recharge induced groundwater flow over a plane sloping bed solutions for steady and transient flow using physical and numerical models 1 the free surface profile and outflow hydrograph for groundwater under conditions of steady uniform recharge followed by recession have been studied in viscous fluid model tests using a sloping bed with a gradient of 0 2 the data have been compared with the nonlinear boussinesq model and a modification of that model simulating the outflow seepage surface obtained from a finite difference solution of the free boundary problem it is shown that for a given bed slope there is close to a linear relationship between outflow and storage raised to a power n where n ranges from almost 2 for zero slopes to just above 1 at a gradient of 0 3 there is also a simple relationship between outflow and storage in the final stage of recession when a drainage front occurs on the bed these results lead to simple algorithms for prediction of the outflow under unsteady recharge conditions

satellite altimetry and current meter velocities in the malvinas current at 41 s comparisons and modes of variations three year long current meter arrays were deployed in the malvinas current at 41 s below a satellite altimeter track at about 10 years intervals surface geostrophic velocities sgv derived from satellite altimetric data are compared with the in situ velocities at the upper current meter 300 m multisatellite gridded sgv compare better with in situ observations than along track sgv in spite of the proximity of the moorings to the complex brazil malvinas confluence bmc region satellite sgv are significantly correlated with the 20 day low passed in situ velocities 0 85 for along isobaths velocities 0 8 for cross isobaths velocities the recent in situ measurement period 2014 2015 stands out in the altimetry record with a long lasting 4 months high level of eddy kinetic energy at the mooring site and a southernmost location of the subantarctic front saf the first two modes of variations of sea level anomaly sla over the bmc remarkably match the first two modes of the low passed in situ velocities the first mode is associated with a latitudinal migration of the saf and the second with a longitudinal displacement of the brazil current overshoot the two modes dominate the 24 year long record of sla in the bmc with energy peaks at the annual and semiannual periods for the first mode and at 3 5 months for the second mode the sla over the southwest atlantic was regressed onto the two confluence modes of sla variations and showed remarkable standing wave train like structures in the argentine basin

observed low frequency variability of the brazil current front 1 the brazil current is a weak western boundary current the southwest component of the south atlantic subtropical gyre which is the main conduit of upper ocean waters in the region the objective of this work is to report on observed low frequency variability of the brazil current front using satellite derived sea height anomaly and sea surface temperature observations during the 1993 2008 period the variability of the front is studied in terms of the separation of the brazil current front from the continental shelf break during the study period estimates of this parameter vary 6 degrees in latitude and the mean monthly estimates exhibit a shift to the south of approximately 1 5 degrees statistically significant changes are not observed in the geostrophic transport of the brazil and malvinas currents suggesting that the low frequency changes of the brazil current front are governed by different mechanisms than the seasonal variability of these surface currents surface drifter trajectories and simulations using synthetic drifters are consistent with the observed shift to the south of the brazil current front trends of eddy kinetic energy sea height anomaly sea surface temperature and wind stress curl are also in agreement with the variability reported here wavelet transform analysis revealed interesting changes in the periodicity of the latitude of separation of the brazil current front from the continental shelf break with periods ranging from semiannual to biannual longer records together with comprehensive numerical experiments will ultimately be needed to determine the origin of these changes

hillslope subsurface flow similarity real world tests of the hillslope peclet number 1 similarity analysis offers the ability to model hydrological response using quantifiable landscape descriptors it is possible to develop similarity indices based on analytical solutions to the governing dynamic equations brutsaert 2005 berne et al 2005 provide derivation of such a similarity index the hillslope peclet number of subsurface flow and saturation for hillslopes with exponential width functions they showed that the hillslope peclet number depends only on geometric properties of the hillslope their work was validated using laboratory experiments conducted on constructed hillslopes with homogeneous soil structure and varying bedrock slope angle this study applies the similarity analysis of berne et al 2005 to two data sets 1 the trench hillslope study at the maimai research catchment conducted by woods and rowe 1996 and 2 the isolated hillslope study near troy idaho united states conducted by brooks et al 2004 the maimai trench study was selected because it provides subsurface flow data from hillslopes with different planform geometries the troy hillslope study was selected because the experimental results of brooks et al 2004 provide an estimate of hydraulic conductivity consistent with the support scale of the hillslope we estimated the hillslope peclet number of the hillslopes on the basis of elevation data and reported values of average soil depth this hillslope peclet number quantifies the geomorphological control on how water moves through these hillslopes and creates a basis for comparison independent of hydraulic properties we then estimated the first and second moments of the characteristic subsurface response function of each hillslope on the basis of subsurface flow data to compare the empirical and theoretical moments the hydraulic properties saturated hydraulic conductivity and drainable porosity of the hillslopes were related using a base flow recession analysis then we were able to derive the dimensionless moments of the hillslopes observed characteristic response function using hydraulic conductivities reported in the literature the agreement between the observed and theoretical moments shows the promise of implementing the hillslope peclet number as a similarity parameter to describe first order hydrological response in humid environments

