discriminating stacked distributary channel from palaeovalley fill sand bodies in foreland basin settings abstract stacked fluvial distributary channel deposits and palaeovalley fills can form major multi storey sand bodies with similar thicknesses and with lateral extents often greater than a single exposure consequently they can be difficult to tell apart from one another using outcrop data this study addresses this problem by quantitatively analysing the architecture of five stacked fluvial distributary channel deposits and two palaeovalley fills from the pennsylvanian pikeville and hyden formations of the central appalachian basin usa the a priori interpretation of the sand bodies as stacked distributary channels and palaeovalley fills is possible because a robust in place coal seam correlation framework allows for the recognition of different basin scale architectures for each type aspect ratios 1000 and a regional basinward facies shift at the bases of palaeovalley fills sand body thickness storey thickness position and length of storey contacts within the sand body are similar in both types however they can be distinguished by different up system to down system changes in their respective architectures stacked distributary channel sand bodies thin down system display a decrease in storey thickness an increase in the mean position of storey heights in the sand body and a decrease in the length of storey contacts these trends are the result of down system decrease in channel size and confinement associated with radially distributive fluvial systems palaeovalley fill sand bodies thicken down system display an increase in storey thickness a decrease in the mean position of storey heights and a decrease in the length of storey contacts the increase in sand body and storey thickness are the result of down system increases in original channel size consistent with trunk axial fluvial systems fed by tributaries that predominate during valley formation the down system increase in amalgamation reflects a down system decrease in accommodation from the higher subsidence rate active margin of the basin and is therefore not necessarily characteristic of palaeovalley fill architectures in all basin settings this study emphasises the requirement for detailed correlation work and quantitative analysis of external and internal architectures before the interpretation of sand bodies as stacked distributary channels or palaeovalley fills

evolution of mid channel bars in a braided river and complex response to reservoir construction an example from the middle hanjiang river china using the middle hanjiang river as an example this paper deals with the development of mid channel bars in a braided river as controlled by channel boundary conditions runoff and sediment load as well as reservoir construction relations have been established between indices describing the mid channel bars and the controlling variables such as the channel width the percentage silt clay content in the channel boundary and the energy expenditure of flowing water bank erosion provides space and material for mid channel bar formation so bank erosion rate can be closely related to mid channel bar indices the middle channel bars exhibit a complex evolutionary response to the reservoir regulated hydrological regime in the middle hanjiang river a descriptive model showing the complex response has been established 1997 john wiley sons ltd

coarse sediment storage and connectivity and off highway vehicle use board camp creek arkansas abstract upper board camp creek bcc in western arkansas drains the wolf pen gap wpg trail complex a designated off highway vehicle ohv area in use since the 1990s the mixed bedrock alluvial channel is quite active with extensive bars and eroding banks present within the higher order main valley channels this study was conducted to determine the relative magnitudes of sediment storage and production within the channel and whether geomorphic changes are synchronous with establishment and increasing ohv use levels on the trail system fourteen geomorphically active reaches within the main valley channels representing the range of conditions of bcc within the wpg complex were examined in detail all sites had significant alluvial storage in the form of point lateral or mid channel bars dominated by cobble and gravel sediment storage volumes ranged from 140 to nearly 10 000 m3 per kilometer of channel with a mean of about 3400 eleven of 14 reaches also had actively eroding banks ten reaches 71 exhibited net sediment storage two are possible net sources and two may be in approximate steady state storage erosion the imbalance between local bank erosion sources and in channel storage and the evidence of activity and mobility of most of the bars indicates a connected system with coarse sediment mobile during banktop flow events and no evidence of sediment starvation finer

shifting surface currents in the northern north atlantic ocean 1 analysis of surface drifter tracks in the north atlantic ocean from the time period 1990 to 2007 provides evidence that warm subtropical waters have recently increased their penetration toward the nordic seas prior to 2000 the warm water branches of the north atlantic current fed by the gulf stream turned southeastward in the eastern north atlantic since 2001 these paths have shifted toward the rockall trough through which the most saline north atlantic waters pass to the nordic seas these surface drifters are able to overcome the ekman drift which would force them southward under the westerly winds dominating the subpolar atlantic yet the changes in path cannot be accounted for by changes in ekman drift eddy kinetic energy from satellite altimetry shows increased energy along the shifted drifter pathways across the mid atlantic ridge since 2001 these near surface changes have occurred during continual weakening of the north atlantic subpolar gyre as seen by altimetry they are also consistent with the observed increase in temperature and salinity of the waters flowing northward into the nordic seas these findings suggest the changes in the vertical structure of the northern north atlantic ocean its dynamics and exchanges with the higher latitudes wind stress and its curl changes are discussed as a possible forcing of the changes in the pathways of the subtropical waters

