery rates in the order of 10 5 10 6 m 3 a 1 the accurate quantification of the relative contribution of debris from the disturbing landslide to overall sediment flux is extremely difficult nonetheless are quantitative estimates of landslide derived sediment production and delivery important data to develop a more comprehensive understanding of the variability in alpine sediment flux such data are essential not only for use in hydraulic engineering or catchment management but also in gauging potential future impacts from rainstorm and earthquake induced landsliding in the southern alps

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

bed aggradation in the lower reach of the jia dhansiri river india abstract this study aims at estimating the rate of bed aggradation of the jia dhansiri river in assam india it is carried out using two methods 1 measurement of channel cross section in the field and 2 measurement of variously dated maps for the period 1995 2006 following these two methods data on parameters pertaining to bed aggradation are generated and authenticated by comparison data on total bed aggradation during 1995 2006 are extrapolated from cross section graphs and again verified with a model proposed in this paper based on average water level of base year and current year and total bed aggradation the rates of bed aggradations are 5 27 cm y at dhansiri khuti village 5 09 cm y at barigain village 5 27 cm y at bagishakash village and 2 64 cm y at thalthali village no degradation zones are found in between during the study period except in minor magnitude and localized cases if these rates of bed aggradation are continued and no significant changes in the channel morphology occur then the river bed may merge with the low river bank after 11 years at dhansiri khuti village 17 years at barigaon village 6 years at bagishakash village and 7 years at thalthali village the average channel aggradation during 11 years of period in the 16 km reach has estimated to be 3 65 cm y again if this rate is continued then the river bed will overtop low banks of the 16 km reach after 16 years at this situation the river may attain a state of geomorphic threshold which may be channel shift following vulnerable slope s

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

field evidence for rapid downstream fining of river gravels through selective transport doubts have been expressed about the ability of either abrasion or sorting to explain strong downstream fining of river gravels we describe pronounced fining over a short distance in a scottish river that has no human disturbance or lateral input of water and sediment measured abrasion rates are far too small to explain observed downstream fining but bed load trap measurements and the dispersion of magnetic tracer pebbles in six subreaches both show sorting during transport the observed downstream fining is also simulated well by a numerical sediment routing model using hydraulic and transport laws consistent with our field measurements the geomorphological cause of the strong fining is slope reduction above a local base level control in this common situation the development of downstream fining is part of the river9s tendency to minimize downstream variation in bed load transport rates and can proceed far more rapidly than the major aggradation otherwise required for equilibration

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

bed load transport measurements with geophones and other passive acoustic methods abstractthis paper reviews the more widely used bed load surrogate acoustic measuring techniques that were tested both in flume experiments and field settings a fair number of these measuring tech

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

radio tracking gravel particles in a large braided river in new zealand a field test of the stochastic theory of bed load transport proposed by einstein hans a einstein initiated a probabilistic approach to modelling sediment transport in rivers his formulae were based on theory and were stimulated by laboratory investigations the theory assumes that bed load movement occurs in individual steps of rolling sliding or saltation and rest periods so far very few attempts have been made to measure stochastic elements in nature for the first time this paper presents results of radio tracing the travel path of individual particles in a large braided gravel bed river the waimakariri river of new zealand as proposed by einstein it was found that rest periods can be modelled by an exponential distribution but particle step lengths are better represented by a gamma distribution einstein assumed an average travel distance of 100 grain diameters for any bed load particle between consecutive points of deposition but larger values of 6 7 m or 150 grain diameters and 6 1 m or 120 grain diameters were measured for two test particle sizes together with other available large scale field data a dependence of the mean step length on particle diameter relative to the d50 of the bed surface was found during small floods the time used for movement represents only 2 7 of the total time from erosion to deposition the increase in percentage of time being used for transport means that it then has to be regarded in stochastic transport models tracing the flow path of bed load particles between erosion and deposition sites is a step towards explaining the interactions between sediment transport and river morphology copyright 2001 john wiley sons ltd

time and the persistence of alluvium river engineering fluvial geomorphology and mining sediment in california abstract river managers need to understand fluvial systems as they change through time many river systems are presently in a state of flux as a result of substantial anthropogenic changes to water and sediment regimes and channel hydraulics yet historical approaches to understanding river systems rarely receive adequate attention because historical methodologies are not conducive to the application of quantitative analysis while there is limited precision in most historical reconstructions the information derived from these studies constrains other interpretations and is essential to a full understanding of the behavior of fluvial systems geomorphology provides a perspective on river systems in which time at various scales is interwoven into practical and theoretical aspects of scientific inquiry thus geomorphology is important to our understanding of not only physical systems but also fundamental concepts of time this study examines channel morphological changes in the bear and american basins brought about by two episodes of sedimentation from hydraulic gold mining the primary event was the production of more than 1 billion m3 of sediment throughout the northern sierra nevada from 1853 to 1884 which caused aggradation in many channels across the sierra foothills and sacramento valley assumptions by both engineers and geomorphologists that morphologic responses to this event were ephemeral that sediment loads have returned to previous levels and that deposits have stabilized are not borne out by field and historical data in the sacramento valley a secondary sedimentation event not previously studied was the production of at least 24 million m3 of sediment during a period of licensed mining from 1893 to 1953 this episode of sedimentation has been largely overlooked as a geomorphic hydrologic or water quality event yet channel morphologic responses in phase with mining during this period are demonstrated systematic changes in stage discharge relationships reflect channel morphological changes that are relevant to flood risk assessments stability of engineering structures on floodplains and geomorphic interpretations

