GM2.2

GM2 EDI
Assessing and monitoring geomorphic processes across scales 

Transport of sediments in geophysical flows occurs in mountainous, fluvial, estuarine, coastal, aeolian and other natural or man-made environments on Earth, while also shapes the surface of planets such as Mars, Titan, and Venus. Understanding the motion of sediments is still one of the most fundamental problems in hydrological and geophysical sciences. Such processes can vary across a wide range of scales - from the particle to the landscape - which can directly impact both the form (geomorphology) and, on Earth, the function (ecology and biology) of natural systems and the built infrastructure surrounding them. In particular, feedback between flow and sediment transport as well as interparticle interactions including size sorting are a key processes in surface dynamics, finding a range of important applications, from hydraulic engineering and natural hazard mitigation to landscape evolution and river ecology.

Specific topics of interest include (but are not restricted to):

A) particle-scale interactions and transport processes:
-mechanics of entrainment and disentrainment (for fluvial and aeolian flows)
-momentum (turbulent impulses) and energy transfer between turbulent flows and particles
-upscaling and averaging techniques for stochastic transport processes
-interaction among grain sizes in poorly sorted mixtures, including particle segregation

B) reach-scale sediment transport and geomorphic processes
-bedform generation, evolution and disintegration dynamics (e.g. for dunes and other formations)
-discrete element modelling of transport processes and upscaling into continuum frameworks
-derivation and solution of equations for multiphase flows (including fluvial and aeolian flows)
-shallow water hydro-sediment-morphodynamic processes

C) large-scale, highly unsteady and complex water-sediment flows:
-flash floods, debris flows and landslides due to extreme rainfall
-natural and build dam failures and compound disasters (due to landslides, debris flow intrusion and downstream flooding)
-reservoir operation schemes and corresponding fluvial processes
-design of hydraulic structures such as fish passages, dam spillways, also considering the impact of sediment
-dredging, maintenance and regulation for large rivers and navigational waterways

Co-organized by GI5/NH1
Convener: Manousos Valyrakis | Co-conveners: Zhixian Cao, Rui Miguel Ferreira, Anita Moldenhauer-RothECSECS, Eric Lajeunesse
Presentations
| Thu, 26 May, 13:20–18:30 (CEST)
 
Room G2

Presentations: Thu, 26 May | Room G2

Chairpersons: Zhixian Cao, Rui Miguel Ferreira, Eric Lajeunesse
13:20–13:33
13:33–13:40
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EGU22-1415
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ECS
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Virtual presentation
Jinxin Liu, Zhixian Cao, and Xichun Li

Flushing is considered as a cost-effective technique for mitigating sediments and constraining environmental problems in sewer systems. Previous mathematical models are almost exclusively based upon simplified governing equations and weak sediment transport assumptions, of which the applicability remains to be theoretically justified. Here a fully coupled one-dimensional model is presented for non-uniform sediment transport in sewer systems, as adapted from recently established shallow water hydro-sediment-morphodynamic models for fluvial processes. The present model is tested for an experimental flushing case in the Des Coteaux catchment system of Paris city. The computational results are compared with measured data, and satisfactory agreements are acquired. It is revealed that the adaptation of bedload sediments to capacity regime can be fulfilled quickly, while the adaptation of suspended sediment transport to capacity regime requires a relatively long time and space, thereby underpinning and warranting the non-capacity modelling paradigm for sewer systems.

How to cite: Liu, J., Cao, Z., and Li, X.: Fully coupled modelling of non-uniform sediment transport in sewer systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1415, https://doi.org/10.5194/egusphere-egu22-1415, 2022.

13:40–13:47
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EGU22-1885
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Presentation form not yet defined
Tian Wang, Jingming Hou, Yu Tong, Jiaheng Zhao, and Feng Wang

Slope erosion is the main source of soil erosion. Simulated slope erosion sediment yield and its development process have great significance for quantitative erosion evaluation at the spatiotemporal scale. In this study, a loess slope erosion experiment was implemented indoors to establish a sediment carrying capacity formula suitable for loess slope erosion. A two-dimensional slope erosion numerical model was developed based on the developed sediment carrying capacity formula, and the model was verified by a simulated indoor slope rainfall erosion experiment. The results showed that the corrected slope sediment transport capacity formula is suitable for loess slopes, which have a higher prediction precision. The developed erosion numerical model simulation was verified by simulated rainfall slope erosion experiments. Regarding the evaluation metrics for slope simulation accuracy, the Nash-Sutcliffe efficiency (NSE) values were 0.83 for the runoff rate and 0.66 for the sediment concentration, R2 values were 0.89 for the runoff rate and 0.73 for the sediment concentration, and the relative bias (RB) values were -5.02% for the runoff rate and -1.02% for the sediment concentration. The spatial contribution rate of slope erosion was analysed based on the simulation results, and the most severely eroded areas were the middle and lower parts of the slope. The erosion contribution rate reached 69.59% on the 1-4 m area of the slope. The research results can further improve loessal slope erosion process simulation and prediction.

How to cite: Wang, T., Hou, J., Tong, Y., Zhao, J., and Wang, F.: A novel two-dimensional numerical model developed for slope soil erosion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1885, https://doi.org/10.5194/egusphere-egu22-1885, 2022.

13:47–13:54
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EGU22-1951
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Virtual presentation
Peng Hu, Binghan Lyu, Ji Li, Qifeng Liu, Youwei Li, and Zhixian Cao

Given that fluvial flows carrying relatively coarse sediments involve strong interactions between the water and the sediment phases, two-phase shallow water hydro-sedi-morphodynamic models have been developed (Li et al. 2019, Advances in Water Resources, 129(JUL.), 338-353; Lyu et al. 2021: EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4258). Here we report improvements over the model by Lyu et al. (2021), which lead to considerably improved numerical accuracies. Specifically, using finite volume method (FVM) to solve the governing equations on unstructured grids, the Harten-Lax-van Leer-Contact (HLLC) Riemann solver is proposed to estimate the inter-cell numerical flux for the flow phase and the sediment phases separately, in contrast to previous two-phase flow models using centered schemes. The improved numerical accuracy is demonstrated by numerically revisiting a series of experimental scenarios including refilling of a dredged trench, and a full dam-break flow in an abruptly widening channel.

How to cite: Hu, P., Lyu, B., Li, J., Liu, Q., Li, Y., and Cao, Z.: A new two-phase shallow water hydro-sedi-morphodynamic model with the HLLC solver for inter-grid numerical flux estimation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1951, https://doi.org/10.5194/egusphere-egu22-1951, 2022.

13:54–14:01
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EGU22-1463
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ECS
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Presentation form not yet defined
Jiaheng Zhao, Jingming Hou, Ilhan Özgen Xian, Tian Wang, and Reinhard Hinkelmann

Extreme rainfall may generate flash floods, which may overtop the flood defences (e.g., dam, dike, and levees) and subsequently lead to structure failure, threatening the safety of the downstream population and properties. This work presents a new two-layer modelling approach to simulate surface water flooding and the subsequent dam/dike breach process caused by overtopping. The new modelling framework simulates the surface water flooding process in the upper layer using a high-resolution hydrodynamic model that also considers sediment transport and morphodynamic change. A cell-based infinite slope model is implemented to identify unstable slope/soil and estimate the sliding depth for the lower layer. And a cellular automaton method based on diffusion-wave assumption is further developed to simulate the dynamics of the resulting bed granular movement. The momentum and bed elevation source terms of the hydrodynamic governing equations (the flood layer) and the soil depth of debris flow (the granular layer) are simultaneously calculated in a fully coupled way. This results in a fully coupled flooding induced breach chain model. The proposed model is validated against experimental and real-world tests with different breach types. And the sensitivities of calibrated parameters and mesh sizes are discussed in detail. The results indicate that the proposed model can simultaneously simulate overtopping flooding and the associated slope failure and breach processes.

