spatial patterns of hyporheic exchange and biogeochemical cycling around cross vane restoration structures implications for stream restoration design 1 natural channel design restoration projects in streams often include the construction of cross vanes which are stone dam like structures that span the active channel vertical hyporheic exchange flux hef and redox sensitive solutes were measured in the streambed around four cross vanes with different morphologies observed patterns of hef and redox conditions are not dominated by a single downstream directed hyporheic flow cell beneath cross vanes instead spatial patterns of moderate 0 4 m d 1 upwelling and downwelling are distributed in smaller cells around pool and riffle bed forms upstream and downstream of structures patterns of biogeochemical cycling are controlled by dissolved oxygen concentrations and resulting redox conditions and are also oriented around secondary bed forms strong downwelling into the hyporheic zone 0 5 3 5 m d 1 was observed immediately upstream of structures but was limited to an area 1 2 m from the cross vane these hyporheic flow paths likely rejoin the stream at the base of cross vanes after residence times too short to alter nitrate concentrations or accumulate reaction products total hyporheic exchange volumes are 0 4 of stream discharge in restored reaches of 45 55 m results show that shallow hyporheic flow and associated biogeochemical cycling near cross vanes is primarily controlled by secondary bed forms created or augmented by the cross vane rather than by the cross vane itself this study suggests that cross vane restoration structures benefit the stream ecosystem by creating heterogeneous patches of varying hef and redox conditions in the hyporheic zone rather than by processing large amounts of nutrients to alter in stream water chemistry

spatial and temporal variations in electrical conductivity in a pro glacial stream system resultats d observations spatio temporelle de la conductivite electrique en ete 1978 et 1981 du systeme d ecoulement proglaciaire du glacier de tsidjiore nouve valais suisse des cycles d echantillonnage a 12 h 24 h et 48 h montrent l existence de cycles diurnes et de caracteristiques de complementarite entre les periodes d ablation entre plusieurs jours ou de jour en jour

distribution of bedrock and alluvial channels in forested mountain drainage basins mountain river networks often consist of both bedrock and alluvial channels1 5 the spatial distribution of which controls several fundamental geomorphological and ecological processes6 7 the nature of river channels can influence the rates of river incision and landscape evolution1 2 as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure8 11 studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands12 here we investigate the distribution of channel types in forested mountain drainage basins and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply in addition we find that valley spanning log jams create alluvial channels hospitable to aquatic life in what would otherwise be bedrock reaches the formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins

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

mixing law versus discharge and electrical conductivity relationships application to an alpine proglacial stream mixing laws have been used in hydrogeology for decades in glacial hydrology they are used to determine the contributions of the different reservoirs supplying the proglacial stream however some assumptions about discharge solute matter and discharge electrical conductivity ec relationships have led to erroneous conclusions analysis of a theoretical example indicated a hyperbolic relationship between discharge and solute matter concentration ec for two reservoirs we applied this approach to experimental data from the baounet glacier savoie france assuming that the proglacial stream is provided by a combination of watershed groundwater flow diurnally stable and with high ec and quick drainage from the glacier low ec and discharge that change very quickly applying mixing laws allowed us to characterise these two flows and to separate the quick flows glacial ablation and rainfalls copyright 2011 john wiley sons ltd

hyporheic exchange due to channel spanning logs 1 the flow of river water around large woody debris lwd creates pressure gradients along the riverbed that drive a large zone of river groundwater mixing or hyporheic exchange flume experiments and numerical simulations show that river water downwells into the riverbed upstream of a channel spanning log and upwells downstream exchange rates are greatest near the log and decay exponentially with distance upstream and downstream we developed equations for bed pressure profiles and hyporheic exchange rates in the vicinity of a channel spanning log that can be used to evaluate the impact of lwd removal or reintroduction on hyporheic mixing the magnitude of pressure disturbance along the bed and thus hyporheic exchange increases with the fraction of channel depth blocked by the log and channel froude number exchange rates are relatively insensitive to relative depth of the log gap ratio at natural densities lwd in lowland streams drives reach averaged hyporheic exchange rates similar to a ripple covered bed however the length scales and residence times of hyporheic exchange due to lwd are greater by removing lwd from streams humans have altered patterns and rates of hyporheic exchange which influence habitat distribution and quality for invertebrates and fish

