hydraulic and sedimentary processes causing anastomosing morphology of the upper columbia river british columbia canada abstract the upper columbia river british columbia canada shows typical anastomosing morphology multiple interconnected channels that enclose floodbasins and lateral channel stability we analysed field data on hydraulic and sedimentary processes and show that the anastomosing morphology of the upper columbia river is caused by sediment bedload transport inefficiency in combination with very limited potential for lateral bank erosion because of very low specific stream power 2 3 w m 2 and cohesive silty banks in a diagram of channel type in relation to flow energy and median grain size of the bed material data points for the straight upper columbia river channels cluster separately from the data points for braided and meandering channels measurements and calculations indicate that bedload transport in the anastomosing reach of the upper columbia river decreases downstream because of lateral channel stability no lateral storage capacity for bedload is created therefore the surplus of bedload leads to channel bed aggradation which outpaces levee accretion and causes avulsions because of loss of channel flow capacity this avulsion mechanism applies only to the main channel of the system which transports 87 of the water and 90 of the sediment in the cross valley transect studied because of very low sediment transport capacity the morphological evolution of most secondary channels is slow measurements and calculations indicate that much more bedload is sequestered in the relatively steep upper anastomosing reach of the upper columbia river than in the relatively gentle lower anastomosing reach with anastomosing morphology and related processes e g crevassing being best developed in the upper reach this confirms the notion of upstream rather than downstream control of upper columbia river anastomosis

reply to van den berg and bledsoe s comment on lewin and brewer 2001 predicting channel patterns geomorphology 40 329 339

preferential flow in a sandy vadose zone 2 mechanism and implications abstract field experiments conducted at the hancock agricultural research station during the 1987 growing season showed that preferential flow paths were the dominant flow pattern in the central sand area of wisconsin csaw the observed preferential flow was different from other preferential flow patterns mentioned in the literature e g short circuiting flow and fingering flow this paper presents a detailed discussion of the mechanism of this preferential flow and its influence on groundwater contamination soil solution sampling and solute transport modeling four factors that will determine the occurrence of a funneled flow are a conductivity of the upper finer layer k b slope of the inclined layer sin c retention potential of the upper finer layer 2 r and d ponding potential g l

variations of the east asian jet stream and asian pacific american winter climate anomalies in this study the authors apply the ncep ncar reanalysis and other observations to depict the association of the asian pacific american climate with the east asian jet stream eajs with an emphasis on boreal winter seasons and on interannual timescales they analyze the variations of the eajs and their relationships with el nino southern oscillation enso and extratropical north pacific sea surface temperature sst and assess the relative connections of the eajs and enso to the anomalies of atmospheric circulation surface temperature and precipitation in the asian pacific american region it is found that the eajs is coupled to a teleconnection pattern spanning the entire asian pacific american region with the strongest signals over east asia and the western pacific this pattern differs significantly from that associated with enso which influences the earth s climate extensively with a strongest impact on the climate over the central pacific and east a strong eajs is associated with an intensification of the weather and climate systems in asia and over the pacific such as deepening of the east asian trough and the aleutian low and strengthening of the east asian winter monsoon it is linked to colder and drier conditions in east asia and stronger convection over the tropical asia australia sector compared with enso the eajs seems to link to the climate signals of asia and the pacific more strongly an intensified eajs is also associated with anomalies of temperature and precipitation in north america due to the related changes in stationary wave patterns while the eajs does not strongly link to the tropical central eastern pacific sst it is significantly associated with the extratropical north pacific sst more specifically the second most dominant mode of the empirical orthogonal function analysis of the sst in addition a strong weak eajs seems to follow a large small meridional gradient of the western pacific sst associated with warming cooling in the tropics subtropics and cooling warming in the extratropics

prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

connections between wintertime jet stream variability oceanic surface heating and transient eddy activity in the north pacific 1 a set of statistical analyses of the fields from the european center for medium range weather forecasts reanalysis era 40 are carried out to investigate the connections between three selected fields namely the wintertime western pacific jet stream wpjs as represented by the zonal wind at 200 hpa the oceanic surface heating represented by the latent and sensible heat fluxes and the synoptic scale transient eddy activity stea over the north pacific first empirical orthogonal function eof analysis is performed to characterize the wintertime wpjs variability further analyses yield the following conclusions 1 the most dominant relationship among the three selected fields is strongly linked to the el nino southern oscillation enso during enso events anomalous zonal wind at 200 hpa downstream of the wpjs main body shown in the first eof is accompanied by stea anomalies around the region of the anomalous midlatitude zonal wind 2 the strengthening weakening of the wintertime wpjs main body shown in the second eof is connected to the surface heating anomalies in the kuroshio and its extension region as well as to stea anomalies in the region downstream of the wpjs main body 3 the northward southward shift of the wintertime wpjs represented in the third eof is closely related to the south north dipolar structure of the surface heating anomalies in the western north pacific the stea spatial displacement is in conjunction with the shift of the jet stream in the same direction due to the dynamical connection between the winds and the eddies furthermore the stea anomalies in winter may cause the wpjs anomalies on the submonthly timescale as a consequence the northward southward shift of the stea is harmoniously in favor of the similar jet shift

midlatitude atmospheric transient eddy feedbacks influenced enso associated wintertime pacific teleconnection patterns in two pdo phases the el nino southern oscillation enso associated wintertime atmospheric teleconnection patterns in two pacific decadal oscillation pdo phases are investigated using era 20c reanalysis data for 1950 2010 a strengthened enso associated pacific north american pna teleconnection pattern presents in pdo positive phase while a west pacific wp pattern over northwestern pacific and a squeezed pna pattern coexist when enso occurs in pdo negative phase the dynamical role of atmospheric transient eddy feedbacks to the teleconnection patterns are highlighted in the present study when enso occurs in pdo positive phase the uniform strengthened westerly jet anomalies downstream of the climatological main body of jet accompany with energetic transient eddy anomalies over northeastern pacific the transient eddy feedbacks largely enhance and favor the strengthened pna pattern when enso occurs in pdo negative phase the strengthened westerly jet anomalies appear to separate into two parts one locating north of the climatological main body of jet and the other at the downstream the accompanied transient eddy anomalies also split into two parts under such conditions the transient eddy feedbacks are limited over northeastern pacific and favor a weak pna pattern however the transient eddy anomalies over northwestern pacific strengthen and the feedbacks also strengthen and largely contribute to the wp pattern moreover the transient eddy anomalies over northwestern pacific seem to be anchored along the anomalously poleward strengthened oceanic subarctic frontal zone safz in pdo negative phase the enhanced atmospheric baroclinicity anomalies coupled with the strengthened safz energize atmospheric transient eddy anomalies and work as the potential maintenance in shaping the wp pattern

influence of a large debris flow fan on the late holocene evolution of squamish river southwest british columbia canada cheekye fan is a large paraglacial debris flow fan in southwest british columbia it owes its origin to the collapse of mount garibaldi a volcano that erupted in contact with glacier ice near the end of the pleistocene epoch the fan extended across howe sound isolating a freshwater lake upstream of the fan from a fjord downstream of it squamish river built a delta into this lake during the holocene we use 28 radiocarbon ages to describe the final infilling of the lake and the subsequent evolution of the squamish river floodplain over the past 3300 years these events are recorded in fine grained lacustrine wetland river channel and overbank sediments exposed in the banks of squamish river over a distance of more than 10 km upstream of the fan we link these deposits to construction persistence and eventual degradation of the dam formed by cheekye fan and a smaller inset fan formed by cheakamus river into which cheekye river flows the coupled cheekye fan squamish river floodplain system is si

interannual and decadal modulations recently observed in the pacific storm track activity and east asian winter monsoon abstract interannual variability of the north pacific storm track observed over 17 recent winters is documented the local storm track activity is measured by a meridional flux of sensible heat associated with the lower tropospheric subweekly fluctuations the interannual variability in the heat flux over the northwestern nw pacific is found to be strongest in midwinter the first empirical orthogonal function of the interannual variability in midwinter captures the decadal tendency toward the enhanced storm track activity in midwinter over the nw pacific in association with the decadal weakening of the east asian winter monsoon siberian high and the aleutian low that occurred in the late 1980s the most marked signature of this enhancement is that the midwinter minimum in the storm track activity which had been apparent in the early to mid 1980s almost disappeared afterward as opposed to linear theory of baroclinic instability the enhanced activity occurred despite the weakening of the pacific j

grain rimming kaolinite in permian rotliegend reservoir rocks upper rotliegend sediments of permian age from the northeast netherlands show moderate to good reservoir

evaluating controls on crevasse splay size implications for floodplain basin filling abstract although crevasse splays are often considered important contributors to floodplain basin filling evidence from modern and ancient fluvial deposits indicates that they may not play a significant role in all river systems in order to better understand controls on the abundance and scale of crevasse splays produced in fluvial systems we used aerial photography to observe crevasse splay deposits along three rivers and conducted a targeted numerical modeling study to explore factors which promote widespread crevasse splay deposition on fluvial floodplains results demonstrate that splay size does not always scale directly with channel size or discharge and that hydrodynamic factors primarily sediment size and floodplain drainage conditions play a significant role in determining whether a fluvial system is likely to produce large floodplain filling splays this work suggests that widespread crevasse splays demand both a large supply of relatively coarse suspended sediment and a steep water surface slope away from the channel across the floodplain without both these conditions the role of crevasse splays in flood basin filling is limited