How to cite: Zhao, J., Hou, J., Özgen Xian, I., Wang, T., and Hinkelmann, R.: An integrated two-layer model for simulating shallow flow, sediment transport and overtopping-induced breach processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1463, https://doi.org/10.5194/egusphere-egu22-1463, 2022.

14:01–14:08
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EGU22-2194
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Virtual presentation
Wei Li, Bingrun Liu, and Peng Hu

Previous studies for numerical representation of aquatic vegetation based on the isotropic porosity shallow water models can not only consider the effects of vegetation resistance and spatial occupation in physics, but also improve the computational efficiency in large-scale modelling. This type of models provides a promising tool to numerically study the vegetated flow and the corresponding sediment transport in practice. However, the characteristics of preferential flow among complex vegetation distributions which are often observed in nature cannot be well captured due to the isotropic assumption. Thus, we make an improvement by introducing the anisotropic porosity method in the shallow water model. Unlike the isotropic porosity method which uses only one porosity parameter to describe the vegetation spatial occupation, the anisotropic porosity method defines a cell-based porosity for volumetric occupation and an edge-based porosity for flux exchange to capture the flow heterogeneity in space. Under the framework of finite volume method, the model is solved explicitly with a hybrid LTS/GMaTS method and the Open MP techniques for fast modelling. The well-balanced property and accuracy of the developed model have been tested by a series of flume experiments with different vegetation distributions over fixed or mobile beds. In general, both velocity and deposition patterns are well reproduced. It shows that a constant vegetation drag coefficient can lead to numerical solutions of comparable accuracy as those complex empirical relations in the anisotropic porosity modelling. In addition, the stem-scale turbulence could be a critical factor affecting the sediment transport inside and around vegetation patches and its appropriate quantification in the shallow water modelling deserves further research.

How to cite: Li, W., Liu, B., and Hu, P.: 2-D fully coupled morphodynamic modelling in vegetated environments based on the anisotropic porosity method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2194, https://doi.org/10.5194/egusphere-egu22-2194, 2022.

14:08–14:15
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EGU22-10656
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ECS
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Highlight
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Presentation form not yet defined
Hamed Farhadi, Yi Xu, Panagiotis Michalis, Zaid AlHusban, and Manousos Valyrakis

Bed particle motion as bedload transport in riverine flows is a topic of interest in scientific and engineering fields as it is responsible for erosion and sedimentation, which are essential for hydraulic structures design and maintenance [1] but also for river and basin management. The physics of particle motion as the bedload is governed by stochastic processes which interrelated various parameters and conditions (i.e., particle-particle and particle-flow interrelations). Therefore, applying physically-based or hydrodynamic modeling is not always intuitive because of the complex dynamics. In these situations, in which physics is complex, data-driven modeling approaches may yield an efficient alternative approach since it solely considers the relations among the data. Artificial intelligence models (as for data-driven approach) have offered robust predictive performance in various fields of study. In addition, for time-series and sequential forecasting, a beneficial approach is to choose a model that relates previous states to predict future events.

This study contributes to developing a Long Short-Time Memory (LSTM) neural network modeling to predict the particle displacements near-threshold conditions. In order to prepare the data needed for the study, experimental tests were conducted in a hydraulic laboratory on a tilting recirculating flume with a 2000 (length) cm × 60 (width) cm dimension. Laser Doppler Velocimetry (LDV) was applied to record the flow velocity time-series upstream of the particle with 350-hertz frequency. Also, a He-Ne laser with a photomultiplier tube was used to track the particle motion [2]. Data were pre-processed with some statistical approaches for outlier detections and normalization purposes [3]. Therefore, different training and validation datasets ratios were considered, and the results were analyzed with some statistical measures (i.e., MAPE and RMSE).

The proposed input-output architecture (based on the hydrodynamic forces acting on the bed particle) was a function of the future particle displacement and local instantaneous streamwise flow velocity (about 1 diameter upstream of it). Accordingly, the proposed LSTM model achieved high particle displacement prediction accuracy even for lower percent data conditions for model training.

 

References

[1] Michalis, P., Saafi, M. and Judd, M. (2012). Wireless sensor networks for surveillance and monitoring of bridge scour. Proceedings of the XI International Conference Protection and Restoration of the Environment - PRE XI. Thessaloniki, Greece, pp. 1345–1354.

[2] Diplas, P., Celik, A.O., Dancey, C.L., Valyrakis, M. (2010). Non-intrusive method for Detecting Particle Movement Characteristics near Threshold Flow Conditions, Journal of Irrigation and Drainage Engineering, 136(11), pp.774-780, DOI:10.1061/(ASCE)IR.1943-4774.0000252.

[3] Valyrakis, M., Diplas, P., Dancey, C.L. (2011). Prediction of coarse particle movement with adaptive neuro-fuzzy inference systems, Hydrological Processes, 25(22). pp.3513-3524, DOI:10.1002/hyp.8228.

How to cite: Farhadi, H., Xu, Y., Michalis, P., AlHusban, Z., and Valyrakis, M.: Predicting coarse particle displacements due to turbulent flows at near-threshold conditions via LSTM models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10656, https://doi.org/10.5194/egusphere-egu22-10656, 2022.

14:15–14:22
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EGU22-3607
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ECS
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Virtual presentation
Yesheng Lu, Nian-Sheng Cheng, and Maoxing Wei

The well-known Shields diagram is developed for unvegetated open channel flows to describe incipient sediment motion by means of critical bed shear stress. Due to difficulties in estimating the bed shear stress in vegetated flows, it is not clear whether the Shields diagram is applicable in the presence of vegetation. By applying the phenomenological theory of turbulence, a new method to evaluate the bed shear stress in vegetated flows is proposed in this study. With this method, the critical bed shear stress subject to vegetated flows is calculated using the published data. The result shows that the calculated critical shear stresses are consistent with the Shields diagram.

How to cite: Lu, Y., Cheng, N.-S., and Wei, M.: Application of the Shields diagram for evaluating critical shear stress for vegetated flows, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3607, https://doi.org/10.5194/egusphere-egu22-3607, 2022.

14:22–14:29
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EGU22-10068
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ECS
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Presentation form not yet defined
Oral Yagci, Murat Aksel, Fatih Yorgun, and Manousos Valyrakis

Oscillatory flows are commonly observed flow conditions in sloshing tanks or at the seabed/river mouths under the effect of gravity and seiche waves. In such environments, particles are exposed to bi-directional oscillation-caused forces. These particles are usually sediments in settling basins under earthquake conditions or deposits on seabed/river mouths.

Physical model tests investigated the hydrodynamic forces acting on a spherical particle. This step is followed by a computational fluid dynamic model (i.e., RANS model), which aims to resolve the pressure and force fluctuations around a rigidly attached spherical particle to the bottom.

The experiments were conducted in a sloshing tank with 28.5cm length, 14.5 cm in width, and 20 cm in depth. A step-type-computer-controlled motor triggered the body of water within the tank. The motion of the mobile component of the tank was measured using two independent devices, i.e., an accelerometer and an ultrasonic distance sensor. The utilization of these measurement devices enables verifying the records of the motion double. Six different cases were conducted to define the error band for each device. These calibration cases emerge as a combination of the “better step motor speed” and “maximum displacement”. The acceleration records constitute a basis as an input for the RANS-based numerical model. During the validation/calibration of the CFD model, video records of the water surface observed during the experiment and the CFD outputs were comparatively analyzed based on an image-processing technique.

Once it was ensured that the CFD model simulated the sloshing process within the tank with an acceptable accuracy, a spherical particle was fixed to the bottom as the second phase of this study. Various sloshing scenarios were performed better to understand the fluctuation of the pressure field around the sphere. Based on these simulations, the variation of drag coefficient around the spherical body which emerges under the oscillatory flow was calculated.

How to cite: Yagci, O., Aksel, M., Yorgun, F., and Valyrakis, M.: Analysis of oscillatory flow around a rigidly attached spherical particle to the bottom in a sloshing tank, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10068, https://doi.org/10.5194/egusphere-egu22-10068, 2022.

