analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers sloping coastal aquifers in reality are ubiquitous and well documented steady state sharp interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the dupuit forchheimer approximation specifically analytical solutions based on the constant flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone analytical solutions for the constant head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant flux inland boundary it is found that for the constant flux inland boundary the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types despite that the geometry of the bottom confining layer determines the location of the interface tip this is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary so the shape of the bed below the interface is irrelevant to the interface position moreover developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable density flow numerical modelling analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer this article is protected by copyright all rights reserved

numerical study of airflow in the unsaturated zone induced by sea tides 1 the air pressures in coastal unsaturated zones fluctuate in response to tidal fluctuations two phase air water flow induced by sea tides in a coastal two layered subsurface system is investigated through numerical simulations the system consists of upper and lower layers with permeabilities of ku and kl respectively a water table exists in the lower layer the study demonstrates that airflow in the unsaturated zone is controlled by permeabilities of both layers and the fluctuation of water level the tide induced water level fluctuation may result in significant air pressure fluctuation in the unsaturated zone in an air confined system that is the permeability of the upper layer is about 2 orders of magnitude lower than that of the lower layer in such an air confined system horizontal airflow is dominant in the lower layer and vertical airflow is dominant in the upper layer the simulation results show that the hydraulic head rather than the sea tide is the direct driving force of the air pressure fluctuation above the water table the study on the relation between the air pressure amplitude and the landward distance demonstrates that the air pressure amplitudes increase to a maximum and then decrease with distance the amplitude of air pressure fluctuation decreases progressively with ku in the lower layer in the upper layer however the amplitude tends to increase with ku when ku is very low and decrease with ku when ku is relatively high overall the air flux fluctuations across the atmosphere soil interface attenuate landward gradually and this attenuation becomes faster as the permeability of the upper layer increases

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

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

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

influence of variable salinity conditions in a tidal creek on riparian groundwater flow and salinity dynamics while recent studies have revealed that tidal fluctuations in an estuary significantly affect groundwater flows and salt transport in the riparian zone only seawater salinity in the estuary has been considered a numerical study is conducted to investigate the influence of estuarine salinity variations on the groundwater flow and salt dynamics in the adjacent aquifer to extend our understanding of these complex and dynamic systems tidal salinity fluctuations synchronous with estuary stage were found to alter the magnitude and distribution of groundwater discharge to the estuary which subsequently impacted on groundwater salinity patterns and residence times especially in the riparian zone the effects of salinity fluctuations were not fully captured by adopting a constant time averaged estuarine salinity the modelling analysis also included an assessment of the impact of a seasonal freshwater flush in the estuary similar to that expected in tropical climates e g mean estuary level during flood significantly greater than average on adjacent groundwater flow and salinity conditions the three month freshwater flushing event temporarily disrupted the salt distribution and re circulation patterns predicted to occur under conditions of constant salinity and tidal water level fluctuations in the estuary the results indicate that the salinity variations in tidal estuaries impact significantly on estuary aquifer interaction and need to be accounted for to properly assess salinity and flow dynamics and groundwater residence times of riparian zones

an image of the columbia plateau from inversion of high resolution seismic data the authors use a method of traveltime inversion of high resolution seismic data to provide the first reliable images of internal details of the columbia river basalt group crbg the subsurface basalt sediment interface and the deeper sediment basement interface velocity structure within the basalts delineated on the order of 1 km horizontally and 0 2 km vertically is constrained to within plus minus 0 1 km s for most of the seismic profile over 5 000 observed traveltimes fit their model with an rms error of 0 018 s the maximum depth of penetration of the basalt diving waves truncated by underlying low velocity sediments provides a reliable estimate of the depth to the base of the basalt which agrees with well log measurements to within 0 05 km 165 ft the authors use image blurring calculated from the resolution matrix to estimate the aspect ratio of images velocity anomaly widths to true widths for velocity features within the basalt from their calculations of image blurring they interpret low velocity zones lvz within the basalts at boylston mountain and the whiskey dick anticline to have widths of 4 5 and 3 km respectively within the upper 1 5 km of the model at greater depth the widths of these imaged lvzs thin tomore approximately 2 km or less they interpret these linear subparallel low velocity zones imaged adjacent to anticlines of the yakima fold belt to be brecciated fault zones these fault zones dip to the south at angles between 15 to 45 degrees less

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 rare earth element chemistry of estuarine surface sediments in the chesapeake bay abstract concentrations of rare earth elements ree were measured in the fine fraction of shallow surface sediments from the lower chesapeake bay as studies suggest that coagulation of colloids dominates the removal of ree from the dissolved load in low salinity regions of estuaries ree in sediments showed spatial heterogeneity both laterally and longitudinally we observed the influence of salinity on the spatial and temporal variability in total ree content and on eu anomalies lower total ree was found in sediments deposited along the eastern shore the chemistry of the mid bay islands was distinct with higher overall ree content and slightly more positive ce anomaly values positive ce ce in the mid bay are attributed to coriolis acceleration restricting freshwater flow towards the west away from the islands leading to oxidative removal of ce from the pore waters to the sediments the presence of positive eu eu in sediments deposited along the eastern shore is linked to salinity we suggest that unique local conditions along the eastern shore possibly including submarine groundwater discharge of nutrient rich reducing waters combined with organic matter decay and the predominance of oceanic water flow toward this region leads to the development of a strong localized salinity gradient this study demonstrates the utility of ree sediment chemistry in identifying and resolving local and estuarine wide geochemical processes

groundwater level fluctuation in the waimea plains new zealand changes in a coastal aquifer within the last 30 years data for the waimea plains new zealand indicate that the lower confined groundwater aquifer is hydraulically homogeneous and that shallow groundwater levels inland are affected mostly by anthropogenic processes while those near the coast are affected more by sea level variation analysis of long term data for new zealand indicates that sea level has increased continuously but trends are not spatially uniform results from non parametric trend analysis show that rising trends for groundwater levels are predominant in the shallow aquifer both inland on the waimea plains and for recent years near the coast while decreasing trends are evident in the underlying confined aquifer near the coast groundwater level change in the shallow aquifer appears to be more affected by climate change than the lower confined aquifer correlation analysis indicated that groundwater levels are more affected by rainfall during the rainy season than the dry season and more influenced by rainfall inland than near the coast groundwater level declines in the lower confined aquifer near the coast which has its major recharge area inland in the catchment may be substantially affected by groundwater abstraction in inland areas as well as sea level variation but there are little evidences of seawater intrusion meanwhile groundwater recharge over the catchment area has great influence on rising groundwater levels in the shallow aquifer and its recharge is estimated to be 417 8 mm year using chloride concentrations of precipitation and groundwater

spatial patterns of groundwater biogeochemical reactivity in an intertidal beach aquifer beach aquifers host a dynamic and reactive mixing zone between fresh and saline groundwater of contrasting origin and composition seawater driven up the beachface by waves and tides infiltrates into the aquifer and meets the seaward discharging fresh groundwater creating and maintaining a reactive intertidal circulation cell within the cell land derived nutrients delivered by fresh groundwater are transformed or attenuated we investigated this process by collecting pore water samples from multilevel wells along a shore perpendicular transect on a beach near cape henlopen delaware and analyzing solute and particulate concentrations pore water incubation experiments were conducted to determine rates of oxygen consumption and nitrogen gas production a numerical model was employed to support field and laboratory interpretations results showed that chemically sensitive parameters such as ph and orp diverged from salinity distribution patterns indicating biogeochemical reactivity within the circulation cell the highest respiration rates were found in the landward freshwater saltwater mixing zone supported by high dissolved inorganic carbon chlorophyll a a proxy for phytoplankton and particulate carbon did not co occur with the highest respiration rates but were heterogeneously distributed in deeper and hypoxic areas of the cell the highest rates of n2 production were also found in the mixing zone coinciding with elevated o2 consumption rates but closer to the lower discharge point model results were consistent with these observations showing heightened denitrification in the mixing zone the results of this work emphasize the relationship between the physical flow processes of the circulation cell and its biogeochemical reactivity and highlight the environmental significance of sandy beaches

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

an evaluation of electromagnetic methods in the presence of geologic noise an important element of electromagnetic em prospecting is survey design numerical modeling algorithms may be used to calculate signal to geologic noise s n ratios to compare different survey configurations and measured responses quantitatively our models consist of a prismatic three dimensional 3 d target in a conductive half space which may contain an overburden conductor the models are energized by a time varying current transmitted in a loop of wire the signal is the scattered or anomalous response of the target while the geologic noise is either the response of the half space or the anomalous response of the overburden conductor for typical loop sizes in exploration the coincident loop configuration has a relatively high s n ratio and thus a relatively high capability to resolve the target in the case of half space noise measurements made with the horizontal loop moving coil configuration can be just as effective if the coil separation is one and one half to two times the depth of buria

experience with the em 60 electromagnetic system for geothermal exploration in nevada lawrence berkeley laboratory lbl conducted controlled source electromagnetic em surveys at three geothermal prospects in northern nevada over 40 soundings were made in panther canyon grass valley near winnemucca soda lakes near fallon and mccoy west of austin to test and demonstrate the applicability of lbl s em 60 system to geothermal exploration the em 60 is a frequency domain system using three component magnetic detection typically 65 a is applied to an 100 m diameter four turn horizontal loop generating a dipole moment 10 sup 6 mks over the frequency range 10 sup 3 to 10 sup 3 hz with such a source loop soundings were made at transmitter receiver separations of up to 4 km providing a maximum depth of penetration of 4 km

electromagnetic mapping of electrical conductivity beneath the columbia basalts sedimentary rocks beneath the columbia river basalt group are recognized as having potential for oil and gas production but the overlying layered basalts effectively mask seismic reflections from the underlying sediments four electromagnetic em methods have been applied on profiles crossing boylston ridge a typical east west trending anticline of the yakima fold belt in an attempt to map the resistivity interface between the basalts and the sediments and to map variations in structure and resistivity within the sediments the em surveys detected strong variations in resistivity within the basalts and in particular the continuous magnetotelluric array profiling emap revealed resistivity lows beneath the surface anticlines these low resistivity zones probably coincide with fracturing in the core of the anticlines and they appear to correlate well with similar zones of low seismic velocity observed on a nearby seismic profile the controlled source em surveys in loop transient long offset transient and variable offset frequency domain were designed in anticipation of relatively uniform high resistivity basalts and were found to have been seriously distorted by the intrabasalt conductors discovered in the field in particular the resistivity sections derived from 1d inversions were found to be inconsistent and misleading the emap survey provided the most information about themore subsurface resistivity distribution and was certainly the most cost effective however both controlled source and emap surveys call for accurate 2d or 3d inversion to accommodate the geological objectives of this project references 18 less

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

megasource time domain electromagnetic sounding methods the colorado school of mines time domain electromagnetic em sounding system makes use of a grounded length of cable powered with high amplitude current square waves to generate an em field for probing the earth the vertical component of magnetic induction is detected at a sounding site located at a relatively large distance compared to the desired depth of investigation with a source moment of a million ampere meters or greater offset distances of several tens of kilometers can be achieved easily providing depths of investigation of up to 10 km the recorded induction field versus time curves are routinely interpreted by comparison with computer generated theoretical curves for a layered earth megasource em surveys have been carried out at the geysers in northern california and near yakima in central washington providing apparently meaningful information on the electrical structure in these areas at depths as great as 10 km

co2 water mineral reactions during co2 leakage geochemical and isotopic monitoring of a co2 injection field test a shallow co2 injection experiment was performed at the co2fieldlab site near svelvik norway in sept 2011 the gas was injected through a 45 inclined well to a target depth of 20 m its aim was to test various geophysical and geochemical monitoring tools for integrated near surface leakage monitoring a total of 1 67 t of co2 was injected over a period of six days groundwater level was at 60 cm depth and a complex salinity stratification with brackish water overlying fresh and saltwater was observed at the beginning of the experiment four water sampling boreholes were located at each corner of a square configuration of 8 m with the nominal injection at the center from baseline conditions to the post co2 injection phase ph temperature and electrical conduc tivity of the groundwater were measured collecting water samples at three different depths 5 10 and 15 m for analyses of major minor and trace elements ca na so4 cl mg al ba mn ni co b li and isotopes 11b 7li 34sso4 18oso4 87sr 86sr 18oh2o 2hh2o significant changes in chemical and isotope signatures of water over the duration of the experiment indicated two processes 1 binary mixing with seawater and rainwa ter as the possible end members due to a near seashore location and 2 co2 water rock interactions enhanced by dissolved co2 causing acid conditions and favoring rock dissolution the relative contribution of those pro cesses was quantified by a mass balance model and equilibrium calculations this comprehensive geochemical and isotope approach allowed discriminating reactive mechanisms from non reactive mixing processes asso ciated with co2 leaks within an aquifer with a strong conductivity stratification and heterogeneous mineralogy and this approach seems promising for investigating co2 leaks at field scale

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

water table shapes and drain flow rates in shallow drainage systems abstract a relationship between drain flow rate elevation and shape of the water table and recharge intensity in shallow drainage systems is developed from an analytical spatial integration of the boussinesq equation in transient conditions drain flow rates are shown to be the sum of three terms the first one is proportional to the maximum water table elevation and more generally to the steady state flow rate at the same water table elevation the second one is a fraction of the recharge rate of the water table depending on the water table shape the third one accounts for possible changes in water storage in the water table due to its shape changes drain flow rates in shallow drainage systems are shown to be fully predicted by one unique variable that is a function of a combination of the hydraulic conductivity k the drainable porosity f and the drain spacing 2l namely k f2l2 this variable also determines the dynamics of changes in the water table shape and in turn the respective parts of the three terms in the equation it is shown that drainage systems with values of 1 m 1 h 1 respond very fast to recharge events water table shape changes occur very quickly so that the third component of the drain flow can be neglected in that case the equation results in a simplified analytical relationship the reliability of the complete and simplified equations to predict drain flow rates in transient conditions is discussed in relation to in situ measurements

submarine discharge of nutrient enriched fresh groundwater at stinson beach california is enhanced during neap tides the influence of fortnightly spring neap tidal variability on submarine discharge of fresh and saline groundwater was examined at stinson beach california stinson beach is a residential community that utilizes on site systems for wastewater disposal fresh shallow groundwater at the site contains high concentrations of nutrients dissolved inorganic nitrogen din soluble reactive phosphate srp and silicate and human fecal bacteria a groundwater derived freshening and nutrification of the surf zone during neap tides was observed followed by a 4 d increase in chlorophyll a concentrations analytical models and a freshwater budget in the surf zone were used to estimate the saline and fresh discharge of submarine groundwater we estimate fresh groundwater discharge between 1 2 and 4 7 l min21 m21 shoreline during neap tides compared with 0 1 and 0 5 l min21 m21 during spring tides this compares with 15 9 and 22 0 l min21 m21 saline groundwater discharge forced by waves and tides during neap and spring tides respectively despite the smaller total fresh saline flux of groundwater during neap compared with spring tides the larger fresh discharge component during neap tides raises surf zone silicate din and srp by 14 3 5 and 27 respectively relative to spring tides this observed fortnightly pulsing of fresh groundwater derived nutrients was consistent with seaward hydraulic gradients across the fresh part of the beach aquifer which varied due to aquifer overheight near the beach face darcy dupuit estimates of seaward fresh groundwater flow in this area agreed well with the fresh discharge results of the mass balance

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

recharge from an ephemeral stream following wetting front arrival to water table after the infiltration wetting front from a river bed of an ephemeral stream in flood reaches the shallow water table the rate of recharge which is also that of infiltration is affected by the development of a groundwater mound the effect is practically immediate if the water content behind the wetting front is close to saturation an approximate analytical solution is developed in that case which predicts the time dependence of the recharge rate comparison with experimental results in the laboratory shows that the solution is excellent in spite of the assumptions necessary in the derivations as long as the ratio of river width over depth to water table exceeds 2 and as long as the ratio of initial saturated thickness over depth to the water table exceeds 2 5 the analytical solution is essentially exact under most field conditions these ratios are largely exceeded consequently the predictive equation for the time dependence of the recharge is both quite simple to use and adequately accurate for field applications

radon 222 budget in catalina harbor california 2 flow dynamics and residence time in a tidal beach we measured the flux of water through a beach at the head of catalina harbor california by monitoring the water table in a transect of wells perpendicular to the shoreline during a 24 h period the volume of sediments filled and drained the tidal wedge was 7 4 m 3 m shoreline 1 and the flux of water pumped across the beach face was 1 0 0 3 m 3 d 1 m shoreline 1 222 rn concentrations measured in four wells were used to calculate the minimum age of water in the beach radon samples collected below the tidal wedge were not in equilibrium with the production rate suggesting vertical mixing across the base of the tidal wedge the age of water ranged from up to 8 0 d landward of the high water mark to less than 2 0 d in the littoral zone this latter age agreed with an independent estimate of 1 7 0 5 d on the basis of a mass balance for radon at the head of the harbor however a mass balance for water in the tidal wedge was significantly greater 3 0 0 5 d the difference was most likely due to evasion of radon from wet unsaturated sediments water draining out of the beach was a mixture of water that infiltrated the beach on the previous high tide and older water from either below or the back of the tidal wedge

tidal effects on sea water intrusion in unconfined aquifers abstract a variable density groundwater model is used to analyse the effects of tidal fluctuations on sea water intrusion in an unconfined aquifer it is shown that the tidal activity forces the sea water to intrude further inland and it also creates a thicker interface than would occur without tidal effects moreover the configuration of the interface is radically changed when the tidal fluctuations are included this is because of the dramatic changes in the flow pattern and velocity of the groundwater near the shoreline for aquifer depths much larger than tidal amplitudes the tidal fluctuation does not have much effect on how far the sea water intrudes into the aquifer nevertheless a significant change in the configuration of concentration contours because of the effect of tidal fluctuations is observed this change is more noticeable at the top of the aquifer near the water table than at the bottom of the aquifer and is caused by the infiltration of salt water into the top of the aquifer at higher tidal levels a flatter beach slope therefore intensifies this phenomenon the interface configurations do not change noticeably over the course of a tidal cycle neglecting tidal fluctuation effects results in an inaccurate evaluation of the water table elevation at the land end of the aquifer although no distinguishable difference is seen between the water tables near the shoreline where the landward boundary condition is a constant head the effects of tidal fluctuations on sea water intrusion are more pronounced than for cases where the landward boundary condition is a specified flux also it is shown that the effects of tidal fluctuations are more significant for a sloping beach than for a vertical shoreline and the salt water intrudes further inland for the sloping case

a carbon isotope method to quantify groundwater discharge at the land sea interface we present a new method to characterize and quantify groundwater discharge to estuaries and the coastal ocean using data from the pages creek estuary in the cape fear region of southeastern north carolina we show that the concentration and carbon isotopic composition d 14 c and d 13 c values of dissolved inorganic carbon dic can provide a tracer of a single well defined component of the surface water groundwater system in coastal regions the integrated freshwater discharge to an estuary from confined aquifers groundwater from the two shallowest confined aquifers in the cape fear region the castle hayne and the peedee has dic d 14 c values ranging from 2282 to 2829 significantly lower than the radiocarbon content of surficial water table groundwater rivers and streams and seawater in the area d 14 c 52 38 to 197 dic additions from salt marsh decomposition and dic removal via photosynthesis and gas evasion can influence estuarine dic concentrations and dic d 13 c values however none of these processes results in strongly depleted dic d 14 c values because artesian springs are the only significant low d 14 c dic input to the pages creek estuary flood ebb 14 c budgets provide a direct measure of the fraction of the total freshwater inputs to the pages creek estuary that is derived from artesian discharge with this method we have observed a striking range in the relative contribution of artesian flow to the pages creek estuary freshwater budget during november 1999 and april 2001 both periods of low precipitation in southeastern north carolina artesian groundwater discharge could account for essentially all of the pages creek freshwater inputs in contrast during july 2000 a period of high precipitation in this region artesian groundwater made a negligible contribution to the creek s freshwater budget

karst channelled intertidal submarine groundwater discharge sgd conditions the form of the rock pool sessile assemblage abstract freshwater submarine groundwater discharge sgd frequently occurs in areas of karst coastline where karst aquifers are hydraulically connected to the sea though up to 25 of the world s coastline is karst little work has been done to determine the ecological impacts of karst channelled freshwater sgd reported herein are the effects of karst channelled freshwater sgd on the rock pool sessile assemblage in the locale of olhos de agua on the south portuguese coast two quadrat surveys were conducted in eight intertidal rock pools which ranged in freshwater sgd content from 0 to 57 3 salinity and nitrogen no3 and no2 concentrations were measured in the eight surveyed rock pools as well as a further three rock pools on the same plateau three inland groundwater boreholes and the adjacent coastal marine environment there was a strong negative correlation between salinity used as a proxy for freshwater sgd and nitrogen concentration r2 0 98 p

quantifying hydrological and tidal influences on groundwater discharges into coastal waters 1 in coastal aquifers the dynamic mixing zone between intruding seawater and fresh groundwater constitutes a zone of salinity transition that may supply brackish groundwater along with chemical

estimation of submarine groundwater discharge from bulk ground electrical conductivity measurements the utility of bulk ground conductivity bgc measurements in the estimation of submarine groundwater discharge sgd was investigated at four sites covering a range of hydrogeological settings namely cockburn sound australia shelter island usa ubatuba bay brazil and flic en flac bay mauritius at each of the sites bgc was surveyed in the intertidal zone and seepage meters were used for direct measurements of sgd flow rates in the presence of detectable salinity gradients in the sediment a negative correlation between sgd and bgc was recorded the correlation is site specific and is dependent on both the type of sediment and the mixing processes for example at shelter island the maximum mean flow rates were 65 cm d 1 at a bgc of 0 ms cm 1 while at mauritius maximum mean flow rates were 364 cm d 1 at a bgc of 0 ms cm 1 bgc measurements are used to estimate sgd over a large scale and to separate its fresh and saline components extrapolating bgc measurements throughout the study sites yields a total discharge of 2 91 1 59 7 16 and 25 4 103 m3 d 1 km 1 of shoreline with a freshwater fraction of 41 24 29 and 63 at cockburn sound shelter island ubatuba bay and flic en flac bay respectively the results demonstrate that ground conductivity is a useful tracer to survey and separate freshwater and recirculated seawater component of sgd the presented investigation is a subset within a series of experiments designed to compare different methods to investigate sgd co organized and carried out by scor loicz ioc and iaea

laboratory scale saltwater behavior due to subsurface cutoff wall artificial subsurface barriers are among several countermeasures proposed to control seawater intrusion into coastal aquifers we performed experimental and numerical studies to investigate the dynamics of residual saltwater trapped in the storage area upon installation of cutoff walls experimental results showed that after wall installation the residual saltwater wedge initially flattened causing its toe to advance and then gradually retreated before being completely removed from the reservoir behind the cutoff wall the seawat model predicted the behavior of the advancing saltwater intrusion wedge and the retreating residual saltwater after cutoff wall installation flow patterns showed that dispersed saltwater flowed with the freshwater discharge along the mixing zone and over the cutoff wall eventually all remaining saltwater in the storage area was flushed out experimental and numerical results showed that a shorter cutoff wall achieved a faster removal rate of residual saltwater than a higher wall simulations of shorter cutoff wall heights show that a minimum height limit on the cutoff wall is needed to achieve complete removal of residual saltwater residual saltwater will be flushed if the wall height exceeds the thickness of the saltwater wedge at that position

groundwater lens dynamics of atoll islands a variable density groundwater model is used to analyze the effects of various controls on the size of the freshwater lens the structure of the transition zone and the propagation of tidal fluctuations in a two layer atoll island groundwater system modeling results indicate that mixing of fresh water and saltwater occurs primarily as a result of oscillating vertical flow due to tidal fluctuations and depends to a lesser extent on transverse dispersion along the dominantly horizontal recharge discharge path of flow the controls on the amount of mixing are 1 the accumulated vertical distance which increases with tidal range and is restricted by vertical permeabilities and 2 vertical longitudinal dispersion comparison of cross sectional simulations of atoll islands using nontidal and tidal models shows that the nontidal model must use artificially high values of transverse dispersivity to compensate for the lack of tidally driven vertical mixing processes although the tidal model has high computational requirements it can be used to calibrate vertical permeabilities and is best suited for problems dealing with groundwater resource evaluations hydrologic events and hydrologic processes the limitations of the nontidal model are that it cannot be used for calibration of vertical permeabilities and will not realistically simulate those cases in which transition zones are thick or recharge low

dynamic hydrologic and biogeochemical processes drive microbially enhanced iron and sulfur cycling within the intertidal mixing zone of a beach aquifer intertidal aquifers host a reactive zone comprised of fe mineral coated sands where fresh and saline groundwaters mix this zone may significantly influence the export of c n p fe and other metals in submarine groundwater discharge sgd toward determining the roles of microbes in fe and s mineralization and the interplay of microbiology with geochemistry and physical hydrology we conducted a biogeochemical study of pore waters at cape shores delaware here fresh groundwater provides fe ii which precipitates as feiiiooh predominantly through microbial fe ii oxidation candidate division op3 was the dominant microbial group associated with fe ii and fe iii rich regions of the aquifer suggesting that this uncharacterized phylum may be involved in fe ii oxidation saline water brings o2 sulfate and organic c into the intertidal mixing zone microbial reduction of sulfate produces sulfide that is transported to the fe mineralized zone leading to the transformation of feooh to fe ii sulfides microbial populations are structured by the availability of chemical species supplied along groundwater flow paths seasonal changes in the relative supply of fresh and saline groundwater affect solute fluxes and therefore microbial controls on the location and composition of the fe mineralized zone ultimately the composition extent and dynamics of the fe mineralized zone will affect the sequestration affinity and residence time of solutes bound for export to coastal oceans through sgd

large explosive source wide recording aperture seismic profiling on the columbia plateau washington clear subsurface seismic images have been obtained at low cost on the columbia plateau washington the columbia plateau is perhaps the most notorious of all bad data areas because large impedance contrasts in surface flood basalts severely degrade the seismic wavefield this degradation was mitigated in this study via a large explosive source wide recording aperture shooting method the shooting method emphasizes the wide angle portion of the wavefield where fermat s principle guarantees reverberation will not interfere with the seismic manifestations of crucial geologic interfaces the basalt diving wave normally discarded in standard common midpoint cmp seismic profiling can be used to image basalt velocity structure via traveltime inversion maximum depth penetration of the diving wave tightly constrains basalt sediment interface depth an arrival observed only at shot receiver offsets greater than 15 km can be used to determine the velocity and geometry of basement via simultaneous inversion

water table fluctuation in soils overlying semi confined aquifers in response to time varying replenishment abstract the water table height in drained agricultural land depends on time varying replenishment that is due to the vertical downward recharge from irrigation or rainfall and in some cases to the upward vertical leakage from a semi confined aquifer the downward recharge may be assumed to vary exponentially with time whereas the upward leakage may be expressed as a function of the unknown water table height furthermore the rising of the water level in the field drainage system that may cause an inverse flow from the drains towards the soil is introduced through a properly defined boundary condition a non homogeneous form of the boussinesq equation that is used to describe this particular drainage problem is solved for three different initial conditions the same drainage problems were solved numerically by using the finite element method comparison between analytical and numerical solutions shows satisfactory agreement from the analytical solutions we obtain the non dimensional water table height at the midpoint between the drains and the non dimensional discharge of the drains per unit drained area as functions of non dimensional time and constants describing the aforementioned drainage conditions variation of these functions has also been illustrated graphically in non dimensional diagrams these can be used to show the sensitivity to various sets of parameter values and to calculate easily the water table height and the drain discharge in practical problems

effects of beach slope breaks on nearshore groundwater dynamics interactions between fresh groundwater and seawater affect significantly the nearshore pore water flow which in turn influences the fate of nutrients and contaminants in coastal aquifers prior to discharge to the marine environment field investigations and numerical simulations were carried out to examine the groundwater dynamics in the intertidal zone of a carbonate sandy aquifer on the tropical island of rarotonga cook islands the study site was featured by distinct cross shore slope breaks on the beach surface measured pore water salinities revealed different distributions under the influences of different beach profiles inland heads and tidal oscillations fresh groundwater was found to discharge around a beach slope break located in the middle area of the intertidal zone the results indicate a strong interplay between the slope break beach morphology and tidal force in controlling the nearshore groundwater flow and solute transport the fresh groundwater discharge location was largely determined by the beach morphology in combination with the tidal force the nearshore groundwater flow can be very sensitive to beach slope breaks which induce local circulation and flow instabilities as slope breaks are a common feature of beaches around the world these results have important general implications for future studies of nutrients transport and transformations in nearshore aquifers and associated fluxes via submarine groundwater discharge

boundary integral solution to seawater intrusion into coastal aquifers the boundary integral equation method is used to solve problems of seawater intrusion into a freshwater aquifer that is being pumped the transient problem of intrusion lens type into a deep aquifer is solved as is the steady state problem of intrusion wedge type into a shallow aquifer both cases are compared with analytical solutions that are available for simple geometries the numerical models uses the dupuit forchheimer approximation to reduce the three dimensional problem to two dimensions it then uses the ghyben herzberg approximation which simplifies the treatment of flow in the saltwater region a special potential eliminates the need to track explicitly the freshwater saltwater interface the numerical program adds to the capability of the general groundwater basin model which was based on the same techniques

modelling of water table variation in response to time varying recharge from multiple basins using the linearised boussinesq equation a mathematical model is presented to describe the variations of the water table in an unconfined aquifer due to time varying recharge applied from four rectangular basins the model is developed by solving the linearised boussinesq equation using the extended finite fourier cosine transform the time varying recharge rate is approximated by a number of piecewise linear elements of different lengths and slopes depending on the nature of the variation in recharge rate application of this model for the prediction of water table fluctuations and in the sensitivity analysis of various controlling parameters on the aquifer response is demonstrated in an example

inverse modelling for freshwater lens in small islands kish island persian gulf a number of challenges including instability nonconvergence nonuniqueness nonoptimality and lack of a general guideline for inverse modelling have limited the application of automatic calibration by generic inversion codes in solving the saltwater intrusion problem in real world cases a systematic parameter selection procedure for the selection of a small number of independent parameters is applied to a real case of saltwater intrusion in a small island aquifer system in the semiarid region of the persian gulf the methodology aims at reducing parameter nonuniqueness and uncertainty and the time spent on inverse modelling computations subsequent to the automatic calibration of the numerical model uncertainty is analysed by constrained nonlinear optimization of the inverse model the results define the percentage of uncertainty in the parameter estimation that will maintain the model inside a user defined neighbourhood of the best possible calibrated model sensitivity maps of both pressure and concentration for the small island aquifer system are also developed these sensitivity maps indicate higher sensitivity of pressure to model parameters compared with concentration these sensitivity maps serve as a benchmark for correlation analysis and also assist in the selection of observations points of pressure and concentration in the calibration process copyright 2012 john wiley sons ltd

advection and diffusion in a variable salinity confining layer a numerical model that simulates groundwater flow and solute transport for cases in which fluid properties are variable was applied in one dimension vertical to the shallow low permeability clayey confining layer in donana national park in southwestern spain the salinity in the 80 m thick confining layer decreases from a brine near the land surface to fresh water near its base results of model simulations indicate that the system could be in or close to a steady state condition the model calibration was very sensitive to small variations in individual model parameters and was nonunique in the sense that equally good calibrations could be achieved by compensatory joint perturbations in the permeability diffusion coefficient and overall governing hydraulic gradient at present there is probably an upward flow of the order of 1 mm yr 1 to 1 cm yr 1 and a balance in the solute flux between upward advection and downward diffusion the time scale of calculated responses to changes in boundary conditions in this low permeability system ranges from thousands to hundreds of thousands of years when considering extremes within the range of uncertainty of values of the evaluated parameters

the columbia river basalts between 17 million and 6 million years ago 200 000 square kilometers of the american northwest were flooded by basaltic lava that erupted through fissures in the crust up to 150 kilometers long larger individual eruptions covered over a third of the columbia plateau in a few days the lavas represent partial melts of the earth s mantle that were only slightly modified by near surface upper crustal processes the abundant chemical and mineralogical data now available offer an opportunity to study mantle composition and the processes involved in the evolution of the earth s crust

water table fluctuation in aquifers overlying a semi impervious layer due to transient recharge from a circular basin summary an analytical solution of a linearised form of boussinesq equation is presented in this paper to describe the water table fluctuation in unconfined aquifers overlying a semi impervious layer in response to transient recharge this solution does not require the common assumption of an impervious formation underlain the unconfined aquifer on the contrary it shows that even when the hydraulic conductivity of the semi impervious layer is several orders of magnitude less than the aquifer hydraulic conductivity downward leakage can be important and can lead to large overestimations of water table heights if it is ignored the rate of recharge is considered to decrease exponentially with time during a single cycle of recharge while two cycles of time varying recharge are approximated by continuous elements described by nth degree polynomials numerical solution of the non linear boussinesq equation was implemented to validate the applied linearisation

electromagnetic sounding in the columbia basin yakima washington a controlled source electromagnetic csem survey was conducted near yakima washington to map the thickness and resistivity of a thick volcanic sequence overlying a sedimentary section and to infer structure in the sediments the survey was conducted with a frequency domain system employing loop transmitters 400 500 m on a side and three component squid magnetometer receivers separated from the loop by 1 to 5 km data collected along a 30 km profile orthogonal to regional strike were interpreted initially with 1 d layered models which were then pieced together to make a geoelectric section induction logs in a 5000 m exploration hole at one end of the profile agree very well with the csem soundings made around the hole the geoelectric section reveals a smoothly varying thickness of volcanics with a pronounced anticlinal structure approximately concordant with a surface topographic ridge to assess the validity of inferring lateral structure from 1 d interpretations we made scale models of an anticlinal structure and of a surface inhomogeneity and conducted csem measurements over the scale models layered model inversions of these data show that the anticlinal structure and its location are very well determined by 1 d inversion but its height and width are not accurately determined csem sounding over the surface inhomogeneity model shows that this feature does not significantly degrade the interpretation of a deep target layer in this setting a geoelectric section made up from 1 d interpretations provides good qualitative measures of subsurface structure and also provides excellent starting models for detailed 2 d or 3 d modeling

saltwater freshwater mixing dynamics in a sandy beach aquifer over tidal spring neap and seasonal cycles the biogeochemical reactivity of sandy beach aquifers is closely linked to physical flow and solute transport processes thus a clearer understanding of the hydrodynamics in the intertidal zone is needed to accurately estimate chemical fluxes to the marine environment a field and numerical modeling study was conducted over a 1 year timeframe to investigate the combined effects of tidal stage spring neap variability in tidal amplitude and seasonal inland water table oscillations on intertidal salinity and flow dynamics within a tide dominated microtidal sandy beach aquifer measured and simulated salinities revealed an intertidal saline circulation cell with a structure and cross sectional mixing zone area that varied over tidal spring neap and seasonal time scales the size of the circulation cell and area of the mixing zone were shown for the first time to be most affected by seasonal water table oscillations followed by tidal amplitude and tidal stage the intertidal circulation cell expanded horizontally and vertically as the inland water table declined displacing the fresh discharge zone and lower interface seaward over monthly spring neap cycles the center of the circulation cell shifted from beneath the backshore and upper beachface to the base of the beach salinity variations in the intertidal zone over semidiurnal tidal cycles were minimal the dynamics of the circulation cell were similar in simulations with and without a berm the highly transient nature of intertidal salinity over multiple time scales may have important implications for the types and rates of chemical transformations that occur in groundwater prior to discharge to the ocean

water table fluctuation in a sloping aquifer with transient recharge abstract an analytical solution of the linearized boussinesq equation with a complex transient recharge function is presented to describe the water table fluctuation in a sloping aquifer of finite width the solution is obtained by using an eigenvalue eigenfunction expansion method some previously known solutions for different recharge functions have been shown to be special cases of the present general solution applications of the solutions in prediction of the spatio temporal distribution of the water table in a ditch drainage system are illustrated with the help of synthetic examples

direct determination of total and fresh groundwater discharge and nutrient loads from a sandy beachface at low tide cape henlopen delaware total groundwater discharge from a sandy seepage site to the delaware bay at cape henlopen delaware was determined together with the associated nutrient loads by trapping the discharge from a length of the shoreline in a tidal pond at low tide and measuring the discharge of the trapped water through a weir at steady state salinity was used to parse the total groundwater discharge from the beachface at low tide into a recycled estuarine component and a new fresh groundwater component based on 16 measurements over 18 months average total discharge and average freshwater discharge at low tide were found to be 2 76 6 1 08 and 0 87 6 0 43 l min21 m21 of shoreline respectively the estuarine component of discharge varied with the maximum height of the immediately preceding high tide owing to the control of freshwater discharge by the average upland hydraulic gradient away from the beach individual measurements of freshwater discharge at low tide represent a good estimate of this discharge component over time scales of hours to days based on the nutrient concentrations in the discharge waters nutrient loads from the beach to the adjacent estuary at low tide were 148 6 79 7 5 6 5 1 and 197 6 101 mmol min21 m21 of shoreline for total dissolved n p and si respectively groundwater discharge and these nutrient fluxes contribute significantly to the unusually productive benthic communities that inhabit the seepage and nearby intertidal zones estuaries receive their primary inputs from fluvial discharges and exchange with the ocean but it is increasingly evident that atmospheric deposition and direct groundwater discharges from uplands also play a significant role in estuarine biogeochemical processes paerl 1997 burnett et al 2003 although groundwater discharge is thought to represent only a small fraction of the total freshwater discharge to estuaries and the ocean there is increasing evidence that nutrients and contaminants associated with this discharge may play a more significant ecological role than implied by the relatively small discharge valiela et al 1992 burnett et al 2003 shaw 2003 this is particularly true in coastal plain settings where nutrient and contaminant inputs to the groundwater from domestic industrial municipal and agricultural practices may be high the hydraulic conductivity of soils and aquifer sediments is large and the topographically driven groundwater flow to shallow upland streams is low submarine groundwater discharge in many settings appears to be associated with productive benthic communities johannes and hearn 1985 bussmann et al 1999 zipperle and reise 2005 and may influence sediment water exchange through the imposition of hydraulic gradients the modification of subbottom flow paths and the alteration of diagenetic reactions and rates moore

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

the motion of coastal groundwater in response to the tide abstract problems of seawater intrusion into confined coastal aquifers under the influence of the tide are analysed with the use of two different models the freshwater saltwater interface model and the dispersion model the freshwater saltwater interface model which describes the motion of the groundwater level and the freshwater saltwater interface in response to the tide is applied to the confined coastal aquifers in the estuary of the naka river and yura district of gogo island in japan the position of the outlet of the confined groundwater into the sea and also the degree of spreading of the aquifer s thickness which is assumed to vary exponentially with horizontal distance are estimated from the non dimensional analysis based on the dispersion model it is found that salt water intrudes furthest inland at the time at which the sea level reaches the mean sea level in the ebb tide stage consistent with the result obtained by the freshwater saltwater interface model and the transition zone from fresh water to salt water becomes widest at that time

response of the mediterranean and dead sea coastal aquifers to sea level variations 1 the present study examines the response of groundwater systems to expected changes in the mediterranean sea rise of 1cm yr and dead sea levels decline of 1 m yr a fast response is observed in the dead sea coastal aquifer exhibited both in the drop of the water levels and in the location of the fresh saline water interface no such effect is yet observed in the mediterranean coastal aquifer as expected numerical simulations using the feflow software show that the effect of global sea level rise depends on the coastal topography next to the shoreline a slope of 2 5 is expected to yield a shift of the interface by 400 m after a rise of 1m 100 years whereas a vertical slope will yield no shift reduced recharge due to climate change or overexploitation of groundwater also enhances the inland shift of the interface

the effect of submarine groundwater discharge on nutrient and salinity regimes in a coastal lagoon off perth western australia abstract submarine groundwater discharge sgd into a coastal lagoon off perth western australia contains nitrate and silicate in concentrations two orders of magnitude higher than those of the receiving waters this discharge delivers enough nitrate to replace that dissolved in the lagoon water mass about every eight days and enough silicate to replace the lagoon silicate in about 48 days the delivery rate of nitrate nitrogen by sgd is equal to about 48 of that required for observed growth rates of lagoon macrophytes surface salinity is lower close to the shore as a result of sgd during calm conditions a salinity front was observed in the lagoon with a nearshore pool of nutrient enriched water floating above the more saline ocean water

exploration in the basalt covered areas of the columbia river basin washington using electromagnetic array profiling emap the electromagnetic array profiling emap exploration method was tested at three basalt covered locations on the columbia plateau in central washington state three 16 km survey lines were located to intersect test wells drilled by shell the data were emap filtered and inverted using a nonlinear 1 d riccati approach developed for conventional magnetotelluric mt processing large and small features on the resulting resistivity cross sections produced by emap filtering near the drill hole closely approximated the electric induction logs sedimentary units within the survey area appear to be thin with some thickening indicated toward the center of the basin structuring within the sediments is mild within the limits of the survey although there is appreciable structure within the miocene flood basalts on one test line

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

numerical and experimental study of seepage in unconfined aquifers with a periodic boundary condition the assessment of groundwater conditions within an unconfined aquifer with a periodic boundary condition is of interest in many hydrological and environmental problems a two dimensional numerical model for density dependent variably saturated groundwater flow sutra voss c i 1984 sutra a finite element simulation model for saturated unsaturated fluid density dependent ground water flow with energy transport or chemically reactive single species solute transport us geological survey national center reston va is modified in order to be able to simulate the groundwater flow in unconfined aquifers affected by a periodic boundary condition the basic flow equation is changed from pressure form to mixed form the model is also adjusted to handle a seepage face boundary condition experiments are conducted to provide data for the groundwater response to the periodic boundary condition for aquifers with both vertical and sloping faces the performance of the numerical model is assessed using those data the results of pressure and mixed form approximations are compared and the improvement achieved through the mixed form of the equation is demonstrated the ability of the numerical model to simulate the water table and seepage face is tested by modelling some published experimental data finally the numerical model is successfully verified against present experimental results to confirm its ability to simulate complex boundary conditions like the periodic head and the seepage face boundary condition on the sloping face c 1999 elsevier science b v all rights reserved

regional scale impact of tidal forcing on groundwater flow in unconfined coastal aquifers summary this paper considers the impact of tidal forcing on regional groundwater flow in an unconfined coastal aquifer numerical models are used to quantify this impact for a wide range of hydrogeological conditions both a shallow and a deep aquifer are investigated with regard to three dimensionless parameter groups that determine the groundwater flow to a large extent analytical expressions are presented that allow for a quick estimate of the regional scale effect of tidal forcing under the same conditions as used in the numerical models quantitatively the results in this paper are complementary to previous studies by taking into account variable density groundwater flow dispersive salt transport and a seepage face in the intertidal area qualitatively the results are in line with previous investigations the time averaged hydraulic head at the high tide mark increases upon a decrease of each of the three considered dimensionless parameter groups r including the ratio of the hydraulic conductivity and the precipitation excess a the slope of the intertidal area and al the ratio of the width of the fresh water lens and the tidal amplitude the relative change of the location and the hydraulic head of the groundwater divide which together characterize regional groundwater flow increase as a and al decrease but decrease as r decreases the difference between the analytical solutions and numerical results is small therefore the presented analytical solutions can be used to estimate the bias that is introduced in a numerical model if tidal forcing is neglected the results should be used with caution in case of significant wave forcing as this was not considered

tidally induced groundwater circulation in an unconfined coastal aquifer modeled with a hele shaw cell we use a scaled hele shaw cell to mimic tidally induced nearshore groundwater motion in an unconfined aquifer the low slope angle of sandy beaches contributes to a strongly asymmetric pattern of fluid exchange across the water sediment interface during tidal cycles this asymmetry leads to a time averaged groundwater circulation centered beneath the low tide level horizontal and vertical components of motion are of the same order horizontal seaward flow extends a significant depth beneath the interface consonant with a time averaged water table that is elevated above mean sea level providing the hydraulic gradient necessary to drive this deeper export of mass equal to the time averaged inflow by infiltration this tidally forced flow behavior likely contributes to observed fluctuations in submarine seepage rates moreover the circulation largely involves a subsurface cycling of seawater that infiltrates during the rising tide measurements of submarine seepage near the tidal zone therefore likely involve this cycled seawater as well as freshwater flows

monitoring of tidal influences on the saline interface using resistivity traversing and cross borehole resistivity tomography summary tidal influences on the saline interface of a shallow unconfined aquifer have been investigated by using both dc resistivity traversing and cross borehole resistivity tomography crt variations in bulk resistivity structure obtained through resistivity traversing provide a clear general picture of the structure of the saline interface and its mixing zone on all three resistivity traverses there are also indications that a small degree of mixing of saline and fresh water is occurring ahead of the main saline boundary for one of the traverses much more detail of variations in resistivity structure is provided by crt utilising three 10 m long electrode strings installed at 10 m separation crt images of the saline mixing zone do not reveal any significant difference between low and high tide for tidal ranges of about 2 m but for a tidal range of approximately twice this clearly show effects due to both increased wave run up and tidal head correlation of the bulk resistivity with fluid resistivity values measured in parallel bores suggests that although there is no apparent widening of the mixing zone during the tidal cycle significant variations in salinity do occur which can be envisaged in terms of the horizontal movement of near vertical salinity contours