measurements of shoaling internal waves and turbulence in an estuary 1 the shoaling of horizontally propagating internal waves may represent an important source of mixing and transport in estuaries and coastal seas including such effects in numerical models demands improvements in the understanding of several aspects of the energetics especially those relating to turbulence generation and observations are needed to build this understanding to address some of these issues in the estuarine context we undertook an intensive field program for 10 days in the summer of 2008 in the st lawrence estuary the sampling involved shore based photogrammetry ship based surveys and an array of moorings in the shoaling region that held both conventional and turbulence resolving sensors the measurements shed light on many aspects of the wave shoaling process wave arrivals were generally phase locked with the m2 tide providing hints about far field forcing in the deeper part of the study domain the waves propagated according to the predictions of linear theory in intermediate depth waters the waves traversed the field site perpendicularly to isobaths a pattern that continued as the waves transformed nonlinearly acoustic doppler velocimeters permitted inference of the turbulent energetics and two main features were studied first during a period of shoaling internal waves turbulence dissipation rates exceeded values associated with tidal shear by an order of magnitude second the evolving spectral signatures associated with a particular wave shoaling event suggest that the turbulence is at least partly locally generated overall the results of this study suggest that parameterizations of wave induced mixing could employ relatively simple dynamics in deep water but may have to handle a wide suite of turbulence generation and transport mechanisms in inshore regions

intermittency of near bottom turbulence in tidal flow on a shallow shelf u s office of naval research n00014 05 1 0245 spanish ministry of education and science fis2008 03608 major state program of china for basic research 2006cb400602 catalan institute for water research icra

electrical resistivity tomography applied to groundwater aquifer at downstream of chih ben creek basin taiwan groundwater resource investigations primarily involve inferring groundwater levels and recharge sources from factors such as the distributed location and range subsurface geological structure and flow paths of groundwater sources this study conducted an investigation on the underground aquifer at the downstream of the chih ben creek basin taiwan in addition convenient rapid and accurate two dimensional electrical resistivity tomography ert was employed for evaluations the cross sectional ert image indicates that the low resistivity region in the stratum at survey line cb01 may be a groundwater deposit or fracture zone this region can be divided into three major segments the segment that is 0 50 m from the survey line exhibits a decreasing trend and is thus inferred to be a recharge source survey line cb02 can be generally divided into four layers with the second layer containing a greater amount of groundwater this layer is an aquifer with a depth of approximately 25 100 m below the ground surface and 75 100 m in thickness the base of the aquifer slopes toward the east and primarily possesses a lithological composition of slate and sandstone with explicit and fractured joints

delineation of saltwater intrusion zones using the time domain electromagnetic method the nabeul hammamet coastal aquifer case study ne tunisia the time domain electromagnetic method tdem is applied to monitor to delineate and to map the saltwater intrusion zones in the mediterranean plio quaternary aquifer forty two tdem soundings were carried out in the coastal plain of nabeul hammamet region ne tunisia tdem resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater seawater transition zone the geoelectric sections showing the vertical configuration of seawater intrusion with the brackish salty saturated zones have a resistivity ranging from 0 1 to 5 m and are detected at a depth lower than 1 5 m the salinized zones are located at nabeul sidi moussa sidi el mahrsi al gasba and mrazgua and at hammamet touristic zone of hammamet north and south baraket essahel and reached a distance of 4 km from the coastline indicating a severe state for the aquifer in these zones these tdem results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells moreover in the northeastern part the presence of a saltwater front located far from the coast and along the nw se major surface fault can be explained by two hypothesis i this fault seems to provide a conduit for seawater to move readily towards the water wells and ii the clay and gypsum infiltration of marine messinian deposits through the fault plane leads to low resistivities finally it comes out from this study that tdem survey has successfully depicted salinized zones of this coastal aquifer copyright 2012 john wiley sons ltd

groundwater salinization in semi arid zones an example from nador plain tipaza algeria the groundwater of nador plain has been overexploited during the last two decades the goal was to meet the demands of intensive agricultural activities and at the same time the supply of drinking water as a result the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated the degradation of the groundwater quality is characterized by salinization phenomena in this project the analysis of the piezometric map indicates a piezometric water level of 0 m inside the plain the chemical analysis of major ions in the groundwater was carried out on the water samples of 24 wells it indicates an electrical conductivity of water exceeding 1 500 s cm and chloride concentrations exceeding 500 mg l in the downstream of the plain presently the groundwater in this coastal sector is used neither for drinking water nor for irrigation in this study 35 vertical electrical soundings ves were carried out in the area with geoelectrical sections and maps of iso resistivity created to delineate the zones that are affected by saltwater intrusion the findings suggest that saltwater intrusion has reached a distance of approximately 1 600 m inside the aquifer

seabed stresses in combined wave and steady flow conditions on the nova scotia continental shelf field measurements and predictions abstract a tripod holding electromagnetic flowmeters at two heights within 1 m above the seabed has been deployed at two shallow sites 25 and 45 m depths on the continental shelf off nova scotia canada wave flows are comparable with the small mean flows at both sites friction velocities have been estimated from the observed spectra of vertical turbulent velocities using a modification of the dissipation method appropriate to low reynolds number conditions the results from each site show no significant change of friction velocity with height as expected for measurements from within the constant stress layer however in each case the observed friction velocities are considerably larger than would be predicted on the basis of the observed bottom roughness and the mean flows alone indicating that the wave flows were important in enhancing the friction velocity the theory of grant and madsen 1979 has been used to predict the friction velocities based on the observed mean and wave velocities and o

effects of short flexible seagrass zostera noltei on flow erosion and deposition processes determined using flume experiments innovative flume experiments were conducted in a recirculating straight flume zostera noltei meadows were sampled in their natural bed sediments in the field at contrasting stages of their seasonal growth the aims of this study were i to quantify the combined effects of leaf flexibility and development characteristics of zostera noltei canopies on their interaction with hydrodynamics and ii to quantify the role of zostera noltei meadows in suspended sediment trapping and bed sediment resuspension related with changes in hydrodynamic forcing caused by the seasonal development of seagrasses velocity within the canopy was significantly damped the attenuation in velocity ranged from 34 to 87 compared with bare sediments and was associated with a density threshold resulting from the flow induced canopy reconfiguration the reduction in flow was higher in dense canopies at higher velocities than in less dense canopies in which the reduction in flow was greater at low velocities these contrasted results can be explained by competition between a rough wall boundary layer caused by the bed and a shear layer caused by the canopy the velocity attenuation was associated with a two to three fold increase in bottom shear stress compared with unvegetated sediment despite the increase in near bed turbulence protection of the sediment against erosion increased under a fully developed meadow while sediment properties were found to be the main factor controlling erosion in a less developed meadow deposition fluxes were higher on the vegetated bed than on bare sediments and these fluxes increased with leaf density fewer freshly deposited sediments were resuspended in vegetated beds resulting in an increase in net sediment deposition with meadow growth however in the case of a very high leaf area index sediment was mostly deposited on leaves which facilitated subsequent resuspension and resulted in less efficient sediment trapping than in the less developed meadow

shear velocity estimates in rough bed open channel flow shear velocity u is an important parameter in geophysical flows in particular with respect to sediment transport dynamics in this study we investigate the feasibility of applying five standard methods the logarithmic mean velocity profile the reynolds stress profile the turbulent kinetic energy tke profile the wall similarity and spectral methods that were initially developed to estimate shear velocity in smooth bed flow to turbulent flow over a loose bed of coarse gravel d 50 15cm under sub threshold conditions the analysis is based on quasi instantaneous three dimensional 3d full depth velocity profiles with high spatial and temporal resolution that were measured with an acoustic doppler velocity profiler advp in an open channel the results of the analysis confirm the importance of detailed velocity profile measurements for the determination of shear velocity in rough bed flows results from all methods fall into a range of 20 variability and no systematic trend between methods was observed local and temporal variation in the loose bed roughness may contribute to the variability of the logarithmic profile method results estimates obtained from the tke and reynolds stress methods reasonably agree most results from the wall similarity method are within 10 of those obtained by the tke and reynolds stress methods the spectral method was difficult to use since the spectral energy of the vertical velocity component strongly increased with distance from the bed in the inner layer this made the choice of the reference level problematic mean shear stress for all experiments follows a quadratic relationship with the mean velocity in the flow the wall similarity method appears to be a promising tool for estimating shear velocity under rough bed flow conditions and in field studies where other methods may be difficult to apply this method allows for the determination of u from a single point measurement at one level in the intermediate range 036 copyright c 2013 john wiley sons ltd

