spreading and convective dissolution of carbon dioxide in vertically confined horizontal aquifers injection of carbon dioxide co2 into saline aquifers is a promising tool for reducing anthropogenic co2 emissions at reservoir conditions the injected co2 is buoyant relative to the ambient groundwater the buoyant plume of co2 rises toward the top of the aquifer and spreads laterally as a gravity current presenting the risk of leakage into shallower formations via a fracture or fault in contrast the mixture that forms as the co2 dissolves into the ambient water is denser than the water and sinks driving a convective process that enhances co2dissolution and promotes stable long term storage motivated by this problem we study convective dissolution from a buoyant gravity current as it spreads along the top of a vertically confined horizontal aquifer we conduct laboratory experiments with analog fluids water and a mixture of methanol and ethylene glycol and compare the experimental results with simple theoretical models since the aquifer has a finite thickness dissolved buoyant fluid accumulates along the bottom of the aquifer and this mixture spreads laterally as a dense gravity current when dissolved buoyant fluid accumulates slowly our experiments show that the spreading of the buoyant current is characterized by a parabola like advance and retreat of its leading edge when dissolved buoyant fluid accumulates quickly the retreat of the leading edge slows as further dissolution is controlled by the slumping of the dense gravity current we show that simple theoretical models predict this behavior in both limits where the accumulation of dissolved buoyant fluid is either negligible or dominant finally we apply one of these models to a plume of co2 in a saline aquifer we show that the accumulation of dissolved co2 in the water can increase the maximum extent of the co2 plume by several fold and the lifetime of the co2 plume by several orders of magnitude

filling box flows in porous media we report upon a theoretical and experimental investigation of a porous medium filling box flow by specifically examining the details of the laminar descending plume and its outflow in a control volume having an impermeable bottom boundary and sidewalls the plume outflow initially comprises a pair of oppositely directed gravity currents the gravity currents propagate horizontally until they reach the lateral sidewalls at y pm l the flow then becomes of filling box type with a vertically ascending first front separating discharged plume fluid below from ambient fluid above the flow details are described analytically by first deriving a new similarity solution for darcy plumes with mathit pe o 1 where mathit pe is the peclet number from the similarity solution so obtained we then derive expressions for the plume volume flux and mean reduced gravity as functions of the vertical distance from the source regarding the plume outflow a similarity solution adopted from huppert woods j fluid mech vol 292 1995 pp 55 69 describes the height and front speed of the gravity currents whereas a semi implicit finite difference scheme is used to predict the first front elevation versus time and horizontal distance as with high reynolds number filling box flows that studied here is an example of a coupled problem the gravity current source conditions are prescribed by the plume volume flux and mean reduced gravity conversely discharged plume fluid may be re entrained into the plume be it soon or long after reaching the bottom impermeable boundary to corroborate our model predictions analogue laboratory experiments are performed with fresh water and salt water as the working fluids our experiments consider as independent variables the porous medium bead diameter and the plume source volume flux and reduced gravity predictions for the gravity current front position and height compare favourably against analogue measured data good agreement is likewise noted when considering either the mean elevation or the profile of the first front results from this study may be adopted in modelling geological plumes for example our equations can be used to predict the time required for discharged plume fluid to return to the point of injection in the case of aquifers closed on the sides and below by impermeable boundaries

the bi azimuthal scattering distribution of an abyssal hill high resolution bistatic images of a typical abyssal hill on the western flank of the mid atlantic ridge are made with a low frequency towed array system operating remotely at 1 2 convergence zone 33 3 km stand off comparison with modeled images generated from high resolution supporting bathymetry sampled at 5 m intervals roughly the wavelength scale reveals that steep scarps return the strongest echoes because they project the largest area along the acoustic path from the source to receiver prominent returns deterministically image scarp morphology when the cross range axis of the system s resolution footprint runs along the scarp axis statistical fluctuations inherent in the scattered field prevent the system from distinguishing smaller scale anomalies on the scarps such as canyons and gullies 100 200 m scale that would otherwise be resolvable in range in certain bistatic geometries the mean bi azimuthal scattering distributions of the two major scarps on the abyssal hill are identical a

on the use of seismic data to monitor the injection of co2 into a layered aquifer abstract one method to monitor the migration of co2 through a confined layered aquifer is to use time lapse seismic reflection data we examine how such information may be combined with a flow model for a co2 plume spreading through a water saturated aquifer to provide constraints on the migration of a plume of injected co2 we focus on the estimation of the partitioning of the injected flux between the different layers in a multi layer geological formation and on estimation of the permeability of each layer since there is a minimum depth of the injected co2 which is detectable seismically we show that even in a one layer formation the model predicts two different possible permeabilities for the formation corresponding to a fast pressure driven flow and a slower buoyancy controlled flow these two estimates of the permeability are sensitive to changes in the seismic detection threshold if there is additional data on the bottom hole well pressure we can distinguish between the solutions in a multi layer system supplied from a single well the non uniqueness in the inversion process leads to uncertainty in both the partitioning of the flux between the layers and the permeability of the different layers in the formation the model constraints lead to a relatively small range of possible distributions of the flux but if there is a lack of information about the relative pressure in the different layers near the well there is a much larger range of possible values for the permeability of each layer we develop some simple bounds on the problem by considering the case in which the near well pressure difference between the layers is related to either the vertical hydrostatic or the vertical co2 static pressure difference we examine the implications of the technique for interpreting the historic data set relating to co2 injection at the sleipner field north sea in which there are nine distinct layers in the formation this leads to estimates for the possible flux partitioning between the layers and also some constraints on the possible range of effective permeability in each layer estimates of the partitioning of the flux can inform estimates of the efficiency of co2 injection in the different layers however the uncertainty in the estimate of the effective permeability leads to uncertainty in estimates of the propagation speed of the flow in each layer and hence assessments of the hazards of leakage and of the rate of capillary trapping or dissolution of co2 following injection

co2 percolation experiment through chlorite zeolite rich sandstone pretty hill formation otway basin australia underground co2 sequestration is highly recommended as an effective means of significantly decreasing co2 concentration in the atmosphere mineral storage is the more secure technology but requires the presence of high concentration of divalent cations in the pore fluid results from co2 percolation experiments through chlorite zeolite rich sandstone samples from the pretty hill formation otway basin australia are presented the dissolution of the laumontite 7 wt and chamosite 7 wt are the potential sources of calcium iron and magnesium required for carbonate precipitation the percolation experiment was setup to reproduce at laboratory scale the in situ temperature and pressure conditions t 95 degrees c and p 10 mpa the fluid injected at constant flow rate is a rock equilibrated brine subsequently enriched in co2 up to partial pressure of 6 mpa we observe feldspars laumontite and chamosite dissolution kaolinite and silica precipitation and a noticeable sink of co2 in the sample which is attributed to the precipitation of both amorphous carbon due to the reduction of co2 and fe rich carbonate permeability decreases of about one order of magnitude due to the localization of the kaolinite precipitation in the main flow paths while porosity increases the high reactivity of this sandstone makes this reservoir a valuable target for co2 mineralization but the associated permeability decrease may limit the injection rate and the spreading of the co2 in the reservoir

time lapse walkaway vertical seismic profile monitoring for co2 injection at the sacroc enhanced oil recovery field a case study abstractgeologic carbon storage involves large scale injections of carbon dioxide into underground geologic formations changes in reservoir properties resulting from co2 injection and migration can be characterized using monitoring methods with time lapse seismic data to achieve economical monitoring vertical seismic profile vsp data are often acquired to survey the local injection area we investigated the capability of walkaway vsp monitoring for co2 injection into an enhanced oil recovery field at sacroc west texas vsp data sets were acquired in 2008 and 2009 and co2 injection took place after the first data acquisition because the receivers were located above the injection zone only reflection data contain the information from the reservoir qualitative comparison between reverse time migration images at different times revealed vertical shifts of the reflectors center indicating the presence of velocity changes we examined two methods to quantify the changes in velocity standard full wa

