Velocity and Turbulence Measurements for Two Overbank Flow Events in River Severn

Babaeyan-Koopaei, K.; Ervine, D. A.; Carling, Paul A.; Cao, Zhixian

doi:10.1061/(asce)0733-9429(2002)128:10(891)

Cited by 67 publications

(38 citation statements)

References 10 publications

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“…The low, 1 Hz sampling frequency represented an important instrumental limitation (Soulsby, 1980), and we were unable to infer specific characteristics of turbulence (i.e., higherorder moments, autocorrelation functions, or power spectra). The 180 s record length allowed for averaging over the passage of several flow structures (Babaeyan-Koopaei et al, 2002), however, and, rather than performing detailed, time-domain analyses of individual measurement locations as in previous studies (e.g., Roy et al, 2004), we used the resulting summary statistics to characterize reach-scale spatial patterns of velocity and turbulence intensity. For the cross-sectional deployment, we approximated the depth-averaged velocity by assuming a logarithmic velocity profile and placing the ADV at 0.6 of the flow depth h where h < 45 cm and at 0.2h and 0.8h where h > 45 cm (Whiting, 2003); summary statistics computed for the two depths were then averaged to provide a single data point for the plan view location.…”

Section: Field Data Collectionmentioning

confidence: 99%

“…Turbulence intensities for each velocity component were quantified by computing root mean square (RMS) values from the ADV time series data (Clifford and French, 1993b). In order to compare flow fields for the three discharges we sampled, we did not use the mean velocity and turbulence intensity components directly but rather scaled them by the friction velocity U * = ghS (Nezu and Nakagawa, 1993;Babaeyan-Koopaei et al, 2002), where g is gravitational acceleration,h is the reach-averaged depth (mean of depths measured at velocity measurement stations), and S is (approximated by) the reach-averaged channel bed slope of 0.041. Scaling the velocity components by U * thus accounted for the effects of increasing flow stage on the depthaveraged velocity.…”

Section: Calculation Of Hydraulic Quantitiesmentioning

confidence: 99%

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Geostatistical analysis of the effects of stage and roughness on reach-scale spatial patterns of velocity and turbulence intensity

2007

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Although previous research has documented well-organized interactions between the turbulent flow field and an irregular boundary, the spatial variability of turbulent flow characteristics at the reach scale remains poorly understood. In this paper, we present detailed field measurements of three-dimensional flow velocities and turbulence intensities in a high-gradient, cobble-bed riffle from three discharges; additional data on sediment grain size and bed topography were used to characterize boundary roughness. An acoustic Doppler velocimeter was used to measure velocities along five cross-sections within a 6 m long reach of the North Fork Cache La Poudre River; vertical profiles were also measured along the channel thalweg. We adopted a spatially explicit stochastic hydraulic approach and focused not on coherent flow structures per se but rather time-averaged, reach-scale variability and spatial pattern. Scaling velocities and turbulence intensities by the reach-averaged friction velocity U * accounted for changes in flow depth and enabled comparisons among the three discharges. We quantified the effects of stage and roughness by assessing differences among probability distributions of hydraulic quantities and by examining geostatistical metrics of spatial variability. We computed semivariograms for both the streamwise and transverse directions and fit parametric models to summarize the spatial structure of each variable at each discharge. Cross-correlograms were also used to describe the local and lagged effects of boundary roughness on flow characteristics. Although the probability distributions yielded some insight, incorporating spatial information revealed important elements of stage-dependent flow structure. The development of secondary currents and flow convergence at higher stages was clearly documented in maps and semivariograms. In general, the spatial structure of the flow field became smoother and more continuous as stage increased and the effects of boundary roughness diminished. Although roughness elements do influence velocities and turbulence intensities, our data suggest that the flow primarily responds to the gross morphology of the channel and that flow depth is the primary control on flow structure. The geostatistical framework proved useful, and our results indicate that a complete stochastic description must also be explicitly spatial.

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Section: Field Data Collectionmentioning

confidence: 99%

Section: Calculation Of Hydraulic Quantitiesmentioning

confidence: 99%

Geostatistical analysis of the effects of stage and roughness on reach-scale spatial patterns of velocity and turbulence intensity

2007

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“…These authors classified the contributions by type of analysis and by topic (flow structure, velocity profiles, microhabitats and numerical model validation). Examples pertinent to the present research and not referred to by Buffin-Bélanger and Roy [11] include the following: Nelson et al [31] described the turbulent structure in the wake formed by the presence of bed forms, which are responsible for the observed deviations in the lower layers of the velocity profile; Baiamonte et al [4] showed the delay effect in the streamwise velocity produced by boulder drag in gravelbed rivers; Smart [44] and Babaeyan-Koopaei et al [3] studied time-averaged velocities, turbulence intensities, shear stresses, bed shear, friction velocity, roughness parameters and velocity spectra; Nikora and Smart [33] investigated the vertical distribution of turbulent energy dissipation and characteristic turbulence scales; Katul et al [26] compared the velocity deviations produced in gravel-bed rivers with the inflected profiles observed in atmospheric flows above the vegetation canopy; Hurther et al [23] documented the existence of coherent structures in rivers and their influence on transport and mixing; Tritico and Hotchkiss [46] described turbulence characteristics in the wake of obstructions. More references to field studies of fluvial hydraulics are given in [36] and in [15], thus extending the list by Buffin-Bélanger and Roy [11].…”

Section: Introductionmentioning

confidence: 99%

Parameterization of the logarithmic layer of double-averaged streamwise velocity profiles in gravel-bed river flows

Franca

Ferreira²,

Lemmin

2008

Advances in Water Resources

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a b s t r a c tThe logarithmic layer of double-averaged (in time and space) streamwise velocity profiles obtained from field measurements made in the Swiss rivers, Venoge and Chamberonne is parameterized and discussed. Velocity measurements were made using a 3D Acoustic Doppler Velocity Profiler. Both riverbeds are hydraulically rough, composed of coarse gravel, with relative submergences (h/D 50 ) of 5.25 and 5.96, respectively. From the observations, the flow may be divided into three different layers: a roughness layer near the bed, an equivalent logarithmic layer and a surface or outer layer. It was found that a logarithmic law can describe the double-averaged profiles in the layer 0.30 < z/h < 0.75. The parameterization of the logarithmic law is discussed. Special emphasis is given to the geometric parameters roughness and zerodisplacement heights and to the equivalent von Karman constant.

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“…The apparent shear stress is the stress due to the difference in velocities between the faster flow in the main channel and the slower flow in the floodplain. The momentum transfer mechanism in terms of apparent shear stress at the interface between the main channel and floodplains is expressed accurately for steady flows (Murota et al 1990;Bousmar & Zech 1999;Abidin 2004;Seckin 2004;Prooijen et al 2005;Ghavasieh et al 2006;Hua et al 2007;Koopaei et al 2007). However, the flow interactions and momentum exchanges between the main channel and floodplains in natural and complex river streams using unsteady flow models have not been well studied.…”

Section: Introductionmentioning

confidence: 99%

Flow modeling and analysis of compound channel in river network with complex floodplains and groynes

Hassan

Tanaka

Tamai

2010

Journal of Hydroinformatics

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Presented here are flow simulations of a network of natural rivers flanked by one or two large and complex floodplains with impermeable groynes and bridge embankments using one-and quasi-two-dimensional dynamic flow models. The effects of the large floodplain storage capacity, momentum transfer interaction and apparent shear stress at the vertical interface between the main channel and floodplain on the flow-simulated discharge and water depth values could be well explained. The two models were tested and validated in the Arakawa River basin, Kanto Region, Japan. The simulated results show that the large floodplain storage capacity greatly affected the flow discharge and water depth results and cannot be neglected. The quasitwo-dimensional river flow model was used in a flow simulation of a compound channel with complex floodplains with groynes and gave more acceptable results. In the simulated case, the average reduction in flood discharge using floodplain groynes was about 7-15%. Thus, floodplain groynes can be effective for flood protection and attenuation.

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Velocity and Turbulence Measurements for Two Overbank Flow Events in River Severn

Cited by 67 publications

References 10 publications

Geostatistical analysis of the effects of stage and roughness on reach-scale spatial patterns of velocity and turbulence intensity

Geostatistical analysis of the effects of stage and roughness on reach-scale spatial patterns of velocity and turbulence intensity

Parameterization of the logarithmic layer of double-averaged streamwise velocity profiles in gravel-bed river flows

Flow modeling and analysis of compound channel in river network with complex floodplains and groynes

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