modelling of the evolution of ground waters in a granite system at low temperature the stripa ground waters sweden abstract from chemical data collected by nordstrom and his colleagues on stripa ground waterswe have tried to model the evolution of the chemical composition of a ground water in a granitic system at low temperature the existence of two end member ground water compositions made it possible first to test the conventional model of a geothermal system according to which an overall equilibrium between the waters and a given mineral assemblage can be defined and then to show that such a model could be extended to low temperatures 10 c conversely if we know the mineral assemblage the equilibration temperature and the charge of the mobile ions in this case cl the composition of the solution is entirely fixed in our model of the stripa ground waters the existence of two end member ground water compositions can be explained by an evolution from a kaolinite albite laumontite equilibrium to a prehnite albite laumontite equilibium the latter requiring less al than the former we have also emphasized the importance of the cl ion concentrions ofof the ground waters because they cab be considered as indicators of the degree of reaction progress between rock and water thus determining the degree of equilibration of the system

fluid inclusions in the stripa granite and their possible influence on the groundwater chemistry fluid inclusions in quartz and calcite of the proterozoic stripa granite central sweden demonstrate that the rock and its fracture fillings have a complex evolutionary history the majority of inclusions indicate formation during a hydrothermal stage following emplacement of the stripa pluton total salinities of quartz inclusions range from 0 18 eq wt nacl for unfractured rock and from 0 10 eq wt for fractured rock vein calcites contain up to 25 eq wt nacl but the inclusion size is larger and the population density is lower homogenization temperatures are 100 150 c for unfractured rock and 100 250 for fractured rock pressure corrections assuming immediate post emplacement conditions of 2 kbar give temperatures about 160 c higher measurements of fluid inclusion population densities in quartz range from about 108 inclusions cm3 in grain quartz to 109 inclusions cm3 in vein quartz residual porosity from inclusion densities has been estimated to be at least 1 which is two orders of magnitude greater than the flow porosity breakage and leaching of fluid inclusions is proposed as an hypothesis for the origin of major solutes na ca cl in the groundwater evidence for the hypothesis is based on 1 mass balance only a small fraction of the inclusions need to leak to account for salt concentrations in the groundwater 2 chemical signatures brcl ratios of fluid inclusion leachates 0 0101 match those ratios for the deep groundwaters 0 0107 3 leakage mechanisms micro stresses from isostatic rebound or mining activities acting on irregular shaped inclusions could cause breakage and provide connection with the flow porosity and 4 experimental studies water forced through low permeability granites leach significant quantities of salt this hypothesis is consistent with the available data although alternate hypotheses cannot be excluded

effects of episodic rainfall on a subterranean estuary numerical simulations were conducted to examine the effect of episodic rainfall on nearshore groundwater dynamics in a tidally influenced unconfined coastal aquifer with a focus on both long yearly and short term daily behaviour of submarine groundwater discharge sgd and seawater intrusion swi the results showed non linear interactions among the processes driven by rainfall tides and density gradients rainfall induced infiltration increased the yearly averaged fresh groundwater discharge to the ocean but reduced the extents of the saltwater wedge and upper saline plume as well as the total rate of seawater circulation through both zones overall the net effect of the interactions led to an increase of the sgd the nearshore groundwater responded to individual rainfall events in a delayed and cumulative fashion as evident in the variations of daily averaged sgd and salt stored in the saltwater wedge quantifying the extent of swi a generalized linear model glm along with a gamma distribution function was developed to describe the delayed and prolonged effect of rainfall events on short term groundwater behaviour this model validated with results of daily averaged sgd and swi from the simulations of groundwater and solute transport using independent rainfall datasets performed well in predicting the behaviour of the nearshore groundwater system under the combined influence of episodic rainfall tides and density gradients the findings and developed glm form a basis for evaluating and predicting sgd swi and associated mass fluxes from unconfined coastal aquifers under natural conditions including episodic rainfall

the extent of lateral water movement in the sediments of a new england salt marsh models of depth averaged hydraulic head are used with data from a water balance study in a new england salt marsh to describe horizontal pore water water fluxes near a creek bank three hydrologically distinct regions are identified in the sediment in the marsh studied semidiurnal tides may drive an oscillating horizontal flux in the narrow region within about 2 5 m of the creek bank farther than 15 m from the creek there is essentially no horizontal water movement in the region between 2 5 and 15 m drainage to the creek is driven by alternating periods of surface flooding and nonflooding due to the spring neap variation in tidal amplitudes there is little or no input of fresh groundwater to the marsh sediment at this site the spatial extent of the drained region depends on the duration of the nonflooded period the morphology of the sediment surface and the ratio of hydraulic conductivity to specific storage of the sediment

groundwater chemistry and water rock interactions at stripa groundwaters from near surface to a depth of 1232 m in the stripa granite have been sampled and analyzed for major and trace constituents the groundwater composition consists of two general types a typical recharge water of ca hco3 type 700 m depth of high ph 8 10 that reaches a maximum of 1250 mg l in total dissolved solids tds intermediate depths show mixtures of the two types that are highly fracture dependent rather than depth dependent any borehole can vary significantly and erratically in tds for either a horizontal or vertical direction the general transition from ca hco3 type to na ca cl type correlates with the depth profile for hydraulic conductivity that drops from 10 8 m s to 10 11 m s or lower thermomechanical stress from heater experiments clearly shows an effect on the groundwater composition that could be caused by changing flow paths leakage of fluid inclusions or both dissolution and precipitation of calcite fluorite and barite aluminosilicate hydrolysis and addition of a saline source possibly fluid inclusion leakage play the major roles in defining the groundwater composition the low permeability of the stripa granite has produced a groundwater composition that appears intermediate between the dilute shallow groundwaters typical of recharge in a crystalline rock terrain and the saline waters and brines typical of cratonic shield areas at depth

progressive failure of aznalcollar dam using the material point method the material point method which combines features of finite element and particle discretisation methods has been extended to solve coupled flow deformation problems in granular media the method is applied to simulate the construction and failure of the aznalcollar dam the brittle foundation clay is characterised by means of a strain softening mohr coulomb elasto plastic model the rupture process of the foundation is associated with a progressive failure mechanism the model predicts the development of a localised shearing band that initiates at the toe of the dam at some intermediate stage of construction and propagates downstream and upstream the shape and position of the failure surface reproduce actual field observations

