flow processes near smooth and rough concave outer banks in curved open channels flow processes near the concave outer bank in curved river reaches are investigated in a laboratory flume with focus on the influence of the bank roughness an outer bank cell of reversed secondary flow occurs for all the investigated roughness configurations of the outer bank the cell widens the outer bank boundary layer which reduces the flow forcing on the bank but also advects high momentum fluid toward the lower part of the bank which enhances the flow forcing on the bank increasing the roughness of the outer bank causes a considerable widening and strengthening of the outer bank cell which amplifies both effects on the flow forcing the widening of the outer bank boundary layer induced by the outer bank cell reduces the effective width of the channel i e the width where most of the discharge is conveyed which increases significantly the sediment transport capacity in the central part of the channel the near bank processes are qualitatively similar but show considerable quantitative variations around the bend the outer bank cell reaches its maximum strength in the zone that is most vulnerable to bed scour and bank erosion which corroborates its morphological relevance the outer cell is mainly generated by reversed near surface gradients in the profile of the streamwise velocity the anisotropy of the cross stream turbulence is the major mechanism opposed to the outer bank cell increasing roughness of the outer bank amplifies all dominant mechanisms but does not modify their relative importance the relevance of the experimental results for natural curved river configurations is discussed

simulation of curved open channel flows by 3d hydrodynamic model a mathematical model of three dimensional 3d free surface flows has been applied to simulate the curved channel flows and mass transport in the horizontal plane a channel fitted curvilinear coordinate system is used whereas in the vertical plane the transformation is adopted to track the free surface and variable bed topography to reduce the numerical diffusion the second order upwind scheme of roe is incorporated to discretize the convection terms the standard k e model has been modified to take account of some anisotropic effects appearing in shallow curved channels i e streamline curvature and the damping effects of free surface and solid walls the governing equations are solved in a collocated grid system by a fractional three step implicit algorithm two test cases from curved flumes have been studied 1 a 270 channel bend with a sloped outer bank and 2 a meandering channel with mass transport the results are compared with the available data which shows generally good agreement

oxygen in the southern ocean from argo floats determination of processes driving air sea fluxes the southern ocean is of outsized significance to the global oxygen and carbon cycles with relatively poor measurement coverage due to harsh winters and seasonal ice cover in this study we use recent advances in the parameterization of air sea oxygen fluxes to analyze nine years of oxygen data from a recalibrated argo oxygen dataset and from air calibrated oxygen floats deployed as part of the southern ocean carbon and climate observations and modeling soccom project from this combined dataset of 150 floats we find a total southern ocean oxygen sink of 183 80 tmol yr 1 positive to the atmosphere greater than prior estimates the uptake occurs primarily in the polar frontal antarctic zone paz 94 30 tmol o2 yr 1 and seasonal ice zone siz 111 9 3 tmol o2 yr 1 this flux is driven by wintertime ventilation with a large portion of the flux in the siz passing through regions with fractional sea ice the subtropical zone stz is seasonally driven by thermal fluxes and exhibits a net outgassing of 47 29 tmol o2 yr 1 that is likely driven by biological production the subantarctic zone saz uptake is 25 12 tmol o2 yr 1 total oxygen fluxes were separated into a thermal and non thermal component the non thermal flux is correlated with net primary production and mixed layer depth in the stz saz and paz but not in the siz where seasonal sea ice slows the air sea gas flux response to the entrainment of deep low oxygen waters

combined influences of seasonal east atlantic pattern and north atlantic oscillation to excite atlantic multidecadal variability in a climate model the physical processes underlying the internal component of the atlantic multidecadal variability amv are investigated from a 1 000 yr pre industrial control simulation of the cnrm cm5 model the low frequency fluctuations of the atlantic meridional overturning circulation amoc are shown to be the main precursor for the model amv the full life cycle of amoc amv events relies on a complex time evolving relationship with both north atlantic oscillation nao and east atlantic pattern eap that must be considered from a seasonal perspective in order to isolate their action the ocean is responsible for setting the multidecadal timescale of the fluctuations amoc rise leading to a warm phase of amv is statistically preceded by wintertime nao and eap from lag 40 20 yrs associated wind stress anomalies induce an acceleration of the subpolar gyre spg and enhanced northward transport of warm and saline subtropical water concurrent positive salinity anomalies occur in the greenland iceland norwegian seas in link to local sea ice decline those are advected by the eastern greenland current to the labrador sea participating to the progressive densification of the spg and the intensification of ocean deep convection leading to amoc strengthening from lag 10 yrs prior an amoc maximum opposite relationship is found with the nao for both summer and winter seasons despite negative lags nao at that time is consistent with the atmospheric response through teleconnection to the northward shift intensification of the inter tropical convergence zone in link to the ongoing warming of tropical north atlantic basin due to amoc rise amv build up nao acts as a positive feedback for the full development of the model amv through surface fluxes but at the same time prepares its termination through negative retroaction on amoc relationship between eap and amoc is also present in summer from lags 30 10 yrs while winter eap is favored around the amv peak based on additional atmospheric forced experiments both are interpreted as the local seasonal dependent atmospheric response to warmer north atlantic finally advection of fresher water from the tropical basin created by local atmosphere ocean anomalous circulation on one hand and from the arctic on the other hand due to large scale sea ice melting leads to decrease of density in the spg and contributes terminating the model amoc amv events all together the combined effects of nao and eap their intertwined seasonal forcing forced role upon by the ocean and the primary role of salinity anomalies associated with oceanic dynamical changes acting as an integrator are responsible in cnrm cm5 for an irregular and damped mode of variability for amoc amv that takes about 35 40 15 20 years to build up dissipate

channel incision evolution and potential recovery in the walla walla and tucannon river basins northwestern usa we evaluated controls on locations of channel incision variation in channel evolution pathways and the time required to reconnect incised channels to their historical floodplains in the walla walla and tucannon river basins northwestern usa controls on incision locations are hierarchically nested a first order geological control defines locations of channels prone to incision and a second order control determines which of these channels are incised channels prone to incision are reaches with silt dominated valley fills which have sediment source areas dominated by loess deposits and channel slopes less than 0 1 area 0 45 among channels prone to incision channels below a second slope area threshold slope 0 15 area 0 8 did not incise once incised channels follow two different evolution models small deeply incised channels follow model i which is characterized by the absence of a significant widening phase following incision widening is limited by accumulation of bank failure deposits at the base of banks which reduces lateral channel migration larger channels follow model ii in which widening is followed by development of an inset floodplain and aggradation in contrast to patterns observed elsewhere we found the widest incised channels upstream of narrower reaches which reflects a downstream decrease in bed load supply based on literature values of floodplain aggradation rates we estimate recovery times for incised channels the time required to reconnect to the historical floodplain between 60 and 275 years restoration actions such as allowing modest beaver recolonization can decrease recovery time by 17 33 per cent published in 2007 by john wiley sons ltd

surface climate variations over the north atlantic ocean during winter 1900 1989 abstract the low frequency variability of the surface climate over the north atlantic during winter is described using 90 years of weather observations from the comprehensive ocean atmosphere data set results are based on empirical orthogonal function analysis of four components of the climate system sea surface temperature sst air temperature wind and sea level pressure an important mode of variability of the wintertime surface climate over the north atlantic during this century is characterized by a dipole pattern in ssts and surface air temperatures with anomalies of one sign cast of newfoundland and anomalies of the opposite polarity off the southeast coast of the united states wind fluctuations occur locally over the regions of large surface temperature anomalies with stronger than normal winds overlying cooler than normal ssts this mode exhibits variability on quasi decadal and biennial time scales the decadal fluctuations are irregular in length averaging 9 years before 1945 and 1

analytical solution of a model of contaminant transport in the advective zone of a river abstractan analytical solution of a model of contaminant transport in the advective zone of rivers is presented and evaluated an existing model that accounts for transport in the advective zone by dividing the channel into flowing and stagnant zones is solved with laplace transforms for the case of a gaussian pulse injected into the center of the channel the effects of the two main parameters of the model the fraction of the channel occupied by the stagnant zone and a transfer coefficient are consistent with expectations from the theory of shear dispersion another parameter which is related to the streamwise width of the initial pulse determines whether a separate pulse appears in the tracer response curves a procedure for determining the parameters from temporal moments of measured concentration curves is described and applied to measurements in the advective zone of a mountain stream predictions from the model of reichert and wanner fit the measurements especially the peak concentration better

surface wave forces acting on submerged logs drag forces exerted on cylindrical simulated logs by flowing water are measured in a laboratory flume drag coefficient values calculated from these data are presented for a range of log submergence and slenderness values drag coefficients for large submergence values are consistent with those previously published however at submergence values less than eight element diameters the observed drag coefficients are consistently higher than those previously published this discrepancy is due to the additional drag created by stationary surface waves which causes the drag coefficient to increase considerably when a log is positioned near the free surface this phenomenon which has not been accounted for in previous studies on large woody debris is shown to depend on log slenderness submergence and froude number