a view of the 1993 1994 california current based on surface drifters floats and remotely sensed data near surface drifters were deployed in the california current system during the period 1993 1994 in order to study mean and eddy currents the deployment scheme allowed a 2 year period where data density was high enough to make meaningful estimates of eddy statistics and of seasonal mean currents and variances on a 5 grid eddy variability which tended to be isotropic was higher near the coast standard deviations around 0 2 m s 1 and decreased offshore down to 0 1 m s 1 seasonal mean surface flow west of california was southward during all seasons if a davidson current existed during 1993 1995 it was probably either short lived or only found closer to the coast than our study area i e within 100 150 km of shore in some cases drifter populations within a discrete feature were high enough to allow some detailed resolution of its behavior we note a tendency for individual eddies which can last for up to 3 5 months to drift westward at rates of o 5 km day 1 not all eddies in the region are surface intensified there is clear evidence for at least the occasional presence of a thin meandering southward jet in the region that can be 1000 km or more long this jet can be identified with that found in the coastal transition zone program in association with cool filaments the jet appears to become broader and slower south of point conception we hypothesize on the basis of others results as well as ours that the eddies that are strongest at the surface result primarily from instabilities on a southward alongshore mean current and that eddies that are maximal at depth are spawned by the northward undercurrent

reshaping of the hyporheic zone beneath river restoration structures flume and hydrodynamic experiments 1 in channel stream restoration structures readjust surface water hydraulics streambed pressure and subsurface hyporheic exchange characteristics in this study we conducted flume experiments pool riffle amplitude of 0 03 m and wavelengths of 0 5 m and computational fluid dynamic cfd simulations to quantify how restoration structures impacted hyporheic penetration depth dp and hyporheic vertical discharge rate qv restoration structures were channel spanning vanes with subsurface footers placed in the gravel bed at each riffle hyporheic vertical discharge rate was estimated by analyzing solute concentration decay data and maximum hyporheic penetration depth was measured as the interface between hyporheic water and groundwater using dye tracing experiments the cfd was verified with literature based flume hydraulic data and with dp and qz observations and the cfd was then used to document how dp and qz varied with flume discharge q ranging from 1 to 15 l s 3e 03 re 5e 04 flume experiments and cfd simulations showed that restoration structures increased qz and decreased dp creating a shallower but higher flux hyporheic zone qz had a positive linear relationship with q while dp initially grew as q increased but then shrunk when a hydraulic jump with low streambed pressured formed downstream of the structure the restoration structures created counter acting forces of increased downwelling head due to backwater effects and increased upwelling due to low streambed pressure and standing waves downstream of the structure

hyporheic flow path response to hydraulic jumps at river steps flume and hydrodynamic models 1 the conceptual model of hyporheic exchange below river steps may oversimplify exchange flow paths if it depicts a uniform pattern of downstream directed upwelling this research used nonmobile porous bed flume experiments and hydrodynamic simulation cfd to characterize hyporheic flow paths below a river step with a hydraulic jump bed slope was 1 step height was 4 cm downstream flow depth was 4 cm substrate was 1 cm median diameter gravel and hydraulic jump length was 25 cm in the flume and cfd experiments with the hydraulic jump flow paths changed to include downwelling beneath the water plunging into the pool and upstream directed upwelling at the base of the step and beneath the length of jump failure to represent the influence of static and dynamic pressures associated with hydraulic jumps leads to erroneous prediction of subsurface flow paths in 75 of the streambed beneath the jump a refined conceptual model for hyporheic flow paths below a step with a hydraulic jump includes reversed hyporheic circulation cells in which downwelling water moves upstream and then upwells and flow reversals in which the larger flow net of downstream directed upwelling encounters a nested flow path of upstream directed upwelling heterogeneity in hyporheic flow paths at hydraulic jumps has the potential to explain field observed mosaics in streambed redox patterns and expand structure function relationships used in river management and restoration

effect of experimental wood addition on hyporheic exchange and thermal dynamics in a losing meadow stream 1 stream restoration structures such as large wood can enhance shallow river groundwater exchange or hyporheic exchange and alter temperature dynamics in restored reaches we added and then removed channel spanning logs in a second order mountain meadow stream to test short term impacts on hyporheic exchange streambed temperatures and surface water temperatures based on vertical seepage measurements and numerical simulations of hyporheic fluid and heat flow large wood addition increased hyporheic exchange and altered streambed temperatures in this losing stream meter scale hyporheic exchange cells formed beneath large wood upwelling pore water downstream of logs stabilized diel temperature cycles across 8 of the streambed creating localized but potentially valuable thermal refuge exchange rates were 0 1 of channel discharge too small to impact the range of diel temperature signals in surface water however the lag between downstream and upstream diel temperature signals was slightly greater with large wood which may indicate that surface storage zones rather than hyporheic storage zones increased thermal retardation losing conditions limited the spatial extent and rates of hyporheic exchange near large wood impacts of large wood reintroduction on hyporheic exchange depend on ambient groundwater discharge or recharge streambed permeability channel froude number large wood blockage ratio and large wood spacing in many streams large wood reintroduction may increase hyporheic habitat volume and complexity but may not increase exchange rates enough to alter surface water temperature or chemistry surface storage zones such as eddies and pools can still influence heat and solute retention in the channel

