sedimentary record and luminescence chronology of palaeoflood events along the gold gorge of the upper hanjiang river middle yangtze river basin china abstract palaeoflood slackwater deposits swds along the river banks have important implications for the reconstruction of the past hydro climatic events two palaeoflood swd beds were identified in the holocene loess soil sequences on the cliff river banks along the gold gorge of the upper hanjiang river by field investigation and laboratory analysis they have recorded two palaeoflood events which were dated by optically stimulated luminescence to 3 2 2 8 ka and 2 1 1 8 ka respectively the reliability of the ages obtained for the two events are further confirmed by the presence of archaeological remains and good regional pedostratigraphic correlation the peak discharges of two palaeoflood events at the studied sites were estimated to be 16 560 17 930 m3 s a correlation with the palaeoflood events identified in the other reaches shows that great floods occurred frequently during the episodes of 3200 2800 and 2000 1700 a bp along the upper hanjiang river valley during the last 4000 years these phases of palaeoflood events in central china are well correlated with the climatic variability identified by 18o record in the stalagmites from the middle yangtze river basin and show apparent global linkages palaeoflood studies in a watershed scale also imply that strengthened human activities during the shang dynasty bce 1600 1100 and han dynasty bce206 ce265 may have caused accelerated soil erosion along the upper hanjiang river valley

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

fluvial sediment budgets in the north carolina piedmont phillips j d 1991 fluvial sediment budgets in the north carolina piedmont geomorphology 4 231 241 sediment budgets for four large 1000 km 2 drainage basins in the piedmont physiographic province of north carolina were estimated from data compiled during erosion and sedimentation surveys budgets for the upper tar upper neuse haw and deep river basins showed broadly similar trends in allocation of eroded sediment among yield and storage sediment yield as a percentage of mean annual gross erosion within the basins averaged 10 this was less than the rate of alluvial storage which averaged 14 of annual gross erosion about 76 of the mean annual erosion was stored as colluvium on hillslopes there are relatively small differences in sediment delivery and storage ratios among the study basins this suggests that the relative order of magnitude of the allocation of eroded sediment for southern piedmont rivers is colluvial storage alluvial storage and yield of the sediment that does reach the streams more than half is stored as alluvium on an average annual basis aggrading channels and floodplains siltation of benthic habitats and sediment pollution problems are thus likely to persist unless dramatic reductions in upland erosion or in sediment delivery to streams are realized with respect to longer term basin evolution results point to the need for an improved understanding of the temporal scales of colluvial and alluvial sediment storage

floodplain storage of sediment contaminated by mercury and copper from historic gold mining at gold hill north carolina usa abstract previous research on the environmental consequences of mining has shown that metal contaminants can have long lasting impacts on water quality and aquatic ecosystems because of the remobilization of sediment associated contaminants that have been stored in floodplains we examined the magnitude and distribution of mercury hg and copper cu contamination of floodplain deposits associated with nineteenth century gold au mining activities in the gold hill mining district north carolina a comparison of post mining metal concentrations in overbank deposits with sediment quality guidelines indicates that overall about 21 are contaminated above the probable effect concentration pec above which adverse effects are expected to occur more often than not for both cu and hg the highest contamination occurs upstream near the mine source where 51 of the samples exceed the pec for hg and 57 exceed the pec for cu of the three different methods used to estimate metal mass storage the most reliable estimate suggests that about 6 8 mg of hg and 619 mg of cu currently reside in floodplain deposits within this watershed although overbank sediment storage increases downstream and with valley width about 75 of the hg and cu mass are stored in the upstream portion of the watershed hg mass storage displays a strong negative relationship with cross sectional stream power but the relationship between cu mass storage and stream power is insignificant we used vertical changes in overbank metal concentrations and the mining history to estimate a mean sedimentation rate of 2 7 cm y 1 during the most intensive period of au mining at gold hill 1842 1856 that is three times the long term 1842 2007 rate of 0 9 cm y 1 long term average rates at gold hill are comparable to those reported elsewhere in the eastern piedmont the downstream increase in long term rates may indicate a spatial and temporal lag effect where the locus of deposition shifts downstream with time