flow turbulence and drag associated with engineered log jams in a fixed bed experimental channel abstract engineered log jams eljs have become attractive alternatives for river restoration and bank stabilization programs yet the effects of eljs on turbulent flow and the fluid forces acting on the eljs are not well known and such information could inform design criteria in this study a fixed bed physical model was constructed to assess the introduction of eljs along the big sioux river sd two elj types were examined referred to as elj 1 and elj 2 both types were deflector jams where elj 1 was rectangular and elj 2 was triangular and oriented with one side attached to the channel bank they were deployed either as single structures or in groups of two or three on the same side of the channel and at different separation distances results show that 1 time mean and turbulent velocities and bed shear stresses were measurably altered near the elj but spatially averaged flow just upstream and downstream of the structure was unaffected 2 streamwise drag forces measured for the eljs were significantly larger than the transverse forces and the derived drag coefficients for the single structures were 2 72 0 19 for elj 1 and 1 60 0 37 for elj 2 and 3 the presence of an upstream structure created a near bank wake region that extended a distance of more than 30 flow depths downstream which greatly reduced drag forces and drag coefficients observed for the downstream structure by as much as 80 these observations are further evidence of the efficacy of eljs in providing near structure scour pool development and bank protection downstream and they can be used to inform and assess the design of eljs for use in river restoration and bank stabilization projects

roughness effects on flow and shear stress near outside bank of curved channel velocity and turbulence distributions are measured in a 270 curved open channel of half trapezoidal section with extra roughness applied to the outside bank slope the purpose of this investigation is to provide some understanding of flow mechanics that may be useful in the design of riprap protection profile averaged velocity and bed shear velocity distributions are calculated a significant variation of bed shear up the slope and a much higher stress near the toe of the slope are found for the roughened outside bank slope it is found that a reasonable correlation of the velocity and bed shear stress on the bank is given by a form of the colebrook equation lateral momentum transfer by secondary flow and turbulent stress are also evaluated and found to be significant in the bank vicinity

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

mediated equilibrium the influence of riparian vegetation and wood on the long term evolution and behaviour of a near pristine river analysis of the contemporary geomorphology vegetation and in channel wood within the relatively pristine thurra river in southeastern australia provides insight into river behaviour prior to european disturbance this sand bed river has an extremely low channel capacity with a pronounced pool riffle morphology lateral migration rates are low 11 24 mm a 1 as are floodplain aggradation rates average d 0 27 mm a 1 sedimentological evidence is used to place contemporary channel dynamics within a 16 ka evolutionary framework the floodplain has continuously aggraded over this interval despite a number of avulsions and numerous meander cutoffs avulsions occur on a timeframe of once in 5 ka or more while cutoffs occur around once in 1 ka the morphology and evolution of the thurra river are appraised in terms of a mediated equilibrium condition in which channel capacity hydraulics bedload transport rates bank erosion rates and in channel deposition are substantially influenced by vegetation and wood within the channel and on the floodplain copyright 2002 john wiley sons ltd

hydrologic and geoenvironmental characterization of wetlands in quarries of the vinalopo mitja alicante spain this paper deals with the environmental characterization of the collao de candela enclave alicante se spain which in the early 1980s reported strong mining activity mainly due to the extraction of marls the subsequent abandonment of such quarries produces floods in depressed areas that are constituted as pools these anthropogenic wetlands are the object of this research in order to characterize the geometry of the studied wetlands a bathymetry was carried out bathymetric data are very important for water managers tasked with assessing wetlands status a chemical and mineralogical characterization has been carried out on the lithologies in the study area a study was also conducted of the physical and chemical parameters of the waters contained in these pools during one hydrologic cycle the climate of the zone having elevated evapotranspiration measurements favors a progressive concentration of salts in the pools consequence of runoff water washing the evaporitic sediments as well as from elevated evaporation the results obtained justify the environmental protection of these marl gypsum mining quarries as potential wetlands

pools channel form and sediment storage in wood restored streams potential effects on downstream reservoirs abstract large wood lw or pieces of dead wood longer than 1 m and thicker than 10 cm in diameter is a key element in forested streams but its abundance has decreased worldwide as a result of snagging and clearing of riparian forests therefore many restoration projects introduce lw into stream channels to enhance geomorphology biotic communities and ecosystem functioning because lw enhances the retention of organic matter and sediments its restoration can reduce siltation in receiving reservoirs although so far little information on this subject is available we studied the effects of restoring the natural loading of lw in four streams in the aiako harria natural park the basque country spain in pool abundance channel form and storage of organic matter and sediments in all reaches log jams induced the formation of new geomorphic features and changes in physical habitat especially an increase in the number and size of pools and in the formation of gravel bars and organic deposits the storage of organic matter increased 5 to 88 fold and streambed level rose 7 4 to 21 4 cm on average resulting in the storage of 35 2 19 7 to 711 375 m 3 733 1400 m 3 ha 1 y 1 of sediment per reach extrapolation of these results to the entire drainage basin suggests that basinwide restoration of lw loading would enhance the retention potential of stream channels by 66 817 27 804 m 3 1075 m 3 ha 1 y 1 of sediment and by 361 t 5 32 t ha 1 y 1 of organic matter which represents 60 of the estimated annual inputs of sediments to the downstream anarbe reservoir and almost twice as much as the annual input of organic matter to the entire river network therefore basinwide restoration of lw loading is a potentially important tool to manage catchments that feed reservoirs where retention of sediments and organic matter can be considered important ecosystem services as they reduce reservoir siltation

where and how long ago was water in the western north atlantic ventilated maximum entropy inversions of bottle data from woce line a20 1 a maximum entropy me method is used to deconvolve tracer data for the joint distribution of locations and times since last ventilation the deconvolutions utilize world ocean circulation experiment line a20 repeat hydrography for cfc 11 potential temperature salinity oxygen and phosphate as well as global ocean data analysis project glodap radiocarbon data combined with surface boundary conditions derived from the atmospheric history of cfc 11 and the world ocean atlas 2005 and glodap databases because of the limited number of available tracers the deconvolutions are highly underdetermined leading to large entropic uncertainties which are quantified using the information entropy of relative to a prior distribution additional uncertainties resulting from data sparsity are estimated using a monte carlo approach and found to be of secondary importance the me deconvolutions objectively identify key water mass formation regions and quantify the local fraction of water of age or older last ventilated in each region ideal mean age and radiocarbon age are also estimated but found to have large entropic uncertainties that can be attributed to uncertainties in the partitioning of a given water parcel according to where it was last ventilated labrador irminger seawater l water is determined to be mostly less than 40 a old in the vicinity of the deep western boundary current dwbc at the northern end of a20 but several decades older where the dwbc recrosses the section further south pointing to the importance of mixing via a multitude of eddy diffusive paths overflow water lies primarily below l water with young waters 40 a at middepth in the northern part of a20 and waters as old as 600 a below 3500 m

flow near sloped bank in curved channel shear and velocity distributions near a sloped bank in a 270 open channel bend are studied data which include detailed velocity and turbulence measurements in both the longitudinal and transverse flow directions are collected with a laser doppler anemometer system the flow adjacent to a 2 1 horizontal vertical and a 3 1 sloped bank is examined the purpose is to examine in unprecedented detail the developing flow near a sloped bank in a curved channel including the effect of varying side slope it is found that the longitudinal flow redistribution is fully developed at the downstream end of this 270 bend although the spiral flow is found to develop much more quickly in the straight reach upstream of the bend it is found that the friction factor on the sloped bank is more dependent on channel shape than a local velocity shear stress relationship within the bend velocities and shear stresses on the sloped bank increase significantly with the shear stress correlating more directly with the loc

calibration of a two dimensional finite element flood flow model using satellite radar imagery the application of numerical models of free surface flow to fluvial flood prediction is currently hampered by the lack of distributed calibration and validation data we address this shortcoming by the use of satellite borne synthetic aperture radar imagery to map a flood on a 15 km reach of the river thames england a finite element numerical model of shallow water flow is constructed over the reach and analysis shows that floodplain friction is the dominant factor affecting inundation extent when compared to channel friction turbulence parameterization and downstream boundary conditions the area of the domain correctly classified by the model is maximized with the constraint of uniform floodplain friction 77 at maximum compared with 70 for a simple planar model of the water free surface a simple distributed calibration scheme is also tested with a minor improvement over the uniform parameterization

origin of water salinity in a lake and coastal aquifer system the studied area is in the algerian northeast a number of interacting factors at the site are able to modify salinity the main influences are 1 the lithology 2 fedzara lake 3 marine waters and 4 a prolonged drought 1 the lithology is very clearly delineated by the outcrop of metamorphic formations gneiss marbles micaschists and quartzites and sedimentary formations limestones clay sandstones and sands all these formations can influence the chemical composition of waters 2 fedzara lake evacuates its salted waters via the wadi meboudja which connects with the wadi seybouse and the phreatic surface these lake waters might induce changes in salinity 3 the marine waters represent the third source of salinity change over pumping of water from wells and drillings can cause an imbalance to the fresh salted water interface 4 the effects of a local prolonged drought of more than 10 years may increase water salinity over pumping to augment water supply generates a fall in water levels and the drier atmosphere increases evapotranspiration both may contribute to increased salinity results of water analysis were used to observe the evolution of these various factors

