lower mantle substructure embedded in the farallon plate the hess conjugate the morphologies of subducted remnants in the lower mantle are essential to our understanding of the history of plate tectonism here we image a high velocity slab like hvsl anomaly beneath the southeastern u s using waveforms from five deep earthquakes beneath south america recorded by the usarray in addition to travel time anomalies the multipathing of s and scs phases at different distances are used to constrain the hvsl model we jointly invert s and scs traveltimes amplitudes and waveform complexities to produce a best fitting block model characterized by a rectangular shape with a 2 5 s wave velocity increase and tapered edges while the farallon slab is expected to dip primarily eastward the hvsl structure apparently dips 40 to 50 to the se and appears to be related to the eclogitized hess conjugate

using borehole logging and electron backscatter diffraction to orient an ice core from upper fremont glacier wyoming usa while glacier fabric reflects the accumulated strain detailed azimuthal information is required to link the microstructure to the flow and this is not easily gathered at depth borehole logging provides a way to obtain a log of azimuthal orientation of tilted stratigraphic features that can be used to orient the core with respect to glacier flow we demonstrate this using acoustic borehole logs and the ice core from a 162 m borehole in upper fremont glacier wind river range wyoming usa we measured the dip of tilted dust and bubble layers in the actual ice core identified them on the borehole log then used their strike to orient the core sections containing them we examined the crystal orientation fabric of our samples using electron backscatter diffraction in a scanning electron microscope when we compared the orientation of the tilted layers in some samples with the fabric we found that the normal to the foliation and the c axes maxima both pointed in the direction of maximum shear stress this illustrates the usefulness of borehole logs for orienting ice cores after removal from the borehole and for developing a better understanding of fabric development

radio echo sounding studies of englacial water movement in variegated glacier alaska une crue glaciaire du variegated a ete enregistree a l aide d un emetteur mono impulsion de 3mhz les discontinuites intraglaciaires ont ete observees dans le domaine des 12 a 30 mhz les changements dans la forme des echos sont interpretes en terme de redistribution de l eau dans les canaux glaciaires et les cavites reliees au lit a quelque distance a l aval

mathematical modelling of sea water intrusion nauru island a two dimensional finite element model for density dependent groundwater flow was calibrated to simulate sea water intrusion in nauru island in the central pacific ocean nauru island occupies an area of 22 km2 and supports a population of 8500 the island has been mined for its phosphate deposits and current reserves indicate that the mine has about eight years life remaining the water supply of the island is about one third dependent on imported water which is also used as ballast on the phosphate ships imported water will not be available in the future and a hydrogeological investigation shows that the island is underlain by a fresh water layer less than 5 m thick the freshwater layer overlies a thick transition zone of brackish water which in turn overlies sea water simulation of several management options shows that it is possible to substitute current importation of fresh water by careful extraction from the groundwater resources of the island

a stationary impulse radar system for autonomous deployment in cold and temperate environments l mingo acknowledges the sr ed tax incentive program of the cra for offsetting some r d costs of the sipr g flowers and d bigelow are grateful to nserc cfi csa nstp pcsp and sfu for funding kluane first nation yukon government and parks canada for access to yukon field sites and s williams l goodwin a pulwicki j crompton f beaud and canadian astronaut d saint jacques for support and field assistance c schoof and c rada provided time lapse imagery and 2017 water pressure data a crawford and d mueller acknowledge funding from nserc transport canada pkc nstp and the garfield weston foundation as well as support from arctic net the ccgs amundsen crew and pilots o talbot a roy and g carpentier

