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Flow Processes (flow + process)
Kinds of Flow Processes Selected AbstractsEvaluation of the MODFLOW-2005 Conduit Flow ProcessGROUND WATER, Issue 4 2010Melissa E. Hill The recent development of the Conduit Flow Process (CFP) by the U.S. Geological Survey (USGS) provides hydrogeologic modelers with a new tool that incorporates the non-Darcian, multiporosity components of flow characteristic of karst aquifers. CFP introduces new parameters extending beyond those of traditional Darcian groundwater flow codes. We characterize a karst aquifer to collect data useful for evaluating this new tool at a test site in west-central Florida, where the spatial distribution and cross-sectional area of the conduit network are available. Specifically, we characterize: (1) the potential for Darcian/non-Darcian flow using estimates of specific discharge vs. observed hydraulic gradients, and (2) the temporal variation for the direction and magnitude of fluid exchange between the matrix and conduit network during extreme hydrologic events. We evaluate the performance of CFP Mode 1 using a site-scale dual-porosity model and compare its performance with a comparable laminar equivalent continuum model (ECM) using MODFLOW-2005. Based on our preliminary analyses, hydraulic conductivity coupled with conduit wall conductance improved the match between observed and simulated discharges by 12% to 40% over turbulent flow alone (less than 1%). [source] MODFLOW-CFP: A New Conduit Flow Process for MODFLOW,2005GROUND WATER, Issue 3 2009Thomas Reimann First page of article [source] Fast and Enantioselective Production of 1-Aryl-1-propanols through a Single Pass, Continuous Flow ProcessADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2008Miquel Abstract A functional polymer 4, obtained by reaction of (R)-2-(1-piperazinyl)-1,1,2-triphenylethanol with a Merrifield resin, has been loaded in a packed bed reactor and used as catalyst for the continuous enantioselective production of 1-arylpropanols by ethylation of aromatic aldehydes. The high catalytic activity depicted by 4 allows the complete conversion of the substrates with the use of stoichiometric reagent ratios and unprecedently short residence times (down to 2.8,min). In practice, a single-pass operation can be used for all the studied aldehydes, and productions of up to 13.0 mol/g,h are recorded. The sequential operation of the flow system for the uninterrupted synthesis of a small library of enantiopure 1-arylpropanols is also reported. [source] ChemInform Abstract: Epoxidation of Alkenes Using HOF·MeCN by a Continuous Flow Process.CHEMINFORM, Issue 30 2009Christopher B. McPake Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Elongational Rheology of Polymer/Clay Dispersions: Determination of Orientational Extent in Elongational Flow Processes,MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2008Eduard A. Stefanescu Abstract The purpose of the present contribution is to provide an efficient method that would help to quantify the orientational levels occurring in polymer/clay dispersions subjected to elongational flow. The extent of internal orientation developed in salt containing montmorillonite/poly(ethylene oxide) gels is investigated, combining shear and elongational rheology methods. Entropic changes indicate that the strength of the transient network present in each gel affects the orientational ability of clay particles and polymer chains. We found that an increased Hencky strain of the hyperbolic die leads to a higher variation of the calculated entropy of the material. [source] Combining Enabling Techniques in Organic Synthesis: Continuous Flow Processes with Heterogenized CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2006Andreas Kirschning Prof. Dr. Abstract The concepts article describes enabling techniques (solid-phase assisted synthesis, new reactor design, microwave irradiation and new solvents) in organic chemistry and emphasizes the combination of several of them for creating new synthetic technology platforms. Particular focus is put on the combination of immobilized catalysts as well as biocatalysts with continuous flow processes. In this context, the PASSflow continuous flow technique fulfils both chemical as well as chemical engineering requirements. It combines reactor design with optimized, monolithic solid phases as well as reversible immobilization techniques for performing small as well as large scale synthesis with heterogenized catalysts under continuous flow conditions. [source] Scanning Electrochemical Microscopy as an In Vitro Technique for Measuring Convective Flow Rates Across Dentine and the Efficacy of Surface Blocking TreatmentsELECTROANALYSIS, Issue 3 2005Julie Abstract Scanning electrochemical microscopy (SECM) is shown to be a powerful technique for both the measurement of local solution velocities through human dentine slices, in vitro, and for assessing quantitatively the effect of surface treatments on the flow process. SECM employs a small ultramicroelectrode (micron dimensions) as an imaging probe to provide information on the topography and transport characteristics of dentine, with high spatial resolution. In these studies the dentine sample is a membrane in a two compartment cell, which contains solutions of identical composition, including a redox active mediator (Fe(CN). In