analysis of river lateral channel movement using quantitative geomorphometric indicators qara sou river iran qara sou river a permanent river in ardabil province iran has recently undergone changes by anthropogenic factors in this research through geomorphometric quantitative methods we have tried to carefully investigate lateral channel movement of qara sou river during the last 12 years so as to provide a comprehensive understanding of these changes and their calculation methods using gis techniques the study area is located 31 km away from qara sou river from the vicinities of qadilou village to the surroundings of la l ganj village the most important geomorphometric indices used in this paper include total bankline change e normalized lateral movement rate n width change dw true migration m and lateral stability index the results of river lateral movement indices show the high level of total bankline change e and low level of true migration m indices this is due to changes in the width change of qara sou river during the last 12 years in fact farming activities and encroachments in bed and riparian of qara sou river have caused channelization of the channel accelerating flooding around the river in addition the results revealed that high mobility in total bankline change e and normalized lateral movement rate n of qara sou river was not related to lateral migration of the river but it had a strong connection with width changes of the channel the calculated true migration rate in the study area for qara sou river was about 0 36 m per year during the last 12 years

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

underlying gravel layers in a large sand bed river and their influence on downstream dam channel adjustment due to the changes in environmental factors during a river s historical development underlying gravel layers are found in many large plain rivers when the buried depth of this gravel layer is within the reach of down cutting by clear water scour after reservoir construction it may be exposed and exert a far reaching influence on channel adjustment in hanjiang river the longest tributary of the yangtze river in china down cutting has been greatly reduced and even stopped due to the total change of bed material composition the exposure of a gravel layer results in a dramatic increase in the bed s hydraulic roughness so the channel slope may increase after a decline during the period prior to the exposure of the gravel layer moreover the exposed gravel layer increases the erosion resistance of bed material making a lower relative erosion resistance of bank to bed material where the bank s erosional resistance is weak this may lead to a tendency towards channel widening

alterations of channel parameters in response to river regulation works since 1840 on the lower tisza river hungary abstract in the last few years an increase in the frequency and magnitude of floods was detected on the tisza river endangering large areas of hungary the causes of these record floods were complex including both natural and human induced factors this paper focuses on river management works and their effect on planimetric and cross sectional parameters with special attention to the flood conductivity changes to the river channel during 19th century river regulation works half of the total length of the tisza river was altered by cut offs while in the 20th century mostly revetments and groynes were constructed subsequently horizontal and vertical channel parameters have changed considerably due to semi natural bed processes in order to reveal changes hydrological map series 1842 1890 1929 1957 1976 and 1999 and cross sectional surveys from the same dates were analysed prior to the intensive human interventions before 1890s the river s course was highly sinuous with some very sharp bends due to cut offs both the length and sinuosity of the tisza river decreased by 35 while the lengths of straight sections and the river s slope doubled as a consequence the river incised by up to 3 8 m until the 1929 survey resulting better flood conductivity which improved flood safety in the 1920s river management favoured bank stabilisation in order to stop the lateral migration of the channel despite these measures meander development has continued however in a distorted manner this is reflected by the opposing processes of lengthening centre line on the one hand and gradually decreasing radius of curvature on the other these processes can be explained by the continuous development of natural point bars on the convex bank and the lack of lateral retreat on the concave stabilised bank the width of the river decreased by 17 45 while its mean and maximum depth increased by 5 48 the area of cross sections influenced by revetments decreased by 6 19 resulting in a 6 15 decline in flood conductivity the non stabilised sections were influenced by upstream revetments therefore their parameters show similar changes but with a smaller rate at present the flood conductivity of the channel is worse than it was in its natural state in all it was found that the ongoing process of cross sectional distortion is a significant factor in increasing flood stage and hazard and high floods can be expected more frequently in the future partly due to this factor

spatial and temporal variations of channel lateral migration rates in the inner mongolian reach of the upper yellow river channel variations of the inner mongolian reach in the upper yellow river are very complicated because of diversity of channel patterns intense changes in water and sediment and enhanced human activities in the last decades it is important to examine the channel migration rates in this river reach based on channel planform changes at 236 digital channel cross sections the present study estimated the channel migration rates in terms of mid channel line shift at the digital channel cross sections during the periods 1975 1990 1990 2000 2000 2006 2006 2010 and 2010 2011 the results show that the average channel migration rate for the whole river reach is 5 0 7 9 5 9 8 6 and 1 0 m 1 in the five different periods respectively in both directions to the right and to the left the highest channel migration rate was always observed in the meandering channels while the lowest channel migration rate was in the whole inner mongolian reach except the sanhuhekou zhaojunfen s z sub reach the temporal variation of channel migration rate was mainly controlled by changing sediment concentration in river flow while the spatial variation along the straight braided and meandering channel reaches was largely affected by material differences of channel banks as reflected by different channel patterns with the highest average lateral migration rate to the left bank the meandering channel reach is extremely vulnerable to lateral migration and needs to be protected with engineering practices because a large population and wide farmland are located on its left floodplain