modeling groundwater with ocean and river interaction we develop and implement the groundwater model saturated unsaturated flow and transport in 3d suft3d to integrate water quantity quality data and simulations with models of other hydrologic cycle components namely rivers and the ocean this work was done as part of the sea air land modeling operational network salmon project supported by the ibm international foundation through its environmental research program the first research steps presented here address the simulation of typical hydrologic conditions to demonstrate suft3d s effectiveness and accuracy the theory behind the modeling of seawater intrusion and groundwater river interaction is summarized along with the numerical methods and characteristics of suft3d the code was applied to different increasingly complex scenarios confined to unconfined conditions local to regional scale homogeneous to increasing heterogeneity two to three dimensional of particular interest were the impacts of different boundary conditions and influence of river interactions on seawater intrusion results are illustrated discussed and compared when possible to those in the literature simulating groundwater exchange between both the river and the ocean has provided interesting results that better depict the dynamics of flow and transport in coastal zone groundwater systems different models can be developed to simulate water flow and quality at large scales in both time and space each part of the hydrological cycle i e ocean surface water groundwater and atmosphere is simulated using models adapted to each particular component usually each model is designed for only one part of the water cycle and interactions with other parts are taken into account by using prescribed input output flux at the boundaries this is commonly considered as satisfactory so that groundwater river and ocean models are usually con nected only by these prescribed boundary conditions how ever the actual water and contaminant fluxes between the models should be simulated more realistically without pre scribing any flux integrated water quantity and quality prob lems in coastal zones were investigated as part of the sea air land modeling operational network salmon project sup ported by the ibm international foundation this research focuses on introducing natural junctions between the differ ent models to adequately compute exchange flux as of 1995 three models ocean beckers 1991 river smitz et al 1997 and groundwater dassargues 1994 had been developed in different departments of the university of liege now these are being connected to form an integrated model able to describe water and contaminant flux over the entire system at regional scales including input from marine river groundwa ter and atmospheric hydrologic cycle components connecting the different models is done through a specific interface called a junction designed to manage data exchange

an automatic approach to delineate the cold temperate transition surface with ground penetrating radar on polythermal glaciers ground penetrating radar has been widely used to map the thermal structure of polythermal glaciers hitherto the cold temperate transition surface cts in radargrams has been identified by a labour intensive and subjective manual picking method we introduce a new automatic approach for picking the cts that uses the difference in signal power exhibited by the cold and temperate ice layers we compare our automatically computed cts depths with manual picks our results show very good agreement between the two methods in most areas r 2 0 7 rmses computed at each trace in two way travel time from three test sites range from 14 to 19 ns 2 4 3 2 m the proposed automated method mostly fails in areas showing a rather gradual transition in signal power at the cts in some areas high power originating from non water sources is misinterpreted by the automatic picking method as temperate ice

temporal englacial water content variability associated with a rapidly retreating glacier this study uses a combination of evidence from ground penetrating radar borehole video and wireless probe data to assess temporal changes in englacial water content associated with briksdalsbreen a rapidly retreating norwegian glacier over a 13 day period in 2006 ice radar wave velocity varied between 0 135 m ns 0 009 and 0 159 m ns 0 003 and water content from 7 8 2 6 2 8 to 2 5 0 9 1 1 derived from the looyenga physica31 3 401 406 1965 formula it is suggested that during warm precipitation free days void spaces within the glacier become filled with water resulting in low radar wave velocity this stored water then drained during cold high precipitation days allowing the radar wave velocity to rise these changes in englacial storage were caused by the enhanced crevassing generated by the newly floating ice margin and were associated with accelerated glacier retreat

observations of englacial water passages a fracture dominated system to test models of the hydraulics and geometry of englacial conduits 48 holes 3900 m of ice were drilled into storglaciaren sweden in search of conduits about 79 of the holes intersected a hydraulically connected englacial feature a video camera was used to examine the features and measure local water flow rates because of the extremely clear ice that surrounded most features their geometry could not be discerned of the remaining features 80 36 were fracture like 16 6 were of complex geometry and 4 2 exhibited a conduit like geometry the fracture like features exhibited steep plunges 708 narrow openings 40 mm and slow water flow speeds 10 mm s 1 we argue that these fracture like features are indeed englacial fractures of unknown origin the depth to fractures intersection varied from near the glacier surface to 96 of local ice depth with a maximum depth of 131 m few hydraulically connected fractures exhibited water motion indicating some preferential flow pathways exist we found one traditional englacial conduit after an intentional search in a field of moulins these results suggest that englacial water flow is conveyed through a ubiquitous network of fractures and that conduits are relatively rare

