a model for a moving interface in a layered coastal aquifer the framework of the present study is the development of a new approach to describe the displacement of fresh water by salt water in a layered coastal aquifer the aquifer is composed of horizontal layers possessing different hydraulic conductivities which are also different in the saltwater and the freshwater zones a one dimensional analysis is performed describing the displacement of the saltwater freshwater interface under the influence of freshwater flow toward the sea several analytical solutions are found revealing the effects of various parameters on the interface displacement process on the basis of these solutions several type curves for different freshwater saltwater hydraulic conductivity are drawn the model is calibrated by matching a type curve with field data taken from an observation well and is further used to predict the evolution of the interface shape and position

artificial tracers for geothermal reservoir studies safe disposal of thermally spent geothermal brines that contain environmentally hazardous constituents is commonly obtained by reinjection the reinjection process also serves to maintain reservoir pressure enhance thermal recovery and eliminate possible compactional subsidence to avoid premature thermal breakthrough of reinjected fluids tracer tests are employed for detection and evaluation of preferential path networks in this paper some promising tracers that have not received much attention in geothermal reservoir studies are discussed and a comprehensive tabulation of field sites of artificial tracer utilization is presented chemical and transport processes responsible for tracer retention by the formation of reservoir solids as well as available tracer detection techniques are emphasized

interpretation of field tracer tests of a single fracture using a transient solute storage model the results and interpretation of five induced gradient tracer tests performed at five different average interborehole fluid velocities in a single fracture in monzonitic gneiss are described the experiments were conducted using radioactive 82br and a fluorescent dye as conservative tracers where the tracers were pulse injected into radial convergent and injection withdrawal flow fields the flow fields were established between straddle packers isolating the fracture in three boreholes over distances of 12 7 29 8 m the tracer breakthrough curves were determined from samples of the withdrawn groundwater and were interpreted using residence time distribution rtd theory and two deterministic simulation models the rtd curves of the tracer experiments were interpreted by fitting to the field data a simple advection dispersion model and an advection dispersion model with transient solute storage in immobile fluid zones both models consider the different flow field geometries associated with injection withdrawal and radial convergent tests comparison of the fits obtained by the simulation models suggest that the initial period of solute transport in single fractures is advection dominated and with increasing tracer residence time or decreasing fluid velocity transport progresses toward more fickian like behavior during the advective dominated period the transient solute storage model is shown to adequately describe the asymmetries and long tails characteristic of the fracture rtds interpretation of the tracer experiments using both simulation models further suggests that induced gradient tracer experiments are likely to underestimate the dispersive characteristics of single fractures under natural flow conditions

subsurface seawater intrusion barrier analysis seawater intrusion barriers are currently being constructed in the coastal aquifers of japan based on the results of a computer model employing finite difference numerical techniques this model provides a practical design and management tool for predicting the likelihood of seawater intrusion through a semipervious subsurface barrier in an unconfined coastal aquifer the analysis assumes an abrupt interface the dupuit approximations and various simplifying boundary conditions the movements of both the water table and the freshwater saltwater interface are numerically simulated in the unsteady state the computed results are validated with observations obtained from a vertical two dimensional sand box model the application of the computer model is illustrated by a site specific analysis for a proposed subsurface barrier location in a limestone coastal aquifer on okinawa jima island in the western pacific ocean from this analysis it is found that the subsurface barrier is able to delay seawater intrusion for about 2 mo under critical conditions of continual pumping of the aquifer without recharge the subsurface barrier is technically feasible and is a viable solution to the problem of seawater intrusion in coastal aquifers

transience of seawater intrusion in response to sea level rise 1 understanding seawater intrusion swi induced by sea level rise slr is important for the future management of many coastal aquifers only simplified steady state sharp interface analyses of generalized slr swi exist in the literature and the important issue of associated time scales has been neglected we employ numerical modeling in order to explore the transience of dispersive slr swi in common unconfined coastal aquifer settings an instantaneous slr is adopted to compare with the instantaneous sea level drop sld case of a previous sld swi analysis temporal asymmetry between the swi responses to slr and sld is observed a slr swi simulation series indicates that toe representative response times time to reach 95 of new steady state range from decades to centuries for a 1 m slr significant discrepancies between the representative response times of various swi quantitative indicators e g toe position wedge center of mass are observed this demonstrates that the indication of steady state swi conditions depends upon the monitoring approach and thus holds implications for studies reporting that swi steady state has been attained we adopt 100 years as a typical planning time frame and compare 100 year and steady state slr swi as expected the simplified steady state sharp interface solution overpredicts the 100 year landward toe shift in most cases however some simulations exhibit temporary overshoot of the steady state interface position this is in contradiction to the presumption that steady state swi is the worst case steady state sharp interface estimates appear to be at best useful as initial approximations of slr swi given that they span 40 250 of 100 year dispersive interface results for the cases considered

break up of the largest arctic ice shelf and associated loss of an epishelf lake 1 field observations and radarsat imagery of the ward hunt ice shelf lat 83 n long 74 w nunavut canada show that it broke in two over the period 2000 to 2002 with additional fissuring and further ice island calving the fracturing caused the drainage of an ice dammed epishelf lake disraeli fiord a rare ecosystem type reductions in the freshwater volume of disraeli fiord occurred from 1967 to the present and accompanied a significant rise in mean annual air temperature over the same period in this far northern region the recent collapse of ice shelves in west antarctica has been interpreted as evidence of accelerated climate change in that region similarly the inferred thinning and observed fragmentation of the ice shelf plus the drainage of the epishelf lake are additional evidence for climate change in the high arctic

effect of climate change on sea water intrusion in coastal aquifers there is increasing debate these days on climate change and its possible consequences much of this debate has focused in the context of surface water systems in many arid areas of the world rainfall is scarce and so is surface runoff these areas rely heavily on groundwater the consequences of climate change on groundwater are long term and can be far reaching one of the more apparent consequences is the increased migration of salt water inland in coastal aquifers using two coastal aquifers one in egypt and the other in india this study investigates the effect of likely climate change on sea water intrusion three realistic scenarios mimicking climate change are considered under these scenarios the nile delta aquifer is found to be more vulnerable to climate change and sea level rise copyright 1999 john wiley sons ltd

variable density flow and solute transport simulation of regional aquifers containing a narrow freshwater saltwater transition zone variable density flow and solute transport simulation of aquifer systems containing narrow transition zones between freshwater and saltwater requires particular attention to certain aspects of the numerical method and its application to be successful typically only cases involving wide transition zones have been simulated with variable density transport models possibly because of inaccuracies in the modeling approaches used the major components of a successful approach are threefold first functionally consistent approximation of terms involved in fluid velocity calculations is necessary in the case of galerkin finite element methodology a significant modification is required to the standard approach in order to achieve consistency second the simulator must be verified in a particular series of tests the usual tests using henry s problem for verification of density dependent transport simulators are inadequate to check for consistency of the velocity approximations and for the accuracy of simulating flow driven by bouyancy forces third adequately fine spatial discretization is required when applying the simulator for spatial stability of the numerical transport solution and to allow accurate representation of narrow transition zones and the effects of low transverse dispersivity the effectiveness of this approach is demonstrated through simulation of the flow of fresh and saline groundwater in the layered basalt aquifer of southern oahu hawaii the transition zone in this regional flow system is narrow except near the discharge area where it is broadly dispersed simulation of this common situation with an inconsistent approximation gives grossly incorrect results while simulation with a consistent model provides a robust tool for analysis of system hydrology

loss of floating glacier tongues from the yelverton bay region ellesmere island canada a total of eight floating glacier tongues have shrunk in area by 85 from the yelverton bay region of northern ellesmere island since 1959 with unusually large losses since 2005 to better understand the causes of these losses this study undertakes the first examination of ice tongue changes in this region including an assessment of changes in surrounding marine ice i e sea ice sikussak and melange and atmospheric and oceanographic forcings from 1959 to 2017 the total ice tongue area decreased by 49 07 km 2 with the majority of this loss occurring from 2005 to 2009 34 68 km 2 the loss of ice tongues since 2005 occurred when open water replaced multi year landfast sea ice mlsi and first year sea ice in the regions adjacent to the ice tongues these changes were accompanied by an increase in mean annual mid depth i e 100 and 200 m ocean temperatures from 0 29 c from 1999 to 2005 to 0 67 c from 2006 to 2012 despite the recent return of ocean temperatures to below pre 2006 levels atmospheric summer temperatures have continued to rise 0 15 c decade 1 between 1948 and 2016 with open water continuing to occur without the sustained presence of mlsi in this region the ice tongues are unable to stabilize making it unlikely that they will re form in the current climate

