HS9.3 | Hydro-morphological processes in open water environments
EDI

Sedimentary processes in aquatic environments, including erosion, transport, and deposition of sediment by hydrodynamic mechanisms, are key features for various research disciplines, e.g., geomorphology and paleoclimatology or hydraulics, river engineering and water resources management and hydrology. Accurate quantification of erosion, transport, and deposition rates, conditioning river channel morphology, and bed composition, is fundamental for adequate development of conceptual sediment budget models and for the calibration and validation of the numerical tools.
The main goal of this session is to bring together the community of scientists, scholars, and engineers, investigating, teaching, and applying novel measurement techniques, numerical modelling and monitoring concepts, which are crucial in determining sedimentary and hydro-morphological processes in rivers, lakes, and reservoirs, estuaries as well as in coastal and maritime environments. It focuses on the quantification of bedload and suspended load, bedforms migration, channel horizontal migration, bed armouring and colmation, but also the transport mode, flocculation, settling, and re-suspension of the sediment particles.
Contributions are welcome with a particular focus on single and combined measurement techniques and numerical modelling, post-processing methods as well as on innovative and advanced monitoring concepts for field and laboratory applications. We welcome contributions containing recent results in a temporal and spatial scale on sediment budgets as well as on sedimentary and morpho-dynamic processes in open water environments.

Co-organized by GM5
Convener: Slaven ConevskiECSECS | Co-conveners: Bernhard Vowinckel, Michele TrevissonECSECS, Wendy GonzalezECSECS, Katharina BaumgartnerECSECS, Kordula Schwarzwälder
Orals
| Tue, 25 Apr, 08:30–12:30 (CEST)
 
Room 2.44
Posters on site
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
Hall A
Posters virtual
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
vHall HS
Orals |
Tue, 08:30
Tue, 14:00
Tue, 14:00

Orals: Tue, 25 Apr | Room 2.44

Chairpersons: Bernhard Vowinckel, Katharina Baumgartner, Slaven Conevski
08:30–08:35
08:35–08:45
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EGU23-3820
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HS9.3
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ECS
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On-site presentation
Harshvardhan Harshvardhan and Deo Raj Kaushal

Scouring at bridge piers is troublesome and inevitable at the same time. Numerous empirical studies have been conducted in the last century to predict scour depth, but they completely ignore the physics of the problem. The physics behind scouring at bridge piers can be best understood in terms of the effect of the flow field around the pier at different stages of scour. This study comprises experimental and numerical parts. Experiments are conducted in the laboratory in which the flow field data at equilibrium is collected using Acoustic Doppler Velocimeter (ADV) and the equilibrium scoured bed is measured around isolated and In-Line Piers. Additionally, the commercial CFD code “FLOW-3D HYDRO 2022 R1” is utilized to simulate the flow field and scour around bridge piers. The FLOW-3D model solves the three–dimensional momentum and continuity equations coupled with the sediment transport equations to calculate and predict the flow field and the equilibrium scoured bed. While the maximum scour depth at equilibrium has been used to validate various CFD codes in the past, point-wise comparison of scour depth is scanty in previous research works. Moreover, the flow field at the equilibrium scour stage obtained using FLOW-3D has also been compared with experimental data available in the literature and experiment conducted in the laboratory. The performance of the CFD model is evaluated, the flow field and scoured bed geometry at equilibrium are analyzed and results are presented.

How to cite: Harshvardhan, H. and Kaushal, D. R.: CFD Modelling of Local Scour and Flow Field around Isolated and In-Line Bridge Piers using FLOW-3D, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3820, https://doi.org/10.5194/egusphere-egu23-3820, 2023.

08:45–08:55
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EGU23-109
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HS9.3
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ECS
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On-site presentation
Cheng-Chia Huang

The formulation of the reservoir desiltitation strategy has been addressed as an essential issue worldwide because the water resources crisis has become serious in recent years. The sediment-releasing operation using the current sluice gates or the bypass tunnel during flooding events can slow down the reservoir deposition and keep the storage capacity. However, the variation of downstream river morphology inevitably affected the channel stability due to the reservoir sediment-releasing operation. The sediment transportation downstream of the reservoir needs to be further investigated to determine the potential risk. This study adopted a calibrated two-dimensional numerical model, SRH-2D, to investigate the river morphology in the Tamshui River in northern Taiwan, East Asia. Three different typhoon events, Typhoon Hinnamnor, Soudelor, and Aere were considered slight, moderate, and severe scenarios. In addition, the original operation, sediment releasing, and bypass joint operation could be represented as the lowest, medium, and highest sediment released rate situation. The simulation shows the erosion and deposition location of different typhoon events and reservoir operations to highlight the potential disaster hotspot. As a result, this research can be a reference to reservoir management to adjust the operation principle to obtain the balance between reservoir storage capacity and downstream river stability.

How to cite: Huang, C.-C.: Simulation of River Morphology Change due to Reservoir Desiltitation Operation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-109, https://doi.org/10.5194/egusphere-egu23-109, 2023.

08:55–09:05
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EGU23-1717
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HS9.3
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On-site presentation
Gaurav Savant, Christopher Denney, and Gary Brown

Habitat structures such as the Interception Rearing Complexes (IRC) are intended to aid endangered species such as the larval pallid sturgeon by increasing the movement of larval sturgeon out of the main river channel and into the channel margin through the construction or modification of river training structures. The studied IRC are designed to create fish pathways that access the lower velocities and generally shallower depths in the channel margin where juvenile sturgeon have a chance to mature in areas with critical food resources. A Two-Dimensional (2D) Adaptive Hydraulics/Sediment Library (AdH/SEDLIB) depth-averaged, shallow-water, finite element model has been created to study the potential effects that the construction of an IRC may have on other factors, such as long-term bed morphology, navigation, velocity distribution, water surface elevations, and potential flood risk. The model simulates a stretch of river under consideration for the construction of IRC structures. First, the model was set up with pre-existing riverbed and structure geometry. The model was validated for a period between 2017-2020. After calibration, the model was run with the implementation of the proposed IRC structure geometry and compared to system behavior without IRC construction. The validated model was used to evaluate the effects of the proposed IRC on other river processes, by performing simulations both with and without the implementation of the IRC and analyzing inter-model comparisons. The presentation will focus on the details of the modeling system including numerics, application and analysis of results.

How to cite: Savant, G., Denney, C., and Brown, G.: Numerical Model Based Analysis of River Training and Habitat Structures on River Processes: Straubs Bend of the Missouri River, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1717, https://doi.org/10.5194/egusphere-egu23-1717, 2023.

09:05–09:15
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EGU23-2270
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HS9.3
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ECS
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On-site presentation
Alireza Khodabakhshi, Sudarshan Konidena, and Bernhard Vowinckel

Intense sediment transport situations such as debris flows and mudslides consisting of fine-grained particles can pose serious threats to human infrastructures and lives. A thorough understanding of the rheology of such cohesive granular flows is crucial to predict the behavior of these types of flow and to mitigate their damaging effects. Whereas the rheology of non-cohesive granular flows has been studied extensively in the literature, the effect of cohesive inter-particle forces on the rheological behavior is still obscure and has not been sufficiently addressed. In this study, employing particle-resolved Direct Numerical Simulations, we simulate non-cohesive and cohesive dense suspensions sheared by moving walls. We perform several high-resolution simulations and compare the rheological parameters of the suspensions for different values of a dimensionless cohesive number, Co. Direct Numerical Simulations enable us to delve into the stress profiles in the vertical and streamwise directions and explore the contribution of different particle and fluid stresses to the total stress in each direction. We will also investigate the microstructure of the suspension and relate the microscopic interactions to macromechanical, rheological behavior of the dense cohesive suspension. 

How to cite: Khodabakhshi, A., Konidena, S., and Vowinckel, B.: Rheological behavior of dense granular suspensions of cohesive particles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2270, https://doi.org/10.5194/egusphere-egu23-2270, 2023.

09:15–09:25
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EGU23-13076
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HS9.3
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On-site presentation
Josef Schneider, Sebastian Gegenleithner, Stefanie Pessenteiner, Oliver Sass, and Wolfgang Schöner

Floods including sediment transport are a significant threat to  communities in Austria. With climate change impacting the Alps, it is crucial to enhance and reassess protective measures. Predictions for the future of the Alpine climate indicate that there will be more winter precipitation and stronger, convective rain in the summer, even if the temperature goals set by the  Paris Agreement are met.

However, analyzing the impact of increased extreme precipitation on flood events in small Alpine catchments remains a challenge, and knowledge of the subsequent impacts on sediment transport is still insufficient. The catchment area of the Schöttlbach and thus the town of Oberwölz (Murtal, Styria) were affected by extreme flood events with extreme sediment transport in both 2011 and 2017, which caused heavy damage. The region was therefore selected to work with local stakeholders (especially the Austrian Torrent and Avalanche Control authorities) to improve the process understanding of flood events and sediment transport in a torrent catchment area and to draw possible climate change scenarios for the future.

It was the aim of the project „RunSed-CC“ (i) to estimate future runoff and sediment transport in an Alpine catchment using the latest climate projections (ÖKS15), (ii) to consider them in the light of the associated model uncertainties, and (iii) the potential for extrapolating the results to other Alpine catchments to test.

One focus of the project was the collection of natural data using a wide variety of measurements in the catchment area of an alpine torrent.The project RunSed-CC developed further a model that connects rainfall and runoff to sediment transport. The  hydrological model WaSiM was used, in combination with data on the  evolution of sediment source areas, to drive the 2D numerical models Telemac-2D (hydrodynamics) & Sisyphe (sediment transport). The main focus of the project was to  understand the potential impacts of future climate change on the  hydrologic regime, changes in sediment dynamics and sediment yield, and  associated uncertainties in the model.

