hydraulic modeling of bed load transport in gravel bed laba river on the basis of a field study of a piedmont braided reach of the gravel bed laba river in the northern caucasus russia an undistorted 1 50 scale mobile bed hydraulic model was constructed in an outdoor experimental plot of the state hydrological institute st petersburg russia channel and hydraulic regimes of the laba river were studied in this model attention was paid to the regime of bed load transport and its relation to the hydraulic characteristics of the flow the same problems were investigated in an 100 m long 1 m wide flume with glass walls also located at the state hydrological institute and in an 18 m long 2 46 m wide steel tilting flume at hr wallingford ltd u k quantitative characteristics of bed load transport were obtained from the laboratory experiments and compared with the field data proximity of the field and scaled up laboratory data demonstrates that the processes of bed load transport of gravel bed rivers can be faithfully reproduced in small scale models and flumes

understanding the temporal dynamics of the wandering renous river new brunswick canada wandering rivers are composed of individual anabranches surrounding semi permanent islands linked by single channel reaches wandering rivers are important because they provide habitat complexity for aquatic organisms including salmonids an anabranch cycle model was developed from previous literature and field observations to illustrate how anabranches within the wandering pattern change from single to multiple channels and vice versa over a number of decades the model was used to investigate the temporal dynamics of a wandering river through historical case studies and channel characteristics from field data the wandering renous river new brunswick was mapped from aerial photographs 1945 1965 1983 and 1999 to determine river pattern statistics and for historical analysis of case studies five case studies consisting of a stable single channel newly formed anabranches anabranches gaining stability following creation stable anabranches and an abandoning anabranch were investigated in detail long profiles hydraulic geometry channel energy grain size and sediment mobility variables were calculated for each channel within the renous study area the frequency of channel formation and abandonment were similar over the 54 years of analysis indicating that the wandering pattern is being maintained eight anabranches were formed through avulsions five were formed through the emergence of islands from channel bars and 11 anabranches were abandoned the stable anabranch pair displayed similar hydraulic geometry and channel energy characteristics while unstable anabranch pairs did not the anabranch pair that gained stability displayed more similar channel energy characteristics than the anabranch pair that was losing stability abandoning it appears that anabranch pairs with similar energy characteristics are more stable than anabranches where these characteristics are out of balance this is consistent with the hypothesis that anabranch pairs of similar length will be more stable than those with dissimilar lengths copyright 2005 john wiley sons ltd

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

morphodynamic signatures of braiding mechanisms as expressed through change in sediment storage in a gravel bed river previous flume based research on braided channels has revealed four classic mechanisms that produce braiding central bar development chute cutoff lobe dissection and transverse bar conversion the importance of these braiding mechanisms relative to other morphodynamic mechanisms in shaping braided rivers has not yet been investigated in the field here we exploit repeat topographic surveys of the braided river feshie uk to explore the morphodynamic signatures of different mechanisms of change in sediment storage our results indicate that when combined the four classic braiding mechanisms do indeed account for the majority of volumetric change in storage in the study reach 61 total chute cutoff traditionally thought of as an erosional braiding mechanism appears to be the most common braiding mechanism in the study river but was more the result of deposition during the construction of diagonal bars than it was the erosion of the chute three of the four classic mechanisms appeared to be largely net aggradational in nature whereas secondary mechanisms including bank erosion channel incision and bar sculpting were primarily net erosional although the role of readily erodible banks in facilitating braiding is often conceptualized we show that bank erosion is as or more important a mechanism in changes in sediment storage than most of the braiding mechanisms and is the most important secondary mechanism 17 of total change the results of this study provide one of the first field tests of the relative importance of braiding mechanisms observed in flume settings