medium and short term channel planform changes on the rivers tay and tummel scotland abstract channel planform change was analysed using a variety of data sources for the medium term 25 years and

hyperconcentrated flow and sediment transport at steep slopes in order to simulate a fine material slurry of a debris flow a clay suspension of various concentrations was recirculated in a steep flume the effect of an increasing fluid density and viscosity on the flow behavior and the bed load transport capacity of the flow was examined viscous effects were found to become important below a limiting particle reynolds number of about 10 above this limiting value density effects cause an increase in the bed load transport rates as compared to similar conditions with clear water as transporting fluid the experimental data in this range can be described with conventional newtonian formulas and is analyzed together with other bed load transport data two different calculation schemes are proposed for the steep slope range is n n 10 where the bed load concentration is significant with respect to the total flow depth below the critical particle reynolds number of 10 the bed load transport rates decreased strongly

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

constraining the long term evolution of the slip rate for a major extensional fault system in the central aegean greece using thermochronology the brittle ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary in this study we examine the slip history of the large scale naxos paros extensional fault system npefs cyclades greece by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime based on apatite and zircon fission track aft and zft and u th he dating we observe variable slip rates across the brittle ductile transition on naxos zft and aft ages range from 11 8 0 8 to 9 7 0 8 ma and 11 2 1 6 to 8 2 1 2 ma and u th he zircon and apatite ages are between 10 4 0 4 to 9 2 0 3 ma and 10 7 1 0 to 8 9 0 6 ma respectively on paros zft and aft ages range from 13 1 1 4 ma to 11 1 1 0 ma and 12 7 2 8 ma to 10 5 2 0 ma while the u th he zircon ages are slightly younger between 8 3 0 4 ma and 9 8 0 3 ma all ages consistently decrease northwards in the direction of hanging wall transport most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of 6 8 km myr 1 on the npefs across the brittle ductile transition even the intrusion of a large granodiorite body into the narrowing fault zone at 12 ma on naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate the data also show that the npefs accomplished a minimum total offset of 50 km between 16 and 8 ma

reconceptualising coarse sediment delivery problems in rivers as catchment scale and diffuse this paper assesses river channel management activities in the context of the interaction between coarse sediment delivery climate change river channel response and flood risk it uses two main sources of evidence 1 an intensive instrumentation of an upland river catchment using both traditional hydrometric and novel sediment sensing methods and 2 a sediment delivery model that combines a treatment of sediment generation from mass failure with a treatment of the connectivity of this failed material to the drainage network the field instrumentation suggests that the precipitation events that deliver sediment from hillslopes to the drainage network are different to those that transfer sediment within the network itself extreme events that could occur at any time in the year i e they are not dependent on wet antecedent conditions were crucial for sediment delivery however sustained high river flows were responsible for the majority of transfer within the river itself application of three downscaling methods to climate model predictions for the 2050s and 2080s suggested a significant increase in the number and potential volume of delivery events by the 2050s regardless of the climate downscaling scenario used first approximations suggested that this would translate into annual bed level aggradation rates of between 0 10 and 0 20 m per year in the downstream main channel reaches second the importance of this delivery for flood risk studies was confirmed by simulating the effects of 16 months of measured in channel simulation with river flows scaled for climate change to the 2050s and 2080s short term sedimentation could result in similar magnitude increases in inundated area for 1 in 0 5 and 1 in 2 year floods to those predicted for the 2050s in relation to increases in flow magnitude finally we were able to develop an alternative approach to river management in relation to coarse sediment delivery based upon reducing the rates of coarse sediment delivery through highly localised woodland planting under the assumption that reducing delivery rates should reduce the rate of channel migration and hence the magnitude of the bank erosion problem thus the paper demonstrates the need to conceptualise local river management problems in upland river environments as point scale manifestations of a diffuse sediment delivery process with a much more explicit focus on the catchment scale if our river systems are to become more insulated from the impacts of future climate changes