This article is intended to provide a brief outline of the results of the extensive project, with a focus on the final findings of the sediment balances at the outlet of the catchment area.

 

How to cite: Schneider, J., Gegenleithner, S., Pessenteiner, S., Sass, O., and Schöner, W.: Determination of runoff and sediment transport in an Alpine torrent in Austria, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13076, https://doi.org/10.5194/egusphere-egu23-13076, 2023.

09:25–09:35
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EGU23-13691
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HS9.3
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ECS
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On-site presentation
Jakob Siedersleben, Stefan Jocham, Robert Klar, and Markus Aufleger

Morphodynamic modelling relies on different types of riverbed surveys. Surveys are essential as the basis of the evaluation of temporal river bed development, mesh creation, and model calibration. Spatial data, for example, obtained by topo-bathymetric airborne laser scanning (ALB) or sonar surveys results in a dense point cloud, providing detailed information on the river bathymetry. However, data gaps can occur due to restrictions in data acquisition (e.g. high water turbidity or water depth for ALB, low water for boat-mounted sonar). In contrast, cross-profiles contain only limited information on the bathymetry strongly dependent on the cross-profile and point spacing.

To assess the effect of the two survey data types on river bed development and morphodynamic predictions, the temporal evolution of a river stretch in the upper Danube at Donauwörth was analysed. The study area contains homogeneous river sections and sections with complex river geometry due to scours, bridge foundations, and river mouths.  Spatial sonar and ALB surveys were conducted from 2013 to 2020 and give detailed documentation of the river bed development. Cross-profiles with a cross-profile spacing of 200 m were derived from the spatial data. The spatial and cross-profile datasets show continuous river bed erosion. However, in this case, cross-profile data overestimate the overall erosion compared to spatial data. The geometry of homogeneous river stretches is depicted very similarly in the two datasets. For cross-profile data two cases exist for reaches with more complex river bed geometry: (i) The geometry lies in between two cross-profiles and it is missed entirely. (ii) The geometry is covered by a cross-profile and the resulting geometry is smeared in between the cross-profiles due to the interpolation process. Both possibilities result in an unsatisfactory depiction of the riverbed geometry.

To analyse the effect of morphological developments two morphodynamic models based either on the spatial or cross-profile datasets were set up. The models were calibrated against the datasets from 2013 to 2020 by adjusting the Strickler value for river sections with a length of 200 m. The Strickler values differ over the entire river stretch and not only in sections where complex river bed geometry occurs, meaning that the calibration errors propagate through the entire study area. Consequently, the deviations in calibration outcomes affect the model predictions, which simulate 7 years. In this case, the general shape of the predicted riverbed is similar, but due to the overestimation of riverbed erosion by cross-profile data, the morphodynamic model overestimates the erosion compared to the spatial data. However, the obtained error is for river reaches with low local variability within an acceptable range. If a project demands a highly accurate depiction of the river bed and the river geometry is known for having complex features, the use of spatial data is strongly advised.

How to cite: Siedersleben, J., Jocham, S., Klar, R., and Aufleger, M.: The Effect of Spatial and Cross-Profile Data on Morphodynamic Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13691, https://doi.org/10.5194/egusphere-egu23-13691, 2023.

09:35–09:45
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EGU23-6198
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HS9.3
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ECS
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On-site presentation
Wessel van der Sande, Pieter Roos, Theo Gerkema, and Suzanne Hulscher

Estuarine sand dunes are primary bedforms existing in many sandy estuaries. They generally have lengths between those of river dunes (tens of meters) and marine sand waves (on the order of hundred meters). Estuaries are known for their complex flow patterns, arising from a mix of riverine and tidal flow, bringing in freshwater from land and salt water from the sea. Two particular flow patterns arising from the interaction between salt- and freshwater are the gravitational circulation and the strain-induced circulation, induced by a longitudinal and a vertical salinity gradient, respectively. Recent research was directed to understanding the influence of these flow patterns on estuarine sand dunes through a linear morphodynamic model ([1], [2]). Linear stability models are capable of capturing initial growth from a flat bed, and yield the system’s preferred bedform length and migration rate.

Here, we build upon the linear modeling approach with a nonlinear morphodynamic model capturing both the subsequent bedform development towards equilibrium, and the effect of dunes on the flow as they develop. The model domain has spatially periodic boundary conditions and a rigid lid at the surface; the hydrodynamic module is non-hydrostatic and is solved with a k-omega turbulence closure. Furthermore, we include bed-load sediment transport with a formulation that contains a slope term. Results show the height, length, shape and migration rate of dunes in an estuarine environment, and reveal the flow- and turbulence patterns over these bedforms. Furthermore, we show the deceleration of the flow with development of dunes, and thus quantify the effect of dunes on flow resistance.

[1]          Van der Sande, W. M., Roos, P. C., Gerkema, T., & Hulscher, S. J. M. H. (2021). Gravitational circulation as driver of upstream migration of estuarine sand dunes. Geophysical Research Letters, 48(14). DOI: 10.1029/2021GL093337

[2]          Van der Sande, W. M., Roos, P. C., Gerkema, T., & Hulscher, S. J. M. H. (in press).  Shorter estuarine dunes and upstream migration due to intratidal variations in stratification. Estuarine, Coastal and Shelf Science. DOI: 10.1016/j.ecss.2023.108216

 

How to cite: van der Sande, W., Roos, P., Gerkema, T., and Hulscher, S.: Finite-amplitude modeling of estuarine sand dunes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6198, https://doi.org/10.5194/egusphere-egu23-6198, 2023.

09:45–09:55
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EGU23-16035
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HS9.3
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ECS
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On-site presentation
Clemens Hiller, Jakob Siedersleben, Sebastian Leistner, Thomas Wibmer, Kay Helfricht, and Stefan Achleitner

Shifting runoff dynamics and highly intensified geomorphic processes are immediate consequences of the evident glacier mass loss in high-alpine headwater catchments. Rapidly retreating glaciers expose unconsolidated sediments to erosion in the proximity of meltwater-fed mountain streams impacting the catchment-scale sediment dynamics. Altering sediment fluxes can have considerable implications for the operation and management of water infrastructure, especially hydro-electric power facilities in otherwise non-regulated glaciated catchments. Bedload-rich outwash plains with typical braided channel networks serve as a deposition area for glacier debris under average runoff conditions. During flood flow conditions, the proglacial areas connect with the downstream catchment, delivering subglacial sediments to lower stream sections.

As such, they represent key elements in high-alpine river systems when considering future discharge and sediment yield from deglaciating catchments. Establishing a numerical model of this important component of the headwater catchment illuminates a data scarce fluvial process domain. Yet, model parametrization and setting boundary conditions for a glacier forefield are challenging. Direct measurements in the paraglacial transition zone of retreating glaciers are usually complicated to achieve, especially since outwash plains are frequently subject to intensive geomorphic processes. Therefore, innovative methods, minimizing labour-intensive and time-consuming manual surveying, are needed to overcome data scarcity in paraglacial environments.

A combined methodological approach to parameterize key boundary conditions of an Alpine proglacial outwash plain (Jamtal valley, Austria) with an area of 0.035 km2 and an average channel inclination of 4.8 % is presented. Measuring discharge in situ is difficult since the braided riverbed is not stable due to frequent relocation of sediment. Therefore, close range sensing techniques based on RGB imagery from hand-held and fixed time-lapse cameras used in combination with maximum water level gauges are used directly in the outwash plain to monitor flood runoff events. A conventional discharge gauge (non-contact flow velocity and water level sensor) was realized 3 km further downstream covering the recent hydrologic summers (2019-2022). UAV-borne RGB imagery was used to detect changes in topography, sediment budget and composition.

We present results on key parameters, essential for numerical modelling of hydraulic flood flow conditions, including: (i) multi-annual high-resolution topographic 3-D models of the frequently changing channel geometry, (ii) hydraulic roughness of surface sediments derived from areal grain size distribution maps (i.e., D50, D84) and (iii) spatio-temporal flood flow maps indicating the annual variability in the surveyed proglacial outwash plain. These interrelated survey results are then used to parameterize and calibrate a 2-D numerical model (TELEMAC 2-D) to simulate hydraulic base and flood flow conditions, demonstrating the applicability and robustness of the presented multi-method approach.

How to cite: Hiller, C., Siedersleben, J., Leistner, S., Wibmer, T., Helfricht, K., and Achleitner, S.: From multi-method monitoring towards numerical simulations of flood flow events in a proglacial outwash plain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16035, https://doi.org/10.5194/egusphere-egu23-16035, 2023.

09:55–10:05
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EGU23-868
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HS9.3
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ECS
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On-site presentation
Gurpinder Singh and Rakesh Khosa

In hydraulic engineering, river discharge estimation is an important requirement for managing and planning the channel flow. Discharge measurements are of utmost importance for the purposes such as water availability analysis, reservoir operation, flood forecasting, designing of hydraulic structures, etc. In the discharge estimation process, the spatial velocity distribution in the transverse cross-section at the desired location of measurement is required. In traditional approaches such as Prandtl-Von Karman logarithmic law and power law, the velocity is employed deterministically, making its utility easier and providing accurate results for the wide channels only. In contrast, Shannon’s information entropy concept, which evaluates random variables probabilistically, is used in hydrology to determine entropy-based velocity distributions. In this approach, the velocity distributions obtained depends on a parameter called as entropy parameter, which is considered to be a fundamental measure of information about the channel characteristics such as channel bed slope and roughness. It provided better results for both the clear water and sediment-laden flow as compared to the former. In the present study, experiments for discharge estimation were performed on the experimental flume to collect the velocity data at different channel bed slope conditions to demonstrate the accuracy of the entropy-based concept. To prove the truthfulness of the entropy-based concept, the results were compared with the ones obtained from the classical method (velocity area method). Both the approaches have their respective advantages and limitations. Therefore, error analysis was necessary to check the efficiency and accuracy of the entropy-based model, which was performed by comparing the percentage error between the observed and computed discharge values. The final results revealed that the entropy model was a quick and accurate technique for discharge estimation as absolute percentage errors were less than 5% and the 95th percentile was 3%.