a study of the sulfur cycle in the antarctic marine boundary layer atmospheric sampling was conducted aboard r v polar duke from march 21 to april 27 1986 in the southern drake passage and in the coastal waters west of the antarctic peninsula average atmospheric concentrations n 6 of sulfur dioxide so2 vapor aerosol methanesulfonate ch3so3 and aerosol non sea salt sulfate nss so4 were 0 36 0 22 and 0 34 nmol m 3 respectively cascade impactor data indicated that more than 85 of the masses of both ch3so3 and nss so4 were on particles of 0 25 m mean aerodynamic radius average concentrations n 8 of ch3so3 and nss so4 in precipitation were 0 09 and 0 57 m respectively box model calculations based on this limited data suggest a total sulfur removal rate from the local marine boundary layer of 0 3 7 2 mol m 2 day 1 this removal approximately balances the oceanic source of dimethylsulfide dms sulfur of 1 2 4 4 mol m 2 day 1 100 estimated by berresheim 1987 from data obtained during the same cruise the box model calculations also suggest that heterogeneous so2 oxidation may be the major pathway for dms to sulfate conversion 75 and or that other sources of sulfate may not be negligible observed mineral aerosol and 222rn concentrations were low but slightly elevated above pure remote marine background levels suggesting a weak but discernible continental character in sampled air uncertainties are large owing to the limited sampling time study area and numbers of samples obtained but overall the sulfur cycle in the coastal antarctic marine boundary layer appears not to differ remarkably from that in other remote marine regions

mechanisms of anabranch avulsion within gravel bed braided rivers observations from a scaled physical model the physical modelling of gravel bed braided rivers using a 1 20 froude scale model permits analysis of the types and relative occurrence of different avulsion mechanisms anabranch avulsion within braided rivers involves three main mechanisms choking avulsion caused by blockage of one channel by a sediment lobe constriction avulsion produced by deflection confinement and subsequent diversion of the flow by a barform and apex avulsion following erosion at the outside of sinuous thalwegs and confined meander bends each avulsion mechanism is described and analysis of the abundance of each type illustrates choking avulsion to be predominant without braided rivers three factors are found to control anabranch avulsions namely flow discharge sediment flux and floodplain topography these are briefly discussed together with the implications of avulsion type for the alluvial architecture of gravelly braided alluvium

the relationship between channel avulsion flow occupancy and aggradation in braided rivers insights from an experimental model experimental modelling of an aggrading braided river has allowed investigation of the relationship between the frequency of channel avulsion a f the duration of time that the braidplain is occupied by flow the spatial pattern of braidplain sedimentation and how these respond to a change in sediment supply s s model results demonstrate a strong positive relationship between s s and a f and that there is no downstream change in a f over the short braidplain distances ca 100 m modelled herein although a f is strongly dependent on s s the degree of channel switching does not influence the rate or spatial pattern of braidplain sedimentation all experiments used a single central input for water and sediment and the channels occupied the centre of the alluvial basin for a longer period of time than the margins for all sediment supply rates and distances downstream despite this spatio temporal pattern in flow occupancy braidplain sedimentation rates were nearly uniform both downstream and across the basin and increased at approximately the same rate as increases in s s as a consequence less frequent and possibly short lived flows at the margins of the braidplain deposited and preserved more sediment per unit time in comparison with the centre of the basin where flow occupancy was higher an approximate order of magnitude change in sediment supply resulted in only a factor of two change in bed slope probably due to both an increase in channelization and adjustment of the channel form that maintained sediment transport through the basin this result suggests that linear diffusion models are unlikely to be applicable in landscape evolution models that possess aggrading multi thread rivers which are capable of self adjustment in channel number and form