14:29–14:36
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EGU22-10116
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Virtual presentation
Zied Driss, Khadija Rahal, Mariem Lajnef, Mohamed Salah Abid, and Manousos Valyrakis

Air-water flow interfaces around and over most hydraulic structures are complex, yet of crucial importance for safeguarding society and the resilience of the built environment. In this context, the present research work reports a computational fluid dynamics (CFD) methodology to accurately predict the complex air-water flow in a large-scale hydraulic test bench. It focuses on the potential of the volume of fluid (VOF) model to predict the free water surface evolution. The simulations were performed using the commercial software ANSYS Fluent 17.0, which utilized a three-dimensional Navier–Stokes equations in the unsteady flow regime. The Standard k-ɛ turbulence model was used, and the finite volume method was considered. The numerical uncertainty was quantified by the grid convergence index (GCI) method. The numerical results were found to be in excellent agreement with the experimental data.

Keywords: CFD, Turbulent Flows, Air-water flows, Hydraulic test bench.

How to cite: Driss, Z., Rahal, K., Lajnef, M., Salah Abid, M., and Valyrakis, M.: Numerical simulation and experimental validation of the air-water flow in a Hydraulic Test Bench, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10116, https://doi.org/10.5194/egusphere-egu22-10116, 2022.

14:36–14:43
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EGU22-4702
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Virtual presentation
Qihang Zhou, Lu Wang, Xingnian Liu, and Ruihua Nie

Storms often cause serious rainfall runoff in mountain river areas, which results large amounts of sediment form upstream hills to downstream channels, leading to a reconstruction of the riverbed and finally water and sediment disasters. High concentration sediment transport may exist during flash floods, and performs unsteady supply process in channels. Based on laboratory experiments, this paper analyzed the responses of riverbed elevation and water level to unsteady sediment supply. The unsteady sediment supply is described as a single triangular sediment process. The sediment supply rate of all tests is greater than the sediment transport capacity of the flow. Results show that the riverbed deposits and water level rises continuously during sediment supply, while the flow depth decreases correspondingly. The greater the rate of sediment supply, the faster the rising of riverbed elevation and water level. After the sediment supply ended, the deposited bed degraded and the rising water level decreased. Compared with the constant sediment supply, the riverbed elevation and water level under unsteady sediment supply rise greatly. In addition, it is found that the flow discharge with saturated sediment supply is much less than that without sediment supply in the same water level. Because the concentration sediment transport increases the flow resistance and then makes the water level sharply rise. The study highlighted the important effects of the unsteady sediment supply on bed morphology and water level surge in water and sediment disasters, and enhanced the understanding of the mechanism caused by the sharply rise of water level in flash floods.

How to cite: Zhou, Q., Wang, L., Liu, X., and Nie, R.: Experimental study on sediment deposition and water level surge under unsteady sediment supply, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4702, https://doi.org/10.5194/egusphere-egu22-4702, 2022.

14:43–14:50
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EGU22-6105
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ECS
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Presentation form not yet defined
Zaid Alhusban, Manousos Valyrakis, and Hamed Farhadi

In the process of sediment exchange from one region of the water column to another, morphological development occurs, as does the transmission of varying sediment concentrations and flow momentum along the stream. Herein, a one-dimensional hydro-morphodynamic model is proposed for simulating water flow over a rolling bed of non-cohesive materials to understand better how water flows. Flow hydrodynamics, sediment movement, and bed growth are all considered in this simulation. The governing equations were solved using first-order accurate Harten Lax-van Leer solvers, and the fluxes at cell sides were determined using a finite volume technique based on a structured rectangular mesh. Adding geometry and bed topography to the equations in both the x and y axes may be used to convert a onedimensional model to a two-dimensional model, which is a common approach to transforming one-dimensional models into two-dimensional models. Experimental measurements are also utilized to test and assess the integrated model.

How to cite: Alhusban, Z., Valyrakis, M., and Farhadi, H.: Simulating water flow over a rolling bed of non-cohesive materials by using a Hydromorphodynamic model., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6105, https://doi.org/10.5194/egusphere-egu22-6105, 2022.

Coffee break
Chairpersons: Rui Miguel Ferreira, Eric Lajeunesse, Anita Moldenhauer-Roth
15:10–15:23
15:23–15:30
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EGU22-7196
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ECS
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Virtual presentation
Yulan Chen and Thomas Pähtz

The downslope component of the gravitational force affects the threshold and direction of sediment transport along an arbitrarily sloped bed. It plays an important role for the shape and stability of river channels, and for the formation, evolution, and morphology of aeolian and fluvial bedforms. Here, we generalize an existing model of the threshold of nonsuspended sediment transport, which unifies aeolian and fluvial transport conditions using an analytical description of flow-driven periodic grain motion, to account for arbitrarily sloped beds. Without any readjustment of the model parameters, the generalized model captures the experimentally measured bed slope effect on the transport threshold much better than previously proposed models based on incipient grain motion, especially for large bed slopes in the direction transverse to the driving flow. This is mostly because drag resistance counteracts the transverse average motion of transported grains, which in the model has the same mathematical effect as a reduction of the transverse bed slope. For aeolian transport, the model predicts substantial gravity-induced transverse diffusion of saltating grains, neglected in previous studies, which may explain why aeolian barchan dunes generally tend to have a larger width than length.

How to cite: Chen, Y. and Pähtz, T.: Threshold of aeolian and fluvial nonsuspended sediment transport along arbitrarily sloped beds from an analytical model of periodic grain motion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7196, https://doi.org/10.5194/egusphere-egu22-7196, 2022.

15:30–15:37
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EGU22-12828
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ECS
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Highlight
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On-site presentation
Solange Mendes, Rodrigo Farias, Rui Aleixo, Michele Larcher, Teresa Viseu, and Rui Ferreira

A granular system is a collection of macroscopic particles that interacts through dissipative collisions and enduring contacts. It can exhibit gas, liquid or solid behaviour. These systems present phase transitions and coexistence of different phases. As for solid-liquid transitions, there is vast literature in thermal and athermal systems but no universal models of first-order or second-order phase transitions.

In particular, dry granular flows (the movement of granular material in fluids of low density and viscosity) can serve as models of debris flows. Mechanical clogging occurs when the mass of granular material is stopped in from of slits or orifices in check dams. There is currently not enough knowledge on the processes that lead to clogging.  

In this research we conducted a series of 31 laboratory experiments of dry granular flows constricted through a vertical gap, adjacent to the side wall, mimicking slit dam conditions. The granular material was composed of monosized polystyrene particles (Ø1.8 mm). The width of the slit was 2 particle diameters. The granular mass was released suddenly in a 1.5 m long chute, tilted at 20°. Instrumentation included two high-speed cameras (300 fps), located upstream, at the gate location, and downstream, at the slit location. Instantaneous velocities were obtained with PTV at the chute wall. In this work we discuss the behaviour or mean longitudinal velocities and of granular temperatures when the clogging occurs. The start of the clogging process was identified as the ts – solidification instant, this instant is defined by the moment the first particles stop moving.

It is shown that the statistical distribution of ts is probably not heavy-tailed. It has a positive asymmetry [0.410] and low flatness [-1.369]. Analysing 0.133 s before and after the solidification instant, it is shown that the mean velocity and the granular temperature of the granular system is constant up to 0.033 s before ts while the solid volume increases. It is not clear which portions of the system are in a gas phase and which are in a liquid phase.

The dissipative nature of the system becomes apparent from ts – 0.033 s. It is postulated that the rate of collisions has substantially increased with the increase of the solid fraction. It is expected that the rate of dissipation of fluctuating energy is a non-linear increasing function of the volume fraction. Hence, from ts – 0.033 onwards, a decrease in granular temperature (granular cooling) becomes evident. A reduction of the mean velocity becomes apparent at the same instant. The decrease of the fluctuating kinetic energy is continuous across the phase transition but appears stronger after ts.  

