HS9.4

EDI
Numerical modelling of hydro-morphological processes in open water environments

Complex hydro-morphological processes, such as sediment erosion, transport, deposition or fan development, affect open water environments, including rivers, estuaries as well as lakes and reservoirs. Consequently, many research tasks as well as practical applications rely on the correct prediction of these processes. During the last decades, numerical models have become a powerful tool in the research fields of hydraulic engineering and geosciences to simulate these hydro-morphological processes. With improved algorithms as well as an ever growing computational power, it became feasible to simulate the interaction of water, sediments and air with high resolution in space and time. In addition, with an increasing quantity and quality of validation data from laboratory experiments and field studies, numerical models are continuously enhanced so that many good examples of sediment transport modelling offer new insights in multiphase processes, e.g. dune development, river bed armoring or density driven transport. Hence, new generations of numerical modelling techniques open up the possibility to explore numerous outstanding research questions related to hydro-morphologic processes.
The main goal of this session is to bring together scientists and engineers, who develop, improve, and apply numerical models of multiphase flows for sediment transport in open water environments. We invite contributions that deal with numerical modelling from small-scale, such as bed structure development, to large-scale interactions, such as long-term development of hydro-morphological processes in rivers, lakes, reservoirs and estuaries.
Contributions may refer, but are not restricted, to:
• Entrainment processes of sediments (from cohesive sediments to armoured river beds)
• Bed load and suspended sediment transport processes (including flocculation processes)
• Simulation of sediment management including planning, operation and maintenance of hydro power plants
• Design and evaluation of restoration measures to revitalize rivers
• Navigation issues, such as sediment replenishment, dredging and erosion induced by ship generated waves
• Flood related issues of long term effects of morphological bed changes on flood security
• Eco-hydraulics such as flow – sediment – vegetation interaction
• Density driven transport

Co-organized by GM3
Convener: Bernhard Vowinckel | Co-conveners: Sándor Baranya, Katharina Baumgartner, Gabriele Harb, Nils Rüther
vPICO presentations
| Tue, 27 Apr, 15:30–17:00 (CEST)

vPICO presentations: Tue, 27 Apr

Chairpersons: Bernhard Vowinckel, Sándor Baranya, Gabriele Harb
15:30–15:35
15:35–15:37
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EGU21-7027
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ECS
Zixiong Zhao, Peng Hu, Wei Li, Zhixian Cao, and Zhiguo He

In recent decades, computational hydraulics and sediment modelling have a great development due to compute technology. Applying a finite-volume Godunov-type hydrodynamic shallow water model with hydro-sediment-morphodynamic processes, this work demonstrates and analysis the ability of single-host parallel computing technology with algorithmic acceleration technology. This model is implemented for high-performance computing using the NVIDIA’s Compute Unified Device Architecture (CUDA) programming framework, using a domain decomposition technique and across multiple cores through an efficient implementation of the Open Multi-Processing (Open MP) architecture, and using an algorithmic acceleration technology named local time stepping scheme (LTS), which is capable of obtain much efficiency improvement via different time step sizes for different grid sizes. The model is applied for three cases, through which we compare the effectiveness of CPU, Open MP, Open MP+LTS, CUDA, and CUDA+LTS, demonstrating high computational performance across CUDA+LTS which can lead to speedups of 40 times with respect to CPU and high-precision results across CUDA +LTS.

KEY WORDS: Hydro-sediment-morphological modeling; local time step; Open MP; CUDA.

How to cite: Zhao, Z., Hu, P., Li, W., Cao, Z., and He, Z.: Research on the single-host parallel computing with the local time step scheme for modeling of hydro-sediment-morphodynamic processes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7027, https://doi.org/10.5194/egusphere-egu21-7027, 2021.

15:37–15:39
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EGU21-9610
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ECS
Ramandeep Jain, Ricardo Rebel, and Jochen Fröhlich

Accurate prediction of sediment transport is highly desirable because of its key importance in many environmental and industrial applications. One way to approach this is to measure the length and height of the jump of a moving particle. This led to many studies dealing with the quantification of a particle jump. Nevertheless, few experiments have been performed to understand the effect of particle shape on its jump. A dataset of jumps of differently shaped particles has been generated by the authors from direct numerical simulations of bedload transport in a turbulent open channel flow. A total of four simulations were performed with a large number of mobile single shaped, mono-disperse particles. Four ellipsoidal shapes were used in these simulations, i.e. oblate, prolate, sphere, and a generally shaped ellipsoid. In the present contribution, statistical properties of the jump trajectories such as ejection and landing angles, flight length, height, and time, etc. will be reported. Mean jump trajectories for different particle shapes were calculated using the Dynamic-Time-Warping algorithm. The analysis provides a quantification of the different behavior of the particles under the present conditions. For example, it is observed that oblate particles travel a maximum distance in a jump, while spherical particles take small jumps but more often.

How to cite: Jain, R., Rebel, R., and Fröhlich, J.: On the dependency of jumps on particle shape in bedload transport of monodisperse non-spherical particles, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9610, https://doi.org/10.5194/egusphere-egu21-9610, 2021.

