the use of multivariate statistics to elucidate patterns of floodplain sedimentation at different spatial scales floodplains are depositional features of riverine landscapes that display complex sedimentation patterns that are amenable to multi scale approaches we examined sedimentation in the lower balonne floodplain queensland australia at three different spatial scales the channel 103 km floodplain process zone 10 km and geomorphic unit 102 m scales and compared scale related patterns evident from stratigraphy with those evident from quantitative multivariate analysis three stratigraphic sequences were found in the lower balonne floodplain generally fining upward episodic fining upward and mud dominated stratigraphical analysis revealed the detailed character of sedimentary sequences embedded within the scale patterns derived from multivariate analysis multivariate statistical analyses of a range of textural and geochemical data revealed different patterns of floodplain sedimentation at each scale at the channel scale sediment texture and geochemistry were more heterogeneous in the culgoa river than in briarie creek at the floodplain process zone scale clear patterns of sediment texture and geochemistry were observed along the upper mid and lower floodplain process zones of briarie creek but not along the culgoa river at the geomorphic unit scale clear patterns of sediment texture and geochemistry were observed among the bank buried channel and flat floodplain units of the culgoa river but were not as clear in briarie creek recognition of rivers as hierarchically organized systems is an emerging paradigm in river science our study supports this paradigm by demonstrating that different sedimentation patterns occur at different scales to reveal a hierarchically organized floodplain environment copyright 2006 john wiley sons ltd

dynamic relations for the deposition of sediment on floodplains and point bars of a freely meandering river abstract fluvial features such as floodplains and point bars are built by sediment deposition and sculpted by erosion long term measurements 38 yr of the cross section topography of active floodplains and point bars along the freely meandering powder river in southeastern montana usa mean daily discharge of 12 5 m3 s 1 were used to develop dynamic relations between annual sediment deposition and peak flood discharge five floodplain sections and five point bar sections were selected from 24 cross sections along a 90 km study reach at each cross section the sediment deposition volume per unit streamwise distance was computed as the difference between two topographic surveys made in consecutive years snowmelt floods were found to be the dominant annual process however other processes such as flash floods ice breakup floods and autumnal floods were important episodically the dynamic relations were linear for both fluvial features the snowmelt deposition discharge relations showed in general that point bars were about two times more efficient at trapping sediment than floodplains each relation had a discharge threshold that must be exceeded before sediment was deposited although these discharge thresholds for floodplains and point bars had essentially the same mean value 69 and 71 m3 s 1 respectively they represented different processes thresholds for other rivers will probably differ from those for powder river because of different channel geometry and sediment characteristics

the geomorphic dynamics and environmental history of an upper deltaic floodplain tract in the sacramento san joaquin delta california usa a multi proxy approach was used to examine the geomorphic dynamics and environmental history of an upper deltaic oodplain tract in the sacramento san joaquin delta california three long cores were collected from the mccormack williamson tract mwt and these cores were analyzed for bulk density loss on ignition ne clay and silt content al concentration magnetic susceptibility pollen and charcoal radiocarbon dates obtained for the cores were converted into calendar years and an age depth model was constructed long term vertical accretion and sedimentation rates were estimated from the age depth model cross core relations show that coarse sediment generally accumulates more rapidly and has greater magnetic susceptibility compared to ne sediment percentage ne and loi data show a strong linear relationship that indicates ooding is the primary mechanism for the deposition of particular organic matter on the oodplain and that landscape wash load has contributed a highly consistent fraction of persistent organic matter averaging 5 5 per cent to the site down core grain size pro les show two hydrological domains in the cores namely millennial ne coarse uctuations superimposed on general up core ning coarse sediment is viewed as channel or near channel overbank deposits whereas ne deposits are considered to be distal overbank ood deposits the coarse ne uctuations are indicative of changing depositional settings as channels migrated laterally across mwt whereas the upward ning trend re ects a combination of self limiting overbank deposition as oodplain elevation increased and decreasing competence as sea level rise reduced ood pulse energy slopes mwt has been cross cut and incised numerous times in the past only to have the channels abandoned and subsequently lled by ne sediment the channels around mwt attained their modern con guration about 4000 years ago mwt likely came under tidal in uence at about 2500 cal bp wetlands have recently developed on mwt but they are inorganic sediment dominated copyright 2004 john wiley sons ltd

holocene floodplain soils along the rio mamore northern bolivia and their implications for understanding inundation and depositional patterns in seasonal wetland settings abstract the llanos de moxos lm in the bolivian amazon basin host one of the largest seasonally inundated savannah landscapes on earth very little is known of this area with regard to sedimentary dynamics soil formation or their relationship to longer term climatic and hydrological variability in this setting here we present a detailed study of three floodplain depositional sequences building up the inundation savannah along the mamore river in the central lm pleistocene sands and silts unit 1 are overlain by thick overbank deposits of mostly holocene age unit 2 on both sides of the mamore river and underline the importance of extensive flooding processes for the late quaternary sedimentary and geomorphic evolution of the lm the fine grained distal overbank sediments show signs of strong modification by hydromorphic processes and reflect spatial and temporal variations in flood inundation patterns in addition widespread dark gray to blackish soil and paleosol horizons are intercalated with the overbank sediments but lack evidence for significant weathering these horizons are likely the result of cumulative incorporation of organic material under conditions of particularly low sedimentation rates therefore their formation should be linked to processes such as channel migration longer term meanderbelt evolution avulsive drainage reorganization changes in sediment supply or climatically induced variations in flooding type frequency or magnitude the common occurrence of these floodplain soils in the early to mid holocene may thus reflect the combined effects of hydrological geomorphic and sedimentary changes during a drier mid holocene

variations in natural levee morphology in anastomosed channel flood plain complexes abstract natural levees are common features of alluvial river systems yet their origin and evolution are poorly understood in this paper we present morphologic and sedimentologic data from two anastomosed rivers and offer a hypothesis of natural levee growth in these systems based on mechanisms of sediment transport in settings where floodbasins fill at the same rate as the channel levees form by turbulent diffusion of suspended sediment away from a high velocity thread into a floodbasin of relatively stagnant water the theory of diffusive transport suggests that these levees should be narrow steep and display abrupt decreases in grain size due to rapid decreases in carrying capacity with distance into the floodbasin in environments where an appreciable water surface slope is maintained between the main channel and the floodbasin levees form by advection of sediment out of the channel and into the floodbasin advective transport theory indicates that these levees should be broad and gently sloped with grain sizes gradually decreasing away from the main channel natural levees occurring in the anastomosed reach of the upper columbia river in se british columbia display significantly different morphology from levees in the cumberland marshes region of the lower saskatchewan river in east central saskatchewan at the upper columbia site the rise in stage of the floodbasin water nearly keeps up with that of the channel water because of good communication between channel and floodbasins through crevasses this inhibits the establishment of a water surface slope and the bulk of the escaping sediment is deposited close to the channel in contrast the cumberland marshes region is characterized by wide and volumetrically large floodbasins these conditions keep floodbasin water surface elevations relatively low and maintain an appreciable elevation head between the channel and its floodbasin fostering levee growth by advective transport

impact of flow regulation on near channel floodplain sedimentation article i nfo article history rates and the spatial extent of near channel floodplain sedimentation on regulated and unregulated reaches in two upland rivers in central vermont u s a are measured using the short lived fallout radionuclide 210 pb we find consistent profiles of 210 pb inventories across all sites inventories are low immediately next to the channel increase to a peak value as the inundation frequency decreases and then asymptotically diminish with distance from the channel to the equilibrium inventory associated with atmospheric deposition alone we infer from our data that flow regulation has impacted sediment deposition to floodplains below the dam total sediment deposition is less and it is constrained to a narrower band immediately along the active channel flow regulation does not appear however to impact the general form of the 210 pb inventory profile suggesting a uniformity of process across regulated and unregulated floodplains

floodplain land cover and flow hydrodynamic control of overbank sedimentation in compound channel flows overbank sedimentation is predominantly due to fine sediments transported under suspension that become trapped and settle in floodplains when high flow conditions occur in rivers in a compound channel the processes of exchanging water and fine sediments between the main channel and floodplains regulate the geomorphological evolution and are crucial for the maintenance of the ecosystem functions of the floodplains these hydrodynamic and morphodynamic processes depend on variables such as the flow depth ratio between the water depth in the main channel and the water depth in the floodplain the width ratio between the width of the main channel and the width of the floodplain and the floodplain land cover characterized by the type of roughness this paper examines by means of laboratory experiments how these variables are interlinked and how the deposition of sediments in the compound channel is jointly determined by them the combination of these compound channel characteristics modulates the production of vertically axised large turbulent vortical structures in the mixing interface such vortical structures determine the water mass exchange between the main channel and the floodplain conditioning in turn the transport of sediment particles conveyed in the water and therefore the resulting overbank sedimentation the existence and pattern of sedimentation are conditioned by both the hydrodynamic variables the flow depth ratio and the width ratio and the floodplain land cover simulated in terms of smooth walls meadow type roughness sparse wood type roughness and dense wood type roughness

