scholarly journals Longitudinal scattering coefficient obtained by hydroacoustic measurement and by conservative tracer

2021 ◽  
pp. 75-86
Author(s):  
Ana F. Nadal ◽  
José M. Díaz Lozada ◽  
Gonzalo P. Barbero Medina ◽  
Karen M. Moro ◽  
Mariana N. Melchiorre ◽  
...  
Keyword(s):  
Dispersion Coefficient ◽  
Flow Characteristics ◽  
Chemical Reactor ◽  
High Flow ◽  
Low Flow ◽  
Flow Conditions ◽  
Dry Period ◽  
Longitudinal Dispersion Coefficient ◽  
Transport Models ◽  
Conservative Tracer

The objective of the present work was to determine the value of the longitudinal dispersion coefficient (DL) of the Chicamtoltina stream (Alta Gracia) by means of two different techniques, in order to compare the values obtained. The first technique consisted of applying a developed formula that includes a detailed description of hydrodynamic parameters obtained by gauging with a hydroacoustic instrument, while the second technique consisted of injecting a conservative tracer, using the same approach as the non-ideal chemical reactor theory of flow with dispersion. This work was carried out at low flow conditions (dry period) and at high flow conditions (wet period). It was found that, either for high flow or low flow, the values of the dispersion coefficient obtained by both techniques have good agreement, fitting better in the dry period than in the wet period. Due to the fact that frequent gauging campaigns are carried out in this stream, it is concluded that with similar flow characteristics and morphology of the section, the gauging data can be used to determine the DL coefficient, in order to incorporate reliable data that can be applied to pollutant transport models.

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.

Estimating the hydrodynamic and morphodynamic characteristics using Entropy theory at the confluence of Negro and Solimões Rivers

2021 ◽  
Author(s):  
Farhad Bahmanpouri ◽  
Silvia Barbetta ◽  
Carlo Gualtieri ◽  
Marco Ianniruberto ◽  
Naziano Filizola ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Flow Characteristics ◽  
Low Flow ◽  
Entropy Theory ◽  
Velocity Data ◽  
Flow Conditions ◽  
Mean Velocity ◽  
Discharge Data ◽  
Confluence Zone ◽  
Error Percentage

&lt;p&gt;When two mega rivers merge the mixing of two flows results in a highly complex three-dimensional flow structure in an area known as the confluence hydrodynamic zone. In the confluence zone, substantial changes occur to the hydrodynamic and morphodynamic features which are of significant interest for researchers. The con&amp;#64258;uence of the Negro and Solim&amp;#245;es Rivers, as one of the largest river junctions on Earth, is the study area of the present research. During the EU-funded Project &amp;#8220;Clim-Amazon&amp;#8221; (2011-2015), velocity data were collected using an ADCP vessel operating under high and low flow conditions in different locations at that confluence (Gualtieri et al., 2019). By applying the Entropy theory developed by Chiu (1988) for natural channels and simplified by Moramarco et al. (2014), the two-dimensional velocity distribution, as well as depth-averaged velocity, were calculated at the different transects along the confluence zone, using only the surface velocities observation. The estimated data yielded 6.6% and 6.9% error percentage for the discharge data related to high and low flow conditions, respectively, and 8.4% and 8.3% error percentage for the velocity data related to high and low flow conditions, respectively. Regardless of the flow condition, these preliminary results also suggest the potential points at the confluence zone for the maximum local scouring. The findings of the current research highlighted the potential of Entropy theory to estimate the flow characteristics at the large river&amp;#8217;s confluence, just starting from the measure of surface velocities. This is of considerable interest for monitoring high flows using&amp;#160;no-contact technology, when ADCP or other contact equipment cannot be used for the safety of operators and risks for equipment loss.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Keywords: Amazon River, Negro/Solim&amp;#245;es Confluence, Entropy Theory, Velocity Distribution, Local Scouring&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Gualtieri, C., Ianniruberto, M., Filizola, N. (2019). On the mixing of rivers with a difference in density: the case of the Negro/Solim&amp;#245;es confluence, Brazil. Journal of Hydrology, 578(11), November 2019, 124029,&lt;/p&gt;&lt;p&gt;Chiu, C. L. (1988). &amp;#8220;Entropy and 2-D velocity distribution in open channels&amp;#8221;. Journal of Hydrologic Engineering, ASCE, 114(7), 738-756&lt;/p&gt;&lt;p&gt;Moramarco, T., Saltalippi, C., Singh, V.P. (2004). &amp;#8220;Estimation of mean velocity in natural channels based on Chiu&amp;#8217;s velocity distribution equation&amp;#8221;. Journal of Hydrologic Engineering, ASCE, 9 (1), pp. 42-50&lt;/p&gt;

Blood Flow in Stented Arteries: A Parametric Comparison of Strut Design Patterns in Three Dimensions

