electrical resistivity imaging of the architecture of substream sediments 1 the modeling of fluvial systems is constrained by a lack of spatial information about the continuity and structure of streambed sediments there are few methods for noninvasive characterization of streambeds invasive methods using wells and cores fail to provide detailed spatial information on the prevailing architecture and its continuity geophysical techniques play a pivotal role in providing spatial information on subsurface properties and processes across many other environments and we have applied the use of one of those techniques to streambeds we demonstrate through two examples how electrical resistivity imaging can be utilized for characterization of subchannel architecture in the first example electrodes installed in riparian boreholes and on the streambed are used for imaging under the river bed the thickness and continuity of a highly permeable alluvial gravel layer overlying chalk in the second example electrical resistivity images determined from data collected using electrodes installed on the river bed provide a constrained estimate of the sediment volume behind a log jam vital to modeling biogeochemical exchange which had eluded measurement using conventional drilling methods owing to the boulder content of the stream the two examples show that noninvasive electrical resistivity imaging is possible in complex stream environments and provides valuable information about the subsurface architecture beneath the stream channels

sedimentary architecture and 3d ground penetrating radar analysis of gravelly meandering river deposits neckar valley sw germany sedimentological outcrop analysis and sub surface ground penetrating radar gpr surveys are combined to characterize the three dimensional sedimentary architecture of quaternary coarse grained fluvial deposits in the neckar valley sw germany two units characterized by different architectural styles are distinguished within the upper part of the gravel body separated by an erosional unconformity i a lower unit dominated by trough shaped depositional elements with erosional concave up bounding surfaces that are filled by cross bedded sets of mainly openwork and filled framework gravel and ii an upper unit characterized by gently inclined sheets of massive and openwork gravels with thin sandy interlayers that show lateral accretion on a lower erosional unconformity the former is interpreted as confluence scour pool elements formed in a multi channel possibly braided river system the latter as extensive point bar deposits formed by the lateral migration of a meandering river channel the lateral accretion elements are locally cut by chute channels mainly filled by gravels rich in fines and by fine grained abandoned channel fills the lateral accretion elements are associated with gravel dune deposits characterized by steeply inclined cross beds of alternating open and filled framework gravel floodplain fines with a cutbank and point bar morphology cover the gravel deposits the gpr images revealing the three dimensional geometries of the depositional elements and their stacking patterns confirm a change in sedimentary style between the two stratigraphic units the change occurred at the onset of the holocene as indicated by 14 c dating of wood fragments and is related to a re organization of the fluvial system that probably was driven by climatic changes the integration of sedimentological and gpr results highlights the heterogeneity of the fluvial deposits a factor that is important for modelling groundwater flow in valley fill aquifers

topographic vorticity generation submesoscale instability and vortex street formation in the gulf stream meanders and eddies are routinely observed in the gulf stream along the south atlantic bight we analyze here the instability processes that lead to the formation of submesoscale eddies on the cyclonic side of the gulf stream at the exit of the florida straits using very high resolution realistic simulations the positive relative vorticity and potential vorticity on the cyclonic side of the gulf stream are strongly intensified in the straits due to topographic drag along the continental slope the bottom drag amplifies the cyclonic shear by generating large positive vertical vorticity values within the sloped turbulent bottom boundary layer downstream from the straits the current becomes unstable to horizontal shear instability rolls up and forms a street of submesoscale vortices the vortices expand as they propagate northward along the shelf where they can generate large vertical displacements and enhance cross shelf exchanges

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

generation of submesoscale frontal eddies in the agulhas current copyright 2019 brill due to copyright restrictions the attached pdf file contains the abstract of the full text item for access to the full text item please consult the publisher s website https agupubs onlinelibrary wiley com doi full 10 1029 2019jc015229

a simple model for sheddies ocean eddies formed from shed vorticity abstractrecent studies show that vertical eddy diffusivity is sufficient on its own to introduce intense horizontal shear layers at sloping ocean margins molemaker et al gula et al dewar et al these layers influence mesoscale energy and potential vorticity budgets but cannot be fully represented in models without sloping boundaries no slip boundary conditions and sufficiently high resolution this paper investigates the detachment of these shear layers and their subsequent rolling up into concentrated eddies these shed eddies or sheddies may have significant oceanographic impacts their growth is considered using a simple point vortex model that adapts the brown michael model of vortex shedding to quasigeostrophic flow and allows detailed consideration of the vorticity fluxes the model shows good qualitative agreement with observations and experimental and numerical results it is applied to a number of examples of well known cases of sheddy formation including the agulhas cyclones calif

characteristics of high resolution hydraulic head profiles and vertical gradients in fractured sedimentary rocks summary accurately identifying the position of vertical hydraulic conductivity k v contrasts is critical to the delineation of hydrogeologic units that serve as the basis for conceptual and numerical models of groundwater flow high resolution head profiles have identified the position and thickness of k v contrasts in clayey aquitards but this potential has not yet been thoroughly evaluated in sedimentary rocks this paper describes an experiment in which head profiles with the highest technically feasible resolution were obtained using westbay multilevel systems mls installed in 15 cored holes at three sedimentary rock research sites with contrasting geologic and flow system conditions mlss were installed to maximum depths between 90 and 260 m with 2 5 monitoring zones per 10 m head profiles were measured over multiyear periods the vertical component of hydraulic gradient i e vertical gradient was calculated for each pair of adjacent monitoring intervals in every mls and then categorized based on its repeatability to facilitate interpretation of k v contrasts and comparisons within boreholes between boreholes at the same site and between sites the head and vertical gradient profiles from all three sites display systematic i e simple geometric shapes defined by repeatable intervals of no to minimal vertical gradient indicating relatively high k v units bounded by shorter depth intervals with large up to 50 m m vertical gradients indicating relatively low k v units the systematic nature of the profiles suggests flow in regular and interconnected fracture networks rather than dominated by a few key fractures with irregular orientations the low k v units were typically thin with their positions and thicknesses not predicted by lithostratigraphy or detailed lithologic geophysical and horizontal hydraulic conductivity data hence the position and thickness of units with contrasting k v would not be evident if mlss with the conventional number of monitoring zones had been used furthermore the detailed profiles can be strongly diagnostic of hydrogeologic unit boundaries or layers and can be used to improve the quantitative assessment of flow system conditions that is foundational to understanding contaminant plume migration

origin of vertical shafts in bedrock along the eramosa river valley near guelph southern ontario numerous vertical to subvertical cylindrical shafts occur in the rugged exposures of the middle silurian amabel formation bedrock along the eramosa river approximately 10 km northeast of guelph these shafts vary from 1 m to 10 m in diameter with depths as great as 12 m they can occur as isolated depressions but more commonly are clustered closely together and many coalesce to form sinuous bedrock walls these depressions may contain soil fine sediment rubble from the surrounding dolomite bedrock and rounded clasts of precambrian basement lithologies till is conspicuously absent these shafts occur in close proximity to cavernous pores that were formed during pre wisconsinan to early wisconsinan time suggesting a possible karstic origin the cylindrical shafts however with their greater midpoint diameters sculpted interiors and inclined axes and their lack of vertical flutes and till are more likely to have originated from glaciofluvial discharge at the end of the late wisconsinan the d

seasonal thermal fronts on the northern south china sea shelf satellite measurements and three repeated field surveys seasonal thermal fronts associated with wind driven coastal downwelling upwelling in the northern south china sea are investigated using satellite measurements and three repeated fine resolution mapping surveys in winter spring and summer the results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons which tend to be approximately aligned with the 20 100 m isobaths driven by the prevailing winter summer monsoon the band shaped fronts were observed with a magnitude exceeding 0 1 degrees c km in the subsurface and accompanied by energetic coastal downwelling upwelling due to shoreward offshore ekman transport the downward upward tilting of seasonal thermoclines across the shelf exceeds 20 m significantly contributing to the development of thermal fronts over the shelf in addition the diagnostic analysis of potential vorticity pv suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling favorable monsoon forcing this is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing at the same time the coastal currents are substantially regulated by the seasonal winds an expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region these results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf

the north atlantic eddy heat transport and its relation with the vertical tilting of the gulf stream axis correlations between temperature and velocity fluctuations are a significant contribution to the north atlantic meridional heat transport especially at the northern boundary of the subtropical gyre in satellite observations and in a numerical model at 1 12 resolution a localized pattern of positive eddy heat flux is found northwest of the gulf stream downstream of its separation at cape hatteras it is confined to the upper 500 m a simple kinematic model of a meandering jet can explain the surface eddy flux taking into account a spatial shift between the maximum velocity of the jet and the maximum cross jet temperature gradient in the gulf stream such a spatial shift results from the nonlinear temperature profile and the vertical tilting of the velocity profile with depth the numerical model suggests that the meandering of the gulf stream could account at least in part for the large eddy heat transport of order 0 3 pw near 36 n in the north atlantic and for its compensation by the mean flow

formation and dynamics of a long lived eddy train in the south china sea a modeling study abstracta process oriented numerical modeling study was conducted to investigate the formation and underlying forcing of an anticyclonic eddy train observed in the northern south china sea observations showed that long lived anticyclonic eddies formed an eddy train along an eastward separated jet across the northern south china sea in summer the eddy train plays a critical role in regulating ocean circulation in the region forced by the southwesterly monsoon and prevailing dipole wind stress curl in the summer the northward coastal jet separates from the west boundary of the south china sea basin and overshoots northeastward into the basin the anticyclonic recirculation of the separated jet forms the first anticyclonic eddy in the eddy train the jet meanders downstream with a strong negative shear vorticity that forms a second and a third anticyclonic eddy along the jet s path these three eddies form the eddy train these eddies weaken gradually with depth from surface but they can extend to appro

mesoscale and submesoscale processes in the southeast atlantic and their impact on the regional thermohaline structure the turbulent processes in the cape basin the southeasternmost gate of the atlantic ocean play a key role in the transport and mixing of upper to intermediate water masses entering the area from the indian ocean making them especially relevant for the indo atlantic transfer of heat and salt in this paper two numerical simulations at different horizontal resolutions are used to study meso and submesoscale dynamics their phenomenology their evolution and their impact on the local water masses submesoscale processes seasonally affect both the upper and intermediate layers but there are clear dynamical differences between the two layers several types of instabilities underline this spatial and temporal variability near the surface mixed layer instabilities occur during winter while mesoscale driven instabilities as the symmetric type prevail in summer the connection between these two seasonal regimes is ensured in anticyclonic eddies and within the mixed layers by charney baroclinic instabilities involved in the local formation and subduction of mode water that we have dubbed as agulhas rings mode water intermediate depths are instead characterized by mesoscale mechanisms of density compensation and lateral stirring of the tracer variance triggering a significant filamentogenesis whose vertical scales are comparable to those mentioned in previous studies this leads to a particularly efficient mixing of antarctic intermediate waters of indian and atlantic origins lagrangian estimates highlight the new and significant role of fine scale structures in setting the water masses properties of upper and lower thermocline waters materializing the indo atlantic exchange and therefore potentially affecting the global ocean circulation

shelf edge tide correlated eddies along the southeastern united states 1 high frequency radar observations in the southeastern united states have revealed sequences of small short lived cyclonic eddies along the shoreward edge of the gulf stream that spin up as the local tide turns alongshelf antiparallel to the stream eddies propagate equatorward along the shelf edge sometimes progressing shoreward before dissipating one to three hours later they are distinctly different from gulf stream meander eddies which propagate poleward in this article radar and mooring data are used to establish three important aspects of these new eddies they represent an instability process operating at a previously unidentified frequency scale and cross stream position they contribute to shoreward momentum fluxes defining a link between gulf stream and outer shelf subtidal variability and illustrating a mechanism to justify locally large horizontal eddy viscosity estimates and they transport properties across the shelf edge importing nutrients onto the shelf and transferring heat between the gulf stream and the coastal ocean

using two and three dimensional georadar methods to characterize glaciofluvial architecture abstract the threat of pollution in the shallow subsurface has led to an increasing need to understand how complex heterogeneities in gravel aquifers influence groundwater transport to characterize these heterogeneities we have conducted extensive two dimensional 2 d and three dimensional 3 d ground penetrating radar gpr or georadar surveys in two quarries within the rhine valley of northeastern switzerland the quarries comprised gravel and sand deposited in a proglacial braided river system that followed the maximum wurm stage glaciation after the surveys the terrace walls beneath the two study sites were photographed as they were being excavated by combining information extracted from the 2 and 3 d georadar images with the outcrop photographs it was possible to correlate georadar facies with the various glaciofluvial architectural elements the dominant elements were scour pools formed at or near the confluences of two stream channels and horizontally bedded and massive gravel sheets deposited during moderate to high water flow conditions and exposed during low flow conditions architectural elements were generally elongated parallel to the mean flow directions of the ancient river system variations in the strike of their long axes reflected lateral and vertical changes in the local flow direction time slices showed structural trends not evident on 2 d georadar images and photographs data interpretation was quicker more complete and less ambiguous when georadar facies analyses were based on a combination of georadar vertical profiles and time slices than when based on georadar vertical profiles alone

eddy topography interactions and the fate of the persian gulf outflow the persian gulf feeds a warm and salty outflow in the gulf of oman northern arabian sea the salt climatological distribution is relatively smooth in the gulf of oman and the signature of a slope current carrying salty waters is difficult to distinguish hundreds of kilometers past the strait of hormuz in contrast to other outflows of the world ocean this study focuses on the mechanisms involved in the spreading of persian gulf water pgw in the gulf of oman using a regional primitive equation numerical simulation the authors show that the dispersion of pgw occurs through a regime that is distinct from for example the one responsible for the mediterranean outflow dispersion the background mesoscale eddy field is energetic and participates actively to the spreading of pgw remotely formed eddies propagate into the gulf of oman and interact with the topography leading to submesoscales formation and pgw shedding eddy topography interactions are isolated in idealized simulations and reveal the formation of intense frictional boundary layers generating submesoscale coherent vortices scvs interactions take place at depths encompassing the pgw depth thus scvs trap pgw and contribute to its redistribution from the boundaries to the interior of the gulf of oman the overall efficiency of these processes is confirmed by a strong contribution of eddy salt fluxes in the interior of the basin and is quantified using particle statistics it is found to be a highly dispersive regime with an approximated eddy diffusivity of inline image

assessment of geophysical surveys as a tool to estimate riverbed hydraulic conductivity summary the goal of this project was to investigate to what extent the vertical hydraulic conductivity k v of a riverbed could be estimated by geophysical methods capable of gathering stratigraphic information of large areas in a relatively short time riverbed k v was investigated at four sites along the great miami river the sites represented a variety of riverbed sediment ranging from clay to cobbles estimates of riverbed k v were obtained using a variety of methods at multiple scales including conventional seepage meter slug tests and modeling of heat and water flow between the river and aquifer estimated riverbed k v values were compared to stratigraphic information obtained from geophysical resistivity continuous seismic electromagnetism profiling to assess the usefulness of the geophysical data in predicting k v values seepage meters were used to estimate k v in the upper 0 3 m of the riverbed and yielded k v values ranging from 0 11 to 5 3 m d slug tests at depths between 0 45 and 11 2 m yielded k v values ranging from 0 0284 to 9 46 m d assuming an anisotropy ratio of 0 1 modeling of groundwater flow and heat transport provided perhaps the best estimates of k v over a larger area and longer period of time model derived estimates of k v agreed well with other methods and ranged from 0 015 to 14 9 m d k v values obtained from conventional seepage slug tests and temperature modeling compared well qualitatively to the stratigraphy inferred from electrical resistivity surveys at three out of four study sites discrepancies associated with the fourth site could be due to the existence of a colmation layer a layer of a coarse sediment matrix clogged with fine sediment these findings suggest that geophysical methods cannot be used alone as a method to assess the appropriate ranges of riverbed k v this might especially be true where municipal pumping contributes to riverbed clogging to correlate the resistivity data with hydraulic conductivity both geophysical and hydrogeological methods should be applied

submesoscale instability and generation of mesoscale anticyclones near a separation of the california undercurrent abstractthe california undercurrent cuc flows poleward mostly along the continental slope it develops a narrow strip of large negative vertical vorticity through the turbulent boundary layer and bottom stress in several downstream locations the current separates aided by topographic curvature and flow inertia in particular near point sur ridge south of monterey bay when this happens the high vorticity strip undergoes rapid instability that appears to be mesoscale in eddy resolving simulations but is substantially submesoscale with a finer computational grid the negative relative vorticity in the cuc is larger than the background rotation f and ertel potential vorticity is negative this instigates ageostrophic centrifugal instability the submesoscale turbulence is partly unbalanced has elevated local dissipation and mixing and leads to dilution of the extreme vorticity values farther downstream the submesoscale activity abates and the remaining eddy motions exhibit an upscale organizati

multifrequency seismic detectability of seasonal thermoclines assessed from argo data seismic oceanography is a developing research topic where new acoustic methods allow high resolution teledetection of the thermohaline structure of the ocean first implementations to study the ocean surface boundary layer have recently been achieved but remain very challenging due to the weakness and shallowness of such seismic reflectors in this article we develop a multifrequency seismic analysis of hydrographic data sets collected in a seasonally stratified midlatitude shelf by argo network floats to assess the detectability issue of shallow thermoclines this analysis for which sensitivity to the data reduction scheme used by argo floats for the transmission of the profiles is discussed allows characterizing both the depth location and the frequency dependency of the dominant reflective feature of such complex structures this approach provides the first statistical distribution of the range of variability of the frequency dependent seismic reflection amplitude of the midlatitude seasonal thermoclines we introduce a new parameter to quantify the overall capability of a multichannel seismic setup including the source strength the fold and the ambient noise level to detect shallow thermoclines seismic source signals are approximated by ricker wavelets providing quantitative guidelines to help in the design of seismic experiments targeting such oceanic reflectors for shallow midlatitude seasonal thermoclines we show that the detectability is optimal for seismic peak frequencies between 200 and 400 hz this means that airgun and sparker sources are not well suited and that significant improvements of source devices will be necessary before seismic imaging of osbl structures can be reliably attempted

characterizing large river history with shallow geophysics middle yukon river yukon territory and alaska abstract changes in longitudinal valley fill thickness can provide inferences about fluvial behaviour over millennia increased thickness of channel deposits may reveal climate induced accelerated sediment supply basin subsidence tectonic displacements or rising downstream base level decreases in thickness expressed as terraces may suggest active uplift decreased sediment flux or falling base level within a reach to date methods to characterize valley fills have depended largely on borehole data however recent developments in shallow geophysics make such investigations possible and provide a practical methodology to investigate alluvial rivers we carried out a longitudinal geophysical survey coupled with floodplain chronologies to characterize a 1000 km reach of the middle yukon river between western yukon territory and central alaska ground penetrating radar gpr and electrical resistivity ground imaging ergi profiles along the middle yukon river between central yukon and alaska coupled with channel bottom echo profiles demonstrates that there is little variation in thickness of gravel fill and depth of active scour holes gpr surveys near the white river the largest sediment source in the upper yukon show no significant longitudinal variation in gravel thickness 8 16 m up to near circle alaska 530 km of wandering channels geophysical profiles across the yukon flats sedimentary basin 430 km of braided and wandering channels show an increase in gravel thickness 25 30 m but this is consistent with compaction of underlying lacustrine sediment and maximum depths of contemporary scour holes from the western margin of the yukon flats to the dalton highway bridge 30 km confined valley with no floodplain or braid bars borehole data at the bridge indicates 6 10 m of gravel on bedrock beneath 3 6 m of water floodplain stratigraphy indicates there is little evidence of fluvial aggradation of the middle yukon during the holocene radiocarbon ages from the gravel overbank silt contact near present river level demonstrate a general vertical stability of the river with a period of rapid eolian accumulation during the late pleistocene and early holocene the consistency of gravel fill and scour hole depth and lack of holocene terraces along the 1000 km reach of the yukon indicate that the river has been in a state of mass balance equilibrium of sediment transport input output over the holocene despite massive sediment influxes from the glacial fed white river and crossing major faults variation in valley fill depth is not significant and further the yukon flats reach shows no evidence of bed aggradation during the pleistocene and has probably existed in equilibrium since the late pliocene

evaluating the structure characteristics of epikarst at a typical peak cluster depression in guizhou plateau area using ground penetrating radar attributes abstract epikarst defined as the skin of karst environment is widely developed in southwest china largely as a result of the subtropical monsoon climate typical sw china karst accommodates a dual hydrogeological structure with surface and subsurface hydrological systems the epikarst ecosystem of karst environments plays a key role in biogeochemical cycling and energy and material storage and transport due to low rates of soil formation derived from carbonate rock weathering the soil layer is shallow and scattered presenting interlocked features within carbonate rock research on epikarst structure is primarily based on section field survey with semi quantitative characterization often lacking a fully quantitative description of soil rock structural characteristics we utilized ground penetrating radar gpr attributes to interpret the structure of epikarst at a peak cluster depression in the guizhou karst plateau two typical types of epikarst slope profiles and one peak cluster depression in maguan town puding county were selected for study we used mala gpr equipment with 500 mhz and 50 mhz antennas to acquire data gpr data was processed conventionally and then average energy attributes average amplitude attributes and coherence attributes were extracted to interpret the structure of the two epikarst profiles and the soil depth of the depression the results show that i energy and coherence attributes can highlight the soil rock structure of the epikarst profiles with relative ease ii compared to the original returned image the energy attributes visualise the soil and rock medium more effectively and iii the coherence attributes can identify the reflection interface between complete bedrock and bedrock containing fissure and grikes epikarst in addition using the 50 mhz antenna we were able to determine the soil depth in depression with coherence attributes indicating a depth of 3 6 m very close to the real depth 3 58 m measured by our auger verification work gpr attributes provide evidence that the epikarst has developed a large number of fissures filled with soil or other materials but that the bedrock under the epikarst has few fractures gpr attributes are therefore helpful for increasing our confidence of studying the structure of slope epikarst structure and depression soil depth

submesoscale cyclones in the agulhas current gliders were deployed for the first time in the agulhas current region to investigate processes of interactions between western boundary currents and shelf waters continuous observations from the gliders in water depths of 100 1000 m and over a period of 1 month provide the first high resolution observations of the agulhas current s inshore front the observations collected in a nonmeandering agulhas current show the presence of submesoscale cyclonic eddies generated at the inshore boundary of the agulhas current the submesoscale cyclones are often associated with warm water plumes which extend from their western edge and exhibit strong northeastward currents these features are a result of shear instabilities and extract their energy from the mean agulhas current jet

a comparison of em induction and gpr methods in areas of karst abstract electromagnetic em induction and ground penetrating radar gpr methods have been used extensively in areas of karst to detect and delineate major structural and solution features and to improve site assessments these methods do not work equally well in all soils and the amount of practical information derived from surveys has varied the choice of the most appropriate method often depends on the electrical properties of the soils this study characterized the use of gpr and em at two contrasting sites in florida and pennsylvania the florida site is underlain by relatively thick layers of electrically resistive sands overlying loamy marine sediments and limestone bedrock gpr was effectively used to determine the thickness of surface layers and the locations of buried solution features multiple contrasting soil horizons and layers weakened relationships and created non unique interpretations for em the pennsylvania site is was underlain by clayey residuum and limestone bedrock the clayey residuum is opaque to gpr and observation depths are severely restricted em induction effectively characterized the depths to bedrock within the pennsylvania site the integrated use of both methods supported by commensurate ground truth verifications helped to increase confidence in interpretations

revealing the temporal dynamics of subsurface temperature in a wetland using time lapse geophysics summary there is growing recognition of the need to understand the subsurface hydrological mechanisms within wetlands given their potentially significant role in the hydrological and biogeochemical function of catchments as well as their effects on the wetland habitat itself conventional subsurface hydrological sampling and monitoring techniques are often limited in such environments because of the invasive nature of such approaches and the sensitivity of the environment in this study we use ground penetrating radar gpr and electrical resistivity tomography ert to characterise the stratigraphy at a small riparian wetland site then through time lapse ert measurements over a 12 month period we demonstrate how changes in resistivity may provide additional value about localised recharge we compare direct measurements of water table depth and pore fluid electrical conductivity and temperature with subsurface resistivity derived from the ert measurements and reveal that temporal fluctuations in temperature of the subsurface dominates the change in resistivity over the monitored period from this we use the ert images of resistivity to estimate spatio temporal changes in subsurface temperature and thus infer localised zones of groundwater recharge due to suppressed seasonal variation in temperature although we focus here on one 2 d vertical profile through the wetland the results highlight the potential value of non invasive time lapse geoelectrical surveys for mapping 3 d thermal patterns within a wetland environment

vertical fracture detection by exploiting the polarization properties of ground penetrating radar signals vertically oriented thin fractures are not always detected by conventional single polarization reflection profiling ground penetrating radar gpr techniques we study the polarization properties of em wavefields and suggest multipolarization acquisition surveying to detect the location and azimuth of vertically oriented fractures we employ analytical solutions 3d finitedifference time domain modeling and field measurements of multipolarization gpr data to investigate em wave transmission through fractured geologic formations for surface based multipolarization gpr measurements across vertical fractures we observe a phase lead when the incident electric field component is oriented perpendicular to the plane of the fracture this observation is consistent for nonmagnetic geologic environments and allows the determination of vertical fracture location and azimuth based on the presence of a phase difference and a phase lead relationship between varying polarization gpr data

characterization of groundwater and surface water mixing in a semiconfined karst aquifer using time lapse electrical resistivity tomography groundwater flow in karst includes exchange of water between large fractures conduits and the surrounding porous matrix which impacts both water quality and quantity electrical resistivity tomography combined with end member mixing analysis emma and numerical flow and transport modeling was used to study mixing of karst conduit and matrix waters to understand spatial and temporal patterns of mixing during high flow and base flow conditions to our knowledge this is the first time emma and synthetic geophysical simulations have been combined here we interpret an 8 week time lapse electrical resistivity data set to assess groundwater surface mixing we simulate flow between the karst conduits and the porous matrix to determine fractions of water recharged to conduits that has mixed with groundwater stored in the pore space of the matrix using a flow and transport model in a synthetic time lapse resistivity inversion comparing the field and synthetic inversions our results enable us to estimate exchange dynamics spatial mixing and flow conditions results showed that mixing occurred at a volumetric flux of 56 m3 d with a dispersivity around 1 69 m during the geophysical experiment for these conditions it was determined that conduit water composition ranged from 75 groundwater during base flow conditions to less than 50 groundwater in high flow conditions though subject to some uncertainties the time lapse inversion process provides a means to predict changing hydrologic conditions leading to mixing of surface water and ground water and thus changes to water quantity and quality as well as potential for water rock reactions in a semiconfined sink rise system

submesoscale cold filaments in the gulf stream abstracta set of realistic very high resolution simulations is made for the gulf stream region using the oceanic model regional oceanic modeling system roms to study the life cycle of the intense submesoscale cold filaments that form on the subtropical gyre interior wall of the gulf stream the surface buoyancy gradients and ageostrophic secondary circulations intensify in response to the mesoscale strain field as predicted by the theory of filamentogenesis it can be understood in terms of a dual frontogenetic process along the lines understood for a single front there is however a stronger secondary circulation due to the amplification at the center of a cold filament filament dynamics in the presence of a mixed layer are not adequately described by the classical thermal wind balance the effect of vertical mixing of momentum due to turbulence in the surface layer is of the same order of magnitude as the pressure gradient and coriolis force and contributes equally to a so called turbulent therm

vorticity balance off the south shore of oahu hawaii derived by high frequency radio doppler current observations abstracthigh frequency radio doppler surface current observations off the south shore of oahu hawaii are used to calculate the vorticity equation at a 2 km spatial resolution in terms of a time

sinkhole structure imaging in covered karst terrain 1 ground penetrating radar gpr and resistivity techniques have been widely used to map the locations of sinkholes in covered karst terrain to determine whether a sinkhole is a likely preferential conduit for groundwater flow however requires higher resolution imaging than that used in conventional sinkhole mapping surveys field observations combined with simulated surveys for a 15 m diameter 3 m deep sinkhole in west central florida are used to assess the resolution of gpr and resistivity surveys targeting the semiconfining unit that floors the sinkhole depression 2d resistivity surveys clearly show the central depression as well as resistivity contrasts between the cover sediments within and outside of the sinkhole but are inadequate for resolving breaches in the semiconfining unit or underlying conduits a 3d gpr survey resolves vertical structure on the order of tens of centimeters within the semiconfining unit as well as indicators of conduits that extend several meters beneath the central depression 3d gpr thus holds promise for imaging hydrologically significant features of sinkholes

traveltime inversion of vertical radar profiles traveltimes of direct arrivals in vertical radar profiles vrps are tomographically inverted to estimate the earth s electromagnetic em velocity between a surface transmitter and a downhole receiver we determine the 1d interval velocity model that best fits the first arrival traveltimes by using a weighted damped least squares inversion scheme we assess the accuracy of the velocity model using synthetic traveltimes from a known velocity distribution model simulating an unconfined aquifer the inverted velocity profile closely matched the velocity profile of the input model in the synthetic examples using vertical radar profile data from an unconfined aquifer near boise idaho we inverted traveltimes to obtain velocity estimates at the well location the velocity change at a depth of 2 0 m corresponds well with the measured depth to the water table of 1 95 m and at depths between 2 and 18 m the velocities ranged between 0 06 and 0 1 m ns our estimates approximately match the velocity distribution determined from neutron derived porosity logs at depths greater than about 2 m an important function of inverse methods is to assess quantitatively and qualitatively the uncertainty of inverted velocity estimates we note that the velocity values in the upper and lower parts of the inverted model are not as well constrained compared to those between the depths of 4 and 13 m from the model resolution and model covariance matrices of the real data inversion we determine theuncertainty in ourvelocity model leading to more reliable interpretations of the subsurface

evaluation of ground penetrating radar gpr and geology survey for slope stability study in mantled karst region engineering geological problems such as slope failure may be a result of the karst process slope stability evaluation is an effective way to minimize the losses caused by slope failure in this study a methodology is developed to evaluate the slope stability first a ground penetrating radar gpr survey is conducted along the survey lines which have a mixed orthogonal distribution in the study area detailed information of the stratum structure and karst feature is presented through gpr profiles interpretation concurrently punctual data are obtained through surface geology investigations borehole surveying and laboratory tests subsequently a series of two dimensional geological cross sections in the horizontal direction and along the topographic dip direction are generated based on the spatial database in the coordinate system relative to the geological map finally numerical simulation is performed utilizing the finite element method the horizontal deformation and distribution of the plastic zone are used to evaluate the cross sectional stability along the topographic dip direction whereas the vertical deformation is chosen as the criterion to evaluate the same in the horizontal direction slope stability analysis is conducted in terms of the above comprehensive analysis to verify the validity of the method an application is performed in nan an district in chongqing city the results of the numerical simulation indicate that a sliding surface is not formed and regional collapse does not occur the results prove that the slope is stable in the study site which is consistent with the actual conditions

entry flux and exit of potential vorticity in ocean circulation the flux form of the potential vorticity pv equation is employed to derive simple expressions for the boundary and interior flux of pv in ocean circulation using bernoulli functions the formulas are discussed and physically interpreted and used to map the flux of pv through a model of ocean circulation

controls and age of cavernous porosity in middle silurian dolomite southern ontario porosity in bioclastic dolomites of the amabel formation in the eramosa river area northeast of guelph ontario is characterized by solution enlarged joints in outcrop kluftkarren and vuggy and cavernous intervals in the subsurface in addition a network of accessible caves has been dissected by recent fluvial incision by the present eramosa river valley porosity development was controlled locally by lithostratigraphy and regionally by the progressive downcutting of a deeply incised buried bedrock valley west of rockwood the amabel formation is capped by the eramosa member of the guelph formation which consists of jointed but relatively nonporous laminated to medium bedded bituminous dolomitized mudstones the vuggy and cavernous porosity in the amabel formation is probably pre wisconsinan to early wisconsinan in age beginning more than 60 75 ka and developed in response to the lowering of hydraulic gradients as the channel of the rockwood buried valley was progressively incised porous inte

diffraction imaging of sub vertical fractures and karst with full resolution 3d ground penetrating radar abstract vertical fractures with openings of less than one centimetre and irregular karst cause abundant diffractions in ground penetrating radar gpr records gpr data acquired with half wavelength trace spacing are uninterpretable as they are dominated by spatially undersampled scattered energy to evaluate the potential of high density 3d gpr diffraction imaging a 200 mhz survey with less than a quarter wavelength grid spacing 0 05 m 0 1 m was acquired at a fractured and karstified limestone quarry near the village of cassis in southern france after 3d migration processing diffraction apices line up in sub vertical fracture planes and cluster in locations of karstic dissolution features the majority of karst is developed at intersections of two or more fractures and is limited in depth by a stratigraphic boundary such high resolution 3d gpr imaging offers an unprecedented internal view of a complex fractured carbonate reservoir model analogue as seismic and gpr wave kinematics are similar improvements in the imaging of steep fractures and irregular voids at the resolution limit can also be expected from high density seismic diffraction imaging

detailed hydraulic head profiles as essential data for defining hydrogeologic units in layered fractured sedimentary rock this paper describes a study in southern wisconsin where vertical hydraulic head profiles measured in exceptional detail provided the key data for defining hydrogeologic units hgus in a layered sequence of sandstone siltstone shale and dolostone the most important data were obtained from corehole mp 6 which was cored 131 m into bedrock and instrumented using a westbay multilevel system with 36 depth discrete monitoring intervals the resulting head profile is consistant over time and shows eight distinct inflections in hydraulic head several of the inflections occur between adjacent permeable units and are likely due to poor vertical connectivity of fracture sets rather than distinct lower permeability layers or aquitards in the conventional sense no other type of data was capable of identifying the position of such distinct hydrogeologic features these zones of abrupt head loss provide the primary dataset for delineation of eleven hgus at mp 6 and are supported by less detailed head profiles at other locations although the detailed head profiles are essential core logs and geophysical logs from other boreholes are nessessary to fully establish the lateral continuity of the hgus

submesoscale vortical wakes in the lee of topography abstractan idealized framework of steady barotropic flow past an isolated seamount in a background of constant stratification with frequency n and rotation with coriolis parameter f is used to

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

application of geophysical prospecting techniques to evaluate geological mining heritage the sinapismo mine la carolina southern spain abstract geological mining heritage is a valuable resource that deserves proper attention given its educational scientific landscape and cultural worth the significant geological and mining wealth of the abandoned metallogenic district of la carolina southern spain is particularly interesting in this regard this study is focused on one of the emblematic veins of this district the sinapismo vein and more specifically on the la paloma drainage adit stretching a total length of 1170 m a geological and geophysical study was conducted in the interior of this drainage structure to assess its heritage value as well as the condition of the mine voids with a view to converting the mine into a site open to the public electrical resistivity imaging eri provides a general characterization of the mine highlighting the vergence of the geological structure and the main faults and veins ground penetrating radar gpr offers higher resolution but provides a limited depth of penetration less than 3 m in this case profiles have been constructed using 500 mhz and 250 mhz shielded antennas to assist the analysis of the lithological alternance quartzites and phyllites layer dip and the various associated fault and vein families the position of the sinapismo shaft with respect to the la paloma drainage adit will permit an itinerary for visitors to be designed along the first 480 m of the tunnel because it will allow for the proper location of two evacuation points the shaft and the entrance to the adit according to the results obtained from eri and gpr studies access to the rest of the drainage tunnel by visitors is inadvisable for safety reasons due to the existing fracture networks and the presence of veining the two geophysical techniques applied in this study eri and gpr provide on the one hand complementary information to the geological observations which can be used to evaluate the geo mining heritage on the other hand they offer information about the geomechanical conditions of the rock mass thus permitting a safety assessment of access to the la paloma adit

bed load transport in bedrock rivers the role of sediment cover in grain entrainment translation and deposition 1 bedrock rivers exert a critical control over landscape evolution yet little is known about the sediment transport processes that affect their incision we present theoretical analyses and field data that demonstrate how grain entrainment translation and deposition are affected by the degree of sediment cover in a bedrock channel theoretical considerations of grain entrainment mechanics and sediment continuity each demonstrate that areas of exposed bedrock and thin sediment depths cause sediment transport to be size independent albeit excluding extreme grain sizes we report gravel and cobble magnetic tracer data from three rivers with contrasting sediment cover the bedrock river calder 20 cover the bedrock south fork eel river 80 and the alluvial allt dubhaig 100 these data sets show that 1 transport distances in the river calder are controlled by sediment patch location whereas in the other rivers transport distances are described by gamma distributions representing local dispersion 2 river calder transport distances are size independent across all recorded shear stresses whereas the other rivers display size selectivity 3 river calder tracers are entrained at a dimensionless shear stress of 0 038 which is relatively low compared to alluvial rivers and 4 virtual grain velocities in the river calder are higher than in a comparable reach of the allt dubhaig these contrasts result from differences in the thicknesses and spatial distribution of sediment in the three rivers and support the theoretical analysis sediment processes in bedrock rivers systematically vary along a continuum between bedrock and alluvial end members citation hodge r a t b hoey and l s sklar 2011 bed load transport in bedrock rivers the role of sediment cover in grain entrainment translation and deposition j geophys res 116 f04028 doi 10 1029 2011jf002032

aquifer architecture analysis using ground penetrating radar triassic and quaternary examples s germany applying the concept of analogue studies long used in reservoir characterization outcrop analogues in two aquifer units of southern germany have been investigated upper triassic keuper alluvial sandstones stubensandstein and quaternary glaciofluvial gravels architectural element analysis of the outcrops is combined with ground penetrating radar profiles derived a few meters behind the outcrop walls such calibration is used to better understand the three dimensional sedimentary architecture many sedimentary units at the same time represent hydraulic flow units and are characterized by specific radar signatures this approach leads to promising results not only in unconsolidated aquifers but also in fully consolidated sedimentary rocks our studies will lead to a database with which more realistic predictions of the hydraulic behaviour of sedimentary aquifers systems needed for numerical hydrogeological simulations will be possible

florida current meandering and evolution of cyclonic eddies along the florida keys reef tract are they interconnected 1 the florida current fc is the branch of the gulf stream system within the straits of florida connected to the loop current in the gulf of mexico cyclonic cold core eddies travel along this oceanic current system entering the straits of florida in the vicinity of the dry tortugas and evolving along the florida keys island chain and coral reefs the development of the high resolution 900 m hydrodynamic model florida straits south florida and florida keys fkeys nested within a gulf of mexico model both based on the hybrid coordinate ocean model has enabled new findings in eddy variability together with high resolution 1 km ocean color imagery multiyear model archives have been employed to study the changes in the position of the fc front and the relationship with eddy evolution it was found that eddy interactions and transformations are common with multiple eddy cells within individual eddies or new cells emerging from existing vortices features in the dry tortugas area previously thought to be semipermanent are shown to be frequently transformed and or replenished a mechanism of local cyclogenesis is also proposed incoming eddies interact with and influence the downstream propagation of previous eddies systems of eddies rather than individual vortices can form the elongated features observed between the fc front and the atlantic florida keys shelf topography plays an important role in eddy dissipation or growth a close synergy between eddy evolution and fc meandering is revealed the results have implications on the connectivity of remote coastal and reef ecosystems

gulf stream dynamics along the southeastern u s seaboard abstractthe gulf stream strongly interacts with the topography along the southeastern u s seaboard between the straits of florida and cape hatteras the dynamics of the gulf stream in this region is investigated with a set of realistic very high resolution simulations using the regional ocean modeling system roms the mean path is strongly influenced by the topography and in particular the charleston bump there are significant local pressure anomalies and topographic form stresses exerted by the bump that retard the mean flow and steer the mean current pathway seaward the topography provides through bottom pressure torque the positive input of barotropic vorticity necessary to balance the meridional transport of fluid and close the gyre scale vorticity balance the effect of the topography on the development of meanders and eddies is studied by computing energy budgets of the eddies and the mean flow the baroclinic instability is stabilized by the slope everywhere except past the bump the flow

full resolution 3d gpr imaging noninvasive 3d ground penetrating radar gpr imaging with submeter resolution in all directions delineates the internal architecture and processes of the shallow subsurface full resolution imaging requires unaliased recording of reflections and diffractions coupled with 3d migration processing the gpr practitioner can easily determine necessary acquisition trace spacing on a frequency wavenumber f k plot of a representative 2d gpr test profile quarter wavelength spatial sampling is a minimum requirement for full resolution gpr recording an intensely fractured limestone quarry serves as a test site for a 100 mhz 3d gpr survey with 0 1 m 0 2 m trace spacing this example clearly defines the geometry of fractures in four different orientations including vertical dips to a depth of 20 m decimation to commonly used half wavelength spatial sampling or only 2d migration processing makes most fractures invisible the extra data acquisition effort results in image volumes with submeter resolution both

focused inversion of vertical radar profile vrp traveltime data the reconstruction of the gpr velocity vertical profile from vertical radar profile vrp traveltime data is a problem with a finite number of measurements and imprecise data analogous to similar seismic techniques such as the shallow down hole test used for s wave velocity profiling or the vertical seismic profiling vsp commonly used in deeper exploration the uncertainty in data accuracy and the error amplification inherent in deriving velocity estimates from gradients of arrival times make this an example of an ill posed inverse problem in the framework of tikhonov regularization theory ill posedness can be tackled by introducing a regularizing functional stabilizer the role of this functional is to stabilize the numerical solution by incorporating the appropriate a priori assumptions about the geometrical and or physical properties of the solution one of these assumptions could be the existence of sharp boundaries separating rocks with different physical properties we apply a method based o

geophysical conceptualization of a fractured sedimentary bedrock riverbed using ground penetrating radar and induced electrical conductivity summary bedrock rivers exhibit very different hydraulic and ecological regimes compared to alluvial rivers groundwater surface water interaction in rivers that flow directly on sedimentary bedrock surfaces with exposed fracture and conduit networks is generally based on alluvial river conceptual models however the dual and triple porosity systems of sedimentary rock e g matrix fractures and vugs leads to highly variable hydraulic pathways and groundwater velocities that in turn result in processes that are very different than those derived from alluvial concepts relative to alluvial rivers there has been very little direct examination of dynamic interactions such as fluxes groundwater velocities and mechanisms affecting water quality across the channel interface this is largely because bedrock rivers are difficult to instrument and monitor given their heterogeneous and anisotropic flow systems in this study we evaluate the capacity of non invasive low impact ground penetrating radar and frequency domain electromagnetic induction methods capable of detecting discrete fracture and conduit features mapping complex distributions of lithostratigraphic interfaces and providing information about formation properties along a partially exposed section of the eramosa river located in ontario canada geophysical data are supported by direct hydrogeologic and geologic information obtained from a nearby borehole piezometer cluster and a continuous 15 m rock core valuable insights were gained into the lateral extent and geometry of structurally controlled whydrostratigraphic units e g dissolution enhanced fractures epikarst and karst features which are expected to strongly influence groundwater and surface water interaction along the channel an integrated application of gpr and emi methods was necessary to fully understand the complex geometry of geologic boundaries and karst features within the shallow bedrock aquifer the identification of epikarst below fluvial sediment and its relationship to the formation of dissolution features exposed fracture conduit networks and sinkholes represents the basis for understanding the dynamic hydraulic responses between the surface water and the shallow bedrock aquifer

submesoscale coherent vortices in the gulf stream seismic images and glider sections of the gulf stream front along the u s eastern seaboard capture deep lens shaped submesoscale features these features have radii of 5 20 km thicknesses of 150 300 m and are located at depths greater than 500 m these are typical signatures of anticyclonic submesoscale coherent vortices a submesoscale resolving realistic simulation which reproduces submesoscale coherent vortices with the same characteristics is used to analyze their generation mechanism submesoscale coherent vortices are primarily generated where the gulf stream meets the charleston bump a deep topographic feature due to the frictional effects and intense mixing in the wake of the topography these submesoscale coherent vortices can transport waters from the charleston bump s thick bottom mixed layer over long distances and spread them within the subtropical gyre their net effect on heat and salt distribution remains to be quantified plain language summary the interior of the ocean is populated by small scale coherent vortices which redistribute water properties on the scale of basins these structures are very difficult to observe they have no surface signature and small dimensions on the order of 1 50 km such that they are missed by satellites and sampled only by chance furthermore climate scale ocean models do not resolve these type of motions and do not take into account their impacts for the large scale transport and distribution of heat nutrients and other materials understanding and parameterizing these phenomena within models is critical for a better prediction of climate here we present new observations of submesoscale coherent vortices from seismic images and glider sections in the region of the gulf stream we use a numerical model at very high resolution to reproduce vortices with the same characteristics and to analyze their generation mechanism these vortices are generated where the gulf stream interacts with a deep topographic feature called the charleston bump due to frictional effects and intense mixing in the wake of the topography these vortices transport waters from the charleston bump s thick bottom mixed layer and act to spread them all around the subtropical gyre

the role of sloping sidewalls in forming potential vorticity contrasts in the ocean interior the role of sidewalls in determining the interior distribution of potential vorticity pv is investigated using eddy resolving isopycnic experiments the layer model is integrated at 1 8 resolution for a wind driven double gyre with either vertical or sloping sidewalls if there are vertical sidewalls eddy stirring leads to pv homogenization within unforced interior density layers if there are sloping sidewalls frictional torques lead to bands of low and high pv being formed along the western boundary of the subpolar and subtropical gyres respectively these regions of low and high pv are transferred into the interior by a separated jet at the intergyre boundary over a limited domain this injection of the pv contrast can prevent eddy homogenization from occurring however over a larger scale domain eddies provide a downgradient transfer of pv reducing the pv contrast downstream along the jet and enabling homogenization to occur for intermediate layers within the basin interior diabatic mixing along the slope can introduce low pv for intermediate layers and even mask the frictional contributions