an experimental study of the relationship between joint spacing and layer thickness abstract two methods for measuring joint spacing are described and compared the area method is a constant for a given outcrop area and is not affected by joint distribution within that area in contrast the line method depends on the location of the linear traverse two kinds of joint sets are distinguished on bedding surfaces 1 a poorly developed set represents the early stages of development when typical joint lengths are less than typical spacing 2 a well developed set represents later stages when lengths are much greater than spacing the area method is applicable to both poorly and well developed sets whereas the line method produces inconsistent results for poorly developed joint sets surface textures on many joints indicate point fracture origins and propagation parallel to bedding whereas most numerical model studies of spacing assume linear origins and propagation perpendicular to bedding the laboratory experiments described in this paper do not suffer from these restrictions an important concept confirmed during these experiments is fracture saturation when the applied strain reaches a certain value fracture spacing stops evolving and remains nearly constant these fracture sets are well developed spacing at saturation is a function of layer thickness but is independent of strain whereas spacing before saturation varies strongly with applied strain thus plotting spacing vs thickness and comparing the slopes of lines fit to such data for poorly developed joint sets in different layers is unlikely to be a diagnostic test for differences in material properties on the other hand spacing may be a sensitive indicator of strain for layers with poorly developed joint sets assessing fracture saturation is a lirst order consideration when gathering spacing data

investigation of groundwater contamination using electric and electromagnetic methods at an open waste disposal site a case study from isparta turkey geophysical methods when integrated with soil chemical and hydrogeological methods can be used to investigate groundwater contamination direct current dc resistivity geo electrical sounding and very low frequency electromagnetic vlf em data were collected at an open waste site used by the municipality of the city of isparta turkey the groundwater at shallow depths in alluvium which is composed of gravel sand and clay were expected to be hazardously contaminated under and around the open waste disposal site in which both household and industrial wastes are known to be disposed of improperly in this study we mapped the spread of groundwater contamination using a vlf em method which allows fast and inexpensive data collection the method complements the results of geo electrical sounding there is a good correlation between the results of the vlf em and the dc resistivity methods employed for the investigation of subsurface structure of the site where soil chemical and previous hydrogeological surveys have indicated high levels of chemical concentrations

assessment of groundwater contamination around active dumpsite in ibadan southwestern nigeria using integrated electrical resistivity and hydrochemical methods investigation of groundwater contamination due to leachate migration in a solid waste disposal site was done using both geophysical and hydrochemical methods the main goals were to delineate groundwater contamination due to leachate percolation and thus assessment of quality of groundwater from nearby hand dug wells bordering the dumpsite for drinking purpose a total of ten resistivity traverses were acquired within and outside the dumpsite using wenner configuration with constant electrode separation ranging from 5 to 25 m the 2d resistivity data were processed and inverted using res2dinv and res3dinv softwares respectively geochemical assessment of groundwater samples were carried out according to apha standards while hydrochemical facies of the sampled groundwater was evaluated using piper trilinear software the inverse resistivity models of the subsurface from 2d and 3d imaging revealed low resistivity value less than 10 m suspected to be leachate while 3d inverse sections allowed delineation of leachate weathered layer bedrock and seepage path from the dumpsite the extent of migration was more pronounced in the southern part of the dumpsite hence possible contamination of shallow groundwater system as dumpsite ages the results of physico chemical analyses showed the groundwater samples to be within the limits of who nsdwq for drinking purpose however higher values of concentrations of most analyzed parameters were noticed in well 1 due to its nearness to dumpsite and well 10 due to agricultural activities respectively interpretation of piper diagram showed cahco3 to be dominant facie in the area while alkaline earth metals text ca 2 text mg 2 and weak acids hco3 co3 are dominant cations and anions during both climatic seasons groundwater in the study area is of hard fresh and alkaline in nature

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

magma propagation at piton de la fournaise from joint inversion of insar and gnss magma propagation is an unsteady process controlled by magma crust interaction to provide information on its dynamics we invert complementary ground deformation data spanning the 8 hr preceding the 26 may 2016 eruption at piton de la fournaise pdf volcano la reunion france data are inverted using 3 d boundary element models combined with a monte carlo inversion method the final geometry of the displacement source is determined based on four interferograms spanning the whole propagation phase while the dynamics of the propagation is inferred from temporal inversion of continuous global navigation satellite system gnss data using the final geometry as an a priori to constrain the source the best modeled magma path consists in a 2 700 m long sill located 800 m above sea level and connected to the eruptive fissure by a subvertical dike the quick opening of the horizontal part of the intrusion could have been favored by limited flank sliding during the early stage of propagation the intrusion then stalled for 5 hr while pressure increased slightly until final upward propagation and eruption volume budget suggests that the eruption was fed by a single batch of magma quickly disconnected from its source the delay prior to the eruption may reflect a limited magma supply finally two mechanisms potentially acting together might have favored the eruption a driving role of magmatic gas and or as often observed at piton de la fournaise an eastward flank slip

the effects of oscillation period on groundwater wave dispersion in a sandy unconfined aquifer sand flume experiments and modelling summary this paper presents a new laboratory sand flume dataset on the propagation of groundwater waves in an unconfined sandy aquifer with a vertical boundary subject to simple harmonic forcing with a wide range of oscillation period from 10 7 s to 909 s the data is unique in that it covers a much wider range of non dimensional aquifer depths n d k where n is the porosity is the angular frequency d is the aquifer depth and k is the hydraulic conductivity than has been previously investigated both the amplitude decay rate and rate of increase in phase lag of the water table waves are observed to monotonically increase with increasing oscillation frequency increasing n d k this is in contrast to existing theoretical dispersion relations which predict 1 zero phase lag or standing wave behaviour and 2 an asymptotic decay rate as the frequency increases possible influences on the experimental data including sand packing measurement location finite amplitude wave effects unsaturated zone truncation and multiple wave mode effects are unable to explain the discrepancy the data was also compared against numerical solutions of richards equation with and without hysteresis and in both cases the same qualitative behaviour as the analytic solutions described above is found the discrepancy between data and predictions remains unexplained and highlights a knowledge gap that requires further investigation these findings relate directly to practical applications in the field of surface groundwater interactions such as the influence of wave forcing of coastal aquifers on contaminant transport sediment mobility and salt water intrusion all of which are influenced by the dispersion of the groundwater wave

integrated use of hydrochemistry and resistivity methods in groundwater contamination caused by a recently closed solid waste site in order to investigate the groundwater contamination by solid waste disposal using both hydrochemical and geophysical methods the halkali i stanbul solid waste disposal site which was closed in 1994 was investigated the disposal site lies on a ridge between two valleys filled with alluvium a total of six boreholes were drilled on two lines across the menekse valley adjacent to the halkali site groundwater samples collected from these boreholes were analyzed for various contaminant parameters the results indicate that tds and chloride concentrations decrease horizontally away from the waste site whereas they increase with depth electrical soundings carried out at 12 locations yielded high resistivity values at the upstream part of menekse valley while lower values were obtained from the locations near the leachate seepage points