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

long term versus short term deformation of the meizoseismal area of the 2008 achaia elia mw 6 4 earthquake in nw peloponnese greece evidence from historical triangulation and morphotectonic data abstract the deformation of the meizoseismal area of the 2008 achaia elia mw 6 4 earthquake in nw peloponnese of the first significant strike slip earthquake in continental greece was examined in two time scales of 102 years based on the analysis of high accuracy historical triangulation data describing shear and of 105 106 years based on the analysis of the hydrographic network of the area for signs of streams offset by faulting our study revealed pre seismic accumulation of shear strain of the order of 0 2 rad year in the study area consistent with recent gps evidence but no signs of significant strike slip induced offsets in the hydrographic network these results confirm the hypothesis that the 2008 fault which did not reached the surface and was not associated with significant seismic ground deformation probably because of a surface flysch layer filtering high strain events was associated with an immature or a dormant recently activated fault this fault about 150 km long and discordant to the morphotectonic trends of the area seems first to contain segments which have progressively reactivated in a specific direction in the last 20 years reminiscent of the north anatolian fault and second to limit an 150 km wide recent shear zone in the internal part of the arc in a region mostly dominated by thrust faulting and strong destructive earthquakes

vertical accretion rates in fluvial systems a comparison of volumetric and depth based estimates a wide range of approaches has been adopted for collecting and reporting vertical accretion rates hence evaluation of results from different catchments or even from different reaches within the same basin is difficult as they may not be directly comparable the present study compares depth and volume based estimates of sediment accumulation for well dated vertical accretion sequences at broomhaugh island in the tyne basin northern england high resolution dating control based on heavy metal stratigraphy and cartography coupled with detailed reconstruction of channel geometry allows accumulation rates to be calculated for the last 300 400 years the results show a marked disparity in the magnitude and pattern of vertical accretion rates between the two approaches the average annual thickness of sediment increases progressively with a six fold difference between the seventeenth and twentieth centuries the volume figures are more consistent with a two fold difference between the highest and lowest rates both of which occurred in the twentieth century a major control on vertical accretion is found to be changing channel shape and capacity enlargement of the channel by 76 per cent since the seventeenth century associated with channel bed incision has resulted in fewer overbank flows hence floods with their associated suspended sediment loads which once inundated the floodplain are now confined within the channel the reduced areal extent of surfaces available for deposition has resulted in greater annual thickness of sediment accumulated despite an overall reduction in volume this study emphasizes that caution is needed when attempting to identify causal linkages between changes in sedimentation rates and catchment land use and or climatic factors and the geomorphological setting of the site must be taken into account copyright 2000 john wiley sons ltd

the characteristics of overbank deposits associated with a major flood event in the catchment of the river ouse yorkshire uk overbank floodplain deposits associated with a major flood which occurred in 1995 were collected shortly after the event from transects at 14 locations within the catchment of the river ouse yorkshire uk at most sites the sediment deposited nearest to the channel consisted primarily of sand sized material and the absolute particle size composition of the mineral fraction of the deposits evidenced fining with increasing distance from the channel most of the sand sized material was deposited within 20 to 40 m of the channel although at some sites sand was present at distances 100 m from the channels there was no obvious downstream trend in the texture of the sediment deposited on the floodplains in most places the overbank sediment was considerably coarser than the suspended sediment transported in the study rivers although at several sites thed50 of the latter was similar to that of overbank sediment deposited furthest from the channel although the c n ratio of the organic fraction of the overbank sediment was approximately constant across the width of the floodplain the organic carbon and137cs content of the deposited sediment increased with distance from the channel and both properties were positively related to the magnitude of the 63 m fraction the texture of sediment in cores collected from two of the sites in 1994 was generally finer than that of the overbank deposits from the 1995 flood at the same locations confirming the extreme nature of the 1995 flood event

joint isotopic mass balance a novel approach to quantifying channel bed to channel margins sediment transfer during storm events the important role of floodplains and the broader riparian zone in providing temporary storage for a large fraction of the annual sediment load of rivers is well established but this understanding is largely based on observations of the long term average behavior of the catchment here we combine measurements of the fallout radionuclides 7be and 210pb and the stable isotopes of hydrogen in water to quantify fine sediment mobilization and storage in a stream and its channel margins during individual intermediate sized storm events with recurrence intervals of a few months or less we demonstrate this method using five storm events in a small 15 km2 undeveloped gravel bedded tributary of the connecticut river usa we estimate that in each storm the mass of sediment deposited onto the margins accounts for almost 90 of the sediment mobilized from the bed with the remainder of the mobilized bed sediment transported downstream as suspended load the result that the bed is a net source of sediment to the stream and the margins a net sink is robust but estimates of the mass of material eroded from the bed and deposited on the margins are less certain the source of sediment to the bed remains unclear as consistent with earlier studies we observe only limited deposition of sediment to the bed during the storm events the suspended sediment is organic rich and thus its source may be associated with in channel organic decay between storm events understanding the coupled interactions between discharge magnitude and frequency and sediment resupply at the event time scale has important implications for stream restoration efforts seeking to connect the channel and the broader riparian zone and for the development of accurate sediment budgets and predictions of sediment flux from a watershed copyright 2015 john wiley sons ltd

in situ measurements of sediment settling characteristics in ﬂoodplains using a lisst st due to a lack of data on settling velocities ws and grain size distributions gsds in oodplain environments sedimentation models often use calibrated rather than measured parameters since the characteristics of suspended matter differ from those of deposited sediment it is impossible to derive the ws and gsd from the latter therefore one needs to measure in situ suspended sediment concentrations sscs settling velocities effective grain sizes and sedimentation uxes for this purpose we used the lisst st a laser particle sizer combined with a settling tube in 2002 twice and 2004 we located the lisst st with an optical backscatter sensor and sediment traps in two oodplains in the netherlands one along the unembanked ijssel river another along the embanked waal river measurements revealed that the ssc in the oodplains varied in relation to the ssc in the river channel smaller ocs dominated the ssc while larger ocs dominated the potential sedimentation uxes the in situ gsd in the ijssel oodplain was signi cantly coarser than in the waal oodplain while the dispersed median grain sizes were equal for both oodplains therefore the dispersed median grain size was two to ve times smaller than the effective one the in situ grain size exhibited a signi cant positive relationship with ws although the ws for the largest ocs showed high variability consequently the variability in sedimentation uxes was also large in the actual sedimentation uxes and hence in sedimentation models in situ grain sizes up to about 20 m can be neglected in oodplain sedimentation models the relation between settling velocity and in situ grain size can be used instead of stokes s law which is only valid for dispersed grain sizes these models should also use adequate data on ow conditions as input since these strongly in uence the suspended sediment characteristics copyright 2005 john wiley sons ltd

elevation change and stability on a prograding delta coastal wetland systems are among the most dynamic landscapes on earth s surface however interrelated processes create wetland platforms that are relatively constant in space and time theoretically stable elevations should maintain themselves through time if the balance of processes creating that elevation remains unchanged at louisiana s prograding wax lake delta we measure landscape change between 2009 and 2013 quantifying volumetric changes to the delta subaerial slope adjustment and an equilibrium elevation of 0 56 m north american vertical datum of 1988 where elevation change on average is zero around which elevations fluctuate we calculate a system average equilibrium time scale of 16 years to describe how long locations will take to approach the stable elevation this time scale increases as a function of distance from channel edge peaks in elevation probability density functions can form for multiple reasons and do not require stability e g peaks can temporarily form at elevations where elevation change rate is locally minimum

overbank sediment deposition patterns for straight and meandering flume channels experiments with the 10 m flood channel facility at hr wallingford uk indicate a fundamental dependency of the overbank deposition pattern of channel suspended sediments on channel planform two experiments 100 and 140 l s 1 in a 1 95 m wide straight channel showed deposition concentrated in a berm along the channel bank little sediment was transferred further onto the floodplain for the larger flow the berm formed further from the channel a single experiment 103 l s 1 with a 1 31 m wide meandering channel showed deposition across the entire floodplain tongue between successive meanders maximum deposition occurred on the downstream side of the meander just past the bend apex these generalized flume results complement the real world but site specific data of field studies copyright 2002 john wiley sons ltd

floodplain river ecosystems lateral connections and the implications of human interference abstract floodplains are ecotones that form a transition between aquatic and terrestrial environments these important ecosystems can be described as dynamic spatial mosaics in which water plays an important role in connecting various patches on the floodplain surface hydrological connections facilitate the exchange of carbon and nutrients between the river channel and the floodplain and therefore influence the productivity of the entire river system this paper examines the influence of hydrological connections on the potential exchange of dissolved organic carbon between a large australian floodplain to a river channel and the effects of land and water developments on these exchanges the paper proposes that an understanding of floodplain ecosystems requires an interdisciplinary approach a recognition of the importance of the three disciplines hydrology geomorphology and ecology large scale water resources and floodplain development has significantly altered the spatial and temporal patterns of hydrological characteristics in the lower balonne floodplain australia the magnitude frequency and duration of flooding events have all been reduced the construction of levees and water storages has also reduced the reactive floodplain surface area the presented data show the impacts of these changes on the potential supply of dissolved organic carbon from the floodplain surface during periods of inundation annual reductions of up to 1293 tonnes of dissolved organic carbon supply were noted and reductions were especially significant for floods with an average recurrence interval of 2 years or less some small flood events no longer facilitate the potential supply of dissolved organic carbon from the floodplain to the river channel because of water resources and floodplain developments

floodplain evolution in a small tectonically active basin of northern california sediment cores were collected along oodplains in the navarro river basin of coastal northern california to examine the controls on oodplain evolution in a tectonically active setting sedimentary strata were subsampled for organic content bulk density and grain size measurements organic samples were analysed for 14c age which yielded net averaged sedimentation rates for all cores overbank deposition rates decreased at all study sites through time and declined in the downstream direction the ability of intermediary order streams to store sediment in oodplains decreased the ability of highest order streams to record sediment pulse events the effects of anthropogenic disturbance primarily logging on long term overbank deposition rates were minimal climatic variability by affecting sediment loading in the channel network is the principal control on oodplain evolution through the holocene a hypothetical model is proposed to explain overbank deposition rates in the navarro basin which may be extrapolated to the northern coastal california region during the late pleistocene and holocene the complexities observed in sediment storage and routing in this study imply that caution should be made when extrapolating sediment yield measurements obtained at river mouths or coastal shelves to geomorphic events within small tectonically active basins

a preliminary investigation of the integration of modelled floodplain hydraulics with estimates of overbank floodplain sedimentation derived from pb 210 and cs 137 measurements this paper investigates the possibility of linking finite element modelled two dimensional hydraulics with floodplain sedimentation rates derived from radionuclide dating techniques the telemac 2d system is used to simulate the full dynamic velocity vector and water depth distributions for a 1 in 12 year flood event for the river culm devon these are compared to patterns of medium term 30 100 years sedimentation rates and a degree of correlation is found to exist this information is used to comment on the complexity of flow and sediment deposition interactions in floodplain environments and to provide a research design for the development of a more fully integrated floodplain morphodynamic model copyright 1999 john wiley sons ltd

