spatial and temporal relationships between mid tertiary magmatism and extension in southwestern arizona cenozoic magmatism in southwestern arizona which is within the basin and range tectonic province occurred almost entirely between 15 and 25 ma volcanic rocks typically consist in ascending order of 1 a thin sequence of mafic to intermediate lava flows 2 voluminous felsic lava flows and pyroclastic rocks with minor to moderate amounts of intermediate to mafic lava flows and 3 basalt and andesite volcanic rock sequences rest disconformably on pre tertiary bedrock in most areas but locally overlie substantial coarse clastic debris that was deposited immediately before and during earliest magmatism prevolcanic clastic debris is interpreted as a consequence of local early normal faulting in most regions tilting related to extension began later and occurred during or after eruption of felsic volcanic rocks and before the end of younger mafic volcanism extension generally ended before about 17 ma except in a northwest trending belt adjacent to the relatively unfaulted and topographically elevated transition zone tectonic province which is adjacent to the colorado plateau rapid cooling of metamorphic core complexes and tilting of young basalts and coarse clastic rocks continued in this belt until as recently as 11 ma extension was extreme in this belt whereas it was generally moderate to slight in other parts of southwestern arizona large magnitude extension was not associated with areas of greatest igneous activity and rapid cooling and exhumation of core complexes postdated local magmatism these relationships are inconsistent with theories that relate genesis of metamorphic core complexes to magma intrusion in the upper crust except for young extension in this northwest trending belt there are no apparent regional migration trends for either magmatism or extension within southwestern arizona lack of substantial extension before magmatism and general lack of magmatism during youngest extension are inconsistent with the hypothesis that magmatism was the product of decompression melting during lithospheric extension the long duration and large magnitude of extension adjacent to the transition zone tectonic province and within an area of earlier crustal thickening are consistent with the hypothesis that extension was driven by the gravitational potential energy of elevated land mass and crustal roots regional magmatic heating apparently weakened the lithosphere and triggered extension but did not control extension locally

the influence of evaporation and rainfall on supratidal groundwater dynamics and salinity structure in a sandy beach evaporation has been recognized as a major driving force affecting coastal aquifer systems however its effects on subsurface flow and salinity structure have not been investigated in sufficient detail this paper presents field measurements and numerical simulations of pore water flow and subsurface salinity structure in the supratidal zone of a sandy beach subjected to evaporation as well as rainfall it was found that evaporation significantly increased pore water salinity up to 85 g l within a shallow layer approximately 10 cm below the beach surface the induced density gradient generated salt fingers near the beach surface which caused local groundwater circulation i e fingering flow however unlike inland aquifers the salt fingering was significantly diminished by tidal action that prompted the horizontal mixing of salt in the beach the subsequent precipitation e g rainfall diluted the evaporation induced high saline plume near the beach surface and drove the plume to migrate further downward the plume gradually dispersed and was diluted along the groundwater pathways the simulation results indicated that evaporation as well as precipitation at the beach surface induced complex driving mechanisms for supratidal groundwater flow depending on the intensity at the beach surface evaporation and rainfall significantly altered the pore water flow and associate solute transport processes in the supratidal zone of the beach

groundwater mineralisation processes in mediterranean semi arid systems cap bon north east of tunisia hydrogeological and geochemical approaches the groundwater of the korba plain represents major water resources in tunisia the plio quaternary unconfined aquifer of the cap bon north east tunisia is subject to the intensive agricultural activities and high groundwater pumping rates due to the increasing of the groundwater extraction the degradation of the groundwater quality is characterized by the salinization phenomena groundwater were sampled and analysed for physic chemical parameters ca2 mg2 na k cl so42 hco3 no3 ph electrical conductivity ec and the temperature t the hydrochemical analysis is coupled with the calculation of the saturation indexes si gypsum si halite si calcite and si dolomite ionic derivation and with the ion correlations compared to chloride concentrations na cl ca2 cl and mg2 cl ratios seawater fractions in the groundwater were calculated using the chloride concentration those processes can be used as indicators of seawater intrusion progression ec methods were also conducted to obtain new informations on the spatial scales and dynamics of the fresh water seawater interface of coastal groundwater exchange the mixing zone between freshwater and saltwater was clearly observed from the ec profile in the investigated area where a strong increase in ec with depth was observed corresponding to the freshwater and saltwater interface results of hydrochemical study revealed the presence of direct cation exchange linked to seawater intrusion and dissolution processes associated with cations exchange these results together with ec investigation indicated that the groundwater is affected by seawater intrusion and is still major actor as a source of salinization of the groundwater in korba coastal plain further isotopic and hydrological investigations will be necessary to identify and more understood the underlying mechanisms copyright 2012 john wiley sons ltd

a mechanistic study of nonlinear solute transport in a groundwater surface water system under steady state and transient hydraulic conditions two laboratory experiments were conducted to investigate the effects of tides and buoyancy on beach hydraulics in the presence of a seaward groundwater flow due to an elevated regional water table in the first experiment case 1 the difference in concentration between the salt water at sea and the water of the regional aquifer was small 2 4 g l 1 such that it did not engender density gradients the salt acts as a tracer in this case in the second experiment case 2 the difference was 32 0 g l 1 which creates a significant density gradient this case corresponds to the presence of fresh groundwater in the subsurface of the coasts of the continental united states the experiments were numerically simulated by the marine unsaturated marun model a numerical model for density and viscosity dependent flows in two dimensional variably saturated media the long term experimental and numerical results showed that the seawater plume entered the beach from the sea and occupied most of the intertidal zone the maximum depth of the seawater plume was near the midsection of the intertidal zone and it decreased near the low and high tide lines when viewed in the context of case 2 these results indicate an inverted salinity distribution in beaches subjected to tides with salt water from sea overtopping the freshwater lens for both cases water from the regional aquifer moved seaward beneath the seawater in the intertidal zone and pinched out near the low tide mark we also noted that beach hydraulics are highly two dimensional with water entering the beach at a near vertical angle and leaving it at a near horizontal angle which casts doubts on analyses of beach hydraulics based on the dupuit assumption findings from this work have direct implications within the practice of bioremediation of oil spills on beaches we found that applying dissolved nutrients on the beach surface at low tide is superior to applying them in a trench landward of the beach this is because the residence time of the nutrient plume in the bioremediation zone of the beach in the prior situation is longer than that in the latter

tide induced seawater groundwater circulation in shallow beach aquifers summary in this paper we investigated the tide induced seawater groundwater circulation in shallow beach aquifers using the finite element model marun the numerical solutions were generalized using a dimensionless formulation from a dimensionless tidal period and a dimensionless beach slope of 10 we obtained results that apply to a wide range of beach permeabilities from 10 4 m s to 10 3 m s beach slopes from 3 16 to 31 6 tidal amplitude 0 3 m 2 m and period diurnal or semidiurnal the numerical simulations demonstrated the following the maximum darcy velocity always occurs at the intersection of the watertable and the beach surface the offshore beach groundwater is almost stagnant compared with the onshore groundwater flow which may explain the previous observations that the major portion of the seaward groundwater seepage usually occurs in the shallow part of the submerged beach the outflow from the seepage face accounts for 41 97 average 55 of the outflow from the intertidal zone the amount of seawater infiltrating into the intertidal zone in a tidal cycle increases with the beach permeability and decreases when the inland recharge increases and ranges from 35 5 m 3 yr 1 m 1 to 505 8 m 3 yr 1 m 1 for all the cases considered smaller beach slopes smaller inland freshwater recharges and or greater beach permeability lead to larger saltwater plumes in the intertidal zone of the beach the results are in line with the existing results of field observations and numerical simulations by previous researchers a 2008 elsevier b v all rights reserved

