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Water Flow (water + flow)
Kinds of Water Flow Terms modified by Water Flow Selected AbstractsFEFLOW: A Finite-Element Ground Water Flow and Transport Modeling ToolGROUND WATER, Issue 5 2007Mike G. Trefry First page of article [source] Fracture Control of Ground Water Flow and Water Chemistry in a Rock AquitardGROUND WATER, Issue 5 2007Timothy T. Eaton There are few studies on the hydrogeology of sedimentary rock aquitards although they are important controls in regional ground water flow systems. We formulate and test a three-dimensional (3D) conceptual model of ground water flow and hydrochemistry in a fractured sedimentary rock aquitard to show that flow dynamics within the aquitard are more complex than previously believed. Similar conceptual models, based on regional observations and recently emerging principles of mechanical stratigraphy in heterogeneous sedimentary rocks, have previously been applied only to aquifers, but we show that they are potentially applicable to aquitards. The major elements of this conceptual model, which is based on detailed information from two sites in the Maquoketa Formation in southeastern Wisconsin, include orders of magnitude contrast between hydraulic diffusivity (K/Ss) of fractured zones and relatively intact aquitard rock matrix, laterally extensive bedding-plane fracture zones extending over distances of over 10 km, very low vertical hydraulic conductivity of thick shale-rich intervals of the aquitard, and a vertical hydraulic head profile controlled by a lateral boundary at the aquitard subcrop, where numerous surface water bodies dominate the shallow aquifer system. Results from a 3D numerical flow model based on this conceptual model are consistent with field observations, which did not fit the typical conceptual model of strictly vertical flow through an aquitard. The 3D flow through an aquitard has implications for predicting ground water flow and for planning and protecting water supplies. [source] Michigan Basin Regional Ground Water Flow Discharge to Three Great LakesGROUND WATER, Issue 4 2002John Robert Hoaglund III Ground water discharge to the Great Lakes around the Lower Peninsula of Michigan is primarily from recharge in riparian basins and proximal upland areas that are especially important to the northern half of the Lake Michigan shoreline. A steady-state finite-difference model was developed to simulate ground water flow in four regional aquifers in Michigan's Lower Peninsula: the Glaciofluvial, Saginaw, Parma-Bayport, and Marshall aquifers interlayered with the Till/"red beds," Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specified-head boundary, formed from lakes Michigan, Huron, St. Clair, and Erie, with the St. Clair and Detroit River connecting channels. The model was developed to quantify regional ground water flow in the aquifer systems using independently determined recharge estimates. According to the flow model, local stream stages and discharges account for 95% of the overall model water budget; only 5% enters the lakes directly from the ground water system. Direct ground water discharge to the Great Lakes' shorelines was calculated at 36 m3/sec, accounting for 5% of the overall model water budget. Lowland areas contribute far less ground water discharge to the Great Lakes than upland areas. The model indicates that Saginaw Bay receives only ,1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only ,2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas. [source] Analytical Studies on the Impact of Land Reclamation on Ground Water FlowGROUND WATER, Issue 6 2001Jiu J. Jiao Land reclamation has been a common practice to produce valuable land in coastal areas. The impact of land reclamation on coastal environment and marine ecology is well recognized and widely studied. It has not been recognized yet that reclamation may change the regional ground water regime, which may in turn modify the coastal environment, flooding pattern, and stability of slopes and foundations. This paper represents the first attempt to examine quantitatively the effect of reclamation on ground water levels. Analytical solutions are developed to study the ground water change in response to reclamation based on two hypothetical models. In the first model, the ground water flow regime changes only in the hillside around the reclamation areas. In the second model, the ground water regime changes in the entire hill. Both models assume that the ground water flow is in a steady state and satisfies the Dupuit assumptions. Hypothetical examples are used to demonstrate how the ground water level, ground water divide and ground water submarine discharge will change with the scale and hydraulic conductivity of the reclamation materials. The results show that the change of ground water regime depends mainly on the length of the reclaimed area and the values of hydraulic conductivity of the reclaimed materials. It is also seen that the reclamation may impact not only the ground water regime near the coast areas around the reclamation site, but also that in the coast areas opposite the reclamation area. A reclamation site near Tseung Kwan O in the New Territories in Hong Kong, China, is used as a case study to discuss the possible modification of the ground water system caused by reclamation. [source] Characteristics of Underground Water Flow at Different Water Levels in Tianshengan Karst Area, Yunnan, ChinaACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2010Janja KOGOV Abstract: Three tracing tests from the same injection point executed at low, medium, and high water levels in the karst aquifer near Tianshengan village, Lunan Stone Forest, Yunnan Province, China, have revealed the basic properties of underground water flow. They showed the