density driven groundwater flow in closed desert basins field investigations and numerical experiments abstract with a numerical model duffy and al hassan demonstrated that free convection of brine could occur under the playa lake in a closed basin since then continued effort has been made to further our understanding of the role of free convection in closed basin hydrology in this paper we present the results of 5 years of field investigation in pilot valley nevada of a literature search for field studies in closed basins around the world and of numerical simulations to examine the effect of heterogeneity on free convection and the effect of climate changes observations along the divide playa transect revealed evidence of forced convective flow and the existence of a hinge line the salinity profile and the inferred flux suggest that diffusion is the dominant solute transport mechanism under the field sites but the stable isotopes o h suggest that free convection of playa brine also occurs we propose a model that explains these observations first free convection could occur farther out on the playa where the density of surface brines is higher second once free convective flow penetrates the surface sediments it could migrate laterally in the more permeable layers of alluvium third free convection could occur during periods of time when brines pond on the surface for extended periods the search for field studies of groundwater processes in other closed basins leads to a few cases where free convection has occurred on a basin scale based on this survey we discuss the geologic and climatic conditions that favor free convection numerical simulations are carried out to examine the effect of basin scale heterogeneity in hydraulic conductivity the results indicate that heterogeneity changes the pattern of flow by creating multiple convection cells finally we address how a closed basin may respond to climate change climate changes alter the salinity of surface brines and the freshwater recharge both acting as boundary conditions for subsurface processes using dimensional analysis and numerical simulations we evaluate the effect of a warming and drying trend on free convection and how the geologic features of a closed basin affect the response 1997 elsevier science b v

interpretation of radio echo returns from internal water bodies in variegated glacier alaska u s a des sondages radios ont revele la presence de cavites remplies d eau dans le glacier variegated alaska discussion sur l origine et les consequences glaciologiques de ces cavites

radio and electrical measurements on glacial streams we discuss the suggestion that small under water transmitters might be used to illuminate the interior of major englacial water channels with radio waves once launched the radio waves would naturally tend to be guided along the channels until attenuated by absorption and by radiative loss receivers placed within the channels or at the glacier surface could be used to detect the signals they would provide valuable information about the connectivity of the water system the electrical conductivity of the water is of crucial importance a surface stream on storglachlren in sweden was found using a low frequency technique to have a conductivity of approximately 4 x 10 4 s m i although this is several hundred times higher than the conductivity of the surrounding glacier ice the contrast is not sufficient to permit us simply to use electrical con ductivity measurements to establish the connectivity of englacial water channels however the water conductivity is sufficiently small that under favourable circumstances radio signals should be detectable after travelling as much as a few hundred metres along an englacial water channel in a preliminary field experiment we demonstrated se mi quantitatively that radio waves do indeed propagate as expected at least in surface streams we conclude that under water radio transmitters could be of real practical value in the study of the englacial water system provided that sufficiently robust devices can be constructed in a subglacial channel however we expect the radio range would be much smaller the environment much harsher and the technique of less practical value

mixed convection processes below a saline disposal basin abstract saline groundwater and irrigation drainage are commonly diverted and stored in both natural and artificial depressions throughout the murray darling basin of australia the disposal basin brines that are formed are often denser than ambient groundwater under certain conditions these dense brines may become unstable causing them to mix with groundwater over distances several orders of magnitude greater than due to diffusion alone a model is developed to study the mixed convection processes below a saline disposal basin located between a recharge and discharge zone numerical simulations are performed in cross section using the 2 d density dependent model sutra saturated unsaturated transport it is shown that the salt front movement is related to both the ability of the dense saline brines to mix convectively with underlying groundwaters rayleigh convection and the strength of the regional advective velocity both homogeneous and heterogeneous aquifer systems are studied and the effects of anisotropy are considered our numerical results suggest that the behaviour of a dense brine plume overlying less dense groundwater in a homogeneous porous medium depends on the magnitude of at least two non dimensional numbers a rayleigh number and modified peclet number defined in terms of basin scale hydrogeologic parameters including dispersion it is shown that the onset of gravitational instabilities and the formation of free convective cells begins when the magnitude of a non dimensional parameter combining the rayleigh and modified peclet number exceeds a certain critical value 1997 elsevier science b v all rights reserved

the effect of salinity dependent hydraulic conductivity on saltwater intrusion episodes abstract the ionic strength of percolating water can greatly alter a soil s hydraulic conductivity this appears to be the result of dispersion and or swelling of clay particles and can alter hydraulic conductivity by several orders of magnitude in this paper the potential effects of salinity dependent changes in hydraulic conductivity during saltwater intrusions are analyzed results are presented to show that this can increase the degree to which brackish water will penetrate a coastal aquifer this can also increase the width of the dispersed salt front and can lead to a much greater circulation of saltwater within the intruding saltwater toe these results may help to explain field observations that have previously been attributed to scale dependent dispersivity and domain heterogeneity