quantifying riparian zone structure from airborne lidar vegetation filtering anisotropic interpolation and uncertainty propagation summary advances in remote sensing technology notably in airborne light detection and ranging lidar have facilitated the acquisition of high resolution topographic and vegetation datasets over increasingly large areas whilst such datasets may provide quantitative information on surface morphology and vegetation structure in riparian zones existing approaches for processing raw lidar data perform poorly in riparian channel environments a new algorithm for separating vegetation from topography in raw lidar data and the performance of the elliptical inverse distance weighting eidw procedure for interpolating the remaining ground points are evaluated using data derived from a semi arid ephemeral river the filtering procedure which first applies a threshold either slope or elevation to classify vegetation high points and second a regional growing algorithm from these high points avoids the classification of high channel banks as vegetation preserving existing channel morphology for subsequent interpolation 2 90 9 21 calibration error 4 53 7 44 error in evaluation for slope threshold eidw which accounts for surface anisotropy by converting the remaining elevation points to streamwise co ordinates can outperform isoptropic interpolation idw on channel banks however performs less well in isotropic conditions and when local anisotropy is different to that of the main channel a key finding of this research is that filtering parameter uncertainty affects the performance of the interpolation procedure resultant errors may propagate into the digital elevation model dem and subsequently derived products such as canopy height models chms consequently it is important that this uncertainty is assessed understanding and developing methods to deal with such errors is important to inform users of the true quality of laser scanning products such that they can be used effectively in hydrological applications

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

frequency and magnitude of bedload transport in a mountain river magnitude and frequency of bedload transport was examined in the lainbach river bavaria using magnetically tagged particles during the study 18 small to moderate events and one major event occurred about 1 per cent of the flow period exceeded the entrainment threshold and at least once every year about 50 per cent of the tagged particles were mobile themajor event which occurred during the study period resulted in the deposition of a thick layer of sediment in parts of the channel and passive burial of most of the recovered particles the step pool pattern which characterized the study site prior to the large event was obliterated however the channel recovered quickly and has returned to a new step pool pattern the event changed the boundary conditions by increasing the availability of loose sediment and creating higher river bed slopes in reaches between breached check dams as a result movement of individual particles measured for events of both the same magnitude and duration occurring before and after the large event yielded different values for events which occurred after the large event the range and the mean distance of movement were about ten times higher

does hydrological connectivity improve modelling of coarse sediment delivery in upland environments modelling the delivery of landslide generated sediment to channel networks is challenging due to uncertainty in the magnitude frequency distribution of failures connected to the channel network here we investigate a simplified treatment of hydrological connectivity as a means for improving identification of coarse sediment delivery to upland rivers sediment generation from hillslopes and channel banks and its delivery to the channel network are modelled based on a modified form of shalstab coupled to a network index version of topmodel the network index treatment has two important hydrological effects a it only allows saturated areas to connect to the hydrological network when there is full saturation along the associated flow path and 2 overland flow associated with unconnected but saturated zones is assumed to remain within the catchment and to contribute to a reduction in the catchment averaged saturation deficit we use this hydrological treatment to restrict sediment delivery to situations where there is surface hydrological connection i e saturation along the complete flow path that connects failure areas to the drainage network this represents an extreme restriction on the possibility of connected failure as it does not allow for failed material to connect if failures are associated with partial saturation or where delivery involves runout across areas where hydrological connection is not maintained the impact of this restriction is assessed by comparing model predictions with field mapping of connected failures and data from continuously recording coarse sediment sensors for two storm events the hydrological connection requirement restricted connected failures to zones closer to the drainage network and resulted in a better level of agreement with the field mapped failures simulations suggested that in the study catchment the majority of sediment inputs occur from hydrologically connected areas close to the channel network during moderate sized rainstorms that occur relatively frequently 2007 elsevier b v all rights reserved

entrainment displacement and transport of tracer gravels the mass and size distribution of grain entrainment per unit bed area may be measured by replacing a volume of the bed with tracer gravels and observing the mass difference before and after a transport event this measure of spatial entrainment is relevant to any process involving size selective exchange of sediment between transport and bed and may be directly used in calculations of sediment transport rate using an elementary relation for fractional transport components presented here this relation provides a basis for evaluating tracer data collected by different methods and may be used to provide physical insight regarding the expected behaviour of tracer grains the variation with grain size of total displacement length l ti depends on the degree of mobilization of the individual fractions on the bed surface l ti is independent of d i for smaller fully mobile sizes and decreases rapidly with d i for larger fractions in a state of partial transport in which a portion of the surface grains remain immobile through the flow event the boundary between fully and partially mobile grain sizes increases with flow strength these inferences are supported by values of l ti calculated from flume experiments and provide a physical explanation for a summary relation between l ti and d i based on field data 1997 john wiley sons ltd

