an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

variability of the north atlantic thermohaline circulation during the last interglacial period studies of natural climate variability are essential for evaluating its future evolution greenland ice cores suggest that the modern warm period the holocene has been relatively stable for the past 9 000 years much less is known about other warm interglacial periods which comprise less than 10 of the climate record during the past 2 5 million years here we present high resolution ocean sediment records of surface and deep water variables from the bermuda rise spanning the last interglacial period about 118 000 127 000 years ago in general deep water chemical changes are coincident with transitions in surface climate at this site the records do not show any substantial fluctuations relative to the much higher variability observed during the preceding and subsequent cool climates the relatively stable interglacial period begins and ends with abrupt changes in deep water flow we estimate using 230 th measurements to constrain the chronology that transitions occur in less than 400 years

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

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

estimation of evaporation from the normally dry lake frome in south australia depth profiles of deuterium composition expressed as delta values have been used to make point estimates of evaporation from the floor of the normally dry lake frome a salt lake in northern south australia values from five sites varying between 90 and 230 mm yr 1 have been used to obtain a relatively crude approximation for mean evaporation rate from the lake of 170 mm yr 1 under the assumption that this represents discharge of water from the regional groundwater system the groundwater inflow into the lake is calculated as 5 108 m3 yr 1 two possible models which describe groundwater inflow into the lake are discussed

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

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

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

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

impacts of evaporation on subsurface flow and salt accumulation in a tidally influenced beach we coupled a mass transfer formulation of evaporation to the density dependent variably saturated finite element model marun to predict the salinity under realistic conditions in a beach in the gulf of mexico the results showed that evaporation almost doubled the pore water salt concentration in the intertidal zone in comparison to the case with no evaporation the results also showed that for the relatively wet atmospheric conditions the maximum evaporation did not occur from the supratidal zone rather from the intertidal zone and it was due to the difference in moisture between pore water and atmosphere the highest salinity occurred during the spring tide period and extended into the neap tide period when the atmospheric condition was assumed to be constant and conducive to large evaporation high temperature and low air humidity the maximum salinity region shifted to the supratidal zone and persisted there due to low mixing the maximum salinity value in the intertidal zone for this case was not larger than that of the variable atmospheric condition case however the maximum was more landward than the more realistic variable atmospheric condition case which suggests that accurate characterization of pore water salinity in tidally influenced beaches requires accurate knowledge of atmospheric conditions in addition to beach and hydraulic properties the constant atmospheric condition simulations suggest that antecedent extreme conditions greatly affect the salinity in the supratidal zone but they are dampened in the intertidal zone

seismic moments local magnitudes and coda duration magnitudes for earthquakes in central california onscale seismograms recorded at stations in the u s geological survey s usgs central california seismic network calnet have been used to estimate the seismic moment m and local magnitude ml for earthquakes of 1 ml 4 located on the san juan bautista and parkfield sections of the san andreas fault the coyote lake section of the calaveras fault the sargent fault and near livermore these data together with m and ml estimates for 4 ml 6 earthquakes in these areas cannot be fit with a single linear log m versus ml relation rather the data are consistent with log m 1 5 ml 16 for 3 ml 6 with log m 1 2 ml 17 for 1 1 2 ml 3 1 2 and with a slope of to 1 fro 1 2 ml 1 1 2 whereas usgs coda duration magnitude md is consistent with ml for 1 1 2 ml 3 md is larger than ml at ml 1 1 2 and smaller than ml at ml 3 log m can be estimated to a precision of 0 2 for 1 md 3 1 2 earthquakes in central california by applying log m 1 2 md 17 to the md that have been routinely published by the usgs

on the computation of darcian velocity and mass balance in the finite element modeling of groundwater flow darcian velocity has been conventionally calculated in the finite element modeling of groundwater flow by taking the derivatives of the computed pressure field this results in discontinuities in the velocity field at nodal points and element boundaries discontinuities become enormous when the computed pressure field is far from a linear distribution it is proposed in this paper that the finite element procedure that is used to simulate the pressure field or the moisture content field also be applied to darcy s law with the derivatives of the computed pressure field as the load function the problem of discontinuity is then eliminated and the error of mass balance over the region of interest is much reduced the reduction is from 23 8 to 2 2 by one numerical scheme and from 29 7 to 3 6 by another for a transient problem

loading effect of water table variation and density effect on tidal head fluctuations in a coastal aquifer system 1 water table variation will result in considerable variation of the weight of the pore water which has loading effects on the groundwater flow in the underlying confined aquifer here we present an analytical solution on such a loading effect in a coastal aquifer system consisting of an unconfined aquifer a confined aquifer and an impermeable layer between them with the two lower layers extending under the sea the solution generalizes several existing ones in the literature the water table variation s loading effects tend to enhance the amplitude and to reduce the phase shift of the tide induced head fluctuation these effects become considerable when the tidal loading coefficient is large the aquifer s offshore extending length is long and the unconfined aquifer has large values of hydraulic conductivity and specific yield numerical examination indicated that the assumption of ignoring the density variation causes an error not greater than 2 5 of the tidal amplitude

convection in groundwater below an evaporating salt lake 2 evolution of fingers or plumes the downward convection of salt fingers or plumes developed from the unstable boundary layer of an evaporating dry salt lake is examined using a numerical model and hele shaw cell experiments in the convecting layer the early small waves evolve into fingerlike or plumelike formations the number of fingers or plumes decreasing with time owing to differential growth and or coalescence comparison of intermediate formational stages of this pattern with the pattern generated by a two dimensional numerical simulation shows good qualitative agreement however there is a significant mismatch of the growth rates at long times in the computer simulation the plume length develops approximately twice as rapidly as it does in the experimental case a simple numerical experiment independent of the salt lake boundary conditions is compared to previously published laboratory scale measures of plume development in hele shaw cells which confirms the retardation of hele shaw plumes by a factor of approximately 50 this departure is attributed to the differences in dimensionality between the hele shaw flow domain and the model domain the data indicated that leading plumes develop isolated behavior at long times and may not be adequately represented in hele shaw analog models and numerical simulation provides a more accurate simulation of field scale behavior

