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

the chronology of holocene alluvial sediments from the wetterau germany provided by optical and 14c dating holocene floodplain chronologies are often hard to establish the principal limitation being the scarc ity of organic remains in the present study optical dating of flood loam was carried out in

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

the paleohydrology of lower cretaceous seasonal wetlands isle of wight southern england abstract the floodplain deposits of the wealden group lower cretaceous of the isle of wight southern england were formed in a seasonal wetland setting a type of environment widespread today along higher order tropical and subtropical river systems but rarely identified in the geological record the unit consists of four main lithofacies sheet sandstones with dinosaur footprint casts green gray mudstones with vertebrate remains abundant lignite pyrite and siderite spectacularly color mottled mudstones with goethite and locally pseudo anticlines and red mudstones with pseudo anticlines hematite and carbonate nodules the sheet sandstones are interpreted as crevasse deposits the green gray mudstones were deposited in shallow ponds on the floodplain which acted as sinks for debris released by local floods following wildfires the mottled mudstones represent surface water gley soils formed in seasonally waterlogged areas and the red mudstones resemble present day vertisols that formed on topographically elevated areas only intermittently flooded these mudstones show vertical transitions from one to another and although they could be interpreted as components of simple catenas the absence of associated facies changes implies that topographic differences were not the only control it is proposed that these three mudstone types formed as seasonal wetland catenas in which differences in soil drainage conditions resulted from variations in the flooding hydroperiod affecting areas with minor relief differences rather than drainage variability simply reflecting static topographic differences such seasonal wetland systems are rarely documented in the stratigraphic record despite being a widespread environment in present day tropical regions and the wealden deposits are used to identify criteria for the recognition of this important environment in the rock record these southern english wetlands are compared with other lower cretaceous wetlands from northern spain enabling hydrological factors which controlled deposition to be recognized

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

simulation of 3d karst conduits with an object distance based method integrating geological knowledge karst conduit shapes have a high influence on fluid flows as these underground hidden systems are partially inaccessible their stochastic simulation is an essential tool to assess the uncertainties related to these highly exploited water resources the object distance simulation method odsim is a hybrid dual scale approach that has been recently proposed to model geological underground structures due to late processes such as dolomitized rocks mineralized veins or karsts using a perturbed euclidean distance field around a curve representing roughly the conduit centre and called a skeleton the resulting shapes are globally cylindrical like 3d envelopes but at a drain scale karstic conduits are elongated along weakness planes such as lithostratigraphic horizons bedding planes fractures or faults in addition to those planes the influence of the water table is added this work presents different improvements of odsim methodology for simulating more realistic shapes in the particular case of karst firstly we propose using a custom distance field computed with a fast marching method considering the velocity field to be proportional to the permeability allows the resulting features to be elongated along the weakness planes secondly to handle specific shapes due to the proximity of the water table such as trenches or notches we impose areas of higher velocity between the skeleton and the water table finally we generate a custom random threshold with several variograms and or distributions depending on the different features integrated in the velocity field applied on different models it is shown that the resulting karst conduits have more realistic shapes than those obtained with the previous workflow while the variability of structures which can be modelled with odsim is preserved

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

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

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

karst aquifer evolution in fractured porous rocks the evolution of flow in a fractured porous karst aquifer is studied by means of the finite element method on a two dimensional mesh of irregularly spaced nodal points flow within the karst aquifer is driven by surface recharge from the entire region simulating a precipitation pattern and is directed toward an entrenched river as a base level during the early phase of karstification both the permeable rock matrix modeled as triangular elements and fractures within the rock matrix modeled as linear elements carry the flow as the fractures are enlarged with time by chemical dissolution within the system calcite carbon dioxide water flow becomes more confined to the fractures this selective enlargement of fractures increases the fracture conductivity by several orders of magnitude during the early phase of karstification thus flow characteristics change from more homogeneous pore controlled flow to strongly heterogeneous fracture controlled flow we study several scenarios for pure limestone aquifers mixed sandstone limestone aquifers and various surface recharge conditions as well as the effect of faulting on the aquifer evolution our results are sensitive to initial fracture width faulting of the region and recharge rate

