GM2.8 | Assessing and monitoring geomorphic processes across scales

GM2.8

EDI
Assessing and monitoring geomorphic processes across scales
Convener: Gordon GiljaECSECS | Co-conveners: Anita Moldenhauer-RothECSECS, Rui Miguel Ferreira, Zhixian Cao, Thomas Pähtz
Orals
| Fri, 28 Apr, 14:00–15:35 (CEST)
 
Room D3
Posters on site
| Attendance Fri, 28 Apr, 16:15–18:00 (CEST)
 
Hall X3
Posters virtual
| Attendance Fri, 28 Apr, 16:15–18:00 (CEST)
 
vHall SSP/GM
Orals |
Fri, 14:00
Fri, 16:15
Fri, 16:15
Transport of sediments in geophysical flows occurs in mountainous, fluvial, estuarine, coastal, aeolian and other natural or man-made environments on Earth, while also shapes the surface of planets such as Mars, Titan, and Venus. Understanding the motion of sediments is still one of the most fundamental problems in hydrological and geophysical sciences. Such processes can vary across a wide range of scales - from the particle to the landscape - which can directly impact both the form (geomorphology) and, on Earth, the function (ecology and biology) of natural systems and the built infrastructure surrounding them. In particular, feedback between flow and sediment transport as well as interparticle interactions including size sorting are a key processes in surface dynamics, finding a range of important applications, from hydraulic engineering and natural hazard mitigation to landscape evolution and river ecology.

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

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

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

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

This session is promoted by the IAHR committee on Experimental Methods and Instrumentation.

Orals: Fri, 28 Apr | Room D3

Chairpersons: Gordon Gilja, Rui Miguel Ferreira, Thomas Pähtz
14:00–14:05
14:05–14:15
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EGU23-10650
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GM2.8
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ECS
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On-site presentation
Megan McKellar, Scott McDougall, Steve Evans, and Andy Take

Dam breach is a large-scale, highly unsteady, and complex water-sediment flow. Dam breach events span scenarios involving natural dams (created following valley blocking landslides) to scenarios involving anthropogenic structures such as water-retaining dams and dams designed specifically to store mine waste (e.g. tailings). Management of the risk posed by a potential breach of a dam structure requires a careful analysis of the consequences of failure. These analyses, often called dam breach studies, aim to improve safety and risk management through the prediction of travel time, flow velocity, and spatial extent of the hazard (e.g. map of depth of inundation) in the event of a breach. These factors in turn define the consequence classification of a dam and guide the development of emergency preparedness plans. The key boundary condition required for flood routing numerical simulations often conducted for dam breach studies is the outflow hydrograph which describes the relationship between outflow of the retained volume with time. In this study we explore the effect of failure mechanism on the characteristics of the outflow hydrograph of otherwise identical physical model dams. Physical model dams of 1 m in height were constructed of fine sand near the midspan of the 36 m long, 2.1 m wide, and 1.2 m high large landslide flume facility at Queen’s University Coastal Engineering Laboratory. Three failure mechanisms are explored; a) notch overtopping, initiated by incising a v-notch into the dam crest and allowing the impounded reservoir to intersect this local low point; b) wide-width overtopping, where a retaining wall placed along the crest of the dam allows for an additional reservoir capacity above the height of the crest that when rapidly removed a full width sheet of water cascades over the dam; and c) geotechnical seepage failure, where closing the toe drain allows a seepage face to develop that causes a failure in the downstream face of the dam. The reservoir surface elevation during breach was monitored with a series of five Akamina AWP-24 wave capacitance height gauges distributed centerline in the upstream reservoir. The evolution of breach shape is captured every 3 s using five Canon EOS Rebel T5 Digital Single-lens Reflex (DSLR) that capture a plan view area of the entire 2.1 m width of the dam and a combined upstream and downstream length of 4.3 m. To further capture the evolution of failure a Blickfeld LiDAR sensor was positioned oblique to the downstream slope to capture a point cloud scan ever 1.4 s. These data sets are then used to compare the physical characteristics of each breach process and the resulting implications for the observed outflow hydrographs for each failure mechanism.

How to cite: McKellar, M., McDougall, S., Evans, S., and Take, A.: Comparison of outflow hydrographs following dam breach arising from overtopping, wide-width overtopping, and geotechnical seepage failure mechanisms., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10650, https://doi.org/10.5194/egusphere-egu23-10650, 2023.