high resolution measurement of bedload transport a bedload movement detector of novel design was installed in a gravel bed stream as a component of the ongoing research on sediment transport dynamics in the stuart takla experimental watersheds in north central british columbia canada the device is designed to collect information on the patterns and timing of bedload transport during a flood event the device is based on a passive magnetic sensor that produces signals of 10 2 to 10 5 v as its magnetic field is disturbed by passing clasts a series of 82 sensors is housed in an aluminum beam placed across the stream inserted such that its surface is flush with the gravel bed the device can be raised or lowered to compensate for bed aggradation and scour a data acquisition system gathers voltage signals from the sensors at rates of 30 to 100 hz this device is sensitive enough to record the movement of most volcanic metamorphic granitic and ultramafic clasts larger than a few millimetres o ne ell creek watershed is a 68 km2 tributary basin of the middle river drainage system in the northern headwaters of the fraser river bedload transport generally occurs twice a year in the stuart takla streams once during spring floods and again during salmon spawning activity bedload moved only during two days in 1998 at the peak of the relatively small nival flood in may nevertheless the device detected at least 3 106 passing clasts a continuous record of bedload transport was obtained showing a pulsating pattern of activity seemingly independent of stage lateral movement of the transport zone and a sudden onset of bed movement with a tapered cessation we anticipate that more sophisticated calibration of the sensors and accelerated sampling rates will provide detailed information on the size and or velocity and magnetic permeability of particles moving over the device and will contribute to a better understanding of bedload transport copyright 2000 john wiley sons ltd

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

the tectonic evolution of the southern alps new zealand insights from fully thermally coupled dynamical modelling summary we present here the results of numerical models of the southern alps in which the thermal and dynamical developments of the orogen are fully coupled to one another this interlinkage allows the use of a wide range of thermal and physical features of the orogen as constraints on the applicability of our models in particular the thermal aspect of this method enables the prediction of the distribution of thermochronological ages at the surface of the model perturbation of the geothermal structure due to rapid uplift and exhumation causes an intrinsic weakening and concentration of strain along the equivalent of the alpine fault zone in these models this thermal weakening of the crust also produces a zone of high strain antithetic to the alpine fault in the upper crust that is comparable to the main divide fault zone within the southern alps the introduction of orographic rainfall and erosional processes into the model leads to the development of high asymmetric topography comparable to that of the southern alps this topographic profile results from the capture of available precipitation by the windward side of the orogen and the resultant rain shadow on the leeward side due to the time required to accumulate suycient topography for this rain capture evect to become significant the establishment of this high asymmetric topography lags the initiation of surface uplift by several million years comparison of the observed thermal history of the southern alps with that seen in models based on divering hypotheses of the tectonic evolution of the south island shows that the present tectonic regime of the orogen most probably developed in a single rapid reorganization of plate motions at approximately 5 ma with relative stability of the tectonic regime since that time the variation in isotopic ages along the southern alps is consistent with that expected from variation in accumulated uplift and exhumation along the orogen arising from the obliquity of convergence of the australian and pacific plates

towards establishing climatic thresholds for slope instability use of a physically based combined soil hydrology slope stability model shallow landslides are often linked to high magnitude rainstorms research has attempted to establish threshold rainfall totals that trigger shallow landslides based mainly on field evidence complications arise because not all regolith has the same hydrological behaviour and research frequently fails to take this into account this paper uses a combination of field and modelling approaches to explore the triggering rainfall thresholds for shallow failures in deforested hill country of new zealand it emphasises the role of variations in regolith hydrology focussing on unsaturated and saturated zone responses by using a modelling approach detailed variations in pore pressure positive and negative responses are investigated developing ideas initially derived from field evidence this paper defines and develops earlier research that establishes values for maximum and minimum probability thresholds for shallow landslides and provides a more generalised model that can be applied more widely hydrological mechanisms for shallow landslides are investigated in greater detail than previously possible using a combined hydrology and stability model chasm

a shallow water model of the diurnal dryline this study explores the diurnal variation in the movement and structure of the dryline using a one dimensional shallow water model the model is adapted to test some common theories of dryline motion including the diurnal variation in surface friction static stability inversion erosion and momentum mixing aloft these mechanisms of diurnal variation are first studied individually and then in unison a diurnal variation in the surface friction produces a model dryline that moves westward during the day in disagreement with observations and has a southerly wind maximum near midnight a diurnal variation in the static stability produces a model dryline that steepens in slope and moves eastward during the day and then surges westward at night with a southerly wind maximum 6 to 9 h after the minimum stability inversion erosion during the day produces a nearly vertical model dry front that moves eastward during the day with surface southwesterlies at sunset the model dryline surges westward with a southerly wind maximum before midnight a diurnal variation of the momentum mixing aloft has no significant effect on the model dryline results show that the combined case with a diurnal variation of surface friction inversion erosion and static stability with terrain most accurately describes the observed dryline system the westward surge depicted in the model is compared to the flow evolution of the corresponding dam break problem for a rotating fluid

