Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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Porosity, Bulk Density, and Volume Reduction During Drying: Review of Measurement Methods and Coefficient Determinations
Qiu, J. ; Khalloufi, S. ; Martynenko, A. ; Dalen, G. van; Schutyser, M.A.I. ; Almeida-Rivera, C. - \ 2015
Drying Technology 33 (2015)14. - ISSN 0737-3937 - p. 1681 - 1699.
pore-size distribution - cooked beef product - mercury porosimetry - physical-properties - structural-properties - vacuum impregnation - image-analysis - porous-media - true density - shrinkage
Several experimental methods for measuring porosity, bulk density and volume reduction during drying of foodstuff are available. These methods include among others geometric dimension, volume displacement, mercury porosimeter, micro-CT, and NMR. However, data on their accuracy, sensitivity, and appropriateness are scarce. This paper reviews these experimental methods, areas of applications and limits. In addition, the concept of porosity, bulk density and volume reduction and their evolution as a function of moisture content during drying is presented. In this study, values of initial porosity (¿0) and density ratio (ß) of some food products are summarized. It has been found that ¿0 is highly dependent on the type of food products, while ß ranges from 1.1 to 1.6. The possibility of calculating solid density based on food compositions has also been validated. The inter-predictions between porosity, bulk density and volume density have been made mathematically evident.
Reactive transport codes for subsurface environmental simulation
Steefel, C.I. ; Appelo, C.A.J. ; Arora, B. ; Kalbacher, D. ; Kolditz, O. ; Lagneau, V. ; Lichtner, P.C. ; Mayer, K.U. ; Meeussen, J.C.L. ; Molins, S. ; Moulton, D. ; Shao, D. ; Simunek, J. ; Spycher, N. ; Yabusaki, S.B. ; Yeh, G.T. - \ 2015
Computational Geosciences 19 (2015)3. - ISSN 1420-0597 - p. 445 - 478.
variably saturated flow - dynamic leaching tests - fluid-rock interaction - porous-media - chemical-reactions - co2 sequestration - biogeochemical processes - geochemical speciation - preferential flow - heterogeneous aquifers
A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, CrunchFlow, MIN3P, and PFLOTRAN. The descriptions include a high-level list of capabilities for each of the codes, along with a selective list of applications that highlight their capabilities and historical development.
Multiscale analysis of structure development in expanded starch snacks
Sman, R.G.M. van der; Broeze, J. - \ 2014
Journal of Physics-Condensed Matter 26 (2014)46. - ISSN 0953-8984
mass-transfer - food materials - bubble-growth - porous-media - systems - polymer - phase - model - simulation - extrusion
In this paper we perform a multiscale analysis of the food structuring process of the expansion of starchy snack foods like keropok, which obtains a solid foam structure. In particular, we want to investigate the validity of the hypothesis of Kokini and coworkers, that expansion is optimal at the moisture content, where the glass transition and the boiling line intersect. In our analysis we make use of several tools, (1) time scale analysis from the field of physical transport phenomena, (2) the scale separation map (SSM) developed within a multiscale simulation framework of complex automata, (3) the supplemented state diagram (SSD), depicting phase transition and glass transition lines, and (4) a multiscale simulation model for the bubble expansion. Results of the time scale analysis are plotted in the SSD, and give insight into the dominant physical processes involved in expansion. Furthermore, the results of the time scale analysis are used to construct the SSM, which has aided us in the construction of the multiscale simulation model. Simulation results are plotted in the SSD. This clearly shows that the hypothesis of Kokini is qualitatively true, but has to be refined. Our results show that bubble expansion is optimal for moisture content, where the boiling line for gas pressure of 4 bars intersects the isoviscosity line of the critical viscosity 10(6) Pa.s, which runs parallel to the glass transition line.