borehole dilution tests in the vicinity of an extraction well abstract a mathematical solution is derived for a borehole dilution test conducted in the proximity of an extraction well under conditions where the theis assumptions are applicable the solution is similar to the steady state velocity case except for a factor that accounts for the transient response of the aquifer to pumping curves calculated from the derived solution show a delay in response that increases with the specific storage of the aquifer and with the radius from the extraction well the delay decreases with increasing values of hydraulic conductivity and aquifer thickness deviations of the response curves from the straight line steady state velocity case can be used to calculate the hydraulic diffusivity while the limiting slope at late time can be used to calculate groundwater flux when borehole dilution tests are conducted at several intervals over the thickness of the aquifer under steady state velocity conditions k z can in principle be calculated using several equations depending on the type of information available two existing methods to account for the distortion of the flow lines near the open test interval are related to well construction and development reasonable estimates of borehole factors can only be obtained for minimally developed wells

volume and area changes of the milne ice shelf ellesmere island nunavut canada since 1950 1 ground penetrating radar gpr surveys of the 205 km2milne ice shelf conducted in 2008 and 2009 are compared with radio echo sounding res data from 1981 to provide the first direct measurements of thinning for any northern ellesmere island ice shelf our results show an average thinning for the ice shelf as a whole of 8 1 2 8 m with a maximum of 30 m over this 28 year period direct line comparisons along a 7 5 km transect near the front of ice shelf indicate a mean thinning of 2 63 2 47 m over the same period reductions in areal extent 29 82 8 4 km2 1950 2009 and volume 13 1 5 0 73 km3 water equivalent w e 1981 2008 2009 indicate that the milne ice shelf has been in a state of negative mass balance for at least the last 59 years a comparison of mean annual specific mass balance measurements with the nearby ward hunt ice shelf whis suggests that basal melt is a key contributor to milne ice shelf thinning glacier inflow to the ice shelf has also reduced markedly over the past 28 years the transition of ice shelf ice to lake ice was the most important source of mass loss a 28 5 km2 epishelf lake now exists on the landward side of the ice shelf given these recent changes disintegration of the milne ice shelf will almost certainly continue in the future

assessment of historical changes 1959 2012 and the causes of recent break ups of the petersen ice shelf nunavut canada aerial photography and satellite imagery of the petersen ice shelf nunavut canada from 1959 to 2012 show that it was stable until june 2005 after which a series of major calving events in the summers of 2005 2008 2011 and 2012 resulted in the loss of 61 of the june 2005 ice shelf area this recent series of calving events was initiated by the loss of extensive regions of 50 year old multi year landfast sea ice from the front of the ice shelf in summer 2005 each subsequent calving event has been preceded by open water conditions and resulting loss of pack ice pressure across the front of the ice shelf and most occurred during record warm summers ground penetrating radar gpr ice thickness measurements and radarsat 2 derived observations of surface motion indicate that tributary glaciers provided total ice input of 1 19 5 65 mt a 1 to the ice shelf from 2011 to 2012 far below the mean surface loss rate of 28 45 mt a 1 with recent losses due to calving and little evidence for current basal freeze on this suggests that the petersen ice shelf will no longer exist by the 2040s or sooner if further major calving events occur

origin and characteristics of brackish groundwater in abu madi coastal area northern nile delta egypt abstract hydrogeochemical and geoelectrical resistivity investigations were carried out to assess the origin and characteristics of a brackish groundwater in abu madi coastal area twenty six surface water shallow and deep groundwater samples were collected and analyzed for various ionic concentrations as well as oxygen and hydrogen stable isotopic contents in addition a total of 20 vertical electrical sounding sites were conducted to investigate layers thicknesses resistivities and to detect the water bearing layers then 2 d electrical resistivity tomography ert along two profiles in the study area was conducted to get information about the surface water effect on recharge the stable isotopic composition and the chloride concentrations strongly suggest that the deep groundwater in abu madi area is dominated by inland freshwater with a minor seawater component this groundwater was recharged during the first and the third holocene humid climatic cycles where the sea surface was about 125 and 25 m below the current sea level respectively the brackish nature and higher piezometric surface of the groundwater as well as the occurrence of vertical low salinity seawater zone in front of the study area support the possibility of submarine groundwater discharge the geoelectrical resistivity surveying on the other hand revealed a number of geoelectrical groundwater bearing layers the main water bearing layer in the study area is represented by the sixth geoelectrical layer which has relatively high resistivity and a considerable thickness being consistent with the hydrogeochemical observations ert results point to the presence of shallow water bearing layers recharged from the surface water drains with low resistivity and surface rain water of moderate resistivity results from the hydrogeochemical analyses and the different hydrogeological data are consistent with the high resistivity values of this geoelectrical layer however the overall high specific conductance and high sodium hazards indicate that the groundwater in the study area should be carefully treated before irrigation and domestic uses through mixing it with surface irrigation water

area change of glaciers across northern ellesmere island nunavut between 1999 and 2015 using a variety of optical satellite scenes this study quantifies the change in the areal extent of 1773 glaciers across northern ellesmere island between 1999 and 2015 our results show that the regional ice coverage decreased by 1705 3 km 2 over the 16 year period a loss of 5 9 ice shelves had the greatest losses relative to their size of 42 4 glaciers feeding into ice shelves reduced in area by 4 7 while tidewater glaciers reduced in area by 3 3 marine terminating glaciers with floating ice tongues reduced in area by 4 9 and 19 of these 27 ice tongues disintegrated causing these glaciers to retreat to their grounding lines land terminating glaciers lost 4 9 of their 1999 area including the complete loss of three small ice caps 2 our study highlights the high sensitivity of the ice cover of northern ellesmere island to recent climate warming and the continued losses that are likely to occur in the future in particular the ice masses most susceptible to further losses are marine terminating glaciers with floating termini and small land terminating ice caps at low elevations

arctic ice shelves and ice islands origin growth and disintegration physical characteristics structural stratigraphic variability and dynamics ice shelves are thick floating ice masses most often associated with antarctica where they are seaward extensions of the grounded antarctic ice sheet and sources of many icebergs however there are also ice shelves in the arctic primarily located along the north coast of ellesmere island in the canadian high arctic the only ice shelves in north america and the most extensive in the north polar region the ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands the tabular icebergs of the arctic ocean the present state of knowledge and understanding of these ice features is summarized in this paper it includes historical background to the discovery and early study of ice shelves and ice islands including the use of ice islands as floating laboratories for polar geophysical research growth mechanisms and age the former extent and the twentieth century disintegration of the ellesmere ice shelves and the processes and mechanisms of ice island calving are summarized surface features thickness thermal regime and the size shape and numbers of ice islands are discussed the structural stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described large scale and small scale dynamics of ice islands are described and the results of modeling their drift and recurrence intervals are presented the conclusion identifies some unanswered questions and future research opportunities and needs

twin lake tracer tests setting methodology and hydraulic conductivity distribution following evaluation of three potential sites a fluvial sand aquifer with high 0 7 1 6 m d 1 linear average groundwater flow velocities was instrumented with a fully penetrating injection well and 82 monitoring installations over a 40 m flow path length two natural gradient tracer migration experiments have employed pulse injections of a nonreactive radioisotope 131i in a study of hydraulic conductivity structure and dispersive characteristics of the flow system the use of a gamma emitting radionuclide in these experiments allowed measurement of tracer distribution by scanning fully penetrating boreholes with a scintillation detector this technique provided many advantages in data collection over conventional tracers including unprecedented resolution of the vertical distribution of tracer measurements without pumping and the attendant concerns for flow system perturbation and minimal manpower for sample analysis tracer breakthroughs at monitors along the axis of flow revealed the presence of heterogeneities in aquifer hydraulic conductivity at two scales over the 40 m path length six regions with hydraulic conductivities substantially different from adjacent strata were identified thicknesses of these regions varied from 0 2 to more than 3 m their lateral extents in the direction of groundwater flow ranged from 15 m to more than 40 m smaller strata with an average thickness of 0 34 m and lengths of less than 10 m were detected within all six of the hydraulic conductivity regions but there was no evidence of increases in local dispersivity with increased transport distance as a result of these variations the six hydraulic conductivity regions do however have measurable effects on whole aquifer dispersion stratification characteristics of the tested aquifer believed to have been deposited in a sandy braided river are consistent with those observed in similar modern environments estimation of the magnitude and spatial structure of hydraulic conductivity variations in aquifers of concern would be greatly aided by studies of the stratification characteristics in well exposed modern or lithified sedimentary analogues