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

characteristics of freshly deposited sand and finer sediments along an island braided gravel bed river the roles of water wind and trees over the past two decades there has been a growing interest in the geomorphological mosaic along large floodplain rivers where channel dynamics are seen to drive habitat patch creation and turnover and to contribute to high biological diversity this has required a new perspective on fluvial geomorphology that focuses on biological scales of space and time this study examines the spatial pattern of surface fine sediment accumulations along a reach of a large gravel bed river the tagliamento river in ne italy an area with a moist mediterranean climate and seasonal flow regime the study investigates changes in sediment characteristics during the summer low flow period between april and september focussing on five areas representing a gradient from open bar braided to wooded island braided morphologies the paper demonstrates the importance of riparian vegetation and aeolian fluvial interactions significant contrasts in particle size distributions and organic content of freshly deposited sand and finer sediments were found between sampling areas geomorphological settings and sampling dates in particular wooded floodplain and established islands supported consistently finer sediment deposits than both open bar surfaces and the lee of pioneer islands and in september significantly finer sediments were also found in deposits located in the lee of pioneer islands than on open bar surfaces overall the september samples had a greater variability in particle size characteristics than those obtained from the same sites in april with a general coarsening of the d5 i e the coarse tail of the particle size distribution also in september crusts of fine sediment 30 m d50 64 m had formed on the surface of some of the open bar and pioneer island deposits within the more open sampling areas along the study reach these crusts possessed similar particle size characteristics to aeolian crusts found in more arid environments they were significantly finer than april samples and september subcrust samples obtained from the same sites and had similar particle size characteristics to some samples taken from wooded floodplain established island surfaces and the lee of pioneer islands that were not crusted local climatological and river level data confirm significant wind and rainfall events during a period of consistently low river levels between the april and september sampling periods these support deflation deposition and rain wash of finer sediment during the summer with windblown sediments being deposited on bar surfaces and in the lee of pioneer islands where wood and young trees provide foci for accelerated sedimentation and island growth as well as on marginal floodplains and established islands we conclude that along braided rivers in moist settings but with a distinct dry season aeolian reworking of sediment deposits may have a more important role in driving habitat dynamics than previously considered

grain size trends used to assess the effective discharge for floodplain sedimentation river waal the netherlands abstract the importance of floods of different magnitude on floodplain sedimentation can be estimated from sedimentation measurements carried out during a series of floods however because these measurements represent sediment accumulation during the entire flood they cannot be used to estimate the importance of individual flood stages on sediment deposition in this study the importance of different flood stages on floodplain sedimentation was assessed from analysis of spatial variations in grain size distributions which are indicative of sediment transport directions as a secondary objective the applicability of grain size trend analysis to fine grained floodplain sediments was tested the grain size trend analyses were carried out in a geographical information system and applied to sediment deposited on an embanked floodplain section along the river waal in the netherlands during a large flood in december 1993 because flow patterns at the studied floodplain section vary with flood stage comparison of the identified sediment transport pathways with computed flow patterns indicates at which discharge most sediment is deposited the results indicate that large discharges with a recurrence time of more than two years are most effective in depositing suspended sediment on floodplain areas enclosed by a minor river dike on floodplain sections that directly border the main channel moderate discharges with a recurrence time of about one year seem to be more efficient contrary to the results of floodplain sedimentation models low but increasing discharges with a recurrence time of less than one year and during which only low lying areas near residual channels are inundated appear important for deposition of suspended sediment in these low lying areas this observation is confirmed by measurements of spatial concentration gradients and by floodplain sedimentation measurements comparison of the trends with additional information on sediment transport directions indicates that trends in which sediment becomes finer better sorted and more negatively skewed when measured in units are most suitable for defining transport pathways on river floodplains trends may however deviate up to 90 from true transport directions flocculation does not seem to have any negative effects on the applicability of grain size trend analysis

trace metals distribution pattern in floodplain sediments of a lowland river in relation to contemporary valley bottom morphodynamics the distribution of trace metals in alluvial sediments depends on their natural background concentrations and on the dynamics of contemporary depositional and erosional mainly flood induced processes geological and geochemical investigations were carried out in the valley of vistula river near magnuszew central poland sediment samples were collected from a depth of 35 cm and comprise sediments of all defined geomorphological features identification and geological interpretation of the morphodynamic sediment features was supported by aerial photographs and high resolution satellite images these studies revealed that the distribution of trace metals is closely linked to the morphogenesis of the alluvial floodplain the highest concentrations of cu co zn v cr and ni were observed in crevasse splays deposits by contrast sr pb and as were concentrated in deposits which fill oxbow lakes partly infilled with organic deposits the lowest concentrations of trace metals were detected in flood sediments deposited within erosional troughs the geomorphological and sedimentological history of the fluvial features explains the pattern of heavy metal distribution on the current floodplain surface copyright 2014 john wiley sons ltd

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

geomorphology and dynamics of the mfolozi river floodplain kwazulu natal south africa abstract the geomorphology and dynamics of the mfolozi river floodplain and estuary located in the subtropical region of northern kwazulu natal south africa were considered with respect to existing models of avulsion and alluvial stratigraphy the mfolozi river floodplain may be divided into regions based on longitudinal slope and dominant geomorphic processes confinement of the mfolozi river above the floodplain has led to the development of an alluvial fan at the floodplain head characterized by a relatively high sedimentation rate and avulsion frequency at a gradient of 0 10 the lower floodplain is controlled by sea level with an average gradient of 0 05 between the two lies an extremely flat region with an average gradient of 0 02 which may be controlled by faulting of the underlying bedrock avulsion occurrences on the mfolozi floodplain are linked to the two main zones of aggradation the alluvial fan at the floodplain head and toward the river mouth in the lower floodplain on the alluvial fan normal flow conditions result in scour from local steepening during infrequent large flood events the channel becomes overwhelmed with sediment and stream flow and avulses the resulting avulsion is regional and affects the location of the channel from the floodplain head to the river mouth deposits resulting from such avulsions contribute significantly to the total volume of sediment stored in the floodplain and tend to persist for long periods after the avulsion contrastingly on the lower floodplain reaching of the avulsion threshold is not necessarily linked to large flood events but rather to long term aggradation on the channel that decreases the existing channels gradient while increasing its elevation above the surrounding floodplain resultant avulsions tend to be local and do not contribute significantly to the overall volume of floodplain alluvium

overbank sand deposition in relation to transport volumes during large magnitude floods in the dutch sand bed rhine river system using aerial photographs and field measurements sandy overbank deposits formed by the large magnitude floods of 1993 94 and 1995 were quantified along two branches of the dutch rhine river system the waal 1993 94 and 1995 and the ijssel 1995 these deposits were laid down intermittently all along the length of these rivers on the top and landward slope of the natural levees and covered about 4 per cent of the embanked floodplain on the waal and about 1 per cent on the ijssel the overbanks and transport mechanism is basically convective by nature the spatial variability of overbank sedimentation points to the important role played by helicoidal currents in determining overbank deposition the presence of embankments and training works appears to influence the sand transport to and morphological development of the floodplains along the dutch rhine river system overbank deposition volumes about equal present estimates of sand transport during a large magnitude flood it appears that studies on sand transport in the dutch rhine carried out so far underestimate sand transport during floods 1998 john wiley sons ltd

floodplain complexity and surface metrics influences of scale and geomorphology abstract many studies of fluvial geomorphology and landscape ecology examine a single river or landscape thus lack generality making it difficult to develop a general understanding of the linkages between landscape patterns and larger scale driving variables we examined the spatial complexity of eight floodplain surfaces in widely different geographic settings and determined how patterns measured at different scales relate to different environmental drivers floodplain surface complexity is defined as having highly variable surface conditions that are also highly organised in space these two components of floodplain surface complexity were measured across multiple sampling scales from lidar derived dems the surface character and variability of each floodplain were measured using four surface metrics namely standard deviation skewness coefficient of variation and standard deviation of curvature from a series of moving window analyses ranging from 50 to 1000 m in radius the spatial organisation of each floodplain surface was measured using spatial correlograms of the four surface metrics surface character variability and spatial organisation differed among the eight floodplains and random fragmented highly patchy and simple gradient spatial patterns were exhibited depending upon the metric and window size differences in surface character and variability among the floodplains became statistically stronger with increasing sampling scale window size as did their associations with environmental variables sediment yield was consistently associated with differences in surface character and variability as were flow discharge and variability at smaller sampling scales floodplain width was associated with differences in the spatial organisation of surface conditions at smaller sampling scales while valley slope was weakly associated with differences in spatial organisation at larger scales a comparison of floodplain landscape patterns measured at different scales would improve our understanding of the role that different environmental variables play at different scales and in different geomorphic settings

sedimentation patterns across a coastal plain floodplain the importance of hydrogeomorphic influences and cross floodplain connectivity abstract the floodplains of large coastal plain rivers in the southeastern u s are important long term storage sites for alluvial sediment and nutrients yet considerable uncertainty surrounds sediment dynamics on many large river floodplains and in particular the local scale factors that affect the flux of sediment and nutrients from rivers onto their floodplains and their subsequent deposition this research quantifies short term rates of sediment deposition from 2012 to 2014 on floodplain sites at congaree national park using feldspar pads sediment deposition rates ranged from 0 1 to 15 6 cm median 1 46 cm and were closely associated with inundation frequency and geomorphic position cross floodplain distributary channels served as particularly important conduits for moving sediment onto the floodplain physical and chemical analyses of soil samples demonstrated that the most flood exposed sites had higher major nutrient and micronutrient levels especially of phosphorus and more diverse nutrient compositions this research advances current understandings of lateral floodplain connectivity by demonstrating the complex effects of regional hydrology and local floodplain environmental characteristics on the supply of sediment and nutrients