processes and forms of an unstable alluvial system with resistant cohesive streambeds as a response to channelization projects undertaken near the turn of the 20th century and in the late 1960s upstream reaches and tributaries of the yalobusha river mississippi usa have been rejuvenated by upstream migrating knickpoints sediment and woody vegetation delivered to the channels by mass failure of streambanks has been transported downstream to form a large sediment debris plug where the downstream end of the channelized reach joins an unmodified sinuous reach classification within a model of channel evolution and analysis of thalweg elevations and channel slopes indicates that downstream reaches have equilibrated but that upstream reaches are actively degrading the beds of degrading reaches are characterized by firm cohesive clays of two formations of palaeocene age the erodibility of these clay beds was determined with a jet test device and related to critical shear stresses and erosion rates repeated surveys indicated that knickpoint migration rates in these clays varied from 0 7 to 12 m a 1 and that these rates and migration processes are highly dependent upon the bed substrate resistant clay beds of the porters creek clay formation have restricted advancement of knickpoints in certain reaches and have caused a shift in channel adjustment processes towards bank failures and channel widening channel bank material accounts for at least 85 per cent of the material derived from the channel boundaries of the yalobusha river system strategies to reduce downstream flooding problems while preventing upstream erosion and land loss are being contemplated by action agencies one such proposal involves removal of the sediment debris plug bank stability analyses that account for pore water and confining pressures have been conducted for a range of hydrologic conditions to aid in predicting future channel response if the sediment debris plug is removed to improve downstream drainage care should be taken to provide sufficient time for drainage of groundwater from the channel banks so as not to induce accelerated bank failures published in 2002 john wiley sons ltd

morphological modelling of rivers with erodible banks a bank erosion mechanism and provisions to account for the associated planform changes and input of bank erosion products are added to a two dimensional depth averaged model of river morphology the model is applied to a reach of the meandering gravel bed river oh e eger in the former state of czechoslovakia the agreement with observations is poor but this can be ascribed to shortcomings in the flow and bed topography submodels rather than to shortcomings in the bank erosion submodel better results are expected when a three dimensional flow model equations for sediment mixtures and a bank accretion mechanism are included this inclusion will have to be preceded by fundamental research on bank accretion mechanisms and on hiding and exposure effects in the relationship for the influence of gravity pull on sediment transport direction 1998 john wiley sons ltd

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

assessment of flow forces on large wood in rivers 1 large wood lw exerts an important influence on the geomorphology and ecology of streams and rivers the magnitudes of flow forces on lw are needed to support stream management activities and are typically computed using time mean lift and drag coefficients determined in laboratory flumes using small smooth cylinders herein we report measurements of forces on lw of varying complexity simple cylinder branching and complex root wad and surface bark roughness made in an outdoor grassed channel under steady and unsteady flows lw orientation relative to the primary flow direction and lw relative submergence were varied drag and lift coefficients for cylindrical unbranched lw followed patterns reported by others for metal cylinders in wind tunnels drag coefficients for cylindrical unbranched lw corrected for blockage effects ranged from 0 05 to 1 29 and lift coefficients ranged from 0 88 to 0 52 varying systematically with lw position relative to the channel bed and incident flow direction measured drag coefficients for the noncylindrical lw corrected for blockage effects ranged from 0 22 to 6 27 while lift coefficients varied from 3 65 to 30 84 systematic relationships between the relative submergence and orientation of branching lw and the drag and lift coefficients were not observed but coefficients were greatest for lw with few branches and converged on smaller values typical of blunt bodies as lw complexity increased for both simple and complex lw maximum lift and drag forces during the rising limb of unsteady flows were about 2 3 times greater than steady flow temporal mean values

eco hydrological role of deep aquifers in the salado sedimentary basin in the province of buenos aires argentina although not well known the eco hydrological functions of deep aquifers those having no contact with surface hydrological events play an important role in the hydrological regime because they can affect the type of habitats the availability of water and nutrients and the salinity of the medium among other environmental features this work aims at characterizing the deep tertiary hydrogeological units of the salado sedimentary basin in the province of buenos aires argentina at a regional scale and to determine their environmental importance in the hydrological cycle the geological characterization of the study area is based on the drilling profiles from oil exploration wells bored by different oil companies between 1948 and 1994 and also from the existing literature the conclusion is that water exchange between quaternary surface aquifers in contact with atmospheric events and deep tertiary aquifers is one of the main processes that keep the hydrologic balance of the region not only is this crucial for the conservation of the numerous and well developed ecosystems in the basin wetlands but also significant for the agricultural and cattle raising activities of the region

large woody debris structures for sand bed channels described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris this method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand in these types of environments buoyancy forces are typically more important factors in woody debris stability than fluid drag buoyant forces are counteracted by the weight of the structure earth anchors and sediment deposits design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37 km watershed large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention construction costs per unit channel length were 23 58 of costs for recent stone bank stabilization projects within the same region during the second year following construction 31 of the structures failed during high flows probably due to inadequate anchoring

3d numerical simulation for water flows and sediment deposition in dam areas of the three gorges project this paper presents a three dimensional 3d mathematical model for suspended load transport in turbulent flows based on the stochastic theory of turbulent flow proposed by dou numerical schemes of reynolds stresses for anisotropic turbulent flows are obtained instead of a logarithmic law a specific wall function is used to describe the velocity profile close to wall boundaries the equations for two dimensional suspended load motion and sorting of bed material have been improved for a 3d case numerical results are in good agreement with the measured data of the gezhouba project the present method has been employed to simulate sediment erosion and deposition in the vicinity of the three gorges dam the size distribution of the deposits and bed material and flow and sediment concentration at different times and elevations are predicted the results agree well with the observations in physical experiments thus a new method is established for 3d simulation of sediment motion in the vicinity of dams

prediction of effects of woody debris removal on flow resistance a simple technique for predicting the darcy weisbach friction factor for river channels with varying amounts of large woody debris was developed first debris density is determined based on measurement or visual estimation of cross sectional areas of debris formations in the plane perpendicular to flow the darcy weisbach friction factor is then computed using debris density channel geometry mean flow velocity and the debris drag coefficient the debris drag coefficient may be computed fom a power function with experimentally determined coefficients for verification of the proposed procedure debris density and friction factors were measured in river reaches in western tennessee and southeastern new south wales australia friction factors computed using the procedure were within 30 of measured values for straight sand bed reaches and within 38 of measured values for sinuous gravel bed reaches the computational procedure explained 84 of the variance in observed values

main flow velocity in short river bends results of a mathematical model for the depth averaged main flow velocity in shallow river bends are compared with measurements in two consecutive sharply curved short bends in the river dommel the netherlands the computed main velocity distribution agrees rather well with the measured one in the larger part of each bend near the bend exits however deviations occur which indicate that secondary flow convection should be included in the mathematical model also the present model is used to verify some qualitative explanations for the skewing of the main velocity distribution towards the inner bank in the first part of a bend outwards further downstream and to show the effect of flow stage variations on the streamline pattern

woody vegetation and channel morphogenesis in low gradient gravel bed streams in the ozark plateaus missouri and arkansas woody vegetation affects channel morphogenesis in ozark streams of missouri and arkansas by increasing local roughness increasing bank strength providing sedimentation sites and creating obstructions to flow variations in physiographic controls on channel morphology result in systematic changes in vegetation patterns and geomorphic functions with increasing drainage basin area in upstream reaches streams have abundant bedrock control and bank heights that typically are less than or equal to the rooting depth of trees in downstream reaches where valleys are wider and alluvial banks are higher vegetation has different geomorphic functions at drainage areas of greater than 100 200 km2 ozarks streams are characterized by longitudinally juxtaposed reaches of high and low lateral channel migration rates referred to as disturbance reaches and stable reaches respectively whereas stable reaches can develop stable forested floodplains if they are not farmed disturbance reaches are characterized by dynamic vegetation communities that interact with erosion and deposition processes disturbance reaches can be subdivided into low gradient and high gradient longitudinal zones low energy zones are characterized by incremental unidirectional lateral channel migration and deposition of gravel and sand bars the bars are characterized by prominent bands of woody vegetation and ridge and swale topography channel monitoring data indicate that densely vegetated bands of woody vegetation formed depositional sites during bedload transporting events the same floods caused up to 20 m of erosion of adjacent cutbanks scoured non vegetated areas between vegetation bands and increased thalweg depth and definition in high energy or riffle zones channel movement is dominantly by avulsion in these zones vegetation creates areas of erosional resistance that become temporary islands as the channel avulses around or through them woody vegetation on islands creates steep root defended banks that contribute to narrow channels with high velocities calculation of hydraulic roughness from density and average diameter of woody vegetation groups of different ages indicates that flow resistance provided by vegetation decreases systematically with group age mainly through decreasing stem density if all other factors remain constant the stabilizing effect of a group of woody vegetation on a gravel bar decreases with vegetation age

characteristics distribution and geomorphic role of large woody debris in a mountain stream of the chilean andes the paper presents an analysis of amounts characteristics and morphological impact of large woody debris lwd in the tres arroyos stream draining an old growth forested basin 9 1 km2 of the chilean southern andes large woody debris has been surveyed along a 1 5 km long channel section with an average slope of 0 07 and a general step pool cascade morphology specific wood storage is very high 656 710 m3 ha 1 comparable to that recorded in old growth forested basins in the pacific northwest half of the lwd elements were located on the active floodplain and around two thirds of lwd elements were found in accumulations different types of log jam were observed some heavily altering channel morphology log steps and valley jams while others just line the channel edges bankfull bench jams log steps represent approximately 22 of all steps whereas the elevation loss due to lwd log steps and valley jams results in 27 loss of the total stream potential energy about 1600 m3 of sediment is stored in the main channel behind lwd structures corresponding to approximately 150 of the annual sediment yield copyright 2007 john wiley sons ltd