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

experimental evidence of dynamic scaling and indications of self organized criticality in braided rivers the evolution of an experimental braided river produced in our laboratory has been monitored and analyzed it has been shown that in addition to the spatial scaling revealed by sapozhnikov and foufoula georgiou 1996a braided rivers also exhibit dynamic scaling this implies that a smaller part of a braided river evolves identically in the statistical sense to a larger one provided the time is renormalized by a factor depending only on the ratio of the spatial scales of those parts the small value of the estimated dynamic exponent z is interpreted as an indication that the evolution of small channels in a braided river system is to a large extent forced by the evolution of bigger channels the presence of dynamic scaling is further interpreted as indicating that braided rivers may be in a critical state and behave as self organized critical systems in a recent paper sapozhnikov and foufoula georgiou 1996a evidence was presented that natural braided rivers ex hibit anisotropic scaling self affinity in their geometrical structure within a range of scales spanning the width of the narrowest channel to the width of the braid plain in simple words within these scales if a small part of a braided river is stretched in a certain way along the mainstream direction and a certain different way along the perpendicular direction then this stretched part looks statistically the same as a bigger part of the river such anisotropically scaled objects are called self affine fractals and are characterized by two fractal exponents nx and ny the ratio nx ny characterizes the scaling anisotropy and the fractal dimension d 5 ny 2 nx 1 1 ny e g see sapozhnikov and foufoula georgiou 1995 indicates how densely the object fills the space in sapozhnikov and foufoula georgiou 1996a three natu ral braided rivers of different scales and different hydrological and sedimentological characteristics aichilik and hulahula in alaska and brahmaputra in bangladesh were analyzed for spatial scaling using the logarithmic correlation integral lci method developed by sapozhnikov and foufoula georgiou 1995 interestingly enough it was observed that despite their different scales 0 5 15 km in braid plain width slopes 7 3 10 23 8 310 25 and types of bed material gravel to sand all three rivers exhibited anisotropic spatial scaling with almost the same fractal exponents nx 5 0 72 0 74 and ny 5 0 51 0 52 the x axis being oriented along the river and the y axis being in the perpendicular direction in simple terms this im plies that if parts of a braided river are stretched by l along the mainstream direction and by l n y n x l 0 7 along the perpen dicular direction the resulting images will look statistically similar to each other similarity within a braided river at the same time the invariance of nx and ny between braided rivers of different sizes and hydrology sedimentology suggests that the same anisotropic scaling as above applied to different riv ers will result in statistically similar images apart possibly from a normalization factor to account for the different mass of each river note that mass here refers to the area i e number of pixels covered with water the presence of such a statistical scale invariance in the spatial structure of braided rivers apart from being interesting in its own right might indicate the presence of universal features in the underlying mechanisms responsible for the formation of braided rivers and deserves further theoretical and experimental investiga tion braided rivers besides their complex geometry at any in stant of time are also highly dynamic systems characterized by intensive erosion sediment transport and deposition and fre quent channel shifting as they evolve predicting the evolution of braided rivers in terms of frequency and magnitude of chan nel shifting is of paramount importance where hydraulic struc tures or land developments are planned or where field use must be made of maps and air photos it is of great practical and theoretical value therefore to study the evolution of braided rivers in addition to their spatial structure in view of the evidence for spatial static scaling in braided rivers the question is asked here as to whether they also show dynamic scaling the presence of dynamic scaling would imply that space and time can be appropriately rescaled such that the evolution of the spatial structure of parts of the river of dif ferent size would be statistically indistinguishable the pres ence of dynamic scaling would also provide a highly desirable integrated framework for studying simultaneously the spatial and temporal structure of braided rivers

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

meteorological transport of continental soot to antarctica an impactor concentrator microdensitometer icm instrument system has been constructed and calibrated this system is sufficiently sensitive to measure the black carbon soot component of antarctic aerosol with a sampling time of four hours the impactor concentrator was exposed to antarctic air at ross island in september 1987 microdensitometer analysis of the collected specimens indicates that the maximum black aerosol concentration was observed concurrently with the arrival of the warmest air accompanying a cyclonic storm this is similar to the concurrence of continental radon and lead isotopes with warm advection measured on the antarctic coast by polian et al 1986 it is possible that continental soot can be transported to the antarctic coast several times each year by this mechanism