integrating geochronologic and instrumental approaches across the bengal basin constraining time is of critical importance to evaluating the rates and relative contributions of processes driving landscape change in sedimentary basins the geomorphic character of the field setting guides the application of geochronologic or instrumental tools to this problem because the viability of methods can be highly influenced by geomorphic attributes for example sediment yield and the linked potential for organic preservation may govern the usefulness of radiocarbon dating similarly the rate of sediment transport from source to sink may determine the maturity and or light exposure of mineral grains arriving in the delta and thus the feasibility of luminescence dating here we explore the viability and quirks of dating and instrumental methods that have been applied in the bengal basin and review the records that they have yielded this immense dynamic and spatially variable system hosts the world s most inhabited delta outlining a framework for successful chronologic applications is thus of value to managing water and sediment resources for humans here and in other populated deltas worldwide our review covers radiocarbon dating luminescence dating archaeological records and historical maps short lived radioisotopes horizon markers and rod surface elevation tables geodetic observations and surface instrumentation combined these tools can be used to reconstruct the history of the bengal basin from late pleistocene to present day the growing variety and scope of bengal basin geochronology and instrumentation opens doors for research integrating basin processes across spatial and temporal scales

sedimentation in the riparian zone of an incising river this paper focuses on one aspect of riparian zone change associated with channel incision it presents information on sedimentation within the riparian zone of the river garonne france derived from both historical and contemporary sources the riparian zone investigated is morphologically complex containing a remnant island and cut off channel information drawn from historical and contemporary sources permits the reconstruction of channel planform and cross profile change as well as an assessment of changes in riparian zone sedimentation rates and patterns very significant changes are identified over the last 50 years a change from a multiple thread to single thread channel planform high rates of riparian zone sedimentation of the order of 0 5 to 2 5 cm a 1 clear spatial patterns in over bank sedimentation reflecting topographic and vegetational variations and flood event magnitude and a reduction in morphological and vegetational diversity through the period which is expected to continue as the zone is transformed into an increasingly homogeneous sediment sink copyright 2001 john wiley sons ltd

salt affected soils on elevated landforms of an alluvial megafan northern pantanal brazil abstract salt affected soils play an important role in the pantanal wetlands ecosystem in brazil but their occurrence on higher landforms is not well understood in order to investigate the major processes involved in salt affected soil formation a trench was opened in a representative transition between the floodplain and a paleochannel paleolevee complex not currently reached by floodwater the trench was 6 meter long and 2 meter deep and 121 soil samples were collected in a 0 25 0 25 m regular grid and submitted for soil particle size ph exchangeable cations and solution extract major cation and anions analyses analytical results were subjected to geostatistical and principal components analyses pca for selected horizons an undisturbed sample was collected to perform thin sections and micromorphology description the presence of degraded carbonates in the soils indicated an ancient formation the regional environmental settings of the alluvial fan and particle size variation along the soil profiles suggested that the sediments of the study site were deposited during the late pleistocene and holocene in a river channel levee complex and an abandoned channel by avulsion processes the depressed topography of the abandoned channel accompanied by moderately drier climates during early holocene likely favored low leaching of salts and higher evapotranspiration enabling the development of salt affected soils later erosion of the region which is expected in older lobes of alluvial fans triggered a relief inversion in the area preserving the more clayey areas as a slightly higher landform with remaining salt affected soils currently the seasonal flooding mainly reaches the footslope of this landform triggering redoximorphic processes expressed as redox concentrations and depletions and solodization processes expressed by lower values of ph cation exchange capacity cec base saturation and exchangeable sodium percentage esp than at the summit thus the occurrence of salt affected soils on higher landforms is the reflection of a complex sedimentological history in this way the genesis of salt affected soils on higher landforms which seems to be poorly understood in many situations worldwide should be carefully investigated in order to address formation mechanisms especially in extremely dynamic environments of tropical wetlands

the interplay of sedimentation and carbon accretion in riparian forests abstract sediment trapping and organic carbon oc accretion in soil are crucial ecosystem services of floodplain forests however interactions between the two processes have scarcely been analyzed at the ecosystem level this study aimed at quantifying oc accretion parameters cap including sedimentation rate oc concentration oc accretion over roughly the last 50 years on both sides of a dike in a danubian floodplain forest in austria additionally we determined soil oc stocks 0 100 cm in depth and modeled both cap and oc stocks in relation to environmental parameters overall mean sedimentation rate and oc accretion of the riparian forest were 0 8 cm y 1 and 3 3 t oc ha 1 y 1 and significantly higher in flooded riparian forest frf 1 0 cm y 1 and 4 1 t oc ha 1 y 1 than in diked riparian forest drf 0 3 cm y 1 and 1 5 t oc ha 1 y 1 in contrast mean oc concentration 0 05 t oc m 3 and oc stocks 238 t oc ha 1 were significantly higher in the drf than in frf 0 05 vs 0 04 t oc m 3 and 286 vs 201 t oc ha 1 modeling revealed tree species fluctuation of groundwater table and the distance to the river as valuable indicators for oc accretion rate the oc concentration and distance to the river were positively and sedimentation negatively correlated with oc stock the dike was consistently ruled out as a significant predictor variable consequently differences among frf and drf seem to be related rather to longer term processes during the last centuries than directly to the dike our findings highlight the relevance of sediment quality i e oc concentration for building up long term soil oc stocks whereas sediment quantity is the main driver of recent oc accretion rates

floods floodplains delta plains a satellite imaging approach abstract thirty three lowland floodplains and their associated delta plains are characterized with data from three remote sensing systems amsr e srtm and modis these data provide new quantitative information to characterize late quaternary floodplain landscapes and their penchant for flooding over the last decade daily proxy records for discharge since 2002 and for each of the 33 river systems can be derived with novel advanced microwave scanning radiometer amsr e methods a descriptive framework based on analysis of shuttle radar topography mission srtm data is used to capture the major landscape scale floodplain elements or zones 1 container valleys with their long and narrow pathways of largely sediment transit and bypass 2 floodplain depressions that act as loci for frequent flooding and sediment storage 3 zones of nodal avulsions common to many continental scale rivers and often located seaward of container valleys and 4 coastal floodplains and delta plains that offer both sediment bypass and storage but under the influence of marine processes the srtm data allow mapping of smaller scale architectural elements in unprecedented systematic manner floodplain depressions were found to play a major role which may largely be overlooked in conceptual floodplain models lastly modis data independently and combined with amsr e allows the tracking of flood hydrographs and pathways and sedimentation patterns on a near daily timescale worldwide these remote sensing data show that 85 of the studied major river systems experienced extensive flooding in the last decade a new quantitative paradigm of floodplain processes honoring the frequency and extent of floods can be develop by careful analysis of these new remotely sensed data

hydraulic controls on the entrapment of heavy metal polluted sediments on a floodplain of variable width the upper vistula river southern poland distribution of heavy metal polluted overbank sediments deposited by a major flood in july 2001 in three gauging sections of different width on the vistula river southern poland was investigated and related to reconstructed pattern of flow velocity during the event the mean velocity of the flow over the floodplain was low and showed a marked contrast with mean velocity in the channel zone in the smolice and the sieroslawice cross sections 4 5 and 9 times wider than the respective channel widths high rates of lateral thinning and fining of overbank deposits were observed at sieroslawice the heavy metal concentrations first rapidly increased with distance from the channel and then remained high over most of the floodplain at smolice concentrations were relatively low within the levee deposits and high over the rest of the floodplain in both cross sections the loads of heavy metals were highest close to the channel margins and decreased exponentially with increasing distance from the channel due to the rapid lateral thinning of the flood deposits the mean velocity of the flow over the floodplain was high in the bielany cross section only 2 6 times wider than the channel width sediments deposited on the narrow floodplain were mostly sand slowly thinning laterally while the concentrations of various heavy metals increased gradually with increasing distance from the channel their loads varied across the floodplain the highest load of some metals occurred near the channel margin and that of others away from the channel this study indicates that floodplain width and the resultant flow hydraulics exert a significant influence on the lateral distribution of floodplain sediments and entrapped heavy metals in wider floodplain sections the largest amounts of heavy metals accumulate near the channel margin and may be remobilized in the future due to bank erosion

sedimentation of overbank floods in the confined complex channel floodplain system of the lower yellow river china the channel boundary conditions along the lower yellow river lyr have been altered significantly since the 1950s with the continual reinforcement and construction of both main and secondary dykes and river training works to evaluate how the confined complex channel floodplain system of the lyr responds to floods this study presents a detailed investigation of the relationship between the tempo spatial distribution of sedimentation erosion and overbank floods occurred in the lyr for large overbank floods we found that when the sediment transport coefficient ratio of sediment concentration of flow to flow discharge is less than 0 034 the bankfull channel is subject to significant erosion while the main and secondary floodplains both accumulate sediment the amount of sediment deposited on the main and secondary floodplains is closely related to the ratio of peak discharge to bankfull discharge volume of water flowing over the floodplains and sediment concentration of overbank flow while the degree of erosion in the bankfull channel is related to the amount of sediment deposited on the main and secondary floodplains water volume and sediment load in flood season the significant increase in erosion in the bankfull channel is due to the construction of the main and secondary dykes and river training works which are largely in a wide and narrow alternated pattern along the lyr such that the water flowing over wider floodplains returns to the channel downstream after it drops sediment for small overbank floods the bankfull channel is subject to erosion when the sediment transport coefficient is less than 0 028 while the amount of sediment deposited on the secondary floodplain is associated closely with the sediment concentration of flow over the entire length of the lyr the situation of erosion in the bankfull channel and sediment deposition on the main and secondary floodplains occurred mainly in the upper reach of the lyr in which a channel wandering in planform has been well developed

