coastal gravel barrier hydrology observations from a prototype scale laboratory experiment bardex abstract a prototype scale laboratory study bardex barrier dynamics experiment was conducted within the 250 m long and 7 m deep delta wave flume the netherlands a 4 m high and 50 m long gravel barrier d50 11 mm was constructed within the central region of the flume enabling a back barrier lagoon to be located at its landward side by the installation of a multi stage pump system the water levels at the sea and lagoon sides of the barrier could be manipulated independently a series of experiments were undertaken to examine the groundwater fluctuations and flow within the barrier system subject to varying lagoon levels and wave conditions in accordance with previous sand experiments the wave induced watertable over height at the beachface was confirmed to be independent of sediment characteristics varying back barrier lagoon levels were observed to have significant effect on both the maximum watertable over height within the barrier and shoreline set up vertical position of the point of intersection between mean water surface through the swash zone and beachface as well as the direction and magnitude of though barrier groundwater flux the effective hydraulic conductivity of the d50 11 mm gravel barrier was determined to be k 0 16 m s 1 at higher reynolds numbers re 40 associated with local watertable gradients exceeding 0 025 and resulting turbulent losses the transition from laminar to turbulent through barrier flow was indicated by a reduction in local k however for the parameter range encountered this effect was modest only

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

swash zone moisture dynamics and unsaturated infiltration in two sandy beach aquifers the intertidal zone of coastal aquifers is a dynamic region of mixing between saline surface water and fresh groundwater groundwater circulation in this zone is affected by complex forcing mechanisms that operate on a range of timescales and can regulate chemical fluxes to marine environments we evaluated wave swash induced infiltration and associated flow dynamics in the unsaturated region of two sandy beach aquifers with differing wave conditions and beach morphologies moisture and pressure sensors were used to measure fluctuations in water content water table elevation and hydraulic gradients at high frequencies 5 hz in the swash zone at mean lower low water mean sea level and mean higher high water water content in the unsaturated region of the swash zone responded to wave overtopping and swash infiltration with a rapid rise in water content followed by a slower decline swash induced unsaturated infiltration rates calculated from water content response were lowest near low tide and increased up the beachface with inflow highest near high tide at both sites consistent with an increase in water table depth up the beach unsaturated infiltration was 1 6 m 3 m per tidal cycle at the wavedominated beach and 0 4 m 3 m per tidal cycle at the tide dominated beach saturated pore pressure measurements show that a water table mound formed as a consequence of swash infiltration that migrated up the beach during rising tide leading to divergent seaward landward groundwater flow the results demonstrate the significant and spatially variable effects of wave swash on moisture dynamics in the unsaturated zone of beach aquifers and show that these effects depend on wave conditions and beach characteristics results have implications for understanding transport and reaction of solutes in this biogeochemically active zone

shallow seismic reflection study of a glaciated valley shallow seismic reflection data were recorded along two long 1 6 km intersecting profiles in the glaciated suhre valley of northern switzerland appropriate choice of source and receiver parameters resulted in a high fold 36 48 data set with common midpoints every 1 25 m as for many shallow seismic reflection data sets upper portions of the shot gathers were contaminated with high amplitude source generated noise e g direct refracted guided surface and airwaves spectral balancing was effective in significantly increasing the strength of the reflected signals relative to the source generated noise and application of carefully selected top mutes ensured guided phases were not misprocessed and misinterpreted as reflections resultant processed sections were characterized by distributions of distinct seismic reflection patterns or facies that were bounded by quasi continuous reflection zones the uppermost reflection zone at 20 to 50 ms 15 to 40 m depth originated from a boundary between

deep seismic reflection profiling in the swiss alps explosion seismology results for line nfp 20 east in september 1986 a 120 km long seismic line was recorded through the swiss alps the line traverses major units involved in thin and thick skinned alpine tectonics our preliminary interpretation indicates that 1 lithologic boundaries such as basement cover contacts although severely deformed during the alpine orogeny can be identified on the seismic sections 2 the top of the aar massif an external basement massif extends deep into the alpine orogen 3 the upper and lower parts of the crust are more or less transparent but are separated by a swarm of reflectors at mid crustal level 4 these mid crustal reflectors might be related to trapped fluids from alpine metamorphism and 5 the moho appears as a bright reflection that steepens from the north toward the south and terminates abruptly near the center of the alpine chain perhaps because of alpine deformation

prestack kirchhoff depth migration of shallow seismic data prestack kirchhoff depth migration is applied successfully to shallow seismic data from a waste disposal site near arnstadt in thuringia germany the motivation behind this study was to locate an underground building buried in a waste disposal the processing sequence of the prestack migration is simplified significantly as compared to standard common cmp data processing it includes only two parts 1 velocity depth model estimation and 2 prestack depth migration in contrast to conventional cmp stacking prestack migration does not require a separation of reflections and refractions in the shot data it still provides an appropriate image our data example shows that a superior image can be achieved that would contain not just subtle improvements but a qualitative step forward in resolution and signal to noise ratio

