radionuclide migration in strongly fissured zones the sensitivity to some assumptions and parameters radionuclides escaping from a repository for high level nuclear waste in crystalline rock may eventually be carried by the flowing water in fissure zones in such zones the rock is broken into blocks of varying sizes and shapes also the water velocity may vary considerably in such zones a previously developed model which lumps the different blocks into a single pseudobody is tested by comparing it with an exact analytical solution which can account for the diffusion into blocks of any size distribution the approximate simplified model which is based on a numerical scheme and thus is more versatile gives errors which are small compared to the normal variation in observed block size distributions and other data a method for determining an average peclet number or dispersion length in a strongly varying velocity field is tested and found to give small errors compared to the present confidence limits in predicting dispersion data for large migration distance a simple criterion is proposed for defining the cutoff limit in the block size distribution below which the blocks can be modeled as if they were in equilibrium with the flowing water a simple sensitivity analysis shows that much can be gained if the confidencemore limits for block size distribution water flow rate dispersion data sorption data and matrix diffusion data can be narrowed down less

tidal fluctuations in a leaky confined aquifer dynamic effects of an overlying phreatic aquifer tidal fluctuations in a leaky confined coastal aquifer are damped significantly due to leakage into an overlying phreatic aquifer jiao and tang 1999 presented an analytical solution to a simple model describing this phenomenon their solution assumes that the tidal fluctuations in the overlying phreatic aquifer are negligible i e a static phreatic aquifer here we examine dynamic effects of the overlying aquifer based on a new approximate analytical solution the numerical results indicate that the dynamic effects can be significant for a relatively large leakage and a high transmissivity of the phreatic aquifer

advection and dispersion of contaminant in a permeable medium embedding fractures in which advection velocity is comparatively slow abstract this paper concerns the advective migration of an aqueous contaminant in a fractured permeable formation calculation and analysis refer to fractures in which advection velocity is comparatively small the slow advective velocity is created by some local cavities or almost vertical orientation of the fractures it is shown that the advective contaminant transport is characterized by two dimensionless parameters 1 the ratio between the permeable block and fracture flow rates termed the mobility number 2 the ratio between the longitudinal advection velocity of the permeable block flow and that of the fracture flow termed the advection velocity ratio for a sufficiently large domain continuum parameters can be applied to characterization of the fractured permeable formation then the mixing between the permeable block flow and the fracture flow is a mechanism leading to contaminant dispersion for very small values of the advection velocity ratio the effective dispersivity is fully determined by the mobility number its value decreases with increase of the mobility number under such conditions the equivalent porosity is constant and its value is identical to that of the permeable blocks a significant value of the advection velocity ratio increases the equivalent porosity of the fractured permeable formation with regard to the effective dispersivity of the domain if the advection velocity ratio is equal to unity then the effective dispersivity vanishes the larger the deviation of the advection velocity from unity the larger is the effective dispersivity of the fractured permeable medium

a successive steady state model for simulating freshwater discharges and saltwater wedge profiles at baffin bay texas submarine groundwater discharges sgd are an important source of freshwater to coastal bays and estuaries in arid and semi arid regions understanding groundwater flows to these ecologically sensitive bodies is important for coastal environmental sustainability a management oriented mathematical model capable of simulating the flow of groundwater into a coastal bay i e submarine groundwater discharge is developed here using the principles of quasi steady state flow and the existence of a sharp interface between the freshwater and the saltwater portions of the aquifer the model is applied to the baffin bay in south texas a hypersaline coastal body with no major river discharges two global sensitivity approaches the one at a time design oat and the grid based monte carlo sensitivity index are used to identify critical model inputs the sensitivity of the model inputs to the nash sutcliffe efficiency nse criterion is calculated making use of synoptic observed sgd measurements made over a period of one tidal cycle the results of the study indicate that global sensitivity analysis methods are particularly sensitive to the number of model realizations the ability of these techniques to screen out insensitive model inputs increased with increasing number of realizations the variability in the identified inputs was more prominent with the oat sensitivity methods than monte carlo based techniques in general the aquifer properties hydraulic conductivity and aquifer thickness as well as fluid properties seawater and fresh water densities along with the antecedent sgd was noted to be the most sensitive parameters this result indicates that the implementation of sharp front coastal aquifer models can be improved through better hydrogeologic characterization and measuring temperature and salinity data to improve density estimation the global sensitivity methods also help identify reasonable values for model inputs which can serve as a starting point for advanced calibrations the results however indicated that the model is likely over parameterized with different input sets yielding similar nse estimates based on these initial parameter estimates the model was able to capture the general trend in the observed sgd but could not capture the dynamic associated with high water levels in the bay pre calibration global sensitivity analysis is recommended in similar applications as it not only provides insights into future data collection efforts but can also help assess the likely success of model calibration however given the variability among the techniques it is suggested that multiple global sensitivity methods be utilized

numerical modeling of tidal effects on groundwater dynamics in a multi layered estuary aquifer system using equivalent tidal loading boundary condition case study in zhanjiang china this paper presents a numerical modeling study of tidal effects on groundwater dynamics of a multi layered estuary aquifer system in this study to generalize the tidal loading effects on the confined aquifer we used equivalent tidal loading boundary condition based on existing analytical solutions for the confined aquifer in a three dimensional numerical model and then good simulated result was obtained using the numerical model the tide induced groundwater level and confined groundwater discharge dynamics were discussed and the following conclusions were obtained the combined action of sea tide and river tide can enhance the tidal response of groundwater level in the aquifer system especially for the confined groundwater the river tidal effect is more significant in the areas away from coastline although the confined aquifer is separated by a layer of clay from the ocean because of the tidal loading effects the confined groundwater discharge also changes periodically displaying a negative correlation with the tide level fluctuations like the unconfined groundwater discharge using linear functions that express the relationship between the mean confined groundwater flux and sea tide level the confined groundwater flux through the tidal loading boundaries can be approximately estimated when the sea tide level is higher than 4 4 m there would be a risk of seawater intrusion into the confined aquifer in the study area this case study is useful for numerical studying of tidal effects on groundwater resource dynamics in a coastal multi layered estuary aquifer system

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

dynamics of submarine groundwater discharge and associated fluxes of dissolved nutrients carbon and trace gases to the coastal zone okatee river estuary south carolina abstract multiple techniques including thermal infrared aerial remote sensing geophysical and geological data geochemical characterization and radium isotopes were used to evaluate the role of groundwater as a source of dissolved nutrients carbon and trace gases to the okatee river estuary south carolina thermal infrared aerial remote sensing surveys illustrated the presence of multiple submarine groundwater discharge sites in okatee headwaters significant relationships were observed between groundwater geochemical constituents and 226 ra activity in groundwater with higher 226 ra activity correlated to higher concentrations of organics dissolved inorganic carbon nutrients and trace gases to the okatee system a system level radium mass balance confirmed a substantial submarine groundwater discharge contribution of these constituents to the okatee river diffusive benthic flux measurements and potential denitrification rate assays tracked the fate of constituents in creek bank sediments diffusive benthic fluxes were substantially lower than calculated radium based submarine groundwater discharge inputs showing that advection of groundwater derived nutrients dominated fluxes in the system while a considerable potential for denitrification in tidal creek bank sediments was noted in situ denitrification rates were nitrate limited making intertidal sediments an inefficient nitrogen sink in this system groundwater geochemical data indicated significant differences in groundwater chemical composition and radium activity ratios between the eastern and western sides of the river these likely arose from the distinct hydrological regimes observed in each area groundwater from the western side of the okatee headwaters was characterized by higher concentrations of dissolved organic and inorganic carbon dissolved organic nitrogen inorganic nutrients and reduced metabolites and trace gases i e methane and nitrous oxide than groundwater from the eastern side differences in microbial sulfate reduction organic matter supply and or groundwater residence time likely contributed to this pattern the contrasting features of the east and west sub marsh zones highlight the need for multiple techniques for characterization of submarine groundwater discharge sources and the impact of biogeochemical processes on the delivery of nutrients and carbon to coastal areas via submarine groundwater discharge