effects of peat on the shapes of alluvial channels examples from the cumberland marshes saskatchewan canada abstract an avulsion of the lower saskatchewan river in the 1870s inundated a large segment of peat covered floodplain that subsequently has become aggraded with a broad 500 km 2 belt of alluvium deposited by the redirected flow routing of water and sediment discharge through the avulsion affected area has been accomplished mainly by networks of sandy bedded anastomosed channels that have formed evolved and abandoned as the alluvial belt prograded down the floodplain slope these processes continue today though at a much reduced rate new channels formed by crevassing and basinward extension of distributaries are initially small and shallow with bottom elevations situated within the avulsive alluvium but above the pre avulsion peat floodplain surface subsequent enlargement and downcutting of many of these channels eventually uncovers the underlying peat layer whose resistance to erosion exerts significant influence on cross sectional shape and further channel development peat floored channels tend to have rectangular cross sections high ratios of average to maximum depth d d max and a large range of width to depth ratios if the channel continues to enlarge the peat layer eventually becomes breached commonly leading to temporarily irregular cross sections caused by localized scouring at the breach sites eventually the peat layer is completely eroded from the channel floor by undercutting and slumping after which channel shape becomes governed mainly by other perimeter characteristics channels unaffected by peat either before the peat layer is encountered during early channel development or after it is entirely removed tend to have low width depth ratios and a large range of d d max values

a study of caprock hydromechanical changes associated with co2 injection into a brine formation a numerical study of hydromechanical changes during a deep underground injection of supercritical co2 in a hypothetical brine aquifer caprock system is conducted the injection process is simulated using a newly developed computer model for multi phase analysis of co2 and brine water flow coupled with heat transfer and rock deformations in this modeling co2 is injected at a constant rate over a 10 year period at a depth of 1 300 1 500 m the injection zone is overlain by a 100 m thick caprock located at 1 200 1 300 m which in one of the studied cases is intersected by a vertical fault the hydraulic mechanical as well as hydromechanical responses caused by the injection are studied this includes the spread of the co2 plume effective stress changes ground surface uplift stress induced permeability changes and mechanical failure analysis the analysis shows that most hydromechanical changes are induced in the lower part of the caprock near its contact with the injection zone whereas the sealing mechanism of the upper part may remain intact despite an injection pressure close to the lithostratic stress value

gravity currents with residual trapping motivated by geological carbon dioxide co 2 storage we present a vertical equilibrium sharp interface model for the migration of immiscible gravity currents with constant residual trapping in a two dimensional confined aquifer the residual acts as a loss term that reduces the current volume continuously in the limit of a horizontal aquifer the interface shape is self similar at early and at late times the spreading of the current and the decay of its volume are governed by power laws at early times the exponent of the scaling law is independent of the residual but at late times it decreases with increasing loss owing to the self similar nature of the current the volume does not become zero and the current continues to spread in the hyperbolic limit the leading edge of the current is given by a rarefaction and the trailing edge by a shock in the presence of residual trapping the current volume is reduced to zero in finite time expressions for the up dip migration distance and the final migration time are obtained comparison with numerical results shows that the hyperbolic limit is a good approximation for currents with large mobility ratios even far from the hyperbolic limit in gently sloping aquifers the current evolution is divided into an initial near parabolic stage with power law decrease of volume and a later near hyperbolic stage characterized by a rapid decay of the plume volume our results suggest that the efficient residual trapping in dipping aquifers may allow co 2 storage in aquifers lacking structural closure if co 2 is injected far enough from the outcrop of the aquifer

modeling leakage pathways in subsurface formations fluid drainage through multiple fractures in porous media insights from hele shaw cell experiments abstract arresting the recent observed warming of the earth s climate is a challenge requiring the reduction of anthropogenic emissions of carbon dioxide one option for reducing emissions into the atmosphere is to capture and sequester the released carbon dioxide in geological formations however potential geological storage first requires a risk assessment of carbon dioxide escaping to overlying layers and back to the atmosphere through leakage pathways in the formation this in turn requires an understanding of fluid flow through the leakage pathways in this study the effect of leakage pathways on the flow of a gravity current was investigated using an analogue system a hele shaw cell fluid was introduced through the top edge of the cell and flowed out through one or more holes in its impermeable base the height of the accumulated fluid above the base of the cell at various points along its length and the outflow rate of fluid through the holes was measured this measurement was conducted with varying conditions of the location number and strength of source as well as the location and number of holes at steady state the fluid motion was in accordance with darcy s law for horizontal flow in a long thin current in another set of experiments in which inflow was stopped and the fluid was allowed to drain out of a single open hole the outflow rate was in accordance with darcy s law for one dimensional flow in the vertical direction until the fluid height above the hole fell below a certain limit this threshold height was found to be 1 3 cm which was similar in magnitude to the length of the hole a time series of photographs tracked the flow of colored dye the photographs demonstrated that at steady state the fluid traveled for some distance beyond the hole before draining through it this implies that contaminants may be transported in a formation even beyond an outlet before finally draining out through it the photographs also documented the shape of the interface between the newly introduced dye and the ambient fluid in the cell these shapes were found to be different in a cell placed horizontally versus one placed on an incline suggesting that the geometry and flow conditions in a formation affecting the transport of an injected fluid these findings may be used as a basis for predicting behavior of a fluid injected into a fractured formation in the subsurface

deterministic reverberation from ocean ridges the deterministic relationship between low frequency reverberation and detailed geomorphology is documented for wide area insonifications of the western mid atlantic ridge charted reverberation registers precisely with extended ridges and has a high correlation with negative transmission loss confirming previous analysis with lower resolution data j acoust soc am 95 1865 1881 1993 for a given ridge prominent returns come from steep escarpments and cliffs that face the bistatic source and receiving arrays this was hypothesized in the above reference but could not be proven without the higher resolution waveforms and more sophisticated charting procedures of the present analysis monostatic and bistatic returns from the same lineated ridge at 1 2 11 2 and 21 2 convergence zone ranges are used to thoroughly document the registration with steep scarps a decrease in resolution of the scattering site is also documented for increasing measurement range ambiguity from the horizontal receiving array is resolved by two independent methods that show close agreement for prominent returns the first is an environmental symmetry breaking esb technique that requires detailed knowledge of bathymetry to be incorporated into a range dependent propagation model the second is a global inversion of reverberation charts obtained from differing receiving array locations and orientations the global inversion requires no a priori environmental information and has not been previously applied to field data

elevation adjustments of paired natural levees during flooding of the saskatchewan river natural levees control the exchange of water between an alluvial channel and its floodplain but little is known about the spatial distribution and evolution of levee heights the summer 2005 flood of the saskatchewan river cumberland marshes east central saskatchewan inundated large areas of floodplain for up to seven weeks forming prominent new deposits on natural levees along main stem channels measurements of flood deposit thickness and crest heights of 61 levee pairs show that the thickest deposits occur on the lower pre flood levee in 80 of the sites though no clear relationship exists between deposit thickness and magnitude of height difference only 16 of the pairs displayed thicker deposits on the higher levee half of which occurred at sites where relatively clear floodbasin waters re entered turbid channels during general flooding difference in crest elevation e between paired levees is approximately log normally distributed both before and after the flood though with different mean values supplemental observations from tank experiments indicate that during near bankfull flows temporally and spatially variable deposition and erosion occur on levees due to backwater effects associated with nearby channel bars and irregular rises of the channel bed forced by channel extension during floods preferential deposition in lows tends to even out crest heights copyright 2009 john wiley sons ltd