a small scale flood plain a miniature 9 m wide floodplain developed along a gravel washing effluent stream shows features such as levees crevasse splays and floodbasins which compare with their larger scale counterparts for sediments deposited overbank median size decreases exponentially with distance from the channel whilst sorting increases with coarser sediment on the outside of a meander bend overbank flows are only a few grain diameters in depth near the channel this study shows potentially useful systematic relationships in floodplain sediment textures but it involves only one of a possible variety of floodplain types dominated by overbank sedimentation this suggests that further exploration of overbank depositional processes is desirable as an aid to field interpretation

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

late holocene flooding records from the floodplain deposits of the yugu river south korea abstract predicting responses of regional hydrological cycles to global warming requires an understanding of past hydrological events on various timescales this study investigated the variability of flooding as recorded in fluvial floodplain deposits the percentage of sand sized material in two cores collected from the floodplain of the yugu river one of the tributaries of the keum river central south korea has been tested as a proxy for the occurrence and magnitude of past flooding the sand fraction of the floodplain deposits in cores kl28 and kl29 which record deposition over the last 3500 years varied on multicentury timescales and suggests several past episodes of higher frequency large floods these clusters of large floods seem to correlate well with northern hemisphere temperature anomalies and suggest that more frequent large floods occurred during the medieval warm period mwp than during the little ice age lia the occurrence of more frequent large floods on the keum river tributary may have been driven by intensified northerly winds over east asia and resultant moisture convergence over korea and or a weakened thermal gradient between the tropical ocean and asian continent furthermore the centennial scale changes in the sand fraction of the floodplain deposits were partly similar to remote el nino southern oscillation enso activity implying a possible link between flooding in central south korea and enso activity this study has demonstrated that floodplain deposits have much potential for recording paleofloods though floodplains can be and quite often are very complex places in terms of their depositional history in regions where natural lakes suitable for the study of paleohydrology and paleoclimate are lacking well controlled time series data for the sand content at multiple sites in fluvial floodplains may be used to understand paleoflooding and extreme precipitation variability in the past

pattern analysis of dune field parameters as a basic form of pattern analysis the parameters of dune spacing defect density crest orientation and crest length are measured from remote images and treated statistically for dunes at white sands in new mexico the algodones in california the agneitir in mauritania and the namib in namibia statistical populations are identified from frequency plots of dune spacing and crest length field scale calculations of defect density and rose diagrams of crest orientation single populations characterize simple dune fields white sands whereas multiple populations characterize compound complex dunes algodones namib and complex dune fields agneitir as time increases dune fields show an increase in dune spacing and crest length a decrease in defect density more tightly clustered crest orientation and a reduction in the variance associated with measurements of these parameters the results are consistent with models of dune fields as self organizing complex systems in which a characteristic pattern emerges as a function of constructional time because pattern evolution is a function of time it may be possible to use pattern analysis to augment current methods of age determination statistically defined populations can be used in geomorphic backstripping to unstack generations of simple patterns that give rise to complex patterns and to reconstruct each generation in terms of construction time and palaeo wind regime copyright 2006 john wiley sons ltd

floodplain storage of mine tailings in the belle fourche river system a sediment budget approach arsenic contaminated mine tailings that were discharged into whitewood creek at lead south dakota from 1876 to 1978 were deposited along the floodplains of whitewood creek and the belle fourche river the resulting arsenic contaminated floodplain deposit consists mostly of overbank sediments and filled abandoned meanders along white wood creek and overbank and point bar sediments along the belle fourche river arsenic concentrations of the contaminated sediments indicate the degree of dilution of mine tailings by uncontaminated alluvium about 13 per cent of the 110 106 mg of mine tailings that were discharged at lead were deposited along the whitewood creek floodplain deposition of mine tailings near the mouth of whitewood creek was augmented by an engineered structure about 29 per cent of the mine tailings delivered by whitewood creek were deposited along the belle fourche river floodplain about 60 per cent of that sediment is contained in overbank deposits deposition along a segment of the belle fourche river was augmented by rapid channel migration the proportions of contaminated sediment stored along whitewood creek and the belle fourche river are consistent with sediment storage along the floodplains of perennial streams in other similar sized watersheds