scaling relations of earthquakes and aseismic deformation in a damage rheology model summary we perform analytical and numerical studies of scaling relations of earthquakes and partition of elastic strain energy between seismic and aseismic components using a thermodynamically based continuum damage model brittle instabilities occur in the model at critical damage level associated with loss of convexity of the strain energy function a new procedure is developed for calculating stress drop and plastic strain in regions sustaining brittle instabilities the formulation connects the damage rheology parameters with dynamic friction of simpler frameworks and the plastic strain accumulation is governed by a procedure that is equivalent to drucker prager plasticity the numerical simulations use variable boundary forces proportional to the slip deficit between the assumed far field plate motion and displacement of the boundary nodes these boundary conditions account for the evolution of elastic properties and plastic strain in the model region 3 d simulations of earthquakes in a model with a large strike slip fault produce scaling relations between the scalar seismic potency rupture area and stress drop values that are in good agreement with observations and other theoretical studies the area and potency of the simulated earthquakes generally follow a linear log log relation with a slope of 2 3 and are associated with stress drop values between 1 and 10 mpa a parameter space study shows that the area potency scaling is shifted to higher stress drops in simulations with parameters corresponding to lower dynamic friction more efficient healing and higher degree of seismic coupling

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

capillary effect on water table fluctuations in unconfined aquifers parlange and brutsaert 1987 derived a modified boussinesq equation to account for the capillary effect on water table dynamics in unconfined aquifers barry et al 1996 solved this equation subject to a periodic boundary condition their solution shows significant influence of capillarity on water table fluctuations which evolve to finite amplitude standing waves at the high frequency limit here we propose a new governing equation for the water table which considers both horizontal and vertical flows in an unsaturated zone of finite thickness an approximate analytical solution for periodic water table fluctuations based on the new equation was derived in agreement with previous results the analytical solution shows that the unsaturated zone s storage capacity permits water table fluctuations to propagate more readily than predicted by the boussinesq equation furthermore the new solution reveals a capping effect of the unsaturated zone on both the amplitude and phase of the water table fluctuations as well as the water table overheight due to the finite thickness of the unsaturated zone the capillary effect on water table fluctuations is modified mainly with reduced amplitude damping and phase shift

evolution of magma conduits during the 1998 2000 eruptions of piton de la fournaise volcano reunion island 1 at basaltic volcanoes magma is transported to the surface through dikes magma filled fractures but the evolution of these dikes as eruptions proceed is rarely documented in march 1998 after five and a half years of quiescence piton de la fournaise volcano reunion island entered into a new eruptive phase characterized by intense eruptive activity coeruptive displacements recorded by interferometric synthetic aperture radar insar for the first five eruptions of the cycle are analyzed using 3 d boundary element models combined with a monte carlo inversion method we show that the eruptions are associated with the emplacement of lateral dikes rooted at depths of less than about 1000 m except for the first march 1998 event where an additional deeper source is required the dikes are located above preeruptive seismic swarms this is consistent with nearly isotropic stress caused by repeated dike intrusions and low confining pressure enhanced by the presence of pores in the shallowest 1000 m of the edifice the volumes of the modeled dikes represent 17 of the volume of emitted lava showing that exogenous growth plays a major role in building the volcano by taking into account the preeruptive seismicity and tilt data together with the results of insar data modeling we find that dikes first propagate vertically from a source region below sea level before being injected laterally at shallow depth this behavior is consistent with the presence of levels of neutral buoyancy at shallow depth in the edifice

the enhancing effect of the elastic storage of the seabed aquitard on the tide induced groundwater head fluctuation in confined submarine aquifer systems summary this paper investigated the tide induced head fluctuation in a coastal confined aquifer with an infinitely extending semipermeable roof the roof is overlain by an unconfined aquifer terminating at the coastline previous analytical studies ignored the effect of the elastic storage of the semipermeable roof our model incorporated this effect the analytical solution indicated that the increase of the elastic storage of the offshore semipermeable roof may significantly enhance the tidal head fluctuation in the confined aquifer at the coastline a threshold leakance exists in the sense that when the leakance is less than the threshold the head fluctuation at the coastline will become insensitive to leakance and the roof can be regarded as impermeable the threshold strongly depends on the roof s elastic storage and decreases as the roof s elastic storage increases indicating that the roof s leakage effect is significantly enhanced by the increase of the roof s elastic storage

formation and interpretation of dilatant echelon cracks the relative displacements of the walls of many veins joints and dikes demonstrate that these structures are dilatant cracks we infer that dilatant cracks propagate in a principal stress plane normal to the maximum tensile or least compressive stress arrays of echelon crack segments appear to emerge from the peripheries of some dilatant cracks breakdown of a parent crack into an echelon array may be initiated by a spatial or temporal rotation of the remote principal stresses about an axis parallel to the crack propagation direction near the parent crack tip a rotation of the local principal stresses is induced in the same sense but not necessarily through the same angle incipient echelon cracks form at the parent crack tip normal to the local maximum tensile stress further longitudinal growth along surfaces that twist about axes parallel to the propagation direction realigns each echelon crack into a remote principal stress plane the walls of these twisted cracks may be idealized as helicoidal surfaces an array of helicoidal cracks sweeps out less surface area than one parent crack twisting through the same angle thus many echelon cracks grow from a single parent because the work done in creating the array as measured by its surface area decreases as the number of cracks increases in cross sections perpendicular to the propagation direction echelon cracks grow laterally each crack overlapping its neighbors until the mechanical interaction of adjacent cracks limits this growth dilation of each crack pinches the tips of adjacent cracks into an asymmetrical form and introduces local stresses that can cause lateral growth along a curving sigmoidal path sigmoidal echelon cracks may link at tip to plane intersections leaving a step in the through going crack wall the geometry of dilatant echelon cracks may be used to infer spatial or temporal changes in the orientation of principal stresses in the earth

rainfall infiltration derived submarine groundwater discharge from multi layered aquifer system terminating at the coastline this article investigates the quantity of submarine groundwater discharge sgd from a coastal multi layered aquifer system in response to constant rainfall infiltration the system comprises an unconfined aquifer a leaky confined aquifer and an aquitard between them and terminates at the coastline an approximate analytical solution is derived based on the following assumptions i flow is horizontal in the aquifers and vertical in the aquitard and ii flow in the unconfined aquifer is described by nonlinear boussinesq equation the analytical solution is compared with numerical solutions of the strictly two dimensional nonlinear model to validate the model assumptions used for the analytical solution the sgd from the leaky confined aquifer increases with the inland rainfall infiltration recharge and the specific leakage of aquitard the maximum sgd ranges from 1 87 to 10 37 m3 per day per meter of shoreline when rainfall infiltration ranges from 18 2 to 182 mm year and the specific leakage of aquitard varies from 10 9 to 10 1 l day copyright 2011 john wiley sons ltd

the capillary fringe and its effect on water table response abstract shallow water tables are often observed to respond in a highly disproportionate manner to precipitation events that is the magnitude of the response is often much greater than would be predicted on the basis of the specific yield of the geologic material and the amount of rainfall physical arguments are presented to show that if the capillary fringe the zone of tension saturation extends to ground surface then the addition of a very small amount of water can result in an immediate and large rise in the water table the arguments are supported by a field experiment in which the addition of 0 3 cm of water caused the water table to rise 30 cm in 0 25 min thus demonstrating the large and highly transient influence of the capillary fringe on the position of the water table the evidence in this study as well as recent work of others suggests that the capillary fringe effect could have a major influence on the process of stream flow generation contaminant transport to surface waters and contaminant transport in hydrogeologic regimes having shallow water tables it is further shown that calculations of groundwater recharge and consumptive use based on water table response and an assumed specific yield could be substantially in error