14:15–14:25
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EGU23-2278
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GM2.8
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On-site presentation
Kaiheng Hu, Lan Ning, Li Wei, and Qiyuan Zhang

Debris flows are the common gravity-driven mass flows in mountain areas that have high sediment concentration, wide grain sizes, and strong impact force.  Erosion or entrainment is the main mechanism by which the flows significantly increase their volume and destructive potential when they progressively move down over colluvial or alluvial beds. However, the scale and mechanism of erosion are poorly understood due to scarcity of field data. We present on-site data of a rare event in which three consolidated landslide dams were incised deeply by debris flows in a small catchment, southwestern China. The highest erosion rate was up to 1.3 m/min or 568 m3 per unit channel length. The channel topographical condition controls transition from erosion to deposition and the locations of local erosion maxima. An outburst-flood erosion model incorporating flow discharge, channel slope and erodibility is adopted to simulate the progressive erosion of these dams. The infrequent case confirms the key role of debris flows in alpine landscape evolution and provides field data (case data) for developing advanced erosion models. This work provides new insights into the role and scale of debris-flow erosion in catchment evolution.

How to cite: Hu, K., Ning, L., Wei, L., and Zhang, Q.: Progressive channel erosional processes of the 2020 Heixiluo debris flow in Dadu River, southwestern China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2278, https://doi.org/10.5194/egusphere-egu23-2278, 2023.

14:25–14:35
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EGU23-7170
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GM2.8
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ECS
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Virtual presentation
Antonio Jodar-Abellan, Efraín Carrillo-López, Joris Eekhout, Carolina Boix-Fayos, Pedro Pérez-Cutillas, and Joris de Vente

Floods cause severe natural disasters over the world generating property and infrastructures damages, poverty and loss of human life, among others. Mediterranean watersheds are especially sensible to floods due to their typical drainage basin features (steep slopes, short concentration times, complex orography, etc.) and the high rainfall intensity typical of convective systems. Knowing channel dimensions and other fluvial morphological features is key to (i) understanding the morphological evolution of the fluvial system in response to changes in land use and climate, and (ii) as an input for hydrological and erosion modelling. The objective of this study is to develop a simple method to obtain reliable estimates of channel dimensions and granulometry of bed material, based on statistical relations with catchment characteristics (e.g. topography, land use, soil properties, lithology, precipitation, connectivity indicators).

First, channel dimensions were estimated based on GIS analysis using a high resolution digital elevation model (2x2m) and ortophotos (50 cm resolution) for the Upper Segura River catchment, a Mediterranean catchment of 2,592 km2 located in the southeast of Spain. These estimates were validated with field measurements of depth and width of bankfull channels in the catchment headwaters. This comparison revealed that there was generally good agreement between channel dimensions obtained with the GIS method and those observed in the field for all evaluated channels (depth: RMSE=0.06; R2=0.93; width: RMSE=0.59, R2=0.45), although with better results for dry channels than for channels with continuous water flow. At each field observation, we also took sediment samples and characterised the granulometry of the channel bed material in the laboratory through dry sieving. Preliminary results show that bed material is composed mainly by gravels (67.8%), followed by sands (31.1%) and clays and silts (1.1%).    

Next, channel dimensions, obtained using GIS analysis across the entire catchment, and granulometry of bed material were used as dependent variables in advanced statistical analyses (such as machine learning algorithms) at sub-basin scale, with catchment characteristics as independent variables. The outcome of this analysis is now being used to make spatially continuous predictions of channel dimensions and granulometry of bed material at the catchment scale. This information will then ultimately serve as input for a coupled model that simulates channel hydraulics and morphodynamics at the catchment level.

Keywords: geomorphology; sediment yield; depth and width of bankfull channels; Mediterranean environment; GIS based tools; southeast of Spain.

We acknowledge funding from the Spanish Ministry of Science and Innovation and ‘Agencia Estatal de Investigación’ (PID2019-109381RB-I00/AEI/10.13039/501100011033).

How to cite: Jodar-Abellan, A., Carrillo-López, E., Eekhout, J., Boix-Fayos, C., Pérez-Cutillas, P., and de Vente, J.: Predicting channel dimensions and bed materials in intermittent Mediterranean rivers., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7170, https://doi.org/10.5194/egusphere-egu23-7170, 2023.

14:35–14:45
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EGU23-13546
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GM2.8
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On-site presentation
Dijana Oskoruš, Karlo Leskovar, and Krešimir Pavlić

Abstract: A very common engineering task we encounter in practice is calculating the annual balance of sediments on some watercourse. This is particularly challenging when assessing the backfilling of river reservoirs that have a multifunctional function.

Trakošćan Lake was built in the period from 1850 to 1862 as a pond and landscape addition to the park and Trakošćan castle. The topographic catchment area of the lake is 10.7 km2, it is about 1.5 km long, and its area is about 17 hectares, with an average depth of about 2.5 meters. The lake's total volume was originally 400,000 cubic meters, and downstream from the dam, the water of the Čemernica stream flows into the Bednja River.

After 61 years, the lake was drained, and in 2022, work began on sediment excavation to improve the lake's ecological condition due to about 200,000 cubic meters of deposited silt in the lake. The projected depth of the lake after cleaning would be about 6 meters.