general directions of water flows; tracer concentrations were observed at six successive points allowing for the calculation of apparent dominant flow velocities at these sections towards the Dalongtan karst spring. For the high water level, the discharge between single sections was between two and 10 times greater than that at low water level. For the medium water level, the flow velocity at different sections was between 1.4 and 3.7 times faster than that at low water level; and for high water level, it was between 1.3 and 2.7 times faster than that at medium water level. The fastest water flow appeared at the first section (23 cm/s at medium water level); and the slowest (0.6 cm/s at low water level) appeared where water flow must cross the Tianshengan fault (north-south direction), and later, a layer of 20-30 m thickness of quartz sandstone and shale clay-stones. It was also possible to calculate the recovery of the tracer for point 4, Dakenyan, where discharge was measured. At the medium water level, 50% of the injected tracer was detected a half-day after its first appearance and at low water level after more than 3 days. The previously published research illustrates the transport velocities of possible contaminants and their solubilities in water at different hydrological conditions. [source] A review of the likely effects of climate change on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta, with particular reference to water temperature and flowJOURNAL OF FISH BIOLOGY, Issue 10 2009B. Jonsson The present paper reviews the effects of water temperature and flow on migrations, embryonic development, hatching, emergence, growth and life-history traits in light of the ongoing climate change with emphasis on anadromous Atlantic salmon Salmo salar and brown trout Salmo trutta. The expected climate change in the Atlantic is for milder and wetter winters, with more precipitation falling as rain and less as snow, decrease in ice-covered periods and frequent periods with extreme weather. Overall, thermal limits for salmonids are species specific. Scope for activity and growth and optimal temperature for growth increase with temperature to an optimal point before constrain by the oxygen content of the water. The optimal temperature for growth decreases with increasing fish size and varies little among populations within species, whereas the growth efficiency may be locally adapted to the temperature conditions of the home stream during the growth season. Indirectly, temperature influences age and size at smolting through its effect on growth. Time of spawning, egg hatching and emergence of the larvae vary with temperature and selective effects on time of first feeding. Traits such as age at first maturity, longevity and fecundity decrease with increasing temperature whilst egg size increases with temperature. Water flow influences the accessibility of rivers for returning adults and speed of both upstream and downstream migration. Extremes in water flow and temperature can decrease recruitment and survival. There is reason to expect a northward movement of the thermal niche of anadromous salmonids with decreased production and population extinction in the southern part of the distribution areas, migrations earlier in the season, later spawning, younger age at smolting and sexual maturity and increased disease susceptibility and mortality. Future research challenges are summarized at the end of the paper. [source] Sizing of throttling device for gas/liquid two-phase flow part 1: Safety valvesPROCESS SAFETY PROGRESS, Issue 4 2004Ralf Diener The calculation of the mass flow rate through throttling devices is difficult when handling two-phase flow, especially when boiling liquids flow into these fittings. Safety valves are typically oversized by a significant extent, if sizing methods like the ,-method (originally developed by J. Leung), are used in case of low-quality inlet flow. Within this method the boiling delay of the liquid and the influence of the boiling delay on the mass flow rate are not considered. In this paper the HNE-DS model is proposed, where the compressibility coefficient , is extended by adding a boiling delay coefficient. It includes the degree of thermodynamic nonequilibrium at the start of the nucleation of small mass fractions of vapor upstream of the fitting. In Part 1 the sizing of safety valves is described. Additionally, the derivation of the HNE-DS method is given in detail. Part 2 considers the mass flow rate through short nozzles, orifices, and control valves. The HNE-DS model can be used for all those fittings. A comparison with experimental results on safety valves with steam/water and air/water flow has emphasized the excellent accuracy of the new model. © 2004 American Institute of Chemical Engineers Process Saf Prog, 2004 [source] Fluid flow in an impacting symmetrical tee junction II: two-phase air/water flowASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2009A. P. Doherty Abstract A universal flow regime map was presented for two-phase flow in a horizontal pipe. Data were given on two-phase gas/liquid flow in a symmetrical impacting tee junction. The flow regimes in the inlet arm of the tee were those expected for a straight pipe. This was not so for the outlet arm where, in most cases, flow regimes occurred earlier than expected. At low liquid outlet flows the stratified regime was reinforced into higher gas flows than expected. The liquid hold-up exhibited variations over the tee junction. The pressure drop in the inlet arm agreed with similar data for the straight pipe, but in the tee outlets was below that expected for the straight pipe. The tee junction pressure drop showed some parallels to the corresponding single-phase flow data but the le/d dimensionless values for the junction pressure drop showed a wide variation, in contrast to the single-phase junction data. A model was presented based on the Lockhard,Martinelli theory that enabled the tee pressure drop to be predicted. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Hydrology and dynamics of a polythermal (mostly cold) High Arctic glacierEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2006Robert G. Bingham Abstract To improve our understanding of the interactions between hydrology and dynamics in mostly cold glaciers (in which water flow is limited by thermal regime), we analyse short-term (every two days) variations in glacier flow in the ablation zone of polythermal John Evans Glacier, High Arctic Canada. We monitor the spatial and temporal propagation of high-velocity events, and examine their impacts upon supraglacial drainage processes and evolving subglacial drainage system structure. Each year, in response to the rapid establishment of supraglacial,subglacial drainage connections in the mid-ablation zone, a ,spring event' of high horizontal surface velocities and high residual vertical motion propagates downglacier over two to four days from the mid-ablation zone to the terminus. Subsequently, horizontal velocities fall relative to the spring event but remain higher than over winter, reflecting channelization of subglacial drainage but continued supraglacial meltwater forcing. Further transient high-velocity events occur later in each melt season in response to melt-induced rising supraglacial meltwater inputs to the glacier bed, but the dynamic response of the glacier contrasts with that recorded during the spring event, with the degree of spatial propagation a function of the degree to which the subglacial drainage system has become channelized. Copyright © 2006 John Wiley & Sons, Ltd. [source] Consequences of hyperconcentrated flow for process-based soil erosion modelling on the Chinese Loess PlateauEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2006Rudi Hessel Abstract High sediment concentrations in runoff are a characteristic feature of the Chinese Loess Plateau, and are probably caused by factors such as the occurrence of erodible materials on steep slopes, the characteristics of the loess and the harsh climate that results in low plant cover. When sediment concentration increases, fluid density increases, viscosity increases and settling velocity decreases. These effects become increasingly important with increasing concentration and can result in flow behaviour that is quite different from that of clear water flow. Although the net effect of these changes on the flow is not always apparent, erosion models that deal with high sediment concentrations should consider such effects and could include corrections for some of these effects. A case study in a small catchment on the Loess Plateau indicated that sediment concentrations were considerable, and literature data suggested that for such sediment concentrations, corrections for settling velocity, fluid density and viscosity are needed. Furthermore, a number of corrections are necessary to be able to compare field measurements with results of soil erosion models: sediment volume should be subtracted from runoff volume and a density correction is needed to use data from a pressure transducer. For flumes that were used to measure discharge from smaller areas inside the catchment, the measured water level should be corrected by subtracting the sediment level in the flume from the water level, while the sediment volume should also be subtracted from the discharge. Finally, measured concentration should be corrected to give concentration expressed as grams per litre of clear water, since soil erosion models express sediment concentration in this way. Copyright © 2006 John Wiley & Sons, Ltd. [source] Effects of size and morphology on swimming performance in juvenile brown trout (Salmo trutta L.)ECOLOGY OF FRESHWATER FISH, Issue 4 2003A. F. Ojanguren Abstract,,, Our study assesses swimming capacity (speed and stamina) and possible morphometric determinants of locomotor performance of juvenile brown trout (Salmo trutta L.). We addressed these issues at the individual level to have an approach of the functional significance of intraspecific variation in morphological design. Both swimming speed and endurance time showed significant positive relationships with fish length. Size-corrected values of speed and endurance time were negatively correlated suggesting a phenotypic trade-off between burst and prolonged swimming. Size was also highly correlated with all the morphological variables measured. Therefore, we used the residuals of the regressions of those variables on fish length to remove the effect of body size. A principal components analysis (PCA) summarised the 12 morphological variables into two factors, which accounted for 44.3% of the variance. PC1 combined several measures of body depth and width, whereas PC2 represented mainly postanal length relative to abdomen length. Relationships between the scores of the two factors and size-corrected values of maximum swimming speed and endurance time were weak. PC2 showed a significant positive relationship with endurance time; that is, individuals with longer caudal regions were able to swim against water flow for longer periods of time. Stoutness (PC1) showed a marginally significant negative correlation with endurance time. The lack of stronger relationships could be because of the low morphometric variability among the test individuals, all proceeding from the same population, reared in a common environment, and measured at the same ontogenetic stage. [source] Impact of stone content on water movement in water-repellent sandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2009E. Urbanek Summary Soils are commonly stony, especially in steep