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

sedimentary facies changes and climatic tectonic controls in a foreland basin the urumqi river tian shan northwest china abstract a sedimentological study was conducted on an interbedded fine gravel and silt succession up to 70 m thick at cangfang gou in northern chaiwopu basin tian shan nw china the succession informally termed urumqi gravel is part of the gravelly basin infill that commenced around 1 87 ma bp in the early pleistocene its upper boundary determined by a magnetostratigraphical study is slightly above the brunhes matuyama b m at 780 ka bp detailed facies analysis indicates that the river underwent multiple cyclic changes from a bed load dominated braided to a suspension load dominated sinuous regime the latter probably adopted a single thread meandering pattern confined within its course and was predominated by overbank accretion of fines without development of distinct point bars the river probably represents the proto urumqi river it appears that the cyclic sequences are climatically controlled their preservation in the succession is largely attributed to the continued aggradation resulted from the subsidence of the chaiwopu basin in the early pleistocene

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

valley confinement as a factor of braided river pattern for the platte river abstract the platte river in nebraska has evolved in the twentieth century from a predominantly braided river pattern to a melange of meandering wandering anastomosed island braided and fully braided reaches identifying the factors that determine the occurrence of a fully braided main channel was the objective of this study aerial photography gage flow data ground surveyed cross sections bed material samples and the results of sediment transport modeling were used to examine factors that control spatial change in main river pattern of the central platte river valley confinement is identified as the determining factor of braided river in nine of eleven divisions of the central platte river flow reduction and the interruption of sediment supply are identified as determining factors preventing fully braided river in the remaining two of eleven reaches valley confinement the topography which limits the width of the floodplain was initially measured as width between historical banks predevelopment river banks this metric was later refined to width between confining features historical banks remnant bars bridge abutments protected banks and levees under existing conditions the main channel of the central platte river is fully braided when valley confinement width between confining features is 600 m or less and begins to divide into the multiple channels of an anastomosed pattern when valley confinement width between confining features exceeds 600 m when platte river flow is divided between two to four major anabranches a fully braided pattern in the main channel of the main anabranch requires a more confined valley of 400 m or less valley confinement is demonstrated to be the dominant factor in determining river pattern in the central platte river although this factor is not normally considered in the continuum of channel pattern model conclusions from this study can be used to increase the occurrence of fully braided main channel in the central platte river to aid habitat recovery for endangered or threatened bird species that favor this river pattern consideration of valley confinement with river continuum factors can aid river managers by improving predictions of river pattern in response to management actions

a synthesis of warm air advection to the south polar plateau surface temperature and wind chronologies of varying length and 10 m snow temperatures have been used to produce a synthesis of airflow into antarctica this synthesis shows relatively warm air over ellsworth land which appears to enter the south polar plateau through a slightly lower lying trough between the summit of the transantarctic mountains and the polar plateau comparison of recent automatic weather station aws records from mount howe 88 5 s 150 w with four aws surrounding south pole at 89 s show that this upslope inflow is a frequent and persistent phenomenon

temporal variations in bedload transport rates associated with the migration of bedforms temporal variations in bedload transport rates that occur at a variety of timescales even under steady flow conditions are accepted as an inherent component of the bedload transport process rarely however has the cause of such variations been explained clearly we consider three data sets obtained from laboratory experiments that refer to measurements of bedload transport made with continuously recording bedload traps each data set is characterized by a predominant low frequency oscillation on which additional higher frequency oscillations generally are superimposed the period of these oscillations as isolated through the use of spectral analysts ranged between 0 47 and 168 minutes and was associated unequivocally with the migration of bedforms such as ripples dunes and bars the extent to which such oscillatory behaviour may be recognized in a data set depends on the duration of sampling and the length of the sampling time with respect to the period of a given bedform several theoretical probability distribution functions have been developed to describe the frequency distributions of relative bedload transport rates that are associated with the migration of bedforms einstein 1937b hamamori 1962 carey and hubbell 1986 these distribution functions were derived without reference to a sampling interval we present a modification of hamamori s 1962 probability distribution function generated by monte carlo simulation which permits one to specify the sampling interval in relation to the length of a bedform comparisons between the simulated and observed frequency distributions that were undertaken on the basis of the data described herein are good significant at the 90 per cent confidence level finally the implications that temporal variability which is associated with the migration of bedforms have for the accurate determination of bedload transport rates are considered