15:39–15:41
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EGU21-1464
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ECS
Christoph Rettinger, Sebastian Eibl, Ulrich Rüde, and Bernhard Vowinckel

With the increasing computational power of today's supercomputers, geometrically fully resolved simulations of particle-laden flows are becoming a viable alternative to laboratory experiments. Such simulations enable detailed investigations of transport phenomena in various multiphysics scenarios, such as the coupled interaction of sediment beds with a shearing fluid flow. There, the majority of available simulations as well as experimental studies focuses on setups of monodisperse particles. In reality, however, polydisperse configurations are much more common and feature unique effects like vertical size segregation.

In this talk, we will present numerical studies of mobile polydisperse sediment beds in a laminar shear flow, with a ratio of maximum to minimum diameter up to 10. The lattice Boltzmann method is applied to represent the fluid dynamics through and above the sediment bed efficiently. We model particle interactions by a discrete element method and explicitly account for lubrication forces. The fluid-particle coupling mechanism is based on the geometrically fully resolved momentum transfer between the fluid and the particulate phase. We will highlight algorithmic aspects and communication schemes essential for massively parallel execution.

Utilizing these capabilities allows us to achieve large-scale simulations with more than 26.000 densely-packed polydisperse particles interacting with the fluid. With this, we are able to reproduce effects like size segregation and to study the rheological behavior of such systems in great detail. We will evaluate and discuss the influence of polydispersity on these processes. These insights will be used to improve and extend existing macroscopic models.

How to cite: Rettinger, C., Eibl, S., Rüde, U., and Vowinckel, B.: Numerical study of sheared mobile polydisperse sediment beds with a coupled lattice Boltzmann - discrete element method, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1464, https://doi.org/10.5194/egusphere-egu21-1464, 2021.

15:41–15:43
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EGU21-4576
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ECS
Fabian Kleischmann, Paolo Luzzatto-Fegiz, Nick Rommelfanger, Eckart Meiburg, and Bernhard Vowinckel

Flocculation processes of clay particles are usually influenced by settling effects due to gravity. This inhibits the investigation of the effects of cohesive forces in isolation and limits our understanding of flocculation processes over long time scales that are more common in aquatic environments. To address this issue, particle-resolved Direct Numerical Simulations (pr-DNS) are conducted to simulate the flocculation processes of a preceding campaign of microgravity experiments that have been performed onboard the International Space Station (ISS). The experiments with clay suspensions of kaolin (8 ppt) in saline water (35 PSU) have been examined in the absence of gravity over a time period of more than 100 days by taking pictures of the suspension at regular time intervals. The results of the image analysis are used to validate the numerical computation of clay aggregate growth over time. The simulations are based on a numerical cohesion model which includes the fluid-particle interaction via the Immersed Boundary Method (IBM) by geometrically resolving the flow field around the suspended particles. To this end, monodisperse spherical primary particles were randomly placed in a triple-periodic box and exposed to an oscillatory flow. This oscillation is used to mimic the jitering motion of the ISS, which may be caused by onboard instruments as well as the drive-line technology. In this talk, we will present the results of these simulations and link them to the observations provided by the microgravity experimtents.

How to cite: Kleischmann, F., Luzzatto-Fegiz, P., Rommelfanger, N., Meiburg, E., and Vowinckel, B.: Particle-Resolved Direct Numerical Simulations of Clay Particles in the Absence of Gravity., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4576, https://doi.org/10.5194/egusphere-egu21-4576, 2021.

15:43–15:45
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EGU21-2438
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ECS
Alexander Metelkin and Bernhard Vowinckel

The dynamics of cohesive sediments under various flow conditions are of special interest in the framework of aquatic ecosystems. Being one of the main sources of transport for minerals and organic matter, the constituents of cohesive sediments are the source of food for many aquatic organisms. Due to the additional complexity of physical mechanisms, there are only a few simulation techniques for cohesive sediments, which do not cover all spatial scales. The primary cohesive clay particles are platelets smaller than 2 μm, which is small enough to experience Brownian motion. Composed together under the influence of van der Waals forces, they shape rounded aggregates also known as microflocs that are rather stable. These microflocs can form fragile, larger macroflocs with complex shapes exceeding 100 μm in size. Owing to the huge difference in the spatial scales, it is almost impossible to simulate macroflocs as the assembly of primary clay particles in the context of cohesive sediment transport modeling. In contrast to separate sediment grains, microflocs represent porous aggregates. To perform direct numerical simulations of microflocs transported in a viscous fluid flow, we are developing a computational model for immersed porous particles. The model resolves the flow outside and inside porous aggregates and accurately computes the hydrodynamic forces on the microflocs. The simulation of macroflocs is also attainable by employing cohesive forces between microflocs, which assembles them into bigger aggregates with the propensity of breaking up under high shear rates. Our computational model solves the system of Navier - Stokes equations directly with an additional Darcy term inside the porous aggregate. Using this approach, it becomes feasible to consider the influence of the flow inside porous media, so that we can study its impact on the mean flow characteristics depending on the properties of the porous flocs. The hydrodynamic forces are calculated implicitly based on the pressure and shear stress distribution. By comparison with methods that use Stokes-based drag coefficients, our approach allows estimating the influence of local flow conditions and the presence of neighboring aggregates on the resulting fluid force.