As a result of this work we will explore the hypothesis that the liquid-solid phase transition, observed in terms of mean velocities and granular temperatures is best modelled as smooth transition.

This work was funded by Portuguese Foundation for Science and Technology (FCT) through Project PTDC / ECI-EGS / 29835/2017 - POCI-01-0145-FEDER-029835, financed by FEDER funds through COMPETE2020, by National funds through FCT, IP. and partially funded by FEDER Project by the FCT Project RECI/ECM-HID/0371/2012.

How to cite: Mendes, S., Farias, R., Aleixo, R., Larcher, M., Viseu, T., and Ferreira, R.: Experimental characterization of mechanical clogging of dry granular flows through sudden constrictions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12828, https://doi.org/10.5194/egusphere-egu22-12828, 2022.

15:37–15:44
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EGU22-6355
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ECS
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On-site presentation
Robert Fliszar and Gordon Gilja

Scouring around bridge piers is considered to be a significant process in rivers because it can alter bridge loading and consequently its stability. Riprap is often deployed as scour countermeasure, and while it does protect the pier from local scouring, it doesn’t completely solve the scouring problem because it deflects the scour hole downstream of the bridge. Riprap is flexible, and flood events can induce five significant failure mechanisms - shear, edge and winnowing failure under clear-water conditions and bedform-induced and bed-degradation-induced failure under live-bed conditions. On the other hand, the thick riprap layer can withstand a partial failure of the layer with the capability of armouring the scour hole. This paper investigates the mechanisms of riprap partial collapsing and its effects on the development of a downstream scour hole. Experiments were conducted on the physical model of scouring around bridge piers protected with riprap built in the Department of Hydroscience and Engineering laboratory under the University of Zagreb. Experimental setup included different pier shapes (rectangular and circular piers) in order to examine the influence of the pier as well as the influence of riprap geometry in different flow conditions.

Acknowledgments

This work has been supported in part by Croatian Science Foundation under the project R3PEAT (UIP-2019-04-4046).

How to cite: Fliszar, R. and Gilja, G.: Evaluation of riprap failure impact on the downstream scour hole, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6355, https://doi.org/10.5194/egusphere-egu22-6355, 2022.

15:44–15:51
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EGU22-12570
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ECS
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Presentation form not yet defined
Zaid Al-Husban, Hamed Farhadi, Khaldoon AlObaidi, Yi Xu, and Manousos Valyrakis

Bed particle motion as bedload entrainment in riverine flows is a topic of interest in scientific and engineering fields. It is responsible for erosion and sedimentation, essential for designing hydraulic structures and river and basin management. Stochastic processes govern the physics of coarse particle motion due to particle-particle (here, bed particles) and fluid-particle interrelations, yet not mainly considered for estimating and describing the bedload flux and motions. Therefore, authentic knowledge of bed particle behavior in different phases of entrainment and transport might lead to a better description of the phenomenon. This study contributes to applying a non-intrusive particle monitoring technique, i.e., an embedded micro-electromechanical system (MEMS) as “smart particle” [1], to explore and monitor the dynamics of the initial and the bed particle motion near- and above threshold conditions.

Additionally, the imaging technique was deployed to track and monitor the instantaneous particle velocity and displacement during the transport, which was also applied as a complementary technique to calibrate and assess the MEMS sensor results [2]. The dynamics of incipient particle motion and particle transport were evaluated in sets of hydraulic flume experiments (by applying the instrumented particle) for different flow conditions, which deliver distinct particle entrainment and transport regimes [3-5]. The stochastic frameworks, which best described the hydrodynamic aspects of the entrainment and transport conditions, were chosen and discussed in relation to the near riverbed surface flow hydrodynamic conditions for better comprehension of the conditions leading to incipient entrainment and relatively low bedload transport stages. 

 

References

[1] Valyrakis, M., Alexakis, A. (2016). Development of a “smart-pebble” for tracking sediment 2transport. River Flow 2016, MO, USA.

[2] Valyrakis, M., Farhadi, H. (2017). Investigating coarse sediment particles transport using PTV and “smart-pebbles”instrumented with inertial sensors, EGU General Assembly 2017, Vienna, Austria, 23-28 April 2017, id. 9980.

[3] Farhadi, H. and Valyrakis, M. (2021). Exploring probability distribution functions best-fitting the kinetic energy of coarse particles at above threshold flow conditions. In EGU General Assembly Conference Abstracts (pp. EGU21-1820).

[4] AlObaidi, K., Xu, Y., and Valyrakis, M. (2020). The Design and Calibration of Instrumented Particles for Assessing Water Infrastructure Hazards, Journal of Sensor and Actuator Networks, 2020, 9(3), pp.36(1-18), DOI: 10.3390/jsan9030036.

[5] AlObaidi, K. and Valyrakis, M. (2021). Linking the explicit probability of entrainment of instrumented particles to flow hydrodynamics. Earth Surface Processes and Landforms, 46(12), pp.2448-2465.

How to cite: Al-Husban, Z., Farhadi, H., AlObaidi, K., Xu, Y., and Valyrakis, M.: Incorporating an instrumented particle to monitor the dynamic processes of bed particle motion from entrainment to low transport stages, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12570, https://doi.org/10.5194/egusphere-egu22-12570, 2022.

15:51–15:58
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EGU22-10620
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ECS
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Presentation form not yet defined
Yi Xu, Hamed Farhadi, Panagiotis Michalis, and Manousos Valyrakis

During extreme river-flow conditions induced by the continually worsening effects of climate change, the riverbed granular surface may get destabilized and can potentially be the cause of infrastructure failures [1]. Such conditions signify the start of the geomorphic change of the river's boundaries, affecting natural river habitat and the built infrastructure in its vicinity, especially near surface water bodies, costing billions of pounds per year globally. Given its importance, identifying the conditions leading to hydraulic infrastructure scour (i.e., scour around abutments and piers) has been a topic of intense focus for hydraulic researchers and engineering practitioners alike, especially over the last decades.

This research aims at studying the conditions leading to the start of hydraulic infrastructure scour by assessing the turbulent energy of flow structures leading to the destabilization of the bed surface around them. Specifically, a physical model of a cylindrical bridge pier is used in a flume to conduct lab experiments for various flow rates, aiming at probing the risk of critical failure of the riverbed surface. The experiments are conducted at a water recirculating laboratory flume with a cylindrical pier under four different flow rates. The experimental setup involves a flat fixed bed surface hydraulically roughened by spherical beads packed closely in a hexagonal arrangement, with a similarly roughened 3D-printed test section, on top of which an instrumented particle [2] can be positioned at distinct distances from the model pier. The risk of bed surface destabilization and scour initiation is assessed by the probability of entrainment of the instrumented particle for the combination of flow rates and distances downstream of the model cylinder [3]. The latter can be estimated as the rate of entrainment of the instrumented particle, monitored from the appropriate post-processing of the fused sensor data and validated from video observations (from a top and side camera). In this work, the 3-axis accelerometers and gyroscopes that offer records to help directly produce estimates of the probability of entrainment are embedded within an instrumented particle with an external diameter of 3.5cm.

These observations are further linked to the flow turbulence energy by aiming to establish correlations of the entrainment risk of the exposed instrumented particle to the probability of occurrence of turbulent eddies shed downstream the cylindrical model pier. Profiles of point flow turbulence measurements are obtained with acoustic Doppler velocimetry (ADV) at distinct distances downstream of the model pier. Flow energy and impulses are calculated from the probed flow velocity data at seven longitudinal distances.

 

References

[1] Michalis P, Xu Y, Valyrakis M (2020). Current practices and future directions of monitoring systems for the assessment of geomorphological conditions at bridge infrastructure. River Flow 2020. In: Proceedings of the 10th Conference on Fluvial Hydraulics, Delft, Netherlands, 7–10 July, pp.1–6. ISBN 9781003110958

[2] AlObaidi, K., Valyrakis, M. (2021). Explicit linking the probability of entrainment to the flow hydrodynamics, Earth Surface Processes and Landforms, DOI: 10.1002/esp.5188.