How to cite: Singh, G. and Khosa, R.: Discharge Estimation for Different Bed Slope Conditions Using Entropy-Based Concept: An Experimental Investigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-868, https://doi.org/10.5194/egusphere-egu23-868, 2023.

10:05–10:15
Coffee break
Chairpersons: Slaven Conevski, Stefan Achleitner, Kordula Schwarzwälder
10:45–10:55
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EGU23-8007
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HS9.3
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ECS
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On-site presentation
Florian Meslard, François Bourrin, Yann Balouin, and Nicolas Robin

Small mountainous rivers provide an important part of the sedimentary inputs to the oceans. The particularity of theses rivers comes from the fact that their inputs take place mostly during brief and intense flood events. While the quantification of fine sediment flux is fairly well known, sandy inputs are very poorly known and field measurements are scarce. River mouth sand discharge is a key variable in the coastal sediment budget as it participates to the coastline evolution and its protection against marine events. Coarse sediments are mainly transported as bedload, making it difficult to estimate with traditional methods such as traps. In this study, a fixed Acoustic Doppler Current Profiler (ADCP Nortek Aquapro 1 MHz) was deployed on a bottom frame, near the mouth of the Têt river (SE France) to estimate near-bottom sediment transport during flood events. In addition, cross sections have been undertaken with a Sontek Hydroboard equipped with a Sontek M9 ADP at different water discharge during several flood events. A calibration of the backscatter index was carried out using gravimetric measurements and granulometric analysis of water samples to estimate the sediment flux and the sand proportion. Sediment fluxes were then compared with the altimetric variations observed from bathymetric surveys. Results allowed to characterize the variability of the boundary layer thickness and the sediment concentrations during flood events. Those results give useful information to estimate sand fluxes from mountainous rivers to the coastal area in a context where these are considered to be low or non-existent compared to large coastal rivers.

How to cite: Meslard, F., Bourrin, F., Balouin, Y., and Robin, N.: Near-bottom sediment transport during flood events on a small mountainous river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8007, https://doi.org/10.5194/egusphere-egu23-8007, 2023.

10:55–11:05
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EGU23-7152
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HS9.3
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On-site presentation
Stefan Haun, Beatriz Negreiros, Sebastian Schwindt, Alcides Aybar Galdos, Markus Noack, and Silke Wieprecht

Many water bodies are, as a result of anthropogenic influences, such as river straightening, river bank fixation, or damming in accordance with the EU Water Framework Directive (2000/60/EC) not in a good ecological state anymore. With the aim to return to a good ecological status for surface waters, restoration measures are implemented in many rivers. However, the success and sustainability of such measures are often site-dependent and require hence an objective assessment.

In this study, the Multi-Parameter Approach to assess Clogging (MultiPAC) was used to assess the suitability and sustainability of different riverbed restoration strategies. MultiPAC is based on several measured physico-chemical parameters, which enable a detailed investigation of in-situ conditions of gravel-bed rivers. The approach includes measurements of the sediment composition for identifying surface and subsurface grain size distributions and fine sediment fractions. In addition, measurements of the porosity are obtained by using Structure-from-Motion and the Water Replacement Method of freeze-core samples. Finally, measurements of the interstitial oxygen concentration and so-called slurping rates, which are converted into hydraulic conductivity, were performed with a double-packer system called VertiCo.

The residual river stretch between Jettenbach and Töging at the Inn River in Germany provided a means to evaluate riverbed restoration measures, implemented in February and March 2020. Investigations were performed for several gravel bars, where sediment was replenished and a mechanical break-up of the bed armour layer was conducted. The MultiPAC investigations were performed before measure implementation, shortly afterwards (March 2020) and in November 2020 to investigate the impact of a flood event with a 10-year return period, which occurred in August 2020, and thus may have influenced the sustainability of the restoration measures.

From the measurements, it can be seen that sediment replenishment and the mechanical break-up of the armour layer significantly improved the ecological functioning of the riverbed. However, it became evident that the increase in the quality of the riverbed was only temporary. Hence, these measures will need to be repeated regularly with the aim of maintaining ecologically-valuable riverbed habitat conditions. The results of this study also showed that MultiPAC provides detailed insights into the riverbed sediments, their composition, and the permeability of the riverbed.

How to cite: Haun, S., Negreiros, B., Schwindt, S., Aybar Galdos, A., Noack, M., and Wieprecht, S.: MultiPAC as a tool to monitor the sustainability of riverbed restoration measures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7152, https://doi.org/10.5194/egusphere-egu23-7152, 2023.

11:05–11:15
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EGU23-8386
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HS9.3
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ECS
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On-site presentation
Juha-Matti Välimäki, Eliisa Lotsari, Tuure Takala, Franziska Wolff, Virpi Pajunen, and Anette Eltner

Northern rivers are responding to global warming by changes in seasonal discharges, sediment transport rates and morphology. Very limited amount of studies about bedload transport rates have been carried out in the winter-season. Traditional methods of measuring bedload transport are limited by their proneness to user error, small spatial scales and uncertainties related to the equipment itself. Computer vision-based particle image velocimetry (PIV) and particle tracking velocimetry (PTV) methods have been successfully applied to measurements of water surface velocities and preliminary results show that they can be applied to underwater sediment transport velocity measurements. 

The aims of this study are to 1) to enhance the bedload calculations, by comparing traditional mechanical methods and computer vision-based particle image velocimetry methods applied to underwater video data sets. Additionally, topography created from underwater imagery is used to scale and  georeference the results with very good precision, and 2) understand the seasonal variation in bedload transport amounts based on both mechanical and image velocimetry methods.

The study is based on field data, measured at sub-arctic Pulmanki river, located in northern Finland. The data has been gathered in 2021 autumn and winter, 2022 spring, 2022 autumn, to cover different possible sediment transport conditions, from low flow ice-covered to high flow open channel periods. The preliminary results are presented. They show that the method is promising in enhancing the understanding of sediment transport processes and the seasonal transported amounts.

How to cite: Välimäki, J.-M., Lotsari, E., Takala, T., Wolff, F., Pajunen, V., and Eltner, A.: Subwater particle image velocimetry and  photogrammetry  as solution for enhanced seasonal measurements of river dynamics (more precisely: bedload transport), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8386, https://doi.org/10.5194/egusphere-egu23-8386, 2023.

11:15–11:25
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EGU23-11614
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HS9.3
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ECS
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On-site presentation
Vivek Kumar Bind and Vikrant Jain

Sediment transport is a fundamental process to understand river morphodynamics. Bedload sediment transport during high flow energy governs channel geometry, though with variable response to flood events. Therefore, the sensitivity of bedload sediment transport to flood events is an important geomorphic query. We analysed the bedload transport process during the extreme flood event in the Purna River, a partial-bedrock river in peninsular India. The Purna River originates from an elevation of ~900 m and drains ~18,450 km2 area. This major tributary of the Tapi River flows ~360 km. The flood events were characterised through flood frequency analysis using the Gumble distribution on peak discharge data from 1980-2016. The bedload sediment transport was assessed for the highest flood event using the Mayer-Peter Muller equation. Daily data of discharge, wetted area, wetted perimeter, grain size (D50) data of pre- and post-monsoon, and the cross-section was obtained from the Central Water Commission (CWC), India. The bed slope was analysed using Manning’s equation. Our analysis shows that the return period for the highest flood at upstream station (Gopalkheda) is 35 years, while it is 136 years for downstream station (Yerly). The average bed shear stress was ~1.04 and ~1.55 times more than the critical shear stress using D50 during the flood event for upstream and downstream reaches, respectively. The average bed shear stress exceeded the equal mobility condition (τeq≈1.45τc) in the downstream reach leading to full mobilisation. Therefore, it causes high bedload transport and scouring of bed level by more than 1 m in the downstream reach. However, at upstream reach, there was low bedload sediment transport and insignificant change in the bed level due to partial mobilisation. Also, the Maximum Flow Efficiency (MFE) at the downstream station is 6-7 times more than the upstream reach, representing high erosion in the downstream reach. Therefore, Purna River is characterised by reach-scale variability in the channel process to the same flood event. The downstream reach is more sensitive than the upstream reach and hence more prone to morphological change. These alterations have implications for designing hydraulic structures, water management, and river ecology.

How to cite: Bind, V. K. and Jain, V.: Bed level variation and channel sensitivity analysis of a river channel to the extreme flood event, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11614, https://doi.org/10.5194/egusphere-egu23-11614, 2023.

11:25–11:35
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EGU23-10815
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HS9.3
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ECS
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On-site presentation
Gergely T. Török and Gary Parker

Low water depth can be a problem for navigation on large rivers. Since the last century, a frequently-used method of river regulation has been the installation of wing dams (wing dikes, spur dikes, groins). With their help, the riverbed narrowed during low water, which created a greater water depth and a higher water level. However, the narrowed flow also generated a higher bed shear stress, which, due to bed erosion, simultaneously increased the water depth and lowered the water level.