In the example of this artificial lake, an estimate of the annual sediment spread by empirical parametric methods was carried out. Furthermore, the results were compared with the results of previous analysis obtained based on geotechnical sediment investigation at Lake Trakošćan.

How to cite: Oskoruš, D., Leskovar, K., and Pavlić, K.: Parametric methods for assessing the production of suspended sediment and its deposition in artificial lakes - an example of Lake Trakošćan, Croatia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13546, https://doi.org/10.5194/egusphere-egu23-13546, 2023.

14:45–14:55
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EGU23-11802
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GM2.8
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ECS
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Highlight
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On-site presentation
Rémi Chassagne, Raphaël Maurin, Julien Chauchat, and Philippe Frey

Bedload transport has major consequences for public safety, water resources and environmental sustainability. In mountains, steep slopes drive an intense transport of a wide range of grain sizes implying size sorting or segregation largely responsible for our limited ability to predict sediment flux and river morphology. Size segregation can lead to very complex and varied morphologies of bed surface and subsurface, including armouring, and can drastically modify the fluvial morphology equilibrium.

In this work, the mobility of bidisperse beds is studied with coupled fluid-Discrete Element Method (DEM) simulations of bedload transport. Initially, a large particle layer is deposited over a 10% slope bed made of small particles. A gravity-driven water free surface flow induces a downslope shear-driven granular flow of the erodible bed. It is observed that, for the same water flow conditions, the bedload transport rate is higher in the bidisperse configuration than in the monodisperse one. Depending on the Shields number and on the depth of the interface between small and large particles, different transport phenomenologies are observed, ranging from no influence of the small particles to small particles reaching the bed surface due to diffusive remixing. In cases where the small particles hardly mix with the overlying large particles and for the range of studied size ratios (r < 4), it is shown that the increase of mobility of the sediment bed is a granular effect, which can be explained within the mu(I) rheology framework. The buried small particles are more mobile than larger particles and play the role of a “conveyor belt” for the large particles at the surface. Based on rheological arguments, a simple predictive model is proposed for the additional transport in the bidisperse case. It reproduces quantitatively the DEM results for a large range of Shields numbers and for size ratios smaller than 4.

Finally, a phenomenological map is proposed. It presents the different transport regimes of bidisperse mixtures, depending on the mechanism responsible for the mobility of the small particles.

How to cite: Chassagne, R., Maurin, R., Chauchat, J., and Frey, P.: Mobility of bi-disperse sediment beds in bedload transport, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11802, https://doi.org/10.5194/egusphere-egu23-11802, 2023.

14:55–15:05
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EGU23-10517
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GM2.8
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ECS
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Highlight
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On-site presentation
Julia Kimball, Elisabeth Bowman, Nico Gray, and Andy Take

Particle size segregation is a phenomenon that generates preferential sorting of particles, based on size, in material flows of non-uniform size distribution. Landslide hazards, such as debris flows, involve materials of non-uniform particle sizes and therefore generate flow structures which arise from particle size segregation. The mobility, distal reach and impact forces associated with these natural hazards are influenced by these processes. Understanding the mechanisms of this phenomenon is essential for acquiring accurate input parameters that are needed to model these flows and properly design debris flow barriers and retaining structures. While the dynamics of particle size segregation in flow and deposition have been furthered through studying granular flows, studies to date have had several limitations. They primarily examine flows of bidispersed material, are small in scale, and rely on observations from flume sidewalls, precluding the study of dynamics along the centreline of flows. In this study, a large scale 6.8 m long and 2.1 m wide slope inclined at 30 degrees was used to generate dry tridispersed granular flows with 0.6 m3 of material. The tridisperse mixture consisted of even proportions by mass of 3 mm, 6 mm and 12 mm diameter spherical particles. Replicate tests were conducted to observe flow dynamics and assess methods for sampling along the internal plane of the test deposit. Image analysis techniques were developed to quantify particle size distributions within the deposit. Flume sidewall and internal observations were found to differ significantly from each other, in that side wall observations contained significantly higher proportions of the largest particle size. Additional replicate tests were conducted with saturated material to further examine the impact of pore fluid on segregation. This work will allow for future calibration of both numerical and theoretical models of particle size segregation and ultimately enable better debris flow modelling and mitigation practices.

How to cite: Kimball, J., Bowman, E., Gray, N., and Take, A.: Assessing Experimental Methods for the Quantification of Particle Size Segregation in Large Scale Flume Tests using Image Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10517, https://doi.org/10.5194/egusphere-egu23-10517, 2023.