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

numerical modelling of tide induced beach water table fluctuations field studies have shown that the elevation of the beach groundwater table varies with the tide and such variations affect significantly beach erosion or accretion in this paper we present a bem boundary element method model for simulating the tidal fluctuation of the beach groundwater table the model solves the two dimensional flow equation subject to free and moving boundary conditions including the seepage dynamics at the beach face the simulated seepage faces were found to agree with the predictions of a simple model turner 1993 the advantage of the present model is however that it can be used with little modification to simulate more complicated cases e g surface recharge from rainfall and drainage in the aquifer may be included the latter is related to beach dewatering technique the model also simulated well the field data of nielsen 1990 in particular the model replicated three distinct features of local water table fluctuations steep rising phase versus flat falling phase amplitude attenuation and phase lagging

review of the modelling of radionuclide transport from u series disequilibria and of its use in assessing the safe disposal of nuclear waste in crystalline rock abstract u series disequilibia from crystalline rocks and u deposits have been used to estimate the timing of hydrogeological events for u and ra mobility and to model the transport rates of u and ra both with some sucess unfortunately activity ratio data alone are not unique to a given process or model and it is shown how inappropriate choice of the model can have quite diverse consequences for interpretation of the data information from other sources is needed to help minimise these non uniqueness problems but as yet the state of methodology is unadequate to assess completely the validity of the models in particular the rate of deposition of u in fractures seems highly dependent upon the availability of trivalent fe and other low temperature minerals whose rates of formation are largely unknown this review reinforces the need to assess closely the suggestion that chemisorption is an effective retardant of fracture borne borne repository source radionuclides

analytical study of hydraulic and mechanical effects on tide induced head fluctuation in a coastal aquifer system that extends under the sea summary head response to sea level fluctuations has been extensively used for characterizing coastal aquifers when the aquifer is semiconfined and extends for a certain distance d under the sea head response results from the superposition of two types of effects hydraulic i e ground water flow connection through aquifer and aquitard and mechanical induced by tidal loading onto the sea floor solutions are available for this problem that has been analyzed before but only for d zero or infinity these solutions do not allow analyzing aquifer systems that extends for a finite d or identifying them which is critical for coastal aquifer management we derive an exact analytical solution that describes separately the mechanical and hydraulic effects the proposed analytical solution is a generalization of most of existing analytical solutions a simpler approximate analytical solution is also obtained for soft aquitards with low permeabilities we find that the impact of the hydraulic component of the aquitard and the mechanical effects in the total head fluctuation at the shoreline is significant but not very sensitive to the properties of the aquitard the amplitude of these fluctuations relative to that of the sea tide ranges approximately between 1 small d and 0 5 large d this implies that aquifer penetration under the sea can indeed be identified if it is below a certain threshold beyond which the system responds as if d was infinity surprisingly the time lag is close to zero regardless of hydraulic parameters of the aquifer system

numerical modeling of colloid facilitated radionuclide decay chain transport in a coupled fracture matrix system a numerical model is developed to simulate the colloid facilitated transport of radionuclides in a single fracture host rock coupled system with planar geometry such a system may be encountered in case of leaching and transport of radionuclides from a high level radioactive waste repository in deep geological formations the presence of colloids in the system reduces the retardation effects on the radionuclide migration and can change the concentration distribution of radionuclides in the system significantly the processes such as advection dispersion surface sorption radioactive decay and diffusive loss to the host rock are considered for transport in the fracture whereas dispersion adsorption and radioactive decay are included for transport in the host rock since the radionuclides to be disposed into the high level waste repository may include a decay chain of progeny the performance assessment methodology must incorporate the ingrowth of progeny with time to carry out realistic estimates the inclusion of decay chain buildup and transport is essential to avoid underestimation with respect to the environmental impact assessment for the repository hence the numerical model based on implicit finite difference scheme is developed with the inclusion of decay chain transport the model is verified by comparing with well known analytical solutions the application of the model is demonstrated by applying it to a five member decay chain of 238u with increase in the concentration of colloids the concentrations of the radionuclides in the fracture water increase and also reach the steady state at an earlier time the concentrations of radionuclides almost become steady throughout the distance of 200 m in the fracture as the colloid concentration reaches 5 kg m 3 or more sensitivity analysis is carried out with respect to various model parameters such as dispersion coefficient in fracture dispersion coefficient in the porous host rock porosity of the host rock and distribution coefficient of radionuclide with respect to the mobile colloids the developed model can be a useful tool for the performance assessment of high level radioactive waste repositories

migration of radionuclides in fissured rock the influence of micropore diffusion and longitudinal dispersion the migration of radionuclides in the fissures in the bedrock surrounding a repository is discussed a one dimensional transport model is presented it includes diffusion of the nuclides into the microfissures of the rock and linear sorption and longitudinal dispersion in the bedrock an analytical solution to the model is given in terms of an infinite integral the integrand is a sometimes highly oscillatory function of the system parameters a special integration method is developed to evaluate the infinite integral the method utilizes the oscillatory behavior of the integrand the assessment of input parameters is discussed in some detail dimensionless breakthrough curves are given for the approximate range of variation of the input parameters calculations are made for a repository of spent fuel surrounded by fissured but fairly good rock kp 10 9 m s and fissure spacing s 50 m longitudinal dispersion may significantly affect the amount of radioactive material reaching the biosphere radionuclides which would decay completely without longitudinal dispersion may arrive in nonnegligible concentrations dispersion effects of the magnitude considered in this study can significantly diminish the retardation effects of matrix diffusion

investigations into the factors influencing long range matrix diffusion rates and pore space accessibility at depth in granite abstract investigations in granite systems have been conducted on 1 diffusion through fissure surfaces 2 the effect of confining pressures on diffusion rates 3 the extent of pore interconnectivity over metre distances and 4 the accessiblity of the pore space to colloidal particles in the size range 0 3 0 09 m diffusion rates through fissure surfaces were found to be greater than or equal to those measured on samples taken well away from such surfaces no evidence for pore blocking by alteration products was found confining pressures of up to 16 mpa reduced diffusion rates at the highest pressures reductions by factors of between 2 and 2 5 compared with diffusion rates measured at ambient pressure were recorded pore connectivity over distances of up to 125 cm on granite cores saturated with 3 m nacl was demonstrated by the measurement of formation factors as a function of core length using a conductivity technique increases in the formation factor for short core lengths 1 cm were ascribed to sample size and pore geometry effects which converted some of the dead end porosity into transport porosity colloidal particles in the size range investigated neither entered the pore structure nor blocked pore apertures to any significant extent

analysis of hydrodynamic dispersion in discrete fracture networks using the method of moments recent field investigations in crystalline rock give strong indications that water flows in largely isolated channels in fissured rock the channels are located in fracture planes and may or may not connect to other channels in the same plane or at fracture intersections in the present paper hydrodynamic dispersion in such fracture networks is investigated using the concepts of residence time distribution theory it is shown that from a set of simple relations at least the first four statistical moments for the system response are easily obtained even for complicated networks in particular an equivalent dispersion coefficient may be calculated from the second central moment variance the effect of channeling generally decreases in systems with many mixing steps a criterion based on the coefficients of skewness and kurtosis is derived for when the response of the system is in accordance with the diffusion dispersion model examples show that this limit may not be obtained under realistic repository conditions in fissured rock

tidal influence on seawater intrusion in unconfined coastal aquifers studies of seawater intrusion in unconfined coastal aquifers typically neglect oceanic oscillations such as tides and assume a static seaward boundary condition defined by the mean sea level laboratory experiments and numerical simulations were conducted to investigate the influence of tidal oscillations on the behavior of the saltwater wedge for the conditions examined the experiments showed that an upper saline plume formed in the intertidal zone due to tide induced seawater circulation the presence of the upper saline plume shifted the fresh groundwater discharge zone seaward to the low tide mark and restricted the intrusion of the saltwater wedge the overall seawater intrusion extent as indicated by the wedge toe location was reduced significantly compared with the nontidal static case results from the numerical model matched these experimental observations and further demonstrated the similar type of tidal influence on the saltwater wedge in a field scale aquifer system the glover 1959 solution for predicting the saltwater wedge was modified to account for the tidal effect by including the tide induced circulation as a recharge to the aquifer the findings highlight the significant impact of the tide in modulating the groundwater behavior and salt freshwater dynamics not only within but also landward of the intertidal zone

