growth by extension and reworking of a south western kalahari linear dune optically stimulated luminescence osl dating studies of linear longitudinal dunes have been used extensively to elucidate late quaternary environments and climates in arid or formerly arid regions yet understanding of the development of such dunes is incomplete in particular conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally the degree to which they rework their own sediment during accumulation and whether they form primarily by extension as opposed to lateral sand movement from adjacent interdunes this study focuses on this last point although the importance of the other controversies is discussed in context a simple linear dune in the south western kalahari which has a prominent termination on a pan playa surface provides an opportunity to directly test hypotheses of dune extension chronostratigraphy along a 600 m transect along the crest of the dune constrained by 42 osl ages reveals that the dune grew by extension on occasions in the late pleistocene and early holocene but has also been subject to reworking along its length which has continued until recent times dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation whereas reworking is largely independent of conditions throughout the last 18 ka and may represent seasonal fluctuations in the position of the dune crest the relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change copyright 2011 john wiley sons ltd

transient hydraulic tomography in a fractured dolostone laboratory rock block experiments 1 the accurate characterization of fractured geologic medium imaging of fracture patterns and their connectivity have been a challenge for decades recently hydraulic tomography has been proposed as a new method for imaging the hydraulic conductivity k and specific storage ss distributions of fractured geologic media while encouraging results have been obtained in the field the method has not been rigorously assessed in a controlled laboratory setting in this study we assess the performance of transient hydraulic tomography tht in a fractured dolomitic rock block the block is characterized through flow through tests and multiple pumping tests the pumping test data were then analyzed with the tht code of zhu and yeh 2005 to image the fracture patterns and their connectivity through the delineation of k and ss distributions or tomograms results show that the tht analysis of pumping tests yields high k and low ss zones that capture the fracture pattern and their connectivity quite well and those patterns become more vivid as additional pumping test data are added to the inverse model the performance of the estimated k and ss tomograms are then assessed by 1 comparing the tomograms obtained from synthetic to real data 2 comparing the tomograms from two different pumping configurations 3 comparing the estimated geometric mean of the hydraulic conductivity kg from the k tomogram to the effective hydraulic conductivity keff estimated from the flow through tests and 4 predicting five independent pumping tests not used in the construction of the k and ss tomograms the performance assessment of the k and ss tomograms reveals that tht is able to image high k and low ss zones that correspond to fracture locations in the fractured rock block and that the tomograms can be used to predict drawdowns from pumping tests not used in the construction of the tomograms with reasonable fidelity

a continuum model for water movement in an unsaturated fractured rock mass the movement of fluids in a fractured porous medium has been the subject of considerable study this paper presents a continuum model that may be used to evaluate the isothermal movement of water in an unsaturated fractured porous medium under slowly changing conditions this continuum model was developed for use in evaluating the unsaturated zone at the yucca mountain site as a potential repository for high level nuclear waste thus its development has been influenced by the conditions thought to be present at yucca mountain a macroscopic approach and a microscopic approach are used to develop a continuum model to evaluate water movement in a fractured rock mass both approaches assume that the pressure head in the fractures and the matrix are identical in a plane perpendicular to flow both approaches lead to a single flow equation for a fractured rock mass the two approaches are used to calculate unsaturated hydrologic properties i e relative permeability and saturation as a function of pressure head for several types of tuff underlying yucca mountain using the best available hydrologic data for the matrix and the fractures rock mass properties calculated by both approaches are similar

bioturbation and the upward movement of sediment particles and archaeological materials comments on bueno et al the literature on bioturbation both from the biological and archaeological points of view is growing steadily available data suggests that ants and termites are responsible for the upward movement of soil sediment particles and archaeological materials it is argued that this could be the most parsimonious explanation for the stratigraphic data presented by bueno et al 2013 given the size range of displaced materials and the environmental setting composed of a sandy soil in a savannah region

modeling complex nonlinear geological processes abstract we review selected geological processes to which numerical modeling has been applied with the aim of describing some of the general approaches and applications of the modeling all of these examples involve multiphase fluid flow in some cases coupled with heat transport and phase changes first we describe modeling approaches to a human made geological system a potential underground radioactive waste repository next we describe recent advances in modeling two phase flow through random heterogeneous porous media we review recent modeling studies of fluid processes in magmatic systems especially focusing on melting and crystallization induced by magma chambers finally several research directions are suggested including improving our understanding of the linkage between small scale and field scale processes coupling across regimes e g surface water and ground water and further developments in the modeling of stochastic geological processes