groundwater response to the tide in wetlands observations from the gillman marshes south australia we present results from a series of piezometers installed in the foreshore flat and mangrove environments of the gillman marshes south australia in an interdisciplinary study of the propagation of the ocean tide into the coastal aquifers a unique feature of the analysis is that all water level records were harmonically analysed so that the behaviour of the four major tidal constituents could be independently examined the main findings were that 1 the decay of the groundwater tide in the coastal aquifers was greater than that predicted by the ferris solution a theoretical model has been developed and applied to the study site the model suggests that this behaviour is due to the occurrence of a time delay in the darcian response in the shelly and muddy sand substrate 2 when the tide is incident over a gently sloping bank the time delay in response gives rise to a spiked signal in which high water is confined to a small fraction of the tidal cycle and 3 at the coastal interface tidal propagation across a sloping bank causes a rise in the water table relative to mean sea level which is proportional to the variance of tidal elevation and inversely proportional to the decay constant of the groundwater tide the model developed in this study is also applicable to other coastal groundwater systems with tidal influence

advective flow through the upper continental shelf driven by storms buoyancy and submarine groundwater discharge data from monitoring wells on the carolina usa continental shelf require a reevaluation of pore water exchange across the seafloor temperature salinity and 226ra data from 3 offshore wells require rapid and frequent pore water exchange to depths of several meters through sands and other permeable sediments the exchange is driven by tidal pumping storms buoyancy and submarine groundwater discharge tidal pumping causes semidiurnal temperature cycles in one well that can only be explained by rapid fluid flow the effect of large storms is evident in sudden temperature changes 2 4 m below the seabed in two wells these changes require considerable pore water exchange sudden cooling of the ocean may cause pore waters to become buoyant with respect to the ocean and trigger pore water convection to several meters depth as observed in one well the wells also display frequent large factor of ten changes in 226ra activity this requires a substantial input of 226ra enriched fluids to replace 226ra that is lost during exchange events these data support a fourth flow process which is groundwater seeping from the underlying limestone the pore spaces in the overlying sand provide a temporary reservoir for these fluids we conclude that pore water residence times in 2 4 m thick sands on this continental margin are on the order of a few months or less

geochemistry and origin of saline groundwaters in the fennoscandian shield chemical and isotopic analyses of water from drill holes and mines throughout the fennoscandian shield show that distinct layers of groundwater are present an upper layer of fresh groundwater is underlain by several sharply differentiated saline layers which may differ in salinity relative abundance of solutes and o h sr and s isotope signature saline groundwater can be classified into four major groups based on geochemistry and presumed origin brackish and saline waters from 50 200 m depth in coastal areas around the baltic sea exhibit distinct marine chemical and isotopic fingerprints modified by reactions with host rocks these waters represent relict holocene seawater inland three types of saline groundwater are observed an uppermost layer of brackish and saline water from 300 900 m depth saline water and brines from 1000 2000 m depth and superdeep brines which have been observed to a depth of at least 11 km in the drill hole on the kola peninsula u s s r electrical and seismic studies in shield areas suggest that such brines are commonly present at even greater depths the salinity of all inland groundwaters is attributed predominantly to water rock interaction the main solutes are cl ca na and mg in varying proportions depending on the host rock lithology the abundance of dissolved gases increases with depth but varies from site to site the main gas components are n2 ch4 up to 87 vol and locally h2 the 13c value for methane is highly variable 25 to 46 and it is suggested that hydrothermal or metamorphic gases trapped within the surrounding rocks are the most obvious source of ch4 the uppermost saline water has meteoric oxygen hydrogen isotopic compositions whereas values from deeper water plot above the meteoric water line indicating considerably longer mean residence time and effective low temperature equilibration with host rocks geochemical and isotopic results from some localities demonstrate that the upper saline water cannot have been formed through simple mixing between fresh water and deep brines but rather is of independent origin the source of water itself has not been satisfactorily verified although superdeep brines at least may contain a significant proportion of relict precambrian hydrothermal or metamorphic fluids

introduction to the hydrogeochemical investigations within the international stripa project abstract the international stripa project 1980 1990 has sponsored hydrogeochemical investigations at several subsurface drillholes in the granitic portion of an abandoned iron ore mine central sweden the purpose has been to advance our understanding of geochemical processes in crystalline bedrock that may affect the safety assessment of high level radioactive waste repositories more than a dozen investigators have collected close to a thousand water and gas samples for chemical and isotopic analyses to develop concepts for the behavior of solutes in a granitic repository environment the stripa granite is highly radioactive and has provided an exceptional opportunity to study the behavior of natural radionuclides especially subsurface production extensive microfracturing low permeability with isolated fracture zones of high permeability unusual water chemistry and a typical granitic mineral assemblage with thin veins and fracture coatings of calcite chlorite seriate epidote and quartz characterize the site preliminary groundwater flow modeling indicates that the mine has perturbed the flow environment to a depth of about 3 km and may have induced deep groundwaters to flow into the mine

aznalcollar dam failure part 1 field observations and material properties the paper describes the failure of aznalcollar dam in southern spain in april 1998 the rockfill dam slid forward and released a flow of acid saturated tailings the geology and geomorphology of the site are described the results of a detailed laboratory testing programme on the tailings material and on the overconsolidated high plasticity foundation clay are given special attention is paid to the identification of cementation of the tailings and to the strength and consolidation properties of the foundation clay failure features are interpreted on the basis of the field evidence taking into account the measured geotechnical properties of the materials involved

post failure stage simulation of a landslide using the material point method abstract traditional numerical methods such as the finite element method are usually used to analyse the slope response in the pre failure and failure stages under the assumption of small deformations however these methods are generally unsuitable for simulating the post failure stage of landslides due to the occurrence of large deformations the material point method mpm is a numerical technique capable to overcome this limitation in the present study mpm is used to carry out a two dimensional analysis of the run out process of the senise landslide that occurred in southern italy in 1986 accuracy of the method is assessed by comparing the final geometry of the landslide observed just after the event and the magnitude of the measured displacements to those provided by the numerical simulation the calculation results match fairly well the observed ones when two slip surfaces detected by the inclinometers are accounted for in the analysis an additional improvement of simulation is achieved taking into account the presence of some buildings and retaining walls existing in that area kinematics of the landslide is also investigated the results show that the senise landslide was a translational slide moving along two planar slip surfaces located in thin layers of clayey silt in addition these results demonstrate that a suitable analysis of the post failure stage can lead to a better understanding of the complex mechanical processes that characterise some landslides and thereby help in establishing the most effective stabilization measures