swash zone moisture dynamics and unsaturated infiltration in two sandy beach aquifers the intertidal zone of coastal aquifers is a dynamic region of mixing between saline surface water and fresh groundwater groundwater circulation in this zone is affected by complex forcing mechanisms that operate on a range of timescales and can regulate chemical fluxes to marine environments we evaluated wave swash induced infiltration and associated flow dynamics in the unsaturated region of two sandy beach aquifers with differing wave conditions and beach morphologies moisture and pressure sensors were used to measure fluctuations in water content water table elevation and hydraulic gradients at high frequencies 5 hz in the swash zone at mean lower low water mean sea level and mean higher high water water content in the unsaturated region of the swash zone responded to wave overtopping and swash infiltration with a rapid rise in water content followed by a slower decline swash induced unsaturated infiltration rates calculated from water content response were lowest near low tide and increased up the beachface with inflow highest near high tide at both sites consistent with an increase in water table depth up the beach unsaturated infiltration was 1 6 m 3 m per tidal cycle at the wavedominated beach and 0 4 m 3 m per tidal cycle at the tide dominated beach saturated pore pressure measurements show that a water table mound formed as a consequence of swash infiltration that migrated up the beach during rising tide leading to divergent seaward landward groundwater flow the results demonstrate the significant and spatially variable effects of wave swash on moisture dynamics in the unsaturated zone of beach aquifers and show that these effects depend on wave conditions and beach characteristics results have implications for understanding transport and reaction of solutes in this biogeochemically active zone

preconditioning an ensemble kalman filter for groundwater flow using environmental tracer observations abstract groundwater resources management requires operational regional scale groundwater models accounting for dominant spatial variability of aquifer properties and spatiotemporal variability of groundwater recharge we test the ensemble kalman filter enkf to estimate transient hydraulic heads and groundwater recharge as well as the hydraulic conductivity and specific yield distributions of a virtual phreatic aquifer to speed up computation time we use a coarsened spatial grid in the filter simulations and reconstruct head measurements at observation points by a local model in the vicinity of the piezometer as part of the observation operator we show that the enkf can adequately estimate both the mean and spatial patterns of hydraulic conductivity when assimilating daily values of hydraulic heads from a highly variable initial sample the filter can also estimate temporally variable recharge to a satisfactory level as long as the ensemble size is large enough constraining the parameters on concentrations of groundwater age tracers here tritium and transient hydraulic head observations cannot reasonably be done by the enkf because the concentrations depend on the recharge history over longer times while the head observations have much shorter temporal support we thus use a different method the kalman ensemble generator keg to precondition the initial ensemble of the enkf on the groundwater age tracer data and time averaged hydraulic head values the preconditioned initial ensemble exhibits a smaller spread as well as improved means and spatial patterns the preconditioning improves the enkf particularly for smaller ensemble sizes allowing operational data assimilation with reduced computational effort in a validation scenario of delineating groundwater protection zones the preconditioned filter performs clearly better than the filter using the original initial ensemble

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

long term persistence of oil from the exxon valdez spill in two layer beaches oil spilt from the tanker exxon valdez more than 20 years ago still persists in the gravel beaches of prince william sound alaska field data and numerical modelling indicate that some of the oil was trapped in the anoxic environment of the lower layers of the beaches when the water table was low oil spilled from the tanker exxon valdez in 1989 refs 1 2 persists in the subsurface of gravel beaches in prince william sound alaska the contamination includes considerable amounts of chemicals that are harmful to the local fauna3 however remediation of the beaches was stopped in 1992 because it was assumed that the disappearance rate of oil was large enough to ensure a complete removal of oil within a few years here we present field data and numerical simulations of a two layered beach with a small freshwater recharge in the contaminated area where a high permeability upper layer is underlain by a low permeability lower layer we find that the upper layer temporarily stored the oil while it slowly and continuously filled the lower layer wherever the water table dropped below the interface of the two layers as a result of low freshwater recharge from the land once the oil entered the lower layer it became entrapped by capillary forces and persisted there in nearly anoxic conditions that are a result of the tidal hydraulics in the two layered beaches we suggest that similar dynamics could operate on tidal gravel beaches around the world which are particularly common in mid and high latitude regions4 5 with implications for locating spilled oil and for its biological remediation

swash infiltration exfiltration and sediment transport field measurements of vertical pore pressure gradients within the bed are used to quantify instantaneous 8 hz rates of swash infiltration exfiltration across the beach face cyclic infiltration exfiltration is associated with individual swash events with observed vertical flow rates o 10 3 m s rates of net swash groundwater exchange i e through bed flow integrated over several swash cycles are two orders of magnitude smaller at the timescale of individual swashes vertical pore pressure gradients within the beach face are much greater than horizontal pore pressure gradients this permits application of the numerical solution of darcy s law for one dimensional vertical flow to model fluctuating pore pressures and hence vertical through bed flow vertical flow through a porous bed modifies sediment mobility in at least two ways 1 seepage forces change the effective weight of surficial sediments and 2 boundary layer thickening or thinning result in altered bed shear stresses by considering these two opposing effects separately a new shields parameter is derived that incorporates terms for through bed flow simulation of time varying seepage force and bed stress effects over an uprush backwash cycle suggests that the effect of altered bed stresses dominates over the change in effective weight and that infiltration exfiltration effects are most important during uprush simulated transport rates are increased by up to 40 of the peak transport rate during uprush and reduced by 10 during backrush in summary swash infiltration exfiltration across a saturated beach face enhances the net upslope transport of sediment

nonlinear interactions of waves and tides in a subterranean estuary previous studies have revealed hysteretic behavior in subterranean estuaries in response to intensified wave conditions caused by offshore storm events showing dependence of submarine groundwater discharge sgd and subsurface salt distribution on historic wave conditions although most shorelines worldwide are also exposed to tidal fluctuations it is unclear how tides moderate wave induced sgd and salinity distribution in subterranean estuaries this study presents numerical simulations that explore the combined influence of intensified wave conditions and tides on groundwater flow and salt transport in a subterranean estuary the results show that tides weaken the hysteretic wave effect on sgd suggesting that a tidally influenced subterranean estuary is less sensitive to intensified wave conditions with respect to the water fluxes across the aquifer sea interface however due to enhancement of salt freshwater mixing tides strengthen the hysteretic wave effect on the salt fluxes across the aquifer sea interface prolonging the recovery of salt distribution in the subterranean estuary to the prestorm state these findings reveal the nonlinear coupling nature of processes driven by oceanic oscillations at different time scales in subterranean estuaries