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

field study of spatial variability in unsaturated flow beneath and adjacent to playas we quantified unsaturated flow beneath playa and adjacent interplaya settings at a site in the southern high plains united states to resolve issues related to where and how water moves through the unsaturated zone this is the first study in which the data density 39 boreholes and the variety of techniques used physical chemical and isotopic were sufficient to quantify spatial variability in unsaturated flow water contents water potentials and tritium eoneentrations were much higher and chloride eoneentrations were much lower beneath playas than in interplaya settings which indicated that playas focus recharge these results refute previous hypotheses that playas act as evaporation pans or that recharge is restricted to the annular region around playas water fluxes estimated from environmental tracers ranged from 60 to 120 mm yr 1 beneath playas and were 0 1 mm yr 1 during the past 2000 5000 years beneath natural interplaya areas not subjected to ponding to evaluate the apparent inconsistency between high recharge rates and thick clay layers beneath playas we applied bromide and fd c blue dye to evaluate flow processes these applied tracer experiments showed preferential flow along roots and desiccation cracks through structured clays in the shallow subsurface in playas

numerical modeling of water flow below dry salt lakes effect of capillarity and viscosity abstract we investigate numerically the effects of capillarity and viscosity on density dependent flows below dry salt lakes the numerical model marun boufadel m c suidan m t venosa a d 1999a a numerical model for density and viscosity dependent flows in two dimensional variably saturated media j contam hydrol 37 1 20 is used to assess the combined and separate effects of capillarity and concentration engendered viscosity on the groundwater dynamics of a two dimensional system simulating a dry lake we found that accounting for concentration engendered viscosity effects under saturated water flow conditions gives totally different groundwater dynamics from the case where these effects are neglected however concentration dependent viscosity effects were minor when unsaturated water flow conditions were present under variably saturated flow conditions capillarity effects gave totally different hydraulics in the porous domain from the saturated flow case upwelling regions observed under saturated flow conditions were downwelling when capillarity effects were present a mesh orientation study revealed that density dependent flows were susceptible to the orientation of the diagonals of the triangular elements a discussion on the accuracy and the efficiency of the marun model in the context of density and viscosity dependent flows in two dimensional variably saturated media is also provided

laboratory scale investigation of saltwater intrusion dynamics 1 experiments were completed in a laboratory scale porous media tank to study the transport patterns of a saltwater wedge in a freshwater aquifer three types of experiments were performed to develop 1 steady state salt wedge data observed under different hydraulic gradient conditions 2 transient salt wedge data observed under intruding wedge conditions and 3 transient salt wedge data observed under receding wedge conditions furthermore flux measurements were made to quantify the flow characteristics of three distinct steady state experiments the saltwater intrusion model seawat was used to simulate these data sets the model results along with the experimental data are presented as benchmark problems for testing density coupled groundwater flow models a worthiness analysis was completed to test the sensitivity of these experimental problems to density coupling effects the results of our analysis show that the proposed benchmark is a more robust alternative to the traditional henry problem these new experimental data sets can be used to assess the performance of saltwater intrusion models under both steady state and transient conditions

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

a dupuit formulation for modeling seawater intrusion in regional aquifer systems 1 a new formulation is presented for the modeling of seawater intrusion in coastal multiaquifer systems the formulation is intended for the simulation of three dimensional regional seawater intrusion starting from a specified salinity distribution the dupuit approximation is adopted and diffusion and dispersion are not taken into account the formulation is based on a vertical discretization of the groundwater into zones of either constant density stratified flow or continuously varying density piecewise linear in the vertical direction the zones are separated from each other by curved surfaces representing interfaces for stratified flow and isosurfaces of the density for variable density flow during a simulation both the change of the elevations of the surfaces and the change in head are computed through consistent application of continuity of flow a simple tip and toe tracking algorithm is applied to simulate the horizontal movement of the surfaces the resulting differential equations are equivalent in form to the differential equation for single density flow the density effects are incorporated through the addition of pseudosource terms this makes it easy to implement the formulation in existing numerical groundwater codes the main advantage of the formulation is the tremendous reduction of the number of cells needed for a simulation because every aquifer may be represented by a single layer of cells the accuracy of the formulation is demonstrated through comparison with existing exact solutions and a numerical solution

vadose zone permeability tests unsteady flow saturated unsaturated flow models are used to simulate transient conditions in four soils during constant head borehole infiltration tests in the vadose zone infiltration rate varies directly with saturated hydraulic conductivity and is also influenced by unsaturated soil properties antecedent moisture conditions anisotropy and borehole conditions the method recommended by the u s bureau of reclamation to determine when to terminate a test may lead to overestimating saturated hydraulic conductivity simple graphical procedures are developed to overcome field problems associated with large water volume requirements or long time required to reach steady state by using early time date to estimate the steady infiltration rate

convection in groundwater below an evaporating salt lake 1 onset of instability convective groundwater motion can be generated in aquifers beneath and adjacent to saline lakes such motions strongly control the subsurface distribution of salts the formation of saline minerals and the distribution of contaminants that may be disposed of in the saline lake in particular schemes to use saline lakes as evaporation basins for irrigation waste waters must consider the groundwater dynamics associated with convection the convection is driven by the evaporative concentration of salts at the land surface leading to an unstable distribution of density however the evaporative groundwater discharge can dynamically stabilize this saline boundary layer and inhibit convection in this work we investigate the nature and onset of convection for a range of boundary conditions typically found in saline lakes processes involved in the accumulation of salt at the surface of a groundwater discharge zone and in the gravitational instability of the near surface groundwater are considered results of theoretical stability analysis are applied through laboratory and numerical experimentation to the more complex geometries typically found in the field these comparisons indicate that for large saline lakes the stability of the saline boundary layer can be parameterized by traditional rayleigh criteria in which the aquifer permeability and the evaporation rate from the lake bed are principal controlling factors for typical saline lake environments convection will dominate in sediments whose permeability exceeds approximately 10 14 m2 below this threshold permeability the boundary layer should be stabilized by the evaporative flux resulting in the accumulation of salts and evaporites at the land surface these results provide insight into the predictive behavior of groundwater dynamics and solute distributions in many natural systems