groundwater flow and salt transport in a subterranean estuary driven by intensified wave conditions a numerical study based on a density dependent variably saturated groundwater flow model was conducted to investigate flow and salt transport in a nearshore aquifer under intensified wave conditions caused by offshore storms temporally varying onshore hydraulic gradients due to wave setup were determined as the seaward boundary condition for the simulated aquifer the results showed a rapid increase in influxes across the aquifer ocean interface in response to the wave event followed by a more gradual increase in effluxes the upper saline plume first widened horizontally as the wave setup point moved landward it then expanded vertically with recirculating seawater pushed downward by the wave induced hydraulic gradient the time for the salt distribution to return to the prestorm condition was up to a hundred days and correlated strongly with the time for seawater to recirculate through the aquifer the pathways of recirculating seawater and fresh groundwater were largely modified by the wave event these pathways crossed through the same spatial locations at similar times indicating significant salt freshwater mixing the flow and salt transport dynamics were more responsive to wave events of longer duration and higher intensity especially in more permeable aquifers with lower fresh groundwater discharge despite their larger response aquifers with higher permeability and beach slope recovered more rapidly postevent the rapid recovery of the flows compared with the salinity distribution should be considered in field data interpretation due to their long lasting impact wave events may significantly influence the geochemical conditions and the fate of chemicals in a subterranean estuary key points intensified waves perturb flow and transport in a subterranean estuary lengthy period months for salinity distribution to recover from a wave event exchange fluxes and flows respond and recover rapidly following a wave event

tide induced recirculation across the aquifer ocean interface a parametric analysis is conducted to examine the influence of tides inland hydraulic conditions and aquifer properties on the rate of tide induced seawater recirculation through the nearshore aquifer understanding such influence is crucial for accurate prediction of subsurface chemical fluxes to coastal waters via groundwater discharge the analysis is based on numerical simulations of density dependent groundwater flow in a coastal aquifer subject to tidal oscillations across a sloping beach face the results reveal that the amplitude of tidal oscillations and the inland hydraulic gradient are the primary parameters controlling the tide induced recirculation rates significant tidal exchange is expected when the ratio of tidal to inland forcing is large the horizontal tidal shoreline excursion and aquifer depth both display asymptotic behavior influencing recirculation rates for only small values where the exchange process is limited by the potential for infiltration and shallowness of the aquifer respectively the analysis also indicates that tidal effects increase density driven recirculation rates due to enhanced convective flow within the saltwater wedge

runout evaluation of the oso landslide with the material point method long runout landslides can cause significant damage and represent one of the most important problems in geotechnical engineering understanding the mechanics of the landslide runout process is impo

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

evaluation of the groundwaters from the stripa mine using stable chlorine isotopes groundwater samples and a rock leachate sample from the stripa mine and south central sweden have been analysed for their 37cl values results reveal that the salinity found at depth in the groundwater is most likely derived form water rock interaction the overall distribution is one of 37cl enrichment with depth and with chloride concentration this trend is comparable to other sites in the fennoscandian shield where it is believed that deep groundwaters derive their 37cl values from the local bedrock

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

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

high cesium concentrations in groundwater in the upper 1 2 km of fractured crystalline rock influence of groundwater origin and secondary minerals abstract dissolved and solid phase cesium cs was studied in the upper 1 2 km of a coastal granitoid fracture network on the baltic shield aspo hard rock laboratory and laxemar area se sweden there unusually high cs concentrations up to 5 6 g l 1 occur in the low temperature 1 median laxemar 3 7 g l 1 and groundwater with marine origin aspo hrl 4 2 g l 1 overall lower but variable cs concentrations were found in other types of groundwater the similar concentrations of cs in the saline groundwater which had a residence time in the order of millions of years and in the marine groundwater which had residence times in the order of years shows that duration of water rock interactions is not the single and primary control of dissolved cs in these systems the high cs concentrations in the saline groundwater is ascribed to long term weathering of minerals primarily cs enriched fracture coatings dominated by illite and mixed layer clays and possibly wall rock micaceous minerals the high cs concentrations in the groundwater of marine origin are in contrast explained by relatively fast cation exchange reactions as indicated by the field data and predicted by 1d solute transport modeling alkali cations with low energy hydration carried by intruding marine water are capable of nh 4 in particular and k to some extent replacing cs on frayed edge fes sites on illite in the fracture coatings the result is a rapid and persistent at least in the order of decades buildup of dissolved cs concentrations in fractures where marine water flows downward the identification of high cs concentrations in young groundwater of marine origin and the predicted capacity of nh 4 to displace cs from fracture solids are of particular relevance in the disposal of radioactive nuclear waste deep underground in crystalline rock

natural radioelement solution by circulating groundwaters in the stripa granite natural radioelement concentrations in groundwaters from the fracture flow regime in the stripa granite were monitored during the period 1977 1986 uranium concentrations from depths of 80 m or less and in minewaters from above the hydraulic sink produced by the deepest mining level 410 m range from 10 to 90 ppb 234u238u activity ratios are characteristic of chemical leaching processes at the shallower depths whilst at about 350 m groundwaters occur which have an additional component of 234u by alpha recoil processes at greater depths u concentrations are indicative of the changed redox conditions and are subject to activity ratio enhancement by the alpha recoil process groundwater residence times may be estimated from the rate of such recoil solution of 234u in zones where chemical leaching of u is not active the 222rn contents of the minewaters are extremely high and can be related to the 222rn flux from fracture surfaces and the fracture width the fracture apertures range from 10 mm for the shallow groundwater zone 222rn contents m for water from the deepest borehole section 222rn content 100 kbq kg 1 the activity ratios 234th238u 210pb222rn and 210po222rn have been used to estimate residence times for th pb and po isotopes solution of ra is controlled by chemical rather than alpha recoil processes the 226ra content of the groundwater increases with salinity and is well correlated with groundwater ca content the 228ra226ra activity ratios in the groundwaters suggest that water rock interaction occurs predominantly with the average granitic matrix rather than with highly uraniferous fracture mineralisation the behaviour of ra th and po isotopes may be used to assess that of homologous fission product and actinide constituents of nuclear wastes in groundwaters

rainfall induced slope collapse with coupled material point method abstract rainfall induced slope failures are a major category of slope failure with incidents likely to increase with the predicted escalation of extreme rainfall events traditional numerical methods such as the finite element method are often restricted in their applicability to small deformation analyses therefore incomplete descriptions of the failure mechanism and failure consequence may be obtained due to the evolving deformations and progressive failure being ignored a one point two phase material point method mpm formulation is proposed to consider the influence of rainfall on slope failure due to the characteristics of mpm in capturing the large deformations the complete failure process from initiation to failure of a slope subjected to rainfall infiltration is presented the soil behaviour is described by a mohr coulomb strain softening model based on bishop s effective stress the two phase analysis shows that the rainfall affected slope is initially stable until the soil shear strength reduces due to the reduction of suction in the slope starting from the surface leading to a superficial failure mode which in turn leads to a complete slope failure friction angle and residual cohesion are shown to play important roles in the development of the slope failure