water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in western australia abstract volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in western australia the filtered volumes were large 19 m 3 m 1 day 1 and 73 m 3 m 1 day 1 on two clean beaches but only 0 4 m 3 m 1 per tidal cycle on a beach covered in kelp and seagrass wrack the mean residence times of this water in the interstitial system and its percolation paths were both short 1 7 h and 2 5 m respectively water input was greater across a beach cusp horn than across a cusp embayment most input occurred in the upper swash zone where the water table was less than 20 cm deep tidal variations in input volumes were evident even with tide ranges of only 20 cm the inshore zone off these beaches filters on average 0 07 m 3 m 2 day 1 at an average depth of 5 5 m under 0 4 m waves of 6 5 s duration the importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore lagoon ecosystem is estimated and discused

stratigraphic controls on fluid and solute fluxes across the sediment water interface of an estuary shallow stratigraphic features such as infilled paleovalleys modify fresh groundwater discharge to coastal waters and fluxes of saltwater and nutrients across the sediment water interface we quantify the spatial distribution of shallow surface water groundwater exchange and nitrogen fluxes near a paleovalley in indian river bay delaware using a hand resistivity probe conventional seepage meters and pore water samples in the interfluve region outside the paleovalley most nitrate rich fresh groundwater discharges rapidly near the coast with little mixing of saline pore water and nitrogen transport is largely conservative in the peat filled paleovalley fresh groundwater discharge is negligible and saltwater exchange is deep 1 m long pore water residence times and abundant sulfate and organic matter promote sulfate reduction and ammonium production in shallow sediment reducing iron rich fresh groundwater beneath paleovalley peat discharges diffusely around paleovalley margins offshore in this zone of diffuse fresh groundwater discharge saltwater exchange and dispersion are enhanced ammonium is produced in shallow sediments and fluxes of ammonium to surface water are large by modifying patterns of groundwater discharge and the nature of saltwater exchange in shallow sediments paleovalleys and other stratigraphic features influence the geochemistry of discharging groundwater redox reactions near the sediment water interface affect rates and patterns of geochemical fluxes to coastal surface waters for example at this site more than 99 of the groundwater borne nitrate flux to the delaware inland bays occurs within the interfluve portion of the coastline and more than 50 of the ammonium flux occurs at the paleovalley margin

a shallow seismic reflection survey in basalts of the snake river plain idaho the objective of this feasibility study was to determine if the seismic reflection method could help to optimize placement of water quality monitoring wells near a radioactive storage facility seismic reflections from depths less than 30 m were recorded along a 500 m long line over a basalt rhyolite and sedimentary sequence in the snake river plain some shallow reflections at 40 to 50 ms on the field files are of exceptional quality with frequency exceeding 150 hz reflections and refractions from selected seismograms along the line possess vastly different normal moveout nmo and apparent velocities as well as wavelet characteristics extreme variations in quality seismic character and reflector geometries observed on seismograms give the appearance of varying geologic settings and are uncommon for such short distances severe surgical muting was necessary for accurate velocity and statics analyses the seismic reflection data show apparent structural lows in a sedimentary layer sandwiched between

a method for computing infiltration and redistribution in a discretized moisture content domain 1 a new one dimensional infiltration and redistribution method is proposed as an alternative to the richards equation re for coupled surface and subsurface models the proposed method discretizes soil water content into hypothetical hydraulically interacting bins the entry and propagation of displacement fronts in each bin are simulated by means of explicit infiltration and drainage approximations based on capillary and gravitational driving forces wetting front advances within bins create water deficits that are satisfied by capillary driven interbin flow the method inherently provides numerical stability by precluding the need to directly estimate nonlinear gradients through numerical schemes comparisons of the performance of this method against re solutions for theoretical laboratory and field data in both well drained and high water table conditions are presented the new method produces infiltration flux estimates with errors less than 10 compared to a widely used re solution in tests on multiple soil textures with and without high water table conditions while providing unconditionally guaranteed conservation of mass

geophysical investigations in the flumendosa river delta sardinia italy seismic reflection imaging a geophysical investigation that included seismic reflection surveying and time domain electromagnetics em was carried out in the flumendosa river delta plain in southeastern sardinia italy the objective was to improve knowledge of geologic and hydrogeologic controls on a highly productive aquifer hosted in thick quaternary deposits and known to be affected by an extensive saltwater intrusion the seismic reflection survey whose results are reported here aimed to image the paleozoic bedrock topography and to obtain detailed structural and stratigraphic information on the sequence of largely fluvial sediments extending from the surface down to bedrock the survey consisted of two inline profiles nearly parallel to the coastline and 1 km inland the sources 0 25 kg of explosives buried at 2 m depth and receivers 50 hz vertical geophones produced a twelvefold data set with common midpoints every 2 5 m detailed integrated velocity analysis constant velocity gathers constant velocity stacks an