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

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

advances in carbonate exploration and reservoir analysis carbonate reservoirs contain an increasingly important percentage of the world s hydrocarbon reserves this volume presents key recent advances in carbonate exploration and reservoir analysis as well as a comprehensive overview of the trends in carbonate over the years the volume focuses on four key areas 1 emerging plays and techniques with special reference to lacustrine plays in syn rift basins and development of super giant heavy oil plays 2 improved reservoir characterization with examples from the middle east and europe and case studies of how outcrop analogues can provide key data for input to geological models 3 impact of fractures and faults in carbonates contributors highlight the need for integrated structural and diagenetic approaches in order to understand how fractures evolve as fluid flow conduits 4 advances in geomodelling of carbonate reservoirs several papers discuss the application of new and innovative geomodelling and geostatistical techniques to carbonate reservoirs

cave development in the swabian alb south west germany a numerical perspective summary the formation of phreatic cave conduits in the carbonate aquifer of the swabian alb south west germany is discussed by means of numerical simulations three active cave conduit systems the blautopf cave the aachtopf cave and the wimsener cave have been partially explored by divers and exhibit a continuous conduit flow path with phreatic loops down to 50 m below the average water table these three systems drain catchments between 50 and 280 km2 and largely follow the dip of the jurassic limestone beds we use the numerical model karst karst aquifer simulation tool to explore the possibility of structural control of the conduit evolution we show that both the dip of the bedding and the frequency of major bedding partings is likely to result in numerical drainage paths which are similar to the observed cave systems

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

crevasse splay processes and deposits in an ancient distributive fluvial system the lower beaufort group south africa abstract up to 12 of the mud prone ephemeral distributive fluvial system stratigraphy in the permo triassic lower beaufort group south africa comprises tabular fine grained sandstone to coarse grained siltstone bodies which are interpreted as proximal to distal crevasse splay deposits crevasse splay sandstones predominantly exhibit ripple to climbing ripple cross lamination with some structureless and planar laminated beds a hierarchical architectural scheme is adopted in which 1 m thick crevasse splay elements extend for tens to several hundreds of meters laterally and stack with other splay elements to form crevasse splay sets up to 4 m thick and several kilometers in width and length paleosols and nodular horizons developed during periods or in areas of reduced overbank flooding are used to subdivide the stratigraphy separating crevasse splay sets deposits from crevasse splays differ from frontal splays as their proximal deposits are much thinner and narrower with paleocurrents oblique to the main paleochannel in order for crevasse splay sets to develop the parent channel belt and the location where crevasse splays form must stay relatively fixed during a period of multiple flood events beaufort group splays have similar geometries to those of contemporary perennial rivers but exhibit more lateral variability in facies which is interpreted to be the result of more extreme fluctuations in discharge regime sharp based crevasse splay packages are associated with channel avulsion but most are characterized by a gradual coarsening upward interpreted to represent progradation the dominance of progradational splays beneath channel belt deposits may be more characteristic of progradational stratigraphy in a distributive fluvial system rather than dominated by avulsion processes in a trunk river system this stratigraphic motif may therefore be an additional criterion for recognition of distributive fluvial systems in the ancient record

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

process like modeling of flank margin caves from genesis to burial evolution abstract a major challenge in groundwater and petroleum modeling is how to represent the diagenesis effect sensu lato and its associated features e g karst cavities porosity and permeability characteristics both geometrical descriptions and genesis are necessary for modeling diagenetic features because they allow the restitution of phenomenon in subsurface settings where they cannot be fully observed this study focuses on flank margin caves developed on carbonate islands as in the case of the bahamian islands over the last twenty years numerous measurements and observations have been carried out on quaternary carbonate islands these together with reasonable hypotheses of genesis fresh water lens dissolution make island karst an appropriate subject for developing concepts and modeling methods which can be then applied to other diagenetic features such as reflux dolomitization and hydrothermal fluid effects the speleogenesis of flank margin caves was modeled following deterministic and stochastic methods to achieve a description of dissolution genesis a fresh water lens surface was built based on the topography of long island bahamas and was then used to simulate virtual development of flank margin caves at several formation phases including uncertainty coefficients applied to both fresh water lens location and stability time by using 3d probability cubes the cave simulations were compared with over sixty bahamian cave surveys in order to substantiate our modeling processes and results finally the model was exposed to a cave collapse situation the likelihood of preservation and the extent of the area affected were measured to provide an evaluation of the spatial distribution of associated petrophysical characteristics e g porosity and permeability the results reveal close resemblance and coherence between modeled and field data including collapse features therefore the optimum method for restituting diagenetic features is by stochastic modeling actively driven by process concepts and most up to date methods