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

the initiation and growth of en echelon veins abstract numerical models are used to understand the evolution of mode i opening fractures from spatially random distributions in a brittle elastic material en echelon arrays commonly develop because mechanical fracture interaction promotes growth for this geometry this provides a new mechanism for en echelon vein formation in rock which is distinctly different than previously proposed mechanisms it is suggested that some macroscopic en echelon vein arrays may have served as zones of weakness that localized later shear zone development in a manner analogous to that observed by experimentalists examining micro cracking and subsequent shear rupture of rocks loaded under compression sigmoidally shaped veins and vein fillings are explicitly modeled showing that they can form in response to the mechanical interaction of neighboring fractures which redirects the propagation path numerical comparison of sigmoidal veins formed by brittle fracture and by ductile shear zones demonstrates some of the pitfalls of failing to correctly identify the mechanism of formation

monitoring of fracture propagation by quartz tiltmeters the growth of a hydrofracture can be monitored by observation of the ensuing deformation of the earth s surface the field data are processed and analyzed to yield a characterization of the deformation source several methods are used for measuring the surface deformation geodetic techniques are used for monitoring slow deformation over large areas where tiltmeters may be used to complement geodetic networks by providing continuous records in this paper two different case studies are presented in which tiltmeters are used for measuring surface deformation the first case deals with measurements of surface tilts obtained during an induced hydraulic fracture experiment the fracture characteristics are obtained by comparing the measured deformation with those provided by a mathematical model nonlinear inversion of surface tilts gave estimates of the fracture geometry depth length and thickness the second case deals with tilts measured during a naturally induced hydraulic fracture in a volcanic area the analysis of field data enabled good understanding of the volcano behavior

an alternative boussinesq equation considering the effect of hysteresis on coastal groundwater waves abstract this paper presents an alternative boussinesq equation considering hysteresis effect via a third order derivative term by introducing an improved moisture pressure retention function this equation describes with reasonable precision groundwater propagation in coastal aquifers subject to dirichlet boundary condition of different oscillation frequencies test results confirmed that it is necessary to consider horizontal and vertical flows in unsaturated zone because of their variable influences on hysteresis hysteresis in unsaturated zone can affect the water table wave number of groundwater wave motion such as wave damping rate and phase lag oscillations with different periods exert different hysteresis effect on wave propagation truncation shrinkage of unsaturated zones also affects the strength of hysteresis these impacts can be reflected in the alternative boussinesq equation by adjusting the parameter representing the variation rate of moisture associated with pressure change as opposed to traditional computationally expensive hysteresis algorithms the present boussinesq equation is simple to use and can provide feasible basis for future coupling of groundwater and surface water models

water table waves in an unconfined aquifer experiments and modeling 1 comprehensive measurements are presented of the piezometric head in an unconfined aquifer during steady simple harmonic oscillations driven by a hydrostatic clear water reservoir through a vertical interface the results are analyzed and used to test existing hydrostatic and nonhydrostatic small amplitude theories along with capillary fringe effects as expected the amplitude of the water table wave decays exponentially however the decay rates and phase lags indicate the influence of both vertical flow and capillary effects the capillary effects are reconciled with observations of water table oscillations in a sand column with the same sand the effects of vertical flows and the corresponding nonhydrostatic pressure are reasonably well described by small amplitude theory for water table waves in finite depth aquifers that includes the oscillation amplitudes being greater at the bottom than at the top and the phase lead of the bottom compared with the top the main problems with respect to interpreting the measurements through existing theory relate to the complicated boundary condition at the interface between the driving head reservoir and the aquifer that is the small amplitude finite depth expansion solution which matches a hydrostatic boundary condition between the bottom and the mean driving head level is unrealistic with respect to the pressure variation above this level hence it cannot describe the finer details of the multiple mode behavior close to the driving head boundary the mean water table height initially increases with distance from the forcing boundary but then decreases again and its asymptotic value is considerably smaller than that previously predicted for finite depth aquifers without capillary effects just as the mean water table over height is smaller than predicted by capillarity free shallow aquifer models so is the amplitude of the second harmonic in fact there is no indication of extra second harmonics in addition to that contained in the driving head being generated at the interface or in the interior

impact of arid surface megacracks on hydrocarbon reservoir properties the megacrack pattern of the ephemeral north panamint dry lake california united states is characterized by variably sized polygons with diameters ranging from hundreds of meters to meters the evolution and subsurface extent of this polygonal pattern and a probable tectonic link are examined by ground resistivity measurements and surface mapping crack development is initiated by the shrinking of clays caused by changes in water content near the surface for crack evolution the following processes are proposed cavities develop at approximately 1 m 3 ft depth during a subsurface phase followed by the collapse of the overburden into the existing cavities to form the surface cracks cracks are filled by wind blown sand and dried out lake sediments from collapsing crack walls following burial differences in competence between crack fill and surrounding playa lake sediments provide zones of structural weakness that might channelize stress release and faulting ground resistivity measurements confirmed the extent of the cracks to a depth of more than 3 m 9 ft the megacrack pattern is compared to a rotliegende upper permian tight gas field located in the southern permian basin of northwestern germany situated in a comparable geologic setting there a multidirectional polygonal pattern is recorded on horizon slices of three dimensional seismic data and compares well to our observations from the panamint valley the rotliegende pattern is associated with low offset faults which are proposed to be responsible for subtle reservoir compartmentalization

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

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

delineation of fluoride contaminated groundwater around a hot spring in nayagarh orissa india using geochemical and resistivity studies geochemical and geoelectrical investigations were carried out around a hot spring near village singhpur nayagarh district of orissa to delineate the extent of fluoride contamination in groundwater fluoride concentration is observed to be very high in both hot spring and groundwater of singhpur village compared with surrounding ones vertical electrical sounding ves studies in the area reveal the presence of two to four prominent litho units the weathered and fractured litho units constitute the main aquifer system spatial distribution of apparent resistivities at different electrode spacing indicates the presence of a low apparent resistivity zone encompassing the hot spring and the villages with fluoride contamination such as singhpur and sagaragan fluoride concentrations of groundwater and hot spring water show an inverse relation with the apparent resistivity of the formation at different electrode spacing the results of geoelectric soundings coupled with the geochemical studies and a well inventory confirm that the fluoride contamination of groundwater is mainly due to venting of thermal water into the regional aquifer system through the fractured and weathered rocks