textural analysis and modelling of a flood deposit river severn u k samples of sediment collected from the severn floodplain between worcester and gloucester following the severe flooding in january and february 1990 were analysed for their grain size distribution the results show that most sand was deposited within 20 m of the channel bank but that fine sand may contribute to flood sediment across the width of the floodplain james 1985 numerical model of overbank sedimentation attempts to predict the transfer of sediment to the floodplain during flooding geometrical and hydraulic data relating to the severn flood are used as input for a computer program of james 1985 model the pattern of sediment concentrations predicted by the model was compared with that obtained from statistical analysis of the flood sediment the patterns were found to be similar so james 1985 model was considered to predict in a relative sense the distribution of flood sediment

floodplain sedimentation and sensitivity summer 1993 flood upper mississippi river valley patterns of overbank sedimentation in the vicinity of and far removed from levee breaks that occurred in response to the 100 year summer 1993 flood in the upper mississippi river valley are elucidated two suites of overbank deposits were associated with the failure of artificial levees within a 70 km long study reach circumjacent sand deposits are a component of the levee break complex that develops in the immediate vicinity of a break site as epitomized by the levee break complex at sny island these features consist of an erosional scoured and or stripped zone together with a horseshoe shaped depositional zone at locales farther removed from the break site the impact of flooding was exclusively depositional and was attributed to the settling of suspended sediment from the water column the overall picture was one of modest scour at break sites and minimal suspended deposition 4 mm at locales farther removed from the breach downriver from the confluence with the missouri river suspended sediment deposition was of a similar magnitude to that observed within the study reach and levee break complexes exhibited a similar morphology but scour at break sites was greatly enhanced and the excavated sand formed extensive deposits on the floodplain surface the different erosional response was probably engendered by the higher sand content and reduced aggregate cohesion of the floodplain soils downriver from the confluence with the missouri river a qualitative comparison serves to highlight the influence that the resistance threshold may have on the sensitivity of floodplains bordering large low gradient rivers to high magnitude floods 1997 john wiley sons ltd

human induced sedimentation patterns of a channelized lowland river channelization of the severely polluted odra and vistula rivers in poland induced intensive accumulation of fine grained deposits rich in organic matter and heavy metals these sediments have been identified in vertical profiles in a narrow zone along river banks both in groyne created basins and on the floodplain grain size organic matter zinc zn lead pb copper cu content and cesium 137 137cs was used for sediment dating and stratigraphy and chemistry have been diagnostic features for these deposits named industrial alluvium in the most polluted river reaches stabilized by bank reinforcements and groynes 2 m thick slack water groyne deposits are composed of uniform strata of polluted silts with organic matter content over 10 zn content over 1000 mg kg and average cu and pb over 100 mg kg the average rate of sediment accretion in groynes is higher than on the floodplain and reaches 5 cm yr stratification which appears at higher levels in the groyne fields and on the levees reflects a change from in channel to overbank deposition and is typified by dark layers separated by bright sandy and less polluted strata stratified 4 m thick sediment sequences have been found in groyne fields of incised river reaches the average rate of sediment accretion in these reaches is of the order of 5 cm yr in stable and relatively less polluted river reaches vertical accretion organic deposits are finely laminated and the average rate of deposition amounts to a few millimeters per year investigations indicate that groyne construction favors conditions for long term storage of sediments at channel banks for this reason groynes should be considered as structures that efficiently limit sudden release of sediment associated heavy metals stored in channels and in floodplains of the historically polluted rivers copyright 2014 john wiley sons ltd

increase in mercury contamination recorded in lacustrine sediments following deforestation in the central amazon1the present investigation is part of an ongoing study the caruso project crdi ufpa uqam initiated to determine the sources fate and health effects of the presence of mehg in the area of the lower tapajos 1 the geochemical study of surface sediments vertical profiles of 30 80 cm from lentic ecosystems of the tapajos river permit the observation of environmental changes responsible for the mercury contamination of aquatic systems exploited by the human riverine population the arapiuns and amazon rivers are compared measurements of mercury textural indicators water content and dry density mineralogic indicators iron and aluminum associated with oxyhydroxides and aluminosilicates and organic indicators carbon nitrogen atomic c rn ratio were performed over the full length of the cores the results demonstrate that soil erosion is responsible for an increase in surficial sediment mercury concentrations in the different aquatic systems of the tapajos and arapiuns rivers this increase is the result of the relative enrichment of the sedimentary deposits in fine particulates rich in aluminosilicates oxyhydroxides and mercury transported in suspension in the water column the oxyhydroxides of iron and aluminum associated with fine clayey particles seem to control the accumulation of heavy metals in the sediments of the tapajos arapiuns and amazon rivers overall the mercury levels in the sediments studied have the same relationship with the aluminosilicates and the texture of the sediments the quantity of aluminosilicates permits the evaluation of diagenetic effects the influence of the clay content and the matrix effect on the levels of mercury in sediments the activity of lead 210 measured in two cores suggests that the superficial sediments originate from eroded soils a preliminary dating using the constant initial concentration model indicates that the environmental changes recorded in the tapajos river sediments would have been initiated some time between the 1950s and 1970s they would then coincide with the important colonization of the brazilian amazon during this period the results presented have important implications for the geochemical interpretation of anthropogenic disturbances in the amazon they demonstrate that the recent colonization of the drainage basins and the growing exploitation of new parcels of land in the

floodplain sedimentation quantities patterns and processes this paper presents the result of measurements of floodplain sedimentation using sediment traps the study was carried out on two embanked floodplains along the rivers rhine and meuse in the netherlands during a 3 day flood in january 1993 raster maps of sediment accumulation were made by interpolating the measurements from the traps using block kriging the sediment maps show clear patterns in sediment accumulation together with the estimated interpolation errors average sediment accumulation ranges between 0 57 and 1 0 kg m 2 high sediment accumulation is found on the levees 4 kg m 2 or more and on low lying areas 1 6 kg m 2 sediment accumulation decreases with distance from the main channel the sedimentation patterns are related to floodplain topography and sediment transporting mechanisms sediment transport by turbulent diffusion as well as by convection can be recognized also flood duration and the process of sediment settling out in ponding water in closed depressions are important the applied method allows comparison of the results with raster based sedimentation models

organic matter processing and soil evolution in a braided river system traditionally braided river research has considered flow sediment transport processes and recently vegetation dynamics in relation to river morphodynamics however if considering the development of woody vegetated patches over a time scale of decades we must consider the extent to which soil forming processes particularly related to soil organic matter impact the alluvial geomorphic vegetation system here we quantify the soil organic matter processing humification that occurs on young alluvial landforms we sampled different geomorphic units ranging from the active river channel to established river terraces in a wandering braided river system for each geomorphic unit soil pits were used to sample sediment soil layers that were analysed in terms of grain size 2 mm and organic matter quantity and quality rock eval method a principal components analysis was used to identify patterns in the dataset results suggest that during the succession from bare river gravels to a terrace soil there is a transition from small amounts of external organic matter supply provided by sedimentation processes e g organic matter transported in suspension and deposited on bars to large amounts of autogenic in situ organic matter production due to plant colonisation this appears to change the time scale and pathways of alluvial succession bio geomorphic succession however this process is complicated by the ongoing possibility of local sedimentation which can serve to isolate surface layers via aggradation from the exogenic supply and erosion which tends to create fresh deposits upon which organic matter processing must re start the result is a complex pattern of organic matter states as well as a general lack of any clear chronosequence within the active river corridor this state reflects the continual battle between deposition events that can isolate organic matter from the surface erosion events that can destroy accumulating organic matter and the early ecosystem processes necessary to assist the co evolution of soil and vegetation a key question emerges over the extent to which the fresh organic matter deposited in the active zone is capable of significantly transforming the local geochemical environment sufficiently to accelerate soil development

storms channel changes and a sediment budget for an urban suburban stream difficult run virginia usa abstract determining erosion and deposition rates in urban suburban settings and how these processes are affected by large storms is important to understanding geomorphic processes in these landscapes sediment yields in the suburban and urban upper difficult run are among the highest ever recorded in the chesapeake bay watershed ranging from 161 to 376 mg km2 y erosion and deposition of streambanks channel bed and bars and deposition of floodplains were monitored between 1 march 2010 and 18 january 2013 in upper difficult run virginia usa we documented the effects of two large storms tropical storm lee september 2011 a 100 year event and super storm sandy october 2012 a 5 year event on channel erosion and deposition variability in erosion and deposition rates for all geomorphic features temporally and spatially are important conclusions of this study tropical storm lee was an erosive event where erosion occurred on 82 of all streambanks and where 88 of streambanks that were aggrading before tropical storm lee became erosional statistical analysis indicated that drainage area explains linear changes cm y in eroding streambanks and that channel top width explains cross sectional area changes cm2 y in eroding streambanks and floodplain deposition mm y a quasi sediment budget constructed for the study period using the streambanks channel bed channel bars and floodplain measurements underestimated the measured suspended sediment load by 61 2130 mg y underestimation of the sediment load may be caused by measurement errors and to contributions from upland sediment sources which were not measured but estimated at 36 of the gross input of sediment eroding streambanks contributed 42 of the gross input of sediment and accounted for 70 of the measured suspended sediment load similar to other urban watersheds the large percentage of impervious area in difficult run and direct runoff of precipitation leads to increased streamflow and streambank erosion this study emphasizes the importance of streambanks in urban suburban sediment budgets but also suggests that other sediment sources such as upland sources which were not measured in this study can be an important source of sediment