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

sensitivity of a hydraulic model to channel erosion uncertainty during extreme flooding recent research into flood modelling has primarily concentrated on the simulation of inundation flow without considering the influences of channel morphology river channels are often represented by a simplified geometry that is implicitly assumed to remain unchanged during flood simulations however field evidence demonstrates that significant morphological changes can occur during floods to mobilize the boundary sediments despite this the effect of channel morphology on model results has been largely unexplored to address this issue the impact of channel cross section geometry and channel long profile variability on flood dynamics is examined using an ensemble of a 1d 2d hydraulic model lisflood fp of the 1 2000 year recurrence interval floods in cockermouth uk within an uncertainty framework a series of simulated scenarios of channel erosional changes were constructed on the basis of a simple velocity based model of critical entrainment a monte carlo simulation framework was used to quantify the effects of this channel morphology together with variations in the channel and floodplain roughness coefficients grain size characteristics and critical shear stress on measures of flood inundation the results showed that the bed elevation modifications generated by the simplistic equations reflected an approximation of the observed patterns of spatial erosion that enveloped observed erosion depths the effect of uncertainty on channel long profile variability only affected the local flood dynamics and did not significantly affect the friction sensitivity and flood inundation mapping the results imply that hydraulic models generally do not need to account for within event morphodynamic changes of the type and magnitude of event modelled as these have a negligible impact that is smaller than other uncertainties e g boundary conditions instead morphodynamic change needs to happen over a series of events to become large enough to change the hydrodynamics of floods in supply limited gravel bed rivers such as the one used in this research

an assessment of engineered log jam structures in response to a flood event in an upland gravel bed river engineered log jams eljs are employed to address river restoration goals and a range of river management problems including coarse sediment movement in the bowmont water a dynamic wandering gravel bed river in the scottish borders 33 previously untested eljs primarily designed to capture and store coarse sediment were installed on a trial basis using repeated topographical surveys and field observations the performance of the eljs in response to a 5 10 year recurrence interval flood that occurred on the 25 september 2012 was evaluated at two reaches with catchment areas of 28 km2 and 57 km2 three of the structures were damaged due to scour of surrounding material that exposed the pile anchors and all the timbers of one structure were completely displaced downstream sixteen structures induced geomorphic responses and only four induced significant deposition 0 3 m above that which would occur naturally within the adjacent active gravel bar deposition zones the placement in gravel bars minor channel blockage ratio created by the structures and their porous nature limited the hydraulic interference and in turn geomorphic responses therefore the elj placement goal of increasing sediment storage was not fully met this study contributes to the empirical evidence base for elj performance evaluation of different designs in a range of physiographic settings needed to validate performance and refine design using these initial findings and knowledge gained from other studies recommendations for improving the design and placement strategy are proposed copyright 2016 john wiley sons ltd

low level jet development during a numerically simulated return flow event the evolution of the southerly low level jet llj during a return flow event is studied using output from the penn state ncar mesoscale model version 4 three geographically different southerly lljs develop in the simulation one over the southern plains of the united states a second southwest of brownsville texas and a third over the western gulf of mexico the llj over the plains is found to form first as an inertial oscillation and later as a response to lee troughing and an elevated mixed layer that develops over the region over mexico the temperature structure over the altiplanicie mexicana mexican high plain is responsible for a locally intense low level pressure gradient east of the high plain which remains nearly stationary over two diurnal cycles the llj over the western gulf of mexico results largely from topographic blocking of the low level southerly flow by the eastern end of the neovolcanic cordillera northwest of veracruz mexico the evolution of the lower troposphere over the southern plains resembles the carlson and ludlam conceptual model for a severe storm environment but the structure of the return flow is complex when midlevel westerlies are weak mesoscale and boundary layer processes govern the development of lljs as the west and southwesterly winds increase with an approaching upper level disturbance synoptic influences overwhelm the mesoscale processes leading to a single larger scale llj

extensional faulting on tinos island aegean sea greece how many detachments zircon and apatite fission track zft and aft and u th he 40ar 39ar hornblende and u pb zircon ages from the granites of tinos island in the aegean sea greece suggest together with published zft data that there are three extensional detachments on tinos the tinos granites crosscut the tinos detachment cooling of the granites was controlled by the livadi detachment which occurs structurally above the tinos detachment our u pb zircon age is 14 6 0 2 ma and two 40ar 39ar hornblende ages are 14 4 0 4 and 13 7 0 4 ma zft and aft ages go from 14 4 1 2 to 12 2 1 0 ma and 12 8 2 4 to 11 9 2 0 ma u th he ages are from 10 4 0 2 to 9 9 0 2 ma zircon and 11 9 0 5 to 10 0 0 3 ma apatite all ages decrease northeastward in the direction of hanging wall transport on the livadi detachment and age distance relationships yield a slip rate of 2 6 3 3 1 0 km ma 1 this rate is smaller than a published slip rate of 6 5 km ma 1 for the vari detachment which is another detachment structurally above the tinos detachment because of the different rates and because published zft ages from the footwall of the vari detachment are 10 ma we propose that the vari detachment has to be distinguished from the older livadi detachment we discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the vari detachment cut down into the footwall of the livadi detachment successively exhuming deeper structural units the thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation

southerly low level jet in the winter cyclones of the southwestern great plains abstract on the basis of 20 cases in the winter half year it is found that a southerly low level jet llj is regularly associated with extratropical cyclones in the southwestern great plains only very weak and short lived lows are not associated with an llj a composite model is constructed that shows the typical sequence of events during the formation of the llj in the texas colorado area this jet is initially dry since it develops over the continent only in the advanced stage 1 2 days after its inception and as it expands over a wide area does the llj start drawing water vapor from the gulf of mexico

needle ice processes and sediment mobilization on river banks the river ilston west glamorgan uk abstract this paper examines the role of needle ice processes in the bank erosion system of a site on the river ilston west glamorgan south wales uk bank retreat rates were monitored with erosion pins over a 2 25 year period concurrent detailed data were also obtained on river flow levels and ambient air and stream temperatures unique data on river bank thermal regimes are presented along with rare information on the morphological properties and sediment yield characteristics of needle ice growths needle ice occurred even with mild freezing temperatures if sufficient bank moisture was present with average growth rates of approximately 1 mm h 1 bank material incorporation and mobilization within needle ice was significant sediment yields of up to 4 02 kg m 2 of bank face were observed and represented between 32 and 43 of total bank erosion recorded most sediment was incorporated within needle ice when growth became stressed because of overrapid cooling and or limited moisture supplies which supports the models of outcalt and fukuda four mechanisms of direct needle ice sediment transport on river banks were identified direct particle fall sediment laden rivulets sliding failures and toppling failures however the indirect preparatory role of needle ice and frost disturbance of bank surfaces is also emphasized and the enhanced fluvial erosion which takes place when bank materials have first been conditioned by frost related processes is noted both indirect and direct effects are expressed in a simple conceptual model and a number of the important system linkages examined combinations of needle ice action and subsequent fluid entrainment of weakened bank material appear to be the dominant mechanism for bank erosion here pronounced and persistent erosional notches in the lower parts of the bank profile were observed showing that in winter even single low magnitude flow events can effect significant channel width adjustment here

evaluation of an experimental lidar for surveying a shallow braided sand bedded river reaches of a shallow 1 0 m braided sand bedded river were surveyed in 2002 and 2005 with the national aeronautics and space administration s experimental advanced airborne research lidar eaarl and concurrently with conventional survey grade real time kinematic global positioning system technology the laser pulses transmitted by the eaarl instrument and the return backscatter waveforms from exposed sand and submerged sand targets in the river were completely digitized and stored for postflight processing the vertical mapping accuracy of the eaarl was evaluated by comparing the ellipsoidal heights computed from ranging measurements made using an eaarl terrestrial algorithm to nearby 0 5 m apart ground truth ellipsoidal heights after correcting for apparent systematic bias in the surveys the root mean square error of these heights with the terrestrial algorithm in the 2002 survey was 0 11 m for the 26 measurements taken on exposed sand and 0 18 m for the 59 measurements taken on submerged sand in the 2005 survey the root mean square error was 0 18 m for 92 measurements taken on exposed sand and 0 24 m for 434 measurements on submerged sand in submerged areas the waveforms were complicated by reflections from the surface water column entrained turbidity and potentially the riverbed when applied to these waveforms especially in depths greater than 0 4 m the terrestrial algorithm calculated the range above the riverbed a bathymetric algorithm has been developed to approximate the position of the riverbed in these convolved waveforms and preliminary results are encouraging

testing bedload transport formulae using morphologic transport estimates and field data lower fraser river british columbia morphologic transport estimates available for a 65 km stretch of fraser river over the period 1952 1999 provide a unique opportunity to evaluate the performance of bedload transport formulae for a large river over decadal time scales formulae tested in this paper include the original and rational versions of the bagnold formula the meyer peter and muller formula and a stream power correlation the generalized approach adopted herein does not account for spatial variability in flow bed structure and channel morphology however river managers and engineers as well as those studying rivers within the context of long term landscape change may find this approach satisfactory as it has minimal data requirements and provides a level of process specification that may be commensurable with longer time scales hydraulic geometry equations for width and depth are defined using morphologic maps based on aerial photography and bathymetric survey data comparison of transport predictions with bedload transport measurements completed at mission indicates that the original bagnold formula most closely approximates the main trends in the field data sensitivity analyses are conducted to evaluate the impact of inaccuracies in input variables width depth slope and grain size on transport predictions the formulae differ in their sensitivity to input variables and between reaches average annual bedload transport predictions for the four formulae show that they vary between each other as well as from the morphologic transport estimates the original bagnold and meyer peter and muller formulae provide the best transport predictions although the former underestimates while the latter overestimates transport rates based on our findings an error margin of up to an order of magnitude can be expected when adopting generalized approaches for the prediction of bedload transport copyright 2005 john wiley sons ltd