2005 ◽  
Vol 127 (4) ◽  
pp. 637-647 ◽  
Author(s):  
Yong He ◽  
Nandini Duraiswamy ◽  
Andreas O. Frank ◽  
James E. Moore
Keyword(s):  
Fluid Dynamics ◽  
Flow Direction ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Three Dimensions ◽  
Low Flow ◽  
Radius Of Curvature ◽  
Shear Stresses ◽  
Stent Design ◽  
Flow Conditions

Background: Restenosis after stent implantation varies with stent design. Alterations in secondary flow patterns and wall shear stress (WSS) can modulate intimal hyperplasia via their effects on platelet and inflammatory cell transport toward the wall, as well as direct effects on the endothelium. Method of Approach: Detailed flow characteristics were compared by estimating the WSS in the near-strut region of realistic stent designs using three-dimensional computational fluid dynamics (CFD), under pulsatile high and low flow conditions. The stent geometry employed was characterized by three geometric parameters (axial strut pitch, strut amplitude, and radius of curvature), and by the presence or lack of the longitudinal connector. Results: Stagnation regions were localized around stent struts. The regions of low WSS are larger distal to the strut. Under low flow conditions, the percentage restoration of mean axial WSS between struts was lower than that for the high flow by 10–12%. The largest mean transverse shear stresses were 30–50% of the largest mean axial shear stresses. The percentage restoration in WSS in the models without the longitudinal connector was as much as 11% larger than with the connector. The mean axial WSS restoration between the struts was larger for the stent model with larger interstrut spacing. Conclusion: The results indicate that stent design is crucial in determining the fluid mechanical environment in an artery. The sensitivity of flow characteristics to strut configuration could be partially responsible for the dependence of restenosis on stent design. From a fluid dynamics point of view, interstrut spacing should be larger in order to restore the disturbed flow; struts should be oriented to the flow direction in order to reduce the area of flow recirculation. Longitudinal connectors should be used only as necessary, and should be parallel to the axis. These results could guide future stent designs toward reducing restenosis.

scholarly journals Remodeling of Resistance Arteries in Renal Failure: Effect of Endothelin Receptor Blockade

2001 ◽  
Vol 12 (10) ◽  
pp. 2040-2050 ◽  
Author(s):  
KERSTIN AMANN ◽  
GABRIEL MIL TENBERGER-MIL TENYI ◽  
AURELIA SIMONOVICIENE ◽  
ANDREAS KOCH ◽  
STEPHAN ORTH ◽  
...  
Keyword(s):  
Renal Failure ◽  
Blood Flow ◽  
High Flow ◽  
Mesenteric Arteries ◽  
Low Flow ◽  
Normal Flow ◽  
Flow Conditions ◽  
First Order ◽  
The Media ◽  
Intimal Thickness

Abstract. Remodeling of vessels is a known feature of renal failure, but it is unclear whether this represents an appropriate or inappropriate response to the known changes in blood flow, shear stress, and wall tension. To investigate remodeling in response to variations in blood flow, first-order mesenteric arteries were exposed to high- and low-flow conditions via the ligation of second-order branches, according to the technique described by Pour-ageaud and De Mey. The resulting changes in vessel geometric features, relative proportions of intima and media, submicroscopic structure, and immunostaining for proliferating cell nuclear antigen (PCNA), endothelin-1 (ET-1), and ETAreceptors were assessed in first-order mesenteric arteries under low-flow and high-flow conditions. Subtotally nephrectomized (SNX) animals were compared with sham-operated rats. Animals either were left untreated or were treated with the ETAreceptor antagonist (ET-RA) LU-135252, because of suggestions in the literature that ET is involved in vascular remodeling in uremia. A highly significant increase in intimal thickness was noted in low-flow arteries (4.21 ± 1.39 μm) of SNX animals, compared with normal-flow arteries (2.06 ± 0.61 μm), but this increase was not observed in sham-operated rats (1.38 ± 0.77 in low-flow arteriesversus2.40 ± 0.35 μm in normal-flow arteries). The increase in intimal thickness in low-flow arteries was abrogated by ET-RA. The medial thickness was increased in untreated SNX animals (19.5 ± 3.61 μm), compared with sham-operated rats, and this increase was also prevented by ET-RA. The medial thickness was not affected by low flow in either sham-operated or SNX animals. In parallel, the number of PCNA-positive intimal cells was higher in low-flow, but not high-flow, arteries of SNX rats, compared with sham-operated rats. No significant change was observed in sham-operated animals. In the media, the number of PCNA-positive cells was higher in untreated SNX animals than in sham-operated rats. The number was even more markedly increased in high-flow, but not low-flow, vessels. This increase was abrogated by ET-RA. It is concluded that, in uremic animals, the response of the intima to low flow and the response of the media to high flow are exaggerated. Both responses are apparently mediated by ET.

ANALYSIS OF LOW-FLOW CONDITIONS IN A HETEROGENEOUS KARST CATCHMENT AS A BASIS FOR FUTURE PLANNING OF WATER RESOURCE MANAGEMENT

2020 ◽  
Author(s):  
Klaudija Sapač ◽  
◽  
Simon Rusjan ◽  
Nejc Bezak ◽  
Mojca Šraj ◽  
...  
Keyword(s):  
Water Resources ◽  
Water Use ◽  
Water Resource Management ◽  
Flow Characteristics ◽  
Low Flow ◽  
Flow Conditions ◽  
Discharge Data ◽  
River Catchment ◽  
Low Flows ◽  
Recession Curves

Understanding and prediction of low-flow conditions are fundamental for efficient water resources planning and management as well as for identification of water-related environmental problems. This is problematic especially in view of water use in economic sectors (e.g., tourism) where water-use peaks usually coincide with low-flow conditions in the summer time. In our study, we evaluated various low-flow characteristics at 11 water stations in the non-homogenous Ljubljanica river catchment in Slovenia. Approximately 90% of the catchment is covered by karst with a diverse subsurface, consisting of numerous karst caves. The streams in the remaining part of the catchment have mainly torrential characteristics. Based on daily discharge data we calculated and analyzed values of 5 low-flow indices. In addition, by analyzing hydrograph recession curves, recession constants were determined to assess the catchment’s responsiveness to the absence of precipitation. By using various calculation criteria, we analyzed the influence of individual criteria on the values of low-flow recession constants. Recession curves are widely used in different fields of hydrology, for example in hydrological models, baseflow studies, for low-flow forecasting, and in assessing groundwater storages which are crucial in view of assessing water availability for planning water resources management. Moreover, in the study we also investigated the possible impact of projected climate change (scenario RCP4.5) on low-flow conditions in two sub-catchments of the Ljubljanica river catchment. For the evaluation we used the lumped conceptual hydrological model implemented in the R package airGR. For periods 2011-2040, 2041-2070, and 2071-2100 low-flow conditions were evaluated based on flow duration curves compared with the 1981-2010 period. The lowest discharges at all water stations in the Ljubljanica river catchment occur mostly during the summer months. Our results for the future show that we can expect a decrease of the lowest low-flows in the first two 30-year periods, while in the last one low-flows could increase by approx. 15%. However, the uncertainty/variability of the results is very high and as such should be taken into account when interpreting and using the results. This study demonstrates that evaluation of several low-flow characteristics is needed for a comprehensive and holistic overview of low-flow dynamics. In non-homogeneous catchments with a high karstic influence, the hydrogeological conditions of rivers should also be taken into account in order to adequately interpret the results of low-flow analyses. This proved to be important even in case of neighboring water stations.

Estimating river water-quality trends under different flow conditions

2021 ◽  
Author(s):  
Qian Zhang ◽  
James Webber ◽  
Douglas Moyer ◽  
Jeffrey Chanat
Keyword(s):  
Water Quality ◽  
River Water ◽  
Total Nitrogen ◽  
Nitrogen Concentration ◽  
High Flow ◽  
River Water Quality ◽  
Low Flow ◽  
Flow Conditions ◽  
Particulate Nitrogen ◽  
Water Quality Trends

&lt;p&gt;A number of statistical approaches have been developed to quantify the overall trend in river water quality, but most approaches are not intended for reporting separate trends for different flow conditions. We propose an approach called FN&lt;sub&gt;2Q&lt;/sub&gt;, which is an extension of the flow-normalization (FN) procedure of the well-established WRTDS (&amp;#8220;Weighted Regressions on Time, Discharge, and Season&amp;#8221;) method. The FN&lt;sub&gt;2Q&lt;/sub&gt;&amp;#160;approach provides a daily time series of low-flow and high-flow FN flux estimates that represent the lower and upper half of daily riverflow observations that occurred on each calendar day across the period of record. These daily estimates can be summarized into any time period of interest (e.g., monthly, seasonal, or annual) for quantifying trends. The proposed approach is illustrated with an application to a record of total nitrogen concentration (632 samples) collected between 1985 and 2018 from the South Fork Shenandoah River at Front Royal, Virginia (USA). Results show that the overall FN flux of total nitrogen has declined in the period of 1985&amp;#8211;2018, which is mainly attributable to FN flux decline in the low-flow class. Furthermore, the decline in the low-flow class was highly correlated with wastewater effluent loads, indicating that the upgrades of treatment technology at wastewater treatment facilities have likely led to water-quality improvement under low-flow conditions. The high-flow FN flux showed a spike around 2007, which was likely caused by increased delivery of particulate nitrogen associated with sediment transport. The case study demonstrates the utility of the FN&lt;sub&gt;2Q&lt;/sub&gt;&amp;#160;approach toward not only characterizing the changes in river water quality but also guiding the direction of additional analysis for capturing the underlying drivers. The FN&lt;sub&gt;2Q&lt;/sub&gt; approach (and the published code) can easily be applied to widely available river monitoring records to quantify water-quality trends under different flow conditions to enhance understanding of river water-quality dynamics. &lt;span&gt;(Journal article: https://doi.org/10.1016/j.scitotenv.2020.143562; R code and data release: https://doi.org/10.5066/P9LBJEY1).&lt;/span&gt;&lt;/p&gt;

Characteristics of sediments in a newly constructed reservoir in Japan

2006 ◽  
Vol 53 (2) ◽  
pp. 73-78 ◽  
Author(s):  
Y. Sakurai ◽  
S. Haruta
Keyword(s):  
High Flow ◽  
Low Flow ◽  
Particulate Phosphorus ◽  
Formation Mechanisms ◽  
Flow Conditions ◽  
Discharge Rates ◽  
Main River ◽  
Sediment Formation ◽  
Specific Discharge ◽  
Land Surfaces

The sediment formation mechanisms of a newly constructed reservoir in Ehime, Japan were evaluated by characterizing the soil particles (SP) and particulate phosphorus (PP) in the runoff and reservoir sediments. The SP and PP loads from the runoffs of the main river in the watershed considerably increased, when the specific discharge rates were over 300 l/s/km2 (high flow conditions). When the specific discharge rates exceeded over 300 l/s/km2, 19% of the watershed generated over 80% of the SP and PP loads. When the specific discharge rates were under 300 l/s/km2 (low flow conditions), the contributions of the previously mentioned 19% area to the SP and PP loads were smaller. Significant amounts of smectite were found in the sediments in the reservoir and in the soil samples obtained at the forest exposed area in this 19% area while it was negligible in citrus orchards and paddy fields that constituted the remaining land surfaces. The forest area exposed by recent landslides was significant for the SP and PP in the reservoir. Judging from the outcomes, land use information alone may not be sufficient to detect critical sources of SP and PP in the runoffs and reservoirs. To identify and confirm crucial areas for the SP and PP in the runoffs, the investigations should be conducted under high flow conditions and the composition of clay minerals in the sediments should be checked against the clay mineral distributions of soils in the watershed.

scholarly journals Flow Characteristics in the Volute and Tongue Region of a Centrifugal Pump

1984 ◽  
Author(s):  
R. B. Brownell ◽  
R. D. Flack
Keyword(s):  
Rotational Speed ◽  
Separation Zone ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
High Flow ◽  
Low Flow ◽  
Flow Rates ◽  
Pressure Profiles ◽  
Instantaneous Position ◽  
Centrifugal Process

A centrifugal process pump was tested at two rotational speeds and five flow rates. Nine piezometer taps around the volute were used to measure time averaged pressure profiles and streak photography was used to visualize the flow patterns near the volute tongue. Flow patterns for four different instantaneous impeller orientations (blade positions) were studied. Nondimensionalized results were independent of rotational speed. At 100% capacity the volute pressures were uniform within 15%. At off-design condition, however, the pressure near the tongue varied by as much as 28% from the average. At 100% capacity the streamlines were smooth and well behaved. At low flow rates the tongue stagnation point moved between the impeller and tongue and a separation zone appeared in the discharge. The instantaneous position of the impeller was seen to affect the streamlines primarily near the impeller, although at high flow rates the separation zone was also seen to depend on the impeller position.

The Tracer Experimental Method for Determining Longitudinal Dispersion Coefficient of Nature River

2013 ◽  
Vol 748 ◽  
pp. 1155-1159 ◽  
Author(s):  
Yong Fan ◽  
Ke Bin Shi
Keyword(s):  
Experimental Method ◽  
Dispersion Coefficient ◽  
Flow Characteristics ◽  
Tracer Experiment ◽  
Longitudinal Dispersion ◽  
Longitudinal Dispersion Coefficient ◽  
Local Conditions ◽  
Practical Applications ◽  
Advantages And Disadvantages ◽  
Natural Rivers

Tracer experiment to obtain flow longitudinal dispersion coefficient is the most direct and reliable method. In this paper, the existing natural rivers longitudinal dispersion coefficient tracer experimental method for calculating is analyzed comprehensively. Focuses on the method of moments, the principles and applications of regression analysis, calculus optimization methods, and analyzes their advantages and disadvantages. In recent years the calculus optimization method is outstanding, determine river longitudinal dispersion coefficient method was developed and applied to an instance of some of the new tracer experiment. Local conditions should combine with topographic flow characteristics to select the appropriate calculation methods in practical applications. Finally, some problems of the natural rivers longitudinal dispersion coefficient study that need further investigation were put forward.

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