surface geoelectrics for groundwater pollution and protection studies abstract surface geoelectrical methods are currently used in solving a range of hydrogeological problems involving both quality and quantity issues this is the first of two papers devoted to the use of applied geophysics in solving problems of groundwater protection and pollution detection in this paper attention is focused on the fundamental principles of geophysical surveying for pollution and protection studies geoelectrical methods in particular resistivity methods which are the most widely applicable geophysical method are analysed in detail relations between geoelectrical and hydrogeological parameters are discussed with a view to groundwater pollution as well as methods of measurements and the principles of geophysical and hydrogeological interpretation of results several examples are given to illustrate the principles a future paper will be devoted to presentation of case histories

fault interaction near hollister california a numerical model is used to study fault stress slip near hollister california the geometrically complex system of interacting faults including the san andreas calaveras sargent and busch faults is approximated with a two dimensional distribution of short planar fault segments in an elastic medium the steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time the resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results in part from geometry a nonsteady simulation is made by introducing in addition stress drops for individual moderate earthquakes a close fit of observed creep with calculated slip on the calaveras and san andreas faults suggests that many changes in creep rate averaged over several months are caused by local moderate earthquakes in particular a 3 year creep lag preceding the august 6 1979 coyote lake earthquake on the calaveras fault seems to have been a direct result of the november 28 1974 thanksgiving day earthquake on the busch fault computed lags in slip rate preceding some other moderate earthquakes in the area are also duemore to earlier earthquakes although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others the long term rate appears to reflect deep slip less

tidally driven groundwater flow and solute exchange in a marsh numerical simulations 1 tidal fluctuations drive groundwater flow in salt marsh sediments this flow could cause significant chemical exchange across the sediment water interface and could affect marsh ecology numerical models of a generalized tidal creek and marsh were constructed to calculate flow patterns and solute exchange between the marsh and creek the governing equation for saturated unsaturated flow was modified to account for tide related changes in total stress groundwater flow occurred primarily in the creek bank even when the marsh platform was inundated at high tide for marsh sediments with a hydraulic conductivity of 10 4 m s 1 groundwater ages in simulations lasting 60 days were on the order of days near the creek bank and increased to 50 60 days with distance into the marsh the volume of water that discharged between high and low tide was 0 22 0 31 m3 per meter length of channel which for a creek drainage density of 0 012 m 1 corresponds to 10 14 l m 2 d 1 sediment permeability and capillarity were important controls on flow and groundwater age in the marsh sediment compressibility affected groundwater age for compressible sediments representative of mud but not for sediments with lower compressibilities representative of sand simulations were relatively insensitive to dispersivity a comparison of simulation results with other estimates of groundwater exchange from the north inlet south carolina suggest that tides could drive observed exchange there only if the pleistocene sands underlying muddy marsh sediments outcrop within the tidal range

submarine groundwater discharge and solute transport under a transgressive barrier island abstract many recent investigations of groundwater dynamics in beaches employed groundwater models that assumed isotropic numerically convenient hydrogeological conditions real beaches exhibit local variability with respect to stratigraphy sediment grain size and associated topographic profile so that groundwater flow may diverge significantly from idealized models we used a combination of hydrogeologic field methods and a variable density saturated unsaturated transient groundwater flow model to investigate sgd and solute transport under cabretta beach a small transgressive barrier island seaward of sapelo island georgia we found that the inclusion of real beach heterogeneity drove important deviations from predictions based on theoretical beaches cabretta beach sustained a stronger upper saline plume than predicted due to the presence of a buried silty mud layer beneath the surface infiltration of seawater was greater for neap tides than for spring tides due to variations in beach slope the strength of the upper saline plume was greatest during spring tides contrary to recent model predictions the position and width of the upper saline plume was highly dynamic through the lunar cycle our results suggest that field measurements of salinity gradients may be useful for estimating rates of tidally and density driven recirculation through the beach finally our results indicate that several important biogeochemical cycles recently studied at cabretta beach were heavily influenced by groundwater flow and associated solute transport

geoelectrical model calculations for two dimensional resistivity distributions for the calculation of geoelectrical model curves for a two dimensional resistivity distribution the potential equation is transformed by means of a fourier cosine transform into a two dimensional helmholtz equation containing the separation parameter the numerical solution of this equation for different values of for an irregular grid is obtained using the method of finite differences combined with the method of overrelaxation the method by which derivatives are replaced by finite differences turned out to be very important especially for high resistivity contrasts after testing several methods designed to deal with any type of resistivity distribution a method of discretization similar to that used by brewitt taylor and weaver 1976 for magnetotelluric modeling for h polarization was found the best examples are given of model curves for schlumberger soundings over a vertical fault covered by overburden the incorrect use of horizontal layer models leads to erroneous interpretations that are more complex than the real subsurface situations

tidal water table fluctuations in a sandy ocean beach tidal water table fluctuations observed for 27 days in a gently sloped ocean beach are predicted well by numerical models based on the boussinesq equation driven with the observed 10 min averaged shoreline ocean beach intersection motion diurnal and semidiurnal water table fluctuations are almost completely damped 100 m landward of the mean shoreline location on this fine grained sand beach but fluctuations at spring neap periods 14 days are attenuated less comparison of the observations with the predictions suggests that the asymmetries in the water table level time series measured in this study result from nonlinearity owing to the large relative to the wavelength horizontal shoreline excursions rather than from nonlinearity owing to finite amplitude water table fluctuations cross shore variations of the aquifer depth are predicted to have a small effect on the landward decay rate of the water table fluctuations the seepage face width is predicted accurately and depends on the nonplanar beach profile in general the development of a seepage face is predicted to have little effect on the water table level landward of the intertidal region

a fully coupled numerical modeling for regional unsaturated saturated water flow summary it is a long lasting challenge in subsurface hydrologic modeling to develop numerically efficient algorithm for coupling unsaturated and saturated flow especially in regional scale modeling in this study a new scheme is developed for coupled numerical simulation of unsaturated saturated water flow at the regional scale the modeling domain is divided into sub areas in horizon according to spatially distributed inputs flow characteristics and topography conditions the unsaturated zone of each sub area is represented by individual one dimensional soil column water balance analysis method is employed to formulate the three dimensional groundwater model the unsaturated and saturated zones are implicitly coupled in space and time through the vertical flow between the unsaturated soil columns and the saturated aquifers in that the heads in the unsaturated and saturated zones are integrated in a single matrix equation the coupling scheme is verified and computational efficiency is evaluated in several hypothetical examples by comparing the simulation results with those of widely used software including hydrus1d swms2d feflow and hydrogeosphere in the real world application numerical results show that the coupling model can obtain satisfactory simulation results with fairly little computational cost compared with existing models the new numerical scheme is more suitable to regional scale modeling with complex domain geometry and alternating recharge or discharge fluxes however due to the assumptions involved in the method development the coupling method has its intrinsic limitations and should be used with caution in cases where the lateral flow is predominant in the unsaturated zone