analytical approximation for the recession of a sloping aquifer an approximation is obtained for the recession of a sloping aquifer the analytical approximation can provide a useful tool to analyze data and obtain physical properties of the aquifer in contrast to the case of a horizontal aquifer when plotting the time derivative of the flux versus the flux on a log scale the result shows that the flux derivative reaches a minimum value and that the curve can have a slope of unity as often observed illustration of the application of the analytical results to the mahantango creek data is also discussed

numerical simulation of flow around a tall isolated seamount part i problem formulation and model accuracy abstract a sigma coordinate ocean circulation model is employed to study flow trapped to a tall seamount in a periodic f plane channel in part i errors arising from the pressure gradient formulation in the steep topography strong stratification limit are examined to illustrate the error properties a linearized adiabatic version of the model is considered both with and without forcing and starting from a resting state with level isopycnals the systematic discretization errors from the horizontal pressure gradient terms are shown analytically to increase with steeper topography relative to a fixed horizontal grid and for stronger stratification as measured by the burger number for an initially quiescent unforced ocean the pressure gradient errors produce a spurious oscillating current that at the end of 10 days is approximately 1 cm s 1 in amplitude the period of the spurious oscillation about 0 5 days is shown to be a consequence of the particular form of the pressure gradient terms in th

interannual to decadal changes in the western south atlantic s surface circulation 1 a combination of surface drifters and altimetry is used to analyze the seasonal to interannual variability of the surface velocity field in the brazil malvinas confluence of the western south atlantic ocean longer term changes are inferred from wind and sea surface temperature fields during the period october 1992 to december 2007 a southward shift of 0 6 to 0 9 decade 1 is found in the confluence latitude of the brazil and malvinas currents a comparable trend is found in the latitude of the maximum wind stress curl averaged across the south atlantic basin allowing a proxy for the confluence latitude to be calculated for the prealtimeter time period this longer time series suggests that the recent trend may be part of a longer term oscillation which has returned to values last sustained in the early 1980s this variation does not appear to be related to the multidecadal trend in the southern annular mode but instead is inversely related to long term variations in the sea surface temperature anomaly in the agulhas benguela pathway of the eastern south atlantic subtropical basin

on the use of the boussinesq equation for interpreting recession hydrographs from sloping aquifers 1 the method of recession analysis proposed by brutsaert and nieber 1977 remains one of the few analytical tools for estimating aquifer hydraulic parameters at the field scale and beyond in the method the recession hydrograph is examined as dq dt f q where q is aquifer discharge and f is an arbitrary function the observed function f is parameterized through analytical solutions to the one dimensional boussinesq equation for unconfined flow in a homogeneous and horizontal aquifer while attractive in its simplicity as originally presented it is not applicable to settings where slope is an important driver of flow or where hydraulic parameters vary greatly with depth we compare analytical solutions to the linearized one dimensional boussinesq equation for a sloping aquifer to numerical solutions of the full nonlinear equation the behavior of the nonlinear boussinesq equation is also assessed when the aquifer is heterogeneous wherein the lateral saturated hydraulic conductivity k varies as a power law with height z above the impermeable layer k zn n constant 0 all of the analytical solutions differ in key aspects from the nonlinear solution when plotted as dq dt f q and thus are inappropriate for a brutsaert and nieber type analysis however new analytical solutions for a sloping aquifer are derived empirically from the numerical simulations that are applicable during the late period of recession when the recession curve converges to dq dt aqb where b 2n 1 n 1 and a is a function of the dimensions and hydraulic properties of the aquifer

theoretical and conceptual models of subsurface hillslope flows 1 theoretical and conceptual models for predicting the subsurface flow in a sloping aquifer are presented one category of models is of the lumped conceptual type that is based on combining the continuity equation with discharge storage relationships derived from the steady state solutions of the linearized boussinesq equation the second categories of models are derived from the linearized unsteady boussinesq equation using the method of green s function the green s function solution determines the water table profile and the aquifer outflow for nonuniform and nonsteady recharge distribution arbitrary initial water table profile and time varying stream level at the downstream end the latter theoretical models pertain to a finite domain and to a semi infinite domain and are of two types depending on the linearization approach the conceptual and theoretical models are used to derive the outflow and the cumulative outflow expressions for a particular set of conditions and a comparative analysis is carried out semi infinite aquifer models generate almost the same results as the more complicated finite aquifer models and the quasi steady state models perform as well as the nonsteady ones for long recharge events the kinematic wave model is also shown to provide a good approximation of boussinesq models for steep slopes and high hydraulic conductivity the application of the various models is also illustrated for three published experimental data the present models can be easily incorporated in catchments models and can provide a suitable framework for aquifer parameter estimation base flow separation and recession analysis and analysis of drainage in landfills