use of mining contaminated sediment tracers to investigate the timing and rates of historical flood plain sedimentation abstract changes in land use practices following european settlement in the 1830s produced accelerated sedimentation on virtually all valley floors in the blue river watershed wisconsin the contamination of sediments by pb and zn mining allowed us to calculate cross valley rates of flood plain sedimentation for three time periods the pre mining period 1830 1900 the mining period 1900 1920 and the post mining period 1920 1997 most of the eight valley floors examined contained multiple presettlement surfaces significantly higher rates of sedimentation occurred on the lower flood plain surfaces while the terraces were high enough to prevent sedimentation from most floods higher rates of sedimentation on the lower surfaces eventually reduced valley floor relief and consequently lateral differences in sedimentation rates tributaries and larger valleys downstream exhibited differences in the timing and rates of historical flood plain sedimentation while rates of sedimentation were high during the pre mining period in tributary valleys the lower valleys were receiving little or no pre mining alluvium little pre mining alluvium was found in mid basin reaches suggesting that most of the pre mining sedimentation was limited to headwater locations during the mining period lateral channel migration and the development of meander belts increased the conveyance capacity of tributary and mid basin channels which decreased overbank flooding and produced lower rates of sedimentation during the post mining period the meander belt channels also had an effect on the lower portion of the watershed by increasing flood magnitudes and the transport of sediment downstream thereby shifting the locus of sedimentation from the tributaries to the larger lower valleys sedimentation rates in the largest most downstream site were an order of magnitude higher during the post mining period than any of the sites upstream

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

three dimensional model of alluvial stratigraphy theory and applications abstract a three dimensional model of alluvial stratigraphy has been developed to simulate the spatial distribution proportion and connectedness of coarse grained channel belt deposits in alluvial strata as a function of channel belt width floodplain width bankfull channel depth channel belt and overbank sedimentation rates avulsion location and period compaction and tectonism tilting and faulting in this model a floodplain surface of variable width and length is occupied by a single channel belt changes in floodplain topography are produced by spatial and temporal variation of channel belt and floodplain deposition rates and by compaction and local or regional tectonism the location and timing of avulsions are determined by local changes in floodplain slope relative to channel b lt slope and by flood magnitude and frequency the diverted channel belt follows the locus of maximum floodplain slope at the end of each simulation architectural parameters are calculated including channel deposit proportion and connectedness and the dimensions of channel belt sandstone bodies three dimensional perspective diagrams mesh surfaces and two dimensional stratigraphic sections can be plotted to illustrate depositional surfaces time planes and the location and geometry of coarse grained channel belt deposits within finer grained overbank deposits the model predicts that channel belt proportion and connectedness and dimensions of sandstone bodies vary as a function of distance from avulsion points and cross section orientation upstream from avulsion points sandstone bodies have low width thickness ratios because of aggradation in a fixed channel belt immediately downstream from avulsion points channel belts tend to be connected resulting in sandstone bodies with high width thickness ratios avulsion sequences develop where points of avulsion shift up valley with a progressive decrease in avulsion period such sequences may produce successions in which channel belt proportion and connectedness vary vertically with a cyclic period of 103 to 105 years down valley increases in aggradation rate or down valley decreases in floodplain slope for example associated with a rise in base level may result in an increase in channel belt proportion and connectedness because of high avulsion frequencies in down valley regions of the floodplain down valley decreases in aggradation rate as in alluvial fans foreland basins and during base level fall may result in high avulsion frequencies in up valley parts of the floodplain tectonic tilting and faulting locally increase avulsion probabilities and channel belts generally shift toward areas of maximum subsidence under certain conditions however depositional topography may cause channels to shift away from areas of maximum subsidence channel deposit proportion and connectedness are gen rally high near downthrown areas of the floodplain but distribution clustering of channel belts may not be a reliable indicator of fault geometry or displacement models of alluvial architecture that consider only sediment accumulation rate as the main controlling factor are oversimplified the three dimensional model presented here predicts many of the features of channel behavior observed in modern rivers but there is a pressing need for better models and adequate natural data to test them