atmospheric response to zonal variations in midlatitude sst transient and stationary eddies and their feedback midwinter storm track response to zonal variations in midlatitude sea surface temperatures ssts has been investigated using an atmospheric general circulation model under aquaplanet and perpetual january conditions zonal wavenumber 1 sst variations with a meridionally confined structure are placed at various latitudes having these sst variations centered at 308n leads to a zonally localized storm track while the storm track becomes nearly zonally uniform when the same sst forcing is moved farther north at 408 and 508n large small baroclinic energy conversion north of the warm cold sst anomaly near the axis of the storm track near 408n is responsible for the large small storm growth the equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction significant stationary eddies form in the upper troposphere with a ridge trough northeast of the warm cold sst anomaly at 308n heat and vorticity budget analyses indicate that zonally localized condensational heating in the storm track is the major cause for these stationary eddies which in turn exert a positive feedback to maintain the localized storm track by strengthening the vertical shear near the surface these results indicate an active role of synoptic eddies in inducing deep tropospheric scale response to midlatitude sst variations finally the application of the model results to the real atmosphere is discussed

natural levee formation along a large and regulated river the danube in the national park donau auen austria abstract we investigated overbank deposition and natural levee formation along the danube east of vienna based on airborne laserscan data als combined with historical information the analyses of equally spaced cross sections hypsographic curves and point elevations revealed the significance of the distance from the river bank the floodplain width and the floodplain flow situation inflow outflow sections for the spatial variability of sediment deposition deposition was high near the banks natural levee formation in wide floodplain sections and in inflow areas the overall pattern was modified by the presence of side channels and the micro relief of the floodplain from the derived sedimentation rates averaged for the past 120 years over the reach of about 11 0 mm yr 1 at the natural levee and about 0 3 mm yr 1 at the flood protection dyke we can estimate an overbank deposit rate of 416 000 m 3 yr 1 for the entire free flowing reach between river km 1921 and 1880 that is between 18 and 20 of the annual transported suspended load an analysis of historical cross sections showed that there was no natural levee along the riverbanks shortly after the regulation about 100 years ago we thus assume that natural levee formation is a consequence of the danube regulation in the late 19th century under natural conditions overbank deposition was balanced and limited by side erosion and lateral channel migration after stabilization of the banks the overbank deposits were not eroded and distinct natural levees formed these levees will develop and grow further and affect flood protection and floodplain ecology we discuss the interplay between floodplain deposition and lateral bank migration under the concept of dynamic equilibrium

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

evaluating competing hypotheses for the origin and dynamics of river anastomosis anastomosing rivers have multiple interconnected channels that enclose flood basins various theories potentially explain this pattern including an increased discharge conveyance and sediment transport capacity of multiple channels deltaic branching avulsion forced by base level rise or a tendency to avulse due to upstream sediment overloading the former two imply a stable anabranching channel pattern whereas the latter two imply disequilibrium and evolution towards a single channel pattern in the absence of avulsion our objective is to test these hypotheses on morphodynamic scenario modelling and data of a well documented case study the upper columbia river proportions of channel and floodplain sediments along the river valley were derived from surface mapping initial and boundary conditions for the modelling were derived from field data a 1d network model was built based on gradually varied flow equations sediment transport prediction mass conservation transverse slope and spiral meander flow effects at the bifurcations the number of channels and crevasse splays decreases in a downstream direction also measured sediment transport is higher at the upstream boundary than downstream these observations concur with bed sediment overloading from upstream which can have caused channel aggradation above the surrounding floodplain and subsequent avulsion the modelling also indicates that avulsion was likely caused by upstream overloading in the model multi channel systems inevitably evolve towards single channel systems within centuries the reasons are that symmetric channel bifurcations are inherently unstable while confluenced channels have relatively less friction than two parallel channels so that more discharge is conveyed through the path with more confluences and less friction furthermore the present longitudinal profile curvature of the valley could only be reproduced in the model by temporary overfeeding

why the western pacific subtropical high has extended westward since the late 1970s the western pacific subtropical high wpsh is closely related to asian climate previous examination of changes in the wpsh found a westward extension since the late 1970s which has contributed to the inter decadal transition of east asian climate the reason for the westward extension is unknown however the present study suggests that this significant change of wpsh is partly due to the atmosphere s response to the observed indian ocean western pacific iwp warming coordinated by a european union s sixth framework programme understanding the dynamics of the coupled climate system dynamite five agcms were forced by identical idealized sea surface temperature patterns representative of the iwp warming and cooling the results of these numerical experiments suggest that the negative heating in the central and eastern tropical pacific and increased convective heating in the equatorial indian ocean maritime continent associated with iwp warming are in favor of the westward extension of wpsh the sst changes in iwp influences the walker circulation with a subsequent reduction of convections in the tropical central and eastern pacific which then forces an enso gill type response that modulates the wpsh the monsoon diabatic heating mechanism proposed by rodwell and hoskins plays a secondary reinforcing role in the westward extension of wpsh the low level equatorial flank of wpsh is interpreted as a kelvin response to monsoon condensational heating while the intensified poleward flow along the western flank of wpsh is in accord with sverdrup vorticity balance the iwp warming has led to an expansion of the south asian high in the upper troposphere as seen in the reanalysis

north atlantic weather regimes response to indian western pacific ocean warming a multi model study 1 the extratropical large scale atmospheric circulation is often described in terms of a few preferred and recurrent patterns referred to as weather regimes here we investigate the influence of the observed indian and western pacific ocean ip warming over the last decades on the frequency of occurrence of north atlantic weather regimes a multi model approach is adopted in which five different atmospheric general circulation models are forced with idealized sea surface temperature patterns mimicking the ip warming despite some discrepancies three models suggest a stronger occurrence of the zonal regime when ip is warm compensated by less frequent greenland anticyclone regimes consistently with the observed positive trend of the north atlantic oscillation the other two models simulate instead an increase in the frequency of occurrence of the atlantic ridge regime variance decomposition into stationary and transient waves suggest two mechanisms at work in the individual models the ar regime favoured occurrence is associated with a strong transient wave activity along the wave guide in the north pacific and downstream in the north atlantic the zonal favoured excitation is interpreted as an indirect response to changes in the tropical atlantic associated with a global alteration of the walker cell

multifractal analysis applied to the study of the accuracy of dem based stream derivation abstract a correct description of river network morphology is very important when it is used to study different features of a river s morphology as well as phenomena related to it such as erosion nitrogen retention or sediment pollution in recent years different algorithms have been developed to extract drainage networks directly from digital elevation models in this paper the suitability of archydro extension developed for arcgis desktop and based on the d8 algorithm to generate river networks has been studied by using multifractal analysis the river networks generated by archydro tools were compared to those provided by photogrammetric restitution for different flow accumulation threshold values one limitation of the d8 algorithm in order to generate the most appropriate river networks is the correct choice of the flow accumulation threshold value multifractal analysis has shown itself to be an efficient approach to determine the most suitable flow accumulation threshold values moreover this approach has allowed characterizing the morphology of river networks and testing the quality of archydro results according to the multifractal spectra the main difference between the networks considered here is the lesser stream density with a low channel order detected for archydro results compared to photogrammetric restitution in addition the relationship between ruggedness number for the largest contributing area and fractal dimensions in each study area has been explored the use of multifractal analysis has been extended to drainage network simulation going beyond the descriptive aim of previous works

controls on natural levee development in the columbia river british columbia canada natural levees of the columbia river near golden british columbia were investigated to identify the mechanisms that control levee development and morphology topographic profiles of 12 levee pairs were surveyed and measurements of water surface elevation flow velocity flow direction and turbidity were obtained during an average magnitude flood 1ae2 years recurrence interval sedimentation rates and grain size distributions were measured from sediment traps placed along levee to floodbasin transects results show that water and sediment exchange between the channel and floodbasin was mainly by advection during flooding local floodbasins behave more as efficient water pathways than water storage features resulting in down valley floodbasin flows capable of limiting basinward growth of levees levee shape results primarily from two independent factors 1 maximum channel water stage which limits levee height and 2 floodbasin hydraulics which control width in the columbia river the competence of floodbasin flows results in relatively narrow and steep levees natural levees grow under two general conditions of deposition as governed by flood stage elevation relative to levee crest elevation front loading and back loading during large floods when crests are inundated front loading preferentially aggrades the proximal portions of levees with sediment directly from the channel thus increasing levee slope during average or below average floods when many levee crests are not overtopped back loading preferentially aggrades the distal levee areas and floodbasin floor reducing levee slope in the study area a balance between front and back loading sustains these narrow and steep levee shapes for long periods reflecting an equilibrium between hydraulic regime floodplain morphology and deposition