modeling tracer transport at the made site the importance of heterogeneity 1 we examine three stochastic transport models of the macrodispersion experiment made site using high resolution conductivity fields derived from a new geostatistical interpretation of the flowmeter data evaluation of the spatial continuity of the hydraulic conductivity data revealed a hole effect structure indicating the occurrence of periodic structures i e clustered lenses or facies alternatively we examine geostatistical models based on indicator variables and found a similarity to bivariate gaussian properties tritium transport was simulated in kriged fields and in random fields generated using different geostatistical models at a grid spacing equal to the vertical support scale of the flowmeter measurements to explicitly represent small scale heterogeneity only those simulations obtained using the hole effect model resulted in a subset of realizations which reproduced the strong anomalous tracer spreading neglecting the hole effect structure of the spatial model in the gaussian simulations resulted in a reduced tailing of the tracer illustrating the importance of preferential flow on anomalous solute transport at the columbus aquifer furthermore we found that a multivariate gaussian random function is adequate to model the spatial distribution of hydraulic conductivity at the made site based on the results of the indicator transport simulations and the univariate and bivariate normality detected in the analysis of the flowmeter data we conclude that when small scale variability of hydraulic conductivity is correctly modeled at the flowmeter measurement support scale the ade is capable of reproducing the tracer spreading results suggest that the main contributor to the operational memory function used in previous successful mass transfer models is mostly a reflection of the suppressed spatial variation of hydraulic conductivity at the model scale

driving mechanisms for groundwater flow and salt transport in a subterranean estuary this paper presents field measurements and numerical simulations of groundwater dynamics in the intertidal zone of a sandy meso tidal beach the study focusing on vertical hydraulic gradients and pore water salinities reveals that tides and waves provide important forcing mechanisms for flow and salt transport in the nearshore aquifer such forcing interacting with the beach morphology enhances the exchange between the aquifer and ocean the spatial and temporal variations of vertical hydraulic gradients demonstrate the complexity and dynamic nature of the processes and the extent of mixing between fresh groundwater and seawater in a subterranean estuary these results provide evidence of a potentially important reaction zone in the nearshore aquifer driven by oceanic oscillations land derived contaminants may undergo important biogeochemical transformations in this zone prior to discharge

exact analytical expressions for the piezometric profile and water exchange between stream and groundwater during and after a uniform rise of the stream level 1 we consider an archetypical problem relevant to a confined aquifer in contact with a stream the model problem consists of an idealized one dimensional region 0 x l where the left boundary at x 0 is held at a fixed piezometric head h0 and the right boundary s piezometric head at x l is increased from hl to h0 at a constant rate exact solutions for all times all points in the aquifer and for any possible constant rate of change of the right boundary piezometric head are presented for the piezometric head and the instantaneous flow rate an exact expression for the exchange volume at the groundwater stream interface for an arbitrary time is also provided this expression shows that there is a specific critical rising rate of the stream level above which the net exchange volume is into the aquifer and below which it is out of the aquifer the solution shows that regardless of the rise rate a certain water volume inversely proportional to the rise rate enters the aquifer

groundwater flow and salt transport in a subterranean estuary driven by intensified wave conditions a numerical study based on a density dependent variably saturated groundwater flow model was conducted to investigate flow and salt transport in a nearshore aquifer under intensified wave conditions caused by offshore storms temporally varying onshore hydraulic gradients due to wave setup were determined as the seaward boundary condition for the simulated aquifer the results showed a rapid increase in influxes across the aquifer ocean interface in response to the wave event followed by a more gradual increase in effluxes the upper saline plume first widened horizontally as the wave setup point moved landward it then expanded vertically with recirculating seawater pushed downward by the wave induced hydraulic gradient the time for the salt distribution to return to the prestorm condition was up to a hundred days and correlated strongly with the time for seawater to recirculate through the aquifer the pathways of recirculating seawater and fresh groundwater were largely modified by the wave event these pathways crossed through the same spatial locations at similar times indicating significant salt freshwater mixing the flow and salt transport dynamics were more responsive to wave events of longer duration and higher intensity especially in more permeable aquifers with lower fresh groundwater discharge despite their larger response aquifers with higher permeability and beach slope recovered more rapidly postevent the rapid recovery of the flows compared with the salinity distribution should be considered in field data interpretation due to their long lasting impact wave events may significantly influence the geochemical conditions and the fate of chemicals in a subterranean estuary key points intensified waves perturb flow and transport in a subterranean estuary lengthy period months for salinity distribution to recover from a wave event exchange fluxes and flows respond and recover rapidly following a wave event

numerical modeling of subsurface release and fate of benzene and toluene in coastal aquifers subjected to tides abstract a numerical study was undertaken to investigate subsurface release and fate of benzene and toluene in a tidally influenced beach the simulations were conducted by using a numerical model biomarun which coupled a multi monod kinetic model biob to a density dependent variably saturated groundwater flow model marun the fate and transport of the contaminant plume were characterized by computing its centroid trajectory spreading area and percentage of biodegradation in beach saturated and unsaturated zone respectively key factors likely affecting this process were investigated including tide amplitude capillarity and hydraulic conductivity it was found that aerobic biodegradation was the major fate of the contaminant plume in the beach tidal action twisted the centroid of the contaminant plume during its migration in the beach which increased the residence time of the plume in the beach high tidal range significantly altered the spatial distribution of the contaminant biodegradation in the beach in contrast the capillary fringe had impacts on the percentage of benzene biodegraded in the saturated and unsaturated zone of the beach the increase in capillary fringe enhanced the percentage of the contaminant biodegraded in the unsaturated zone up to 40 which is comparable to that in the saturated zone hydraulic conductivity seemed to have large impacts on the biodegradation rate of the contaminant in the beach higher hydraulic conductivity induced faster contaminant biodegradation in the beach

dynamic groundwater flows and geochemistry in a sandy nearshore aquifer over a wave event dynamic coastal forcing influences the transport of pollutants in nearshore aquifers and their ultimate flux to coastal waters in this study field data are presented that show for the first time the influence of a period of intensified wave conditions wave event on nearshore groundwater flows and geochemistry in a sandy beach field measurements at a freshwater beach allow wave effects to be quantified without other complex forcing that are present along marine shorelines e g tides pressure transducer data obtained over an isolated wave event reveal the development of transient groundwater flow recirculations the groundwater flows were simulated in feflow using a phase averaged wave setup approach to represent waves acting on the sediment water interface comparison of measured and simulated data indicates that consideration of wave setup alone is able to adequately capture wave induced perturbations in groundwater flows while prior studies have shown sharp ph and redox spatial zonations in nearshore aquifers this study reveals rapid temporal variations in conductivity ph and redox orp in shallow sediments up to 0 5 m depth in response to varying wave conditions comparison of head gradients with calculated conductivity and ph mixing ratios indicates the controlling effect of the wave induced water exchange and flows in driving the observed geochemical dynamics while we are not able to conclusively determine the extent to which temporal variations are caused by conservative mixing versus reactive processes the ph and orp variations observed will have significant implications for the fate of reactive pollutants discharging through sandy nearshore aquifers