effects of peat compaction on delta evolution a review on processes responses measuring and modeling abstract peat is most compressible of all natural soils compaction of peat layers potentially leads to substantial amounts of land subsidence peat is common in many distal parts of holocene deltas which are often densely populated it is known that land subsidence due to peat compaction may have serious societal implications in such areas as it may cause damage to construction works and lead to land inundation effects of peat compaction on the natural evolution of deltas are however poorly understood whereas this might be an important control on delta evolution at both local and regional scales the main objective of this paper is to review current knowledge concerning the peat compaction process and its effect on delta evolution in holocene settings and to identify gaps in this knowledge an overview is given regarding 1 the compaction process 2 presumed and potential effects of peat compaction on delta evolution 3 field methods to quantify peat compaction and 4 numerical models to calculate the amount and rate of peat compaction peat compaction and formation influence channel belt elevation channel belt geometry and channel belt configuration last mentioned aspect mostly concerns the influence of peat compaction on avulsion which is one of the most important processes controlling delta evolution interactions between peat compaction peat formation and avulsion have seldom been studied and remain unclear partly because factors such as peat type organic matter content sediment sequence composition and groundwater table fluctuation are so far not taken into account peat compaction and formation potentially influence avulsion as 1 a decrease in accommodation space created by peat compaction underneath a channel causes superelevation and or an increase in lateral migration 2 the high cohesiveness of peat banks inhibits lateral migration which increases bed aggradation decreases sediment transport capacity and hence increases crevassing frequencies which possibly evolve into an avulsion although the low regional gradient in peatlands will hinder this and 3 peat compaction and oxidation in flood basins following groundwater table lowering leads to relief amplification of channel belts at delta scale variations in compaction rates might stimulate the occurrence of nodal avulsions to quantify effects of peat compaction on delta evolution and to determine the relative importance of different factors involved field research should be combined with numerical models describing peat compaction and formation the model should be validated and calibrated with field data

spatial and temporal evolution of injected co2 at the sleipner field north sea time lapse three dimensional 3d seismic surveys have imaged an accumulation of injected co 2 adjacent to the sleipner field in the north sea basin the changing pattern of reflectivity suggests that co 2 accumulates within a series of interbedded sandstones and mudstones beneath a thick caprock of mudstone nine reflective horizons within the reservoir have been mapped on six surveys acquired between 1999 and 2008 these horizons have roughly elliptical planforms with eccentricities ranging between two and four in the top half of the reservoir horizon areas grow linearly with time in the bottom half horizon areas initially grow linearly for about eight years and then progressively shrink the central portions of deeper reflective horizons dim with time amplitude analysis of horizons above within and below the reservoir show that this dimming is not solely caused by acoustic attenuation instead it is partly attributable to co 2 migration and or co 2 dissemination which reduce the impedance contrast between sandstone and mudstone layers growth characteristics and permeability constraints suggest that each horizon grows by lateral spreading of a gravity current this model is corroborated by the temporal pattern of horizon velocity pushdown beneath the reservoir horizon shrinkage may occur if the distal edge of a co 2 filled layer penetrates the overlying mudstone if the buoyant plume draws co 2 upward or if the effective permeability of deeper mudstone layers increases once interstitial brine has been expelled topographic control is evident at later times and produces elliptical planforms especially toward the top of the reservoir our results show that quantitative mapping and analysis of time lapse seismic surveys yield fluid dynamical insights which are testable shedding light on the general problem of co 2 sequestration

controls on the dissolution of co2 plumes in structural traps in deep saline aquifers 1 sequestration of carbon dioxide in deep saline aquifers has been proposed and investigated as a viable solution to help mitigate carbon emissions from fossil fuels much research has been directed at understanding the transitions of supercritical co2 from being a mobile fluid phase to being trapped by capillarity or dissolved in groundwater such transitions lead to a reduction in mobility of co2 and hence in the risk of leakage to the surface following injection buoyant plumes of co2 migrate updip towards structural traps in the geological strata however some of this co2 may be capillary trapped in pore spaces or dissolved in groundwater en route since co2 saturated groundwater only has a small co2 concentration the dissolution of any large structurally trapped plumes of co2 may be controlled by the availability of unsaturated groundwater in an aquifer of finite vertical extent this may be rate limited by a combination of i the background hydrological flow coupled with ii the slow lateral exchange of relatively dense co2saturated groundwater with unsaturated groundwater in an inclined aquifer this may be controlled by the slow along aquifer component of gravity structurally trapped plumes of co2 may therefore persist for many thousands of years and since they are potentially highly mobile may represent an important contribution to the long term risks associated with co2 sequestration at particular sites

modelling carbon dioxide accumulation at sleipner implications for underground carbon storage an analytical solution to the equations describing the flow of a buoyant fluid released into a porous medium below a horizontal impermeable boundary is used to model the growth of co2 accumulations beneath thin mudstone beds in the utsira sand reservoir at sleipner in the north sea here supercritical co2 has been injected at a rate of 1 mt yr since 1996 and imaged by time lapse seismic data in 1999 2001 and 2002 the co2 rises as a narrow plume and is partially trapped by a number of thin mudstones before reaching the caprock to the reservoir the radii of the individual layers of trapped co2 increase as the square root of time since initiation as predicted by the modelling for constant input flux however apparent negative initiation times for horizons low in the reservoir suggests that net input fluxes for these layers have decreased with time most probably as the spreading layers have increased their leakage rates accumulation of co2 in the layers higher in the reservoir was initiated up to 3 yr after injection started modelling of the thickness profiles across three of the higher layers suggests that their net input fluxes have increased with time the observation that the central thicknesses of the deeper layers have remained approximately constant or have slightly decreased since first imaged in 1999 is consistent with the model predictions that the central thickness is directly proportional to net input flux however estimates of the permeability of the reservoir from the rate of increase of the radii of the co2 accumulations are an order of magnitude less than measured permeabilities on the reservoir sandstone permeabilities estimated from the modelling of layer thickness changes scatter in the same range these discrepancies may arise from 1 approximations in the model not being valid 2 the measured permeabilities not being representative of the permeability for two phase flow on the scale of the reservoir or considered less likely 3 that much less co2 is being stored in the imaged co2 accumulations than estimated from the seismic reflection profiles the most probable cause of the discrepancy is that the relative permeability for the co2 phase is significantly reduced at lower co2 saturations

an inverse method for estimating thickness and volume with time of a thin co2 filled layer at the sleipner field north sea migration of co 2 through storage reservoirs can be monitored using time lapse seismic re ection surveys at the sleipner field injected co 2 is distributed throughout nine layers within the reservoir these layers are too thin to be seismically resolvable by direct measurement of the separation between re ections from the top and bottom of each layer here we develop and apply an inverse method for measuring thick ness changes of the shallowest layer our approach combines di erences in traveltime down to a speci c re ection together with amplitude measurements to determine layer thicknesses from time lapse surveys a series of synthetic forward models were used to test the robustness of our inverse approach and to quantify uncertainties in the absence of ambient noise this approach can unambiguously resolve layer thickness if a realistic ambient noise distribution is included layer thicknesses of 1 6 m are accurately retrieved with an uncertainty of 0 5 m we used this approach to generate a thickness map of the shallowest layer the delity of this result was tested using measurements of layer thickness determined from the 2010 broadband seismic survey the calculated volume of co 2 within the shallowest layer increases at a rate that is quadratic in time despite an approximately constant injection rate into the base of the reser voir this result is consistent with a diminished growth rate of the areal extent of underlying layers finally the relationship between caprock topography and layer thickness is explored and potential migration pathways that charge this layer are identi ed