age origin and climatic controls on vegetated linear dunes in the northwestern negev desert israel abstract the stabilized northwestern nw negev vegetated linear dunes vld of israel extend over 1300 km 2 and form the eastern end of the northern sinai nw negev erg this study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology stratigraphy and optically stimulated luminescence osl dating thirty five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and osl dating enabling spatial and temporal elucidation of the nw negev dunefield evolution in a global perspective the nw negev dunefield is relatively young though sporadic sand deposition has occurred during the past 100 ka dunes began to accumulate over large portions of the dunefield area only at 23 ka three main chronostratigraphic units corresponding to three osl age clusters were found throughout most of the dunefield indicating three main dune mobilizations late to post last glacial maximum lgm at 18 11 5 ka late holocene 2 0 8 ka and modern 150 8 years the post lgm phase is the most extensive and it defined the current dunefield boundaries it involved several episodes of dune incursions and damming of drainage systems dune advancement often occurred in rapid pulses and the orientation of vld long axes indicates similar long term wind directions the late holocene episode included partial incursion of new sand reworking of late pleistocene dunes as well as limited redeposition the modern sand movement only reactivated older dunes and did not lengthen vlds this aeolian record fits well with other regional aeolian sections we suggest that sand supply and storage in sinai was initiated by the late pleistocene exposure of the nile delta sands late pleistocene winds substantially stronger than those usually prevailing since the onset of the holocene are suggested to have transported the dune sands across sinai and into the northwestern negev our results demonstrate the sensitivity of vegetated linear dunes located along the northern fringe of the sub tropical desert belt to climate change i e wind and sediment supply

buried in ashes site formation processes at lapa do santo rockshelter east central brazil few archaeological sites in the americas contain high concentrations of human burials dating back to the early holocene the tropical karstic region of lagoa santa in central brazil state of minas gerais is one of the richest bioanthropological records available to study the behaviors and funerary practices of early holocene south americans with more than 200 skeletons found so far one of the key locations to examine the history of human settlement in lagoa santa is the site of lapa do santo a rockshelter known to contain the oldest rock art and the earliest evidence of funerary complexity in the continent in this geoarchaeological investigation we focus on the early holocene settlement at lapa do santo 7 9 12 7 cal kybp applying high resolution geoarchaeological techniques such as micromorphology organic petrology and ftir on both archaeological modern reference and experimental samples this is the first time that a micro contextual approach integrated with experimental geoarchaeology has been applied to study the formation of rockshelter deposits in a tropical setting our results show that the stratigraphic sequence formed under the dual influence of anthropogenic sedimentation through continuous combustion activities and geogenic sedimentation in the form of oxisol aggregates which fell from above the limestone cliff into the rockshelter intact hearths and remobilized combustion debris possibly hearth rake out are close to the graves suggesting repeated burning activities as part of the ritual behavior of early holocene south americans large amounts of ash are intermixed with heated and unheated oxisol aggregates heated termite mound fragments were also found mixed within the sediments post depositional alteration of the site includes limited bioturbation and localized low energy surface water and sub surface concentrations of moisture leading to precipitation of dense secondary carbonates the age inversions can be attributed to the human action of reworking the ashy sediments and not to post abandonment processes despite this the overall preservation of the sediments is good and most human burials can be considered to be in primary context

some exact solutions to the nonlinear shallow water wave equations these exact solutions correspond to time dependent motions in parabolic basins a characteristic feature is that the shoreline is not fixed it is free to move and must be determined as part of the solution in general the motion is oscillatory and has the appropriate small amplitude limit for the case in which the parabolic basin reduces to a flat plane there is a solution for a flood wave these solutions provide a valuable test for numerical models of inundating storm tides

liquid release tests in unsaturated fractured welded tuffs ii numerical modeling abstract we have carried out a numerical modeling study in conjunction with the in situ liquid release experiment described in salve et al j hydrol 257 2001 the experiment site is a highly fractured welded tuff accessed from the exploratory studies facility an underground laboratory in the unsaturated zone at yucca mountain nevada the experiment examines the effect of the rock matrix on liquid flow and transport that occurs primarily through the fracture network the purpose of the modeling is to aid in experimental design predict experimental results and study the physical processes accompanying liquid flow through unsaturated fractured welded tuff the model uses cubic elements arranged in a regular three dimensional grid to represent a 24 m3 block of fractured tuff high permeability fracture elements located deterministically preserve the connectivity of the fracture network which is crucial to its ability to conduct fluid because element thickness is much greater than fracture aperture fracture elements are assigned properties of a fracture continuum rather than of an individual fracture the fracture network is constructed using fracture geometry data taken from a fracture map of the walls and ceiling of the alcove adjacent to the field test site the network is then refined using the results of air permeability tests model results suggest that it may not be sufficient to conceptualize the fractured tuff as consisting of high permeability fractures embedded in a low permeability matrix the need to include a secondary fracture network with distinct characteristics from the network of larger mapped fractures is demonstrated by comparison to the liquid flow observed in the field

on fluid reserves and the production of superheated steam from fractured vapor dominated geothermal reservoirs vapor dominated geothermal reservoirs produce saturated or superheated steam and vertical pressure gradients are close to vapor static these observations have been generally accepted as providing conclusive evidence that the liquid saturation must be rather small 50 in order that liquid may be nearly immobile this conclusion ignores the crucial role of conductive heat transfer mechanisms in fractured reservoirs for vaporizing liquid flowing under two phase conditions we have developed a multiple interacting continuum method minc for numerically simulating two phase flow of a homogeneous fluid in a fractured porous medium application of this method to reservoir conditions representative of the geysers california and results from an analytical approximation show that for matrix permeability less than a critical value 2 5 to 5 microdarcies the mass flux of water from the matrix to the fractures will be continuously vaporized by heat transported due to conduction this gives rise to production of superheated steam even when the matrix has nearly full liquid saturation simple estimates also show that heat driven steam water counterflow can maintain a nearly vapor static vertical pressure profile in the presence of mobile liquid water in a reservoir with low vertical matrix permeability the implication of these findings is that the fluid reserves of vapor dominated geothermal reservoirs may be larger by a factor of about 2 than has generally been believed in the past