the absence of an applied pressure, the transport-limited current response at the probe electrode is due to diffusion of Fe(CN) to the UME, which depends on the probe to sample separation. Under an applied hydrostatic pressure, hydrodynamic flow across the sample enhances mass transport to the UME. With this methodology it was possible to accurately measure effective fluid velocities, by recording tip currents with and without pressure, and assess the efficacy of potential flow retarding agents for the treatment of dentinal hypersensitivity. For native dentine, the solution velocity was found to vary dramatically with location on the sample. The application of a glycerol monooleate - base paste treatment to the surface of dentine was found to lower local flow velocities significantly. This electroanalytical methodology is simple to implement and is generally applicable to assessing the efficacy and mode of action of a wide variety of potential fluid flow retarding agents. [source] On-line cell lysis and DNA extraction on a microfluidic biochip fabricated by microelectromechanical system technologyELECTROPHORESIS, Issue 9 2008Xing Chen Dr. Abstract Integrating cell lysis and DNA purification process into a micrototal analytical system (,TAS) is one critical step for the analysis of nucleic acids. On-chip cell lysis based on a chemical method is realized by sufficient blend of blood sample and the lyzing reagent. In this paper two mixing models, T-type mixing model and sandwich-type mixing model, are proposed and simulation of those models is conducted. Result of simulation shows that the sandwich-type mixing model with coiled channel performs best and this model is further used to construct the microfluidic biochip for on-line cell lysis and DNA extraction. The result of simulation is further verified by experiments. It asserts that more than 80% mixing of blood sample and lyzing reagent which guarantees that completed cell lysis can be achieved near the inlet location when the cell/buffer velocity ratio is less than 1:5. After cell lysis, DNA extraction by means of a solid-phase method is implemented by using porous silicon matrix which is integrated in the biochip. During continuous flow process in the microchip, rapid cell lysis and PCR-amplifiable genomic DNA purification can be achieved within 20,min. The potential of this microfluidic biochip is illustrated by pretreating a whole blood sample, which shows the possibility of integration of sample preparation, PCR, and separation on a single device to work as portable point-of-care medical diagnostic system. [source] Hydrometeorological controls and erosive response of an extreme alpine debris flowHYDROLOGICAL PROCESSES, Issue 19 2009Lorenzo Marchi Abstract On 29 August, 2003, an intense convective storm system affected the Fella River basin, in the eastern Italian Alps, producing rainfall peaks of approximately 390 mm in 12 h. The storm triggered an unusually large debris flow in the ungauged Rio Cucco basin (0·65 km2), with a volume of approximately 78 000 m3. The analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network. Detailed geomorphological field surveys, carried out both before and after the flood of August 2003, and the application of a distributed hydrological model have enabled assessment of flood response, estimation of erosion volumes and sediment supply to the channel network. The accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event. Liquid peak discharge estimates cluster around 20 m3 s,1 km,2, placing this event on the flood envelope curve for the eastern Italian Alps. The hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount, required to exceed the large initial losses, and the large rainfall intensities at hourly temporal scales, required to generate high flood response at the considered basin scale. Observations on the deposits accumulated on the alluvial fan indicate that, although the dominant flow process was a debris flow, sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris-flow lobes and redistributing sediment on the fan surface. This points out to the large discharge values during the recession phase of the flood, implying an important role for subsurface flow on runoff generation of this extreme flash flood event. Copyright © 2009 John Wiley & Sons, Ltd. [source] The Use of Copper Flow Reactor Technology for the Continuous Synthesis of 1,4-Disubstituted 1,2,3-TriazolesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2009Andrew Abstract A library of 1,4-disubstituted 1,2,3-triazoles was synthesized using a copper flow reactor. Organic azides, generated in situ from alkyl halides and sodium azide, were reacted with acetylenes using the copper-catalyzed Huisgen 1,3-dipolar cycloaddition. This process eliminates both the handling of organic azides and the need for additional copper catalyst and permits the facile preparation of numerous triazoles in a continuous flow process. [source] Spatial and temporal variations in bank erosion on sand-bed streams in the seasonally wet tropics of northern AustraliaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2006M. J. Saynor Abstract Bank erosion rates and processes across a range of spatial scales are poorly understood in most environments, especially in the seasonally wet tropics of northern Australia where sediment yields are among global minima. A