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

the isotope geochemistry of carbon in groundwater at stripa the carbon isotopic composition of the total dissolved inorganic carbon in groundwater associated with a granitic pluton at stripa sweden reflects both inorganic and organic carbon sources following the uptake of soil carbon dioxide calcite dissolution dominates the geochemical evolution of shallow groundwater calcite saturation is reached at a depth of about 100 m in deeper waters geochemical release of ca and increasing ph cause calcite precipitation radiocarbon contents suggest carbon and water ages in excess of 20 000 years for waters at 300 400 m depth in deep groundwaters with enhanced salinities organic carbon is added to the dissolved inorganic carbon either through bacterial activity e g sulphate reducing bacteria or the oxidation of organic compounds such as methane the lowest radiocarbon contents were measured at the 300 400 meter levels and not in the deepest fluids the distribution of 13c in the deep groundwaters suggests the existence of well defined flowsystems with limited active hydraulic interaction isotope analyses on fracture calcites substantiate the complex geochemical history of the pluton

science society and the coastal groundwater squeeze coastal zones encompass the complex interface between land and sea understanding how water and solutes move within and across this interface is essential for managing resources for society the increasingly dense human occupation of coastal zones disrupts natural groundwater flow patterns and degrades freshwater resources by both overuse and pollution this pressure results in a coastal groundwater squeeze where the thin veneers of potable freshwater are threatened by contaminant sources at the land surface and saline groundwater at depth scientific advances in the field of coastal hydrogeology have enabled responsible management of water resources and protection of important ecosystems to address the problems of the future we must continue to make scientific advances and groundwater hydrology needs to be firmly embedded in integrated coastal zone management this will require interdisciplinary scientific collaboration open communication between scientists and the public and strong partnerships with policymakers

chlorine isotope distribution in formation waters texas and louisiana theoretically the chlorine isotope ratio 37cl 35cl can aid in identifying chloride sources and in distinguishing chloride transport mechanisms among formation waters if ratio differences exist among samples we measured the chlorine ratios of 18 formation water samples from oil fields along the texas louisiana gulf coast representing depths between 2 016 and 4 267 m chloride concentrations of samples ranged from 4 to 94 874 g l the chlorine ratios ranged from 1 24 to 0 58 pmil with respect to standard mean ocean chloride or smoc precision 0 12 pmil and enrichment of 37cl correlates with increasing concentration we also compared the isotope ratios of samples from within the weeks island salt dome with adjacent formation waters in louisiana all ratio measurements on the salt are between 0 1 and 0 3 pmil and for the formation waters are between 0 0 and 0 22 pmil the probability that the salt measurements differ from the waters is 99 we conclude that significant chlorine isotope ratio differences exist among formation waters and between the waters and potential sources in the gulf coast region and that the chlorine ratio will be a valuable tool in interpreting chloride geochemistry in this region

storm driven groundwater flow in a salt marsh 1 storms can cause significant groundwater flow in coastal settings but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer we have little information about the effects of smaller storms on coastal flow and how storm induced variability affects key tidal wetlands like salt marshes which may remain saline throughout a storm here we show that even the distant passage of a moderate storm can strongly increase groundwater flow and transport in salt marsh ecosystems and adjacent barrier islands groundwater monitoring and radium isotope tracer analyses revealed significant influx of saline creek water into the confined aquifer below the marsh platform driven by storm surge this pulse of fluids reached depths exceeding 5 m and surge enhanced tides propagated through the aquifer to affect flow in the upland 100 m from the creek bank groundwater discharge from the marsh varied significantly prior to the storm doubling during inundating tides compared to a period of noninundating neap tides storm surge then caused groundwater discharge to decline 50 compared to similar inundating tides ra and nutrient poor creek water that entered the confined aquifer below the marsh was quickly enriched in nutrients and carbon even on 12 h tidal cycles so that nutrient discharge was likely proportional to groundwater discharge storm related flow could also drive significant contaminant discharge from developed coastlines the enhanced transport and variability observed here likely affected hundreds of kilometers of the coastline impacted by the storm

seasonality of major redox constituents in a shallow subterranean estuary abstract the subterranean estuary ste the subsurface mixing zone of outflowing fresh groundwater and infiltrating seawater is an area of extensive geochemical reactions that determine the composition of groundwater that flows into coastal environments this study examined the porewater composition of a shallow ste

trends in large deformation analysis of landslide mass movements with particular emphasis on the material point method traditional geotechnical analyses for landslides involve failure prediction i e onset of failure and the design of structures that can safely withstand the applied loads the analyses provide limited information on the post failure behaviour modern numerical methods are able to simulate large mass movements and there is an opportunity to utilise such methods to evaluate the risks of catastrophic damage if a landslide occurs in this paper various large deformation analysis methods are introduced and their applicability for solving landslide problems is discussed since catastrophic landslides often involve seepage forces consideration of the coupled behaviour of soil and pore fluid is essential two approaches to model soil pore fluid coupling in large deformation analysis using the material point method mpm are introduced an example simulation is presented for each approach one on a model levee failure and the other on a natural cut slope failure the selborne experiment conducted by cooper and co workers in 1998 in the levee failure case mpm simulation was able to capture a complex failure mechanism including the development of successive shear bands the simulation was also able to predict excess pore pressure generation during the failure propagation and the subsequent consolidation stage the simulations demonstrated the importance of the dilation characteristics of soil as well as changes in geometry for the post failure behaviour in the selborne case mpm was able to simulate the progressive failure of brittle overconsolidated clay the evolution of shear stresses along the failure surface was also captured by the mpm the changes in the pore pressure and the actual shape of the failure surface were simulated by the mpm the importance of accurately modelling the shear band within the mpm framework is highlighted