suspended sediment transport under seiches in circular and elliptical basins abstract enclosed bodies of water such as lakes or harbours often experience large scale oscillatory motions seiching as a simple model of such flow we investigate exact solutions to the shallow water equations which represent oscillatory flow in an elliptical basin with parabolic cross section specifically we consider two fundamental modes of oscillation in one of which the flow is parallel to the axis of the ellipse while in the other it is radial we obtain periodic analytical solutions for sediment transport including erosion deposition and advection under either mode of oscillation and present a method for obtaining such solutions for a more general class of flow fields and sediment transport models our solutions provide estimates of the morphodynamical importance of seiching motions and also reveal a characteristic pattern of net erosion and deposition associated with each mode in particular we find that a net flux of suspended sediment can be transported from the deeper to the shallower regions of the basin these transport patterns which are driven essentially by settling lag are highly robust to the formulation of the sediment transport relation and appear not to be substantially affected by the omission of frictional terms in the hydrodynamics they should thus provide considerable insight into sediment transport in less idealised systems

evaluating natural site formation processes in eolian dune sands a case study from the krmpotich folsom site killpecker dunes wyoming abstract eolian dune sands commonly contain archaeological material in both surface and buried contexts however because of the dynamic nature of dunes the original context of an archaeological site can be severely modified or destroyed as a result of post occupational geomorphic processes this paper examines a folsom occupation associated with a buried soil in the killpecker dunes in southwestern wyoming field and labortory data are compared to determine the likely scenario of natural site formation processes responsible for the current context of the archaeological assemblage two primary eolian stratigraphic units are present at the site and are separated by the buried artefact bearing soil radiocarbon and optical luminescence ages indicate that the folsom artefacts occur across a temporal hiatus and that the buried soil is late holocene in age sedimentological data indicate that the highest frequencies of artefacts by depth are associated with an erosional contact characterized by a concentration of coarse grained material thus the folsom assemblage appears to have been vertically displaced as a result of post occupational erosion and deflation this case study indicates that evaluating the context of an archaeological occupation in a dune setting is best carried out utilizing multiple lines of evidence derived from both field and laboratory work

modeling of thermally driven hydrological processes in partially saturated fractured rock 1 this paper is a review of the research that led to an in depth understanding of flow and transport processes under strong heat stimulation in fractured porous rock it first describes the anticipated multiple processes that come into play in a partially saturated fractured porous volcanic tuff geological formation when it is subject to a heat source such as that originating from the decay of radionuclides the rationale is then given for numerical modeling being a key element in the study of multiple processes that are coupled the paper outlines how the conceptualization and the numerical modeling of the problem evolved progressing from the simplified to the more realistic examples of numerical models are presented so as to illustrate the advancement and maturation of the research over the last 2 decades the most recent model applied to in situ field thermal tests is characterized by 1 incorporation of a full set of thermal hydrological processes into a numerical simulator 2 realistic representation of the field test geometry in three dimensions and 3 use of site specific characterization data for model inputs model predictions were carried out prior to initiation of data collection and the model results were compared to diverse sets of measurements the approach of close integration between modeling and field measurements has yielded a better understanding of how coupled thermal hydrological processes produce redistribution of moisture within the rock which affects local permeability values and subsequently the flow of liquid and gases the fluid flow in turn will change the temperature field we end with a note on future research opportunities specifically those incorporating chemical mechanical and microbiological factors into the study of thermal and hydrological processes

sand sheet dynamics and quaternary landscape evolution of the selima sand sheet southern egypt abstract the selima sand sheet occupies more than 120 000 km 2 of the hyperarid uninhabited darb el arba in desert centered at the border of egypt and sudan at latitude 22 n and is characterized by a featureless surface of lag granules and fine sand broken only by widely separated dune fields and giant ripples of varying height and wavelength monitoring of the largest of these chevron shaped ripples using repeat orbital images and field surveys indicates migration rates of 500 1000 m yr accompanied by 0 2 0 cm erosion or deposition of the youngest sand sheet stratigraphic units beneath this active surface several developmental stages of sand sheet sediments have undulatory upper contacts and varying degrees of pedogenic alteration the younger stages retain their horizontal lamination and have cracking patterns indicative of past wetter conditions while older stages have lost their laminar structure through pedogenesis historical remains in the desert as well as 14 c and uranium series dating indicate that the younger strata of the sand sheet have a very low accumulation rate despite the active movement of the surface the lower strata were extensively modified during mid and late pleistocene pluvials resulting in an initial undulatory surface that set the stage for later accumulation of sand sheet below these quaternary sediments lies irregular topography dissected by channels of mid tertiary drainage the selima sand sheet is neither the result of net aggradation nor degradation but results from inheritance of an initial fluvial landscape increasingly modified during climatic cycles wet periods led to local drainage and deposition while the increasingly severe arid periods of the late pleistocene and holocene resulted in deposition of the blanketing bimodal sediments of the sand sheet