structure and hydraulics of natural woody debris jams 1 numerous studies exist on the hydraulics of woody debris jams and the mechanisms driving their geomorphic influence while most hydraulic studies treat jams as single solid objects jams are clearly not individual cylindrical logs but rather an accumulation of pieces ranging in size from leaves and twigs to entire trunks here we treat debris jams as complex and porous accumulations of heterogeneous material to understand the relative importance of the different size fractions comprising a jam we systematically dismantled three deflector debris jams in four stages removing a total of 17 783 individual wood pieces to experimentally manipulate jam porosity we measured the surrounding velocity shear stress and drag force fd the assumption of nonporosity can result in a 10 20 overestimation of fd back calculated values of the combined drag coefficient and frontal area term cdaf calc represented the drag characteristics of natural debris jams whereas separating frontal area af emp and drag coefficient cd contributions in natural jams is misleading values of cdaf calc for each jam at each stage of removal captured the effects of size and composition of the jam wood piece size in debris jams dictates the surface area to volume relationship this association in turn determines the rate at which fd and cdaf calc change with the addition of material only low porosity jams produce the geomorphic and hydraulic characteristics commonly associated with deflector jams our results on natural debris jams also illustrate the importance of employing variable wood size fractions when using woody debris jams for river restoration

interdecadal water mass changes in the southern ocean between 30 e and 160 e interdecadal water mass changes in the indian western pacific sectors of the southern ocean were investigated using the japanese antarctic research expeditions and historical hydrographic observations from the 1950s to 1990s freshening and cooling occurred on the neutral density surfaces of 27 0 kgm3 equatorward of sub antarctic front results for the area south of the polar front show warm and saline anomalies and oxygen decreases on the surfaces around 27 9 kgm3 which correspond to the upper circumpolar deep water these latter anomalies are most simply explained by the mixing of these shallow waters with warmer and fresher surface waters steric sea level has also increased with an average change of 1mmyr1 from the 1970s to 1990s the changes are larger north of the sub antarctic front implying a strengthening of the antarctic circumpolar current it appears that the observed changes are consistent with the results from coupled climate model results for a similar period

north atlantic oceanic decadal variability in the hadley centre coupled model the hadley centre coupled model is used to investigate the relationship between the north atlantic oscillation nao labrador sea deep convection and sea surface temperature variability it is shown that the model is capable of simulating many features of the observed variability in particular the model reproduces the observed relationship between decadal variations in labrador sea convection and the nao it also has surface temperature anomalies that propagate along the path of the north atlantic current nac with a timescale close to that of observed anomalies a number of sensitivity experiments are performed with the coupled model to understand the underlying mechanisms simulations in which the labrador sea convection is artificially enhanced and surpressed illustrate a time lagged impact on the nac and therefore on sea surface temperature in that region further simulations with a sinusoidal forcing of convection confirm the role of labrador sea water lsw in determining the timescale for propagation of the surface temperature anomalies the timescale of surface anomalies moving along the path of the nac is determined by the movement of lsw at intermediate depths

meander migration and the lateral tilting of floodplains the response of a meandering river to lateral tilting of the floodplain that supports the river is studied theoretically here the lateral direction is perpendicular to the overall direction of the river on the floodplain it is found that for most natural meandering rivers the river will migrate down the tilt direction to a lower elevation however the theory also shows that under some conditions especially when the froude number of the flow in the channel is very small the river migration is biased in the opposite direction two major contributions to the response of the river to lateral tilting identified in the theory are 1 perturbation of the cross section averaged flow velocities and 2 modification of the near bank flow velocity variation along the channel the theory is one of the first attempts to develop a quantitative understanding of the effects of floodplain tilting on meandering rivers and it provides a framework for future studies

modulation of outer bank erosion by slump blocks disentangling the protective and destructive role of failed material on the three dimensional flow structure the three dimensional flow field near the banks of alluvial channels is the primary factor controlling rates of bank erosion although submerged slump blocks and associated large scale bank roughness elements have both previously been proposed to divert flow away from the bank direct observations of the interaction between eroded bank material and the 3 d flow field are lacking here we use observations from multibeam echo sounding terrestrial laser scanning and acoustic doppler current profiling to quantify for the first time the influence of submerged slump blocks on the near bank flow field in contrast to previous research emphasizing their influence on flow diversion away from the bank we show that slump blocks may also deflect flow onto the bank thereby increasing local shear stresses and rates of erosion we use our measurements to propose a conceptual model for how submerged slump blocks interact with the flow field to modulate bank erosion

a depth averaged two dimensional model for flow sediment transport and bed topography in curved channels with riparian vegetation 1 a depth averaged two dimensional numerical model has been developed to simulate flow sediment transport and bed topography in river channels with emergent and submerged rigid vegetation and large woody debris the effect of helical flow in bends is considered by adopting an algebraic model for the dispersion terms in the depth averaged two dimensional momentum and suspended sediment transport equations and by adjusting the bed load transport angle the governing equations are discretized using the finite volume method on a nonstaggered curvilinear grid model validity has been assessed using experimental data observed in both fixed and movable bed laboratory flumes and a natural channel with submerged and emergent rigid vegetation in general mean flow velocities sediment transport rates and changes in bed topography predicted by the model agree well with the experimental observations for laboratory and field cases root mean square relative errors for velocities were less than about 13 and 44 respectively and about 50 of errors for changes in bed topography were less than 14 5 and 8 of the flow depth respectively

on the link between the two modes of the ocean thermohaline circulation and the formation of global scale water masses a close link between the formation of global scale water masses such as north atlantic deep water nadw and antarctic intermediate water aaiw and two stable modes of the thermohaline circulation thc is investigated in a coupled model in the upper 2 3 km of the atlantic the thc modes are characterized by meridional overturning circulations of opposite sign with either a dominance of the aaiw cell over the nadw cell off thc mode or vice versa on thc mode a transition between these thc modes is controlled by the relationship between the densities in the source regions of formation of aaiw and nadw water masses this is shown by applying a freshwater perturbation in the region of enhanced aaiw formation in the southern ocean to obtain a hysteresis loop of the nadw circulation transitions between the two modes of the thc occur when the densities in the source regions of aaiw and nadw become comparable to each other

multidecadal warming and shoaling of antarctic intermediate water antarctic intermediate water aaiw is a dominant southern hemisphere water mass that spreads from its formation regions just north of the antarctic circumpolar current acc to at least 20 s in all oceans this study uses an isopycnal climatology constructed from argo conductivity temperature depth ctd profile data to define the current state of the aaiw salinity minimum its core and thence compute anomalies of aaiw core pressure potential temperature salinity and potential density since the mid 1970s from ship based ctd profiles the results are used to calculate maps of temporal property trends at the aaiw core where statistically significant strong circumpolar shoaling 30 50 dbar decade 1 warming 0 05 0 15 c decade 1 and density reductions up to 0 03 kg m 3 decade 1 are found these trends are strongest just north of the acc in the southeast pacific and atlantic oceans and decrease equatorward salinity trends are generally small with their sign varying regionally bottle data are used to extend the aaiw core potential temperature anomaly analysis back to 1925 in the atlantic and to 1960 elsewhere the modern warm aaiw core conditions appear largely unprecedented in the historical record biennially and zonally binned median aaiw core potential temperatures within each ocean basin are with the notable exception of the subtropical south atlantic in the 1950s 70s 0 2 1 c colder than modern values zonally averaged sea surface temperature anomalies around the aaiw formation latitudes in each ocean and sectoral southern annular mode indices are used to put the aaiw core property trends and variations into context

the geomorphic and ecological effectiveness of habitat rehabilitation works continuous measurement of scour and fill around large logs in sand bed streams abstract geomorphologists ecologists and engineers have all contributed to stream rehabilitation projects by predicting the physical effect of habitat restoration structures in this study we report the results of a stream rehabilitation project on the snowy river se australia that aims to improve fish habitat and facilitate migration associated with scour holes around large wood in the streambed whilst engineering models allow us to predict maximum scour the key management issue here was not the maximum scour depth but whether the holes persisted at a range of flows and if they were present when fish actually required them this led to the development of a new method to continuously monitor scour in a sand bed using a buried pressure transducer in this study we monitored fluctuations in the bed level below three large logs 1 m diameter on the snowy river each log had a different scour mechanism a plunge pool a horseshoe vortex analogous to a bridge pier and a submerged jet beneath the log the continuous monitoring demonstrated a complex relationship between discharge and pool scour the horseshoe vortex pool maintained a constant level whilst contrary to expectations both the plunge pool and the submerged jet pool gradually filled over the 12 months filling was associated with the average rise in flows in winter and occurred despite several freshes and discharge spikes the plunge pool showed the most variation with bed levels fluctuating by over 1 m a key factor in pool scour here may not be the local water depth at the log but the position of the log in relation to larger scale movements of sand waves in the stream these results question assumptions on the relative importance of small floods or channel maintenance flows that lead to beneficial scour around large wood in sand bed streams further the continuous measurement of scour and fill around the logs suggested the presence of pool scour holes would have met critical requirements for australian bass macquaria novemaculeata during the migration period whereas less frequent monitoring typical of rehabilitation trials would have suggested the contrary the results of this study have demonstrated that geomorphic effectiveness is not always synonymous with biological effectiveness whilst physical models emphasise extreme changes such as maximum scour the key biological issue is whether scour occurs at the critical time of the life cycle continuous measurement of sand levels is an example of a geomorphic technique that will help to develop models that predict biologically meaningful processes not just extremes