analysis and interpretation of single well tracer tests in stratified aquifers this study deals with the definition and measurement of the dispersive properties of a stratified aquifer based on the single well tracer test knowledge of such dispersive properties are of fundamental importance to the evaluation analysis and simulation of contaminant migration in groundwater a subject of great interest in recent years in the single well test tracer is pumped into the formation for a period of time and then pumped out concentration data are obtained from the injection withdrawal well and from one or more sampling observation wells which may be multilevel our analysis of such a test is based on a lagrangian eulerian numerical model which considers the depth dependent advection in the radial direction and local hydrodynamic dispersion in the vertical and radial directions results show that the movement of an injected tracer in a stratified aquifer may be accurately simulated without resorting to the use of a scale dependent full aquifer dispersivity if the flow field is known in sufficient detail when the advection process is simulated accurately the values of local dispersivity will be small constant and on the order of those measured in the field or laboratory at individual levels in the aquifer the full aquifer breakthrough curves measured in observation wells in a single well test in a stratified aquifer are determined by the hydraulic conductivity profile in the region between the injection withdrawal well and the observation well if the travel distance between these wells is typical of most test geometries however the relative concentration versus time data recorded at the injection withdrawal well during the withdrawal phase is primarily a measure of mixing in the aquifer due to local dispersion which has taken place during the experiment the amount of mixing will depend on both the hydraulic conductivity distribution in the aquifer and the size of the experiment as the experiment scale increases the effects of local vertical dispersion will become larger compared to the effects of local radial dispersion local vertical dispersion will cause a solute traveling in a high conductivity layer in an aquifer to migrate into adjacent low conductivity layers where its movement will be relatively slow in comparison in the initial design of a tracer test it is important to have some idea of the type of nonhomogeneity with which one is dealing more information of a broad nature concerning the types or classifications of nonhomogeneities that exist in natural aquifers would be very useful future research in this area is needed

analytical solutions to non fickian subsurface dispersion in uniform groundwater flow abstract analytical solutions are obtained by the fourier transform technique for the one two and three dimensional transport of a conservative solute injected instantaneously in a uniform groundwater flow these solutions account for dispersive non linearity caused by the heterogeneity of the hydraulic properties of aquifer systems and can be used as building blocks to construct solutions by convolution principle of superposition for source conditions other than slug injection the dispersivity is assumed to vary parabolically with time and is thus constant for the entire system at any given time two approaches for estimating time dependent dispersion parameters are developed for two dimensional plumes they both require minimal field tracer test data and therefore represent useful tools for assessing real world aquifer contamination sites the first approach requires mapped plume area measurements at two specific times after the tracer injection the second approach requires concentration versus time data from two sampling wells through which the plume passes detailed examples and comparisons with other procedures show that the methods presented herein are sufficiently accurate and easier to use than other available methods

an experimental and numerical study of evaporite mineral dissolution and density driven flow in porous media abstract subsurface mineral dissolution problems exhibit complex behaviors which are difficult to model and validate numerically controlled physically validated experimental problems can be used to better understand mineral dissolution and subsequent numerical representation bridging the gap between numerical models and field observations the objective of this work was to collect the first controlled physical measurements in a porous aquifer overlying an evaporite mineral and to create a numerical model of the system the problem studied was modified from the classic hydrocoin level 1 case 5 problem three flow gradients in a porous aquifer were investigated in duplicate in a 2 d box problem the duplicate measurements had high variability shown by numerical modeling to be a result of initial conditions variable flux representing dissolution sharp gradients and variable dispersivity the physical measurements of parameters and fields were important for calibration success the numerical models including sensitivity analyses were capable of simulating flow patterns observed concentrations and peaks resulting from observed initial conditions the numerical models were a key tool in understanding factors influencing the flow and spread of salt within the system the models were limited by the ability to detail physical observations difficult in both the laboratory and for potential field applications the results provided insight in the hydrocoin level 1 case 5 numerical simulations with flow appearing to be swept forward however observed concentrations were lower than commonly modeled

solute advection in stratified formations advection dominated solute movement in stratified formations is investigated using a lagrangian interpretation of particle motion a probability density function pdf for particle position quantifies the expected depth integrated resident concentration a pdf for particle arrival time quantifies the expected depth integrated rate of mass arrival from which the flux averaged concentration can be defined the difference between the flux averaged and resident concentrations is shown to be significant for the variability in the hydraulic conductivity that is commonly encountered in field applications the influence of porosity variations on the advection dominated solute movement in stratified porous media is shown to be notable only for large variability in the effective porosity

an analysis of dispersion in a stratified aquifer the dispersion of a conservative solute produced as a result of vertical variations of hydraulic conductivity in a horizontal stratified aquifer of finite thickness is analyzed by applying the moment method of aris to solve the governing advection dispersion equation describing mass transport in the analysis it is assumed that the aquifer is of constant thickness and of infinite lateral extent the hydraulic conductivity is a known function of the vertical coordinate only and the flow is unidirectional parallel to the stratification the applicable aris moment equations are developed in a suitable nondimensional form analytical solutions are obtained for the zeroth and first moments and for the time derivative of the second moment of the longitudinal concentration distribution for the case of an instantaneous plane source for several idealized hydraulic conductivity profiles parabolic linear step function and cosine profiles and their even periodic extensions the analysis gives the time dependent variation of the longitudinal macrodispersivity for these idealized cases throughout the transient development of the dispersion process the results of the analysis are applied to a field measured hydraulic conductivity profile and predicted values of the longitudinal macrodispersivity are compared with field results an important conclusion from the analyses is that nonuniformities in the hydraulic conductivity profile which persist over long distances may produce rather large values of longitudinal macrodispersivity which are comparable to those observed in some aquifers and which are much larger than those predicted by some previous stochastic analyses implications of the analytical results for field dispersion problems are discussed

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

marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs principles methodologies and limitations the possibility of a time domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated the method operates on source receiver offsets which are several times less than the depth of the reservoir geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field the basics of the method as well as its sensitivity resolution and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths are analyzed for the analysis 1d and 3d geoelectric models of hydrocarbon reservoirs are used it is shown that under existing technologies of excitation and measurement of vertical electric fields the highest accessible depth of soundings can be up to 4 km technology for the inversion and interpretation of transient responses is demonstrated on experimental data

a multi level pore water sampler for permeable sediments abstract the construction and operation of a multi level piezometer multisampler designed to collect pore water from permeable sediments up to 230 cm below the sediment water interface is described multisamplers are constructed from 1 inch schedule 80 pvc pipe one quarter inch flexible pvc tubing leads from eight ports at variable depths to a 1 inch tee fitting at the top of the pvc pipe multisamplers are driven into the sediment using standard fence post drivers water is pumped from the pvc tubing with a peristaltic pump field tests in banana river lagoon florida demonstrate the utility of multisamplers these tests include collection of multiple samples from the permeable sediments and reveal mixing between shallow pore water and overlying lagoon water

transition zone width in ground wateron ocean atolls an analytical solution for the thickness of the transition zone between fresh and seawater in aquifers on ocean islands is presented the interface is treated as a mixing layer similar to a laminar boundary layer between fluids moving at different velocities the method requires assumptions of homogeneous isotropic dispersion uniform hydraulic conductivity and steady flow all water withdrawal is assumed to occur at the water table the slope of the sharp interface is used in the solution for the mixing layer and the sharp interface is determined using dupuit forchheimer assumptions of horizontal flow the method presented efficiently estimates the transition zone thickness thus providing information not available from sharp interface models the method is illustrated by application to the freshwater lens on an island of the tarawa atoll in the pacific ocean and is used to show the effects of different pumping arrangements on the width of the mixing layer