geomorphological patterns in a linear dune field and ages of the linear dunes in the northern kumtagh desert northwest china the unique linear dunes in the northern kumtagh desert of northwest china have inspired enthusiastic debate among aeolian geomorphologists over their origins and classification their uniqueness lies not only in their morphology but also in their geomorphological patterns in this paper the geomorphological patterns and ages of the linear dunes in the northern kumtagh desert are analyzed using the pattern analysis method that was recently adopted by geomorphologists the analysis suggests that these linear dunes have developed since 13 ka bp during the late part of the most recent deglaciation stage when the region s dry climate was favorable for dune formation the differences in dune construction time within this region result from the complex factors that control their formation and spatial variations in the local environment but these factors were not strong enough to prevent us from estimating the dune age recorded by the geomorphological patterns with acceptable precision it is also suggested that the pattern analysis method can be used to estimate dune ages in the absence of more reliable dating methods

a centennial tribute to g k gilbert s hydraulic mining debris in the sierra nevada abstract g k gilbert s 1917 classic monograph hydraulic mining debris in the sierra nevada is described and put into the context of modern geomorphic knowledge the emphasis here is on large scale applied fluvial geomorphology but other key elements e g coastal geomorphology are also briefly covered a brief synopsis outlines key elements of the monograph followed by discussions of highly influential aspects including the integrated watershed perspective the extreme example of anthropogenic sedimentation computation of a quantitative semidistributed sediment budget and advent of sediment wave theory although gilbert did not address concepts of equilibrium and grade in much detail the rivers of the northwestern sierra nevada were highly disrupted and thrown into a condition of nonequilibrium therefore concepts of equilibrium and grade for which gilbert s early work is often cited are discussed gilbert s work is put into the context of complex nonlinear dynamics in geomorphic systems and how these concepts can be used to interpret the nonequilibrium systems described by gilbert broad basin scale studies were common in the period but few were as quantitative and empirically rigorous or employed such a range of methodologies as pp105 none demonstrated such an extreme case of anthropogeomorphic change

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

an antarctic circumpolar wave in surface pressure wind temperature and sea ice extent the southern ocean is the only oceanic domain encircling the globe it contains the strong eastward flow of the antarctic circumpolar current and is the unifying link for exchanges of water masses at all depths between the world s major ocean basins1 as these exchanges are an important control on mean global climate the southern ocean is expected to play an important role in transmitting climate anomalies around the globe interannual variability has been often observed at high southern latitudes and observations of sea ice extent suggest that such features propagate eastwards around the southern ocean2 3 here we use data from a variety of observational techniques to identify significant interannual variations in the atmospheric pressure at sea level wind stress sea surface temperature and sea ice extent over the southern ocean these anomalies propagate eastward with the circumpolar flow with a period of 4 5 years and taking 8 10 years to encircle the pole this system of coupled anomalies which we call the antarctic circumpolar wave is likely to play an important role in climate regulation and dynamics both within and beyond the southern ocean