variability of the lower circumpolar deep water in drake passage 1926 2004 lower circumpolar deep water lcdw is an important component of the global overturning circulation as it upwells south of the antarctic circumpolar current acc renewing the ocean interior the lcdw also aids the transport of water properties between the major ocean basins the property variability of the lcdw salinity maximum layer was examined using 37 meridional sections across drake passage between 1926 2004 within the limits of experimental error and high frequency variability the core properties of this layer have remained constant between 1926 2004 a comparison of modern sections and the 1932 discovery ii cruise indicates that this observation may be true for lcdw throughout the southern ocean the significance of this result in terms of the observations of decadal changes in the southern ocean intermediate and mode waters is that these changes are most likely due to contemporary atmospheric forcing and not due to variations in the source water properties

changes in dissolved oxygen in the southern ocean with climate change 1 climate models predict that increasing greenhouse gases in the atmosphere will change our climate however the range of observations available to assess these model predictions is limited we have utilized an ocean biogeochemical model to project the impact of climate change on the oxygen cycle in the ocean and the air sea exchange of oxygen with climate change our model predicts an outgassing of oxygen from the ocean in the model the southern ocean is the region that displays the largest change in the air sea exchange of oxygen with climate change the reduced oxygen uptake in the southern ocean is dominated by a reduction in convective mixing and in the subduction rate of bottom water which decreases the amount of dissolved oxygen in the southern ocean our model results suggest that dissolved oxygen is sensitive to changes in southern ocean circulation revealing the potential to use dissolved oxygen to test model predictions of climate change from southern ocean observations collected 28 years a part we observed a decrease in dissolved oxygen that was consistent with model climate change simulation this provides credibility to the climate model predictions additional analysis and observations of dissolved oxygen are needed to substantiate our climate model simulations

antarctic intermediate water circulation in the tropical and subtropical south atlantic recent hydrographic data from the south atlantic ventilation experiment cruises and others are combined with historical data and used to map the isopycnal properties corresponding to the antarctic intermediate water aaiw in the atlantic ocean the low salinity of the aaiw extends eastward across the south atlantic just south of the equator 3 4 s evidence of a weak eastward flow just north of the equator 1 2 n is also shown lateral and vertical homogenization of properties in the aaiw is found at the equator between 2 s and 2 n there is no clear zonal gradient in salinity just along the equator these observations suggest enhanced mixing within the equatorial baroclinic deformation radius the south atlantic tropical gyre is shown to consist of the following three cells one cyclonic cell centered at about 7 s another centered at about 19 s in the west and 23 s in the east and one anticyclonic cell centered at about 13 s these cells are associated with a westward extension at 10 s of high salinity and low oxygen which originates in the eastern tropical south atlantic and a front in these properties at about 15 s in the west and about 20 s in the east

hooked and tubular coralline algae indicate seagrass beds associated to mediterranean messinian reefs poniente basin almeria se spain abstract abundant hooked and tubular crustose coralline algae cca record early messinian late miocene seagrass beds on the northern margin of the poniente basin in southeastern spain hooked and tubular shapes in cca result from their epiphytic growth over seagrass leaves and stems the lower messinian deposits consist of a thin retrograding subunit overlain by sigmoidal bed packages that prograded to the southwest at least 650 m from the basin margin seagrass deposits mainly occur as bivalve cca packstone to rudstone and cca floatstone seawards of a conglomerate facies belt in the retrograding subunit and downslope of coral reefs and serpulid packstone to rudstone in the prograding sigmoidal beds fragments of contorted foliose cca algal flakes some hooked or tubular are common components in the seagrass deposits they mainly belong to an unidentified species of mesophyllum like their present day counterparts the epiphytic cca grew attached to seagrass by the initial parts of their thalli and displayed unattached projections or open frameworks of contorted foliose plants in a few cases hooked cca occur attached to halimeda plates small benthic foraminiferal assemblages are further evidence of macrophyte vegetation hooked contorted foliose cca can be a helpful tool for the identification of ancient seagrass beds especially in mediterranean neogene and quaternary deposits in which foraminiferal taxa fully indicative of seagrass ecosystems are scarce

unobstructed and obstructed turbulent flow in gravel bed rivers an acoustic doppler velocimeter was used to characterize turbulence in two gravel bed rivers data were collected in unobstructed flow and compared to recent investigations additional data collected in the wake of emergent boulders indicate that mean flow velocity turbulent kinetic energy gradients in the streamwise velocity and reynolds stress downstream from large rocks deviate from unobstructed flow results but similar turbulence patterns are found behind each boulder results of this study are discussed with regard to natural channel design and fish habitat

holocene changes in antarctic intermediate water flow strength in the southwest atlantic abstract antarctic intermediate water aaiw is an essential component of the atlantic meridional overturning circulation amoc contributing to balance the southward flow of north atlantic deep water nadw however the role of aaiw in holocene abrupt climate changes remains poorly understood here we reconstruct changes in the flow strength of aaiw based on a high temporal resolution paleocurrent record from the southwest atlantic superimposed on a slight increase in aaiw strength at 7 ka bp a succession of millennial scale aaiw variations is recognized in our paleocurrent records indicating a highly variable intermediate water circulation throughout the holocene although variations in the strength and position of the southern westerlies winds sww are proposed to greatly influence the formation and circulation of aaiw we cannot confirm such a potential sww aaiw linkage since our records of aaiw flow strength do not correlate to holocene shifts of the sww across the atlantic however our data shows a good correspondence with abrupt variations in the amoc with enhanced reduced northward advection of aaiw during periods of reduced enhanced nadw circulation these results provide evidence for a holocene aaiw nadw see saw thus although the exact forcing mechanism remains unresolved we suggest that holocene perturbations in aaiw exerted a significant impact on the amoc

spatial density and characteristics of woody debris in five mountain rivers of the dolomites italian alps abstract this research quantifies amounts and characteristics of woody debris in mountain channels of the alps all pieces of woody debris greater than 5 cm diameter and 0 3 m length have been surveyed along five channels of the dolomites italian alps with channel slopes ranging from 0 04 to 0 26 basin area 2 2 51 km2 during the survey channels were divided into uniform reaches and the mean gradient bankfull width and depth of flow were measured overall 4900 woody debris pieces single and jam forming were measured and classified with respect to several qualitative attributes such as presence absence of rootwads orientation to flow and position in the channel results show that very large variations in the volume of woody debris per unit area of the streambed occur even within single streams and that inputs mainly result from slope instabilities adjacent to the channels amounts of woody debris are low compared to most previous data published from different world regions but match with other mountain rivers of the alps debris transport seems to be of minor importance compared to local inputs from the slopes because reach characteristics are poorly correlated with the volume of woody debris in a reach a strong negative correlation is however observed between basin area and average density of woody debris in the five channels but debris removal in the larger channels likely affects such a trend finally the frequency of log steps is inversely correlated to drainage area and positively related to the density of debris

bed surface adjustments to spatially variable flow in low relative submergence regimes in mountainous rivers large relatively immobile grains partly control the local and reach averaged flow hydraulics and sediment fluxes when the flow depth is similar to the size of these grains low relative submergence heterogeneous flow structures and plunging flow cause spatial distributions of bed surface elevations textures and sedimentation rates to explore how the bed surface responds to these flow variations we conducted a set of experiments in which we varied the relative submergence of staggered hemispheres simulated large boulders between runs all experiments had the same average sediment transport capacity upstream sediment supply and initial bed thickness and grain size distribution we combined our laboratory measurements with a 3d flow model to obtain the detailed flow structure around the hemispheres the local bed shear stress field displayed substantial variability and controlled the bedload transport rates and direction in which sediment moved the divergence in bed shear stress caused by the hemispheres promoted size selective bedload deposition which formed patches of coarse sediment upstream of the hemisphere sediment deposition caused a decrease in local bed shear stress which combined with the coarser grain size enhanced the stability of this patch the region downstream of the hemispheres was largely controlled by a recirculation zone and had little to no change in grain size bed elevation and bed shear stress the formation development and stability of sediment patches in mountain streams is controlled by the bed shear stress divergence and magnitude and direction of the local bed shear stress field