alpine subglacial hydrology abstract the size and shape of subglacial flow pathways exert a strong influence over the pressure and speed at which meltwaters are routed through glaciers these characteristics in turn influence glacier sliding velocity and the quantity and quality of bulk meltwaters discharging from glaciers in this paper we summarise four empirical research approaches that have been developed to improve our understanding of the subglacial hydrology of predominantly temperate based alpine glaciers investigations of bulk meltwater discharge and chemistry tracer studies proglacial bedrock investigations and borehole investigations as a result of linking these studies to conceptual or numerical models three arborescent and four non arborescent or distributed subglacial drainage configurations are described these drainage networks may be neither spatially nor temporally persistent but may compete with and replace each other on a seasonal basis a qualitative model of the temporal and spatial evolution of a typical alpine subglacial drainage system is advanced on the basis of research conducted at haut glacier d arolla switzerland

the effects of discharge and slope on hyporheic flow in step pool morphologies this paper focuses on surface subsurface water exchange in a steep coarse bedded stream with a step pool morphology we use both flume experiments and numerical modelling to investigate the influence of stream discharge channel slope and sediment hydraulic conductivity on hyporheic exchange the model step pool reach whose topography is scaled from a natural river consists of three step pool units with 0 1 m step heights discharges ranging between base and over bankfull flows scaled values of 0 3 4 5 l s and slopes of 4 and 8 results indicate that the deepest hyporheic flow occurs with the steeper slope and at moderate discharges and that downwelling fluxes at the base of steps are highest at the largest stream discharges in contrast to findings in a pool riffle morphology those in this study show that steep slopes cause deeper surface subsurface exchanges than gentle slopes numerical simulation results show that the portion of the hyporheic zone influenced by surface water temperature increases with sediment hydraulic conductivity these experiments and numerical simulations emphasize the importance of topography sediment permeability and roughness elements along the channel surface in governing the locations and magnitude of downwelling fluxes and hyporheic exchange our results show that hyporheic zones in these steep streams are thicker than previously expected by extending the results from streams with pool riffle bed forms copyright 2014 john wiley sons ltd

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

hyporheic flow path response to hydraulic jumps at river steps hydrostatic model simulations 1 this research examined hydrostatic groundwater model modflow predictive adequacy and sensitivity in simulating hyporheic flow paths across a river step with a hydraulic jump in a companion paper we used flume and hydrodynamic model analysis to develop a refined conceptual model depicting these flow paths with zones of downwelling and upstream directed flux below the step the previous coarse conceptual model predicted uniform downstream directed upwelling below the step the hydrostatic model accurately predicted the downwelling and upstream directed fluxes beneath the wave and jump but failed to predict the plunge pool downwelling which is driven by dynamic pressures sensitivity tests varied riverbed topography and water surface profile geometry for a river with 1 slopes 10 cm flow depths and 50 150 cm long jets and jumps the flow paths below the jet jump region were driven by hydrostatic pressures and were highly sensitive to water surface profile and riverbed topography parameters failure to simulate the hydraulic jump caused errors in hyporheic flow path predictions beneath the jump region 1 m long by 0 5 m deep if the jump was poorly parameterized several meters of riverbed flow paths could be erroneously modeled as pointing upstream the hyporheic zone may contain a spatial mosaic of aerobic and anaerobic waters regulating nutrient transformations and biologic productivity accurate parameterization of hydraulic jumps in hyporheic simulation has the potential to improve predictions and explain heterogeneous subsurface flow paths and associated nutrient patterns and ecosystem functions

mixing of surface and groundwater induced by riverbed dunes implications for hyporheic zone definitions and pollutant reactions 1 the hyporheic zone is often defined as where mixing of surface water and groundwater occurs in shallow sediments beneath and adjacent to rivers this mixing is credited with creating unique biogeochemical conditions that can attenuate contaminants from either upstream surface water or groundwater under gaining conditions however reactions of contaminants upwelling from groundwater may be more dependent on such mixing than contaminants from surface water we numerically modeled mixing between hyporheic flow paths induced by riverbed dunes and flow paths of adjacent upwelling of deeper groundwater results show that only 12 7 or less tracer mass upwelling from deeper groundwater dispersed across into hyporheic flow paths originating in surface water the spatial extent of a mixing defined hyporheic zone was smaller than a hyporheic zone defined as hydrologic flow paths leaving and returning to surface water mixing dependent reactions will therefore be localized within a thin mixing zone yet vary considerably with site conditions for example mixing in homogeneous sediments was controlled most by variation in hydraulic conductivity and upwelling flow rate which primarily affected mixing zone length by contrast introduction of heterogeneity increased mixing primarily by increasing mixing zone thickness consistent with studies of flow focusing in aquifers finally dispersivity is a critical parameter for which data are needed for shallow sediments our results help clarify hyporheic zone definitions and potential for mixing dependent reactions in particular the biogeochemically reactive portion of riverbed sediments from the perspective of upwelling contaminants does not necessarily spatially coincide with more traditional hydrologic conceptions of the hyporheic zone