Performance assessment of nitrate leaching models for highly vulnerable soils used in low-input farming based on lysimeter data
Groenendijk, P. ; Heinen, M. ; Klammler, G. ; Fank, J. ; Kupfersberger, H. ; Pisinaras, V. - \ 2014
Science of the Total Environment 499 (2014). - ISSN 0048-9697 - p. 463 - 480.
long-term experiments - hydraulic-properties - hydrological models - standardized assessment - nitrogen dynamics - simulation-models - organic-matter - porous-media - drain flow - water
The agricultural sector faces the challenge of ensuring food security without an excessive burden on the environment. Simulation models provide excellent instruments for researchers to gain more insight into relevant processes and best agricultural practices and provide tools for planners for decision making support. The extent to which models are capable of reliable extrapolation and prediction is important for exploring new farming systems or assessing the impacts of future land and climate changes. A performance assessment was conducted by testing six detailed state-of-the-art models for simulation of nitrate leaching (ARMOSA, COUPMODEL, DAISY, EPIC, SIMWASER/STOTRASIM, SWAP/ANIMO) for lysimeter data of the Wagna experimental field station in Eastern Austria, where the soil is highly vulnerable to nitrate leaching. Three consecutive phases were distinguished to gain insight in the predictive power of the models: 1) a blind test for 2005–2008 in which only soil hydraulic characteristics, meteorological data and information about the agricultural management were accessible; 2) a calibration for the same period in which essential information on field observations was additionally available to the modellers; and 3) a validation for 2009–2011 with the corresponding type of data available as for the blind test. A set of statistical metrics (mean absolute error, root mean squared error, index of agreement, model efficiency, root relative squared error, Pearson's linear correlation coefficient) was applied for testing the results and comparing the models. None of the models performed good for all of the statistical metrics. Models designed for nitrate leaching in high-input farming systems had difficulties in accurately predicting leaching in low-input farming systems that are strongly influenced by the retention of nitrogen in catch crops and nitrogen fixation by legumes. An accurate calibration does not guarantee a good predictive power of the model. Nevertheless all models were able to identify years and crops with high- and low-leaching rates.
Compensation in Root Water Uptake Models Combined with Three-Dimensional Root Length Density Distribution
Heinen, M. - \ 2014
Vadose Zone Journal 13 (2014)2. - ISSN 1539-1663 - 9 p.
hydraulic architecture - integrated approach - porous-media - absorption - conductivity - systems - soils
A three-dimensional root length density distribution function is introduced that made it possible to compare two empirical uptake models with a more mechanistic uptake model. Adding a compensation component to the more empirical model resulted in predictions of root water uptake distributions similar to those predicted by the more complex model. Because root water uptake is a considerable component in the soil water balance, a lot of attention has been paid to defining and applying root water uptake models. These models can be grouped into empirical vs. mechanistic root uptake models. Intermodel comparisons are valuable in understanding the different concepts used. Such a comparison is sometimes difficult because the level of information required by the models is different, for example, information on the root length density distribution. Here a three-dimensional root length density distribution function is introduced that makes it possible to compare two empirical uptake models with a more mechanistic uptake model. Adding a compensation component to the more empirical model results in prediction of root water uptake distributions in the root zone similar to those predicted by the more complex model.
Improved management of winter operations to limit subsurface contamination with degradable deicing chemicals in cold regions
French, H.K. ; Zee, S.E.A.T.M. van der - \ 2014
Environmental Science and Pollution Research 21 (2014)15. - ISSN 0944-1344 - p. 8897 - 8913.
penetrating radar data - solute transport - spatial variability - soil heterogeneity - dc resistivity - porous-media - water - snow - flow - polarization
This paper gives an overview of management considerations required for better control of deicing chemicals in the unsaturated zone at sites with winter maintenance operations in cold regions. Degradable organic deicing chemicals are the main focus. The importance of the heterogeneity of both the infiltration process, due to frozen ground and snow melt including the contact between the melting snow cover and the soil, and unsaturated flow is emphasised. In this paper, the applicability of geophysical methods for characterising soil heterogeneity is considered, aimed at modelling and monitoring changes in contamination. To deal with heterogeneity, a stochastic modelling framework may be appropriate, emphasizing the more robust spatial and temporal moments. Examples of a combination of different field techniques for measuring subsoil properties and monitoring contaminants and integration through transport modelling are provided by the SoilCAM project and previous work. Commonly, the results of flow and contaminant fate modelling are quite detailed and complex and require post-processing before communication and advising stakeholders. The managers’ perspectives with respect to monitoring strategies and challenges still unresolved have been analysed with basis in experience with research collaboration with one of the case study sites, Oslo airport, Gardermoen, Norway. Both scientific challenges of monitoring subsoil contaminants in cold regions and the effective interaction between investigators and management are illustrated.
