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HS9.4

EDI
Hydro-morphological processes in open water environments - numerical modelling

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 armouring or density-driven transport. Hence, new generations of numerical techniques open the possibility to explore numerous outstanding research questions related to hydro-morphologic processes. Artificial Intelligence procedures offer an additional alternative to hydro-morphological studies, e.g., determining particle size or floodplain vegetation cover.
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 GM2
Convener: Gergely T. TörökECSECS | Co-conveners: Bernhard Vowinckel, Katharina BaumgartnerECSECS, Sándor Baranya, Gabriele Harb
Presentations
| Mon, 23 May, 10:20–11:48 (CEST)
 
Room 2.17

Mon, 23 May, 10:20–11:50

Chairpersons: Bernhard Vowinckel, Gabriele Harb, Gergely T. Török

10:20–10:26
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EGU22-1172
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ECS
wenlong chen et al.

Introduction: Erosion has become an urgent problem to society due to the increasing intensity and frequency of disturbances, e.g. storms, wave energy and rainfall. Yet, a universal model to predict erosion thresholds for cohesive sediment is still missing. Short range interaction of clays is recognized as the source of cohesion and adhesion of cohesive sediment. The interaction of negatively charged (i.e., montmorillonite (MMT) and beidellite (BD)) and neutral clay particles (i.e., kaolinite (KL)) are traditionally simulated through DLVO theory and van der Waals interaction[1]. However, the applicability of DLVO theory at short range (i.e., at distance less than 3 nm) has been increasingly challenged in molecular dynamics simulations[2]. A suitable description of short-range clay particle interaction is crucial for the prediction of cohesive sediment erodibility. The aim of this study was to determine how clay mineralogy and water chemistry influence clay particle interactions at short range to affect inter-particle attraction and stability under imposed forces.

Methods: Molecular dynamics models of clay minerals and water were created using LAMMPS to simulate the interactions between water, clay and dissolved salt to investigate the forces determining clay cohesion, i.e. attractive force between clay particles [3]. A 2-layer model was used in this study, which is a simplification of the multi-layer particles found in nature. A multifactorial design was used with two factors: mineralogy and salinity. For clay mineralogy, kaolinite (KL), beidellite (BD) and montmorillonite (MMT) with sodium (Na) counter ions were tested. Three types of salt were considered, i.e., KCl, NaCl and CaCl2, with concentration ranging from 1% to 4%. Clay particle interactions with bulk water containing salt solution were simulated for 5 ns. Clay swell, i.e. the increase in the interlayer distance (d the distance between the mass center of two adjacent layers) and the underlying forces were quantified. The resistance of clay particles to imposed force was also investigated. 

Results and Discussion: First, for most negatively charged MMT and BD treatments, positively charged cations act as a bridge to hold clay layers together, which contrasts with the swelling predicted by DLVO theory. Second, Na-MMT with -0.375, -0.5, and -0.625 e/unit swelled in pure water, induced by the breakdown of cation bridges rather than osmotic swell pressure. Third, low concentrations of dissolved salt (i.e. KCl, NaCl or CaCl2) inhibit the swelling of MMT, by increasing the cation bridge strength. Fourth, non-charged KL did not swell because of strong van der Waals interaction. Finally, stable clay particles were more resistant to external pull and shear forces. These novel molecular dynamics simulations are helping to uncover the mechanisms controlling clay cohesion to support new formulations to predict the erodibility of cohesive sediment. 

Acknowledgements: The support of the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/T001100/1. 

References: [1] Grabowski et al. (2011) Earth Sci Rev 105:101-120; [2] Shen and Bourg (2020) J. Colloid Interface Sci. 584:610-621 [3] Chen et al. (2022) ACS omega (accepted).

How to cite: chen, W., Grabowski, R., and Goel, S.: Modelling short-range interaction of clay particles to improve erodibility prediction, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1172, https://doi.org/10.5194/egusphere-egu22-1172, 2022.

