pilot scale field validation of the long electrode electrical resistivity tomography method a validation experiment carried out in a scaled field setting was attempted for the long electrode electrical resistivity tomography method in order to demonstrate the performance of the technique in imaging a simple buried target the experiment was an approximately 1 17 scale mock up of a region encompassing a buried nuclear waste tank on the hanford site the target of focus was constructed by manually forming a simulated plume within the vadose zone using a tank waste simulant the long electrode results were compared to results from conventional point electrodes on the surface and buried within the survey domain using a pole pole array both point and long electrode imaging techniques identified the lateral extents of the pre formed plume with reasonable fidelity but the long electrode method was handicapped in reconstructing vertical boundaries the pole dipole and dipole dipole arrays were also tested with the long electrode method and were shown to have the least favourable target properties including the position of the reconstructed plume relativetotheknownplumeandtheintensityoffalsepositivetargets thepoorperformance of the pole dipole and dipole dipole arrays was attributed to an inexhaustive and non optimal coverage of data at key electrodes as well as an increased noise for electrode combinations with high geometric factors however when comparing the model resolution matrix among the different acquisition strategies the pole dipole and dipole dipole arrays using long electrodes were shown to have significantly higher average and maximum values within the matrix than any pole pole array the model resolution describes how well the inversion model resolves the subsurface given the model resolution performance of the pole dipole and dipole dipole arrays it may be worth investing in tools to understand the optimum subset of randomly distributed electrode pairs to produce maximum performance from the inversion model

an assessment procedure for glacial hazards in the swiss alps glacial hazards such as ice avalanches glacial lake outburst floods and debris flows have caused severe damage in populated mountain regions such as the swiss alps assessment of such hazards mus

saline tracer visualized with three dimensional electrical resistivity tomography field scale spatial moment analysis 1 cross well electrical resistivity tomography ert was used to monitor the migration of a saline tracer in a two well pumping injection experiment conducted at the massachusetts military reservation in cape cod massachusetts after injecting 2200 mg l of sodium chloride for 9 hours ert data sets were collected from four wells every 6 hours for 20 days more than 180 000 resistance measurements were collected during the tracer test each ert data set was inverted to produce a sequence of 3 d snapshot maps that track the plume in addition to the ert experiment a pumping test and an infiltration test were conducted to estimate horizontal and vertical hydraulic conductivity values using modified moment analysis of the electrical conductivity tomograms the mass center of mass and spatial variance of the imaged tracer plume were estimated although the tomograms provide valuable insights into field scale tracer migration behavior and aquifer heterogeneity standard tomographic inversion and application of archie s law to convert electrical conductivities to solute concentration results in underestimation of tracer mass such underestimation is attributed to 1 reduced measurement sensitivity to electrical conductivity values with distance from the electrodes and 2 spatial smoothing regularization from tomographic inversion the center of mass estimated from the ert inversions coincided with that given by migration of the tracer plume using 3 d advective dispersion simulation the 3 d plumes seen using ert exhibit greater apparent dispersion than the simulated plumes and greater temporal spreading than observed in field data of concentration breakthrough at the pumping well

a review of catastrophic drainage of moraine dammed lakes in british columbia abstract moraine dammed lakes are common in the high mountains of british columbia most of these lakes formed when valley and cirque glaciers retreated from advanced positions achieved during the little ice age many moraine dams in british columbia are susceptible to failure because they are steep sided have relatively low width to height ratios comprise loose poorly sorted sediment and may contain ice cores or interstitial ice in addition the lakes commonly are bordered by steep slopes that are prone to snow and ice avalanches and rockfalls moraine dams generally fail by overtopping and incision the triggering event may be a heavy rainstorm or an avalanche or rockfall that generates waves that overtop the dam the dam can also be overtopped by an influx of water caused by sudden drainage of an upstream ice dammed lake jokulhlaup melting of moraine ice cores and piping are other possible failure mechanisms failures of moraine dams in british columbia produce destructive floods orders of magnitude larger than normal streamflows most outburst floods are characterized by an exponential increase in discharge followed by an abrupt drop to background levels when the water supply is exhausted peak discharges are controlled by dam characteristics the volume of water in the reservoir failure mechanisms and downstream topography and sediment availability for the same potential energy at the dam site floods from moraine dammed lakes have higher peak discharges than floods from glacier dammed lakes the floodwaters may mobilize large amounts of sediment as they travel down steep valleys producing highly mobile debris flows such flows have larger discharges and greater destructive impact than the floods from which they form moraine dam failures in british columbia and elsewhere are most frequent following extended periods of cool climate when large lateral and end moraines are built a period of protracted warming is required to trap lakes behind moraines and create conditions that lead to dam failure this sequence of events occurred only a few times during the holocene epoch most notably during the last several centuries glaciers built large moraines during the little ice age mainly during the 1700s and 1800s and lakes formed behind these moraines when climate warmed in the 1900s twentieth century climate warming is also responsible for recent moraine dam failures in mountains throughout the world warming from the late 1800s until about 1940 and again from 1965 to today destabilized moraine dams with interstitial or core ice the warming also forced glaciers to retreat prompting ice avalanches landslides and jokulhlaups that have destroyed some moraine dams