soil formation and its implications for stabilization of soil organic matter in the riparian zone abstract riparian woodlands consist of different landscape units characterized by different hydroecomorphological site conditions that are reflected in the distribution of soils and tree species these conditions are determined by flooding frequency and duration distance to river channels elevation and water flow velocity the influence of these environmental drivers on the stabilization of soil organic matter som has as yet not been investigated hence the aim of our study is to link soil formation and its drivers with stabilizing processes of som in riparian floodplain forests we investigated soils and sediments at two sites in the ash maple elm oak alluvial forest zone ameo sites and two sites in the willow poplar alluvial forest zone wip sites within the riparian zone of the danube near vienna austria sediments and soils were characterized based on texture contents of organic carbon oc nitrogen fe oxides and soil ph density fractionation was used to separate oc fractions in terms of stabilization process and resulting organic matter om turnover time the free light fraction fast turnover the light fraction occluded in aggregates intermediate turnover and the heavy fraction of om associated tightly to mineral surfaces slow turnover at both sites soil and sediment properties reflect the hydroecomorphological site conditions for formation of the landscape units in the riparian zone soils at ameo sites develop during constant deposition of fine textured sediment while water flow velocity is low progressing soil development causes a continuous decrease in oc content with increasing soil depth mainly from fractions with fast and intermediate turnover as a consequence the heavy fraction clearly dominates with around 90 of oc temporally variable flooding conditions with occurring turbulences found at wip sites result in a discontinuous change of soil properties with increasing soil depth former topsoil horizons buried by huge amounts of sediments seem to keep the oc fractionation typical for topsoil horizons with extraordinarily high amounts of light fraction om free and occluded representing 20 40 of total oc the presented results confirm that sedimentation and soil formation are simultaneous processes at ameo sites at wip sites both processes seem uncoupled with alternate phases of sedimentation and soil formation thus the frequent burial of topsoil material formed at wip sites seems to enable the conservation of unstable organic matter fractions at this part of active floodplains

use of fallout 137cs in investigations of overbank sediment deposition on river floodplains abstract river floodplains have been recognised as important sinks for storing suspended sediment and associated contaminants mobilised from the upstream catchment however information on contemporary rates of overbank sedimentation is difficult to obtain using conventional methods measurements of the 137cs content of floodplain sediments provide an alternative approach to obtaining estimates of medium term rates ca 40 years of overbank sediment deposition the 137cs approach requires only a single site visit and minimum sample preparation furthermore it is capable of providing information on spatial patterns of sediment deposition on floodplains which is needed to improve our understanding of the processes involved in overbank flow and sediment deposition this paper reviews the basis for using 137cs measurements in floodplain sedimentation studies and presents improved procedures for interpreting 137cs profiles in floodplain sediments and for obtaining estimates of sedimentation rates from single measurements of the total 137cs inventories of bulk sediment cores the results obtained from a case study undertaken on the floodplain of the river stour dorset uk are presented

floodplain sediment disconnectivity at a tributary junction and valley constriction site in the fitzroy river basin queensland australia abstract many catchment scale sediment models assume connectivity from the top to the bottom of the catchment the purpose of this study is to provide evidence that particular topographic features can affect catchment connectivity and the transfer of sediment through the catchment this study investigates floodplain sediment deposition in a valley bottom constriction and tributary junction site within the fitzroy river basin a large semiarid subtropical catchment in ne australia these sites can cause backwater effects during flooding that enhance sediment deposition isotope analysis of floodplain sediment cores for cesium 137 and plutonium 239 240 is used to determine deposition rates since the 1960s results show overall higher deposition rates across the lower tributary floodplain proximal to the confluence and within the valley constriction reach deposition rates in the upper constriction reach were less than in the constriction reach but similar to rates reported by other studies in the fitzroy river basin however evidence suggests that the region of influence of the valley constriction on sediment deposition is dependent on flood size with large floods depositing sediment further upstream than the sampling sites of this study nevertheless the study shows evidence that backwater inducing features such as confluences of disparate channels can promote sediment deposition and cause a disconnection in the transfer of sediment from tributary to main channel the effect of these processes on storing sediment needs to be considered in catchment scale sediment budget models

coarse grained floodplain deposits in the seasonal tropics towards a better facies model abstract floodplain deposits in semiarid and subhumid settings with erratic rainfall may contain relatively high proportions of sand because of climatically controlled patterns of discharge and vegetation cover ancient formations with abundant floodplain sands may record fluvial systems with extreme discharge variability of this type but are difficult to interpret because of the paucity of published modern analogues the lower burdekin and haughton river alluvial and delta plains of north queensland australia are used here to illustrate this type of fluvial architecture the modern burdekin and haughton channels have gravelly sand beds and transport a mixed load in the wet season the channels have low relief levees that decrease in amplitude downstream across the low gradient floodplains tropical cyclone activity results in high magnitude short duration sediment charged floods that inundate large areas of the coastal lowland bankfull discharge is infrequently exceeded return interval 25 years because the channels are enlarged by major cyclone induced runoff events and between these events flows are too small to modify the channel form significantly suspended sediment loads and the proportions of these that are sand are particularly high when intense rainfall occurs after prolonged drought when vegetation cover is reduced as a consequence of these factors most of the deposition on the levees and floodbasins occurs in very large discharge events with significant suspended sand load these floods carry a lot of sand out of the channel and efficiently in suspension over the floodplains because of deep inundation boreholes drilled in these floodplains encountered sharply bounded and gradationally bounded sand beds that fine upward or show no vertical grain size trend these are interbedded with thin silt clay and minor gravel beds holocene paleochannels make up about 30 of the floodplain area and consist predominantly of coarse sand that is similar to modern channel bed deposits the overbank sand in contrast is predominantly fine medium grained and beds have distinctly different granulometry from each other and from channel floor deposits efficient sediment partitioning in the runoff and extreme variation in flood magnitude explain variations in sand bed granulometry in the alluvial valley and upper delta plain individual sand beds are difficult to correlate between adjacent boreholes even over very short distances tens of meters in contrast on the lower delta plain overbank sands have a more sheet like geometry this is explained by the lower lying landscape negligible levee development greater inundation depths and reduced surface roughness in addition the channel bodies are thinner and wider and may be connected to overbank sand wings

impact of natural reforestation on floodplain sedimentation in the dragonja basin sw slovenia changes in floodplain sediment dynamics have profound effects on riverine habitats and riparian biodiversity depopulation due to socio economic changes in the dragonja catchment 91 km2 in southwestern slovenia resulted in the abandonment of agricultural fields followed by natural reforestation since 1945 this profoundly changed the water and sediment supply to the streams as well as floodplain sediment deposition this paper presents a reconstruction of the development of the dragonja floodplain due to these land use changes during the last 60 years the reconstruction is based on dating of floodplain sediments using 137cs profiles measurement of actual sedimentation rates using artificial grass sedimentation mats and linking this information to the present day hydrological behaviour of the river the sedimentation mats showed that floodplain sedimentation was restricted to peak flows of considerable magnitude due to the reforestation the return period of such high flows increased from 0 31 year in the period 1960 1985 to 0 81 year between 1986 and 2003 with commensurate changes in sedimentation rates at the 1 5 m river terrace formed about 60 years ago 137cs based sedimentation rates 1960 1986 were roughly twice the rates inferred from the artificial grass mats 2001 2003 this finding matches the increase in the return period for larger peak events during the 1986 2003 period which caused fewer major inundations at this level conversely sedimentation rates determined for the lowest terrace at 0 5 m were similar for both techniques and periods because the return periods of the peak events responsible for sediment deposition at this lower level did not change much over the period 1986 2003

measuring sediment deposition and accretion on anthropogenic marshland part ii the adaptation capacity of the north frisian halligen to sea level rise abstract low coastlands marshlands and islands all over the world are challenged by rising water levels due to climatic changes the adaptation capacity of such lowlands is based on frequent inundations and according sedimentation processes exemplarily a system of small islands west of northern germany was investigated over three years at three out of ten so called halligen located in the wadden sea the adaptation capacity of the anthropogenic marshland was determined the halligen hooge langeness and nordstrandischmoor have surface elevations only a few decimetres above mean high water and have to cope with an inundation frequency of nowadays up to 22 times per year by use of methods introduced in schindler et al 2014 this volume in combination with a 137 cs and 210 pb dating campaign on 12 sediment cores vertical accretion rates were measured and detailed sediment accretion patterns presented a good agreement was found between the used methods to calculate long term and short term marshland accretion rates sediment deposition and vertical marshland accretion is mainly controlled by the high tide events single storm surges coastal protection structures established in the early 20th century decrease the inundation frequency and hinder the efficiency of the sediment transport by the tidal channel system on the halligen vertical marshland accretion based on 210 pb dating for the time span 1915 2011 1 0 0 3 mm a hooge 1 2 0 3 mm a langeness and 2 6 0 9 mm a nordstrandischmoor is in disequilibrium with the fast increasing mean high water level mhw 5 0 0 3 mm a projections until 2100 revealed that the extreme values highest high waters hhw tend to rise much faster than the mhw or relative mean sea level rmsl therefore an increasing hazard potential for the halligen has to be expected if vertical marshland accretion does not accelerate in the future

