scholarly journals Contribution of flow conditions and sand addition on hyporheic zone exchange in gravel beds

2019 ◽  
Vol 50 (3) ◽  
pp. 878-885
Author(s):  
H. Marttila ◽  
S. Tammela ◽  
K.-R. Mustonen ◽  
P. Louhi ◽  
T. Muotka ◽  
...  
Keyword(s):  
Hyporheic Zone ◽  
Headwater Streams ◽  
Transport Model ◽  
Tracer Test ◽  
Breakthrough Curves ◽  
Flow Conditions ◽  
One Dimensional ◽  
Gravel Beds ◽  
Negative Effect ◽  
Tracer Methods

Abstract We conducted a series of tracer test experiments in 12 outdoor semi-natural flumes to assess the effects of variable flow conditions and sand addition on hyporheic zone conditions in gravel beds, mimicking conditions in headwater streams under sediment pressure. Two tracer methods were applied in each experiment: 2–5 tracer-pulse tests were conducted in all flumes and pulses were monitored at three distances downstream of the flume inlet (0 m, 5 m and 10 m, at bed surface), and in pipes installed into the gravel bed at 5 m and 10 m distances. The tracer breakthrough curves (total of 120 tracer injections) were then analysed with a one-dimensional solute transport model (OTIS) and compared with data from the gravel pipes in point-dilution pulse tests. Sand addition had a strong negative effect on horizontal fluxes (qh), whereas the fraction of the median travel time due to transient storage (F200) was determined more by flow conditions. These results suggest that even small additions of sand can modify the hyporheic zone exchange in gravel beds, thus making headwater streams with low sediment transport capacity particularly vulnerable to sediments transported into the stream from catchment land use activities.

One-Dimensional Mixed Poroelastic-Transport-Swelling (MPHETS) Finite Element Models for Soft Tissues

2000 ◽  
Author(s):  
Jason W. Nichol ◽  
Bruce R. Simon ◽  
Stuart K. Williams
Keyword(s):  
Finite Element ◽  
Soft Tissues ◽  
Transport Model ◽  
Element Model ◽  
Solid Matrix ◽  
Finite Element Models ◽  
Flow Conditions ◽  
One Dimensional ◽  
Dimensional Finite Element ◽  
Water Species

Abstract A hydrated soft tissue structure can be viewed as a poroelastic transport model, or specifically a porous, incompressible, fibrous solid matrix, which is saturated by an incompressible fluid (water) containing both positively and negatively charged species. We present a one-dimensional finite element model (FEM), derived from a Mixed-Poro-HyperElastic-Transport-Swelling (MPHETS)model. This FEM can be used to model various soft tissues, such as arteries, and provides a powerful tool to study coupled ion transport under various mechanical loading and water/ species flow conditions.

scholarly journals Phosphorus Transport in a Lowland Stream Derived from a Tracer Test with 32P

Water ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1030
Author(s):  
Damian Zięba ◽  
Przemysław Wachniew
Keyword(s):  
Rural Areas ◽  
Transport Model ◽  
Tritiated Water ◽  
Tracer Test ◽  
Breakthrough Curves ◽  
Transient Storage ◽  
Phosphorus Transport ◽  
Lowland Stream ◽  
Beaver Dam ◽  
Small Streams

Small streams in urbanized rural areas receive loads of P from various, often episodic, sources. This paper addresses, through a tracer test with 32P, retention and transport of a pulse input of phosphorus in a 2.6 km long stretch of a channelized second-order lowland stream. Tritiated water was introduced alongside the 32P-labelled ortophosphate in order to isolate the influence of the hydrodynamic factors on P behavior. Tracer concentrations in unfiltered water samples were measured by liquid scintillation counting. Four in-stream and five hyporheic breakthrough curves were collected at four points along the stream, two of which encompass a beaver dam impoundment. The overall retention efficiency of 32P along the studied reach was 46%. The transient storage transport model OTIS-P provided reasonable fits for in-stream breakthrough curves (BTCs) but failed at reproducing the hyporheic BTCs. The overall small effect of transient storage on solute transport was higher in the stretch with a more pronounced surface storage. Transient storage and phosphorus retention were not enhanced in the beaver dam impoundment.

scholarly journals Multi-level qualification of Parafluvial Exchange within the Hyporheic Zone Affected by River Sinuosity and Seasonal Change using Multi-tracer Methods

2017 ◽  
Author(s):  
Amin reza Meghdadi ◽  
Morteza Eyvazi
Keyword(s):  
Stable Isotope ◽  
Hyporheic Zone ◽  
Dry Season ◽  
Water Type ◽  
Flow Conditions ◽  
Groundwater Hydrochemistry ◽  
Tracer Methods ◽  
Multi Level ◽  
Spatio Temporal ◽  
Groundwater Outflow

Abstract. Exchange of water in the parafluvial zone, located along the boundaries of meandering streams, arises in response to seasonal variation and spatial distribution. Remarkably, few studies have applied multi-tracer methods for qualitative scrutiny of losing (recharge) or gaining (discharge) reaches along the parafluvial zone. Hence, the main objective of this study is to qualitatively characterize the spatio-temporal alteration in parafluvial exchange within the hyporheic zone (PEHZ) by simultaneous application of multi-tracer methods. For this approach, first, Hierarchical Cluster Analysis (HCA) in conjunction with groundwater hydrochemistry analysis was used to evaluate the representativeness of parafluvial assessment network. Then, water stable isotope compositions (δ18O and δ2H), radioisotope (222Rn), and environmental tracers (Temperature and EC) were measured at multiple depths (20 cm to 100 cm depths below streambed) during the wet and dry season to qualitatively elucidate the PEHZ in the Ghezel-Ozan River, a third order river located in the northwest of Iran. By groundwater hydrochemistry assessment identified, NaHCO3 and CaHCO3 as the dominant water type in dry and wet season, respectively. Moreover, the HCA approach designed two different clusters for each season for accurate interpretation of PEHZ. Results obtained from stable isotope and environmental tracer analysis of bore water, surface water, and parafluvial water distinguished stream-aquifer connectivity with highly seasonal and spatial variations. In the dry season, for example, δ18O, δ2H, and EC varied from −3.59 to −1.88 (‰ VSMOW), −31.08 to −24.06 (‰ VSMOW), and 234 to 740.65  μS/cm respectively. Also, the results acquired from the integration of δ18O and EC revealed complex spatio-temporal stream-aquifer connectivity (PEHZ). In low flow conditions, groundwater outflow mainly occurred at 100 cm depth while the dominance of groundwater outflow at 20 cm depth prevailed during high flow conditions. The continuous and point scale measurements of temperature and 222Rn were highly in accordance with the results of δ18O and EC. Furthermore, diel temperature fluctuation, as well as radon activity variations at multi-level scale, expressed the PEHZ (especially at depth greater than 60 cm) are affected by large-scale regional flow-field which is embedded within. The synthesized approaches used in this study provide a useful insight into the spatiotemporal changes of stream-aquifer connectivity which make the more efficient monitoring and interpretation of hydrological processes possible. They can be, furthermore, utilized to pinpoint the losing/gaining reaches accurately to tackle environmental problems such as monitoring the transport of anthropogenic contaminants in a system.

Parameter Determination for Chloride and Tritium Transport in Undisturbed Lysimeters during Steady Flow

1992 ◽  
Vol 23 (2) ◽  
pp. 89-104 ◽  
Author(s):  
Ole H. Jacobsen ◽  
Feike J. Leij ◽  
Martinus Th. van Genuchten
Keyword(s):  
Experimental Data ◽  
Unsaturated Flow ◽  
Transport Model ◽  
Time Moment ◽  
Breakthrough Curves ◽  
Coarse Sand ◽  
Retardation Factor ◽  
Parameter Determination ◽  
Model Parameters ◽  
Water Fraction

Breakthrough curves of Cl and 3H2O were obtained during steady unsaturated flow in five lysimeters containing an undisturbed coarse sand (Orthic Haplohumod). The experimental data were analyzed in terms of the classical two-parameter convection-dispersion equation and a four-parameter two-region type physical nonequilibrium solute transport model. Model parameters were obtained by both curve fitting and time moment analysis. The four-parameter model provided a much better fit to the data for three soil columns, but performed only slightly better for the two remaining columns. The retardation factor for Cl was about 10 % less than for 3H2O, indicating some anion exclusion. For the four-parameter model the average immobile water fraction was 0.14 and the Peclet numbers of the mobile region varied between 50 and 200. Time moments analysis proved to be a useful tool for quantifying the break through curve (BTC) although the moments were found to be sensitive to experimental scattering in the measured data at larger times. Also, fitted parameters described the experimental data better than moment generated parameter values.

scholarly journals Interaction of equivalence ratio fluctuations and flow fluctuations in acoustically forced swirl flames

2021 ◽  
pp. 175682772110155
Author(s):  
Vincent Kather ◽  
Finn Lückoff ◽  
Christian O. Paschereit ◽  
Kilian Oberleithner
Keyword(s):  
Equivalence Ratio ◽  
Transfer Functions ◽  
Transport Model ◽  
Mode Conversion ◽  
Fuel Injector ◽  
One Dimensional ◽  
Flow Fluctuations ◽  
Non Linear ◽  
Non Local ◽  
Acoustic Forcing

The generation and turbulent transport of temporal equivalence ratio fluctuations in a swirl combustor are experimentally investigated and compared to a one-dimensional transport model. These fluctuations are generated by acoustic perturbations at the fuel injector and play a crucial role in the feedback loop leading to thermoacoustic instabilities. The focus of this investigation lies on the interplay between fuel fluctuations and coherent vortical structures that are both affected by the acoustic forcing. To this end, optical diagnostics are applied inside the mixing duct and in the combustion chamber, housing a turbulent swirl flame. The flame was acoustically perturbed to obtain phase-averaged spatially resolved flow and equivalence ratio fluctuations, which allow the determination of flux-based local and global mixing transfer functions. Measurements show that the mode-conversion model that predicts the generation of equivalence ratio fluctuations at the injector holds for linear acoustic forcing amplitudes, but it fails for non-linear amplitudes. The global (radially integrated) transport of fuel fluctuations from the injector to the flame is reasonably well approximated by a one-dimensional transport model with an effective diffusivity that accounts for turbulent diffusion and dispersion. This approach however, fails to recover critical details of the mixing transfer function, which is caused by non-local interaction of flow and fuel fluctuations. This effect becomes even more pronounced for non-linear forcing amplitudes where strong coherent fluctuations induce a non-trivial frequency dependence of the mixing process. The mechanisms resolved in this study suggest that non-local interference of fuel fluctuations and coherent flow fluctuations is significant for the transport of global equivalence ratio fluctuations at linear acoustic amplitudes and crucial for non-linear amplitudes. To improve future predictions and facilitate a satisfactory modelling, a non-local, two-dimensional approach is necessary.

scholarly journals Soil microbial inoculation during flood events shapes headwater stream microbial communities and diversity

2021 ◽  
Author(s):  
Florian Caillon ◽  
Katharina Besemer ◽  
Peter Peduzzi ◽  
Jakob Schelker
Keyword(s):  
Microbial Diversity ◽  
Bacterial Diversity ◽  
Soil Water ◽  
Headwater Streams ◽  
High Flow ◽  
Low Flow ◽  
Flood Events ◽  
Flow Conditions ◽  
Soil Microbial ◽  
Microbial Inoculation

AbstractFlood events are now recognized as potentially important occasions for the transfer of soil microbes to stream ecosystems. Yet, little is known about these “dynamic pulses of microbial life” for stream bacterial community composition (BCC) and diversity. In this study, we explored the potential alteration of stream BCC by soil inoculation during high flow events in six pre-alpine first order streams and the larger Oberer Seebach. During 1 year, we compared variations of BCC in soil water, stream water and in benthic biofilms at different flow conditions (low to intermediate flows versus high flow). Bacterial diversity was lowest in biofilms, followed by soils and highest in headwater streams and the Oberer Seebach. In headwater streams, bacterial diversity was significantly higher during high flow, as compared to low flow (Shannon diversity: 7.6 versus 7.9 at low versus high flow, respectively, p < 0.001). Approximately 70% of the bacterial operational taxonomic units (OTUs) from streams and stream biofilms were the same as in soil water, while in the latter one third of the OTUs were specific to high flow conditions. These soil high-flow OTUs were also found in streams and biofilms at other times of the year. These results demonstrate the relevance of floods in generating short and reoccurring inoculation events for flowing waters. Moreover, they show that soil microbial inoculation during high flow enhances microbial diversity and shapes fluvial BCC even during low flow. Hence, soil microbial inoculation during floods could act as a previously overlooked driver of microbial diversity in headwater streams.

Diabatic Nozzle Flow with Constant Small Stage Efficiency

1960 ◽  
Vol 64 (598) ◽  
pp. 632-635 ◽  
Author(s):  
R. A. A. Bryant
Keyword(s):  
Gas Flow ◽  
Nozzle Flow ◽  
Flow Conditions ◽  
One Dimensional ◽  
Real Flow ◽  
Stage Efficiency ◽  
Frictional Effects

The concept of small stage efficiency is introduced when studying one-dimensional gas flow in nozzles in order to permit a closer approximation of real flow conditions than is possible from an isentropic analysis. It is more or less conventional to assume the flow conditions are adiabatic whenever the small stage efficiency is used. That is to say, small stage efficiency is generally considered in relation to flows contained within adiabatic boundaries, in which case it becomes a measure of the heat generated by internal frictional effects alone.

Mathematical Analysis for Off-Design Performance of Cryogenic Turboexpander

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Subrata K. Ghosh ◽  
R. K. Sahoo ◽  
Sunil K. Sarangi
Keyword(s):  
Pressure Ratio ◽  
Expansion Ratio ◽  
Flow Conditions ◽  
Flow Properties ◽  
Dimensional Solution ◽  
One Dimensional ◽  
Design Performance ◽  
Fluid Properties ◽  
The Mean ◽  
Inlet Conditions

A study has been conducted to determine the off-design performance of cryogenic turboexpander. A theoretical model to predict the losses in the components of the turboexpander along the fluid flow path has been developed. The model uses a one-dimensional solution of flow conditions through the turbine along the mean streamline. In this analysis, the changes of fluid and flow properties between different components of turboexpander have been considered. Overall, turbine geometry, pressure ratio, and mass flow rate are input information. The output includes performance and velocity diagram parameters for any number of given speeds over a range of turbine pressure ratio. The procedure allows any arbitrary combination of fluid species, inlet conditions, and expansion ratio since the fluid properties are properly taken care of in the relevant equations. The computational process is illustrated with an example.

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