Kooperativer Bibliotheksverbund

Berlin Brandenburg

and
and

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Ground water  (89)
Type of Medium
Language
Year
  • 1
    In: Water Resources Research, July 2010, Vol.46(7), pp.n/a-n/a
    Description: Biodegradation of continuously emitted compounds that need a dissolved reaction partner, which is not jointly introduced with the contaminant into the subsurface, is mainly controlled by transverse dispersive mixing. Previous analytical approaches of evaluating mixing‐controlled bioreactive transport in steady state have been based on the assumption that the bulk aqueous‐phase concentration of the reactants is directly available to the specific biomass catalyzing the reaction. These models predict a very narrow stripe of active biomass with high specific biomass concentration. Experimental studies have indicated that such behavior may be unrealistic, particularly for anaerobic biodegradation. I extend the previous analysis to include kinetic solute uptake by the biomass, expressed as a first‐order mass‐transfer process coupled to dual Monod kinetics in the bio‐available domain. The approach is based on the evaluation of conservative components undergoing advective‐dispersive transport, the solution of a quadratic speciation problem within the immobile bio domain, and iterative simulation of linear transport of a single reactive constituent in steady state. Convergence is typically achieved within less than ten iterations. The comparison with simulations assuming instantaneous solute uptake by the biomass indicate that mass‐transfer kinetics may explain larger overlap of reactive constituents and a wider spatial distribution of specific biomass observed in experiments. Depending on the rate coefficient of mass transfer, the overall transformation of the contaminant may be significantly reduced or only slightly shifted to a region farther downstream.
    Keywords: Biodegradation ; Kinetic Mass Transfer ; Reactive Transport ; Monod Kinetics
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Language: English
    In: Journal of Hydrology, February 2017, Vol.545, pp.42-54
    Description: Groundwater resources management requires operational, regional-scale groundwater models accounting for dominant spatial variability of aquifer properties and spatiotemporal variability of groundwater recharge. We test the Ensemble Kalman filter (EnKF) to estimate transient hydraulic heads and groundwater recharge, as well as the hydraulic conductivity and specific-yield distributions of a virtual phreatic aquifer. To speed up computation time, we use a coarsened spatial grid in the filter simulations, and reconstruct head measurements at observation points by a local model in the vicinity of the piezometer as part of the observation operator. We show that the EnKF can adequately estimate both the mean and spatial patterns of hydraulic conductivity when assimilating daily values of hydraulic heads from a highly variable initial sample. The filter can also estimate temporally variable recharge to a satisfactory level, as long as the ensemble size is large enough. Constraining the parameters on concentrations of groundwater-age tracers (here: tritium) and transient hydraulic-head observations cannot reasonably be done by the EnKF because the concentrations depend on the recharge history over longer times while the head observations have much shorter temporal support. We thus use a different method, the Kalman Ensemble Generator (KEG), to precondition the initial ensemble of the EnKF on the groundwater-age tracer data and time-averaged hydraulic-head values. The preconditioned initial ensemble exhibits a smaller spread as well as improved means and spatial patterns. The preconditioning improves the EnKF particularly for smaller ensemble sizes, allowing operational data assimilation with reduced computational effort. In a validation scenario of delineating groundwater protection zones, the preconditioned filter performs clearly better than the filter using the original initial ensemble.
    Keywords: Data Assimilation of Hydraulic Heads ; Ensemble Kalman Filter ; Kalman Ensemble Generator ; Groundwater-Age Tracers ; Phreatic Aquifer ; Groundwater Recharge ; Hydraulic Conductivity ; Specific Yield ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Language: English
    In: Journal of Hydrology, 27 November 2014, Vol.519, pp.3386-3399
    Description: The travel-time distribution between rivers and groundwater observation points and the mixing of freshly infiltrated river water with groundwater of other origin is of high relevance in riverbank filtration. These characteristics usually are inferred from the analysis of natural-tracer time series, typically relying on a stationary input–output relationship. However, non-stationarity is a significant feature of the riparian zone causing time-varying river-to-groundwater transfer functions. We present a non-stationary extension of nonparametric deconvolution by performing stationary deconvolution with windowed time series, enforcing smoothness of the determined transfer function in time and travel time. The nonparametric approach facilitates the identification of unconventional features in travel-time distributions, such as broad peaks, and the sliding-window approach is an easy way to accommodate the method to dynamic changes of the system under consideration. By this, we obtain time-varying signal-recovery rates and travel-time distributions, from which we derive the mean travel time and the spread of the distribution as function of time. We apply our method to electric-conductivity data collected at River Thur, Switzerland, and adjacent piezometers. The non-stationary approach reproduces the groundwater observations significantly better than the stationary one, both in terms of overall metrics and in matching individual peaks. We compare characteristics of the transient transfer function to base flow which indicates shorter travel times at higher river stages.