effects of kinetic mass transfer and transient flow conditions on widening mixing zones in coastal aquifers 1 the width of a mixing zone between freshwater and seawater is important primarily because it directly reflects the extent of mixing and the growth and decay of the mixing zone indicates changes of the flow regime and water exchange between freshwater and coastal seawater wide mixing zones have been found in many coastal aquifers all over the world however the mechanisms responsible for wide mixing zones are not well understood this work examines the hypothesis that kinetic mass transfer coupled with transient conditions which create the movement of the mixing zone may widen mixing zones in coastal aquifers the hypothesis is tested by conducting two dimensional numerical simulations based on a variable density groundwater model for a scaled tank model and a field scale model periodic water levels representing periodic tidal motion and freshwater table fluctuations are imposed at the seaward and landward boundary respectively which cause the movement of the mixing zone both the scaled tank model and the field model show that the combination of the moving mixing zone and kinetic mass transfer may significantly enhance the extent of mixing and create a wider mixing zone than the models without kinetic mass transfer in addition sensitivity analyses indicate that a larger capacity ratio immobile porosity mobile porosity of mass transfer leads to a wider mixing zone and the maximum width of the mixing zone may be reached for a given capacity ratio when the mean retention time scale in the immobile domain the reciprocal of mass transfer rate and the period of water level fluctuations are comparable

performance analysis and simulation of a two well tracer test at the mobile site during the late summer of 1984 a two well tracer test was performed which involved travel distances of 38 3 m to 90 m a bromide tracer slug was injected at one well while groundwater was simultaneously pumped from the other well the two well test which required 32 days to complete was then simulated by geotrans inc using a three dimensional advection dispersion model with a longitudinal dispersivity of 0 15 m a transverse dispersivity of 0 05 m and the permeability distribution being measured independently in a single well test single well test results which involved a travel distance of 5 5 m indicated that the hydraulic conductivity varied by about a factor of 4 throughout the aquifer thickness the two well test simulation made without knowledge of the test results and without any calibration was remarkably good local hydrodynamic dispersion was negligible so that the concentration versus time breakthrough at the withdrawal well could be simulated just as well with a quasi three dimensional advection model having zero hydrodynamic dispersion this implies that over the travel distances applicable to the two well test the spreading of the slug in the aquifer depended mainly on macroscopic velocity variations that were quantifiable in terms of the inferred permeability distribution this result which pertains to an aquifer in a fluvial terrace deposit of quaternary age is similar to that observed by pickens and grisak in a sandy glaciofluvial aquifer near the chalk river nuclear laboratories in canada such flow systems can result in fully three dimensional plumes with high concentrations of contaminant moving over large horizontal distances in the higher permeability zones

a density dependant finite element model for analysis of saltwater intrusion in coastal aquifers summary saltwater intrusion is a serious problem in coastal regions all over the world it is one of the processes that degrade water quality by raising salinity to levels exceeding acceptable drinking water standards it may occur due to human activities and or by natural events over abstraction is considered the main cause of saltwater intrusion moreover climate change and sea level rise speed up saltwater intrusion this paper presents the development and validation of a coupled transient finite element model for simulation of fluid flow and solute transport in saturate and unsaturated soils with application to study saltwater intrusion in coastal aquifers the model includes coupling of water flow air flow heat flow and solute transport furthermore transient density dependent flow is included in the model and the dependency of dispersion on velocity is considered different mechanisms that govern solute transport in porous media including advection diffusion dispersion adsorption chemical reactions and biological degradation are included in the model the governing equation of the solute transport is solved together with three balance equations for water flow air flow and heat transfer the nonlinear system of governing differential equations is solved using the finite element method in the space domain and a finite difference scheme in the time domain the model is validated by application to a standard case study from the literature henry s problem and then applied to predict saltwater intrusion in a coastal aquifer the results of the model predictions are presented and discussed

a field example of measuring hydrodynamic dispersion in a single fracture a field example of measuring the dispersive properties of a single fracture in fractured plutonic rock is presented the experimental technique involves injecting a slug of conservative tracer into a steady groundwater flow field established between a pumping and recharging borehole and monitoring the tracer breakthrough by sampling the withdrawal water directly the breakthrough curves from two experiments were analyzed with a model which describes the flow field geometry either analytically or numerically and solves for hydrodynamic dispersion analytically a longitudinal dispersivity of 1 40 m was estimated by fitting the model to each set of field data the magnitude of the dispersion was determined to be independent of dispersive effects created by flow through the borehole instrumentation and thought to be purely hydrodynamic in nature

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

electromagnetic fields induced at the seafloor by rayleigh stoneley waves we model oceanic acoustic and seismic disturbances as rayleigh stoneley waves in the layered medium consisting of ocean sediment and rock the waves induce electromagnetic fields because of motion of conducting materials through the geomagnetic field low frequency disturbances in deep water are efficient electromagnetic generators because the motions are coherent over large volumes of highly conducting seawater for wave frequencies below 0 1 hz in deep water the geomagnetic field is nearly frozen to the moving water consequently the electric field measured by a voltmeter attached to the seabed is approximately u f where u is the difference between the velocity of the water and of the voltmeter itself as it is moved by the motion of the seafloor and f is the geomagnetic field this result applied to love waves suggests that the electric field will result largely from the movement of the detector but detailed calculations have not been made although the fields are weak they should be detectable because the main interference is from ionospheric sources and the fields from these sources are greatly attenuated at the seabed by the overlying oceanic shield the effectiveness of the shield diminishes sharply at frequencies below 0 03 hz at high frequencies the principal limitation to detectability is in the inherent noise level of detectors whether electric or magnetic at present electric detectors are more effective than magnetic they appear to be competitive with accelerometers for seismic detection in the deep ocean in a restricted frequency band near 0 05 hz a layer of unconsolidated sediment underlying the ocean profoundly affects the dispersion relation of rayleigh stonely waves and thereby affects the electromagnetic induction process the shunting effect of a normal deep ocean sediment layer is not large on the electric field but the low shear modulus of the sediments influences sea bottom motions and therefore greatly changes the fields sensed by bottom mounted instruments especially at higher frequencies

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

twin lake tracer tests longitudinal dispersion two natural gradient dispersion tests were conducted at the chalk river nuclear laboratories ontario in 1982 and 1983 in order to quantify field scale dispersion processes over a 20 and 40 m distance of a radiotracer migration the patterns of dispersion that were observed in the field using a dry access tube monitoring technique were compared with patterns predicted by the advection dispersion model with constant parameters analysis of the time concentration profiles of the tracer at observation wells located along the mean direction of the longitudinal spreading showed that the dispersion model adequately describes the dispersion patterns actually observed and averaged over the aquifer depth the values of longitudinal dispersivity determined from continuous time concentration profiles were virtually equal to those obtained from laboratory scale columns the dispersive properties of the aquifer were characterized at the local scale by a constant independent of travel distance dispersivity value of 0 0045 m averaging the test data over the aquifer depth analogous to the information provided by a fully penetrating pumping well yielded a full aquifer dispersivity varying in an irregular fashion from 0 16 to 0 06 m the scale effect observed between local scale and full aquifer dispersivities is the result of inhomogeneity of the aquifer and the concentration averaging produced by the sampling instrumentation the results of two tracer tests also showed that the use of the dry access tube monitoring technique for field experimentation provides detailed representation of spatial and temporal distribution of a radiotracer s activity and consequently provides a practical means to determine the groundwater velocity field and dispersive properties of porous materials

surface mass balance of the ward hunt ice rise and ward hunt ice shelf ellesmere island nunavut canada 1 the ward hunt ice rise and ward hunt ice shelf located on ellesmere island canada are two of the northernmost land ice masses on the north american continent surface mass balance measurements excluding calving and subice processes began in 1959 on the ice rise and in 1966 on the ice shelf but were frequently interrupted most recently between 1986 and 2002 the surface balance of the ice rise and ice shelf follows the temporal pattern seen on other measured high arctic glaciers the overall surface mass losses over the last 45 years have been comparatively low 1 68 m water equivalent w eq for the ice rise and 3 1 m w eq for the ice shelf which reflects their proximity to the arctic ocean nevertheless the ice shelf appears to have weakened sufficiently in recent years to raise concerns about its possible disintegration in the near future the 2002 2003 balance year was the most negative year on record 0 33 m w eq for the ice rise and 0 54 m w eq for the ice shelf dynamical stresses related to wind wave and tidal action may further accelerate this process as open water conditions on the arctic ocean become more prevalent the ward hunt ice rise has so far remained in a reasonably healthy state in terms of its overall surface mass balance although its long term survival is also threatened by current and predicted future climatic conditions