[3] Valyrakis, M., Diplas, P., Dancey C.L. (2011). Entrainment of coarse grains in turbulent flows: an extreme value theory approach, Water Resources Research, 47(9), W09512, pp.1-17, DOI:10.1029/2010WR010236.

How to cite: Xu, Y., Farhadi, H., Michalis, P., and Valyrakis, M.: Assessing the risk of infrastructure scour due to turbulence, using miniaturized instrumented particles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10620, https://doi.org/10.5194/egusphere-egu22-10620, 2022.

15:58–16:05
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EGU22-4631
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On-site presentation
Gordon Gilja, Robert Fliszar, Antonija Harasti, and Nikola Adžaga

Experiments conducted in the hydraulic flume provide a controlled flow environment, which often provides means for prompt qualitative investigation of general flow structure. Under the R3PEAT project (www.grad.hr/r3peat), research focus is on the scour at bridge piers protected by the riprap sloping structure – investigated using both physical and 3D numerical model. Experimental data, while constrained by the flume dimensions and the pump capacity, measured with high frequency Vectrino Profiler’s provide detailed insight into turbulence around the structure. Experimental models are set-up as segments of the river extruded from the bathymetric and hydraulic surveys, corresponding to the flume size and selected scaling. Based on the experimental data, 3D numerical model will be calibrated in order to investigate flow conditions for the relevant floods with design return period, exceeding the flume capacity. Physical model therefore must reliably present the prototype bridge, through resulting flow field in the pier vicinity. This paper presents verification of the physical model using field ADCP measurements. ADCP velocities are compared to experimental data on the 4 cross-sections adjacent to the bridge, adapted to the relative flume streamwise orientation. Advantages and disadvantages of the physical model usage as benchmark for numerical model setup are discussed.

Acknowledgments
This work has been supported in part by Croatian Science Foundation under the project R3PEAT (UIP-2019-04-4046).

How to cite: Gilja, G., Fliszar, R., Harasti, A., and Adžaga, N.: Verification of the pier scour development in the experimental environment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4631, https://doi.org/10.5194/egusphere-egu22-4631, 2022.

16:05–16:12
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EGU22-4883
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Virtual presentation
Wen Zhang, Lu Wang, Xingnian Liu, and Ruihua Nie

Rock weirs are river restoration structures used for grade control, raising upstream water level and restoring river habitat. This paper presents an experimental study of local scour at rocks weirs under live-bed scour condition. The effects of approaching bedform, flow intensity, weir height and void ratio on the scour depth at rock weirs are analyzed and discussed. Under clear-water scour condition, scour occurs only at the downstream of rock weirs; the equilibrium scour depth increases with increased flow intensity and weir height, but decreases with increased void ratio. Under live-bed scour condition, scour occurs both upstream and downstream of rock weirs. The equilibrium upstream scour depth increases first and then decreases with increased flow intensity, decreases with increased weir height, and has a complex relationship with increased void ratio. The equilibrium downstream scour depth decreases first and then increases with flow intensity, increases with increased weir height, and decreases with increased void ratio.

How to cite: Zhang, W., Wang, L., Liu, X., and Nie, R.: Impacts of approach bedforms on live-bed scour at rock weirs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4883, https://doi.org/10.5194/egusphere-egu22-4883, 2022.

16:12–16:19
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EGU22-10252
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ECS
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On-site presentation
Manish Pandey, Yi Xu, Panagiotis Diplas, and Manousos Valyrakis

The development and generation of scour holes around hydraulic infrastructures, such as bridge piers, can affect their stability and lead to their structural failure. Bridge scour is becoming increasingly challenging to tackle, especially under the context of climate change, increased urbanization pressures, and lack of adequate funding to inspect and maintain aging built infrastructure near water surface bodies [1,2]. As a result, many infrastructure failures are driven by the formation of scour holes due to strong enough turbulent flows. Traditionally, the research community has explored infrastructure scour by aiming to identify correlations between phenomenologically relevant parameters, such as the pier characteristics and the mean flow conditions around it. However, such bridge pier scour prediction models and relevant formulas are developed focusing on idealized lab experiments using bulk/averaged parameters. Thus, they may receive criticism due to their relatively limited generalization ability and their capacity to be validated with field data.

This study adopts a new paradigm assuming that it is rather meaningful to study scour as a dynamic process stemming from the interplay of the highly turbulent three-dimensional eddies stemming downstream of the pier with the granular material comprising the bed around it. Motivated by this observation and recent relevant research, the current study aims to shed more light on the role of impulse induced by the dynamics of flow energy acting on individual particles and setting them in motion [2], leading to the scour hole formation.

To the above goal, experimental tests are conducted in a water-recirculating flume with a depth of 50cm, a width of 90cm, and a length of 700cm. The generated scour hole developed past different cylindrical pier models is studied. Flow impulses are calculated from high resolution (200Hz) flow velocimetry data collected over a finely spaced grid downstream of the bridge pier model. This study is a first attempt to demonstrate the application of the impulse criterion towards predicting scour depth - as opposed to all past phenomenological models that employ bulk flow and pier parameters.

 

References

[1] Pandey, M., Valyrakis, M., Qi, M., Sharma, A., Lodhi, A.S. (2020). Experimental assessment and prediction of temporal scour depth around a spur dike, International Journal of Sediment Research, 36(1), pp.17-28, DOI: 10.1016/j.ijsrc.2020.03.015.

[2] Khosronejad, A., Diplas, P., Angelidis, D., Zhang, Z., Heydari, N., Sotiropoulos, F. (2020). Scour depth prediction at the base of longitudinal walls: A combined experimental, numerical, and field study, Environmental Fluid Mechanics, 20, pp.459–478, DOI: 10.1007/s10652-019-09704-x.

[3] Valyrakis, M., Diplas, P., Dancey, C.L. (2013). Entrainment of coarse particles in turbulent flows: An energy approach, Journal of Geophysical Research, 118(1), pp.42-53, DOI:10.1029/2012JF002354.

How to cite: Pandey, M., Xu, Y., Diplas, P., and Valyrakis, M.: Some observations on the prediction of bridge scour from first principles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10252, https://doi.org/10.5194/egusphere-egu22-10252, 2022.

16:19–16:26
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EGU22-8006
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Presentation form not yet defined
Christopher Unsworth, Martin Austin, and Katrien Van Landeghem

Predicting sediment transport near the threshold of mobility is a particular challenge in coastal environments, due in part to turbulence in the wake of bedforms and infrastructure but also due to variable grain size distributions and biological processes affecting mobility. Understanding the relevant processes and having the ability to accurately predict sediment transport in shallow shelf seas are currently of pivotal importance due to the prevalence of offshore wind infrastructure being built on mobile seabeds with mixtures of sediment grain sizes.  

Bridging the gap between the small-scale detail of sediment transport to large-scale modelling is a key challenge for the community. Using a set of novel observations of suspended sediment concentration (via a multifrequency acoustic backscatter system) and turbulence (via Nortek’s Aquadopp High Resolution Doppler Profiler) from a coastal site (~15 m depth) with sandy bed sediments, we revisit the threshold of motion from the perspective of Grass’ 1970’s work by investigating the overlaps of bed shear stress and initiation of motions for the bed sediments. A section of electricity cable was attached to the seabed instrument frame so that on ebb tides turbulent wakes and sediment suspensions from interactions with the cable and frame were measured, and on flood tides a clear boundary layer flow was measured.

We create a distribution of initiation of motions from bed sediment data, and from the ADCP data we calculate distributions of bed shear stresses using a temporal filter based on the large eddy turnover time. We investigate the overlap between the two distributions to assess the temporal mobility of the sediments, and discuss how estimating these distributions (and their overlap) can be an important way of improving our predictive capability of sediment transport beyond the usual median grain size and bed shear stress methods – especially important when there are turbulent wakes from bedforms and sea bed infrastructure.