salt freshwater dynamics in a subterranean estuary over a spring neap tidal cycle this paper presents field measurements and numerical simulations of pore water salinities and groundwater flow in the intertidal zone of an unconfined coastal aquifer over a spring neap tidal cycle the study provides insight into the extent and time scales of mixing between fresh groundwater and recirculating seawater in a tidally influenced subterranean estuary salt freshwater dynamics in subterranean estuaries are currently not well understood despite their potentially important implications for fluxes of chemicals to coastal waters via submarine groundwater discharge the data and simulation results show that changes in the tidal shoreline excursion over the spring neap cycle induce significant variations in the intertidal salinity structure observed higher frequency salinity fluctuations demonstrate further the intensity and complexity of the salt freshwater mixing process in contrast with the salinity variations fresh groundwater was found to discharge around a distinct intertidal beach slope break throughout the spring neap period this suggests that the slope break may affect significantly groundwater flow and salt transport near the shore measurements of ph and dissolved oxygen distributions revealed important biogeochemical zonations in the system these zonations are expected to strongly influence the fate of many reactive chemicals in the nearshore aquifer and their subsequent discharge to coastal waters

deuterium oxygen 18 and tritium in stripa groundwater deuterium oxygen 18 and tritium determinations show that groundwaters in the fractures of the stripa granite are of meteoric origin not affected by secondary isotope effects evaporation or isotope exchange deep ground waters have lower 18o and 2h contents than recent shallow groundwaters the differences are most likely due to recharge during cooler climatic conditions however no age information can be derived because recharge could have occurred before the last major climatic improvement following the last deglaciation during minor climatic variations during the more recent past or could be the result of regional groundwater flow low 18o contents are paralleled by increasing salinities with highest salinities limited to a narrow fracture zone at a depth of about 800 m below ground surface most saline waters sampled appear to represent mixtures of a saline component with an isotopically depleted water and local fresh water the presence of young groundwaters is indicated by bomb produced 3h all surface boreholes contain tritium indicating residence times 35 years however tritium is also found in some boreholes drilled at the 300 m mine levels and its presence may be due to flows induced in response to heater tests low but detectable 3h contents about 0 1 to 1 tu in v2 at about 850 m below groundsurface are discussed either as subsurface production and or as a result of admixtures of small amounts of recent water to old groundwater

comparison of the sr isotopic signatures in brines of the canadian and fennoscandian shields abstract a synthesis of sr isotope data from shallow and deep groundwaters and brines from the fennoscandian and canadian shields is presented a salinity gradient is evident in the water with concentrations varying from approximately 1 75 g l 1 below 1500 m depth in the fennoscandian shield and from 10 up to 300 g l 1 below 650 m depth in the canadian shield strontium isotope ratios were measured to assess the origin of the salinity and evaluate the degree of water rock interaction in the systems in both shields the sr concentrations are enriched relative to cl defining a positive trend parallel to the seawater dilution line and indicative of sr addition through weathering processes the depth distribution for sr concentration increases strongly with increasing depth in both shields although the variation in sr isotope composition does not mirror that of sr concentrations strontium isotope compositions are presented for surface waters and groundwaters in several sites in the fennoscandian and canadian shields numerous mixing lines can be drawn reflecting water rock interaction a series of calculated lines links the surface end members surface water and shallow groundwater and the deep brines these mixing lines define a range of 87 sr 86 sr ratios for the deep brines in different selected sites all sites show a specific 87 sr 86 sr signature and the occurrence of large 87 sr 86 sr variations is site specific in both shields in canadian shield brines the sr isotope ratios clearly highlight large water rock interaction that increases the 87 sr 86 sr ratio from water that could have been of marine origin in contrast to the canadian shield groundwater does not occur in closed pockets in the fennoscandian and the well constrained 87 sr 86 sr signatures in deep brines should correspond to a large well mixed and homogeneous water reservoir whose sr isotope signature results from water rock interaction

climate driven sea level anomalies modulate coastal groundwater dynamics and discharge 1 to better understand the physical drivers of submarine groundwater discharge sgd in the coastal ocean we conducted a detailed field and modeling study within an unconfined coastal aquifer system we monitored the hydraulic gradient across the coastal aquifer and movement of the mixing zone over multiple years at our study site sea level dominated over groundwater head as the largest contributor to variability in the hydraulic gradient and therefore sgd model results indicate the seawater recirculation component of sgd was enhanced during summer while the terrestrial component dominated during winter due to seasonal changes in sea level driven by a combination of long period solar tides temperature and winds in one year sea level remained elevated year round due to a combination of enso and nao climate modes hence predicted changes in regional climate variability driven sea level may impact future rates of sgd and biogeochemical cycling within coastal aquifers

aqueous sulphates from the stripa groundwater system abstract the isotopic composition of aqueous sulphate in the groundwater in the stripa pluton reflects the geochemical history of the groundwater as well as the origin of the sulphur or sulphate in shallow modern groundwater sulphate originates from fallout and the oxidation of pyrite or other reduced forms of sulphur at intermediate depths sulphate of surface origin is lost through bacterial reduction the origin of sulphate of the deep and more saline water is not clearly defined but could be derived from a sedimentary brine which was subject to substantial modification through rock water interaction bacterial sulphate reduction also occurs locally at depths below about 800 m

what time scales are important for monitoring tidally influenced submarine groundwater discharge insights from a salt marsh submarine groundwater discharge sgd varies significantly across time scales ranging from hours to years but studies that allow quantitative comparisons between different time scales are few most of these studies have focused on beach settings where the combined variations in fresh and saline sgd can be difficult to interpret we calculated variations in saline sgd based on a 1 year record of hydraulic head in a salt marsh where we could isolate variations in saline tidally driven sgd observed sgd varied by an order of magnitude over the course of the year groundwater discharge was proportional to tidal amplitude and varied by at least a factor of 2 between spring and neap tides monthly average sgd was inversely proportional to average sea level it increased by nearly a factor of 2 as sea level declined by 50 cm from late summer to late winter this variation was far larger than that predicted by analytic models owing to the flat topography and inundation of the marsh platform the effect of short term days variations in sea level associated with wind events and storms was small in comparison sgd is probably proportional to tidal amplitude in nearly all coastal settings including beaches seasonal variations in sea level may not affect the volume of sgd as significantly in coastal settings where the slope of the intertidal zone is relatively constant but such variations have the potential to strongly affect the composition of sgd