incorporating the concept of equivalent freshwater head in successive horizontal simulations of seawater intrusion in the nile delta aquifer egypt summary a new approach to study seawater intrusion problems in coastal aquifers is presented the approach is demonstrated for the case of the nile delta aquifer in egypt feflow a 3d finite element variable density model is employed however because of the lack of 3d data and to demonstrate the proposed approach the simulations are performed in 2d horizontal views the concept of equivalent freshwater head usually implemented in 2d vertical simulations is adapted in the horizontal areal simulations after calibration against field observations the simulations are conducted at four horizontal sections located at different levels 100 200 300 and 400 m below the mean seawater level the depth of the horizontal section is identified through assigning an appropriate pressure equivalent freshwater head at the boundaries the study domain is modified for the horizontal sections at 300 and 400 m respectively to account for the aquifer geometry at these depths the effect of freshwater recharge from the nile river on the seawater intrusion is observed in the upper layer around its two main branches the results of the horizontal simulations clearly demonstrate the variation of water concentration in the vertical direction as the depth increases the transition zone in which the concentration varies from the seawater to the freshwater concentration is shifted toward the landside and become more extensive at the lower levels of the nile delta aquifer the seawater migrates much further inland as compared to the shallower levels the concept of horizontal simulations at different levels is further developed to produce meaningful concentration distributions in the vertical sections this approach allows for a better realization of seawater intrusion in coastal aquifers

holocene dynamics of the arctic s largest ice shelf ice shelves in the arctic lost more than 90 of their total surface area during the 20th century and are continuing to disintegrate rapidly the significance of these changes however is obscured by the poorly constrained ontogeny of arctic ice shelves here we use the sedimentary record behind the largest remaining ice shelf in the arctic the ward hunt ice shelf ellesmere island canada to establish a long term context in which to evaluate recent ice shelf deterioration multiproxy analysis of sediment cores revealed pronounced biological and geochemical changes in disraeli fiord in response to the formation of the ward hunt ice shelf and its fluctuations through time our results show that the ice shelf was absent during the early holocene and formed 4 000 years ago in response to climate cooling paleoecological data then indicate that the ward hunt ice shelf remained stable for almost three millennia before a major fracturing event that occurred 1 400 years ago after reformation 800 years ago freshwater was a constant feature of disraeli fiord until the catastrophic drainage of its epishelf lake in the early 21st century

airborne uhf radar sounding of glaciers and ice shelves northern ellesmere island arctic canada more than 2000 line kilometres of ice were sounded in 1981 using an 840 mhz pulsed radar system the surveyed regions include mt oxford ice cap disraeli glacier milne glacier ward hunt ice shelf and milne ice shelf in northern ellesmere island arctic canada the maximum ice thickness that was reliably recorded was 750 m for milne glacier in addition to ice thickness interpretation the power reflection coefficient prc and propagation loss rate were estimated from the data measured basal prc s differ for ice shelves floating glaciers and grounded glaciers spatial variations of prc have been used to infer a composite structure for the ice shelves ward hunt ice shelf proved difficult to sound probably because of its known saline and brackish chemistry excellent results were obtained for milne ice shelf and its depth was found to average roughly 70 m in places attaining 100 m bottom side crevasses were observed within milne ice shelf the characteristic ridge and trough topography of the ice

characterization of hydrogeologic properties for a multi layered alluvial aquifer using hydraulic and tracer tests and electrical resistivity survey a multi layered aquifer typical of riverbank alluvial deposits in korea was studied to determine the hydrologic properties the geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units silt sand highly weathered and fresh bedrock layers the electrical resistivity survey supplied information on lateral extension of hydrogeologic strata only partially identified by a limited number of the geologic loggings the laboratory column tracer test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5 00 10 2 cm s the slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4 32 7 72 10 4 cm s hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2 08 10 3 and 2 44 10 2 cm s with a geometric mean of 6 89 10 3 cm s which is 7 times smaller than that from the laboratory column experiment the trend of increasing hydraulic conductivity with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity zone as more of the aquifer is tested the combined hydrogeologic site characterization using hydraulic tests tracer tests and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties of the multi layered alluvial aquifer

study of tracer movement through unsaturated sand abstract a column of 100 cm length and 15 4 cm diameter was filled with sand a solute displacement experiment using tritium as a tracer was conducted under saturated water flow conditions analysis of the observed effluent concentration resulted in an estimated dispersivity of 0 094 cm solute displacement experiments under unsaturated water flow conditions were conducted by leaching the column intermittently on a daily basis with constant amounts of water as soon as the amount drained from the column was equal to the daily input tritium was added to the infiltrating water for some period three such experiments were conducted with different amounts of water infiltrated daily these amounts were small enough for the water flow to remain unsaturated the parameters of the hydrodynamic dispersion equation were fitted to the observed effluent concentrations very large dispersion coefficients were obtained with a dispersivity of about 7 3 cm a possible explanation of this phenomenon is the presence of immobile water pockets during unsaturated flow for all experiments it was found that about 36 of the water in the unsaturated column could be considered as immobile the exchange of solute between the mobile and immobile phases explains very well the large dispersion observed in the experiments conducted under unsaturated conditions

a millennial scale record of arctic ocean sea ice variability and the demise of the ellesmere island ice shelves 1 sea ice ice shelves at the apex of north america 80 n constitute the oldest sea ice in the northern hemisphere we document the establishment and subsequent stability of the ward hunt ice shelf and multiyear landfast sea ice in adjacent fiords using 69 radiocarbon dates obtained on holocene driftwood deposited prior to coastal blockage these dates 47 of which are new record a hiatus in driftwood deposition beginning 5500 cal yr bp marking the inception of widespread multiyear landfast sea ice across northern ellesmere island this chronology together with historical observations of ice shelf breakup 1950 to present provides the only millennial scale record of arctic ocean sea ice variability to which the past three decades of satellite surveillance can be compared removal of the remaining ice shelves would be unprecedented in the last 5500 years this highlights the impact of ongoing 20th and 21st century climate warming that continues to break up the remaining ice shelves and soon may cause historically ice filled fiords nearby to open seasonally

seawater groundwater mixing in and fluxes from coastal sediment overlying discrete fresh seepage zones a modeling study submarine fresh groundwater discharging from discrete zones such as conduits overlain by thick sediment remains poorly documented and understood despite common anecdotal accounts of it we analyzed this phenomenon by a suite of variable density variably saturated groundwater flow simulations guided by field studies the field observations included point flux and salinity measurements using seepage meters spread across the intertidal and the subtidal zones the discretely measured seepage fluxes in the subtidal region were as high and the salinity was as fresh as those from the intertidal zone both fluxes and salinities varied with tides two dimensional simulations of the idealized beach ocean vertical section with discrete freshwater springs at the base showed the development of seawater recirculation cells along the edge of freshwater discharge plumes emanating from the outlets causing mixing brackish water discharges at the sediment water interface above where the plume mixes with the recirculating seawater sensitivity analyses showed that stronger terrestrial fresh groundwater flow increases the freshwater plume size but does not affect the mixing zone width tidal oscillations and a dynamic fresh groundwater flow widened the mixing zones and increased porewater flux across the sediment water interface sediment thickness had a minor effect on the width of both the freshwater plume and its surrounding mixing zone the subtidal freshwater plume and mixing zone likely represent a unique but potentially ubiquitous setting which hosts dramatic ecological and chemical gradients their local biogeochemical niche and coastal scale ecosystem impacts will need to be considered in investigations of coastlines

analysis of saltwater upconing beneath a pumping well abstract aquifer systems that contain freshwater and saltwater are usually stratified with the more dense saltwater underlying the freshwater a groundwater well discharging from the freshwater zone causes the saltwater to move upwards towards the well this phenomenon is known as saltwater upconing two methods of analysis the sharp interface method and the fluid density dependent solute transport method are used to simulate saltwater upconing numerical experiments including comparisons of the two methods indicate 1 for low to moderate pumpages the 50 isochlor and sharp interface correlate well 2 the well can discharge significant concentrations of saltwater even though a stable cone according to the sharp interface method exists below the well screen 3 an almost linear relationship exists between the well discharge rate and the concentration of the discharge at low pumping rates that maintain a stable cone and 4 upconing is sensitive to transverse dispersivity whereas it is insensitive to longitudinal dispersivity a simulation of upconing at test site no 4 truro cape cod massachusetts indicates that the appropriate field value of transverse dispersivity is very small this supports the validity of the sharp interface assumption for analyzing the behavior of systems with thin saltwater freshwater transition zones