10:26–10:32
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EGU22-1888
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ECS
Rui Zhu et al.

We investigate the submerged collapse of weakly polydisperse, loosely packed cohesive granular columns, as a function of aspect ratio and cohesive force strength, via grain-resolving direct numerical simulations. The cohesive forces act to prevent the detachment of individual particles from the main body of the collapsing column, reduce its front velocity, and yield a shorter and thicker final deposit. All of these effects can be accurately captured across a broad range of parameters by piecewise power-law relationships. The cohesive forces significantly reduce the amount of available potential energy released by the particles. For shallow columns, the particle and fluid kinetic energy decreases for stronger cohesion. For tall columns, on the other hand, moderate cohesive forces increase the maximum particle kinetic energy, since they accelerate the initial free-fall of the upper column section. Only for larger cohesive forces do the peak kinetic energy of the particles decrease. Computational particle tracking indicates that the cohesive forces reduce the mixing of particles within the collapsing column, and it identifies the regions of origin of those particles that travel the farthest. The simulations demonstrate that cohesion promotes aggregation and the formation of aggregates. They furthermore provide complete information on the temporally and spatially evolving network of cohesive and direct contact force bonds. While the normal contact forces are primarily aligned in the vertical direction, the cohesive bonds adjust their preferred spatial orientation throughout the collapse. They result in a net macroscopic stress that counteracts deformation and slows the spreading of the advancing particle front.

How to cite: Zhu, R., He, Z., Zhao, K., Vowinckel, B., and Meiburg, E.: Grain-resolving simulations of submerged cohesive granular collapse, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1888, https://doi.org/10.5194/egusphere-egu22-1888, 2022.

10:32–10:38
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EGU22-2382
kang yongde

Erosion is an important issue in soil science and is related to many environmental problems, such as soil erosion and sediment transport. Establishing a simulation model suitable for soil erosion prediction is of great significance not only to accurately predict the process of soil separation by runoff, but also improve the physical model of soil erosion. In this study, we develop a graphic processing unit (GPU)-based numerical model that combines two-dimensional (2D) hydrodynamic and Green-Ampt (G-A) infiltration modelling to simulate soil erosion. A Godunov-type scheme on a uniform and structured square grid is then generated to solve the relevant shallow water equations (SWEs). The highlight of this study is the use of GPU-based acceleration technology to enable numerical models to simulate slope and watershed erosion in an efficient and high-resolution manner. The results show that the hydrodynamic model performs well in simulating soil erosion process. Soil erosion is studied by conducting calculation verification at the slope and basin scales. The first case involves simulating soil erosion process of a slope surface under indoor artificial rainfall conditions from 0 to 1000 s, and there is a good agreement between the simulated values and the measured values for the runoff velocity. The second case is a river basin experiment (Coquet River Basin) that involves watershed erosion. Simulations of the erosion depth change and erosion cumulative amount of the basin during a period of 1–40 h show an elevation difference of erosion at 0.5–3.0 m, especially during the period of 20–30 h. Nine cross sections in the basin are selected for simulation and the results reveal that the depth of erosion change value ranges from –0.86 to –2.79 m and the depth of deposition change value varies from 0.38 to 1.02 m. The findings indicate that the developed GPU-based hydrogeomorphological model can reproduce soil erosion processes. These results are valuable for rainfall runoff and soil erosion predictions on rilled hillslopes and river basins.

How to cite: yongde, K.: Two-dimensional hydrodynamic robust numerical model of soil erosion based on slopes and river basins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2382, https://doi.org/10.5194/egusphere-egu22-2382, 2022.