hydraulic and thermal effects of in stream structure induced hyporheic exchange across a range of hydraulic conductivities in stream structure induced hyporheic exchange and associated thermal dynamics affect stream ecosystems their importance is controlled by spatial variability of sediment hydraulic conductivity k we calibrated a computational fluid dynamics cfd model of surface and groundwater hydraulics near a channel spanning weir represents log dams boulder weirs to field data and varied k from 10 7 to 10 2 m s silt to gravel surface water stopped cresting the weir for k 10 3 m s non darcy hyporheic flow was also prevalent for k 10 3 m s and velocity errors using non cfd models ranged up to 32 2 we also modeled weir induced heat transport during summer as k increased from 10 7 to 10 3 m s weir induced hyporheic heat advection steadily increased cooling and buffering along hyporheic flow paths decreased with increasing k particularly above k 10 5 and 10 4 m s respectively vertical heat conduction between surface water and groundwater near the weir decreased with increasing k particularly for k 10 5 m s conduction between hyporheic flow paths and adjacent groundwater helped cool hyporheic flow downstream surface water cooling by hyporheic advection increased steadily with k as increases in hyporheic flow overwhelmed decreases in cooling along hyporheic flow paths yet such effects were small 0 016 c even at k 10 3 m s the largest thermal effect of weir induced exchange was therefore spatial expansion of subsurface diel variability particularly for k 10 5 m s which affects benthic habitat and chemical reactions the specific values of k where such trend shifts occur is likely variable among streams based on flow conditions but we expect the presence of such trend shifts to be widespread

in stream geomorphic structures as drivers of hyporheic exchange 1 common in stream geomorphic structures such as debris dams and steps can drive hyporheic exchange in streams exchange is important for ecological stream function and restoring function is a goal of many stream restoration projects yet the connection between in stream geomorphic form hydrogeologic setting and hyporheic exchange remains inadequately characterized we used the models hec ras modflow and modpath to simulate coupled surface and subsurface hydraulics in a gaining stream containing a single in stream geomorphic structure and to systematically evaluate the impact of fundamental characteristics of the structure and its hydrogeologic setting on induced exchange we also conducted a field study to support model results model results indicated that structure size background groundwater discharge rate and sediment hydraulic conductivity are the most important factors determining the magnitude of induced hyporheic exchange followed by geomorphic structure type depth to bedrock and channel slope model results indicated channel spanning structures were more effective at driving hyporheic flow than were partially spanning structures and weirs were more effective than were steps across most structure types downwelling flux rate increased linearly with structure size yet hyporheic residence time exhibited nonlinear behavior increasing quickly with size at low structure sizes and declining thereafter important trends in model results were observed at the field site and also interpreted using simple hydraulic theory thereby supporting the modeling approach and clarifying underlying processes

neighborhood matters patterns and controls on wood distribution in old growth forest streams of the colorado front range usa abstract we surveyed wood characteristics along four headwater channel segments of the colorado front range with drainage areas of 8 82 km2 stream lengths surveyed range from 3025 to 8980 m and together include a total of 15 706 pieces of wood time since last disturbance in the form of a stand killing fire varied from 31 to 500 years individual pieces of wood were highly aggregated at length scales of 1 to 150 m trends among jams were more weakly developed but jams tended to be more segregated at lengths 300 m with jams along individual channels being aggregated segregated or random multiple linear regressions failed to produce highly predictive models to explain the response variables of wood load piece dimensions or characteristics of jams other than jam volume which correlated with drainage area and wood load but examination of downstream patterns suggests that local valley and channel geometry valley bottom width gradient and sequence of longitudinal channel changes exert a stronger influence on patterns of wood distribution than either time since last forest disturbance or progressive downstream trends associated with increasing drainage area the longitudinal sequences of wood recruitment sources forest stand age and channel geometry together exert an important control on reach scale wood load and aggregation wood loads in streams draining old growth 250 years forests of the colorado front range are low compared to old growth sites in other regions of the world which we interpret to reflect decreased retention of wood recruited to the streams

heat transport in hyporheic zones due to bedforms an experimental study heat transport in hyporheic zones is critical for many temperature sensitive physical chemical and biological processes it also plays a role in the energy balance of rivers to complement previous theoretical studies we investigated the effects of hyporheic flow due to bed topography on hyporheic thermal dynamics through flume experiments diel temperature cycles were imposed in the channel and propagation of temperature signals into the sediment was examined for three different bed morphologies flat bed pool riffle pool and rippled bed three channel flow rates and two sediment grain sizes results show that the downwelling upstream and downstream of the bedforms and upwelling focused near the crest caused substantial advective heat transport and distinct thermal patterns in the sediment with downwelling zones reflecting most of the surface water diel thermal range whereas upwelling zones were more buffered increasing permeability and channel flow rates increased advective transport the results corroborate previous theoretical models further showing that hyporheic flow distinctly affects thermal patchiness in sediment the results also have implications for heat tracing using analytical models which work well for flow fields without pronounced divergence and convergence and minimal dispersion features atypical of hyporheic flow