morphology hydrology and evolution of the anastomosing ovens and king rivers victoria australia anastomosing channels form the characteristic stream pattern of the riverine plain of southeastern australia investigations of the ovens and king rivers in northeastern victoria show that the individual channels and reaches of channels vary markedly in channel morphology and age young channels have large bankfull flows low sinuosity large meander wavelength steep gradients and are unstable they are incised channels that are rapidly eroding their bed and banks old channels however have small bankfull flows high sinuosity small meander wavelength gentler gradients and are relatively stable the multiple channels develop by avulsion as individual channels become older and more sinuous they also become more hydraulically inefficient thus increasing proportions of flood discharge are displaced overbank this overbank flow concentrates in relatively straight flood plain depressions and it erodes a new channel which develops by both up and down valley incision down valley incision is initiated at outflow points and up valley incision is initiated where the overbank flow rejoins the main channel with time both channel segments join to form a new anabranch of the anastomosing channel system large anastomosing channel networks have been identified in ancient rocks by stratigraphers and sedimentologists on the basis of studies of the anastomosing ovens and king rivers it is very likely that these channel networks are composed of channels of different ages hence even at one stratigraphic level not all of the anabranches functioned simultaneously nevertheless as a result of anabranch incision which intersects older channels at depth a three dimensional network of paleochannels can form that permits fluid flow throughout the network

enhancement of lower tropospheric winter synoptic temperature variations in southwest china and the northern indochina peninsula after 2010 in this study long term change in winter synoptic temperature variations in southwest china and the northern indochina peninsula from 1979 to 2017 39 years is documented a sharp increase in synoptic temperature variation is found after 2010 indicating stronger day to day temperature change in the last decade the increasing variation is attributed to stronger horizontal wind on a synoptic timescale after 2010 on the other hand transient eddies show stronger intensity after 2010 when approaching southwest china and the northern indochina peninsula swcnip contributing to the stronger synoptic horizontal wind according to the eddy kinetic energy budget the stronger horizontal wind is due primarily to the larger baroclinic energy conversion from eddy potential energy to eddy kinetic energy after 2010 furthermore a larger potential energy conversion from the mean flow to transient eddies is observed in swcnip after 2010 this plays an important role in sustaining the intensity of transient eddies it is also noted that the intensification of transient eddies after 2010 is caused by warming in the western tropical pacific and the bay of bengal and strengthened synoptic eddies along the southern part of the tibetan plateau

response of northern hemisphere storm tracks to indian western pacific ocean warming in atmospheric general circulation models with 40 years integration output of two atmospheric general circulation models gamil iap and hadam3 ukmo forced with identical prescribed seasonally varying sea surface temperature this study examines the effect of the observed indian western pacific ocean iwp warming on the northern hemisphere storm tracks both models indicate that the observed iwp warming tends to cause both the north pacific storm track npst and the north atlantic storm track nast to move northward such a consistent effect on the two storm tracks is closely associated with the changes in the low level atmospheric baroclinicity high level jet stream and upper level geopotential height the iwp warming can excite a wavelike circum global teleconnection in the geopotential height that gives rise to an anticyclonic anomaly over the midlatitude north pacific and a positive phase nao anomaly over the north atlantic these geopotential height anomalies tend to enhance upper level zonal westerly winds north of the climatological jet axes and increase low level baroclinicity and eddy growth rates thus favoring transient eddy more active north of the climatological storm track axes responsible for the northward shift of the both storm tracks the iwp warming induced northward shift of the nast is quite similar to the observed suggesting that the iwp warming can be one of the key factors to cause decadal northward shift of the nast since the 1980s however the iwp warming induced northward shift of the npst is completely opposite to the observed implying that the observed southward shift of the npst since the 1980s would be primarily attributed to other reasons although the iwp warming can have a cancelling effect against those reasons

north atlantic oscillation response to anomalous indian ocean sst in a coupled gcm the dominant pattern of atmospheric variability in the north atlantic sector is the north atlantic oscillation nao since the 1970s the nao has been well characterized by a trend toward its positive phase recent atmospheric general circulation model studies have linked this trend to a progressive warming of the indian ocean unfortunately a clear mechanism responsible for the change of the nao could not be given this study provides further details of the nao response to indian ocean sea surface temperature sst anomalies this is done by conducting experiments with a coupled ocean atmosphere general circulation model oagcm the authors develop a hypothesis of how the indian ocean impacts the nao

interchannel hydraulic geometry and hydraulic efficiency of the anastomosing columbia river southeastern british columbia canada the morphodynamics of the anastomosing channel system of upper columbia river in southeastern british columbia canada is examined using an adaptation of conventional hydraulic geometry termed interchannel hydraulic geometry interchannel hydraulic geometry has some of the characteristics of downstream hydraulic geometry but differs in that it describes the general bankfull channel form and hydraulics of primary and secondary channels in the anastomosing channel system interchannel hydraulic geometry generalizes these relationships and as such becomes a model of the geomorphology of channel division and combination interchannel hydraulic geometry of upper columbia river based on eld measurements of ow velocity and channel form at 16 test sections is described well by simple power functions wbf 3 24qbf0 64 dbf 1 04qbf0 19 vbf 0 30qbf0 17 these results with other related measurements of ow resistance imply that channel splitting leads to hydraulic inef ciency higher ow resistance on the anastomosing columbia river because these ndings differ from those reported in studies elsewhere we conclude that hydraulic ef ciency does not provide a general explanation for anabranching in river channels copyright 2003 john wiley sons ltd

bifurcation dynamics and avulsion duration in meandering rivers by one dimensional and three dimensional models at river bifurcations water and sediment are divided over two branches the dynamics of the bifurcation determine the long term evolution centuries of the downstream branches potentially leading to avulsion but the dynamics are poorly understood the long term evolution can only be studied by one dimensional models because of computational costs for such models a relation describing the sediment division is necessary but only few relations are available and these remain poorly tested so far we study the division of sediment and the morphodynamics on a timescale of decades to centuries by idealized three dimensional modeling of bifurcations with upstream meanders and dominantly bed load transport an upstream meander favors one bifurcate with more sediment and the other with more water leading to destabilization the bifurcations commonly attain a highly asymmetrical division of discharge and sediment after a few decades to a few centuries depending on combinations of the relevant parameters although past work on avulsions focused on slope advantage we found that bifurcations can be quasibalanced by opposing factors such as a bifurcate connected to the inner bend with a downstream slope advantage nearly balanced bifurcations develop much slower than unbalanced bifurcations which explains the observed variation in avulsion duration in natural systems which branch becomes dominant and the timescale to attain model equilibrium are determined by the length of the downstream bifurcates the radius of the upstream bend a possible gradient advantage for one bifurcate and notably the width depth ratio the latter determines the character of the bars which may result in overdeepening and unstable bars the distance between the beginning of the upstream bend and the bifurcation determines the location of such bars and pools which may switch the dominant bifurcate in fact when the bifurcation is quasibalanced by opposing factors any minor disturbance or a different choice of roughness or sediment transport predictor may switch the dominant bifurcate the division of sediment is nearly the same as the division of flow discharge in most runs until the discharge division becomes very asymmetrical so that a bifurcate does not close off entirely this partly explains the sustained existence of residual channels and existence of anastomosing rivers and the potential for reoccupation of old channel courses we develop a new relation for sediment division at bifurcations in one dimensional models incorporating the effect of meandering the flow and sediment divisions predicted by two existing relations and the new relation for one dimensional models are in qualitative agreement with the three dimensional model these one dimensional relations are however of limited value for wider rivers because they lack the highly three dimensional bar dynamics that may switch the direction of bifurcation evolution the potential effects of bed sediment sorting bank erosion and levee formation on bifurcation stability and avulsion duration are discussed

laboratory and numerical modeling of water balance in a layered sloped soil cover with channel flow pathway over mine waste rock macropores developed in barrier layers in soil covers overlying acid generating waste rock may produce preferential flow through the barrier layers and compromise cover performance however little has been published on the effects of preferential flow on water balance in soil covers in the current study an inclined layered soil cover with a 10 cm wide sand filled channel pathway in a silty clay barrier layer was built over reactive waste rock in the laboratory the channel or preferential flow pathway represented the aggregate of cracks or fissures that may occur in the barrier during compaction and or climate induced deterioration precipitation runoff interflow percolation and water content were recorded during the test a commercial software vadose w was used to simulate the measured water balance and to conduct further sensitivity analysis on the effects of the location of the channel and the saturated hydraulic conductivity of the channel material on water balance the maximum percolation 80 1 of the total precipitation was obtained when the distance between the mid point of the channel pathway and the highest point on the slope accounted for 71 of the total horizontal length of the soil cover the modeled percolation increased steadily with an increase in the hydraulic conductivity of the channel material percolation was found to be sensitive to the location of the channel and the saturated hydraulic conductivity of the channel material confirming that proper cover design and construction should aim at minimizing the development of vertical preferential flow in barrier layers the sum of percolation and interflow was relatively constant when the location of the channel changed along the slope which may be helpful in locating preferential flow pathways and repairing the barrier

shift in the summer rainfall over the yangtze river valley in the late 1970s 1 the summer rainfall over the middle lower valley of the yangtze river and over the whole eastern china experienced a notable regime shift in about 1979 this change is consistent with a simultaneous jump like change in the 500 hpa geopotential height 500 over the northern pacific the rainfall over the yangtze river valley is closely related to the 500 averaged over the area 20 25 n 125 140 e with a correlation coefficient of 0 66 for the period 1958 1999 since 1980 the subtropical northwestern pacific high snph has enlarged intensified and extended southwestward the changes in the snph are strongly associated with the variations of the sea surface temperatures ssts of the eastern tropical pacific and tropical indian ocean the anomalies of these ssts responsible primarily for the shift of the summer rainfall over the yangtze river through the changes in snph precede the 500 signals with different leading times