 

How to cite: Metelkin, A. and Vowinckel, B.: A numerical method for simulations of cohesive, porous sediments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2438, https://doi.org/10.5194/egusphere-egu21-2438, 2021.

15:45–15:47
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EGU21-36
Joshua Er Addi Iparraguirre Ayala, Estibene Pool Vásquez Choque, Carlos Lenin Benavente Escobar, Flor de María Zanini Maldonado, and Hugo Dulio Gómez Velásquez

The Peruvian coast is one of the driest in the world, but it is continuously affected by extraordinary rains associated with El Niño and/or La Niña phenomenon. During these periods of intense rainfall, high flow rates are registered and gravitational processes are reported along the valleys, such as: landslides, debris flow, rock falls, avalanches, among others.

This work presents the first estimation of the Stream Power, relationship between the energy, the flow, the slope of the channel and the density of the flow of the Chancay - Lambayeque basin, with the objective of determining the energy of the main rivers in the basin and relating with gravitational processes and damage to infrastructures.

We use two softwares: LSDTopoTools and ArcSWAT (version for ArcGIS 10.6). Using high resolution Digital Elevation Models (Alos Palsar, 12.5 m) we delimit the basin, its drainage area, water network and slope using LSDTopoTools. Subsequently, we use the SWAT program.

First, the sub-basins were delimited. Second, the Hydrological Response Units (HRU) were obtained, applying the Land Use data and the FAO base guide on soil types updated by the Ministry of Agriculture and Irrigation of Peru (MINAGRI). Third, we process data on temperature, wind speed, humidity, solar radiation and rainfall from 1970 - 2018 from five meteorological stations distributed in the study basin, whose data were provided by the National Meteorology and Hydrology Service of Peru (SENAMHI). Next, we include in the analyzes the flow data from the Tinajones reservoir (6° 38´S, 79° 29´W). Finally, the annual flow rates (Hm3/s) were simulated and adjusted using SWATCup.

The results show an average flow for the year 2018 that varies from 13 Hm3/s - 49 Hm3/s. This means that the Stream Power varies from 1.3x1012Kw-4.8x1012Kw, the maximum power coinciding with the location of the Tinajones reservoir in the middle basin.

These results have allowed us to identify that 73% of the critical zones (zones with presence of gravitational processes) are in the sections where the rivers register high Stream Power; and in the same way in these sections geological dangers predominate such as flows and rock falls. In addition, infrastructures were located that may be susceptible to being damaged (e.g. three bridges, where flows range between ~22-35 Hm3/s) and/or may compromise the health of the inhabitants (e.g. five mining deposits located along the basin, considered high risk).

And to conclude, because the Tinajones reservoir is reaching its maximum capacity, a possible area was identified where a new reservoir can be housed (complying with all technical conditions), whose location would be 20 km to the east, in the province of Chumbil Alto (Cajamarca - Peru).

How to cite: Iparraguirre Ayala, J. E. A., Vásquez Choque, E. P., Benavente Escobar, C. L., Zanini Maldonado, F. D. M., and Gómez Velásquez, H. D.: Stream Power determination along of a basin: First trial in the Chancay-Lambayeque basin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-36, https://doi.org/10.5194/egusphere-egu21-36, 2020.

15:47–15:49
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EGU21-3753
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ECS
Runye Zhu and Ryota Tsubaki

Braiding is among the most dynamic landscape on Earth. It provides diverse habitats for freshwater creatures. Unfortunately, the number of braided rivers is reducing affected by human activities in the Anthropic period. The increase of the vegetation cover within the river corridor is one important factor, which is induced by flow regime change, land-use change, or alien vegetation invasion. Vegetation clearance could be a promising measure to mitigate vegetation overexpansion. Several previous research suggested vegetation clearance may induce geomorphological metamorphosis. However, quantitative prediction of the morphological change resulted from the vegetation clearance is still an open question to date. We simulated the river morphological response of vegetated braided river with gravel bed to the vegetation clearance using the Nays2DH model combined with a vegetation module. Except for vegetation removal, the developed conceptual model considered vegetation colonization and the destruction induced by floods. Multiple scenarios have been tested, considering two vegetation types (strong and weak vegetation), two clearance methods (full clearance and partial clearance), and two maximum discharge. The full clearance scenario stood for the removal of above-ground and underground biomass simultaneously, and the partial clearance scenario stood for the removal of above-ground biomass. Braided rivers had developed for both no vegetation and river with weak vegetation cover. The bedform affected by strong vegetation coverage consisted of a main channel and small channels on the floodplain, which was consistent with previous experimental results. The distinctive morphology of developed bed form depended on the dominant factor in the vegetation-geomorphology interaction: vegetation dominant or physical process dominant. River morphology responded differently to the vegetation control measure based on the dominating factor. For the vegetation dominated river, the developed main channel tended to be braiding after the vegetation removal, and the river morphology change was sensitive to the vegetation clearance method. By contrast, river morphology changed insignificantly by vegetation colonization and after vegetation removal if the river physical process was dominant. We also found that the small channels on the floodplain promoted sediment transport from the floodplain to the main channel after the vegetation clearance. Thus, the morphological response to the vegetation clearance method was also affected by the reduction of maximum discharge because the connectivity between floodplain and channel was reduced. To improve vegetation clearance effectiveness, we recommend increasing the connectivity between the floodplain and the main channel, such as excavating small channels on the floodplain.

