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1

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.

2

Form induced stresses over rough gravel-beds

Aberle J., Koll K., Dittrich A.

Acta Geophysica

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2008

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Vol. 56, no. 3

584-600

EN

This paper presents an analysis of spatial flow heterogeneity over rough gravel beds for shallow flows in terms of form induced stresses. Data from experiments specifically designed with the intention to analyze the flow data with the double-averaging methodology are used to investigate the nature of form induced stresses. It is shown that spatial flow heterogeneity is small at greater distances to the roughness tops (z 100), increases slightly towards z 100, and increases significantly below z 100. Form induced stresses determined over the same bed and with the same slope are found to be independent of discharge. The influence of the number of measuring verticals on the magnitude of form induced stresses is discussed. The distributions of form induced stresses - are used to define the geodetic level of the roughness crest for rough, irregular beds from hydraulic data.

3

Measurements of armour layer roughness geometry function and porosity

Aberle J.

Acta Geophysica

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2007

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Vol. 55, no. 1

23-32

EN

The roughness geometry function of the interfacial sublayer of a gravel-bed armour layer was measured directly by filling water stepwise into a laboratory flume and indirectly from a digital elevation model (DEM) of the surface. The re-sults of both methods are compared and show that the DEM can be used to reliably estimate the roughness density function for a wide range of the interfacial sublayer. The direct measurements revealed an absolute minimum of porosity at the level of the roughness trough which is significantly smaller than porosity in the undisturbed subsurface and porosity estimates obtained from relationships found in the litera-ture. The significance of the results for hydraulic engineering and ecological appli-cations is highlighted.

4

Shear velocity estimation in hydraulic research

Rowiński P., Aberle J., Mazurczyk A.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 4

567-583

EN

Various methods for determination of shear velocity and bed shear stress in hydraulic research are discussed, comprising gravity method, logarithmic profile method, near-bed Reynolds-stress method, turbulent kinetic energy method, Prandtl based method, Saint Venant method, power law method, pipe flow method, Shields method, and direct methods. These methods are, where applicable, used to estimate shear velocity and/or bed shear stress in different fields of hydraulic research, ranging from flows in compound channels, gravel bed rivers, and cohesive sediment erosion studies to flows under unsteady conditions.

5

Sediment budget of a heathland sand-bed river

Schulte-Rentrop A., Koll K., Aberle J., Dittrich A.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 4

553-565

EN

The paper presents methodologies to quantify sediment sources in order to determine the sediment budget of a river. The methods are applied to assess the morphological state of the heathland River Wuemme. The results emphasize that de-tailed knowledge of the sediment budget is a prerequisite for the development of successful river restoration strategies.