physical behaviour of cretaceous calcareous nannofossil ooze insight from flume studies of disaggregated chalk geomorphic features such as drifts sediment waves and channels have been documented in the upper cretaceous of north west europe these features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition there is limited knowledge on the processes that govern nannofossil ooze mobility thus forcing uncertainty onto numerical models based on sedimentological observations this article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes a fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity erosion characteristics labelled as erosion types vary with total bed porosity and applied shear stress 0 high porosity ooze 80 is characterized by constant erosion rates em at 77 however erosion characteristics showed greater variance surface erosion was typically followed by transitional erosion with asymptotically decreasing em and stages of erosion with constant and exponential erosion rates the estimated erosion thresholds c vary from ca 0 05 to 0 08 pa for the onset of surface erosion and up to ca 0 19 pa for the onset of constant erosion of 60 to 85 variability of deposition thresholds cd from ca 0 04 to 0 13 pa reflects the influence of variable suspended sediment concentration and 0 on settling particle size due to the identified potential for chalk ooze aggregation and flocculation additionally deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity lastly slow sediment transport without resuspension occurred in high porosity ooze as surface creep forming low relief sedimentary features resembling ripples this process represents a previously undescribed mode of fine grained nannofossil ooze transport

induced seismicity in mines in canada an overview monitoring of mine induced seismicity in canada has improved with the expansion of regional seismograph networks into areas of active mining however the severity and in some cases the frequency of mine induced tremors has increased as mining extends to greater depths and at accelerated rates of extraction because of the complex design and large areal extent of many mines potash coal and metalliferous the most feasible and practical way to monitor these tremors at the present time is to deploy a network of seismometers in and on the surface above mines experiencing microearthquake activity a few of these mines already have a network of seismometers deployed around them and plans are under way to deploy seismograph networks around other mines that have experienced some rather severe tremors in recent times six possible mechanisms for mine induced tremors are described and the associated p and s wave radiation patterns presented a comparison of actual seismic radiation patterns with theoretical predictions is a quick way to diagnose the potential source mechanisms in addition recognizing the pattern of microearthquake activity preceding larger tremors can be used to mitigate the potential effects of severe tremors

mining induced microseismicity monitoring and applications of imaging and source mechanism techniques the study of microseismicity in mines provides an ideal method for remote volumetric sampling of rock masses the nature and uniqueness of microseismic monitoring is outlined in the context of acquisition hardware and software requirements several topics are used to highlight the potential for novel applications of microseismicity and to outline areas where further study is required these topics reflect some of the current interest areas in seismology namelyb values and source parameters fault plane solutions modes of failure and moment tensor inversion imaging and seismicityvelocity correlations these studies suggest potential correlations between zones of high seismic velocity high microseismic activity and maximal stress drops which can be interpreted spatially to be the locations of highly stressed ground with a potential for rock bursting fault plane solutions are shown to be useful in determining the slip potential of various joint sets in a rock mass source parameter studies and moment tensor analysis clearly show the importance of non shear components of failure andb values for microseismicity appear to be magnitude limited and related to spatial rather than temporal variations in effective stress levels

comparing different methods of bed shear stress estimates in simple and complex flow fields bed shear stress is a fundamental variable in river studies to link ow conditions to sediment transport it is however dif cult to estimate this variable accurately particularly in complex ow elds this study compares shear stress estimated from the log pro le drag reynolds and turbulent kinetic energy tke approaches in a laboratory ume in a simple boundary layer over plexiglas and over sand and in a complex ow eld around de ectors results show that in a simple boundary layer the log pro le estimate is always the highest over plexiglas the tke estimate was the second largest with a value 30 per cent less than the log estimate however over sand the tke estimate did not show the expected increase in shear stress in a simple boundary layer the reynolds shear stress seems the most appropriate method particularly the extrapolated value at the bed obtained from a turbulent pro le in a complex ow eld around de ectors the tke method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent uctuations close to the de ectors it is suggested that when single point measurements are used to estimate shear stress the instrument should be positioned close to 0 1 of the ow depth which corresponds to the peak value height in pro les of reynolds and tke shear stress copyright 2004 john wiley sons ltd

mapping groundwater conditions in different geological environments in the northern area of uae using 2d earth resistivity imaging survey a water resources database was developed and used to characterize the geological and hydrogeological settings of groundwater aquifers in the northern part of the united arab emirates an intensive 2d earth resistivity imaging eri survey was conducted in selected areas to assess the available groundwater resources and delineate the salt water intrusion drilling information of the existing monitoring wells as well as their records of water table elevations and groundwater salinity were used to measure the horizontal and vertical variations in lithology degree of saturation and groundwater salinity and thus to improve the interpretation of eri data the results of the chemical analyses of water samples collected from the wells along with the 2d eri survey profiles were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids this relationship was used along with the true resistivity sections resulting from the inversion of 2d eri data to identify and map three zones of water bearing formation fresh brackish and salt water zones in the coastal areas the results indicated that the depth to the fresh brackish interface exceeded 50 m at the upstream of the wadies and was in the order of 10 m or less in the vicinity of shoreline because of the high resistivity contrast between dry and water saturated fractured rocks this method was very successful in detecting water filled fractures and cavities in the carbonate aquifer the application of this method was unsuccessful in clayey aquifers as it was not possible to isolate lenses of gravel and or saturated with saline or brackish water from the surrounding clayey materials

evidence for remotely triggered microearthquakes during salt cavern collapse summary microseismicity is a good indicator of spatio temporal evolution of physical properties of rocks prior to catastrophic events like volcanic eruptions or landslides and may be triggered by a number of causes including dynamic characteristics of processes in play or and external forces we show evidence of triggered microseismicity observed in the vicinity of an underground salt cavern prone to collapse by a remote m 7 2 earthquake which occurred 12 000 km away high dynamic range broad band records reveal the strong time correlation between a dramatic change in the rate of local high frequency microseismicity and the passage of low frequency seismic waves including body love and rayleigh surface waves pressure was lowered in the cavern by pumping operations of brine out of the cavern we demonstrate the near critical state of the cavern before the collapse by means of 2 d axisymmetric elastic finite element simulations on this basis we show that the increment of stress necessary for the failure of the dolomite layer which ensures the stability of the whole system is of the same order of magnitude as the maximum dynamic stress magnitude observed during the passage of the earthquakes waves this suggests that the stress oscillations due to the seismic waves correlated with the recorded microearthquakes induced damage of the overburden which eventually led to the collapse of the salt cavern we show that the contribution of rayleigh waves is the most efficient to trigger microseismicity at periods close to the natural fundamental frequency of the cavern system found at about 10 20 s by investigating the impulse response of the cavern overburden brine system