How to cite: Unsworth, C., Austin, M., and Van Landeghem, K.: Using a natural laboratory to quantify sediment mobility in the turbulent wake of instrument frames and offshore infrastructure. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8006, https://doi.org/10.5194/egusphere-egu22-8006, 2022.

16:26–16:33
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EGU22-8428
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ECS
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Virtual presentation
Fotios Konstantinidis, Panagiotis Michalis, and Manousos Valyrakis

Various sectors of the built environment (BE) are threatened by deterioration processes that have an increasing trend due to ageing infrastructure, current extreme climatic conditions, increasing urban population, and limited financial resources [1]. Digitalization has the potential to transform the current processes of managing and sharing critical information that can enhance decision-making and, in the long term, enable efficient and sustainable BE. However, despite the recent technological advancements, BE, and particularly critical infrastructure systems are still managed following a traditional approach in both technological but also organizational, and institutional aspects. As a result, they do not take full advantage of the recent technological developments that can enable a more sophisticated approach that involves the incorporation of real-time data streams and the employment of advanced analytical methods for efficient management of resources and risks. To overcome this challenge, the utilization of technologies and advancements provided by Civil Infrastructure 4.0 (CI4.0) [2] accelerate the digitalization of the BE focusing on critical infrastructure systems.

 

This study focuses on providing an overview of the pillars for the next generation BE, which aims to enable an interconnected and collaborative ecosystem across cities, infrastructure, and societies. Various case studies are presented, including large residential regions, transportation networks across waterways, and buildings in which digitalization can play a pivotal role in providing instantly information to the BE stakeholders for enhanced decision-making. These are based on obtaining real-time data from the surrounding environment to assist in predicting the current and future states of BE. For example, obtained information derived from advanced microcontrollers measure the deteriorating performance of the ageing infrastructure systems over waterways and the flood levels in real-time. At the same time, datasets are incorporated into a high-performance machine hosted in cloud and deep-learning algorithms to predict the upcoming states of the infrastructure and climatic risk. In the case of an emergency state (e.g., river overflow, flash floods, or infrastructure disruption), the management system generates an alarm. At the same time, the models also predict infrastructure deterioration to inform critical stakeholders promptly to take action and adapt the societal functions accordingly. Digitalization is expected to enable a flourishing society and physical and natural environment across our cities and infrastructure, which play a significant role in the upcoming Society 5.0.

References

[1] Pytharouli, S., Michalis, P. and Raftopoulos, S. (2019). From Theory to Field Evidence: Observations on the Evolution of the Settlements of an Earthfill Dam, over Long Time Scales. Infrastructures 2019, 4, 65. https://doi.org/10.3390/infrastructures4040065

[2] Michalis, P., Konstantinidis, F. and Valyrakis, M. (2019). The road towards Civil Infrastructure 4.0 for proactive asset management of critical infrastructure systems. Proceedings of the 2nd International Conference on Natural Hazards & Infrastructure (ICONHIC), 23–26 June, Chania, Greece, pp. 1-9.

How to cite: Konstantinidis, F., Michalis, P., and Valyrakis, M.: Coupling physical and digital built environments for proactive asset management, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8428, https://doi.org/10.5194/egusphere-egu22-8428, 2022.

16:33–16:40
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EGU22-12375
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ECS
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Presentation form not yet defined
Khaldoon AlObaidi, Yi Xu, Hamed Farhadi, Panagiotis Michalis, and Manousos Valyrakis

One of the most vulnerable elements of the built environment is critical infrastructure constructed near water bodies, as flowing water negatively impacts their performance [1]. Water-related hazards can increase degradation effects which can be the leading cause for their structural failure. The current practice to assess the condition of structures is typically based on visual inspections, which in many cases are carried out in challenging environmental conditions posing threats for the health and safety of inspectors, among other issues [2]. Important key points about the safety of the structures are often not captured by the visual inspections because these areas of interest are not accessible or visible by inspectors. Real-time monitoring of flood events together with other environmental and structural-related datasets are considered key to better understanding essential aspects of degradation effects at infrastructure. The difficulty in detecting seepage processes inside the body of geo-infrastructure with conventional methods also leads to irreversible impacts with significant disruption and costs to road asset owners, maintainers, and users. The need to obtain real-time information about the evolution of natural and climatic hazards is therefore considered necessary considering the ageing infrastructure, constructed near geomorphologically active rivers, and the extreme shifting climatic conditions.

This work investigated the development of a new risk-monitoring ecosystem to remotely assess the condition of infrastructure. The development of two sensing units with complementary characteristics to provide information about flood risk at bridge sites and seepage processes at road embankments is presented. The sensing system is based on a cloud-based interface with a web-based visualization tool that enables asset owners to monitor in real-time the health of infrastructure systems and receive early warnings when incoming data exceed predetermined threshold levels [1,2,3]. Finally, the potential application location of the sensing units is also discussed alongside the proposed threshold levels that will provide information about the low, medium, high, and very high-risk probability.

References

[1] Michalis, P., Saafi, M. and Judd, M. 2012. Wireless sensor networks for surveillance and monitoring of bridge scour. Proceedings of the XI International Conference Protection and Restoration of the Environment - PRE XI. Thessaloniki, Greece, pp. 1345–1354.

[2] Michalis, P. Xu., Y. and Valyrakis M. (2020). Current practices and future directions of monitoring systems for the assessment of geomorphological conditions at bridge infrastructure. River Flow 2020. Proceedings of the 10th Conference on Fluvial Hydraulics, Delft, Netherlands, 7-10 July. pp. 1-6.

[3] AlObaidi, K. and Valyrakis, M. (2021). Explicit linking the probability of entrainment to the flow hydrodynamics, Earth Surface Processes and Landforms, DOI: 10.1002/esp.5188.

How to cite: AlObaidi, K., Xu, Y., Farhadi, H., Michalis, P., and Valyrakis, M.: A New Risk Monitoring Approach to Assess Infrastructure Performance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12375, https://doi.org/10.5194/egusphere-egu22-12375, 2022.

Coffee break
Chairpersons: Eric Lajeunesse, Rui Miguel Ferreira, Anita Moldenhauer-Roth
17:00–17:07
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EGU22-1685
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ECS
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Presentation form not yet defined
Zhiwei Li, Peng Gao, and Bang Chen

Cutoff occurrence is a pivotal process of the forward long-term evolution of meandering river. Here a neck cutoff occurred unexpectedly in a highly sinuous bend of a meandering river in the Zoige basin on the Qinghai-Tibet Plateau in July 2018. Nonetheless, for protecting the grassland inside this bend, subsequently two artificial embankments reversed this neck cutoff (backward evolution) in 2018-2019 and strongly affected three-dimensional flow structure according to field surveys using an unmanned aerial vehicle and acoustic Doppler Current Profiler from 2018 to 2021. This rare case for inhibiting natural cutoff remains an unknown geomorphic process, and furthermore the inverse impact of human intervention on an occurred cutoff is still unclear. The artificial earth embankment was breached in the 2019 flood season and left the broken debris at both ends. Soon afterwards the second rockfill embankment was built in the late 2019 to force the flow back to the original bend so far. Some main results are summarized: (i) Flow structure in the new cutoff channel was intensely adjusted in combination with locally increased channel slope by the cutoff and the first earth embankment built in 2019. Conversely, flow velocity and circulation in the upstream straight reach was less affected by neck cutoff and artificial embankments, while the flow velocity in the bend section was obviously adjusted after neck cutoff and two embankments built. The lateral distribution of the maximum velocity and circulation intensity at the apex of the bend are altered. (ii) After the cutoff occurred, the separate zone shifted to the erosion side of the new cutoff channel in 0.3 times channel width in 2019. At the cross-section of the apex, the clockwise circulation was generated with the maximum streamwise velocity close to the outer bank. The maximum streamwise velocity moved to 0.2 times channel width. (iii) The artificial embankment is a driving factor to generate the strong alteration on the bend completeness and hydrodynamic adjustment along the course in this unique case. It is of great importance on understanding the inverse process for implementing engineering measures to restore the original sinuous flow path and sustain an intact meander landscape after a cutoff occurred. Given that the intervention of reversing neck cutoff is a mandatory task required by local people, it is a better choice to wait 2-3 years until the cutoff channel reaching the quasi-equilibrium state.