How to cite: Zhu, R. and Tsubaki, R.: Impact of vegetation control measures on the bedform of braided gravel-bed river, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3753, https://doi.org/10.5194/egusphere-egu21-3753, 2021.

15:49–15:51
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EGU21-6016
|
ECS
Tatiana Fedorova, Vitaly Belikov, and Andrei Alabyan

The retrospective simulation of the Pyoza river (Arkhangelsk region, Russia) meander cut-off in 2003-2008 has been undertaken. As a result of the river bend straightening two large villages were cut off from the road network of the region.

The initial data for modeling were obtained by analyses of archive satellite images for the period from 1997 together with the runoff data, as well as by the field survey of September 2019. The simulation was performed by the latest version of the STREAM_2D CUDA software, using a new method for the numerical solution of two-dimensional Saint-Venant equations [1]. It was adapted for the complicated bottom topography typical for a wide floodplain with a meandering channel flooded in high water stage.

The mass-exchange equations for three layers of sediment over the unerodible bed were solved together with the hydrodynamic equations. When calculating channel deformations, the gravitational effect due to bottom slope and the influence of secondary currents on the sediment shift were taken into account [2].

The Pyoza river is the lowest large tributary of the Mezen’ river flowing into the White sea. It is distinguished by a typical alluvial channel, meandering along wide floodplain composed by sands and sandy loams. The maximum runoff usually corresponds to spring snow-melting and can reach 1500-2000 m3/s.

To schematize the computational domain of the Pyoza river section of 13 km long, a hybrid grid of irregular structure was constructed, consisting of 37 329 cells of a quadrangular shape for the channel and a triangular one for the floodplain.

The simulation started at the year 1997 when where was no any rill across the meander neck. The time step of calculation was taken to be one day.

Modeling made it possible to simulate realistically the essential steps and mechanisms of the meander cut-off: the development of a pioneer straightening rill, its widening and deepening, as well as blocking of the old channel by a point bar in its upper reaches, as well as its further silting and aggradation.

1. Aleksyuk A.I., Belikov V.V. (2017): Simulation of shallow water flows with shoaling areas and bottom discontinuities. Computational Mathematics and Mathematical Physics, Volume 57, issue 2, pp. 318–339. https://doi.org/10.1134/S0965542517020026

2. Aleksyuk А. I., Belikov V. V., Borisova N. M., Fedorova T. A. (2018): Numerical modeling of non-uniform sediment transport in river channels. Water Resources, Volume 45, Special Issue S1, pp. 11–17. http://dx.doi.org/10.1134/S0097807818050275

How to cite: Fedorova, T., Belikov, V., and Alabyan, A.: Simulation of the meander cut-off by 2D hydrodynamic model for erodible bed, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6016, https://doi.org/10.5194/egusphere-egu21-6016, 2021.

15:51–15:53
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EGU21-8900
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ECS
Wendy Gonzalez, Diogo Mees Delfes Varela, and Frank Seidel

The importance of water reservoirs has been increasing with population growth and the need of water supply. Understanding the environmental processes in these water bodies is essential for the correct management performed by stakeholders. In this context, numerical models appear as a great tool for simulating hydrodynamics and sediment related processes and presenting them in way easy to understand. However, a wide range of data is required as input for a good performance of these models and its quality have a direct influence on the simulations results. Long term high resolution input data is the ideal case for simulations, but in developing countries this is usually not the case due to the absence of measured or simulated data to be used as input. The main objective of this research is to understand how the reduction of input data resolution and/or use of wrong datasets may influence final results of the processes taking place in reservoirs regarding the hydrodynamics, water temperature and sedimentation. Passaúna reservoir located in Curitiba, Brazil, is used as a study case with high resolution measured and simulated datasets which will be implemented as input data for numerical simulations using Delft3D. For the simulation of the horizontal velocities and the water temperature, parameters related to heat flux calculations showed the strongest influences on the results. A specific important parameter was the secchi depth, which is a single value used as input data and shows great differences for the reproduction of periods with mixed or stratified water column. On the other hand, sediment simulations showed sensitivity to the main river flow discharge temporal resolution and its corresponding sediment concentrations. Reanalysis data used as heat flux parameters and wind presented great differences from the use of measured datasets, but in cases where measured data is not available, this source may be the best choice for users.

How to cite: Gonzalez, W., Mees Delfes Varela, D., and Seidel, F.: Study on the complexity reduction of the input data for 3D numerical modeling of the hydrodynamics and sediment transport in a Brazilian reservoir  , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8900, https://doi.org/10.5194/egusphere-egu21-8900, 2021.