linkage between turbulent kinetic energy waves and suspended sediment concentrations in the nearshore zone abstract knowledge about the tradeoffs among turbulent kinetic energy tke waves and suspended sediment concentrations sscs in the nearshore zone is relevant for understanding beach morphodynamics at different temporal and spatial scales a field measurement lasting for nearly three tidal cycles was conducted to holistically discern couplings between tke waves and sscs with further evaluation of the relative significance of tke and waves on sscs under various wave conditions over a meso macro tidal beach yintan to the north of beibu gulf china the results showed a dramatic increase in wave groupiness intensity from the shoaling wave condition to the breaking wave condition and a clear decrease further into the surf bore condition the near bed tkes under the surf bore condition were an order of magnitude larger than those under the breaking and shoaling wave conditions at the measurement position the averaged sscs in the near bed approximately 10 cm under the surf bore condition were 1 5 and 4 5 times larger than those under breaking and shoaling wave conditions respectively the variations in relative wave height were a decisive indicator for the differences in tke intensities among different wave conditions while the occurrence of peak tkes at the wave front within the intrawave cycle was associated with flow acceleration regardless of wave conditions mean sscs were well correlated with waves in terms of both incident wave scale and wave group scale which was limited to the shoaling wave condition and the occurrence of near bed intrawave peak sscs was always related to the offshore wave phase further tke contributed more effectively to sediment suspension at the wave group scale than at the incident wave scale especially under broken wave condition among the hydrodynamic factors tke played the most important role in the variations in sscs for all wave conditions flow acceleration served as the second most important factor under the broken wave condition while wave group single wave and advection were equivalent and less important factors for sscs

a traversing system to measure bottom boundary layer hydraulic properties this study describes a new convenient and robust system developed to measure benthic boundary layer properties with emphasis placed on the determination of bed shear stress and roughness height distribution within estuarine systems by using velocity measurements this system consisted of a remotely operated motorised traverser that allowed a single adv to collect data between 0 and 1 m above the bed as a case study we applied the proposed traversing system to investigate bottom boundary layer bbl hydraulic properties within coombabah creek queensland australia four commonly employed techniques 1 log profile lp 2 reynolds stress rs 3 turbulent kinetic energy tke and 4 inertial dissipation id used to estimate bed shear stresses from velocity measurements were compared bed shear stresses estimated with these four methods agreed reasonably well of these the lp method was found to be most useful and reliable additionally the lp method permits the calculation of roughness height which the other three methods do not an average value of bed shear stress of 0 46 n m2 roughness height of 4 3 mm and drag coefficient of 0 0054 were observed within coombabah creek results are consistent with that reported for several other silty bed estuaries

microseismic monitoring of a controlled collapse in field ii at ocnele mari romania several decades of faulty exploitation of salt through solution mining led to the creation of an underground cavern containing several million cubic meters of brine to eliminate the huge hazard near a densely inhabited area a technical solution was implemented to resolve this instability concern through the controlled collapse of the roof while pumping the brine out and filling the cavern with sterile to supervise this an area of over 1 km2 was monitored with a staggered array of 36 one component 15 hz geophones installed in 12 boreholes about 160 360 m deep a total of 2 392 seismic events with mw 2 6 to 0 2 occurred from july 2005 to march 2006 located within an average accuracy of 18 m the b value of the frequency magnitude distribution exhibited a time variation from 0 5 to 1 and from there to 1 5 suggesting that the collapse initiated as a linear fracture pattern followed by shear planar fragmentations and finally a 3 d failure process the brunching ratio of seismicity is indicative of a super critical process except for a short period in mid february when temporary stability existed event relocation through the use of a collapsing technique outlines that major clusters of seismicity were associated with the main cavern collapse whereas smaller clusters were generated by the fracturing of smaller size nearby caverns it is shown that one component recordings allow for stable and reliable point source event mechanism solutions through automatic moment tensor inversion using time domain estimates of low frequency amplitudes with first polarities attached detailed analysis of failure mechanism components uses 912 solutions with conditional number cn 0 5 the largest pure shear dc components characterize the events surrounding the cavern ceiling which exhibit normal and strike slip failures the majority of mechanism solutions include up to 30 explosional failure components which correspond to roof caving under gravitational collapsing the largest vertical deformation rate relates closely to the cavern roof and floor as well as the rest of the salt formation whereas the horizontal deformation rate is most prominent in areas of detected collapses

use of vertical electrical soundings to delineate seawater intrusion in a coastal area of byunsan korea to delineate spatial extent of seawater intrusion in a small experimental watershed in the coastal area of byunsan korea electrical resistivity surveys with some evaluation core drillings and chemical analysis of groundwaters were conducted the vertical electrical sounding ves method was applied which is useful to identify variations in electrical characteristics of layered aquifers the drilling logs identified a three layered subsurface including reclamation soil weathered layer and relatively fresh sedimentary bedrock the upper two layers are the main water bearing units in this area a total of 30 electrical sounding curves corresponded mostly to the h type and they were further divided into three classes highly conductive intermediate and low conductive according to the observed resistivity values of the most conductive weathered layer in addition groundwater samples from 15 shallow monitoring wells were analyzed and thus grouped into two types based on hco3 cl and ca na molar ratios with tds levels which differentiated groundwaters affected by seawater intrusion from those not or less affected according to relationships between the three classes of the sounding curves and groundwater chemistry locations of the monitoring wells with low hco3 cl and ca na ionic ratios coincided with the area showing the highly conductive type curve while those with the high ratios corresponded to the area showing low conductive curve type both the low electrical resistivity and the low ionic ratios indicated effects of seawater intrusion from this study it was demonstrated that the ves would be useful to delineate seawater intrusion in coastal areas

microseismic investigation of an unstable mountain slope in the swiss alps 1 risks associated with unstable rocky slopes are growing as a result of climate change and rapid expansions of human habitats and critical infrastructure in mountainous regions to improve our understanding of mountain slope instability we developed a microseismic monitoring system that operates autonomously in remote areas afflicted by harsh weather our microseismic system comprising 12 three component geophones was deployed across 60 000 m 2 of rugged crystalline terrain above a huge 30 million m 3 recent rockfall in the swiss alps during its 31 month lifetime signals from 223 microearthquakes with approximate moment magnitudes ranging from 2 to 0 were recorded determining the hypocenters was challenging for several reasons 1 p wave velocities were highly heterogeneous varying abruptly from 3 8 km s 2 first break picks were either inaccurate or lacking for some microearthquakes 3 there were no reliable s wave picks 4 numerous microearthquakes occurred just outside the network boundaries these issues were addressed by using a three dimensional 3 d p wave velocity model of the mountain slope determined from refraction tomography in a nonlinear inversion for hypocenter parameters and their probability density functions recordings from geophones at different altitudes and in boreholes constrained microearthquake depth estimates most microearthquakes were concentrated within 50 100 m of the surface in two zones one that followed the recent rockslide scarp and one that spanned the volume of highest fracture zone fault density these two active zones delineated a mass of rock that according to geodetic measurements has moved toward the scarp at 1 2 cm yr

induced seismicity monitoring of an underground salt cavern prone to collapse within the framework of a large research project launched to assess the feasibility of microseismic monitoring of growing underground caverns this specific work focuses on the analysis of the induced seismicity recorded in a salt mine environment a local seismic network has been installed over an underground salt cavern located in the lorraine basin northeast of france the microseismic network includes four 3 components and three single component geophones deployed at depths between 30 and 125 m in cemented boreholes drilled in the vicinity of the study area the underground cavern under monitoring is located within a salt layer at 180 m depth and it presents a rather irregular shape that can be approximated by a cylindrical volume of 50 m height and 180 m diameter presently the cavern is full of saturated brine inducing a significant pressure on its walls 2 0 mpa to keep the overburden mechanically stable nevertheless some small microseismic events were recorded by the network and analyzed approximately 2 000 events in 2 years of recording in october 2005 and april 2007 two controlled pressure transient experiments were carried out in the cavern in order to analyze the mechanical response of the overburden by tracking the induced microseismicity the recorded events were mainly grouped in clusters of 3 30 s of signal duration with emergent first arrivals and rather low frequency content between 20 and 120 hz some of these events have been spatially located by travel time picking close to the actual cavern and its immediate roof preliminary spectral analysis of isolated microearthquakes suggests sources with non negligible tensile components possibly related to fluid filled cracks rock debris falling into the cavern from delamination of clay marls in the immediate roof is probably another source of seismic excitation this was later confirmed when the most important seismic swarms occurred at the site during may 2007 accompanied by the detachment of more than 8 104 m3 of marly material on top of the cavern roof in any case no clear evidence of classical brittle ruptures in the most competent layers of the overburden has been observed during the analyzed period current work is focused on the discrimination of all these possible mechanisms to better understand the damage processes in the cavern overburden and to assess its final collapse hazard