oxygen influx and geochemistry of percolate water from reactive mine waste rock underlying a sloping channelled soil cover an ideal engineered soil cover can mitigate acid rock drainage ard by limiting water and gaseous o2 ingress into an underlying waste rock pile however the barrier layer in the soil cover almost invariably tends to develop cracks or fractures after placement these cracks may change water flow and o2 transport in the soil cover and decrease performance in the long run the present study employed a 10 cmwide sand filled channel installed in a soil barrier layer silty clay to model the aggregate of cracks or fractures that may be present in the cover the soil cover had a slope of 20 oxygen transport through the soil cover and oxidation of the underlying waste rock were investigated and compared to a controlled column test with bare waste rock without soil cover moreover gaseous o2 transport in the soil cover with channel and its sensitivity to channel location as well as the influence of the saturated hydraulic conductivity of the channel material were modeled using the commercial software vadose w the results indicted that the waste rock underlying the soil cover with channel had a lower oxidation rate than the waste rock without cover because of reduced o2 ingress and water flushing in the soil cover with channel which meant a partial soil cover might still be effective to some extent in reducing ard generation gaseous o2 ingress into the covered waste rock was more sensitive to the channel location than to the saturated hydraulic conductivity of the material filling the channel aqueous equilibrium speciation modeling and scanning electron microscopy with energy dispersive x ray analysis indicated that secondary minerals formed as a result of the oxidation of the waste rock included gypsum and goethite in the covered waste rock and schwertmannite and other fe oxides in the uncovered waste rock the findings of the study provided insight into the effect of channel flow on o2 transport and oxidation of the covered waste rock which may help to improve soil cover design and construction to minimise the generation of preferential flow in the barrier layer

pdo related wintertime atmospheric anomalies over the midlatitude north pacific local versus remote sst forcing abstractobserved wintertime atmospheric anomalies over the central north pacific associated with the pacific decadal oscillation pdo are characterized by a cold trough warm ridge structure tha

upstream and downstream controls of recent avulsions on the taquari megafan pantanal south western brazil avulsion the natural relocation of a river is a key process in the evolution of subaerial fans river floodplains and deltas the causes of avulsion are poorly understood which is partly due to the scarcity of field studies of present avulsions at present two avulsions are occurring on the middle and lower taquari megafan pantanal basin south western brazil here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes the middle fan avulsion started in 1997 1998 is a result of upstream control overbank aggradation was caused by the variable input of sandy sediment into the system which caused channel belt superelevation and also created an easily erodible subsurface favouring bank retreat crevassing and scour of deep floodplain channels the sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage the lower fan avulsion started c 1990 results from interplay of upstream and downstream controls the latter being related to the local base level the paraguay river floodplain at the toe of the fan channel and overbank aggradation on the lower fan was influenced by fan sub lobe progradation and channel backfilling fan sub lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel avulsions are commonly supposed to be preferentially triggered by high magnitude floods when there is considerable channel belt superelevation however both avulsions studied by us were triggered by small to average floods with modest channel belt superelevation we conclude that flood magnitude and channel belt superelevation have been overrated as causes of avulsion and demonstrate additional causes that influence the growth of crevasses into avulsions

representation of northern hemisphere winter storm tracks in climate models northern hemisphere winter storm tracks are a key element of the winter weather and climate at mid latitudes before projections of climate change are made for these regions it is necessary to be sure that climate models are able to reproduce the main features of observed storm tracks the simulated storm tracks are assessed for a variety of hadley centre models and are shown to be well modelled on the whole the atmosphere only model with the semi lagrangian dynamical core produces generally more realistic storm tracks than the model with the eulerian dynamical core provided the horizontal resolution is high enough the two models respond in different ways to changes in horizontal resolution the model with the semi lagrangian dynamical core has much reduced frequency and strength of cyclonic features at lower resolution due to reduced transient eddy kinetic energy the model with eulerian dynamical core displays much smaller changes in frequency and strength of features with changes in horizontal resolution but the location of the storm tracks as well as secondary development are sensitive to resolution coupling the atmosphere only model with semi lagrangian dynamical core to an ocean model seems to affect the storm tracks largely via errors in the tropical representation for instance a cold sst bias in the pacific and a lack of enso variability lead to large changes in the pacific storm track extratropical sst biases appear to have a more localised effect on the storm tracks

upstream control of river anastomosis by sediment overloading upper columbia river british columbia canada anastomosing rivers systems of multiple interconnected channels that enclose floodbasins constitute a major category of rivers for which various sedimentary facies models have been developed while the sedimentary products of anastomosing rivers are relatively well known their genesis is still debated a rapidly growing number of ancient alluvial successions being interpreted as of anastomosing river origin including important hydrocarbon reservoirs urge the development of robust models for the genesis of anastomosis to facilitate better interpretation of ancient depositional settings and controls the upper columbia river british columbia canada is the most studied anastomosing river and has played a key role in the development of an anastomosing river facies model two hypotheses for the origin of upper columbia river anastomosis include the following i downstream control by aggrading cross valley alluvial fans and ii upstream control by excessive bedload input from tributaries both upstream and downstream control may force aggradation and avulsions in the upper columbia river in order to test both hypotheses long term millennia scale floodplain sedimentation rates and avulsion frequencies are calculated using 14c dated deeply buried organic floodplain material from cross valley borehole transects the results indicate a downstream decrease in floodplain sedimentation rate and avulsion frequency along the anastomosed reach which is consistent with dominant upstream control by sediment overloading the data here link recent avulsion activity to increased sediment supply during the little ice age ca 1100 to 1950 ad this link is supported by data showing that sediment supply to the upper columbia study reach fluctuated in response to holocene glacial advances and retreats in the hinterland upstream control of anastomosis has considerable implications for the reconstruction of the setting of interpreted ancient anastomosing systems the present research underscores that anastomosing systems typically occur in relatively proximal settings with abundant sediment supplied to low gradient floodplains a situation commonly found in intermontane and foreland basins

the behavior of inclined covers used as oxygen barriers covers with capillary barrier effects ccbe have been recently proposed as a viable option for gas migration barriers however the effect of geometry on ccbe performance has not been clearly demonstrated in this paper the results of a laboratory study performed with an original apparatus called the inclined box are presented the results obtained show that the hydraulic behavior of layered covers is influenced by the inclination of the slope generally the upper part of the slope contains less water than the lower part this means that the upper part is less efficient than the lower part for limiting gas migration the authors have also studied an existing site where a ccbe was built on a sloping surface after validation of the numerical model with in situ measured data the model was used to perform a parametric study to quantify the influence of the main ccbe parameters on its performance the results obtained confirm those measured in the lab and clearly show how geometry influences the performan

discrimination of alluvial and mixed bedrock alluvial multichannel river networks this paper explores the use of planview morphological metrics to quantitatively describe and distinguish mixed bedrock alluvial multichannel networks from alluvial multichannel networks the geometries of the channel planforms of two bedrock constrained networks mekong and orange rivers are compared with the classic alluvial anastomosed upper columbia river and the wandering ganga river widely recognised indices utilized include channel link count and channel sinuosity with additional emphasis being given to the less common metrics network bifurcation angles and island shape characteristics i e aspect ratio compactness roundness and convexity link count data with one notable exception conform to theoretical expectations bifurcation angles for all four multichannel rivers are significantly greater than angles reported for braiding rivers island convexity clearly discriminates the two alluvial rivers from the two bedrock influenced rivers the width of the macrochannel in which each network develops has a positive influence on the number of channel links and is further related to channel slope variations which in turn are influenced by terrain structure revealed using trend surface analysis the geometry of multichannel networks are often laterally constrained such that the values of channel bifurcation angles and link sinuosity values reduce as the network intensifies and channel links are shortened these latter observations go some way to explain the oft noted relatively straight links seen within multichannel networks which are a necessary adjustment to space filling constraints placed on a network