spatial and temporal variability in sedimentation rates associated with cutoff channel infill deposits ain river france floodplain development is associated with lateral accretion along stable channel geometry along shifting rivers the floodplain sedimentation is more complex because of changes in channel position but also cutoff channel presence which exhibit specific overflow patterns in this contribution the spatial and temporal variability of sedimentation rates in cutoff channel infill deposits is related to channel changes of a shifting gravel bed river ain river france the sedimentation rates estimated from dendrogeomorphic analysis are compared between and within 14 cutoff channel infills detailed analyses along a single channel infill are performed to assess changes in the sedimentation rates through time by analyzing activity profiles of the fallout radionuclides 137cs and unsupported 210pb sedimentation rates are also compared within the channel infills with rates in other plots located in the adjacent floodplain sedimentation rates range between 0 65 and 2 4 cm a1 over a period of 10 to 40 years the data provide additional information on the role of distance from the bank overbank flow frequency and channel geometry in controlling the sedimentation rate channel infills lower than adjacent floodplains exhibit higher sedimentation rates and convey overbank sediment farther away within the floodplain additionally channel degradation aggradation and bank erosion which reduce or increase the distance between the main channel and the cutoff channel aquatic zone affect local overbank flow magnitude and frequency and therefore sedimentation rates thereby creating a complex mosaic of sedimentation zones within the floodplain and along the cutoff channel infills last the dendrogeomorphic and 137cs approaches are cross validated for estimating the sedimentation rate within a channel infill

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

preservation of exceptional vertebrate assemblages in middle permian fluviolacustrine mudstones of kotel nich russia stratigraphy sedimentology and taphonomy the kotel nich locality in european russia has long been a rich source of high quality tetrapod fossils including pareiasaurs dicynodonts gorgonopsians and theriodonts the age of the kotel nich locality has been debated but it corresponds to early severodvinian in the russian stratigraphic scheme equivalent to the late capitanian late middle permian on the international time scale remarkably the majority of specimens are complete quite unlike those from most russian permo triassic red bed localities commonest of all are 1 2 metre long pareiasaur skeletons of the genus deltavjatia preserved in hollows on top of a consolidated palaeosol horizon previous taphonomic scenarios in the russian literature have included suggestions that the animals were overwhelmed beneath sand dunes mired in soft fluviatile sediments caught at the bottom of a deep lake trapped in burrows or dumped in fluviatile scours it is probable that the pareiasaurs were searching for water in a time of catastrophic aridification and died weakened in shallow hollows in this case we also emphasise the importance of floodplain microtopography in creating the sedimentary conditions necessary for the preservation of exceptional vertebrate assemblages in a slowly aggrading fluviolacustrine setting

detection of karst conduit patterns via hydraulic tomography a synthetic inverse modeling study abstract karst aquifers are geologic media that consist of enlarged solution conduits the geometry of such conduits is very difficult to delineate and its hydraulic parameters such as hydraulic conductivity k and specific storage ss are difficult to estimate hydraulic tomography ht shown to successfully map the hydraulic heterogeneity of porous and fractured rock aquifers may also be effective in karst aquifers in this study we utilize two synthetic karst aquifers with the branchwork and network conduit patterns bcp and ncp to explore the ability of ht to map conduit patterns and their hydraulic parameters prior to the ht analysis forward models are built to study groundwater flow through synthetic karst aquifers to generate data and to gain insights into flow patterns forward modeling results reveal that 1 flow rates at the outlet of the bcp model is higher than the ncp model even when the same water injection rates are applied at the wells 2 the location of the injection well has a significant impact on the flow rate at the outlet and 3 flow lines mainly follow the conduit pattern these results suggest that the accurate mapping of karst networks is critical next the ht analysis of these data is conducted using a set of six models bcp and ncp to map the heterogeneity of different conduit systems under steady state and transient flow conditions inverse modeling results reveal that the estimated k maps become more reliable as the number of injection tests and the corresponding monitoring data are increased in the ht analysis moreover the results of the bcp model is closer to the original conduit pattern in comparison to the ncp model a comparative study of three inverse models with different number of observation wells and assuming the availability of geological data has shown that a more reliable pattern of the conduits can be mapped by adding geological information even when a small number of observation wells are available overall our results confirm the feasibility of ht in detecting major conduits as well as being able to differentiate between the bcp and ncp network types