15:53–15:55
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EGU21-9676
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ECS
Jason Duguay, Pascale Biron, and Thomas Buffin-Bélanger

The large-scale turbulent structures that develop at confluences fall into three main categories: vertically orientated (Kelvin-Helmholtz) vortices, large-scale secondary flow helical cells and smaller strongly coherent streamwise orientated vortices. The causal mechanisms of each class, how they interact with one another and their respective contributions to mixing is still unclear. Our investigation emphasises the role played by the instantaneous flow field in mixing at a mesoscale confluence (Mitis-Neigette, Quebec, Canada) by complementing aerial drone observations of turbulent suspended sediment mixing processes with results from a high-resolution eddy-resolved numerical simulation. The high velocity near-surface flow of the main channel (Mitis) separates at the crest of the scour hole before downwelling upon collision with the slower tributary (Neigette). Fed by incursions of lateral momentum of the Mitis, shear generated Kelvin-Helmholtz instabilities expand as they advect along the mixing-interface. As the instabilities shed, water from the deeper Neigette passes underneath the fast, over-topping Mitis, causing a large portion of the Neigette’s discharge to cross under the mixing-interface in a short distance. The remaining flow of the tributary crosses over inside large-scale lateral incursions farther downstream. The downwelling Mitis, upwelling Neigette and recirculatory cell interact to generate coherent streamwise vortical structures which assist in rapidly mixing the waters of the two rivers in the vicinity of the mixing-interface. Evidence of large-scale helical cells were not observed in the flow field. Results suggest that flow interaction with bathymetry, and both vertical and streamwise orientated coherent turbulent structures play important roles in mixing at confluences. Our findings strongly suggest that investigating mixing at confluences cannot be based solely on mean flow field variables as this approach can be misleading. Visualization of a confluence’s mixing processes as revealed by suspended sediment gradients captured in aerial drone imagery complemented with eddy-resolved numerical modelling of the underlying flow is a promising means to gain insights on the role of large-scale turbulent structures on mixing at confluences.

How to cite: Duguay, J., Biron, P., and Buffin-Bélanger, T.: Study of turbulent mixing processes at a mesoscale confluence through aerial drone imagery and eddy-resolved modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9676, https://doi.org/10.5194/egusphere-egu21-9676, 2021.

15:55–15:57
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EGU21-14255
Tatyana Lyubimova, Anatoliy Lepikhin, Yanina Parshakova, Stuart Lane, Carlo Gualtieri, and Bernard Roux

River confluences are characterized by complex 3D changes in flow hydrodynamics and bed morphology and provide important ecological functions. The current literature on river confluences suggests that their hydrodynamics and morphodynamics are controlled by three aspects: (1) the geometry (planform and junction angle) of the confluence, (2) the momentum flux ratio of the tributaries and (3) the level of concordance between channel beds at the confluence entrance. However, the difference in water densities between the tributaries, and the associated stratification, potentially may impact on hydrodynamics and mixing as well, but such aspects has received less attention by far, and has not yet been subject to systematic investigation.

The objective of this study is to investigate hydrodynamics and mixing within the confluence zone of the Kama and Vishera rivers (Russia). During the warm period, the water densities in these rivers are similar due to the peculiarities of their hydrological basins. Hence density effects are negligible. However, in winter, the mineralization level of waters in the Vishera river significantly exceeds that in the Kama river. Even due to a significant decrease in the discharge of these rivers, the densimetric Froude number Fr is of the order of unity. This condition provided the motivation for investigating the effects of density differences on hydrodynamic and mixing at such river confluence.

The study of these effects was carried out on the basis of full-scale field measurements and numerical experiments in a full 3D formulation (i.e. with no hydrostatic approximation). Both the field measurements and the numerical results suggest that hydrodynamics processes at the confluence in the absence and in the presence of density stratification are fundamentally different.. At large densimetric Froude numbers (at small density differences) the waters of the Vishera and Kama rivers flow, practically without mixing, for several kilometers in the form of two parallel streams and at Fr of the order of unity, the more mineralized (more dense) waters of the Vishera river flow under the less dense waters of the Kama river leading to much more rapid mixing.

The reported study was funded by Russian Foundation for Basic Research (RFBR) and Perm Krai (grant 20-45-596028) and by RFBR (grant 19-41-590013).

How to cite: Lyubimova, T., Lepikhin, A., Parshakova, Y., Lane, S., Gualtieri, C., and Roux, B.: Hydrodynamic aspects of large river confluence with different water densities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14255, https://doi.org/10.5194/egusphere-egu21-14255, 2021.

15:57–15:59
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EGU21-9799
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ECS
Behnam Balouchi, Nils Rüther, Mahmood Shafaei Bejestan, Kordula Valerie Anne Schwarzwälder, and Hans Bihs

Channel confluence is one of the important sections of channel networks which is also common encountered in nature. Six different zones exist at a channel confluence: 1) stagnation zone, 2) flow deflection zone, 3) flow separation zone, 4) maximum velocity zone, 5) flow recovery zone and 6) shear layers between combining flows zone. Due to the complexity of flow pattern at channel confluence, this location is always interesting among researchers. Although there are a number of studies on the flow and sediment pattern at confluences, there are still some gaps to be studied. Hence, a calibrated numerical model should be a good tool for evaluating the various effective parameters on flow and sediment patterns. The numerical 2D shallow-water model used in this paper is SFLOW which was developed by NTNU. Besides, the model calibration part of the current study is done by using a set of data from laboratory experiments.