the effect of a fissure on storage in a porous medium we consider the two dimensional buoyancy driven flow of a fluid injected into a saturated semi infinite porous medium bounded by a horizontal barrier in which a single line sink representing a fissure some distance from the point of injection allows leakage of buoyant fluid our studies are motivated by the geological sequestration of carbon dioxide co2 and the possibility that fissures in the cap rock may compromise the safe long term storage of co2 a theoretical model is presented that accounts for leakage through the fissure using two parameters which characterize leakage driven both by the hydrostatic pressure within the overriding fluid and by the buoyancy of the fluid within the fissure we determine numerical solutions for the evolution of both the gravity current within the porous medium and the volume of fluid that has escaped through the fissure as a function of time a quantity of considerable practical interest is the efficiency of storage which we define as the amount of fluid remaining in the porous medium relative to the amount injected this efficiency scales like t 1 2 at late times indicating that the efficiency of storage ultimately tends to zero we confirm the results of our model by comparison with an analogue laboratory experiment and discuss the implications of our two dimensional model of leakage from a fissure for the geological sequestration of co2

modelling carbon dioxide sequestration in layered strata motivated by the geological sequestration of carbon dioxide co2 we study the propagation of gravity currents in a porous medium bounded by a thin layer of much lower permeability we formulate a model for drainage assuming that the fluid remains simply connected throughout using this model we examine the propagation of both two dimensional and axisymmetric currents numerically we find that for the fixed flux situation solutions approach a steady state which is described analytically the approach to this final solution depends on both the permeability contrast and thickness of the thin layer and in many cases the current first overshoots before relaxing back to its ultimate steady state finally we examine propagation along multiple thin lower permeability layers as a reduced order model of the plume of co2 currently being injected at sleipner in the north sea

using image warping for time lapse image domain wavefield tomography abstracttime lapse seismic data are widely used for monitoring subsurface changes a quantitative assessment of how reservoir properties have changed allows for better interpretation of fluid substitution and fluid migration during processes such as oil and gas production and carbon sequestration full waveform inversion fwi has been proposed as a way to retrieve quantitative estimates of subsurface properties through seismic waveform fitting however for some monitoring systems the offset range versus depth of interest is not large enough to provide information about the low wavenumber component of the velocity model we evaluated an image domain wavefield tomography idwt method using the local warping between baseline and monitor images as the cost function this cost function is sensitive to volumetric velocity anomalies and it is capable of handling large velocity changes with very limited acquisition apertures where traditional fwi fails we described the theory and workflow of our method la

natural levee deposition during the 2005 flood of the saskatchewan river abstract in summer 2005 a controlled flood of the saskatchewan river east central saskatchewan canada resulted in general floodplain inundation and extensive natural levee deposition along a 60 km reach extending from 40 km below the e b campbell dam to cumberland lake levee crests along channel banks were inundated for up to 7 weeks in some areas of the floodplain new deposits on levee crests varied from 0 to 70 cm in thickness displaying large variations both along reach and in opposing sites across channels mean grain sizes mainly silt and very fine sand likewise varied considerably among sample sites pre and post flood surveys of channel cross sections along the flooded reach permitted assessments of relationships between channel area changes and patterns of levee sedimentation in this system in which virtually all new flood sediment was derived by channel scour results show that both net deposition and net erosion occurred within the channel cross sections but that on average net channel enlargement of 4 2 prevailed over the entire survey reach when weighted by cross section size over the 60 km flooded reach zones of thick levee deposition occur at or just downstream of two areas of major channel enlargement and an intermediate zone of thin levee deposits is associated with an intermediate area of net channel aggradation this bimodal distribution of flood deposit thickness is inferred to have resulted from differences in sediment supply produced locally by the different extents of channel perimeter erosion two other factors 1 position of interfacial zones between clear floodbasin water and turbid channel water and 2 difference in pre flood levee heights contributed to the poor correspondence in thickness and grain size between opposing levees at some sites additional features of the new levee deposits including increases in transverse slopes abrupt basinward fining and paucity of deposition in distal areas due to clear floodbasin waters are characteristic of strong front loading that results when suspended sediment production is restricted to channel erosion processes

buoyancy driven flow from a waning source through a porous leaky aquifer we develop a series of models to describe the migration of a buoyant fluid through a layered permeable rock following release from a localized waning source in particular if the fluid is injected into a high permeability layer bounded above by a layer of lower permeability a plume migrates along the interface with some draining into the low permeability layer if the current is sufficiently deep to overcome the capillary entry pressure we show the motion of the fluid is controlled by a number of key factors with the dominant dimensionless numbers being the time scale for the source to decay compared to the time scale for draining through the low permeability layer the residual saturation of the gas and water in the formation as that phase is displaced by the other phase and the capillary entry pressure as measured by the critical depth of the current required for draining as compared to the initial depth of the current simplified analytical models are presented to illustrate some of the key controls on and transitions in the flow and the models are used to explore leakage and trapping prior to flow reaching a fault zone

the influence of large scale seafloor slope and average bottom sound speed on low grazing angle monostatic acoustic scattering variations in large scale seafloor slope and average seabed sound speed account for a significant portion of the variations in scattering intensity observed in low grazing angle monostatic reverberation numerical modeling using a finite difference solution to the elastic wave equation is used to quantify the effect of these large scale parameters in interpretations of reverberation data for hard rough seafloor e g basalt the results of the modeling suggest that the monostatic backscattering strength increases with increasing large scale seafloor slope up to a slope of about 15 dipping toward the incident direction once the grazing angle of the incident wavefield exceeds the critical grazing angle for the flat reference seafloor the backscattering intensity increases only slowly with increasing grazing angle similarly average subseafloor sound speed has a significant effect seafloor with low sound speeds characteristic of soft bottoms e g sediment generate significantly weaker backscatter signals than seafloor with sound speeds characteristic of hard bottoms e g basalt the difference is that the shear waves can always be passed into soft bottoms because even for a flat seafloor there is no shear wave critical grazing angle

similarity solutions for fluid injection into confined aquifers fluid injection into the deep subsurface such as injection of carbon dioxide co 2 into deep saline aquifers often involves two fluid flow in confined geological formations similarity solutions may be derived for these problems by assuming that a sharp interface separates the two fluids by imposing a suitable no flow condition along both the top and bottom boundaries and by including an explicit solution for the pressure distribution in both fluids when the injected fluid is less dense and less viscous than the resident fluid as is the case for co 2 injection into a resident brine gravity override produces a fluid flow system that is captured well by the similarity solutions the similarity solutions may be extended to include slight miscibility between the two fluids as well as compressibility in both of the fluid phases the solutions provide the location of the interface between the two fluids as well as drying fronts that develop within the injected fluid applications to cases of supercritical co 2 injection into deep saline aquifers demonstrate the utility of the solutions and comparisons to solutions from full numerical simulations show the ability to predict the system behaviour

influence of bank vegetation on channel morphology in rural and urban watersheds stream bank vegetation significantly influences the morphology of streams in the piedmont region of the united states we surveyed the morphology of 26 paired stream reaches in southeastern pennsylvania northern maryland and delaware one member of each pair has a forested riparian zone whereas the other has a riparian zone composed pri marily of grass the paired reaches are nearly contiguous so all significant channel forming variables except riparian vegetation are held constant the extent of urban development of the watersheds upstream of the paired reaches also varies considerably allowing us to determine the combined influence of riparian vegetation and urbanization on channel morphology statistical analyses indicate that 1 channels with forested riparian zones are wider than channels with nonforested riparian zones 2 channels in urbanized watersheds are wider than channels in nonurbanized watersheds and 3 the effect of riparian vegetation is independent of the level of urbanization