patterns and processes of wood debris accumulation in the queets river basin washington field surveys in the 724 km 2 queets river basin on the west slope of the olympic mountains in nw washington reveal basin wide patterns of distinctive wood debris wd accumulations that arise from different mechanisms of wd recruitment hydraulic geometry and physical characteristics of wd individual pieces of wd in an accumulation or jam can be separated into key racked and loose members ten types of wd accumulations are identified based on the mode of recruitment and the orientation of key racked and loose debris relative to the channel axis although some types of wd accumulation have few geomorphic effects others form stable in stream structures that influence alluvial morphology at both subreach and reach length scales ranging from less than 1 to greater than 10 channel widths in the queets river stable accumulations of wd directly influence channel anabranching planform geometry flood plain topography and establishment of long term riparian refugia for old growth forest development the classification of wood debris accumulations in the queets river basin is based on physical observations that offer a template potentially applicable to other forested mountain regions d 2002 elsevier science b v all rights reserved

changes in hyporheic exchange flow following experimental wood removal in a small low gradient stream 1 we investigated the response of hyporheic exchange flow hef to wood removal in a small low gradient gravel bed stream in southeast alaska using a series of groundwater models built to simulate hef for the initial conditions immediately after wood removal and 1 month 2 years 4 years and 16 years following wood removal the models were based on topographic surveys of the stream channel and surrounding floodplain and surveyed water surface elevations wses were used to assign stream boundary conditions using the groundwater flow model modflow and the particle tracking model modpath we calculated hyporheic exchange fluxes their residence time distributions and both longitudinal and plan view spatial patterns of downwelling and upwelling zones in the first few years streambed scour and sediment deposition smoothed the streambed and wse profile reducing hef also large contiguous patches of downwelling or upwelling were fragmented nearly doubling the total number of patches present on the streambed as the stream continued to adjust to the loss of wood those trends began to reverse accretion of sediment onto alternating bars resulted in better developed pool riffle morphology enhanced hef and increased residence times and also resulted in downwelling and upwelling zones coalescing into elongated patches along bar margins this study showed that the hyporheic zone is sensitive to changes in wood loading and that initial changes in hef resulting from the direct effects of wood removal were contrary to longer term channel adjustments to changes in wood loading

comments on the use of chemically based mixing models in glacier hydrology the assumptions involved in the use of chemically based mixing models for analysis of flow routing of meltwaters in glacierized basins are critically evaluated the assumption that glacial drainage systems consist of only two primary flow components is arbitrary and must be supported by independent evidence recent studies of the processes by which meltwaters acquire solute indicate that the assumption that flow components have unique and constant chemical compositions is unlikely to lie correct source water composition and weathering potential will vary over the course of a melt season and the extent of subglacial weathering is strongly dependent upon such factors as meltwater residence time and the availability of reactive sediment both of which are known to vary on diurnal to seasonal time scales mixing of flow components does not appear to be confined to the terminal regions of glaciers and is therefore unlikely to be conservative as assumed a multi parameter mixing model is applied to the analysis of data on the chemistry of waters sampled from bureholes drilled through haut glacier d arolla switzerland to demonstrate the range of dissolved species for which the assumption of conservative mixing is violated the consequences of this violation for quantitative hydrograph separation are shown to be highly significant the utility of mixing models as a tool for the investigation of glacier hydrological systems is questionable and the results of previous studies are unreliable

numerical modeling of flow and scour below a pipeline in currents part ii scour simulation abstract a vertical two dimensional 2d numerical model for time dependent local scour below offshore pipelines subject to unidirectional steady flow is developed the governing equations for the flow and sediment transport are solved by using finite difference method in a general curvilinear coordinate system the performance of two turbulence models the standard k model and smagorinsky subgrid scale sgs model on modeling time dependent scour processes is examined both suspended load and bed load are considered in the scour model the suspended load model is verified against two channel sediment transport cases the change of bed level is calculated from the continuity equation of total sediment transport a new time marching scheme and a sand slide scheme are proposed for the scour calculation it is found that the proposed time marching scheme and sand slide model work well for both clear water and live bed scour situations and the standard k turbulence closure is more preferable than the sgs model in the 2d scour model developed in this study

effect of instream wood on vertical water flux in low energy sand bed flume experiments 1 in streams interaction of current with bed forms and solid objects can produce vertical water flux across the streambed instream wood is a major obstacle to flow and alters the bed topography of natural sand bed streams in the present experimental study in large circulating flumes simulating sand bed streams with low constant slope we compared systems with and without natural quantities of wood the introduction of wood resulted in the production of irregular bed forms as a result flow resistance tripled and vertical water flux across the streambed increased by a factor of 1 8 to 2 5 the mixing depth was spatially variable and seemed unrelated to the local bed form after the addition of wood surface water mixed deeper into the sediments and the total sediment pore water volume involved in mixing increased by factors of 1 2 to 1 5 the practice of increasing instream wood should be a valuable tool for hyporheic rehabilitation of degraded sand bed streams

modeling vertical and horizontal diffusivities with the sigma coordinate system abstract the use of diffusive terms in numerical ocean models is examined relative to different coordinate systems the conventional model for horizontal diffusion is found to be incorrect when bottom topographical slopes are large a new formulation is suggested which is simpler than the conventional formulation when transformed to a sigma coordinate system and makes it possible to model realistically both surface ekman and bottom boundary layers

