Simulation of natural levee laboratory experiments with TELEMAC-2D/SISYPHE

Hydrodynamic

Technical Note: On the Production and Accuracy of CNC-Manufactured Hydraulic Scale Models

This Technical Note addresses the workflow for the production of hydraulic scale models using a Computer Numerically Controlled (CNC) production technique and investigates the possibilities to accurately reproduce topographical roughness features. Focusing on the construction of three scale models of unlined rock blasted tunnels, their accuracy is evaluated based on the comparison of differences between scaled prototype point clouds obtained by terrestrial laser scanning, spatially filtered meshes that served as input for the milling of the models, and digital twins of the constructed models that were created by Structure from Motion photogrammetry. The direct comparison between the point clouds and meshes as well as the comparison of derived statistical parameters show that the models could be reproduced with a high degree of accuracy. Observed deviations between the point clouds of the milled models and the milling meshes, as well as the scaled original point cloud, are identified and discussed in light of the production technique and the accuracy of the applied methods for the comparison

Fluvial levees in compound channels: a review on formation processes and the impact of bedforms and vegetation

Natural levees are wedge-shaped morphological features developing along the boundaries of mass flows. When they form in fluvial landscapes, they can have multiple implications for river management of trained inland rivers. This paper summarizes the present knowledge in regard to the formation and evolution of so-called fluvial levees of trained inland river sections and provides novel hypotheses in regard to the significance of bedforms and vegetation strips along the floodplain on levee formation, evolution, and characteristics. The hypotheses that (i) bedforms contribute to levee formation by altering the interface hydraulics between the main channel and the floodplain and enhancing entrainment of sediment into suspension and (ii) vegetation stripes along the floodplain additionally affect the interface hydraulics resulting in a changed levee geometry are supported by combining existing knowledge on bedform dynamics and flow-vegetation-sediment interaction with results reported in recent flume studies

Directional dependency of flow resistance in an unlined rock blasted hydropower tunnel

The dependency of the friction factor on the flow direction was investigated experimentally in a milled scale model of an unlined rock blasted tunnel under pressurized flow conditions by reversing the flow direction. The experimental data were used to highlight the significance of anisotropic roughness structures and variations in the cross-sectional area on the flow resistance. It is hypothesized that local sudden expansions of the cross-sectional area, which are followed by gradual contractions, contribute significantly to the directional dependency of the friction factor due to potential flow separation. For the reversed case, i.e. when sudden large-scale contractions were followed by gradual expansions, 15% lower friction factors were observed. The results were also used to highlight the scale dependency of these topographical features, the dependency of the friction factor from the tunnel driving direction, and to show the need for the development of methods that can be used to parameterize the directional dependency of hydraulic roughness and friction factors

Impacts on alternate bar geometry and dynamics in a trained sand bed river

This study investigates the occurrence and dynamics of single row alternate bars forming in a particular reach of the sand bed Elbe River in Germany. Although the formation and dynamics of alternate bars have been intensively investigated in the literature, there exists only a limited number of studies focusing on the characteristics of alternate bars forming under complex field conditions. This is particular the case for bars forming in trained sand bed rivers, as most previous field studies have focused on gravel bed rivers. Moreover, little is known on the impact of river training structures on bar characteristics in anthropogenic rivers. To close this gap, we present a comprehensive bed elevation data set that was collected over a period of 10 years within a 30 km long reach of the lower Elbe River in Germany by the Federal Waterways and Shipping Administration (WSV). The reach is characterized by a sand bed, has curved as well as straight parts, and exhibits a section that is less trained by groins than the neighboring sections. For our analyses, we propose a novel approach to estimate bar characteristics based on statistically derived geometrical parameters. The outcomes of the approach are used to show that bars in Elbe River belong to the free bar type and that their origin of formation and characteristics depend on hydrological and geometrical boundary conditions. The results reveal that the active width of the river bed, defined as the distance between the groin heads, is a crucial parameter for the occurrence of alternate in the reach. We further highlight the impact of river bends on bar characteristics, as bars in the outer bend were longer and higher than their inner bend counterparts. Finally, we show that simple predictors for bar formation can be successfully applied to predict bar formation in sand bed rivers but that care needs to be taken when applying such approaches to more complex boundary conditions

Fluvial levees in compound channels: a review on formation processes and the impact of bedforms and vegetation

Natural levees are wedge-shaped morphological features developing along the boundaries of mass flows. When they form in fluvial landscapes, they can have multiple implications for river management of trained inland rivers. This paper summarizes the present knowledge in regard to the formation and evolution of so-called fluvial levees of trained inland river sections and provides novel hypotheses in regard to the significance of bedforms and vegetation strips along the floodplain on levee formation, evolution, and characteristics. The hypotheses that (i) bedforms contribute to levee formation by altering the interface hydraulics between the main channel and the floodplain and enhancing entrainment of sediment into suspension and (ii) vegetation stripes along the floodplain additionally affect the interface hydraulics resulting in a changed levee geometry are supported by combining existing knowledge on bedform dynamics and flow-vegetation-sediment interaction with results reported in recent flume studies

A flume study to investigate the contribution of main-channel bedforms on levee formation

Natural levees can be observed worldwide in nearly all river systems characterized by frequent flooding in combination with the transport of suspended bed material. Several parameters and processes have been suggested to explain the formation and the highly variable geometry of natural levees. However, the effect of bedforms migrating in the main-channel has not been amongst the studied parameters and processes. To fill this gap, this study investigates the relationship between bedforms and natural levee formation by flume experiments. Experiments were conducted in a 2 m wide and 30 m long sediment recirculating flume, monitoring the bed level elevation in the main channel by ultrasonic sensors as well as recording the levee development on the floodplain by a camera. The effect of different bed configurations on the developed levees is compared, and discussed, showing that bedforms could enhance levee formation

A flume study to investigate the contribution of main-channel bedforms on levee formation

Natural levees can be observed worldwide in nearly all river systems characterized by frequent flooding in combination with the transport of suspended bed material. Several parameters and processes have been suggested to explain the formation and the highly variable geometry of natural levees. However, the effect of bedforms migrating in the main-channel has not been amongst the studied parameters and processes. To fill this gap, this study investigates the relationship between bedforms and natural levee formation by flume experiments. Experiments were conducted in a 2 m wide and 30 m long sediment recirculating flume, monitoring the bed level elevation in the main channel by ultrasonic sensors as well as recording the levee development on the floodplain by a camera. The effect of different bed configurations on the developed levees is compared, and discussed, showing that bedforms could enhance levee formation

Technical Note: On the Production and Accuracy of CNC-Manufactured Hydraulic Scale Models

This Technical Note addresses the workflow for the production of hydraulic scale models using a Computer Numerically Controlled (CNC) production technique and investigates the possibilities to accurately reproduce topographical roughness features. Focusing on the construction of three scale models of unlined rock blasted tunnels, their accuracy is evaluated based on the comparison of differences between scaled prototype point clouds obtained by terrestrial laser scanning, spatially filtered meshes that served as input for the milling of the models, and digital twins of the constructed models that were created by Structure from Motion photogrammetry. The direct comparison between the point clouds and meshes as well as the comparison of derived statistical parameters show that the models could be reproduced with a high degree of accuracy. Observed deviations between the point clouds of the milled models and the milling meshes, as well as the scaled original point cloud, are identified and discussed in light of the production technique and the accuracy of the applied methods for the comparison