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

tide induced ground water flow in deep confined aquifer water elevation variation in rivers can be large due to tides even far away from the coastline for deep confined aquifers the possibility of leakage from rivers is small nevertheless the fluctuation of river elevation can induce a stress change in soil and in turn can induce ground water flow below the present study focuses on the effect of the fluctuation assuming the time scale for consolidation is much larger than that of the ground water the total stress change in the deep confined aquifer affects the water pressure head through deformable soil medium if the subsurface profile contains only one dominant confined aquifer a vertically averaged one dimensional problem with periodic total stress change and constant line pumping is examined the governing equation is a linear diffusion equation with time varying forcing terms laplace transform and fourier transform are invoked the response distribution in space is of the error function type the pumping effect can be superimposed due to linearity away from the loading deeper aquifers rather than those close to the ground surface are affected by the dynamic loading pressure peaks appear earlier for location farther away from the loading field data support the model

contaminant advection and spreading in a fractured permeable formation part 1 parametric evaluation and analytical solution abstract this paper concerns contaminant transport phenomena in aquifers comprising fractured permeable formations in contrast to deep rock formations with tight almost impermeable matrix rock we consider fractures embedded in permeable rock blocks it is shown that in many cases e g in sandstone formations the advective transport of contaminants in permeable blocks can be identified as the major process leading to contaminant exchange between fractures and blocks in the framework of the present study a simplified conceptual model of the fractured formation is adopted the conceptual model is formulated by sets of space linear differential equations subject to time dependent boundary conditions a closed form analytical solution of these sets of differential equations is developed calculations of the contaminant distribution along the fracture network are utilized to obtain breakthrough curves concerning the time variation of the average contaminant concentration in certain cross sections of the fractured permeable medium characteristics of the contaminant transport phenomena originating from the contaminant advection and the mixing between the fracture flow and the permeable block flow are determined and possibilities of considering the fractured permeable formation as a continuum are discussed

dynamic response of surface water groundwater exchange to currents tides and waves in a shallow estuary 1 in shallow fetch limited estuaries variations in current and wave energy promote heterogeneous surface water groundwater mixing benthic exchange which influences biogeochemical activity here we characterize heterogeneity in benthic exchange within the subtidal zone of the delaware inland bays by linking hydrodynamic circulation models with mathematical solutions for benthic exchange forced by current bedform interactions tides and waves benthic fluxes oscillate over tidal cycles as fluctuating water depths alter fluid interactions with the bed maximum current driven fluxes 1 10 cm d occur in channels with strong tidal currents maximum wave driven fluxes 1 10 cm d occur in downwind shoals during high energy storms simulated wave pumping rates increase by orders of magnitude demonstrating the importance of storms in solute transfer through the benthic layer under moderate wind conditions 5 m s integrated benthic exchange rates due to wave current and tidal pumping are each 1 10 m3 s on the order of fluid contributions from runoff and fresh groundwater discharge to the estuary benthic exchange is thus a significant and dynamic component of an estuary s fluid budget that may influence estuarine geochemistry and ecology

tidal groundwater level fluctuations in l shaped leaky coastal aquifer system this paper presents an analytical solution to describe tidal groundwater level fluctuations in a coastal leaky aquifer system bounded by water land boundaries that form a right angle referred to as l shaped coastlines the system consists of an unconfined aquifer a confined aquifer and a leaky layer between them previously published analytical solutions that discuss only single aquifer constitute a special case of the new solution when the permeability of leaky layer approaches zero a simple approximate solution without integral is presented error analysis and hypothetical example show that the approximate solution has adequate accuracy for both groundwater level prediction and parameter estimation for an l shaped leaky aquifer system q 2002 elsevier science b v all rights reserved

alluvial fan facies in the miocene pliocene coastal plain sands niger delta nigeria abstract a 30 m thick alluvial fan developed in the lower part of the coastal plain sand miocene pliocene in southeastern nigeria comprises four intergradational lithofacies quartz pebble conglomerate pebbly sandstone interstratified pebbly sandstone and parallel to cross stratified sandstone the quartz pebble conglomerate facies consists of massive pebble packed beds set in a matrix of coarse to very coarse sand unordered poorly developed fabric with rare imbrication is characteristic deposition by debris flow on the proximal zone of the fan is interpreted for this facies the pebbly sandstone facies is a structureless unit composed of pebbles dispersed through a medium to coarse grained sand with no significant pebble to pebble contact reversed distribution grading as well as cut and fill structures are common deposition by debris flow within the medial section of the fan is proposed the interstratified pebbly sandstone and sandstone facies comprises relatively thin alternations of pebbly sandstone and horizontally stratified sandstone beds alternate deposition by sheet floods and or debris flows in the distal part of the fan is suggested parallel and cross stratified fine to medium sand facies represents sheet flood deposits in the most distal part of the fan these facies characteristics are similar to arid semi arid and temperate alluvial fans fault scarp and or non tectonic base level change may have provided the necessary relief for the formation of the fan the absence of braided stream deposits associated with the alluvial fan appears to support the earlier contentions that alluvial fan and braided stream deposits could be separate in space at any given time

a two dimensional analytical solution for groundwater flow in a leaky confined aquifer system near open tidal water groundwater in coastal areas is commonly disturbed by tidal fluctuations a two dimensional analytical solution is derived to describe the groundwater fluctuation in a leaky confined aquifer system near open tidal water under the assumption that the groundwater head in the confined aquifer fluctuates in response to sea tide whereas that of the overlying unconfined aquifer remains constant the analytical solution presented here is an extension of the solution by sun for two dimensional groundwater flow in a confined aquifer and the solution by jiao and tang for onedimensional groundwater flow in a leaky confined aquifer the analytical solution is compared with a two dimensional finite difference solution on the basis of the analytical solution the groundwater head distribution in a leaky confined aquifer in response to tidal boundaries is examined and the influence of leakage on groundwater fluctuation is discussed copyright 2001 john wiley sons ltd

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

a two dimensional analytical solution of groundwater response to tidal loading in an estuary a two dimensional transient groundwater flow equation for a confined nonleaky aquifer is solved analytically with an estuary tidal loading boundary condition the amplitude and phase of the tide varies with position and time respectively these variations called the damping coefficient for amplitude and separation constant for phase along the coastline are considered in the analysis the solution presented is more advanced than the traditional one dimensional analytical solution with a one dimensional tidal loading boundary condition the damping coefficient and separation constant in the application study are obtained from the harmonic analysis of the observed tidal level in apalachicola bay florida the analytical solution is compared to a two dimensional finite difference solution a numerical simulation illustrates the response of piezometric head to tidal loading the piezometric head and phase from both solutions match closely the analytical and numerical solutions show that a piezometric head along both sides of the estuary can be predicted given a tidal elevation at the entry of an estuary the fluctuation of piezometric head in response to tidal loading diminishes rapidly inland and diminishes slowly along the coastline of an estuary there are also obvious phase shifts associated with spatial variations as the wave propagates

simulating the influence of groundwater seepage on sediment transported by the sweep of the swash zone across macro tidal beaches abstract a numerical model is developed to simulate the influence of groundwater seepage on swash zone sediment transport across macro tidal beaches the emergence of equilibrium profile morphology is examined in response to varying tide sediment and initial profile characteristics due to the unresolved complexities of boundary layer flow and corresponding shear stresses in the swash zone sediment transport across the beach face is modelled by incorporating an uprush phase described by the shallow water wave equations within an heuristic model of equilibrium beach face slope a new parameter termed the m net transport parameter is defined to parameterize the net flux of sediment per uprush backrush cycle the definition of differing equilibrium gradients across saturated versus unsaturated regions of the intertidal profile permits the saturation characteristics of the bed to be incorporated the dynamics of the watertable exit point on the beach face is central to the scheme as this defines the time varying extent of saturated and unsaturated regions of the intertidal profile the sensitivity of coastal seepage face development to tide profile and sediment characteristics is highlighted through the derivation of a new seepage face parameter the simulation model is found to successfully reproduce key aspects of observed profile adjustment and resulting equilibrium morphology complex morphodynamic feedback is observed between the tidal stage net transport per uprush backrush cycle profile slope and the dynamics of the watertable outcrop net upper profile steepening and lower profile lowering is simulated on beaches composed of medium to coarse sand this results in the emergence of a distinctive break in slope within the intertidal profile such morphology is commonly observed on macro tidal coasts

