correlation of porosity and permeability of reservoirs with well oscillations induced by earth tides summary periodic gravity perturbations known as earth tides produce minute expansions and contractions of subsurface geologic formations the motions induce water level oscillations in wells connected to the deep reservoirs and a measurable phase lag occurs between the maximum gravity and the maximum water level the amplitude of the water level oscillations induced by the small harmonic gravity variations of the earth tides and the phase lag relative to the tide are related to the reservoir porosity and permeability the motions of an elastic subsurface reservoir are analysed by considering an axially symmetric system of finite volume which is activated by oscillations of a rigid rock mass overlying the reservoir the geometric parameters involved are the thickness of the reservoir radial extent depth and fluid level in the well the physical parameters for which data are available or satisfactory estimates can be made are the fluid viscosity densities temperature compressibilities and shear modulus these properties refer to in situ conditions at large overburden pressure permeability and porosity at in situ conditions are not directly measurable and methods of indirect estimation are of practical interest this analysis correlates these two parameters with the amplitude and phase lag of the induced well fluid oscillation for the very small strains and fluid volume fraction changes induced by the tides slow flow of a viscous fluid through an isotropic porous matrix is assumed an axially symmetric analysis for a uniform permeable layer perturbed by the oscillations of the rigid overburden rock yields explicit expressions for the oscillation amplitude and phase in the well selected results from numerical solutions having a wide range of realistic parameter values are presented the results clearly show the dependence of amplitude and phase lag on the dimensionless permeability and the near proportionality of the amplitude on the reciprocal of the porosity porosity has no other significant influence finally it is shown how asymptotic approximations of the direct solution allow an inversion which determines the permeability and porosity in terms of the amplitude and phase lag given the other reservoir properties

analytical and numerical solutions on the response of pore pressure to cyclic atmospheric loading with application to horonobe underground research laboratory japan during the long term stability assessment of underground disposal repositories buried in sedimentary formations one of crucial scientific problems is to determine parameters of site formations the analysis of response of the pore pressure due to atmospheric loading provides a possible way of accurate estimation of formation parameters in this paper an analytical solution of response of the pore pressure to atmospheric loading was derived starting from the biot s poroelasticity and its corresponding numerical solutions were developed by finite element methods for 1d and 2d situations with comparison to the analytical solution the experimental results show that the numerical schemes sound reasonable to implement the assessment of response of the pore pressure in horizontal multilayer sedimentary formations in particular it is effective for a 2d model over large area with consideration of background horizontal groundwater flow a highlight of this work is to construct a reasonable approach to capture responses of the pore pressure to atmospheric loading and at the same time to provide the feasibility of integrated analysis of well monitoring data of pore pressure variance in horonobe underground research laboratory url hokkaido japan

constraints on hydraulic parameters and implications for groundwater flux across the upland estuary interface abstract analyses of independent laboratory and field scale measurements from two sites on sapelo island georgia reveal heterogeneity in hydraulic parameters across the upland estuary interface regardless of the method used short duration pumping tests amplitude attenuation of tidal pumping data sediment grain size distributions and falling head permeameter tests we obtain hydraulic conductivity of 10 4 m s 1 for the fine grained well sorted clean sands that make up the upland areas proximal to the upland estuary boundary the tidal pumping analyses and permeameter tests suggest that hydraulic conductivities decrease by more than two orders of magnitude a result consistent with the presence of a clogging layer such a clogging layer may arise due to a variety of physical chemical or biological processes the extent and orientation of the layers of reduced hydraulic conductivity near the upland estuary boundary influence the nature of the aquifer s response to tidal forcing where the lower conductivity layer forms a relatively flat creek bank tidal pumping produces a primarily mechanical response in the adjacent aquifer where the creek bank is nearly vertical there is a more direct hydraulic connection between the tidal creek and the adjacent aquifer the clogging layer likely contributes to the development of complicated flow pathways across the upland estuary boundary effective flow paths calculated from tidal pumping data terminate within the marsh beyond the boundary of the upland aquifer suggesting a diffuse regime of groundwater discharge in the marsh we postulate that in many settings submarsh flow may be as important as seepage faces for groundwater discharge into the marsh estuary complex

transient changes in well water level in bore wells in western india due to the 2004 mw 9 3 sumatra earthquake large water level changes were observed in six bore wells in the koyna region in western india following the great sumatra earthquake of m w 9 3 on 2004 december 26 this earthquake occurred at 00 58 50 coordinated universal time utc off the coast of sumatra located about 3000 km from the koyna region the arrival time of the p wave recorded at the koyna seismic station was 01 04 24 45 utc the anomalous water level changes were observed at 01 15 utc at all of these wells where the sampling rate was 15 min no abnormal changes were noticed in the preceding sampling time at 01 00 utc clearly indicating that these changes occurred due to the passage of seismic waves generated by the sumatra earthquake however due to the large sampling interval it is difficult to correlate the water level changes either to shear or surface waves no local earthquake was recorded by the network during this period the anomalous water level changes were of the order of 2 65 cm and show either a spikelike or a steplike change these types of changes are attributed to the dynamic strain induced by the passage of seismic waves most probably long period surface waves

atmospheric pumping a mechanism causing vertical transport of contaminated gases through fractured permeable media as the barometer falls gases are drawn upward out of the permeable earth into the atmosphere conversely a rising barometer pushes air downward in a homogeneous permeable medium these cyclical gas motions are piston like and nearly reversible so they contribute only modestly to the net transport of contaminant gases in a fractured permeable medium however the fractures will generally serve as breathing passages for all of the gas filled porosity greatly increasing the amplitude and nonuniformity of vertical motions the resulting transport process may be orders of magnitude more significant than molecular diffusion according to the theoretical analysis presented here analytical solutions are first derived for the sinusoidal pressure response of a medium containing identical vertical fractures equally spaced by slabs of permeable matrix material these solutions are then used to constrain the relationship between fracture aperture and fracture spacing based on field comparisons between surface and subsurface pressure variations the final phase of the analysis addresses the diffusive and advective transport of an inert trace gas which is carried by an oscillatory flow along a fracture having permeable walls a maximum rate of transport is predicted to occur for an intermediate fracture spacing which is typically a few meters

frequency dependence of the groundwater discharge at an artesian well as recognized from tidal fluctuation records groundwater discharge temperature and electrical conductivity of an artesian well were measured at nishiawakura okayama prefecture southwest japan the discharge ranged from 2 10 4 to 5 10 4 m3 s and showed tidal fluctuations of about 5 10 5 m3 s induced by strain although the groundwater temperature reflected the same tidal fluctuations as the discharge the electrical conductivity did not manifest tidal fluctuations the discharge slightly leads the theoretical tidal strain and its response to the strain of the diurnal constituents is different from that of the semidiurnal constituents the discharge fluctuations induced by atmospheric loading also have some frequency dependence these can be explained by the vertical or horizontal groundwater flow leakage from the aquifer which has been used in the explanation of the well water level fluctuations induced by tidal strain and atmospheric loading