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

understanding the interdecadal variability of east asian summer monsoon precipitation joint influence of three oceanic signals abstracteast asian summer monsoon precipitation easmp features complicated interdecadal variability with multiple time periods and spatial patterns using century long datasets of hadisst cru precipitation and era 20c reanalysis this study examines the joint influence of three oceanic interdecadal signals i e pacific decadal oscillation pdo atlantic multidecadal oscillation amo and indian ocean basin mode iobm on the easmp which however is found not to be simply a linear combination of their individual effects when pdo and amo are out of phase the same sign sst anomalies occur in north pacific and north atlantic and a zonally orientated teleconnection wave train appears across the eurasian mid high latitudes propagating from north atlantic to northern east asia along the asian westerly jet waveguide correspondingly the interdecadal precipitation anomalies are characterized by a meridional tripole mode over eastern china when pdo and amo are in phase with opposite sign sst anomal

middle holocene avulsion belt deposits in the central rhine meuse delta the netherlands abstract the schoonrewoerd fluvial system in the central rhine meuse delta was active as a rhine distributary between 3900 and 3800 14c years bp based on planform patterns cross sectional facies architecture reconstructed paleodischarge and its short period of activity the schoonrewoerd fluvial system is interpreted to represent a failed avulsion the schoonrewoerd system consists of a complex of ribbon channel sand bodies encased in a lens of clayey deposits and it can be traced for more than 35 km in a downstream direction prominent features of the system are longitudinal facies architecture change with channel sand body width thickness ratio decreasing downstream from 40 to 5 and high lateral facies variability multiple anastomosing sand bodies occur in its upper and middle reaches paleodischarge reconstruction indicates that the schoonrewoerd system was only a minor distributary within the rhine meuse deltaic system specific stream power in the lower reach is estimated to have been low 0 5 to 1 8 w m2 the short period of activity of the schoonrewoerd system suggests that very high floodplain sedimentation rates were associated with the avulsion process with the formation of meters thick fine grained sedimentary successions in 100 years the facies architecture of the short lived schoonrewoerd system is interpreted to reflect the first stages of avulsion broadly analogous to the modern saskatchewan river avulsion in canada smith et al 1989 sedimentology v 36 p 1 23 having escaped from later erosion by a more mature channel belt many other systems often partly eroded with similar facies architecture exist in the west central rhine meuse delta suggesting that avulsion belt deposits are a major component of the holocene delta deposits the facies architecture model of the schoonrewoerd avulsion belt deposits presented in this paper may provide clues for the interpretation of fine grained sedimentary successions in ancient fluviodeltaic deposits

modelling and field measurements of water percolation through an experimental soil cover on mine tailings a composite soil cover constructed on acid producing tailings was evaluated for its ability to retain a high degree of water saturation and low hydraulic conductivity the cover consisted of a 60 c

predicting channel patterns brewer paul lewin j 2001 predicting channel patterns geomorphology 40 pp 329 339 rae2008

evolution of a bifurcation in a meandering river with adjustable channel widths rhine delta apex the netherlands rivers may dramatically change course on a fluvial plain such an avulsion temporarily leads to two active channels connected at a bifurcation here we study the effect of dynamic meandering at the bifurcation and the effect of channel width adjustment to changing discharge in both downstream branches on the evolution of a bifurcation and coexisting channels as an example we reconstructed the last major avulsion at the rhine delta apex we combined historical and geological data to reconstruct a slowly developing avulsion process spanning 2000 years and involving channel width adjustment and meandering at the bifurcation based on earlier idealised models we developed a one dimensional model for long term morphodynamic prediction of upstream channel and bifurcates connected at the bifurcation node the model predicts flow and sediment partitioning at the node including the effect of migrating meanders at the bifurcation and channel width adjustment bifurcate channel width adaptation to changing discharge partitioning dramatically slows the pacing of bifurcation evolution because the sediment balance for width adjustment and bed evolution are coupled the model further shows that meandering at the bifurcation modulates channel abandonment or enlargement periodically this explains hitherto unrecognised reactivation signals in the sedimentary record of the studied bifurcation meander belts newly identified in our geological reconstruction historical maps show that bifurcation migration due to meander bend dynamics increases the bifurcation angle which increases the rate of closure of one bifurcate the combination of model and reconstruction identifies the relevant timescales for bifurcation evolution and avulsion duration these are the time required to fill one downstream channel over one backwater length the time to translate one meander wavelength downstream and for strong river banks the adaptation timescale to adjust channel width the findings have relevance for all avulsions where channel width can adjust to changing discharge and where meandering occurs copyright 2011 john wiley sons ltd

parameter estimation for a karst aquifer with unknown thickness using the genetic algorithm method the thickness of an aquifer b is a critical hydrogeologic parameter in understanding groundwater system especially in a karst aquifer where the high heterogeneity in this parameter brings more uncertainty to the evaluation of groundwater resources in this study the genetic algorithm ga method was used to estimate b as well as five other parameters including k r horizontal hydraulic conductivity k z vertical hydraulic conductivity s storativity s y specific yield and delayed coefficient of a karst aquifer based on a pumping test the search bounds of the six parameters for the ga method were obtained from numerous hypothetic numerical tests the feasibility of the ga method for parameter estimation was verified by the results obtained from the gradient method in terms of a pumping test conducted in the platte river valley in nebraska then this approach was used to estimate the hydraulic parameters in a karst aquifer with unknown aquifer thickness based on a pumping recovery test conducted in the houzhai karst basin southwestern china the results show that the k r k z and the anisotropy ratio of k r to k z are strongly affected by b the differences between the estimated parameter values at two observation wells indicate the existence of high heterogeneity in the karst aquifer the parameter b has the highest absolute normalized sensitivity among these variables implying that the estimated b may be more reliable as compared to other parameters this study demonstrates that the ga method is an alternative method of parameter estimation with the unknown aquifer thickness

middle to late holocene delta plain evolution of the kimotsuki lowland kyushu southern japan abstract the evolution of delta plains and coastal floodplains is commonly believed to be influenced by sea level and climate changes however regional climate change influences on the evolution of delta plains and floodplains are poorly understood compared with responses to rapid sea level rise since the last deglaciation this study investigated the kimotsuki lowland delta plain evolution kyusyu southern japan including allogenic controls based on 28 auger cores and 28 radiocarbon ages large scale crevasse splay deposition occurred at 7000 6000 cal yr bp in response to sea level rise or increased sediment supply following a volcanic eruption afterwards widespread peat was formed in the absence of substantial fluvial sedimentation decreased precipitation from a weakened east asian summer monsoon may have dried the peatlands around 4000 cal yr bp with increasing precipitation and storminess around 2000 cal yr bp peat formation resumed at areas further from the kimotsuki river while increased overbank flows deposited organic rich mud near the river these changes may reflect an increased frequency of la nina events and higher ocean surface temperatures of the kuroshio extension the increased storminess around 2000 cal yr bp may have produced similar influences on delta plain and coastal floodplain evolution across the east asia region the results of this study suggest that regional climate change in the late holocene has a potential to control the evolution of coastal floodplains and delta plains

midwinter suppression of baroclinic wave activity in the pacific abstract seasonal variations in baroclinic wave activity and jet stream structure in the northern hemisphere are investigated based upon over 20 years of daily data baroclinic wave activity at each grid point is represented for each day by an envelope function the lowpass filtered time series of the squared highpass filtered geopotential height baroclinic wave activity over the atlantic exhibits a single maximum in january whereas in the pacific it exhibits peaks in late autumn and in early spring and a significant weakening in midwinter which is more evident at the tropopause level than near the surface this suppression occurs despite the fact that the low level baroclinity and the intensity of the jet stream are strongest in midwinter based on the analysis of 31 day running mean fields for individual winters it is shown that over both the oceans baroclinic wave activity is positively correlated with the strength of the upper tropospheric jet for wind speeds up to 45 m s 1 when the strength of t

anisotropic shear strength characteristics of a tailings sand the deposition process of tailings in a tailings dam may lead to the anisotropy of mechanical properties of tailings to investigate the anisotropic shear strength characteristics of a tailings sand samples deposited under gravity were sheared in a modified direct shear apparatus along different orientations of the shear planes relative to the bedding plane the experimental results reveal that the anisotropy has a substantial effect on the peak shear strength of the tailings sand leading to a variation in peak friction angle of 10 it is found that the effect of anisotropy on the peak shear strength of the tailings sand is mainly attributed to the effect of anisotropy on soil dilatancy on the other hand the effect of anisotropy on the residual friction angle of the tailing sand is relatively smaller likely due to the partial erasure of anisotropy at large shear deformation the degree of anisotropy is reduced by an increase in normal stress to achieve more accurate stability analysis of tailings dams it is suggested to take into account the shear strength anisotropy of tailings soils

the fluvial record of climate change fluvial landforms and sediments can be used to reconstruct past hydrological conditions over different time scales once allowance has been made for tectonic base level and human complications field stratigraphic evidence is explored here at three time scales the later pleistocene the holocene and the historical and instrumental period new data from a range of field studies demonstrate that croll milankovitch forcing dansgaard oeschger and heinrich events enhanced monsoon circulation millennial to centennial scale climate variability within the holocene probably associated with solar forcing and deep ocean circulation and flood event variability in recent centuries can all be discerned in the fluvial record although very significant advances have been made in river system and climate change research in recent years the potential of fluvial palaeohydrology has yet to be fully realized to the detriment of climatology public health resource management and river engineering

simulating the seasonal cycle of the northern hemisphere storm tracks using idealized nonlinear storm track models abstract in this study an idealized nonlinear model is used to investigate whether dry dynamical factors alone are sufficient for explaining the observed seasonal modulation of the northern hemisphere storm tracks during the cool season by construction the model does an excellent job simulating the seasonal evolution of the climatological stationary waves yet even under this realistic mean flow the seasonal modulation in storm track amplitude predicted by the model is deficient over both ocean basins the model exhibits a stronger sensitivity to the mean flow baroclinicity than observed producing too large midwinter eddy amplitudes compared to fall and spring this is the case not only over the pacific where the observed midwinter minimum is barely apparent in the model simulations but also over the atlantic where the october april eddy amplitudes are also too weak when the january amplitude is tuned to be about right the nonlinear model generally produces stronger eddy amplitude with stronger b