a similarity framework to assess controls on shallow subsurface flow dynamics in hillslopes 1 an understanding of the dominant controls on water fluxes through landscapes at scales smaller than the resolution of a hydrologic model is useful for choosing appropriate parameterizations and for developing a classification system for landscape hydrology the links between these controls and the parameters in hillslope scale models of subsurface lateral saturated flow have been treated implicitly in both physical e g characteristic response function and empirical formulations such as power law storage discharge relations in particular the controls exerted by the boundary condition at the toe of the hilslope and the temporal variability of the recharge have not been integrated with the understanding of the controls of topography and soil properties in this work we develop a dimensionless similarity framework for assessing these controls on the subsurface flow dynamics based on the boussinesq equation in an idealized hillslope system using this framework we demonstrate the relationship between 1 the exponents of the storage discharge relations 2 the boundary conditions and 3 the characteristic storage thickness used in the characteristic response function parameterization we use the concept of hydrologic regimes to incorporate information about the population of recharge events that drive the system and set up the initial condition of saturated storage for each storm event the analysis demonstrates that for planar hillslopes with uniform soil properties exponents range between 0 when the flow through the hillslope is dominated by the topographic gradients and is in the early stages of draining and 2 when the flow is driven by water table gradients and the thickness of the aquifer at the seepage face is small compared to the average thickness the similarity framework can be used to make first order predictions of these exponents and classify hillslopes using a simple typology of subsurface flows based on two components of the behavior the relative dominance of the topographic and water table gradients and the responsiveness of the hillslope discharge to temporal variability of the recharge inputs

generality of drought flow characteristics within the arkansas river basin drought flow measurements from 11 river basins contained within and surrounding the cooperative atmosphere surface exchange study cases in the walnut river watershed in kansas were subjected to a recession slope analysis this analysis was based on the dupuit boussinesq groundwater formulation and made use of the historical streamflow daily values published by the u s geological survey the long and short term response features of the riparian aquifers were found to be practically identical to those observed in an earlier study in the washita river basin in oklahoma as both study areas lie within the osage section of the central lowland physiographic province these findings support the applicability of regionalization and scaling of low streamflow related basin characteristics within the same geomorphic domain

characterization functioning and classification of two volcanic soil profiles under different land uses in central mexico volcanic soils constitute an important resource for agriculture and forestry in central mexico as well as in various world regions they exhibit unique properties and high productive potential related to the amorphous materials they contain the relationship between amorphous materials soil characteristic and functioning has not been well studied the objectives of the present work were to assess the influence of land use agricultural and forest topography and other soil forming factors on physical chemical and mineralogical characteristics and pedological processes responsible for soil genesis and soil classification of two volcanic soil profiles derived from andesitic parent material located 150 m away from each other within the same toposequences the toposequence is located in the trans mexican volcanic belt tmvb a highly populated region of central mexico that provides part of the water for mexico city megapolis a series of field and laboratory techniques including physical chemical micromorphological x ray diffraction xrd transmission electron microscopy tem infra red analysis mossbauer spectroscopy were used the main factor affecting the present morphology of the soil profiles was the topography the mineralogical features of the upper layers of the maize profile pachic andosol indicate redistribution of soil material from the upper part of the toposequence the land use change favored this redistribution deeper horizons of this profile were developed from volcanic ashes deposited in situ hematite and ferrihydrite considered markers of evolution in redistributed soil material were observed in this profile associated with allophane the presence of hematite has been reported for the first time in mexican andosols the present characteristics of the forest profile dystric cambisol are mainly due to the pedological process of the volcanic ash layers remaining in situ after the redistribution and volcanic breccia it was concluded that the forest profile evolved from an andosol to an inceptisol which was evidenced by desaturation loss of silica and organic carbon in this profile the fe minerals were associated with the presence of gibbsite and halloysite the position in the toposequence and the physical and chemical characteristics of these profiles define their present functioning such as losses by erosion and c dynamics

power law catchment scale recessions arising from heterogeneous linear small scale dynamics 1 power law recession behavior has typically been attributed to the hydraulics of subsurface flows in the landscape e g the boussinesq equation many catchments exhibit enormous heterogeneity in their characteristics such as the permeability of soils hillslope length and gradient and soil mantle thickness in the paper we demonstrate using a simple linear flow model that the between hillslope heterogeneity alone can give rise to observed apparently nonlinear recession slope curves the degree of nonlinearity represented by the exponent fitted to the recession slope curve is shown to increase with the degree of heterogeneity of catchment hydraulic properties in sufficiently heterogeneous catchments the recession is also sensitive to the history of recharge events tending to increase when the past events have built up a storage of water in the slow parts of the catchment the models based on the catchment heterogeneity were fitted to data from the panola mountain research watershed yielding a good fit and allowing us to infer how the heterogeneity in catchment properties varies with scale the range of exponents explained by this theory overlaps with the range explained by the hydraulics of subsurface flow which raises doubts about our ability to extract catchment hydraulic parameters on the basis of recession curves so long as the heterogeneity is not accounted for in general the results presented here have enabled us to show how the heterogeneity of landscape characteristics is upscaled and manifested in the apparent nonlinear relationship at the catchment scale