effects of alongshore morphology on groundwater flow and solute transport in a nearshore aquifer variations of beach morphology in both the cross shore and alongshore directions associated with tidal creeks are common at natural coasts as observed at a field site on the east coast of rarotonga cook islands field investigations and three dimensional 3 d numerical simulations were conducted to study the nearshore groundwater flow and solute transport in such a system the results show that the beach morphology combined with tides induced a significant alongshore flow and modified local pore water circulation and salt transport in the intertidal zone substantially the bathymetry and hydraulic head of the creek enabled further and more rapid landward intrusion of seawater along the creek than in the aquifer which created alongshore hydraulic gradient and solute concentration gradient to drive pore water flow and salt transport in the alongshore direction within the aquifer the effects of the creek led to the formation of a saltwater plume in groundwater at an intermediate depth between fresher water zones on a cross shore transect the 3 d pore water flow in the nearshore zone was also complicated by the landward hydraulic head condition resulting in freshwater drainage across the inland section of the creek while seawater infiltrating the seaward section these results provided new insights into the complexity intensity and time scales of mixing among fresh groundwater recirculating seawater and creek water in three dimensions the 3 d characteristics of nearshore pore water flow and solute transport have important implications for studies of submarine groundwater discharge and associated chemical input to the coastal sea and for evaluation of the beach habitat conditions

numerical study of solute transport in shallow beach aquifers subjected to waves and tides a numerical study was conducted to investigate the fate of solute in a laboratory beach in response to waves and tides a new temporal upscaling approach labeled net inflow was introduced to address impacts of waves on solute transport within beaches numerical simulations using a computational fluid dynamic model were used as boundary conditions for the two dimensional variably saturated flow and solute transport model marun the modeling approach was validated against experimental data of solute transport due to waves and tides exchange fluxes across the beach face and subsurface solute transport e g trajectory movement speed and residence time were quantified simulation results revealed that waves increased the exchange fluxes and engendered a wider exchange flux zone along the beach surface compared to tide only forcing waves superimposed on tide caused the plume to be deeper into the beach and to migrate more seaward the infiltration into the beach was found to be directly proportional to the general hydraulic gradient in the beach and inversely proportional to the matrix retention or capillary capacity the simulations showed that a higher inland water table would attenuate wave caused seawater infiltration which might impact beach geochemical processes e g nutrient recycle and redox condition especially at low tide zone the concept of biochemical residence time maps brtm was introduced to account for the net effect of limiting concentration of chemicals on biochemical reactions it was found that waves shifted the brtms downward and seaward in the beach and subsequently they engendered different biochemical conditions within the beach

a comparative study of three dimensional hydraulic conductivity upscaling at the macro dispersion experiment made site columbus air force base mississippi usa simple averaging simple laplacian laplacian with skin and non uniform coarsening are the techniques investigated in this comparative study of three dimensional hydraulic conductivity upscaling the reference is a fine scale conditional realization of the hydraulic conductivities at the macro dispersion experiment site on columbus air force base in mississippi usa this realization was generated using a hole effect variogram model and it was shown that flow and transport modeling in this realization at this scale can reproduce the observed non fickian spreading of the tritium plume the purpose of this work is twofold first to compare the effectiveness of different upscaling techniques in yielding upscaled models able to reproduce the observed transport behavior and second to demonstrate and analyze the conditions under which flow upscaling can provide a coarse model in which the standard advection dispersion equation can be used to model transport in seemingly non fickian scenarios specifically the use of laplacian based upscaling technique coupled with a non uniform coarsening scheme yields the best results both in terms of flow and transport reproduction for this case study in which the coarse blocks are smaller than the correlation ranges of the fine scale conductivities

swash groundwater dynamics in a sandy beach laboratory experiment abstract experiments are carried out in a wave basin in order to study the swash groundwater interaction a set of wave gages and pressure sensors are used to monitor the free surface and groundwater dynamics the study is based on the comparison of two selected cases which differ by the gravity and infragravity forcing conditions the features of wave breaking in the surf zone the presence of a standing wave attached to the beach face and the wave setup at the shoreline significant differences are observed in the response of the swash groundwater system the water table overheight appears to be controlled by the amount of infragravity energy available at the shore cyclic beach drainage processes can be observed when the water table is low significant time averaged and time resolved flows are observed into the sand depending on the swash hydrodynamics the presence of a gravity standing wave modulation attached to the shore is shown to affect swash and groundwater dynamics most of the pressure gradients observed under the swash zone are related to infiltration flows and are thus related to moderate increase of the sediment relative weight

reply to comment by f molz et al on investigating the macrodispersion experiment made site in columbus mississippi using a three dimensional inverse flow and transport model

numerical experiments on interactions between wave motion and variable density coastal aquifers a comprehensive two dimensional cross shore process based numerical model of nearshore hydrodynamics based on the navier stokes equations k e turbulence closure and the volume of fluid method beach morphology and variable density groundwater flow seawat 2000 was developed this model which was applied at the field scale relaxes simplifications in existing models that do not include such detailed mechanistic descriptions numerical experiments were conducted to investigate the effects of varying aquifer beach and wave characteristics e g inland groundwater head sand grain size different wave heights and periods on the coupled system spilling and plunging breakers on dissipative and intermediate beaches were simulated for a given set of boundary conditions the model was run for 1 y without the hydrodynamic sub model to achieve a realistic salt freshwater interface then the hydrodynamic component was run for 15 min and the model results analyzed the main features considered were groundwater circulation saltwater wedge position in exfiltration across the beach face and beach morphology the predictions of the numerical model agree well with existing understanding and experimental measurements for an inland watertable that is lower than the still water level swl such that the groundwater flow is mainly landward on both coarse and fine sand beaches the addition of wave motion moves the saltwater wedge further landward for an inland watertable that is higher than the swl the opposite behavior occurred the numerical experiments showed that more sediment transport takes place on intermediate beaches than on dissipative beaches in addition beach profile variations are greater under plunging breakers while coarse sand beaches are steeper than fine sand beaches for the same wave conditions there is a strong correlation between in exfiltration and beach face deposition erosion for the coarse beaches while in exfiltration has a slight effect on sediment transport for fine beaches the model is capable of simulating the short term evolution of foreshore profile changes and beach watertable and saltwater wedge movement due to interactions between wave motion and coastal groundwater

numerical modeling of water flow and salt transport in bare saline soil subjected to evaporation summary a numerical study based on a density dependent variably saturated groundwater flow model marun was conducted to investigate subsurface flow and salt transport in bare saline aquifers subjected to evaporation which was simulated using the bulk aerodynamic formulation as evaporation was assumed to depend on the pore moisture the evaporation flux evolved gradually causing a gradual increase in the pore salinity this is in contrast to prior studies where the high salinity was imposed instantaneously on the ground surface key factors likely affecting subsurface hydrodynamics were investigated including saturated hydraulic conductivity capillary drive relative humidity in the air and surrounding groundwater replenishment the simulations showed two temporal regimes where the first consists of rapid evaporation for a duration of hours followed by slow evaporation until evaporation ceases in the absence of surrounding groundwater replenishment evaporation induced density gradient generated an upward water flow initially and then the flow decreased at which time a high density salt finger formed and propagated downwards capillary properties and atmospheric condition had significant impacts on subsurface moisture distribution and salt migration in response to the evaporation the results also suggested that the presence of subsurface water replenishment to the evaporation zone tended to produce a steady evaporation rate at the ground surface