influence of sea level rise on iron diagenesis in an east florida subterranean estuary abstract subterranean estuary occupies the transition zone between hypoxic fresh groundwater and oxic seawater and between terrestrial and marine sediment deposits consequently we hypothesize in a subterranean estuary biogeochemical reactions of fe respond to submarine groundwater discharge sgd and sea level rise porewater and sediment samples were collected across a 30 m wide freshwater discharge zone of the indian river lagoon florida usa subterranean estuary and at a site 250 m offshore porewater fe concentrations range from 0 5 m at the shoreline and 250 m offshore to about 286 m at the freshwater saltwater boundary sediment sulfur and porewater sulfide maxima occur in near surface oc rich black sediments of marine origin and dissolved fe maxima occur in underlying oc poor orange sediments of terrestrial origin freshwater sgd flow rates decrease offshore from around 1 to 0 1 cm day while bioirrigation exchange deepens with distance from about 10 cm at the shoreline to about 40 cm at the freshwater saltwater boundary doc concentrations increase from around 75 m at the shoreline to as much as 700 m at the freshwater saltwater boundary as a result of labile marine carbon inputs from marine sgd this labile doc reduces fe oxides which in conjunction with slow discharge of sgd at the boundary allows dissolved fe to accumulate upward advection of fresh sgd carries dissolved fe from the fe oxide reduction zone to the sulfate reduction zone where dissolved fe precipitates as fe sulfides saturation models of fe sulfides indicate some fractions of these fe sulfides get dissolved near the sediment water interface where bioirrigation exchanges oxic surface water the estimated dissolved fe flux is approximately 0 84 m fe day per meter of shoreline to lagoon surface waters accelerated sea level rise predictions are thus likely to increase the fe flux to surface waters and local primary productivity particularly along coastlines where groundwater discharges through sediments

shallow seismic reflection mapping of the overburden bedrock interface with the engineering seismograph some simple techniques where unconsolidated overburden exceeds 20 m in thickness the reflection method may be efficiently used with a 12 channel engineering seismograph to map topography on the overburden bedrock interface as well as possible structure within the overburden the two techniques we suggest are the simplest forms of reflection profiling which can be applied with a minimum amount of equipment which we suggest is a 12 channel enhancement seismograph a 12 geophone array and a hammer source these techniques require good transmission characteristics of the overburden as well as a sharp velocity discontinuity at the overburden bedrock interface for data processing and display a microcomputer is essential

comparison of surface seismic sources at the co2sink site ketzin germany 3d seismic time lapse surveys 4d seismics are an essential tool for large scale reservoir characterization the target reservoir of the ketzin pilot project for co2 storage is a saline aquifer of the heterogeneous stuttgart formation upper triassic in the northeast german basin the focus of this project is on testing and further developing monitoring co2 storage technologies for time lapse seismic monitoring three seismic surface sources were characterized with respect to s n signal to noise ratios signal penetration and frequency content by analysis of raw shot gathers and stacked sections along two lines at the ketzin site differences in reflectivity between these 2d lines reflect the differences in the nature of the sources tested and how they influence the signal bandwidth resolution and signal energy all three sources image the target horizon the weight drop source was recommended as the primary source for 3d surveys based mainly on logistics and cost results of processing including equalization of a 4d 3d time lapse data set from the ketzin site and cross correlation indicate that the injected co2 can be monitored the highly irregular amplitude response on the time lapse data can be attributed to the reservoir heterogeneity time lapse seismic processing petrophysical measurements on core samples and geophysical logging of co2 saturation levels allow for an estimate of the total amount of co2 visible in the seismic data to be made in spite of some uncertainty the close agreement between the injected and observed amount is encouraging for quantitative monitoring of a co2 storage site using seismic methods by integrating seismic modeling and multiphase fluid flow simulations the impact of the reservoir temperature on the 4d seismic data from ketzin was estimated the modeled time lapse seismic differences for two temperature scenarios present in the reservoir are minor regarding the qualitative analysis however the influence of temperature on the volumetric estimation of the co2 using the 4d seismic data is significant future issues to be considered include expanding the temperature range 34 38 c in this study to be investigated and the resulting effects on the seismic response as well as the role of the reservoir heterogeneity in addition it would be important to investigate the impact of temperature on the co2 storage at other sites with favorable p t conditions in the reservoir further seismic modeling using results of petrophysical experiments for estimating the effect of the co2 injection at the ketzin site on the ava avo response on time lapse seismic data was performed two effects were considered the co2 saturation and the pore pressure related effects the results indicate that it is worth investigating if it is possible to discriminate between these effects on future 3d repeat surveys at the ketzin site

the role of swash infiltration in determining the beachface gradient a numerical study on sand and gravel beaches the increase of the gradient of the beachface with increasing sediment size has been attributed to swash infiltration the present study uses a process based numerical model to examine in detail the role of swash infiltration in determining the beachface gradient it is found that swash infiltration increases the onshore asymmetry in the swash flow thereby enhancing onshore sediment transport and resulting in relatively steep beachface gradients however the accretionary effects of swash infiltration are only evident when the rate of infiltration is sufficiently large i e when the total infiltration volume over a wave cycle exceeds c 2 of the uprush volume this threshold is attained when the hydraulic conductivity exceeds 1 cm s which is approximately equivalent to a grain size coarser than 1 5 mm this finding suggests that the correlation between beachface gradient and sediment size observed on sandy beaches is not due to enhanced swash asymmetry caused by swash infiltration for gravel beaches however swash infiltration is likely to be the dominant factor in controlling the beachface gradient with increased hydraulic conductivity i e sediment size resulting in steeper beachface gradients c 2001 elsevier science b v all rights reserved