upland or heavily degraded sites. The hydrological effect of large stone contents has been previously investigated in wettable but not in water-repellent soils. For the latter, the focus has instead been on the impact of other soil characteristics (e.g. cracks and macropores) likely to promote water percolation. This paper investigates stone effects on water flow in water-repellent sand under laboratory conditions. Seventy-five experiments were performed on a water-repellent sand mixed with a range of quantities of different-sized wettable and water-repellent stones. The time taken for water to pass through each sand,stone mix, the percolated water volumes and numbers of dry and wet stones following each 60-minute experiment were recorded. At large stone contents (> 55% or > 65% by weight, depending on stone wettability), percolation occurred relatively quickly and in comparatively large quantities. At intermediate stone contents (45,65%) percolation response was variable and at stone contents < 45% for wettable and < 55% for water-repellent soils no water percolation occurred. We argue that with large stone contents flow pathways develop along sand,stone interfaces and a continuous preferential flow path can form provided there are sufficient stone-to-stone connections. The distribution and alignment of the stones, especially at intermediate stone contents, are important for promoting water movement. Water repellency determinations based only on the fine sediment component in stony soils could therefore be misleading as regards determining their hydrological response: the influence of the clastic component must also be considered. [source] Scaling of water flow through porous media and soilsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008K. Roth Summary Scaling of fluid flow in general is outlined and contrasted to the scaling of water flow in porous media. It is then applied to deduce Darcy's law, thereby demonstrating that stationarity of the flow field at the scale of the representative elementary volume (REV) is a critical prerequisite. The focus is on the implications of the requirement of stationarity, or local equilibrium, in particular on the validity of the Richards equation for the description of water movement through soils. Failure to satisfy this essential requirement may occur at the scale of the REV or, particularly in numerical simulations, at the scale of the model discretization. The latter can be alleviated by allocation of more computational resources and by working on a finer-grained representation. In contrast, the former is fundamental and leads to an irrevocable failure of the Richards equation as is observed with infiltration instabilities that lead to fingered flow. [source] Simulation of water flow and solute transport in free-drainage lysimeters and field soils with heterogeneous structuresEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2004H. M. Abdou Summary Lysimeters are valuable for studying the fate and transport of chemicals in soil. Large-scale field lysimeters are used to assess pesticide behaviour and radionuclide transport, and are assumed to represent natural field conditions better than laboratory columns. Field lysimeters are usually characterized by a free-draining lower boundary. As a result, the hydraulic gradient is disrupted, and leachate cannot be collected until the bottom of the lysimeter becomes saturated. We compared heterogeneously structured, free-drainage lysimeters and field soils with respect to water flow and solute transport. Numerical simulations were carried out in a two-dimensional heterogeneous sandy soil under unsaturated water flow conditions with the CHAIN_2D code. Three different soil structures (isotropic, horizontal, and vertical) were generated, and Miller,Miller similitude was used to scale the hydraulic properties of the soil. The results showed that ponding occurs at the bottom of the lysimeter for the three soil structures and that it occurred faster and was more pronounced with the vertical structure (preferential flow effect). Breakthrough curves of a conservative solute (bromide) showed that solutes are moving faster in the field than in the lysimeters. Fewer differences between lysimeters and field soils were found with the horizontal soil structure than with the isotropic and vertical structures. [source] Non-equilibrium water flow characterized by means of upward infiltration experimentsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2001Summary Upward infiltration experiments under tension were used to demonstrate the presence of non-equilibrium flow in soils, the phenomenon that has important implications for the accelerated movement of fertilizers, pesticides, non-aqueous liquids, and other pollutants. Data obtained from these experiments were analysed using the single-porosity Richards equation, as well as a variably saturated, dual-porosity model and a dual-permeability model for characterizing non-equilibrium water flow. The laboratory experiments were carried out on 0.10-m-long soil cores having an internal diameter of 0.10 m. Constant pressure heads of ,0.10 and ,0.01 m were used as the lower boundary condition. Each infiltration was followed by a single-rate evaporation experiment to re-establish initial conditions, and to obtain the drying soil hydraulic properties. Pressure heads inside the cores were measured using five tensiometers, while evaporative water loss from the top was determined by weighing the soil samples. The data were analysed to estimate parameters using a technique that combined a numerical solution of the governing flow equation (as implemented in a modified version of the Hydrus-1D software) with a Marquardt,Levenberg optimization. The objective function for the parameter estimation was defined in terms of pressure