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

salt freshwater dynamics in a subterranean estuary over a spring neap tidal cycle this paper presents field measurements and numerical simulations of pore water salinities and groundwater flow in the intertidal zone of an unconfined coastal aquifer over a spring neap tidal cycle the study provides insight into the extent and time scales of mixing between fresh groundwater and recirculating seawater in a tidally influenced subterranean estuary salt freshwater dynamics in subterranean estuaries are currently not well understood despite their potentially important implications for fluxes of chemicals to coastal waters via submarine groundwater discharge the data and simulation results show that changes in the tidal shoreline excursion over the spring neap cycle induce significant variations in the intertidal salinity structure observed higher frequency salinity fluctuations demonstrate further the intensity and complexity of the salt freshwater mixing process in contrast with the salinity variations fresh groundwater was found to discharge around a distinct intertidal beach slope break throughout the spring neap period this suggests that the slope break may affect significantly groundwater flow and salt transport near the shore measurements of ph and dissolved oxygen distributions revealed important biogeochemical zonations in the system these zonations are expected to strongly influence the fate of many reactive chemicals in the nearshore aquifer and their subsequent discharge to coastal waters

saltwater freshwater mixing fluctuation in shallow beach aquifers abstract field measurements and numerical simulations demonstrate the existence of an upper saline plume in tidally dominated beaches the effect of tides on the saltwater freshwater mixing occurring at both the upper saline plume and lower salt wedge is well understood however it is poorly understood whether the tidal driven force acts equally on the mixing behaviours of above two regions and what factors control the mixing fluctuation features in this study variable density saturated unsaturated transient groundwater flow and solute transport numerical models are proposed and performed for saltwater freshwater mixing subject to tidal forcing on a sloping beach a range of tidal amplitude fresh groundwater flux hydraulic conductivity beach slope and dispersivity anisotropy are simulated based on the time sequential salinity data the gross mixing features are quantified by computing the spatial moments in three different aspects namely the centre point length and width and the volume or area in a two dimensional case simulated salinity distribution varies significantly at saltwater freshwater interfaces mixing characteristics of the upper saline plume greatly differ from those in the salt wedge for both the transient and quasi steady state the mixing of the upper saline plume largely inherits the fluctuation characteristics of the sea tide in both the transverse and longitudinal directions when the quasi steady state is reached on the other hand the mixing in the salt wedge is relatively steady and shows little fluctuation the normalized mixing width and length mixing volume and the fluctuation amplitude of the mass centre in the upper saline plume are in general one magnitude order larger than those in the salt wedge region in the longitudinal direction tidal amplitude fresh groundwater flux hydraulic conductivity and beach slope are significant control factors of fluctuation amplitude in the transverse direction tidal amplitude and beach slope are the main control parameters very small dispersivity anisotropy e g l t 5 could greatly suppress mixing fluctuation in the longitudinal direction this work underlines the close connection between the sea tides and the upper saline plume in the aspect of mixing thereby enhancing understanding of the interplay between tidal oscillations and mixing mechanisms in tidally dominated sloping beach systems

subsurface processes generated by bore driven swash on coarse grained beaches 1 large scale laboratory experiments presented in this paper involved bore driven swash on permeable immobile coarse grained beaches two different sediments were used d50 1 5 and 8 5 mm resulting in different beach permeability and surface roughness the experiments yielded detailed measurements of swash depth and velocities wetting front pressure and groundwater levels across the swash zone this paper is focused on the processes occurring within the beach the measurements provide the shape of the wetting front and the groundwater table and reveal the behavior of air in the unsaturated region of the beach air is initially at atmospheric pressure but the pressure builds up when air becomes encapsulated between the saturated region formed below the swash and the groundwater table for the 1 5 mm beach entrapped air significantly affected the water exchange between the swash and the subsurface the considerable buildup of interstitial air pressure reduced vertical hydraulic gradients and thus infiltration rates at the lower end of the beach the hydraulic gradients even became negative indicating flow reversal and exfiltration in contrast for the 8 5 mm beach the rate of infiltration was only slightly affected by the buildup of pore air pressure the vertical hydraulic gradients were more than twice the magnitude of those within the 1 5 mm beach the results presented in the paper clarify the mechanisms that drive and impede the water exchange between the surface and subsurface flow in particular infiltration into the initially unsaturated part of the beach and the resulting air entrapment play a significant role in swash and similar flows

construction of geostatistical aquifer models integrating dynamic flow and tracer data using inverse technique natural aquifers are heterogeneous and geostatistical methods are widely used to simulate the heterogeneity of aquifer properties due to limited available data it is essential to integrate as much information as possible to reduce the uncertainty in aquifer models and flow predictions traditional geostatistical techniques efficiently consider static hard and soft information such as core data and seismic data however dynamic flow and transport data such as flow rates pressure and tracer breakthrough are important information that are not easily considered with the traditional techniques integrating such dynamic data into a model requires the solution of a difficult inverse problem since dynamic data and aquifer properties are related to each other through the non linear flow and transport equations a recently developed geostatistically based inverse technique the sequential self calibration ssc method is introduced to integrate those dynamic data the ssc method is an iterative inverse technique that is coupled with an optimization procedure it provides for fast generation of multiple realizations of aquifer property models that jointly match pressure and tracer breakthrough data yet display the same geostatistical characteristics this method is flexible computationally efficient and robust the main features of ssc include 1 a master point concept that reduces the number of parameters 2 a perturbation mechanism based on kriging that accounts for the spatial correlation of the aquifer properties 3 a fast streamline based tracer flow simulator for integration of tracer data and 4 a new semi analytical streamline based method for computing sensitivity coefficients of tracer breakthrough applications of the ssc method are demonstrated with a synthetic data set results show that tracer breakthrough data carry important information on the spatial variation of aquifer permeability in the inter well areas as a contrast pressure data provide information at near well bore areas only integrating pressure and breakthrough data jointly leads to significant improvement in the aquifer heterogeneity representation and a reduction in the uncertainty of aquifer model the accuracy of flow and transport predictions can be dramatically improved by integrating dynamic data

hydrodynamics in a gravel beach and its impact on the exxon valdez oil 1 this paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach field observations of water table pore water salinity were performed the two dimensional finite element model marun was used to simulate observed water table and salinity based on field observations and model calibrations a two layered beach structure was identified which is characterized by a high permeability surface layer underlain by a low permeability lower layer the salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone the presence of the two layers prevented the presence of a freshwater discharge tube between the upper saline plume and salt wedge this is in contrast with the previous works where freshwater discharge tube was observed the tide induced submarine groundwater discharge sgd was estimated at 9 m3 d 1 m 1 a large value that is probably due to the large tidal range of 4 8 m and the very permeable surface layer the freshwater seawater dynamics revealed here may provide new insights into the complexity intensity and time scales of mixing between fresh groundwater and seawater in tidal beaches the simulated water table of the beach was higher than the interface between the surface layer and the lower layer which prevented exxon valdez oil from penetrating into the lower layer in 1989