10:38–10:44
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EGU22-3306
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ECS
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Highlight
qiji zhang and xin qian

Microplastics have been reported in environmental media for decades, but gaps in our knowledge about them still remain. We investigated the third biggest freshwater lake in China – Taihu Lake – and the 30 major rivers around it. Microplastics were detected in lake water and sediment, and in river water, at abundances varying from 1.7 to 8.5 items/L, 460 to 1380 items/kg and 1.8 to 18.2 items/L, respectively. Inflow rivers were more polluted with microplastics than outflow rivers. The most common shape was fragment. Microplastic sizes of < 100 μm dominated in inflow rivers, 100–200 μm dominated in lake water and outflow rivers. The average size of microplastics in outflow rivers (200.4 μm) was larger than that in inflow rivers (166.2 μm). Microplastics of < 100 μm only accounted for 28% in the lake surface water but were as high as 70% in the sediment, indicating that smaller microplastics may more easily settle in the lake. The main components of the microplastics were identified as being polyvinyl chloride and polyethylene. There were about 1.2× 106 items/s microplastics entered Taihu Lake. Four main rivers located at northwestern lake accounted for 79% of the total inflow microplastic fluxes.

How to cite: zhang, Q. and qian, X.: Distribution and Sedimentation of Microplastics in Taihu Lake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3306, https://doi.org/10.5194/egusphere-egu22-3306, 2022.

10:44–10:50
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EGU22-4742
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ECS
Andreas C. T. Müller et al.

The European Water Framework Directive aims to achieve a good ecological status for all European rivers by 2027. Since the majority of rivers in Germany are in a highly altered state, large-scale restoration projects have been promoted by the federal and state governments. To plan and implement river restoration implies the integration of different interests and constraints such as flood protection, water supply, recreational use and ecology. In particular in urban environments, or otherwise spatially restricted conditions, there are serious problems to reach the ecological objectives which are set by authorities. Thus, the planning engineer is confronted with additional difficulties, especially from human-made contiguous infrastructures. Consequently, it is not possible to develop watercourses through their own dynamics. In these cases, purposefully selected instream structures can be used as alternative means to achieve morphodynamic development and improve the ecological conditions in the existing riverbed.

Until now, many restoration measures by means of instream structures have been implemented empirically according to the experiences by river engineers and technical staff. As a consequence, the guidelines for instream structures provide suitable hydraulic conditions and focus on the technical implementation rather than indicating which type of river habitat can be restored by the selected instream structure. The used measures often showed morphodynamic changes. However, in many cases habitat quality shows only negligible improvement compared to the initial conditions. This demonstrates a lack of scientifically derived solutions that can specifically induce morphodynamic changes and thus create fish and macroinvertebrates habitats in a targeted manner.

At KIT we investigate artificial measures to create functional habitats in pre-alpine to lowland rivers. The investigation is made in close collaboration with governmental bodies who locally specify the ecological objectives guided by the EU Water Framework Directive. An analysis of ecological needs determines the lack of several habitat types in the examined river systems. Together with the state authorities, several types of hydraulic structures such as groynes and other instream structures are then evaluated regarding their ability of habitat replacement.

The selected designs are examined according to state-of-the-art methods of hybrid hydraulic modelling, including mobile bed experiments, complementary numerical simulations and monitoring field campaigns. Based on the hydraulic findings the habitat suitability for all relevant flow conditions is derived through aquatic habitat simulation. The promising variants are then optimized and evaluated in terms of their ecological impact as well as hydraulic requirements, e.g. flood and bank protection for all morphologically relevant discharges.

The current research shows that nature-based solutions, inspired by practical empiricism and improved scientifically, can be used for developing instream structures that generate purposefully ecologically favourable conditions in rivers. In our presentation we will discuss that with optimization through scientific methods we expect to improve the planning reliability and ecological benefits of the use of instream structures for the enhancement of river habitats.

How to cite: Müller, A. C. T., Kannen, C., Seidel, F., and Franca, M. J.: Use of nature-based solutions for the enhancement of river habitats – transfer of practical experience to scientifically optimized solutions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4742, https://doi.org/10.5194/egusphere-egu22-4742, 2022.