on the evolution of salt lakes episodic convection beneath an evaporating salt lake 1 the transient evolution of salt lake brines and the accompanying underlying groundwater salinity distribution with depth is discussed a convective diffusive equation with a novel surface source term modeling the evaporative process is introduced and an approximate analytical solution of this equation is obtained using a perturbation approach a linear stability analysis of the resulting solution is carried out for typical field scale parameters the model predicts that instability may initially occur within timescales on the order of weeks or decades and that a near surface layer of salty fluid whose thickness is on the order of decimeters is responsible for the initial onset of convection furthermore the analysis indicates that when convection starts the decimeter layer mixes and this results in the loss of the destabilizing force in this period the salty fluid diffuses downward this results in a return to a hydrologic system where the salt profile is then well mixed throughout but now with a background concentration with a higher average salinity the process can then repeat for an extensive but finite period as the surface layer and subsurface groundwater concentration eventually become hypersaline and where salt precipitation occurs we have called this phenomenon episodic convection variable density groundwater flow and solute transport modeling experiments of a field based salt lake system confirm the existence of episodic convection and semiquantitatively validate the findings of the analytical approach

impact of layered heterogeneity on transient saltwater upconing in coastal aquifers abstract this research investigated the effect of layered heterogeneity on transient saltwater upconing in a laboratory scale coastal aquifer the experiments were conducted in a 2d laboratory flow tank and the response of the saltwater wedge to pumping was analysed in a heterogeneous aquifer system where a low permeability layer was constructed in the middle of the aquifer the seawat code was used for validation and to perform additional simulations to explore the sensitivity of the critical pumping rate and the critical time to the main parameters characterising the low permeability layer which included its permeability thickness and position the experimental results showed that the presence of layered heterogeneity noticeably altered the shape and the intrusion length of the upconing wedge without inducing a change in the abstraction rate triggering saltwater upconing mechanism compared to the homogeneous case the numerical results of the layered aquifer provided excellent agreement with the experimental data for both the transient toe length and the shape of the steady state saltwater wedges the sensitivity analysis revealed that the critical pumping rate and the critical time was found to decrease considerably with decreasing hydraulic conductivity and thickness of the middle layer which evidences the higher vulnerability of such layered aquifer systems to the saltwater upconing in comparison to idealised homogeneous systems the results nonetheless showed that varying the position of the interlayer induced very little change on the critical pumping rate but the critical time would tend to decrease as the low permeability layer was moved deeper away from the pumping well particularly for smaller middle layer thickness

regression models for hydraulic conductivity and field test of the borehole permeameter the saturated hydraulic conductivity ks of sediments in the vadose zone is an important parameter in predicting the seepage rates of water and contaminants the borehole permeameter is an in situ technique to test a relatively large sample size at any depth solutions are presented which account for the effects of unsaturated flow these solutions are derived from a regression analysis of results of numerical simulations in which unsaturated hydraulic conductivity is represented by one or two parameters the results of a borehole permeameter test in a uniform sand are compared with field ponding tests and air entry permeameter tests the regression based solutions for the borehole permeameter which account for capillarity provide very good agreement with other permeameter results depending upon the approach used to solve the borehole problem ks values determined by methods which neglected and included capillary effects varied by a factor of only about two for the soil tested

spatial variability and hydrologic evolution of australian lake basins analogue for pleistocene hydrologic change and evaporite formation abstract processes evident in basins across hydrologic gradients from humid to arid regions today provide analogues for systems that may have operated in some individual basins during periods of past hydrologic change thus lakes in humid regions today with low salinity sedimentary facies and with morphology controlled largely by wave action may closely resemble past lacustral pluvial phases experienced in zones which today are relatively arid and saline conversely playas controlled today by groundwater and in some cases subject to defletion may resemble those arid and dune building stages experienced by basins in sub humid regions today as they underwent glacial age desiccation in any such sequence of spatial or temporal gradients from humid to more arid conditions the frequency of basin filling and drying modulates the rate of evaporitive loss of interstitial waters from the exposed basin surface this in turn controls the salinity evolution of the interstitial and local groundwaters the notion of closed systems for terminal lakes while satisfactory for analysis of surface water budgets is quite inapplicable to the evolution of brines where surfacewater groundwater exchange during the high salinity drying stages becomes a controlling factor affecting all salt budgets in these systems evaporites may only be preserved when the sub surface waters have evolved to salinites near saturation for the salts concerned if sub surface waters are frequently diluted by surfacewater groundwater exchange evaporites will not be preserved in the record even though the surface system appears hydrologically closed the process of interstitial water evolution which controls efflorescence deflation and salt weathering exerts a dominating influence on basin geomorphic expression as well as on hydrochemical fractionation

role of salinity derived variable density flow in the displacement of brine from a shallow regionally extensive aquifer portions of many regional scale aquifers in midcontinent sedimentary basins exhibit large salinity gradients that significantly impact the velocity field and solute distribution through time a two dimensional numerical transport model was constructed to examine the role of salinity derived variable density flow on changes in the velocity field and solute distributions in a near surface regionally extensive aquifer as brine is displaced by infiltrating meteoric water the silurian devonian carbonate aquifer in the western portion of the appalachian basin was used as a framework to insure that realistic flow velocities and salinities were used in the assessment the variable density effects on brine displacement are observed by examining the differences in the velocity fields and solute distributions produced by uniform density and variable density simulations the effects include the change from an intraformational displacement pattern to a cross formational displacement pattern with the development of flow reversals and partitioning of regional flow cells into smaller flow cells variable density effects also are manifest in the solute distributions by slowing the displacement of brine and influencing the magnitude of the salinity gradient a sensitivity analysis used to examine the influence of flow and transport parameters on the transient development and migration of salinity gradients shows that increasing cross formational leakage into the regional aquifer causes flow velocities to decrease which magnifies the influence of the variable density behavior by slowing the displacement of brine the sensitivity analysis also shows that increasing the value of dispersivity causes an increase in the variable density effects however the effects of variable density flow are relatively insensitive to changes in values of horizontal and vertical anisotropy assigned to the aquifer or to the presence of an overlying transmissive layer