From a flood protection point of view, questions arise as to how wing dam fields change flood levels as a result of the bed change caused by such intervention. The complexity of the answer increases if we examine the problem not only in a cross-section (or short reach scale), but at long scale, as in the case of the Mississippi River, USA, where a system of wing dams hundreds of kilometers long was installed.

We analyzed the problem in two steps: we apply a 3D sediment transport model on a local scale, and the results are then upscaled and implemented in a 1D model to enable study of the problem at large spatio-temporal scale (hundreds of km, several centuries).

How to cite: Török, G. T. and Parker, G.: Study of morphodynamic change caused by wing dams at large spatio-temporal scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10815, https://doi.org/10.5194/egusphere-egu23-10815, 2023.

11:35–11:45
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EGU23-13887
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HS9.3
|
ECS
|
On-site presentation
Hannes Zöschg, Tobias Bacher, Max Boschi, Christine Fey, Johannes Schöber, Robert Reindl, Martin Schletterer, and Markus Aufleger

In the 19th and 20th centuries, numerous alpine rivers were modified into straightened and monotonous channels by river regulations, which had significant negative effects on the ecology of the river systems and their floodplains. River revitalisations aim to restore river sections in order to create stepping stones in anthropogenic altered rivers. A large-scale example are the measures along the alpine Inn River between Stams and Rietz in Tyrol (Austria) over a length of about 3 river kilometres, which are implemented within the extension project of the hydropower plant Sellrain-Silz. During two low-water periods (October - April), starting in 2021, the existing bank protections were removed to a large extent, the river bed was widened up to 75 meters and a back water zone as well as a branch were created. As a result, the river stretch can develop by its own dynamics and ecologically valuable areas such as shallow water zones as well as gravel and sand banks are supposed to be formed.

In order to assess the morphodynamics and ecological functionality of these measures, while also maintaining flood protection, a comprehensive monitoring program is being conducted. This includes nine photogrammetric surveys using an unmanned aerial vehicle (UAV) between March and October 2022. The UAV data were used to generate ortho-images and digital elevation models. The accuracy was assessed by comparison with airborne LiDAR data from one flight in March 2022. The objective is to quantify the erosion and deposition processes in the area of the measures and to determine the sedimentological processes that occurred during the survey period using the UAV results and hydro-morphological data (e.g., hydrograph, suspended sediment concentration) from nearby gauging stations on the Inn River. In addition, the suitability of high-resolution data from UAV surveys for monitoring sediment and bedload dynamics in alpine rivers will be evaluated. First results show that deposition processes dominated in the area of the measures, while relatively low discharge values were recorded throughout the study period. Based on the data analysis, we elaborate a suggestion for further monitoring in addition to the cross-section surveys already conducted since 1980, i.e., one UAV flight per year at low-flow conditions in order to establish a long term monitoring of morphodynamics.

How to cite: Zöschg, H., Bacher, T., Boschi, M., Fey, C., Schöber, J., Reindl, R., Schletterer, M., and Aufleger, M.: UAV-based monitoring of sedimentary processes at a large-scale revitalisation of an alpine river – concept and outlook, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13887, https://doi.org/10.5194/egusphere-egu23-13887, 2023.

11:45–11:55
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EGU23-14612
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HS9.3
|
On-site presentation
Thomas Hoffmann

Suspended sediment transport is an integral part of river systems and provides important services for ecological functioning and human use of river channels. Thus, measuring and monitoring suspended sediment is of great importance to understand the implications of suspended sediment transport and to improve sustainable river management. Suspended sediment in the German waterways is monitored at 62 monitoring stations by the German Water and Shipping Authorities staring in the 1960ties. The dataset provides valuable information on the long-term developments of suspended sediment transport in Germany. After the analysis of suspended sediment rating (Hoffmann et al. 2020) and the long-term trend (Hoffmann et al. 2022) based on the extensive suspended sediment dataset, we present first results on the seasonal variation and the seasonal shifts of suspended sediment transport in Germany. The results indicate that river systems in Germany are characterized by strongly differential seasonal behavior despite modest spatial variations of climatic conditions in Germany. These results will be discussed in terms of seasonal shifts during the last 50 years and the expected changes of the sediment regimes in German river systems due to future climate changes.

 

References:

Hoffmann, T.O., Baulig, Y., Fischer, H., Blöthe, J., 2020. Scale breaks of suspended sediment rating in large rivers in Germany induced by organic matter. Earth Surface Dynamics, 8(3), 661-678.

Hoffmann, T.O., Baulig, Y., Vollmer, S., Blöthe, J., Fiener, P., 2022. Back to pristine levels: a meta-analysis of suspended sediment transport in large German river channels. Earth Surf. Dynam. Discuss., 2022, 1-28.

How to cite: Hoffmann, T.: Seasonal variability and seasonal shifts of suspended sediment transport in large German river system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14612, https://doi.org/10.5194/egusphere-egu23-14612, 2023.

11:55–12:05
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EGU23-8056
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HS9.3
|
ECS
|
On-site presentation
Ivan Pascal, Raphaël Miazza, Bob de Graffenried, and Christophe Ancey

Although the importance of studying channel bifurcations is widely recognised, their hydraulic behaviour in shallow, rough mountain rivers has so far received little attention from researchers. Understanding the specific hydraulics of such units is essential for predicting and interpreting their morphodynamic evolution. Water discharge measurements in the incoming channel and distributaries are often difficult to perform in steep streams characterised by high relative roughness (grain size to depth ratio d/h > 0.1), aerated flow, and marked free-surface waves. Nonetheless, recent advances in Acoustic Doppler Current Profiler (ADCP) technologies open new possibilities for studying the flow configuration at stream bifurcations.

We monitored the flow repartition in a bifurcation of a mountain gravel-bed river by deploying an ADCP specifically designed for shallow flow conditions. This field campaign was combined with photogrammetric surveys for documenting the geomorphological evolution of the river bed, its surface grain size distribution and structure. Integrating data from these different sources provided useful information on the bifurcation evolution and hydrodynamics. During a period in which the river bed did not undergo noticeable elevation changes, we observed that the water discharge ratio of the distributaries was approximately constant for sensibly different total discharge values. Such result was compared with the outcomes of numerical simulations.

How to cite: Pascal, I., Miazza, R., de Graffenried, B., and Ancey, C.: Bifurcations in mountain rivers: insights on their hydraulics from field measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8056, https://doi.org/10.5194/egusphere-egu23-8056, 2023.

12:05–12:15
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EGU23-14726
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HS9.3
|
On-site presentation
|
Nino Ohle, Suleman Shaikh, Thomas Thies, Thomas Strotmann, and Ulrich Schmekel

For future strategies in water depth maintenance in the Port of Hamburg, determining the navigability limit (i.e. the nautical safe depth) is of major importance. For this purpose, a project "Nautical Depth" was set up at the Hamburg Port Authority (HPA), which is dedicated to dealing with this issue. The aim is to measure a nautical safe depth under various boundary conditions and to identify limits for a safe passage of high concentrated soil suspensions. Among other things within the project monitoring data of suspended sediment fluxes and data from multibeam echo-sounders and sub-bottom profilers were analysed and compared.

Therefore, the backscatter along the cross-section of a long-term H-ADCP monitoring station was analysed and calibrated with water samples and data of optical backscatter sensors. The standard monitoring frequency of the data is 1 minute. The data were aggregated and summarized as half-tide values and flood-tide, ebb-tide and the residual sediment fluxes were calculated. These data sets were compared with hydroacoustic measurements of the bathymetry, including sub-bottom profilers, in the harbour basin Köhlfleethafen nearby the cross-section of the H-ADCP monitoring station. In a defined and shaped area volumetric calculations, layer densities and the amount of sedimented dry matter of the bottom layer were analysed.

The presentation will give a closer look to the sampling, monitoring and interpretation of the data. The data sets of sediment fluxes derived by the H-ADCP will be compared with the data sets of the hydroacoustic measurements. The influence of dredging campaigns will be shown, and an interpretation of the data will be given. The investigations also show, that the soil properties and analysed data sets are dependent from local and regional boundary conditions, as flow velocity, grain size distribution and especially in Hamburg from the organic matters and nutrients within the suspended and the soil material. All data sets are used to optimize the maintenance strategies of the nautical bottom in the Köhlfleethafen area, especial regarding sediment conditions methods with bed levellers or water injection dredgers.

References:

Nino Ohle, Thomas Thies, Rolf Lüschow, and Ulrich Schmekel - Sediment sampling and soil properties of sediments in the Hamburg port and the river Elbe in comparison with hydro-acoustic measurements , Proceedings of the EGU2020-16468, https://doi.org/10.5194/egusphere-egu2020-16468

Ahmad Shakeel, Claire Chassagne, Jasper Bornholdt, Nino Ohle, and Alex Kirichek - From fundamentals to implementation of yield stress for nautical bottom: Case study of the Port of Hamburg, Ocean Engineering, Volume 266, Part 2, 2022, 112772, ISSN 0029-8018, https://doi.org/10.1016/j.oceaneng.2022.112772

How to cite: Ohle, N., Shaikh, S., Thies, T., Strotmann, T., and Schmekel, U.: Monitoring of suspended mater with H-ADCP devices and comparison with sedimentation rates and soil properties in the Köhlfleethafen harbour basin of the Hamburg port, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14726, https://doi.org/10.5194/egusphere-egu23-14726, 2023.