river stage tomography a new approach for characterizing groundwater basins received 19 june 2008 revised 16 february 2009 accepted 12 march 2009 published 9 may 2009 1 data from tomographic surveys make an inverse problem better posed in comparison to the data from a single excitation source a tomographic survey provides different coverages and perspectives of subsurface heterogeneity nonfully redundant information of the subsurface fusion of these pieces of information expands and enhances the capability of a conventional survey provides cross validation of inverse solutions and constrains inherently ill posed field scale inverse problems basin scale tomography requires energy sources of great strengths spatially and temporally varying natural stimuli are ideal energy sources for this purpose in this study we explore the possibility of using river stage variations for basin scale subsurface tomographic surveys specifically we use numerical models to simulate groundwater level changes in response to temporal and spatial variations of the river stage in a hypothetical groundwater basin we then exploit the relation between temporal and spatial variations of well hydrographs and river stage to image subsurface heterogeneity of the basin results of the numerical exercises are encouraging and provide insights into the proposed river stage tomography using naturally recurrent stimuli such as river stage variations for characterizing groundwater basins could be the future of geohydrology however it calls for implementation of sensor networks that provide long term and spatially distributed monitoring of excitation as well as response signals on the land surface and in the subsurface

multi level slug tests in highly permeable formations 1 modification of the springer gelhar sg model a multi level slug test model and a method for the evaluation of vertical profiles of hydraulic conductivity in highly permeable formations are developed a double packer system is employed to estimate local hydraulic conductivity depending on the formation and double packer system parameters the water level recovery in the tested well can exhibit a monotonic or oscillatory response to discern information on aquifer properties from artifacts introduced by the measurement system the theory of flow in an aquifer and a double packer system is developed the mathematical model incorporates features of the springer and gelhar 1991 model and reduces to the bouwer and rice 1976 model in a special case the model involves equations of momentum and mass conservation for the double packer system with quasi steady well aquifer interaction equations the method is uniformly applicable for both monotonic and oscillatory well responses and can produce profiles of hydraulic conductivity for the tested well the criterion is given to determine the type of well response for given slug test conditions

land subsidence due to groundwater withdrawal potential damage of subsidence and sea level rise in southern new jersey usa land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region groundwater withdrawal results in fluid pressure change in the layers the pressure change in the layers induces both elastic and inelastic land compaction the elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent groundwater response to barometric pressure change is used to estimate the elastic compaction in this study the storativity specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal the discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern new jersey the estimated subsidence is about 2 3 cm near the location of monitoring wells in atlantic camden cumberland and cape may counties over the past 20 years if the current trend of water level drop continues the average subsidence in southern new jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years the rise of global sea level is about 2 mm year on average because of the very gentle slope in southern nj the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period this combination will also accelerate the coastal flooding frequency and the erosion rate of the new jersey coastal plain and pose a serious threat to the coastal economy

determining fault permeability from subsurface barometric pressure measured barometric pressure fluctuations in a borehole drilled 600 m into the unsaturated zone at a site on the eastern slope of yucca mountain nevada are used to compute pneumatic diffusivities and air permeabilities of layered tuffaceous rocks of particular interest is the occurrence of increasing pressure amplitude and decreasing phase lags observed at several deep stations the pressure amplitude increases by 13 and the pressure peak arrives 65 to 72 h earlier as the depth of the unsaturated zone increases from 407 to 436 m this observation is inconsistent with a conventional 1d downward pressure decay model but can be explained by hypothesizing the existence of a lateral pneumatic flow path from a nearby fault a 2d numerical model has been constructed to test this lateral flow hypothesis the modeling results indicate that a leaky fault hypothesis can reconcile the measured barometric data with other geologic mapping and permeability measurements at the site the inferred fault permeability r

five decades of triggered earthquakes in koyna warna region western india a review abstract we review reservoir triggered seismicity rts in the koyna warna region of india since the impoundment of the koyna reservoir in 1962 until the year 2015 we include seismicity that occurred farther south in response to the impoundment of warna reservoir in 1993 about 35 km to the south of koyna reservoir the on going earthquake activity for more than five decades in a small seismic volume of about 30 20 10 km3 has characterized the koyna warna region as globally unique and significant to date 22 earthquakes of m 5 about 200 earthquakes of m 4 and several thousand smaller earthquakes have been recorded by a dense network of stations in the region various seismological geophysical and hydrological studies have been carried out to understand the phenomenon of triggered seismicity including source mechanism fault geometry crustal structure earthquake processes causal relationship with reservoir water level changes and anomalous water level fluctuations in cased bore wells the present review takes stock of all such studies undertaken so far to summarise the understanding on various geo scientific issues and milestone achievements with regard to mechanism of triggered seismicity and source processes fault plane solutions commensurate with geometry of faulting source parameters seismogenic depth crustal structure and the role of reservoir water level two stage increase in seismic energy release coinciding with peaks of annual filling and draining cycle of reservoir with one month delay vis a vis spurt of moderate earthquakes m 5 due to i rapid rise in reservoir level 12 m week ii reservoir water level exceeding the previous maxima and iii duration for which high reservoir level is retained are characteristic features numerical models simulating diffusion of pore fluid pressure fronts during the filling stage of reservoir suggest stress perturbations of the order of 0 75 2 25 bar at hypocentral depth triggering earthquakes on critically stressed pre existing faults in the year 2005 a 13 station digital seismometers network became functional that characterized the distribution of epicentres in the area with increased accuracy and suggested four major seismic zones with well defined clusters scientific drilling carried out recently provide several new information regarding the subsurface geology and structure in the koyna region such as i thickness of deccan traps 933 in the koyna area and 1185 m in the warna area ii presence of granite gneiss basement directly underlying the deccan traps iii absence of infratrappean sediments and iv temperature not exceeding 150 c at hypocentral depth it is planned to establish a deep borehole observatory close to the seismic source zone for direct measurements of physical and mechanical properties of rocks pore fluid pressure hydrology thermal condition and other parameters of an intra plate active fault zone in the near field of earthquakes before during and after their occurrence results from such experiment and long term in situ monitoring of critical parameters would enhance our understanding on the mechanism of triggered earthquakes and the role of reservoir water level fluctuations