a coupled sediment routing and lateral migration model for gravel bed rivers we describe additions made to a multi size sediment routing model enabling it to simulate width adjustment simultaneously alongside bed aggradation incision and fining coarsening the model is intended for use in single thread gravel bed rivers over annual to decadal timescales and for reach lengths of 1 10 km it uses a split channel approach with separate calculations of flow and sediment transport in the left and right sides of the channel bank erosion is treated as a function of excess shear stress with bank accretion occurring when shear stress falls below a second low threshold a curvature function redistributes shear stress to either side of the channel we illustrate the model through applications to a 5 6 km reach of the upper river wharfe in northern england the sediment routing component with default parameter values gives excellent agreement with field data on downstream fining and down reach reduction in bedload flux and the width adjustment components with approximate calibration to match maximum observed rates of bank shifting give plausible patterns of local change the approach may be useful for exploring interactions between sediment delivery river management and channel change in upland settings

combining impact sensor field and laboratory flume measurements with other techniques for studying fluvial bedload transport in steep mountain streams the timing and rate of fluvial bedload transport are of central importance within sediment budget studies and in many applications in river science and engineering during the years 2010 2011 and 2012 detailed field measurements with portable impact sensors as a non invasive technique for indirectly determining fluvial bedload transport intensity were conducted in two instrumented and supply limited drainage basin systems erdalen and bodalen in the fjord landscape in western norway additional field measurements with portable impact sensors were carried out in 2010 and 2011 in selected transport limited fluvial systems in the coast mountains of western canada the collected impact sensor field data were calibrated with laboratory flume experiments the data from the impact sensor field measurements in western norway and the flume experiments were combined with field data from continuous discharge monitoring repeated surveys of channel morphometry and sediment texture particle tracer measurements helley smith samplings underwater video filming and biofilm analyses the combination of methods and techniques applied provides insights into the temporal variability and intensity of fluvial bedload transport in the selected mountain streams i in the transport limited systems with generally high bedload transport rates during high discharge and with bedload material moving in clusters over the impact sensor plates impact sensor data based on a 1 s measuring interval provide the opportunity to detect the start and end of bedload transport thus to identify discharge thresholds for sediment entrainment and to roughly estimate the intensity and relative intensity of change of bedload transport during the measuring period ii in the supply limited systems with low bedload transport rates and bedload components moving separately as single particles over the impact sensor plates impact sensor data with a 1 s measuring interval allow the detection of the start and end of transport of bedload components 11 3 mm thus the identification of discharge thresholds for possible entrainment of particles the quantification of the number of particles 11 3 mm moving over the impact sensor plates during the measuring period the rough estimation of grain sizes of the particles moving separately over the impact sensor plates and the calculation of the total mass of the bedload material 11 3 mm moving over the impact sensor plates during the measuring period iii when combined with other methods and techniques helley smith sampling particle tracer measurements biofilm analyses underwater video filming which provide information on the active bedload transport channel width on discharge thresholds for possible entrainment of particles of different grain sizes and on transport rates of bedload material 11 3 mm total rates of fluvial bedload transport covering all given grain sizes of the bedload material can be calculated for the supply limited mountain streams with generally low bedload transport the higher measured annual bedload yield in bodalen 13 6 t km 2 yr 1 compared to erdalen 2 6 t km 2 yr 1 reflects a higher level of slope channel coupling in bodalen than in erdalen

geochronology and geochemistry of high pressure granulites of the arthur river complex fiordland new zealand cretaceous magmatism and metamorphism on the palaeo pacific margin the arthur river complex is a suite of gabbroic to dioritic orthogneisses in northern fiordland new zealand the arthur river complex separates rocks of the median tectonic zone a mesozoic island arc complex from palaeozoic rocks of the palaeo pacific gondwana margin and is itself intruded by the western fiordland orthogneiss new shrimp u pb single zircon data are presented for magmatic metamorphic and deformation events in the arthur river complex and adjacent rocks from northern fiordland the arthur river complex orthogneisses and dykes are dominated by magmatic zircon dated at 136 129 ma a dioritic orthogneiss that occurs along the eastern margin of the complex is dated at 154 4 3 6 ma and predates adjacent plutons of the median tectonic zone rims on zircon cores from this sample record a thermal event at c 120 ma attributed to the emplacement of the western fiordland orthogneiss migmatitic palaeozoic orthogneiss from the arthur river complex 346 6 ma is interpreted as deformed wall rock very fine rims 5 20 lm also indicate a metamorphic age of c 120 110 ma a post tectonic pegmatite 81 8 1 8 ma may be related to phases of crustal extension associated with the opening of the tasman sea the arthur river complex is interpreted as a batholith emplaced at mid crustal levels and then buried to deep crustal levels due to convergence of the median tectonic zone arc and the continental margin