12:15–12:25
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EGU23-17507
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HS9.3
|
On-site presentation
Melanie Diaz, Henko Stigter, Benjamin Gillard, Iason-Zois Gazis, Jochen Mohrmann, Karl Heger, Matthias Baeye, Laurenz Thomsen, and Jens Greinert

Where fine-grained marine sediments are being brought in suspension and become subject to transport by currents, aggregation of cohesive primary particles (flocculation) can occur. By changing the inherent particle properties, flocculation processes play an important role in speeding up settling and redeposition of sediment particles. However, while numerous laboratory experiments have been conducted to understand properties and behavior of flocs, so far, there is not yet an appropriate method to monitor flocculation in-situ. Gaining a better understanding of the flocculation process and how it will affect the dispersion of man-made sediment plumes is important to assess the impact of human activities on the environment, for example in the context of deep-sea mining or offshore dredging.
In this study, the inherent acoustical and optical properties of sediment particles are studied using in-situ plume monitoring data collected by the MiningImpact2 project consortium during the first deep-sea mining trial of a pre-prototype polymetallic nodule collector vehicle. The trial was conducted in April 2021 at 4500 m water depth in the Clarion-Clipperton Zone (eastern equatorial Pacific Ocean) by the Belgian contractor DEME-GSR. During this trial, one of the main goals was to monitor the spatiotemporal evolution of the sediment plume generated by the mining vehicle. For this purpose, numerous sensors were deployed around the test area including ADCPs of different frequencies, OBSs and deep-sea particle camera. In this study, the main interest is to use this dataset to gain knowledge on the variability of particle properties and to monitor flocculation in the generated plume.
The monitoring array of sensors proved successful in measuring the dispersion of the plume around the mining site. In the data recorded in the plume, a gradient in optical and acoustic response was found, suggesting a change in inherent particle properties such as their size and shape induced by flocculation. The evolution of particle size as inferred by the particle camera recordings (PartiCam) corroborated this finding. In combination with currents and environmental measurements, this dataset provided valuable information to better understand the flocculation process.

How to cite: Diaz, M., Stigter, H., Gillard, B., Gazis, I.-Z., Mohrmann, J., Heger, K., Baeye, M., Thomsen, L., and Greinert, J.: Monitoring flocculation during a deep-sea mining test in the Clarion-Clipperton Zone, eastern equatorial Pacific Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17507, https://doi.org/10.5194/egusphere-egu23-17507, 2023.

12:25–12:30

Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall A

Chairpersons: Slaven Conevski, Bernhard Vowinckel, Katharina Baumgartner
A.166
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EGU23-16306
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HS9.3
|
ECS
Slaven Conevski, Paul Alberto Quintanilla, Siri Stokseth, Massimo Guerrero, and Nils Ruther

The Cheves hydroelectric power plant (HPP) is located in the Andes Mountains in Peru near Lima. The operation of the Statkraft asset is heavily influenced by sediment transport during the rainy season (February to June), both by bed load and suspended load. To avoid sediments from filling up the reservoir, sediment routing during rainy season is applied. However, during the routing, high water velocities through the gates are causing flab abrasion resulting in high maintenance costs. In addition, the water being transferred to the head race tunnel is of high sediment concentration and causes severe erosion of the turbine blades, resulting in low efficiency. This occurs despite desanders are operating continuously during rainy season.

To optimize the operation of the power plant, both during power production and during sediment routing, a sediment monitoring instrument was installed at four locations on the HP system. The positions were chosen to provide accurate information on sediment inflow to all major units of HP, such as the desilting units, reservoir, forebay, headrace tunnel, and turbine outlets. Both acoustic (e.g., 8 MHz, acoustic backscatter) and optical (e.g., optical backscatter) instruments will be installed to accurately estimate suspended sediment concentration (SSC). The AoBS, manufactured by Sequoia AS, provides both acoustic-optical measurements and a proprietary method for combining the measurements and determining the SSC in mg/l. To validate SSC, a pump sampler was installed at each location to sample once a day in dry season and twice a day in the wet season. The water samples were analyzed using both the typical filter method and the laser diffraction method.

The initial results (in the dry season) confirmed that the combination of optical and acoustic methods provided the most accurate results, although the Sequoia AS method appears to underestimate by 30-50%. Another method based on a weighted summation of both results is under development and promises better results for the existing data. Based on these results, four indicators have been developed: i) intensity of sediment inflow in the turbine, ii) coarseness of particles at all positions (optics vs acoustics scattering index), iii) sediment discharge, iv) desander performance (sediment input from the desanders). Further testing needs to be conducted in the wet season to validate the indicators as well as the method of combined acoustic-optical sediment data collection.

How to cite: Conevski, S., Quintanilla, P. A., Stokseth, S., Guerrero, M., and Ruther, N.: Monitoring sediment transport by means of optic-acoustic system to optimize the operation of a hydropower plant, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16306, https://doi.org/10.5194/egusphere-egu23-16306, 2023.

A.167
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EGU23-512
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HS9.3
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ECS
Bidhan Kumar Sahu and Pranab Kumar Mohapatra

Studying bedload transport is essential for analysing erosion and deposition processes in the channels and designing hydraulic structures. Impact plate systems are indirect devices deployed to measure bedload consisting of a metal plate. When the bedload sediments strike the plate, they create vibrations which are recorded as signals by an acoustic sensor attached to the plate. The signal acquired is then processed to find the bedload properties. Flow velocity and mode of bedload transport can affect the signal. The effect of velocity on the impact plate signals is well documented in the literature. However, the role of channel bed roughness which hugely influences the mode of transportation of bedload, is yet to be studied in detail. This study investigates the effect of channel roughness on the mode of bedload transport and the signal registered in an impact plate in a laboratory flume. The impact plate is placed at the downstream end such that the top plate of the box is aligned with the bed of the flume. An accelerometer sensor is attached to the underside of the plate to record the vibrations. The bed of the flume 2.5m upstream of the impact plate is composed of a replaceable “rough” section. Four different tests are conducted considering four separate rough sections (smooth, 2mm, 5mm, and 10 mm). The bedload particles are sorted into five classes based on their size, from 2.36mm to 20mm. In each test, the particles from a particular grain size class are manually released 5m upstream of the impact plate. The signal generated from the bedload strike is used to develop a calibration equation relating to bedload size and channel roughness. A digital camera is used to capture the bedload movement over the plate to link the mode of bedload transport with the signal.

How to cite: Sahu, B. K. and Mohapatra, P. K.: Effect of Channel Bed Roughness on the Mode of Bedload Transport and Signal Response of Impact Plate with an Accelerometer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-512, https://doi.org/10.5194/egusphere-egu23-512, 2023.

A.168
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EGU23-4383
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HS9.3
Anurag Handique, Shakti Kalyani, Arup Kumar Sarma, and Rajib Kumar Bhattacharjya

Confluences of rivers are classified as one of the most intricate hydrodynamic environments. The convergence of incoming flows at confluences generated by two rivers or subchannels in large braided rivers creates complex fluid motion patterns, including the growth of large-scale turbulence formations. A study on the dynamics of flow mixing and propagation from the adjoining channels could be tricky as the channels consisting of the confluence usually acts as a flow barrier to each other. The flow in the dominant channel would initially act as a virtual barrier to the incoming channel, intercepting its free movement to the main channel. Post this stagnation, the less dominant flow gain energy because of a temporary rise in its level due to flow accumulation and eventually merge into the main stream in due course of time. However, when the confluence involves two channels of relatively similar strengths, primarily observed in large complex braided rivers, the complete or partial flow stagnation is observed in both the sub-channels alternatively in subsequent times. This distinctive flow phenomenon was first observed by our research team during 2004 while doing a hydrographic survey for modelling purpose in the Brahmaputra River of Assam, India, and is popularly called “Hamol” by the riverine community. Owing to this peculiar occurrence, there can be several implications on the river, such as changes in sediment dynamics, influencing the aquatic biota and habitat alterations, etc. For numerical river flow modelling, accurately simulating confluence hydrodynamics is a significant challenge. In this work, this phenomenon is investigated in a confluence composed of two sub-channels with different strengths through a mathematical model study. The model is simulated in the Brahmaputra River near Bahari, Barpeta from the viewpoint of its complex braiding patterns existent in this stretch. A TVD McCormack predictor corrector technique is used in the mathematical model to solve a modified form of boundary fitted shallow water equations in the MATLAB environment. The stability of the model is governed by the Courant criteria, with the Courant number being less than unity. Through the model study, the variations of the depth-averaged streamwise velocities and the simulated flow depths in the grid points prior to the confluence juncture in the less dominant channel are compared in different timesteps. Alongside, the characteristic of such transitions is examined for different discharge ratios of the two adjoining channels. The study indicated the efficacy of the mathematical model in capturing the “Hamol” phenomenon observed practically in the field.

How to cite: Handique, A., Kalyani, S., Sarma, A. K., and Bhattacharjya, R. K.: Investigating Intermittent Flow Stagnation at Channel Confluence of Braided River, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4383, https://doi.org/10.5194/egusphere-egu23-4383, 2023.