the formation and failure of natural dams of the numerous kinds of dams that form by natural processes dams formed from landslides glacial ice and late neoglacial moraines present the greatest threat to people and property landslide dams form in a wide range of physiographic settings the most common types of mass movements that form landslide dams are rock and debris avalanches rock and soil slumps and slides and mud debris and earth flows the most common initiation mechanisms for dam forming landslides are excessive rainfall and snowmelt and earthquakes landslide dams can be classified into six categories based on their relation with the valley floor type i dams 11 of 184 landslide dams from around the world that we were able to classify do not reach from one valley side to the other type ii dams 44 span the entire valley floor in some cases depositing material high on opposite valley sides type iii dams 41 move considerable distances both upstream and downstream from the landslide failure type iv dams 1 are rare and involve the contemporaneous failure of material from both sides of a valley type v dams 1 also are rare and are created when a single landslide sends multiple tongues of debris into a valley and forms two or more landslide dams in the same reach of river type vi dams 3 involve one or more failure surfaces that extend under the stream or valley and emerge on the opposite valley side many landslide dams fail shortly after formation in our sample of 73 documented landslide dam failures 27 of the landslide dams failed less than 1 day after formation and about 50 failed within 10 days over topping is by far the most common cause of failure the timing of failure and the magnitude of the resulting floods are controlled by dam size and geometry material characteristics of the blockage rate of inflow to the impoundment size and depth of the impoundment bedrock control of flow and engineering controls such as artificial spill ways diversions tunnels and planned breaching by blasting or conventional excavation glacial ice dams can produce at least nine kinds of ice dammed lakes the most dangerous are lakes formed in main valleys dammed by tributary glaciers failure can occur by erosion of a drainage tunnel under or through the ice dam or by a channel over the ice dam cold polar ice dams generally drain supraglacially or marginally by downmelting of an outlet channel warmer temperate ice dams tend to fail by sudden englacial or subglacial breaching and drainage late neoglacial moraine dammed lakes are located in steep mountain areas affected by the advances and retreats of valley glaciers in the last several centuries these late neoglacial dams pose hazards because 1 they are sufficiently young that vegetation has not stabilized their slopes 2 many dam faces are steeper than the angle of repose 3 these dams and lakes are immediately downslope from steep crevassed glaciers and near vertical rock slopes and 4 downstream from these dams are steep canyons with easily erodible materials that can be incorporated in the flow and increase flood peaks the most common reported failure mechanism is overtopping and breaching by a wave or series of waves in the lake generated by icefalls rockfalls or snow or rock avalanches melting of ice cores or frozen ground and piping and seepage are other possible failure mechanisms natural dams may cause upstream flooding as the lake rises and downstream flooding as a result of failure of the dam although data are few for the same potential energy at the dam site ownstream flood peaks from the failure of glacier ice dams are smaller than those from landslide moraine and structed earth fill and rock fill dam failures moraine dam failures appear to produce some of the largest downstream flood peaks for potential energy at the dam site greater than 1011 1012 joules differences in flood peaks natural dam failures appear to be controlled by dam characteristics and failure mechanisms

electrical resistivity tomography of vadose water movement cross borehole electrical resistivity tomography ert was used to image the resistivity distribution before and during two infiltration experiments in both cases water was introduced into the vadose zone and the change in resistivity associated with the plume of wetted soil was imaged as a function of time the primary purpose of this work was to study the capabilities and limitations of ert to image underground structure and ground water movement in the vadose zone a secondary goal was to learn specifics of unsaturated flow in a complex geologic setting tomographs of electrical resistivity taken before infiltration image coarser well drained soils sands and gravels as more resistive zones whereas finer grained soils silts and clays which hold more water by capillarity are imaged as more conductive images of changes in resistivity during infiltration show growth of the water infiltration plume with time that is consistent with known geology in the ert images we see the effects of capillary barriers and infer differences between capillary driven flow through fine sediments and gravity driven flow through very permeable sediments images are consistent with numerical flow simulations using hydrological parameter values consistent with soil types inferred from well logs ert can be a useful tool to monitor movement of circuitous moisture fronts in a heterogeneous field setting that would go undetected by borehole measurements