geomorphological origin of recession curves 1 we identify a previously undetected link between the river network morphology and key recession curves properties through a conceptual physical model of the drainage process of the riparian unconfined aquifer we show that the power law exponent of dq dt vs q curves is related to the power law exponent of n l vs g l curves which we show to be connected to hack s law where l is the downstream distance from the channel heads n l is the number of channel reaches exactly located at a distance l from their channel head and g l is the total length of the network located at a distance greater or equal to l from channel heads using digital terrain models and daily discharge observations from 67 us basins we find that geomorphologic estimates match well the values obtained from recession curves analyses finally we argue that the link between recession flows and network morphology points to an important role of low flow discharges in shaping the channel network

trends in the brazil malvinas confluence region observations show abrupt changes in the oceanic circulation of the southwestern atlantic these studies report a southward drift of the brazil malvinas confluence bmc and a change in the spectral characteristics of the malvinas current mc transport we address the cause of these changes using the result of a high resolution numerical experiment the experiment which is consistent with observations shows a southward bmc displacement at a rate of 0 62 decade between 1993 and 2008 and a shift of the spectral characteristics of the mc transport after 1999 we find that these changes are driven by a weakening of the northern branch of the antarctic circumpolar current which translates to a weakening of the mc transport and a southward bmc drift the drift changes the spectral characteristics of the mc transport which becomes more influenced by annual and semiannual variations associated with the bmc

kinematic subsurface stormflow this paper builds on the analysis of henderson and wooding 1964 in comparing simplified models of subsurface stormflow for the case of a sloping soil mantle in which the hydraulic conductivity is constant throughout it is shown that models based on a kinematic wave formulation may be good approximations for those based on the extended dupuit forchheimier assumptions for values of the nondimensional parameter 4i cos k sin2 less than about 0 75 in terms of predicting both water table profiles and subsurface stormflow hydrographs by using this critical value of the range of values of slope angle and saturated hydraulic conductivity for which the kinematic approximation is valid can be specified a comparison is made with slope angles and hydraulic conductivities at field sites where subsurface stormflow has been shown to be an important component of catchment storm response it is concluded that the kinematic approximation may be useful for cases of practical interest

investigation of the brazil current front variability from altimeter data the southwestern atlantic ocean is characterized by the confluence of the brazil and malvinas currents which form very strong surface and subsurface fronts that can be detected from hydrographic and remote sensing observations three data sets consisting of topex poseidon derived sea height anomalies the climatologically derived depth of the 10 c isotherm and reduced gravity are used in conjunction with a two layer dynamical ocean scheme to monitor the brazil current front and to investigate its variability during a 6 year period 1993 1998 results reveal that the fronts exhibit motions that are larger zonally than meridionally showing strong interannual variability with annual mean amplitudes that range from 1 to 6 the annual and semiannual components account for more than 75 of the variability of the frontal oscillations in the annual cycle the frontal motions appear to be related closely to fluctuations in the baroclinic transport of the brazil current and are only influenced by the malvinas current when the brazil current transport is very small

drying front in a sloping aquifer nonlinear effects 1 the profiles for the water table height h x t in a shallow sloping aquifer are reexamined with a solution of the nonlinear boussinesq equation we demonstrate that the previous anomaly first reported by brutsaert 1994 that the point at which the water table h first becomes zero at x l at time t t c remains fixed at this point for all times t t c is actually a result of the linearization of the boussinesq equation and not as previously suggested brutsaert 1994 verhoest and troch 2000 a result of the dupuit assumption rather by examination of the nonlinear boussinesq equation the drying front i e the point x f at which h is zero for times t greater than or equal to t c actually recedes downslope as physically expected this points out that the linear boussinesq equation should be used carefully when a zero depth is obtained as the concept of an average depth loses meaning at that time