a dual porosity model for water level response to atmospheric loading in wells tapping fractured rock aquifers a fractured rock aquifer may be viewed as a permeable fracture network embedded within a less permeable porous matrix this permeability contrast gives rise to distinct pressure fields in the pore space and fractures and therefore to a response to atmospheric loading different from that of nonfractured porous media assuming that fracture sizes and orientations are uncorrelated and sufficiently random to ensure homogeneous and isotropic elastic behavior of the rock mass at the continuum scale an effective stress model proposed by tuncay and corapcioglu 1995 is used to develop a linear elastic stress strain relationship for dual porosity media elastic constants of the fractured rock mass required by the model are estimated using theoretical relations derived by budiansky and o connell 1976 the stress strain relationship and the coupled continuity equations for flow in deformable fractured media are combined to derive expressions for the undrained static confined barometric efficiency of a dual porosity medium two limiting cases are considered the initial instantaneous pressure response in the pore space and fractures due to a change of confining stress and the later stage of pressure equilibrium between the two phases the dual porosity response model developed here may be used to characterize hydraulic properties in fractured aquifers including low porosity and low permeability media the model is evaluated on water level hydrograph data from a borehole tapping fractured volcanic rocks water level and barometric data are supplemented by independent measurements of matrix porosities fracture spacing and rock elastic properties allowing an assessment of total porosity and specific storage at the site for the observed static confined barometric efficiency of 0 78 the instantaneous pressure response model yields plausible values for both parameters

borehole water level response to barometric pressure as an indicator of aquifer vulnerability the response of borehole water levels to barometric pressure is a function of the confining layer and aquifer properties this study aims to use this response as an aid towards quantitative assessment of groundwater vulnerability applying the techniques to the confined semi confined part of the chalk aquifer in east yorkshire uk time series analysis techniques are applied to data collected from twelve monitoring boreholes to characterize and remove components contributing to the borehole water level signal other than barometric pressure such as recharge and earth tides barometric response functions are estimated using the cross spectral deconvolutionaveraging technique performed with up to five overlapping frequency bands a theoretical model was then fitted to the observed barometric response functions in order to obtain estimates of aquifer and confining layer properties derived ranges for pneumatic and hydraulic diffusivities of the confining layer vary over four orders of magnitudes 0 9 to 128 0 m2 day and 10 0 to 5 0 104 m2 day respectively indicating that the aquifer is nowhere purely confined discrepancies between estimates of aquifer transmissivity derived from the barometric response function and pumping tests have been explored using slug tests and results suggest that aquifer model transmissivity are highly sensitive to borehole construction a simple flow model constructed to test the potential impact of confining layer heterogeneity on the barometric response function shows that while high frequencies reflect the immediate vicinity of the borehole low frequencies detect confining layer properties up to some 500 meters distant from the borehole a characteristic time scale is introduced as a function of derived properties of the confining layer and is used as a quantitative measure of the degree of aquifer confinement it is concluded that barometric response functions are sensitive to confining layer properties and thus can provide a useful tool for the assessment of aquifer vulnerability

detecting the vulnerability of groundwater in semi confined aquifers using barometric response functions summary the use of barometric response functions brfs for detecting the presence of fully penetrating highly conductive bodies within aquifer confining layers that present potential pathways for contaminants is explored brfs are determined from borehole water level wl and barometric pressure bp records past studies have shown that confining layer properties can be estimated from brfs providing a potential link between brfs and the concept of groundwater vulnerability existing analytical models that predict the brf from system properties assume homogeneity within the aquifer and its confining layer conditions which are seldom satisfied in nature the impact of partially and fully penetrating high diffusivity heterogeneities within a confining layer representing potential high flow pathways for contaminants on the brf is investigated through a suite of three dimensional transient numerical simulations of the confining layer aquifer system the results are interpreted through comparison with a modified pre existing analytical model for the brf comparison of numerically and analytically calculated brfs reveals that the key effect of a localised fully penetrating high diffusivity heterogeneity within a low diffusivity confining layer is to reduce the brf gain with only minor changes to the phase this impact on the brf decreases with increasing distance from the heterogeneity the importance of heterogeneity size is secondary to distance from the borehole and partially penetrating heterogeneities affect the brf to only a minor extent data from a study of the chalk aquifer e yorkshire england which is semi confined by heterogeneous glacial sediments display variations in brfs which are qualitatively similar to those shown by the numerical results it is suggested that the variation in brfs estimated from borehole records across a semi confined aquifer could be used to assess the degree of spatial continuity of low diffusivity lithologies within the confining layer which protect the aquifer against surface sourced contamination and thus provide a tool to improve groundwater vulnerability assessment

a study on the mechanism of coseismic groundwater changes interpretation by a groundwater model composed of multiple aquifers with different strain responses in order to research the coseismic and postseismic groundwater changes for a groundwater system consisting of multiple aquifers we studied the mechanism of coseismic groundwater changes at yudani hot spring which is an artesian well supplied by at least three aquifers in tottori prefecture japan we observed the changes in discharge and water temperature at this site in response to earthquakes tides and atmospheric pressure changes for the groundwater system of yudani hot spring a realistic model composed of three aquifers having different frequency dependencies of groundwater responses to crustal strain and atmospheric pressure was adopted the tidal and barometric responses of the discharges from the three aquifers which were cyclic responses over a limited frequency band were calculated and the physical parameters of the three aquifers were estimated by fitting a theoretical model to the observed responses then using the strain response over the whole frequency determined by the estimated physical parameters the theoretical responses of the discharges from the three aquifers to step like volumetric strain changes were calculated as a result the three aquifer model with different frequency dependencies quantitatively explained the observed groundwater changes at yudani hot spring due to earthquakes in addition the values of the coseismic volumetric strain steps were estimated based on groundwater changes at yudani hot spring these values did not agree with the theoretical coseismic volumetric strain changes at yudani hot spring due to the earthquake fault slips which were calculated under the assumption that the earth s crust is a homogeneous elastic half space medium it is possible that a local strain release such as aseismic slip at a fault near yudani hot spring might have caused the large strain changes estimated from the coseismic groundwater changes

determination of aquifer transmissivity from earth tide analysis the water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by earth tide dilatation of the aquifer because a finite amount of time is needed for water to flow into and out of the well there exists a phase shift or time lag between the tidal dilatation of the aquifer and the water level response in the well we derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity storage coefficient well radius and the period of the harmonic disturbance this solution is rather insensitive to the storage coefficient thus if the phase shift is known for a harmonic disturbance the transmissivity can be calculated given a rough estimate of the storage coefficient theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying as in the case of earth tides this opens the possibility of estimating aquifer transmissivity from water level records that show earth tide fluctuations a case study using data from a site near parkfield california is presented to illustrate application of the theory phase shifts of the o1 25 82 hour period and m2 12 42 hour period tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure a brief error analysis suggests that the computed o1 phase shift is subject to large uncertainty while the computed m2 phase shift is substantially more accurate based on an assumed storage coefficient range of 10 4 to 10 6 the estimated transmissivity range is 8 10 6 to 2 10 5 m2 s while hydraulic tests have not been performed to validate these estimates the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake

considering barometric pressure in groundwater flow investigations 1 water level elevation measurements in wells are commonly used as a basis to delineate groundwater flow patterns i e flow direction and hydraulic gradient barometric pressure fluctuations however can have a discernible impact on well water levels these barometric effects may lead to erroneous indications of hydraulic head within the aquifer total hydraulic head within the aquifer not well water level elevation is the hydrologic parameter for determining groundwater flow direction and hydraulic gradient conditions for low gradient unconfined aquifer sites exhibiting variable vadose zone characteristics e g thickness pneumatic diffusivity barometric pressure fluctuations can cause temporal changes in lateral flow direction and flow velocity discrete water level measurements used to determine the average or long term groundwater flow conditions therefore may provide nonrepresentative results calculation of the barometric response characteristics for individual wells provides the basis to account for the temporal effects of barometric pressure fluctuations from monitor well measurements so that average long term groundwater flow pattern behavior can be determined

a rainfall loading response recorded at 300 meters depth implications for geological weighing lysimeters abstract static pore water pressures in confined aquifers vary in response to ground surface loading changes including precipitation and evaporation under certain hydrogeological conditions such aquifers can function as giant natural weighing lysimeters referenced here as geological weighing lysimeters the extent of the land area weighed increases with aquifer depth and it is of interest to establish at what depth it is still possible to monitor surface water budgets an 86 mm rainfall event produced a clear loading signal in a well in western kansas at 300 m depth the loading effect is quantitatively consistent with elastic deformation induced by the rainfall mass and suggests that geological weighing lysimeters could operate at considerably greater depths thereby monitoring water budgets over a significant land area

characterizing subsurface hydraulic heterogeneity of alluvial fan using riverstage fluctuations strategic environmental research and development program serdp er 1365 environmental security and technology certification program estcp er201212 nsf ear from the united state 1014594 jilin university from department of education china global expert award through tianjin normal university from the thousand talents plan of tianjin city from china taiwan typhoon and flood research institute national applied research laboratories natural science foundation of china 51409029

structural characterization of an island aquifer via tidal methods 1 a set of water level time series collected along a transect through a sedimentary island aquifer was used to test the utility of various simple models of ocean tidal propagation in bounded one dimensional aquifers fourier spectra were calculated for the ocean tidal modes and compared with spectra measured in wells along the island transect other sources of fluctuation could be neglected an observed spatial bias in the well responses attenuations and lags could not be modeled by a homogeneous aquifer theory a theory involving composite heterogeneity accounted well for the spatial bias yielding estimates of aquifer transmissivities and storage coefficients indicating a fivefold difference in hydraulic diffusivity along the transect a lack of well locations toward one end of the transect reduced the statistical significance of this result with correlations between regression parameters evident at the same time a second bias was seen involving the ratio of signal amplitude and lag with penetration distance into the aquifer as observed in prior tidal studies a brief set of numerical experiments showed that horizontal layering in aquifer properties was the most probable cause of this propagation bias application of these results to the island data set supported a conceptual stratigraphic model of a highly conductive sloping stratum underlying a less conductive superficial sand layer this model is inconsistent with well logs along the island transect but is supported by additional off transect well logs it was concluded that one dimensional tidal propagation models may be useful in inverse characterization of aquifers with macroscale hydrogeological structures and that the analysis of measured propagation bias has the potential to yield extra information on aquifer properties in the vertical direction

the response of water level in a well to a time series of atmospheric loading under confined conditions the water level in a well that penetrates a confined aquifer can fluctuate in response to changes in atmospheric pressure the response varies with the well casing and screen dimensions the transmissivity and compressibility of the aquifer and to a small extent its storativity recently this loading response problem has been solved in terms of a frequency response function that characterizes how attenuation and phase shifts in the response signal vary with frequency the counterpart of this solution in the time domain is an impulse response function this solution has the immediate appeal that it can be used directly to filter raw loading and water level records via serial convolution where the response at any time is a weighted aggregate of the previous loading signal the impulse response function derives from well known solutions to the slug test problem when based on the cooper bredehoeft papadopulos solution the response function is precise but computationally intensive based on the hvorslev solution the response function is computationally simple but applicable only to aquifers with small storativity simulations and a field example clearly illustrate the dominating influence of transmissivity in dampening and lagging the response of a confined aquifer to a loading signal and how both effects increase with higher frequency the results also illustrate the weak influence of storativity in modulating the response signal

groundwater strain coupling before the 1999 mw 7 6 taiwan chi chi earthquake summary the coupling of pre earthquake anomalous phenomena between long term groundwater levels recorded at 42 monitoring stations and time varying surface strain derived from 16 gps stations was found in the choshuichi alluvial fan before the 1999 m w 7 6 chi chi earthquake in taiwan the noise free groundwater level anomalies consistently comprised by a sequence of decrease rise and flat phases which agree very well with changes in strain rates computed from the gps stations these coupling agreements show that in addition to compression tension can be generated before a thrust earthquake occurrence as well this case demonstrates that short term surface deformation as signals against noise and accuracy of pre earthquake anomalous phenomena can be simultaneously examined by using multiple parameter crosscheck for significantly reducing the uncertainty of earthquake precursory evaluation

annual fluctuations of groundwater levels as a result of loading by surface moisture abstract long term hydrographs for deep confined aquifers in southern saskatchewan canada show annual fluctuations characterized by a gradual rise in head from october to may june and a rapid drop from may june to october these fluctuations are distinctly different from the seasonal fluctuations observed in surficial and shallow semi confined aquifers which reflect the response of these aquifers to recharge derived from snow melt and early spring rains on the basis of field data and theoretical considerations it is demonstrated that seasonal fluctuations of the water table are not transmitted down to the deep aquifers provided the confining layers are thick and have sufficiently low hydraulic diffusivity the annual fluctuations in the deep aquifers thus do not reflect seasonal recharge to these aquifers plots of moisture accumulation i e precipitation minus calculated areal evapotranspiration are strikingly similar to the observed hydrographs for the deep aquifers in timing and magnitude of the annual fluctuations it is postulated that the annual head fluctuations in the deep confined aquifers reflect changes of the mechanical load on the formations caused by seasonal changes of the soil moisture snow and storage at the water table the deep confined aquifers thus act as large scale inexact weighing lysimeters

a new technique for obtaining high resolution pore pressure records in thick claystone aquitards and its use to determine in situ compressibility 1 laboratory tests are commonly used to determine properties vertical compressibility specific storage ss and vertical hydraulic conductivity kv of claystone aquitards however whether data representative of in situ conditions can be obtained from disturbed samples is questionable here we present a method to determine the in situ and ss of a thick sequence of cretaceous aged claystone by estimating the loading efficiency of a formation from pore pressure responses to barometric pressure fluctuations we installed 10 vibrating wire pressure transducers at different depths 25 325 m below ground in a thick claystone aquitard by placing them directly within the cement bentonite grout two years of continuous transducer records using this method appeared to provide pore pressure data with a resolution of better than one part in 105 equivalent to millimeter of hydraulic head change pore pressure responses to barometric pressure changes earth tides and precipitation events can be clearly identified and the barometric responses can be easily analyzed the resulting values of 0 6 0 93 2 5 10 7 to 2 2 10 6 kpa 1 and ss 2 6 10 5 to 4 5 10 6 m 1 all decrease with depth the results are comparable with the limited existing data for in situ estimates of ss and are as much as an order of magnitude smaller than laboratory estimates of ss for similar aquitard deposits our findings suggest that the fully grouted transducer method can provide an accurate and reliable means to monitor pore pressure changes and to determine in situ parameters for bedrock aquitard systems