is unique scaling of aquifer macrodispersivity supported by field data spreading of conservative solutes in groundwater due to aquifer heterogeneity is quantified by the macrodispersivity which was found to be scale dependent it increases with travel distance stabilizing eventually at a constant value however the question of its asymptotic behavior at very large scale is still a matter of debate it was surmised in the literature that macrodispersivity scales up following a unique scaling law attempts to define such a law were made by fitting a regression line in the log log representation of an ensemble of macrodispersivities from multiple experiments the functional relationships differ among the authors based on the choice of data our study revisits the data basis used for inferring unique scaling through a detailed analysis of literature marcodispersivities in addition values were collected from the most recent tracer tests reported in the literature we specified a system of criteria for reliability and reevaluated the reliability of the reported values the final collection of reliable estimates of macrodispersivity does not support a unique scaling law relationship on the contrary our results indicate that the field data can be explained as a collection of macrodispersivities of aquifers with varying degree of heterogeneity where each exhibits its own constant asymptotic value our investigation concludes that transport and particularly the macrodispersivity is formation specific and that modeling of transport cannot be relegated to a unique scaling law instead transport requires characterization of aquifer properties e g spatial distribution of hydraulic conductivity and the use of adequate models

determination of longitudinal dispersivity in an unconfined sandy aquifer study of the mobility of contaminants in an aquifer is an important issue for the proper remediation of contaminated groundwater determination of associated solute transport parameters therefore is essential for investigation of the extent to which groundwater can be contaminated this study aimed at determining solute transport parameters for an unconfined sandy aquifer at a laboratory scale through various tracer tests using a conservative solute as a tracer tracer tests consisted of both well tracer tests single and double wells and an aquifer tracer test using a plume capturing device such as time domain reflectometry tdr the results showed that longitudinal dispersivities estimated from the single and double well tracer tests were 2 2 cm and 13 5 cm for a travel distance of 9 3 cm and 13 5 cm from the injection point respectively these results agreed reasonably well with the results of the aquifer tracer test the solute transport parameters obtained at multiple points in the aquifer through the aquifer tracer test revealed that the dispersivity length was proportional to the travel distance by a factor of 0 3 which was moderately higher than the value of 0 1 given in the literature copyright 2002 john wiley sons ltd

simulating fluoride evolution in groundwater using a reactive multicomponent transient transport model application to a crystalline aquifer of southern india abstract overexploitation of crystalline aquifers in a semi arid climate leads to a degradation of water quality with the main processes responsible for the observed salt loads probably being irrigation return flow irf and a high evaporation rate the present study has focused on modelling the f accumulation caused by irf below rice paddy fields in the small endorheic maheshwaram watershed andhra pradesh southern india the transient simulation was performed with a 1d reactive transport phreeqc column and took into account irf evaporation kinetically controlled mineral dissolution precipitation ion adsorption on fe hydroxides and mixing with fresh groundwater the results revealed the role of cationic exchange capacity cec in ca na exchange and calcite precipitation both favouring a decrease of the ca 2 activity that prevents fluorite precipitation iron hydroxide precipitation offers a not inconsiderable adsorption capacity for f immobilization the principal sources of f are fluorapatite dissolution and to a lesser extent allanite and biotite dissolution anthropogenic sources of f such as fertilizers are probably very limited after simulating an entire dry season irrigation cycle 120 days the results are in good agreement with the observed overall increase of cl in the maheshwaram groundwater the model enables one to decipher the processes responsible for water resource degradation through progressive salinization it shows that f enrichment of the groundwater is likely to continue in the future if groundwater overexploitation is not controlled

reconstructing hydrographic change in petersen bay ellesmere island canada inferred from sar imagery abstract synthetic aperture radar sar satellite imagery was used to reconstruct the change in limnological conditions adjacent to an arctic ice shelf by examining the backscatter values of coastal ice in mid winter scenes high sar backscatter values 6 db suggest that an ice dammed lake was present adjacent to the south coast of petersen bay from 1992 until 2005 following a large calving event of the adjacent petersen ice shelf 8 07 km2 in august 2005 the lake drained through a region where the ice shelf had separated from the coastline this loss of freshwater and replacement of lake ice with sea ice along the southern coast of petersen bay were confirmed from analyses of ice core samples and conductivity temperature depth ctd profiles the exception to this pattern was one distinct area where terrestrial streams entered the edge of petersen bay and freshwater continued to collect from 2006 to 2008 however this ephemeral area of freshwater has not reformed since 2009 due to the persistence of open water events in petersen bay observed in optical satellite imagery which likely facilitated mixing of freshwater with sea water based on the continued break ups of petersen ice shelf and the frequency of open water events it is unlikely that this ice dammed lake will reform the results of this study underscore the utility of sar for reconstructing past hydrographic conditions in the water column below

the impeller meter for measuring aquifer permeability variations evaluation and comparison with other tests a knowledge of the variation of horizontal hydraulic conductivity with vertical position k z is important in understanding the transport and dispersive properties of aquifers using an impeller meter to measure the discharge distribution in a screened well while pumping at a constant rate is a promising technique for obtaining the k z function such an application is described herein and the resulting k z functions are compared with those obtained previously using tracer tests and multilevel slug tests impeller meter data were the most convenient to obtain and tracer data the most difficult the k z functions obtained by the three methods were not identical but quite similar overall this similarity between both borehole tests and the larger scale tracer test showed that nonstationary hydraulic conductivity trends in a stochastic hydrologic sense exist in the test aquifer the impeller meter method was better able to detect the higher k layers than was the multilevel slug approach overall the results suggest that a practical strategy for fitting impeller meter tracer or multilevel slug test data to a given aquifer is to use the selected testing procedure to obtain a dimensionless distribution and then a standard pumping test to measure combining both types of information enables dimensional values for k z to be calculated in low permeability aquifers or near the bottom of a test well the fluid velocity due to pumping may be below the stall velocity of an impeller thus there is a definite need for the commercial development of more sensitive flow measuring devices such as heat pulse flowmeters hess 1986 which will extend the resolution of this field method

measurements of the magnetic fluctuations associated with ocean swell compared with weaver s theory fluctuations in the earth s magnetic field caused by ocean swell have been measured above the ocean s surface with total field magnetometers the magnetic field measurements were made both from an oceanographic research tower and from a dual magnetometer system on an aircraft the results are consistent with the theory of magnetic fields associated with ocean waves and swell as developed by weaver 1965 aeromagnetic measurements give a good estimate of the period of the dominant ocean swell and its direction of propagation

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

the impact of an intense summer cyclone on 2012 arctic sea ice retreat 1 this model study examines the impact of an intense early august cyclone on the 2012 record low arctic sea ice extent the cyclone passed when arctic sea ice was thin and the simulated arctic ice volume had already declined 40 from the 2007 2011 mean the thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms during the storm ice volume decreased about twice as fast as usual owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport this increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer driven by strong winds and rapid ice movement a comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone enhanced bottom melt strongly reduces ice extent for about 2 weeks with a declining effect afterward the simulated arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0 15 106 km2 4 4 thus without the storm 2012 would still have produced a record minimum

the dipole flow test a new single borehole test for aquifer characterization a new single borehole measurement technique for confined aquifers the dipole flow test yields the vertical distributions of the horizontal hydraulic conductivity the vertical hydraulic conductivity and the specific storativity when applied to different borehole intervals the test utilizes straddle packers to isolate two chambers in the borehole pressure transducers to monitor drawdown in them and a small pump to create a dipole flow pattern in the aquifer by pumping water at a constant rate from the aquifer into one chamber transferring it within the well to the next chamber and finally injecting it back to the aquifer a mathematical model describing the drawdown in each chamber is derived for the transient as well as the steady state cases the aquifer parameters may be estimated from data produced by the dipole flow test alone or in conjunction with conventional pumping tests the dipole flow regime reaches a steady state relatively quickly especially in well permeable aquifers a robust computational methodology for estimating the aquifer parameters suitable for automatization is based on the newton raphson algorithm applied to a system of up to three nonlinear equations each describing the well drawdown at a different judiciously chosen time due to the relatively small drawdownmore it invokes the dipole flow test may be applicable to unconfined aquifers as well less