laboratory experiments on heat driven two phase flows in natural and artificial rock fractures water flow in partially saturated fractures under thermal drive may lead to fast flow along preferential localized pathways and heat pipe conditions at the potential high level nuclear waste repository at yucca mountain water flowing in fast pathways may ultimately contact waste packages and transport radionuclides to the accessible environment sixteen experiments were conducted to visualize heat driven liquid flow in fracture models that included 1 assemblies of roughened glass plates 2 epoxy replicas of rock fractures and 3 a fractured specimen of topopah spring tuff continuous rivulet flow was observed for high liquid flow rates intermittent rivulet flow and drop flow for intermediate flow rates and film flow for lower flow rates and wide apertures heat pipe conditions vapor liquid counterflow with phase change were identified in five of the seven experiments in which spatially resolved thermal monitoring was performed but not when liquid vapor counterflow was hindered by very narrow apertures and when inadequate working fluid volume was used

the formation process of a paleoindian open air site in central brazil integrating lithic analysis radiocarbon and luminescence dating abstract lithic analysis radiocarbon dating and luminescence dating are applied to a stratified open air paleoindian site in central brazil lending some balance to a published record dominated by rock shelter sites most lithics are found in two discrete occupation layers lithics found outside these layers are attributed to post depositional movement of small flakes mainly upwards single grain luminescence dating on quartz grains also suggest post depositional movement both wind and bioturbation are suspected mechanisms the luminescence analysis does not provide precise depositional dates in this situation but does support such dates suggested by radiocarbon

lapa das boleiras rockshelter stratigraphy and formation processes at a paleoamerican site in central brazil abstract lapa das boleiras rockshelter a paleoamerican archaeological site in central brazil was intensely occupied by humans from 10 000 14c bp 11 8 cal kyr bp until approximately 7500 14c bp 8 4 cal kyr bp in this paper we present some interpretations about the formation processes operating on the site one of our main conclusions is that the bulk of accumulated sediments at the site is of anthropogenic origin they are constituted by volumetrically significant quantities of plant ash remains what is somewhat unexpectedly in view of prevailing models about the lifestyle of paleoamerican hunter gatherers in south america the evidence we discuss below is also consistent with paleoenvironmental data that suggest a dry period during the mid holocene in the region probably leading to a decrease in human occupation araujo a g m neves w pilo l b atui j p 2005 holocene dryness and human occupation in brazil during the archaic gap quaternary research 64 298 307 we surmise that both factors underpin a surprising reduction in sediment accumulation at the site during the mid holocene

1822 earthquake triggered homogenite in lake le bourget nw alps high resolution textural signatures of an earthquake induced historical homogenite layer are presented as well as its 3d distribution this homogeneous deposit is correlated with the ad 1822 event vii viii msk intensity the main historical earthquake of the french outer alps using 210pb dating and historical chronicles during this earthquake a violent lake water oscillation was reported seiche effect in the present study we discuss the influence of lake water oscillations during earthquake induced subaqueous slide through a pluridisciplinary analysis of subbottom sediments including high resolution seismic sidescan sonar and short gravity coring

post closure investigation of engineered test covers on acid generating waste rock at whistle mine ontario three engineered test covers were installed at the whistle mine test site near capreol ontario and monitored over 4 years each cover was a two layer system consisting of a 0 90 m noncompacted g

on fine sediment transport by long waves in the swash zone of a plane beach we calculate suspended sediment transport erosion and deposition under reflected long waves on a plane beach our method employs the shallow water equations and is based on the calculation of the concentration field in lagrangian coordinates this allows results to be obtained readily throughout the whole domain including the often troublesome shoreline region these results suggest that the tendency of wave dominated muddy shores to export sediment and erode over long time scales is not due to wave forcing at infragravity frequencies since the sediment transport under such waves is localized close to the shoreline and is principally directed shorewards they also provide easily reproduced test cases against which to validate the numerical methods used in more detailed studies of coastal sediment transport and morphodynamics

numerical model of water flow in a fractured basalt vadose zone box canyon site idaho a numerical model of a fractured basalt vadose zone has been developed on the basis of the conceptual model described by faybishenko et al his issue the model has been used to simulate a ponded infiltration test in order to investigate infiltration through partially saturated fractured basalt a key question addressed is how the fracture pattern geometry and fracture connectivity within a single basalt flow of the snake river plain basalt affect water infiltration the two dimensional numerical model extends from the ground surface to a perched water body 20 m below and uses an unconventional quasi deterministic approach with explicit but highly simplified representation of major fractures and other important hydrogeologic features the model adequately reproduces the majority of the field observation and provides insights into the infiltration process that cannot be obtained by data collection alone demonstrating its value as a component of field studies