an experimental and numerical investigation of saltwater movement in coupled saturated partially saturated systems 1 a combined experimental and numerical analysis is used to examine the movement and interaction of saltwater and freshwater in unconfined porous media particular emphasis is placed on flow phenomena in the partially saturated region above the water table and along the interface between the saturated and partially saturated regions while some numerical models are apparently capable of simulating these phenomena there is still a significant lack of experimental data with which to verify the models here a series of laboratory scale experiments is considered to evaluate density dependent saltwater freshwater flow patterns in both the saturated and partially saturated zones the laboratory experiments demonstrate clearly that significant lateral flows and coupled density driven flow effects may take place in the partially saturated region above the water table and at the interface between the saturated and partially saturated zones in parallel a finite element numerical model is developed the model reproduces effectively the observed flow behaviors the quality of the results suggests that the numerical model has the capacity to provide realistic predictions

surface water groundwater interaction near shallow circular lakes flow geometry in three dimensions steady flow regimes for three dimensional lake aquifer systems are studied via idealized mathematical models that are extensions of earlier simplified vertical section models of interaction between shallow lakes and underlying aquifers the present models apply to a shallow circular lake at the surface of a rectangular aquifer of finite depth yielding a truly three dimensional representation of the resulting flow system flux boundary conditions are applied at the ends of the aquifer with net vertical recharge or evapotranspiration at the water table the lake is defined by a region with constant head by determining and visualizing solutions to the discretized saturated flow equations a range of possible flow regimes is identified and their topological properties are studied tools for analyzing flow regimes are described including a method for locating and mapping three dimensional dividing surfaces within steady flow fields results show strong similarities between two and three dimensional systems including a large number of flow through recharge and discharge regimes and reverse flow cells flow lines calculated on a vertical plane through the middle of a lake resemble but are not identical to two dimensional streamlines for a range of aquifer flow and recharge conditions estimates of the widths and depths of capture and release zones for various lake aquifer geometries are asymptotic to earlier results for two dimensional systems numerical predictions are compared with analytical results for certain limiting flow regimes

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

comment on mixed convection processes below a saline disposal basin by simmons c t narayan k a 1997 journal of hydrology 194 263 285

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

parameter estimation for determining hydraulic properties of a fine sand from transient flow measurements a cone penetrometer method for measuring hydraulic conductivity of unsaturated soils at depth is under development successful advancement of this method hinges on using parameter estimation to obtain hydraulic parameter values from pore water pressure and flow rate data a finite element model is employed to predict flow responses and objective functions describe differences between true and simulated responses contour plots in parameter space show the relative sensitivity of objective functions to field saturated hydraulic conductivity kfs field saturated moisture content fs and the van genuchten hydraulic parameters and n principal curvatures and directions in parameter space describe the nature of objective functions near true parameter values an objective function based on flow rate and pore water pressures does not provide better parameter sensitivity than one based on pore water pressures alone it appears possible to obtain estimates of kfs and but unlikely that the other parameters will be identifiable

development of a discrete continuum vdfst cfp numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system a hybrid discrete continuum numerical model variable density flow and solute transport conduit flow process vdfst cfp is developed to simulate seawater intrusion to a coastal karst aquifer with a conduit network the darcy weisbach equation is applied to simulate the nonlaminar groundwater flow in the conduit system that is conceptualized as pipes while the darcy equation is used for laminar groundwater flow in the continuum porous medium density dependent groundwater flow with appropriate additional density terms in the conduit is analytically derived the flow and transport equations are coupled and numerically solved by the finite difference method with an implicit iteration procedure two synthetic benchmarks are developed to compare the vdfst cfp model results with other numerical models such as the variable density seawat constant density continuum modflow mt3dms and constant density discrete continuum cfpv2 umt3d models the vdfst cfp model compares reasonably well with the other model results in both conduit and porous medium domains and well describes water and salt exchange between the two systems under turbulent flow conditions within the conduit the darcy weisbach equation calculates the flow rate more accurately without overestimation by the darcy equation sensitivity analysis indicates that conduit diameter friction factor matrix hydraulic conductivity and effective medium porosity are important parameters in the vdfst cfp model the pros and cons of the vdfst cfp model are discussed including the model assumptions and simplifications limitations of the discrete continuum modeling method and the convergence criteria in general the newly developed vdfst cfp model provides a new numerical modeling method for simulating seawater intrusion in a coastal karst aquifer with conduits

magnitude and seismic moment scales in western yunnan peoples republic of china abstract seismograms and accelerograms from 77 earthquakes in 1982 to 1984 near the northwest end of the red river fault in western yunnan province peoples republic of china have been used to calculate seismic moment m 0 and local magnitude m l using techniques established in california for 1 1 2 m l 3 1 2 log m 0 16 97 1 17 0 05 m l consistent with the log m 0 m l relation appropriate for central california a comparison of these m l values and the coda duration magnitudes m and s wave amplitude magnitudes m assigned by the seismological bureau of yunnan province suggests that m and m values are generally larger than the m l values for 1 7 m 5 3 m l 0 49 0 67 0 04 m and log m 0 17 30 0 86 0 04 m for 2 0 m 5 4 m l 0 24 0 76 0 05 m and log m 0 17 06 0 95 0 05 m

characterising flow regime and interrelation between surface water and ground water in the fuente de piedra salt lake basin by means of stable isotopes hydrogeochemical and hydraulic data summary this research reports the characterisation of ground and surface water interaction in the fuente de piedra salt lake basin in southern spain by a combined approach using hydraulic hydrogeochemical and stable isotope data during three sampling campaigns february 2004 2005 and october 2005 ground and surface water samples were collected for stable isotope studies 18 o d and for major and minor ion analysis hydraulic measurements at multilevel piezometers were carried out at four different locations around the lake edge conductivity logs were performed at four piezometers located along a profile at the northern lake border and at two deeper piezometers in the miocene basin at a greater distance from the lake to describe processes that control the brine evolution different hydrogeochemical simulations were performed hydrogeochemical data show a variety of brines related to thickness variations of lacustrine evaporites around the lake salinity profiles in combination with stable isotope and hydraulic data indicate the existence of convection cells and recycled brines furthermore restricted ground water inflow into the lake was detected dedolomitisation processes were identified by hydrogeochemical simulations and different brine origins were reproduced by inverse modelling approaches