dispersion in unconsolidated aquatic sediments inert tracer breakthrough experiments were used to parameterize hydrodynamic dispersion in undisturbed cores of surface sediment from lacustrine estuarine and marine depositional environments the sediments studied cover wide ranges of composition porosity 46 to 83 mean grain size 10 5to 10 2 cm and sorting 0 48 1 26 as expected hydrodynamic dispersion depends on the average longitudinal fluid flow velocity through the sediment plug at linear flow velocities exceeding 10 4 cm s 1 mechanical dispersion exceeds diffusion in all sediment cores studied compared to the classical studies on dispersion in sand columns however peclet numbers based on particle size measurements do not provide a reliable guide for predicting the transition from molecular diffusion dominated to mechanical dispersion dominated flow regimes in the sediments it is believed that the influence of pore structure on dispersion is much larger than that of particle size and that the characteristic pore lengths in the finest highly porous sediments are orders of magnitude larger than the mean grain size aggregation microlaminations and a heterogeneous pore size distribution may all contribute to non ideal flow conditions in the sediments tailing of the breakthrough curve occurred occasionally in fine grain sediment signifying micro and macro scale dispersion and non ideal flow behavior experiments showing significant non ideal flow through the sediment plug were not used for calculation of hydrodynamic dispersion coefficient

simulations of two well tracer tests in stratified aquifers at the chalk river and the mobile sites a simulation study of two well injection withdrawal tracer tests in stratified granular aquifers at two widely separated sites is presented the first site is located near the chalk river nuclear laboratories in canada and the second site is located in mobile alabama field data and test conditions at these sites are substantially different in terms of vertical distributions of hydraulic conductivity well spacings flow rates test durations and tracer travel distances furthermore the test at the chalk river site was conducted in a recirculating mode whereas the test at the mobile site was conducted in a nonrecirculating mode simulations of these tests were performed in three dimensions using the curvilinear finite element model developed in the previous paper of this series the simulations incorporated measured vertical variations in relative hydraulic conductivity and local dispersivity values that are small fractions between 1 1000 and 1 100 of the spacing between the injection and the withdrawal wells the local dispersivities are used to account for local hydrodynamic dispersion and are chosen independently so that they are not affected by the scales of the tests simulation results obtained from the model are presented interpretation of these results is made in conjunction with measured breakthrough curves at the withdrawal well and multilevel observation wells for the chalk river site predicted and measured breakthrough curves at the withdrawal well are in good agreement over the earlier part of the test duration deviation of the field data from the model prediction occurs over the second part where the predicted breakthrough curves show a declining trend but the field data plot does not for the mobile site predicted and measured breakthrough curves at the withdrawal well show similar trends throughout the entire test duration and are in good agreement overall model predictions of the effect of hydraulic conductivity stratification on temporal distributions of concentration are generally consistent with data from multilevel observation wells at both sites the model results also show interesting effects of stratification on spatial distributions of concentration and on the evolution and spreading pattern of tracer plumes these effects have not been fully assessed in the field measurement and should be investigated further

a multilayered sharp interface model of coupled freshwater and saltwater flow in coastal systems model development and application a quasi three dimensional finite difference model that simulates freshwater and saltwater flow separated by a sharp interface has been developed to study layered coastal aquifer systems the model allows for regional simulation of coastal groundwater conditions including the effects of saltwater dynamics on the freshwater system vertically integrated freshwater and saltwater flow equations incorporating the interface boundary condition are solved within each aquifer leakage through confining layers is calculated by darcy s law accounting for density differences across the layer the locations of the interface tip and toe within grid blocks are tracked by linearly extrapolating the position of the interface the model has been verified using available analytical solutions and experimental results application of the model to the soquel aptos basin santa cruz county california illustrates the use of the quasi three dimensional sharp interface approach for the examination of freshwater saltwater dynamics in regional systems simulation suggests that the interface today is still responding to long term pleistocene sea level fluctuations and has not achieved equilibrium with present day sea level conditions

seeking a seafloor magnetic signal from the antarctic circumpolar current summary motional electromagnetic induction by ocean currents is a basic phenomenon of geophysics with application to the monitoring of ocean transport one of earth s strongest ocean currents is the antarctic circumpolar current acc this paper explores the magnetic signals that should be generated by the acc and reports an experiment in which a magnetometer recorded natural variations of earth s magnetic field on the floor of the southern ocean for some five months in 1996 magnetometer records from kingston tasmania and from macquarie island give reference information concerning magnetic storms and substorms the instrument was sited in the region of the major oceanographic subantarctic flux and dynamics experiment safde where the acc passes south of tasmania between the major topographic features of the south tasman rise and the australia antarctica spreading ridge the safde records give comprehensive control on the actual ocean current flow at the time of the magnetic recording and allow a magnetic signal to be predicted in terms of the seafloor conductance the seafloor conductance for the area is however low and the amplitude of the predicted signal is low the seafloor observations confirm that the signal is weak against the effects of ionospheric signals in future experiments the choice of sites with thicker seafloor sedimentation would increase the acc magnetic signal to be observed the magnetometer measurements have a result relevant for the safde in confirming that the correction of electric data for seafloor conductance is small there is also the result for seafloor magnetic observatories for which motional induction effects are unwanted that such an observatory can operate even under the acc and be substantially protected from motional induction effects by low seafloor conductance

offshore continuation of coastal groundwater systems predictions using sharp interface approximations and variable density flow modelling analytical sharp interface solutions and numerical variable density flow and transport modelling are used to study how far into the offshore the influence of meteoric continental groundwater systems extends under steady state flow and transport conditions results show that factors which favour the development of an extensive fresh water wedge in the offshore are 1 a high head or fresh water discharge at the coastline 2 a thick semi confined high permeability submarine aquifer 3 optimum but not necessarily maximum and minimum values for the thickness and permeability of the confining layer near the seafloor respectively sharp interface models tend to overpredict the seaward extent of fresh water considerably because in distal parts upward seepage rates through the overlying confining layer are too small to prevent salinisation by diffusion from the overlying sea and ensuing convective mixing by density differences within underlying aquifers the overprediction is particularly large for relatively low heads at the coastline and low permeabilities of the confining layer under favourable conditions fresh water connected to continental flow systems is predicted to occur up to several tens of kilometers offshore comparison of model predictions with observational data demonstrates that relatively fresh submarine pore waters off the coasts of new jersey us and suriname south america occur too far offshore to be explained by active flow systems indicating that they are paleo waters which formed during the pleistocene when sea levels were lower than at present

vertical and horizontal components of the electric background field at the sea bottom the natural e field variations measured at the sea bottom and the magnitude of the different field components compared in the light of the theory for induction caused by ocean surface waves at shallow sea depths of 107 122 meters only the vertical component carries an observable effect of ocean waves whereas the horizontal field is dominated by the larger magnetotelluric noise this agrees well with theoretical predictions

sr isotopic ratios trace mixing and dispersion in co2 push pull injection experiments at the co2crc otway research facility australia abstract analysis of 87sr 86sr ratios and modelling of formation water injection water and produced water compositions from the co2crc otway research facility in victoria australia are used to test tracer behaviour and response in push pull experiments such experiments are an essential pre requisite to understanding the controls imposed by reservoir heterogeneities on co2 dissolution rates which may be an important stabilising mechanism for geological carbon storage the experiments otway stage 2b extension in 2014 comprised two sequential tests in which 100 t of co2 saturated water was injected with combinations of sr and br or li and fluorescein tracers each injection being followed by two staged extractions of 10 t and a final extraction of 50 t all spaced at 10 day intervals analysis of the 87sr 86sr ratios of the produced fluids from the first injection spiked with srcl2 and nabr is consistent with sr behaving conservatively this contrasts with previous interpretations in which br was argued to have behaved conservatively while sr which dilutes three times as fast as br was thought to be lost to a mineral phase such sr loss cannot explain the evolution of 87sr 86sr ratios the analysis of 87sr 86sr ratios in the waters produced after the second injection episode spiked with licl and fluorescein tracers allows calculation of the fractions of the formation waters and the injection waters from both tests 1 and 2 the sr li and so4 tracers the later formed by oxidation of formation sulphide all indicate similar rates of dilution that is consistent with conservative behaviour the results of the two injection episodes with spaced extractions are compared with two subsequent push pull injections in which the produced waters spiked with methanol were extracted continuously these continuous extraction experiments exhibited significantly less dilution over the same range of produced to injected water volumes up to only 0 6 than the earlier experiments with spaced extractions this implies that some process related to the pauses in extraction enhances mixing of injected and formation waters achieving the objective of using push pull experiments to assess reservoir heterogeneities and co2 dissolution rates will require better assessment of the various tracers to establish which behave conservatively followed a proper understanding of the causes of the variations in mixing as fluids are extracted from the formations