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

field study of dispersion in a heterogeneous aquifer 3 geostatistical analysis of hydraulic conductivity observations of the spatial variability of hydraulic conductivity at a tracer test site located at columbus air force base in mississippi are presented direct measurements of hydraulic conductivity of the heterogeneous alluvial aquifer at the site were made using borehole flowmeter logging slug tests and a laboratory permeameter to test undisturbed soil cores indirect methods estimating hydraulic conductivity were also evaluated including soil grain size analyses surface geophysical surveys and mapping of sediment facies the spatial covariance of the 2187 hydraulic conductivity values obtained with the borehole flowmeter method was examined the log hydraulic conductivity variance ln2k and the horizontal and vertical correlation scales h and v of 4 5 12 8 m and 1 6 m respectively were estimated assuming second order stationarity of the conductivity field the covariance parameters are uncertain with bounding values that are 24 76 above or below the estimate covariance parameters estimated with more limited nonflowmeter data were within the same magnitude as those obtained using the extensive flowmeter data suggesting that data from a variety of methods may be used to provide approximate values of the autocovariance parameters nonstationarity of the ln k field was examined by removing three dimensional polynomial trend surfaces and calculating variograms of the residuals significantly lower estimates for ln2k h and v of 2 7 4 8 m and 0 8 m respectively were obtained from the third order log conductivity residuals after trend removal the bounding parameter values differ 15 44 from the estimated values accounting for unsteady flow and the uncertainty in the covariance parameters of the third order log conductivity residuals the calculated longitudinal and horizontal transverse macrodispersivities ranged from 1 5 m to 1 8 m and 0 3 m to 0 6 m respectively

modeling transient groundwater flow by coupling ensemble kalman filtering and upscaling 1 the ensemble kalman filter enkf is coupled with upscaling to build an aquifer model at a coarser scale than the scale at which the conditioning data conductivity and piezometric head had been taken for the purpose of inverse modeling building an aquifer model at the support scale of observations is most often impractical since this would imply numerical models with many millions of cells if in addition an uncertainty analysis is required involving some kind of monte carlo approach the task becomes impossible for this reason a methodology has been developed that will use the conductivity data at the scale at which they were collected to build a model at a much coarser scale suitable for the inverse modeling of groundwater flow and mass transport it proceeds as follows 1 generate an ensemble of realizations of conductivities conditioned to the conductivity data at the same scale at which conductivities were collected 2 upscale each realization onto a coarse discretization on these coarse realizations conductivities will become tensorial in nature with arbitrary orientations of their principal components 3 apply the enkf to the ensemble of coarse conductivity upscaled realizations in order to condition the realizations to the measured piezometric head data the proposed approach addresses the problem of how to deal with tensorial parameters at a coarse scale in ensemble kalman filtering while maintaining the conditioning to the fine scale hydraulic conductivity measurements we demonstrate our approach in the framework of a synthetic worth of data exercise in which the relevance of conditioning to conductivities piezometric heads or both is analyzed

beach water table fluctuations due to wave run up capillarity effects high frequency beach water table fluctuations due to wave run up and run down have been observed in the field waddell 1976 such fluctuations affect the infiltration exfiltration process across the beach face and the interstitial oxygenation process in the beach ecosystem accurate representation of high frequency watertable fluctuations is of importance in the modeling of 1 the interaction between seawater and groundwater more important the effects on swash sediment transport and 2 the biological activities in the beach ecosystem capillarity effects provide a mechanism for high frequency water table fluctuations previous modeling approaches adopted the assumption of saturated flow only and failed to predict the propagation of high frequency fluctuations in the aquifer in this paper we develop a modified kinematic boundary condition kbc for the water table which incorporates capillarity effects the application of this kbc in a boundary element model enables the simulation of high frequency water table fluctuations due to wave run up numerical tests were carried out for a rectangular domain with small amplitude oscillations the behavior of water table responses was found to be similar to that predicted by an analytical solution based on the one dimensional boussinesq equation the model was also applied to simulate the water table response to wave run up on a sloping beach the results showed similar features of water table fluctuations observed in the field in particular these fluctuations are standing wave like with the amplitude becoming increasingly damped inland we conclude that the modified kbc presented here is a reasonable approximation of capillarity effects on beach water table fluctuations however further model validation is necessary before the model can confidently be used to simulate high frequency water table fluctuations due to wave run up

rate limited mass transfer or macrodispersion which dominates plume evolution at the macrodispersion experiment made site we present a model of solute transport that explains the large scale behavior of the solute tracer test plumes at the macrodispersion experiment made site as the result of advection and rate limited mass transfer between mobile and small scale immobile domains this model does not consider the process of dispersion and yet provides an alternative explanation of the evolution of the observed concentration profiles compared to the macrodispersion model the mass transfer model better represents the change in mobile dissolved mass with time the peak of the concentration profile and the profile asymmetry specifically unlike the macrodispersion model the mass transfer model explains the facts that the observed mass of the plume was greater than the injected mass in early snap shots of the plume and less than the injected mass at late times we suggest that the injected mass advects through the mobile domain and diffuses into and out of the immobile domain the immobile domain consists of a combination of low permeability zones on the scale of centimeters to decimeters the darcy scale immobile domain and intragranular porosity dead end pores and surface sorption the pore scale immobile domain we suggest that the mobile domain was sampled preferentially when water was extracted therefore at early times relatively clean water in the immobile domain was not sampled and incorrectly assumed to contain high solute concentrations similarly the mass at late times was underestimated because solute trapped in the pore scale immobile domain was not extracted during sampling and therefore ignored the combination of advection and slow mass transfer is consistent with the fact that the peak of the plume migrated only 5 m by the termination of the experiment as well as the different behavior of bromide and tritium tracers

numerical model of swash motion and air entrapment within coarse grained beaches abstract the paper presents a numerical model for bore driven swash on permeable coarse grained beaches the surface flow module is modelled using the non linear shallow water equations nlswes solved using the godunov based finite volume ader scheme which is suitable for handling steep bores as well as large source terms in the nlswes the subsurface flow comprises i infiltration and exfiltration modelled as vertical piston like flow ii horizontal pore air movement within the unsaturated region of the beach iii the horizontal groundwater flow model predictions of the surface and subsurface flow are in good agreement with measurements from large scale laboratory experiments for swash on permeable immobile beaches in these simulations air velocity was sufficiently small to justify using darcy s resistance law for the air flow whereas the quadratic forchheimer law had to be used for the infiltration and groundwater flow the validated numerical model provides insight into the surface subsurface water exchange for bore driven swash on coarse grained beaches the impact of air entrapped between the wetting front and the groundwater level on the water exchange is examined in particular