baseflow recession and recharge as nonlinear storage processes discharge in many rivers is often fed by outflow from a shallow groundwater reservoir it is becoming clear that the outflow from this aquifer is not linearly proportional to storage as is commonly assumed in many algorithms numerical analysis of flow recession curves from about 100 river gauging stations instead reveals a nonlinear relationship between baseflow q and storage s for which the equation s aqb was adopted values of the exponent b are found by calibration to be between 0 and 1 but with a high concentration around 0 5 which is in accordance with the findings of other studies and theoretical approaches yielding b 0 5 for unconfined aquifers and relating the coefficient a to catchment properties primarily area and shape of basin pore volume and transmissivity this non linear reservoir function is proposed as a more realistic alternative to the linear reservoir function the relatively fast response of groundwater flow to rainfall is mainly a result of the increase of hydraulic head of the groundwater reservoir accelerating the exfiltration of old pre event water into the river bed as fissure and pore volumes communicate hydraulically it appears physically reasonable to model the system by one non linear reservoir for catchments or parts of them instead of applying independent parallel linear reservoirs the non linear reservoir algorithms are supported by an analytical derivation they are extended for the automatic separation of baseflow from a time series of daily discharge in rivers and the computation of storage and effective recharge of groundwater in river basins by inverse nonlinear reservoir routing the time series obtained allow the identification and quantification of long term changes to the water balance relationships between computed groundwater storage and observed groundwater level can also be established copyright 1999 john wiley sons ltd

on the origins of the variability of the malvinas current in a global eddy permitting numerical simulation 1 this article investigates the origins of the variability of the malvinas current mc transport using the results of an eddy permitting ocean general circulation model first the dynamical links between the variabilities of the mc and the antarctic circumpolar current acc transports at the drake passage are established time series analyses indicate that the connection between the transport variations of the acc and the mc is masked by high frequency oscillations although a substantial portion of this highfrequency variability is produced and dissipated locally there are also anomalies that propagate between those regions the most conspicuous of these signals has an average speed of 6 7 cm s 1 and a period of 150 days second the contribution of the wind forcing to the variability of the acc and the mc is determined from principal estimator patterns analysis the analysis indicates that the variance of the transport of both currents is more directly related to the variability of the wind stress than to the wind stress curl the transport variability is particularly sensitive to zonal wind stress anomalies in the latitudinal range of the drake passage that extends farther north over the south indian ocean a rather counterintuitive result of our analysis is that the wind stress forcing over the south atlantic ocean is unimportant to the variability of the mc transport

the patagonian shelf circulation drivers and variability abstract a high resolution ocean model is used to characterize the local and remote driving mechanisms of the variability of the patagonian shelf circulation local forcing includes the effects of tides buoyancy fluxes and wind while remote forcing represents the impact of the adjacent deep ocean currents there is an abrupt change of the dynamical characteristics of the shelf circulation at 40 s south of 40 s the seasonal variations of the shelf circulation are out of phase with the local wind stress and are driven by deep ocean inflows originated in the drake passage the inter annual variability of the shelf circulation is principally driven by the wind and shows a significant correlation with the time variations of the southern annular mode index the variability of the circulation and upwelling at the shelfbreak region are modulated by the variability of the malvinas current transport at low frequency periods higher than two years and by the local wind stress at higher frequencies north of 40 s the local wind forcing drives the seasonal variations of the shelf transport the inter annual variability of the flow is driven by the combined action of the rio de la plata discharge significantly correlated with the el nino southern oscillation local wind stress and the brazil malvinas confluence in the outer shelf in agreement with previous studies we show that while the position of the confluence marks the location of the largest offshelf transports it does not determine their magnitude the offshelf transport variability is controlled by the local wind at high frequency periods less than a year and by the equatorward inflow of southern waters at longer periods our simulation indicates that the variability of the subtropical shelf front is modulated by the local wind stress forcing position of the brazil malvinas confluence and the equatorward inflow of subantarctic waters

late time drainage from a sloping boussinesq aquifer numerical solutions to the nonlinear boussinesq equation applied to a steeply sloping aquifer and assuming uniform hydraulic conductivity indicate that late time recession discharge decreases nearly linearly in time when recession discharge is characterized by dq dt aqb this is equivalent to constant dq dt or b 0 this result suggests that a previously reported exponential decrease with time b 1 of modeled recession discharge from a similar sloping aquifer represented by the same equation appears to be an artifact of the numerical solution scheme and its interpretation because the linearly decreasing recession discharge b 0 is not known from field studies these findings challenge the application of a nonlinear boussinesq framework assuming uniform conductivity and geometric similarity to infer hydraulic properties of sloping aquifers from observations of streamflow this finding also questions the validity of the physical interpretation of the exponential decline in late time resulting from the commonly used linearized form of the boussinesq equation opposed to the full nonlinear equation when applied under these conditions for this reason application of the linearized equation to infer hydraulic properties of sloping aquifers is also challenged even if the observed recession is consistent with that of the linearized boussinesq equation

effects of unsaturated flow on hillslope recession characteristics recession flow analysis is usually conducted to infer hydraulic parameters of hillslope aquifers various boussinesq equation based models both linear and nonlinear have been used to analyze the recession curves for sloping aquifers with a focus on the long time recession behavior based on a modified boussinesq equation with capillarity incorporated we demonstrate the significant effect of unsaturated flow on the recession curve which result in three instead of two power law regimes with two transition points instead of one corresponding to the formation of a fully unsaturated zone at the adjacent area of the upslope boundary and across the whole domain respectively the results show that the power of the second and third recession regime is variable depending on the slope angles soil types and hillslope geometries the unsaturated flow effects also lead to the absence of drastic drop of formula presented at the transition between the first and second regime which was predicted by previous numerical models but has not been observed in the field or laboratory experiments these findings have important implications for recession flow analysis in studies of hillslope aquifers