a geoelectrical and hydrogeological study for the assessment of groundwater resources in wadi al bih uae drilling information historical water table levels groundwater salinity records of the existing water wells in wadi al bih area united arab emirates were stored in a geodatabase and used to characterize the geological and hydrogeological settings of this area a 2d earth resistivity imaging survey was conducted for the first time in the northern uae to determine the potential of the quaternary aquifer and its groundwater quality in the areas where there are no monitoring wells the results of the chemical analyses of the collected groundwater samples together with the inversion results of the resistivity data were used to draw a total salinity map and determine the spatial variations in groundwater quality the inversion results of the 2d earth resistivity imaging data indicated that the quaternary aquifer in the study area is in a good connection with the underlying carbonate aquifer it also indicated that the carbonate aquifer is of major regional and vertical extension and it contains the fresh water in this area the data stored in the developed database were used to produce different types of geopotential maps

examining the generality of τ0 tke for gravel and cobble beds with sand fill abstractturbulence measurements over rough beds are used for a variety of purposes including studies of habitat diversity for aquatic organisms stream restoration efforts and assessment of drag induced by vegetation turbulent kinetic energy tke has been used to estimate bed shear stress by use of a proportionality constant of 0 19 0 21 the tke method of bed shear stress estimation is less sensitive to flow misalignment relative to reynolds stress or mean velocity measurements but it has not been tested across a broad range of hydraulic conditions in the work reported here tke was compared to bed shear stresses for gravel d50 35 mm and cobble d50 156 mm beds with varying discharges and levels of sand fill d50 0 3 mm the ratio of bed shear stress 0 with tke was not strongly affected by mean velocity for either the gravel or cobble beds but it was affected by bed roughness the mean of the median values of 0 tke across three mean velocities was 0 24 for gravel with no sand in the bed

on the salt water intrusion into the durusu lake istanbul a joint central loop tem and multi electrode ert field survey durusu lake is the biggest and most important freshwater source supplying drinking water to the european side of istanbul in this study electrical resistivity tomography ert and transient electromagnetic tem measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of durusu lake the ert and tem measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier tem data were interpreted using different 1 d inversion methods such as occam marquardt and laterally constrained inversion lci ert data were interpreted using 2 d inversion techniques the inversion results of ert and tem data were shown as resistivity depth sections including topography the sand layer spreading over the basin has a resistivity of 150 400 omega m with a thickness of 5 10 m the sandy layer with clay silt and gravel has a resistivity of 15 100 omega m and a thickness of 10 40 m followed by a clay layer of a resistivity below 10 omega m when the inversion of these data is interpreted along with the hydrogeology of the area it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close using information from boreholes around the lake it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses

geoelectrical and hydrogeochemical studies for delineating seawater intrusion in the outlet of wadi ham uae the quaternary aquifer of wadi ham uae has been overexploited during the last two decades to meet the increasing water demands as a result the dynamic balance between freshwater and seawater has been disturbed and the quality of the groundwater has deteriorated in this paper a 2d earth resistivity survey was conducted in wadi ham in the area between fujairah and kalba to delineate the seawater intrusion existing monitoring wells were used to measure the horizontal and vertical variations in water salinity and thus to improve the interpretation of earth resistivity imaging data results of vertical electrical soundings and chemical analyses of collected water samples were used to obtain an empirical relationship between the inferred earth resistivity and the amount of total dissolved solids this relationship was used along with the true resistivity sections resulting from the inversion of 2d resistivity data to identify three zones of water bearing formation fresh brackish and salt water zones along the four 2d resistivity profiles the depth to the fresh brackish interface exceeded 50 m at the western part of the area and was in the order of 10 m or less in the eastern side near the shoreline depth to the brackish saline water interface reached about 70 m in the western side and was in the order of 20 m in the eastern side the thickness of the fresh water zone decreases considerably in the farming areas toward kalba and thus the degree of seawater intrusion increases

application of resistivity and gpr techniques for the characterization of the coastal litho stratigraphy and aquifer vulnerability due to seawater intrusion abstract the objective of this study is to identify geological properties and structural settings allowing salt water intrusion to the aquifers in oceanic originated rock formations of the south andaman island to evaluate the impact of seawater in groundwater aquifer several geophysical surveys using ground penetrating radar gpr and resistivity sounding were performed through the most significant sites located near coastal areas tidal channels and agriculture land high resolution gpr images were obtained and combined with resistivity sounding which allows to identify the mixing transition zone of fresh and saline groundwater and also successfully delineated the structural geometry and litho stratigraphic details of aquifers we show that the sedimentary formations are highly susceptible to seawater intrusion than the mantle originated ophiolites further potential impacts from seawater intrusion are higher along the west coast than the east coast because of macro pore tendency of soils allows seawater filtration

stabilizing effects of bacterial biofilms eps penetration and redistribution of bed stability down the sediment profile biofilms consisting of microorganisms and their secreted extracellular polymeric substances eps serve as ecosystem engineers stabilizing sedimentary environments natural sediment bed provides an excellent substratum for biofilm growth the porous structure and rich nutrients allow the eps matrix to spread deeper into the bed a series of laboratory controlled experiments were conducted to investigate sediment colonization of bacillus subtilis and the penetration of eps into the sediment bed with incubation time in addition to eps accumulation on the bed surface eps also penetrated downwards however eps distribution developed strong vertical heterogeneity with a much higher content in the surface layer than in the bottom layer scanning electron microscope sem images of vertical layers also displayed different micro morphological properties of sediment eps matrix in addition colloidal and bound eps exhibited distinctive distribution patterns after the full incubation the bio sedimentary beds were eroded to test the variation of bed stability induced by biological effects this research provides an important reference for the prediction of sediment transport and hence deepens the understanding of the biologically mediated sediment system and broadens the scope of the burgeoning research field of biomorphodynamics

locating pyroclastic flows on soufriere hills volcano montserrat west indies using amplitude signals from high dynamic range instruments pyroclastic flows are located using amplitude signals from a seven station high dynamic range seismograph array located 1 9 6 1 km from soufriere hills volcano in montserrat west indies locations are determined by measuring the seismograph signal amplitude for an event recorded at several stations in a moving time window analysis for a given window the measured amplitudes are corrected to a trial source location by removing the effect of the surface wave geometric spreading instrument gain and the attenuation at calculated travel times the trial source location is then compared to other trial locations via an iterative localised grid search where the root mean squared amplitude residual a is minimised the process is repeated for subsequent time steps resulting in a best fit event location and size through time the method has been tested on four small events occurring on april 8 1999 august 12 1999 february 25 2001 and july 4 2001 when visual observations of pyroclastic flows coincided with good seismograph station coverage number of stations 5 azimuthal gap 160 based on the location results the four events propagated 0 5 1 4 1 3 and 1 0 km from the dome and had maximum attenuation corrected reduced displacements drq of 9 0 2 8 6 9 and 2 3 cm2 and maximum pyroclastic flow velocities of 7 30 20 and 8 ms 1 respectively a time lapse video of the event of august 12 1999 shows that amplitude based location through time closely matches the observed run out distance and velocity in contrast amplitude based locations for the events of april 8 1999 and july 4 2001 underestimated the actual flow run out by 1 5 km underestimation of the true run out distance is probably due to both the increased distribution of sources as coherent dome material disaggregates into many blocks and signal contamination from other sources results indicate that pyroclastic flows and rockfalls can be located using amplitude signals from high dynamic range seismograph stations yielding estimates of size and trajectory regardless of visibility conditions on the volcano this new method is being tested as a hazard mitigation and research tool on montserrat