15:05–15:15
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EGU23-385
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GM2.8
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ECS
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Highlight
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On-site presentation
Xiuqi Wang, Geert Campmans, Thomas Weinhart, Anthony Thornton, Stefan Luding, and Kathelijne Wijnberg
In coastal areas, aeolian sediment transport could show significant spatio-temporal variability as a result of varying beach surface properties. The observed morphological patterns also vary with surface conditions. Surface moisture is one of the most important factors limiting the sediment transport process [1]. Moisture between the sand grains can influence both the mechanism of aerodynamic entrainment and the momentum transfer upon the collision between a saltating particle and the bed. Next to those, the saltation features are likely to be different from those in dry cases, hence different subsequent bed form patterns [2].
To understand the intrinsic variability of large-scale sediment transport on moist beach and the features of morphological processes, it is necessary to quantify the sediment transport properties on the grain scale first. From the information on the grain-scale dynamic behaviour, the up-scaling from discrete state of transport to a continuum description of bed forms could be realized through a novel transport formula. With this aim, this study investigates the effect of surface moisture on the grain-scale transport mechanism by CFD-DEM coupling. The open-source package MercuryDPM is used for DEM simulation [3]. This includes a 1D RANS model for air flow field calculation and a liquid bridge model that simulates the liquid between the particles. From this study, it is found that particles behave differently in the lift-off process by wind and collision process because of the cohesion induced by liquid bridge. The moisture could change the critical wind condition for transport initiation, as well as the cessation threshold for saturated transport to be sustained. The dependencies of transport rate on the wind strength and moisture level are studied as well.

(1) Ellis, J. T.; Sherman, D. J.; Farrell, E. J.; Li, B. Aeolian Research 2012, 3, 379–387.
(2) Swann, C.; Lee, D.; Trimble, S.; Key, C. Aeolian Research 2021, 51, 100712.
(3) Weinhart, T.; Orefice, L.; Post, M.; van Schrojenstein Lantman, M. P.; Denissen, I. F.; Tunuguntla, D. R.; Tsang, J.; Cheng, H.; Shaheen, M. Y.; Shi, H., et al. Computer physics communications 2020, 249, 107129.
 
 
 

How to cite: Wang, X., Campmans, G., Weinhart, T., Thornton, A., Luding, S., and Wijnberg, K.: Discrete element modelling of grain-scale aeolian sediment transport on moist beach surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-385, https://doi.org/10.5194/egusphere-egu23-385, 2023.

15:15–15:25
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EGU23-15236
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GM2.8
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ECS
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On-site presentation
Giovanni Di Lollo, Claudia Adduce, Moisés Brito, Rui M.L. Ferreira, and Ana Ricardo

ABSTRACT: Gravity currents are flows generated by density differences within two contacting fluids. In this work the interaction between lock-release gravity currents propagating over a horizontal rectangular channel and an emergent cylinder is analyzed through velocity measurements obtained through PIV. Two-dimensional instantaneous velocity fields are measured in a plane perpendicular to the bottom along the center axis of the channel upstream of the obstacle. The experiments were also conducted without the cylinder for comparison purposes and ten repetitions were carried out for each configuration. The analyses focus on the effects that the presence of an adverse pressure gradient has on both the mean velocity field and the turbulence of the leading part of the current, the head, before the impact. The mean velocity field is not affected by the presence of the obstacle and since no differences were found in the spatial distribution of the mean velocity components, the necessary cylinder-induced deceleration occurs uniformly. Turbulence is studied through the components of the Reynolds stress tensor and their fluxes within the head. In the configuration with the cylinder, there are no fluxes of Reynolds stresses in the inner part of the section. Consequently, the Reynolds stress intensity decreases inside the head compared to the configuration without the obstacle. In conclusion, the presence of an adverse pressure gradient stops the mechanism of Reynolds stress distribution from the main source of production, i.e. the front region, to the inner region of the flow. This leads to a decrease in Reynolds stresses in the inner part of the head and an increase in the frontal region.

Acknowledgements: This work was partially supported by Foundation for Science and Technology's through funding UIDB/04625/2020 (CERIS research unit).

Keywords: Gravity currents, lock release, Particle Image Velocimetry, adverse pressure gradient, Reynolds stress.

How to cite: Di Lollo, G., Adduce, C., Brito, M., Ferreira, R. M. L., and Ricardo, A.: Reynolds stresses in gravity currents approaching an obstacle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15236, https://doi.org/10.5194/egusphere-egu23-15236, 2023.