    Keywords: Travel-Time Distribution ; Bank Filtration ; Non-Stationarity ; Nonparametric Inference ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Language: English
    In: Journal of Hydrology, 15 November 2013, Vol.505, pp.352-363
    Description: Dissolved oxygen (DO) is an important groundwater-quality parameter, especially within the context of drinking-water production by riverbank filtration. In riverbank sediments, a strong decrease of DO over the distance of a few meters has frequently been observed. The consumption rates may vary in time, which puts the representativeness of common, sporadic DO measurements in groundwater, based on monthly or even yearly sampling, into question. We present a new modeling approach that allows efficiently estimating DO concentrations in alluvial groundwater from measured DO concentrations in the river under various temperature and discharge conditions. The model is based on the stochastic–convective reactive approach and assumes a time-invariant lognormal travel-time distribution of the stream tube ensemble connecting the river and a groundwater observation well. DO consumption, resulting from aerobic respiration, is modeled by zero-order kinetics. According to high-resolution DO time series measured in the Thur River (NE-Switzerland) and an adjacent observation well, the DO consumption rate appears to depend on river temperature and discharge. While the temperature dependence of aerobic respiration is well known, the discharge dependence is probably related to an increased trapping of particulate organic matter (POM) within the riverbed during high-discharge events, thus enhancing the POM availability and DO consumption rate. We propose an empirical equation that quantifies the dependence between discharge and the DO consumption rate. The estimated parameterization at our field site suggests that an increasing discharge within the narrow window of 20–50 m /s enhances the DO consumption rate by a factor of 4. By considering the measured DO in the river and including the dependence of the DO consumption rate on both discharge and temperature, the model was able to capture the diurnal, short-term (days to weeks), and seasonal dynamics of the observed DO within the alluvial aquifer. The temperature dependence of the DO consumption rate was found to be more important on a seasonal time scale, while the effect of discharge dominated the DO behavior during hydrological events extending over a few days to weeks. The presented modeling approach can be transferred to other riverbank-filtration systems to efficiently estimate DO concentrations in alluvial aquifers under various climatic and hydrologic conditions and, hence, assess the risk of approaching anoxic conditions in a changing climate.
    Keywords: Riverbank Filtration ; Climate Change ; Oxygen Consumption ; Stochastic–Convective Reactive Transport ; POM ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Source: ScienceDirect Journals (Elsevier)
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Language: English
    In: Journal of Hydrology, 2010, Vol.380(1), pp.154-164
    Description: Vertical temperature profiling in the river beds of losing streams has been shown to be useful in obtaining seepage rates. We present a method for high-resolution vertical temperature profiling in surface-water sediments for detailed quantification of seepage flux over depth and time. The method is based on fiber-optic distributed temperature sensing, in which temperature profiles along an optical fiber are obtained by making use of Raman scattering. An optical fiber was wrapped around a 2 in. PVC tube and installed vertically within the streambed sediment. The wrapping transfers the spatial resolution along the fiber of 1 m to a vertical resolution of about 5 mm. The high-resolution temperature profiler was tested at a losing reach of the Swiss prealpine River Thur resulting in a 20-day long temperature time series with a temporal resolution of 10 min. The time series are analyzed by means of dynamic harmonic regression to obtain the diurnal contributions of the measured time series at all depths and time points. The time for the diurnal temperature signal to reach the observation depth and the associated attenuation of the signal are calculated from the phase angles and amplitudes of the diurnal contributions. The time shift results in an apparent celerity of diurnal temperature propagation, which is converted into an apparent seepage rate by fitting the data to the analytical solution for convective–conductive heat transfer in a semi-infinite, uniform, one-dimensional domain with a sinusoidal surface temperature. The high spatial resolution allows the location of discontinuities in the river bed which would have remained undetected if temperature had been measured only at a few individual depths to be identified. This is a particular strength of the fiber-optic high-resolution temperature profiler. The time series also give evidence of sporadic high infiltration rates at times of high water tables.