borehole to surface electrical resistivity monitoring of a salt water injection experiment a field experiment was conducted at the university of california richmond field station to demonstrate the sensitivity of borehole to surface resistivity measurements in groundwater investigations a quantity of saline water was injected into a fresh water aquifer while the resistivity was monitored using a multichannel borehole to surface system two experiments were conducted using pole pole and pole dipole receiver electrode arrays the data from the pole pole experiment were superimposed to simulate a dipole pole array and the data from the pole dipole array were superimposed to simulate a dipole dipole array this superposition of the data was done to enhance the anomaly and facilitate interpretation a numerical modeling study was performed in conjunction with the field experiment in order to interprete the results a three dimensional modeling program was used to simulate the geological setting of the field experiment and the salt water injection this modeling revealed that an asymmetric displacem

hydrogeophysical tracking of three dimensional tracer migration the concept and application of apparent petrophysical relations 1 direct estimation of groundwater solute concentrations from geophysical tomograms has been only moderately successful because 1 reconstructed tomograms are often highly uncertain and subject to inversion artifacts 2 the range of subsurface conditions represented in data sets is incomplete because of the paucity of colocated well or core data and aquifer heterogeneity and 3 geophysical methods exhibit spatially variable sensitivity we show that electrical resistivity tomography ert can be used to estimate groundwater solute concentrations if a relation between concentration and inverted resistivity is used to deal quantitatively with these issues we use numerical simulation of solute transport and electrical current flow to develop these relations which we call apparent petrophysical relations they provide the connection between concentration or local resistivity and inverted resistivity which is measured at the field scale based on ert for media containing ionic solute the apparent petrophysical relations are applied to tomograms of electrical resistivity obtained from field measurements of resistance from cross well ert to create maps of tracer concentration on the basis of synthetic and field cases we demonstrate that tracer mass and concentration estimates obtained using these apparent petrophysical relations are far better than those obtained using direct application of archie s law applied to three dimensional tomograms from ert which gives severe underestimates

imaging and quantifying salt tracer transport in a riparian groundwater system by means of 3d ert monitoring abstractdetermining groundwater flow paths of infiltrated river water is necessary for studying biochemical processes in the riparian zone but their characterization is complicated by strong temporal and spatial heterogeneity we investigated to what extent repeat 3d surface electrical resistance tomography ert can be used to monitor transport of a salt tracer plume under close to natural gradient conditions the aim is to estimate groundwater flow velocities and pathways at a site located within a riparian groundwater system adjacent to the perialpine thur river in northeastern switzerland our ert time lapse images provide constraints on the plume s shape flow direction and velocity these images allow the movement of the plume to be followed for 35 m although the hydraulic gradient is only 1 43 the ert time lapse images demonstrate that the plume s center of mass and its front propagate with velocities of 2 10 4 m s and 5 10 4 m s respectively these velocities are compatible with groundwate

remote sensing based assessment of hazards from glacier lake outbursts a case study in the swiss alps glacier lakes are a common phenomenon in high mountain areas outbursts from glacier lakes have repeatedly caused the loss of human lives as well as severe damage to local infrastructure in several high mountain ranges around the world a grave uncertainty about the hazard potential of glacier lakes still exists especially with respect to the effects of accelerating rates of glacier retreat as a consequence of atmospheric warming area wide detection and modeling of glacier lake hazard potentials is therefore a major challenge in this study an approach integrating three scale levels allows for the progressive focus on critical glacier lakes remote sensing methods for application in glacier lake hazard assessment are presented and include channel indexing data fusion and change detection each method matches the requirements of a certain scale level for estimating potential disaster amplitudes assessments must be made of maximum discharge and runout distance of outbursts floods and debris flows existing empirical relations are evaluated and complementary ones as derived from available data are proposed tests with observations from a recent outburst event from a moraine dammed lake in the swiss alps show the basic applicability of the proposed techniques and the usefulness of empirical relations for first hazard assessments in particular the observed runout distance of the debris flow resulting from the outburst does not exceed the empirically estimated maximum runout distance a list of decision criteria and related remote sensing techniques are discussed in conclusion such a list is an essential tool for evaluating the hazard potential of a lake a systematic application of remote sensing based methods for glacier lake hazard assessment is recommended

performance of aster and srtm dems and their potential for assessing glacial lakes in the lunana region bhutan himalaya to assess the potential volume of a glacial lake outburst flood glof more precisely than in previous studies we analyze ground survey data and remote sensing digital elevation models dems around glacial lakes in the lunana region bhutan based on a dem generated from differential gps ground surveys we first evaluate the relative accuracies of dems produced by the advanced spaceborne thermal emission and reflection radiometer aster and the shuttle radar topography mission srtm root mean square errors of the altitudinal difference between these dems and ground survey data were 11 0 m for aster and 11 3 m for srtm these errors are similar to those of previous studies we show that a topographical classification allows a better estimate of elevation on lakes ponds riverbeds and glaciers due to their flat surfaces while the relative accuracy is worse over moraines and hill slopes due to their narrow ridges and steep slopes using the optical satellite images and the ground survey data we re evaluate the glof volume in 1994 as 17 2 5 3 10 6 m 3 we show glof related information such as distance altitudinal difference and gradient at possible outburst points where the lake level is higher than the neighboring riverbed and or glacial lake