15:25–15:35
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EGU23-14619
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GM2.8
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Virtual presentation
Manousos Valyrakis and Yi Xu

The risk of scour of hydraulic infrastructure, such as bridge piers and abutments, may considerably rise during extreme weather events. The removal of coarse bed material and consequent critical failure of the riverbed surface layer's protective layer against scour can result from sufficiently energetic flow structures, which normally scale with their cross-sectional lengthscale [1] (typically a naturally formed armour layer or implemented rip-rap protection, comprising of cobbles and rocks). This study intends to directly monitor the likelihood of entrainment of an instrumented particle [2] that is properly positioned on the riverbed surface near a bridge pier, in order to evaluate the probability of critical failure of the scour protection layer. By directly observing (visually with an underwater camera) as well as monitoring with inertial sensors within the instrumented particle its likelihood of being entrained, this study seeks to evaluate and validate the risk of a critical failure of the scour protection layer close to build hydraulic infrastructure (here, a model bridge pier). As the physical model of a bridge pier is laid downstream, a series of flume experiments (four flow rates) are conducted under carefully controlled flow conditions to evaluate the change in entrainment frequencies of the instrumented particle. The experimentally obtained highly resolved (at 200Hz) time series of the instrumented particle's entrainment, are validated with the camera placed underwater, for the various flow conditions. The instances of instrumented particle entrainment - from which the rate of entrainment is found (matching the probability of bed surface destabilization [3]) - are derived from the analysis of fused raw data from the calibrated embedded sensors (accelerometer, magnetometer, and gyroscope) to identify entrainment events. Acoustic Doppler velocimetry (ADV) under proper configurations [4], is used to collect flow profiles at various distances downstream of the model pier in an initial effort to connect the local and dynamic driving processes for particle entrainment to the phenomenologically significant bulk flow and pier characteristics (such as pier lengthscale, average flow velocity and depth, the median size of armour layer particles). In order to examine the incipient destabilization of riverbed material, typically leading to the disruption of the bed surface protective layer and catastrophic scour, this research effectively demonstrates the employment of purpose designed instrumented particles, showcasing it as a method that is affordable, non-intrusive, long-lasting, and with readily accessible results.

 

References

  • 1. Xu, Y., Valyrakis, M., Gilja, G., Michalis, P., Yagci, O., Przyborowski, L. (2022). Assessing riverbed surface destabilization risk downstream isolated vegetation elements, Water, 14(18):2880. DOI: 10.3390/w14182880.
  • 2. AlObaidi, K., Valyrakis, M. (2021). A sensory instrumented particle for environmental monitoring applications: development and calibration, IEEE Sensors, 21(8), pp.10153-10166, DOI: 10.1109/JSEN.2021.3056041.
  • 3. AlObaidi, K., Valyrakis, M. (2021). Linking the explicit probability of entrainment of instrumented particles to flow hydrodynamics, Earth Surface Processes and Landforms, 46(12), pp. 2448-2465 DOI: 10.1002/esp.5188.
  • 4. Liu, D., AlObaidi, K., Valyrakis, M. (2022). The assessment of an Acoustic Doppler Velocimetry profiler from a user’s perspective, Acta Geophysica, 70, pp. 2297-2310. DOI: 10.1007/s11600-022-00896-3.

How to cite: Valyrakis, M. and Xu, Y.: Using instrumented particles for monitoring the likelihood of bridge scour protection destabilization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14619, https://doi.org/10.5194/egusphere-egu23-14619, 2023.

Posters on site: Fri, 28 Apr, 16:15–18:00 | Hall X3

Chairpersons: Gordon Gilja, Rui Miguel Ferreira, Thomas Pähtz
X3.9
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EGU23-14688
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GM2.8
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ECS
Yulan Chen, Thomas Pähtz, and Katharina Tholen

Most aeolian sand transport models incorporate a so-called “splash function” that describes the number and velocity of particles ejected by the splash of an impacting particle. It is usually obtained from experiments or simulations in which an incident grain is shot onto a static granular packing. However, it has recently been discovered that, during aeolian sand transport, the bed cannot be considered as static, since it cannot completely recover between successive impacts. This leads to a correction of the splash function accounting for cooperative effects, which is responsible for an anomalous third-root scaling of the sand flux with the particle-fluid density ratio s [1]. Here, we present a two-species saltation model that incorporates this correction. In contrast to the model by [1], it does not only quantitatively reproduce sand fluxes but also transport thresholds from measurements and discrete element method-based sand transport simulations across several orders of magnitude of s.

[1] Tholen, Pähtz, Kamath, Parteli, Kroy, Anomalous scaling of aeolian sand transport reveals coupling to bed rheology, Physical Review Letters, accepted.

How to cite: Chen, Y., Pähtz, T., and Tholen, K.: A two-species model of aeolian saltation incorporating cooperative splash, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14688, https://doi.org/10.5194/egusphere-egu23-14688, 2023.

X3.10
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EGU23-16245
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GM2.8
Thomas Pähtz, Katharina Tholen, Sandesh Kamath, Eric Parteli, and Klaus Kroy

Authors: Thomas Pähtz, Katharina Tholen, Sandesh Kamath, Eric Parteli, Klaus Kroy

Title: Anomalous scaling of aeolian sand transport reveals coupling to bed rheology

Predicting transport rates of windblown sand is a central problem in aeolian research, with implications for climate, environmental, and planetary sciences. Though studied since the 1930s, the underlying many-body dynamics is still incompletely understood, as underscored by the recent empirical discovery of an unexpected third-root scaling in the particle-fluid density ratio [1]. Here, by means of grain-scale simulations and analytical modeling, we elucidate how a complex coupling between grain-bed collisions and granular creep within the sand bed yields a dilatancy-enhanced bed erodibility. Our minimal saltation model robustly predicts both the observed scaling and a new undersaturated steady transport state that we confirm by simulations for rarefied atmospheres [2].