A.169
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EGU23-5093
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HS9.3
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ECS
Tamara Kuzmanić, Klaudija Lebar, Mateja Klun, and Simon Rusjan

Optical sensors are widely used for turbidity measurements in suspended sediment concentration studies. When conducting continuous measurements of turbidity in the field with optical sensors, results are determined according to the calibration curve (relationship between suspended sediment concentration and turbidity readings from the optical sensors). The calibration curve is developed based on the samples of the material present in and/or around the investigated stream. The concentration data are useful in water-quality-related investigations as well as for evaluating the amounts of transported (flushed, eroded) material from the catchments as suspended load. The amounts and particle sizes of transported material depend on the hydrological conditions. Usually, the particles’ size is not directly considered when developing the calibration curve. However, different particle sizes of the material from the same study site can result in different turbidity readings. Taking into account one general calibration curve for suspended sediment concentration determination can lead to misestimation of the transported material amounts. Here, the results of turbidity sensor calibration for different particle size classes are presented. Additionally, the uncertainty of the suspended material concentrations due to this effect is estimated. Further, we show how different calibration curves affect the assessment of the amount of the transported suspended load from the selected experimental catchment.

How to cite: Kuzmanić, T., Lebar, K., Klun, M., and Rusjan, S.: Investigating the relationship between particle size of suspended sediments and optical sensor turbidity readings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5093, https://doi.org/10.5194/egusphere-egu23-5093, 2023.

A.170
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EGU23-6764
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HS9.3
|
ECS
Theresa Himmelsbach, Bernhard Gems, Katharina Baumgartner, and Markus Aufleger

While hydraulic models belong to the standard toolkit of engineers, numerical models for bed load transport in mountain rivers, here defined by steep slopes and coarse bed material, still lack reliability. On one hand, this is attributed to the complex processes in mountain rivers due to highly turbulent flows, changing flow conditions and higher form and spill drag due to immobile boulders compared to gravel-bed rivers. And on the other hand, the models highly depend on underlying input terrain data such as river section data, which in an alpine environment is generally difficult to access. The ongoing advances in remote sensing techniques, in particular in the field of topo-bathymetric laser scanning offer high-resolution bathymetry data. Compared to terrestrial laser scanning, topo-bathymetric laser scanning also captures the structure below the water surface. A water-penetrating laser system, using the green region of the electromagnetic spectrum (wavelength of 532 nm), provides valuable information across the whole river section. Depending on the conditions, such as turbidity and white water, the data achieves up to 20 - 50 survey points per square meter. Generally, the laser scanners are carried by aircrafts (manned or unmanned) to deliver large-scale high-resolution bathymetric survey data. The current research investigates the advances of high-resolution and spatially continuous bathymetry laser scanner data on sediment transport models for mountain rivers. Besides the general application as terrain data for bedload transport models, the research interest is also on the derivation of form drag through different parameters such as grain size D84 and standard deviation σz from the point cloud. For this research, available data from a mountain river in South Tyrol (Italy), covering a length of about 1.5 km over the whole river width with about 40 points/m², is applied. The river section has a slope of about 2 %, an anthropogenic-influenced cascade section in the upper part with single exposed boulders and a plan-bed character in the lower section. The mean particle size of the surface layer is about d90 = 0.10 m. With this data, the current research aims to derive extensive grain size and flow resistance information from topo-bathymetric laser scanner data and compare it with the traditional reference measurements from field data. Both data sets, from the remote-sensing and the field measurements, are tested on different approaches for bed-load transport capacity, form drag and critical flow, with particular respect to flow resistance. It is expected, that the higher information on a reach scale greatly improves the estimation of the flow resistance of mountain rivers and thus, improves the estimation of sediment transport rates in alpine environments. The contribution shows the first results of this research.

How to cite: Himmelsbach, T., Gems, B., Baumgartner, K., and Aufleger, M.: Remotely sensed data in bed load transport models of mountain rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6764, https://doi.org/10.5194/egusphere-egu23-6764, 2023.

A.171
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EGU23-8077
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HS9.3
|
ECS
Wei-Min Shen and Christina W. Tsai

    Sediment dynamics is a key mechanism of the interaction between sediment particles and fluid particles. Therefore, the stochastic Diffusion Particle Tracking Model (SD-PTM), a Langevin equation-based model, was introduced to randomly simulate suspended sediment particles' movement by incorporating Brownian Motion (BM) in the Langevin equation.

    Under the framework of Kolmogorov's turbulence theory, large-scale eddies with a high Reynolds number (Re) show similarity while continuing to break into smaller eddies. A correlation thus exists between time increments. In addition, according to the bursting process near the bed region, we assume that sweep events with eddies of various sizes contribute mainly to the resuspension mechanism. Consequently, a generalized stochastic process is required to incorporate the correlation, interpreted as either a memory effect or long-range dependency. Fractional Brownian Motion (fBm), a continuous and centered Gaussian process characterized by the Hurst parameter(H), can describe the long-range dependency more precisely. Moreover, we seek to develop a relationship between the H-parameter and turbulent intensity.

    In addition, the dependent increment assumption invalidates the Ito formula. As such, advanced stochastic calculus should be adopted as an alternative. The Malliavin derivative and Skorohod integral, defined in Weiner space, are introduced to fulfill the assumption and to maintain the fundamental rules in the Riemann integral to a random variable. This study further introduces the Wick-Ito expansion with Hermit Polynomial to overcome the abovementioned computational issue; thus, both the fractional Brownian Motion and the stochastic ordinary differential equation (SODE) can be simulated.

    Last, to build a physically based SODE for sediment transport in open channel turbulent flow, we aim to more comprehensively determine the diffusion coefficient and Hurst parameter by the turbulent properties. In addition, the turbulent sweep events are known to entrain the sediment particles back into the water column in the near-wall region. Therefore, when including the particle memory effect attributed to turbulent sweep events by introducing fBm to the resuspension mechanism, particles in the near-wall region impacted by the sweep events can be more precisely simulated.

How to cite: Shen, W.-M. and Tsai, C. W.: Incorporating the resuspension mechanism into suspended sediment particle tracking by fractional Brownian Motion with Malliavin calculus, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8077, https://doi.org/10.5194/egusphere-egu23-8077, 2023.

A.172
|
EGU23-9781
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HS9.3
Alban Gilletta de Saint Joseph, Julien Chauchat, Cyrille Bonamy, and Marie Robert

The coastal environment is meeting numerous anthropogenic changes especially with the increased implementation of bottom-fixed Offshore Wind Farms. Few feedbacks are available for these recent infrastructures facing a complex turbulent marine environment made of combined waves and currents. In the presence of a pile, strong hydrodynamical eddies structures form that are responsible for the scour process which may lead to the failure of the wind turbine. Former two-phase flow simulations of this problem [1] have been performed using the Reynolds-Averaged Navier-Stokes approach for turbulence modelling and they have shown some limitations to reproduce the main features of the scour process. Turbulence modelling was argued to be the major bottleneck. In order to further investigate this problem, an extensive study of the numerical simulation of the flow hydrodynamic around a wall-mounted cylinder has been carried out using a hierarchy of turbulence models including RANS, hybrid RANS-LES and LES. The range of Reynolds numbers is too large to allow for a well-resolved LES and therefore hybrid RANS-LES is essential to reproduce main hydrodynamical features at an affordable cost. In this study we evaluated the k-omega SST model coupled with the Improved Delayed Detached Eddy Simulation [2] and the Scale-Adaptative Simulation [3]. All the simulations have been performed using OpenFOAM an open-source Computational Fluid Dynamics toolbox. Our simulations suggest that the k-ω SST SAS is the best model for this configuration. It has been adapted for the two-phase flow Eulerian-Eulerian approach and implemented in sedFOAM [4]. Preliminary results of the two-phase simulation of Roulund and co-worker experiments [5] shows very encouraging results in terms of morphological features at short-time scales. These results will be presented during the conference together with in-depth analysis of the sediment transport fluxes.

References

[1] Nagel T., Chauchat J., Bonamy C., Liu X., Cheng Z. and Hsu T. - J., Three-dimensional scour simulations with a two-phase flow model, Advances in Water Resources (2020).

[2] M. S. Gritskevich, A. V. Garbaruk, J. Schütze and F. R. Menter, Development of DDES and IDDES Formulations for the k-ω SST Model, Flow Turbulence Combust (2012).

[3] F. R. Menter and Y. Egorov, A scale-adaptative simulation model using two-equation models, American Institute of Aeronautics and Astronautics Paper (2005).

[4] J. Chauchat, Z. Cheng, T. Nagel, C. Bonamy, and T.-J. Hsu, Sedfoam-2.0: a 3-d two-phase flow numerical model for sediment transport, Geoscientific Model Development (2017).

[5] Roulund A., Sumer B. M., Fredsøe J. and Michelsen J., Numerical and experimental investigation of flow and scour around a circular pile, Journal of Fluid Mechanics (2005).

How to cite: Gilletta de Saint Joseph, A., Chauchat, J., Bonamy, C., and Robert, M.: Two-phase simulation of scour using a hybrid RANS-LES turbulence model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9781, https://doi.org/10.5194/egusphere-egu23-9781, 2023.

A.173
|
EGU23-10102
|
HS9.3
Julia Mullarney, Rémi Chassagne, and Vinay Nelli

In vegetated areas, water flow and sediment transport are highly influenced by their interactions with vegetation. The induced vegetation drag force reduces the water flow velocity but increases the TKE (turbulent kinetic energy). Recent laboratory experiments of flow within array of rigid cylinders have shown that the fluid bed shear stress, and consequently the sediment transport rate, are correlated with the TKE instead of with the depth-average velocity.

In this context, modeling sediment transport in vegetated areas represents a major challenge for the prediction of the geomorphic evolution of coastlines. In this study, a three-phase flow model for sediment transport in vegetation is presented. The governing equations are obtained from a double averaging procedure: a spatial and turbulence (Favre) averaging. The model is based on the sedFOAM solver, in which the particle phase is represented as a continuum with constitutive laws based on the kinetic theory of granular flows and a turbulence model is required for the fluid phase. The vegetation is represented as a passive phase which interacts with the other phases through a drag force.