long range backscatter from the mid atlantic ridge acoustic backscatter returns measured with a vertical source and horizontal receiving array are beamformed and charted to respective scattering sites on the western flank of the mid atlantic ridge mar well defined patterns of high level backscatter resembling bottom morphology occur within the direct path and at convergence zone ranges measured backscatter is compared with modeled two way transmission loss using the wide angle parabolic equation pe and high resolution supporting bathymetry the level of backscatter is found to be strongly dependent upon two way transmission loss tl specifically tl selects prominent bathymetric features from which high backscatter is returned with backscatter maxima corresponding to tl minima scattering strength estimated for the wide area surveyed shows low variance and relatively minimal spatial variation apparently distinct scattering contributions are so well mixed in long range backscatter that dominant variations are generally due to propagation these

anatomy and dimensions of fluvial crevasse splay deposits examples from the cretaceous castlegate sandstone and neslen formation utah u s a abstract crevasse splay deposits form a volumetrically significant component of many fluvial overbank successions up to 90 in some successions yet the relationships between the morphological form of accumulated splay bodies and their internal facies composition remains poorly documented from ancient successions this work quantifies lithofacies distributions and dimensions of exhumed crevasse splay architectural elements in the campanian castlegate sandstone and neslen formation mesaverde group utah usa to develop a depositional model fluvial crevasse splay bodies thin from 2 1 m average to 0 8 m average and fine from a coarsest recorded grain size of lower fine sand to fine silt away from major trunk channel bodies internally the preserved deposits of splays comprise laterally and vertically variable sandstone and siltstone facies associations proximal parts are dominated by sharp and erosional based sandstone prone units which may be structureless or may comprise primary current lineation on beds and erosional gutter casts medial parts comprise sets of climbing ripple strata and small scale deformed beds distal parts comprise sets of lower stage plane beds and complex styles of lateral grading into fine grained floodbasin siltstones and coals lithofacies arrangements are used to establish the following i recognition criteria for crevasse splay elements ii criteria for the differentiation between distal parts of crevasse splay bodies and floodplain fines and iii empirical relationships with which to establish the extent ca 500 m long by 1000 m wide and overall semi elliptical planform shape of crevasse splay bodies these relationships have been established by high resolution stratigraphic correlation and palaeocurrent analysis to identify outcrop orientation with respect to splay orientation this permits lateral changes in crevasse splay facies architecture to be resolved facies models describing the sedimentology and architecture of crevasse splay deposits preserved in floodplain successions serve as tools for determining both distance from and direction to major trunk channel sandbodies

linking microseismic event observations with geomechanical models to minimise the risks of storing co2 in geological formations abstract for carbon capture and storage ccs in geological formations to be scientifically viable we must be able to model and monitor the effects of geomechanical deformation on the integrity of the caprock excess deformation may open fractures providing pathways for co2 leakage from the reservoir an acceptable geomechanical model must provide a good match with field observations microseismic activity is a direct manifestation of mechanical deformation so it can be used to constrain geomechanical models the aim of this paper is to develop the concept of using observations of microseismic activity to help ground truth geomechanical models microseismic monitoring has been ongoing at the weyburn co2 storage and monitoring project since 2003 we begin this paper by presenting these microseismic observations less than 100 events have been recorded documenting a low rate of seismicity most of the events are located close to nearby producing wells rather than the injection well a pattern that is difficult to interpret within the conventional framework for injection induced seismicity many events are located in the overburden without geomechanical simulation it is difficult to assess what these observations mean for the integrity of the storage formation to address these uncertainties we generate numerical geomechanical models to simulate the changes in stress induced by co2 injection and use these models to predict the generation of microseismic events and seismic anisotropy the initial geomechanical model that we generate using material properties based on laboratory core measurements does not provide a good match with either event locations or s wave splitting measurements made on the microseismic events we find that an alternative model whose reservoir is an order of magnitude softer than lab core sample measurements provides a much better match with observation as it leads shear stresses to increase above the production wells promoting microseismicity in these areas and generates changes in effective horizontal stresses that match well with s wave splitting observations this agreement between geophysical observations and a softer than lab measurements reservoir model highlights the difficulties encountered in upscaling lab scale results there is a strong need to link geomechanical models with observable manifestations of deformation in the field such as induced seismicity for calibration only then can we accurately assess the risks of leakage generated by mechanical deformation

geological carbon storage storage of the carbon dioxide that is produced by burning fossil fuels is one way to avoid the damaging consequences of climate change a range of observations suggests that geological carbon storage is much less risky than unabated carbon emissions to the atmosphere

stream channels in peatlands the role of biological processes in controlling channel form while some aspects of peatlands are well studied understanding of the hydrology and geomorphology of the associated surface drainage networks is quite limited this paper attempts to describe some of the basic attributes of stream channels in peatlands and asks whether the form and the mechanisms behind development represent a significant departure from self forming alluvial streams we use three approaches to better understand these poorly studied systems an examination of the geomorphology of allequash creek wisconsin a survey of aerial photographs of similar peatland stream complexes in northern wisconsin and a review of the existing literature on peat influenced and wetland channels distinct features of allequash creek and other wisconsin streams in peatlands include absence of mineral substrates low width depth ratio presence of lateral pool like structures along the channel margin long straight reaches and acute angle bends further the lateral location of the thalweg was apparently independent of planform or cross sectional form and no flow zones often occurred along both edges of channel cross sections collectively these features represent a distinct departure from characteristic forms of alluvial channels deep peat samples from allequash creek and aerial photographs from other sites indicate that these streams represent remnant lake systems whose basins filled with peat thus we suggest that the processes responsible for channel form in these low energy peatland systems are largely governed by groundwater hydrology and the biology of peat accumulation and decomposition in this manner biological forces not just physical drivers such as channel discharge and sediment supply are central to the understanding of stream geomorphology in peatlands

imaging ocean basin reverberation via inversion a technique for imaging large areas of the ocean floor by inverting reverberation data is presented acoustic returns measured on a horizontally towed line array have right left ambiguity about the array s axis and decreasing cross range resolution for off broadside beams and more distant scattering sites by optimal use of data taken with differing array locations and orientations right left ambiguity is eliminated and resolution is maximized this is accomplished via a global inversion using the array s known resolving properties the output of the inversion can be optimally resolved reverberation scattering coefficient or physical properties of the seafloor depending upon the formulation simulations are presented to show the general superiority of this approach to data averaging

propagation and analysis issues in the prediction of long range reverberation data collected from the office of naval research special research program onr srp bottom reverberation research cruises consist of various environmental measurements sound speed profiles bottom properties etc extensive bathymetric mapping of the 300 km 150 km natural laboratory and high quality acoustic reverberation data recorded in both monostatic and bistatic geometries the analysis of the acoustic data and the effects of propagation are investigated accurate gps tracking of the participating research vessels provided the precision necessary to attempt to correlate spiky reverberation events with bathymetric features understanding the limitations of our ability to resolve such features due to imperfect signal processing environmental variability and complex multipath structures is the main objective of this work using a simplified time to range conversion the measured reverberation data can be displayed over the local bathymetry this process shows good correlation between large scal

