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Flow Paths (flow + paths)
Kinds of Flow Paths Selected AbstractsModerate Bioclogging Leading to Preferential Flow Paths in BiobarriersGROUND WATER MONITORING & REMEDIATION, Issue 3 2006Katsutoshi Seki Permeable reactive barriers (PRBs) are an alternative technique for the biological in situ remediation of ground water contaminants. Nutrient supply via injection well galleries is supposed to support a high microbial activity in these barriers but can ultimately lead to changes in the hydraulic conductivity of the biobarrier due to the accumulation of biomass in the aquifer. This effect, called bioclogging, would limit the remediation efficiency of the biobarrier. To evaluate the effects bioclogging can have on the flow field of a PRB, flow cell experiments were carried out in the laboratory using glass beads as a porous medium. Two types of flow cells were used: a 20- × 1- × 1-cm cell simulating a single injection well in a one-dimensional flow field and a 20- × 10- × 1-cm cell simulating an injection well gallery in a two-dimensional flow field. A mineral medium was injected to promote microbial growth. Results of 9 d of continuous operation showed that conditions, which led to a moderate (50%) reduction of the hydraulic conductivity of the one-dimensional cell, led to a preferential flow pattern within the simulated barrier in the two-dimensional flow field (visualized by a tracer dye). The bioclogging leading to this preferential flow pattern did not change the hydraulic conductivity of the biobarrier as a whole but resulted in a reduced residence time of water within barrier. The biomass distribution measured after 9 d was consistent with the observed clogging effects showing step spatial gradients between clogged and unclogged regions. [source] Empirical prediction of debris-flow mobility and deposition on fansEARTH SURFACE PROCESSES AND LANDFORMS, Issue 2 2010Christian Scheidl Abstract A new method to predict the runout of debris flows is presented. A data base of documented sediment-transporting events in torrent catchments of Austria, Switzerland and northern Italy has been compiled, using common classification techniques. With this data we test an empirical approach between planimetric deposition area and event volume, and compare it with results from other studies. We introduce a new empirical relation to determine the mobility coefficient as a function of geomorphologic catchment parameters. The mobility coefficient is thought to reflect some of the flow properties during the depositional part of the debris-flow event. The empirical equations are implemented in a geographical information system (GIS) based simulation program and combined with a simple flow routing algorithm, to determine the potential runout area covered by debris-flow deposits. For a given volume and starting point of the deposits, a Monte-Carlo technique is used to produce flow paths that simulate the spreading effect of a debris flow. The runout zone is delineated by confining the simulated potential spreading area in the down slope direction with the empirically determined planimetric deposition area. The debris-flow volume is then distributed over the predicted area according to the calculated outflow probability of each cell. The simulation uses the ARC-Objects environment of ESRI© and is adapted to run with high resolution (2·5,m × 2·5,m) digital elevation models, generated for example from LiDAR data. The simulation program called TopRunDF is tested with debris-flow events of 1987 and 2005 in Switzerland. Copyright © 2009 John Wiley & Sons, Ltd. [source] Percolation characteristics of a water-repellent sandy forest soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2008G. Wessolek Summary In a tracer experiment TDR transect measurements were made to study percolation behaviour in a 120-year-old pine stand (Pinus sylvestris) on a water-repellent sandy soil (Haplic Arenosol). The experiment (with potassium iodide) showed an 80% labelling of the total flow in organic layers, whereas the area of transport in the mineral soil was sharply reduced to 12,30%. The average diameters of these preferential flow paths were about 8,15 cm. The TDR measurements indicate a homogeneous flow only for a short period from February until April. At this time of the year preferential flow is insignificant, because the soil is at approximately field capacity and not repellent to water. During summer (May to September) the soil dries out, and most precipitation results in preferential flow during this period. For any daily rainfall exceeding 10 mm, water infiltrates down to 1 m depth in the soil, which nevertheless, is still within the root zone. This kind of deep percolation results in the subsoil's wetting to field capacity (pF 1.8) earlier than the topsoil. A one-dimensional numerical model (SWAP) was used to simulate mean water balance with hydraulic functions with and without a water-repellency term. From the results of our tracer experiment we showed that the de-watering process in spring could be simulated well using the traditional piston flow concept, while the rewetting behaviour could be described more realistically using the mobile,immobile concept for water repellency. [source] Mass fractal dimension of soil macropores using computed tomography: from the box-counting to the cube-counting algorithmEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003J.S. Perret Summary Transport phenomena in porous media depend strongly on three-dimensional pore structures. Macropore networks enable water and solute to move preferentially through the vadose zone. A complete representation of their geometry is important for understanding soil behaviour such as preferential flow. Once we know the geometrical, topological and scaling attributes of preferential flow paths, we can begin computer simulations of water movement in the soil. The