tidal influence on behaviour of a coastal aquifer adjacent to a low relief estuary the tidal influence on groundwater hydrodynamics salt water intrusion and submarine groundwater discharge from coastal estuarine aquifers is poorly quantified for systems with a mildly sloping beach in contrast to the case where a vertical beach face is assumed we investigated the effect of beach slope for a coastal aquifer adjacent to a low relief estuary where industrial waste was emplaced over the aquifer the waste was suspected to discharge leachate towards the estuary field observations at various locations showed that tidally induced groundwater head fluctuations were skewed temporally frequency analysis suggested that the fluctuation amplitudes decreased exponentially and the phase lags increased linearly for the primary tidal signals as they propagated inland salinisation zones were observed in the bottom part of the estuary and near the beach surface flow and transport processes in a cross section perpendicular to the estuary were simulated using seawat 2000 which is capable of depicting density dependent flow and multi species transport the simulations showed that the modelled water table fluctuations were in good agreement with the monitored data further simulations were conducted to gain insight into the effects of beach slope in particular the limiting case of a vertical beach face was considered the simulations showed that density difference and tidal forcing drive a more complex hydrodynamic pattern for the mildly sloping beach than the vertical beach as well as a profound asymmetry in tidally induced water table fluctuations and enhanced salt water intrusion the simulation results also indicated that contaminant transport from the aquifer to the estuary was affected by the tide where for the mildly sloping beach the tide tended to intensify the vertical mass exchange in the vicinity of the shoreline

a particle tracking approach to simulating transport in a complex fracture 1 nearly all of the studies of flow and transport in fractured rocks have assumed that each fracture can be modeled as an open space between two surfaces with constant or variable separation field observations of rock fractures have shown that a fracture in the field can be rather more complex recent studies indicate that a complex fracture can be characterized as a thin fracture zone having several interconnected subfractures which can contain mechanically dislodged and chemically altered materials with an enhanced porosity this paper proposes a particle tracking approach to calculate solute transport in a complex fracture with structures in the fracture thickness normal to the fracture plane these structures include subfractures dead end pores gouge materials small matrix blocks and the adjacent rock matrix all providing material in which solute diffusion and sorption can occur the method is described an example is provided to show its feasibility and the reasonableness of its parameter dependence and finally direction for its further development is discussed

an upstream finite element method for solution of transient transport equation in fractured porous media a finite element method for the solution of two dimensional transient dispersive convective transport of nonconservative solute species in fractured porous media is presented a two nodal point one dimensional transport element for fractures is developed which provides a number of advantages relative to conventional fracture representation by two dimensional continuum elements to eliminate the oscillatory behavior of convective dominated transport which is a more likely occurrence in fracture a very efficient one dimensional upstreaming method along with a two dimensional method is implemented validity of the numerical scheme is established by comparison with existing one and two dimensional analytic solutions

determining the length of confined aquifer roof extending under the sea by the tidal method abstract the main task in studying saline intrusion into an aquifer is to determine the position of the saline water freshwater interface for a confined aquifer this position is determined mainly by the roof length of the aquifer extending under the sea this information can be obtained from fluctuations of the groundwater level caused by tidal fluctuations of the sea in this paper a mathematical model of confined groundwater level fluctuations is constructed on the condition that the roof length is finite taking account of the continuity of flow between the inland and offshore aquifers allows a general formula to be calculated for the groundwater level fluctuations in terms of the tidal fluctuations and the length of the confined aquifer under the sea the actual roof length can be computed by comparison of the observed groundwater level fluctuations with those computed by the formula under various assumptions concerning the roof length the method is applied to an aquifer on the beihai peninsula in the guangxi province of china

tidal variations in groundwater storage and associated discharge from an intertidal coastal aquifer 1 we applied a hydrogeological numerical simulation to investigate spatial and temporal variations in groundwater flow and discharge at a well studied tidal flat margin in the german wadden sea the simulation was forced by high resolution sea level boundary conditions accuracy of the simulation was checked by comparing simulated with measured pressure heads obtained from direct burial pressure sensor measurements overall discharge calculated from the simulation for a time period of almost 12 month averages 0 97 m3 per meter of margin length per tide but may vary significantly most pronounced with the spring neap tide cycle the simulation predicts that the maximum hydraulic gradient at ebb tide controls the magnitude of discharge whereas duration of ebb tide is less important additionally simulated and measured pressure gradients can be used to investigate the influence of varying lithology on the groundwater flow regime the presence of a low permeable holocene silt layer ubiquitous in the study area creates a layered unconfined semiconfined aquifer system both parts of the aquifer are hydraulically connected to the deeply incising tidal creek but show a different response to the tidal forcing groundwater flow in the upper unconfined margin sediments can be described as a circulation of seawater where inflow and outflow are coupled to changes in saturation sediments below the confining layer release groundwater from storage during falling and ebb tide and recharge during rising and high tide we can show that tidally driven water exchange between semiconfined aquifers and coastal waters may have a major impact on total groundwater discharge

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

simple model representations of transport in a complex fracture and their effects on long term predictions 1 a complex fracture model for fluid flow and tracer transport that incorporates many of the important physical effects of a realistic fracture including advection through a heterogeneous fracture plane partitioning of flow into multiple subfractures in the third dimension and diffusion and sorption into fracture filling gouge small altered rock matrix blocks within the fracture zone and the unaltered semi infinite rock matrix on both sides of the fracture zone was previously developed it is common however to represent the complex fracture by much simpler models consisting of a single fracture with a uniform or heterogeneous transmissivity distribution over its plane and bounded on both sides by a homogeneous semi infinite matrix simple model properties are often inferred from the analysis of short term one to a few days site characterization sc tracer test data the question addressed in this paper is how reliable is the temporal upscaling of these simplified models are they adequate for long term calculations that cover thousands of years in this study a particle tracking approach is used to calculate tracer test breakthrough curves btcs in a complex fracture model incorporating all the features described above for both a short term sc tracer test and a 10 000 year calculation the results are considered the real world next two simple fracture models one uniform and the other heterogeneous are introduced properties for these simple models are taken either from laboratory data or found by calibration to the short term sc tracer test btcs obtained with the complex fracture model then the simple models are used to simulate tracer transport at the long term timescale results show that for the short term sc tracer test the btcs calculated using simple models with laboratory measured parameters differ significantly from the btcs obtained with the complex fracture model by adjusting model properties the simple models can be calibrated to reproduce the peak arrival time and height of the complex fracture model btcs but the overall match remains quite poor using simple models with short term sc calibrated parameters for long term calculations yields btcs with order of magnitude errors peak arrival time is 10 to 100 times too late and peak height is 50 to 300 times too small on the other hand using simple models with laboratory measured properties of unfractured rock samples for 10 000 year calculations yields btcs with peak arrivals and heights up to a factor of 50 too early and large respectively the actual magnitudes of the errors made by using the simple models depend on the parameter values assumed for the complex fracture model but in general simple models are not expected to provide reliable long term predictions the paper concludes with some suggestions on how to improve long term prediction calculations

estimation of aquifer parameters using tide induced groundwater level measurements in a coastal confined aquifer aquifer parameters are useful for modeling sea water intrusion and other groundwater management issues in coastal areas oscillations in tide induced groundwater levels contain important information of the properties of coastal aquifers and measurements of tidal effects can be employed to estimate the aquifer parameters the solution to the transient groundwater flow model in a coastal confined aquifer with a sinusoidal fluctuation of the tide shows that the amplitude of groundwater levels is smaller than the tide the tidal efficiency decreases exponentially with distance from the coast and the time lag increases linearly with distance from the coast the aquifer property described by the ratio of storativity to transmissivity can be estimated if the amplitude or tidal efficiency and the time lag of groundwater levels are obtained based on filed measurements of tidal effects principle of these tidal methods is presented in this article including those with one observation well and two observation wells hourly observations of the tide and groundwater levels at 14 observation wells in the coastal aquifer near beihai china are used to illustrate the application of these methods the estimated ratio of storativity to transmissivity of the confined aquifer ranges from 1 66 10 7 to 4 84 10 7 d m2 for a given transmissivity of 750 m2 d the storativity of the aquifer is in the range 1 245 10 4 to 3 63 10 4