interannual and interdecadal variability of atmospheric synoptic scale activity in the southern hemisphere 1 a rotated empirical orthogonal function analysis was applied to anomalies of july atmospheric short time scale variability or storm tracks over the southern hemisphere sh using ncep reanalyses the study reveals the existence of two leading modes of storm track variations the first one describing storm track changes along the subtropical pacific and the second one associated with variations over southeast pacific ocean the principal components of both modes exhibit significant variability on interannual 2 7 years and interdecadal longer than 7 years time scales the interannual variation of the first mode is closely linked to enso variability the corresponding signal on sst anomalies shows a conspicuous maximum over central equatorial pacific while the signature on geopotential height anomalies shows the typical pacific south america pattern characterized by a rossby wave train propagating poleward from the tropics on interdecadal time scales the first mode is related to sst anomalies over the subtropical portions of the pacific atlantic and indian oceans and to a rossby wave train with strongest signals over the southeast pacific and the antarctic peninsula the second mode that represents storm track changes west of the antarctic peninsula is related on interannual time scales to sst anomalies over western pacific between 40 s and 20 s while on interdecadal time scales it does not seem to be significantly related to sst changes in any of the basins in particular the spatial signature of the reof2 interdecadal variability on the sh circulation corresponds to the well known high latitude mode characterized by a monopole over the antarctica and a three wave pattern at middle latitudes

sedimentology of a fine grained aggrading floodplain abstract historical land use changes accelerated both soil erosion and subsequent floodplain alluviation within the galena river basin wisconsin a cross valley transect in a low gradient downstream section of this watershed permitted documentation of the lateral and vertical sedimentological properties occurring during this aggradational phase mechanical and statistical analyses of 97 sediment samples reveal two dominant controls determining the resulting floodplain sedimentology firstly the initial fine grained loessial texture dominated the particle size of the early post settlement alluvium generally yielding fine textured sediments across the valley bottom further landscape de stabilization promoted upland gullying into coarser textured residuum below the loess with a concomitant particle size increase in the foodplain alluvium thus the resulting foodplain stratigraphy exhibits a coarsening upward sequence secondly distance from the stream channel exerts a strong control on overall sedimentological properties distal settings possess massive high clay content sediments usually with less than 1 sand samples become coarser and more stratified near the modern stream channel with channel fill facies containing approximately 20 sand in the upper sections the fine grained loessial sediment source affected numerous sedimentological properties of the deposited alluvium sorting correlates negatively with particle size because all particle sizes were entrained during large overbank floods dominance of silt in this loess mantled basin maintains the maintains the median of the particle size distribution within a fairly narrow range only the tails of the distribution vary and they are primarily controlled by the distance to the stream channel in distal settings the fine tail emerges whereas the coarse tail appears in the channel fill and proximal settings although all sediments were deposited in an overbank floodplain environment passega s cm diagrams erroneously indicate a pelagic depositional environment

accelerated overbank accumulation after nineteenth century river regulation works a case study on the maros river hungary abstract in the nineteenth century the meandering rivers of the carpathian basin were extensively regulated and their large up to 100 km wide floodplains were confined by artificial levees on the narrow 0 5 4 km artificial floodplains confined by these levees overbank sedimentation has become the dominant geomorphological process resulting in rising floodplain levels during the last century the maros river is an extreme example of this process as it carries a significant amount of suspended sediment 4 6 10 6 m 3 y and because its lowland reach was drastically shortened by cutoffs resulting in bed scour and an increased sediment load simultaneously a flood embankment system was constructed reducing the floodplain width by 70 80 the resulting accelerated overbank sediment accumulation increases the flood hazard along the river the aim of this study is to determine the spatial and temporal pattern of overbank sediment accumulation on the artificial floodplain of the lower maros river over the last 150 years and to identify its influencing factors the lateral slope of the protected natural floodplain was projected towards the present day channel allowing the volume m 3 and rate cm y of overbank sedimentation to be calculated using digital terrain modelling dtm changes in the rate of sedimentation were determined by pollen analysis the studied reach was divided into five sections based on the rate of aggradation i the distal surface of the alluvial fan where no sedimentation was measured only incision ii the original front of the alluvial fan 1 0 0 4 cm y iii the recently formed secondary alluvial fan 1 4 0 3 cm y iv the low lying floodplain 0 4 0 2 cm y and v the outlet unit 2 0 0 5 cm y the aggradation rate was slower on elevated forms such as the pre regulation natural levee 0 2 cm y and greater on the low lying floodplain 0 6 cm y the greatest accumulation rate 1 3 2 4 cm y was measured in cutoffs the sedimentation rate was high during the regulation period 1 9 2 4 cm y but later decreased to 0 5 0 9 cm y the rate of aggradation was determined by the width height and slope conditions of the floodplain the impoundment of the main river and the land use in the area