memory of past random wave conditions in submarine groundwater discharge submarine groundwater discharge sgd is an integral part of the hydrological cycle and represents an important aspect of land ocean interactions we used a numerical model to simulate flow and salt transport in a nearshore groundwater aquifer under varying wave conditions based on yearlong random wave data sets including storm surge events the results showed significant flow asymmetry with rapid response of influxes and retarded response of effluxes across the seabed to the irregular wave conditions while a storm surge immediately intensified seawater influx to the aquifer the subsequent return of intruded seawater to the sea as part of an increased sgd was gradual using functional data analysis we revealed and quantified retarded cumulative effects of past wave conditions on sgd including the fresh groundwater and recirculating seawater discharge components the retardation was characterized well by a gamma distribution function regardless of wave conditions the relationships between discharge rates and wave parameters were quantifiable by a regression model in a functional form independent of the actual irregular wave conditions this statistical model provides a useful method for analyzing and predicting sgd from nearshore unconfined aquifers affected by random waves key points cumulative effects of antecedent wave conditions on sgd long memory of past wave conditions back to over a hundred days found in the sgd wave effects characterized well by a gamma distribution function

chlorine isotopes of thermal springs in arc volcanoes for tracing shallow magmatic activity the evaluation of the status of shallow magma body i e from the final intrusion stage to quiescence and back to activity one of the key parameters that trigger and sustain volcanic eruptions has been challenging in modern volcanology among volatile tracers chlorine cl uniquely exsolves at shallow depths and is highly hydrophilic consequently cl enrichment in volcanic gases and thermal springs has been proposed as a sign for shallow magmatic activities however such enrichment could also result from numerous other processes e g water evaporation dissolution of old chloride mineral deposits seawater contamination that are unrelated to magmatic activity here based on stable isotope compositions of chloride and dissolved inorganic carbon as well as previous published 3he 4he data obtained in thermal springs from two recently erupted volcanoes la soufriere in guadeloupe and montagne pelee in martinique in the lesser antilles arc we show that the magmatic cl efficiently trapped in thermal springs displays negative 37cl values 0 65 0 65 consistent with a slab derived origin but distinct from the isotope compositions of chloride in surface reservoirs e g seawater local meteoric waters rivers and cold springs displaying common 37cl values of around 0 using this 37cl difference as an index of magmatic cl we further examined thermal spring samples including a 30 year archive from two thermal springs in guadeloupe covering samples from its last eruption in 1976 1977 to 2008 and an island wide sampling event in martinique in 2008 to trace the evolution of magmatic cl in the volcanic hydrothermal systems over time the results show that magmatic cl can be rapidly flushed out of the hydrothermal systems within 30 to 80 years after the eruption much quicker than other volatile tracers such as co2 and noble gases which can exsolve at greater depths and constantly migrate to the surface because arc volcanoes often have well developed hydrothermal systems where magmatic cl is easily transferred to the surface following its exsolution from shallow magma body we suggest that 37cl has great potential to be a unique proxy to monitor the cessation and revival of infrequent arc volcanoes particularly at centennial time scales

cosmogenic radiogenic and stable isotopic constraints on groundwater residence time in the nubian aquifer western desert of egypt measurements of radiochlorine sup 36 cl radiogenic noble gases sup 4 he and sup 40 ar and stable chlorine isotope ratios were obtained to assess the residence time of groundwater in the nubian aquifer of the western desert of egypt measured sup 36 cl cl ratios yield apparent residence times from approx 0 2 to 1 2 x 10 sup 6 years in the deep 600 1200 m groundwater assuming constant cl and le 0 16 x 10 sup 6 years in the shallow 600 m groundwater values of delta sup 37 cl in the groundwater strengthen the application of the sup 36 cl dating method by constraining cl sources and identifying groundwater mixing dissolved gases were measured in some of the deep groundwater samples measured sup 4 he concentrations indicate accumulation of radiogenic sup 4 he that is qualitatively consistent with the age progression indicated by the sup 36 cl cl ratios but the flux of external sup 4 he from the underlying crust has not been quantified and is not constant throughout the aquifer concentrations of sup 40 ar range from 3 3 to 6 7 x 10 sup 4 ccstp g and indicate excess air incorporation at recharge measured sup 40 ar sup 36 ar ratios do not exceed the atmospheric ratio a two dimensional numerical hydrodynamic transect of the aquifer was modeled from the areamore of the uweinat uplift to the northern bahariya oasis predicted groundwater velocities in the deep portion of the aquifer are 0 5 3 5 m yr with groundwater residence times up to 9 x 10 sup 5 years residence times up to 1 3 x 10 sup 6 years are predicted in the confining shale aquifer properties are estimated by using the model to fit the measured sup 36 cl cl ratios under these conditions hydrodynamic residence times are within about 30 percent of those calculated from sup 36 cl when mixing of cl sup is accounted for in the highest cl sup deep groundwaters by mutually calibrating multiple methods hydrodynamic sup 36 cl and sup 4 he a consistent picture of the nubian aquifer has emerged in which lateral flow from a southern recharge area dominates the deep horizons while shallow horizons contain younger autochthonous recharge less

tidal impacts on riparian salinities near estuaries groundwater dependent riparian biota is known to be sensitive to changes in soil and groundwater salinity in estuarine systems the groundwater flow and salinity behaviour in a phreatic aquifer adjoining a partially penetrating tidal estuary is investigated through two dimensional numerical experiments for a lateral cross section which explore the influence of factors such as aquifer and soil materials tidal amplitudes and regional groundwater hydraulic gradients the density contrast between estuarine water and the fresh groundwater drives saltwater penetration of the aquifer even in the case of a marked groundwater hydraulic gradient towards the estuary we show that tidal fluctuations in estuaries can significantly affect the groundwater salinity distribution in adjacent density stratified phreatic aquifers this has consequences for the expected distribution of salinity sensitive biota in the hyporheic zone as well as vegetation and fauna dependent on water in the riparian soil and aquifer the shape of the dense saltwater wedge propagating into the adjacent groundwater system is also modified by the estuarine tidal signal although this effect appears to have only minor influence on the maximum distance penetrated into the aquifer i e location of the toe of the wedge tide induced changes to riparian groundwater salinity are advection driven as evidenced by the modified time averaged groundwater flow dynamics