bedload hysteresis in a glacier fed mountain river sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before counterclockwise hysteresis or after clockwise hysteresis the peak of bedload hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions respectively hysteresis has been mainly explored for the case of suspended sediment transport but it was rarely reported for bedload transport in mountain streams this work focuses on the temporal variability of bedload transport in an alpine catchment saldur basin 18 6 km2 italian alps where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0 5m long steel pipe runoff dynamics are dominated by snowmelt in late spring early summer mostly by glacier melt in late summer early autumn and by a combination of the snow and glacier melt in mid summer the results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin on the contrary counterclockwise hysteresis tend to be more frequent during late glacier melting period possibly due to the time lag needed for sediment provided by the glacial and peri glacial area to be transported to the monitoring section however intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis thus indicating the activation of different sediment sources these results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams

using sediment impact sensors to improve the morphological sediment budget approach for estimating bedload transport rates constructing a sediment budget from morphological channel change typically measured using repeat cross sectional surveys has proven a useful technique for estimating mean bedload transport rates in gravel bed rivers we apply and suggest improvements to the approach using new data sources from an intensely monitored 5 6 km reach of an upland gravel bed river in northern england sediment impact sensors were placed in the bed to record the instantaneous passage of grains during transport events these sensors provide valuable information for the budget including 1 a downstream budget limit from which the rest of the budget can be calculated 2 estimates of sediment input from tributaries and 3 a better indication of active transport time used in the calculation of average transport rates further information collected from field studies include estimates of lateral inputs from the banks using field surveys and bank erosion pins and estimates of the variability of sediment porosity from bed grain size distributions budget calculations for different locations and time periods demonstrate large spatial and temporal variabilities in bedload transport rates over a short distance 3 km whilst some uncertainty in the new data sources remains this work highlights some limitations of the traditional budget approach and some potential solutions in particular the value of sediment impact sensors for sediment transport studies

spatial pattern of flow competence and bed load transport in a divided gravel bed river a 14 month continuous record of the spatial variation in the incidence and magnitude of bed load transport was provided by nine pit traps sunk into the bed of a 21 m wide upland gravel bed river the bed load data are related to a simultaneous record of average bed shear stress derived from the depth slope product the study reach is straight and includes a small low relief mid channel bar which represents the divide between two zones of markedly different bed structure and stability he bed of the left channel and bar tail is loose with an open framework while that of the bar head and right channel is tightly interlocking and well imbricated bed surface grain size is similar throughout the reach the two zones of contrasting bed structure have a strong influence on the threshold of sediment movement c and consequently the spatial pattern of bed load transport entrainment thresholds for the tightly structured bed are up to seven times higher than those for the loosely structured bed sediment transport is therefore most frequent in the left channel and over the bar tail where flows with excess shear stresses c peaking at 8 c constitute 19 of the flow record this is in marked contrast to the right channel and bar head where excess shear stresses of maximum 1 4 c total only 1 3 of the flow record however despite the marked difference in the magnitude and duration of competent flows between the two contrasting bed areas little difference in bed load yield is observed between the nine traps when averaged over the 14 month study period this study shows that different zones of bed structure and stability in a channel will control the incidence and spatial pattern of bed load transport but not necessarily the medium and long term bed load yield this has important implications for local and short term bed load sampling programs and the numerical modeling of sediment budgets and zone to zone bed load transfer

large floods alluvial overprint and bedrock erosion depending on their behaviour during extreme floods streams can be divided into two distinct classes which derive from a simple threshold model of transport dynamics flood cleaning streams erode during high flows and deposit during small and medium flows flood depositing streams deposit during high flows and erode during small and medium flows using published descriptions of the geomorphic effects of large floods rivers with a wide range of drainage areas and other characteristics are classified as either flood cleaning or flood depositing in bedrock channels this behaviour can lead to a feedback effect the overprint effect between sediment transport processes and bedrock erosion which can modulate long term bedrock erosion rates the overprint effect arises when alluvium covers the bedrock and typical alluvial channel forms e g meandering or braiding patterns armour layers or bedforms develop which influence sediment transport rates this effect may accelerate or decelerate sediment export from a reach causing increased or decreased long term bedrock erosion rates the overprint effect is illustrated using field data from the erlenbach switzerland and its implications for channel dynamics and bedrock erosion are discussed copyright 2012 john wiley sons ltd