identification prediction and mitigation of sinkhole hazards in evaporite karst areas sinkholes usually have a higher probability of occurrence and a greater genetic diversity in evaporite terrains than in carbonate karst areas this is because evaporites have a higher solubility and commonly a lower mechanical strength subsidence damage resulting from evaporite dissolution generates substantial losses throughout the world but the causes are only well understood in a few areas to deal with these hazards a phased approach is needed for sinkhole identification investigation prediction and mitigation identification techniques include field surveys and geomorphological mapping combined with accounts from local people and historical sources detailed sinkhole maps can be constructed from sequential historical maps recent topographical maps and digital elevation models dems complemented with building damage surveying remote sensing and high resolution geodetic surveys on a more detailed level information from exposed paleosubsidence features paleokarst speleological explorations geophysical investigations trenching dating techniques and boreholes may help in investigating dissolution and subsidence features information on the hydrogeological pathways including caves springs and swallow holes are particularly important especially when corroborated by tracer tests these diverse data sources make a valuable database the karst inventory from this dataset sinkhole susceptibility zonations relative probability may be produced based on the spatial distribution of the features and good knowledge of the local geology sinkhole distribution can be investigated by spatial distribution analysis techniques including studies of preferential elongation alignment and nearest neighbor analysis more objective susceptibility models may be obtained by analyzing the statistical relationships between the known sinkholes and the conditioning factors chronological information on sinkhole formation is required to estimate the probability of occurrence of sinkholes number of sinkholes km2 year such spatial and temporal predictions frequently derived from limited records and based on the assumption that past sinkhole activity may be extrapolated to the future are non corroborated hypotheses validation methods allow us to assess the predictive capability of the susceptibility maps and to transform them into probability maps avoiding the most hazardous areas by preventive planning is the safest strategy for development in sinkhole prone areas corrective measures could be applied to reduce the dissolution activity and subsidence processes a more practical solution for safe development is to reduce the vulnerability of the structures by using subsidence proof designs

hydrochemical geophysical and multivariate statistical investigation of the seawater intrusion in the coastal aquifer at phetchaburi province thailand abstract seawater intrusion in coastal regions is an imperative ecological issues and results in an undesirable consequence on future groundwater resources to assess and mitigate seawater intrusion the affected aquifers need to be characterized by integrating geophysical investigation and multivariate statistical analysis of hydrochemical data seawater intrusion into coastal aquifers at cha am district in phetchaburi province thailand as a model area that is adversely affected by this problem was evaluated the vertical electrical sounding ves survey study was conducted at 80 locations and then 47 ves locations were used to create four pseudo cross section lines in a west east direction the geophysical results were described together with the hydrochemical analysis of 57 groundwater samples revealed that seawater intrusion occurred in the quarternary colluvial sediment aquifer at an average depth of 50 60 m a resistivity value of

identifying seawater intrusion in coastal areas by means of 1d and quasi 2d joint inversion of tdem and ves data abstract seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes sea level rise extreme phenomena like flooding and droughts and groundwater depletion near to the coastline to evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion geophysical methods are the most appropriate tool to address these researches among all geophysical techniques electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater freshwater and geological layers the combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods in this investigation joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the ferragudo albufeira aquifer system algarve south of portugal for this purpose two profiles combining electrical resistivity tomography ert and time domain electromagnetic tdem methods were measured and the results were compared with the information obtained from exploration drilling three different inversions have been carried out single inversion of the ert and tdem data 1d joint inversion and quasi 2d joint inversion single inversion results identify seawater intrusion although the sedimentary layers detected in exploration drilling were not well differentiated the models obtained with 1d joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined finally the quasi 2d joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling this study demonstrates that the quasi 2d joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas

estimating shear stress from moving boat acoustic doppler velocity measurements in a large gravel bed river 1 moving boat acoustic doppler current profiling adcp is increasingly used to measure discharge in large rivers we investigate whether useful information about bed shear stress can be recovered from such data alternative ways to estimate local bed shear stress using the logarithmic law of the wall and spatial averaging are tested using adcp transects across lower fraser river canada repeatability is assessed by comparing estimates from outward and return boat tracks the most precise method uses the vertically averaged mean velocity and a zero velocity height based on bed grain size information the accuracy of the assumed zero velocity height can be judged by consistency between estimates using mean velocity and near bed velocity shear stress estimates from unconstrained log law fits are less repeatable and tend to overpredict and mean shear stress estimates using the depth slope product are unreliable in this river because of nonuniform flow

imaging the dynamics of magma propagation using radiated seismic intensity 1 at shallow depth beneath the earth s surface magma propagates through strongly heterogeneous volcanic material inversion of buoyancy and or solidification have strong impacts on the dynamics of propagation without any change of magma supply in this paper we study the spatial and time evolution of magma intrusions using induced seismicity we propose a new method based on ratio analysis of estimates of radiated seismic intensities recorded at different stations during seismic swarms by applying this method to the january 2010 piton de la fournaise volcano eruption we image complex dike propagation dynamics which strongly differ from a model of constant velocity dike propagation we provide a new method to image in real time the dynamics of dike propagation and to infer the position of eruptive fissures

dynamic response of the chamousset rock column western alps france 1 this paper investigates the variation of the first resonance frequency of the chamousset limestone column 21 000 m3 vercors french alps before its collapse in november 2007 the site was instrumented with seismometers and extensometers during a 4 month period with some gaps in the measurements experimental results and numerical modeling showed that the resonance frequency of a prone to fall column can be derived from the spectra of continuous seismic noise records at the chamousset site the evolution of the resonance frequency appeared to be strongly controlled by the temperature when temperatures were positive slight resonance frequency variations correlated well with thermal fluctuations irreversible damage can occur during freeze thaw cycles and to a lesser extent during strong wind it coincided with a significant drop in resonance frequency which was interpreted as the result of rock bridge breakage this hypothesis is supported by fresh rupture observations after the collapse seismic event records and numerical modeling this study suggests that seismic noise recording could be used for assessing the potential failure of unstable columns in rigid rocks

a comparison of flow intensities in alluvial rivers characteristics and implications for modelling flow processes this paper compares flow intensity data obtained with different instruments from a variety of fluvial environments it examines associations between the root mean square of longitudinal velocity fluctuations flow intensity local mean velocity relative depth and boundary resistance results indicate systematic differences in the behaviour of flow intensity which scale with respect to position in the boundary layer deep sand bedded rivers boundary grain resistance shallow river environments with coarse beds and possibly form resistance shallower sand bedded rivers preliminary approaches to prediction and modelling of variations in flow intensity are suggested based upon linear regression relationships intensity values are also compared with theoretical and empirical limits to the use of taylor s substitution which allows time and frequency properties of a single point velocity time series to be used to yield a flow length scale in general limits are exceeded in all environments for near boundary flow measurements but are met for y d 0 3 in most cases in sand bed rivers and for y d 0 4 in some gravel bed environments 1998 john wiley sons ltd

in situ monitoring of rock fracturing using shear wave splitting analysis an example from a mining setting summary changing stress conditions are well known to cause rupturing of rock this is well constrained on a small scale from laboratory experiments and inferred on a much larger scale from tectonic earthquakes here we present a study of rock fracturing induced by changes in stress state during block caving operations in an australian mine this intermediate scale study provides further evidence of the scalability of processes involved in rock fracturing and thus helps to link laboratory and seismological observations we analyse the temporal evolution of rock fracturing during a production cycle using the analysis of fracture induced anisotropy fracturingoftherockmassismonitoredusingevidenceofseismicanisotropyfromestimates of shear wave splitting and their subsequent inversion for fracture parameters the data set consists of more than 40 000 three component seismograms recorded by an array of sensors which provides excellent ray coverage we applied a novel automatic quality assessment technique to handle this large data set and find that anisotropy and thus fracturing correlates strongly with the excavation process we then perform a grid search over a series of synthetic models based on rock physics to invert the splitting parameters for fracture orientation and density finally by applying a sliding window on our results we are able to identify production related fracture evolution during production the fracture density increases with horizontal fracture density being stronger than the vertical fracture density this can be explained by the removal of the supporting rock during caving during short intervals of reduced production the horizontal fracture density decreases whereas vertical fracture density increases we relate this to change in stress regime with reducing overburden mass during cavity collapse this scenario is similar to a collapsing caldera or the inverse of an inflating magma chamber