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

vertical velocities and dynamical balances in gulf stream meanders a triangular array of current meter moorings was deployed within the cyclonic flank of the gulf stream in the south atlantic bight from september 1981 to april 1982 using velocity and temperature data and the nondiffusive heat equation a time series of vertical velocity was derived a mean vertical velocity of 0 013 cm s 1 and standard deviation of 0 078 cm s 1 were obtained to better understand the subsurface structure of gulf stream meanders the time series of horizontal and vertical velocities and temperature were examined at times when events were passing through the array the flow along the trailing edge of a gulf stream meander and within the leading portion of a cold core frontal eddy was found to have an upward component positive w while that within the trailing portion of the frontal eddy and along the leading edge of a meander had a downward component negative w using the horizontal and vertical velocity time series cross stream and along stream momentum balances were calculated the downstream flow was found to be in geostrophic balance in contrast the coriolis and nonlinear terms were found to contribute equally to the determination of the cross stream flow

hyporheic zone hydrologic science a historical account of its emergence and a prospectus the hyporheic zone defined by shallow subsurface pathways through river beds and banks beginning and ending at the river is an integral and unique component of fluvial systems it hosts myriad hydrologically controlled processes that are potentially coupled in complex ways understanding these processes and the connections between them is critical since these processes are not only important locally but integrate to impact increasingly larger scale biogeochemical functioning of the river corridor up to the river network scale thus the hyporheic zone continues to be a growing research focus for many hydrologists for more than half the history of water resources research this manuscript partly summarizes the historical development of hyporheic zone hydrologic science as gleaned from papers published in water resources research from the birth of the concept of the hyporheic zone as a hydrologic black box sometimes referred to as transient storage zone to its adolescent years of being torn between occasionally competing research perspectives of interrogating the hyporheic zone from a surface or subsurface view to its mature emergence as an interdisciplinary research field that employs the wide array of state of the art tools available to the modern hydrologist the field is vibrant and moving in the right direction of addressing critical fundamental and applied questions with no clear end in sight in its growth there are exciting opportunities for scientists that are able to tightly link the allied fields of geology geomorphology hydrology geochemistry and ecology to tackle the many open problems in hyporheic zone science

numerical treatment of cross shelf open boundaries in a barotropic coastal ocean model abstract using a barotropic coastal ocean model with a straight coastline and uniform cross shelf bottom slope seven different cross shelf open boundary conditions four of which are applied in either implicit or explicit form are compared in three numerical experiments 1 a mound of water is allowed to collapse and radiate waves toward the open boundaries 2 a uniform alongshelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment 3 a uniform cross shelf wind stress is applied at zero time over the entire shelf and held constant for the duration of the experiment the boundary condition which is most transparent to waves consists of a sponge at the outer edge of the model domain with an orlanski radiation condition at the outer edge of the sponge several open boundary conditions perform adequately in the wind stress experiments but the orlanski radiation condition alone without a sponge appears to give the best total performance of thes

hyporheic exchange in a karst conduit and sediment system a laboratory analog study summary karst conduits are often partly filled by clastic sediments flow through such sediments can have a strong impact on the fate of sediment entrapped contaminants in contrast to stream bed sediments hyporheic flow in karst sediments has received little attention so far for karst sediments conduit bends could induce hyporheic flow in addition to bedforms or obstacles the main aim of this study was to investigate flow processes in a conduit sediment system using a laboratory model resembling a siphon and numerical modeling in the laboratory system zones with forward and reserve flow occurred in the sediment due to the conduit bends as demonstrated with sediment source tracer test entrapped solutes were generally flushed out more rapidly at a higher flow rate and steeper conduit angle numerical modeling assuming pressure continuity across the conduit sediment interface reproduced the flow patterns and breakthrough curves btcs well based on the model the magnitude of hyporheic exchange is expected to increase linearly with the flow rate and was higher for a steeper conduit angle however the increase in flushing intensity was not evenly distributed throughout the sediments but occurred mainly adjacent to the conduit bends consistent with observations from tracer tests this study confirms that conduit bends could have a strong influence on hyporheic flow in karst sediments