hydrologic dynamics and geochemical responses within a floodplain aquifer and hyporheic zone during hurricane sandy storms dominate solute export budgets from catchments and drive hydrogeochemical changes in the near stream environment we captured near stream hydrogeochemical dynamics during an intense storm hurricane sandy october 2012 by instrumenting a riparian hyporheic zone transect of white clay creek in the christina river basin critical zone observatory with pressure transducers redox probes and pore water samplers in the floodplain aquifer preferential vertical flow paths such as macropores facilitated rapid infiltration early in the storm water table rose quickly and promoted continuous groundwater discharge to the stream floodplain hillslope topography controlled poststorm aquifer drainage rates as the broad western floodplain aquifer drained more slowly than the narrow eastern floodplain aquifer adjacent to a steep hillslope these changes in groundwater flow drove heterogeneous geochemical responses in the floodplain aquifer and hyporheic zone vertical infiltration in the floodplain and hyporheic exchange in the streambed increased doc and oxygen delivery to microbially active sediments which may have enhanced respiration resulting geochemical perturbations persisted from days to weeks after the storm our observations suggest that groundwater borne solute delivery to streams during storms depends on unique interactions of vertical infiltration along preferential pathways perturbations to groundwater geochemistry and topographically controlled drainage rates

field study of dispersion in a heterogeneous aquifer 1 overview and site description results are presented for a large scale natural gradient tracer experiment conducted in a heterogeneous alluvial aquifer at a site near columbus mississippi the study was initiated with a 48 hour pulse injection of 10 m3 of groundwater containing bromide and three organic tracers pentaflourobenzoic acid o trifluoromethylbenzoic acid and 2 6 diflourobenzoic acid over a 20 month period seven comprehensive samplings of the tracer plume were performed at approximately 1 to 4 month intervals using an extensive three dimensional sampling well network the dominant feature of the tracer plume that evolved during the study was the highly asymmetric concentration distribution in the longitudinal direction this asymmetry was produced by accelerating groundwater flow along the plume travel path that in turn resulted from an approximate 2 order of magnitude increase in the mean hydraulic conductivity between the near field and far field regions of the site the columbus study is distinct from previous natural gradient experiments because of the extreme heterogeneity of the aquifer the large scale spatial variations in groundwater velocity and the extensive set of hydraulic conductivity measurements for the aquifer

large wave simulation of three dimensional cross shore and oblique spilling breaking on constant slope beach in this work the large wave simulation lws method is adapted for application in spilling wave breaking over a constant slope beach according to lws large scales of velocities pressure and free surface elevation are numerically resolved while the corresponding unresolved scale effects are taken into consideration by a subgrid scale sgs model for wave and eddy stresses the model may be not fully applicable in very shallow water close to the shoreline where the unresolved turbulent free surface oscillation is of the same order with the water depth time integration of the euler equations is achieved by a two stage fractional scheme combined with a hybrid scheme for spatial discretization consisting of finite difference and pseudospectral approximation methods model parameters are calibrated by comparison to available experimental data of free surface elevation and velocities in the surf zone for cross shore incoming waves the action of the wave sgs stresses in the outer coastal and surf zones initiates breaking and generates appropriate vorticity in the form of an eddy structure surface roller at the breaking wavefront at incipient breaking both advection and gravity contribute to the vorticity flux at the free surface while only after the full development of the surface roller the effect of advection becomes stronger the sgs model is also utilized to simulate propagation refraction and breaking of oblique incoming waves the gradual breaking and dissipation of wave crestlines and the surface roller structure along the breaking wavefront are automatically captured without any empirical input such as data for the roller shape or the wave propagation angle at breaking

semi analytical solution of land derived solute transport under tidal fluctuation in a confined aquifer abstract a one dimensional semi analytical solution of land derived solute transport subject to tidal fluctuation in a coastal confined aquifer was derived using the generalized integral transform technique gitt to investigate the plume migration of land derived contaminants within a tidally influenced aquifer both spatially and temporally varying expressions of the darcy velocity and dispersion coefficients obtained from the analytical solution of the groundwater head response which were subject to sinusoidal boundary conditions due to tidal fluctuation were considered this new semi analytical solution was verified against a numerical solution as well as the peak location trajectory obtained using the predictor corrector method sensitivity analyses of tidal amplitude hydraulic conductivity and storage coefficient using the proposed solution were performed to understand plume behavior with regard to plume shape plume spatial moments and macrodispersion coefficients to gain a better understanding of the transport mechanisms as the tidal amplitude hydraulic conductivity and storage coefficient were increased the peaks were travelled faster and peak concentrations were decreased in addition an increase in tidal amplitude hydraulic conductivity and storage coefficient caused an increase in variance as well as the macrodispersion coefficient it was observed that negative macrodispersion appeared when the storage coefficient was largest as well as when the difference between landward directed advective velocity at the leading and trailing edges of the plume was greatest this newly developed semi analytical solution provides a useful mathematical tool for validating numerical models and understanding the physical mechanism of the migration of plume discharge to the sea or estuaries within a tidally influenced aquifer

impact of upscaling on solute transport traveltimes scale dependence of dispersivity and propagation of uncertainty 1 efficiency constraints in applying numerical models to real problems force the use of a coarse discretization of the domain compared with the detailed scale required for the most adequate description of the system upscaling encompasses the methods that transfer small scale information to the computational scale the loss of small scale information by upscaling aquifer properties to construct a numerical model largely modifies the true heterogeneous structure of the aquifer compromising the final predictions of solute transport we present extensive monte carlo solute transport simulations in heterogeneous porous media to investigate 1 the impact of upscaling on the evolution of solute plumes and 2 the propagation of uncertainty through upscaling in doing this we analyze the benefits of using enhanced block dispersion tensors in the advection dispersion equation to compensate for the loss of information it is shown that upscaling does not affect the median traveltimes of particles reaching a control location but the tail of breakthrough curves is largely underestimated it is also observed that normal upscaled transport models can largely underestimate the spreading of solute plumes even if block dispersivities are calculated as being representative of within block heterogeneity discrepancies are mainly attributed to the mass transfer interaction between grid blocks of the numerical model and the use of a simplistic representation of the block hydraulic conductivity tensor using the small perturbation stochastic approach we found that mass transfer effects are still significant even for block sizes of the numerical model greater than 30 correlation scales moreover upscaling is shown to have a substantial impact on the uncertainty predicted by solute transport models which is not compensated by the use of enhanced block dispersion tensors for very heterogeneous media simulation results showed the inability of the classical advection dispersion equation to simultaneously reproduce the tail of the breakthrough curve and its uncertainty in the upscaled model in those cases results indicated that either a mass transfer model allowing solute mass exchange between high and low conductivity zones encountered within a grid block of the numerical model or the continuous time random walk model expressing the retardation of solute particles passing through low conductivity regions inside a grid block by means of a transition time distribution function might suppose a better upscaled transport model

coupled surface subsurface hydrologic measurements reveal infiltration recharge and discharge dynamics across the swash zone of a sandy beach swash groundwater interactions affect the biogeochemistry of beach aquifers and the transport of solutes and sediment across the beachface improved understanding of the complex coupled dynamics of surface and subsurface flow processes in the swash zone is required to better estimate chemical fluxes to the sea and predict the morphological evolution of beaches simultaneous high frequency measurements of saturation water table elevation and the cross shore locations of runup and the boundary between the saturated and unsaturated beachface surface saturation boundary were collected on a sandy beach to link groundwater flow dynamics with swash zone forcing saturation and lysimeter measurements showed the dynamic response of subsurface saturation to swash events and permitted estimation of infiltration rates surface and subsurface observations revealed a decoupling of the surface saturation boundary and the intersection between the water table and the beachface surface measurements alone were insufficient to delineate the infiltration and discharge zones which moved independently of the surface saturation boundary results show for the first time the motion and areal extent of infiltration and recharge zones and constrain the maximum size of the subaerial discharge zone over swash and tidal time scales the width of the infiltration zone was controlled by swash processes and subaerial discharge was controlled primarily by tidal processes these dynamics reveal the tightly coupled nature of surface and subsurface processes over multiple time scales with implications for sediment transport and fluid and solute fluxes through the hydrologically and biogeochemically active intertidal zone of sandy beaches