box-counting method is used in three dimensions (i.e. cube-counting algorithm) to characterize the mass fractal dimension of macropore networks using X-ray computed tomography (CT) matrices. We developed an algorithm to investigate the mass fractal dimension in three dimensions and to see how it compares with the co-dimensions obtained using the box-counting technique in two dimensions. For that purpose, macropore networks in four large undisturbed soil columns (850 mm × 77 mm diameter) were quantified and visualized, in both two and three dimensions, using X-ray CT. We observed an increasing trend between the fractal dimension and macroporosity for the four columns. Moreover, similar natural logarithm functions were obtained for the four cores by a least squares fit through plots of mass fractal dimension against macroporosity. [source] The influence of poorly interconnected fault zone flow paths on spring geochemistryGEOFLUIDS (ELECTRONIC), Issue 2 2008J. C. ROWLAND Abstract Thermal springs commonly occur along faults because of the enhanced vertical permeability afforded by fracture zones. Field and laboratory studies of fault zone materials document substantial heterogeneities in fracture permeabilities. Modeling and field studies of springs suggest that spatial variations in permeability strongly influence spring locations, discharge rates and temperatures. The impact of heterogeneous permeability on spring geochemistry, however, is poorly documented. We present stable isotope and water chemistry data from a series of closely spaced thermal springs associated with the Hayward Fault, California. We suggest that substantial spatial variations observed in ,18O and chloride values reflect subsurface fluid transport through a poorly connected fracture network in which mixing of subsurface waters remains limited. Our measurements provide insight into the effect of fracture zone heterogeneities on spring geochemistry, offer an additional tool to intuit the nature of tectonically induced changes in fault zone plumbing, and highlight the need to consider local variations when characterizing fracture zone fluid geochemistry from spring systems with multiple discharge sites. [source] Infiltration of basinal fluids into high-grade basement, South Norway: sources and behaviour of waters and brinesGEOFLUIDS (ELECTRONIC), Issue 1 2003S. A. Gleeson Abstract Quartz veins hosted by the high-grade crystalline rocks of the Modum complex, Southern Norway, formed when basinal fluids from an overlying Palaeozoic foreland basin infiltrated the basement at temperatures of c. 220°C (higher in the southernmost part of the area). This infiltration resulted in the formation of veins containing both two-phase and halite-bearing aqueous fluid inclusions, sometimes with bitumen and hydrocarbon inclusions. Microthermometric results demonstrate a very wide range of salinities of aqueous fluids preserved in these veins, ranging from c. 0 to 40 wt% NaCl equivalent. The range in homogenization temperatures is also very large (99,322°C for the entire dataset) and shows little or no correlation with salinity. A combination of aqueous fluid microthermometry, halogen geochemistry and oxygen isotope studies suggest that fluids from a range of separate aquifers were responsible for the quartz growth, but all have chemistries comparable to sedimentary formation waters. The bulk of the quartz grew from relatively low ,18O fluids derived directly from the basin or equilibrated in the upper part of the basement (T < 200°C). Nevertheless, some fluids acquired higher salinities due to deep wall-rock hydration reactions leading to salt saturation at high temperatures (>300°C). The range in fluid inclusion homogenization temperatures and densities, combined with estimates of the ambient temperature of the basement rocks suggests that at different times veins acted as conduits for influx of both hotter and colder fluids, as well as experiencing fluctuations in fluid pressure. This is interpreted to reflect episodic flow linked to seismicity, with hotter dry basement rocks acting as a sink for cooler fluids from the overlying basin, while detailed flow paths reflected local effects of opening and closing of individual fractures as well as reaction with wall rocks. Thermal considerations suggest that the duration of some flow events was very short, possibly in the order of days. As a result of the complex pattern of fracturing and flow in the Modum basement, it was possible for shallow fluids to penetrate basement rocks at significantly higher temperatures, and this demonstrates the potential for hydrolytic weakening of continental crust by sedimentary fluids. [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] TOPCAT-NP: a minimum information requirement model for simulation of flow and nutrient transport from agricultural systemsHYDROLOGICAL PROCESSES, Issue 14 2008P. F. Quinn Abstract Future catchment planning requires a good understanding of the impacts of land use and management, especially with regard to nutrient pollution. A range of readily usable tools, including models, can play a critical role in underpinning robust decision-making. Modelling tools must articulate our process understanding, make links to a range of catchment characteristics and scales and have the capability to reflect future land-use management changes. Hence, the model application can play an important part in giving confidence to policy makers that positive outcomes will arise from any proposed land-use changes. Here, a minimum information requirement (MIR) modelling approach is presented that creates simple, parsimonious models based on more complex physically based models, which makes the model more appropriate to catchment-scale applications. This paper shows three separate MIR models that represent flow, nitrate losses and phosphorus losses. These models are integrated into a single catchment model (TOPCAT-NP), which has the advantage that certain model components (such as soil type and flow paths) are shared by all three MIR models. The integrated model can simulate a number of land-use activities that relate to typical land-use management practices. The modelling process also gives insight into the seasonal and event nature of nutrient losses exhibited at a range of catchment scales. Three case studies are presented to reflect the range of applicability of the model. The three studies show how different runoff and nutrient loss regimes in different soil/geological and global locations can be simulated using the same model. The first case study models intense agricultural land uses in Denmark (Gjern, 114 km2), the second is an intense agricultural area dominated by high superphosphate applications in Australia (Ellen Brook, 66 km2) and the third is a small research-scale catchment in the UK (Bollington Hall, 2 km2). Copyright © 2007 John Wiley & Sons, Ltd. [source] Hydrochemical behaviour of dissolved nitrogen and carbon in a headwater stream of the Canadian Shield: relevance of antecedent soil moisture conditionsHYDROLOGICAL PROCESSES, Issue 3 2008Julie M. L. Turgeon Abstract This paper examines the impact of contrasting antecedent soil moisture conditions on the hydrochemical response, here the changes in dissolved nitrogen (NO3,, NH4+ and dissolved organic nitrogen (DON)) and dissolved organic carbon (DOC) concentrations, of a first-order stream during hydrological events. The study was performed in the Hermine, a 5 ha forested watershed of the Canadian Shield. It focused on a series of eight precipitation events (spring, summer and fall) sampled every 2 or 3 h and showing contrasted antecedent moisture conditions. The partition of the eight events between two groups (dry or wet) of antecedent moisture conditions was conducted using a principal component analysis (PCA). The partition was controlled (first axis explained 86% of the variability) by the antecedent streamflow, the streamflow to precipitation ratio Q/P and by the antecedent groundwater depth. The mean H+, NO3,, NH4+, total dissolved nitrogen and DOC concentrations and electrical conductivity values in the stream were significantly higher following dry antecedent conditions than after wetter conditions had prevailed in the Hermine, although the temporal variability was high (17 to 138%). At the event scale, a significantly higher proportion of the changes in DON, NO3,, and DOC concentrations in the stream was explained by temporal variations in discharge compared with the seasonal and annual scales. Two of the key hydrochemical features of the dry events were the synchronous changes in DOC and flow and the frequent negative relationships between discharge and NO3,. The DON concentrations were much less responsive than DOC to changes in discharge, whereas NH was not in phase with streamflow. During wet events, the synchronicity between streamflow and DON or NO3, was higher than during dry events and discharge and NO3, were generally positively linked. Based on these observations, the hydrological behaviour of the Hermine is conceptually compatible with a two-component model of shallow (DON and DOC rich; variable NO3,) and deep (DON and DOC poor; variable NO3,) subsurface flow. The high NO3, and DOC levels measured at the early stages of dry events reflected the contribution from NO3, -rich groundwaters. The contribution of rapid surface flow on water-repellent soil materials located close to the stream channel is hypothesized to explain the DOC levels. An understanding of the complex interactions between antecedent soil moisture conditions, the presence of soil nutrients available for leaching and the dynamics of soil water flow paths during storms is essential to explain the fluxes of dissolved nitrogen and carbon in streams of forested watersheds. Copyright © 2007 John Wiley & Sons, Ltd. [source] Hillslope-swamp interactions and flow pathways in a hypermaritime rainforest, British ColumbiaHYDROLOGICAL PROCESSES, Issue 15 2003D. F. Fitzgerald Abstract The process of water delivery to a headwater stream in a hypermaritime rainforest was examined using a variety of physical techniques and tracing with dissolved organic carbon (DOC) and the stable isotopes of water. Headwater swamps, often the major discharge zones for water draining off steep forest slopes, strongly affect the physical and chemical character of streamflow in the region. The headwater swamp selected for detailed investigation was sustained by relatively constant groundwater input from the steep colluvial slopes that maintained the water table above the ground surface. During significant storm events the water table rose quickly and the swamp expanded to engulf marginal pools that developed rapidly on the adjacent ground surfaces. The corresponding release of surface water directly to the stream typically comprised up to 95% of total stream discharge. The proportion of groundwater seepage to the stream by matrix flow (<1%) and via macropore-fed springs (up to 73%) increased during the recession period, but could not be sustained over the longer term. In more protracted drying periods, deep groundwater contributions to the stream were routed first to the headwater swamp. Dissolved organic carbon (DOC) in the stream, measured daily or more frequently during storm events, was found to be directly proportional to discharge, owing to the domination of DOC-rich headwater-swamp water sources. Although ,18O and ,2H composition of rainwater, groundwater and stream flow were found to be similar, deuterium excess (d ,2H , 8,18O) of water components was often found to be distinct, and suggested short water residence times of roughly 12 days for one event. Overall, observations of a typical headwater swamp reveal that the groundwater regime is dominated by rapid infiltration and short, emergent flow paths. With a relatively short