Evaluation of friction velocity in unsteady flow experiments

Mrokowska, Magdalena M.; Rowiński, Paweł M.; Kalinowska, Monika B.

doi:10.1080/00221686.2015.1072853

Cited by 16 publications

(18 citation statements)

References 31 publications

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“…It is more difficult to control and evaluate water surface slope than the flowrate in unsteady flow, which has been broadly discussed in the literature (Dottori et al, 2009;Mrokowska et al, 2015b;Perumal et al, 2004). Moreover, water surface slope results are very sensitive to the fluctuations of water level data.…”

Section: Evaluation Of Water Surface Slopementioning

confidence: 99%

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Laboratory studies on bedload transport under unsteady flow conditions

Mrokowska

Rowiński

Książek

et al. 2017

Journal of Hydrology and Hydromechanics

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Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m 3 s -1 to 0.0456 m 3 s -1 , water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.

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Section: Evaluation Of Water Surface Slopementioning

confidence: 99%

“…S w may be evaluated as a difference quotient, provided spatial measurements of water level in several locations along the channel are available (Mrokowska et al, 2015b).…”

Section: Evaluation Of Water Surface Slopementioning

confidence: 99%

Laboratory studies on bedload transport under unsteady flow conditions

Mrokowska

Rowiński

Książek

et al. 2017

Journal of Hydrology and Hydromechanics

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“…Equation 1 contains the flow depth gradient, which is extremely difficult to determine. Mrokowska et al (2015aMrokowska et al ( , 2015b recently discussed this issue and claimed it was highly sensitive to the method used for computations. In this study, to calculate β, the variation in water depth along the flow direction (∂H/∂x) was determined from the continuous water surface profile, adjusted by a spline fitting technique to the flow depth measurements.…”

Section: Laboratory Experiments and Field Measurementsmentioning

confidence: 99%

Non-uniform flow over cobble bed with submerged vegetation strip

Afzalimehr

Barahimi

Sui

2019

Proceedings of the Institution of Civil Engineers - Water Manag

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2 3To better understand the influence of non-uniform flow in coarse-bed streams with a submerged vegetation strip on flow characteristics, data were collected from experiments in a laboratory flume and field investigations in a cobblebed river reach in central Iran. The results of the experiments and field observations showed that the velocity profiles for non-uniform flows in cobble-bed streams with vegetation strips can be divided into either two or three sub-zones. The velocity profiles of non-uniform flows in the laboratory flume and cobble-bed stream deviated from the log law in the wake and mixing zones, but fitted approximately in the log-law layer zone. The distribution of Reynolds stress for non-uniform flows was influenced by the vegetation strip and showed a non-concave shape. Near the channel bed, sweep motion occurred more frequently than the ejection process. Close to the top of vegetation strip, the correlation coefficient (r u 0 w 0 ) was negative, indicating downward momentum transport due to sweep and ejection processes. However, r u 0 w 0 was positive near the water surface, indicating upward momentum by the vegetation strip due to inward and outward interactions. The study shows that laboratory results cannot be easily applied to natural rivers without considerable assumptions.

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“…On the other hand, the authors have claimed that the distance between cross sections should be large enough to perform a robust evaluation of the flow depth gradient. The impact of distance between cross sections on the gradient of flow depth has been studied in Mrokowska et al (2015) with reference to dynamic waves generated in a laboratory flume. The results have shown that with a too long distance, the gradient in the region of the wave peak is misestimated due to the linear character of approximation.…”

Section: Linear Approximation Based On Two Cross Sectionsmentioning

confidence: 99%

“…In Mrokowska et al (2015) it has been stated that for better representation of ϑ the central difference quotient should be applied. Due to insufficient measurement cross sections for the Olszanka watercourse, in this study only a two-point difference quotient is applied.…”

Section: Linear Approximation Based On Two Cross Sectionsmentioning

confidence: 99%

A methodological approach of estimating resistance to flow under unsteady flow conditions

Mrokowska

Rowiński

Kalinowska

2015

Hydrol. Earth Syst. Sci.

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Abstract. This paper presents an evaluation and analysis of resistance parameters: friction slope, friction velocity and Manning coefficient in unsteady flow. The methodology to enhance the evaluation of resistance by relations derived from flow equations is proposed. The main points of the methodology are (1) to choose a resistance relation with regard to a shape of a channel and (2) type of wave, (3) to choose an appropriate method to evaluate slope of water depth, and (4) to assess the uncertainty of result. In addition to a critical analysis of existing methods, new approaches are presented: formulae for resistance parameters for a trapezoidal channel, and a translation method instead of Jones' formula to evaluate the gradient of flow depth. Measurements obtained from artificial dam-break flood waves in a small lowland watercourse have made it possible to apply the method and to analyse to what extent resistance parameters vary in unsteady flow. The study demonstrates that results of friction slope and friction velocity are more sensitive to applying simplified formulae than the Manning coefficient (n). n is adequate as a flood routing parameter but may be misleading when information on trend of resistance with flow rate is crucial. Then friction slope or friction velocity seems to be better choice.

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Evaluation of friction velocity in unsteady flow experiments

Cited by 16 publications

References 31 publications

Laboratory studies on bedload transport under unsteady flow conditions

Laboratory studies on bedload transport under unsteady flow conditions

Non-uniform flow over cobble bed with submerged vegetation strip

A methodological approach of estimating resistance to flow under unsteady flow conditions

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