sudden end of an interglacial for the past 9 000 years or so the world has experienced an interglacial period with in terms of geological time an anomalously warm and stable climate but how stable are interglacials and what processes might bring them to a sudden close evidence from a 53 metre long sediment core retrieved from the bermuda rise in the western north atlantic now gives us the most detailed picture yet of events during the previous interglacial the results date the period concerned to between 129 000 and 119 000 years ago most notably however its termination seems to have been marked by a sudden reduction in the ocean conveyor circulation which today carries ocean heat north from the tropics and warms much of europe

impacts of the 2004 tsunami on groundwater resources in sri lanka the 26 december 2004 tsunami caused widespread destruction and contamination of coastal aquifers across southern asia seawater filled domestic open dug wells and also entered the aquifers via direct infiltration during the first flooding waves and later as ponded seawater infiltrated through the permeable sands that are typical of coastal aquifers in sri lanka alone it is estimated that over 40 000 drinking water wells were either destroyed or contaminated from february through september 2005 a team of united states sri lankan and danish water resource scientists and engineers surveyed the coastal groundwater resources of sri lanka to develop an understanding of the impacts of the tsunami and to provide recommendations for the future of coastal water resources in south asia in the tsunami affected areas seawater was found to have infiltrated and mixed with fresh groundwater lenses as indicated by the elevated groundwater salinity levels seawater infiltrated through the shallow vadose zone as well as entered aquifers directly through flooded open wells our preliminary transport analysis demonstrates that the intruded seawater has vertically mixed in the aquifers because of both forced and free convection widespread pumping of wells to remove seawater was effective in some areas but overpumping has led to upconing of the saltwater interface and rising salinity we estimate that groundwater recharge from several monsoon seasons will reduce salinity of many sandy sri lankan coastal aquifers however the continued sustainability of these small and fragile aquifers for potable water will be difficult because of the rapid growth of human activities that results in more intensive groundwater pumping and increased pollution long term sustainability of coastal aquifers is also impacted by the decrease in sand replenishment of the beaches due to sand mining and erosion

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

chalk dolomitization beneath localized subsiding tertiary depressions in a marginal marine setting in the paris basin france abstract dolomitization of the late cretaceous chalk in the southeastern paris basin forms kilometer size bodies that crosscut bedding these diagenetic structures were first identified during petroleum exploration of intra chalk seismic discordances and then they were cored down to 700 m the high velocity chalk forms kilometer size hill shaped structures between 150 and 600 m depth similarly the top of the chalk shows kilometer size domes and depressions with an average amplitude of 50 m and slopes over 3 whereas the base of the chalk shows only very gentle dip two drill cores 2 km apart intersecting the seismic discordances allowed us to establish that these structures correspond to dolomitized chalk and porosity reduction detailed biostratigraphic correlations between the two drill cores show that 1 the seismic discordances are not related to the stratigraphy and 2 dolomitization of the chalk coincides with an apparent compaction of the whole unit the overlying early and middle eocene formations vary spatially between 20 and 100 m thickness the distribution of their sedimentary facies indicates that the dome and depression structures at the top of the chalk developed during the middle eocene the depression structures and localized middle eocene depocenters directly overlie the dolomitized diagenetic structures in the chalk furthermore the depressions commonly correspond to zones where sand channels are cut through the early eocene claystone down to chalk groundwater circulation within the chalk may have been linked to the tertiary sand channels such circulation might have been responsible for the dolomitization of the chalk and concurrent dissolution and or compaction leading to differential subsidence in the tertiary deposits the link between tertiary localized depocenters and dolomitization constrains the chalk diagenesis to the eocene and to nearsurface environments stable isotope compositions of the dolomites indicate that sea water of normal salinity was likely the dolomitizing fluid dolomitization was apparently triggered by recharge of the chalk groundwater with sea water entering the chalk in depression areas lastly the diagenetic processes result in sharp seismic reflectors that cut across stratigraphy these seismic reflectors first interpreted as deep intra chalk erosional surfaces do not follow any depositional stratigraphy at all consequently such structures cannot be interpreted in terms of sequence stratigraphy

unstable convection flow as a controlling process of increasing salinity in the saline lake coastal aquifers case of maharlu lake coastal aquifer deterioration of freshwater aquifers adjacent to saline lakes is a serious environmental and water resources management problem generally different phenomena including saltwater intrusion upconing free and forced convection flow can lead to the salinization of fresh aquifers in the vicinity of saline lakes the severity of this problem depends on hydrogeological and hydrogeochemical conditions of coastal saline lake aquifers accordingly maharlu lake in the southeast of shiraz plain is one of these saline lakes and has an important impact on its adjacent fresh aquifers so that the salinity of these aquifers has increased in recent years since the lake has special conditions such as very flat and low permeable floor and variable water level fluctuation during a year with the onset of the rainy season after a long term well pumping in the adjacent aquifer the lake water covers a wide extent of the lake area in a short time then because of the higher permeability of the surface of the lake in its southeast margin conditions for convection flow are provided there in this study salinity distribution in one of the aquifers bokat aquifer in the southeast of the lake is investigated using resistivity tomography along several profiles interpretation of inverse models of these profiles showed that convection flow is an important process in increasing the salinity of fresh aquifer comparison of the results of geo tomography sections with convection index map of the bokat aquifer showed that getting closer to the lake free convection flow becomes the dominant process in the salinity distribution in addition in farther distances relative to the lake due to increasing the pumping rate of the extraction wells forced convection flow is an important process

hydro mechanical properties of unsaturated residual soil from a flysch rock mass abstract rainfall is a major triggering factor of landslides in flysch deposits along europe physical and mechanical changes of flysch rock masses caused by the weathering process result in a complex soil profile with residual soil typically present at the slope surface the research encompasses residual soils from the rjecina river valley in croatia built in flysch deposits the valley is known for several deep seated and shallow historical landslides this manuscript presents the hydro mechanical properties of the soil existing in unsaturated zone of the slope that could play an important role in landslide activation on flysch slopes presented unsaturated soil property functions are essential for modelling of the transient rainfall infiltration process and how it affects the stability of flysch slopes in time for the first time shear strength and hydraulic conductivity determination were performed in saturated and unsaturated soil conditions using both the intact as well as remolded samples of the residual soil form flysch rock mass the results indicate that in order to correctly define hydraulic and mechanical properties of the in situ soil measurements have to be performed on intact samples also the presented results highlight the importance of hysteresis effects and hydraulic paths that fine grained residual soil has been subjected to in the past