head readings, the cumulative infiltration rate, and the final total water volume in the core during upward infiltration. The final total water volume was used, as well as the pressure head readings during the evaporation part. Analysis of flow responses obtained during the infiltration experiment demonstrated significant non-equilibrium flow. This behaviour could be well characterized using a model of physical non-equilibrium that divides the medium into inter- and intra-aggregate pores with first-order transfer of water between the two systems. The analysis also demonstrated the importance of hysteresis. [source] The dispersal and deposition of hydrochorous plant seeds in drainage ditchesFRESHWATER BIOLOGY, Issue 10 2010HESTER SOOMERS Summary 1. Surface water is an important dispersal vector for wetland plant species. However, most previous studies on hydrochory (i.e. water dispersal) have focused on ecosystems with relatively rapid water flow. Therefore, there is a need to study such dispersal in slow-flowing or stagnant waterbodies, such as drainage ditches, which might act as dispersal corridors between habitat patches. 2. To gain insight into the mechanisms by which seeds are transported in drainage ditches, the effect of the velocity of wind and water on the rate of transport of floating seeds of three wetland species (Carex pseudocyperus L., Iris pseudacorus L. and Sparganium erectum L.) was investigated. Furthermore, in release and retrace experiments with painted C. pseudocyperus seeds, a number of factors potentially determining the probability of seed deposition were investigated. 3. Net wind speed was found to be the main factor determining the rate at which seeds are transported in drainage ditches. No relation between water flow at middepth in the ditches and seed transport was found. Wind speed and flow at the water surface were positively related. The effect of wind speed on the rate of transport of floating seeds was greater for S. erectum seeds, because a greater ratio of their volume protrudes from the water, than for C. pseudocyperus and I. pseudacorus seeds. 4. The principal factors that determine seed deposition were aquatic plant cover, ditch slope and indentations in the ditch bank. Seeds changed direction if the wind direction changed, or if there was a bend in the ditch. The final pattern of deposition was related to mean net wind speed. Mean transport distance after 2 days varied between 34 and 451 m. 5. Unlike in rivers, seed transport in ditches was determined by wind speed and direction, enabling multidirectional seed dispersal. We conclude that in slow-flowing waters, wind is a more important driver for hydrochorous seed transport than the flow of water. This sheds a new light on hydrochory and has important consequences for the management of otherwise fragmented wetland remnants. [source] Organic matter availability structures microbial biomass and activity in a Mediterranean streamFRESHWATER BIOLOGY, Issue 10 2009JOAN ARTIGAS Summary 1. We compared microbial biomass (bacteria, fungi, algae) and the activity of extracellular enzymes used in the decomposition of organic matter (OM) among different benthic substrata (leaves, coarse and fine substrata) over one hydrological year in a Mediterranean stream. 2. Microbial heterotrophic biomass (bacteria plus fungi) was generally higher than autotrophic biomass (algae), except during short periods of high light availability in the spring and winter. During these periods, sources of OM shifted towards autochthonous sources derived mainly from algae, which was demonstrated by high algal biomass and peptidase activity in benthic communities. 3. Heterotrophic activity peaked in the autumn. Bacterial and fungal biomass increased with the decomposition of cellulose and hemicellulose compounds from leaf material. Later, lignin decomposition was stimulated in fine (sand, gravel) and coarse (rocks, boulders and cobbles) substrata by the accumulation of fine detritus. 4. The Mediterranean summer drought provoked an earlier leaf fall. The resumption of the water flow caused the weathering of riparian soils and subsequently a large increase in dissolved organic carbon and nitrate, which led to growth of bacteria and fungi. [source] Riverine landscapes: taking landscape ecology into the waterFRESHWATER BIOLOGY, Issue 4 2002JOHN A. WIENS 1.,Landscape ecology deals with the influence of spatial pattern on ecological processes. It considers the ecological consequences of where things are located in space, where they are relative to other things, and how these relationships and their consequences are contingent on the characteristics of the surrounding landscape mosaic at multiple scales in time and space. Traditionally, landscape ecologists have focused their attention on terrestrial ecosystems, and rivers and streams have been considered either as elements of landscape mosaics or as units that are linked to the terrestrial landscape by flows across boundaries or ecotones. Less often, the heterogeneity that exists within a river or stream has been viewed as a `riverscape' in its own right. 