an objective frequency domain method for quantifying confined aquifer compressible storage using earth and atmospheric tides the groundwater hydraulic head response to the worldwide and ubiquitous atmospheric tide at 2 cycles per day cpd is a direct function of con ned aquifer compressible storage the ratio of the responses of hydraulic head to the atmospheric pressure change is a measure of aquifer barometric e ciency from which formation compressibility and aquifer speci c storage can be determined in situ rather than resorting to laboratory or aquifer pumping tests the earth tide also impacts the hydraulic head response at the same frequency and a method is developed here to quantify and remove this interference as a result the barometric e ciency can be routinely calculated from 6 hourly hydraulic head atmospheric pressure and modeled earth tide records where available for a minimum of 15 days duration this new approach will be of critical importance in assessing worldwide problems of land subsidence or groundwater resource evaluation that both occur due to groundwater abstraction

frequency characteristics of the response of water pressure in a closed well to volumetric strain in the high frequency domain 1 oscillations of water pressures and crustal strains due to the seismic waves of the 2010 chile earthquake were observed in japan the oscillations of water pressures observed over the frequency range of 0 002 to 0 1 hz were negative proportional to the oscillations of volumetric strains the responses of water pressures in closed wells are frequency dependent the expression for the response of water pressure in a closed well to crustal strain is developed based on the poroelastic theory the expression developed in the present paper describes the frequency characteristics of the responses the response is useful for the estimation of rock properties in addition the responses of water pressure due to tidal volumetric strain are estimated and compared with the responses due to the seismic waves

capillary effects on groundwater response to earth tides author s wang cy zhu ay liao x manga m wang lp abstract 2019 american geophysical union all rights reserved the response of unconfined aquifers to earth s solid tides earth tides has been used to study a number of hydrogeological environmental and ecological processes the traditional interpretation of such responses has been based on a model that assumes free flow of groundwater to the water table even though capillary effects have long been recognized to influence the response of coastal aquifers to ocean tides here we study the capillary effect on the response of unconfined aquifers to earth tides using a numerical procedure that couples groundwater flow and poroelastic strain in both the saturated and the unsaturated zones we show that when the water table rises to the surface and the capillary zone disappears the predicted tidal response is identical to that predicted by the traditional model but when the capillary zone is present when the water table falls below the surface the predicted amplitude ratio and phase shift depart notably from those predicted by the traditional model we apply the model to a field case where large seasonal changes of tidal response have been documented we show that the large seasonal changes in the tidal response may be due to the change of the water table from a capillary affected state to a capillary free state when the water table rises annually to the ground surface thus the omission of the capillary effects in the interpretation of the response of unconfined aquifers to earth tides may lead to incorrect inference of subsurface processes and properties

application of wavelets for specifying tsunami from tide a comprehensive study on the 1945 makran tide gauge records abstract in tide gauge records the separation of tidal from non tidal contents is in general done by specialists after applying high pass or bandpass filtering techniques however there is always a tradeoff between losing some valuable contents of the signal while trying to remove the tide in this manuscript we deal with two significant tide gauge records of the 1945 makran tsunami the importance of these data is well known for researchers since these are the only valid tide gauge data for any evaluation of tsunami in the western makran region wavelet decomposition technique was applied as a tool by us to minimize the influence of tidal contents on these data several parameters were set and applied to several types of wavelets in various temporal series and frequency ranges the goal was to find the most appropriate wavelet parameter and type to distinguish tsunami data from tidal contents our results show that the application of wavelets in comparison to conventional methods yields to lesser rms errors before the arrival of the tsunami wave and therefore produces minor data loss after applying moreover after applying suitable wavelets to data we have noticed a sudden decrease in the sea level before the arrival of tsunami waves which is consistent with eyewitness reports the result of our work is beneficial for further evaluation of tsunami modeling in western makran the procedure introduced can be applied at any tide gauge data for tidal analysis with wavelet decomposition techniques

on phase shifts in periodic well fluctuations summary for the case of a well completely penetrating a confined aquifer of infinite extent an analysis is made of the flow processes in the well aquifer system due to periodic pressure variations like earth tides and barometric tides it is shown that the earth tides lead to well fluctuations with a negative phase difference phase lag while the barometric tides cause well fluctuations with a positive phase difference phase advance in both cases the amplitudes and phases of the well fluctuations depend on frequency and are therefore different for the individual components of the tidal spectra these frequency characteristics need to be studied more carefully than is the case now a schematic model of a device is described that could not only be used for this purpose but also for the determination of the specific storage ss and the conductivity k the method would be closely related to the well known slug or bail tests

seven year history of vertical hydraulic diffusivity related to excavation around an underground facility abstract significant amounts of groundwater drain induced by the excavation of an underground facility will influence various site formation parameters such as permeability in this study a spectral analysis was applied to long term records of pore pressure responses to atmospheric loading in order to clarify the history of rock permeability changes at the horonobe underground research laboratory url in japan this study revealed that excavation of the url influenced nearby aquifers and reduced their vertical hydraulic diffusivity at a point approximately 130 m distant from the url it was found that hydraulic diffusivity has decreased by approximately 7 to 55 in the five years since the excavation started at a point approximately 860 m distant from the url the vertical hydraulic diffusivity was found to have decreased by approximately 26 even though pore pressure had not changed significantly this study confirmed that long term permeability changes could be monitored via pore and atmospheric pressure records more specifically during the development of a geological disposal system which can take several tens of years the vertical permeability of the site can be continuously monitored from the period before the start of the excavation through to the repository s post closure period

transfer functions of the well aquifer systems response to atmospheric loading and earth tide from low to high frequency band 1 the transfer functions of the well aquifer systems response to atmospheric loading and earth tide can be used to calculate the well aquifer properties due to the low signal to noise ratio the study on barometric response at frequencies higher than 8 cycles per day cpd for short is almost blank using the recorded water level and barometric pressure as well as the corresponding theoretical tidal volumetric strain at 17 well stations in china we obtained continuous barometric and tidal responses of the well aquifer systems by cross spectra estimation it shows that the barometric responses are stable at low frequencies 0 1 0 5 cpd while fluctuate at tidal frequencies 0 5 8 cpd in the high frequency band 8 30 cpd by stacking the transfer functions to suppress the noise we obtained stable barometric responses for the first time according to the low and high frequency barometric responses we can better judge whether the aquifers are confined in the timescale that we focused and whether the wellbore storage effect can be ignored and expect to determine the fluid flow properties of the aquifers more reliably for the three aquifers whose water table drainage and wellbore storage effects are ignored we used the barometric and tidal responses to estimate their formation properties which are consistent with previous results the tidal strain sensitivities are related to the aquifer lithology which are mainly controlled by the compressibility of the porous matrixes with different porosities and different aspect ratio fractures

spectral decomposition of periodic ground water fluctuation in a coastal aquifer this research accomplished by the descriptive statistics and spectral analysis of six kinds of time series data gives a complete assessment of periodic fluctuation in significant constituents for the huakang shan earthquake monitoring site spectral analysis and bandpass filtering techniques are demonstrated to accurately analyse the significant component variation in relative ground water heads with a period of 12 6 h is found to be highly related to seawater level fluctuation time lag is estimated about 3 78 h based on these phenomena the coastal aquifer formed in an unconsolidated formation can be affected by the nearby seawater body for the semi diurnal component fluctuation in piezometric heads is found to correspond at a rate of 1000 m h 1 atmospheric pressure presents the significant components at periods of 10 8 h and 7 2 h in a quite different type compared to relative ground water head and seawater level copyright 2008 john wiley sons ltd

fracture characterization using earth tide analysis summary wells tapping confined aquifer systems are known to commonly produce water level fluctuations caused by strain induced earth tides in this investigation a straightforward methodology is presented for quantifying the specific storage and secondary porosity of a fractured fault zone aquifer system using earth tides water level and barometric pressure head data are smoothed and then filtered to remove low frequency responses the resulting tidal signals are used in the program baytap g to yield amplitude and phase shifts of all the major tidal groups the resulting tidal parameters can be used to compute the time dependent volumetric strain caused by the m 2 and o 1 tides stress strain hysteresis loops are produced when the reduced water levels are compared to the volumetric strain induced by these tides for amplification factors near unity representing the ratio of pressure response to tidal loading in the fracture to water level response in the well the slopes of the loops represent the specific storage of the fracture the barometric efficiency and specific storage can then be used to estimate a secondary porosity and other parameters of the aquifer system this analysis was carried out at the fractured rock research site frs in the blue ridge physiographic province in floyd county virginia

estimating aquifer parameters from analysis of forced fluctuations in well level an example from the nubian formation near aswan egypt 3 diffusivity estimates for saturated and unsaturated zones atmospheric pressure variations provide a broadband signal that may force a sympathetic response in well water levels in this paper time series analysis techniques are used to estimate the response as a frequency dependent admittance function which is then modeled to provide estimates of the fluid transport properties of strata the data derive from five cased piezometer wells sampling aquifers in the nubian formation southwest of aswan egypt three shallow wells 100 140 m deep sample a water table aquifer a fourth w3 400 m deep samples a basal aquifer in the same area that behaves in a confined manner up to a period of several years the fifth well samples another basal aquifer and shows evidence of partial blockage nontidal water level variations in the shallow wells are due almost entirely to barometrically driven flow of air and water using a simple model to fit the observed barometric admittance spectra we obtain estimates of horizontal and vertical permeabilities for water in the saturated zone local horizontal permeability is constrained by modeling the effects of flow induced pressure gradients near the screen for the w3 deep well sampling the basal aquifer the resulting values 0 15 0 3 2 are marginally lower than the large scale 5 km estimates 0 32 0 43 2 derived in a previous paper however the values for the three wells sampling the water table aquifer although consistent among themselves 0 2 0 5 2 are significantly lower than the large scale estimate 1 0 1 5 2 this is contrary to what might be expected given that the wells are preferentially screened in clean sandstones vertical permeability estimated by modeling partial confinement effects is constrained for only one well a low value was obtained because of the presence of claystone beds in the diffusion path between screen and water table at this well the effects of air wave diffusion are clearly manifest in the spectra of one well where the water table lay at a depth of about 40 m the form of the spectra was well fit by ascribing a uniform pneumatic diffusivity of 1 75 10 m 3m2 s to the unsaturated zone however it was also necessary to include an apparent attenuation of the air wave at the capillary fringe of about 0 5 we propose that the effect is due not to attenuation but that it reflects compression of the phreatic surface arising from the presence of trapped air pockets in the underlying saturated zone a 40 m rise in the water table at the site during the decade prior to the measurements might explain the presence of significant quantities of trapped air this rise in water table together with the arid climate might be taken to suggest that the moisture content of the unsaturated zone is negligible except within a meter or so of the water table however calculation of the intrinsic rock permeability from pneumatic diffusivity assuming zero moisture content yields an estimate which is considered to be too low the likely explanation is that the assumption of zero moisture content is in error despite conditions which are as favorable as are ever likely to be realized under field conditions

earth tide forcing of glacier drainage 1 fourier analysis reveals that winter electrical self potential sp water pressure pw and electrical conductivity ec time series collected beneath haut glacier d arolla switzerland are forced by earth and atmospheric tides forcing is dominant during periods of expanding bedrock consistent with glacier substrate deformation periodically driving water from the ice body into the bed this may modify the strength of subglacial sediments and could therefore influence glacier drainage and motion on a global scale

sensitivity of the response of well aquifer systems to different periodic loadings a comparison of two wells in huize china abstract groundwater well can be used as a seismograph or as strainmeter since the well water level is sensitive to seismic waves and other crustal strains through mechanical coupling between rock and groundwater the use of the groundwater level in monitoring tectonic strain however is hindered by the enigmatic response discrepancy among wells different responses may be recorded by even closely clustered wells therefore understanding the factors that control the sensitivity of well aquifer systems in response to different periodic loadings is important in this paper we analyzed two closely located wells that show no response to seismic waves and respond differently to earth tides and barometric pressure we discuss these wells sensitivity of response to periodic loadings by using the spectrum barometric response function tidal response and slug test methods our results show that the different response characteristics are due to the differences in permeability and confinement of the well aquifer systems well aquifer systems with a low permeability cannot record coseismic responses even if they can record clear tidal and barometric signals in addition periodic loading signals in shallow aquifers will be easily masked by the interference from the surface for example rainfall or pumping which diminishes the signal to noise ratio of the tectonic activity thus the hydrogeological and tectonic settings are the two key factors that should be considered in choosing a suitable monitoring well location for tectonic strain monitoring