bed shear stress estimation on an open intertidal flat using in situ measurements abstract accurate estimations for the bed shear stress are essential to predict the erosion and deposition processes in estuaries and coasts this study used high frequency in situ measurements of water depths and near bed velocities to estimate bed shear stress on an open intertidal flat in the yangtze delta china to determine the current induced bed shear stress c the in situ near bed velocities were first decomposed from the turbulent velocity into separate wave orbital velocities using two approaches a moving average ma and energy spectrum analysis esa c was then calculated and evaluated using the log profile lp turbulent kinetic energy tke modified tke tkew reynolds stress rs and inertial dissipation id methods wave induced bed shear stress w was estimated using classic linear wave theory the total bed shear stress cw was determined based on the grant madsen wave current interaction model wci the results demonstrate that when the ratio of significant wave height to water depth hs h is greater than 0 25 cw is significantly overestimated because the vertical velocity fluctuations are contaminated by the surface waves generated by high winds in addition wind enhances the total bed shear stress as a result of the increases in both w and c generated by the greater wave height and reinforcing of vertical turbulence respectively from a comparison of these various methods the tkew method associated with esa decomposition was found to be the best approach because 1 this method generates the highest mean index of agreement 2 it uses vertical velocities that are less affected by doppler noise and 3 it is less sensitive to the near bed stratification structure and uncertainty in bed location and roughness

understanding the hydrogeology of the venice lagoon subsurface with airborne electromagnetics abstract the occurrence of alternating dry wet conditions in transitional environments such as wetlands deltas and lagoons usually challenges the use of traditional direct and geophysical surveys for comprehensive hydrogeologic investigations moreover significant mixing between continental fresh groundwater and marine salty surface waters generally takes place in these flat coastal areas airborne electromagnetics aem is a promising tool in this respect as it provides in a fast and cost effective manner large scale distribution of bulk electrical conductivities that can be used profitably to develop hydrogeologic models the results of a skytem aem survey in the venice lagoon italy show the capability of this technique to significantly improve the knowledge of the hydrogeologic setting of the lagoon and nearby coastland subsurface irrespective of the different features characterizing the area the environment consists of salt marshes mud flats shallows tidal channels islands together with reclaimed farmlands crossed by natural watercourses and drainage channel networks in particular the aem shows i the presence of fresh water with resistivity larger than 20 m underneath the central part of the lagoon at depths from 10 to 25 m below m s l ii the interface between different relevant stratigraphic units e g the clayey layer bounding the holocene pleistocene sedimentation and iii the occurrence of areas with possible submarine fresh groundwater discharge moreover the source and inland extent of the saltwater contamination in the shallow coastal aquifers along the southern margin of the lagoon are clearly revealed aem data were complemented with very high resolution seismic vhrs acquisitions the integrated analysis of the two data sets allows distinguishing between lithostratigraphic heterogeneity and variability of the subsurface fluids

estimating bottom stress in tidal boundary layer from acoustic doppler velocimeter data bed stresses in the bottom boundary layer of the york river estuary virginia were estimated from three dimensional near bottom velocities measured by acoustic doppler velocimeters advs and also by a profiling array of electromagnetic current meters by assuming the measurements were made in a constant stress layer four methods of stress estimation were evaluated using advs direct covariance cov measurement turbulent kinetic energy inertial dissipation utilizing the kolmogorov spectrum and log profile the four methods yielded similar estimates of frictional velocity u based on adv output from both 14 cm and 44 cm above bed all eight estimates of average u were consistent with the overall mean of 1 10 cm s to within the 95 confidence interval for individual burst estimates the cov method worked slightly better nearer the bed possibly because of the sensitivity of cov to the upper limit of the constant stress layer the inertial dissipation method performed marginally well at 14 cm above bed likely because of sediment induced stratification and insufficient separation of turbulent production and dissipation scales the log profile method was the most variable and appeared most sensitive to stratification and to the thickness of the constant stress layer the turbulent kinetic energy method was the most consistent at both heights and appears most promising for further development results encourage future use of the adv in estuarine environments but also favor the simultaneous use of several methods to estimate bottom stress

estimation of the bed shear stress in vegetated and bare channels with smooth beds the shear stress at the bed of a channel influences important benthic processes such as sediment transport several methods exist to estimate the bed shear stress in bare channels without vegetation but most of these are not appropriate for vegetated channels due to the impact of vegetation on the velocity profile and turbulence production this study proposes a new model to estimate the bed shear stress in both vegetated and bare channels with smooth beds the model which is supported by measurements indicates that for both bare and vegetated channels with smooth beds within a viscous sublayer at the bed the viscous stress decreases linearly with increasing distance from the bed resulting in a parabolic velocity profile at the bed for bare channels the model describes the velocity profile in the overlap region of the law of the wall for emergent canopies of sufficient density frontal area per unit canopy volume a 4 3 m 1 the thickness of the linear stress layer is set by the stem diameter leading to a simple estimate for bed shear stress

the heterogeneity of mudflat erodibility the prediction of the erosion of mudflats is hampered by inaccurate estimates of the erodibility distribution of the sediment bed to investigate how erodibility varies in space and what the vertical distribution over the sediment depth is comprehensive observations of the sediment properties hydrodynamics and bed level changes were conducted on an intertidal flat in the western scheldt estuary the netherlands the erosion potential on a mudflat is determined by the critical shear stress for erosion e erosion rate coefficient m and local hydrodynamic conditions a clear difference in hydrodynamic forcing was observed leading to significant bed level variations at the low water line where erosion often occurs during very shallow water condition and a nearly constant bed level at the upper part the erosion parameters e and m could be determined over a sediment bed of 12 cm at the low water line the erosion coefficient m can be considered constant with depth although there is a large spreading a clear vertical variation of e was found e increased significantly downward from 0 10 pa at the sediment surface to 1 13 pa at 12 cm below the surface additionally there was a strong indication that the presence of diatoms enhanced e in the upper 2 mm of sediment by five times of the abiotic e from 0 09 pa to 0 46 pa these findings lead to the following improvement for predicting morphological changes of tidal mudflats 1 very shallow conditions should be better simulated 2 the vertical distribution of e should be considered otherwise erosion rates can be overestimated especially during extreme events because exposure of the deeper well consolidated layer likely occurs and 3 an appropriate description of the effect of diatoms should be considered as part of the bottom boundary condition

turbulence based measurements of wave friction factors under irregular waves on a gravel bed very few studies have quantified the wave friction factor fw for coarse sediments at field scale to address this shortcoming high frequency measurements of turbulence obtained within the boundary layer of irregular waves over gravel in the delta flume have been used to calculate values of fw using different evaluation methods in the field scale laboratory experiments reported here three velocimeters were deployed on the seaward side of a 4 m high 5 m wide and 55 m long gravel barrier subject to a jonswap spectrum of waves with significant wave heights ranging from 0 8 m to 1 3 m and peak periods of 3 0 s to 10 s and offshore water depths ranging from 1 75 m to 3 75 m the deployment area was essentially flat with little or no predicted or observed sediment movement under the wave conditions investigated the turbulent kinetic energy method was found to be the most suitable approach for calculating the bed shear stress which can be related to fw wave friction factor values under the conditions tested here fell in the range 0 01 and 0 27 although fw predicted by an existing equation agrees well with the mean measured fw value the application of a new predictor for fw is recommended for improved parameterisation of skin friction over the range of relative roughness values encountered in this study this approach combines the wave reynolds number wave steepness and relative depth to provide a simple expression to assist assessments of coarse sediment transport by waves for uses within a range of practical engineering applications