10:56–11:02
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EGU22-7976
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ECS
Cong Jiang et al.

A large-scale water erosion and sediment transport model is introduced and applied to predict continental-scale hydrological transport processes at the Yellow River Basin in China. Our model couples the Atmospheric and Hydrological Modelling System (AHMS) with the CASCade 2 Dimensional SEDiment (CASC2D-SED), by considering a scale-adaptive water erosion parameterization and eight possible flow directions of the channel routing model. Here, the AHMS-SED is applied to simulate the water erosion processes in the Yellow River Basin over 10 years with a spatial resolution of 20 km. The simulated daily sediment fluxes from four major hydrological stations along the Yellow River (namely, Tangnaihe, Lanzhou, Toudaoguai and Huayuankou) are compared with corresponding observations. There is a quantitative agreement between these observations and modelling results at all stations. Our results demonstrate the good performance of the new scale-adaptive parameterization and the integrated AHMS-SED, paving the way for the studies of water erosion and sediment transport at large scales. We also show how of our numerical simulations can be used to predict the evolution of sediment transport in the Yellow River Basin under consideration of specific climate change scenarios.

How to cite: Jiang, C., J. R. Parteli, E., and Shao, Y.: A model for continental-scale water erosion and sediment transport and its application to the Yellow River Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7976, https://doi.org/10.5194/egusphere-egu22-7976, 2022.

11:02–11:12
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EGU22-6773
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solicited
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Highlight
Gary Parker and Li Zhang

River networks are ubiquitous in nature. The example of the Amazon River, South America, is shown below.

Typically, channel branches farther upstream tend to be steeper than branches farther downstream. Here we explain this tendency via a simple model of lowland sand-bed stream networks. Any given downstream branch bifurcates into two branches upstream, here each assumed to have discharges equal to half of the downstream branch. . Each branch satisfies (at bankfull flow) a relation each for flow resistance, sand transport and sediment mobility Shields number. We show that if the transport rate of sand increases downstream in proportion to the water discharge, the river slope must be the same everywhere, so that the long profile following any path shows no upward concavity. When the sand load increases downstream at a lower rate than the water discharge, on the other hand, upward concavity is manifested. The bifurcations are allowed to continue upstream until a specified drainage density is reached. The inverse of drainage density scales the distance from any channel to the nearest ridge; at an appropriately low value, it is assumed that sediment can be delivered to the nearest stream solely through overland processes. We use the above conditions to determine the extent of the spatial network, and also the spatial variation of network denudation rate.

 

How to cite: Parker, G. and Zhang, L.: Morphodynamics of Lowland River Networks Modeled as Simple Binary Trees, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6773, https://doi.org/10.5194/egusphere-egu22-6773, 2022.

11:12–11:18
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EGU22-8597
Evgeniya Panchenko and Andrei Alabyan
11:18–11:24
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EGU22-8118
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ECS
Carolina Isabel Saldana Espinoza et al.

Norway's authorities are delayed in implementing the European Water Framework Directive (EU-WFD). A common challenge for the implementation of EU-WFD is finding natural reference conditions in water bodies, which can be challenging for lakes that have been regulated and used for hydropower production before any physical variables were made. Hydrological modelling of unregulated lakes can be a solution.  Modelling water level fluctuations in unregulated lakes allow us to determine the ecological functioning of the lake and the water storage that could be used for different sectors such as hydropower, agriculture and others.