[1] Pähtz, Durán, Scaling laws for planetary sediment transport from DEM-RANS numerical simulations, https://arxiv.org/abs/2203.00562

[2] Tholen, Pähtz, Kamath, Parteli, Kroy, Anomalous scaling of aeolian sand transport reveals coupling to bed rheology , Physical Review Letters, accepted.

How to cite: Pähtz, T., Tholen, K., Kamath, S., Parteli, E., and Kroy, K.: Anomalous scaling of aeolian sand transport reveals coupling to bed rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16245, https://doi.org/10.5194/egusphere-egu23-16245, 2023.

X3.11
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EGU23-16037
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GM2.8
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ECS
Ana Margarida Bento, Luís Mendes, and Rui Ferreira

Scour monitoring in experimental environments relies primarily on visual point-wise measurements that may provide less accurate estimates of scour and its effects. To fulfil these issues many studies and methods has been developed to analyse scour surfaces. Recently, the use of 3D point clouds and digital elevation models has proven to be an effective method for describing scour around bridge foundations with a high degree of accuracy. This is especially true under drained conditions. Therefore, it has become necessary to develop a system that can continuously monitor the development of scour at bridge foundations without interrupting the flow. 

Few studies have addressed continuous monitoring of the scouring process. These include: (i) photogrammetry-based methods using two cameras and algorithms for image calibration, rectification, and stereo-triangulation, and (ii) a laser-based approach using both a laser source and a camera. As a result of these studies, further researches need to be developed in order to effectively monitor scouring process by using the increasing technology of submersible cameras and underwater processing capabilities. In this study, a novel method for acquiring 2D scour profiles was developed to enable continuous monitoring of the scour phenomenon. The developed technique uses a computer vision technique, namely homography transformation, which relates the coordinates of points in one image to the coordinates of corresponding points in another image through a Python routine. This algorithm also considered the critical issues inherent in any underwater image processing technique, such as correcting for perspective, distortion, scaling, and camera lens rotation. 

In the laboratory, four cameras were used to collect synchronized underwater images of the scour holes formed and the affected surrounding areas around an oblong bridge pier model due to the local scour phenomenon. By processing each image sequence and running the Python code to measure the depth of the border line between the sand and the bridge foundation model at specific times during the scouring experiment, it was possible to obtain the evolution of the scour holes in the form of 2D bed profiles. The accuracy of the developed algorithm to study the bed morphology in the vicinity of bridge piers during the scouring process showed promising results compared to point-wise scour depth measurements.

This work was partially funded by the Portuguese Foundation for Science and Technology (FCT) through Project DikesFPro PTDC/ECI-EGC/7739/2020 and through CERIS funding UIDB/04625/2020.

How to cite: Bento, A. M., Mendes, L., and Ferreira, R.: Homography-based continuous bridge scour depth estimation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16037, https://doi.org/10.5194/egusphere-egu23-16037, 2023.

X3.12
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EGU23-2197
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GM2.8
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ECS
Yufang Ni

As different from traditional large dams, the hydraulic lifting dam is a kind of low-head movable weir, which can be partly lifted to impede water while the rest part of the weir collapsed to surpass water, resulting in a rather complicated terrain. Therefore, the flow structure around a hydraulic lifting dam might become complex and highly three-dimensional (3D). Generally, depth-averaged two-dimensional (2D) models are employed in the prediction of riverine morphodynamic processes. However, in the vicinity of a hydraulic lifting dam, the 2D models not only lose the turbulence details, but also neglect the impacts of turbulence on sediment transport and hence bed deformation. Here, a comparison study is conducted by using a 2D and a 3D model, respectively. The 2D model is a validated depth-averaged hydro-sediment-morphodynamic model using Finite Volume Method on unstructured meshes. The 3D model adopts a Reynolds-averaged Navier-Stokes (RANS) based turbulence model or a delay detached eddy simulation (DDES) model under the framework of OpenFOAM. The results show that the flow details, which cannot be reproduced by a 2D model, have a great potential of modifying the morphodynamic processes, so a 3D model is desperately required for resolving flow structure as well as sediment transport and morphological changes in the vicinity of a hydraulic lifting dam.

How to cite: Ni, Y.: Flow structure around a hydraulic lifting dam and its implication for sediment transport and morphological changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2197, https://doi.org/10.5194/egusphere-egu23-2197, 2023.