an evaporated seawater origin for the ore forming brines in unconformity related uranium deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions abstract analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity related uranium deposits from the paleoproterozoic athabasca basin canada were performed in order to determine the origin of chloride in the ore forming brines microthermometric analyses show that samples contain variable amounts of a nacl rich brine cl concentration between 120 000 and 180 000 ppm and a cacl2 rich brine cl concentration between 160 000 and 220 000 ppm molar cl br ratios of fluid inclusion leachates range from 100 to 900 with most values between 150 and 350 cl br ratios below 650 seawater value indicate that the high salinities were acquired by evaporation of seawater most 37cl values are between 0 6 and 0 seawater value which is also compatible with a common evaporated seawater origin for both nacl and cacl2 rich brines slight discrepancies between the cl concentration cl br 37cl data and seawater evaporation trends indicate that the evaporated seawater underwent secondary minor modification of its composition by i mixing with a minor amount of halite dissolution brine or re equilibration with halite during burial ii dilution in a maximum of 30 of connate and or formation waters during its migration towards the base of the athabasca sandstones iii leaching of chloride from biotites within basement rocks and iv water loss by hydration reactions in alteration haloes linked to uranium deposition the chloride in uranium ore forming brines of the athabasca basin has an unambiguous dominantly marine origin and has required large scale seawater evaporation and evaporite deposition although the direct evidence for evaporative environments in the athabasca basin are lacking due to the erosion of 80 of the sedimentary pile cl br ratios and 37cl values of brines have behaved conservatively at the basin scale and throughout basin history

post failure analysis of the maierato landslide using the material point method abstract the 15 february 2010 maierato landslide has become the symbol of the hydrogeological instability of the calabria region southern italy it occurred after a long period of rain in an area prone to landslides some videos filmed during the event documented the high velocity and the flow like character of this landslide after the slope failure several studies focused on the pre failure and failure stages of the maierato landslide in order to interpret its failure mechanism and to establish the main factors of triggering however none of these studies analysed the post failure stage of this landslide in the present study the material point method mpm is used to simulate the run out process of the maierato landslide and provide a possible explanation of this process different scenarios are considered and for each of them the simulated post failure configuration of the displaced material is compared to that detected after the event numerical results match fairly well the observed ones when a severe reduction in the shear strength of the involved soil is accounted for in the analysis this strength reduction is attributed herein to the high excess pore water pressures generated by the large distortions of the moving soil mass moreover the back calculated post failure strength is consistent with that found in several case histories of slope failures involving liquefied materials

subtidal advective water flux as a potentially important nutrient input to southeastern u s a saltmarsh estuaries an initial study was conducted to assess the importance of the advective movement of interstitial water from subtidal creek sediments in enriching the overlying creek water of the estuary the process of advection was measured in two creeks of a south carolina estuarine saltmarsh and results indicated that significant amounts of inorganic nutrients nh4 and po4 3 were added to the overlying creek water by this process the nutrient concentrations in the advected water were as much as an order of magnitude higher than in the overlying water column a comparison of runoff from the marsh surface during low tide to advection from subtidal creek bottoms indicated the importance of the latter in contributing nh4 and po4 3 to the estuarine water column data indicated however that runoff from the marsh surface appeared to be a greater source of no3 no2 to the tidal creek waters mean n 5 sites advective flux across one of the creeks was 3 1 mg nh4 n m 2 tide 1 0 02 mg no3 no2 n m 2 tide 1 and 0 31 mg po4 3 p m 2 tide 1 which was 6 times and 2 5 times higher for nh4 and po4 3 respectively than surface runoff a process known to export nutrients to tidal creek water from the nearby vegetated marsh when normalized over the areal extent of subtidal creek bottom in the estuary subtidal advection is estimated to contribute approximately 3 times as much nh4 and 1 3 times as much po4 3 to the estuarine water column than low tide runoff from the vegetated marsh surface

seasonal cycles in radium and barium within a subterranean estuary implications for groundwater derived chemical fluxes to surface waters abstract there is increasing evidence that submarine groundwater discharge sgd is an important source of water and dissolved materials to the ocean one of the primary tracers of this process is the quartet of radium isotopes 223 ra 224 ra 226 ra and 228 ra whereby excess activities in surface waters can often be attributed to an input supplied via sgd this approach requires the radium end member activity to be well constrained however natural variability in groundwater radium may span several orders of magnitude therefore this variability is usually the main driver of uncertainties in volumetric sgd estimates to investigate the physical and biogeochemical controls on groundwater radium activities we conducted a three year time series of radium and barium a chemical analogue for radium within the subterranean estuary of a coastal aquifer waquoit bay ma usa gonneea et al 2013 demonstrated that movement of the salinity interface within the subterranean estuary is driven by changes in the hydraulic gradient between groundwater level and sea level height for waquoit bay seasonal scale sea level change not groundwater level was the main driver in hydraulic gradient fluctuations seasonal changes in groundwater chemistry can be attributed to the resulting movement of the salinity transition zone between terrestrial and marine groundwater landward movement of the interface results in a large release of radium isotopes 226 ra 1400 dpm 100 l 1 and barium 3000 nmol kg 1 associated with an increase in groundwater salinity the magnitude of these releases cannot be explained by in situ production or weathering alone but is likely due to salinity driven desorption from surface bound sediment inventory the timing of these peak concentrations is not always in phase with model derived estimates of sgd as a result the groundwater concentration rather than the water flux is the main driver of ra and ba inputs to waquoit bay surface waters the behavior of the subterranean estuary as an ion exchange reservoir has important implications for the timing and flux of various nutrients and pollutants that transit this region prior to discharge in addition to modulating chemical fluxes via submarine groundwater discharge on seasonal time scales transgression of the subterranean estuary may alter the input of chemicals to the ocean on decadal and longer time scales during this study the observed excess flux of 226 ra and ba from the subterranean estuary can be accounted for with sorbed sediment pools and accelerating rates of sea level rise in this region

the material point method for unsaturated soils the paper describes a three phase single point material point method formulation of coupled flow water and air for hydro mechanical analysis of geotechnical problems involving unsaturated soils the governing balance and dynamic momentum equations are discretised and adapted to material point method characteristics an eulerian computational mesh and a lagrangian analysis of material points general mathematical expressions for the terms of the set of governing equations are given a suction dependent elastoplastic mohr coulomb model expressed in terms of net stress and suction variables is implemented the instability of a slope subjected to rain infiltration inspired from a real case is solved and discussed the model shows the development of the initial failure surface in a region of deviatoric strain localisation the evolution of stress and suction states in some characteristic locations the progressive large strain deformation of the slope and the dynamics of the motion characterised by the hi