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

southwest pacific ocean water mass changes between 1968 69 and 1990 91 abstract water mass changes are estimated in the southwest pacific ocean by comparing a meridional hydrographic section along 170 w between 60 s and the equator occupied in 1968 69 during the southern cross cruise and again in 1990 during a noaa climate and global change cruise another comparison is made using a hydrographic section along 35 s between the date line and 169 w occupied in 1969 during usns eltanin cruise 40 and again in 1991 during a mapkiwi cruise the most robust change consists of cooling and freshening on isopycnals with peak differences exceeding 1 0 c 0 25 pss at the base of the subtropical thermocline the cooling and freshening starts above the stratification minimum of the subantarctic mode water and persists to below the salinity minimum of the antarctic intermediate water amplitudes are largest at 48 s near where these water masses subduct and decay toward 20 s near the axis of the subtropical gyre this change is likely the result of surface warming and or freshening

fluvial geomorphological analysis of the recruitment of large woody debris in the yalobusha river network central mississippi usa abstract the management of large woody debris lwd should be based on a rational assessment of its recruitment rate relative to its natural decay and removal lwd recruitment may be controlled by natural episodic terrestrial factors or by in channel geomorphological controls related to the rate of bank erosion the geomorphological controls are hard to quantify in laterally migrating channels but in incising channels a conceptual model may be developed based on the density of riparian trees relative to the knickpoint migration rate and bank stability analyses that predict the post knickpoint width of the channel the yalobusha river network in central mississippi usa has twice been destabilised by channel straightening for flood defence and land drainage most recently in 1967 system wide rejuvenation has followed through a series of upstream migrating knickpoints several metres high that have caused mass failure of streambanks and the recruitment of large volumes of trees to the channel lwd recruitment is maximised at the transition between stage iii and stage iv channels focusing attention on 11 sites in the network the sites are upstream of knickzones ranging between 2 2 and 5 4 m high and migrating at rates of 0 13 8 m year 1 based on 23 30 months of monitoring riparian conditions in 500 m2 plots on each bank upstream of the knickpoints range from treeless to forested containing 0 98 trees with an average diameter at breast height of 0 18 m and average maximum height of 14 0 m the average volume of wood on each bank is 0 02 m3 m 2 under rapid drawdown conditions bank stability analyses suggest that the channels will widen in amounts ranging from 1 8 to 31 5 m combined with the knickpoint migration rates riparian land losses are estimated to range from 8 0 to 433 8 m year 1 resulting in the recruitment of almost 28 m3 of wood or 100 trees annually from the 11 sites assuming this lwd recruitment rate a model is developed for the in situ potential for debris dam initiation and growth based on the ratio of tree height to channel width under current and post knickpoint conditions the annual delivery of large trees and the annual total of lwd recruitment by volume a longer term model is also developed based on knickpoint severity and vegetation density in upstream and headwater riparian zones of each tributary the 11 study sites are classified into groups with similar lwd management concerns based on these analyses the models developed in this research provide the first precise quantification of lwd recruitment according to geomorphological controls and standing vegetation and a rational assessment of its meaning but further research is required to improve the accuracy of such estimates

distorted froude scaled flume analysis of large woody debris this paper presents the results of a movable boundary distorted froude scaled hydraulic model based on abiaca creek a sand bedded channel in northern mississippi the model was used to examine the geomorphic and hydraulic impact of simplified large woody debris lwd elements the theory of physical scale models is discussed and the method used to construct the lwd test channel is developed the channel model had bed and banks moulded from 0 8 mm sand and flow conditions were just below the threshold of motion so that any sediment transport and channel adjustment were the result of the debris element dimensions and positions of lwd elements were determined using a debris jam classification model elements were attached to a dynamometer to measure element drag forces and channel adjustment was determined through detailed topographic surveys the fluid drag force on the elements decreased asymptotically over time as the channel boundary eroded around the elements due to locally increased boundary shear stress total time for geomorphic adjustment computed for the prototype channel at the q2 discharge discharge occurring once every two years on average was as short as 45 hours the size depth and position of scour holes bank erosion and bars created by flow acceleration past the elements were found to be related to element length and position within the channel cross section morphologies created by each debris element in the model channel were comparable with similar jams observed in the prototype channel published in 2001 john wiley sons ltd

properties of small instream wood as a logjam clogging agent implications for clogging dynamics based on wood density water content and depositional environment abstract in cooperation with large instream wood lw within logjams small instream wood sw can control downstream flux of sediment and particulate organic matter and can play an important role for stream ecosystems however information regarding the density and moisture content of sw which affects wood transport wood decay and mass loading is limited here we investigated the sw properties i e density under field conditions in situ density basic density volumetric water content and depositional environment of sw sampled from five logjams and their backwater areas in two headwater streams second and third order streams surrounded by mixed broadleaf conifer forests in western japan the in situ density ranged from 0 49 to 1 25 g cm 3 and pieces with densities 1 0 g cm 3 accounted for 45 of all samples additionally the in situ density of sw closely related to the volumetric water content r2 0 76 rather than the basic density as an index of solidity or decay condition of wood the sw that was partially submerged in water had a higher volumetric water content than sw exposed to air these results indicate that a nonfloating transport cannot be ignored as an important mechanism for sw movement and that in situ density depends not on the solidity of the wood but on water sorption by sw however waterlogged sw should be well decayed because it has a lower basic density than air exposed and sediment buried sw we conclude that the moisture conditions of the depositional environment can affect subsequent transport and decay processes of sw moreover most waterlogged and sediment buried sw because of its high in situ density 1 0 g cm 3 may contribute to clogging between the channel bed and lw that initiate a logjam during future movements

estimation of the bed shear stress in vegetated and bare channels with smooth beds the shear stress at the bed of a channel influences important benthic processes such as sediment transport several methods exist to estimate the bed shear stress in bare channels without vegetation but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production this study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds the model which is supported by measurements indicates that for both bare and vegetated channels with smooth beds within a viscous sublayer at the bed the viscous stress decreases linearly with increasing distance from the bed resulting in a parabolic velocity profile at the bed for bare channels the model describes the velocity profile in the overlap region of the law of the wall for emergent canopies of sufficient density frontal area per unit canopy volume a 4 3 m 1 the thickness of the linear stress layer is set by the stem diameter leading to a simple estimate for bed shear stress

predicting floodplain inundation raster based modelling versus the finite element approach we compare two approaches to modelling floodplain inundation a raster based approach which uses a relatively simple process representation with channel flows being resolved separately from the floodplain using either a kinematic or diffusive wave approximation and a finite element hydraulic model aiming to solve the full two dimensional shallow water equations a flood event on a short c 4 km reach of the upper river thames in the uk is simulated the models being validated against inundation extent as determined from satellite synthetic aperture radar sar imagery the unconstrained friction parameters are found through a calibration procedure where a measure of fit between predicted and observed shorelines is maximized the raster and finite element models offer similar levels of performance both classifying approximately 84 of the model domain correctly compared with 65 for a simple planar prediction of water surface elevation further discrimination between models is not possible given the errors in the validation data the simple raster based model is shown to have considerable advantages in terms of producing a straightforward calibration process and being robust with respect to channel specification copyright 2001 john wiley sons ltd

validation of a three dimensional numerical code in the simulation of pseudo natural meandering flows validation of a three dimensional finite volume code solving the navier stokes equations with the standard k epsilon turbulence model is conducted using a high quality and high spatial resolution data set the data set was collected from a large scale meandering channel with a self formed fixed bed and comprises detailed bed profiling and laser doppler anemometer velocity measurements comparisons of the computed primary and secondary velocities are made with those observed and it is found that the lateral momentum transfer is generally under predicted at the apices this results in the predicted position of the primary velocity maximum having a bias towards the channel center compared to the position where it has been measured using a simplified two zone roughness distribution whereby a separate roughness height was prescribed for the channel center and channel sides relative to a single distributed roughness height generally led to a slightly improved longitudinal velocity distribution the higher velocities were located nearer to the outside of the bend improving both the free surface calculation and scheme for discretization of the convection terms led to no appreciable difference in the computed velocity distributions a more detailed study involving turbulence measurements and bed form height distribution should discriminate whether using distributed roughness height is a precursor to using an anisotropic turbulence representation for the accurate prediction of three dimensional river flows

effects of bed forms and large protruding grains on near bed flow hydraulics in low relative submergence conditions in mountain rivers bedforms large relatively immobile grains and bed texture and topographic variability can significantly alter local and reach averaged flow characteristics the low relative submergence of large immobile grains causes highly three dimensional flow fields that may not be represented by traditional shear stress flow velocity and turbulence intensity equations to explore the influence of large protruding grains and bedforms on flow properties we conducted a set of experiments in which we varied the relative submergence while holding the sediment transport capacity and upstream sediment supply constant flow and bed measurements were conducted at the beginning and end of each experiment to account for the absence or presence of bedforms respectively detailed information on the flow was obtained by combining our measurements with a 3d numerical model commonly used velocity profile equations only performed well at the reach scale when shallow flow effects and the roughness length of the relatively mobile sediment were considered however at the local scale large deviations from these profiles were observed and simple methods to estimate the spatial distribution of near bed shear stresses are likely to be inaccurate zones of high turbulent kinetic energy occurred near the water surface and were largely controlled by the immobile grains and plunging flow the reach averaged shear stress did not correlate to depth or slope as commonly assumed but instead was controlled by the relative boulder submergence and degree of plunging flow for accurate flow predictions in mountain rivers the effects of bedforms and large boulders must be considered

the influence of geomorphology on large wood dynamics in a low gradient headwater stream understanding large wood dynamics is critical for a range of disciplines including flood risk management ecology and geomorphology despite the importance of wood in rivers our understanding of the mobility of large wood remains limited in this study individual pieces of large wood were tagged and surveyed over a 32 month period within a third and fourth order lowland forest river individual pieces of wood were found to be highly mobile with 75 of pieces moving during the survey period and a maximum transport distance of 5 6 km multivariate analyses of data from this study and two other published studies identified dimensionless wood length as the important factor in explaining likelihood of movement a length threshold of 2 5 channel widths is identified for near functional immobility with few pieces above this size moving in addition for this study wood type branching complexity location and dimensionless wood diameter were found to be important in determining mobility only for sinuous reaches with readily inundated floodplains where logjams persist over multiple years they were shown to be reworked with component pieces being transported away and replaced by newly trapped pieces the findings of this study have implications for river management and restoration the high mobility observed in this study demonstrates that only very large pieces of wood of length greater than 2 5 channel widths should be considered functionally immobile for pieces of wood of length less than the channel width the possibility of high rates of mobility and long transport distances should be anticipated