First, simulations without sediment are performed and compared with measurements from existing laboratory experiments. The model demonstrates a very good capacity to predict the fluid bed shear stress and the turbulence intensity. The model is also compared with new high-resolution field data (Cook’s beach, New-Zealand). Secondly, sediment transport simulations are performed and compared with laboratory experiments. The results of the model are used to analyze the physics of sediment transport within vegetative regions and to discuss the next necessary steps toward larger-scale modeling.

How to cite: Mullarney, J., Chassagne, R., and Nelli, V.: Modeling sediment transport in vegetative areas with a two-phase flow approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10102, https://doi.org/10.5194/egusphere-egu23-10102, 2023.

A.174
|
EGU23-11987
|
HS9.3
|
ECS
Matthias Renaud, Julien Chauchat, Cyrille Bonamy, and Olivier Bertrand

Erosion due to scouring processes around hydraulic structures is a major topic in hydraulic engineering. Despite more than a century
of active research, its accurate prediction remains poor and its numerical modelling is still a major challenge for civil engineers.
Different studies have particularly identified scouring phenomenon as a major cause for bridge failures making its forecasting of
outermost importance to assess bridge safety and resiliency to extreme events. Numerical prediction of scour around an obstacle
requires the accurate simulation of the complex turbulent fluid flow in the vicinity of the structure as well as its interactions with
the surrounding sediment and the bed morphology. This involves a wide variety of processes such as bed-load transport, turbulent
suspension and gravity-driven avalanches. The classical morphodynamics models used in the industry, although adapted to study
sediment transport at large scales, often fail to accurately simulate the scour process as well as the flow around hydraulic structures.
A detailed comparison of the flow hydrodynamics around a wall-mounted cylinder using TELEMAC-3D and OpenFOAM will be
presented. Furthermore, scour processes concern a wide range of structures with complex geometries that geophysical numerical
models are not able to consider e.g. vertical non-emerging structures or structures with pressurized flows. Other models better
reproduce the local physical processes such as SedFoam, based on a two fluid approach where the sediment is modeled as a continuum.
Unfortunately, the computational cost of such a model remain to high for engineering purposes. Those considerations emphasize the
need for an intermediate-scale model, able to solve the different turbulent flow structures associated with scouring at an affordable cost.
The development of such a model is the main objective of the present study and as first step, idealized benchmarks on sedimentation,
turbulent suspension and dune migration will be presented. In the future, ongoing work using SedFoam will be used to develop new
closures, that will be tested in the present model, which will be made open source.
This thesis work is carried out within the framework of the Oxalia Hydraulics Chair of the Grenoble INP Foundation.

How to cite: Renaud, M., Chauchat, J., Bonamy, C., and Bertrand, O.: Ongoing development of a three-dimensional sedimenttransport model for local scour study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11987, https://doi.org/10.5194/egusphere-egu23-11987, 2023.

A.175
|
EGU23-11215
|
HS9.3
Bernhard Vowinckel, Christoph Schwarzmeier, Christoph Rettinger, Samuel Kemmler, Jonas Plewinski, Franciso Núñez-González, Harald Köstler, and Ulrich Rüde

Antidunes are an important feature in the morphodynamics of streams over steep slopes. These bed forms are short-wave periodic disturbances that develop on the surface of loose granular beds in response to the interaction with supercritical and near-critical shallow, turbulent flows. They arise in fluvial, coastal, and submarine environments and are closely tied to the resulting flow resistance, turbulence, and sediment transport. Antidunes are the only type of bedform that can migrate upstream under the presence of a free surface. This seems counterintuitive and has caught strong interest in hydraulic research. However, up to date little is known about the migration mechanism in connection to turbulence, bed morphology, and sediment transport, because of the challenging supercritical flow conditions, often associated to low submergences. This is in part related to the inherent technical challenges to reproduce rapid flows over an erodible bed in laboratory flumes, as well as to the difficulties to perform non-intrusive measurements. Consequently, experimental data sets in published literature are scarce. Numerical simulations of supercritical flows above an erodible bed can therefore constitute a methodological alternative for the study of antidunes. Such simulations, however, need to properly reflect the interplay of the fluid phase, the sediment particles, and the gas phase above the free surface. In this work we propose to use particle-resolved direct numerical simulations (pr-DNS) in conjunction with a deformable fluid surface to simulate the formation and propagation of upstream migrating antidunes in supercritical flows with high fidelity. We aim to numerically reproduce the experimental campaign recently reported by Pascal et al. (2021), who managed to measure the propagation of upstream migrating antidunes with a high spatial and temporal resolution. For this, we combine the lattice Boltzmann method with the discrete element method to simulate the fluid–particle and particle–particle dynamics (Rettinger & Rüde, 2022) and extend it with a volume of fluid scheme (Schwarzmeier et al., 2023) to track the strongly deformable free fluid surface. The parameter choices of Pascal et al. (2021), with coarse sediment grains and low relative submergence of the particles, allow for a direct overlap of experimental conditions with pr-DNS. In this manner, our simulations successfully close the gap between river morphodynamics experiments and pr-DNS, to couple bedform and free-surface interactions with large-scale simulations consisting of a sediment bed comprising thousands of particles in unidirectional, supercritical turbulent flows.

Schwarzmeier, C., Holzer, M., Mitchell, T., Lehmann, M., Häusl, F. & Rüde, U. (2023). Comparison of free-surface and conservative Allen–Cahn phase-field lattice Boltzmann method. Journal of Computational Physics 473, 111753 .

Rettinger, C., & Rüde, U. (2022) An efficient four-way coupled lattice Boltzmann – discrete element method for fully resolved simulations of particle-laden flows. Journal of Computational Physics 453, 110942

Pascal, I., Ancey, C., & Bohorquez, P. (2021). The variability of antidune morphodynamics on steep slopes. Earth Surface Processes and Landforms, 46(9), 1750-1765.

How to cite: Vowinckel, B., Schwarzmeier, C., Rettinger, C., Kemmler, S., Plewinski, J., Núñez-González, F., Köstler, H., and Rüde, U.: Particle-resolved simulations of antidune migration in supercritical flows, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11215, https://doi.org/10.5194/egusphere-egu23-11215, 2023.

A.176
|
EGU23-16014
|
HS9.3
|
ECS
Emese Nyiri, Gergely Tihamér Török, and Sándor Baranya

Significant river regulation activities have been carried out on the Upper Hungarian Danube since the end of the 19th century. First, a main channel was created in the natural braided channel to improve the navigational conditions. Later, already in the 20th century, in order to facilitate the erosion of larger deposits, groin fields (wing dam system) were installed helping navigation and flood drainage. Finally, at the end of the 20th century, the Gabcikovo dam was built (10 km upstream from the Slovakian-Hungarian border section), which caused a lack of sediment in the examined section due to sediment trapping. These were the most relevant measures, however, other activities, such as dredging, have also been implemented.

Due to the lack of past measurement data, it is impossible to accurately reconstruct the original morphodynamic state of the river. Even the contribution of individual measures to the morphodynamic processes is unclear. For example, what effect the modification of the braided channel system could have had on the high water levels. Or which intervention contributed to what extent to the significant drop in river bed level experienced in the last century.

In our study, we built a schematic 1D morphodynamic model, which approximates the dynamic equilibrium state based on the bankfull stage. The concept was to implement the morphodynamic effect of the individual interventions in the model. The validation confirmed that the 1D model concept is a promising manner for the qualitative examination of the impact of interventions on morphodynamic processes.

How to cite: Nyiri, E., Török, G. T., and Baranya, S.: Impact assessment of river regulations of the past century using 1D morphodynamic modeling on the Upper Hungarian Danube, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16014, https://doi.org/10.5194/egusphere-egu23-16014, 2023.

A.177
|
EGU23-16388
|
HS9.3
|
ECS
Naji Alwani, Gyozo Jordan, Péter Szabó, and Geza Hitka

Mining activities inevitably generate contaminants in high quantities that can pose a risk at soil, water, biota and humans. This article describes a systematic method to understand the geochemical properties of various mine waste heaps and to investigate the waste material of a flotation mud and a waste rock heap coming from a high-sulphidation epithermal mineralization of the Recsk Mining Area, Hungary, and an application of a risk evaluation technique is presented.

Field sampling took place in the Recsk Mining Area on the H2 tailings heap and on the H7 waste rock heap where a total of 48 samples were collected. The geochemical properties of the waste material were assessed to shed light on the behavior of the potential toxic elements. The element concentration of the samples was determined by inductively coupled plasma mass spectrometry (ICP-MS) inductively coupled plasma optical emission spectrometry (ICP-OES) and ion chromatography. In addition, the mineral phases present were detected by X-ray diffraction (XRD). Ranking of potential toxic mining waste was calculated using two indicators: the index of contamination (IC) and the Hazard Average Quotient (HA) which was used to calculate the Toxicity Factor (TF). The mobility of each element was estimated using a simple formula followed by univariate and bivariate data analysis methods.

Results show that the potentially toxic elements are present in varying concentrations in the two studied wase heaps, even though they are originating from the same mineralization. They also behave differently on the studied waste heaps in terms of mineral composition. The calculated IC values were very high, exceeding the limits, and TF values were low for mining waste according to the legislative concentration pollution limits. A unique approach is needed for each type of waste heap in order to facilitate a successful remediation or secondary raw material extraction.