turnover time, potential disturbances to the system by harvesting of upslope areas can be expected to occur rapidly. Forest managers can mitigate some of the harmful effects of logging operations by respecting the integrity of headwater wetland systems. The nature and magnitude of such perturbations will require further study. Copyright © 2003 John Wiley & Sons, Ltd. [source] Determining long time-scale hyporheic zone flow paths in Antarctic streamsHYDROLOGICAL PROCESSES, Issue 9 2003Michael N. Gooseff Abstract In the McMurdo Dry Valleys of Antarctica, glaciers are the source of meltwater during the austral summer, and the streams and adjacent hyporheic zones constitute the entire physical watershed; there are no hillslope processes in these systems. Hyporheic zones can extend several metres from each side of the stream, and are up to 70 cm deep, corresponding to a lateral cross-section as large as 12 m2, and water resides in the subsurface year around. In this study, we differentiate between the near-stream hyporheic zone, which can be characterized with stream tracer experiments, and the extended hyporheic zone, which has a longer time-scale of exchange. We sampled stream water from Green Creek and from the adjacent saturated alluvium for stable isotopes of D and 18O to assess the significance and extent of stream-water exchange between the streams and extended hyporheic zones over long time-scales (days to weeks). Our results show that water residing in the extended hyporheic zone is much more isotopically enriched (up to 11, D and 2·2, 18O) than stream water. This result suggests a long residence time within the extended hyporheic zone, during which fractionation has occurred owing to summer evaporation and winter sublimation of hyporheic water. We found less enriched water in the extended hyporheic zone later in the flow season, suggesting that stream water may be exchanged into and out of this zone, on the time-scale of weeks to months. The transient storage model OTIS was used to characterize the exchange of stream water with the extended hyporheic zone. Model results yield exchange rates (,) generally an order magnitude lower (10,5 s,1) than those determined using stream-tracer techniques on the same stream. In light of previous studies in these streams, these results suggest that the hyporheic zones in Antarctic streams have near-stream zones of rapid stream-water exchange, where ,fast' biogeochemical reactions may influence water chemistry, and extended hyporheic zones, in which slower biogeochemical reaction rates may affect stream-water chemistry at longer time-scales. Copyright © 2003 John Wiley & Sons, Ltd. [source] Wavelet analysis of inter-annual variability in the runoff regimes of glacial and nival stream catchments, Bow Lake, AlbertaHYDROLOGICAL PROCESSES, Issue 6 2003Melissa Lafrenière Abstract Continuous wavelet analyses of hourly time series of air temperature, stream discharge, and precipitation are used to compare the seasonal and inter-annual variability in hydrological regimes of the two principal streams feeding Bow Lake, Banff National Park, Alberta: the glacial stream draining the Wapta Icefields, and the snowmelt-fed Bow River. The goal is to understand how water sources and flow routing differ between the two catchments. Wavelet spectra and cross-wavelet spectra were determined for air temperature and discharge from the two streams for summers (June,September) 1997,2000, and for rainfall and discharge for the summers of 1999 and 2000. The diurnal signal of the glacial runoff was orders of magnitude higher in 1998 than in other years, indicating that significant ice exposure and the development of channelized glacial drainage occurred as a result of the 1997,98 El Niño conditions. Early retreat of the snowpack in 1997 and 1998 led to a significant summer-long input of melt runoff from a small area of ice cover in the Bow River catchment; but such inputs were not apparent in 1999 and 2000, when snow cover was more extensive. Rainfall had a stronger influence on runoff and followed quicker flow paths in the Bow River catchment than in the glacial catchment. Snowpack thickness and catchment size were the primary controls on the phase relationship between temperature and discharge at diurnal time scales. Wavelet analysis is a fast and effective means to characterize runoff, temperature, and precipitation regimes and their interrelationships and inter-annual variability. The technique is effective at identifying inter-annual and seasonal changes in the relative contributions of different water sources to runoff, and changes in the time required for routing of diurnal meltwater pulses through a catchment. However, it is less effective at identifying changes/differences in the type of the flow routing (e.g. overland flow versus through flow) between or within catchments. Copyright © 2003 John Wiley & Sons, Ltd. [source] Towards integrating tracer studies in conceptual rainfall-runoff models: recent insights from a sub-arctic catchment in the Cairngorm Mountains, ScotlandHYDROLOGICAL PROCESSES, Issue 2 2003Chris Soulsby Abstract Hydrochemical tracers (alkalinity and silica) were used in an end-member mixing analysis (EMMA) of runoff sources in the 10 km2 Allt a' Mharcaidh catchment. A three-component mixing model was used to separate the hydrograph and estimate, to a first approximation, the range of likely contributions of overland flow, shallow subsurface storm flow, and groundwater to the annual hydrograph. A conceptual, catchment-scale rainfall-runoff model (DIY) was also used to separate the annual hydrograph in an equivalent set of flow paths. The two approaches produced independent representations of catchment hydrology that exhibited reasonable agreement. This showed the dominance of overland flow in generating storm runoff and the important role of groundwater inputs throughout the hydrological year. Moreover, DIY was