How to cite: Li, Z., Gao, P., and Chen, B.: Impact of embankments for reversing neck cutoff on flow structure in a Zoige meandering river, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1685, https://doi.org/10.5194/egusphere-egu22-1685, 2022.

17:07–17:14
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EGU22-3387
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ECS
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Presentation form not yet defined
Wei Huang, Deliang Shi, Hongyan Wei, Yufang Ni, and Wengang Duan

Dike breaching is the main component of flood defending system. To temporally enhance the capacity of the river, small levees will be build on the dike crown to increase the elevation of the dike crest. Also, the dike top usually be paved with concrete as transportation road. Under these two condition, break mechanism are different from those without complex measures on the crown, which has not been investigated yet. Large-scale experiment has been carried to investigate the breaching mechanism. Results show that with small levees, the flow forms a little fall at the downstream edge of the levee top and a much larger fall on the downstream face of the dike. The “headcut” backward retreat is the main breaching mechanism in the early stage of breaching. During the rapid development stage of breaching, the vertical erosion, lateral erosion and gravity collapse are the breaching mechanism. The existence of the external small levee protected the top of the dike from erosion for a long time, which largely delayed the breaching processes. As the top was paved, the breaching processes likes that of dike with small levees. Two falls forms at the edge of the road and at the downstream face respectively. When the backward retreat of “headcut” at the downstream face of the dike reaches the base of the dike, the underneath soil is washed away and lead to concrete of the road collapse. Once the road is collapsed completely, two falls merged into one, thereafter the breaching processes likes dikes without complex measures on the crown. The paved road also delayed the breaching processes. This study can provide scientific support to dike breaching emergency management.

How to cite: Huang, W., Shi, D., Wei, H., Ni, Y., and Duan, W.: Large-scale experiment on dike breaching with complex measures on the crown, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3387, https://doi.org/10.5194/egusphere-egu22-3387, 2022.

17:14–17:21
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EGU22-4258
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ECS
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Presentation form not yet defined
Yufang Ni, Wei Huang, and Wengang Duan

The events of barrier lake outburst have been frequently reported under the impacts of earthquakes, climate change and human activities, which usually brought tremendous disaster to the downstream regions. Dredging a channel is one of the main measures to deal with the barrier lake risk. However, the effects of the channel geometry on the outburst have been unclear. Therefore, we conducted a series of large-scale field experiments on the barrier lake outburst responding to different geometry profiles of dredged channels. Results show that the barrier lake outburst with dredged channel has four development stages, i.e., erosion alongside the dredged channel, backward headcut erosion, rapid development and weak development. For all cases in this work, the peak stage in the reservoir appears earlier than the peak discharge. The rates of the enlargement of the dredged channel are similar among all the cases, while the start time of the enlargement and the final width of the breach are different. Digging of a small notch advances the enlargement of the breach.

How to cite: Ni, Y., Huang, W., and Duan, W.: The effects of dredged channel geometry on the barrier lake outburst, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4258, https://doi.org/10.5194/egusphere-egu22-4258, 2022.

17:21–17:28
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EGU22-9689
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ECS
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Virtual presentation
zhao zhou and yaojun cai

Aimed at the engineering problems of uncontrollable outburst flood process and large outburst flood peak in a high risk barrier lake, this paper successively adjusts the lateral and longitudinal spillway structure through an indoor physical model and then investigates the consequent outburst flood process differences between the trapezoidal spillway, the compound spillway and the vertical scarp spillway. The results show that the outburst flood process for all kinds of spillway can be successively divided into four typical stages, the initial stage, the retrospective stage, the swift failure development stage and the recovery stage. Compared to the relatively hysteretic initial stage in the trapezoidal spillway, the compound spillway can effectively accelerate the development of initial stage by decreasing down the overtopping elevation, thereby shortening the outburst flood process and cutting down the outburst flood peak by 17.0%. Moreover, the vertical scarp spillway can artificially make a vertical scarp to increase the local velocity at the retrospective stage and further accelerate the initial outburst process, thus significantly shortening the water storage time with upstream maximum water level greatly down. Correspondingly, the barrier body in the vertical scarp spillway would collapse slightly faster due to the excessively accelerated initial outburst process, but the maximum outburst flood peak can still be 11.4% lower than that of the trapezoidal spillway. These investigations can provide reasonable and abundant choices for the emergency disposal in the high risk barrier lake.

How to cite: zhou, Z. and cai, Y.: Influence of spillway structure upon the outburst flood process in a high risk barrier lake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9689, https://doi.org/10.5194/egusphere-egu22-9689, 2022.

17:28–17:35
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EGU22-6898
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Presentation form not yet defined
Min Zhang

Since Xiaolangdi Reservoir began to retained sediment in 1999, the Lower Yellow River (LYR) has deepened and widened continuously. The bankfull discharge has increased obviously, and the average depth has increased 1.3m~3.3m. The incoming water was abundant in recent four years from 2018 to 2021, and the peak discharge in the four year were all greater than 4000m3/s. The maximum discharge of Xiaolangdi station has reached 5500m3/s, which is the largest one since 1996. The evolution of channel bar in wandering reach is always the focus in sediment-laden rivers, especially in erosion period. Therefore, to appraise the changes in wandering reach of LYR in the erosion period, this study presents a detailed investigation of the channel bar changes in recent typical floods form 2018 to 2021. We described the bar pattern formation and sensitivity in wandering reach of LYR. Furthermore, we analyzed the numbers and area of channel bars based on the remote sensing images. We convert the channel bar at the same level from the relationship between the area of channel bar and water level at low water period. The results show that the channel sinuosity has decreased from 1.25 to 1.22, while the radius of curvature has increased from 2.80 to 2.96km. The number and area of channel bar have increased slightly. This phenomenon was affected mainly by the operation of Xiaolangdi Reservoir. The clear water and few bankfull discharge in 21 years since 1999, the channel erosion efficiency has decreased in the first ten years. So the erosion in recent four years floods was fewer. And the changes of channel bar slightly in recent four years. But the channel bar and channel pattern evolution dramatically from 1999 to 2021. 

How to cite: Zhang, M.: Changes of channel bars in the wandering reach of the lower Yellow River from 2018 to 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6898, https://doi.org/10.5194/egusphere-egu22-6898, 2022.

17:35–17:42
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EGU22-1419
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Presentation form not yet defined
Junhao Zhang, Yining Sun, Zhixian Cao, and Ji Li

Fluvial flow with high sediment load may plunge into the reservoir to form turbidity current, which may feature strong interaction with inflow from a tributary. However, to date, the understanding of confluent flow structure with high sediment load has remained poor. Here, a computational fluid dynamic software, Flow-3D, is applied to resolve such flows for a series of cases at laboratory-scale by solving unsteady, 3D Reynolds-averaged Navier-Stokes and sediment transport equations, based on finite difference method with structured meshes. The 3D results are compared with those due to a recently established 2D double layer-averaged shallow water hydro-sediment-morphodynamic model. One distinctive flow structure pattern is generated at the confluence with the intrusion of reservoir turbidity current from the main channel into the tributary. Apparent bed aggradation occurs inside the tributary mouth after a long-term hydro-sediment-morphodynamic process. The present finding has a more profound influence on sediment transport and morphological evolution at a reservoir–tributary confluence with high sediment load.

How to cite: Zhang, J., Sun, Y., Cao, Z., and Li, J.: Flow structure at reservoir-tributary confluence with high sediment load, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1419, https://doi.org/10.5194/egusphere-egu22-1419, 2022.

17:42–17:49
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EGU22-7110
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ECS
|
Virtual presentation
Martina Lacko, Kristina Potočki, and Gordon Gilja

The estimation of baseflow is one of the essential tasks in water resources management and hydrologic research to assess the impacts of climate change and to describe and predict flood events based on the flood hydrograph characteristics (peak flow, duration and volume). Several methods have been developed to separate baseflow from direct flow, and in recent years they have been automated through the use of available R packages. In this work R programming language packages “EcoHydRology” and “lfstat” were used to separate baseflow from direct flow on the historical daily discharge time series of the several gauging stations on the two large lowland rivers in Croatia: the Sava River and the Drava River. The aim of this study is to determine the appropriate baseflow separation method for gauging stations on Sava River and Drava River in order to evaluate the baseflow separation method for future multivariate analysis of flood events under the R3PEAT project (www.grad.hr/r3peat) that explores pier scour development next to the bridges crossing large rivers in Croatia with installed scour countermeasures.

How to cite: Lacko, M., Potočki, K., and Gilja, G.: Determination of the appropriate baseflow separation method for gauging stations on the two lowland rivers in Croatia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7110, https://doi.org/10.5194/egusphere-egu22-7110, 2022.

17:49–17:56
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EGU22-10189
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ECS
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Presentation form not yet defined
Ridwan Raquib, Lukasz Przyborowski, and Manousos Valyrakis

Since the early times of plastic production, the relative change increased approximately about 391,050%. It went from a cumulative production of 2 million tons in 1950 to 7.82 billion tons in 2015. Even though there are variable recycling methods at present, not all discarded plastic gets recycled. The vast majority of the waste plastic makes its way to the ocean through specific pathways, with one of the most dominant being transport via fluvial networks. Moreover, a relatively minimal amount of data is available on the transport of riverine plastic. Plastics found in rivers can accumulate, causing flow blockages and potentially affecting flow routing (intensifying flooding and other climate risks). They can also affect water quality and ecology, including biota that may ingest these through the leakage of chemicals. Out of the various types of plastic, buoyant macro plastic is a major polluter, and understanding its flow in rivers can help us reduce plastic pollution in the long run.

This study focuses on getting a better understanding of how floating plastics debris is transported in rivers with aquatic vegetation by undertaking well-controlled lab flume experiments. Specifically, the transport of floating plastic debris in a river system was studied through a series of flume experiments, using instream simulated vegetation. Vegetation patches of different densities were used to assess their effect on the flow field carrying buoyant plastics of variable sizes. The video camera is used to record the transport process of plastic along the flume until they impinge on the simulated vegetation patch. Obtained video files of the flume experiments are analyzed to assess the effect of vegetation density on the transport efficiency of the plastic. Preliminary results focus on using specific transport metrics, particle velocity before contact with the vegetated patch, focusing on the size of plastics being transported. Altered according to various flow conditions and river morphology, the results of this study will help engineers in the future to design and produce more resilient methods of vegetation patches and engineering structures in order to exploit the trapping effects of macro plastics.

How to cite: Raquib, R., Przyborowski, L., and Valyrakis, M.: Assessment of the transport capacity of floating plastics through fluvial systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10189, https://doi.org/10.5194/egusphere-egu22-10189, 2022.

17:56–18:03
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EGU22-3043
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ECS
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On-site presentation
Marie Vulliet, Eric Lajeunesse, and Jerome A. Neufeld
Seepage erosion occurs when groundwater emerges at the surface of a granular heap. A
spring forms and feeds a river which entrains sediments, thus changing the groundwater
flow.
 
We reproduce this phenomenon in the laboratory using a quasi-2D aquifer filled with glass
beads, by imposing a water level at one end of the pile. Water flows through the aquifer and
emerges at the surface of the granular bed. For large enough water levels this river erodes
its bed and the spring progressively ascends the heap. We investigate its trajectory, the
evolution of the groundwater discharge and the river depth. Intriguingly, we find that after an
initial erosive period the river attains a new equilibrium profile, with an elevated spring.
 
We model the flow in the aquifer using Darcy's law, predicting the shape of the water table,
the position of the spring and the groundwater discharge. By applying Coulomb’s frictional
law to the forces experienced by a grain we predict a threshold for the onset of erosion as a
function of reservoir height and aquifer length. This prediction provides a dynamical theory
for the erosional dynamics of the river. Our combined theoretical and experimental approach
thereby helps constrain the response of an idealized erosive river-catchment system to
steady forcing.

How to cite: Vulliet, M., Lajeunesse, E., and Neufeld, J. A.: Erosional dynamics of a river driven by groundwater seepage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3043, https://doi.org/10.5194/egusphere-egu22-3043, 2022.

18:03–18:10
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EGU22-4162
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Virtual presentation
Hualin Wang, Shan Zheng, and Chenge An

Abstract: Many rivers worldwide have suffered great degradation after large reservoirs construction. By investigating the Yichang-Chenglingji reach downstream of the Three Gorges Dam, we identified and analyzed the erosion centers (sub-reach with most severe erosion intensity) which migrated downstream along the river with the rate of 7.5 km/yr. To simulate the phenomenon and study the factors influencing the migration rate of erosion centers, a one-dimensional river morphodynamic model is implemented using field data (including water and sediment regimes and grain size of bed material) of Yichang-Chenglingji reach based on the active layer theory. We set three values for the thickness of active layer and designed four groups of grain size distribution of the sub-layer based on the drill data and the grain size distribution of bed surface material at Yichang station. The simulation results show that the main cause of the erosion centers is bed armoring. A high-speed bed armoring process is instrumental in the formation and migration of erosion centers, as the armoring of bed surface inhibits the further degradation in the upper reach. The thinner the active layer and the coarser the sub-layer, the faster the process of bed armoring. Under the condition that the thickness of the active layer is 1.5m and the sediment of sub-layer is the field data of bed surface material at Yichang station in 2020, the migration rate (13km/yr.) of erosion centers in simulation results are most in agreement with the actual erosion centers. Our results may deepen the understanding of the river evolution after the abrupt sediment reduction.

Key words: Three Gorges Dam; Yichang-Chenglingji Reach; Morphological evolution; Erosion centers; Spatial clustering; Numerical model

How to cite: Wang, H., Zheng, S., and An, C.: Morphodynamic model of the Yichang-Chenglingji Reach: migration of erosion centers downstream of the Three Gorges Dam, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4162, https://doi.org/10.5194/egusphere-egu22-4162, 2022.

18:10–18:17
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EGU22-4448
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ECS
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On-site presentation
Predrag Popovic, Olivier Devauchelle, Anais Abramian, and Eric Lajeunesse

Understanding how rivers adjust to the sediment load they carry is critical to predicting the evolution of landscapes. Presently, however, no physically based model reliably captures the dependence of basic river properties, such as its shape or slope, on the discharge of sediment, even in the simple case of laboratory rivers. Here, we show how the balance between fluid stress and gravity acting on the sediment grains, along with cross-stream diffusion of sediment, determines the shape and sediment flux profile of laminar laboratory rivers that carry sediment as bedload. Using this model, which reliably reproduces the experiments without any tuning, we confirm the hypothesis, originally proposed by G. Parker (1978), that rivers are restricted to exist close to the threshold of sediment motion (within about 20%). This limit is set by the fluid–sediment interaction and is independent of the water and sediment load carried by the river. Thus, as the total sediment discharge increases, the intensity of sediment flux (sediment discharge per unit width) in a river saturates, and the river can transport more sediment only by widening. In this large discharge regime, the cross-stream diffusion of momentum in the flow permits sediment transport. Conversely, in the weak transport regime, the transported sediment concentrates around the river center without significantly altering the river shape. If this theory holds for natural rivers, the aspect ratio of a river could become a proxy for sediment discharge—a quantity notoriously difficult to measure in the field.

How to cite: Popovic, P., Devauchelle, O., Abramian, A., and Lajeunesse, E.: Sediment load determines the shape of rivers , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4448, https://doi.org/10.5194/egusphere-egu22-4448, 2022.

18:17–18:30