Keywords: mining waste; geochemistry; contamination, index of contamination, Hazard Average Quotient

How to cite: Alwani, N., Jordan, G., Szabó, P., and Hitka, G.: Ranking methodology and geochemical character of different waste materials of an epithermal mineralization from the Recsk Mining Area, Hungary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16388, https://doi.org/10.5194/egusphere-egu23-16388, 2023.

Posters virtual: Tue, 25 Apr, 14:00–15:45 | vHall HS

Chairpersons: Wendy Gonzalez, Katharina Baumgartner
vHS.33
|
EGU23-14867
|
HS9.3
|
ECS
|
Pratik Chakraborty, Daniel Valero, Andrés Vargas-Luna, Francesco Bregoli, and Alessandra Crosato

Bank erosion in riverine systems is one of the most complex, yet rampant, morphodynamic processes with significant implications for riparian activities and thereby the population. Therefore, it is an important aspect of the geomorphological evolution of a river reach that must be taken into consideration by river engineers while planning training, restoration or other engineering works of interest. Erosion of river banks are in essence a result of a combination of bank material entrainment by the river flow and mass failure.

In particular, it has been found that bank accretion on one river side could play an important role in triggering erosion of the opposite bank. Such bank accretion could be a result of a natural bar formation due to morphodynamic instability or even forced by an intervention, such as a groyne. To understand this process, we conducted a computational fluid dynamics (CFD) numerical study.  We set up a high-resolution 3D Large Eddy numerical model replicating data-rich experiments which have been previously conducted in a large flume with a mobile bed, where bank erosion has been observed opposite to a bar formation.

The CFD hydrodynamic model takes as input the boundary conditions and the high-resolution bed topography data which had been collected during the experiment at given time intervals. The hydrodynamic simulation runs until steady-state, thus provides the flow field at that given time of the experiment, i.e., for a particular bed topography configuration. Thereafter, the next time-instances, with an updated bed topography, are simulated similarly. This provids a set of flow-field data for each time instance. The evolution of the flow field can then be related to the evolution of the opposite bank erosion. Various flow field variables and parameters such as near-bank velocities and Q-criterion, were analysed so as to determine the process driving factors. Furthermore, the large eddy simulations allowed for the identification of coherent turbulent structures and their role in driving bank erosion. Results are here presented and discussed.

How to cite: Chakraborty, P., Valero, D., Vargas-Luna, A., Bregoli, F., and Crosato, A.: Correlating flow field with river bank erosion opposite to an accreting bank: a large-eddy simulation approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14867, https://doi.org/10.5194/egusphere-egu23-14867, 2023.

vHS.34
|
EGU23-15527
|
HS9.3
|
Usman Ali Khan, Renato Vacondio, Susanna Dazzi, Alessia Ferrari, and Roberto Valentino

The accuracy and reliability of sediment transport models is crucial for understanding and predicting geomorphological changes in river systems, which can have important implications for conserving riverine ecosystem. This information can be used to make better informed decisions about the management of the river, as well as to predict and prepare for potential hazards such as flash flooding. In the past, various approaches have been used to model these processes for suspended and bedload sediment transport. However, many of these models have limitations including spatial and temporal scales, data requirements, model complexity, numerical stability and computational cost, particularly when it comes to simulating the transport of bedload sediments.

In this study, we tried to address these limitations by testing a 2D weakly coupled numerical model for bedload transport in a real application. The model was implemented by adopting schemes presented in previous works (Vacondio et al. 2014, doi.org/10.1016/j.envsoft.2014.02.003; Juez et al. 2014, doi.org/10.1016/j.advwatres.2014.05.014). The advantage of using a weakly coupled model is that it is flexible, computationally efficient and can be used to simulate bedload transport in large-scale systems while producing consistent and reliable results over time. It is based on the finite-volume method and uses the Shallow water and Exner equations for the liquid and solid phases, respectively. High computational efficiency is guaranteed by parallelization on Graphics Processing Units.

We selected the case study of the Baganza River (Italy), characterized by a catchment area of 228 km2 and a total length of 55 km. We focused on the 28 km-long stretch between Calestano and Parma, with an average slope in the order of 0.8-1.5% and grain sizes in the order of 2-30 mm. For the topography, we used high-resolution digital elevation model (DEM) from 2008, while grain size distribution data were obtained through a hybrid technique combining field sediment sampling and photogrammetry. The adopted approach for the characterization of fluvial sediments at different points along the river is desirable in order to accommodate the full range of particle sizes inside the riverbed. The inflow boundary condition is the 2008-2014 series of floods on the Baganza River, including a destructive flood that occurred in October 2014.The riverbed topography resulting from the numerical simulation was compared with the one extracted from the DEM provided by a LiDAR survey carried out after the October 2014 event. The overall fair agreement between measured and simulated results suggests the usefulness of 2D weakly coupled numerical model for simulating hydro-geomorphological processes in the Baganza River. Moreover, the hybrid technique adopted for the grain characterization provides realistic representation of the sediments and increases the accuracy and reliability of the model predictions.

How to cite: Khan, U. A., Vacondio, R., Dazzi, S., Ferrari, A., and Valentino, R.: Modelling Of Hydro-Geomorphological Processes Related To Sediment Transport: Case Study of the Baganza River (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15527, https://doi.org/10.5194/egusphere-egu23-15527, 2023.

vHS.35
|
EGU23-300
|
HS9.3
|
ECS
|
Thallam Prashanth and Sayantan Ganguly

Fluvial geomorphology is the study of various landforms while analyzing the changes that are happening on the earth surface due to climate change and anthropogenic activities. Fluvial geomorphological parameters change due to natural processes like erosion, transportation, and deposition of sediments. It also changes due to manmade activities such as the construction of dams, canals, irrigation projects, etc. In this regard, the present study aims to analyze the changes in various fluvial geomorphological parameters of the Godavari River basin such as sinuosity index, braiding index, channel length index, channel count index, etc. using the Landsat images at a frequency of every 2 years from 2000 to 2022, along the length of the channel in the Godavari River, India. The second objective of this study is to perform a river bank stability analysis by using the Automatic Water Extraction Index (AWEI) at different time scales. Thirdly, we aim to quantify length, areal and relief parameters using ALOS PALSAR Digital Elevation Model (DEM) for different sub-basins of the Godavari. Due to the changes in the geomorphology, cross-section of the river is altered; the silt content increases near the hydraulic structures, the velocity of the water changes, the sinuosity (meandering) increases and it tends to the formation of oxbow lakes. This analysis helps to investigate the performance of the sub-basins of Godavari River and how much sensitive they are to erosion. An economical river bank stabilization technique can be suggested based on the rate of river bank shift and type of soil information obtained from Food and Agricultural Organization.

How to cite: Prashanth, T. and Ganguly, S.: Analyzing the behavioural changes of various fluvial geomorphological parameters using multi-temporal satellite images for the Godavari River, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-300, https://doi.org/10.5194/egusphere-egu23-300, 2023.

vHS.36
|
EGU23-15323
|
HS9.3
|
Gubash Azhikodan, Pan Ei Phyu, and Katsuhide Yokoyama

The sediments transported by the rivers are the primary source of materials to the downstream estuaries and tidal flats. Hence, human activities and increased natural forcing (driven by climate change) can strongly influence the sediment supply by the rivers to the downstream. This can directly impact the existence of tidal flat areas, the rate of bank erosion, and the health of the aquatic ecosystem. A quantitative analysis of the changes in river morphology on a long-term basis is necessary to understand the current situation and develop management strategies. Therefore, this study aims to analyze the long-term (1953-2020) changes in the riverbed elevation of the Chikugo River, Japan. This 143 km long river has a macrotidal estuary downstream (0-23 km). The bathymetric data measured at 200 m intervals from the river mouth (0 km) to the upstream (64 km) for 68 years (1953-2020) was collected from the Japanese government. Further, topographic data in the upstream estuary (10.2-17 km from the river mouth) at 1 km intervals were surveyed for 17 years (2005-2021).

Based on the time of human activities and disasters occurrence, the study period was divided into three periods: (1) the period of human activities (1953-1998), (2) the period of no human activities and no disasters (1998-2003), and (3) period of disasters (2003-2020). During period-1, the riverbed of the whole river was lowered, with maximum degradation occurring between 20-30 km. This was caused by extensive human activities such as dredging for flood control and land reclamation and sand mining for commercial use. During period-2, the riverbed (23-64 km) became stable because the dredging was stopped. However, bed elevation in the estuary (0-23 km) increased by nearly 1 m due to tide-induced landward sediment transport. During period-3, extreme floods and landslide disasters supplied massive sediments into the Chikugo River, which was deposited between 30 to 64 km and increased the riverbed elevation. However, the riverbed between 23 to 30 km was almost stable and the bed elevation in the estuary was (6-23 km) decreased. It seemed that sediments supplied by disasters were trapped by a bed sill located at 28.7 km and were not enough to reach the estuary. Further, the extreme flood discharge was strong enough to erode the sediment deposited upstream of the estuary by the tidal forcing and transport back downstream. The erosion of existing deposits and lack of sediment supply from the upstream caused the decreased bed elevation of estuarine areas. According to the results, the river is redistributing and restoring the sediments supplied by disasters at the place of extracted sediments in the past, which has reached mid-stream currently and is expected to arrive at the estuary and downstream soon.

How to cite: Azhikodan, G., Phyu, P. E., and Yokoyama, K.: Long-term (1953-2020) changes in morphology of Chikugo River, Japan in response to natural and anthropogenic forces, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15323, https://doi.org/10.5194/egusphere-egu23-15323, 2023.