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

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

floodplain sedimentation in the upper mississippi valley natural versus human accelerated abstract understanding the time scales and pathways for response and recovery of rivers and floodplains to episodic changes in erosion and sedimentation has been a long standing issue in fluvial geomorphology floodplains are an important component of watershed systems because they affect downstream storage and delivery of overbank flood waters and they also serve as sources and temporary sinks for sediments and toxic substances delivered by river systems here 14c and 137cs isotopic dating methods are used along with ages of culturally related phenomena associated with mining and agriculture to determine rates of sedimentation and morphologic change for a reach of the upper mississippi river and adjacent tributaries in southwestern wisconsin and northwestern illinois the most important environmental change that influenced fluvial activity in this region during last 10 000 years involved the conversion of a late holocene mosaic of prairie and forest to a landscape dominated by cropland and pastureland associated with euro american settlement results presented herein for the upper mississippi valley umv show that the shift from pre agriculture natural land cover to landscape dominance by agricultural land use of the last 175 200 years typically increased rates and magnitudes of floodplain sedimentation by at least an order of magnitude accelerated overbank flooding led to increased bank heights on tributary streams and in turn contributed to more frequent deep flows of high energy these high energy flows subsequently promoted bank erosion and lateral channel migration and the formation of a historical meander belt whose alluvial surface constitutes a new historical floodplain inset against the earlier historical floodplain the new historical floodplain serves as a flume like channel that provides efficient downstream transport of water and sediment associated with moderate and large magnitude floods floodplains on lower tributaries however continue to experience rates of overbank sedimentation that are of anomalously high magnitude given improved land cover and land conservation since about 1950 this lower valley anomaly is explained by minimal development of historical agriculture period meander belts because of relatively low stream power in these channel and floodplain reaches of relatively low gradient in general long term pre agriculture rates of vertical accretion between about 10 000 and 200 years ago averaged about 0 2 mm yr 1 in tributary watersheds smaller than about 700 km2 and about 0 9 mm yr 1 on the floodplain of the upper mississippi river where the contributing watershed area increases to about 170 000 km2 on the other hand rates of historical vertical accretion during the period of agricultural dominance of the last 200 years average between 2 and 20 mm yr 1 with short episodes of even higher rates during times of particularly poor land conservation practices significant hydrologic effects of mining and agricultural started by the 1820s and became widespread in the study region by the mid 19th century the hydrologic and geomorphic influences of mining were relatively minor compared to those related to agriculture high resolution dating of floodplain vertical accretion deposits shows that large floods have frequently provided major increments of sedimentation on floodplains of tributaries and the main valley upper mississippi river the relative importance of large floods as contributors to floodplain vertical accretion is noteworthy because global atmospheric circulation models indicate that the main channel upper mississippi river should experience increased frequencies of extreme hydrologic events including large floods with anticipated continued global warming instrumental and stratigraphic records show that coincident with global warming a shift to more frequent large floods occurred since 1950 on the upper mississippi river and these floods generally contributed high magnitudes of floodplain sedimentation

the significance of particle aggregation in the overbank deposition of suspended sediment on river floodplains abstract the effects of suspended sediment aggregation on rates of overbank deposition and on the grain size composition of deposited sediment were investigated using a combined field measurement and numerical modelling approach measurements of the in situ grain size characteristics of the suspended sediment load termed the effective size distribution of the river culm devon were obtained using a custom built water elutriation system samples of suspended sediment and of sediment deposited on the floodplain were analysed in the laboratory to determine the size distributions of their constituent discrete mineral particles termed the ultimate size distribution interpretation of these field data was aided by the development of a two dimensional finite difference model of flood hydraulics and suspended sediment dispersion and deposition field measurements and model predictions show that particle aggregation results in higher relative contributions of fine size fractions to overbank deposits aggregation may also provide a mechanism for explaining the poor agreement between theoretical and observed trends in relationships between mean deposit grain size and distance from the main channel suspended sediment aggregation is shown to cause significant increases in rates of floodplain deposition increases in deposition rates resulting from aggregation may however be less than expected because of the effects of aggregate shape and density the latter may offset increases in particle size so that the settling velocities of the largest aggregates do not increase appreciably with particle diameter