evaluating freshwater lens morphology affected by seawater intrusion using chemistry resistivity integrated technique a case study of two different land covers in carey island malaysia freshwater lenses are vital to small island communities but are susceptible to seawater intrusion due to the physical changes in the shoreline land cover the effect of seawater intrusion and irrigation water on a coastal unconfined aquifer beneath naturally preserved mangrove and deforested mangrove barren belt was investigated in carey island analysis of the total dissolved solids tds and earth resistivity er using a geochemistry electrical integrated technique gave a tds er relationship capable of predicting freshwater lens morphology affected by sea irrigation water the study result shows freshwater was fourfold thicker in close proximity of the mangrove forest than the mangrove barren area the further the shoreline from the mangrove thickest section the less vulnerable was the seawater intrusion and the more fresh the irrigation water and hence the greater the freshwater availability potential

volcanic tremor location during the 2004 mount etna lava effusion 1 a lava emission started at mt etna italy on 7 september 2004 neither earthquake seismicity heralded or accompanied the opening of the fracture field from which the lava poured out nor volcanic tremor changed in amplitude and frequency content at the onset of the effusive activity to highlight long term changes we propose a method for the location of the tremor source based on a 3d grid search using the amplitude decay of the seismic signal from january to november 2004 we find the centroid of the tremor source within a zone close to and partially overlapped with the summit craters pre effusive phase which extended up to 2 km south of them effusive phase the depths are of between 1698 and 2387 m a s l we hypothesize the lava effusion stemmed from a degassed magma body although we find evidence of temporary magma overpressure conditions such as those documented on 25 september

great differences in the critical erosion threshold between surface and subsurface sediments a field investigation of an intertidal mudflat jiangsu china abstract understanding of bottom sediment erodibility is necessary for the sustainable management and protection of coastlines and is of great importance for numerical models of sediment dynamics and transport to investigate the dependence of sediment erodibility on degree of consolidation we measured turbidity waves tidal currents intratidal bed level changes and sediment properties on an exposed macrotidal mudflat during a series of tidal cycles we estimated the water content of surface sediments in the uppermost 2 cm of sediment and sub surface sediments at 2 cm below the sediment surface bed shear stress values due to currents c waves w and combined current wave action cw were calculated using a hydrodynamic model in this study we estimate the critical shear stress for erosion using two approaches and both of them give similar results we found that the critical shear stress for erosion ce was 0 17 0 18 n m2 in the uppermost 0 2 cm of sediment and 0 29 n m2 in sub surface sediment layers depth 2 cm as determined by time series of cw values and intratidal bed level changes and values of ce obtained using the water content of bottom sediments were 0 16 n m2 in the uppermost 2 cm and 0 28 n m2 in the sub surface depth 2 cm sediment these results indicate that the value of ce for sub surface sediments depth 2 cm is much greater than that for the uppermost sediments depth 0 2 cm and that the ce value is mainly related to the water content which is determined by the extent of consolidation our results have implications for improving the predictive accuracy of models of sediment transport and morphological evolution by introducing variable ce values for corresponding sediment layers and can also provide a mechanistic understanding of bottom sediment erodibility at different sediment depths on intertidal mudflats as related to differences in the consolidation time

bed level changes on intertidal wetland in response to waves and tides a case study from the yangtze river delta short term bed level variability in tidal wetlands has important implication both for ecology and engineering in this study we combined in situ measurements with model simulations to quantify short term bed level changes on a meso macrotidal wetland in the yangtze river delta on the middle flat we observed erosion during neap to mean tides under onshore moderate to strong winds and bed recovery during subsequent spring tides when winds were both offshore and weaker suggesting that winds can overturn the neap spring cyclicity of bed level changes even on meso macrotidal mudflats the magnitude of bed level changes was smaller on both sides of the middle flat while the smallest changes occurred on the salt marsh observed bed level changes were reconstructed using a single point bed level change model which incorporates in situ measured parameters of hydrodynamics waves and currents suspended sediment concentrations and bed sediment properties we conclude that the relative importance of waves and tides in intertidal wetland erosion and accretion can vary temporally due to changes in balance between wave and tidal energies and spatially because of changes in elevation and vegetation in the cross shore profile our study also reflects the advantage of combination of in situ measurement with simulation in detecting short term variability of tidal flats

evaluation of landfill disposal boundary by means of electrical resistivity imaging this paper deals with an employment of electrical resistivity imaging eri for survey of leachate content on the waste disposal site in northern israel the research consisted of conducting ten eri lines and drilling investigation wells data simulation used a 2d earthimager inversion program analysis of 2d eri interpretation results shows that determination of the boundary between the landfill body bottom intensively saturated with leachates and underlying layers of highly water saturated fat nonconsolidated clays presents a challenge however statistical analysis of eri data indicates that standard deviation and confidence interval of a set of resistivity data measured in the landfill body are significantly larger than those in underlying clays moreover maximum changes of these parameters are found on the boundary between landfill body and underlying soil thus reflecting natural differences in scattering of resistivity data measured in these two objects

turbulent and advective momentum fluxes in streams 1 the scope of the present paper is the evaluation of the exchange of momentum in natural streams to explore the contribution that turbulence and secondary currents have on the shear stress distributions within the flow and hence evaluate the overall hydraulic resistance existing methods for the evaluation of shear stresses in rivers are examined with respect to their applicability to complex flow fields and a new mathematical formulation for analyzing the shear stresses affecting the longitudinal velocity distribution is presented this new method enables one to estimate the time averaged principal shear stress and its particular components due to turbulence and secondary currents directly from three dimensional velocity data an acoustic doppler velocimeter adv was used to measure the currents and turbulence at five cross sections of two field sites over a wide range of discharges the results of the cross sectional measurements reflect the nonuniformity of the river bed roughness cross sectional form and planform limited applicability was found for methods based on the theory of two dimensional boundary layer flows shear stresses estimated using the new method emphasize the dominance of secondary currents on the total momentum flux momentum fluxes caused by secondary currents were an order of magnitude larger than momentum fluxes due to turbulence

seabed stress determinations using the inertial dissipation method and the turbulent kinetic energy method direct measurements of seabed stress are difficult especially in field conditions several methods for estimating these stresses using current meter data are available two of these methods the inertial dissipation method and the turbulent kinetic energy method are described below and a matlab program is used to analyse data from a wave current environment

spectral estimates of bed shear stress using suspended sediment concentrations in a wave current boundary layer 1 high resolution time series of suspended sediment profiles have been obtained using an acoustic backscatter system at an inner shelf site north carolina where flows are dominated by wind driven currents and waves we analyzed the spatial and temporal structure of near bed turbulence in particle transporting flows and scalar like fluctuations of suspended sediment concentrations an important element of our analysis is a new inertial dissipation method for passive tracers to estimate the shear stress acting on the seabed using the spectral properties of suspended sediment concentrations observed by acoustic backscatter sensors in flows that provide adequate separation of the scales of turbulence production and dissipation a sufficiently thick constant stress wall layer and significant sediment suspension frequency or associated wave number spectra of near bed sediment concentration exhibit a 5 3 slope in the inertial subrange that spans frequencies of order 1 hz this observation suggests that the suspended sediment is effectively a passive tracer of turbulent fluid motions inversion of the relevant kolmogorov scaling equations yields estimates of the shear velocity that agree reasonably well with other independent and widely used measures high and low frequency limits on application of the inertial dissipation method to sediment concentration are related to the inertial response time of sediment particles and the sediment settling timescale we propose that in future applications the inertial dissipation method for passive tracers can be used to estimate either the shear velocity effective settling velocity of suspended sediment or equivalent particle size or dynamic bed roughness if two of these three quantities are independently known

