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

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

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

aeolian sand drift from the intertidal zone on a temperate beach potential and actual rates this paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force with actual measured amounts the actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months along a 1760 m section of foredune on braunton burrows southwest england the calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation white 1979 the results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates the resulting corrected potential movement rates are a closer estimate to the actual rates but there remains much unexplained variance

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

seismic anisotropy under extended crust evidence from upper mantle xenoliths cima volcanic field california abstract a model of p wave velocity anisotropy and shear wave splitting for upper mantle under extended crust is derived from comparisons of seismic field measurements and observed xenolith anisotropies seismic velocity measurements and anisotropies calculated from petrofabric measurements of 15 upper mantle xenoliths from the cima volcanic field eastern mojave desert california show average maximum anisotropies of 6 9 for v p and 4 5 for v s xenolith compressional wave velocities corrected for upper mantle temperature and pressure agree well with field observations in the vicinity of the cima volcanic field the velocities calculated from the olivine fabrics suggest that upper mantle foliations beneath the region are horizontal and lineations trend ene the fabrics are believed to originate from early cenozoic extension in the area which had the same trend as the lineations the unusually high upper mantle temperatures in this region apparently have not significantly affected upper mantle fabrics

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

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

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

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

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

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

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

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

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