Multiscale modeling in food engineering
Ho, Q.T. ; Carmeliet, J. ; Datta, A.K. ; Defraeye, T. ; Delele, M.A. ; Herremans, E. ; Opara, L. ; Ramon, H. ; Tijskens, E. ; Sman, R.G.M. van der; Liedekerke, P. Van; Verboven, P. ; Nicolai, B.M. - \ 2013
Journal of Food Engineering 114 (2013)3. - ISSN 0260-8774 - p. 279 - 291.
dissipative particle dynamics - lattice-boltzmann simulations - ray computed-tomography - random-field parameters - subsp mitis wallr. - mass-transfer - porous-media - moisture transport - discrete element - air-flow
Since many years food engineers have attempted to describe physical phenomena such as heat and mass transfer that occur in food during unit operations by means of mathematical models. Foods are hierarchically structured and have features that extend from the molecular scale to the food plant scale. In order to reduce computational complexity, food features at the fine scale are usually not modeled explicitly but incorporated through averaging procedures into models that operate at the coarse scale. As a consequence, detailed insight into the processes at the microscale is lost, and the coarse scale model parameters are apparent rather than physical parameters. As it is impractical to measure these parameters for the large number of foods that exist, the use of advanced mathematical models in the food industry is still limited. A new modeling paradigm - multiscale modeling - has appeared that may alleviate these problems. Multiscale models are essentially a hierarchy of sub-models which describe the material behavior at different spatial scales in such a way that the sub-models are interconnected. In this article we will introduce the underlying physical and computational concepts. We will give an overview of applications of multiscale modeling in food engineering, and discuss future prospects. (C) 2012 Elsevier Ltd. All rights reserved.
Modeling cooking of chicken meat in industrial tunnel ovens with the Flory-Rehner theory
Sman, R.G.M. van der - \ 2013
Meat Science 95 (2013)4. - ISSN 0309-1740 - p. 940 - 957.
water-holding capacity - protein cross-linking - cod gadus-morhua - mass-transfer - moisture transport - porous-media - heat-transfer - theoretical aspects - capillary-pressure - structural-changes
In this paper we present a numerical model describing the heat and mass transport during the cooking of chicken meat in industrial tunnels. The mass transport is driven by gradients in the swelling pressure, which is described by the Flory-Rehner theory, which relates to the water holding capacity (WHC). For cooking temperatures up to boiling point and practical relevant cooking times, the model renders good prediction of heat and mass transport and the total loss of moisture. We have shown that for cooking temperatures above boiling point, the model has to be extended with the dynamic growth of capillary water (drip) channels. Furthermore, we discuss that the Flory-Rehner theory provides the proper physical basis for describing the change of the WHC by a wide variety of factors like salt and pH. (C) 2013 Elsevier Ltd. All rights reserved.
Investigation of Lattice Boltzmann wetting boundary conditions for capillaries with irregular polygonal cross-section
Sman, R.G.M. van der - \ 2013
Computer Physics Communications 184 (2013)12. - ISSN 0010-4655 - p. 2751 - 2760.
binary fluids - porous-media - simulations - flows - model - equation - configurations - dynamics - schemes
We have investigated the performance of an alternative wetting boundary condition for complex geometries in a phase field Lattice Boltzmann scheme, which is an alternative to the commonly used formulation by Yeomans and coworkers. Though our boundary condition is much simpler in its implementation, all investigated schemes show proper droplet spreading behaviour following the Cox-Voinov law. Still, numerical artefacts like spurious velocities or chequer board effects in the pressure field can be significantly reduced by the use of a two-relaxation-time (TRT) scheme, likewise recent studies by the Yeomans group. The outstanding property of our implementation is the presence of an (artificial) thin wetting layer, which influences the relation between the saturation (S-w) and capillary pressure p(cap) in channels with irregular polygonal cross section. The p(cap) (S-w) relation from our simulation follows the shifted-Young-Laplace (sYL) law, showing that the physics of this wetting layer is similar to precursor films due to Van der Waals forces. With the knowledge of the thickness of the wetting layer, simulation results can be translated back to realistic pore configurations with thinner wetting layers. (C) 2013 Elsevier B.V. All rights reserved.