an efficient solver for nearshore flows based on the waf method abstract we describe an efficient and robust flow solver for the integration of the classic nonlinear shallow water equations nswe on a beach of arbitrary topography on the basis of the shock capturing weighted average flux waf method a numerical code is implemented which employs a space splitting technique to integrate the nswe over a horizontally two dimensional domain 2dh special care is put in handling the moving shoreline and a new efficient formulation of the shoreline boundary conditions is presented this is based on the hydrodynamic equivalent of the cavitation condition used in gas dynamics model capabilities are illustrated by means of a number of tests both 1dh and 2dh these reveal that though primarily conceived for modelling nearshore hydrodynamics the solver can be successfully adopted even for studying the run up of large tsunami waves

a reactive transport model of neptunium migration from the potential repository at yucca mountain abstract characterization and performance assessment studies for the potential high level nuclear waste repository at yucca mountain have identified 2 3 7 np as a radionuclide of concern for the proposed repository to predict the migration of neptunium after a repository breach an understanding of the relevant hydrologic and geochemical processes is required the hydrologic flow in the unsaturated zone at yucca mountain is dependent on the infiltration rate the stratigraphy of the vadose zone and the heat generated by the decaying radioactive waste the geochemical processes that strongly affect 2 3 7 np migration include solubility limited release of 2 3 7 np from the near field environment aqueous speciation of neptunium into non sorbing carbonate hydroxy complexes and the sorbing npo 2 cation sorption of neptunium onto the zeolitic tuffs via an ion exchange mechanism and radioactive decay the finite element heat and mass transfer fehm code was used to investigate the coupled effects of chemical interactions and heat on neptunium transport from the potential repository to the water table the selective coupling method is introduced to solve these reactive transport problems the simulations indicate that in the absence of irreversible changes in the hydrologic and transport properties the heat pulse does not significantly affect the migration of neptunium as the time scale of heat pulse propagation is shorter than the time scales associated with neptunium release and migration water chemistry particularly ph calcium and sodium concentration significantly affect the retardation of neptunium by the zeolitic rocks between the repository and the water table

hydrologic mechanisms governing fluid flow in a partially saturated fractured porous medium in contrast to the saturated zone within which fluid moves rapidly along fractures the fractures with apertures large relative to the size of matrix pores will desaturate first during the drainage process and the bulk of fluid flow would be through interconnected pores in the matrix within a partially drained fracture the presence of a relatively continuous air phase will produce practically an infinite resistance to liquid flow in the direction parallel to the fracture the residual liquid will be held by capillary force in regions around fracture contact areas where the apertures are small normal to the fracture surfaces the drained portion of the fractures will reduce the effective area for liquid flow from one matrix block to another matrix block a general statistical theory is constructed for flow along the fracture and for flow between the matrix blocks to the fractures under partially saturated conditions results are obtained from an aperture distribution model for fracture saturation hydraulic conductivity and effective matrix fracture flow areas as functions of pressure the effects of distortion of flow paths by the air pockets are taken into account by a phase separation constriction factor in a generalized cubic law for fracture flow under a partially saturated condition the reduction of matrix fracture flow area is taken into account by summing the aperture distribution function to a saturation cutoff aperture which is inversely proportional to the suction head drainage from a column of fractured tuff is simulated using available parameters for the densely welded tuff of the topopah spring member at yucca mountain southern nevada the column is bounded by discrete vertical fractures and dissected by horizontal fractures with the fracture spacings determined by the frequencies and orientations of fractured cores the fraction of fracture surfaces with coatings is assumed to correspond to the fraction of in situ fracture contact area the characteristic curves for the matrix are based on laboratory measurements of tuff samples from the cases simulated for the fractured porous columns with discrete vertical and horizontal fractures and porous matrix blocks explicitly taken into account it is observed that the highly transient changes from fully saturated conditions to partially saturated conditions are extremely sensitive to the fracture properties however the quasi steady changes of the fluid flow of a partially saturated fractured porous system could be approximately simulated without taking the fractures into account

holocene eolian activation as a proxy for broad scale landscape change on the gila river indian community arizona abstract eolian sediments are common within the middle gila river valley southern arizona and reflect variability in eolian and fluvial processes during the late holocene this study focuses on deciphering the stratigraphic record of eolian deposition and associated luminescence dating of quartz extracts by single aliquot regeneration sar protocols stratigraphic assessment coupled with luminescence ages indicates that there are four broad eolian depositional events at ca 3145 220 yr 1950 1360 yr 800 100 yr and 690 315 yr this nascent chronology correlated with regional archeological evidence and paleoclimate proxy datasets leads to two general conclusions 1 loess deposits transverse dune formation and sand sheet deposition in the late holocene are probably linked to flow variability of the gila river though the last two events are concordant with regional megadroughts and 2 the stability of eolian landforms since the 19th century reflects the lack of eolian sediment supply during a period of fluvial incision resulting in entisol formation on dunes the prime catalyst of eolian activity during the late holocene is inferred to be sediment supply driven by climate periodicity and variable flow within the gila river catchment