X3.13
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EGU23-6811
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GM2.8
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ECS
Antonija Harasti and Gordon Gilja

This paper investigates effect of scour adjacent to the bridge piers with installed riprap as the scour countermeasure. A riprap sloping structure is a conical placement of launchable stones around the bridge pier commonly used as erosion protection. Riprap sloping structure affects the flow in similar manner to groynes, shifting the scour hole downstream of the toe of the structure. Assuming that the installation of the riprap erosion protection deflects the scour hole development downstream of the bridge, experimental model is developed to represent natural environment under different flow scenarios. The 3D model requires calibration of numerical parameters to accurately simulate the prototype conditions – e.g. cell mesh size, turbulence model, and roughness associated with natural riverbed and the riprap sloping structure. Calibration of the Flow-3D numerical model was performed against the flow measurements conducted during field campaign. Flow measurements were collected using Acoustic Doppler current profiler on 20 transects along the river section adjacent to the bridge. Two independent surveys were conducted: for 30 % flow duration and 60 % flow duration (mean flow conditions). After obtaining the results, cross-sectional velocities were analyzed in 3 characteristic transects (upstream, downstream and at the bridge opening). Finally, good agreement was achieved between the model and measured flow field across all transects, enabling numerical setup to be reliable for simulating rare flood events, and associated scour development.

 

Acknowledgments:

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

How to cite: Harasti, A. and Gilja, G.: Simulation of equilibrium scour hole development around riprap sloping structure using the numerical model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6811, https://doi.org/10.5194/egusphere-egu23-6811, 2023.

X3.14
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EGU23-11405
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GM2.8
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ECS
Armano Cibaric, Nikola Troskot, Maja Veseljak, Mateja Vukovac, and Gordon Gilja

Bridges with elements interacting the flow, such as piers constructed in the main river channel or approach embankments blocking the overbanks, alter the flow conditions and initiate local and contraction scour in the bridge profile. Scour countermeasures are often placed around the bridge piers with goal to scour and associated risk of bridge failure. Effectiveness of scour countermeasures depend on its influence on the surrounding riverbed – in case that countermeasures obstruct significant area, flow can be concentrated and accelerated, inducing scour of the banks. Long-term effects of the scour countermeasures on the river morphology can lead to flow redistribution and lateral shifting of the river cross-section, altering the design conditions in the bridge vicinity. Aim of this work is to compare the flow environment at 4 distinctive bridge locations simulated in HEC-RAS model under characteristic hydraulic scenarios that induce scour. Results show that for all bridges current flow environment differs from the design state, so that additional intervention in the riverbed geometry doesn’t significantly change the flow conditions. Flow environment was simulated with sill placed on different distances downstream or excavation of the riverbed to reduce flow velocity. In all scenarios main flow remain concentrated similar to the current state, showing that countermeasures have to be substantial in order to be effective.

 

Acknowledgments

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

How to cite: Cibaric, A., Troskot, N., Veseljak, M., Vukovac, M., and Gilja, G.: Flow pattern around the bridge piers with installed scour countermeasures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11405, https://doi.org/10.5194/egusphere-egu23-11405, 2023.

X3.15
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EGU23-11685
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GM2.8
Gordon Gilja, Luka Drandić, Robert Fliszar, and Antonija Harasti

Rapid development of the instantaneous flow velocity instruments allows for high frequency measurement of turbulent flow field in the hydraulic flume. To obtain accurate and reliable flow measurement it is necessary to correctly configure the instrument using the manufacturer’s general guidelines. When instruments are used in highly turbulent flows, such as flows around bridge piers, selection of parameters is not straightforward and it generally requires validation against known data. In this study, experimental flow velocity data was collected in the hydraulic flume at three characteristic cross-sections – bridge profile, and upstream, and downstream profile. Velocity was measured on 10 points for each cross-section using Nortek Vectrino Profiler. Velocity measurements were processed to calculate turbulent kinetic energy at discrete points, after which TKE map was interpolated over the entire cross-section using QGIS. Results of TKE maps are compared for two characteristic flow rates and changes in TKE distribution respective to the flow downstream analyzed to quantify influence of the bridge pier and scour protection on the flow in the bridge vicinity.

 

Acknowledgments

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

How to cite: Gilja, G., Drandić, L., Fliszar, R., and Harasti, A.: Experimental study of turbulent kinetic energy of flow over scoured riverbed, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11685, https://doi.org/10.5194/egusphere-egu23-11685, 2023.

Posters virtual: Fri, 28 Apr, 16:15–18:00 | vHall SSP/GM

Chairpersons: Gordon Gilja, Rui Miguel Ferreira, Thomas Pähtz
vSG.1
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EGU23-9197
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GM2.8
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ECS
Zaid Alhusban, lorenzo rovelli, and Andreas Lorke

When it comes to plastic manufacturing worldwide, more than half of what is produced gets dumped into the world's oceans and rivers. The rivers are the primary pathways for plastics to reach the seas. The infiltration behavior of plastic particles into mobile sediment beds (coarse sand) with median diameters (d50) between 0.4 and 0.8 mm was studied using flume experiments with varying plastic particle parameters (such as density and size) under a variety of controlled hydraulic settings.