mapping shallow faults at the evrona playa site using high resolution reflection method a shallow high resolution seismic reflection survey was carried out at the evrona playa site in the southern arava valley israel the aim of the survey was to detect and map faults in the shallow subsurface upper 100 150 m and establish the relationship of the morphological features revealed by aerial photographs and surface geological mapping with the faults detected in the subsurface the survey included three seismic lines shot using the p wave technique and one sh wave line which overlapped one of the p wave lines the seismic energy source on all the lines was a sledge hammer the acquired reflection data were of good quality and did not require special processing efforts the seismic sections along the lines show a sequence of reflected events within the 8 150 m range at several locations continuity of the events is interrupted by a system of faults these faults form flower structures apparently related to strike slip motions typical of the region comparison of the faults mapped on the seismic sections with those expressed by surface morphological features generally show good correspondence the results of the seismic survey provide important information for the study of paleoseismicity and seismic hazards in the investigated area

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

onshore high resolution seismic profiling applied to sedimentology high resolution seismic profiling is a valuable method for the exploration of the shallow subsurface currently a resolution of 0 5 m can be attained this resolution is sufficient to recognize small sedimentary features channels dunes linear ridges etc and to reconstruct the environment of deposition the surveys described in this paper were carried out under favorable conditions on intertidal flats and beaches

rapid water table fluctuations within the beach face implications for swash zone sediment mobility abstract to incorporate groundwater infiltration exfiltration in the description of swash zone sediment transport it is required that the details of groundwater dynamics within the beach face be clarified field measurements of the vertical pore pressure structure within the bed identify capillarity effects as the primary mechanism driving rapid and relatively large magnitude water table fluctuations within the swash zone when the upper extent of the fully saturated capillary fringe coincides with the beach face surface wave runup produces near instantaneous increase in pore pressures across the capillary fringe corresponding to a rapid rise of the phreatic surface i e the surface where pore pressure atmospheric pressure to the sand surface therefore counter to previous conclusions in the literature the rapid rise and fall of the water table under the swash zone do not equate to regions of the beach face alternating between states that favor sediment deposition unsaturated and erosion saturated similar reports that rapid fluctuations of the water table within the beach face correspond to rapid rates of vertical flow and hence bed fluidization are also a misinterpretation field measurements and a careful consideration of saturation and pore pressure characteristics within the beach face demonstrate that rapid water table rise is associated with minute downwards swash infiltration rather than rapid upwards groundwater exfiltration the cause of the pressure fluctuations and phreatic surface oscillations is the alternating appearance and disappearance of meniscuses at the sand surface which generate pressure head fluctuations of decimeters due to the addition of millimeters of water

seismic reflection investigations of sinkholes beneath interstate highway 70 in kansas seismic reflection studies were performed across actively developing sinkholes located astride interstate highway 70 in russell county kansas results indicate that high resolution seismic reflection surveys are useful in the subsurface investigation of some sinkholes in particular we were able to delineate the subsurface vertical and horizontal extent of the sinkholes because of the excellent acoustical marker bed characteristics of the stone corral anhydrite the seismic reflection evidence presented here combined with borehole information from 1967 suggest that the stone corral anhydrite has been down dropped within one of the sinkholes as much as 30 m in 13 years the seismic reflection method is potentially useful in engineering studies of other sinkholes and karst features the seismic data presented here were obtained in the presence of relatively heavy highway traffic i e up to a few dozen vehicles per minute using the minisosie recording technique

swash groundwater dynamics in a sandy beach laboratory experiment abstract experiments are carried out in a wave basin in order to study the swash groundwater interaction a set of wave gages and pressure sensors are used to monitor the free surface and groundwater dynamics the study is based on the comparison of two selected cases which differ by the gravity and infragravity forcing conditions the features of wave breaking in the surf zone the presence of a standing wave attached to the beach face and the wave setup at the shoreline significant differences are observed in the response of the swash groundwater system the water table overheight appears to be controlled by the amount of infragravity energy available at the shore cyclic beach drainage processes can be observed when the water table is low significant time averaged and time resolved flows are observed into the sand depending on the swash hydrodynamics the presence of a gravity standing wave modulation attached to the shore is shown to affect swash and groundwater dynamics most of the pressure gradients observed under the swash zone are related to infiltration flows and are thus related to moderate increase of the sediment relative weight

wave induced water table fluctuations sediment transport and beach profile change modeling and comparison with large scale laboratory experiments coastal groundwater systems can have a considerable impact on sediment transport and foreshore evolution in the surf and swash zones process based modeling of wave motion on a permeable beach taking into account wave aquifer interactions was conducted to investigate the effects of the unconfined coastal aquifer on beach profile evolution and wave shoaling on the water table the simulation first dealt with wave breaking and wave runup rundown in the surf and swash zones nearshore hydrodynamics and wave propagation in the cross shore direction were simulated by solving numerically the two dimensional navier stokes equations with a k e turbulence closure model and the volume of fluid technique the hydrodynamic model was coupled to a groundwater flow model based on seawat 2000 the latter describing groundwater flow in the unconfined coastal aquifer the combined model enables the simulation of wave induced water table fluctuations and the effects of infiltration exfiltration on nearshore sediment transport numerical results of the coupled ocean aquifer simulations were found to compare well with experimental measurements wave breaking and infiltration exfiltration increase the hydraulic gradient across the beachface and enhance groundwater circulation inside the porous medium the large hydraulic head gradient in the surf zone leads to infiltration across the beachface before the breaking point with exfiltration taking place below the breaking point in the swash zone infiltration occurs at the upper part of the beach and exfiltration at the lower part the simulations confirm that beaches with a low water table tend to be accreted while those with a high water table tend to be eroded

measurements and modeling of swash induced pressure gradients in the surface layers of a sand beach field measurements of swash induced hydraulic pressure gradients in the surface layers of a sand beach are presented and compared to a one dimensional diffusion model the model provides a description of flow through a porous quasi saturated sediment and is driven by the time varying swash depth on the beach surface the field measurements broadly show four different types of pressure propagation behavior which appear dependent on cross shore position in the swash zone the hydraulic gradients within the surface layers of the beach are typically found to be much greater than those likely to be generated by tidally induced groundwater flow in these instances the diffusion model generally provides a good description of the data however very large hydraulic gradients are frequently observed just below the beach surface and these cannot be adequately described by the diffusion model a mechanism is proposed through which these large hydraulic gradients could be generated

observations of wave run up and groundwater seepage line motions on a reflective to intermediate meso tidal beach abstract swash sw and ground water seepage line gwsl motions have been recorded at an exposed meso tidal reflective to intermediate beach using a coastal video monitoring system during a 15 month period the monitoring period allowed the collection of imagery under a wide variety of wave and beach morphological conditions and sw and gwsl velocities were extracted on a wave by wave basis the continuous double bounded kumaraswamy kw probability distribution is proposed to parameterize the sw and gwsl height distributions and since the distribution shape of the latter was shown to be influenced by the tidal elevation generic tidal elevation dependent kw pdfs are proposed the beach face slope more than any other factor tested was found to apply certain control to the mean uprush backwash and gwsl velocities the results also indicate that in reflective to intermediate beaches the gwsl lies between the mean and 2 exceedance swash elevation with the occurrence of swash running above a saturated beach face being controlled by the tidal gradient and the significant wave height

large scale laboratory investigation into the effect of varying back barrier lagoon water levels on gravel beach morphology and swash zone sediment transport abstract it is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea specifically a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion while the reverse is thought to hold for a high beach groundwater table here we use the results of a carefully designed series of tests conducted in the delta flume the netherlands as part of the barrier dynamics experiment bardex to unequivocally demonstrate the validity of this assertion during the experiment a 4 m high and 50 m long gravel barrier d 50 11 mm was constructed within the central region of the 250 m long and 7 m deep wave flume enabling a back barrier lagoon to be located at its landward side the groundwater table in the beach was manipulated by lowering and raising the lagoon level and the gravel beach was subjected to variable wave conditions and sea lagoon levels using as the initial beach profile the morphology resulting from 90 min of wave forcing with the sea and lagoon at the same level the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion the divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the bulk swash hydrodynamics i e based on single point velocity measurements arising from a difference in the amount of swash infiltration into the unsaturated beach instead application of a sediment transport model that accounts for the effects of in exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface due to the large hydraulic conductivity of gravel k o 0 1 m s 1 the effect of altered shear stresses due to in exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches

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

applications of land based high resolution seismic reflection analysis to quaternary and geomorphic research abstract the availability in the last few years of low cost microcomputers and multichannel seismographs has made possible the application of high resolution digital seismic reflection profiling to quaternary problems seismic analysis of the subsurface can provide continuous two dimensional sections containing detailed structural and stratigraphic information a review of the general principles of shallow seismic reflection methods includes the nature of seismic sources the use of shotgun shells the application of the optimum offset method data processing and the issue of site dependency a brief overview is provided of seismic and sequence stratigraphy four case studies illustrate the application of reflection seismic profiling 1 champlain sea sediments late wisconsinan on the flank of the gatineau hills near quyon quebec 2 the definition of bedrock valleys beneath pleistocene deposits near shawville quebec 3 the fill of a linear depositional basin okanagan valley british columbia 4 the seismic signatures of topset and foreset beds slope failures and a distributary channel of the fraser river delta british columbia

a workshop examination of shallow seismic reflection surveying in september 1996 the office of basic energy sciences of the u s department of energy doe sponsored a research workshop in berkeley california where approximately 20 participants analyzed the potential and limitations of near surface seismic reflection methods

trace element cycling in a subterranean estuary part 2 geochemistry of the pore water abstract submarine groundwater discharge sgd is an important source of dissolved elements to the ocean yet little is known regarding the chemical reactions that control their flux from sandy coastal aquifers the net flux of elements from sgd to the coastal ocean is dependent on biogeochemical reactions in the groundwater seawater mixing zone recently termed the subterranean estuary this paper is the second in a two part series on the biogeochemistry of the waquoit bay coastal aquifer subterranean estuary the first paper addressed the biogeochemistry of fe mn p ba u and th from the perspective of the sediment composition of cores charette et al charette m a sholkovitz e r hansell c m 2005 trace element cycling in a subterranean estuary part 1 geochemistry of the permeable sediments geochim cosmochim acta 69 2095 2109 this paper uses pore water data from the subterranean estuary along with bay surface water data to establish a more detailed view into the estuarine chemistry and the chemical diagenesis of fe mn u ba and sr in coastal aquifers nine high resolution pore water groundwater profiles were collected from the head of the bay during july 2002 there were non conservative additions of both ba and sr in the salinity transition zone of the subterranean estuary however the extent of sr release was significantly less than that of its alkaline earth neighbor ba pore water ba concentrations approached 3000 nm compared with 25 50 nm in the surface waters of the bay the pore water sr salinity distribution suggests a 26 elevation in the amount of sr added to the subterranean estuary the release of dissolved ba to the mixing zone of surface estuaries is frequently attributed to an ion exchange process whereby seawater cations react with ba from river suspended clay mineral particles at low to intermediate salinity results presented here suggest that reductive dissolution of mn oxides in conjunction with changes in salinity may also be an important process in maintaining high concentrations of ba in the pore water of subterranean estuaries in contrast pore water u was significantly depleted in the subterranean estuary a result of sgd driven circulation of seawater through reducing permeable sediments this finding is supported by surface water concentrations of u in the bay which were significantly depleted in u compared with adjacent coastal waters using a global estimate of sgd we calculate u removal in subterranean estuaries at 20 106 mol u y 1 which is the same order of magnitude as the other major u sinks for the ocean our results suggest a need to revisit and reevaluate the oceanic budgets for elements that are likely influenced by sgd associated processes

glaciotectonized quaternary sediments at dinas dinlle gwynedd north wales and their bearing on the style of deglaciation in the eastern irish sea abstract the sedimentology and structure of late quaternary sediments exposed in a coastal section at dinas dinlle north wales are described the deposits from two small hills the northern one being more prominent and containing northward dipping units of gravel and diamicton bounded by clay lined thrust faults the southern hill comprises complex folded sands and gravels overlying a basal till surface high resolution seismic surveys along the beach 50 m west of the cliffs show a roughly horizontal rockhead lying some 35 m below beach level and demonstrate that thrust faults penetrate the entire quaternary sequence to a detachment immediately above rockhead thrust units in the exposed cliff section show excellent correlation with the seismic sequence 50 m to the west indicating a strike of 080 260 balanced cross section techniques were applied to an initial simple layered sequence comprising a lower irish sea till overlain by a coarsening upwards sand to gravel unit followed by upper till mixed lithology including welsh and northern provenance and finally an upper gravel unit shortening of approximately 54 is estimated within the thrust sequence it is concluded that the two isolated hills at dinas dinlle are erosional remnants of a formerly more extensive push moraine extending westwards into caernarfon bay which has now been truncated by coastal retreat deglaciation of the area was interrupted by ice sheet readvance towards 170 across a proglacial surface

temporal variability of exchange between groundwater and surface water based on high frequency direct measurements of seepage at the sediment water interface 1 seepage at the sediment water interface in several lakes a large river and an estuary exhibits substantial temporal variability when measured with temporal resolution of 1 min or less already substantial seepage rates changed by 7 and 16 in response to relatively small rain events at two lakes in the northeastern usa but did not change in response to two larger rain events at a lake in minnesota however seepage at that same minnesota lake changed by 10 each day in response to withdrawals from evapotranspiration seepage increased by more than an order of magnitude when a seiche occurred in the great salt lake utah near the head of a fjord in puget sound washington seepage in the intertidal zone varied greatly from 115 to 217 cm d 1 in response to advancing and retreating tides when the time averaged seepage was upward at 43 cm d 1 at all locations seepage variability increased by one to several orders of magnitude in response to wind and associated waves net seepage remained unchanged by wind unless wind also induced a lake seiche these examples from sites distributed across a broad geographic region indicate that temporal variability in seepage in response to common hydrological events is much larger than previously realized at most locations seepage responded within minutes to changes in surface water stage and within minutes to hours to groundwater recharge associated with rainfall likely implications of this dynamism include effects on water residence time geochemical transformations and ecological conditions at and near the sediment water interface

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

numerical model of swash motion and air entrapment within coarse grained beaches abstract the paper presents a numerical model for bore driven swash on permeable coarse grained beaches the surface flow module is modelled using the non linear shallow water equations nlswes solved using the godunov based finite volume ader scheme which is suitable for handling steep bores as well as large source terms in the nlswes the subsurface flow comprises i infiltration and exfiltration modelled as vertical piston like flow ii horizontal pore air movement within the unsaturated region of the beach iii the horizontal groundwater flow model predictions of the surface and subsurface flow are in good agreement with measurements from large scale laboratory experiments for swash on permeable immobile beaches in these simulations air velocity was sufficiently small to justify using darcy s resistance law for the air flow whereas the quadratic forchheimer law had to be used for the infiltration and groundwater flow the validated numerical model provides insight into the surface subsurface water exchange for bore driven swash on coarse grained beaches the impact of air entrapped between the wetting front and the groundwater level on the water exchange is examined in particular

heat transport dynamics at a sandy intertidal zone 1 intertidal zones are spatially complex and temporally dynamic environments coastal groundwater discharge including submarine groundwater discharge may provide stabilizing conditions for intertidal zone permeable sediments in this study we integrated detailed time series temperature observations porewater pressure measurements and two dimensional electrical resistivity tomography profiles to understand the coupled hydraulic thermal regime of a tropical sandy intertidal zone in a fringing coral reef lagoon rarotonga cook islands we found three heating patterns across the 15 m study transect over tidal and diel periods 1 a highly variable thermal regime dominated by swash infiltration and changes in saturation state in the upper foreshore with net heat import into the sediment 2 a groundwater supported underground stable cool region just seaward of the intertidal slope break also importing heat into the subsurface and 3 a zone of seawater recirculation that sustained consistently warm subsurface temperatures that exported heat across the sediment water interface simple calculations suggested thermal conduction as the main heat transport mechanism for the shallow intertidal sediment but deeper and or multidimensional groundwater flow was required to explain temperature patterns beyond 20 cm depth temperature differences between the distinct hydrodynamic zones of the foreshore site resulted in significant thermal gradients that persisted beyond tidal and diel periods the thermal buffering of intertidal zones by coastal groundwater systems both at surface seeps and in the shallow subsurface can be responsible for thermal refugia for some coastal organisms and hotspots for biogeochemical reactions

an ultrashallow sh wave seismic reflection experiment on a subsurface ground model an sh wave seismic reflection experiment was conducted to evaluate the feasibility and cost effectiveness of reflection imaging ultrashallow targets commonly encountered in engineering groundwater and environmental investigations it was carried out on a purpose built subsurface ground model consisting of a concrete layer at a depth from 2 85 5 m and a low velocity overburden 80 and 150 m s for s and p waves respectively constituted of filling material with the water table 2 60 m deep high quality cdp data acquired by using a 10 kg sledgehammer and newly designed horizontal detectors allowed us to obtain an extremely detailed stacked section with a minimal amount of processing uncertainty in determining the depth and horizontal dimensions of the concrete model was estimated to be 0 2 and 0 3 m respectively however the dominant frequencies lower than 150 hz the low transmission coefficient at the upper interface and the relatively high velocity 900 m s of the concrete layer prevented

seismic investigation of near surface geological structure in the paducah kentucky area application to earthquake hazard evaluation abstract seismics method were used to evaluate shallow geological conditions at 33 sites in the vicinity of paducah kentucky a combined set of p and s wave seismic refraction and reflection soundings were used in addition to local borehole information to produce structure maps of 1 a shallow 160 m deep shear wave velocity contrasts across the shallow unconformity were generally 2 to 1 while the contrast at the top of the paleozoic bedrock exceeds 5 to 1 these seismic boundaries have been determined to be very important in modelling and interpreting earthquake ground motion amplification in the paducah area the quality and accuracy of the data and the cost effective nature of the methods suggest that other communities in areas at risk to damage from seismic activity with foundation conditions comparable to paducah might benefit from similar characterization in order 1 to identify seismically hazardous near surface geological conditions and 2 to develop geological models that could be used in computer simulations of site response

shallow to very shallow high resolution reflection seismic using a portable vibrator system in shallow engineering geophysical applications there is a lack of controlled nondestructive high resolution mapping tools particularly for the target depth that ground penetrating radar cannot reach but which is too shallow for other conventional geophysical methods for soft soil this corresponds to a depth of 2 to 30 m we have developed a portable high frequency p wave vibrator system that is capable of bridging this gap as far as the important contribution of the seismic source is concerned penetration and resolution can be individually controlled through easy modulation of the sweep signal generated by this electromagnetic vibrator the feasibility of this system has been tested in shallow 10 50 m to very shallow 0 10 m applications seven field data sets representing varying geology site conditions and exploration targets are presented to illustrate the applicability the first three examples show the potential of this portable vibrator source in shallow applications under favorable

comparison of standard horizontal geophones and newly designed horizontal detectors to increase the speed and efficiency of shallow seismic sh wave data recording and to decrease acquisition costs we have designed constructed and tested a new velocity tool that detects horizontal movements better than standard horizontal geophones a comparative evaluation of significant characteristics and field performances of this new detector was conducted through laboratory and field tests on two sets of receivers one consisting of 24 prototypes of the new detector and the other consisting of 24 standard horizontal geophones laboratory measurements revealed similar behaviors of impedance curves and geophone responses for the two types of detectors but the impedance amplitudes and the frequency response amplitudes of the new detector were twice those of the standard geophones however comparison of the horizontal to vertical response ratios proved that the new detector better discriminates 6 db on average between the horizontal and vertical excitements field data proved that the energy

shallow seismic reflection in a mine gallery abstract the technique of seismic reflection was used to survey the mineral deposits in a copper mine exploiting the sulfide minerals galena pyrite and chalcopyrite this approach required the adaptation of seismic reflection techniques to the specific features of the mine which are thin mineral bearing layers variable thickness of overlying strata and innaccessible rock faces field measurements were made according to a four fold multiple coverage after an initial survey we were able to develop a model that allowed the evaluation of the optimal offset based on synthetic traces deconvolution considerably improved the procedure together with the definition and the ability to determine the depth of the upper contact of the mineral deposit finally the application of complex traces analysis mainly of instantaneous amplitude permitted us to specify the degree of continuity in the mineral horizon under survey

swash infiltration exfiltration and sediment transport field measurements of vertical pore pressure gradients within the bed are used to quantify instantaneous 8 hz rates of swash infiltration exfiltration across the beach face cyclic infiltration exfiltration is associated with individual swash events with observed vertical flow rates o 10 3 m s rates of net swash groundwater exchange i e through bed flow integrated over several swash cycles are two orders of magnitude smaller at the timescale of individual swashes vertical pore pressure gradients within the beach face are much greater than horizontal pore pressure gradients this permits application of the numerical solution of darcy s law for one dimensional vertical flow to model fluctuating pore pressures and hence vertical through bed flow vertical flow through a porous bed modifies sediment mobility in at least two ways 1 seepage forces change the effective weight of surficial sediments and 2 boundary layer thickening or thinning result in altered bed shear stresses by considering these two opposing effects separately a new shields parameter is derived that incorporates terms for through bed flow simulation of time varying seepage force and bed stress effects over an uprush backwash cycle suggests that the effect of altered bed stresses dominates over the change in effective weight and that infiltration exfiltration effects are most important during uprush simulated transport rates are increased by up to 40 of the peak transport rate during uprush and reduced by 10 during backrush in summary swash infiltration exfiltration across a saturated beach face enhances the net upslope transport of sediment

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

swash aquifer interaction in the vicinity of the water table exit point on a sandy beach the coupling of sandy beach aquifers with the swash zone in the vicinity of the water table exit point is investigated through simultaneous measurements of the instantaneous shoreline swash front location pore pressures and the water table exit point the field observations reveal new insights into swash aquifer coupling not previously gleaned from measurements of pore pressure only in particular for the case where the exit point is seaward of the observation point the pore pressure response is correlated with the distance between the exit point and the shoreline in that when the distance is large the rate of pressure drop is fast and when the distance is small the rate decreases the observations expose limitations in a simple model describing exit point dynamics which is based only on the force balance on a particle of water at the sand surface and neglects subsurface pressures a new modified form of the model is shown to significantly improve the model data comparison through a parameterization of the effects of capillarity into the aquifer storage coefficient the model enables sufficiently accurate predictions of the exit point to determine when the swash uprush propagates over a saturated or a partially saturated sand surface potentially an important factor in the morphological evolution of the beach face observations of the shoreward propagation of the swash induced pore pressure waves ahead of the runup limit shows that the magnitude of the pressure fluctuation decays exponentially and that there is a linear increase in time lags behavior similar to that of tidally induced water table waves the location of the exit point and the intermittency of wave runup events is also shown to be significant in terms of the shore normal energy distribution seaward of the mean exit point location peak energies are small because of the saturated sand surface within the seepage face acting as a rigid lid and limiting pressure fluctuations landward of the mean exit point the peak energies grow before decreasing landward of the maximum shoreline position

downhole seismic logging for high resolution reflection surveying in unconsolidated overburden downhole seismic velocity logging techniques have been developed and applied in support of high resolution reflection seismic surveys for shallow high resolution reflection surveying within unconsolidated overburden velocity depth control can sometimes be difficult to achieve as well unambiguous correlation of reflections with overburden stratigraphy is often problematic data obtained from downhole seismic logging can provide accurate velocity depth functions and directly correlate seismic reflections to depth the methodologies described in this paper are designed for slimhole applications in plastic cased boreholes minimum id of 50 mm and with source and detector arrays that yield similar frequency ranges and vertical depth resolutions as the surface reflection surveys compressional p wave logging uses a multichannel hydrophone array with 0 5 m detector spacings in a fluid filled borehole and a high frequency in hole shotgun source at the surface overlapping array positions downhole result