water table outcropping on macro tidal beaches a simulation model abstract during the fall of the tide the coastal water table within a beach may become decoupled from the ocean resulting in the formation of a seepage face where water outcrops on the inter tidal profile a simulation model called seep is developed to simulate the point of decoupling and the subsequent motion of the seepage face as it continues to fall across the inter tidal profile the model is based entirely on the dynamics of an isolated water particle on the seepage face i e the pressure distribution within the beach is ignored sensitivity analysis of the seep model to beach face slope and permeability characteristics suggests that small variations to these parameters can result in significantly differing rates of exit point motion and hence seepage face extent to test the predictive capability of the seep model results are presented from a field investigation of exit point dynamics on a macro tidal beach north queensland australia the simulation model is found to accurately reproduce the observed seepage face motion at this field site in addition a re analysis of seepage face extent reported in nielsen 1990 from a protected micro tidal environment shows similarly strong agreement between the reported and modelled exit point elevation

sea level periodic change and its impact on submarine groundwater discharge rate in coastal aquifer abstract this study focused on the interaction between groundwater and seawater and the effect of temporal scale of sea level fluctuation on submarine groundwater discharge sgd rate the numerical code feflow diersch 2005 was used to evaluate the influence of periodic changes in sea level on an increase in sgd at various time scales from diurnal to glacial cycles simulation results showed that not only amplitude but also period of the sea level fluctuation controls total amount of sgd the increase ratio of recirculated submarine groundwater discharge rsgd was found to generally be proportional to the amplitude of sea level and the square root of specific storage of an aquifer while inversely proportional to the square root of hydraulic conductivity of an aquifer and period of sea level fluctuation a nondimensional number p that incorporates combined effect of sea level oscillation and aquifer properties is used to represent the magnitude of periodic forcing from sea boundary into an aquifer as a mechanism for enhancement of rsgd simulation results demonstrate that increase ratios of rsgd are well fitted by an exponential curve as a function of p and variations in rsgd occur only when p exceeds a critical number the dimensionless inland recharge rate where recharge rate is divided by hydraulic conductivity was shown to be important in determining the critical number this implies that sea level fluctuation does not lead to enhancement of rsgd until the specified condition is reached and groundwater recharge rate and aquifer hydraulic conductivity are the key factors controlling the increase of rsgd

contaminant advection and spreading in a fractured permeable formation part 2 numerical simulation abstract in a companion paper referred to as paper i the transport of contaminants in a fractured permeable formation was characterized and formulated it was shown that advective movements in the fracture flow and the permeable block flow as well as mixing between these two types of flow are the most significant factors affecting contaminant transport and spreading in such formations the basic formulation and the closed form analytical solution developed in paper i invite the use of numerical schemes for a further analysis of the contaminant transport processes in the framework of the present paper this target is achieved a numerical solution scheme stemming from the conceptual model of paper i is developed simulations are performed by considering the various properties of the discrete fracture flow and the permeable block flow the results of the present study indicate that fractured permeable formations can be represented by single continuum models provided that a sufficiently large number of sectors is included in the representative elementary volume rev the minimum number of sectors depends on the ratio between the specific discharge of the permeable block flow and that imposed by the fracture presence this ratio is named the mobility number the larger the mobility number the smaller the number of sectors which should be incorporated in the rev equivalent properties of the continuum representing the fractured permeable formation such as the equivalent porosity and dispersivity are determined and evaluated

application of genetic algorithm technique to inverse modeling of tide aquifer interaction modeling of tide aquifer interaction plays a vital role in the management of coastal aquifer systems a novel and robust methodology is presented in this paper for estimating aquifer parameters of coastal aquifers from tide aquifer interaction data using tide aquifer interaction model and genetic algorithm ga two stand alone computer programs were developed to optimize hydraulic diffusivities of unconfined and confined coastal aquifers at multiple sites using ga technique and tide aquifer interaction model and considering two approaches lumped tidal component approach and multi tidal component approach five sets of real world tide aquifer interaction data at two sites of an unconfined aquifer and one set of tide aquifer interaction data at three sites of a confined aquifer were used to demonstrate the efficacy of the methodology the analysis of the ga based inverse modeling results indicated that the multi tidal component approach yields more accurate and reliable hydraulic diffusivities for the unconfined aquifer rmse 0 0129 0 0521 m nse 0 70 0 97 and d1 0 91 0 99 as well as for the confined aquifer rmse 0 0204 0 0545 m nse 0 95 0 97 and d1 0 99 compared with the lumped tidal component approach a comparative evaluation of data size revealed that the short duration datasets of the unconfined aquifer provide more reliable estimate of hydraulic diffusivity than the long duration datasets further it was found that the spring and neap tidal data yield unreasonable values of hydraulic diffusivity with considerably high values of rmse and very low values of r 2 nse and d1 thereby suggesting that spring and neap tidal data are not suitable for aquifer parameter estimation overall it is concluded that the ga based tide aquifer interaction model following multi tidal component approach is the most efficient tool for estimating aquifer parameters of unconfined and confined aquifers from tide aquifer interaction data the developed methodology is also applicable to other coastal basins of the world irrespective of hydrogeological settings

application of tracer injection tests to characterize rock matrix block size distribution and dispersivity in fractured aquifers the complexity of mass transfer processes between the mobile and immobile zones in geohydrologic settings and the limitations that currently exist in the characterization of contaminated sites demand the development of improved models in this work we present a model that describes the mass transfer in structured porous media this model considers divergent radial advective dispersive transport in fractures and diffusive mass transfer inside rock matrix blocks the heterogeneous nature of fractured formations is included with the integration of various distributions of rock matrix block sizes into the transport model breakthrough curves generated based on the developed model are analyzed to investigate the effects of the rate of injection dispersivity and the immobile to mobile porosity ratio on mass transfer between mobile and immobile zones it is shown that the developed model in conjunction with tracer data collected from a monitoring well can be used to estimate the dispersivity and fracture intensity results reveal that the dispersivity is independent of the rock matrix block size distribution for dispersion dominant transport in fractures these findings are used to develop a methodology to characterize rock matrix block size distribution in fractured aquifers and to estimate dispersivity based on a tracer test which will improve our decisions concerning the remediation of contaminated sites

migration of radionuclides from a granite repository migration of radionuclides in the fracture of a host rock matrix surrounding a high level waste repository is discussed in terms of two coupled one dimensional equations one for the fracture and the other for the porous rock matrix the processes considered are advection dispersion radioactive decay and adsorption on the surface of the fracture and diffusion radioactive decay and adsorption in the microfissures of the host rock the temporal and spatial distribution of concentration and flux at the outlet of the fracture for some typical radionuclides encountered in high level radioactive waste has been computed using two component leaching from the waste matrix and budgeting the total inventory it is observed that the concentration of 90sr and 239pu markedly decreases with distance along the fracture due to sorption and decay however either travel time or sorption do not present enough delay for significant decay of 129i in fracture water while the peak flux of 129i shows insignificant variation at different fracture lengths for varied fracture apertures that of 239pu has functional dependence on both parameters

lumped mass transfer coefficient for divergent radial solute transport in fractured aquifers summary dispersion plays an important role in transport of contaminants and tracers in fractured aquifers in this work we develop a model for the lumped mass transfer coefficient by including dispersion in the fracture network for slab cylindrical and spherical shapes of the aggregates for the immobile zone coupled transport equations of mobile and immobile zones are solved to develop a first order lumped mass transfer coefficient an equivalent fracture aperture uniform rock matrix block size and constant volumetric water contents mobile and immobile zones with no adsorption desorption are used to represent the aquifer results reveal that geometry of the rock matrix blocks and dispersivity have important effects on the upscaled mass transfer coefficient it is found that field scale simulations of transport processes without including the dispersion in fractures are not valid for the whole range of practical injection rates 10 4 6 however modeling of laboratory scale experiments less than one meter in length without including dispersion in the mobile zone may be valid at high injection rates pe 10 5 it is confirmed that the upscaled lumped mass transfer coefficient is a function of scale and the rate of injection of the tracer these findings will find applications in modeling of transport processes of contaminated sites remediation and waste disposal

an analytical solution and case study of groundwater head response to dual tide in an island leaky confined aquifer 1 this paper presents an analytical solution of groundwater head response to dual tide fluctuation in the transect of an island leaky aquifer system comprising a confined aquifer and its overlying semipermeable confining layer both layers terminate at the coastlines on two sides of the island solution analysis indicates that the tidal waves from the two sides of the island transect interfere at the middle of the island and the interference decreases to zero as the horizontal length of the aquifer increases to infinity the leakage of the overlying confining layer enhances the landward attenuation of the tidal head fluctuation and shortens the time lag between the head and tide fluctuations the solution agreed well with the observations in eight piezometers in garden island on the continental shelf of western australia reported by trefry and bekele 2004