depositional patterns following the 1870s avulsion of the saskatchewan river cumberland marshes saskatchewan canada abstract the avulsion of the saskatchewan river cumberland marshes east central saskatchewan canada has resulted in new floodplain deposition over an area of more than 500 km2 since beginning in the 1870s the avulsion deposits are predominantly fine grained and could be otherwise classifiable as overbank sediments in alluvial floodplains presumed to be supplied by intermittent flooding of dominant master channels the north angling and cadotte channels are older pre existing channels that were intercepted and appropriated by the expanding avulsion following annexation of the north angling channel stable cohesive banks inhibited channel enlargement and crevassing forcing the increasing discharges to be accommodated by overbank flow and in the process enhancing new levee aggradation these levee deposits coarsen upward and thin downstream as a result of greater competence and higher proximal deposition rates brought on by the larger flows in contrast the cadotte channel responded to increasing discharges by levee breaching giving rise to splay progradation and floodbasin filling the cadotte splay complex formed from the avulsively annexed cadotte channel represents a small but typical area of the avulsion belt facies characteristics and interrelationships examined from auger borings and vibracores are presented to illustrate patterns of deposition and floodplain development avulsive flooding initially raised local water surface elevations deepening small existing lakes and creating new shallow 1 2 m deep lakes on the floodplain surface deposition began when levees of the cadotte channel were breached allowing water and coarser sediment to spread as sheet like flows while finer sediment was carried and deposited farther into the basin later as the proximal splay sheets coalesced and grew basinward flows became channelized and progradation of mouth bars into marshes and shallow lakes together with deposition of interchannel fines became dominant forming coarsening upward sequences further floodplain aggradation developed by overbank flooding when splay channels became stabilized and bordered by levees gradual abandonment was accompanied by deposition of organic rich fine grained sediment on top of the progradational sequences throughout the avulsion the north angling channel has stood as an older alluvial ridge separating two broad areas of avulsive deposition its recent levee deposits now grade basinward into these new floodplain sediments composed of thicker heterogeneous predominantly upward coarsening and rapidly deposited facies of the avulsion

capillary entry pressure and the leakage of gravity currents through a sloping layered permeable rock we examine the motion of a buoyant fluid injected into a water saturated porous rock as it spreads along a thin inclined low permeability barrier we account for leakage of the fluid across the barrier once the current is sufficiently deep so that the pressure exceeds the capillary threshold we show that at some distance from the source the pressure decreases below this threshold and all the remaining flux spreads laterally along the barrier we examine the controls on the partitioning of the flow between the draining flux and the laterally spreading flux and also the controls on the lateral extent of the draining region for the case of an instantaneous release and a maintained release of fluid we consider the implications of our work for the dispersal of co 2 plumes which may be sequestered in deep saline aquifers

the effect of drainage on the capillary retention of co2 in a layered permeable rock buoyant plumes of co 2 spreading through water saturated permeable rock bounded by layers of lower permeability tend to spread laterally as they advance they may gradually leak through fractures or discontinuities in the lower permeability boundary leading to a gradual waning of the original plume and dispersal of co 2 higher in the formation with a finite release of co 2 the trailing edge of the plume recedes with time and capillary forces tend to trap a fraction of this co 2 within the pore space this also leads to a gradual waning of the plume with time and limits the mass of co 2 which can leak through the boundary and rise higher into the formation we explore the balance between these two effects and calculate some of the controls on the fraction of the co 2 plume which becomes trapped within the original layer of rock

factors affecting the accumulation of organic rich deposits in a modern avulsive floodplain examples from the cumberland marshes saskatchewan canada since the 1870s the saskatchewan river at the cumberland marshes east central saskatchewan canada has been undergoing progradational avulsion resulting in development of a 500 km2 avulsion belt the avulsion belt consists of an unstable network of active and abandoned channels splays and floodbasins some containing small shallow lakes fine grained deposits of varying total organic content toc are currently accumulating within floodbasins inside adjacent to and outside the avulsion belt the toc of these deposits depends on factors that control the amount of siliciclastic sediment received by floodbasins five factors that affect toc content are identified distance from an active channel position relative to the avulsion belt presence of alluvial ridges changes in local channel activity and developmental stage of avulsion a channel to basin trend of increasing toc is present at many locations reflecting greater suspended sediment loads received by near channel areas and locations within the avulsion belt generally accumulate sediment with lower toc than those adjacent to or outside the belt alluvial ridges locally act as barriers to floodbasin deposition and channel abandonment reduces suspended sediment to adjacent floodbasins both of which increase toc of sediment finally as avulsion wanes less siliciclastic sediment is distributed throughout the avulsion belt resulting in increased toc in the geological record such fine grained avulsion deposits are likely to appear as intervals of mudrock between thin beds of coal or carbonaceous shale formed from organic rich sediment deposited between avulsion events a succession that is common in many ancient alluvial strata

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

on the flow of buoyant fluid injected into a confined inclined aquifer we study the dispersal of a plume of incompressible buoyant fluid injected into a confined sloping aquifer which has an outflow at a single fault which may be up dip up slope or down dip down slope from the point of injection we develop a long time asymptotic solution for the motion of the injected fluid we show that for the case in which the outflow fault is up dip from the point of injection there is a critical injection rate above which the injected fluid floods the full depth of the aquifer and we show that for the case in which the outflow fault is down dip from the point of injection there is a critical injection rate below which all injected fluid initially flows up dip our analysis leads to expressions for the lateral extent of the injected fluid as a function of time and we consider the implications of the model for the dispersal of supercritical carbon dioxide injected into deep saline aquifers the work also indicates that the geometry of the system may have a significant effect on i the total volume of carbon dioxide which it is possible to sequester in a faulted aquifer and ii the interpretation of the dispersed position of any injected tracers

a comparison of bistatic scattering from two geologically distinct abyssal hills the bistatic scattering characteristics of two geologically distinct abyssal hills located on the western flank of the mid atlantic ridge known as b and c are experimentally compared using data acquired with low frequency towed array systems at 12 convergence zone 33 km stand off the comparison is significant because the abyssal hills span the two classes of elevated seafloor crust that cover the mid atlantic ridge the highly lineated b feature is representative of abyssal hills composed of outside corner crust the most commonly occurring category whereas the domed c promontory is representative of the rougher low aspect ratio abyssal hills composed of inside corner crust the latter are less common and usually restricted to segment valley margins the mean biazimuthal scattering distributions of the two abyssal hills each exhibit lambertian behavior with comparable albedos suggesting that the distinction between abyssal hills composed of differing crust is not significant in modeling long

holocene avulsion styles and sedimentation patterns of the saskatchewan river cumberland marshes canada abstract this paper describes the styles and sedimentation patterns of holocene avulsions of the saskatchewan river at the cumberland marshes predating the most recent 1870 s avulsion holocene avulsions involved two major styles 1 progradation of lacustrine deltas and splay complexes and 2 local reoccupation or appropriation of preavulsive channels most avulsions were progradational and occurred in floodplain lakes occupying floodbasin areas between elevated alluvial ridges the two most recent avulsions old channel and 1870 s diverted mainly into inundated peatland progradational avulsions were accompanied by deposition of avulsion belt sediments associated with multiple channel networks the characteristics of avulsion belt deposits include 1 sediments dominated by poorly sorted silt and very fine sand 2 lateral continuity in transverse and longitudinal directions with subhorizontal upper and lower boundaries 3 predominantly nonerosional contacts with underlying sediments 4 coarsening upward successions 5 consistent radiocarbon dates for the tops of preavulsive substrates and 6 occurrence beneath levee and overbank deposits of the associated major channel belt indicating that avulsion belt deposition occurs prior to the development of a new master channel the width of ancient avulsion belts reaches 18 km with typical thicknesses of 2 3 m avulsion belt deposition accompanied by many small channels was followed by flow reversion to a few larger channels and eventually to one single channel accompanied by deposition of levee and channel deposits reoccupational avulsions were not accompanied by deposition of widespread avulsion belt sediments and led mainly to the modification of pre existing channel belts the sedimentation patterns of holocene avulsions of the saskatchewan river reveal that avulsion belt sediments represent major components of the floodplain deposits supporting the model developed from observations of the 1870 s avulsion