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

design and operation of a portable digital impulse radar we have constructed a back portable impulse radar instrument that weighs roughly 12 kg can be powered by dry cells and records and stores data digitally the radar is controlled by an on board purpose built microcomputer that ensures simple field operation facilitates modifications and allows unattended operation when investigating time varying targets the transmitting unit is triggered from the receiver via an optical link and generates an electromagnetic wavelet by discharging two high voltage capacitors through back to back silicon controlled rectifiers into a resistively loaded dipole antenna successful field operations carried out during the summers of 1986 and 1987 include depth profiling as well as studies of englacial and subglacial targets on several temperate and sub polar glaciers

mixed convection and density dependent seawater circulation in coastal aquifers 1 density dependent circulation of seawater in coastal aquifers results in submarine groundwater discharge sgd across the seabed that is a mixture of terrestrial groundwater and former marine water in this study the controls of the relative amount of seawater to freshwater in sgd were investigated numerically using the feflow and sutra codes it was found that the key controls could be expressed in the form of a single nondimensional recirculation number that incorporates the combined effects of free convection forced convection and hydrodynamic dispersion on convective overturn within the coastal salt wedge anisotropy effects were incorporated into the recirculation number with limited success based on the principle of equivalent isotropic hydraulic conductivity the type of boundary condition employed along the seabed was shown to be important convective overturn was substantially increased if backward dispersion of salt into the aquifer from along the outflowing portion of the seabed boundary was prevented overall the results demonstrated a strong dependence of convective overturn on the aquifer dispersivities suggesting that results from numerical simulations are problematic to apply to real aquifer systems that typically exhibit uncertain scale dependent dispersion properties

acoustic televiewer logging in glacier boreholes the acoustic televiewer is a geophysical logging instrument that is deployed in a water filled borehole and operated while trolling it generates a digital magnetically oriented image of the borehole wall that is developed from the amplitudes and transit times of acoustic waves emitted from the tool and reflected at the water wall interface the transit time data are also converted to radial distances from which cross sectional views of the borehole shape can be constructed because the televiewer is equipped with both a three component magnetometer and a two component inclinometer the borehole s trajectory in space is continuously recorded as well this instrument is routinely used in mining and hydrogeologic applications but in this investigation it was deployed in two boreholes drilled into upper fremont glacier wyoming u s a the acoustic images recorded in this glacial setting are not as clear as those typically obtained in rocks due to a lower reflection coefficient for water and ice than for water and rock results indicate that the depth and orientation of features intersecting the boreholes can be determined but that interpreting their physical nature is problematic and requires corroborating information from inspection of cores nevertheless these data can provide some insight into englacial structural characteristics additional information derived from the cross sectional geometry of the borehole as well as from its trajectory may also be useful in studies concerned with stress patterns and deformation processes

a radar transparent layer in a temperate valley glacier bench glacier alaska radar surveys of bench glacier alaska collected over five field seasons between 2002 and 2006 reveal a surface layer of radar transparent ice in this temperate valley glacier the transparent layer covers the up glacier half of the ablation zone and is defined by a distinct lack of the radar scattering events considered typical of temperate ice radar scattering ice underlies the transparent zone and extends to the surface elsewhere on the glacier we observed the layering in constant offset radar surveys conducted with characteristic frequencies ranging from 5 mhz to 100 mhz the radar transparent layer extends from the surface to 20 m depth on average but up to 50 m in some places bench glacier s transparent layer appears similar to the cold surface layer of polythermal glaciers however observations in over 50 boreholes on bench glacier suggest there is no cold ice corresponding to the radar transparent layer we conclude that spatially extensive radar transparent layers normally used to identify cold ice in polythermal glaciers are present in some temperate glaciers copyright 2009 john wiley sons ltd