inquiry of levee formation by grain size analysis a case study from the warta river central poland abstract levees were the most easily recognised depositional forms developed after two subsequent floods that occurred in summer 2010 and winter 2010 2011 in the warta river valley central poland the levees are built of mainly by fine grained well sorted massive or climbing ripple laminated sands the forms were sampled in 3 pits 0 75 1 1 m deep samples were collected every 5 cm in vertical profiles the main aim of the study was to investigate changes in the grain size of the sands deposited during one flood episode analyses indicated slight differences in the grain size of the deposits with a mean ranging from 1 9 to 2 5 phi however a detailed grain size analysis of sand samples showed that a single flood event was represented by a coarsening upward sequence it is generally assumed that such a trend indicates an increasing energy of the transporting medium therefore the deposits recorded the rising flood stage in scatter plots of mean vs skewness and mean vs kurtosis the examined deposits show a v shaped point arrangement it may indicate the mixing of grain subpopulations differences in flow energy observed mainly within the channel banks resulted in mixing sediment transported in saltation with sediment transported in graded suspension the paper proposes a model sequence for levee deposition during flood event it is directly related to the flood progress 1 beginning of the flood fine grained sand 2 rapid rise of water level up to the inflection point inverse grading deposits and 3 slow rise and stabilisation of the water level up to the culmination point fining upward deposits the subsequent phase of falling water level does not involve deposition therefore a single flood particularly the rising phase is represented by a pensymmetric sequence however the uppermost part of the sequence is sometimes lacking in the fossil record which results in an upward coarsening sequence

spatial hydrogeomorphological influences on sediment and nutrient deposition in riparian zones observations from the garonne river france abstract this paper investigates the influence of geomorphological setting on riparian zone sedimentation within a reach of the river garonne france during three major floods the sampling design was stratified to reflect landforms constructed by fluvial processes e g floodplain lateral benches islands side channels and point bars observed sedimentation varied significantly with flood event planform context landform type and associated vegetation cover and in some cases with sample location within the landform lowest sedimentation was associated with the flood with the smallest peak discharge peak sediment concentration and sediment load sites under natural riparian vegetation experienced higher sedimentation than poplar plantations sites on concave outer banks received less sedimentation than those on convex inner banks sedimentation on floodplain sites and higher benches was lower than on low benches point bars and side channels there was considerable interdependence among these patterns reflecting the underlying geomorphological forms and processes meandering rivers tend to evolve through erosion of concave banks and deposition on convex banks point bar features tend to be built along convex banks whilst concave banks are eroded into higher floodplain and bench features as a result concave banks tend to be bordered by higher riparian margins that are less frequently flooded than convex banks where river margins are developed for agriculture the higher less frequently flooded sites are preferentially selected analyses of the quantity calibre nutrient and carbon content of the deposited sediment reveal further significant relationships which reflect the geomorphological structure of the riparian zone sediment particle size coarsens in locations with higher amounts of sedimentation the quantities of total organic carbon toc total organic nitrogen ton and total phosphorus tp all increase as the quantity of deposited sediment increases the concentration of toc and ton also increased significantly with an increase in the percentage of silt plus clay in the deposited sediments based upon the above observations a conceptual model is proposed which considers the spatial pattern in riparian zone sedimentation according to riparian morphology and flood magnitude the implications of channel incision for the functioning of the model are also discussed

geodynamic regimes of intra oceanic subduction implications for arc extension vs shortening processes abstract 40 of the subduction margins of the earth are intra oceanic they show significant variability in terms of extension and shortening we investigated numerically the physical controls of these processes using a 2d petrological thermo mechanical intra oceanic subduction model with spontaneous volcanic arc growth and deformation we varied the fluid and melt related weakening the ages of both the subduction slab and the overriding plate the subducting plate velocities and the cohesive strength of rocks three main geodynamic regimes were identified retreating subduction with opening of a backarc basin stable subduction and advancing compressive subduction the main difference between these regimes is the degree of rheological coupling between plates which is governed by the intensity of rheological weakening induced by fluids and melts retreating subduction regimes require plate decoupling which results from strong weakening due to both fluids and melts spreading centers nucleate either in forearc or in intraarc regions episodic trench migration is often due to variations of plate coupling with time which is caused by fore arc deformation stable subduction regime with little variation in the trench position forms at an intermediate plate coupling and shows a transient behavior from the retreating to advancing modes the advancing subduction regime results from strong plate coupling at the mature stage this subduction mode is associated with both partial fragmentation and subduction of the previously serpentinized forearc region forearc subduction is typically associated with a magmatic pulse which is caused by dehydration of subducted serpentinized forearc fragments our models demonstrate distinct differences in thermal and lithological structure of subduction zones formed in these different geodynamic regimes results compare well with variations observed in natural intra oceanic arcs

sedimentary facies and geomorphic evolution of a blocked valley lake lake futululu northern kwazulu natal south africa blocked valley lakes are formed when tributaries are impounded by the relatively rapid aggradation of a large river and its floodplain these features are common in the landscape and have been identified in the floodplains of the solimoes amazon brazil and fly strickland rivers papua new guinea for example but their inaccessibility has resulted in studies being limited to remotely sensed image analysis this paper documents the sedimentology and geomorphic evolution of a blocked valley lake lake futululu on the mfolozi river floodplain margin in south africa while also offering a context for the formation of lakes and wetlands at tributary junctions the study combines aerial photography elevation data from orthophotographs and field survey and longitudinal sedimentology determined from a series of cores which were sub sampled for organic content and particle size analysis radiocarbon dating was used to gauge the rate and timing of peat accumulation results indicate that following the last glacial maximum rising sea levels caused aggradation of the mfolozi river floodplain by 3980 years bp aggradation on the floodplain had impounded the futululu drainage line creating conditions suitable for peat formation which has since occurred at a constant average rate of 0 13 cm year 1 continued aggradation on the mfolozi river floodplain has raised the base level of the futululu drainage line resulting in a series of back stepping sedimentary facies with fluvially derived sand and silt episodically prograding over lacustrine peat deposits blocked valley lakes form where the trunk river has a much larger sediment load and catchment than the tributary stream similarly when the relative difference in sediment loads is less palustrine wetlands rather than lakes may be the result in contrast where tributaries drain a steep well connected catchment they may impound much larger trunk rivers creating lakes or wetlands upstream

the impact of land use and climate change on late holocene and future suspended sediment yield of the meuse catchment abstract in this study we investigate the relative importance of changes in land use and climate on suspended sediment yield sy on millennial timescales in the meuse basin we use a spatially distributed soil erosion and sediment delivery model watem sedem to simulate sy in three time periods 4000 3000 bp minimal anthropogenic influence 1000 2000 ad includes land use and climate change and the 21st century changes in climate are based on climate model output ecbilt clio vecode for the 21st century the model is forced according to two emission scenarios of the intergovernmental panel on climate change ipcc namely the sres scenarios a2 and b1 these scenarios lie towards the higher and lower end of the full ipcc scenario range respectively for 4000 3000 bp the basin is assumed to be almost fully forested for 1000 2000 ad land use is reconstructed using corine data historical sources and land use modelling and for the 21st century land use is based on the european land use change project eururalis whilst rainfall erosivity increases by only 3 between 4000 3000 bp and 1000 2000 ad sy increases from ca 92 000 mg a 1 to ca 306 000 mg a 1 this model prediction is in agreement with the limited regional multi proxy data available our simulations show that almost all of this increase is due to the conversion of forest to agricultural land over the period 1000 1900 ad sy shows a significant increasing trend with a peak of ca 388 000 mg a 1 in the 19th century due to continuing deforestation in the 20th century reforestation and rapid urbanisation result in a decrease to ca 281 000 mg a 1 sensitivity analyses show that although land use change acts as the primary control on long term changes in sy the sensitivity of sy to changes in climate increases as the percentage of deforested land increases for the 21st century the results are highly sensitive to the scenarios used due to relatively large increases in rainfall erosivity sy increases by 12 compared to the 20th century according to scenario a2 or by 8 according to b1 however the associated land use change scenarios cause decreases in sy by 26 a2 and 46 b1 the net effect is thus a decrease of sy this study highlights the potentially significant efficacy of land use planning as a tool to mitigate the negative effects of soil erosion and sediment delivery to rivers

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

cumulative effects of channel correction and regulation on floodplain terrestrialisation patterns and connectivity abstract one of the main drivers of overbank fine deposition and floodplain formation is the hydrological connectivity between the channel and the floodplain channel correction i e groyne field construction within the main flow channel and secondary channel disconnections and flow regulation can typically lead to a disconnection of riverine floodplains and disturbances that directly affect terrestrialisation channel correction and flow regulation can sometimes occur successively and it is challenging to distinguish the roles of each this work attempts to assess the respective effects of two phases of channel regulation correction versus flow regulation on floodplain terrestrialisation by comparing three bypassed reaches of the rhone france pierre benite peage de roussillon and donzere mondragon we applied a transversal methodology coupled with gis analysis old maps orthophotos dem s etc to understand processes of channel planform evolution conducted a sediment survey metal rod to assess floodplain terrestrialisation and performed sediment sampling manual auger to obtain surface sediment metal content levels x ray fluorescence and inductively coupled plasma mass spectrometry we found a general trend of channel narrowing within the three reaches among which approximately 40 was found to be associated with correction works while 20 was attributed to flow lowering caused by channel bypassing the number of flowing channels in all sections declined significantly and local anabranching reaches evolved into very stable single thread channels overbank sedimentation declined significantly over the period with very high sedimentation levels observed immediately after correction works and with very low sedimentation levels observed after diversion we also found overbank flooding in the number of days per year decreased while fine sediment thickness increased similarly the highest concentrations of metals zc pb and cu were found to be associated with a low connection frequency and vice versa when similar 2 staged terrestrialisation patterns are observed in all three reaches they differ in chronology and driving factors because of their longitudinal positioning and specific local conditions

spatial and temporal variations in the grain size characteristics of historical flood plain deposits blue river wisconsin usa this study examined vertical lateral and downstream variations in the grain size characteristics of historical post 1830 overbank deposits in a watershed that has experienced high rates of accelerated flood plain sedimentation more than 800 samples were collected from 53 cores along nine flood plain transects overbank deposits exhibit a coarsening upward sequence attributed to historical changes in the sand content of source materials the erosion of loess capped soils increased the exposure erosion and transport of sandy parent materials the average sand content of near channel cores increases moderately downstream along two of the reaches because sandy source materials are increasingly exposed in larger main valleys in the northern part of the watershed the two northernmost reaches are coarser overall but do not display significant downstream trends the sand content of surface and early historical overbank deposits generally decreases laterally as an exponential function of distance from the channel suggesting transport by turbulent diffusion the presence of sand throughout the transects and lateral coarsening at two of the transects however suggests that sediment transport by convection is also important