a study of thermally induced convection near a high level nuclear waste repository in partially saturated fractured tuff we present simple estimates for velocities of buoyancy driven flow of liquid and gas phases near a hypothetical high level nuclear waste repository in partially saturated fractured tuff these estimates indicate that gas phase convection could take place with appreciable velocity of the order of 20 m year while liquid convection is expected to be very slow of the order of 0 1 mm year detailed numerical simulations using an effective continuum approximation to represent fracture effects confirm these estimates and demonstrate a sensitivity of gas convection to the strength of binary diffusion

preserving the palaeoenvironmental record in drylands bioturbation and its significance for luminescence derived chronologies luminescence osl dating has revolutionised the understanding of late pleistocene dryland activity however one of the key assumptions for this sort of palaeoenvironmental work is that sedimentary sequences have been preserved intact enabling their use as proxy indicators of past changes this relies on stabilisation or burial soon after deposition and a mechanism to prevent any subsequent re mobilisation as well as a dating technique osl especially at the single grain level can be used to gain an insight into post depositional processes that may distort or invalidate the palaeoenvironmental record of geological sediment sequences this paper explores the possible impact of bioturbation the movement of sediment by flora and fauna on luminescence derived chronologies from quaternary sedimentary deposits in texas and florida usa which have both independent radiocarbon chronologies and archaeological evidence these sites clearly illustrate the ability of bioturbation to rejuvenate ancient weathered sandy bedrock and or to alter depositional stratigraphies through the processes of exhumation and sub surface mixing of sediment the use of multiple osl replicate measurements is advocated as a strategy for checking for bioturbated sediment where significant osl heterogeneity is found caution should be taken with the derived osl ages and further measurements at the single grain level are recommended observations from the linear dunes of the kalahari show them to have no bedding structure and to have osl heterogeneity similar to that shown from the bioturbated texan and florida sites the kalahari linear dunes could have therefore undergone hitherto undetected post depositional sediment disturbance which would have implications for the established osl chronology for the region

numerical investigation of steady liquid water flow in a variably saturated fracture network numerical simulation was used to study steady liquid water movement in a 5 m by 5 m vertical section containing a hypothetical fracture network under conditions of variable saturation the fracture network was assumed to be embedded within an impermeable rock matrix three variations of a network were considered the mixed network consisted of two fracture sets a subvertical set containing five 125 m average aperture fractures and a subhorizontal set containing four 25 m average aperture fractures the other two networks had identical fracture orientation and contained either all 125 m or all 25 m average aperture fractures the tough simulator was used to calculate the total steady liquid water flux through the network the flux through individual fracture segments and the pressure head at each fracture segment a unit hydraulic gradient was imposed on the network by applying fixed pressure head boundaries ranging from 0 25 to 0 0 m of water of equal value to the top and bottom saturation and permeability versus pressure head relations for the two sets of fractures were determined with the vsfrac model which assumed that aperture was variable within an individual fracture results showed that the spatial distributions of pressure head and flux within the network as well as the location of the dominant pathways depended strongly on the prescribed boundary pressure head for the mixed network both pressure head and flux tended to become more spatially uniform when the boundary pressure head approached the pressure head at which the permeability thickness products of the large and small aperture fractures are equal the crossover pressure head these results imply that for systems similar to the one considered here interpretation of actual measurements of pressure head and flux may be quite complex and that representation of variably saturated fracture networks as an equivalent continuum may be more valid for some ranges in pressure head than for others equivalent permeability as a function of pressure head was calculated for the fracture network illustrating how information collected on individual fractures may be used to estimate the flow properties of rock at larger scales

archaeology of the pleistocene holocene boundary in brazil abstract after a short history of brazilian research about pleistocene peopling the late pleistocene early holocene changes of climate and resources are discussed claims for a very ancient presence of man before 13 000 bp itaborai toca da esperanca pedra furada and lapa vermelha sites are polemic because putative structures and artifacts could have been made by natural processes in central and northeastern brazil some sites dated between 14 000 and 10 000 bp provide clear evidence of human activities and coexistence with huge pleistocene mammals in a synthesis of our present knowledge about the 12 000 8000 bp period biological aspects of the lagoa santa people and their subsistence are discussed the main regional traditions are umbu with bifacial projectile points and humaita with heavy implements in the southern part of brazil in the central and northeastern regions the itaparica tradition is characterized by typical retouched flakes and limaces although projectile points are generally thought to be absent in the earliest levels of this tradition some have been found in boquete cave in amazonia some cultural aspects seem to have been the same as in central brazil

on the transport of suspended sediment by a swash event on a plane beach we develop solutions for the transport of suspended sediment by a single swash event following the collapse of a bore on a plane beach and we investigate the morphodynamical role that such transport may play although the intrinsic asymmetry between uprush and backwash velocities tends to encourage the export of sediment we find that swash events may be effective in distributing across the swash zone much or all of the sediment mobilised by bore collapse additionally settling lag effects may promote a weak onshore movement of sediment we quantify both effects in terms of the properties of the sediment and of the swash event and comment on the relationship between our findings and recent field studies of swash zone sediment transport