Previous studies showed that lakes had a strong influence on the performance of models when using the Hydrological Predictions for the Environment (HYPE) model. This study aims to develop model strategies for improving lake dynamic modelling with natural flow conditions in terms of discharge and water stage in HYPE. We modelled seven lakes in Norway with areas more than 5 km2 and a gauging station at the output. Each lake was calibrated independently, and each model was set up from an existing one for the mainland of Norway. Stepwise calibration was implemented to create separate discharge and water stage models. Rating curves for lakes were calculated and introduced to the model for water discharge and stage calibration following the equation Q=k(w-wo)p. Where w is the observed water level, wo is the reference water level, k is the rate, and p is the exponent. The model performance was evaluated in terms of Kling–Gupta efficiency (KGE). Preliminary results showed improvement of model performance for water stage modelling when employing a pre-calibrated model with discharge time series data. Also, improved model performance in discharge was found when using rating curves for calibration

How to cite: Saldana Espinoza, C. I., Schönfelder, L., and Seidel, J.: Study of unregulated flow conditions in Norwegian rivers- Strategy for improving lake outflow using HYPE model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8118, https://doi.org/10.5194/egusphere-egu22-8118, 2022.

11:30–11:36
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EGU22-12820
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ECS
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Highlight
Diwash Lal Maskey
11:36–11:42
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EGU22-12058
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ECS
Martin Glas et al.

Large physical experiments require - among others - scaling of channel geometry and sediments in order to fit to the available laboratory infrastructure. In this study, scaling effects were investigated with the help of a 3D numerical model (RSim-3D) and a coupled sediment transport model (iSed). Numerical experiments were based on the geometries of two physical scale experiments conducted at the University of Natural Resources and Life Sciences, Vienna, Austria. The large-scale experiments (1:1) were conducted in an open-air research channel with a channel width of 5 m. The small-scale experiments (1:5) were performed inside the Hydraulic Engineering Laboratory with a flume width of 1 m. The large-scale experiments (1:1) include sediments typical for the Austrian Danube River in the section East of Vienna and the small-scale experiments were conducted with a sediment size scaled by 1:5. Results from the physical scale experiments including a submerged and attracting groyne layout with varying groyne heights and water levels were used for calibration and validation of the numerical models. Numerical model results were analyzed with respect to scale influences. In contrast to the relatively small influence of scale on the determined normalized flow velocities, normalized turbulent kinetic energy was found to increase by up to 10 times within the outdoor research channel (1:1) in comparison to the smaller scale (1:5). Moreover, the scale effect was larger in the main stream than in the groyne field. Morphodynamic equilibrium was affected by the scale of the experiment, too, leading to enhanced erosions in the 1:1 scale experiment. The findings are relevant for future hydraulic engineering measures investigated by physical scale experiments and will help to avoid underestimations of hydrodynamic and morphodynamic processes induced by scale influences.

How to cite: Glas, M., Tritthart, M., Sindelar, C., Pessenlehner, S., Buchinger, M., Lichtneger, P., and Habersack, H.: Numerical investigation of scale influences on hydrodynamics and morphodynamics in a groyne field experiment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12058, https://doi.org/10.5194/egusphere-egu22-12058, 2022.

11:42–11:48
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EGU22-12845
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ECS
Antonio Annis et al.

Among the DTM-based parsimonious floodplain delineation methods, hydrogeomorphic scaling laws, providing consistent flood flow depth estimations as a function of contributing drainage areas, are widely used. Recent advances in this field demonstrated the suitability of hydrogeomorphic floodplain delineation models from basin to continental scale across diverse climatic and morphological settings. However, the sensitivity of scaling law parameterizations and performance in semi-arid to humid and low-gradient to steep basins is still unknown. In this work we determined flow depths – contributing areas scaling law parameters with varying basin slope and average annual rainfall across eleven basins in the west-central United States. These variable scaling law parameters were used to test the performance of the GFPLAIN hydrogeomorphic floodplain delineation model in the study area adopting largely and freely available global climate and topographic datasets. Outcomes of this analysis show improved performances and effectiveness of the GFPLAIN model with varying morphometric and climatic factors suggesting room for improvement for the current continental and global hydrogeomorphic floodplain datasets.

How to cite: Annis, A., Morrison, R., and Nardi, F.: Hydrogeomorphic floodplain mapping across different morphometric and climate settings , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12845, https://doi.org/10.5194/egusphere-egu22-12845, 2022.