an idealized model study relevant to the dynamics of the midwinter minimum of the pacific storm track the synoptic variability of a two level quasigeostrophic flow in response to plausible changes in the forcing of a localized baroclinic jet is investigated in the context of the midwinter minimum of the pacific storm track mwm the changes in the model forcing are introduced in terms of a reference potential vorticity field that is associated with plausible changes in the global baroclinicity zonal variation of the baroclinicity and horizontal deformation over the pacific from early winter to midwinter conditions it is found that the modal instability growth rate of perturbation in such a localized jet is significantly reduced in spite of an increase in the local baroclinicity the dynamical nature of such an effect can be interpreted as a generalized barotropic governor effect on localized baroclinic instability the existence of three instability regimes is established on the basis of energetics characteristics the intensity of the nonlinear model storm track is reduced by about 30 in response to a change in the forcing condition from early to midwinter the characteristics of the linear model storm track and nonlinear model storm track are compared the overall results support a hypothesis that mwm could stem from a sufficiently large increase in the stabilizing influence of the local barotropic process in spite of a simultaneous increase in its local baroclinicity in the pacific jet from early to midwinter

morphology of fluvial levee series along a river under human influence maros river hungary abstract the development and morphometry of fluvial levees reflect the connection between channel and overbank processes which can be altered by various human activities the aims of this study are to investigate the morphology and spatial characteristics of fluvial levees and evaluate the role of some local and catchment scale human activities on their medium term 150 years development this study applies lidar data along a 53 km long reach of the maros river in hungary six fluvial levee types are identified based on the beginning and end of their evolution these levee types were generated by local nineteenth century channel regulation works cutoffs and mid twentieth century channel narrowing which was caused by gravel mining and water impoundment in the upstream sections however other human activities also influenced the development of active fluvial levees because their horizontal evolution could have been limited by embanked flood protection levees or the widening of low lying floodplain benches that were generated by channel narrowing additionally revetment constructions influenced their vertical parameters as higher fluvial levees developed along the fixed banks generally the older active fluvial levees are wider while the younger active levees are narrower with steeper slopes but not always lower on the low lying floodplain levels benches the youngest fluvial levees evolved quite rapidly and consist of coarser material currently only 9 8 to 38 year return period floods could cover the fluvial levees contributing to their evolution this fact and the development of fluvial levee series with two three members reflect a gradual decoupling of the channel from the floodplain

post closure investigation of engineered test covers on acid generating waste rock at whistle mine ontario three engineered test covers were installed at the whistle mine test site near capreol ontario and monitored over 4 years each cover was a two layer system consisting of a 0 90 m noncompacted g

anastomosing river deposits sedimentation rates and basin subsidence magdalena river northwestern colombia south america situated in a tectonically active foreland basin the magdalena river consists of vertically accreting levee confined channels and adjacent extensive wetlands which are interpreted as an anastomosing river sedimentary system equivalent rates of basin filling and subsidence average 3 8 mm yr 1 based on 18 14c dates from five bore holes drilled to depths of 55 m and sediment transport budgets from 35 years of measurement located in a savanna tropical climate anastomosing river deposits of the magdalena are remarkably similar to the anastomosing deposits of the upper columbia river in a temperate cold climate in western canada suggesting that climate is not a controlling factor of anastomosis the geometry of anastomosing channel fills in the magdalena consists of stratigraphically non uniform low sinuous narrow stringers of sand up to 30 m thick by 600 m wide a width depth ratio of 20 thin 1 2 m off channel crevasse splay sand sheets extend laterally up to 10 km distance when buried both sand deposits become encased by lacustrine or marsh mud to form stratigraphic traps while there are few modern anastomosing river systems as compared to braiding and meandering there may be a disproportionately large number of ancient anastomosed fluvial rock sequences due to the rapid rate of vertical accretion such a different depositional style and geometry of sand bodies have considerable significance in the interpretation of some ancient fluvial rock sequences because it provides an alternative to the meandered and braided river deposition models

discontinuous drainage systems formed by highland precipitation and ground water outflow in the navua valles and southwest hadriacus mons regions mars abstract the navua valles are systems of paleodrainages located north of dao vallis which empty into hellas planitia the largest impact basin on mars in this study we mapped and characterized the navua valles region s individual drainage systems including drainages along the southwestern flank of hadriacus mons and one valley network from the same source as navua valles but flowing in the opposite direction the major drainage systems share morphological characteristics common to both outflow channels and valley networks the slopes in this region are dissected by two major navua drainage systems here navua a and b and several shorter sub parallel valleys formed on the highest gradient approximately 20 m km 1 15 slopes at the lowest part of hellas basin s rim the two major drainage systems originate in the highlands and empty into the basin our mapping suggests that water in navua valles reached the basin floor in a complicated descent and included several episodes of surface ponding surface runoff infiltration subsurface flow and subsequent outflow the most prominent channel system navua a forms a repetitive sequence of deep incision into bedrock followed by a transition into broad channels in erodible materials and then into unconfined deposits this successive erosion transport deposition sequence continues to repeat along the valley s entire length forming a discontinuous pattern that is consistent with classical fluvial process models the channels cut into volcanic plains likely emplaced from the formation of tyrrhenus and hadriacus montes the dendritic source valleys of navua a originate from the rim of a highland crater while the rest of this subsystem consists of a single discontinuous channel which is consistent with a single water source zone that likely supplied water for all channels downslope these drainages may have formed as discontinuous channels revealing the potential existence of subsurface drainage pathways located within an approximately 1 5 10 5 km 2 area water transported underground emerged in segments that are either isolated or aligned downslope from each other we have identified several causes of discontinuities located the zones of potential ground water discharge and recharge and a site of localized precipitation at the headwaters of navua a

using mean flow change as a proxy to infer interdecadal storm track variability abstract several recent studies based mainly on analyses of reanalysis data have suggested that the northern hemisphere storm tracks have intensified during the second half of the twentieth century however comparisons with rawinsonde observations over land areas suggest that eddy variance covariance statistics may contain spurious jumps that had led to an exaggeration of the storm track secular trend in this study storm track variations are inferred from mean flow anomalies using canonical correlation analysis cca a cca model relating storm track anomalies to mean flow anomalies is derived using recent more reliable data the model is then applied to infer storm track anamalies using mean flow anomalies for earlier periods when storm track analyses are deemed more suspect or even nonexistent results of the cca analyses suggest that the strong secular trend observed over the atlantic basin and europe is consistent with mean flow anomalies while cca predictions based on mean flow changes sugg

combining historical and process perspectives to infer ranges of geomorphic variability and inform river restoration in a wandering gravel bed river restoration approaches such as dam removal and channel reconstruction have moved beyond the realm of small streams and are being applied to larger rivers this development has substantial economic and ecological implications but may test gaps in our understanding of larger river systems and of restoration science we examine how information about historical ranges of geomorphic variability can inform stream restoration in the context of the clark fork river montana focusing on a study reach where one of the largest restoration projects to date was implemented upstream of the recently removed milltown dam analysis of historical sources and aerial photographs of the clark fork river s pre mining mining and more recent history suggest that a wandering channel pattern has persisted despite variations in sediment supply and transport capacity predictive metrics for channel pattern also suggest a wandering pattern transitional between braided and meandering in this geomorphic setting these analyses suggest that the creation of a single thread meandering channel which incorporates structures to limit erosion and channel movement is inconsistent with the historical range of variability in this reach the perils of restoring channels to a condition different than the historical range of variability for their geomorphic setting were illustrated on the clark fork by flood induced avulsions of the restored channel that occurred soon after project construction application of an experimental approach to restoration founded on the method of multiple working hypotheses provides a means for embracing uncertainty can maximize the potential for site specific restoration success and can foster advances in restoration science copyright 2012 john wiley sons ltd

anastamosing channels in the lower neches river valley texas active and semi active anastomosing holocene channels upstream of the delta in the lower valley of the meandering neches river in southeast texas represent several morphologically distinct and hydrologically independent channel systems these appear to have a common origin as multi thread crevasse channels strongly influenced by antecedent morphology levee breaching leads to steeper cross valley flows toward floodplain basins associated with pleistocene meander scars creating multi thread channels that persist due to additional tributary contributions and ground water inputs results are consistent with the notion of plural systems where main channels tributaries and sub channels may have different morphologies and hydrogeomorphic functions the adjacent trinity and sabine rivers have similar environmental controls yet the trinity lacks evidence of extensive anastomosing channels on its floodplain and those of the sabine appear to be of different origin the paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy copyright 2014 john wiley sons ltd

trapping of synoptic scale disturbances into the north pacific subtropical jet core in midwinter 1 over the northwestern nw pacific a subtropical jet stream develops at 30 n in midwinter as the east asian winter monsoon intensifies eddies with subweekly periods propagating through the midlatitude tropopause into the nw pacific storm track tend to be trapped into the jet core 1000 km away from a surface baroclinic zone at 40 n while lifted up by 3 km the trapping appears to weaken the interaction of the upper level eddies with the baroclinic zone thus acting against eddy amplification and thereby contributing to the midwinter minimum in the eddy activity as observed before the late 1980s since then under the reduced trapping effect by the weakened jet upper level eddies tended to propagate right above the surface baroclinic zone while strongly interacting it even in midwinter as in fall and spring this midwinter tendency acted to enhance the eddy amplification that led to the recent disappearance of the activity minimum