This study attempt to simulate bed changes at channel confluences with a 2D shallow-water modeling under non-hydrostatic pressure, and show the applicability of the SFLOW model for this complex flow pattern. SFLOW solving the depth-averaged Navier-Stokes equations which is equipped with cutting-edge solvers. Besides, SFLOW modeled turbulency with depth-averaged two-equation RANS. In comparison with other codes, one of the interesting features of SFLOW is solving the non-hydrostatic pressure besides of hydrostatic part. This leads to a more realistic representation of the complex flow and sediment patterns of channel confluences, and consider less computational power than full 3D models.

How to cite: Balouchi, B., Rüther, N., Shafaei Bejestan, M., Valerie Anne Schwarzwälder, K., and Bihs, H.: 2D numerical simulation of shallow water and bedload transport in channel confluences by considering the non-hydrostatic pressure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9799, https://doi.org/10.5194/egusphere-egu21-9799, 2021.

15:59–16:01
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EGU21-16114
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ECS
Diwash Lal Maskey and Nils Ruther

Floating units/booms are used to trap or guide floating debris in watercourses. In a relatively shallow depth, these floats could affect the velocity distribution, sediment transport and channel bed deformation.  A three-dimensional non-hydrostatic numerical modelling was performed in a 180 degree channel bend with floats to see the effects in flow distribution and bed deformation as a conceptual study. Different configurations of the floats were simulated. The results showed that the flow velocity increased and deposition decreased at the inner bank of the bend. Use of floating units could be studied to alter sediment deposition pattern and sediment transport phenomenon in watercourses.

How to cite: Maskey, D. L. and Ruther, N.: Numerical modelling of sediment transport in a channel bend with floating units, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16114, https://doi.org/10.5194/egusphere-egu21-16114, 2021.

16:01–16:03
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EGU21-14680
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ECS
Jakob Siedersleben, Marco Schuster, Dennis Ties, Benjamin Zwick, Markus Aufleger, and Stefan Achleitner

The presented work is part of the optimization of the sediment management at the hydroelectric powerplants in Reutte/Höfen in Austria. The weirs of the two powerplants are situated at the alpine river Lech, located about 3 km upstream of the Lechaschau gauge (A=1012.2 km²). Totally five sluice gates and a fixed overflow weir are controlling the upstream reservoir, being subjected to high rates of coarse bed load material. In frame of a coupled approach of physical and numerical modelling, different options to (i) avoid/minimize sediment deposition and (ii) allow improved sediment flushing were tested and optimized. Besides a lowering of energy losses (reduced spilling times) the reduction of depositions downstream close to the turbine outlet were considered.

The physical model covers the hydropower and weir system of both power plants within a stretch of 400m / 150m using a model scale of 1:25. Investigated situations covered periods of reservoir sedimentation, flushing of the reservoir and typical flood flow situations (e.g. HQ1 and an unsteady HQ5 event). For model parametrization, sediment samples to quantify size distribution were taken in the field. Sediment inputs to the model were realized dynamically and were required (due to scaling effects) to exclude cohesive fractions having a minimum particle size of 0.5 mm. The full-area surface measurement of the river bed was made by means of airborne laser bathymetry and echo sounding.

As part of an optimization of the overall sediment management strategy, the focus of the presented research is on the western located runoff power plant Höfen. Via a lateral water intake, a maximum design flow of 15 m³/s is withdrawn causing that the intake structure is subjected to sediment depositions. Within the described scale model (1:25) and a partial scale model (1:15) covering the western side, several management options and configurations of sediment guiding walls were tested. Erosion and deposition as well as the transported material are assessed by 3D laser scanning and permanent monitoring of transported sediment load entering and leaving the scale model.

Complementary, a 2D hydro numerical model using a layer based multi fraction approach for sediment transport is set up for an extended area to simulate the morpho-dynamic behavior. The numerical model covers the whole weir system and 750 m of the upstream part of the Lech. The simulations made were realized at nature scale and allowed to mimic the erosion and deposition pattern obtained within the physical modelling for different tested options. Regardless of a chosen guiding wall setup, the results showed that each one is compromise between sediment defense and the effectiveness of the subsequent flushing processes.

How to cite: Siedersleben, J., Schuster, M., Ties, D., Zwick, B., Aufleger, M., and Achleitner, S.: Physical and numerical modelling of sediment guiding walls in an alpine river, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14680, https://doi.org/10.5194/egusphere-egu21-14680, 2021.

16:03–16:05
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EGU21-13319
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ECS
Spyros Pritsis, Nils Ruther, Kordula Schwarzwälder, and Anastasios Stamou

Nowadays, the aquatic biodiversity is highly under pressure due to anthropogenic changes of the rivers such hydraulic structures changing the diversity of flow and aquatic fauna as well as sediment continuity. This can have severe consequences on the fish population in the river reach. Fish are strongly depending on a certain substrate composition throughout all their life stages. Juveniles for example are depending on a certain availability of shelter in the substrate in order to survive this stage.