estimating spatially variable representative elementary scales in fractured architecture using hydraulic head observations 1 water resources within large scale fractured aquifers are typically evaluated using continuum models while any arbitrary scale of continuum can be imposed to represent fracture architecture using the representative elementary volume eliminates errors that result from estimating network connectivity in traditional theory representative elementary scales res are equal in magnitude and geometry throughout a domain and are normally determined using a structural indicator such as porosity or effective hydraulic conductivity we present a fluid based methodology analyzing scale dependent energy variation to estimate res using relatively low cost readily available hydraulic head data hydraulic head predictions of res hyres reveal a spatial variation in elementary scale consistent with the flow field and fracture architecture porosity predictions of res porres incorporate the structural effect of disconnected fracture regions but do not account for fluid behavior res estimated from hydraulic conductivity kres are sensitive to fracture connectivity which controls fluid movement but are difficult to quantify because of scale and spatial variability hyres may be the superior approach for evaluating water resources because it is sensitive to fracture connectivity and avoids complications with scale and spatially dependent averaging our method is sensitive to fracture density clustering connectivity and flow direction but is insensitive to the magnitude of hydraulic gradient hyres is a novel approach to estimating spatially variable res that improves water resource evaluation and flow characterization in fractured aquifers

late quaternary environmental and climatic changes in central brazil paleoenvironmental changes dating back to 30 000 yr b p documented in a pollen record from central brazil lat 19 s permit the reconstruction of climatic changes related to shifts of the antarctic polar fronts the paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution taking into account present day climatic parameters at 30 000 yr b p the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest from 17 000 to 14 000 yr b p the climate was drier although tree pollen percentages were relatively high after 12 000 yr b p araucaria forest elements increased suggesting a moister and cooler climate the araucaria forest disappeared during a short interval between 11 000 and 10 000 yr b p this could be related to the younger dryas event at the beginning of the holocene the climate became cool and moist again as indicated by the reexpansion of the araucaria forest the latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr b p at 5000 yr b p an arid interval was followed by the expansion of mesophytic semideciduous forest elements

a new estimation of equivalent matrix block sizes in fractured media with two phase flow applications in dual porosity models single and multiphase flows in fractured porous media at the scale of natural reservoirs are often handled by resorting to homogenized models that avoid the heavy computations associated with a complete discretization of both fractures and matrix blocks for example the two overlapping continua fractures and matrix of a dual porosity system are coupled by way of fluid flux exchanges that deeply condition flow at the large scale this characteristic is a key to realistic flow simulations especially for multiphase flow as capillary forces and contrasts of fluid mobility compete in the extraction of a fluid from a capacitive matrix then conveyed through the fractures the exchange rate between fractures and matrix is conditioned by the so called mean matrix block size which can be viewed as the size of a single matrix block neighboring a single fracture within a mesh of a dual porosity model we propose a new evaluation of this matrix block size based on the analysis of discrete fracture networks the fundaments rely upon establishing at the scale of a fractured block the equivalence between the actual fracture network and a warren and root network only made of three regularly spaced fracture families parallel to the facets of the fractured block the resulting matrix block sizes are then compared via geometrical considerations and two phase flow simulations to the few other available methods it is shown that the new method is stable in the sense it provides accurate sizes irrespective of the type of fracture network investigated the method also results in two phase flow simulations from dual porosity models very close to that from references calculated in finely discretized networks finally calculations of matrix block sizes by this new technique reveal very rapid which opens the way to cumbersome applications such as preconditioning a dual porosity approach applied to regional fractured reservoirs

estimating liquid fluxes in thermally perturbed fractured rock using measured temperature profiles a new temperature profile method was recently developed for analyzing perturbed flow conditions in superheated porous media the method uses high resolution temperature data to estimate the magnitude of the heat driven liquid and gas fluxes that form as a result of boiling condensation and recirculation of pore water in this paper we evaluate the applicability of this new method to the more complex flow behavior in fractured formations with porous rock matrix in such formations with their intrinsic heterogeneity the porous but low permeable matrix provides most of the mass and heat storage capacity and dominates conductive heat transfer fractures on the other hand offer highly effective conduits for gas and liquid flow thereby generating significant convective heat transfer after establishing the accuracy of the temperature profile method for fractured porous formations we apply the method in analyzing the perturbed flow conditions in a large scale underground heater test conducted in unsaturated fractured porous tuff the flux estimates for this test indicate a significant reflux of water near the heat source on the order of a few hundred millimeter per year much larger than the ambient percolation flux of only a few millimeter per year

a semianalytical solution for steady infiltration in unsaturated fractured rock a semi analytical solution is developed for one dimensional steady infiltration in unsaturated fractured rock the differential form of the mass conservation equation is integrated to yield an analytical expression relating elevation to a function of capillary pressure and relative permeability of the fracture and rock matrix constitutive relationships for unsaturated flow in this analysis are taken from van genuchten 1980 and mualem 1976 but alternative relations can also be implemented in the integral solution expressions are presented for the liquid saturations and pore velocities in the fracture matrix and effective continuum materials as a function of capillary pressure and elevation results of the analytical solution are applied to examples of infiltration in fractured rock consisting of both homogeneous and composite layered domains the analytical results are also compared to numerical simulations to demonstrate the use of the analytical solution as a benchmarking tool to address computational issues such as grid refinement