electrical characterization of non fickian transport in groundwater and hyporheic systems 1 recent work indicates that processes controlling solute mass transfer between mobile and less mobile domains in porous media may be quantified by combining electrical geophysical methods and electrically conductive tracers whereas direct geochemical measurements of solute preferentially sample the mobile domain electrical geophysical methods are sensitive to changes in bulk electrical conductivity bulk ec and therefore sample ec in both the mobile and immobile domains consequently the conductivity difference between direct geochemical samples and remotely sensed electrical geophysical measurements may provide an indication of mass transfer rates and mobile and immobile porosities in situ here we present 1 an overview of a theoretical framework for determining parameters controlling mass transfer with electrical resistivity in situ 2 a review of a case study estimating mass transfer processes in a pilot scale aquifer storage recovery test and 3 an example application of this method for estimating mass transfer in watershed settings between streams and the hyporheic corridor we demonstrate that numerical simulations of electrical resistivity studies of the stream hyporheic boundary can help constrain volumes and rates of mobile immobile mass transfer we conclude with directions for future research applying electrical geophysics to understand field scale transport in aquifer and fluvial systems subject to rate limited mass transfer

vadose zone flow model parameterisation using cross borehole radar and resistivity imaging cross borehole geoelectrical imaging in particular electrical resistivity tomography ert and transmission radar tomography can provide high resolution images of hydrogeological structures and in some cases detailed assessment of dynamic processes in the subsurface environment through appropriate petrophysical relationships these tools offer data suitable for parameterising and constraining models of groundwater flow this is demonstrated using cross borehole radar and resistivity measurements collected during a controlled vadose zone tracer test performed at a field site in the uk sherwood sandstone both methods show clearly the vertical migration of the tracer over a 200 h monitoring period by comparing first and second spatial moments of changes in moisture content predicted from a numerical simulation of vadose zone flow with equivalent statistics from two and three dimensional ert and cross borehole radar profiles the effective hydraulic conductivity is estimated to be approximately 0 4 m d such a value is comparable to field estimates from borehole hydraulic tests carried out in the saturated zone at the field site and provides valuable information that may be utilised to parameterise pollutant transport models of the site

the application of time lapse electrical tomography in groundwater studies recently various techniques of electrical tomography have been refined and fast efficient commercial systems are now available new inversion algorithms produce electrical images that more accurately model a two dimensional or three dimensional subsurface than ever before over the past three years electrical tomography surveys in germany the u k and the u s have produced remarkable results

performance analysis and simulation of a two well tracer test at the mobile site during the late summer of 1984 a two well tracer test was performed which involved travel distances of 38 3 m to 90 m a bromide tracer slug was injected at one well while groundwater was simultaneously pumped from the other well the two well test which required 32 days to complete was then simulated by geotrans inc using a three dimensional advection dispersion model with a longitudinal dispersivity of 0 15 m a transverse dispersivity of 0 05 m and the permeability distribution being measured independently in a single well test single well test results which involved a travel distance of 5 5 m indicated that the hydraulic conductivity varied by about a factor of 4 throughout the aquifer thickness the two well test simulation made without knowledge of the test results and without any calibration was remarkably good local hydrodynamic dispersion was negligible so that the concentration versus time breakthrough at the withdrawal well could be simulated just as well with a quasi three dimensional advection model having zero hydrodynamic dispersion this implies that over the travel distances applicable to the two well test the spreading of the slug in the aquifer depended mainly on macroscopic velocity variations that were quantifiable in terms of the inferred permeability distribution this result which pertains to an aquifer in a fluvial terrace deposit of quaternary age is similar to that observed by pickens and grisak in a sandy glaciofluvial aquifer near the chalk river nuclear laboratories in canada such flow systems can result in fully three dimensional plumes with high concentrations of contaminant moving over large horizontal distances in the higher permeability zones

electrical resistance tomography electrical resistance tomography ert is a method that calculates the subsurface distribution of electrical resistivity from a large number of resistance measurements made from electrodes for in situ applications ert uses electrodes on the ground surface or in boreholes it is a relatively new imaging tool in geophysics the basic concept was first described by lytle and dines as a marriage of traditional electrical probing introduced by the schlumberger brothers and the new data inversion methods of tomography development of both the theory and practice of ert was confined mostly to the late 1980s and the 1990s tomographic inversion added important new capabilities as it was more general accurate and rigorous at spatial imaging of geophysical electrical resistance data than earlier pseudosection or curve fitting methods

fully coupled hydrogeophysical inversion of a laboratory salt tracer experiment monitored by electrical resistivity tomography 1 we perform a salt tracer experiment monitored by time lapse electrical resistivity tomography in a quasi two dimensional sandbox with the aim of determining the hydraulic conductivity distribution in the domain we use sodium chloride as a tracer together with cochineal red for visual monitoring the time series of observed resistance for each electrode configuration is characterized by its temporal moments we invert the mean arrival time of electrical potential perturbations and a few steady state hydraulic head measurements using the fully coupled hydrogeophysical approach recently introduced by pollock and cirpka 2010 this is the first application of the approach to experimental data the results obtained show a reasonable agreement between the estimated hydraulic conductivity field and the pattern of the actual sandbox filling using this estimation a transient simulation is performed to compute the propagation of the salt tracer plume through the sandbox the latter is compared to pictures taken during the experiment these results show an even better agreement indicating that the lenses of different sand types are not entirely homogeneous and some unexpected preferential flow paths are present we conclude that temporal moments of potential perturbations obtained during salt tracer tests provide a good basis for inferring the hydraulic conductivity distribution by fully coupled hydrogeophysical inversion

late quaternary crustal deformation and coastal changes in finland abstract the crustal deformation which has been occurring in finland since the last ice age is principally caused by glacio isostatic uplift as a result of which the highest postglacial shorelines in the country are located over 200 m above the present sea level the uplift rate was well over ten times higher during and immediately after deglaciation in each region than it is today so that numerous vertical faults were created in the northern part of fennoscandia in the period 9000 8500 bp in addition to this isostatic land uplift the fluctuations in water level immediately after deglaciation were also affected by elastic rebound geoid deformation and fluctuations occurring in the baltic sea basin independently of those taking place in the oceans in general there was a marked decrease in the rate of uplift at 8500 8000 bp and the highest rate recorded currently in finland is just over 8 mm year this figure is estimated to include a 10 20 contribution from a tectonic component arising from the mid atlantic ridge uplift has moved the shoreline outwards towards the sea particularly on the flat west coast of finland which has a high rate of uplift a large number of raised shorelines lie at different levels above sea level and the effect of wave action is particularly evident in the glaciofluvial sand and gravel of eskers

electrical properties of partially saturated sandstones novel computational approach with hydrogeophysical applications 1 electric and electromagnetic geophysical tools are suitable methods for investigating moisture content transport and storage properties of the subsoil with noninvasive surveys interpretation of field data is still based on empirical or semiempirical equations which must be calibrated with complex time consuming laboratory measurements in this paper we develop pore scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters grain size distribution and porosity we compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions we compare the simulated results with experimental data from sherwood sandstone uk and discuss the effect of these assumptions on the effective conductivity simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data we also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements

imaging and characterisation of subsurface solute transport using electrical resistivity tomography ert and equivalent transport models abstract we assess the usefulness of electrical resistivity tomography ert in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers a field tracer experiment was conducted at the krauthausen test site germany the spatial and temporal evolution of the injected nabr solute plume was monitored in a 2d ert image plane located downstream of the injection well for 90 days since ert maps changes in bulk electrical conductivity the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation the concentration maps are then analysed using an equivalent convection dispersion model cdm which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity as demonstrated by associated synthetic model studies ert resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm since for heterogeneous media local concentrations within the plume deviate from those predicted by the equivalent cdm we also interpret the ert derived pixel breakthrough curves in terms of an equivalent stream tube model stm the stm represents transport in the aquifer by a set of 1d convection dispersion processes allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified we believe that the observed tracer plume is satisfactorily described by the equivalent cdm probably because the tracer plume was small relative to the heterogeneity scale of the aquifer even though application of the stm revealed some deviation from the ideal homogeneous case the equivalent dispersivity in the stm matches the longitudinal dispersivity of the cdm closely consistent with predominantly homogeneous mixing however the stm analysis illustrates how ert results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers

a tracer test in a shallow heterogeneous aquifer monitored via time lapse surface electrical resistivity tomography we illustrate a case study of a saline tracer test in a shallow highly heterogeneous aquifer monitored by means of surface time lapse ert the test was aimed at identifying the system s hydraulic properties some of the expected limitations of the method particularly caused by the strong decrease in ert resolution with depth and the consequent problems with mass balance and moment calculation could be partly balanced by the use of direct measurements of groundwater electrical conductivity and tracer concentration at one selected location the vast heterogeneity of the system ranging in lithology from clay to gravel at a scale of meters to tens of meters reflects itself in the tracer migration and distribution over time the tracer is trapped in the low permeability regions and from these it is slowly released over time high resolution surface ert proves effective at picturing this system behavior over time the extreme heterogeneity is also a challenge in the attempt to translate bulk electrical

potential of electrical resistivity tomography to infer aquifer transport characteristics from tracer studies a synthetic case study 1 with time lapse electrical resistivity tomography ert transport processes in the subsurface can be imaged and monitored the information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ert is generally underdetermined and that ert data acquisition is often limited to two dimensional 2 d image planes to address this problem we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2 d image plane perpendicular to the mean flow direction using time lapse ert the tracer breakthrough patterns in the image plane were interpreted using equivalent transport models an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves equivalent parameters derived from simulated and from ert inverted concentrations showed a good agreement which demonstrates the potential of ert to characterize subsurface transport using first order approximate solutions of stochastic flow and transport equations equivalent model parameters and their spatial variability were interpreted in terms of the local scale dispersion and the spatial variability of the hydraulic conductivity the spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related consequently the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions which can be observed with sufficiently high spatial resolution using ert

assessment of local hydraulic properties from electrical resistivity tomography monitoring of a three dimensional synthetic tracer test experiment 1 in recent years geophysical methods have become increasingly popular for hydrological applications time lapse electrical resistivity tomography ert represents a potentially powerful tool for subsurface solute transport characterization since a full picture of the spatiotemporal evolution of the process can be obtained however the quantitative interpretation of tracer tests is difficult because of the uncertainty related to the geoelectrical inversion the constitutive models linking geophysical and hydrological quantities and the a priori unknown heterogeneous properties of natural formations here an approach based on the lagrangian formulation of transport and the ensemble kalman filter enkf data assimilation technique is applied to assess the spatial distribution of hydraulic conductivity k by incorporating time lapse cross hole ert data electrical data consist of three dimensional cross hole ert images generated for a synthetic tracer test in a heterogeneous aquifer under the assumption that the solute spreads as a passive tracer for high peclet numbers the spatial moments of the evolving plume are dominated by the spatial distribution of the hydraulic conductivity the assimilation of the electrical conductivity 4d images allows updating of the hydrological state as well as the spatial distribution of k thus delineation of the tracer plume and estimation of the local aquifer heterogeneity can be achieved at the same time by means of this interpretation of time lapse electrical images from tracer tests we assess the impact on the performance of the hydrological inversion of i the uncertainty inherently affecting ert inversions in terms of tracer concentration and ii the choice of the prior statistics of k our findings show that realistic ert images can be integrated into a hydrological model even within an uncoupled inverse modeling framework the reconstruction of the hydraulic conductivity spatial distribution is satisfactory in the portion of the domain directly covered by the passage of the tracer aside from the issues commonly affecting inverse models the proposed approach is subject to the problem of the filter inbreeding and the retrieval performance is sensitive to the choice of k prior geostatistical parameters

a multi disciplinary study of deformation of the basaltic cover over fine grained valley fills a case study from eastern sardinia italy the pliocene to early pleistocene volcanic activity which generated the basaltic plateau of the orosei dorgali area in eastern sardinia led to the disruption of the local hydrographic network by damming some tracts of the fluvial valleys incised in the granite basement this resulted in the formation of lacustrine basins whose fine grained fills were partly interfingered and eventually covered by younger lava flows in the sw part of the plateau close to the galtelli village a number of unknown depressions locally named paules were formed in order to reconstruct their subsurface structure two electrical resistivity tomography surveys were carried out across these depressions the geophysical results which demonstrate the existence of a disrupted layered system were used to build a numerical geomechanical model that suggest the depressions originated by local collapses of the basaltic cover due to the compaction of the underlying fine grained valley fills

time lapse mise a la masse measurements and modelling for tracer test monitoring in a shallow aquifer abstract the main goal of this study is to evaluate the reliability of the mise a la masse malm technique associated with saline tracer tests for the characterization of groundwater flow direction and velocity the experimental site is located in the upper part of the alento river alluvial plain campania region southern italy in this paper we present the hydrogeological setting the experimental setup and the relevant field results subsequently we compare those data against the simulated results obtained with a 3d resistivity model of the test area coupled with a model describing the advection dispersion equation for continuous tracer injection in particular we calculate a series of 3d forward solutions starting from a reference model all derived from electrical tomography results but taking into consideration different values of mean flow velocity and directions each electrical resistivity 3d model is used to produce synthetic voltage maps for malm surveys finally the synthetic malm voltage maps are compared with the ones measured in the field in order to assess the information content of the malm dataset with respect to the groundwater field characteristics the results demonstrate that the information content of the malm data is sufficient to define important characteristics of the aquifer geometry and properties this work shows how a combination of three dimensional time lapse modeling of flow tracer transport and electrical current can substantially contribute towards a quantitative interpretation of malm measurements during a saline tracer test this approach can thus revive the use of malm as a practical low cost field technique for tracer test monitoring and aquifer hydrodynamic characterization

detecting himalayan glacial lake outburst floods from landsat time series abstract several thousands of moraine dammed and supraglacial lakes spread over the hindu kush himalayan hkh region and some have grown rapidly in past decades due to glacier retreat the sudden emptying of these lakes releases large volumes of water and sediment in destructive glacial lake outburst floods glofs one of the most publicised natural hazards to the rapidly growing himalayan population despite the growing number and size of glacial lakes the frequency of documented glofs is remarkably constant we explore this possible reporting bias and offer a new processing chain for establishing a more complete himalayan glof inventory we make use of the full seasonal archive of landsat images between 1988 and 2016 and track automatically where glofs left shrinking water bodies and tails of sediment at high elevations we trained a random forest classifier to generate fuzzy land cover maps for 2491 images achieving overall accuracies of 91 we developed a likelihood based change point technique to estimate the timing of glofs at the pixel scale our method objectively detected ten out of eleven documented glofs and another ten lakes that gave rise to previously unreported glofs we thus nearly doubled the existing glof record for a study area covering 10 of the hkh region remaining challenges for automatically detecting glofs include image insufficiently accurate co registration misclassifications in the land cover maps and image noise from clouds shadows or ice yet our processing chain is robust and has the potential for being applied on the greater hkh and mountain ranges elsewhere opening the door for objectively expanding the knowledge base on glof activity over the past three decades

investigations into the relationship between changes in internal moisture regimes and rock surface deterioration in cavernous sandstone features cavernous features commonly develop in sandstone but their development over time remains enigmatic it has been suggested that moisture movements within the rock mass play a key role in the location development and dynamics of cavernous features in this research the role of internal moisture movement is tested through monitoring moisture and surface deterioration dynamics in april 2008 and april 2009 within two large cavernous features mega tafoni in the golden gate highlands national park south africa gghnp data are presented from surveys of internal moisture using electrical resistivity tomography ert surface moisture using a protimeter and deterioration using surface hardness as recorded with an equotip as a proxy for surface deterioration across five 2 45 m long transects in addition a high resolution temperature record is presented to assess the influence of micro climates within the caverns the results indicate consistency in the gross spatial pattern of moisture flow within the rock mass over a one year period but significant changes in mean moisture contents and in the fine detail of moisture patterning some noticeably weakened areas had developed within the central parts of the cavernous features often linked to wetter subsurface conditions supporting the theory that core softening is a main driver of cavernous feature formation however in some areas surface hardening is also found to be associated with wetter subsurface conditions supporting the theory that case hardening is a main driver of cavernous feature formation in addition the presence of well established biofilms suggests an even more complex interaction between moisture surface development and biological activity a model is presented therefore which integrates this paradox by proposing a non linear relationship between moisture dynamics facilitation of biofilm formation and deterioration within cavernous features

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

rapid changes of the estonian coast during the late glacial and holocene abstract estonia s shoreline 3780 km long underwent rapid changes since the late glacial in some places ancient shorelines are located up to 150 km inland from the present day shoreline while there is widespread evidence of rapid changes in the sea level and coastal erosion pattern resulting mainly from glacioisostatic and climatic factors rapid changes on the contemporary coasts are mainly due to heavy storms and ice push actions

quantitative assessment of electrical resistivity tomography for monitoring dnapls migration comparison with high resolution light transmission visualization in laboratory sandbox abstract real time monitoring of dense non aqueous phase liquids dnapls migration and distribution is essential for the decision of an effective remediation strategy light transmission visualization ltv has shown its accuracy and efficiency for measuring dnapls saturation and water content in the laboratory but it cannot be implemented in three dimensional sandbox or field scale sites recently developed electrical resistivity tomography ert has been applied in monitoring the migration and distribution of dnapls in bench and field scale studies however the evaluation of the ability of ert for monitoring dnapls migration by a direct comparison of ert with high resolution techniques such as ltv within an experimental system is still lacking two sandbox experiments with different permeability conditions are conducted to quantitatively assess the capability of ert for monitoring the dnapls migration during the injections ltv method is used to visualize the dnapls migration and provide high resolution saturation data while ert method is applied to capture the change of resistivity the results from the comparison between ltv and ert methods show that ert is successful in detecting the accumulation and flow bypassing phenomenon around the low permeability lenses as well as the penetration through the high permeability lenses there is a fair correlation between the resistivity and saturation with overall correlation coefficients above 0 6 except at last stage however using classical regularization techniques based on smoothness the area of dnapls plume determined by ert is commonly overestimated compared to the plume around the low permeability lenses the plume around the high permeability lenses estimated by ert is more extensive due to larger resistivity contrasts in addition ert measurements indicate that the resistivity increase caused by the low saturation dnapls is not apparent enough which is likely to be covered up under the changing hydrogeochemical environments in field investigations

hydrodynamic characteristics of the tam pokhari glacial lake outburst flood in the mt everest region nepal the tam pokhari glacial lake outburst flood glof which occurred in 1998 in the mt everest region of nepal was evaluated using hydrodynamic models to gain a better understanding of the flow behaviour the flood wave was analysed separately under rigid and erodible boundary conditions in both cases the calculated dam breach hydrograph which had a peak discharge of about 10 000 m3 s was routed through the inkhu river which originates from the lake the morphologic changes along the river were also analysed and the results were compared with satellite images field observations and recorded data in the case of rigid boundaries the routing procedure gradually attenuated the peaks of the hydrographs to account for hydraulic pooling in narrow gorges and storage in the channel in the case of erodible boundaries such effects were minimized due to the increment in channel capacity associated with erosion by debris flow the study revealed that the glof event produced a large scale debris flow additionally the results revealed that erosion and deposition took place intermittently but that approximately 440 000 m3 of sediment was deposited about 14 km downstream from the lake mouth the calculated peak of the water and sediment mixture at 14 4 km was found to be 30 000 m3 s which is almost 6 times as large as that observed when the rigid boundary conditions were used further the increase in the peaks of the hydrographs due to sediment transport was the primary reason for the destruction associated with the glof these findings suggest that the local sedimentology and topography as well as other geo hazard conditions in the area should be carefully evaluated before recommending any control measures against glofs in the himalayan region copyright 2009 john wiley sons ltd

field study of dispersion in a heterogeneous aquifer 1 overview and site description results are presented for a large scale natural gradient tracer experiment conducted in a heterogeneous alluvial aquifer at a site near columbus mississippi the study was initiated with a 48 hour pulse injection of 10 m3 of groundwater containing bromide and three organic tracers pentaflourobenzoic acid o trifluoromethylbenzoic acid and 2 6 diflourobenzoic acid over a 20 month period seven comprehensive samplings of the tracer plume were performed at approximately 1 to 4 month intervals using an extensive three dimensional sampling well network the dominant feature of the tracer plume that evolved during the study was the highly asymmetric concentration distribution in the longitudinal direction this asymmetry was produced by accelerating groundwater flow along the plume travel path that in turn resulted from an approximate 2 order of magnitude increase in the mean hydraulic conductivity between the near field and far field regions of the site the columbus study is distinct from previous natural gradient experiments because of the extreme heterogeneity of the aquifer the large scale spatial variations in groundwater velocity and the extensive set of hydraulic conductivity measurements for the aquifer

an assessment of conditions before and after the 1998 tam pokhari outburst in the nepal himalaya and an evaluation of the future outburst hazard on 3 september 1998 a glacial lake outburst flood glof that originated from tam pokhari occurred in the hinku valley of the eastern nepal himalaya this study analyses the lake s geomorphic and hydrologic conditions prior to the outburst and evaluates the conditions that could contribute to a future flood through photogrammetric techniques we processed high resolution corona kh 4a 2 7 m and alos prism 2 5 m stereo images taken before and after the glof event and produced detailed topographic maps 2 m contour interval and dems 5 m 5 m we re constructed lake water surfaces before 4410 5 m and after 4356 5 m the outburst and reliably estimated the lake water surface lowering 54 5 m and the water volume released 19 5 2 2 106 m3 from the lake showing good agreement with the results obtained from ground based measurements the most relevant conditions that may have influenced the catastrophic drainage of tam pokhari in 1998 include the presence of i a narrow 75 6 m steep up to 50 and high 120 5 m moraine dam ii high lake level 8 5 m of freeboard and iii a steep overhanging glacier 40 the lake outburst substantially altered the immediate area creating a low and wide 500 m outwash plain below the lake a wide lake outlet channel 50 m and a gentle channel slope 3 5 our new data suggest that the likelihood of a future lake outburst is low our results demonstrate that the datasets produced by photogrammetric techniques provide an excellent representation of micro landform features on moraine dams lake water surfaces and the changes in both over time thereby allowing highly accurate pre and post glof volumetric change analysis of glacial lakes furthermore it enables precise measurement of several predictive variables of glofs that can be useful for identifying potentially dangerous glacial lakes or prioritizing them for detailed field investigations copyright 2015 john wiley sons ltd

large scale natural gradient tracer test in sand and gravel cape cod massachusetts 1 experimental design and observed tracer movement a large scale natural gradient tracer experiment was conducted on cape cod massachusetts to examine the transport and dispersion of solutes in a sand and gravel aquifer the nonreactive tracer bromide and the reactive tracers lithium and molybdate were injected as a pulse in july 1985 and monitored in three dimensions as they moved as far as 280 m down gradient through an array of multilevel samplers the bromide cloud moved horizontally at a rate of 0 42 m per day it also moved downward about 4 m because of density induced sinking early in the test and accretion of areal recharge from precipitation after 200 m of transport the bromide cloud had spread more than 80 m in the direction of flow but was only 14 m wide and 4 6 m thick the lithium and molybdate clouds followed the same path as the bromide cloud but their rates of movement were retarded about 50 relative to bromide movement because of sorption onto the sediments