tide induced fluctuations of salinity and groundwater level in unconfined aquifers field measurements and numerical model the responses of the fresh saline water interface fsi and the groundwater level gwl to the mediterranean sea tide were monitored in the coastal aquifer of israel modeled numerically and analyzed using cross correlation analysis different time lags between sea level fluctuations and hydraulic head and salinity fluctuations were detected for the fsi and the gwl at the fsi the time lag of hydraulic head behind the sea level is much shorter than the lag of the salinity at the same point surprisingly similar time lags behind the sea level were measured for both the hydraulic head at the gwl and the salinity at the fsi both at the same distance from the shoreline results from a numerical model simulating the flow and transport processes at the field scale agree with field measurements in both the gwl and the salinity in the fsi fluctuate almost simultaneously while the hydraulic head in the fsi reacts faster to sea level fluctuations the actual movement of the fresh water body which is controlled by the unsaturated flow in the capillary fringe capillary effect lags behind the pressure head fluctuations in the deeper parts of the aquifer which is controlled by saturated parameters of the aquifer the overall results agree with the conceptual mechanism suggested by levanon et al 2016 in which the effect of sea tide on the coastal groundwater system comprises two main processes 1 tidal fluctuations at the sea floor boundary which cause pressure wave propagation into the aquifer and 2 attenuation at the gwl due to the capillary effect which control also the change in the salinity and the actual movement of the fsi

delineating subsurface heterogeneity at a loop of river steinlach using geophysical and hydrogeological methods stratigraphic heterogeneity is a key controlling factor for flow and transport in groundwater systems in this case study we have combined two and three dimensional images of electric resistivity with hydrogeological data to delineate such stratigraphic heterogeneity at a loop of river steinlach close to tubingen germany where we estimated spatially varying aquifer parameters using established evaluation techniques we developed a three layer stratigraphic model consisting of heterogeneous sandy gravel overlain by a fine alluvium including top soil and underlain by sandstone weathered at its top the sandy gravel makes up the aquifer unit while we interpret the sandstone as aquitard we classified the area into two stratigraphic segments based on resistivity data the southern segment consists of a thicker alluvium where the aquifer material contains more clay than in the northern segment two different stratigraphic structures were also delineated at the southern and northern segments respectively these structures are visible in inversion results as low resistivity features trending in the se nw in the southern segment and ne nw in the northern segment both structures may be previous flow paths of river steinlach and the low permeability material overlying them may impair flow exchange in the area we performed slug and pumping tests to estimate the hydraulic conductivity k of the aquifer the k distributions show slight variation with higher values obtained at wells within the northern segment and close to the river bank a qualitative comparison of measured hydraulic conductivities with the resistivity distribution shows good agreement of the spatial patterns the stratigraphic and hydraulic heterogeneities delineated in this work are important for experimental and modeling studies of flow transport and hyporheic exchange at the site

steady periodic flow through a rectangular dam for unsteady free surface flow in a rectangular dam a simple integral relation which connects the pressure integral with the movement of the free surface is derived in the case of steady periodic movement driven by oscillating reservoir levels the time average of the pressure integral can be found which leads to an average discharge formula which is a generalization of the dupuit forchheimer discharge formula for periodic fluctuations of groundwater in a coastal aquifer in response to tidal oscillations a corollary is that the equilibrium water level far from the sea is equal to the root mean square of the sea level independent of the validity of the dupuit forchheimer assumptions

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

steepness expansion for free surface flows in coastal aquifers free surface flow of groundwater in aquifers has been studied since the early 1960s previous investigations have been based on the boussinesq equation derived from the non linear kinematic boundary condition in fact the boussinesq equation is the zeroth order equation in the shallow water expansion a key assumption in this expansion is that the mean thickness of the aquifer is small compared with a reference length normally taken to be the linear decay length in this study we re examine the expansion scheme for free surface groundwater flows and propose a new expansion wherein the shallow water assumption is replaced by a steepness assumption a comparison with experimental data shows that the new model provides a better prediction of water table levels than the conventional shallow water expansion the applicable ranges of the two expansions are exhibited

groundwater response to tidal fluctuation in a two zone aquifer summary a coastal aquifer may consist of two zones of distinctly different hydraulic properties with the coastal zone of limited width and the inland zone of infinite width the analytical solutions for groundwater level response to tidal fluctuation in such a two zone aquifer are derived and the underlying physical meanings are discussed a dimensionless zone contrast parameter r is introduced which is controlled by ratio between the product of the transmissivity and storativity of the inland zone and that of the coastal zone in the coastal zone the amplitude of groundwater head fluctuation attenuates more quickly when r becomes greater the amplitude declines exponentially with distance from the coastline and the phase lag increases linearly only when r 1 in the inland zone however the head fluctuation always exhibits an exponential attenuation of the amplitude and a linear increase of the phase lag for any value of r thus the diffusivity of the inland zone can be readily assessed with measurements of fluctuation amplitudes or lags as are frequently used when estimating aquifer parameters in homogeneous aquifers compared with jacob 1950 solution for a semi infinite homogeneous aquifer the existence of the coastal zone reduces the amplitude in the inland zone by a spatially constant coefficient and increases the phase lag by a spatially constant shift inverse estimation of aquifer parameters are discussed based on the analytical solutions the analytical solutions are used to estimate the aquifer parameters in a coastal two zone aquifer located in the west part of dongzhai harbor hainan province china

a hydrogeophysical model for relations between electrical and hydraulic properties of aquifers abstract factors influencing relations between electrical and hydraulic properties of aquifers and aquifer materials are discussed both direct and inverse relations are shown to be possible and to exist a general hydrogeophysical model is outlined for aquifer scale relations which are shown to depend primarily on two factors the character of the material level relationship and the mutual relation between the direction of groundwater flow aquifer layering and hydrogeophysical conditions in the aquifer

periodic seepage face formation and water pressure distribution along a vertical boundary of an aquifer detailed measurements of the piezometric head from sand flume experiments of an idealised coastal aquifer forced by a simple harmonic boundary condition across a vertical boundary are presented the measurements focus on the pore pressures very close to the interface view the mathml source and throw light on the details of the boundary condition particularly with respect to meniscus suction and seepage face formation during the falling tide between the low and the mean water level the response is consistent with meniscus suction free models in terms of both the vertical mean head and oscillation amplitude profiles and is consistent with the observation that this area of the interface was generally within the seepage face above the mean water level the influence of meniscus formation is significant with the mean pressure head being less than that predicted by capillary free theory and oscillation amplitudes decaying faster than predicted by suction free models the reduced hydraulic conductivity in this area due to partial drainage of pores on the falling tide also causes a delay in the response to the rising tide the combined influence of seepage face formation meniscus suction and reduced hydraulic conductivity generate higher harmonics with amplitudes of up to 26 of the local main harmonic to model the influence of seepage face formation and meniscus suction a numerical solution of the richards equation was developed and evaluated against the data the model data comparison shows a good agreement with the behaviour high above the water table sensitive to the choice of moisture retention parameters

groundwater waves in a coastal aquifer a new governing equation including vertical effects and capillarity groundwater waves that is water table fluctuations are a natural phenomenon in coastal aquifers they represent an important part of the interaction between the ocean and aquifer and affect the mass exchange between them this paper presents a new groundwater wave equation because it includes the effects of vertical flows and capillarity the new equation is applicable to both intermediate depth aquifers and high frequency waves compared with the wave equation derived by nielsen et al 1997 the present equation provides a closer representation of groundwater waves in particular it predicts high frequency water table fluctuations as observed in the field a validation of the new equation has been carried out by comparing the analytical solutions to it with predictions from direct simulations using the numerical model sutra the effects of various physical parameters and their relative importance are also discussed

frequency dependent hydraulic properties estimated from oscillatory pumping tests in an unconfined aquifer summary oscillatory pumping tests were conducted at the boise hydrogeophysical research site a periodic pressure signal is generated by pumping and injecting water into the aquifer consecutively and the pressure response is recorded at many points around the source we present and analyze the data from the field test after applying fourier analysis we then match the data with a recently derived analytical solution for homogeneous formations to estimate the equivalent aquifer properties conductivity k specific storage s s and specific yield s y the estimated values are shown to be in agreement with previous estimates conducted at this site we observe variations in the estimated parameters with different oscillation periods of pumping the trend of the parameters with changing period is discussed and compared to predictions by existing theory and laboratory experiments dealing with dynamic effective properties it is shown that the results are qualitatively consistent with recent works on effective properties of formations of spatially variable properties in oscillatory flow to grasp the impact of heterogeneity a simple configuration is proposed helping explain the observed increase in effective conductivity with decreasing period

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

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

boundary conditions for rock fracture analysis using the boundary element method successful numerical models of faults joints and other fractures in a rock mass require specification of appropriate boundary conditions but the choice may not be obvious to illustrate potential pitfalls a single two dimensional fracture is modeled by the displacement discontinuity method of boundary elements using both displacement boundary conditions and traction boundary conditions the results are compared with the analytical solution for a mode i opening crack it is shown that the traction boundary conditions can provide a satisfactory solution while displacement boundary conditions applied to a problem with both continuous and discontinuous displacement components can introduce significant errors

mapping groundwater contamination using dc resistivity and vlf geophysical methods a case study geophysical methods can be helpful in mapping areas of contaminated soil and groundwater electrical resistivity and very low frequency electromagnetic induction vlf surveys were carried out at a site of shallow hydrocarbon contamination in utah county utah previously installed monitoring wells facilitated analysis of water chemistry to enhance interpretation of the geophysical data the electrical resistivity and vlf data correlate well and vertical cross sections and contour maps generated from these data helped map the contaminant plume which was delineated as an area of high interpreted resistivities

overlapping spreading centers implications from crack growth simulation by the displacement discontinuity method overlapping spreading centers osc s are a fundamental aspect of accretionary processes at intermediate and fast spreading centers and typically occur at deep points along the axial depth profile they have a characteristic geometry consisting of two en echelon overlapping curving ridges separated by an elongated depression the length to width ratio of this overlap basin is typically 3 1 we have been successful in reproducing the overlapping spreading center geometry by modelling the growth of two initially parallel elastic cracks of given length and offset in a tensile stress field at infinity a boundary element displacement discontinuity method was used to solve this problem our calculated results are compared with seafloor observations in terms of the size and shape of the overlap region for small osc s there is a very good agreement between calculations and observations but for large ones the overlap basin tends to be longer than our predicted results indicate this suggests that the assumptions made in the model i e perfectly elastic isotropic and homogeneous medium are perhaps valid for the brittle lid above the magma chamber that underlies osc s with small offsets 2 km but oversimplified for osc s with large offsets our modelling shows that the initial interaction of closely spaced surface ruptures along spreading centers is to deflect away from one another as they approach the deflection will be the greatest for small misalignments of the fracture systems thus even minor misalignments of the spreading centers may result in the development of osc s where the misalignment is less than the width of the cracking front the fracture systems may meet head on creating a saddle point along the axial depth profile our results support the hypothesis suggested by macdonald et al 1984 in which overlapping spreading centers develop where two magmatic pulses migrate toward each other along the strike of the spreading center following fracture systems and magmatic conduits which are imperfectly aligned

effects of vadose zone on groundwater table fluctuations in unconfined aquifers summary above a shallow unconfined aquifer a considerable amount of water is stored in the vadose zone through water exchange with the underlying unconfined aquifer the vadose zone affects the groundwater table dynamics and overall behavior of the aquifer in this paper we examine tide induced groundwater table fluctuations in unconfined aquifers influenced by vadose zone of finite thickness under the condition of small aquifer thickness d compared with the groundwater wavelength l i e 2 d l 2 1 and small boundary oscillation amplitude a i e e a d 1 where 2 and e are two parameters an approximate analytical solution was derived to quantify systematically the vadose zone effects with a particular consideration of capping by the ground surface i e the upper boundary of the vadose zone depending on the extent to which the capillary rise is truncated by the ground surface the vadose zone enhances the groundwater table fluctuations in an unconfined aquifer however the mean groundwater table height and exchange between surface water and groundwater are reduced due to the presence of the vadose zone these effects are intensified with increased capillary rise but weakened as the vadose zone thickens this study provides a criterion for assessing the importance of vadose zone in modulating the response of unconfined aquifers to low frequency forcing oscillations such as tides

spring neap tide induced beach water table fluctuations in a sloping coastal aquifer predictions of water table fluctuations in coastal aquifers are needed for numerous coastal and water resources engineering problems most previous investigations have been based on the boussinesq equation for the case of a vertical beach in this note an analytical solution based on shallow water expansion for the spring neap tide induced water table fluctuations in a coastal aquifer is presented unlike most previous investigations multitidal signals are considered with a sloping coastal aquifer the new solution is verified by comparing with field observations from ardeer scotland on the basis of the analytical approximation the influences of higher order components on water table elevation are examined first then a parametric study has been performed to investigate the effects of the amplitude ratio lambda frequency ratio omega and phases delta 1 and delta 2 on the tide induced water table fluctuations in a sloping sandy beach

effects of unsaturated flow on hillslope recession characteristics recession flow analysis is usually conducted to infer hydraulic parameters of hillslope aquifers various boussinesq equation based models both linear and nonlinear have been used to analyze the recession curves for sloping aquifers with a focus on the long time recession behavior based on a modified boussinesq equation with capillarity incorporated we demonstrate the significant effect of unsaturated flow on the recession curve which result in three instead of two power law regimes with two transition points instead of one corresponding to the formation of a fully unsaturated zone at the adjacent area of the upslope boundary and across the whole domain respectively the results show that the power of the second and third recession regime is variable depending on the slope angles soil types and hillslope geometries the unsaturated flow effects also lead to the absence of drastic drop of formula presented at the transition between the first and second regime which was predicted by previous numerical models but has not been observed in the field or laboratory experiments these findings have important implications for recession flow analysis in studies of hillslope aquifers

tide induced seawater groundwater circulation in a multi layered coastal leaky aquifer system abstract mean groundwater levels of a multi layered coastal leaky aquifer system are considered the system consists of an unconfined aquifer a confined aquifer and a semi permeable layer between them both exact asymptotic solutions and approximate perturbation solutions are derived for multi sinusoidal component sea tide at inland places far from the coastline the perturbation solutions show a good agreement with the exact asymptotic solutions due to the watertable dependent transmissivity of the unconfined aquifer the mean groundwater levels of the aquifer system stand considerably above the mean sea level even in the absence of net inland recharge of groundwater and rainfall these lead to landward positive gradients of both the mean watertable and mean head in the region near the coastline which consequently results in a seawater groundwater cycle seawater is pumped into the unconfined aquifer by the sea tide and divided into two parts one part returns to the sea driven by the mean watertable gradient the rest part leaks into the confined aquifer through the semipermeable layer and returns to the sea through the confined aquifer driven by the mean head gradient the total discharge through the confined aquifer is significant for coastal leaky aquifer system with typical parameter values this seawater groundwater cycle has impacts on better understanding of submarine groundwater discharge and exchange of various chemicals such as nutrients and contaminants in coastal areas if the observed mean water levels in coastal areas are used for estimating the net inland recharge the enhancing processes of sea tide on the mean groundwater levels should be taken into account otherwise the net inland recharge will be overestimated

a new analytical solution of tidal water table fluctuations in a coastal unconfined aquifer this paper presents a new perturbation solution of the non linear boussinesq equation for one dimensional tidal groundwater flow in a coastal unconfined aquifer built upon the work of parlange et at parlange j y stagnitti f starr j l braddock r d 1984 free surface flow in porous media and periodic solution of the shallow flow approximation j hydrol 70 251 263 the solution adopts a new perturbation parameter that is by definition less than unit and thus is applicable to a wider range of physical conditions within the constraint of the boussinesq approximation this approach avoids a secular term in the third order perturbation equation of parlange et at 1984 enabling the derivation of the third and higher order solutions in comparison with a numerical exact solution the new perturbation solution is shown to be slightly more accurate than that of parlange et at 1984 with the second order approximation the obtained third order solution exhibits considerable improvement in accuracy in relatively simple analytical forms the present perturbation solution will help to understand better the non linear characteristics of tidal water table fluctuations as modeled by the non linear boussinesq equation in coastal unconfined aquifers c 2007 elsevier b v all rights reserved

influence of hysteresis on groundwater wave dynamics in an unconfined aquifer with a sloping boundary in this paper the influence of hysteresis on water table dynamics in an unconfined aquifer was examined using a numerical model to solve richards unsaturated flow equation the model was subject to simple harmonic forcing across a sloping boundary with a seepage face boundary condition time series from both hysteretic and non hysteretic models were subject to harmonic analysis to extract the amplitude and phase profiles for comparison with existing sand flume data cartwright et al 2004 the results from both model types show good agreement with the data indicating no influence of hysteresis at the oscillation period examined t 348 s the models were then used to perform a parametric study to examine the relationship between oscillation period and hysteresis effects with periods ranging from 3 min to 180 min at short oscillation periods t 180 s the effects of hysteresis were negligible with both models providing similar results as the oscillation period increased the hysteretic model showed less amplitude damping than the non hysteretic model for periods greater than t 60 min the phase lag in the non hysteretic model is greater than for the hysteretic one for periods less than t 60 min this trend is reversed and the hysteretic model produced a greater phase lag than the non hysteretic model these findings suggest that consideration of hysteresis dynamics in richards equation models has no influence on water table wave dispersion for short period forcing such as waves t 10 s whereas for long period forcing such as tides t 12 25 h or storm surges t days hysteresis dynamics should be taken into account

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

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

a numerical procedure for unsaturated seepage analysis in rock mass containing fracture networks and drainage holes abstract it is computationally difficult to model unsaturated flow through a highly fractured rock system that contains porous rock matrix densely distributed fracture networks and narrowly spaced drainage holes we present an efficient numerical procedure that uses a three dimensional finite element model to solve richards equation with embedded zero thickness elements for fractures and line elements for drainage holes a mixed boundary condition is applied at potential seepage surfaces and a water retention relation with extremely narrow unsaturated zone is specified to precisely locate the phreatic surface the procedure compares favorably with results from other numerical solutions and experimental data a case study is developed to evaluate seepage through a densely fractured rock slope the simulated results demonstrate that fractures disorder the hydraulic potential distribution with fracture patterns acting as significant influential factors and drainage holes dramatically lower the phreatic surface due to the effects of drainage and depressurization the proposed numerical procedure shows to be capable of investigating the unsaturated flow in highly fractured rock mass

tidally driven multiscale pore water flow in a creek marsh system intertidal wetlands are complex hydrological systems characterized by strong dynamic interactions between coastal surface water and groundwater driven particularly by tides we simulated such interactions with a focus on three dimensional variably saturated pore water flow in a creek marsh system that bordered a tidally dominated main channel simulated intra tidal groundwater dynamics exhibited significant flow asymmetry with non zero mean flow velocities over the tidal period the tidally averaged flow led to pore water circulation with three dimensionality linked strongly to the marsh topography over a range of spatial scales near the creek bank around the creek meander and over long marsh sections inclined towards the main channel particle tracking revealed that time scales associated with these circulations differed by orders of magnitude under the simulated conditions the creek served as the main outlet of the pore water circulation paths especially those linked with infiltration into the upper marsh surface areas away from the main channel local net efflux influenced by the creek channel curvature varied along the creek but produced a total discharge largely proportional to the creek length water infiltrating the soil in the lower marsh surface areas away from the creek tended to discharge directly to the main channel however the total discharge to the main channel was much less than that into the creek this study highlights the hydrological complexity of intertidal marshes and the need for further research on interactions among marsh morphology hydrology and ecology which underpin the functionalities of these wetland systems

two dimensional vertical moisture pressure dynamics above groundwater waves sand flume experiments and modelling this paper presents a new laboratory dataset on the moisture pressure relationship above a dispersive groundwater wave in a two dimensional vertical unconfined sand flume aquifer driven by simple harmonic forcing a total of five experiments were conducted in which all experimental parameters were kept constant except for the oscillation period which ranged from 268 s to 2449 s between tests moisture content and suction head sensor pairings were co located at two locations in the unsaturated zone both approximately 0 2 m above the mean watertable elevation and respectively 0 3 m and 0 75 m from the driving head boundary for all oscillation periods except for the shortest t 268s the formation of a hysteretic moisture pressure scanning loop was observed consistent with the decay of the saturated zone groundwater wave the size of the observed moisture pressure scanning loops decayed with increasing distance landward and the decay rate is larger for the shorter oscillation periods at the shortest period t 268s the observed moisture pressure relationship was observed to be non hysteretic but with a capillary capacity that differs from that of the static equilibrium wetting and drying curves this finding is consistent with observations from existing one dimensional vertical sand column experiments the relative damping of the moisture content with distance landward is higher than that for the suction head consistent with the fact that transmission of pressure through a porous medium occurs more readily than mass transfer this is further supported by the fact that observed phase lags for the unsaturated zone variables i e suction head and moisture content relative to the driving head are greater than the saturated zone variables i e piezometric head harmonic analysis of the data reveals no observable generation of higher harmonics in either moisture or pressure despite the strongly non linear relationship between the two in addition a phase lag of moisture content relative to the suction head was observed indicating that the response time of the moisture content to watertable motion is greater than that of the pore water pressure the observed moisture pressure dynamics are qualitatively reproduced using a hysteretic richards equation model however quantitative differences exist which are likely to be due to previous findings that demonstrated that the richards equation model is unable to accurately reproduce the observed watertable wave dispersion particularly at shorter period oscillations

a new model for coupling surface and subsurface water flows with an application to a lagoon summary built upon the work of yuan et al yuan d lin b falconer r a 2008 simulating moving boundary using a linked groundwater and surface water flow model journal of hydrology 349 524 535 we present in this note an integrated vertically averaged numerical model based on an unstructured finite volume finite difference method for simulating coupled surface and subsurface water flows in a coastal hydrological system the modelled domain was divided into a surface water flow layer and a groundwater flow layer with the former overlying the latter across the interface in contrast to the work of yuan et al 2008 the governing equations for describing these two different flows were discretised using an unstructured triangular mesh and then assembled into a single set of linear algebraic equations for computing the solutions a semi implicit eulerian lagrangian method was used to deal with the momentum convection term of the surface flow equation in this method the constraint on the model s time step imposed by the courant friedrichs lewy condition for stable solutions is relaxed the model was validated against the results of a previous experiment on the interaction of surface and subsurface flows in a coastal lagoon this showed that the new model retained the same degree of accuracy in its predictions even with time steps increased by two orders of magnitude from those allowed in the model of yuan et al 2008 the resulting increase of computational efficiency will enable model applications to large scale hydrological systems commonly encountered in the coastal zone

inversion of coeval shear and normal stress of piton de la fournaise flank displacement the april 2007 eruption of piton de la fournaise was the biggest volcano eruptive crisis of the 20th and 21st centuries interferometric synthetic aperture radar insar captured a large coeruptive seaward displacement on the volcano s eastern flank which continued for more than a year at a decreasing rate coeruptive uplift and posteruptive subsidence were also observed while it is generally agreed that flank displacement is induced by fault slip we suggest that this flank displacement might have been induced by a sheared sill based on observations of sheared sills at piton des neiges to test this hypothesis we develop a new method to invert a quadrangular curved source submitted to simultaneous pressure and shear stress changes this method based on boundary elements is applied to data acquired along six envisat orbits covering a 14 month period subsequent to the april 2007 eruption posteruptive displacement is well explained by closure and slip of a large 5 km by 8 km and shallow 500 m trapezoidal fracture parallel to the flank and probably coincident with a lithological discontinuity we investigate whether thermal contraction or degassing of a coeruptive sill can explain the displacement such a sill would have to be 10 times thicker than inferred from the coeruptive uplift and solidification time 10 times shorter 20 days than the duration of the posteruptive subsidence 24 to 33 months instead we propose that the posteruptive eastern flank displacement is due to the compaction and ongoing slow slip on a shallow detachment fault

analysis of tide and offshore storm induced water table fluctuations for structural characterization of a coastal island aquifer analysis of water table fluctuations can provide important insight into the hydraulic properties and structure of a coastal aquifer system including the connectivity between the aquifer and ocean this study presents an improved approach for characterizing a permeable heterogeneous coastal aquifer system through analysis of the propagation of the tidal signal as well as offshore storm pulse signals through a coastal aquifer offshore storms produce high wave activity but are not necessarily linked to significant onshore precipitation in this study we focused on offshore storm events during which no onshore precipitation occurred extensive groundwater level data collected on a sand barrier island sable island ns canada show nonuniform discontinuous propagation of the tide and offshore storm pulse signals through the aquifer with isolated inland areas showing enhanced response to both oceanic forcing signals propagation analysis suggests that isolated inland water table fluctuations may be caused by localized leakage from a confined aquifer that is connected to the ocean offshore but within the wave setup zone two dimensional groundwater flow simulations were conducted to test the leaky confined unconfined aquifer conceptualization and to identify the effect of key parameters on tidal signal propagation in leaky confined unconfined coastal aquifers this study illustrates that analysis of offshore storm signal propagation in addition to tidal signal propagation provides a valuable and low resource approach for large scale characterization of permeable heterogeneous coastal aquifers such an approach is needed for the effective management of coastal environments where water resources are threatened by human activities and the changing climate

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

the morphology of strike slip faults examples from the san andreas fault california fault zones are seldom straight nor are fractures within them continuous permanent strain fields are imprinted near a fault of complex geometry as a result of continued slip these strain fields may be manifest as vertical deformation near the fault strain fields that increase area result in subsidence and strain fields that reduce area result in uplift although these effects are modified by erosion and deposition the general features of fault zone morphology are a consequence of the geometry and slip distribution along strike graphical views of strain fields associated with simple vertical strike slip faults are derived using boundary element methods if the fault is straight and parallel to the applied shear strain the hills and valleys resulting from finite fault rupture are separated by the fault trace this is rarely observed in nature instead strike slip faults cut through hills and valleys apparently of their own making we show this to be a consequence of segments of the fault being nonparallel to each other and to the overall applied shear strain coseismic strains are large but transient since they are substantially annulled by rupture on contiguous fault segments we test our theory with examples from parts of the san andreas fault system in california the morphologies of the parkfield region and the southern san andreas fault in the coachella valley are shown to be consistent with plausible distributions of slip on mapped surface faults the location of the salton sea appears to be a consequence of a reduction of slip on the san andreas fault toward the brawley seismic zone

improvement of the hillslope storage boussinesq model by considering lateral flow in the unsaturated zone unsaturated flow is an important factor that affects groundwater motion among various drainage models the nonlinear hillslope storage boussinesq hsb model has been commonly used to predict water flux along a slope in this study we improved this model by considering lateral flow in the unsaturated zone using modified van genuchten functions we analytically expressed the concept of equivalent propagation thickness in the vadose zone this analytical expression was then incorporated into the hsb model to reflect two different stages of the drainage process and to simulate the hillslope drainage process more accurately the model results indicated that lateral flow has significant effects in the unsaturated zone during the hillslope drainage process even in sandy aquifers the amount of water contributed by the unsaturated zone is a key factor that enables a decrease in the water table during the middle and late stages of the process a comparison between the measured and simulated results based on both convergent type and divergent type hillslope drainage processes revealed that the thickness of the saturated zone decreases as the unsaturated flow increases this study emphasizes the necessity of considering unsaturated flow in the hsb model to improve the accuracy of predicting groundwater outflow rates and develop more accurate hydrographs the concept of equivalent propagation thickness also provides a criterion for assessing the importance of unsaturated lateral flow for future drainage research

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

vertical electrical sounding ves and multi electrode resistivity in environmental impact assessment studies over some selected lakes a case study a combined geophysical investigation consisting of vertical electrical sounding ves and multielectrode system was carried out to map the subsurface resistivity in all major lakes which are highly polluted by the discharge of sewage and other chemical effluents in greater hyderabad india the structural features identified in the study area play a major role in groundwater flow and storage the interpretation of geophysical data and lithologs indicates that a silt clay zone predominantly silt has a thickness of 5 10 m all along the drainage from patelcheruvu to the musi river the silt clay zone inferred close to the lakes is a mixture of clay silt and sand with more silt content as indicated from the lithologs during drilling the low resistivity values obtained can be attributed to the pollutant accumulated in the silt which can reduce the resistivity values further the tds of the water samples in these wells are more than 1 000 mg l which further confirms the above scenario the pollution spread is less in the upstream areas whereas it is more in the downstream which can be attributed to the shallow water table conditions and also due to the interaction of surface water and groundwater