using the radium quartet for evaluating groundwater input and water exchange in salt marshes the fluxes of 226ra half life 1600 years and 228ra half life 5 7 years from the north inlet salt marsh to the sea are much larger than can be supported by decay of their th parents in the surface marsh sediments these fluxes are sustained almost entirely by groundwater flow through the marsh an average groundwater flow of approximately 10 cm3 cm 2 day 1 is indicated if the groundwater activities we have measured are representative the fluxes of 223ra half life 11 4 day and 224ra half life 3 6 day are factors of 22 and ten more than those expected from the flux of 226ra groundwater also sustains most of the flux of the short lived isotopes the measured ra activity ratio pattern in the marsh creeks matches the groundwater signature but is distinct from the pattern of the parent thorium isotopes in the sediment we present a model to explain the anomalous distribution pattern of these isotopes despite their large throughput the inventories of desorbable 226ra and 228ra in the top 15 cm sediment layer are very low nevertheless the activities of 226ra and 228ra in the porewaters are large indicating a low distribution coefficient 10 for radium and a short retention time 10 days in the surface sediment layer we surmise that groundwater flow may be a significant source of radium isotopes in the waters of shallow estuaries and coastal margins this source must be recognized while considering mass balance of any tracer be it radium nutrients other metals or 18o

measurement of submarine groundwater discharge in kahana bay o ahu hawai i submarine groundwater discharge sgd is neither well understood nor commonly investigated in hawai i but it is recognized as a potential pollution source to coastal environments between 1998 and 2000 this study located and quantified both total sgd and the terrestrial sgd fraction ftgw in kahana bay o ahu ctd casts were used to profile the water structure and identify potential areas of sgd impact in the bay lee type seepage meters were used to measure sgd rates and collect samples of sgd directly radon 222 si cl 2 and total alkalinity ta were used as natural tracers to measure the terrestrial groundwater fraction within sgd nutrient concentrations were also measured to calculate total nutrient fluxes into the bay via sgd ninety percent of the sgd in kahana bay occurs in the inner bay within 1 km of the shoreline the average total sgd flux measured was 90 3 10 6 ld 21 16 of which was terrestrial groundwater by comparison the average annual surface runoff from kahana river is 90 7 3 10 6 ld 21 estimated fluxes of total dissolved phosphorus and nitrogen by sgd to the bay were 500 and 200 greater than fluxes via surface runoff respectively thus sgd in kahana bay has proved to be a significant source of both freshwater and total nutrient input comparable to that from the surface runoff of kahana river submarine groundwater discharge sgd is the seepage of any fluids from coastal submarine sediments into the overlying coastal ocean in this respect coastal submarine sediments act as a subterranean estuary an aquifer separate unto itself with a unique chemistry distinguishing it from either the meteoric or marine hydrologic systems moore 1999 sgd is neither well understood nor commonly investigated in hawai i however sgd has recently become recognized as a potential pollution source because it can include meteoric groundwater anywhere a terrestrial aquifer with positive head is in contact with the shoreline in 1997 the scientific 1

anisotropic radio wave scattering from englacial water regimes mýrdalsjokull iceland colinear polarized 5 mhz radar profiling data were obtained on m rdalsjokull a temperate glacier in iceland radar transects and therefore polarization planes were aligned approximately parallel transverse and oblique to the ice flow direction echoes from the shallower half to two thirds of the ice were 10 20db stronger on the oblique and longitudinal transects than those on the transverse transects anisotropy as a function of depth is clearly seen at the sites where the transects cross strong scattering on longitudinal transects apparently caused extinction of a radar reflecting layer that was continuously profiled on the transverse transects a radio wave scattering model shows that scattering from a longitudinal water filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo we conclude that low frequency mhz radio waves can help to characterize englacial water regimes