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 2 effective continuum approximation this paper presents an effective continuum approximation for modeling of fluid and heat flow in fractured porous media the approximation is based on the thermohydrologic behavior observed in detailed simulations with explicit consideration of fracture effects see the companion paper part 1 the crucial concept in the development of an effective continuum approximation is the notion of local thermodynamic equilibrium between rock matrix and fractures where applicable it provides a substantial simplification of the description of fluid and heat flow in fractured porous media we derive formulas for effective continuum characteristic curves relative permeabilities and capillary pressures in terms of the properties of fracture and matrix continua respectively numerical simulations demonstrate that under favorable conditions the effective continuum approximation closely matches predictions obtained from an explicit modeling of fracture effects it is also demonstrated that the approximation breaks down under unfavorable conditions very tight rock matrix a simple criterion for the applicability of an effective continuum approximation is derived from consideration of diffusive processes a quantitative evaluation shows the criterion to be consistent with results of our numerical simulations

a probabilistic analysis of episodic preferential flow into superheated fractured rock the amount of water seeping into waste emplacement tunnels is important for the long term performance of the proposed geologic nuclear waste repository at yucca mountain nevada the repository site is located in thick partially saturated fractured tuff that will be heated to above boiling temperatures as a result of heat generation from the decay of nuclear waste since water infiltrating down towards the repository will be subject to vigorous boiling for a significant time period the superheated zone i e rock temperature above the boiling point of water may form an effective vaporization barrier that reduces the possibility of water arrival at emplacement drifts in this paper we analyze the behavior of episodic preferential flow events that penetrate down into the hot fractured rock zone and evaluate the impact of such flow behavior on the effectiveness of the vaporization barrier the characteristic features of episodic preferential flow are estimated from laboratory experiments and described by appropriate probability distributions a semi analytical solution is utilized to determine the complex flow processes in the hot rock environment the solution is applied at several discrete times after emplacement in order to cover the time period of strongly elevated temperatures at yucca mountain

penetration of liquid fingers into superheated fractured rock 1 water infiltrating down a fracture in unsaturated rock experiences complex fluid flow and heat transfer phenomena when entering above boiling rock temperature regions such conditions are expected for example after emplacement of heat generating nuclear waste in underground repositories a new efficient semianalytical method is proposed in this paper that simulates the flow processes of infiltration events subject to vigorous boiling from the adjacent hot rock it is assumed that liquid flow forms in localized preferential flow paths and that infiltration events are typically short in duration but large in magnitude relative to the average net infiltration the new solution scheme is applied to several test cases studying sensitivity to a variety of input parameters sample simulations are performed for conditions representative of the potential nuclear waste repository at yucca mountain nevada a characteristic parameter is introduced that provides a quick estimate of the relative significance of boiling at a given location of interest

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 1 simulation studies with explicit consideration of fracture effects we have performed modeling studies on the simultaneous transport of heat liquid water vapor and air in partially saturated fractured porous rock formation parameters were chosen as representative of the potential nuclear waste repository site in the topopah spring unit of the yucca mountain tuffs the presence of fractures makes the transport problem very complex both in terms of flow geometry and physics the numerical simulator used for our flow calculations takes into account most of the physical effects believed to be important in multiphase fluid and heat flow it has provisions for handling the extreme nonlinearities that arise in phase transitions component disappearances and capillary discontinuities at fracture faces we model a region around an infinite linear string of nuclear waste canisters taking into account both the discrete fractures and the porous matrix thermohydrologic conditions in the vicinity of the waste packages are found to depend strongly on relative permeability and capillary pressure characteristics of the fractures which are unknown at the present time if liquid held on the rough walls of drained fractures is assumed to be mobile strong heat pipe effects are predicted under these conditions the host rock will remain in two phase conditions right up to the emplacement hole and formation temperatures will peak near 100 c if it is assumed that liquid cannot move along drained fractures the region surrounding the waste packages is predicted to dry up and formation temperatures will rise beyond 200 c a substantial fraction of waste heat can be removed if emplacement holes are left open and ventilated as opposed to backfilled and sealed emplacement conditions comparing our model predictions with observations from in situ heater experiments reported by zimmerman and coworkers some intriguing similarities are noted however for a quantitative evaluation additional carefully controlled laboratory and field experiments will be needed

swash overtopping a truncated plane beach swash on a plane beach is modelled by using a solution of the shallow water equations due to shen meyer 1963 the equations are used in a form appropriate for a plane at a finite angle to the horizontal the beach is cut off at a level below that of the maximum run up and the water is taken to fall freely over the end of the beach an explicit solution is found which permits evaluation of the overtopping flow and total volume for one swash event