Therefore, we investigate the effects of changes in the sediment composition at a hydropower plant in Switzerland on the availability of potential shelter for juvenile fish. By utilizing the observed correlation between parameters describing the fine tail of a riverbed’s grain size distribution and shelter abundance for juvenile Atlantic salmon, we predict the available shelter in a river reach by using a 3D hydrodynamic numerical model directly coupled to a morphodynamic model. The initial substrate composition was assumed to be spatially uniform, its parameters based on a grain size distribution curve derived from collected sediment samples.

This model can now be used for habitat improvement scenario modeling. Based on the assumption that a specific mixture of sediment coming from upstream travelling through the river reach will positively influence the potential shelter availability, different scenarios can be investigated. The baseline for comparison was the simulation of the bed changes without any sediment supply from upstream. The baseline discharge was set to 100 m3 /s and was applied for 24 hours. The resulting bed changes create a map of the potential shelter availability of this grain size mixture. Then, two scenarios with sediment inflow from the upstream boundary were simulated. One coarse and one fine mixture of sediment were chosen as inputs, with the goal of investigating their impact on shelter abundance. The former designed to have a positive effect while the latter expected to reduce interstitial voids in the substrate and have a negative effect on available shelter.

The investigation is conducted as part of the EU Horizon 2020 funded project FIThydro (funded under 727830)

How to cite: Pritsis, S., Ruther, N., Schwarzwälder, K., and Stamou, A.: Modeling shelter abundance for juvenile Atlantic salmon in a residual flow reach of a hydro power plant using SSIIM 2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13319, https://doi.org/10.5194/egusphere-egu21-13319, 2021.

16:05–16:07
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EGU21-14894
Natalia Dorozhko, Katsiaryna Cidorkina, Alexander Svetashev, and Leonid Turishev

The study is devoted to numerical simulating the 3D fields of biologically active solar light irradiance at deep water layers of natural reservoirs.

A numerical model has been developed on the basis of the discrete ordinate and Monte-Carlo stochastic methods which allows simulating the propagation of solar radiation in the inhomogeneous atmosphere and water media.

A software package has been elaborated enabling to numerically simulate both the irradiance of the reservoir surface by the total (direct and diffused) solar radiation in the spectral range of λ = 280 - 800 nm under various conditions (season, zenith angle, cloud cover, aerosol parameters, etc.) and the radiation propagating in the heterogeneous water media including absorbing pigments, phytoplankton and particles of the organic residues.

The software package combines atmospheric and water modules being able to function both jointly and separately thus allowing one to use spectral irradiance or integrated signals experimentally measured by ground-based devices and immersion photometric systems to validate the results of numerical calculations and model calibration.

To compute three-dimensional scenes of water body irradiation the super-cluster hardware and parallelization algorithms were used as well as the option to trace back in the Monte-Carlo method implementation.

A set of numeric experiments were made to simulate the 3D irradiance field in the water media of the Naroch group lakes using the measured transparency spectra of natural water probes.

The research was focused on propagating the UV-B, UV-A solar radiation, having the main abiogenic effects such as DNA or the immunity suppression.

The numerical simulation exploiting the refined model of UV transparency and irradiances of water layers at various depths was in a good agreement with experimental data.

How to cite: Dorozhko, N., Cidorkina, K., Svetashev, A., and Turishev, L.: Simulating irradiance of water layers of natural reservoirs by solar radiation in various spectral ranges, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14894, https://doi.org/10.5194/egusphere-egu21-14894, 2021.

16:07–16:09
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EGU21-10446
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ECS
Kaveh Purkiani, Benjamin Gillard, André Paul, Matthias Haeckel, Sabine Haalboom, Jens Greinert, Henko de Stigter, Martina Hollstein, Matthias Baeye, Annemiek Vink, Laurenz Thomsen, and Michael Schulz

Prediction of the dispersion of sediment plumes induced by potential mining activities is still very limited due to operational limitations on in-situ observations required for a thorough validation and calibration of numerical models. Here we report on a plume dispersion experiment carried out in the German License Area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean. The dispersion of a sediment plume induced by a dredging experiment in April 2019 was investigated by employing a hydrodynamic high-resolution regional ocean model coupled to a sediment transport module.

Various aspects including sediment characteristics and ocean hydrodynamics are examined to obtain the best statistical agreement between observation and model results. Results show that the model is capable to reproduce suspended sediment concentration and re-deposition patterns observed in the dredging experiment. Due to a strong southward current during the experiment, the model predicts no sediment deposition and plume dispersion north of the dredging tracks. The sediment re-deposition thickness reaches up to 9 mm at the dredging tracks and 0.01 mm at far-field at a distance of about 500 m from the dredging tracks.

The model results suggest that seabed topography and variable sediment release heights above the seafloor cause significant changes especially for the low sedimentation pattern in the far-field region due to different current regimes. The termination of seawater stratification can rise sediment plume above the seafloor and spread it in a larger vertical distances up to 10 m from the seafloor.

How to cite: Purkiani, K., Gillard, B., Paul, A., Haeckel, M., Haalboom, S., Greinert, J., de Stigter, H., Hollstein, M., Baeye, M., Vink, A., Thomsen, L., and Schulz, M.: Numerical simulation of the dispersion of a sediment plume induced by seabed dredging in the northeastern tropical Pacific Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10446, https://doi.org/10.5194/egusphere-egu21-10446, 2021.