total of 177 erosion pins was installed at 45 sites on four sand-bed streams (Tributaries North and Central, East Tributary and Ngarradj) in the Ngarradj catchment in the Alligator Rivers Region. Bank erosion was measured for up to 3·5 years (start of 1998/99 wet season to end of 2001/02 wet season) at three spatial scales, namely a discontinuous gully (0·6 km2) that was initiated by erosion of a grass swale between 1975 and 1981, a small continuous channel (2·5 km2) on an alluvial fan that was formed by incision of a formerly discontinuous channel between 1964 and 1978, and three medium-sized, continuous channels (8·5,43·6 km2) with riparian vegetation. The bank erosion measurements during a period of average to above-average rainfall established that substantial bank erosion occurred during the wet season on the two smaller channels by rapid lateral migration (Tributary Central) and by erosion of gully sidewalls due to a combination of within-gully flows and overland flow plunging over the sidewalls (Tributary North). Minor bank erosion also occurred during the dry season by faunal activity, by desiccation and loss of cohesion of the sandy bank sediments and by dry flow processes. The larger channels with riparian vegetation (East Tributary and Ngarradj) did not generate significant amounts of sediment by bank erosion. Deposition (i.e. negative pin values) was locally significant at all scales. Bank profile form and channel planform exert a strong control on erosion rates during the wet season but not during the dry season. Copyright © 2006 Commonwealth Government of Australia. [source] 1H and 19F nuclear magnetic resonance microimaging of water and chemical distribution in soil columnsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2007Myrna J. Simpson Abstract Nuclear magnetic resonance (NMR) microimaging is a noninvasive and nondestructive technique that has great potential for the study of soil processes. Hydrogen-1 NMR microimaging techniques were used to examine the distribution of water in four different soil cores. Fluorine-19 NMR microimaging is also used to study the transport of three model contaminants (hexafluorobenzene, sodium fluoride, and trifluralin) in soil columns. The 1H water distribution studies demonstrate that NMR microimaging can provide unique detail regarding the nature and location of water in soils. Image distortion (magnetic susceptibility) was observed for soil samples low in water (20,28% by weight) and that contained an iron content of 0.73 to 0.99%. Highly resolved images were obtained for the organic-rich soil (Croatan sample) and also facilitated the analysis of bound and unbound soil water through varying spin echo times. The contaminant studies with 19F NMR demonstrated that preferential flow processes can be observed in soil cores in as little as 16 h. Studies with hexafluorobenzene produced the highest quality images whereas the definition decreased over time with both trifluralin and sodium fluoride as the compounds penetrated the soil. Nonetheless, both 1H and 19F NMR microimaging techniques demonstrate great promise for studying soil processes. [source] Preferential flow and transport in soil: progress and prognosisEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008B. E. Clothier Summary Soil is the first filter of the world's water; its buffering and filtering determine the quality and quantity of our reserves of subterranean and surface water. Preferential flow can either enhance, or curtail, the capacity of the soil to buffer and filter, and it can compromise, or boost, other ecosystem services. We ask ,when do preferential flow and transport matter?' We identify 12 of 17 ecosystem services that benefit from preferential flow and three that are affected detrimentally. We estimate by simple arithmetic the value of preferential flow to ecosystem services to be globally some US$304 billion (109) per year. We review the 1989 Monte Verità meeting on preferential flow processes and summarize the 2006 presentations, some of which are published in this issue of the Journal. New technologies and innovative experiments have increased our understanding of the conditions that initiate and sustain preferential flows. We identify contemporary exigencies, and suggest avenues for their resolution. We are progressing through observation-led discovery. Our prognosis is that new data will enable us to develop better models, and more aptly to parameterize existing models, and thereby predict the impact, benefits and detriments of preferential flow in soil. [source] Geomorphology Fluid Flow Modelling: Can Fluvial Flow Only Be Modelled Using a Three-Dimensional Approach?GEOGRAPHY COMPASS (ELECTRONIC), Issue 1 2008R. J. Hardy The application of numerical models to gain insight into flow processes is becoming a prevalent research methodology in fluvial geomorphology. The advantage of this approach is that models are particularly useful for identifying emergent behaviour in the landscape where combinations of processes act over several scales. However, there are a wide range of available models and it is not always apparent that methodological approach should be chosen. The decision about the amount of process representation required needs to be balanced against both the spatial and temporal scales of interest. In this article, it is argued that in order to gain a