seasonal and interannual variability of currents and temperature off central chile results are reported for continuous 6 year records of current and temperature from a continental slope station at 308s off chile these observations for november 1991 to november 1997 span the moderate weak and strong el nino events of 1991 1992 1994 and 1997 and the la nina event of 1995 1996 results for current and temperature are analyzed together with observations of wind along the south american coast from the ers 1 and 2 satellite scatterometers wind from a local coastal site sea level from northern and central chile sea surface temperature anomalies from the south pacific region and traditional el nino indices mean poleward flow of 12 8 cm s 21 was observed for the 6 year period in the core of the peru chile undercurrent 220 m mean flow in the depth range of antarctic intermediate water 750 m was equatorward at 1 1 cm s 21 intraseasonal scale variability associated with coastal trapped waves was weaker during the austral winter greatest during el nino events and weakest during the la nina event winds adjacent to the coast showed a strong annual cycle with a southward progression of maximum equatorward upwelling favorable winds alongshore flow over the slope exhibited strong semiannual and weaker annual variations poleward flow in the undercurrent was strongest in the austral spring and fall and weakest in the winter near the bottom 750 m seasonal scale variability was less intense but led that higher up in the water column 220 m by 1 month strong interannual variability of alongshore current and temperature was found at all depths over the slope whereby changes at depth led changes higher up a rapid warming event was observed at the end of 1996 beginning of 1997 over the slope this event also seen in sea level and sea surface temperature off chile led el nino indices by several months and may be best explained by local wind anomalies coupled to atmospheric teleconnections from the western tropical pacific at the onset of el nino some aspects of our current and temperature observations are consistent with results from eastern boundary current models our results indicate that both ocean and atmosphere pathways from the equatorial pacific contribute significantly to interannual scale variability of alongshore flow and thermocline depth off chile

flow separation on zongo glacier cordillera real bolivia meltwaters collected from the proglacial stream escaping from zongo glacier 2 1 km2 bolivia 16 s have been monitored in order to analyse the internal drainage system of an andean glacier electrical conductivity has been measured sporadically between february 1995 and march 1996 during 16 one day field surveys under various meteorological conditions in summer and winter the mixing model technique based on the electrical conductivity is used for a quantitative separation of discharge which is derived from continuous water level registration tracer experiments mainly uranine dye and nacl salt have been carried out from march to june 1997 to obtain information about the internal drainage system in the tropical andes accumulation only occurs in austral summer whereas ablation occurs throughout the year and is higher during the accumulation season between november and march the assumptions involved in the use of mixing models for analysis of glacial drainage structure are applicable for tropical glaciers because glacial conduits do not suffer complete closure and are permanently supplied by meltwaters even in wintertime two components of discharge are separated an englacial flow originating from surface meltwater which is routed without chemical enrichment and offering low electrical conductivity and a subglacial one routed in contact with bedrock or sediments showing high ionic concentrations electrical conductivity of meltwater varies diurnally inversely to discharge fluctuations according to this behaviour total discharge is mainly formed by the englacial component the drainage structures for englacial and subglacial flow have to be widely interconnected as indicated by diurnal variations of the subglacial discharge comparison of hydrograph separation based on conductivity and on 18o isotope confirms that the subglacial flow is influenced by surface melting a hydrograph separation of the subglacial flow is proposed between a diurnal variable component composed of water coming from the englacial network and a base flow which may vary seasonally the dye tracing experiments confirm the drainage complexity of zongo glacier and demonstrate the interest of identifying three main drainage components 1998 john wiley sons ltd

a numerical study of the seasonal variability in the circulation off central chile the princeton ocean model is used to study the coastal ocean circulation off central chile between 30 and 45 s and its seasonal transitions in response to monthly mean climatological wind stress and surface heat flux the model reproduces many of the dominant circulation features including an equatorward coastal current coastal upwelling and a poleward undercurrent to get the correct seasonal variability in the undercurrent it was necessary to prescribe the inflow of the undercurrent on the northern model boundary meanders and eddies form throughout the simulation period seaward of the coastal current in response to baroclinic instability of the flow the flow associated with the meanders shows upwelling in the shoreward flow and downwelling in the seaward flow this upwelling downwelling pattern is explained by conservation of relative vorticity in the flow the upwelling velocity associated with the meanders corresponds to a vertical migration of 15 30 m over a typical timescale of the meanders of 1 2 months it is argued that this upwelling may be important for maintaining observed high phytoplankton biomass and primary production seaward of the coastal zone directly affected by wind driven upwelling