A Paradigm Shift in Drying of Food Materials via Free-Volume Concepts
Sman, R.G.M. van der; Jin, X. ; Meinders, M.B.J. - \ 2013
Drying Technology 31 (2013)15. - ISSN 0737-3937 - p. 1817 - 1825.
water-vapor absorption - moisture transport - simultaneous heat - mass-transfer - porous-media - meat - polymers - behavior - sorption - models
We give an overview of the prediction of thermodynamics of food materials, and the kinetics of water transport in them using universal theories based on free volume concepts. These material properties are highly relevant to the prediction of food drying. These presented theories are shown to hold for a large class of polysaccharides and proteins. These different food materials apparently follow the soft matter paradigm that materials' behavior at length scales larger than the molecular scale are dominantly determined by physical characteristics rather than their chemical details. We pose that for food and other bio-materials hydrogen-bonding is largely determining their physical behavior, as in drying. [Supplementary materials are available for this article. Go to the publisher's online edition of Drying Technology for the following free supplemental resource(s): Data sets.]
The impact of aquifer heterogeneity on the performance of aquifer thermal energy storage
Sommer, W.T. ; Valstar, J.R. ; Gaans, P. van; Grotenhuis, J.T.C. ; Rijnaarts, H. - \ 2013
Water Resources Research 49 (2013)12. - ISSN 0043-1397 - p. 8128 - 8138.
heat-transport - solute transport - porous-media - hydraulic conductivity - geothermal systems - field - simulation - flow - macrodispersion - dispersion
Heterogeneity in hydraulic properties of the subsurface is not accounted for in current design calculations of aquifer thermal energy storage (ATES). However, the subsurface is heterogeneous and thus affects the heat distribution around ATES wells. In this paper, the influence of heterogeneity on the performance of a doublet well system is quantified using stochastic heat transport modeling. The results show that on average, thermal recovery decreases with increasing heterogeneity, expressed as the lognormal standard deviation of the hydraulic conductivity field around the doublet. Furthermore, heterogeneity at the scale of a doublet ATES system introduces an uncertainty in the amount of expected thermal interference between the warm and cold storage. This results in an uncertainty in thermal recovery that also increases with heterogeneity and decreases with increasing distance between ATES wells. The uncertainty in thermal balance due to heterogeneity can reach values near 50 percent points in case of regional groundwater flow in excess of 200 m/yr. To account for heterogeneity whilst using homogeneous models, an attempt was made to express the effect of heterogeneity by an apparent macrodispersivity. As expected, apparent macrodispersivity increases with increasing heterogeneity. However, it also depends on well-to-well distance and regional groundwater velocity. Again, the uncertainty in thermal recovery is reflected in a range in the apparent macrodispersivity values. Considering the increasing density of ATES systems, we conclude that thermal interference limits the number of ATES systems that can be implemented in a specific area, and the uncertainty in the hydraulic conductivity field related to heterogeneity should be accounted for when optimizing well-to-well distances.
MRI of plants and foods
As, H. van; Duynhoven, J.P.M. van - \ 2013
Journal of Magnetic Resonance 229 (2013). - ISSN 1090-7807 - p. 25 - 34.