16:09–16:11
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EGU21-1329
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ECS
Sardar Ateeq-Ur-Rehman, Nils Broothaerts, Ward Swinnen, and Gert Verstraeten

Numerical hydro-morphodynamic models can simulate the impact of future changes in climate and land cover on river channel dynamics. Accurate predictions of the hydro-morphological changes within river channels require a realistic representation of controlling factors and boundary conditions (BC), such as the sediment load. This is, in particular, true where simulations are run over longer timescales and when sparse data on sediment load is available. Using sediment rating curves to reconstruct the missing sediment load data can lead to poor estimates of temporal variations in sediment load, and hence, erroneous predictions of channel morphodynamics. Furthermore, when simulating channel morphological changes at longer timescales, this comes at a high computational cost making it impossible to run various scenarios of changing boundary conditions to long river reaches with sufficient spatial detail.  Here, we apply different methods (morphological factors (MFs) and wavelet transform (WT)) to overcome these problems and to arrive at faster and more accurate predictions of long-term morphodynamic simulations.

 

We modelled river channel bed level changes of the River Dijle (central Belgium) from 1969 to 1999. Detailed cross-sectional surveys every 20 to 25 m along the river axis were collected in 1969, 1999 and 2018. Since 1969, the river has been incised by about 2 m most probably as a response to land-use/land-cover changes and subsequent changes in discharge and sediment load.  Daily discharge and water level measurements are available for the entire period; however, daily suspended sediment load was only collected between 1998 and 2000. Therefore, WTs were coupled with artificial neural networks (WT-ANN) to calculate long-term sediment load BCs (1969-1999) from the short-term collected suspended sediment concentration samples. Sediment load predictions with sediment rating curves only obtain an R2 of 0.115, whereas WT-ANN predictions of suspended sediment load data show an R2 of 0.902.

 

Using MFs the reference hydrograph was condensed with a factor of 10 and 20. WT is a mathematical tool that can convert time-domain signals into time-frequency domain signals by passing through low and high-level filters. Passing sediment load time series through these filters create another synthetic BCs containing the frequential and spatial information with half the original signal's temporal length. Thus we also compare the modelling performance using WT generated synthetic BCs with MFs. Similarly, 36x1 to 36x10 processors of an HPC was used to simulate 16 km river reach containing 3,33,305 mesh nodes (with 1.5 m mesh resolution).  Interestingly, with a significant reduction in computational cost, there was a mild difference (R2=0.802 using MFs 10 and R2=0.763 using MFs 20) in model performance without using MFs during initial trials. Surprisingly, generating a synthetic time series using WT did not perform well. Therefore, hydrograph compression using MFs is found the best option to reduce the computational cost, significantly. Although the computational time reduced from 30 days to only 3 days using MFs and more precise BCs calibrated model with R2=0.70, WT poor performance needs to be still investigated.

How to cite: Ateeq-Ur-Rehman, S., Broothaerts, N., Swinnen, W., and Verstraeten, G.: Numerical modelling of hydro-morphodynamic channel processes at decadal timescales using optimization methods: an application to the Dijle River, Belgium, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1329, https://doi.org/10.5194/egusphere-egu21-1329, 2021.

16:11–16:13
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EGU21-15334
Yanina Parshakova, Tatyana Lyubimova, and Lepikhin Anatoliy

Due to the active development of the Verkhnekamskoye deposit of potassium and magnesium salts (Russia) not only watercourses - wastewater receivers, but also water bodies that are not directly affected by technogenic impact fall into the zone of its influence. This impact, due to the high density of brines, is very important from an environmental point of view, but it is not recorded within the framework of traditional production monitoring. The carried out field observations show that the content of macrocomponents in water is significantly heterogeneous in depth and is characterized by the presence of a sharp jump of density. The concentration of salts in the near-bottom horizon is more than an order of magnitude higher than their content in the near-surface layer.

The situation is significantly complicated by the fact that during spring floods and during the passage of rain floods, less mineralized, fresh waters "slide" without mixing with more "dense" water masses located below the density jump layer. Therefore, the efficiency of washing of these reservoirs is significantly reduced. Since water intake for production purposes, as a rule, is made from the bottom horizons, this stratification creates serious problems with ensuring sustainable water supply to production facilities.

To solve these applied problems, the study of the formation of stable density structures was carried out on the basis of combined field studies and computational experiments performed on the basis of a hydrodynamic model in a full 3D formulation in a non-hydrostatic approach. The studies carried out made it possible to evaluate and compare various technologies for increasing the sustainability of technical water supply from these water bodies, to choose the most efficient of them.

The study was supported by Russian Science Foundation (grant 17-77-20093).

How to cite: Parshakova, Y., Lyubimova, T., and Anatoliy, L.: Investigation of stable vertical density structures formed in water bodies in zones of active technogenesis on an example of the Solikamsk-Bereznikovsky industrial hub (RF), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15334, https://doi.org/10.5194/egusphere-egu21-15334, 2021.

16:13–17:00