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

braidplain evolution in the pennsylvanian south bar formation sydney basin nova scotia canada abstract the south bar formation is a 1 km thick alluvial succession in the pennsylvanian morien group of the sydney basin nova scotia that fines upward from conglomerate to pebbly sandstone to sandstone facies assemblages the conglomerate assemblage comprises mainly massive to horizontally stratified conglomerate and planar cross stratified sandstone attributed to deposition in proximal braided rivers confined between bedrock ridges the sandstone assemblage shows uniformity of facies and paleocurrents across the basin and is interpreted as a distal braidplain deposit the pebbly sandstone assemblage is transitional between the other two both sandstone assemblages are dominated by trough cross stratified sandstone formed by dune migration in channel tracts about 4 m deep this succession differs markedly from platte river and icelandic sandy braidplain deposits which are mainly planar cross stratified sands formed by broad shallow flow the south bar sandstones are more like south saskatchewan river deposits but differ in 1 greater abundance of trough sets and 2 rarity of planar sets and other components of shallow water channel fill these features are ascribed to 1 inheritance of relatively deep channels from confined upstream reaches 2 maintenance of deep flow in active tracts by local confinement between temporary banks and 3 rapid avulsive abandonment of active tracts which inhibited development of channel fill sequences evidence for local temporary confinement is preserved as in situ and slumped channel margin mudrock units lateral and vertical transitions from the upper south bar formation to the mud rich waddens cove and sydney mines formations are ascribed to changes in channel pattern from braided to meandering the former is attributed to decreased slope the latter to eustatic rise in sea level

the three metamorphic belts of the hellenides a review and a kinematic interpretation summary new results obtained in the three metamorphic belts of the hellenides suggest that each belt has a different structure geotectonic setting and evolution the external metamorphic belt of peloponnesus crete has probably resulted from nappe movement in the vicinity of an evolving island arc system the blueschists occurring within this external belt are allochthonous and have been transported with other nappes over the external carbonate platform of the pre apulian plattenkalk ionian tripolitza almyropotamos units this implies that there was only one true blueschist domain initiated in the cycladic area during early eocene the kinematic interpretation is based on the distinction of a and b structures and on the nature of the shear zones between the different domains especially that between the metamorphic hellenides below and the non metamorphic hellenides above the existence of the probably lower palaeozoic meta sedimentary sequence of kastoria in the northern pelagonian zone indicates that the overlying ophiolite bearing almopias unit has been derived from within the hercynian domain the kastoria sedimentary sequence the ophiolites of vertiskos and the carbonate platform of pangeon are considered to be most likely elements of a probable hercynian orogeny

record high temperatures in the antarctic a synoptic case study abstract during the period 23 29 december 1978 abnormally high temperatures were recorded at several antarctic stations new records were set at south pole memurdo and vostok and near record high temperatures were reached at coastal stations in east antarctica synoptic scale events accompanying these unprecedented high temperatures were investigated using surface satellite and radiosonde data the high temperatures were associated with two intrusions of warm air which penetrated the continent from the atlantic and indian ocean sectors warming at south pole occurred with the passage of a jet like feature and its accompanying baroclinic zone