nuclear-magnetic-resonance - distance water transport - stem diameter variations - nmr-spectroscopy - imaging system - self-diffusion - porous-media - rheo-nmr - pfg-nmr - flow
The importance and prospects for MRI as applied to intact plants and to foods are presented in view of one of humanity's most pressing concerns, the sustainable and healthy feeding of a worldwide increasing population. Intact plants and foods have in common that their functionality is determined by complex multiple length scale architectures. Intact plants have an additional level of complexity since they are living systems which critically depend on transport and signalling processes between and within tissues and organs. The combination of recent cutting-edge technical advances and integration of MRI accessible parameters has the perspective to contribute to breakthroughs in understanding complex regulatory plant performance mechanisms. In food science and technology MRI allows for quantitative multi-length scale structural assessment of food systems, non-invasive monitoring of heat and mass transport during shelf-life and processing, and for a unique view on food properties under shear. These MRI applications are powerful enablers of rationally (re)designed food formulations and processes. Limitations and bottlenecks of the present plant and food MRI methods are mainly related to short T-2 values and susceptibility artefacts originating from small air spaces in tissues/materials. We envisage cross-fertilisation of solutions to overcome these hurdles in MRI applications in plants and foods. For both application areas we witness a development where MRI is moving from highly specialised equipment to mobile and downscaled versions to be used by a broad user base in the field, greenhouse, food laboratory or factory. (C) 2013 Elsevier Inc. All rights reserved.
Hydrological effects of buried palaeosols in eroding landscapes: A case study in South Africa
Temme, A.J.A.M. ; Schaap, J.D. ; Sonneveld, M.P.W. ; Botha, G.A. - \ 2012
Quaternary International 265 (2012). - ISSN 1040-6182 - p. 32 - 42.
pleistocene-holocene transition - hydraulic conductivity - pedotransfer functions - retention characteristics - porous-media - northern - climate - evolution - soils - flow
Palaeosols have long been studied as valuable records of past climate and landscape changes. The influence of palaeosols on the functioning of present-day landscapes is receiving closer attention due to the relevance of palaeosols on long-term hydrological processes and the future hydrological and erosive response of catchments. This study describes a sequence of interbedded colluvial sedimentary deposits and buried palaeosols exposed by gully erosion in the Drakensberg escarpment foothills in KwaZulu-Natal province, South Africa. Model simulations are then presented that explore present-day hydrological effects of pedogenetic and textural differentiation under conditions of groundwater lowering caused by gully erosion at 14 sites. The results suggest that the colluvial deposits and palaeosols cause a significant increase in total annual drainage from most of the 14 studied sites compared with similar sites without textural or structural differentiation. In the simulations, sediment deposition, not palaeosol formation, has the most profound influence on the present-day hydrological functioning of the catchment: a true deposystem service. The effects of the limited observed palaeosol development on soil water holding capacity and actual soil water storage appear to be negligible
Modelling the effect of aggregates on N2O emission from denitrification in an agricultural peat soil
Stolk, P.C. ; Hendriks, R.F.A. ; Jacobs, C.M.J. ; Moors, E.J. ; Kabat, P. - \ 2011
Biogeosciences 8 (2011)9. - ISSN 1726-4170 - p. 2649 - 2663.
nitrous-oxide emissions - covariance flux measurements - water-flow - structured soils - porous-media - new-zealand - simulation - grassland - field - dynamics
Nitrous oxide (N2O) emissions are highly variable in time, with high peak emissions lasting a few days to several weeks and low background emissions. This temporal variability is poorly understood which hampers the simulation of daily N2O emissions. In structured soils, like clay and peat, aggregates hamper the diffusion of oxygen, which leads to anaerobic microsites in the soil, favourable for denitrification. Diffusion of N2O out of the aggregates is also hampered, which leads to delayed emissions and increased reduction of N2O to N-2. In this model simulation study we investigate the effect of aggregates in soils on the N2O emissions. We present a parameterization to simulate the effects of aggregates on N2O production by denitrification and on N2O reduction. The parameterization is based on the mobile-immobile model concept. It was implemented in a field-scale hydrological-biogeochemical model combination. We compared the simulated fluxes with observed fluxes from a fertilized and drained peat soil under grass. The results of this study show that aggregates strongly affect the simulated N2O emissions: peak emissions are lower, whereas the background emissions are slightly higher. Including the effect of aggregates caused a 40% decrease in the simulated annual emissions relative to the simulations without accounting for the effects of aggregates. The new parameterization significantly improved the model performance regarding simulation of observed daily N2O fluxes; r(2) and RMSE improved from 0.11 and 198 g N2O-N ha(-1) d(-1) to 0.41 and 40 g N2O-N ha(-1) d(-1), respectively. Our analyses of the model results show that aggregates have a larger impact on the reduction than on the production of N2O. Reduction of N2O is more sensitive to changes in the drivers than production of N2O and is in that sense the key to understanding N2O emissions from denitrification. The effects of changing environmental conditions on reduction of N2O relative to N2O production strongly depend on the NO3 content of the soil. More anaerobic conditions have hardly any effect on the ratio of production to reduction if NO3 is abundant, but will decrease this ratio if NO3 is limiting. In the first case the emissions will increase, whereas in the second case the emissions will decrease. This study suggests that the current knowledge of the hydrological, biogeochemical and physical processes may be sufficient to understand the observed N2O fluxes from a fertilized clayey peatland. Further research is needed to test how aggregates affect the N2O fluxes from other soils or soils with different fertilization regimes.