reach scale characterization of large woody debris in a low gradient midwestern u s a river system abstract addition of large woody debris lwd to rivers has increasingly become a popular stream restoration strategy particularly in river systems of the midwestern united states however our knowledge of lwd dynamics is mostly limited to high gradient montane river systems or coastal river systems the lwd related management of low gradient midwestern river systems is thus largely based on higher gradient analogs of lwd dynamics this research characterizes fluvial wood loads and investigates the relationships between fluvial wood channel morphology and sediment deposition in a relatively low gradient semiconfined alluvial river the lwd and channel morphology were surveyed at nine reaches along the big river in southeastern missouri to investigate those relationships in comparison to other regions wood loads in the big river are low 3 114 m 3 100 m relative to those of higher gradient river systems of the pacific northwest but high relative to lower gradient river systems of the eastern united states wood characteristics such as size and orientation suggest that the dominant lwd recruitment mechanism in the big river is bank erosion also ratios of wood geometry to channel geometry show that the big river maintains a relatively high wood transport capacity for most of its length although lwd creates sites for sediment storage the overall impact on reach scale sediment storage in the big river is low

bank and near bank processes in an incised channel abstract gravitational forces acting on in situ bank material act in concert with hydraulic forces at the bank toe to determine rates of bank erosion the interaction of these forces control streambank mechanics hydraulic forces exerted by flowing water on in situ bank toe material and failed cohesive material at the bank toe are often sufficient to entrain materials at relatively frequent flows and to maintain steep lower bank profiles seepage forces exerted on in situ bank material by groundwater downward infiltration of rainwater and lateral seepage of streamflow into and out of the bank are critical in determining bank strength data from a study site on goodwin creek ms usa clearly show the temporal variability of seepage forces and the lag time inherent in reductions in shear strength due to losses of matric suction and generation of positive pore water pressures negative pore water pressures matric suction have also been shown to increase the resistance of failed cohesive blocks to entrainment by fluid shear a stable bank can be transformed into an unstable bank during periods of prolonged rainfall through 1 increase in soil bulk unit specific weight 2 decrease or complete loss of matric suction and therefore apparent cohesion 3 generation of positive pore water pressures and therefore reduction or loss of frictional strength 4 entrainment of in situ and failed material at the bank toe and 5 loss of confining pressure during recession of stormflow hydrographs relatively small frequent flows during the winter have the ability to erode failed bank materials maintain oversteepened unstable bank surfaces and promote prolonged periods of bank retreat channel migration and high yields of fine grained sediment confining pressures provided by stormflow are not as significant in maintaining bank stability as the counteracting force of fluid shear on the bank toe which steepens the bank for example more than 2 m of bank retreat occurred during the study period at the research site on goodwin creek northern mississippi the loss of matric suction negative pore pressures due to infiltrating precipitation has been found to be as significant as the development of excess pore pressures in contributing to mass bank instability apparent cohesion friction angle soil bulk unit weight and moisture content were measured in situ matric suction was measured continuously in situ with a series of five pressure transducer tensiometers a bank failure algorithm which combines the mohr coulomb approach for saturated conditions and the fredlund modification for unsaturated conditions was developed for layered cohesive streambanks the resulting equation has been used successfully to investigate the role of matric suction positive pore water pressures and confining pressure for layered streambanks composed of cohesive materials

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

interaction of aquifer wetland in a zone of intensive agriculture the case of campo de dalias almeria se spain the campo de dalias almeria south eastern spain was the backdrop for the development of intensive agricultural activity during the 1970s due to the poor natural soil development the agriculturalists opted for a system that involved quarrying silt and clay deposits that could be used as soil in the greenhouses in parallel poor water quality in the upper aquifer caused the gradual abandonment of boreholes and a generalised rise in piezometric levels these factors have favoured the formation of a series of artificial wetlands in the abandoned clay pits onayar cabriles and balsa del sapo toad pond being the most significant in balsa del sapo the water column rose 3 5 m between october 2007 and february 2011 there has been a continuous fall in the electrical conductivity of the surface water which has gone from 14 500 s cm 1 in 2004 to 4 100 s cm 1 in 2013 the most recent concentrations are close to those found in the groundwater the same situation is detected for cl so4 and na ion concentrations in the surface and groundwater these data show the groundwater surface water interaction in the balsa del sapo nevertheless the sharp rise in surface water level has created a flood hazard due to the shallow topography of the area both for people living in the vicinity and their property this is an endorheic zone where a number of ramblas gullies draining the southern face of the sierra de gador mountains converge the campo de dalias is a spectacular example of the changes that can occur in a semiarid agricultural area as a result of intensive groundwater abstraction these changes are directly related to the management of water resources the most recent consequence of which is the increased risk of flooding hence there is a need to consider the management of these water resources to achieve a more sustainable use which is compatible with the environmental protection of the wetland and which will give some guarantee of flood protection for people and property

resistance equation for large scale roughness a theory of flow resistance for large scale roughness is developed the main points of which are supported by a flume study from which the outline of a process based resistance equation is determined rivers with large scale roughness have steep slopes and depths of the same order of magnitude as the bed material size flow resistance depends on the form drag of the roughness elements and their disposition in the channel theoretical considerations show resistance to be a function of reynolds number froude number roughness geometry and channel geometry these processes are examined using the results of flume experiments based on five different roughness beds and a wide range of flows semi empirical analysis supports the theory and allows the development of a theoretical power law resistance equation which accounts for most of the processes a summary of the data is presented for use in other research studies

response of the antarctic circumpolar current to atmospheric variability abstract historical hydrographic profiles combined with recent argo profiles are used to obtain an estimate of the mean geostrophic circulation in the southern ocean thirteen years of altimetric sea level anomaly data are then added to reconstruct the time variable sea level and this new dataset is analyzed to identify and monitor the position of the two main fronts of the antarctic circumpolar current acc during the period 1993 2005 the authors relate their movements to the two main atmospheric climate modes of the southern hemisphere the southern annular mode sam and the el nino southern oscillation enso the study finds that although the fronts are steered by the bathymetry which sets their mean pathway on first order in flat bottom areas the fronts are subject to large meandering because of mesoscale activity and atmospheric forcing while the dominant mode of atmospheric variability in the southern hemisphere sam is relatively symmetric the oceanic response of the fronts is not show

estimates of the regional distribution of sea level rise over the 1950 2000 period abstract topex poseidon satellite altimeter data are used to estimate global empirical orthogonal functions that are then combined with historical tide gauge data to estimate monthly distributions of large scale sea level variability and change over the period 1950 2000 the reconstruction is an attempt to narrow the current broad range of sea level rise estimates to identify any pattern of regional sea level rise and to determine any variation in the rate of sea level rise over the 51 yr period the computed rate of global averaged sea level rise from the reconstructed monthly time series is 1 8 0 3 mm yr 1 with the decadal variability in the computed global mean sea level it is not possible to detect a significant increase in the rate of sea level rise over the period 1950 2000 a regional pattern of sea level rise is identified the maximum sea level rise is in the eastern off equatorial pacific and there is a minimum along the equator in the western pacific and in the eastern indian ocean a g

relation between mean and maximum velocities in a natural river the cross sectional mean velocity is an important variable in open channel hydraulics whereas the maximum velocity in a channel cross section is mentioned very little however the maximum velocity in a channel cross section might be as important as the cross sectional mean velocity this is because the measurable maximum velocity can be considered as a signal from which one can know the range of the velocity in a channel cross section this study explored the relation between the cross sectional mean and maximum velocities in a natural river by using velocity data collected from the mississippi river the relation of the maximum velocity to the cross sectional mean velocity on different straight reaches in the mississippi river is perfectly linear the relation of the maximum velocity to the cross sectional mean velocity on different river bends is still linear and changes with the rc b value slightly the conclusions are preliminary because of the limited amount of data

the effect of a northward shift in the southern hemisphere westerlies on the global ocean we examine the effect of a northward shift in the position of the southern hemisphere subpolar westerly winds swws on the vertical and horizontal distribution of temperature and salinity in the world ocean a northward shift of the swws causes a latitudinal contraction of the subpolar gyres in the southern hemisphere sh in the indian and pacific this leads to subsurface warming in the subtropical thermocline as the southern margins of the gyres move into latitudes characterised by warmer surface air temperature sat the layers at mid depth below 400 m depth become ventilated by warmer water we characterize the approximation of the ventilated thermocline in our coarse resolution model using a set of passive tracer experiments and illustrate how the northward shift in the swws causes an equatorward shift in the latitude of origin of water ventilating layers deeper than 400 m in the indian and pacific leaving the total surface ventilation of the upper 1200 m unchanged in contrast the latitudinal constraint on the antarctic circumpolar current posed by the drake passage causes a cooling and freshening throughout the atlantic thermocline here subsurface thermocline water originates from higher latitudes under the wind shift on longer timescales atlantic cooling and freshening is reinforced by a reduction in north atlantic deep water nadw formation and surface salinification of the indian and pacific oceans in effect the latitude of zero wind stress curl in the swws regulates the relative importance of the cold water route via the drake passage and the warm water route associated with thermocline water exchange via the indian ocean thus a more northward location of the swws corresponds with a reduced salinity contrast between the indian pacific oceans and the atlantic this results in reduced nadw formation also a more northward location of the swws facilitates the injection of cool fresh antarctic intermediate water into the south atlantic subtropical gyre beyond these changes on a millennial timescale the deep ocean warms throughout the water column in response to the wind shift global salinity stratification also becomes less stable as more saline water remains at the surface and accumulates in the indian and pacific thermocline the freshening of the deep ocean reflects a reduced stirring of the global ocean due to reduced net circulation arising from a misalignment between the westerlies and the topographically constrained acc our results lend support to the idea that a more equatorward location of the sww maximum during glacial climates contributed to cooler and fresher conditions in the atlantic inhibiting nadw