    Keywords: River–Groundwater Interaction ; Fiber-Optic Distributed Temperature Sensing ; Time Series Analysis ; Seepage Flux ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Language: English
    In: Water Resources Management, Sept, 2013, Vol.27(12), p.4349(20)
    Description: Byline: Ashutosh Singh (1), Claudius M. Burger (1), Olaf A. Cirpka (1) Keywords: Urban hydrogeology; Groundwater management; MODFLOW; Numerical modeling; Response matrix; Optimization Abstract: In rapidly developing urban areas of emerging countries, increased water demand has led to enormous groundwater withdrawal, calling out for sustainable groundwater management. We suggest implementing a sustainable pumping rate concept based on numerical modeling of the managed aquifer. Sustainability is achieved by constraints regarding (1) a minimum groundwater discharge rate to gaining rivers (ecological constraint) and (2) a maximum drawdown along the city boundaries (social constraints) to prevent excessive groundwater depletion in the neighboring peri-urban and rural areas. The total groundwater extraction is maximized subject to these constraints, leading to specific extraction patterns throughout the city, depending upon the values set for the constraints. The optimization is performed by linear programming. For a given extraction rate, the two constraints can be traded off by the groundwater manager, causing different wells to be activated or deactivated. We demonstrate the applicability of the methodology by the example of the city of Lucknow, India, but it can be transferred to other cities facing conflicts of managing groundwater resources. Author Affiliation: (1) Center for Applied Geoscience (ZAG), University of Tubingen, Holderlinstr. 12, 72074, Tubingen, Germany Article History: Registration Date: 05/08/2013 Received Date: 15/03/2013 Accepted Date: 05/08/2013 Online Date: 18/08/2013
    Keywords: Hydrogeology -- Models ; Water Resource Management -- Models ; Aquifers -- Models ; Groundwater -- Models ; Developing Countries -- Models
    ISSN: 0920-4741
    E-ISSN: 15731650
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    In: Water Resources Research, January 2012, Vol.48(1), pp.n/a-n/a
    Description: We perform a salt tracer experiment, monitored by time‐lapse electrical resistivity tomography, in a quasi‐two‐dimensional sandbox with the aim of determining the hydraulic conductivity distribution in the domain. We use sodium chloride as a tracer, together with cochineal red for visual monitoring. The time series of observed resistance for each electrode configuration is characterized by its temporal moments. We invert the mean arrival time of electrical potential perturbations and a few steady state hydraulic head measurements using the fully coupled hydrogeophysical approach recently introduced by Pollock and Cirpka (2010). This is the first application of the approach to experimental data. The results obtained show a reasonable agreement between the estimated hydraulic conductivity field and the pattern of the actual sandbox filling. Using this estimation, a transient simulation is performed to compute the propagation of the salt tracer plume through the sandbox. The latter is compared to pictures taken during the experiment. These results show an even better agreement, indicating that the lenses of different sand types are not entirely homogeneous and some unexpected preferential flow paths are present. We conclude that temporal moments of potential perturbations obtained during salt tracer tests provide a good basis for inferring the hydraulic conductivity distribution by fully coupled hydrogeophysical inversion. Use temporal moments to invert ERT monitoring data of salt‐tracer experiments Application to laboratory experiments has been successful Inverted results may be better than intended zonation of filling pattern
    Keywords: Electrical Resistivity Tomography ; Fully Coupled Inversion ; Salt Tracer Tests ; Temporal Moments
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    In: Water Resources Research, July 2011, Vol.47(7), pp.n/a-n/a
    Description: The hyporheic zone has been identified as important for river ecology, natural biogeochemical turnover, filtration of particles, degradation of dissolved pollutants—and thus for the self‐cleaning capacity of streams, and for groundwater quality. Good estimation of the traveltime distribution in the hyporheic zone is required to achieve a better understanding of transport in the river system. The transient‐storage model has been accepted as an appropriate tool for reach‐scale transport in rivers undergoing hyporheic exchange, but the choice of the best parametric function for the hyporheic traveltime distribution has remained unclear. We present an approach to obtaining hyporheic traveltime distributions from synchronous conservative and “smart” tracer experiments that does not rely on a particular functional form of the hyporheic traveltime distribution, but treats the latter as a continuous function. Nonnegativity of the hyporheic traveltime distribution is enforced by the application of Lagrange multipliers. A smoothness parameter, needed for regularization, and uncertainty bounds are obtained by the expectation‐maximization method relying on conditional realizations. The shape‐free inference provides the opportunity for capturing unconventional shapes, e.g., multiple peaks, in the estimation. We test the approach by applying it to a virtual test case with a bimodal hyporheic traveltime distribution, which is recaptured in the inversion of noisy data. No particular functional shape of hyporheic travel distribution is assumed Reactive tracers help separating different mixing process in streams Uncommon features in hyporheic traveltime distribution can be revealed