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

aspects of numerical and representational methods related to the finite difference simulation of advective and dispersive transport of freshwater in a thin brackish aquifer abstract the simulation of the transport of injected freshwater in a thin brackish aquifer overlain and underlain by confining layers containing more saline water is shown to be influenced by the choice of the finite difference approximation method the algorithm for representing vertical advective and dispersive fluxes and the values assigned to parametric coefficients that specify the degree of vertical dispersion and molecular diffusion that occurs computed potable water recovery efficiencies will differ depending upon the choice of algorithm and approximation method as will dispersion coefficients estimated based on the calibration of simulations to match measured data a comparison of centered and backward finite difference approximation methods shows that substantially different transition zones between injected and native waters are depicted by the different methods and computed recovery efficiencies vary greatly standard and experimental algorithms and a variety of values for molecular diffusivity transverse dispersivity and vertical scaling factor were compared in simulations of freshwater storage in a thin brackish aquifer computed recovery efficiencies vary considerably and appreciable differences are observed in the distribution of injected freshwater in the various cases tested the results demonstrate both a qualitatively different description of transport using the experimental algorithms and the interrelated influences of molecular diffusion and transverse dispersion on simulated recovery efficiency when simulating natural aquifer flow in cross section flushing of the aquifer occurred for all tested coefficient choices using both standard and experimental algorithms

studies of quaternary saline lakes iii mineral chemical and isotopic evidence of salt solution and crystallization processes in owens lake california 1969 1971 abstract as a consequence of the 1969 1970 flooding of normally dry owens lake a 2 4 m deep lake formed and 20 of the 2 m thick salt bed dissolved in it its desiccation began august 1969 and salts started crystallizing september 1970 ending august 1971 mineralogic brine composition and stable isotope data plus field observations showed that while the evolving brine composition established the general crystallization timetable and range of primary and secondary mineral assemblages it was the daily monthly and seasonal temperature changes that controlled the details of timing and mineralogy during this depositional process deuterium analyses of lake brine interstitial brine and hydrated saline phases helped confirm the sequence of mineral crystallizations and transformations and they documented the sources and temperatures of waters involved in the reactions salts first crystallized as floating rafts on the lake surface natron and mirabilite salts whose solubilities decrease greatly with lowering temperatures crystallized late at night in winter when surface water temperatures reached their minima trona nahcolite burkeite and halite salts with solubilities less sensitive to temperature crystallized during the afternoon in summer when surface salinities reached their maxima however different temperatures were generally associated with crystallization at the surface and accumulation on the lake floor because short term temperature changes were transmitted to surface and bottom waters at different rates consequently even when solubilities were exceeded at the surface salts were preserved or not as a function of bottom water temperatures halite a nearly temperature insensitive salt was always preserved monitoring the lake brine chemistry and mineralogy of the accumulating salts shows 1 an estimated 0 9 10 6 tons of co 2 was released to the atmosphere or consumed by the lake s biomass prior to most salt crystallization 2 after deposition some salts reacted in situ to form other minerals in less than one month and all salts except halite decomposed or recrystallized at least once in response to seasons 3 warming in early 1971 caused solution of all the mirabilite and some of the natron deposited a few months earlier a deepening of the lake though the lake surface lowered and an increase in dissolved solids 4 phase and solubility index data suggest that at the close of desiccation na 2 co 3 7h 2 o never reported as a mineral could have been the next phase to crystallize

relation of subtropical atlantic temperature high latitude ice rafting deep water formation and european climate 130 000 60 000 years ago abstract a new high resolution record of sea surface temperature from the subtropical western north atlantic documents a series of abrupt coolings within marine isotope stage 5 which can be objectively correlated with marine core evidence for increased ice sheet discharge at subpolar latitudes and reduced north atlantic deep water formation these results indicate that ice sheet forcing of deep ocean circulation influenced surface temperatures over much of the north atlantic a proposed correlation to the pollen record of grande pile france indicates that each cold event seen in the pollen sequence has a unique counterpart in the record of subtropical ocean temperature if this correlation is correct it suggests that the warmest part of the european eemian ended suddenly in response to oceanographic changes and that the subsequent post temperate phase of the eemian extended well into the interval of ice sheet growth corresponding to marine isotope substage 5d

past changes to isotopic and solute balances in a continental playa clues from stable isotopes of lacustrine carbonates in many salt lakes around the world the relative abundance of preserved authigenic minerals is different from that predicted from solute mass balance calculations conventional mass balance models assume that chloride behaves conservatively over long periods of time and fail to take into account the role of diffusion deflation and fractional crystallisation dissolution of salts an alternative approach is to use oxygen isotopes as these reflect directly water molecule rather than solute concentrations and have the added advantage of providing a palaeohydrological record in lacustrine carbonates we present a steady state stable isotope model in conjunction with stable isotopic measurements of sub surface brines regional groundwaters and carbonate deposits from the lake malata lake greenly playa complex in south australia to estimate the apparent leakage and palaeoleakage from these superficially closed playa lakes the steady state model calculations using the present and compositions of the lake brines and inflowing groundwater suggest that the apparent present day leakage for the complex is 75 to 90 of inflow 35 times that calculated from cl and br under such conditions only low magnesian calcite precipitates and the lake water experiences reduced effects of evaporation gas and vapour exchange and consequently reduced isotopic and chemical enrichment further our model shows that calcite becomes increasingly mg rich until leakage is reduced to 55 to 70 of inflow a condition favourable for dolomitisation and of the lacustrine carbonates show excursions on the order of 5 over the length of a 2 3 m core indicating that the lake complex has varied from being throughflow dominated presence of low mg calcite relatively depleted in and to evaporation dominated high mg calcite dolomite relatively enriched in and throughout late quaternary our estimates of leakage fractions are consistent with the observed mineralogical suite but there remains a discrepancy between apparent closure indicated by the presence of the highly saline brine reservoir 1 leakage and high rates of throughflow inferred from stable isotope data we propose that the brine was formed by winter time re solution of a seasonal halite crust which forms during summer dominated evaporative discharge recirculation of the secondary brine and mixing with regional groundwater may decouple the solute cycle from the water cycle in many playa lakes the end result is a partially mixed brine characterised by nearly conserved solutes but with isotopic signatures indicative of brine rainfall groundwater interactions