successfully adapted to simulate stream chemistry (alkalinity) at daily time steps. Sensitivity analysis showed that whilst a distinct groundwater source at the catchment scale could be identified, there was considerable uncertainty in differentiating between overland flow and subsurface storm flow in both the EMMA and DIY applications. Nevertheless, the study indicated that the complementary use of tracer analysis in EMMA can increase the confidence in conceptual model structure. However, conclusions are restricted to the specific spatial and temporal scales examined. Copyright © 2003 John Wiley & Sons, Ltd. [source] Baseflow and peakflow chemical responses to experimental applications of ammonium sulphate to forested watersheds in north-central West Virginia, USA,HYDROLOGICAL PROCESSES, Issue 12 2002Pamela J. Edwards Abstract Stream water was analysed to determine how induced watershed acidification changed the chemistry of peakflow and baseflow and to compare the relative timing of these changes. Two watersheds in north-central West Virginia, WS3 and WS9, were subjected to three applications of ammonium sulphate fertilizer per year to induce acidification. A third watershed, WS4, was the control. Samples were collected for 8 years from WS9 and for 9 years from WS3. Prior to analyses, concentration data were flow adjusted, and the influence of natural background changes was removed by accounting for the chemical responses measured from WS4. This yielded residual values that were evaluated using robust locally weighted regression and Mann,Kendall tests. On WS3, analyte responses during baseflow and peakflow were similar, although peakflow responses occurred soon after the first treatment whereas baseflow responses lagged 1,2 years. This lag in baseflow responses corresponded well with the mean transit time of baseflow on WS3. Anion adsorption on WS3 apparently delayed increases in SO4 leaching, but resulted in enhanced early leaching losses of Cl and NO3. Leaching of Ca and Mg was strongly tied, both by timing and stoichiometrically, to NO3 and SO4 leaching. F -factors for WS3 baseflow and peakflow indicated that the catchment was insensitive to acid neutralizing capacity reductions both before and during treatment, although NO3 played a large role in reducing the treatment period F -factor. By contrast, the addition of fertilizer to WS9 created an acid sensitive system in both baseflow and peakflow. On WS9, baseflow and peakflow responses also were similar to each other, but there was no time lag after treatment for baseflow. Changes in concentrations generally were not as great on WS9 as on WS3, and several ions showed no significant changes, particularly for peakflow. The lesser response to treatment on WS9 is attributed to the past abusive farming and site preparation before larch planting that resulted in poor soil fertility, erosion, and consequently, physical and chemical similarities between upper and lower soil layers. Even with fertilizer-induced NO3 and SO4 leaching increases, base cations were in low supplies and, therefore, unavailable to leach via charge pairing. The absence of a time lag in treatment responses for WS9 baseflow indicates that it has substantially different flow paths than WS3. The different hydrologies on these nearby watersheds illustrates the importance of understanding watershed hydrology when establishing a monitoring programme to detect ecosystem change. Published in 2002 by John Wiley & Sons, Ltd. [source] Characteristics of preferential flow and groundwater discharge to Shingobee Lake, Minnesota, USAHYDROLOGICAL PROCESSES, Issue 10 2002Hans F. Kishel Abstract Small-scale heterogeneities and large changes in hydraulic gradient over short distances can create preferential groundwater flow paths that discharge to lakes. A 170 m2 grid within an area of springs and seeps along the shore of Shingobee Lake, Minnesota, was intensively instrumented to characterize groundwater-lake interaction within underlying organic-rich soil and sandy glacial sediments. Seepage meters in the lake and piezometer nests, installed at depths of 0·5 and 1·0 m below the ground surface and lakebed, were used to estimate groundwater flow. Statistical analysis of hydraulic conductivity estimated from slug tests indicated a range from 21 to 4·8 × 10,3 m day,1 and small spatial correlation. Although hydraulic gradients are overall upward and toward the lake, surface water that flows onto an area about 2 m onshore results in downward flow and localized recharge. Most flow occurred within 3 m of the shore through more permeable pathways. Seepage meter and Darcy law estimates of groundwater discharge agreed well within error limits. In the small area examined, discharge decreases irregularly with distance into the lake, indicating that sediment heterogeneity plays an important role in the distribution of groundwater discharge. Temperature gradients showed some relationship to discharge, but neither temperature profiles nor specific electrical conductance could provide a more convenient method to map groundwater,lake interaction. These results suggest that site-specific data may be needed to evaluate local water budget and to protect the water quality and quantity of discharge-dominated lakes. Copyright © 2002 John Wiley & Sons, Ltd. [source] Controls on old and new water contributions to stream flow at some nested catchments in Vermont, USAHYDROLOGICAL PROCESSES, Issue 3 2002James B. Shanley Abstract Factors controlling the partitioning of old and new water contributions to stream flow were investigated for three events in four catchments (three of which were nested) at Sleepers River Research Watershed in Danville, Vermont. In the 1993 snowmelt period, two-component isotopic hydrograph separations showed that new water (meltwater) inputs to the stream ranged widely from 41 to 74%, and increased with catchment size (41 to 11 125 ha) (with one exception) and with open land cover (0,73%). Peak dissolved organic carbon concentrations and relative alkalinity dilution in stream water ranked in the same order among catchments as the new water fractions, suggesting that new water followed shallow flow paths. During the 1994 snowmelt, despite similar timing and magnitude of melt inputs, the new-water contribution to stream flow ranged only from 30 to 36% in the four catchments. We conclude that the uncommonly high and variable new water fractions in streamwater during the 1993 melt were caused by direct runoff of meltwater over frozen ground, which was prevalent in open land areas during the 1993 winter. In a high-intensity summer rainstorm in 1993, new water fractions were smaller relative to the 1993 snowmelt, ranging from 28 to 46%, but they ranked in the identical catchment order. Reconciliation of the contrasting patterns of new,old water partitioning in the three events appears to require an explanation that invokes multiple processes and effects, including: 1.topographically controlled increase in surface-saturated area with increasing catchment size; 2.direct runoff over frozen ground; 3.low infiltration in agriculturally compacted soils; 4.differences in soil transmissivity, which may be more relevant under dry antecedent conditions. These data highlight some of the difficulties faced by catchment hydrologists in formulating a theory of runoff generation at varying basin scales. Copyright © 2002 John Wiley & Sons, Ltd. [source] A conceptual model of preferential flow systems in forested hillslopes: evidence of self-organizationHYDROLOGICAL PROCESSES, Issue 10 2001Roy C. Sidle Abstract Preferential flow paths are known to be important conduits of subsurface stormflow in forest hillslopes. Earlier research on preferential flow paths focused on vertical transport; however, lateral transport is also evident in steep forested slopes underlain by bedrock or till. Macropores consisting of decayed and live roots, subsurface erosion, surface bedrock fractures, and animal burrows form the basis of a ,backbone' for lateral preferential flow in such sites. Evidence from field studies in Japan indicates that although individual macropore segments are generally <0·5 m in length, they have a tendency to self-organize into larger preferential flow systems as sites become wetter. Staining tests show clear evidence of interconnected macropore flow segments, including: flow within decayed root channels and subsurface erosion cavities; flow in small depressions of the bedrock substrate; fracture flow in weathered bedrock; exchange between macropores and mesopores; and flow at the organic horizon,mineral soil interface and in buried pockets of organic material and loose soil. Here we develop a three-dimensional model for preferential flow systems based on distributed attributes of macropores and potential connecting nodes (e.g. zones of loose soil and buried organic matter). We postulate that the spatially variable and non-linear preferential flow response observed at our Japan field site, as well as at other sites, is attributed to discrete segments of macropores connecting at various nodes within the regolith. Each node is activated by local soil water conditions and is influenced strongly by soil depth, permeability, pore size, organic matter distribution, surface and substrate topography, and possibly momentum dissipation. This study represents the first attempt to characterize the spatially distributed nature of preferential flow paths at the hillslope scale and presents strong evidence that these networks exhibit complex system behaviour. Copyright © 2001 John Wiley & Sons, Ltd. [source] Quantifying contributions to storm runoff through end-member mixing analysis and hydrologic measurements at the Panola Mountain Research Watershed (Georgia, USA)HYDROLOGICAL PROCESSES, Issue 10 2001Douglas A. Burns Abstract The geographic sources and hydrologic flow paths of stormflow in small catchments are not well understood because of limitations in sampling methods and insufficient resolution of potential end members. To address these limitations, an extensive hydrologic dataset was collected at a 10 ha catchment at Panola Mountain Research Watershed near Atlanta, GA, to quantify the contribution of three geographic sources of stormflow. Samples of stream water, runoff from an outcrop, and hillslope subsurface stormflow were collected during two rainstorms in the winter of 1996, and an end-member mixing analysis model that included five solutes was developed. Runoff from the outcrop, which occupies about one-third of the catchment area, contributed 50,55% of the peak streamflow during the 2 February rainstorm, and 80,85% of the peak streamflow during the 6,7 March rainstorm; it also contributed about 50% to total streamflow during the dry winter conditions that preceded the 6,7 March storm. Riparian groundwater runoff was the largest component of stream runoff (80,100%) early during rising streamflow and throughout stream recession, and contributed about 50% to total stream runoff during the 2 February storm, which was preceded by wet winter conditions. Hillslope runoff contributed 25,30% to peak stream runoff and 15,18% to total stream runoff during both storms. The temporal response of the three runoff components showed general agreement with hydrologic measurements from the catchment during each storm. Estimates of recharge from the outcrop to the riparian aquifer that were independent of model calculations indicated that storage in the riparian aquifer could account for the volume of rain that fell on the outcrop but did not contribute to stream runoff. The results of this study generally indicate that improvements in the ability of mixing models to describe the hydrologic response accurately in forested catchments may depend on better identification, and detailed spatial and temporal characterization of the mobile waters from the principal hydrologic source areas that contribute to stream runoff. Copyright © 2001 John Wiley & Sons, Ltd. [source] Investigating mechanisms of stormflow generation by natural tracers and hydrometric data: a small catchment study in the Black Forest, GermanyHYDROLOGICAL PROCESSES, Issue 2 2001E. Hangen Abstract The importance and interaction of various hydrological pathways and identification of runoff source areas involved in solute transport are still under considerable debate in catchment hydrology. To reveal stormflow generating areas and flow paths, hydrometric behaviour of throughfall, soil water from various depths, runoff, and respective concentrations of the environmental tracers 18O, Si, K, SO4 and dissolved organic carbon were monitored for a 14-week period in a steep headwater catchment in the Black Forest Mountains, Germany. Two stormflow hydrographs were selected and, based on 18O and Si, chemically separated into three flow components. Their sources were defined using mixing diagrams. Additional information about stormflow generating mechanisms was derived from recession analyses of the basin's complete 5-year hydrograph record. By providing insight into storage properties and residence times of outflowing reservoirs of the basin, recession analysis proved to be a valuable tool in runoff model conceptualization. Its results agreed well with hydrometric and hydrochemical data. Supported by evaluation of 30 hillslope soil profiles a coherent concept of stormflow generation could be derived: whereas in many steeply sloped basins in the temperate region soil water from hillslopes appears to have an immediate effect on the shape of the stormflow hydrograph, its role at this basin is basically restricted to the recharge of the groundwater reservoir in the near-channel area. Storm hydrograph peaks appear to be derived from a small direct runoff component supplemented by a fast delivery of baseflow from the groundwater reservoir in the valley bottom. Copyright © 2001 John Wiley & Sons, Ltd. [source] Investigation of nonuniformity in a liquid,solid fluidized bed with identical parallel channelsAICHE JOURNAL, Issue 1 2010Long Fan Abstract Previous work has demonstrated that multiphase flow through identical parallel channels and multiple cyclones can give rise to significant nonuniformity among the flow paths. This article presents results from a study where the distribution of voidage and flux through parallel channels in liquid,solid fluidized beds is investigated. Experiments and computational fluid dynamics simulations were performed with 1.2 mm glass beads fluidized by water where a cross baffle divided a 191 mm diameter column into four identical parallel channels. Voidages were measured by optical fiber probes. Simulations from a three-dimensional unsteady-state Eulerian,Eulerian model based on FLUENT software showed good agreement with the experimental results. Despite the symmetrical geometry of the system, the average voidage and particle velocities in one channel differed somewhat from those in the others. Increasing the superficial liquid velocity could increase voidage greatly and affect the degree of nonuniformity in the four channels. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] A depth filtration model of straining within the void networks of stainless steel filtersAICHE JOURNAL, Issue 12 2009John C. Price Abstract A depth filtration model has been developed, based on the three-dimensional void network model Pore-Cor. The geometry of the void network is fitted, by means of an eight-dimensional Boltzmann annealed amoeboid simplex, to the porosity and percolation characteristics of stainless steel sintered filters measured by mercury porosimetry. Preferential and critical flow paths through the network are calculated. Particles from an experimental size distribution are fed along these flow-biased paths, and when straining occurs, the flow paths are re-calculated. We show that the model usefully reproduces experimental filtration efficiencies as a function of pressure drop, measured by single pass tests. We also offer a critique of current measurements of filtration efficiency, suggesting the use of a new "alpha efficiency" rather than the standard beta efficiency. The model is currently being adapted to accept porometry as well as porosimetry data, hence avoiding the use of mercury. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] In defence of the meltwater (megaflood) hypothesis for the formation of subglacial bedform fields,JOURNAL OF QUATERNARY SCIENCE, Issue 3 2010John Shaw Abstract Characteristics of large-scale fluting and hummocky terrain on the Canadian Prairies test glacial and meltwater hypotheses for landform genesis. These tests defend the meltwater model. Neither sedimentary nor glaciotectonic processes can fully explain such erosional landforms. Province-scale flow paths, which mark palaeo-ice streams and subglacial flood routes, contain large-scale fluting with flanking hummock terrain. Antecedent relief causes these paths to differ from other flood landscapes such as the Scablands. Proponents of the glacial hypothesis use an invalid analogy between Icelandic and Prairie landsystems. They suggest that groove-ploughing formed large-scale fluting, and that ice pushing created hummocky terrain. However, landform location, form, and extent, surface lags, truncated architecture, and landform associations favour the meltwater hypothesis. A simple thought experiment and clear understanding of the principle of least number of assumptions answer the criticisms that meltwater forms cannot cross-cut and that the meltwater hypothesis disregards proper hypothesis testing. An example of cross-cutting erosional marks supports this theory. No narrow tract of smoothed terrain with fluting terminates at the glacially thrust Neutral Hills, negating an important point in the glacial hypothesis. While neither the glacial hypothesis nor postglacial winnowing explain boulder and cobble lags with percussion marks, meltwater processes explain them well. Copyright © 2009 John Wiley & Sons, Ltd. [source] WATERSHED WEIGHTING OF EXPORT COEFFICIENTS TO MAP CRITICAL PHOSPHOROUS LOADING AREAS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2003Theodore A. Endreny ABSTRACT: The Export Coefficient model (ECM) is capable of generating reasonable estimates of annual phosphorous loading simply from a watershed's land cover data and export coefficient values (ECVs). In its current form, the ECM assumes that ECVs are homogeneous within each land cover type, yet basic nutrient runoff and hydrological theory suggests that runoff rates have spatial patterns controlled by loading and filtering along the flow paths from the upslope contributing area and downslope dispersal area. Using a geographic information system (GIS) raster, or pixel, modeling format, these contributing area and dispersal area (CADA) controls were derived from the perspective of each individual watershed pixel to weight the otherwise homogeneous ECVs for phosphorous. Although the CADA-ECM predicts export coefficient spatial variation for a single land use type, the lumped basin load is unaffected by weighting. After CADA weighting, a map of the new ECVs addressed the three fundamental criteria for targeting critical pollutant loading areas: (1) the presence of the pollutant, (2) the likelihood for runoff to carry the pollutant offsite, and (3) the likelihood that buffers will trap nutrients prior to their runoff into the receiving water body. These spatially distributed maps of the most important pollutant management areas were used within New York's West Branch Delaware River watershed to demonstrate how the CADA-ECM could be applied in targeting phosphorous critical loading areas. [source] Simulation of Agglomerate Dispersion in Cubic Cavity FlowMACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2009Mahdi Salami Hosseini Abstract Agglomerate dispersion and deformation is simulated and studied in a cavity flow, as a typical three-dimensional flow field, using Stokesian dynamics and macroscopic flow analysis. The break-up and deformation behaviors of two different agglomerate structures , loose, with fractal dimension FD,=,1.8, and dense, with FD,=,2.6 , are examined in different flow paths. The interparticle forces are calculated using van der Waals and Born forces. Results show that agglomerates with a dense structure break-up through detachment, while ones with a loose structure deform and break into fragments through rupture. It was also found that the rearrangement of particles in the agglomerate can postpone break-up in flow fields where rotation occurs, since it can dissipate stress through rearrangements. [source] Cavity balance for plastic injection moldingPOLYMER ENGINEERING & SCIENCE, Issue 6 2000Y. C. Lam Cavity balancing is the process of altering the flow front within a cavity through thickness and design changes such that a desired fill pattern is achieved. This paper reports the preliminary research undertaken in developing an automated method for cavity balancing of two-dimensional cavities. The aim of the automated cavity balancing routine is to reduce product development time and to improve product quality. This will lower the level of prerequisite expert knowledge necessary for successful mold and part design. The automated cavity balancing routine has been developed using the concept of flow paths. The hill-climbing algorithm was employed on the cavity fill pattern for generation of the flow paths. Replacing the flow paths generated using the straight flow path assumption in previous work, this method was found to be more versatile and suitable to automation. No special considerations or routines were required to overcome the presence of inserts within the cavity. The method has been implemented in a computer program running as an external loop to the Moldflow software. The models analyzed demonstrate that the proposed method is viable and robust. [source] Comprehensive analysis of advanced solar cell contacts consisting of printed fine-line seed layers thickened by silver platingPROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 2 2009D. Pysch Abstract This work presents a detailed analysis of a new two-layer process to contact industrial solar cells. However, most of the results seem to be transferable to standard screen print paste contacts. The seed layer was created by a pad or screen printer and thickened by light-induced plating (LIP) of silver. These contact structures were investigated microscopically to gain a better understanding of the observed electrical parameters. A review of the present microscopic contact formation model for flat surfaces is presented. This model was extended and applied to surfaces textured with random pyramids. This analysis has revealed two new types of silver crystallites which can be described by a crystallographic model. The dependence of the silver crystallite density on the surface doping concentration was investigated. Next, the dependence of the contact resistance on the width of the seed layer was measured showing that the contact resistivity increases with a reduction of the seed layer width. These results have been further approved by an analysis of SEM images of wet-chemically etched contacts examining the density of crystallites and the fraction of removed SiNx layer. Contact resistance RC measurements before and after LIP of silver showed surprisingly a positive influence of the plating process on RC. A detailed microscopical analysis revealed four new possible current flow paths due to the LIP of a conventional contact or a seed layer. The results led to an extension of the existing model for a screen-printed contact. Copyright © 2008 John Wiley & Sons, Ltd. 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