    Keywords: Bayesian Analysis ; Hyporheic Exchange ; Nonnegativity ; Transient‐Storage Model
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    In: Water Resources Research, February 2011, Vol.47(2), pp.n/a-n/a
    Description: Macroscopic transport models calibrated by flux‐averaged breakthrough curves of conservative compounds do not necessarily characterize mixing well because such breakthrough curves do not provide information on fluctuations of concentration within the solute flux, which may influence mean reaction rates. We numerically examine the validity of macroscopic transport models, which are capable of describing all details of flux‐averaged breakthrough curves, for predicting a mixing‐controlled bimolecular precipitation reaction in heterogeneous media. We consider a homogeneous, isotropic medium with an elliptical, low‐permeability inclusion and random heterogeneous fields. For the single‐inclusion case, slow advection through the inclusion results in a multimodal breakthrough curve with enhanced tailing. We vary the hydraulic conductivity contrast and Peclet number to investigate the performance of a “perfect” macroscopic transport model for predicting the total precipitated mass within the domain and the peak concentration difference between the conservative and reactive cases at the outflow boundary. The results indicate that such a model may perform well in media with either very small or very high permeability contrast or at low Peclet number. In the high‐contrast case, most flow takes place in preferential flow paths, resulting in a small variance of the flux‐weighted concentration, even though the offset in the breakthrough between the slow and fast travel paths is substantial. Maximum relative errors in terms of total precipitated mass and the peak concentration difference between the conservative and reactive cases occur at intermediate permeability contrasts and large Peclet numbers. Numerical simulations on random heterogeneous fields confirm the finding of the single‐inclusion case. Thus, in cases with intermediate hydraulic conductivity contrast, making macroscopic models fit flux‐averaged concentration breakthrough curves better may not improve the prediction of mixing‐controlled reactive transport, and it becomes necessary to quantify and account for the variability of conservative concentrations in the flux in order to formulate an appropriate macroscopic transport model that predicts mixing‐controlled reactive transport.
    Keywords: Reactive Mixing ; Low‐Permeability Inclusion ; Breakthrough Tailing ; Heterogeneous Field
    ISSN: 0043-1397
    E-ISSN: 1944-7973
    Source: John Wiley & Sons, Inc.
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 10
    In: Ground Water, July 2010, Vol.48(4), pp.569-579
    Description: In most groundwater applications, measurements of concentration are limited in number and sparsely distributed within the domain of interest. Therefore, interpolation techniques are needed to obtain most likely values of concentration at locations where no measurements are available. For further processing, for example, in environmental risk analysis, interpolated values should be given with uncertainty bounds, so that a geostatistical framework is preferable. Linear interpolation of steady‐state concentration measurements is problematic because the dependence of concentration on the primary uncertain material property, the hydraulic conductivity field, is highly nonlinear, suggesting that the statistical interrelationship between concentration values at different points is also nonlinear. We suggest interpolating steady‐state concentration measurements by conditioning an ensemble of the underlying log‐conductivity field on the available hydrological data in a conditional Monte Carlo approach. Flow and transport simulations for each conditional conductivity field must meet the measurements within their given uncertainty. The ensemble of transport simulations based on the conditional log‐conductivity fields yields conditional statistical distributions of concentration at points between observation points. This method implicitly meets physical bounds of concentration values and non‐Gaussianity of their statistical distributions and obeys the nonlinearity of the underlying processes. We validate our method by artificial test cases and compare the results to kriging estimates assuming different conditional statistical distributions of concentration. Assuming a beta distribution in kriging leads to estimates of concentration with zero probability of concentrations below zero or above the maximal possible value; however, the concentrations are not forced to meet the advection‐dispersion equation.
    Keywords: Hydrogeology -- Analysis ; Hydrogeology -- Models ; Groundwater -- Analysis ; Groundwater -- Models ; Advection (Earth sciences) -- Analysis ; Advection (Earth sciences) -- Models;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. Further information can be found on the KOBV privacy pages