effects of wave forcing on a subterranean estuary wave and tide are important forcing factors that typically co exist in coastal environments a numerical study was conducted to investigate individual and combined effects of these forces on flow and mixing processes in a near shore subterranean estuary a hydrodynamic model based on the shallow water equations was used to simulate dynamic sea level oscillations driven by wave and tide the oscillating sea levels determined the seaward boundary condition of the coastal aquifer where variably saturated variable density flow was modeled the simulation results showed that waves induced an onshore upward tilt in the phase averaged sea level wave set up the resulting hydraulic gradient generated pore water circulations in the near shore zone of the coastal aquifer which led to formation of an upper saline plume usp similar to that due to tides however mixing of recirculating seawater in the usp with underlying fresh groundwater was less intensive under the high frequency wave oscillations in the case of combined forcing wave induced circulations coupled with the intra tidal flows strengthened the averaged circulating pore water flows in the near shore zone over the tidal period the circulating flows increased exchange between the subterranean estuary and ocean contributing 61 of the total submarine groundwater discharge for the simulated condition in comparison with the 40 and 49 proportions caused by the same but separate tidal and wave forcing respectively the combined forces also created a more extensive usp with the freshwater discharge zone shifted further seaward the freshwater flow paths in the intertidal subterranean estuary were altered with a significant increase of associated transit times the interplay of wave and tide led to increased mixing between discharging fresh groundwater and recirculating seawater these results demonstrated the complexity of near shore groundwater systems and have implications for future investigations on the fate of land sourced chemicals in the subterranean estuary prior to discharge to the ocean

iron isotope fractionation in subterranean estuaries dissolved fe concentrations in subterranean estuaries like their river seawater counterparts are strongly controlled by non conservative behavior during mixing of groundwater and seawater in coastal aquifers previous studies at a subterranean estuary of waquoit bay on cape cod usa demonstrate extensive precipitation of groundwater borne dissolved ferrous iron and subsequent accumulation of iron oxides onto subsurface sands waquoit bay is thus an excellent natural laboratory to assess the mechanisms of fe isotope fractionation in redox stratified environments and determine potential fe isotope signatures of groundwater sources to coastal seawater here we report fe isotope compositions of iron coated sands and porewaters beneath the intertidal zone of waquoit bay the distribution of pore water fe shows two distinct sources of fe one residing in the upward rising plume of fe rich groundwater and the second in the salt wedge zone of pore water the groundwater source has high fe ii concentration consistent with anoxic conditions and yield 56fe values between 0 3 and 1 3 in contrast sediment porewaters occurring in the mixing zone of the subterranean estuary have very low 56fe values down to 5 these low 56fe values reflect fe redox cycling and result from the preferential retention of heavy fe isotopes onto newly formed fe oxyhydroxides analysis of fe oxides precipitated onto subsurface sands in two cores from the subterranean estuary revealed strong 56fe and fe concentration gradients over less than 2m yielding an overall range of 56fe values between 2 and 1 5 the relationship between fe concentration and 56fe of fe rich sands can be modeled by the progressive precipitation of fe oxides along fluid flow through the subterranean estuary these results demonstrate that large scale fe isotope fractionation up to 5 can occur in subterranean estuaries which could lead to coastal seawater characterized by very low 56fe values relative to river values

metallogeny of the zoujiashan uranium deposit in the mesozoic xiangshan volcanic intrusive complex southeast china insights from chemical compositions of hydrothermal apatite and metal elements of individual fluid inclusions abstract the zoujiashan u deposit in the mesozoic xiangshan volcanic intrusive complex is one of the largest volcanic related type u deposits in china chemical composition of hydrothermal apatite and metal contents in individual fluid inclusions of quartz and fluorite are investigated in order to understand the precipitation mechanism of u and to further constrain the origin of u and ore forming fluids of the zoujiashan deposit illitization hematitization and u mineralization successively occurred within rhyolite and porphyritic lava three types of hydrothermal apatite are identified apatite type 1 ap1 and apatite type 2 ap2 are both euhedral subhedral crystals found in hematitization zone while only ap2 shows evident irregular chemical zoning along its rims apatite type 3 ap3 occurs as anhedral aggregates closely associated with u minerals in u ore veins implying synchronous precipitation of ap3 and u ores comparable chemical compositions of ap1 and cores of ap2 including similar high cl content indicate both of them were precipitated from a cl rich fluid that induced hematitization the elevated f contents of ap3 and rims of ap2 implies that a f rich fluid was involved and altered ap2 during the main stage of u deposition ap1 and cores of ap2 have lower mn contents than ap3 and rims of ap2 indicating an oxidized character for the cl rich fluid and a reducing character for the f rich fluid metal contents of fluid inclusions in fluorite and quartz occurring in u ores suggest that two end members of fluids including a u rich and a u poor were involved in the main stage of u mineralization mixing between these two fluids led to the deposition of u and th minerals through oxidation reduction reactions and destabilization of th f complexes respectively the u rich fluid is depleted in th and sr compared with the u poor fluid based on comparison of chemical compositions of apatite and fluid inclusions we suggest that the cl rich fluid precipitating ap1 and ap2 corresponds to the u rich end member fluid while the f rich fluid precipitating ap3 represents a mixture between the two end members the high u 12 7 58 5 ppm in the u rich end member fluid is in agreement with a relatively high oxygen fugacity and a surface derived origin the u poor end member fluid has lower rb cs than the u rich end member and the unaltered host rocks indicating the u poor fluid was derived from a mantle wedge that experienced addition of cs by fluids generated from the devolatilization of the subducted paleo pacific slab

trace element and sr nd isotope geochemistry of fluorite from the xiangshan uranium deposit southeast china the trace element and sr nd isotope geochemistry of fluorite have been investigated in the xiangshan volcanic rock hosted uranium deposit in southeast china detailed sr nd isotope data of the hydrothermal fluorite closely associated with the uranium mineralization suggest that ore forming fluids were a combination of mantle derived fluid and fluids equilibrated with basement metamorphic rocks this model is consistent with previously published h o isotope data and is incompatible with meteoric water as the only ore forming fluid trace element geochemical profiles across the uranium orebody can be interpreted to reflect reaction between the host rocks and a mantle derived fluid containing high u and th with low th u ratios the mantle derived fluid is considered to have been u f and carbonate rich mixing with shallowly circulated meteoric water within the fractures of the host volcanic rocks caused dilution and cooling of the ore forming fluid and subsequent precipitation of fluorite and uranium ore