an algorithm for 3d simulation of branchwork karst networks using horton parameters and application to a synthetic case this paper presents a method to stochastically simulate 3d karstic networks and more specifically branchwork pattern cave systems considering that they can be compared with 3d fluvial networks the topological classification of strahler and the corresponding ratios of horton are used to define three morphometric parameters these parameters are integrated in an algorithm that computes branches hierarchically to obtain a final network organized around the main observed inlet and outlet with a branching complexity controlled by the user each branch corresponds to a low cost path between two points calculated with the a graph search algorithm speleogenetic information on inception horizons palaeo water tables and fractures is accounted for by adapted definitions of the searching functions of a the method is demonstrated on a 3d synthetic case with discrete fractures networks inception horizons and a palaeo water table the simulated karsts have a realistic geometry and are geologically consistent simulation

use of fallout 137cs for documenting the chronology of overbank sediments from the river sava croatia and interpreting their geochemical patterns this paper attempts to determine the impact of former pb zn ba mining activities in slovenian drainage basin on overbank sediments of the sava river west croatia among the four studied sequences s7 s8 s9 s10 the most upstream profile s7 showed the most pronounced impact of ore mining mercury was enriched more than 100 fold pb and zn had a strong positive correlation r 0 99 two factor models clearly revealed the pb ba hg association in the lower lying carbonate ca population of all four profiles but only in the overlying silicate si population of profile s7 factor analysis confirmed this association in the total sediment 90 samples as well as separately in the ca 33 samples and si 57 samples populations based on a comparison with an undisturbed soil profile the vertical distribution of 137cs in profile s7 was interpreted to be the combination of caesium deposition caused by a flood in 1964 and by post depositional redistribution

obtaining isochrones from pollution signals in a fluvial sediment record a case study in a uranium polluted floodplain of the ploucnice river czech republic abstract uranium mining and processing in the watershed of the ploucnice river in the czech republic during a well defined time interval 1969 1989 allowed for a study of pollutant fates in sediments of a meandering river that is otherwise in a nearly natural state a considerable part of the primary pollution is present in hotspots in the floodplain 10 15 km downstream from the mining district one of the hotspots was characterised using geoinformatic geophysical and geochemical means the floodplain geomorphology and architecture and river channel dynamics were studied to develop an understanding of the formation of the hotspot and evaluate further movement of pollutants in the river system local background functions with rb or ti as a predictor and local enrichment factors lefs were obtained for ba ni pb u and zn concentrations in unpolluted sediments from the deeper strata of the active floodplain an abandoned floodplain and an ancient terrace the most recent 2013 overbank fines in the study area are still considerably enriched in ni u and zn lef 3 6 and 8 respectively and thus pollution by heavy metals several km downstream of the hotspots continuously increases even though the primary source of pollution was terminated more than 20 years ago the onset of the primary pollution the base of the polluted strata is hence clearly identified in the distal floodplain sediments as persistent and a potentially isochronous pollution signal in the fluvial record whereas a secondary pollution signal overwrites the expected primary pollution climax and pollution improvement signals that inertia of the fluvial system can also be expected in other river systems with both laterally and vertically deposited sediments the ploucnice case study allowed for further elaboration of the concept of local enrichment factors in pollution assessment of fluvial sediments which efficiently reduces the grain size effects the impact of hydraulic sorting and hence allows for reconstruction of the pollution history