The results are thought to be very useful for improving our understanding of and research into how microplastic particles with different characteristics infiltrate into rivers and streams (in mobile beds) with different bedload rates and stay there. The findings showed that microplastic particles were present in both the stationary and mobile sediment layers of the moving sandy bedforms. The number of particles that infiltrate into the sediment is influenced by particle sizes, densities, and bedform characteristics. In general, it was found that the distributions of microplastic particles of different types and sizes in migrating sandy sediment were heterogeneous, although certain trends could be seen, such as a reduction in infiltration rate and average infiltration depth with increasing bedform celerity. Higher infiltration depths and infiltration percentages are also seen for denser and smaller particles. Additionally, the ratio of infiltrated particles in stationary layers of bedforms to total infiltrated (%) decreases as bedform celerity increases. Using the project's findings, future research and numerical modeling studies on plastic particles' accumulation, distribution, and pathways will be able to inform better decisions about how to clean up future microplastic sediment pollution, as well.

 

How to cite: Alhusban, Z., rovelli, L., and Lorke, A.: Studying the effect of moving sandy bedforms on the infiltration behavior of microplastic particles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9197, https://doi.org/10.5194/egusphere-egu23-9197, 2023.

vSG.2
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EGU23-15846
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GM2.8
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ECS
Yi Xu and Manousos Valyrakis

One of the main causes of destabilizing bridge piers has been identified as the process of scour due to the action of the turbulent flows around them, rendering it as one of the most frequent and costly infrastructure failure events all around the world. The challenge of scour-induced catastrophes will keep increasing, affecting the resilience of our society, as extreme weather intensifies affecting the exposed hydraulic infrastructure, such as bridge piers, abutments and spur dikes [1], and aquatic vegetation [2, 3]. Therefore, research into the highly dynamic scour processes that surround hydraulic infrastructure is becoming increasingly valuable. Researchers have investigated maximum scour depth estimation extensively over the past few decades, combining mean flow parameters, bridge pier, and riverbed materials characteristics using phenomenological or empirical methodologies. The precise cause of the formation and amplification of scour-holes that result in bridge pier failure are yet unknown. This study's main goal is to offer new insights on the dynamical interactions of flow structures shed downstream model bridge piers with bed surface particles, that are strong enough to remove them, thus causing the formation of scour holes. This study specifically intends to better understand the interactions between the coarse bed surface particles and the energetic events of the turbulent flow field, as modified by a cylindrical bridge pier. Extreme impulses (flow impulses above a critical impulse level [4]), are modelled using appropriately fitted probability density functions in order to generate new scour depth predictive equations. The tests are carried out in a research flume that circulates water under the same flow conditions using model bridge piers of various model pier diameters. High-resolution acoustic Doppler velocimetry is used to gather flow velocity profiles downstream of the bridge pier. The patterns of flow structures will change as the morphology of the riverbed next to a pier changes. Based on the velocity profiles captured by ADV, the study presents the variation in flow structures, including velocity (U), turbulence intensity, and turbulent kinetic energy (TKE), downstream of the four bridge pier diameters used in the experiments.

 

References

  • 1. Pandey, M., Valyrakis, M., Qi, M., Sharma, A., Lodhi, A.S. (2020). Experimental assessment and prediction of temporal scour depth around a spur dike, International Journal of Sediment Research, 36(1), pp.17-28, DOI: 10.1016/j.ijsrc.2020.03.015.
  • 2. Yagci O., Celik, F., Kitsikoudis, V., Ozgur Kirca, V.S., Hodoglu, C., Valyrakis, M., Duran, Z., Kaya S. (2016). Scour patterns around individual vegetation elements, Advances in Water Resources, 97, pp.251-265, DOI: 10.1016/j.advwatres.2016.10.002.
  • 3. Xu, Y., Valyrakis, M., Gilja, G., Michalis, P., Yagci, O., Przyborowski, L. (2022). Assessing riverbed surface destabilization risk downstream isolated vegetation elements, Water, 14(18):2880. DOI: 10.3390/w14182880.
  • 4. Valyrakis, M., Diplas, P., Dancey C.L. (2011). Entrainment of coarse grains in turbulent flows: an extreme value theory approach, Water Resources Research, 47(9), W09512, pp.1-17, DOI:10.1029/2010WR010236.

How to cite: Xu, Y. and Valyrakis, M.: Stochastic modelling of the extreme flow impulses leading to bridge pier scour, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15846, https://doi.org/10.5194/egusphere-egu23-15846, 2023.