confirmation of a short time expression for the hydrograph rising limb of an initially dry aquifer using laboratory hillslope outflow experiments the objective of this study is to assess the validity of a theoretical expression for the outflow from an initially dry aquifer subject to recharge this equation states that for small values of time this outflow is proportional to the square root of time here we report on experiments performed with two laboratory hillslopes in the wageningen rainfall simulator three different aquifer slopes were investigated with four replicates for each slope the relations between the measured outflows and the square root of time exhibited very high coefficients of determination all but one 0 9 the aquifer saturated hydraulic conductivity k and drainable porosity were determined using a base flow recession analysis with k being consistent with soil physical laboratory measurements the recharge rates obtained using the coefficient of the short time expression and the steady state discharge were consistent as well overall these results confirm the theoretical relationship between the aquifer outflow for the hydrograph rising limb and the square root of time

a two way nested simulation of the oceanic circulation in the southwestern atlantic this article presents the results of a high resolution 1 12 two way nested simulation of the oceanic circulation in the southwestern atlantic region a comparison between the model results and extant observations indicates that the nested model has skill in reproducing the best known aspects of the regional circulation e g the volume transport of the acc the latitudinal position of the bmc the shelf break upwelling of patagonia and the zapiola anticyclone sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the brazil malvinas confluence and the transport of the zapiola anticyclone the transport of the brazil current strengthens during the austral summer and weakens during the austral winter these variations are driven by the wind stress curl over the southwestern atlantic the variations of the transport of the malvinas current are out of phase with those of the brazil current most of the seasonal variability of this current is concentrated in the offshore portion of the jet the inshore portion has a weak seasonality that modulates the magnitude of the patagonian shelf break upwelling using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the patagonian shelf and along the inshore boundary of the brazil current shelf waters are preferentially detrained near the brazil malvinas confluence consistent with previous studies our simulation also shows that south of 42 s the malvinas current is composed of two jets which merge near 42 s to form a single jet farther north

on the dynamics of the zapiola anticyclone recent observations obtained in the south atlantic suggest the existence of a strong anticyclonic flow positioned over a major bottom topographic feature known as the zapiola drift here a numerical simulation of the south atlantic is described in which this anticyclone is reproduced and the model is used to diagnose the dynamics maintaining this flow with a mean barotropic transport of 140 sv and bottom velocities of 10 cm s 1 the simulated zapiola anticyclone compares well with in situ observations furthermore the model surface eddy kinetic energy shows a local minimum over the drift in agreement with observations from topex poseidon numerical experiments show that the circulation feature is sensitive to the intensity of the eddy field and to the particular value of the bottom friction both of these tendencies are in agreement with a theoretical explanation of the zapiola anticyclone that has recently appeared elsewhere thus we argue that the anticyclone is maintained by eddy driven potential vorticity fluxes accelerating flow within topographically closed ambient potential vorticity contours as far as we know this is the first south atlantic simulation to reproduce the zapiola anticyclone in a realistic fashion the quantitative success of this experiment is attributed to the use of a topography following sigma coordinate in a spatially well resolved model

vadose zone influences on aquifer parameter estimates of saturated zone hydraulic theory aquifer drainage was numerically simulated by a coupled unsaturated saturated flow equation the effect of the vadose zone on aquifer parameter predictions of classical hydraulic theory was investigated saturated zone hydraulic theory was shown to be fairly robust in estimating the saturated hydraulic conductivity but less so in estimating drainable porosity mainly because of the much tighter possible range for the latter application of the coupled flow equation may explain discrepancies between predictions of classical saturated zone theory and observations

on the upwelling of downwelling currents abstract the term downwelling currents refers to currents with a downslope mass flux in the bottom boundary layer examples are the malvinas and southland currents in the southern hemisphere and the oyashio in the northern hemisphere although many of these currents generate the same type of highly productive ecosystems that is associated with upwelling regimes the mechanism that may drive such upwelling remains unclear in this article it is postulated that the interaction between a downwelling current and the continental slope generates shelfbreak upwelling the proposed mechanism is relatively simple as a downwelling current flows along the continental slope bottom friction and lateral diffusion spread it onto the neighboring shelf thus generating along shelf pressure gradients and a cross shelf circulation pattern that leads to shelfbreak upwelling at difference with previous studies of shelfbreak dynamics e g gawarkiewicz and chapman chapman and lentz and pickart the shelfbreak upwelli