statistical analysis of lateral migration of the rio grande new mexico abstract the lateral migration rates of alluvial rivers are affected by changes in water and sediment regimes the rio grande downstream from cochiti dam exhibits spatial and temporal variability in lateral movement rates documented since 1918 a tremendous database exists that documents planform bed material size channel geometry and water and sediment regimes a statistical analysis reveals that migration rates primarily decreased with decreasing flow energy r2 0 50 p 60 the findings show that lateral movement increases with increasing flow energy and with degree of braiding

river morphology and thresholds the regime geometry and channel patterns of alluvial rivers are analyzed wing an energy approach together with physical relationships of flow continuity flow resistance and sediment transport because of the discontinuity in flow resistance and thus in power expenditure between lower and upper flow regimes the adjustment in river regime consists of sudden changes in channel geometry channel pattern and sometimes silt clay content when such a discontinuity is crossed thresholds or discontinuities in river morphology are obtained in the analysis in accordance with such thresholds rivers of distinct morphological features are classified into four regions based upon the bankfull discharge channel slope and median size of bed sediment their respective features are described and certain regime relationships for channel width and depth are established the predicted channel geometries are compared with river data

evidence of stream response to holocene climatic change in a small wisconsin watershed abstract during the holocene moderate climatic and vegetational changes triggered several episodes of adjustment in the brush creek fluvial system the alluvial chronology includes an episode of erosion at 7800 5700 yr b p corresponding to the mid holocene precipitation minimum and an episode of floodplain construction at 5700 5000 yr b p corresponding to a rapid increase in precipitation holocene climatic changes have influenced the sedimentology of the alluvial deposits and soil development on them fluvial adjustment is caused primarily by hydrologic and hydraulic changes related to climatic change but there is no simple model for fluvial response to climatic change the relationship between the direction of climatic change and the type of fluvial response is complex

statistical models of fluvial systems abstract statistical methods have dominated quantitative analyses of fluvial systems over the last 40 years this paper assesses the utility of statistical models by examining methodological issues associated with empirical analysis of hydraulic and channel geometry relationships it also describes and presents examples of advanced statistical models that promise to enhance our understanding of the structure and dynamics of fluvial systems bivariate and multivariate power function models of fluvial systems provide objective numerical descriptions of the relationship between channel geometry and hydrologic hydraulic sedimentologic and biotic controls traditional regression models are limited in that they only describe simple input output relations between the states of dependent and independent variables advanced statistical models transcend these limitations simultaneous equation models continuously varying parameter models and distributed lag models are statistical tools for explicitly analyzing 1 mutual adjustments among fluvial variables 2 the factors controlling the spatial structure of channel geometry flow relations and 3 the equilibrium or disequilibrium dynamics of fluvial systems respectively these advanced statistical techniques can be used to empirically test conceptual models of fluvial systems at a variety of spatial and temporal scales

causes of planform stability of a low energy meandering gravel bed river cher river france abstract for at least two centuries the lateral mobility of the meandering reaches of the cher river france has been very low this article aims to identify the main causes of this behavior two not mutually exclusive explanatory hypotheses are proposed under the first hypothesis the natural mechanisms of loop migration would have been inhibited or blocked by the presence of bank protections under the second hypothesis a decrease in the frequency and or intensity of morphogenic hydrological events since the nineteenth century would have reduced the frequency of bedload mobilization and or reduced the capacity of the river to erode its banks to test these hypotheses the diachronic evolution of the planform was reconstituted at different time scales using a gis and field surveys morphological transformations were characterized and quantified eroded and vegetated areas length of eroded banks rates of bank retreat and the critical discharges of bedload mobilization and of lateral erosion were estimated engineering works in the riverbed were identified and when possible dated the results show that meander morphodynamics have been highly constrained and disrupted by engineering works probably for over a century however the meanders still have noticeable potential for bedload mobility and lateral erosion and hence for self restoration