role of stratigraphy in governing pore water seepage from salt marsh sediments 1 numerical modeling experiments have been used to study the effects of marsh stratigraphy on the seepage of pore water into tidal channels if the mud sand contact lies at the elevation of the channel bottom and the hydraulic conductivity of the basal sand is at least an order of magnitude greater than the overlying mud the locus of maximum seepage shifts from the tide line as in a purely mud marsh to the toe of the creek bank the ratio of creek bank seepage to bottom seepage also shifts from greater than to less than one furthermore as the ratio of the hydraulic conductivities of sand to mud increases the ratio of the total seepage from the sand mud marsh to that from a pure mud marsh increases in a nonlinear fashion reaching an asymptotic limit of about 20 at a conductivity ratio of about 1000 if the mud sand boundary is progressively lowered so that mud also lies beneath the channel the seepage dynamics gradually revert toward those of a purely mud marsh the ecological implications of these results for regularly flooded low marshes are discussed

measuring pore water oxygen of a high energy beach using buried probes abstract we conducted six field campaigns to investigate the spatial and temporal evolution of pore water oxygen content on a high energy sandy beach aquifer during several tidal cycles at different seasons we buried autonomous probes in intertidal sands to record dissolved oxygen saturation salinity temperature and water head at a 2 10 min frequency oxygen concentrations display significant changes both with time tide and seasons and space cross shore and vertical variations seawater circulation in tidal sands forms a saline pore water circulation cell with oxygen saturated pore water in the zone of seawater recharge oxygen depleted pore water in the lower beach is the result of in situ respiration processes that occur during seawater circulation oxygen depletion varies throughout the year and anoxic conditions are reached at the end of spring as planktonic organic matter becomes abundant in seawater and more organic matter is therefore supplied to pore water on a shorter time scale weeks to minutes oxygen variations are driven directly by physical forcing tidal amplitude affects the extent of the saltwater circulation cell and the associated location of the recharging and discharging zones of the beach the evolution of the water table level during the tidal cycle influences the circulation of pore water in the sand and ultimately the timing of oxygen variations during flood and ebb this first in situ study in a high energy sandy beach shows that the dynamics of pore water oxygen are governed by biogeochemical processes at the seasonal scale and by physical forcing at the time scale of minutes to a few days

downhill progressive landslides in long natural slopes triggering agents and landslide phases modeled with a finite difference method a large landslide in tuve gothenburg sweden 1977 initiated the development of a model for slope stability analysis taking the deformation softening of soft sensitive clays into consideration the model studies triggering agents and five phases in progressive slope failure are identified 1 in situ 2 disturbance 3 unstable dynamic 4 transitory or permanent equilibrium and 5 global failure the clay resistance in these phases may differ widely mostly due to different rates of loading two time dependent failure criteria are defined i the triggering load condition in the disturbance phase 2 and ii the transitory equilibrium in phase 4 indicating whether minor downhill displacements or a veritable landslide catastrophe will occur the analysis explains why downhill landslides tend to spread over vast areas of almost horizontal ground further downslope the model has been applied to landslides in scandinavia and canada three case studies are briefly discussed the model is a finite difference approach where local downhill deformations caused by normal forces is maintained compatible with deviatory shear deformations above and if relevant below the potential or the established failure surface software and an easy to use spreadsheet are introduced as well as recent developments

aznalcollar dam failure part 2 stability conditions and failure mechanism an analysis of the conditions that led to the failure of the aznalcollar dam is made in the paper pore water pressures prevailing in the foundation clay at the time of the failure have been established on the basis of piezometric observations made after the failure a simplified consolidation analysis is first presented to interpret pore water pressure generation and dissipation and to evaluate the evolution of shear stresses along the potential failure plane both limit equilibrium and finite element analysis are used to back analyse the failure and to derive representative strength parameters along the failure surface three dimensional effects introduced by the layered nature of the foundation clay are then described they provide an explanation for the location of the slide which affected only the south eastern portion of the embankment the failure is examined in the final part of the paper from the perspective offered by the current knowledge of the strength behaviour of brittle clays the signifi

aznalcollar dam failure part 3 dynamics of the motion the motion of the aznalcollar dam slide after the initiation of the failure is examined in the paper the moving mass remained essentially rigid and newton s second law provides the basic equation to determine the resulting dam displacement velocity and acceleration resisting forces have been derived from a previous analysis of the conditions leading to failure pore water pressures induced by the forward motion of the dam are approximated as an undrained loading of the clay driving forces and their evolution in time derive from the liquefaction of tailings and the condition of constant volume of liquefied tailings pushing the moving dam forward the stable cliff left by the motion inside the tailings lagoon supports this hypothesis the model is able to reproduce closely the distance travelled by the dam it shows a low sensitivity with respect to reasonable changes of the main parameters the model computes that the slide motion lasted about 15 s and that the maximum acceleration experienced by

methanotrophy controls groundwater methane export from a barrier island abstract methane concentrations can be high in coastal groundwater resulting in methane export driven by submarine groundwater discharge however the magnitude of this methane flux depends significantly on the rate of methanotrophy the often overlooked process of microbial methane consumption that occurs within coastal aquifer sediments here we describe a zone of methanogenesis within the freshwater lens of a barrier island aquifer and investigate the methane source sink behavior of the barrier island system as a whole the median concentration of methane dissolved in fresh groundwater beneath the center of the island was 0 6 mm supported by high rates of potential methanogenesis 22 mmol m 2 day 1 however rates of microbial methane consumption were also elevated in surrounding sediments 18 mmol m 2 day 1 groundwater flowing from the zone of methanogenesis to the point of discharge into the ocean had a long residence time within methanotrophic sediments 195 days such that the majority of the methane produced within the barrier island aquifer was likely consumed there

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter

analysis of piezocone penetration under different drainage conditions with the two phase material point method abstractthe piezocone penetration test cptu is commonly used to identify a soil s profile and estimate its material properties depending on the soil type ranging from clay to sand undrained partially drained or drained conditions may occur during cone penetration in silt and sand clay mixtures the cptu penetration is characterized by partially drained conditions which are often neglected in data interpretation the effect of drainage on cptu measurements has been mainly studied experimentally numerical analyses are rare because taking into account large soil deformations soil water and soil structure interactions and nonlinear soil behavior is still a challenging task this paper presents and discusses numerical simulations of cptu in saturated soils with the two phase material point method soil behavior is described with the modified cam clay model this study investigates the effects of pore pressure dissipation during penetration cone roughness and horizontal stress state comparing the