Alternative Analytical Expressions for the General van Genuchten-Mualem and van Genuchten-Burdine Hydraulic Conductivity Models
Neto, D.D. ; Lier, Q.D. van; Genuchten, M.T. van; Reichardt, K. ; Metselaar, K. ; Nielsen, D.R. - \ 2011
Vadose Zone Journal 10 (2011)2. - ISSN 1539-1663 - p. 618 - 623.
unsaturated soils - porous-media - permeability - flow
The van Genuchten expressions for the unsaturated soil hydraulic properties, first published in 1980, are used frequently in various vadose zone flow and transport applications assuming a specific relationship between the m and n soil hydraulic parameters. By comparison, probably because of the complexity of the hydraulic conductivity equations, the more general solutions with independent m and n values are rarely used. We expressed the general van Genuchten-Mualem and van Genuchten-Burdine hydraulic conductivity equations in terms of hypergeometric functions, which can be approximated by infinite series that converge rapidly for relatively large values of the van Genuchten-Mualem parameter n but only very slowly when n is close to one. Alternative equations were derived that provide very close approximations of the analytical results. The newly proposed equations allow the use of independent values of the parameters m and n in the soil water retention model of van Genuchten for subsequent prediction of the van Genuchten-Mualem and van Genuchten-Burdine hydraulic conductivity models, thus providing more flexibility in fitting experimental pressure-head-dependent water content, theta(h), and hydraulic conductivity, K(h), or K(theta) data.
Scales in single root water uptake models: a review, analysis and synthesis
Metselaar, K. ; Lier, Q.D. van - \ 2011
European Journal of Soil Science 62 (2011)5. - ISSN 1351-0754 - p. 657 - 665.
zea-mays l - soil-water - plant-roots - porous-media - hydraulic conductivity - computed-tomography - system architecture - nutrient-uptake - sample-size - volume
Scales in transport of water to roots are compared with the length and volume scales by using the concepts associated with the representative elementary volume (REV). The possibility of a mismatch between model scale and system scale when using a Darcy-Buckingham-based model to describe soil water transport to a single root is evaluated. In the absence of a mismatch, the replication requirements for evaluating the Darcy-Buckingham-based model near a single root are discussed by using a synthesis of the elementary scales involved, including those for soil, plant and roots, and of the measurement device. By using REV scales from lattice-Boltzmann simulations, the effective half-root mean distance and the available measurement techniques, the evaluation of Darcy-based single root uptake models is possible in roughly 50% of the combinations of soil- and root-system properties. On the basis of an assessment of the scale characterizing natural soil variability, the number of replicates required to assess the average root water uptake profile near a single root is large, and either requires miniaturization of the measurement methods for the hydraulic transport characteristics, or very homogeneous (artificial) growing media with little variability. Variability of water uptake per unit root length will increase the number of samples required.