migration of backscatter data from the mid atlantic ridge in studies of low frequency reverberation within the marine environment a central concern is the relationship between reverberation events and morphological features of the seafloor a time domain migration algorithm for the reverberation intensity field is developed that produces scattering coefficient maps coregistered with a bathymetry database the algorithm is tailored to broadband transient sources with good range resolution and was developed to analyze an extensive set of reverberation records from a 200 255 hz source collected on the flanks of the mid atlantic ridge the precise sample by sample tracking of wavefronts across elements of the bathymetry database that forms the foundation of the algorithms implementation results in reverberation maps that show a clear and detailed correlation between scattering and morphology with narrow scarp slopes consistently highlighted environmentally induced asymmetries in transmission loss and incidence angle are exploited to break the inherent left righ

a geochemical clogging model with carbonate precipitation rates under hydrothermal conditions abstract a step wise numerical calculation method was developed to provide predictions of when and where carbonate deposits might be found through reservoirs during co 2 sequestration flow experiments through porous media using a supersaturated carbonate fluid were also performed in order to observe flow rates in order to evaluate precipitation rates and permeability change in the formation calculated flow rates based on the proposed geochemical clogging model were compared with the experimentally observed data both high and low temperature cases were studied to understand how hydrothermal conditions can affect precipitation rates of carbonate according to chemical kinetics growth rates of minerals are generally proportional to the saturation index s i that depends on temperature thus a supersaturated fluid has the advantage of improving the filtration and the amount of c fixation however when the ratio of filtration coefficient to pore fluid velocity u increases the permeability around the injection point tends to be significantly reduced by carbonate accumulation and thus this might result in insufficient injection of co 2 therefore it is essential to understand how to control both and u so that the precipitation of carbonate can be located as far away from the inlet as possible

fine grained splay deposition in the avulsion belt of the lower saskatchewan river canada abstract in or about 1883 a northward avulsion of the meandering lower saskatchewan river at the cumberland marshes initiated a broad belt of alluvial sedimentation that has continued to evolve to the present and now covers some 500 km2 the avulsion belt comprises a complex alluvial terrain dominated by individual and coalesced splays and associated wetlands connected by networks of active and abandoned channels of various sizes the windy lake splay a predominantly fine grained feature typical of large parts of the avulsion belt was examined to investigate the relationships between splay evolution and facies development the splay now largely inactive mostly formed over a 35 year period depositing nearly 2 m of sediment over a 7 2 km2 area the splay surface is ch racterized by stable well defined anastomosed distributary channels that separate interchannel wetland basins heights of channel levees diminish downstream and the levees merge with channel mouth bars whose progradation forms the locus of lakeward channel extension and the base for subsequent subaerial levee deposition the anastomosed channel pattern was created when the mouth bars of separate distributary channels merged during progradation vibracore and soil probe profiles show the splay to be dominated by upward coarsening lacustrine prodeltaic mouth bar facies sequences capped by levees and organic rich interchannel wetland deposits channels now containing sand only sporadically in narrowed or slightly migrated reaches will eventually fill with fine sediment when abandonment s complete the windy lake splay is typical of stage iii splays smith et al 1989 whose deposits and associated lacustrine fills form at least half of the avulsion belt thin widespread predominantly upward coarsening sequences capped by either nondepositional horizons or true overbank fines may be characteristic of many avulsive suites in the ancient alluvial record

modeling of the acoustic reverberation special research program deep ocean seafloor scattering experiments using a hybrid wave propagation simulation technique quantitative modeling of bottom interacting ocean acoustic waves is complicated by the long propagation ranges and by the complexity of the scattering targets we employ a two dimensional 2 d hybrid technique combining gaussian beam finite difference and kirchhoff integral solutions of the wave equation to simulate ocean acoustic experiments within half of a convergence zone in the sofar channel the 2 d modeling approach is reasonable due to the one dimensional 1 d velocity distribution in the water column and the strong lineation of the seafloor morphology parallel to the mid ocean ridges full waveform modeling of ocean acoustic data requires that the topography and the material properties of the seafloor are available at scales that are several orders of magnitude smaller than typical bathymetric sampling rates we have therefore investigated the effects on the ocean acoustic response of a stochastic interpolation scheme used to generate seafloor models for typical grazing angles of the incident wave field approximately 5 20 we found that different stochastic realizations of the same seafloor segment sampled at 200 m yield an intrinsic uncertainty of the order of 3 8 db in amplitude and 0 1 0 3 s in time for individual prominent events in the reverberant acoustic field hybrid simulations are compared to beam formed ocean acoustic data collected during the acoustic reverberation special research program arsrp cruises side lobe noise in the observed acoustic data is simulated by adding band limited white noise at 30 db relative to the maximum intensity in the synthetic data numerical simulations can be limited to the response of only one of the mirror azimuth beams provided that the experimental geometry is suitably chosen for the 2 d approximation to be valid the cross range resolution of the observed data must be smaller than the characteristic scale of seafloor lineations and the beams of interest must be approximately perpendicular to the dominant structural grain under these premises the arrival time and maximum intensity of the observed backscattered acoustic events can be modeled within 0 3 s and 5 10 db respectively the mismatch in arrival time is interpreted to be due predominantly to intrinsic uncertainties in the stochastic interpolation of the seafloor profiles whereas the fact that the intensity of the backscattered events is systematically overestimated is attributed to 3 d effects within the footprint of the beam and or to underestimated noise levels

depositional development of the muskeg lake crevasse splay in the cumberland marshes canada crevasse splays are common geomorphological features in alluvial and deltaic floodplains although crevasse splays can develop into full avulsions thereby transforming large areas of floodbasins little is known about their sedimentary and geomorphological development at the decadal scale and their avulsion potential we used aerial photography and lithological cross sections to reconstruct crevasse splay formation in the largely unmanaged floodplain of the saskatchewan river in the cumberland marshes saskatchewan canada based on surface geomorphology and subsurface deposits various stages of crevasse splay development were described which were linked to both external forcing and internal morphodynamics initial splay deposition following a levee breach during a large flood occurred as a broad but relatively thin sandy sheet in a down basin direction in the receiving backswamp area in a next phase these primary crevasse splay deposits blocked local down basin flow thereby forcing the crevasse splay channel in a direction perpendicular to the parent channel and original floodbasin gradient this created an asymmetrical splay sequence composition which differs in appearance from more commonly observed dendritic crevasse splays it is concluded that sedimentation patterns in the splay have been influenced by inherited effects of previously formed deposits feedbacks of the original floodbasin gradient and earlier stages of splay formation are suggested as prominent mechanisms in creating the current morphology orientation and architecture of its deposits

topographic controls on gravity currents in porous media we present a theoretical and experimental study of the propagation of gravity currents in porous media with variations in the topography over which they flow motivated in part by the sequestration of carbon dioxide in saline aquifers we consider cases where the height of the topography slopes upwards in the direction of the flow and is proportional to the nth power of the horizontal distance from a line or point source of a constant volumetric flux in two dimensional cases with n 1 2 the current evolves from a self similar form at early times when the effects of variations in topography are negligible towards a late time regime that has an approximately horizontal upper surface and whose evolution is dictated entirely by the geometry of the topography for n 0 result in a transition from an early time similarity solution towards a topographically controlled regime that has an approximately horizontal free surface we also analyse the evolution over topography that can vary with different curvatures and topographic exponents between the two horizontal dimensions finding that the flow transitions towards a horizontally topped regime at a rate which depends strongly on the ratio of the curvatures along the principle axes finally we apply our mathematical solutions to the geophysical setting at the sleipner field concluding that topographic influence is unlikely to explain the observed non axisymmetric flow