tracage par 13c 2h i et uranine dans la nappe de la craie senonienne en ecoulement radial convergent bethune france abstract the behaviour of four labelled solutions h213co3 2h2 o i and uranine is analysed through a field experiment solutions are injected using a pulse condition into a dynamic radial flow runs are performed on 10 22m of a semi confined aquifer senonian chalk aquifer in the bethune s france institute of technology area using the form and position parameters of the break through curves pure convective transfer time tc mean residence time t and the dispersivity it is shown that 1 i and 2h2o have a nearly identical behaviour 2 uranine presents a faster convective and dispersive transfer than the other tracers specially 2h2o and 3 the retardation of 13c h13co 3 is greater than those of 2h2 o and i this retardation suggests a fixation of h13co 3 onto the solid matrix furthermore the transfer disparity of these compounds is due to the difference of their diffusion rates to the stationary liquid phase of the chalk matrix which lead to apparent distinct mean velocity for each tracer

a potential theory based finite element algorithm for freshwater recharge of saline aquifers a sharp interface model the size and shape of the freshwater lens developed during the freshwater recharge of thick unconfined saline aquifers was investigated through a potential theory based finite element method implicit difference in time scheme in which the air freshwater free surface and the fresh saltwater interface boundary conditions have been integrated in the galerkin s finite element formulation of the flow equation through green s theorem in an iterative scheme using a sharp interface assumption the model can also be applied to locate the positions of the fresh saltwater interface and the air freshwater free surface for recharge of strip oceanic islands the model results are verified through experimental studies conducted on a hele shaw analogue

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

comparison of the low frequency variations of the vertical and horizontal components of the electric background field at the sea bottom natural electric field variations are measured at the sea bottom over long periods of time by means of stationary vertical and horizontal galvanic antennas we compare the power spectra of the vertical and horizontal field components and the extent to which they may be reduced by standard averaging techniques although the raw spectra of the vertical and horizontal components do not differ greatly the difference in the spectra after averaging is significantly greater most significantly in the frequency range between 0 0005 and 0 03 hz this averaging scheme suppresses the vertical electric field component more strongly than the horizontal component

hypoaigic influences on groundwater flux to a seasonally saline river hypoaigic zones are aquifer volumes close to and beneath the shores of saline surface water bodies and are characterized by the presence of time dependent natural convection and chemical stratification when transient and cyclic processes are involved there is significant potential for complex flow and reaction in the near shore aquifer presenting a unique challenge to pollutant risk assessment methodologies this work considers the nature of some hypoaigic processes generated by the seasonally saline canning river of western australia near a site contaminated by petroleum hydrocarbons a dissolved hydrocarbon plume migrates within the shallow superficial aquifer to the nearby bank of the canning river beneath the river bank a zone of complex fluid mixing is established by seasonal and tidal influences understanding this complexity and the subsequent ramifications for local biogeochemical conditions is critical to inferring the potential for degradation of advecting contaminants a range of modelling approaches throws light on the overall topographic controls of discharge to the river on the saline convection processes operating under the river bank on the potential for fluid mixing and on the various important time scales in the system saline distributions simulated within the aquifer hypoaigic zone are in at least qualitative agreement with previous field measurements at the site and are strongly affected by seasonal influences groundwater seepage velocities at the shoreline are found to be positively correlated with river salinity calculations of fluid age distributions throughout the system show sensitivity to dispersivity values however maximum fluid ages under the river appear to be diffusion limited to a few decades the saline convection cell in the aquifer defines a zone of strong dispersive dilution of aged many decades deep aquifer fluids with relatively young several months riverine fluids seasonal recharge and river salinity cycles induce regular perturbations to the convection cell yielding intra annual variations of 50 in seepage velocity and almost 30 in wedge penetration distance at the plume location

rapid loss of the ayles ice shelf ellesmere island canada 1 on august 13 2005 almost the entire ayles ice shelf 87 1 km 2 calved off within an hour and created a new 66 4 km 2 ice island in the arctic ocean this loss of one of the six remaining ellesmere island ice shelves reduced their overall area by 7 5 the ice shelf was likely weakened prior to calving by a long term negative mass balance related to an increase in mean annual temperatures over the past 50 years the weakened ice shelf then calved during the warmest summer on record in a period of high winds record low sea ice conditions and the loss of a semi permanent landfast sea ice fringe climate reanalysis suggests that a threshold of 200 positive degree days year 1 is important in determining when ice shelf calving events occur on n ellesmere island

analysis of solute transport in a divergent flow tracer test with scale dependent dispersion it has been known for many years that dispersivities increase with solute displacement distance in a subsurface the increase of dispersivities with solute travel distance results from significant variation in hydraulic properties of porous media and was identified in the literature as scale dependent dispersion in this study laplace transformed analytical solutions to advection dispersion equations in cylindrical coordinates are derived for interpreting a divergent flow tracer test with a constant dispersivity and with a linear scale dependent dispersivity breakthrough curves obtained using the scale dependent dispersivity model are compared to breakthrough curves obtained from the constant dispersivity model to illustrate the salient features of scale dependent dispersion in a divergent flow tracer test the analytical results reveal that the breakthrough curves at the specific location for the constant dispersivity model can produce the same shape as those from the scale dependent dispersivity model this correspondence in curve shape between these two models occurs when the local dispersivity at an observation well in the scale dependent dispersivity model is 1 3 times greater than the constant dispersivity in the constant dispersivity model to confirm this finding a set of previously reported data is interpreted using both the scale dependent dispersivity model and the constant dispersivity model to distinguish the differences in scale dependence of estimated dispersivity from these two models the analytical result reveals that previously reported dispersivity distance ratios from the constant dispersivity model should be revised by multiplying these values by a factor of 1 3 for the scale dependent dispersion model if the dispersion process is more accurately characterized by scale dependent dispersion copyright 2007 john wiley sons ltd

modes of seawater intrusion during transgressions analytical methods and numerical experiments are used to study salinization of groundwater in response to sea level rise the system that is studied involves a saturated porous medium with an inclined upper surface the upper surface is progressively inundated during sea level rise to simulate transgression the landward migration of the shoreline four modes of seawater intrusion are distinguished 1 horizontal intrusion for slow transgression and a relatively high permeability substrate 2 vertical intrusion by seawater fingering for fast transgression and a sand silt substrate 3 vertical intrusion by diffusion for fast transgression and a low permeability clay substrate 4 vertical intrusion by combined diffusion and low salinity fingering for fast transgression and a clay layer at the seafloor overlying an aquifer these four modes are characterized by the development of very distinctive transition zones between the fresh and salt groundwater domains an analytical expression is derived for the critical transgression rate which separates horizontal mode 1 from dominantly vertical modes 2 4 intrusion for modes 3 and 4 salinization significantly lags behind sea level rise the results are consistent with observations of fossil fresh brackish groundwater beneath many continental shelves and shallow seas

the importance and challenge of hyporheic mixing the hyporheic zone is the interface beneath and adjacent to streams and rivers where surface water and groundwater interact the hyporheic zone presents unique conditions for reaction of solutes from both surface water and groundwater including reactions which depend upon mixing of source waters some models assume that hyporheic zones are well mixed and conceptualize the hyporheic zone as a surface water groundwater mixing zone but what are the controls on and effects of hyporheic mixing what specific mechanisms cause the relatively large 1m mixing zones suggested by subsurface solute measurements in this commentary we explore the various processes that might enhance mixing in the hyporheic zone relative to deeper groundwater and pose the question whether the substantial mixing suggested by field studies may be due to the combination of fluctuating boundary conditions and multi scale physical and chemical spatial heterogeneity we encourage investigation of hyporheic mixing using numerical modeling and laboratory experiments to ultimately inform field investigations

a two dimensional finite element model for dispersion 2d fed in coastal aquifers abstract a two dimensional finite element model is developed to simulate the saltwater intrusion phenomena in confined and leaky coastal aquifers under steady state conditions the governing equations are combined into two nonlinear coupled partial differential equations in only two variables namely the concentration and the equivalent freshwater piezometric head the galerkin technique is employed with the computation scheme based on the relaxation method heterogeneity and anisotropy of the aquifer are considered the dispersion coefficient is taken to be velocity dependent the model is verified on two prepublished problems unlike existing models this model is also applied to simulate saltwater intrusion in a large aquifer the nile delta aquifer in egypt equiconcentration and equipotential lines are constructed in the nile delta aquifer