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

an ancient submarine canyon in the oligocene miocene of the western niger delta abstract an anomalous sequence of thick fossiliferous marine shale of late oligocene early miocene age here termed the opuama shale member occurs within the paralic agbada formation in the subsurface of the western niger delta the opuama shale fills a deep palaeochannel which was cut into eocene early oligocene paralic beds planktonic and benthic foraminifera suggest that deposition in the channel began in the late oligocene early miocene at outer shelf slope depths and that by the late early miocene the channel had filled to shallow neritic depths the channel which is believed to be of submarine origin is termed the opuama canyon the opuama canyon originated during the pronounced early middle oligocene drop in sea level and was cut by turbidity currents it was filled during the major late oligocene early miocene rise of sea level the location of the opuama canyon in the western re entrant of the niger delta supports burke s 1972 conclusion that the western and eastern where ancient submarine canyon fills are known re entrants of the delta are potential sites for ancient submarine canyons burke based his conclusion on the observation that the eastern and western re entrants of the modern delta are areas where opposing longshore drifts converge and generate turbidity currents which cut submarine canyons

wind induced salt wedge intrusion in the tiber river mouth rome central italy the wind effect on river water quality was illustrated by means of thermohaline measurements carried out in the tiber river in may 2012 the survey was carried out using a boat in stations located in the two tiber branches fiumara grande and traiano canal thermohaline variables salinity and temperature were used to describe the water type patterns and to define the salt wedge position although the river flow rate was rather high saltwater intrusion happened wind data suggested that the more probable cause of salt wedge intrusion was the wind action especially wind speeds higher than 4 m s are able to dominate the sea current at surface layers determining an increase in the sea level therefore westerly winds determined a seawater inflow in the river mouths

terrestrial originated submarine groundwater discharge through deep multilayered aquifer systems beneath the seafloor a large quantity of submarine groundwater discharge sgd of about 1000 m3 day 1 m 1 of the 600 km long shoreline of south atlantic bight has been estimated by moore global biogeochemical cycles 2010b 24 gb4005 doi 10 1029 2009gb003747 however there is great uncertainty in estimating the percentage of net land originated groundwater recharge of sgd moreover most previous studies considered the homogeneous case for the coastal superficial aquifers here we investigated the terrestrial originated sgd through a multilayered submarine aquifer system which comprises two confined aquifers and two semi permeable layers the inland recharge includes a constant part representing the annual average and a periodical part representing its seasonal variation an analytical solution was derived and used to analyse the distributions of the terrestrial originated sgd from the multilayered aquifers along the winyah bay transect south atlantic bight it is found that the width of the zone of sgd from the upper aquifer ranges from 0 8 to 8 0 km depending on the leakance of the seabed semi permeable layer a head of the upper aquifer at a coastline 1 0 m higher than the mean sea level will cause a sgd of 1 82 18 3 m3 day 1 m 1 from that aquifer as the seabed semi permeable layer s leakance varies from 0 001 to 0 1 day 1 providing considerable possibility for considerable land originated sgd seasonal terrestrial originated sgd variations predicted by the analytical model provide consistent explanation of the seasonal variation of 226ra observed by moore journal of geophysics 2007 112 c10013 doi 10 1029 2007jc004199 the contribution of the lower aquifer to sgd is only 1 2 12 of that of the upper aquifer copyright 2014 john wiley sons ltd

rates controls and sand body geometries of transgressive regressive cycles cretaceous moosebar and gates formations british columbia the moosebar and gates formations lower cretaceous in northeastern british columbia consist of seven transgressive regressive sequence nonmarine sediments are thickest in the south and pinch out northward the sequences are laterally persistent extending east from the foothills for 240 km 150 mi the orientation of maximum transgressive and regressive limits in five cycles occurs within an east west trending zone 30 40 km 19 25 mi wide a recurring northward bulging sediment depocenter near the alberta british columbia border was fed by a series of stacked northerly flowing rivers the rivers were a major source of sediment for gravel beaches to the north and east isopach maps of marine sandstone and conglomerate show a series of west northwest east southeast o iented sand bodies 60 70 km 37 43 mi wide parallel with the shorelines each coastline prograded northward as a shoreline attached strand plain and a series of arcuate or cuspate deltas gates formation marine nonmarine cyclicity is a series of fourth order cycles superimposed on a major third order cycle the cyclicity and lateral extent of the sequences can be explained as a result of tectonic thrusting and loading superimposed on the trend of the peace river arch the influence of eustatic sea level variations and sedimentologic switching of point sources had minimal effect coastal retreat ranged from 437 to 875 m 1 000 years 1 433 to 2 780 ft 1 000 years coastal progradation ranged from 218 to 437 m 1 000 years 175 to 1 433 ft 1 000 years the duration of several transgressive regressive cycles was 103 000 275 000 years

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

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

temporal variability of freshwater and pore water recirculation components of submarine groundwater discharges at baffin bay texas submarine groundwater discharges sgds are an important source of freshwater as well as nutrients and other chemicals to bays and estuaries sgds are particularly important for coastal bodies in arid and semi arid regions that are not fed by perennial streams the baffin bay tx is a shallow coastal water body that is weakly connected to the gulf of mexico and has no major rivers or streams draining into it a year long submarine groundwater discharge measurement study was carried out at the loyola beach of the baffin bay during the months of july 2005 june 2006 a total of 23 synoptic sgd sampling events were carried out with most events collecting sgd data continuously over a period of 24 h at a 1 min temporal resolution using an ultrasonic seepage meter the median sgd was noted to be 3 83 cm d with an inter quartile range iqr of 11 36 cm d four sampling events had anomalously high sgd values 27 48 cm d which are hypothesized to be due to the geologic heterogeneity of the sea bed and meteorological effects eight of the 23 sampling events had a negative average sgd flux indicating landward flow the short term diurnal variability of sgd was comparable or sometimes higher than the longer term and between events variability no long term trend could be inferred in the short term sgd measurements showed considerable persistence and the effective sample size analysis indicated each sampling event consisting of over 1 000 samples yielded only a handful of statistically independent measurements of sgd the measured sgd values exhibited both negative hydraulically controlled and positive wave set up controlled correlations with the bay water levels marine controls appeared to be the most significant sgd drivers and are in turn controlled by prevailing aeolian forcings the salinity of the sgds were estimated from measured sonic velocities and used in conjunction with the end member mixing models to estimate fresh meteoric and re circulated pore water fractions the freshwater fraction of the sgd was estimated to vary between nearly 4 and 89 with a median value of 9 96 and an iqr of 7 16 three events were noted to have abnormally high freshwater fractions 28 50 and 84 which are likely artifacts caused by bay water freshening from rainfall and plausible thermal expansion the meteoric and pore water partitioning was sensitive to the assumed end member concentrations this study provides preliminary estimates for sgds along the south texas coast line and is useful for calibrating groundwater flow models and understanding the relative importance of terrestrial and marine controls on sgd however the heterogeneous nature of the sedimentary geology of the texas gulf coast implies the sgd fluxes are likely to exhibit considerable spatial variation that has not been characterized yet therefore the study provides useful insights for such future data collection and monitoring activities the measured sgd values at baffin bay tx are comparable to those reported at other parts of the gulf of mexico