variably saturated modeling of transient drainage sensitivity to soil properties abstract numerical analysis of a transient two dimensional rectangular symmetry unconfined drainage problem using a variably saturated flow model shows that the location of the phreatic surface and the height of the seepage face are functions of the capillary forces exerted in the vadose zone a sensitivity analysis investigating the effects of independent variations in the saturated hydraulic conductivity and the two van genuchten parameters is compared to one performed where the saturated hydraulic conductivity is functionally related to the van genuchten parameters the relationship between these descriptive soil parameters which may be used to describe the pore size density function of a porous medium and the saturated hydraulic conductivity is surmised based upon limited empirical evidence expressing the permeability as a function of these soil properties reverses the sensitivities of the variably saturated model to the van genuchten parameters from the preliminary work performed herein consideration of the number of degrees of freedom used when performing a sensitivity analysis is shown to warrant great care if the predicted sensitivities are to have meaningful physical interpretations

on a test case for density dependent groundwater flow and solute transport models the salt lake problem like any other computer model density dependent mathematical groundwater models must be verified to ascertain that they accurately represent the physics implied by a governing set of equations very few test cases for density dependent groundwater numerical models exist as such there is still a need for new and more robust tests of these modeling codes in this paper a numerical model of an idealized evaporating salt lake is produced using the two dimensional density dependent saturated unsaturated transport sutra model the results of which are compared with an equivalent laboratory hele shaw cell system developed by wooding et al 1997a b evaporation results in dense brine overlying less dense fluid which is hydrodynamically unstable and leads to downward convection of salt fingers or plumes a comparison of experimental and numerical plume growth shows good spatial and temporal agreement the numerically generated plume pattern is sensitive to changes in random noise level applied just below the evaporation surface that serves as a trigger for the growth of instabilities experimental plume patterns were best matched with a noise level corresponding to 1 of the total salinity difference between boundary layer and background fluid concentrations at saturation in a second comparison the stream function based finite difference model described by wooding et al 1997a b which differs significantly in principle from sutra is shown after revision to give good spatial and temporal agreement with experimental results this test for density dependent groundwater models appears to be the most comprehensive and detailed available to date

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

numerical investigation of coupled density driven flow and hydrogeochemical processes below playas numerical modeling approaches with varying complexity were explored to investigate coupled groundwater flow and geochemical processes in saline basins long term model simulations of a playa system gain insights into the complex feedback mechanisms between density driven flow and the spatio temporal patterns of precipitating evaporites and evolving brines using a reactive multicomponent transport model approach the simulations reproduced for the first time in a numerical study the evaporite precipitation sequences frequently observed in saline basins bull s eyes playa specific flow evapo concentration and chemical divides were found to be the primary controls for the location of evaporites formed and the resulting brine chemistry comparative simulations with the computationally far less demanding surrogate single species transport models showed that these were still able to replicate the major flow patterns obtained by the more complex reactive transport simulations however the simulated degree of salinization was clearly lower than in reactive multicomponent transport simulations for example in the late stages of the simulations when the brine becomes halite saturated the non reactive simulation overestimated the solute mass by almost 20 the simulations highlight the importance of the consideration of reactive transport processes for understanding and quantifying geochemical patterns concentrations of individual dissolved solutes and evaporite evolution this article is protected by copyright all rights reserved

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

saline groundwater in mono basin california 1 distribution mono lake california is a perennial closed basin saline lake up to 2 km of sediments have accumulated below the lake and a well log shows that saline groundwater of concentration 18 000 ppm extends to the bottom of the basin fill we investigated the groundwater system with the variable density flow and solute transport code sutra to determine if the basin s recharge and inferred groundwater salinity are consistent with observational data steady state model predictions of the position and shape of the interface separating saline from fresh groundwater are consistent with the salinity profile derived from the spontaneous potential sp log of a geothermal well on the lake s shoreline we also inferred the basin wide saline groundwater distribution and concentration from experiments with a steady state model of the entire basin groundwater system hydrologic variations around the lake determine the position of the saline fresh groundwater interface higher recharge rates characteristic of the sierra nevada shoreline push the interface far beneath the lake the interface probably lies below the shoreline around much of the rest of the lake on the low recharge northeastern shoreline the interface top may lie outside the lake edge this positions the saline groundwater discharge zone just below the playa surface and contributes to development of salt flats on the recently exposed former lake bed simulations suggest that the basin fill permeability may not have significant anisotropy possibly owing to extensive faulting which increases vertical permeability for an anisotropic basin fill the resultant increased channeling of recharge beneath the lake readily overcomes the opposing force of the saline groundwater density and it is flushed out of the basin sediments a simple permeability representation of the basin lithology with low permeability below the lake and an anisotropic transition to higher permeability outside the lake reasonably represents the well and spring water salinity observations

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

steady seepage in trenches and dams effect of capillary flow steady seepage from two dimensional domains is investigated using a dimensionless formulation for variably saturated media that depends on three dimensionless parameters m n and the parameter m is the product of the anisotropy ratio and the squared ratio of the vertical length scale to the horizontal length scale the parameter n increases with the uniformity of the pore sizes and represents the ratio of the domain height to the height of the capillary fringe our modeling results show that the seepage face height in rectangular domains is always larger than the seepage face height computed from saturated flow models the results also show that the seepage face height increases with increasing m increasing n and or decreasing the outflows computed from the present model are always larger than the outflows computed by the dupuit assumption nomographs for rectangular and trapezoidal domains simulating trenches and dams are presented