leakage from gravity currents in a porous medium part 2 a line sink we consider the propagation of a buoyancy driven gravity current in a porous medium bounded by a horizontal impermeable boundary the current is fed by a constant flux injected at a point and leaks through a line sink at a distance from the injection point this is an idealized model of how a fault in a cap rock might compromise the geological sequestration of carbon dioxide the temporal evolution of the efficiency of storage defined as the instantaneous ratio of the rate at which fluid is stored without leaking to the rate at which it is injected is of particular interest we show that the efficiency of storage decays like t 2 5 for times t that are long compared with the time taken for the current to reach the fault this algebraic decay is in contrast to the case of leakage through a circular sink neufeld et al j fluid mech vol 2010 where the efficiency of storage decays more slowly like 1 ln t the implications of the predicted decay in the efficiency of storage are discussed in the context of geological sequestration of carbon dioxide using parameter values typical of the demonstration project at sleipner norway we show that the efficiency of storage should remain greater than 90 on a time scale of millennia provided that there are no significant faults in the cap rock within about 12 km of the injection site

the 1870s avulsion of the saskatchewan river several major avulsions of the saskatchewan river have occurred in the cumberland marshes east central saskatchewan during the past few thousand years the most recent avulsion occurred in about the 1870s converting over 500 km2 of floodplain into a belt of anastomosing channels splay complexes and small lakes a region that is still evolving today the avulsion began near the tip of a large meander bend by following a small outflowing creek sturgeon river which in turn followed an abandoned former channel of the saskatchewan river flow began to permanently divert out of the saskatchewan when a narrow strip of floodplain separating the sturgeon river from the nearby torch river became breached diversion into the connected sturgeon torch began to increase sometime in the 1870s and probably culminated around 1882 the triggering event for the avulsion may have been a chute cutoff of the meander bend shown by numerical modeling experiments to have significantly raised water surface elevations at th

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

localizing co2 at sleipner seismic images versus p wave velocities from waveform inversion abstractthe presence of injected co2 in the utsira sand at the sleipner site norway is associated with a high negative p wave velocity anomaly that is a low postinjection velocity and a strong seismic response time lapse seismic imaging of co2 injection at sleipner is thus a viable monitoring tool of the injected co2 the work flow usually involves conventional seismic processing including stacking and results in seismic images multiple reflections interference effects such as tuning and the velocity pushdown effect due to co2 injection render these seismic images ambiguous in terms of the localization and the quantification of the co2 in the utsira sand nonetheless seismic images often form the basis for analyses that aim to quantify the injected co2 we employed elastic 2d full waveform inversion to invert prestack seismic sleipner data from preinjection 1994 and postinjection 1999 and compared the resulting postinjection p wave velocity model with the corresponding seismic image we fou

chrysotile dissolution rates implications for carbon sequestration abstract serpentine minerals e g chrysotile are a potentially important medium for sequestration of co2 via carbonation reactions the goals of this study are to report a steady state far from equilibrium chrysotile dissolution rate law and to better define what role serpentine dissolution kinetics will have in constraining rates of carbon sequestration via serpentine carbonation the steady state dissolution rate of chrysotile in 0 1 m nacl solutions was measured at 22 c and ph ranging from 2 to 8 dissolution experiments were performed in a continuously stirred flow through reactor with the input solutions pre equilibrated with atmospheric co2 both mg and si steady state fluxes from the chrysotile surface and the overall chrysotile flux were regressed and the following empirical relationships were obtained f mg 0 22 ph 10 02 f si 0 19 ph 10 37 f chrysotile 0 21 ph 10 57 where fmg fsi and fchrysotile are the log10 mg si and molar chrysotile fluxes in mol m2 s respectively element fluxes were used in reaction path calculations to constrain the rate of co2 sequestration in two geological environments that have been proposed as potential sinks for anthropogenic co2 carbon sequestration in chrysotile tailings at 10 c is approximately an order of magnitude faster than carbon sequestration in a serpentinite hosted aquifer at 60 c on a per kilogram of water basis a serpentinite hosted aquifer however provides a larger sequestration capacity the chrysotile dissolution rate law determined in this study has important implications for constraining potential rates of sequestration in serpentinite hosted aquifers and under accelerated sequestration scenarios in mine tailings

fitting straight lines and planes with an application to radiometric dating conventional practice in geochronology is to fit a straight line or isochron to data consisting of two isotopic ratios by a method e g that of 1 2 or perhaps the more modern version of titterington and haliday 1979 that takes into account that fact that both ratios are measured with error in this paper we use matrix algebra to lay out a general method for fitting linear relations between any number of variables all subject to errors with known variances and covariances and the well known newton raphson method to do the optimization this leads to a good computational algorithm which may also be used e g to check whether coefficients in several linear relations are the same in many fields of science one needs to fit linear relations so our method is of wide utility its use is in no way restricted to radiometric dating

sedimentology facies architecture and chemostratigraphy of a continental high latitude paleocene eocene succession the chickaloon formation alaska abstract the paleocene eocene chickaloon formation of southern alaska represents rapid deposition in a floodbasin setting contains abundant and diverse fossil plant material and spans the paleocene eocene thermal maximum petm sedimentologic lithofacies and chemostratigraphic analyses of exposures of the chickaloon formation were conducted in order to provide a contextual framework for this late paleocene early eocene high latitude sedimentary succession and to test if hyperthermal conditions are recorded in the unit at the main study area in the evan jones coal mine strata represent an alluvial sequence dominated by floodplain channel sandstone crevasse lobe crevasse channel and mire deposition floodplain environments are represented by medium gray commonly nodular and or carbonate cemented shaly siltstone and centimeter scale thick sheet sandstone interbeds most channel sandstone deposits are interpreted to be crevasse channels and are generally small 2 5 m thick rarely coarser than medium grained sandstone and sand grains are commonly coated with fe oxides carbonaceous shale and coal are localized and indicate a high rate of organic carbon accumulation in the area 13c analyses of bulk organic carbon from the succession at the evan jones mine are internally consistent with this interpretation they yield uniformly negative values that are typical of continental organic matter 21 7 to 28 5 x 25 4 fossil plant material is also very common and includes leaves wood seeds and resins from broad leaf angiosperms conifers ferns and sphenopsids considered together lithologic and paleontologic data suggest that these strata represent a floodbasin environment the observed crevasse channels probably originate from a main channel located within several kilometers of the depocenter ash fall tuffs punctuate the studied sequence and contain abundant reworked or recycled zircons indicating that the depocenter was proximal to a volcanic source across all of these chickaloon depositional environments a significant negative isotopic shift 5 8 occurs which we hypothesize to represent a short lived perturbation associated with a global hyperthermal event

heave of a surficial rock layer due to pressures generated by injected fluids 1 this paper examines the problem of heave developed in a surface or caprock layer of a storage formation due to the injection of pressurized fluids at depth the problem is of interest to the deep geologic disposal of hazardous wastes and the geologic sequestration of carbon dioxide by injection the paper develops a mathematical model that assumes elastic behavior of the storage medium while the surface rock layer is modeled as a thin plate elastic solutions are developed for the axisymmetric flexure deflections of the surface layer during internal pressurization over a flat circular region the model provides a convenient tool for the preliminary estimation of the influence of injection pressures on the integrity of surface rock layers