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

sediment load and floodplain deposition rates comparison of the fly and strickland rivers papua new guinea 1 rates of aggradation and infilling of accommodation space along lowland channels in response to postglacial sea level rise should depend on sediment supply the strickland and fly rivers join at just 6 m above sea level and have experienced the same holocene sea level rise historically the strickland has carried about 7 times the sediment load and 1 4 times the water discharge as the fly therefore we hypothesize that the lowland strickland floodplain should be more developed and consequently should presently be capturing proportionately less sediment than the floodplain of the lowland fly river we use mine derived elevated pb and ag concentrations in 111 shallow 1 m floodplain cores collected in 2003 to determine deposition rates across the lower strickland floodplain sediment deposition rates decrease across the floodplain with distance from the channel bank and the average rate of deposition is 1 4 cm a over the first 1 km overbank deposition along the lowland sandbedded strickland results in 13 loss of the total load 0 05 km of channel length of the main stem deposition rates over the first 1 km from the channel bank on the strickland are about 10 times those on the fly for estimated natural sediment loads however the proportional loss per channel length on the strickland is less than that on the fly 0 09 km of main stem channel length because of an extensive network of tributary and tie channels that convey sediment to the floodplain on the fly furthermore the lateral migration of the strickland channel is 5 times that on the fly such that most overbank deposits on the strickland are returned to the channel causing the net loss of sediment to the floodplain to be small we conclude that the strickland river which has a much higher overbank deposition rate than the fly river as a function of distance from channel bank nonetheless has significantly less net accumulation than the fly because 1 a large proportion of the sediment load is conveyed up tributaries and tie channels on the fly and 2 lateral migration which presumably results from the higher load on the strickland sweeps sediment back into the channel hence our field observations support our initial hypothesis though the primary reason for this is because of active lateral migration rather than low overbank deposition rates

speleogenesis geometry and topology of caves a quantitative study of 3d karst conduits karst systems are hierarchically spatially organized three dimensional 3d networks of conduits behaving as drains for groundwater flow recently geostatistical approaches proposed to generate karst networks from data and parameters stemming from analogous observed karst features other studies have qualitatively highlighted relationships between speleogenetic processes and cave patterns however few studies have been performed to quantitatively define these relationships this paper reports a quantitative study of cave geometries and topologies that takes the underlying speleogenetic processes into account in order to study the spatial organization of caves a 3d numerical database was built from 26 caves corresponding to 621 km of cumulative cave passages representative of the variety of karst network patterns the database includes 3d speleological surveys for which the speleogenetic context is known allowing the polygenic karst networks to be divided into 48 monogenic cave samples and classified into four cave patterns vadose branchwork vb water table cave wtc looping cave lc and angular maze am eight morphometric cave descriptors were calculated four geometrical parameters width height ratio tortuosity curvature and vertical index and four topological ones degree of node connectivity and graph indices and ramification index respectively the results were validated by statistical analyses kruskal wallis test and pca the vb patterns are clearly distinct from am ones and from a third group including wtc and lc a quantitative database of cave morphology characteristics is provided depending on their speleogenetic processes these characteristics can be used to constrain and or validate 3d geostatistical simulations this study shows how important it is to relate the geometry and connectivity of cave networks to recharge and flow processes conversely the approach developed here provides proxies to estimate the evolution of the vadose zone to epiphreatic and phreatic zones in limestones from the quantitative analysis of existing cave patterns

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

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

measurements of erosion of undisturbed bottom sediments with depth a unique flume that measures the erosion of sediments at high shear stresses and with sediment depth has been designed constructed and used experiments in this flume sedflume can be done either with reconstructed sediments or with relatively undisturbed sediments from the field with either kind of sediment two different types of experiments can be conducted the first type determines the critical stress for erosion of the sediment as a function of depth while the second type determines the erosion rate of the sediment as a function of both shear stress and depth measurements of the erosion rates of sediments from the trenton channel of the detroit river in michigan and the lower fox river in wisconsin were made by use of sedflume at sediment depths up to 2 m representative results of these measurements are presented here these results demonstrate the capabilities of sedflume and also illustrate the large differences in erosion rates at different sites and the large variations in erosion rates with depth and as a function of shear stress