complete, high resolution process understanding of flow within the fluvial system a full three-dimensional modelling approach with a complete physical basis is required. [source] Modular Microreaction Systems for Homogeneously and Heterogeneously Catalyzed Chemical SynthesisHELVETICA CHIMICA ACTA, Issue 1 2005Daniel Until now, microreaction devices designed for a specific type of reaction were used mainly for highly exothermic, very fast reactions. Described is a modular microreaction system and its application to representative homogeneous and heterogeneous reactions important in organic synthesis. The modular microreaction system allows continuous flow processes to be optimized and employed effectively in the chemical laboratory. The modular microreaction systems proved also versatile for syntheses requiring moderate reaction times, thus extending their application to a large fraction of organic reactions. The use of the modular and cleanable microreaction systems to rapidly develop optimized reaction conditions provides an excellent basis for the development of many chemical transformations scalable from milligram to ton production quantities. [source] Influence of pore size and geometry on peat unsaturated hydraulic conductivity computed from 3D computed tomography image analysisHYDROLOGICAL PROCESSES, Issue 21 2010F. Rezanezhad Abstract In organic soils, hydraulic conductivity is related to the degree of decomposition and soil compression, which reduce the effective pore diameter and consequently restrict water flow. This study investigates how the size distribution and geometry of air-filled pores control the unsaturated hydraulic conductivity of peat soils using high-resolution (45 µm) three-dimensional (3D) X-ray computed tomography (CT) and digital image processing of four peat sub-samples from varying depths under a constant soil water pressure head. Pore structure and configuration in peat were found to be irregular, with volume and cross-sectional area showing fractal behaviour that suggests pores having smaller values of the fractal dimension in deeper, more decomposed peat, have higher tortuosity and lower connectivity, which influences hydraulic conductivity. The image analysis showed that the large reduction of unsaturated hydraulic conductivity with depth is essentially controlled by air-filled pore hydraulic radius, tortuosity, air-filled pore density and the fractal dimension due to degree of decomposition and compression of the organic matter. The comparisons between unsaturated hydraulic conductivity computed from the air-filled pore size and geometric distribution showed satisfactory agreement with direct measurements using the permeameter method. This understanding is important in characterizing peat properties and its heterogeneity for monitoring the progress of complex flow processes at the field scale in peatlands. Copyright © 2010 John Wiley & Sons, Ltd. [source] Hydrometeorological controls and erosive response of an extreme alpine debris flowHYDROLOGICAL PROCESSES, Issue 19 2009Lorenzo Marchi Abstract On 29 August, 2003, an intense convective storm system affected the Fella River basin, in the eastern Italian Alps, producing rainfall peaks of approximately 390 mm in 12 h. The storm triggered an unusually large debris flow in the ungauged Rio Cucco basin (0·65 km2), with a volume of approximately 78 000 m3. The analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network. Detailed geomorphological field surveys, carried out both before and after the flood of August 2003, and the application of a distributed hydrological model have enabled assessment of flood response, estimation of erosion volumes and sediment supply to the channel network. The accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event. Liquid peak discharge estimates cluster around 20 m3 s,1 km,2, placing this event on the flood envelope curve for the eastern Italian Alps. The hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount, required to exceed the large initial losses, and the large rainfall intensities at hourly temporal scales, required to generate high flood response at the considered basin scale. Observations on the deposits accumulated on the alluvial fan indicate that, although the dominant flow process was a debris flow, sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris-flow lobes and redistributing sediment on the fan surface. This points out to the large discharge values during the recession phase of the flood, implying an important role for subsurface flow on runoff generation of this extreme flash flood event. Copyright © 2009 John Wiley & Sons, Ltd. [source] A new saturated/unsaturated model for stormwater infiltration systemsHYDROLOGICAL PROCESSES, Issue 25 2008Dale Browne Abstract Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one-dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front-tracking model that innovatively combines a soil-moisture-based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non-iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hydrological behaviour and modelling of a volcanic tropical cultivated catchmentHYDROLOGICAL PROCESSES, Issue 22 2008Jean-Baptiste Charlier Abstract The hydrological behaviour of the cultivated Féfé catchment (17·8 ha) on the tropical volcanic island of Guadeloupe was studied to identify flow paths, to quantify water