modelling flood hydraulics and overbank deposition on river floodplains this paper outlines a numerical model for the prediction of floodplain inundation sequences overbank deposition rates and deposit grain size distributions the model has two main components first a simplified hydraulic scheme which predicts floodwater flow depths and velocities and second a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates these relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains the model is applied to a 600 m reach of the river culm devon u k using data derived from a range of field and laboratory techniques continuous records of river stage and suspended sediment concentration provide the model s upstream boundary input requirements these are supplemented by measurements of the in situ settling characteristics of the suspended sediment load the model s sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period the model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition which are largely a product of the complex topography of the floodplain these results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry 1997 by john wiley sons ltd

long term variation of the antarctic circumpolar wave 1 during the period 1968 1999 the character of circum antarctic anomalies in sea level pressure sea ice edge and sea surface temperature changed substantially an antarctic circumpolar wave acw is only clearly visible in the period 1985 1994 before and perhaps after this the signal particularly in sea level pressure is quite different with no clear sign of precession accompanying the change from precessional to nonprecessional modes is a change in the spatial pattern of variability and a change in the predictability of atmospheric anomalies from oceanic forcing evidence from general circulation model integration suggests that during the precessional mode of the acw there is enhanced predictability as would be required to support a coupled ocean atmosphere interaction

spatial patterns of historical overbank sedimentation and floodplain evolution blue river wisconsin abstract increased soil erosion and overbank flooding associated with land use changes following european settlement have buried pre settlement floodplain surfaces in many driftless area watersheds with as much as several meters of alluvium this paper examines the processes influencing spatial variations in the storage of post settlement vertical accretion alluvium and the impact on floodplain evolution in the blue river watershed wisconsin the cross sectional area of historical vertical accretion sediments stored on floodplains was measured at 41 cross valley transects in the 208 km2 watershed the storage of historical overbank sediments is influenced by valley width stream power and the development of meander belts post settlement alluvial storage increases with valley width and decreases with cross sectional stream power in a multivariate regression model valley width and cross sectional stream power explain 67 of the variance in the amount of post settlement alluvium the development of meander belts enlarged channels confined between alluvial terraces by accelerated lateral channel migration influences historical floodplain storage by decreasing the influence of valley width and modifying stream power characteristics for flows greater than bankfull meander belts are located in headwater and mid basin valley reaches where high stream power produces rapid lateral channel migration whereas low gradient channels in downstream valleys lack the power necessary to migrate laterally and develop meander belts meander belts influence the spatial pattern of historical sedimentation by 1 containing large magnitude floods and preventing overbank flow 2 increasing sediment transport capacities 3 initiating the erosion of previously deposited historical sediments 4 reducing the attenuation of flood peaks and 5 increasing the amount of sediment routed downstream to wide low gradient valley bottoms lacking meander belts continued high rates of lateral channel migration will eventually be damped as widening of the meander belt decreases flow depths and stream power