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

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

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

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

the use of multi temporal lidar to assess basin scale erosion and deposition following the catastrophic january 2011 lockyer flood se queensland australia advances in remote sensing and digital terrain processing now allow for a sophisticated analysis of spatial and temporal changes in erosion and deposition digital elevation models dems can now be constructed and differenced to produce dems of difference dod which are used to assess net landscape change for morphological budgeting to date this has been most effectively achieved in gravel bed rivers over relatively small spatial scales if the full potential of the technology is to be realised additional studies are required at larger scales and across a wider range of geomorphic features this study presents an assessment of the basin scale spatial patterns of erosion deposition and net morphological change that resulted from a catastrophic flood event in the lockyer creek catchment of se queensland seq in january 2011 multitemporal light detection and ranging lidar dems were used to construct a dod that was then combined with a one dimensional flow hydraulic model hec ras to delineate five major geomorphic landforms including inner channel area within channel benches macrochannel banks and floodplain the lidar uncertainties were quantified and applied together with a probabilistic representation of uncertainty thresholded at a conservative 95 confidence interval the elevation change distribution ecd for the 100 km2 study area indicates a magnitude of elevation change spanning almost 10 m but the mean elevation change of 0 04 m confirms that a large part of the landscape was characterised by relatively low magnitude changes over a large spatial area mean elevation changes varied by geomorphic feature and only two the within channel benches and macrochannel banks were net erosional with an estimated combined loss of 1 815 149 m3 of sediment the floodplain was the zone of major net deposition but mean elevation changes approached the defined critical limit of uncertainty areal and volumetric ecds for this extreme event provide a representative expression of the balance between erosion and deposition and importantly sediment redistribution which is extremely difficult to quantify using more traditional channel planform or cross sectional surveys the ability of lidar to make a rapid and accurate assessment of key geomorphic processes over large spatial scales contributes to our understanding of key processes and as demonstrated here to the assessment of major geomorphological hazards such as extreme flood events

deposition and storage of fine grained sediment within the main channel system of the river tweed scotland thispaperassessestheimportanceofdepositionandstorageoffine grained c 150m sedimentonthefloodplainsand bedsofthemain non tidal channelsoftherivertweed 4390km 2 scotland andtwoofitstributaries riverteviotand ettrick water caesium 137 analysis of floodplain sediment cores has been used to estimate average rates of overbank sedimentation during the last 30 to 40 years average values for individual transects ranged from 016 to 218 kg m 2 a 1 013to2 2m ma 1 themeanforthe10transectsinvestigatedwas129kgm 2 a 1 1 3m ma 1 thetotalamountoffine sediment deposited was estimated to be about 44 000 t a 1 the fine grained sediment stored in the channel bed was quantifiedusingresuspensiontechniques averagevaluesforindividualsitesrangedfrom012to096kgm 2 themeanfor the10sitesinvestigatedwas056kgm 2 thetotalamountofsedimentstoredonthechannelbedofthemainchannelsystem at the time of sampling was estimated to be about 4300 t comparison of these estimates of floodplain and channel storage with the estimated suspended sediment loadfor the river tweed at the downstream gauging site atnorham indicates that floodplainsedimentationandchannelbedstoragerepresentabout40and4percent respectively oftheannualloadoffine sedimentdeliveredtothemainchannelsystem erosionofchannelbankswillreintroducetheequivalentofabout30percent of the floodplain deposited sediment back into the channel the residence time of the fine grained sediment stored on the channel bed is probably less than one year but that of sediment deposited on the floodplain is likely to be considerably longer conveyance losses associated with overbank deposition have important implications for the routing of sediment throughfluvialsystemsandtheinterpretationofdownstreamsedimentyields copyright 1999johnwiley sons ltd

geomorphological and sedimentological analysis of flash flood deposits the case of the 1997 rivillas flood spain on the basis of the description of the 1997 rivillas flood deposits a morphosedimentary feature classification is proposed mapping of the main morphosedimentary deposits in seven reaches along the basin has provided abundant data for each defined typology and for a better adjustment of their stability fields because of their unstable preservation environment immediate post flood field surveys with descriptions of erosive and depositional features were undertaken up to 18 features were classified as either sedimentary or erosive and mapped according to their genetic environments anthropic interference such as land use changes produce modification of sediment supply and in channel and floodplain erosive processes causing flash floods to be more catastrophic erosive features are dominant over sedimentary ones as the sedimentary budget in the river is negative by means of hec ras hydrologic engineering center modelling we were able to obtain mean values of the main variables limiting feature stability velocity depth stream powers and shear stress these provide information regarding maximum stability threshold and peak flood discharge the ephemeral nature of riverine flash flood deposits in this type of setting does not mean that they are not significant and their interpretation after recent floods can significantly improve interpretation of the event dynamics and its flood hydrology and also be useful for flood risk mapping

use of fallout pb 210 measurements to investigate longer term rates and patterns of overbank sediment deposition on the floodplains of lowland rivers the potential for using fallout unsupported pb 210 210pb measurements to estimate rates of overbank sediment deposition on the floodplains of lowland rivers is explored a model which distinguishes the contribution from direct atmospheric fallout and the catchment derived input associated with the deposition of suspended sediment has been developed to interpret the fallout pb 210 inventories at floodplain sampling sites and to estimate average sediment accumulation rates over the past 100 years the approach has been successfully used to estimate rates of overbank sedimentation on the floodplains of the rivers culm and exe in devon u k a detailed investigation of the pattern of longer term sedimentation rates within a small reach of the floodplain of the river culm indicated a range of deposition rates between 0 07 and 0 59 g cm 2 a 1 which was in close agreement with estimates of current sedimentation rates obtained using sedimentation traps

high resolution evaluation of recent bank accretion rate of the managed rhone a case study by multi proxy approach abstract we determined the sedimentation rates near a managed embankment on the lower rhone for the second half of the twentieth century this was carried out using a combination of chronological indicators 137 cs 241 am dendrochronology and archived data and sedimentological measurements a high resolution chronological sequence has emerged from these data sets the average annual sedimentation rate of 14 cm has increased progressively over the last 50 years and at a much faster rate than observed elsewhere on this river this is probably due to a combination of factors such as the size of the river abundance and coarse texture of the solid load and local impact of river engineering works we also studied hydrological and sedimentological characteristics for a number of flood events

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

patterns of floodplain sediment deposition along the regulated lower roanoke river north carolina annual decadal centennial scales abstract the lower roanoke river on the coastal plain of north carolina is not embayed and maintains a floodplain that is among the largest on the mid atlantic coast this floodplain has been impacted by substantial aggradation in response to upstream colonial and post colonial agriculture between the mid eighteenth and mid nineteenth centuries additionally since the mid twentieth century stream flow has been regulated by a series of high dams we used artificial markers clay pads tree ring dendrogeomorphic techniques and pollen analyses to document sedimentation rates amounts over short intermediate and long term temporal scales respectively these analyses occurred along 58 transects at 378 stations throughout the lower river floodplain from near the fall line to the albemarle sound present sediment deposition rates ranged from 0 5 to 3 4 mm y and 0 3 to 5 9 mm y from clay pad and dendrogeomorphic analyses respectively deposition rates systematically increased from upstream high banks and floodplain to downstream low banks reaches except the lowest reaches conversely legacy sediment deposition a d 1725 to 1850 ranged from 5 to about 40 mm y downstream to upstream respectively and is apparently responsible for high banks upstream and large wide levees along some of the middle stream reaches dam operations have selectively reduced levee deposition while facilitating continued backswamp deposition a gis based model predicts 453 000 mg of sediment is trapped annually on the floodplain and that little watershed derived sediment reaches the albemarle sound nearly all sediment in transport and deposited is derived from the channel bed and banks legacy deposits sources and regulated discharges affect most aspects of present fluvial sedimentation dynamics the lower river reflects complex relaxation conditions following both major human alterations yet continues to provide the ecosystem service of sediment trapping