fluxes, and finally, to build a lumped model to simulate discharge and piezometer levels. The approach combined two steps, an experimental step and a modelling step, which covered two time scales, the annual and the storm event scale. The hydrological measurements were conducted over 2 years. The Féfé catchment is characterized by heavy rainfall (4229 mm year,1) on permeable Andosols; the results showed that underground flow paths involved two overlapping aquifers, and that the annual water balance in 2003 was shared among outflows of the deep aquifer (42%), evapotranspiration (31%), and streamflow (27%). On the event scale, the surface runoff coefficient ranges between 6·2% and 24·4% depending on antecedent dry or wet moisture conditions. Hortonian overland flow predominated over subsurface and saturation overland flow processes. Recharge of the shallow aquifer is mainly governed by a constant infiltration capacity of the Andosols with depth in the vadose zone. Outflows of this shallow aquifer were the baseflow of the main stream and the recharge of the deep aquifer. Volcanic deposits at Féfé promoted the underground flow path, and cultivated areas seemed to explain the high stormflow values relative to other tropical small catchments under rain forest. A conceptual lumped model integrating runoff, infiltration, evapotranspiration, and fluctuations of the two overlapping aquifers was developed. The model has six parameters and was calibrated and validated on the hydrograph at the outlet and on the two piezometers of the shallow and the deep aquifers. The results show fair to good agreement between measured and simulated variables, and consequently, the model was consistent with the main hydrological processes observed from experimental results in wet conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Application of a coil-type TDR probe for measuring the volumetric water content in weathered granitic bedrockHYDROLOGICAL PROCESSES, Issue 6 2008Shin'ya Katsura Abstract As a first step toward describing water flow processes in bedrock, a coil-type time domain reflectometry (TDR) probe capable of measuring volumetric water content, ,, in weathered bedrock at three depths was prepared. Because the coil-type TDR probe is large in diameter (19 mm), it can be installed even in highly weathered bedrock more easily and appropriately than conventional TDR probes that consists of two or three rods of small diameter (5-8 mm). The probe calibrations suggest that the values measured by the probe are very sensitive to changes in ,. Using the calibrated probe together with commercially available profile soil moisture sensors, the , profile was monitored for 1 year. Even rainfall events with relatively small cumulative rainfall of 15 mm increased the bedrock ,, and the increments were comparable to those in the soil. After the end of the rainfall events, the bedrock , displayed a more rapid drop than the soil, and varied little during the period of no rainfall. The water storage showed similar tendencies. These observations suggest that the bedrock , is controlled by clearly distinguishable macropores and micropores within the bedrock. It is concluded that the coil-type TDR probe is very effective in determining , in weathered bedrock, and that bedrock, conventionally defined by conducting cone penetration tests and treated as impermeable, does conduct and hold substantial amounts of water, and therefore contribute greatly to hydrological processes in headwater catchments. Copyright © 2007 John Wiley & Sons, Ltd. [source] The impact of groundwater,surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern GermanyHYDROLOGICAL PROCESSES, Issue 2 2007Stefan Krause Abstract The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time-variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM-ETH-I with the three-dimensional finite-difference-based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km2), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km2 catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain-dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd. [source] Hydrology and nitrogen balance of a seasonally inundated Danish floodplain wetlandHYDROLOGICAL PROCESSES, Issue 3 2004Hans Estrup Andersen Abstract This paper characterizes a seasonally inundated Danish floodplain wetland in a state close to naturalness and includes an analysis of the major controls on the wetland water and nitrogen balances. The main inputs of water are precipitation and percolation during ponding and unsaturated conditions. Lateral saturated subsurface flow is low. The studied floodplain owes its wetland status to the hydraulic properties of its sediments: the low hydraulic conductivity of a silt,clay deposit on top of the floodplain maintains ponded water during winter, and parts of autumn and spring. A capillary fringe extends to the soil surface, and capillary rise from groundwater during summer maintains near-saturated conditions in the root zone, and allows a permanently very high evapotranspiration rate. The average for the growing season of 1999 is 3·6 mm day,1 and peak rate is 5·6 mm day,1. In summer, the evapotranspiration is to a large degree supplied by subsurface storage in a confined peat layer underlying the silt,clay. The floodplain sediments are in a very reduced state as indicated by low sulphate concentrations. All