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

dynamics of the stationary anomalies associated with the interannual variability of the midwinter pacific storm track the roles of tropical heating and remote eddy forcing abstract the leading mode of interannual variability of the midwinter pacific storm track is such that the storm track is weaker during the winters when the pacific jet is strong and stronger when the jet is weak in this paper experiments are conducted using a stationary wave model as well as an idealized global circulation model to explore the roles of anomalous tropical heating and eddy fluxes in forcing the observed pacific jet anomalies it is found that enhanced tropical heating over the region 60 e to the date line 25 s to 25 n acts to force a stronger and narrower pacific jet on average tropical heating may account for about one third of the strong jet anomaly but there is significant year to year variability moreover tropical heating does not appear to contribute to the weak jet anomaly much of the pacific jet anomalies are forced by anomalous eddy fluxes by examining the regional contributions from the pacific the atlantic and asia it is found that local eddy feedback over the paci

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

interdecadal variations in northern hemisphere winter storm track intensity abstract in this paper the interannual variations in the northern hemisphere winter storm tracks have been examined based on 51 winters december january february of ncep ncar reanalysis data the leading empirical orthogonal function eof corresponds to the simultaneous strengthening weakening of both the pacific and atlantic storm tracks interannual and month to month variations in the pacific and atlantic storm tracks are found to be significantly correlated the principal component associated with the leading hemispheric eof exhibits pronounced interdecadal variability there appears to be a transition during the early 1970s from a weak storm track state prior to 1972 73 to a strong storm track state subsequently decadal mean storm track intensity during the 1990s is about 30 stronger than that during the late 1960s and early 1970s the relationship between variations in storm track intensity and low frequency seasonal mean flow anomalies has also been examined it is shown that storm track va

effect of boreal spring precipitation anomaly pattern change in the late 1990s over tropical pacific on the atmospheric teleconnection observational evidence showed that the leading mode of precipitation variability over the tropical pacific during boreal spring experienced a pronounced interdecadal change around the late 1990s characterized by a precipitation pattern shift from an eastern pacific ep type to a central pacific cp type the distinct impacts of such a precipitation pattern shift on the extratropical atmospheric teleconnection were examined an apparent poleward teleconnection extending from the tropics to the north atlantic region was observed after 1998 while there was no significant teleconnection before 1998 to understand why only the cp type precipitation mode is associated with a striking atmospheric teleconnection after 1998 diagnostic analyses with the eliassen palm flux and rossby wave source rws based on the barotropic vorticity equation were performed the results show that for the ep type precipitation mode no significant rws anomalies appeared over the subtropical pacific due to the opposite effect of the vortex stretching and absolute vorticity advection processes for the cp type precipitation mode however there are both significant vorticity forcing source over the subtropical cp and clear poleward propagation of rossby wave the spatial distribution of the cp type precipitation pattern tends to excite a conspicuous anomalous southerly and a well organized negative vorticity center over the subtropical cp where both the mean absolute vorticity gradient and mean divergence flow are large hence the interaction between the heating induced anomalous circulation and the basic state made the generation of rossby waves conceivable and effective such corresponding teleconnection responses to the prescribed heating were also examined by using a linear baroclinic model lbm it turned out that significant poleward teleconnection pattern is only caused by the cp type precipitation mode rather than by the ep type precipitation mode further sensitive experiments demonstrated that the change in spring basic state before and after 1998 played a relatively minor role in exciting such a teleconnection pattern when compared with the tropical precipitation anomaly pattern change

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

multichannel systems in an ancient river dominated delta case study of the lower yanchang formation southwest ordos basin china distributary channels in large deltas can form a channel pattern similar to braided fluvial system or anastomosed fluvial system that have multichannel systems although both systems are of general

northern hemisphere midlatitude cyclone variability in gcm simulations with different ocean representations the impact of different ocean models or sea surface temperature sst and sea ice concentrations on cyclone tracks in the northern hemisphere midlatitudes is determined within a hierarchy of model simulations a reference simulation with the coupled atmosphere ocean circulation model echam hope is compared with simulations using echam and three simplified ocean and sea ice representations 1 a variable depth mixed layer ml ocean 2 forcing by varying sst and sea ice and 3 with climatological sst and sea ice the latter two are from the coupled echam hope integration the reference simulation reproduces the observed cyclone tracks the cyclones are tracked automatically by a standard routine and the variability of individual cyclone trajectories within the storm tracks is determined by a cluster approach in the forced simulation with varying sst the geographical distribution and the statistics of the cyclones are not altered compared to the coupled reference simulation in the ml and the climatological simulation deviations of the mean cyclone distribution are found which occur mainly in the north pacific and can partially be traced back to missing el nino southern oscillation enso variability the climatological experiment is superior to the ml experiment the variability of the individual cyclone trajectories as determined by the cluster analysis reveals the same types and frequencies of propagation directions for all four representations of the lower boundary the largest discrepancies for the cluster occupations are found for the climatological and the ml simulation

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

modelling the bulk flow of a bedrock constrained multi channel reach of the mekong river siphandone southern laos the general nature of bulk flow within bedrock single channel reaches has been considered by several studies recently however the flow structure of a bedrock constrained large river with a multiple channel network has not been investigated previously the multiple channel network of the siphandone wetlands in laos a section of the mekong river was modelled using a steady one dimensional hydraulic model the river network is characterized by a spatially varying channel form leading to significant changes in the bulk flow properties between and along the channels the challenge to model the bulk flow in such a remote region was the lack of ideal boundary conditions the flow models considered both low flow high inbank and overbank flows and were calibrated using spot satellite sensor imagery and limited field data concerning water levels the application of the model highlighted flow characteristics of a large multi channel network and also further indicated the field data that would be required to properly characterize the flow field empirically important results included the observation that adjacent channels within the network had different water surface slopes for the same moments in time thus calibration data for modelling similar systems needs to account for these significant local differences further the in channel hydraulic roughness coefficient strongly varied from one cross section to the next manning s n range 0 01 to 0 10 these differences were amplified during low flow but persisted in muted form during high discharges

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

avulsions channel evolution and floodplain sedimentation rates of the anastomosing upper columbia river british columbia canada ages of channels of the anastomosing upper columbia river south eastern british columbia canada were investigated in a cross valley transect by c 14 dating of subsurface floodplain organic material from beneath levees the avulsion history within the transect was deduced from these data and morphological stages in channel development were recognized additionally floodplain sedimentation rates were established the new data demonstrate that the upper columbia river is a long lived dynamic anastomosing system results show that anastomosis at the study location has persisted since at least 2700 cal years bp with avulsions occurring frequently at least nine channels have formed in the studied cross valley transect within the past 3000 years channel lifetimes from formation to abandonment appear to be highly variable ranging from approximately 800 to 3000 years log jams provoking avulsions and or silting up of old channels are proposed as reasons for this variability long term average floodplain sedimentation rates appear to be significantly lower than previously proposed by smith 1983 int assoc sedimentol spec publ 6 155 168 a long term 4550 years average of 1 75 mm per year after compaction was based on c 14 dates whilea short term sedimentation rate of 0 8 mm was determined for a single relatively small seasonal flood in 1994 using sediment traps however short term sedimentation rates vary considerably over the floodplain with levees aggrading up to four times faster than floodbasins channels of the upper columbia river anastomosed reach follow a consistent pattern in their development with each stage being characterized by different morphology and processes channel evolution comprises the following succession 1 avulsion stage in which a crevasse splay channel deepens by scour and levee sedimentation 2 widening and deepening stage in which bank slumping and bed scouring dominates 3 infilling stage in which either channel narrowing bank accretion or channel shallowing bed accretion takes place and 4 abandonment stage in which the residual remnant channel is filled exclusively by silt clay and organic material vertical stacking super imposition of active channels on recent channel fill sand bodies is a notable feature of the upper columbia river which suggests that reoccupation of residual channels is a common process

a study of infiltration on three sand capillary barriers the capillary barrier effect was investigated by conducting infiltration tests on three soil columns of fine sand over medium sand medium sand over gravelly sand and fine sand over gravelly sand

funneled flow mechanisms in a sloping layered soil laboratory investigation artificial capillary barriers are being used to divert water away from sensitive underground regions conversely funneled flow over natural capillary barriers may increase the danger of groundwater contamination by decreasing the travel time and contact area there have been relatively few experimental studies of capillary barrier flow patterns in this study water was applied uniformly across the top surface of a backlit tilting chamber 1 cm thick 110 cm high and 180 cm long in which a coarse sand layer was imbedded in a fine sand bedding slope and water application rates were varied between 0 and 12 and 1 and 3 cm h 1 respectively after attaining steady state matric potential was measured along the textural interface and photos of dye traces were taken in order to visualize streamlines the funneled flow was characterized by three discrete regions an initial capillary diversion a breakthrough region and a toe diversion the breakthrough region consisted of a significant zone of partial breakthrough where the vertical flux into the coarse layer was less than the water application rate the lateral distance of the capillary diversion was explained well by previously published relationships when the water entry value at the textural interface was replaced by lower observed matric potential at which breakthrough occurred at the most upslope point the length of the capillary diversion was overpredicted using the air entry value finally the toe of the coarse layer had significant observed effects on funneled flow patterns which have previously received little if any attention the results of this study imply that the slope of the coarse layer and infiltration rate will largely govern the effectiveness of capillary barriers and that capillary barriers are less effective than previously assumed