effects of inland water level oscillation on groundwater dynamics and land sourced solute transport in a coastal aquifer abstract inland groundwater level variation widely exists but is usually neglected when conducting research on flow and solute transport in coastal aquifers a variable saturation and variable density flow and transport model feflow is applied to investigate groundwater dynamics and land sourced solute transport in a coastal aquifer under the influence of groundwater level oscillation at inland boundary and tidal fluctuation at seaward boundary over a period of two years the wave number shows that the damping rate of the seasonal oscillation at the inland boundary when propagating in the aquifer is much smaller than that of the tidal fluctuation thus the seasonal oscillation can propagate a longer distance the damping forms of the amplitude of both signals are exponential when propagating in the aquifer even though the amplitudes and the periods are different for the base conditions simulated the size of the upper saline plume usp i e recirculated seawater driven by tidal fluctuation fluctuates periodically in response to the groundwater level oscillation at inland boundary the fluctuation of the usp controls the movement of freshwater discharge tube fdt and the upper part of seawater wedge sw therefore the sw freshwater interface shows a rotating instead of parallel movement as groundwater system in a coastal aquifer is a mixed convection system a modified rayleigh number is adopted to investigate the density induced instabilities associated with the transport of dense solute under the effect of groundwater level oscillation at inland boundary and tidal fluctuation the more obvious gravity induced instabilities i e stronger solute downwelling and freshwater upwelling are observed at lower groundwater level the finger plume and the upwelled freshwater mix well when approaching the discharge zone where strongly affected by tidal fluctuation consequently the high concentration of the plumes is diluted when migrating toward the sea sensitive analysis indicates that the hydraulic conductivity and the density of the solute are the dominant impact factors for the morphology horizontal and vertical movements of the land sourced solute plume the amplitude and period of the fluctuating signal at the inland boundary have minor influence on the morphology and instabilities of the finger plume

modelling density dependent flow and solute transport at the lake tutchewop saline disposal complex victoria abstract intercepted saline groundwaters and drainage effluent from irrigation are commonly stored in both natural and artificial saline disposal basins throughout the murray darling basin of australia their continued use as wastewater evaporation sites requires an understanding of existing groundwater dynamics the useful of individual basins their sustainability and possible environmental impacts remain largely unknown in this work the movement of salt to the underlying groundwater system from lake tutchewop a saline disposal complex in north central victoria was modelled in cross section due to the salinity contrast between the hypersaline basin waters and the regional groundwater it was necessary to simulate density dependent flow behaviour under certain conditions these density stratified systems may become unstable leading to the onset of convective behaviour which greatly increases the movement of salt from the basin to the groundwater system modelled concentration profiles in the aquifer system and calculated seepage rates from the basin show that lake tutchewop is stable under its present operating regime the downward movement of salt is mainly controlled by diffusion and dispersion the calibrated model was used to assess the impact of several management scenarios using time dependent boundary conditions for lake salinity and water levels the influence of heterogeneous basin linings on ensuing salt flux rates is examined and results show that increased solute transport will occur under such conditions a sensitivity analysis performed on governing variables showed that salt fluxes were most sensitive to lake salinity levels a solute rayleigh number defined in terms of basin salinity and hydrogeologic parameters is seen to be an effective tool for predicting the long term behaviour of such saline disposal basins the models and concepts developed in this work may find application in the design and management of saline disposal complexes

evidence of free convection in groundwater field based measurements beneath wind tidal flats free convection caused by salinity differences had not been conclusively detected or measured in the field a field experiment at wind tidal flats on padre island national seashore texas documents salinity driven free convection with both direct head and salinity data and indirect time lapse 3 d resistivity methods evaporative concentration of groundwater near the water table created unstable inverted density gradients reduced groundwater levels and reversed hydraulic gradients these factors allowed plumes or fingers of more saline denser fluid to flow downward into less dense fluid as observed in monitoring wells and 3 d surveys the development of density inversions can overcome the dissipating forces of dispersion and diffusion to create a sufficiently large unstable gradient to induce free convection the development of free convective flow of variable density fluids in groundwater can be detected and monitored through field techniques

steady state freshwater seawater mixing zone in stratified coastal aquifers summary the mixing zone between freshwater and intruding seawater which controls regional groundwater flow dynamics and reactive transport processes is the most important component in coastal aquifers laboratory experiments and numerical simulations were conducted to investigate the effects of aquifer stratification on the thickness of a steady state freshwater seawater mixing zone a series of experiments were implemented in a laboratory tank packed with three layers of coastal sands and manipulated by two flow cells for maintaining constant head boundary conditions packed aquifers included a homogenous aquifer a high hydraulic conductivity k low k high k stratified aquifer and a low k high k low k stratified aquifer both tank scale and field scale density dependent models were developed to simulate the laboratory experiments and to systematically investigate aquifer stratification effects on the thickness of a steady mixing zone with varying layer configurations results showed that when an aquifer layer with a low k overlies a layer with a relatively high k slanting upward flow of diluted saltwater and re circulated seawater flow are refracted at the interface between the two layers resulting in streamline separation and a broad mixing zone in the low k layer by contrast the mixing zone in a high k layer is slightly narrowed when it overlies a layer with a relatively low k because flow refraction squeezes the streamlines within the mixing zone the mixing zone profile in head controlled systems is a function of k contrast but independent of the magnitude of k our results demonstrated the significant impact of aquifer stratification on controlling groundwater flow and solute transport in coastal subsurface environments and would have significant implications for studying physical chemical and biological processes in coastal subsurface environments as aquifer stratification is naturally prevalent

vadose zone permeability tests steady state results free surface and saturated unsaturated flow models are applied to the problem of constant head borehole infiltrat1on tests for determining saturated hydraulic conductivity above a water table the free surface model follows the same general approach employed to develop analytical solutions but this model does not suffer from some of the many simplifying assumptions regarding boundary conditions nonetheless the results of steady state simulations with the free surface model agree rather well with the analytical solutions the free surface approach provides a distorted view of the infiltration process saturated unsaturated models used to simulate quasi steady state conditions indicated that only a small volume of soil in the vicinity of the borehole is completely saturated with water based on saturated unsaturated simulations in four different homogeneous isotropic soils an empirical solution is developed for deep water table conditions to estimate saturated hydraulic conductivity with improved accuracy due to the effects of borehole geometry unsaturated soil characteristics water table depth heterogeneity and anisotropy it is extremely difficult to develop a completely general formula