a sensitivity analysis of 2d fed a model for seawater encroachment in leaky coastal aquifers abstract in a previous study a two dimensional finite element model for dispersion 2d fed was developed and verified for some previously published problems the model was applied to predict the shape of equiconcentration and equipotential lines in coastal aquifers in this paper the 2d fed model is used to study the effect of several parameters on the simulated dispersion zone and flow pattern in leaky coastal aquifers the aquifer thickness greatly affects the dispersion zone as well as the equipotential lines except for certain ranges the effects of isotropic and anisotropic permeability coefficients and anisotropic dispersivities are relatively small cyclic flow is found near the shore boundary in many cases selection of a proper mesh size especially near the seaside is found to be very important to avoid instability problems

interpretation of radio echoes from storglaciaren northern sweden analyse des echos d ondes metriques et decimetriques a l aide d une theorie d onde scalaire de la diffraction et d une statistique simple on peut par exemple etudier les rugosites du lit et les orientations des diffuseurs a l interieur de la glace

englacial and subglacial water flow at skalafellsjokull iceland derived from ground penetrating radar in situ glacsweb probe and borehole water level measurements we reconstruct englacial and subglacial drainage at skalafellsjokull iceland using ground penetrating radar gpr common offset surveys borehole studies and glacsweb probe data we find that englacial water is not stored within the glacier water content 0 0 3 instead the glacier is mostly impermeable and meltwater is able to pass quickly through the main body of the glacier via crevasses and moulins once at the glacier bed water is stored within a thin 1 m layer of debris rich basal ice 2 water content and the till the hydraulic potential mapped across the survey area indicates that when water pressures are high most of the year water flows parallel to the margin and emerges 3 km down glacier at an outlet tongue gpr data indicates that these flow pathways may have formed a series of braided channels we show that this glacier has a very low water storage capacity but an efficient englacial drainage network for transferring water to the glacier bed and therefore it has the potential to respond rapidly to changes in melt water inputs

seasonal changes in ground penetrating radar signature observed at a polythermal glacier bylot island canada in recent years ground penetrating radar gpr has been increasingly used for characterization of subglacial and englacial environments at polythermal glaciers the geophysical method is able to exploit the dielectric difference between water air sediment and ice allowing delineation of subsurface hydrological thermal and structural conditions more recent gpr research has endeavoured to examine temporal change in glaciers in particular the distribution of the cold ice zone at polythermal glaciers however the exact nature of temporal change that can be identified using gpr has not been fully examined this research presents the results of three gpr surveys conducted over the course of a summer ablation season at a polythermal glacier in the canadian arctic a total of approximately 30 km of gpr profiles were collected in 2002 repeatedly covering the lower 2 km of stagnation glacier bylot island 72 58 n 78 22 w comparison between profiles indicated changes in the radar signature including increased noise appearance and disappearance of englacial reflections and signal attenuation in the latter survey further an area of chaotic returns in up glacier locations which was interpreted to be a wet temperate ice zone showed marked recession over the course of the ablation season combining all the temporal changes that were detected by gpr results indicate that a polythermal glacier may exhibit strongly seasonal changes in hydrological and thermal characteristics throughout the ice body including the drainage of 17 000 m 3 of temporarily stored intra glacial meltwater it is also proposed that the liquid water content in the temperate ice zone of polythermal glaciers can be described as a fraction of a specific retention capacity copyright 2006 john wiley sons ltd

automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls kulessa b a d booth a hobbs and a l hubbard 2008 automated monitoring of subglacial hydrological processes with ground penetrating radar gpr at high temporal resolution scope and potential pitfalls geophysical research letters 35 24 l24502

an assessment of the importance of some parameters for seawater intrusion in aquifers and a comparison of dispersive and sharp interface modelling approaches abstract the problem considered is that of determining the location and shape of the steady interface in a coastal aquifer discharging fresh water to the sea for homogeneous isotropic aquifers the location of the interface is obtained by the boundary integral method for an abrupt interface model these results are compared with the distribution of salt in the dispersion zone where the two fluids meet as determined by a finite difference solution of the flow and convective dispersion equations considerations are restricted to a rectangular section of isotropic homogeneous aquifer and examples are limited to those showing the effects of different convection to dispersion ratios including anisotropic dispersion different fresh water flow gradients and different relative densities of seawater these examples give an indication of the relative accuracy of the abrupt interface model for different ratios of convection to dispersion and enable the influence of various parameters on the shape and extent of the dispersion zone to be studied

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods