field observations on hydrodynamic and coastal geomorphic processes off harilaid peninsula baltic sea in winter and spring 2006 2007 abstract investigations of multi layer current regime variations in sea level and wave parameters using a bottom mounted rdcp recording doppler current profiler during 20 december 2006 23 may 2007 were integrated with surveys on changes of shorelines and contours of beach ridges at nearby harilaid peninsula saaremaa island a w storm with a maximum average wind speed of 23 m s 1 occurred on 14 15 january with an accompanying sea level rise of at least 100 cm and a significant wave height of 3 2 m at the 14 m deep rdcp mooring site it appeared that in practically tideless estonian coastal waters doppler based vertical velocity measurements reflect mainly site dependent equilibrium between resuspension and sedimentation the mooring site 1 5 km off the kelba spit of harilaid was located in the accumulation zone where downward fluxes dominated and fine sand settled as a result of storms in january and april the distal part of the accumulative gravel spit advanced by 50 m whereas a 30 50 m retreat of the shoreline in the western and northern parts occurred at cape kiipsaare the location of the beach ridges shows that the development of the spit occurs through relatively short period but infrequent storm events roughly 2 3 times each decade

measuring flow velocity and sediment transport with an acoustic doppler current profiler an acoustic doppler current profiler adcp measures three dimensional velocity profiles within the water column using the doppler shift principle whilst the bottom tracking function and acoustic backscatter can be used to measure bed load velocity and estimate suspended sediment concentration the adcp offers many advantages over traditional single point current meters and sediment samplers including deployment from a moving launch a single instrument for both velocity and sediment transport measurements profiles of three dimensional velocity and suspended sediment and the ability to map an entire flow field limitations of adcps include a large sampling diameter close to the bed coarse measurement of vertical velocity fragmented bottom track records a poor understanding of the relation between bottom tracking and the mechanisms of sediment transport and sensitivity of the acoustic backscatter to particle size

paleohydrological implications of late quaternary fluvial deposits in and around archaeological sites in syria abstract the importance of fluvial processes to the development of late quaternary landforms in arid regions is well established particularly for the american southwest in contrast much less information exists about past fluvial processes for other arid regions such as arabic countries in the middle east this paper reviews the characteristics of late quaternary fluvial deposits and landforms in syria an arid country with little previous quaternary geomorphic research relatively detailed information has been obtained from areas adjacent to archaeological sites because of collaborative activities with geomorphologists and other geoscientists such activities have resulted in intensive field surveys and associated results of complementary archaeological studies of lithic artifacts are useful for establishing the chronology of fluvial deposits although the number of existing studies is limited the available information points to marked changes in the mode of fluvial processes in response to late quaternary climatic change fluvial sedimentation was enhanced during the wet periods of mis 3 4 the pleistocene holocene transition and the mid holocene in contrast the lgm was characterized by limited fluvial sedimentation under a drier climate as well as enhanced carbonate precipitation near the land surface to form calcrete and oncoids

ground penetrating radar response to fracture fluid salinity why lower frequencies are favorable for resolving salinity changes time lapse ground penetrating radar gpr surveys exploit signal amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths however the relationships between gpr signal amplitude phase and frequency with fracture aperture and fluid electrical conductivity are not well understood we used analytical modeling numerical simulations and field experiments of multifrequency gpr to investigate these relationships for a millimeter scale aperturefracturesaturatedwithwaterofvaryingsalinity we found that the response of lower frequency radar signals detects changes in fluid salinity better than the response of higher frequency signals increasing fluid electrical conductivity decreases low frequency gpr signal wavelength which improves its thin layer resolution capability we concluded that lower signal frequencies such as 50 mhz and saline tracers of up to 1 s m conductivity are preferablewhenusinggprtomonitorflowinfracturedrock furthermore we found that gpr amplitude and phase responsesaredetectableinthefieldandpredictablebyemtheory and modeling therefore they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured rockflowandtransportproperties

acoustic doppler current profiler measurements in coastal and estuarine environments examples from the tay estuary scotland acoustic doppler current profilers adcps provide a means to measure the components of water current velocities in three dimensions such instruments have been used widely by the oil industry in deep offshore waters but their application to nearshore coastal and estuarine environments has been principally confined to the usa using examples of adcp datasets acquired from the macrotidal tay estuary eastern scotland the principles of field deployment data acquisition and forms of output are critically summarised it is shown for the first time in the tay estuary that vertical current velocities are significant and are particularly so in downwelling zones associated with the development and passage of axially convergent tidal fronts the improved understanding of three dimensional water and suspended sediment dynamics in coastal and estuarine waters is crucial to inter alia the sustainable management of effluent discharges and in more general terms it is predicted on the basis of the tay case study that adcp measurements afford significant opportunities to refine understanding of geomorphological processes in a variety of aquatic environments worldwide

plinian pumice fall deposit of the campanian ignimbrite eruption phlegraean fields italy abstract a plinian pumice fall deposit associated with the campanian ignimbrite eruption 36 ka phlegraean fields caldera italy occurs at the base of the distal grey ignimbrite in 15 localities spread over an area exceeding 1500 km2 between benevento and the sorrentina peninsula in the thickest stratigraphic section at voscone 130 cm 45 km east of the phlegraean caldera centre pozzuoli the deposit consists of two units the lower fall unit lfu is well sorted exhibits reverse size grading and is composed of equidimensional light grey pumice clasts with very subordinate accidental lithics the upper fall unit ufu is from well to poorly sorted crudely stratified richer in lithics and composed of both equidimensional and prolate pumice clasts the two fall units show slightly different dispersal axis n90 for the lfu and n95 for the ufu volumes calculated with the method of pyle 1989 are about 8 km3 for the lfu and 7 km3 for the ufu the maximum height of the eruptive columns are estimated using the model of the maximum lithic clasts dispersal at 44 km for the lfu and 40 km for the ufu classifying both fall units as ultraplinian in character reverse size grading within the lfu suggests an increase of the height of the column and magma discharge rate with time moderate sorting and crude stratification of the ufu are consistent with short period oscillation of the column possibly associated with repeated partial column collapses sharp increases in lithic content at the transition to ufu and within the ufu suggest that changes in the eruptive behaviour was produced by a dramatic increase in conduit vent erosion the phase of column instability preceded the emplacement of widely dispersed pyroclastic flow the ultraplinian nature of the fall fits well with the wide dispersal of the campanian ignimbrite with an estimated aspect ratio of 3 4 10 4 lari

a multi disciplinary study of frontal systems in the tay estuary scotland the results of a remote sensing study of tidal mixing processes in the tay estuary have been correlated with the results of mathematical and physical models and ground sampling data in an attempt to assess the nature the spatial and temporal extent and the variability in the formation of convergent fronts in the tay estuary the application of remote sensing methods to the study of estuarine mixing processes in the tay estuary supported by ground measurements has discovered convergent front mechanisms and complex hydrodynamic processes which had not previously been recognized in the tay estuary this integrated approach has enabled the various features and mixing mechanisms found in the lower section of the estuary to be interrelated the limitations of using a two dimensional mathematical and a physical model to predict the complex mixing processes affecting water quality in the tay estuary are discussed

high resolution measurements made across a tidal intrusion front high spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the james river estuary virginia during the first few hours of flood the current measurements were made with a surface towed acoustic doppler current profiler which was used in both profile and side scan configurations the profile data show a 30 50 cm s 1 inflow of water from the chesapeake bay a time evolving across front density gradient and downward velocity beneath the front of about 15 cm s 1 the side scan observations directly measure the across front change in current and provide a view of the three dimensional character of the frontal interface the near surface horizontal strain rate a critical parameter for understanding the modulation of surface waves across the front is estimated to be about 0 04 s 1 using phillips 1984 theory as a guide fronts with such large strain rates as these should be discernible in imagery from the ers 1 c band synthetic aperture radar for wind speeds of 4 m s 1

discrete dual porosity model for electric current flow in fractured rock the identification of fractures and the characterization of their properties are of critical importance in a wide variety of research fields and applications to this end geophysical methods are of significant interest as they can provide information regarding the spatial distribution of a number of subsurface physical properties in a rapid and noninvasive manner electrical resistivity surveying in particular has been shown in several previous investigations to exhibit sensitivity to the presence of fractures suggesting that geoelectrical experiments may contain important information regarding how fractures are distributed and connected in the subsurface however a lack of suitable numerical modeling tools for electric current flow in fractured media has prevented a detailed and systematic exploration of this concept to address this issue we present a novel discrete dual porosity modeling approach that is specifically tailored to the electrical resistivity problem with our approach an analytical formulation for fracture matrix current flow exchange at the fracture scale is integrated into a discrete fracture network model which is then combined with a block scale finite volume representation of the rock matrix our methodology allows for low cost and accurate simulation of electric current flow through both the fractures and matrix and is readily applicable to complex fracture networks at relatively large scales although formulated here in two dimensions this work represents an important first step toward investigating the effect of fracture network characteristics on bulk electrical properties as well as toward the simulation of geoelectrical survey data in realistic fractured rock environments

which fractures are imaged with ground penetrating radar results from an experiment in the aspo hardrock laboratory sweden abstract identifying fractures in the subsurface is crucial for many geomechanical and hydrogeological applications here we assess the ability of the ground penetrating radar gpr method to image open fractures with sub mm apertures in the context of future deep disposal of radioactive waste gpr experiments were conducted in a tunnel located 410 m below sea level within the aspo hard rock laboratory sweden using 3 d surface based acquisitions 3 4 m 19 m with 160 mhz 450 mhz and 750 mhz antennas the nature of 17 identified gpr reflections was analyzed by means of three new boreholes bh1 bh3 9 9 5 m deep out of 21 injection and outflow tests in packed off 1 m sections only five provided responses above the detection threshold with the maximum transmissivity reaching 7 0 10 10 m2 s most gpr reflections are situated in these permeable regions and their characteristics agree well with core and optical televiewer data a 3 d statistical fracture model deduced from fracture traces on neighboring tunnel walls show that the gpr data mainly identify fractures with dips between 0 and 25 since the gpr data are mostly sensitive to open fractures we deduce that the surface gpr method can identify 80 of open sub horizontal fractures we also find that the scaling of gpr fractures in the range of 1 10 m2 agrees well with the statistical model distribution indicating that fracture lengths are preserved by the gpr imaging no measurement bias our results suggests that surface gpr carries the resolution needed to identify the most permeable sub horizontal fractures even in very low permeability formations thereby suggesting that surface gpr could play an important role in geotechnical workflows for instance for industrial scale siting of waste canisters below tunnel floors in nuclear waste repositories

three dimensional tidal flow around headlands field measurements of tidal flow around a headland indicate secondary circulation induced by flow curvature the secondary flow defined to be the flow in the plane normal to the direction of the vertically averaged current is directed toward the headland near the bottom and seaward near the surface consistent with theoretical predictions the strength of the secondary flow varies from 5 to 15 of the streamwise flow it is strongest when the water column is stratified because of both the enhanced shear of the streamwise flow and the reduced frictional damping of the secondary flow the transverse exchange accomplished by the secondary flow significantly influences the structure of the streamwise flow causing a broadening of the transverse shear and changing the horizontal and vertical distributions of momentum it may also have a significant influence on horizontal dispersion in the vicinity of headlands

acoustic doppler current profiler measurements of possible lee waves south of key west florida acoustic doppler current profiler measurements made while underway in 200 240 m of water south of key west florida show wavelike signals with about 1 km horizontal wavelength and 3 5 cm s 1 amplitude vertical velocity vertical displacements of about 5 m are inferred from coherent oscillations in surfaces of constant acoustic backscatter in features associated with the width of the peak in the doppler spectrum and in fine structure of vertical current shear while the sampling was limited all the measurable waves occurred over irregular bathymetry in the presence of an east northeastward mean flow u 1 m s 1 averaged over 30 to 90 m depth the peak strain rate associated with the waves was nearly 1 10 3 s 1 at 12 m depth and this could have produced bands of smooth and rough water observed at the surface we tentatively identify the waves as being topographically forced by the florida current flowing over a rough continental margin

comparing flux averaged and resident concentration in a fractured bedrock using ground penetrating radar this is the published version copyright 2010 by the american geophysical union all rights reserved

single hole gpr reflection imaging of solute transport in a granitic aquifer 1 identifying transport pathways in fractured rock is extremely challenging as flow is often organized in a few fractures that occupy a very small portion of the rock volume we demonstrate that saline tracer experiments combined with single hole ground penetrating radar gpr reflection imaging can be used to monitor saline tracer movement within mm aperture fractures a dipole tracer test was performed in a granitic aquifer by injecting a saline solution in a known fracture while repeatedly acquiring single hole gpr sections in the pumping borehole located 6 m away the final depth migrated difference sections make it possible to identify consistent temporal changes over a 30 m depth interval at locations corresponding to fractures previously imaged in gpr sections acquired under natural flow and tracer free conditions the experiment allows determining the dominant flow paths of the injected tracer and the velocity 0 4 0 7 m min of the tracer front

time lapse imaging of saline tracer transport in fractured rock using difference attenuation radar tomography 1 accurate characterization of fractured rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater hydrology we demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests cross well differenceattenuation ground penetrating radar was used to monitor saline tracer migration in an experiment at the u s geological survey fractured rock hydrology research site in grafton county new hampshire radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests an innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection the inverse algorithm minimizes a combination of two functions the first is the sum of weighted squared data residuals second is a measure of solution complexity based on an a priori space time covariance function subject to constraints that limit radarattenuation changes to regions of the tomograms traversed by high difference attenuation ray paths the time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures these results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site index terms 0910 exploration geophysics data processing 0915 exploration geophysics downhole methods 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1894 hydrology instruments and techniques keywords radar tomography fractured rock ground penetrating radar geophysics hydrogeophysics

comparison of alternative methodologies for identifying and characterizing preferential flow paths in heterogeneous aquifers one of the main difficulties encountered when characterizing the hydrodynamic properties of a fractured aquifer is to identify the preferential flow paths within it different methods may be applied to determine the variability of the permeability at the borehole scale and to image the structure of the main flow zones between boreholes in this paper we compare the information obtained from different measurement techniques performed in a set of three 100 m depth wells well to well spacing 5 10 m in a fractured crystalline rock setting geophysical logging and borehole wall imaging are used to identify open and closed fractures intersecting the boreholes and their orientation the comparison with flowmeter and single packer tests shows that few of the fractures interpreted as open from geophysical logs are significantly transmissive cross borehole connectivity is first investigated from single packer tests with pressure monitoring in adjacent boreholes to determine fracture zone connectivity we propose a methodology simply based on the variation with packer depth of the ratio of the drawdown in the observation well and the drawdown in the pumping well the results are compared to the analysis of cross borehole flowmeter tests we show that both methods provide consistent results with a similar level of information on connectivity

four dimensional mapping of tracer channelization in subhorizontal bedrock fractures using surface ground penetrating radar 1 to observe flow channeling in situ surface ground penetrating radar gpr was used to detect a saline tracer moving through a sub horizontal bedrock fracture the tracer is mapped using amplitude variations resulting from the significant difference in electromagnetic properties between the tracer and natural ground water within the fracture results show that hydrogeophysical investigations using gpr can successfully image tracer movement in a variety of flow configurations in three spatial dimensions through time hence 4d observed tracer travel paths demonstrated meter scale spatial variability that may be attributed to heterogeneity in fracture aperture

structure of an axial convergence zone from acoustic doppler current profiler measurements abstract an acoustic doppler current profiler was used to measure the current distribution in a convergence zone located in the piscataqua river a well mixed estuary in new hampshire u s a the convergence zone was distributed along a line parallel to the channel axis and could be located visually by accumulated debris observations of transverse circulation during the flood tide along a transect crossing the front are presented results show surface currents directed towards the centre of the channel sinking in the middle and divergence towards the sides of the channel at the bottom conductivity and temperature measurements indicate accompanying higher densities in the centre of the channel a simple mathematical model is developed applied and compared with the data major features of the frontal circulation are reproduced indicating that transverse circulation is driven primarily by the cross channel density gradients

fracture network characterization using stress based tomography information on structural features of a fracture network at early stages of enhanced geothermal system egs development is mostly restricted to borehole images and if available outcrop data however using this information to image discontinuities in deep reservoirs is difficult wellbore failure data provides only some information on components of the in situ stress state and its heterogeneity our working hypothesis is that slip on natural fractures primarily controls these stress heterogeneities based on this we introduce stress based tomography in a bayesian framework to characterize the fracture network and its heterogeneity in potential egs reservoirs in this procedure first a random initial discrete fracture network dfn realization is generated based on prior information about the network the observations needed to calibrate the dfn are based on local variations of the orientation and magnitude of at least one principal stress component along boreholes a markov chain monte carlo mcmc sequence is employed to update the dfn iteratively by a fracture translation within the domain the markov sequence compares the simulated stress profile with the observed stress profiles in the borehole evaluates each iteration with metropolis hastings acceptance criteria and stores acceptable dfn realizations in an ensemble finally this obtained ensemble is used to visualize the potential occurrence of fractures in a probability map indicating possible fracture locations and lengths we test this methodology to reconstruct simple synthetic and more complex outcrop based fracture networks and successfully image the significant fractures in the domain

hydrogeophysical characterization of transport processes in fractured rock by combining push pull and single hole ground penetrating radar experiments the in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes such as dispersion channeling trapping matrix diffusion ambient and density driven flows we attempted to reduce this uncertainty by coupling push pull tracer experiments with single hole ground penetrating radar gpr time lapse imaging the experiments involved different injection fractures chaser volumes and resting times and were performed at the fractured rock research site of ploemeur in france h network hplus ore fr en for the gpr acquisitions we used both fixed and moving antenna setups in a borehole that was isolated with a flexible liner during the fixedantenna experiment time varying gpr reflections allowed us to track the spatial and temporal dynamics of the tracer during the push pull experiment during the moving antenna experiments we clearly imaged the dominant fractures in which tracer transport took place fractures in which the tracer was trapped for longer time periods and the spatial extent of the tracer distribution up to 8 meters at different times this demonstrated the existence of strongly channelized flow in the first few meters and radial flow at greater distances by varying the resting time of a given experiment we identified regions affected by density driven and ambient flow these experiments open up new perspectives for coupled hydrogeophysical inversion aimed at understanding transport phenomena in fractured rock formations