solute transport in fracture channel and parallel plate models many studies of flow and solute transport in fractured rocks are based on a conceptual model whereby flow occurs between parallel plates which approximate the fracture walls recently it has been observed that this representation is not consistent with actual fractures real fractures are actually composed of a complex system of void spaces of varying aperture and contact areas which are closed to flow in such fractures flow takes place through a network of channels and dead end regions the present investigation analyzes and compares the behavior of solute breakthrough curves in these channels and parallel plate representations numerical experinents show that breakthrough curves obtained with channel models are characterized by a long tail and jumps in the solute concentration consistent with those observed experimentally it is concluded that the considered channel models provide a sound explanation for the behavior of real breakthrough curves which cannot be reproduced by parallel plate models

an analytical solution of groundwater response to tidal fluctuation in a leaky confined aquifer an analytical solution is derived to investigate the influence of leakage on tidal response in a coastal leaky confined aquifer system the analytical solution developed here is more general than the traditional solution obtained by ferris 1951 which can be regarded as a special case of the solution presented in this paper this solution is based on a conceptual model under the assumption that the groundwater level in the confined aquifer fluctuates in response to sea tide while that of the overlying unconfined aquifer remains constant this conceptual model is supported by numerous field studies by previous researchers which have demonstrated that the tidal response in an unconfined aquifer may be negligible compared to that in a confined aquifer the leakage has a significant impact on the tidal behavior of the confined aquifer hypothetical studies indicate that both tidal amplitude of groundwater head in the aquifer and the distance over which the aquifer can be disturbed by the sea tide will be considerably reduced because of the existence of leakage this analytical solution is used to investigate the tidal and piezometer data at the chek lap kok airport hong kong special administrative region people s republic of china

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

a continuum approach for modeling mass transport in fractured media a continuum approach has been developed for modeling mass transport in fractured rocks it involves a new application of a particle tracking method in which physical transport is simulated in terms of velocity and the variations in velocity statistics describing the particle motion come from observing the actual pattern of particle motion in a discrete subdomain this subdomain is a small but representative piece of the much larger continuum in effect particle motion in the continuum is forced to mimic that in the discrete subdomain the model successfully duplicates patterns of anisotropic dispersion predicted by de josselin de jong 1972 and breakthrough curves simulated with a discrete fracture model applications demonstrate that the de josselin de jong approach for estimating dispersivities for idealized networks cannot generally be applied to networks formed from sets of finite irregularly spaced fractures in addition this study reinforces indications from earlier studies about the complexity of dispersion in fractured media factors that contribute to spreading in the major and minor principal directions change with the orientation of the network relative to the mean hydraulic gradient

the afam clay member a lower miocene incised channel in the south eastern niger delta abstract this paper describes a lower miocene incised channel system and its lithic fill within the niger delta sedimentary succession stratigraphic cross sections which clearly show the base to be generally asymmetric and very sharp with erosive characteristics in places suggest a channel configuration for the base of the afam clay the geometry of the channel and its lithic fill supports this interpretation the channel was cut by fluvial processes into pre existing unconsolidated eocene miocene sediments of the benin and agbada formations during a period of low sea level the imo river proto channel is thought to have aided the channelling the channel was subsequently enlarged by marine processes associated with a middle miocene rise in sea level the lithic fill of the afam channel is dominated by clay beds with localized development of sand bodies in time and space analysis of the spatial distribution of the sand units and their sp shapes supports the hypothesis of sand input from the north east central and west central flanks of the channel these are interpreted to reflect sand contributions from tributaries that fed the main channel the faunal lithological and textural characteristics of the afam sediments suggest a predominance of marine conditions in the south paralic conditions in the central area and fluvial processes in the north in addition the southern flanks of the channel may constitute truncation stratigraphic traps for hydrocarbons and it is proposed that these flanks should be fully explored

matching a field tracer test with some simple models simple models of fluid flow and dispersion in a porous rock matrix are compared and used to match the results of tracer tests at the wairakei new zealand geothermal field it is found that models which allow transient diffusion from fractures into the surrounding rock matrix give a better match to test results than either a model which allows only longitudinal dispersion or a pseudo steady state double porosity model for some tests a model which includes two fractures is required to match the field data

influence of submarine groundwater discharge on seawater properties in rovanjska modric karst region croatia coastal karst aquifers are dynamic hydrogeological systems with substantial hydrological geomorphological and ecological impacts on the marine and coastal karst ecosystems mostly induced by the submarine groundwater discharge sgd this paper presents complex hydrogeological settings of the rovanjska modric coastal karst region on the eastern adriatic coast characterized by 1 high temporal and spatial variations in seawater properties 2 significantly reshaped coastal bottom morphology and 3 plethora of associated biocenoses from fresh water brackish marine and cave assemblages with the aim of resolving spatiotemporal interconnections of sgd and marine environment changes we conducted field prospection and seasonal measurements of different water properties on and off shore obtained results pointed to 1 the composite recharge system consisting of numerous sinking rivers in the distant hinterland with different climate settings and local precipitation input 2 specific discharge settings highly governed by a complicated karst conduits network the hydrological situation in the hinterland and local meteorological conditions i e one system that permanently feeds coastal and probably submarine springs while the other operates periodically 3 disturbed winter isothermy and three layered summer stratification of the seawater column and 4 slightly changed trophic settings all of that is the consequence of extreme heterogeneity of the coastal karst aquifer characteristic for the eastern adriatic coast

transverse dispersion of contaminants in fractured permeable formations abstract our interest in understanding some of the mechanisms involved in the mineralization of the great bend prairie aquifer of kansas by salt water originating from permian bedrock formations which are fractured sandstones has prompted this basic study the fractured permeable formatiodis represented by a simplified conceptual model incorporating two sets of oblique and parallel fractures embedded in permeable blocks the domain is initially divided into a completely freshwater zone overlying a completely saline water zone however the sharp interface originally existing between the saline and fresh water is subject to dispersion because of mixing in fracture intersections and between the fracture flow and the permeable block flow simulations based on the use of an appropriate numerical model developed in the present study have helped us to characterize dispersion of the sharp interface and creation of the transition zone relationships of transverse and longitudinal dispersion in the domain are also determined

tide induced groundwater level fluctuation in coastal aquifers bounded by l shaped coastlines 1 this paper presents an analytical solution to describe tidal groundwater level fluctuations in an aquifer bounded by two water land boundaries that form a right angle the aquifer configuration can represent the situation of a right angle corner in an island when the tidal boundaries are the same along both boundaries or the estuary situation if the amplitude damps with distance along one boundary river and the amplitude along the other boundary sea does not change spatially the two dimensional flow equation subject to periodic boundary conditions is changed into a time independent elliptic problem using complex transform the elliptic problem is then solved using the green s function method li et al 2000 obtained a nonperiodic solution to the same problem with an additional hypothetical initial condition their solution includes a time dependent integral the solution presented here is a significant improvement over theirs in the sense that the solution is periodic and computationally efficient since the integral involved is independent of time an approximate solution without integral is also derived an error analysis and a case study in hong kong demonstrate that the approximate solution is adequate for most field problems index terms 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1899 hydrology general or miscellaneous 3384 meteorology and atmospheric dynamics waves and tides keywords periodic groundwater flow analytical solution coastal aquifer sea tide l shaped coastline

convergent radial dispersion in a double porosity aquifer with fracture skin analytical solution and application to a field experiment in fractured chalk an exact laplace transform solution to the problem of dispersion advection and adsorption of a tracer due to its injection in a steady horizontal radially convergent flow field in a densely fractured porous formation double porosity aquifer is presented the porous blocks were assumed to be covered with a layer of material fracture skin of negligible volume and storage capacity that provides a resistance to diffusion in the rock matrix longitudinal dispersion advection and adsorption dominate transport of the tracer in the fractures and diffusion and adsorption dominate movement of the tracer in the blocks dimensionless breakthrough curves are used to illustrate the influence of various aquifer and tracer properties in support of the model a detailed analysis is performed of a published multitracer field test conducted in a layer of densely fractured chalk in bethune france of the three tracers analyzed two are nonsorptive but have widely different free water diffusion coefficients and one is slightly sorptive analysis of measured breakthrough curves matched by trial and error to theoretical responses reveals that by allowing for fracture skin on block surfaces one can obtain 1 pure advection arrival times that are independent of the tracer used 2 values of mass recovery consistent with measured values and 3 relative values of effective diffusion coefficients that are consistent with known free water diffusion coefficients for the separate tracers reasonable estimates of longitudinal dispersivity and fracture porosity are also obtained