wandering miramichi rivers new brunswick canada abstract six rivers within the miramichi basin of new brunswick display long sections with multiple channels that surround semi permanent islands linked by single channels this type of anabranching river may be termed wandering displaying a similar planimetric pattern to wandering rivers in western canada this research addresses three objectives 1 to provide a detailed description of the location pattern characteristics and boundary conditions of wandering miramichi rivers 2 to compare the pattern characteristics among wandering rivers within the miramichi basin and to other wandering meandering and braided rivers and 3 to investigate formative processes for wandering miramichi rivers wandering rivers within the miramichi region occur in larger valleys located downstream of an abrupt change in bedrock from resistive to more erosive bedrock lithology larger rivers display greater braid indices than smaller rivers wandering miramichi rivers display more similarities to meandering rivers than braided rivers exhibit an anabranching pattern yet have characteristics markedly different from anastomosed rivers energy levels mid channel bar formation migration rates and width depth ratios are all within the meandering range lower than braided and higher than anastomosed once anabranches are created larger rivers apparently maintain a greater number of anabranches because of greater discharge wandering miramichi rivers may represent another anabranching river pattern type different from anastomosed and previously described wandering rivers

architectural analysis of fluvial sequences in the northwestern part of kyongsang basin early cretaceous se korea abstract the northwestern part of kyongsang basin early cretaceous largely comprises interbedded sandstones and mudstones of fluvial depositional environments with local basin margin conglomeratic deposits of alluvial fan systems these non marine successions are divided into 5 successive stratigraphic units each of which is unique in facies assemblages and architecture of sandstone bodies one stratigraphic unit sinpyong anpyong unit is documented in this paper with detailed architectural analysis of sandstone bodies the deposits of the sinpyong anpyong unit are divided into three major components thick sandstone thin sandstone and mudstone dominated bodies the thick sandstone bodies 2 47 m thick comprise stacked element groups bounded by laterally persistent erosional surfaces probably representing superposition of channel belts within individual element groups elements are laterally superposed indicating growth and superposition of bars and movement of associated channels the thickness of bar deposits and dip angles of laterally inclined strata suggest that channels were a few to 10 m in depth and 9 m to several tens of meters in width paleocurrent data indicate southward or southeastward draining channel systems the thin sandstone bodies generally the thick sandstone bodies formed in major channels and channel belts are characterized by lateral superposition of numerous bar and channel deposits limited extent of individual lateral accretion sets and the presence of mid channel bar deposits suggesting deposition in braided rivers detailed reconstruction of bars and channels reveals a range of processes including growth coalescence and erosion of bars and migration switching and filling of channels lateral accretion of bars and the associated channel migration might have been principal processes in the sinpyong anpyong river systems bars were commonly coalesced by lateral superposition forming large bar complexes

avulsion mechanisms on the okavango fan botswana the control of a fluvial system by vegetation a study of the avulsion of a major distributory channel on the alluvial fan 22 000 km2 in area of the okavango river in northern botswana has revealed that channels serve as arterial systems distributing water which sustains large areas of permanent swamp the channels are vegetatively confined a primary channel defined here as a channel which receives water and sediment directly from the fan apex aggrades vertically as a result of bedload deposition the rate of aggradation increases downchannel and may exceed 5 cm yr 1 in the distal reaches rapid aggradation is associated with a decline in flow velocity this initiates a series of feedback mechanisms involving invasion of the channel by aquatic plants which trap floating plant debris further reducing flow rate and causing the channel water surface to become elevated thereby increasing rate of water loss from the channel accelerating blockage and aggradation the channel ultimately fails enhanced water loss from the channel promotes the growth of flanking swamp vegetation which confines the failing channel increased flow through the swamp erodes pre existing hippopotamus trails producing a secondary channel system which overlaps but does not connect directly to the failing reach of the primary channel the region of failure of the primary channel migrates upstream accompanied by headward propagation of the secondary channel system the swamp distal to the failed primary channel dessicates and is destroyed by peat fires secondary channels are stable and not prone to blockage comparison with avulsions described in other river systems indicates that the influence of plants in the okavango river system is exceptionally strong

sediment dynamics across gravel sand transitions implications for river stability and floodplain recycling data collection was funded through a nerc gcrf building resilience grant ne p015905 1 to h d s and an epsrc gcrf institutional grant ep p510944 1 to m a sampling equipment was lent by ed tipper and bob hilton the rtk gps was loaned from the nerc geophysical equipment facility

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