effects of hydraulic conductivity variability on hillslope scale shallow subsurface flow response and storage discharge relations 1 an important problem in scientific hydrology is accounting for the effect of small scale heterogeneity in lumped representations of flow through landscapes in this work we investigate the effect of lateral variations in hydraulic conductivity on saturated subsurface lateral flow through hillslopes using an idealized model based on the boussinesq equation the model simulates flow over an impervious planar base through heterogeneous conductivity fields in response to simple recharge inputs and periodic recharge events the results indicate that the hillslope scale response depends on the relative importance of topographic and water table potential gradients driving flow the relative magnitude of these drivers is related to a dimensionless variable where water table gradients dominate a network of flow paths channel flow through the hillslope toward high conductivity areas and the response is primarily dependent on the boundary condition at the toe of the hillslope where the topographic gradients dominate the flow is delayed by low conductivity areas producing a power law like response suggesting that high exponents in observed storage discharge relations may be traced to the presence of heterogeneity in the landscape these observations suggest that the nature of the lumped hillslope scale hydrologic models depends on the emergent behaviors that arise at that scale as a result of the interactions between hillslope properties including their variability in space the relationship between the hillslopes and their surrounding landscape elements through the boundary conditions and the temporal variability of the recharge that enters the system

variations in the malvinas current volume transport since october 1992 1 we present a set of new current meter measurements collected to monitor the malvinas current mc near its merger with the brazil current at 40 41 s from december 2001 to february 2003 below a jason 1 altimeter track these measurements are compared to former measurements obtained 8 years earlier at the same location they also provide new information on the core of the mc on the continental slope above the 1000 m isobath where a mooring had been previously lost there most of the velocity variation is along isobath 80 of the variance and shows a significant annual cycle the two data sets provide coherent means and statistical parameters on the vertical structure of the flow a 14 year long time series of mc volume transport is derived using satellite altimetry the good correlation between the altimetry derived transport and the transport estimated from the current meter data persists in time over 0 7 for each measurement period a spectacular shift in the spectral composition of transport variations was observed from 1992 until the end of 1997 transport variations occurred at rather short periods 50 90 days and to some degree around 180 days whereas after year 2000 longer periods including a seasonal cycle predominated altimetry derived anomalies of surface geostrophic velocities along the core of the mc show a similar shift in spectral composition suggesting a remote forcing origin

hillslope storage boussinesq model for subsurface flow and variable source areas along complex hillslopes 1 formulation and characteristic response 1 hillslope response to rainfall remains one of the central problems of catchment hydrology flow processes in a one dimensional sloping aquifer can be described by boussinesq s hydraulic groundwater theory most hillslopes however have complex three dimensional shapes that are characterized by their plan shape profile curvature of surface and bedrock and the soil depth field studies and numerical simulation have shown that these attributes are the most significant topographic controls on subsurface flow and saturation along hillslopes in this paper the boussinesq equation is reformulated in terms of soil water storage rather than water table height the continuity and darcy equations formulated in terms of storage along the hillslope lead to the hillslope storage boussinesq hsb equation for subsurface flow solutions of the hsb equation account explicitly for plan shape of the hillslope by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function we investigate the behavior of the hsb model for different hillslope types uniform convergent and divergent and different slope angles under free drainage conditions after partial initial saturation drainage scenario and under constant rainfall recharge conditions recharge scenario the hsb equation is solved by means of numerical integration of the partial differential equation we find that convergent hillslopes drain much more slowly compared to divergent hillslopes the accumulation of moisture storage near the outlet of convergent hillslopes results in bell shaped hydrographs in contrast the fast draining divergent hillslopes produce highly peaked hydrographs in order to investigate the relative importance of the different terms in the hsb equation several simplified nonlinear and linearized versions are derived for instance by recognizing that the width function of a hillslope generally shows smooth transition along the flow direction or by introducing a fitting parameter to account for average storage along the hillslope the dynamic response of these reduced versions of the hsb equation under free drainage conditions depend strongly on hillslope shape and bedrock slope angle for flat slopes of the order of 5 only the simplified nonlinear hsb equation is able to capture the dynamics of subsurface flow along complex hillslopes in contrast for steep slopes of the order of 30 we see that all the reduced versions show very similar results compared to the full version it can be concluded that the complex derivative terms of width with respect to flow distance play a less dominant role with increasing slope angle comparison with the hillslope storage kinematic wave model of troch et al 2002 shows that the diffusive drainage terms of the hsb model become less important for the fast draining divergent hillslopes these results have important implications for the use of simplified versions of the hsb equation in landscapes and for the development of appropriate analytical solutions for subsurface flow along complex hillslopes

the unit response of groundwater outflow from a hillslope subsurface flow from a hillslope can be described by hydraulic groundwater theory as formulated by the boussinesq equation solution of its linear version brings out some of the essential features of this phenomenon arbitrary inputs can be accommodated by simple convolution of the sudden drawdown problem the relative magnitude of the driving mechanisms namely the streamwise pressure gradient resulting in diffusion and gravity i e slope resulting in advection can be determined by a simple dimensionless parameter