three dimensional versus two dimensional bed form induced hyporheic exchange the hyporheic zone is often a critical component of river systems hyporheic exchange is generally forced by variation in riverbed topography such as due to bed forms most previous research on bed form driven hyporheic flow has focused on two dimensional 2 d dunes and ripples while little has been done on their three dimensional 3 d counterparts here we compared hyporheic exchange and associated metrics for a previously studied pair of corresponding 2 d and 3 d bed forms to accomplish this a series of multiphysics computational fluid dynamics models were conducted both in 2 d and 3 d with similar open channel reynolds numbers re results show that the pressure gradient along the sediment water interface is highly sensitive to the spatial structure of bed forms which consequently determines hyporheic flow dynamics hyporheic flux is a function of re for both 2 d and 3 d dunes via a power law however the equivalent 3 d dunes have a higher flux since the 3 d form induces more drag the hyporheic zone depths and volumes are only slightly different with the 3 d case having a larger volume the mean fluid residence times for both cases are related to re by an inverse power law relationship with the 3 d dune having smaller residence times at moderate to high re the effects of increasing flux on residence time in 3 d dunes are partly modulated by a slightly increasing hyporheic volume our results suggest that a 2 d idealization is a reasonable approximation for the more complex 3 d situation if local details are unimportant but that development of predictive models for mean fluxes and residence times which are critical for biogeochemical processes based on 2 d models may be insufficient

hyporheic flow and dissolved oxygen distribution in fish nests the effects of open channel velocity permeability patterns and groundwater upwelling many fish lay their eggs in nests or redds which they construct in sediment the viability of eggs depends on many factors particularly their oxygenation because dissolved oxygen is typically saturated within the stream channel the dissolved oxygen distribution within the redd depends on whether or not hyporheic flow and transport occur within the sediment we conducted a series of flume and numerical flow and age transport modeling experiments with the aim of understanding the effects of salmonid redds on the hyporheic transport of young oxygenated water hyporheic flow was visualized directly through dye injections dissolved oxygen throughout the fish nest was measured using a planar optode experiments were conducted at various open channel flow velocities in order to understand their effect on dissolved oxygen and computational simulations considered various sediment textures and ambient groundwater upwelling rates to add process level insight we found that as also shown by previous studies the redd topography induces multiscale hyporheic flow that effectively flushes the egg pocket location with younger presumably oxygenated water older water upwells and forms anoxic zones this pattern persists even at the lowest channel flow rates and at small upwelling velocities of older ambient groundwater which splits the multiscale hyporheic flow cells into isolated pockets large groundwater upwelling rates can shut down all the hyporheic flushing the relatively coarse texture of the redd further promotes hyporheic flushing of the redd sediment with oxygenated water thus redd morphology and sediment texture optimally combine to induce hyporheic exchange flow that delivers young oxygenated water to the egg pocket

influence of large woody debris on morphological evolution of incised sand bed channels this paper documents the influence of large woody debris lwd on the morphological evolution of unstable degrading sand bed rivers in the yazoo basin north mississippi usa the study was performed as part of the demonstration erosion control dec project twenty three river reaches were studied with the aim of determining whether the presence of lwd was beneficial or detrimental to the recovery of stability in degrading sand bed river systems and to provide the geomorphic understanding necessary to underpin enhanced lwd management strategies the results demonstrate that locations of lwd inputs volumes of lwd stored in different reaches and number of jams per unit channel length are causally related to the morphological processes occurring during different stages of adjustment in these unstable incised fluvial systems and may be explained using a channel evolution model cem the net impact of lwd jams on reach scale sediment budgets was found in general to be positive that is jams trap more sediment than they mobilise this suggests that lwd probably accelerates rather than retards recovery of a stable longitudinal profile and channel configuration following incision field typing of lwd jams based on their impacts on the flow pattern reveals that jam type is a function of the size of large key elements in the jam in relation to the channel width a debris jam classification scheme is proposed on this basis with the spatial relationship between jam type and drainage basin area expressed using a dimensionless function of the ratio between channel width and average riparian tree height the scheme features four jam types underflow dam deflector and flow parallel bar head each of which has a different morphological impact on local channel geometry these jam types may be used to classify lwd jams as an aid in determining appropriate management strategies according to their location within the drainage basin

hyporheic temperature dynamics and heat exchange near channel spanning logs 1 the flow of river water around large woody debris lwd creates pressure gradients along the riverbed that drive river groundwater mixing or hyporheic exchange and heat transport within the hyporheic zone we quantify hyporheic fluid and heat exchange induced by current interaction with channel spanning logs using two approaches laboratory flume experiments and numerical simulations that link turbulent open channel fluid flow porous fluid flow and heat transport flume and numerical experiments show that logs produce a characteristic diel temperature pattern within sediment that shifts with log blockage ratio a fraction of the channel depth blocked by the log channel froude number and sediment permeability upstream of a log downwelling water transports the river s diel thermal signal deep into the sediment downstream upwelling water from shallow flow paths has a thermal signal similar to the surface water while upwelling water from deep flow paths forms a wedge of buffered low amplitude temperatures since most hyporheic water emerges from shallow flow paths upwelling water has limited potential to buffer surface water temperature because of historic channel clearing practices modern rivers have unnaturally low densities of lwd a key implication is that lwd removal has contributed to thermal homogenization and potential degradation of hyporheic habitats lwd reintroduction is a promising strategy to improve vertical connectivity in rivers and increase thermal patchiness within the hyporheic zone however hyporheic exchange near lwd may not impact diel surface water temperatures at the reach scale

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications