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Flow Characteristics over a Gravel Bedform: Kaj River Case Study

Maddahi M. R., Afzalimehr H., Rowiński P. M.

Acta Geophysica

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2016

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Vol. 64, no. 5

1779--1796

EN

The present study deals with the turbulence structure in order to better understand the interaction of bedform and flow characteristics in a gravel-bed river. Data measured above a bedform is used to analyze the importance of coherent structures in turbulent transfer. The Reynolds stress and turbulence intensity in stream-wise direction illustrate significant difference along the bedform, showing a three-layer distribution at the crest and a convex one at the downstream of bedform. Quadrant analysis technique is used to picture momentum exchange above the considered bedform and to find the dominant event in bursting process of the gravel bedform. Quadrant analysis demonstrates that the mechanisms of bedforms generation in sand and gravel-bed rivers are similar and sweep is the dominant event in both rivers.

2

Experimental Analysis of Horizontal Turbulence of Flow over Flat and Deformed Beds

Termini D.

Archives of Hydro-Engineering and Environmental Mechanics

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2015

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Vol. 62, nr 3-4

77--99

EN

Laboratory experiments in a straight flume were carried out to examine the evolution of large-scale horizontal turbulent structures under flat-bed and deformed-bed conditions. In this paper, the horizontal turbulence of flow under these conditions is analyzed and compared. The conditioned quadrant method is applied to verify the occurrence of turbulent events. The distributions of horizontal Reynolds shear stress and turbulent kinetic energy are also presented and discussed. Results show the occurrence of an “initial” sequence of horizontal vortices whose average spatial length scales with the channel width. Under deformed-bed conditions, this spatial length does not change.

3

Struktura koryta Potoku Huncowskiego w słowackich Tatrach Wysokich

Szymczuk P.

Woda-Środowisko-Obszary Wiejskie

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2013

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T. 13, z. 2

133-145

PL

W pracy scharakteryzowano strukturę koryta Potoku Huncowskiego w słowackich Tatrach Wysokich. Bazując na klasyfikacji Buffingtona i Montgomery’ego oraz zmianach spadku koryta, ciek podzielono na szesnaście odcinków. Następnie, wykorzystując metodę kartowania koryt rzek górskich wg instrukcji zaproponowanej przez Kamykowską i in., dokonano pomiaru erozyjnych i akumulacyjnych mezoform występujących w korycie. Na podstawie ich rozkładu przestrzennego wnioskowano o dominującym procesie i przypisano typ koryta: erozyjny, tranzytowy, tranzytowo-akumulacyjny. W celu przedstawienia szczegółowej charakterystyki struktury koryta pod względem wielkości form, litologii i spadku koryta wprowadzono podtypy. Stwierdzono, że struktura koryta Potoku Huncowskiego jest uwarunkowana litologią i spadkiem koryta. Podjęto próbę oceny stabilności koryta. Na podstawie zebranych danych stwierdzono, że koryto jest stabilne i Potok Huncowski nie zagraża działalności człowieka.

EN

The study presents characteristics of the Huncowski Stream channel structure in the Slovak High Tatra Mountains. Considering the arrangement of river bed forms the channel was divided into three types: erosive, transitional and transitional-accumulative. Subtypes that characterize channel with respect to the size of bed forms, lithology and channel slope were also distinguished. Factors affecting the structure of the Huncowski Stream channel are lithology and channel slope. Lithology determines the occurrence of bed forms and channel slope determines the frequency and size of bed forms. The Huncowski Stream was found to have a stable channel and to be not dangerous for human activity.

4

Bedform effect on the reorganization of surface and subsurface grain size distribution in gravel bedded channels

Singh A., Guala M., Lanzoni S., Foufoula-Georgiou E.

Acta Geophysica

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2012

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Vol. 60, no. 6

1607-1638

EN

Quantification of river bedform variability and complexity is important for sediment transport modeling as well as for characterization of river morphology. Alluvial bedforms are shown to exhibit highly nonlinear dynamics across a range of scales, affect local bed roughness, and vary with local hydraulic, hydrologic, and geomorphic properties. This paper examines sediment sorting on the crest and trough of gravel bedforms and relates it to bed elevation statistics. The data analysed here are the spatial and temporal series of bed elevation, grain size distribution of surface and subsurface bed materials, and sediment transport rates from flume experiments. We describe surface topography through bedform variability in height and wavelength and multiscale analysis of bed elevations as a function of discharge. We further relate bedform migration to preferential distribution of coarse and fine sediments on the troughs and crests, respectively, measuring directly surface and subsurface grain size distributions, and indirectly the small scale roughness variations as estimated from high resolution topographic scans.

5

Bed load transport by bed form migration

Aberle J., Coleman S., Nikora V.

Acta Geophysica

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2012

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Vol. 60, no. 6

1720-1743

EN

A theoretically-based methodology is presented for the determination of bed load transport from high-resolution measurements of bed surface elevations for steady-state or developing dunes. The methodology is based on the general form of the Exner equation for sediment continuity and requires information on the distribution of sediment volume concentration as well as the migration velocity of bed layers. In order to determine layer speeds, a new method based on cross-correlation analysis of elevation slices is proposed. The methodology is tested using artificiallycreated data as well as data from a physical model and from a flume study of developing bed forms. The analyses show the applicability of the method to determine bed load transport without the need to introduce assumptions about the form of the migrating surface. It is shown that predicted transport rates match measured or theoretical transport rates for steadily moving bed forms of an arbitrary shape. The method can also be used to predict transport rates over deforming bed forms, with the reasons for potential deviations between predicted and measured or theoretical transport rates for deforming bed forms identified and discussed. It is further shown that a simplified bulk-surface approach, that is relatively straightforward to apply and in which it is assumed that bed-layer velocity is constant with depth, gives results that are comparable to analyses based on determined bed-layer velocity variation with depth.

6

Wybrane problemy związane z powstawaniem piaszczysto-żwirowych form dennych w ujściowym odcinku rzeki podgórskiej

Radecki-Pawlik A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2008

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Vol. 17, No. 2

98--116

EN

In the paper the research results of forming observations of sand-gravel dunes developing on the riverbed along the outlet reach of the highland type of river. The subject of subaquatic river forms one can find in many scientific works, however most of the existing papers cover sand dunes and ripples found in the lowland rivers. Moreover, the majority of research was conducted in laboratory flumes, since all fieldworks need very complex research, complicated logistic as well as is extremely money consuming (hiring ships, diving bell, long time echosounding etc.). Thus there is a nowadays need to present field data covering a subject of the river bed forms which still could be considered as dunes but are built up with material coarser then 2 mm (which is fine gravel) and coarser. The research reach described along the present paper is lying in the region of confluence of the Raba and the Vistula Rivers, within the outlet of the Raba River, close to Uscie Solne, just below the Polish Carpathians mountains line. The research results show such parameters as: length, height and granulometric composition of the dunes found along that reach as well as the hydrodynamics parameters such as: shear velocity, shear stresses and resistant coefficients. Having gathered in one place the field measurements results many relationships between mentioned parameters are presented. The work could be useful for river engineers, fluvial geomorphologists, geologists and ecologists working with river channels.

7

Experimental Analysis of Relations Between Coherent Turbulent Structures and Formation of Bedforms

Termini D., Sammartano V.

Archives of Hydro-Engineering and Environmental Mechanics

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2008

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Vol. 55, nr 3-4

125-143

EN

The present paper describes an experimental investigation on the interactions between flow turbulence and sediment motion. During the experiments, detailed measurements of flow velocity components were carried out using an Acoustic Doppler Velocimeter (ADV). The occurrence of turbulent events (inward interaction, ejection, sweep and burst) was verified through conditioned quadrant analysis. The quantitative information on the spatial and temporal evolution of turbulent events was obtained through space-time correlations of the conditioned data. As the primary objective was to analyse how turbulent structures influence formation of bedforms, the spatial scale of turbulent event evolution has been compared with the wavelength of bed-forms (alternate bars) observed on the bed. The analysis has essentially highlighted that such spatial scale compares well with the wavelength of the bars.