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

holocene changes in flooding frequency in south korea and their linkage to centennial to millennial scale el nino southern oscillation activity to trace past changes in flooding frequency we investigated fluvial sediments in the middle reach of the nakdong river south korea sediments with larger grain size lower total organic carbon percentage and depleted 13 c values in the recovered sediment cores were interpreted as periods of more frequent flooding patterns of decreased long term flooding frequency and vegetation changes during the early to late holocene were similar to the decreasing regional summer monsoon intensity multicentennial frequent flooding periods in the study area 2900 3400 cal yr bp 3600 3900 cal yr bp 4600 5300 cal yr bp and 5800 6400 cal yr bp corresponded to stronger el nino southern oscillation enso activity periods based on previous studies showing that high frequency tropical typhoon driven coastal inundation along the western coast of japan during the middle to late holocene was coupled with stronger enso activity it is likely that the observed centennial to millennial scale flood frequency change in south korea was influenced mainly by changes in the genesis and tracks of tropical typhoons at centennial to millennial time scales this suggests that the centennial to millennial scale hydrologic changes in east asia were linked to the remote atmospheric oceanic circulation changes represented by an enso like pattern

multidecadal warming of subsurface temperature in the indian sector of the southern ocean 1 long term variations of subsurface layer temperature were examined for 32 years 1966 1998 of continuous observations in the indian sector of the southern ocean the data analyzed consist of observations from japanese antarctic research expeditions and also from other countries significant warming trends of about 0 004 c yr 1 were observed at all depths from 200 to 900 m to the north of the southern antarctic circumpolar current acc front orsi et al 1995 the rates of warming increase with increasing depth from 0 003 c yr 1 at 200 m to 0 012 c yr 1 statistically significant at 900 m in the region close to the front these warming trends were also found after applying a technique to correct for differences in the data sampling locations the warming tendency in the frontal region is consistent with the assumption of a southward shift of the front and may have a relationship with the observed retreat of sea ice edge

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

raked linear dunes in the kumtagh desert china abstract linear dunes are extensive in sand seas and dune fields around the world but they take a range of forms due to the complex factors that control their development raked linear dunes composed of primary ridges and subsidiary ridges that lie almost perpendicular to the primary ridges were recently identified in the northern part of china s kumtagh desert the primary ridges are typical linear dunes but the subsidiary ridges display vestiges of barchan dunes the subsidiary ridges are sufficiently short that they do not greatly affect the general appearance of the linear dunes however the raked linear dunes in the kumtagh desert have several unique characteristics that distinguish them from typical linear dunes these dunes develop in an environment that is deficient in available sediment and under a wind regime typical of linear dunes an environment with a high wind energy and a directional variability index rdp dp around 0 5 the raked linear dunes appear to have evolved from barchans following a modified form of tsoar s 1984 model barchans formed under a northern wind regime were modified by an eastern wind regime oriented at an oblique angle to the barchans the strengths of the two wind regimes are similar under these conditions the barchans became reoriented with the limbs farthest from the eastern winds extending to form subsidiary ridges and the limbs closest to the eastern winds forming the primary ridges which appear to form mainly from dune collisions

investigating spatial patterns of medium term overbank sedimentation on floodplains a combined numerical modelling and radiocaesium based approach abstract a numerical model of overbank deposition of fine grained suspended sediment is presented and employed to predict spatial patterns of mean annual floodplain sedimentation within a small reach of the river culm devon uk the model incorporates a deposition function which is calibrated with the aid of a dataset of measured deposition amounts obtained from nine flood events over a 13 month period model predictions of mean annual deposition rates are then compared against an independent dataset comprising estimates of longer term ca 35 years average sedimentation rates derived from caesium 137 measurements on 200 floodplain sediment cores collected from two floodplain locations the numerical model is found to adequately reproduce the spatial patterns of overbank sedimentation documented by the 137cs data however where maximum rates of deposition occur the model is found to seriously underpredict the 137cs derived estimates the simulation model employed here might be improved upon by incorporating more sophisticated 2d or 3d numerical treatments of flow hydraulics and suspended sediment transport and settling processes such numerical schemes may offer the potential to provide not only more accurate predictions of sedimentation rates but also more realistic representations of overbank processes while models of this type are now becoming more widely available in order for the benefits associated with increased model complexity to be realised in future greater emphasis must be placed upon testing models against distributed datasets of hydraulic and sedimentological variables obtained through intensive field monitoring programmes the use of 137cs measurements appears to offer considerable potential in this respect