avulsion frequency avulsion duration and interavulsion period of holocene channel belts in the rhine meuse delta the netherlands abstract avulsion parameters greatly influence alluvial architecture because they determine channel density and interconnectedness reliable data on avulsion parameters is still scarce from a detailed reconstruction of the holocene avulsion history of the whole rhine meuse delta we determined quantitative values for the avulsion parameters avulsion frequency avulsion duration and interavulsion period in the rhine meuse delta the number of coeval channels is related to the avulsion frequency calibrated 14c intensity histograms are used to analyze 14c dates of beginning and ending river activity the histograms show that instantaneous and gradual avulsions were almost equally important in the rhine meuse delta a high avulsion frequency occurred from 8000 to 7300 cal yr bp a total of 17 avulsions i e 2 43 avulsions 100 years during this period the avulsion frequency was related to the high rate of sea level rise which induced fluvial sedimentation in the present near coastal area after 7300 cal yr bp avulsion frequency decreased as a result of a continuously decreasing rate of sea level rise from 7300 to 3200 cal yr bp avulsion frequency was low 35 avulsions took place within 4100 years 0 85 avulsions 100 years approximately 5000 cal yr bp the coastal barriers became closed and large scale peat formation occurred this resulted in fixation of the river channels and low cross valley gradients reducing the chances for avulsion between 3200 and 1400 cal yr bp avulsion frequency was high again a total of 34 avulsions i e 1 89 avulsions 100 years as a result of increased discharge and or within channel sedimentation which enhanced chances for avulsion the period of activity of channel belts shows no significant trend on the time scale of the holocene it is highly variable and averages 1280 820 cal yr the avulsion duration fluctuates between less than 200 and 1250 cal years and averages 335 cal years the avulsion duration shows no significant trend through time and remained constant until at least 1900 cal yr bp avulsion duration seems not to be influenced by aggradation rate average interavulsion period is shorter than the period of activity of channel belts and is approximately 945 cal years in the rhine meuse delta on the time scale of the holocene interavulsion period and avulsion duration are on average constant therefore the number of coeval channels is directly related to avulsion frequency available evidence from other rivers and deltas around the world however suggests that the relationship between these avulsion parameters is not everywhere the same

necessary conditions for a meandering river avulsion there is as yet no rational basis for predicting the conditions leading to avulsion of a meandering river here we present a conceptual model and quantify it under simplifying assumptions as a first step toward the construction of a stability diagram for avulsion initiation it is assumed initially that a rectangular crevasse channel of arbitrary depth is cut into the levee of a meandering river because the water entering the crevasse channel is derived from relatively high in the main flow it contains low concentrations of suspended solids consequently the crevasse flow is under capacity and the entrance is eroded deepening of the entrance increases the crevasse channel discharge and the concentration of suspended solids supplied because more sediment laden waters are tapped from the deeper flow in the main channel the crevasse entrance is predicted to deepen until its sediment carrying capacity is satisfied by the suspended solids entering from the main channel whether an avulsion will occur for a particular combination of initial conditions depends upon whether there exists steady state hydraulic and sediment transport conditions for crevasse channel depths that are equal to or less than the main channel depth this conceptual model is quantified by writing the unsteady gradually varied one dimensional conservation of mass and momentum equations for water and sediment transport through a main and crevasse channel sediment transport is computed as the integral of a cross sectional mean velocity and a rouse concentration profile solutions show that stable crevasse channels exist only for particular combinations of the initial height of the crevasse bed relative to the water depth in the main channel and the ratio of initial crevasse bed slope to main channel slope

elemental and biomarker characteristics in a pleistocene aquifer vulnerable to arsenic contamination in the bengal delta plain india an elevated level of arsenic as in the indo gangetic delta plain aquifers has been reported since the 1990s organic matter om present in groundwater and aquifer sediments supports the microbial communities in these aquifers during installation of a drinking water well 26 sediment intervals of 6 m each were retrieved up till 156 m from a pleistocene brown sand aquifer bsa grain size distribution sequential extraction of metals and total extractable lipids were analyzed in each sample these parameters were statistically correlated in order to establish relationship between the physical vs inorganic and organic characteristics and how these properties affected the distribution of as in bsas the aquifer sediments consisted of medium to coarse sand except the surface sediments and those at the bottom of the well which had high clay and slit content arsenic as concentration in sediments ranged from 2 to 21 mg kg and indicated a strong correlation with grain size arsenic was mostly associated with crystalline oxides and silicate rich minerals arsenic showed significant correlation with fe in all fractions and suggests presence of pyrite bound as bearing minerals in these sediments the diagnostic sedimentary lipid biomarkers indicated presence of compounds derived from vascular plants and microbial cell wall this inference was supported by various diagnostic lipid ratios the biomarkers were abundant in surface and deeper layers which had high clay and silt content the bsa sediments indicated preferential preservation of n alkanes over other functional compounds which were more reactive and subject to degradation the thick clay layer at 132 156 m contained visible plant fragments and om in this layer indicated preferential preservation of organic carbon most likely due to the absence of specific microbial communities that degraded these compounds and mobilized as statistical analyses indicated the influence of selective inorganic and organic components as fe and fatty acids controlling the co distribution of various inorganic and organic components in the aquifer

channel networks within lava flows formation evolution and implications for flow behavior new high resolution maps of hawaiian lava flows highlight complex topographically controlled channel networks network geometries range from distributary systems dominated by branching around local obstacles to tributary systems constricted by topography we combine 2 d network analysis tools developed for river systems and neural networks with 3 d lidar morphologic analysis and historical records of flow emplacement to investigate both the origins of channel networks and their influence on flow morphology and behavior we find that network complexity is a function of underlying slope and that the degree of flow branching network connectivity and longevity of individual channels all influence the final flow morphology flow and channel widths and levee heights furthermore because channel networks govern the distribution of lava supply within a flow changes in the channel topology can dramatically alter the effective volumetric flux in any one branch which affects both flow length and advance rate specifically branching will slow and shorten flows while merging can accelerate and lengthen them consideration of channel networks is thus important for predicting lava flow behavior and mitigating flow hazards with diversion barriers observed relationships between network geometry flow parameters and morphology also offer insight into the interpretation of these features elsewhere on earth and other terrestrial planets

defining large river channel patterns alluvial exchange and plurality abstract large rivers have anabranching channels with components that may be defined as braided meandering or straight this paper shows that application of such holistic terminologies is complicated by recognition of within type and transitional type variety a confusingly varied use of terms and a coverage of pattern characteristics that for many large rivers is incomplete in natural states big rivers can be plural systems in which main accessory tributary and floodplain channels and lakes differ functionally and vary in terms of morphological dynamics a distinction is drawn between the hydrological and geomorphological connectivity of components in big river plural systems at any one time even at flood stage only some channels are geomorphologically active six types of geomorphological connectivity are described that range from coupled through to partially coupled and decoupled the interplay between geomorphological and hydrological connectivity in large rivers is shown to determine habitat status and therefore ecological diversity for improved understanding of the dynamics as well as the forms of these large composite systems it is helpful to 1 adopt element level specification not only for sediment bodies but also for functioning channels 2 track the sediment transfer processes and exchanges that produce channel forms over the highly varied timescales operating within large rivers and 3 recognise the ways in which partially coupled and connected geomorphological systems produce naturally a composite set of forms at different rates such augmenting information will provide an improved platform for both river management and ecological understanding

electrical resistivity imaging of anastomosing river subsurface stratigraphy and possible controls of fluvial style change in a graben like basin czech republic abstract subject to frequent channel avulsions due to the increased frequency of floods rise of base level and or sediment overloading anastomosing rivers are sensitive to external climatic or tectonic forcing in sedimentary basins the morava river czech republic shows a well developed holocene anastomosis confined to the pull apart type upper morava basin umb we studied the stratigraphy and aggradation rates of the umb using electrical resistivity tomography ert dipole electromagnetic profiling demp core data and radiocarbon ages with the aim of identifying factors triggering the anastomosis at the pleistocene holocene transition the ert and demp proved to be excellent tools to visualize the shape and thickness of floodplain depositional units abandoned meanders scroll bars etc the major geophysical surfaces identified are the base of the late weichselian braided stream deposits osl age 34 53 3 42 ka interpreted as a palaeo stream gradient of the morava river and their transition to holocene floodplain deposits in the late weichselian the river aggraded at an average rate of 0 2 mm yr the holocene oldest 14c age 7 066 0 072 ka short term aggradation rates reached up to 13 7 mm yr but the average long term rates 0 07 to 0 4 mm yr are comparable to the late weichselian the stratigraphy and sediment ages indicate that the onset of anastomosis was not likely associated with accelerated basin subsidence possible controls of the anastomosis include upstream control by numerous tributaries large wood debris in the floodplain forests and changes in land use the tectonic and geomorphic context of the umb pull apart basin probably favoured the development of the anastomosis