applicability of method to estimate transmissivity based on yield drawdown analysis in mountainous fractured rock aquifers a case study in taiwan abstract the observation of yield drawdown response in the course of pumping test as well as its derived application for aquifer characterization is an essential practice in a geotechnical investigation on the basis of that for providing a reasonable estimate of aquifer transmissivity on site a number of empirical models have therefore been proposed yet the majority of previous studies are conducted based on investigations at homogeneous alluvial plain very few particularly in the case of taiwan are carried out focusing on mountainous fractured rock aquifers aiming to address this problem the observation data of 53 pumping tests obtained from a multi years in situ geological investigation program are analyzed and the applicability of empirical log log linear relationship between t and q s is examined our analysis reveals that the yield drawdown responses derived from different geologic formations are quantitatively distinct and those empirical rules derived from the alluvial landform should be used with care when applying in mountainous fractured rock aquifers based on the analysis of statistical results in our study with a systematic investigation and clarification of the q s relationship in advance a satisfactory and cost effective solution is obtained

response of the water level in a well to earth tides and atmospheric loading under unconfined conditions the response of the water level in a well to earth tides and atmospheric loading under unconfined conditions can be explained if the water level is controlled by the aquifer response averaged over the saturated depth of the well because vertical averaging tends to diminish the influence of the water table the response is qualitatively similar to the response of a well under partially confined conditions when the influence of well bore storage can be ignored the response to earth tides is strongly governed by a dimensionless aquifer frequency q u the response to atmospheric loading is strongly governed by two dimensionless vertical fluid flow parameters a dimensionless unsaturated zone frequency r and a dimensionless aquifer frequency qu the differences between q u and qu are generally small for aquifers which are highly sensitive to earth tides when q u and qu are large the response of the well to earth tides and atmospheric loading approaches the static response of the aquifer under confined conditions at small values of q u and qu well response to earth tides and atmospheric loading is strongly influenced by water table drainage when r is large relative to qu the response to atmospheric loading is strongly influenced by attenuation and phase shift of the pneumatic pressure signal in the unsaturated zone the presence of partial penetration retards phase advance in well response to earth tides and atmospheric loading when the theoretical response of a phreatic well to earth tides and atmospheric loading is fit to the well response inferred from cross spectral estimation it is possible to obtain estimates of the pneumatic diffusivity of the unsaturated zone and the vertical hydraulic conductivity of the aquifer

theory for the effects of free gas in subsea formations on tidal pore pressure variations and seafloor displacements loading of the seafloor by regional scale pressure variations such as those imposed by ocean tides is supported by both the rock matrix and interstitial fluid the nature of the partitioning of the support between the two depends primarily on the compressibility of the fluid and the compressibility and fluid transport properties of the rock matrix in this paper we examine theoretically the influence of free gas on pore fluid compressibility on the nature of time dependent load partitioning and on the consequent vertical rock deformation and seafloor displacement an example is the gas trapped below deep sea gas hydrate we have derived an expression for the steady state compressibility of pore fluid considering the influence of gas solubility in water the effect of gas solubility is seen to be important at low such as tidal loading frequencies and thus must be included when observations of tidally induced pore fluid pressure variations or seafloor displacements are used to constrain gas content for very low gas concentrations ng much less than 0 1 the steady state fluid compressibility can be enhanced by gas solution dissolution over the loading cycle by several factors at high ambient pressure and more than an order of magnitude at low ambient pressures 2 the fluid compressibility increases sensitively with ng and greatly affects the tidal response of the pore fluid pressure regardless of the solubility thus with careful experimental design tidally induced pore pressure variations may be used to detect very small amounts of free gas and constrain the quantity if ng 2 this method is complementary to using acoustic velocity to constrain the quantity of free gas which works well in the ng 0 2 2 range we have also given an expression for the vertical deformation of subsea formations and hence of the seafloor displacement under tidal loading the presence of free gas enhances tidally induced seafloor displacement but the maximum effect is limited by the compressibility of the matrix frame given relatively low frame compressibility tidally induced seafloor displacement is small of the order of 1 mm which is presently difficult to detect at tidal frequencies

determination of fluid flow properties from the response of water levels in wells to atmospheric loading the water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading the magnitude and character of this response is partly governed by the well radius the lateral hydraulic diffusivity of the aquifer the thickness and vertical pneumatic diffusivity of the unsaturated zone and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer these key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response in many cases the response of a well to atmospheric loading can be broken up into a high intermediate and low frequency response the high frequency response is governed largely by the well radius and lateral diffusivity of the aquifer the intermediate frequency response is governed by the loading efficiency of the aquifer the low frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer cross spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters these estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone the lateral permeability of the aquifer and the composite vertical hydraulic diffusivity of the overlying saturated materials

hydraulic head in a clayey sand till over multiple timescales this paper presents an analysis of hydraulic head data measured every 2 h for 2 years in the leading edge of a drumlin that consists of weathered brown clayey sand till and underlying unweathered

groundwater storage inferred from earthquake activities around east asia and west pacific ocean abstract groundwater is a necessary and indispensable resource in the gradual depletion of the amount in the world groundwater storage is an important indicator to evaluate the capability of volume of water can be released from the aquifer this research highlights a new assessment to infer the storage of aquifer using earthquakes activated around east asia and the ring of fire at west pacific ocean ten significant seismic events are used to evaluate the groundwater storage at an observation station by analyzing the spectra of groundwater level and seismogram it is evident that the period varied in 7 25 s of rayleigh waves significantly dominate propagation from the epicenter of earthquakes to the observation station the storage coefficient is then shown in the order of 10 4 10 3 the major innovation of this study suggests that to concretely deduce the groundwater storage by earthquake activity has become feasible

age and identity of the oldest pine fossils comment in their study of charred conifer twigs from the lower cretaceous chaswood formation of canada falcon lang et al 2016 established the species pinus mundayi that they interpreted as a two needled pine and the oldest stratigraphic evidence for the extant genus pinus this is based on their interpretation of what they thought was distinctive wood anatomy and paired needle bases of pinus evident in their fossils while the valanginian age ca 140 133 ma is based on revised palynostratigraphy if correctly interpreted this material predates the oldest known species pinus yorkshirensis from the hauterivian barremian transition at ca 131 129 ma ryberg et al 2012 and pushes back the earliest occurrence of the genus by 4 11 m y however we consider that a more thorough examination reveals that p mundayi is from the valanginian barremian ca 140 125 ma and that falcon lang et al have misinterpreted the anatomy of their fossils and erroneously assigned them to the genus pinus

avoiding confusion between pressure front pulse displacement and groundwater displacement illustration with the pumping test in a confined aquifer two distinct phenomena may be distinguished and defined during a pumping test conducted in a confined aquifer the pressure front pulse displacement and the groundwater displacement this scientific briefing examines and clarifies the difference between the pressure wave displacement and the groundwater displacement by stating the differences in their respective transit times and velocities the pressure front pulse displacement is controlled by the diffusivity of the aquifer whereas groundwater displacement is controlled by the pumping flow rate and the effective porosity of the aquifer to calculate the transit time and velocity of each type of displacement several equations are presented and compared an example is provided to illustrate the differences in velocity between the pressure front pulse displacement and the groundwater displacement