migration of radionuclides in fissured rock analytical solutions for the case of constant source strength an analytical solution is derived for the problem of radionuclide migration in fissured rock where the rock blocks are modelled as spheres the solution differs from a previous one mainly in the inlet boundary condition in the present paper the case of constant source strength is treated instead of a decaying step release the solution developed here is considerably more complex processes that are accounted for are advection and longitudinal dispersion in the fissures external and internal diffusion into spherical rock blocks sorption onto the fissure surfaces and sorption within the matrix and radioactive decay the solution is obtained in the form of an infinite single integral depending in general on six dimensionless parameters the steady state solution includes five dimensionless quantities a comparison with previously published results for a system of parallel fractures is made it is shown that if the area to volume ratio of the slabs and the spherical rock blocks is the same identical breakthrough curves are produced for short and long contact times in the intermediate range the solution with spherical rock blocks will give earlier breakthrough and higher steady state concentrations it is shown that the analytical solution for parallel fractures previously given as an infinite double integral may be derived as an infinite single integral the numerical evaluation is thereby considerably simplified examples demonstrate the impact of hydrodynamic dispersion and water transport time on radionuclide transport in situations considered to be realistic repository conditions

analytical and approximate solutions to radial dispersion from an injection well to a geological unit with simultaneous diffusion into adjacent strata analytical and approximate solutions are developed for radial dispersion in aquifers with simultaneous diffusion into adjacent strata contaminants from the injection well are transported within the main aquifer by advection and mechanical dispersion assuming a steady state and radially diverging ground water flow field the leakage of contaminants from the main aquifer to the aquitards is accounted for by molecular diffusion a mathematical model consisting of two coupled differential equations is proposed to investigate concentration distributions in the main aquifer as well as in the adjacent aquitards by making use of laplace transforms analytical solutions valid for small time periods are obtained without difficulty to complement these analytical solutions concentration distributions for intermediate and large time intervals are determined approximately by numerically inverting the appropriate transformed solution in the laplace domain with the stehfest algorithm excellent agreement exists between analytical solutions and approximate solutions for small time intervals supporting the validity of approximate solutions for intermediate and large time periods it is shown that the diffusive leakage may significantly delay contaminant movement within the main aquifer at relatively large time periods the solutions can be applied to study radial dispersion in granular aquifers bounded by relatively low permeability aquitards or in planar fractures contained in porous formations

tide induced groundwater fluctuation in a coastal leaky confined aquifer system extending under the sea this paper presents the analytical solution of groundwater response to tidal fluctuation in a coastal multilayer aquifer system consisting of a leaky confined aquifer a semipermeable layer and an unconfined aquifer the semipermeable layer or the roof of the leaky confined aquifer extends under the sea comparisons are made with solutions derived previously which considered only a single aquifer zero extension of the roof or infinite roof length and demonstrate that the previous solutions are special cases of the solution presented here a hypothetical example is used to discuss the impact of the dimensionless roof length dimensionless leakage and tidal efficiency on the groundwater level fluctuations in the inland part of the confined aquifer the fluctuation decreases significantly with the roof length when the roof length is small but is insensitive to the change of roof length when the roof length is greater than a threshold the impacts of leakage from the offshore and inland portions of the confining unit are different leakage from the offshore portion tends to increase the fluctuation of the groundwater level while leakage from the inland portion tends to decrease the fluctuation the fluctuation increases as the tidal efficiency increases this fact is significant only when the roof length is great and leakage is small

methodological study of submarine groundwater discharge from a karstic aquifer in the western mediterranean sea summary a multiproxy approach of complementary techniques is applied to localise and quantify submarine groundwater discharge sgd from el maestrazgo jurassic aquifer an example of widespread carbonate coastal aquifer of the western mediterranean sea castellon spain unconventional water resources are critical in this area where highly populated resorts have been developed the aquifer has two main features of particular interest a karstic system with a deep saturated zone reaching 450 m and with no significant surface discharge occurring within the continental area on the other hand sgd can alter the condition of coastal marine environments reducing salinities and providing nutrients that can cause eutrophication and algal blooms the applied combined techniques make it possible to detect groundwater outflows using airborne thermal infrared tir images to monitor physico chemical anomalies in the sea and to quantify the submarine groundwater discharges by means of direct measurements and radium isotopic analyses three main coastal areas affected by sgd and a submarine spring located at 3 km from the coast which seems to be associated with tectonic discontinuities were localised the calculated fresh sgd from ra isotopes 375 mm 3 y 1 is in agreement with the mean aquifer recharge obtained by hydrogeological methods 394 mm 3 y 1

migration of radionuclides from a high level radioactive waste repository in deep geological formations the paper presents the development of an analytical model to estimate the migration of radionuclides through a single fracture with right circular cylinder geometry from a high level radioactive waste repository in deep geological structures the processes considered are advection dispersion surface sorption and radioactive decay for transport in the fracture diffusive loss to the host rock radial diffusion adsorption and radioactive decay for transport in the host rock the model is applied to a typical case of high level radioactive waste repository in deep geological rock formations the concentrations showed an increasing trend with increasing dispersion in fracture or reducing dispersion in the host rock or reducing porosity it is shown that the models which do not consider the dispersion of radionuclides within the fracture underestimate the radionuclide concentrations in the fracture water also the effect of dispersion reduces with increase in fracture water velocity the concentration of radionuclides in the fracture water in general increases with increase in fracture radius until a critical radius is reached the model development is targeted for the performance assessment of high level radioactive waste repositories

groundwater monitoring at a building site of the tidal flood protection system mose in the lagoon of venice italy to protect venice against tidal flooding the mose system experimental electro mechanic module has been under construction since 2003 this safeguarding system is composed of four batteries of mobile barriers at the lagoon s inlets lido malamocco chioggia which will be lifted before the occurrence of exceptional high tides 1 10 m above the mean sea level isolating the venetian lagoon from the sea the end of the construction work is foreseen by 2016 in this paper the results of the groundwater monitoring at the building site of punta sabbioni at the lido inlet are described a large dewatered basin tura formerly occupied by the sea and close to the shoreline was used for the precasting of the mobile barriers and the impact of groundwater control was therefore monitored in the phreatic and shallow confined aquifers although a slurry wall barrier was excavated to isolate the tura a drawdown cone in the confined aquifer was observed extending to 1 km from the construction site in contrast the phreatic aquifer was only influenced by tides rainfall and evapotranspiration and the slurry wall of the tura had a positive effect of decreasing the groundwater salinity by limiting the seawater intrusion as confirmed by the electrical conductivity profiles measured inside the piezometers the monitoring activity was successful in assessing the impacts of the construction work on the aquifer system and in distinguishing them from the effects of natural driving forces

tidal wave propagation in a coastal aquifer effects of leakages through its submarine outlet capping and offshore roof summary this paper considers a leaky aquifer system comprising an unconfined aquifer a confined aquifer and a confining layer the aquifer s roof the unconfined aquifer terminates at the coastline the confined aquifer and its roof extend under the sea for a certain distance the aquifer s submarine outlet is covered by a thin layer of sediment referred to as the outlet capping hereafter with properties dissimilar to the aquifer previous studies either neglected the leakage through the aquifer s roof or the outlet capping this paper considers both effects and gives an analytical solution to describe the tide induced head fluctuation in the aquifer system for aquifers with zero or infinite offshore length or with impermeable roof or outlet capping or without the outlet capping existing solutions in the literature are obtained we defined the threshold value for the offshore aquifer length which was found to be less than 5 km for typical coastal aquifer systems for an aquifer with its offshore length greater than the threshold the inland head fluctuation becomes insensitive to variations of this length and the outlet capping s leakance the leakage through the offshore roof decreases the threshold value when the offshore confined aquifer is short the inland head fluctuation increases with the outletcapping s leakance in this case negative phase shift occurs near the coastline only for aquifers with small leakages through the offshore roof and the outlet capping in general