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

floodplain development in an engineered setting engineered flood bypasses or simplified conveyance floodplains are natural laboratories in which to observe floodplain development and therefore present an opportunity to assess delivery to and sedimentation within a specific class of floodplain the effects of floods in the sacramento river basin were investigated by analyzing hydrograph characteristics estimating event based sediment discharges and reach erosion deposition through its bypass system and observing sedimentation patterns with field data sediment routing for a large iconic flood suggests high rates of sedimentation in major bypasses which is corroborated by data for one bypass area from sedimentation pads floodplain cores and sediment removal reporting from a government agency these indicate a consistent spatial pattern of high sediment accumulation both upstream and downstream of lateral flow diversions and negligible sedimentation in a hydraulic shadow directly downstream of a diversion weir the pads located downstream of the shadow recorded several centimeters of deposition during a moderate flood in 2006 increasing downstream to a peak of 10 cm thick and thinning rapidly thereafter flood deposits in the sediment cores agree with this spatial pattern containing discrete sedimentation layers from preceding floods that increase in thickness with distance downstream of the bypass entrance to several decimeters thick at the peak and then thin downstream these patterns suggest that a quasi natural physical process of levee construction by advective overbank transport and deposition of sediment is operating the results improve understanding of the evolution of bypass flood control structures the transport and deposition of sediment within these environments and the evolution of one class of natural levee systems copyright 2008 john wiley sons ltd

storage of sediment associated heavy metals along the channelized odra river poland the importance of long term storage of heavy metals in groyne fields functioning over 150 years is investigated for the river odra oder western poland construction of groynes along the odra preceded rapid development of heavy industrialization in the largest coal mine districts in poland and the czech republic that resulted in persistent riverine pollution the 187 km long middle odra reach was repeatedly channelized from the first half of the eighteenth century to the turn of the twentieth century during which time partially filled groyne fields were dissected by new bank lines and groyne systems with older groyne fields partially keyed into the floodplain consequently concentrations of zinc lead cadmium and copper within historically deposited groyne field sediments exceed local geochemical background levels by more than 60 40 15 and 10 times respectively sediments contaminated with heavy metals occur within three distinctive geomorphic zones zone i is up to 250 m wide and furthest from the present channel comprising decimeter thick polluted sediments overlying eighteenth century sand and gravel bars zone ii represents the former nineteenth century groyne fields with widths between 10 and 100 m filled with as much as 3 m of polluted sediments zone iii represents the twentieth century groyne fields which are several to a dozen metres wide and filled with polluted sediments averaging depths of more than 2 m this investigation indicates that large and extensive sediment quantities of moderately polluted sediments are stored immediately along the banks of the river odra these sediments could be a significant secondary pollution source and therefore careful maintenance of contemporary bank protection structures is required copyright 2009 john wiley sons ltd

recent and historic sediment dynamics along difficult run a suburban virginia piedmont stream abstract suspended sediment is one of the major concerns regarding the quality of water entering the chesapeake bay some of the highest suspended sediment concentrations occur on piedmont streams including difficult run a tributary of the potomac river draining urban and suburban parts of northern virginia accurate information on catchment level sediment budgets is rare and difficult to determine further the sediment trapping portion of sediment budget represents an important ecosystem service that profoundly affects downstream water quality our objectives with special reference to human alterations to the landscape include the documentation and estimation of floodplain sediment trapping present and historic and bank erosion along an urbanized piedmont stream the construction of a preliminary sediment balance and the estimation of legacy sediment and recent development impacts we used white feldspar markers to measure floodplain sedimentation rates and steel pins to measure erosion rates on floodplains and banks respectively additional data were collected for from legacy sediment thickness and characteristics mill pond impacts stream gaging station records topographic surveying and sediment density texture and organic content data were analyzed using gis and various statistical programs results are interpreted relative to stream equilibrium affected by both post colonial bottomland sedimentation legacy and modern watershed hardening associated with urbanization six floodplain channel sites from high to low in the watershed were selected for intensive study bank erosion ranges from 0 to 470 kg m y and floodplain sedimentation ranges from 18 to 1369 kg m y m refers to meters of stream reach upstream reaches are net erosional while downstream reaches have a distinctly net depositional flux providing a watershed sediment balance of 2184 kg m y trapped within the system the amounts of both deposition and erosion are large and suggest nonequilibrium channel conditions both peak discharge and number of peaks above base have substantially increased since the mid 1960s when urbanization of the watershed began deposition patterns are most closely correlated with channel gradient sinuosity and channel width floodplain width for recent and historic periods the substantial amounts of fine grained sediment deposited on the floodplain over the past two centuries or so do not appear to be closely related to historic mill pond presence or location the floodplain continues to provide the critical ecosystem service of sediment trapping in the face of multiple human alterations trends in sediment deposition erosion may react rapidly to land use practices within the watershed and offer a valuable barometer of the effects of management actions

hydrologic modeling of flood conveyance and impacts of historic overbank sedimentation on west fork black s fork uinta mountains northeastern utah usa abstract this study assesses historic overbank alluvial sedimentation along a low gradient reach of west fork black s fork in the northern uinta mountains utah in this previously glaciated setting an alluvial floodplain that is approximately 400 m wide by 1500 m long has been modified by the combined effects of valley morphometry and the recent history of clear cut logging during the late 19th and early 20th centuries to quantify the effects on sedimentation and flow conveyance three natural streambank exposures were sampled and analyzed for nuclear bomb fallout 137 cs the distribution of 137 cs within the three profiles suggests that a remnant outwash terrace exerts a first order control over the deposition of overbank alluvium upstream from a constriction in the floodplain caused by the terrace remnant as much as 40 cm of overbank alluvium has been deposited since the beginning of clear cut logging immediately downstream of that constriction no evidence exists for any overbank sedimentation during that same period vibracore samples and oakfield soil probe sampling throughout the study reach quantified the geographic extent and thicknesses of the historic alluvial package flood conveyance through the study area was modeled using the u s army corps of engineers hec ras modeling program model simulations were run for modern conditions using surveyed topography and for prehistoric conditions using the modern topography less the historic alluvial package determined by 137 cs analyses model results indicate that the floodplain constriction caused a significant impediment to flood conveyance at even modest discharges during prehistoric conditions this promoted ponding of floodwaters upstream of the constriction and deposition of alluvium this has increased bank heights upstream of the constriction to the point that under modern conditions 1 to 5 year recurrence interval floods are largely confined within the channel these results confirm the validity of this new approach of combining 137 cs dating of alluvial sediments with hec ras flow modeling to compare flood conveyance along a single stream reach prior to and since an abrupt change in alluvial sedimentation patterns

late quaternary floodplain reworking and the preservation of alluvial sedimentary archives in unconfined and confined river valleys in the eastern interior of south africa abstract in this study geomorphological sedimentological and geochronological work was conducted on unconfined and confined reaches of three rivers in the eastern interior of south africa in order to quantify the relative rates of floodplain reworking and alluvial preservation along river courses with variable valley confinement and lithology using optically stimulated luminescence osl dating techniques new chronologies for the schoonspruit and mooi river were created and the existing klip river chronology was expanded the results suggest that floodplains in both unconfined and confined reaches preserve complex spatial and temporal patterns of alluviation although differences in boundary conditions lead to variation in the processes and rates of floodplain construction and reworking on the klip and mooi rivers where local base levels are stable channels in unconfined reaches rework floodplain sediments through slow lateral migration punctuated by local erosion during avulsion events on the schoonspruit where base level has lowered the channel in the unconfined reach is incised the floodplain is abandoned and a large gully has formed in the confined reaches of all three rivers the narrow floodplains are reworked by scour and fill activity and limited lateral migration the osl results suggest that unconfined reaches preserve relatively continuous alluvial records that extend into the pleistocene while the floodplains in the confined reaches preserve relatively discontinuous alluvial records biased toward the late holocene the alluvial geochronologic records in these systems preserve signals of changes in local base level controlled by variation in lithology and incision rather than climate change by defining the processes rates and patterns of floodplain reworking in reaches with different degrees of valley confinement and channel incision the findings contribute to understanding how rivers build modify and preserve alluvial sedimentary archives

effects of watershed management practices on the relationships among rainfall runoff and sediment delivery in the hilly gully region of the loess plateau in china abstract the relationships among rainfall runoff and sediment delivery are significant in predicting soil erosion and in evaluating the benefits of watershed management practices wmp on the hilly gully regions of the loess plateau hydrologic data 1987 to 2010 were analyzed for variations in precipitation runoff and sediment delivery at annual and event scale these data were obtained from the qiaozi east watershed qe and the qiaozi west watershed qw with and without wmp respectively results indicated that the runoff coefficients of the watersheds decreased significantly although the runoff coefficient of qe was less than half of that of qw sediment delivery decreased more in qe than in qw mainly because of the increase in vegetation cover in both watersheds in qe the relationship between runoff and sediment delivery did not change significantly from 1987 to 2006 although the variation was significant from 2007 to 2010 in qw the relationship between runoff and sediment delivery was not notably altered from 1987 to 2010 this finding suggested that vegetation practices and engineering measures on the hillslope did not strongly affect the relationship between runoff and sediment delivery in the watersheds but the construction of check dams reduced gully erosion and the suspended sediment concentration hence control practices for gully erosion significantly influenced the relationship between runoff and sediment delivery this study suggests that a combination of hillslope and gully erosion control practices effectively reduces erosion and sediment delivery in the hilly gully regions of the loess plateau