Analysis of the thickness of a fresh water lens and of the transition zone
Eeman, S. ; Leijnse, A. ; Raats, P.A.C. ; Zee, S.E.A.T.M. van der - \ 2011
Advances in Water Resources 34 (2011)2. - ISSN 0309-1708 - p. 291 - 302.
geohydrologie - watervoerende lagen - zoet water - zout water - delta's - geohydrology - aquifers - fresh water - saline water - deltas - submarine groundwater discharge - porous-media - coastal aquifer - brine transport - barrier-island - interface - flow - infiltration - dispersion - intrusion
In regions with saline groundwater, fresh water lenses may develop due to rainwater infiltration. The amount of fresh water that is available for e.g. agricultural crops depends on the thickness of the lens and the extent of mixing between fresh and saline water. In this paper, we consider the mixing of fresh water and upward moving saline ground water in low-lying deltaic areas. The parameters that dominate the flow and transport problem are investigated using dimensionless groups and scaled sensitivities. We characterize the numerically simulated thicknesses of the lens and of the mixing zone by spatial moments. Rayleigh number and mass flux ratio, which is the ratio of the salt water seepage and the precipitation, determine the thickness of the fresh water lens. The local thickness of the mixing zone is mainly influenced by the dispersive/diffusive groups and the mass flux ratio. In addition, convergence of streamlines towards an outflow boundary affects the thickness, particularly in the vicinity of this boundary. Analytical and numerical steady state solutions for lens thickness are compared, taking into account upward seepage, for the two cases with and without a density difference between lens and underlying groundwater. Agreement between the numerical and analytical solutions for the lens thickness is good except when the mass flux ratio becomes small. For zero mass flux ratio, it is implicitly assumed in the analytical solution that salt water is stagnant, and that is unrealistic. Relative contributions of longitudinal and transversal hydrodynamic dispersion and diffusion to the thickness of the mixing zone are quantified numerically for different phases of lens formation. Longitudinal dispersion dominates in the early stages of lens formation, while diffusion and transversal dispersion dominate at steady state
Effort to improve coupled in situ chemical oxidation with bioremediation: a review of optimization strategies
Sutton, N.B. ; Grotenhuis, J.T.C. ; Langenhoff, A.A.M. ; Rijnaarts, H.H.M. - \ 2011
Journal of Soils and Sediments 11 (2011)1. - ISSN 1439-0108 - p. 129 - 140.
polycyclic aromatic-hydrocarbons - catalyzed hydrogen-peroxide - contaminated soil - fentons reagent - permanganate oxidation - reductive dechlorination - potassium-permanganate - field demonstration - porous-media - source-area
Purpose - In order to provide highly effective yet relatively inexpensive strategies for the remediation of recalcitrant organic contaminants, research has focused on in situ treatment technologies. Recent investigation has shown that coupling two common treatments-in situ chemical oxidation (ISCO) and in situ bioremediation-is not only feasible but in many cases provides more efficient and extensive cleanup of contaminated subsurfaces. However, the combination of aggressive chemical oxidants with delicate microbial activity requires a thorough understanding of the impact of each step on soil geochemistry, biota, and contaminant dynamics. In an attempt to optimize coupled chemical and biological remediation, investigations have focused on elucidating parameters that are necessary to successful treatment. In the case of ISCO, the impacts of chemical oxidant type and quantity on bacterial populations and contaminant biodegradability have been considered. Similarly, biostimulation, that is, the adjustment of redox conditions and amendment with electron donors, acceptors, and nutrients, and bioaugmentation have been used to expedite the regeneration of biodegradation following oxidation. The purpose of this review is to integrate recent results on coupled ISCO and bioremediation with the goal of identifying parameters necessary to an optimized biphasic treatment and areas that require additional focus. Conclusions and recommendations - Although a biphasic treatment consisting of ISCO and bioremediation is a feasible in situ remediation technology, a thorough understanding of the impact of chemical oxidation on subsequent microbial activity is required. Such an understanding is essential as coupled chemical and biological remediation technologies are further optimized
Uncertainty in the determination of soil hydraulic parameters and its influence on the performance of two hydrological models of different complexity
Baroni, G. ; Facchi, A. ; Gandolfi, C. ; Ortuani, B. ; Horeschi, D. ; Dam, J.C. van - \ 2010
Hydrology and Earth System Sciences 14 (2010)2. - ISSN 1027-5606 - p. 251 - 270.
support vector machines - pedo-transfer functions - padano-veneta region - pedotransfer functions - water-retention - functional-evaluation - bulk-density - unsaturated soils - organic-matter - porous-media
Data of soil hydraulic properties forms often a limiting factor in unsaturated zone modelling, especially at the larger scales. Investigations for the hydraulic characterization of soils are time-consuming and costly, and the accuracy of the results obtained by the different methodologies is still debated. However, we may wonder how the uncertainty in soil hydraulic parameters relates to the uncertainty of the selected modelling approach. We performed an intensive monitoring study during the cropping season of a 10 ha maize field in Northern Italy. The data were used to: i) compare different methods for determining soil hydraulic parameters and ii) evaluate the effect of the uncertainty in these parameters on different variables (i.e. evapotranspiration, average water content in the root zone, flux at the bottom boundary of the root zone) simulated by two hydrological models of different complexity: SWAP, a widely used model of soil moisture dynamics in unsaturated soils based on Richards equation, and ALHyMUS, a conceptual model of the same dynamics based on a reservoir cascade scheme. We employed five direct and indirect methods to determine soil hydraulic parameters for each horizon of the experimental profile. Two methods were based on a parameter optimization of: a) laboratory measured retention and hydraulic conductivity data and b) field measured retention and hydraulic conductivity data. The remaining three methods were based on the application of widely used Pedo-Transfer Functions: c) Rawls and Brakensiek, d) HYPRES, and e) ROSETTA. Simulations were performed using meteorological, irrigation and crop data measured at the experimental site during the period June – October 2006. Results showed a wide range of soil hydraulic parameter values generated with the different methods, especially for the saturated hydraulic conductivity Ksat and the shape parameter a of the van Genuchten curve. This is reflected in a variability of the modeling results which is, as expected, different for each model and each variable analysed. The variability of the simulated water content in the root zone and of the bottom flux for different soil hydraulic parameter sets is found to be often larger than the difference between modeling results of the two models using the same soil hydraulic parameter set. Also we found that a good agreement in simulated soil moisture patterns may occur even if evapotranspiration and percolation fluxes are significantly different. Therefore multiple output variables should be considered to test the performances of methods and models
Estimating seepage intensities from groundwater level time series by inverse modelling: a sensitivity analysis on wet meadow scenarios
Cirkel, D.G. ; Witte, J.P.M. ; Zee, S.E.A.T.M. van der - \ 2010
Journal of Hydrology 385 (2010)1-4. - ISSN 0022-1694 - p. 132 - 142.
hydraulic conductivity - porous-media - uncertainty - flow - calibration - parameters - precipitation - optimization - netherlands - prediction
Mesotrophic wet meadows with an upward seepage of fresh, alkaline groundwater are famous for their high species richness. However, due to the lack of seepage data on an appropriate spatial scale, no quantitative relationships have been established as yet between seepage and the occurrence of seepage-dependent plant communities. Since there is no established method to directly measure upward seepage in the field, we investigated the possibility of inferring the seepage intensity by using measurable hydrological quantities such as ground and surface-water levels. To this end, we designed 16 representative plots of virtual hydrological situations, using known sets of geohydrological parameters. Then we applied the integrated soil-water-atmosphere-plant model SWAP to generate 'measured' time series of ground and surface-water levels for these plots. Finally, using the SCEM-UA optimisation algorithm, we calibrated parameters that affect seepage onto these time series. We analysed how the accuracy and uncertainty of calibrated seepage fluxes depend on the measurement interval of input data and on the accuracy and uncertainty of inferred local geohydrological parameters and boundary conditions. Our analysis shows that it is possible to make reliable estimates of seepage intensities from data provided by easy to place piezometers and water level gauges. For application on real datasets, the analysis gives insight into the limitations of both the approach and the data requirements. For example, data supplied every fortnight was found to be just as valuable for seepage estimation as modern high frequency measurements. When setting up a monitoring programme, our method can help to decide what and when to measure. Furthermore, our method can be used establish quantitative relationships between seepage and plant communities on an appropriate spatial scale
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