faulted hybrid joints an example from the campo de dalias betic cordilleras spain abstract the development of hybrid and faulted joints has not been studied in detail in natural outcrops this field study in the campo de dalias betic cordilleras establishes the distinctive features of these structures as compared with those predicted by theoretical studies hybrid joints appear as two sets of vertical joints forming variable angles but generally about 25 with opening directions orthogonal to joint planes their development requires low differential stresses with a tensile minimum stress the main criteria that indicate the existence of faulted joints are 1 the presence of subvertical fault planes with oblique slip forming a complex pattern of dextral and sinistral faults developed under a single stress regime 2 faults with similar geometries as joints in the same outcrop showing an inconsistent cross cutting relationship and 3 the development of small basins with variable polarity of asymmetric wedge filling a permutation in stress orientation since the tortonian in the campo de dalias was responsible for the development of a faulted hybrid joint system with a constant ene wsw extension trend and a switch of 1 between nnw sse and vertical

hydraulic evaluation of w weir for river restoration various structural measures have been advocated for river restoration and habitat improvement schemes the w weir is one such structure that can be used in mobile bed alluvial rivers to diversify habitat and provide grade control laboratory studies have been carried out in a large scale meandering channel with a mobile bed to investigate their effects on flow and sediment transport processes a w weir placed immediately downstream of a riffle section created a strongly three dimensional flow pattern and high turbulence zones two adjacent scour holes of different depths and substrate are formed under clearwater and live bed conditions the continuity of sediment transport along the channel was not interrupted by the structure and the upstream afflux is minimal overbank flow significantly influenced the action of the weir and the scour hole was shifted closer to the structure in a relatively tight bend followed by a short crossover reach the weir may affect bed load transport pathways in the downstream bend finally the study provides insights to guide their design for restoration projects

an anomalous recent acceleration of global sea level rise abstract tide gauge data are used to estimate trends in global sea level for the period from 1955 to 2007 linear trends over 15 yr segments are computed for each tide gauge record averaged over latitude bands and combined to form an area weighted global mean trend the uncertainty of the global trend is specified as a sampling error plus a random vertical land motion component but land motion corrections do not change the results the average global sea level trend for the time segments centered on 1962 90 is 1 5 0 5 mm yr 1 standard error in agreement with previous estimates of late twentieth century sea level rise after 1990 the global trend increases to the most recent rate of 3 2 0 4 mm yr 1 matching estimates obtained from satellite altimetry the acceleration is distinct from decadal variations in global sea level that have been reported in previous studies increased rates in the tropical and southern oceans primarily account for the acceleration the timing of the global acceleration

flow and grainsize pattern in a sharply curved river bend the main characteristics of river flow and grainsize in a bend of the sand bedded meandering river dommel the netherlands are presented measurements were carried out at a relatively low discharge in a sharply curved bend following a long straight reach in the studied bend secondary circulation is restricted to the thalweg area only in the downstream part of the bend it exists over the entire cross section therefore on the entire pointbar platform which comprises the larger part of the bend the median sedimentation diameter of the bedload material is governed by the distribution of the longitudinal components of the bed shear stress only

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

north atlantic climate responses to perturbations in antarctic intermediate water recent observations suggest antarctic intermediate water aaiw properties are changing the impact of such variations is explored using idealised perturbation experiments with a coupled climate model hadcm3 aaiw properties are altered between 10 and 20 s in the south atlantic maintaining constant potential density the perturbed aaiw remains subsurface in the south atlantic but as it moves northwards it surfaces and interacts with the atmosphere leading to density anomalies due to heat exchanges for a cooler fresher aaiw there is a significant decrease in the mean north atlantic sea surface temperature sst of up to 1 c during years 51 100 in the north atlantic current region there are persistent cold anomalies from 2 000 m depth to the surface and in the overlying atmosphere atmospheric surface pressure increases over the mid latitude atlantic and precipitation decreases over northwest africa and southwest europe surface heat flux anomalies show that these impacts are caused by changes in the ocean rather than atmospheric forcing the sst response is associated with significant changes in the atlantic meridional overturning circulation moc after 50 years there is a decrease in the moc that persists for the remainder of the simulation resulting from changes in the column averaged density difference between 30 s and 60 n rather than showing a linear response a warmer saltier aaiw also leads to a decreased moc strength for years 51 100 and resulting cooling in the north atlantic the non linearity can be attributed to opposing density responses as the perturbed water masses interact with the atmosphere

temporal variability of the atlantic meridional overturning circulation at 26 5 n the vigor of atlantic meridional overturning circulation moc is thought to be vulnerable to global warming but its short term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain we combine continuous measurements of the moc beginning in 2004 using the purposefully designed transatlantic rapid climate change array of moored instruments deployed along 26 5 n with time series of gulf stream transport and surface layer ekman transport to quantify its intra annual variability the year long average overturning is 18 7 5 6 sverdrups sv range 4 0 to 34 9 sv where 1 sv a flow of ocean water of 106 cubic meters per second interannual changes in the overturning can be monitored with a resolution of 1 5 sv

rules of the road a qualitative and quantitative synthesis of large wood transport through drainage networks abstract to effectively manage wood in rivers we need a better understanding of wood mobility within river networks here we review primarily field based and some numerical studies of wood transport we distinguish small medium large and great rivers based on wood piece dimensions relative to channel and flow dimensions and dominant controls on wood transport we suggest further identification and designation of wood transport regimes as a useful way to characterize spatial temporal network heterogeneity and to conceptualize the primary controls on wood mobility in diverse river segments we draw analogies between wood and bedload transport including distinguishing eulerian and lagrangian approaches exploring transport capacity and quantifying thresholds of wood mobility we identify mobility envelopes for remobilization of wood with relation to increasing peak discharges stream size and dimensionless log lengths wood transport in natural channels exhibits high spatial and temporal variability with discontinuities along the channel network at bankfull flow and when log lengths equal channel widths although median mobilization rates increase with increasing channel size maximum mobilization rates are greatest in medium sized channels most wood is transported during relatively infrequent high flows but flows under bankfull can transport up to 30 of stored wood we use conceptual models of dynamic equilibrium of wood in storage and of spiralling wood transport paths through drainage networks as well as a metaphor of traffic on a road to explore discontinuous wood movement through a river network the primary limitations to describing wood transport are inappropriate time scales of observation and lack of sufficient data on mobility from diverse rivers improving models of wood flux requires better characterization of average step lengths within the lifetime travel path of a piece of wood we suggest that future studies focus on i continuous or high frequency monitoring of wood mobility ii monitoring changes in wood storage iii using wood characteristics to fingerprint wood sources iv quantifying volumes of wood buried within river corridors v obtaining existing or new data from unconventional sources such as citizen science initiatives and vi creating online interactive data platforms to facilitate data synthesis

velocity redistribution in curved rectangular channels the main velocity redistribution in steady flow through curved conduits of shallow rectangular cross section is considered its mechanism is analysed using a mathematical model of steady incompressible laminar flow in coiled rectangular pipes the transverse transport of main flow momentum by the secondary circulation is shown to be the principal cause of this velocity redistribution the importance of the side wall regions even in shallow channels is assessed and the neglect of the influence of the side walls in the commonly applied simplified models of flow through shallow curved channels is shown to be strongly limiting in case of long bends with a rectangular cross section

characterising flow regime and interrelation between surface water and ground water in the fuente de piedra salt lake basin by means of stable isotopes hydrogeochemical and hydraulic data summary this research reports the characterisation of ground and surface water interaction in the fuente de piedra salt lake basin in southern spain by a combined approach using hydraulic hydrogeochemical and stable isotope data during three sampling campaigns february 2004 2005 and october 2005 ground and surface water samples were collected for stable isotope studies 18 o d and for major and minor ion analysis hydraulic measurements at multilevel piezometers were carried out at four different locations around the lake edge conductivity logs were performed at four piezometers located along a profile at the northern lake border and at two deeper piezometers in the miocene basin at a greater distance from the lake to describe processes that control the brine evolution different hydrogeochemical simulations were performed hydrogeochemical data show a variety of brines related to thickness variations of lacustrine evaporites around the lake salinity profiles in combination with stable isotope and hydraulic data indicate the existence of convection cells and recycled brines furthermore restricted ground water inflow into the lake was detected dedolomitisation processes were identified by hydrogeochemical simulations and different brine origins were reproduced by inverse modelling approaches