tidal responses and earthquake related changes in the water level of deep wells monitoring of the water level has been continued in 100 m deep and 500 m deep wells in the southern kanto district japan to examine the relationship between changes in the well water level and earthquake occurrence by using a bayesian approach the observed data were decomposed into four components tidal response barometric response trend drift and irregular noise components loading effects of the ocean tide on aquifer dilatation were evaluated by using schwiderski s ocean tide models and the harmonic constants compiled by the international hydrographic bureau well aquifer properties were examined based on the tidal and barometric responses of the water level coseismic water level steps were detected in both wells for two earthquakes during the observation period from april 1985 to december 1989 by calibrating the strain sensitivity of the well water levels based on the tidal responses strain changes equivalent to the coseismic steps in the water levels were estimated the coseismic strain changes obtained for the deeper well can be explained reasonably by earthquake fault models in a viscoelastic half space however those observed in the shallower well were too large and in the wrong direction to be explained by the earthquake fault models

pore pressure variation as a precursory phenomenon the need for and a list of supplementary data abstract pore pressure variations are believed to play a dominant role in the earthquake cycle well level fluctuations that reflect possible pore pressure anomalies prior to earthquakes have been reported by many authors the evaluation of the reliability of hydrologie precursors and appropriate fault models is however difficult because the background information provided with the published data is generally sparse following the idea of roeloffs 1988 an extended list of recommendations for improved documentation of hydrologic precursors is presented the list includes basic information on the construction of the well the well s hydrologic environment the pore fluid fluctuations of the well level and other signals and earthquake related information

groundwater recharge in a hard rock aquifer a conceptual model including surface loading effects knowledge about the groundwater recharge is essential for the prediction of impacts of groundwater withdrawal and underground construction recharge in the bedrock is however difficult to estimate the objectives of this thesis were to increase the understanding of groundwater recharge in crystalline bedrock to investigate how the recharge could be estimated and to develop new models to describe the recharge the study was based on three approaches groundwater dating using chlorofluorocarbons cfcs geohydraulic field measurements and mathematical modelling low concentrations of cfc 11 and cfc 113 were found in the bedrock groundwater which in combination with low dissolved oxygen levels indicated anaerobe degradation the cfc 12 and tritium concentrations agreed fairly well which means that apparent ages could be true ages the results suggest that cfc dating may not be reliable at forested humid sites covered by fine grained soil a quick response in hydraulic head to precipitation was observed in the studied bedrock despite the 10 m thick till cover a substantial portion of observed head variations was found to be loading effects involving no storage changes or water flow the loading efficiency of the bedrock was estimated from the air pressure response to be 0 95 the surface loading was calculated from measurements of air pressure water in the soil and snow about 20 of the seasonal variation of the hydraulic head was estimated to be related to loading changes only a simple conceptual model could be used to simulate the observed hydraulic heads the loading effect had to be included to properly describe individual recharge events numerical experiments were performed with a soil bedrock profile when the rock was modelled as a heterogeneous continuum unsaturated zones developed at high hydraulic gradients the phenomenon appeared in areas where low conductive zones were located upstream of high conductive zones decreasing the effective hydraulic conductivity of the material

storage in confined aquifer spectral analysis of groundwater responses to seismic rayleigh waves summary it is frequently found that the fluctuations observed in aquifer well systems demonstrate high coherence to nearby boundary disturbances or more specific in response to the vertical motion of seismic rayleigh waves this study derives the spectral relationship between groundwater head and vertical displacement disturbed by rayleigh waves in the time frequency domain essentially the groundwater storage property e g storage coefficient or specific storage representing the amount of water released from storage when the head changes from water expansion and aquifer compression occur they can be determined using the spectral representation of the factors associated to groundwater head and rayleigh waves for this study the sumatra andaman islands earthquake with magnitude 9 at ut 2004 12 26 00 58 53 45 is used as the seismic source while a groundwater monitoring well and a seismological station located on the east of taiwan acted as the receivers the time series data associated with the observed groundwater head and vertical displacement of rayleigh waves are used to evaluate spectral response analyzing the autospectral density cross spectral density and coherence between them the resultant spectral estimates can be used to determine the storage coefficient and specific storage of the case site to be on the order of 10 3 and 10 4 m 1 respectively in addition the matrix bulk modulus also demonstrated a linear trend with porosity by taking the value of standard water modulus it suggests that the storage of an aquifer can be robustly estimated using spectral representations and responses from head changes in groundwater and vertical displacement of rayleigh waves

the estimation of fluid flow properties from the response of water levels in wells to the combined atmospheric and earth tide forces the water level in an open well tapping a confined formation is influenced by natural forces including the solid earth tide set and atmospheric pressure variation apv the spectral method is used to analytically derive a model for well response to both random and periodic components of the combined set and apv forcings csa an inverse theory and algorithm are developed in order to provide improved results when using the model to estimate the hydraulic parameters associated with a given formation an examination of the response surface of the estimation criterion reveals a uniqueness problem in estimating storativity s since there is little correlation between the transmissivity t and s estimators a good estimate for t is still possible independent of having accurate knowledge of s an estimate of t is possible only if the data contain sufficient information so that the analysis occurs within an identifiability window the csa estimation methodology is compared to individual set and apv schemes the csa scheme gives the greatest probability that sufficient information is contained in a data record so that t is indeed identifiable the results of applications to synthetic data indicate that the csa scheme gives a t estimate with the most precision and also that it requires collecting fewer observations these results are discussed in light of practical considerations when designing data collection procedures

hydrological response to earthquakes in the haibara well central japan i groundwater level changes revealed using state space decomposition of atmospheric pressure rainfall and tidal responses summary for the groundwater level observed at the haibara well shizuoka prefecture central japan time series analysis using state space modelling is applied to extract hydrological anomalies related to earthquakes this method can decompose observed groundwater level time series into five components atmospheric pressure tidal and precipitation responses observation noise and residual water level the decomposed responses to atmospheric pressure and precipitation are independently determined and are consistent with the expected response to surface loading in the groundwater level at the haibara well 28 coseismic changes can be discerned during the period from 1981 april to 1997 december there is a threshold in the relationship between earthquake magnitude and the well hypocentre distance above which earthquakes cause coseismic changes in the residual water level all of the coseismic water level changes at the haibara well are decreases although 33 per cent of the estimated coseismic volumetric strain steps are contraction which would be expected to cause water level increases the coseismic changes in groundwater level are more closely proportional to the estimated ground motion than to coseismic volumetric strain steps suggesting that ground motion due to earthquakes is the major cause of the coseismic water level drops and that the contribution from static strain is rather small possible pre or inter earthquake water level changes have occurred at the haibara well and may have been caused by local aseismic crustal deformation