a note on groundwater flow along a hillslope 1 particular cases of groundwater flow along a hillslope are studied using the groundwater hydraulic theory e g dupuit approximation described by the boussinesq equation analytical solutions are found as simple transformations of known similarity solutions in particular the expressions for phreatic surface level and volume flux and the corresponding loop rating curve for the flow of a groundwater mound as well as the travelling wave solutions of the boussinesq equation are described in detail

analytical approximations of discharge recessions for steeply sloping aquifers in alpine catchments the validity and applicability of various methods to infer hydraulic properties of sloping aquifers in alpine settings using the power law relationship between the discharge recession and its first time derivative is explored for this purpose a synthetic spring catchment implemented in the numerical groundwater flow model modflow as well as the example of a relict rock glacier in an alpine setting is examined the various approaches are found to differ particularly in the late time domain whereas most of them agree fairly well in the early time domain and at the transition point between the two time domains as the early recession may be affected by uncertainties from inappropriate initial conditions it is proposed to use the transition point for estimating aquifer thickness and transmissivity using only prolonged winter recessions in the analysis of the field data from the relict rock glacier yields estimates of aquifer thickness and hydraulic conductivity consistent with results from a geophysical survey and tracer tests respectively in the other seasons the recession is frequently interrupted by minor recharge events and using the lower envelope of the entire data is found to yield estimates that are too high in the given case it is thus recommended to focus on the winter recession in the analysis of hydrograph data from alpine settings

estimation of aquifer lower layer hydraulic conductivity values through base flow hydrograph rising limb analysis 1 the estimation of catchment averaged aquifer hydraulic conductivity values is usually performed through a base flow recession analysis relationships between the first time derivatives of the base flow and the base flow values themselves derived for small and large values of time are used for this purpose however in the derivation of the short time equations an initially fully saturated aquifer without recharge with sudden drawdown is assumed which occurs very rarely in reality it is demonstrated that this approach leads to a nonnegligible error in the parameter estimates a new relationship is derived valid for the rising limb of a base flow hydrograph succeeding a long rainless period application of this equation leads to accurate estimates of the aquifer lower layer saturated hydraulic conductivity further it has been shown analytically that if base flow is modeled using the linearized boussinesq equation the base flow depends on the effective aquifer depth and the ratio of the saturated hydraulic conductivity to the drainable porosity not on these three parameters separately the results of the new short time expression are consistent with this finding as opposed to the use of a traditional base flow recession analysis when base flow is modeled using the nonlinear boussinesq equation the new expression can be used without a second equation for large values of time to estimate the aquifer lower layer hydraulic conductivity overall the results in this paper suggest that the new methodology outperforms a traditional recession analysis for the estimation of catchment averaged aquifer hydraulic conductivities

time space variability of the local dynamics of the malvinas brazil confluence as revealed by inverted echo sounders two inverted echo sounders have been deployed for approximately 8 months in the region of the confluence of western boundary currents in the south atlantic 37 58 7 s 51 56 4 w and 37 29 3 s 53 49 3 s the confluence of the subtropical brazil current with the sub antarctic malvinas current creates a strong sharp thermohaline front from the time series obtained with the sounders two parameters are obtained and analyzed dynamic height from the surface relative to 800 m and the position of the front the time series of dynamic height indicates the presence of a cold intrusion during november the southward extension of the brazil current and northward extension of the malvinas current during january and a simultaneous warming of the area at both moored locations 0 04 dyn m month from march through june from the dynamic height time series mean geostrophic velocities are calculated the mean value from mid december through mid june is 14 cm s representative of an average southward transport of 10 106 m3 s the maximum southward transport 23 106 m3 s is during january the front oscillates around its mean position with a period of about 1 month and an amplitude that varies from 10 to 50 km the velocity of the displacement reaches values up to 10 km d atmospherically forced oscillations are detected in the records a 21 day oscillation in the time series obtained with the instrument located on the slope of the continental shelf is associated with a coastally trapped wind forced response

a base flow separation algorithm based on the linearized boussinesq equation for complex hillslopes 1 the separation of base flow from discharge records is an important issue in hydrology the objective of this paper is to develop a base flow separation algorithm based on groundwater theory in which the shape of the aquifer is taken into account and for which the parameters can be estimated from river discharge measurements for this purpose an analytical solution to the linearized boussinesq equation for realistic aquifer shapes and temporally variable recharge rates is derived this solution is combined with a mass balance at the land surface in order to construct the base flow separation algorithm the parameters of the base flow filter are calculated on the basis of the same analytical solution comparison of the results of the new algorithm to existing base flow separation methods shows the need for a physical basis for base flow filters