nitrate transported into the wetland is thus denitrified. However, owing to modest water exchange with surrounding groundwater and surface water, denitrification is low; 71 kg NO3,N ha,1 during the study period of 1999. Reduction of nitrate diffusing into the sediments during water ponding accounts for 75% of nitrate removal. Biomass production and nitrogen uptake in above-ground vegetation is high,8·56 t dry matter ha,1 year,1 and 103 kg N ha,1 year,1. Subsurface ammonium concentrations are high, and convective upward transport into the root zone driven by evapotranspiration amounted to 12·8 kg N ha,1year,1. The floodplain wetland sediments have a high nitrogen content, and conditions are very favourable for mineralization. Mineralization thus constitutes 72% of above-ground plant uptake. The study demonstrates the necessity of identifying controlling factors, and to combine surface flow with vadose and groundwater flow processes in order to fully comprehend the flow and nitrogen dynamics of this type of wetland. Copyright © 2004 John Wiley & Sons, Ltd. [source] A decision scheme to indicate dominant hydrological flow processes on temperate grasslandHYDROLOGICAL PROCESSES, Issue 2 2003Simon Scherrer Abstract A decision scheme has been developed to indicate the likely dominant runoff forming on temperate grassland hill slopes. The decision scheme was developed from data collected from sprinkler experiments on 60 m2 plots at a number of grassland sites in Switzerland. The scheme requires input of hydrological properties of the surface and each major horizon of the soil. Worked examples of the application of the decision scheme to determine the dominant hydrological processes and runoff types are given for three actual grassland hill slopes. Copyright © 2003 John Wiley & Sons, Ltd. [source] A physical, mechanistic and fully coupled hillslope hydrology modelINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005David A. Raff Abstract We present the mathematical development and numerical solution of a new model of flow processes on an infiltrating hillslope. We also present validation and sample applications. The model is a distributed, mechanistic, physically based hillslope hydrologic model. The model describes the small-scale processes associated with overland flow, erosion, and sediment transport on an infiltrating surface and is capable of capturing small-scale variations in flow depth, flow velocities, interactive infiltration, erosion rates, and sediment transport. The model couples the fully two-dimensional hydrodynamic equations for overland flow, the one-dimensional Richards equation for infiltration, and a sediment detachment and transport model. Two simulations are presented highlighting the model's ability to capture and describe the interaction between precipitation, overland flow, erosion and infiltration at very small scales. Results of the two-dimensional simulations indicate the system of equations produces hillslopes possessing characteristics of self-organization as observed in real world systems. Copyright © 2005 John Wiley & Sons, Ltd. [source] Application of a Bayesian Approach to the Tomographic Analysis of Hopper FlowPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2005Krzysztof Grudzien Abstract This paper presents a new approach to the analysis of data on powder flow from electrical capacitance tomography (ECT) using probability modelling and Bayesian statistics. The methodology is illustrated for powder flow in a hopper. The purpose, and special features, of this approach is that ,high-level' statistical Bayesian modelling combined with a Markov chain Monte Carlo (MCMC) sampling algorithm allows direct estimation of control parameters of industrial processes in contrast to usually applied ,low-level', pixel-based methods of data analysis. This enables reliable recognition of key process features in a quantitative manner. The main difficulty when investigating hopper flow with ECT is due to the need to measure small differences in particle packing density. The MCMC protocol enables more robust identification of the responses of such complex systems. This paper demonstrates the feasibility of the approach for a simple case of particulate material flow during discharging of a hopper. It is concluded that these approaches can offer significant advantages for the analysis and control of some industrial powder and other multi-phase flow processes. [source] Fine-Scale Spatial Genetic Structure of the Distylous Primula veris in Fragmented HabitatsPLANT BIOLOGY, Issue 3 2007F. van Rossum Abstract: In Flanders (northern Belgium), the distylous self-incompatible perennial herb Primula veris is common, but mainly occurs in fragmented habitats. Distyly, which favours disassortative mating, is characterized in P. veris by two genetically determined floral morph types (pin or thrum). Using 18 polymorphic loci, we investigated fine-scale spatial genetic structure (SGS) and spatial distribution of the morphs within four populations from two regions that differ in degree of habitat fragmentation. We studied the contributions made by sexual reproduction and clonal propagation and compared the SGS patterns between pin and thrum morph types. Clonal growth was very restricted to a few individuals and to short distances. One population showed a non-random spatial distribution of the morphs. Pin