2.,Landscape ecology can be unified about six central themes: (1) patches differ in quality (2) patch boundaries affect flows, (3) patch context matters, (4) connectivity is critical, (5) organisms are important, and (6) the importance of scale. Although riverine systems differ from terrestrial systems by virtue of the strong physical force of hydrology and the inherent connectivity provided by water flow, all of these themes apply equally to aquatic and terrestrial ecosystems, and to the linkages between the two. 3.,Landscape ecology therefore has important insights to offer to the study of riverine ecosystems, but these systems may also provide excellent opportunities for developing and testing landscape ecological theory. The principles and approaches of landscape ecology should be extended to include freshwater systems; it is time to take the `land' out of landscape ecology. [source] The Role of Surface Water Drainage in Environmental Change: a Case Example of the Upper South East of South Australia; an Historical ReviewGEOGRAPHICAL RESEARCH, Issue 3 2001Kathryn H. Taffs The role of surface water drainage in environmental change in Australia is rarely appreciated. Drains can modify surface water hydrology, not only altering flow regimes but also rapidly dispersing contaminants and altering the natural hydrological balance of associated flora and fauna. Yet drainage continues to be considered a viable management strategy rather than as a cause of land degradation. The impact of surface water drainage in an inherently saline area of South Australia, the Upper South East, is investigated. Surface water drains were constructed by developers in an attempt to increase the area of land available and viable for agricultural land use. Drainage strategies altered the natural direction, magnitude and frequency of surface water flow. The Upper South East has experienced periods of both increased surface water and flooding, and surface water deficit, in the past one hundred years. The region now receives less surface water than under pre-European conditions, but local runoff is channelled into and through the wetlands more rapidly than before European settlement. Future management strategies are likely to continue this trend, to the detriment of remnant natural wetlands. [source] Streaming potential dependence on water-content in Fontainebleau sandGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010V. Allègre SUMMARY The electrokinetic potential results from the coupling between the water flow and the electrical current because of the presence of ions within water. The electrokinetic coefficient is well described in fluid-saturated media, however its behaviour under unsaturated flow conditions is still discussed. We propose here an experimental approach to investigate streaming potential variations in sand at unsaturated conditions. We present for the first time continuous records of the electrokinetic coefficient as a function of water content. Two drainage experiments have been performed within a column filled with a clean sand. Streaming potential measurements are combined with water pressure and water content measurements every 10 cm along the column. In order to model hydrodymanics during the experiments, we solve Richards equation coupled with an inverse problem to estimate the hydraulic parameters of the constitutive relations between hydraulic conductivity, water pressure and water content. The electrokinetic coefficient C shows a more complex behaviour for unsaturated conditions than it was previously reported and cannot be fitted by the existing models. The normalized electrokinetic coefficient increases first when water saturation decreases from 100 to about 65,80 per cent, and then decreases as the water saturation decreases, whereas all previous works described a monotone decrease of the normalized electrokinetic coupling as water saturation decreases. We delimited two water saturation domains, and deduced two different empirical laws describing the evolution of the electrokinetic coefficient for unsaturated conditions. Moreover, we introduce the concept of the electrokinetic residual saturation, Sr,ekw, which allows us to propose a new model derived from the approach of the relative permeability used in hydrodynamics. [source] The hydroelectric problem of porous rocks: inversion of the position of the water table from self-potential dataGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2004A. Revil SUMMARY The self-potential (SP) method is a fast and cheap reconnaissance tool sensitive to ground water flow in unconfined aquifers. A model based on the use of Green's functions for the coupled hydroelectric problem yields an integral equation relating the SP field to the distribution of the piezometric head describing the phreatic surface and to the electrical resistivity contrast through this phreatic surface. We apply this model to SP data measured on the south flank of the Piton de la Fournaise volcano, a large shield volcano located on Réunion island, Indian ocean. The phreatic surface, inverted with the help of the Simplex algorithm from the SP data, agrees well with the available information in this area [one borehole and electromagnetic (EM) data]. This interpretation scheme, which we call electrography, has many applications to the crucial problem of water supply in volcanic areas where drilling is expensive. [source] Solute and Heat Transport Model of the Henry and Hilleke Laboratory ExperimentGROUND WATER, Issue 5 2010Christian D. Langevin SEAWAT is a coupled version of MODFLOW and MT3DMS designed to simulate variable-density ground water flow and solute transport. The most recent version of SEAWAT, called SEAWAT Version 4, includes new capabilities to represent simultaneous multispecies solute and heat transport. To test the new features in SEAWAT, the laboratory experiment of Henry and Hilleke (1972) was simulated. Henry and Hilleke used warm fresh water to recharge a large sand-filled glass tank. A cold salt water boundary was represented on one side. Adjustable heating pads were used to heat the bottom and left sides of the tank. In the laboratory experiment, Henry and Hilleke observed both salt water and fresh water flow systems separated by a narrow transition zone. After minor tuning of several input parameters with a parameter estimation program, results from the SEAWAT simulation show good agreement with the experiment. SEAWAT results suggest that heat loss to the room was more than expected by Henry and Hilleke, and that multiple thermal convection cells are the likely cause of the widened transition zone near the hot end of the tank. Other computer programs with similar capabilities may benefit from benchmark testing with the Henry and Hilleke laboratory experiment. [source] Reconstruction of the Water Table from Self-Potential Data: A Bayesian ApproachGROUND WATER, Issue 2 2009A. Jardani Ground water flow associated with pumping and injection tests generates self-potential signals that can be measured at the ground surface and used to estimate the pattern of ground water flow at depth. We propose an inversion of the self-potential signals that accounts for the heterogeneous nature of the aquifer and a relationship between the electrical resistivity and the streaming current coupling coefficient. We recast the inversion of the self-potential data into a Bayesian framework. Synthetic tests are performed showing the advantage in using self-potential signals in addition to in situ measurements of the potentiometric levels to reconstruct the shape of the water table. This methodology is applied to a new data set from a series of coordinated hydraulic tomography, self-potential, and electrical resistivity tomography experiments performed at the Boise Hydrogeophysical Research Site, Idaho. In particular, we examine one of the dipole hydraulic tests and its reciprocal to show the sensitivity of the self-potential signals to variations of the potentiometric levels under steady-state conditions. However, because of the high pumping rate, the response was also influenced by the Reynolds number, especially near the pumping well for a given test. Ground water flow in the inertial laminar flow regime is responsible for nonlinearity that is not yet accounted for in self-potential tomography. Numerical modeling addresses the sensitivity of the self-potential response to this problem. [source] Importance of Unsaturated Zone Flow for Simulating Recharge in a Humid ClimateGROUND WATER, Issue 4 2008Randall J. Hunt Transient recharge to the water table is often not well understood or quantified. Two approaches for simulating transient recharge in a ground water flow model were investigated using the Trout Lake watershed in north-central Wisconsin: (1) a traditional approach of adding recharge directly to the water table and (2) routing the same volume of water through an unsaturated zone column to the water table. Areas with thin (less than 1 m) unsaturated zones showed little difference in timing of recharge between the two approaches; when water was routed through the unsaturated zone, however, less recharge was delivered to the water table and more discharge occurred to the surface because recharge direction and magnitude changed when the water table rose to the land surface. Areas with a thick (15 to 26 m) unsaturated zone were characterized by multimonth lags between infiltration and recharge, and, in some cases, wetting fronts from precipitation events during the fall overtook and mixed with infiltration from the previous spring snowmelt. Thus, in thicker unsaturated zones, the volume of water infiltrated was properly simulated using the traditional approach, but the timing was different from simulations that included unsaturated zone flow. Routing of rejected recharge and ground water discharge at land surface to surface water features also provided a better simulation of the observed flow regime in a stream at the basin outlet. These results demonstrate that consideration of flow through the unsaturated zone may be important when simulating transient ground water flow in humid climates with shallow water tables. [source] Analytical Methods for Transient Flow to a Well in a Confined-Unconfined AquiferGROUND WATER, Issue 4 2008Li-Tang Hu Concurrent existence of confined and unconfined zones of an aquifer can arise owing to ground water withdrawal by pumping. Using Girinskii's potential function, Chen (1974, 1983) developed an approximate analytical solution to analyze transient ground water flow to a pumping well in an aquifer that changes from an initially confined system to a system with both unconfined and confined regimes. This article presents the details of the Chen model and then compares it with the analytical model developed by Moench and Prickett (1972) for the same problem. Hypothetical pumping test examples in which the aquifer undergoes conversion from confined to water table conditions are solved by the two analytical models and also a numerical model based on MODFLOW. Comparison of the results suggests that the solutions of the Chen model give better results than the Moench and Prickett model except when the radial distance is very large or aquifer thickness is large compared with drawdown. [source] Fracture Control of Ground Water Flow and Water Chemistry in a Rock AquitardGROUND WATER, Issue 5 2007Timothy T. Eaton There are few studies on the hydrogeology of sedimentary rock aquitards although they are important controls in regional ground water flow systems. We formulate and test a three-dimensional (3D) conceptual model of ground water flow and hydrochemistry in a fractured sedimentary rock aquitard to show that flow dynamics within the aquitard are more complex than previously believed. Similar conceptual models, based on regional observations and recently emerging principles of mechanical stratigraphy in heterogeneous sedimentary rocks, have previously been applied only to aquifers, but we show that they are potentially applicable to aquitards. The major elements of this conceptual model, which is based on detailed information from two sites in the Maquoketa Formation in southeastern Wisconsin, include orders of magnitude contrast between hydraulic diffusivity (K/Ss) of fractured zones and relatively intact aquitard rock matrix, laterally extensive bedding-plane fracture zones extending over distances of over 10 km, very low vertical hydraulic conductivity of thick shale-rich intervals of the aquitard, and a vertical hydraulic head profile controlled by a lateral boundary at the aquitard subcrop, where numerous surface water bodies dominate the shallow aquifer system. Results from a 3D numerical flow model based on this conceptual model are consistent with field observations, which did not fit the typical conceptual model of strictly vertical flow through an aquitard. The 3D flow through an aquitard has implications for predicting ground water flow and for planning and protecting water supplies. [source] Analysis of Steady Ground Water Flow Toward Wells in a Confined-Unconfined AquiferGROUND WATER, Issue 4 2006Chen Chong-Xi A confined aquifer may become unconfined near the pumping wells when the water level falls below the confining unit in the case where the pumping rate is great and the excess hydraulic head over the top of the aquifer is small. Girinskii's potential function is applied to analyze the steady ground water flow induced by pumping wells with a constant-head boundary in a mixed confined-unconfined aquifer. The solution of the single-well problem is derived, and the critical radial distance at which the flow changes from confined to unconfined condition is obtained. Using image wells and the superposition method, an analytic solution is presented to study steady ground water flow induced by a group of pumping wells in an aquifer bounded by a river with constant head. A dimensionless function is introduced to determine whether a water table condition exists or not near the pumping wells. An example with three pumping wells is used to demonstrate the patterns of potentiometric surface and development of water table around the wells. [source] Multilayer Analytic Element Modeling of Radial Collector WellsGROUND WATER, Issue 6 2005Mark Bakker A new multilayer approach is presented for the modeling of ground water flow to radial collector wells. The approach allows for the inclusion of all aspects of the unique boundary condition along the lateral arms of a collector well, including skin effect and internal friction losses due to flow in the arms. The hydraulic conductivity may differ between horizontal layers within the aquifer, and vertical anisotropy can be taken into account. The approach is based on the multilayer analytic element method, such that regional flow and local three-dimensional detail may be simulated simultaneously and accurately within one regional model. Horizontal flow inside a layer is computed analytically, while vertical flow is approximated with a standard finite-difference scheme. Results obtained with the proposed approach compare well to results obtained with three-dimensional analytic element solutions for flow in unconfined aquifers. The presented approach may be applied to predict the yield of a collector well in a regional setting and to compute the origin and residence time, and thus the quality, of water pumped by the collector well. As an example, the addition of three lateral arms to a collector well that already has three laterals is investigated. The new arms are added at an elevation of 2 m above the existing laterals. The yield increase of the collector well is computed as a function of the lengths of the three new arms. [source] Ground water vistas: A graphical user interface for the MODFLOW family of ground water flow and transport modelsGROUND WATER, Issue 2 2005Christian D. Langevin First page of article [source] Validation of Numerical Ground Water Models Used to Guide Decision MakingGROUND WATER, Issue 2 2004Ahmed E. Hassan Many sites of ground water contamination rely heavily on complex numerical models of flow and transport to develop closure plans. This complexity has created a need for tools and approaches that can build confidence in model predictions and provide evidence that these predictions are sufficient for decision making. Confidence building is a long-term, iterative process and the author believes that this process should be termed model validation. Model validation is a process, not an end result. That is, the process of model validation cannot ensure acceptable prediction or quality of the model. Rather, it provides an important safeguard against faulty models or inadequately developed and tested models. If model results become the basis for decision making, then the validation process provides evidence that the model is valid for making decisions (not necessarily a true representation of reality). Validation, verification, and confirmation are concepts associated with ground water numerical models that not only do not represent established and generally accepted practices, but there is not even widespread agreement on the meaning of the terms as applied to models. This paper presents a review of model validation studies that pertain to ground water flow and transport modeling. Definitions, literature debates, previously proposed validation strategies, and conferences and symposia that focused on subsurface model validation are reviewed and discussed. The review is general and focuses on site-specific, predictive ground water models used for making decisions regarding remediation activities and site closure. The aim is to provide a reasonable starting point for hydrogeologists facing model validation for ground water systems, thus saving a significant amount of time, effort, and cost. This review is also aimed at reviving the issue of model validation in the hydrogeologic community and stimulating the thinking of researchers and practitioners to develop practical and efficient tools for evaluating and refining ground water predictive models. [source] | |||||||||||||||||||||||||||||||||||||