logistic analysis of channel pattern thresholds meandering braiding and incising a large and geographically diverse data set consisting of meandering braiding incising and post incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds of channel pattern and instability an energy based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics the strong significance of the 74 statistical models examined suggests that logistic regression analysis is an appropriate and effective technique for associating basic hydraulic data with various channel forms the probabilistic diagrams resulting from these analyses depict a more realistic assessment of the uncertainty associated with previously identified thresholds of channel form and instability and provide a means of gauging channel sensitivity to changes in controlling variables

vegetative impacts on hydraulics and sediment processes across the fluvial system summary vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape interactions occur among flow hydraulics sediment deposition and erosion and plant morphology density and biomechanics interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years this interest is partially driven by the popularity of stream restoration activities worldwide that include re vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes we present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel on channel banks and over the floodplain we illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

planform channel dynamics and bank migration hazard assessment of a highly sinuous river in the north eastern zone of bangladesh rivers or watercourses in sylhet plain of bangladesh are very dynamic over time the aim of the present study is to investigate the channel planform dynamics the prediction of future lateral migration of the bankline and assessment of the hazards associated with manu river bangladesh the name manu river represents the river study reach from tripura india to moulvibazar bangladesh of 41 6 km channel contraction and expansion are very frequent in this river studies had shown that the sinuosity of the river varies from 1 36 to 2 48 also the meandering ratio of the river ranges from 0 32 to 1 67 satellite data were collected and analyzed to determine the planform characteristics meandering parameters and bankline migration rates between 1975 and 2013 the study is based on the landsat satellite imagery of 1975 1988 1999 2003 and 2005 and aerial photograph of 2009 and 2013 which were accumulated from united states geological survey specific critical bends have been elected where bank erosion and accretion rates were severe the purpose of this paper is to show the erosion rate behavior and pattern of upstream side of manu river bangladesh through the study period of 38 years from 1975 to 2013 by comparing its different geomorphological parameters this study has contributed to develop a model for bankline migration prediction of the forthcoming years and address the physical hazard to provide a risk surface present assessment has revealed that there are some critical regions where erosion would be up to 29 18 hectares in 2025

stream curvature and bank erosion a model based on the momentum equation based on the momentum equation of flow the force per unit area which the flow exerts radially on the outer bank of a stream bend is expressed by an equation in which the force is explicitly related to the curvature ratio r w curve radius channel width a dimensionless curvature coefficient c alpha is defined which is dependent on r w and the coefficient of dynamic bedload friction tan alpha exploring the changes of c alpha with r w reveals a functional relationship which for the known values of tan alpha shows maximal values of c alpha for r w values between 2 and 4 the theoretical results agree with field measurements of the relationship between r w and the rate of channel migration

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

hydrological controls on the morphogenesis of low energy meanders cher river france summary river restoration is a key issue for european hydrosystems that were modified over centuries by human activities this is particularly true for numerous low energy rivers flowing in the plateaus of western europe because of this limited energy their potential in terms of autogenic restoration a priori appears strongly restricted this study examines the conditions under which the morphogenesis on one of these systems occurs in relation to various hydrologic conditions two complementary approaches are combined on three reaches of the meandering cher river france firstly we examine at a pluri decadal scale the control of duration frequency and intensity of floods on the planimetric erosion bank retreat mainly secondly we estimate the range of effective discharge for bedload transport the results show that the morphogenesis is controlled by low magnitude hydrological events two major controlling factors are suggested low differential of energy between small and large floods peculiar to low energy rivers of mid latitude and low critical discharges for lateral erosion and bedload mobilization for these reasons the ability of the alluvial cher river to self restore its fluvial dynamics seems to be relatively high

reconstruction of a pleistocene meandering river in east hungary by vhr seismic images and its climatic implications abstract the upper 20 30 m of the pleistocene alluvial sequence on the tisza river hungary is investigated by 200 km of vhr single channel seismic sections frequent internal configurations such as 1 bundles of inclined reflections 2 trough shaped converging and 3 horizontal parallel reflections are interpreted respectively as lateral accretion of point bars abandoned channel fills and floodplain deposits the series of 5 8 m thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43 47 ka in the late pleistocene according to osl data newly recorded quasi 3d seismic profiles reveal that each 1 3 km long inclined series correlates with an individual point bar continuously migrating in the same direction small deviations in the direction of migration are caused by natural wandering of the meander bend morphometric parameters of point bars are used to calculate ancient channel parameters width and depth of 200 500 m and 5 8 m respectively values imply a channel forming discharge of q 400 900 m 3 s these results imply a greater amount of runoff and supply in the basin during mis3 compared to the present day long lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in nw europe our data support the thesis of the three axis drainage system for the basin new evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of danube and tisza rivers contrary to the present day two axis drainage pattern