and thrum individuals differed in SGS patterns at a small scale, suggesting intrapin biparental inbreeding, also related to high plant densities. This may be explained by partial self-compatibility of the pin morph combined with restricted seed dispersal and pollinator behaviour. There is an indication of more pronounced SGS when populations occur in highly fragmented habitats. From our findings, we may hypothesize disruption of the gene flow processes if these large populations evolve into patchworks of small remnants, but also a possible risk for long-term population survival if higher intrapin biparental inbreeding leads to inbreeding depression. Our study emphasizes the need for investigating the interactions between the heterostylous breeding system, population demographic and genetic structure for understanding population dynamics in fragmented habitats and for developing sustainable conservation strategies. [source] Subsurface sediment remobilization and fluid flow in sedimentary basins: an overviewBASIN RESEARCH, Issue 4 2010Mads Huuse ABSTRACT Subsurface sediment remobilization and fluid flow processes and their products are increasingly being recognized as significant dynamic components of sedimentary basins. The geological structures formed by these processes have traditionally been grouped into mud volcano systems, fluid flow pipes and sandstone intrusion complexes. But the boundaries between these groups are not always distinct because there can be similarities in their geometries and the causal geological processes. For instance, the process model for both mud and sand remobilization and injection involves a source of fluid that can be separate from the source of sediment, and diapirism is now largely discarded as a deformation mechanism for both lithologies. Both mud and sand form dykes and sills in the subsurface and extrusive edifices when intersecting the sediment surface, although the relative proportions of intrusive and extrusive components are very different, with mud volcano systems being largely extrusive and sand injectite systems being mainly intrusive. Focused fluid flow pipes may transfer fluids over hundreds of metres of vertical section for millions of years and may develop into mud volcano feeder systems under conditions of sufficiently voluminous and rapid fluid ascent associated with deeper focus points and overpressured aquifers. Both mud and sand remobilization is facilitated by overpressure and generally will be activated by an external trigger such as an earthquake, although some mud volcano systems may be driven by the re-charge dynamics of their fluid source. Future research should aim to provide spatio-temporal ,injectite' stratigraphies to help constrain sediment remobilization processes in their basinal context and identify and study outcrop analogues of mud volcano feeders and pipes, which are virtually unknown at present. Further data-driven research would be significantly boosted by numerical and analogue process modelling to constrain the mechanics of deep subsurface sediment remobilization as these processes can not be readily observed, unlike many conventional sediment transport phenomena. [source] Local Velocity and Concentration of the Single Components in Water/Oil Mixtures Monitored by Means of MRI Flow Experiments in Steady Tube FlowCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 1 2003J. Götz Abstract In this paper the spatially resolved determination of velocities in two-phase systems consisting of water and oil by means of nuclear magnetic resonance (NMR) imaging (MRI) techniques is described and applied to steady tube flows with regard to the total flow rate. As MRI offers the possibility to study the flow of multiphase materials spatially resolved with various forms of contrast, even optically opaque water/oil mixtures can be studied in the interior of the material. Besides snapshot images of the actual flow pattern also local velocity and concentration fields of both phases can be obtained separately. The insight into the inner micro flow processes and microstructure allows to characterize fluid mixtures or emulsions. Flow rate and preparation/mixing method were varied in order to realize changes of the flow pattern and the structure of the mixture during flow. Physical models of the flow behavior and physical stability of these complex systems can be based upon this information. [source] Combining Enabling Techniques in Organic Synthesis: Continuous Flow Processes with Heterogenized CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2006Andreas Kirschning Prof. Dr. Abstract The concepts article describes enabling techniques (solid-phase assisted synthesis, new reactor design, microwave irradiation and new solvents) in organic chemistry and emphasizes the combination of several of them for creating new synthetic technology platforms. Particular focus is put on the combination of immobilized catalysts as well as biocatalysts with continuous flow processes. In this context, the PASSflow continuous flow technique fulfils both chemical as well as chemical engineering requirements. It combines reactor design with optimized, monolithic solid phases as well as reversible immobilization techniques for performing small as well as large scale synthesis with heterogenized catalysts under continuous flow conditions. [source] | ||||||||||||||||||||||