mass settling flux of fine sediments in northern european estuaries measurements and predictions abstract this study describes a new flocculation model which was based entirely on observations of settling floc spectra and turbulent shear stresses acquired primarily from a series of in situ experiments conducted in several european estuaries the synthesis identified that the key components which best quantitatively describe a floc population are the changes in the macrofloc 160 m and microfloc settling velocities ws macroem and ws microem together with how the suspended matter is distributed across each floc sub population spm ratioem the ws macroem algorithm displayed an increase in settling velocity at low shear stresses due to flocculation enhanced by shear and floc disruption at higher stresses for the same concentration the transition being a turbulent shear stress of about 0 36 n m 2 the combination of the three algorithms into a single equation to predict mass settling flux msf em estimated the total flux of the 157 measured floc samples with a cumulative error 1 and 5 mm s 1 were both in error by an average of 86 and 41 respectively a concentration settling parameterisation and the van leussen techniques under predicted the total cumulative flux by 35 and 38 respectively furthermore the analysis indicated that the various existing methods all incurred high predictive errors at times under estimating by over 70 as concentration levels rose in close proximity to the bed the findings of this study demonstrate the new manning floc settling velocity mfsv empirical model has flexibility in adapting to a wide range of both turbulent shear stress and suspended sediment concentration estuarine conditions

floc properties in the turbidity maximum of a mesotidal estuary during neap and spring tidal conditions in order to improve the understanding of how fine cohesive matter behaves during different tidal conditions within an estuary turbidity maxima high quality in situ data is of a prime requirement as part of the european commission cosinus project a series of measurements were carried out in the upper reaches of the tamar estuary to investigate how flocculated mud properties vary within the turbidity maximum zone floc populations were sampled at regular intervals using the optical inssev instrument the floc data was supplemented by simultaneous time series of near bed profiles of turbulent shear stress and suspended particulate matter the proportion of macroflocs 160 m changed significantly across the turbidity maximum before the passage of the turbidity maximum the total floc mass tended to be equally divided between the macroflocs and microflocs on neaps whilst on springs the macroflocs contributed 60 70 at spring tides a peak near bed spm concentration of 6 g l 1 was measured in the turbidity maximum this was over an order of magnitude higher than observed at neaps the turbulence measurements showed significant drag reduction at spm concentration gradients above 3 6 kg m 4 within the turbidity maximum the macrofloc proportion rose rapidly until they contributed at least 75 of the floc dry mass during neap conditions and at spring tides this reached in excess of 90 96 an abundance of fast settling macroflocs from spring tides accounted for a time series average of 83 of the mass settling flux where as during neap tides the macroflocs contributed 15 less to the settling flux rate this was partly due to a time series averaged macrofloc settling velocity of 3 9 mm s 1 from the spring tidal data 2 1 mm s 1 higher than for neap tide conditions during the turbidity maximum passage at springs macroflocs reached 2 2 mm in diameter these flocs had settling velocities of up to 16 6 mm s 1 but effective densities were less than 50 kg m 3 which means they would be prone to break up when settling to a region of high shear at the opposite and of the scale low turbidity and quiescent slack water conditions severely restricted floc production

in situ estimation of erosion and deposition thresholds by acoustic doppler velocimeter adv abstract field based estimations of bed shear stress have been made using sontek ysi 10 mhz advs a coustic d oppler v elocimeter at the kongsmark mudflat danish wadden sea in order to test if it was possible to estimate erosion and deposition thresholds in situ by use of unidirectional tidal and orbital wave currents the results were promising and erosion thresholds were in the same range as those observed in eromes erosion experiments carried out at the same site similarly the short term erosion rates which could be calculated matched closely those obtained with eromes and were in the same range as those published for a large annular flume sea carousel from another fine grained site this indicates that the erosion rates obtained with those two erosion instruments are reasonable estimates of the actual erosion taking place under natural tidal current and waves one advantage of the use of advs to characterize sediment erodibility is that measurements can be carried out for long periods which makes it possible to examine the temporal variation of erosion threshold erosion rate and sedimentation the maximum bed shear stresses which was observed during a strong storm in january 2005 was only 0 7 n m 2 which is three to four times lower than the highest thresholds measured by eromes experiments on sediment with biofilms during previous studies this shows that such strong biofilms at this site will not get eroded unless degraded or physically disrupted by some other mechanism a prerequisite for the determination of any of the erodibility and sedimentation parameters is that the actual bed level changes at the measuring site are known in detail this information is obtained automatically by the advs used in the present study accurate estimates of the bed shear stress under waves in very shallow water are difficult to obtain and in the present study a simple method based on instantaneous velocities and assumption of a logarithmic velocity profile was used further field studies are required of the boundary layer under these extreme conditions in order to refine this simple method of calculating bed shear stresses

cross validation of geo electrical and hydrogeological models to evaluate seawater intrusion in coastal aquifers 1 the validation of variable density flow models simulating seawater intrusion in coastal aquifers requires information about concentration distribution in groundwater electrical resistivity tomography ert provides relevant data for this purpose however inverse modeling is not accurate because of the non uniqueness of solutions such difficulties in evaluating seawater intrusion can be overcome by coupling geophysical data and groundwater modeling first the resistivity distribution obtained by inverse geo electrical modeling is established second a 3 d variable density flow hydrogeological model is developed third using archie s law the electrical resistivity model deduced from salt concentration is compared to the formerly interpreted electrical model finally aside from that usual comparison validation the theoretical geophysical response of concentrations simulated with the groundwater model can be compared to field measured resistivity data this constitutes a cross validation of both the inverse geo electrical model and the groundwater model

an integrated magnetotelluric and gamma exploration of groundwater in fractured granite for small scale freshwater supply a case study from the boshan region shandong province china exploration and use of groundwater in hard rocks is a difficult but yet a significant issue especially when the local surface water source is polluted in this study integrated geophysical and nuclear methods are used to delineate groundwater bearing zones in a granite terrain in the boshan region shandong province china structural analysis showed that fractures extend in a nw se direction which is the same as the direction of river valley a controlled source audio frequency magnetotelluric survey conducted along the river valley indicated several different low resistivity anomalies or potential water bearing fracture zones they are seated at depth ranges down to 400 m from the surface along the river valley the locations of deep water bearing zones were further confirmed by higher gamma radiation measurements found near the river valley a fault with a nw se strike near the river was deduced as an anomalous water bearing zone two tube wells were drilled targeting at the water bearing zone that has achieved single well water yield greater than 360 m3 day the well water was sampled for water chemistry and stable isotope analyses shallow groundwater samples show similar water chemistry and isotopic feature to river water indicating connection between the two deep groundwater from the water bearing fracture zones is not hydraulically connected with shallow groundwater ensuring safety of the deep groundwater in the granite from being affected by the polluted shallow groundwater or river water integrated geophysical and gamma exploration methods helped to identify two disconnected groundwater systems offering an alternative freshwater source for the region if shallow groundwater or surface water is polluted

location of microseismic swarms induced by salt solution mining ground failures caving processes and collapses of large natural or man made underground cavities can produce significant socio economic damages and represent a serious risk envisaged by the mine managements and municipalities in order to improve our understanding of the mechanisms governing such a geohazard and to test the potential of geophysical methods to prevent them the development and collapse of a salt solution mining cavity was monitored in the lorraine basin in northeastern france during the experiment a huge microseismic data set similar to 50 000 event files was recorded by a local microseismic network 80 per cent of the data comprised unusual swarming sequences with complex clusters of superimposed microseismic events which could not be processed through standard automatic detection and location routines here we present two probabilistic methods which provide a powerful tool to assess the spatio temporal characteristics of these swarming sequences in an automatic manner both methods take advantage of strong attenuation effects and significantly polarized p wave energies at higher frequencies 100 hz the first location approach uses simple signal amplitude estimates for different frequency bands and an attenuation model to constrain the hypocentre locations the second approach was designed to identify significantly polarized p wave energies and the associated polarization angles which provide very valuable information on the hypocentre location both methods are applied to a microseismic data set recorded during an important step of the development of the cavity that is before its collapse from our results systematic spatio temporal epicentre migration trends are observed in the order of seconds to minutes and several tens of meters which are partially associated with cyclic behaviours in addition from spatio temporal distribution of epicentre clusters we observed similar epicentre migration in the order of hours and days all together we suggest that the recorded microseismicity mainly represents detachment and block breakage processes acting at the cavity s roof indicating a zone of critical state of stress and where partial fractures cause chain reaction failures as a result of stress redistribution processes