GM – Geomorphology

GM1.1 – Frontiers In Geomorphology - Earth surface interactions, couplings and feedbacks

EGU22-4290 | Presentations | GM1.1 | GM Division Outstanding ECS Award Lecture 2020

Accounting for landslide-channel interactions in landscape evolution and hazards

Georgina Bennett

Landslides are prevalent in mountain landscapes and interact with the river network in a myriad of ways with impacts on flood and debris flow hazards and landscape evolution. Floods in mountainous regions often coincide with a high density of landslides triggered by heavy rainfall. However, the impacts of landslide-delivered sediment on flood dynamics are not typically considered in flood hazard assessment. Higher up in the river network, landslide sediment supply is a key component of debris flows. Yet, assessments of climate change impacts on debris flows to date have focused on likely changes in rainfall triggering potential of debris flows, overlooking the role of landslide sediment supply.

In a first case study, I demonstrate with an example from the Colorado Front Range how landslide-channel feedbacks can significantly amplify channel erosion and flood risk. We used a combination of field analysis and modelling with a multiphase flow model R.avaflow to test the hypotheses that landslide-flood interactions amplified channel erosion during a major flood event in 2013 by (1) bulking of the flow and (2) dam formation and failure dynamics.

In a second case study, I demonstrate with an example from the Swiss Alps, how landslide sediment supply limits debris flow hazard in a warming climate. We forced the sediment cascade model, SedCas, with climate simulations to disentangle the interactions between hydrological triggering, landslide sediment supply and elevation on mountain basin sediment transfer and debris flow hazard over the 21st century. 

How to cite: Bennett, G.: Accounting for landslide-channel interactions in landscape evolution and hazards, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4290, https://doi.org/10.5194/egusphere-egu22-4290, 2022.

EGU22-2798 | Presentations | GM1.1 | GM Division Outstanding ECS Award Lecture 2022

Coastal wetlands and seagrass dynamics with environmental change

Nicoletta Leonardi

Hard engineering solutions are becoming economically unviable due to the high costs of construction, maintenance and adaptation to changes in sea level and storms. ‘Engineering with Nature’ (including the creation of salt marshes, seagrass beds) offers a more economically viable alternative for coastal protection.

However, despite the growing recognition of the necessity to move towards this greener alternative for coastal protection, there are still large uncertainties about factors determining the resilience of these systems to environmental change. As a consequence of sea-level rise, and of the increased occurrence of extreme weather conditions, coastal habitats are at risk of degradation and possible recession.  Human interactions add a layer of complexity to natural processes. Among the others, the sediment delivery to coastal areas has significantly changed over the years, for instance due to changes in catchment management, with consequences for the resilience of coastal systems.

This work uses numerical models to investigate the morphological and hydrodynamic features of coastal systems with environmental change. These numerical tools consist of hydrodynamic models coupled with morphological and sediment transport modules. Results investigate feedbacks between the shape of existing shorelines, wetlands resilience and external forcing such as tidal currents and wind waves. Results provide information useful for the study and management of ‘Engineering with Nature’ interventions and highlights the importance of a whole-system approach for the correct management of coastal areas.

How to cite: Leonardi, N.: Coastal wetlands and seagrass dynamics with environmental change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2798, https://doi.org/10.5194/egusphere-egu22-2798, 2022.

GM2.1 – New approaches for monitoring and modelling sediment transport

EGU22-9016 | Presentations | GM2.1 | Highlight

Rocks and Rivers that Remember:  Using Smartrocks To Constrain Bedload Transport Statistics and Evolving Thresholds of Motion in Natural Mountain Rivers

Joel Johnson, Kealie Pretzlav, Lindsay Olinde, D. Nathan Bradley, and Claire Masteller

Instrumented “smartrock” tracer clasts hold the potential to quantify unique and useful sediment transport statistics from the point of view of each grain--a Lagrangian reference frame.  In this presentation we synthesize lessons learned based on two successful smartrock field deployments in natural mountain rivers during snowmelt floods. Our sensors contain accelerometers, data loggers and batteries.  We have primarily used smartrock data to simply measure the exact timing of grain rests and motions, although future analyses and additional sensors could be used to measure many more aspects of transport.  In addition to methodological suggestions and challenges, we show how smartrock data can be used to measure (a) rest and hop time scaling over a range of timescales, and (b) changes in thresholds of motion through time as a function of discharge.  In data from Halfmoon Creek, Colorado, USA, and Reynolds Creek, Idaho, USA, rest duration scaling is heavy-tailed and varies systematically with both timescale and shear stress.  The shear stress dependence suggests that bedload clast dispersal becomes less superdiffusive as flood size becomes larger. We identify several likely diffusion regimes, and hypothesize how timescales of flow variability from turbulence to daily discharge cyclicity may cause scaling breaks over minutes to hours.  In addition, thresholds of motion tend to increase with cumulative flow (reducing transport rates over time), but also decrease with increases in discharge (increasing transport rates until grains restabilize at the higher flow). The threshold data are used to calibrate and partially validate a new model for discharge-dependent threshold evolution. Finally, we brainstorm ways in which smartrocks could be used to explore sediment transport questions in other Earth surface environments.

How to cite: Johnson, J., Pretzlav, K., Olinde, L., Bradley, D. N., and Masteller, C.: Rocks and Rivers that Remember:  Using Smartrocks To Constrain Bedload Transport Statistics and Evolving Thresholds of Motion in Natural Mountain Rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9016, https://doi.org/10.5194/egusphere-egu22-9016, 2022.

EGU22-10289 | Presentations | GM2.1 | Highlight

SENSUM project, Smart SENSing of landscapes Undergoing hazardous hydrogeomorphic Movement

Kyle Roskilly, Georgina Bennett, Robin Curtis, Martina Egedusevic, Joshua Jones, Michael Whitworth, Benedetta Dini, Chunbo Luo, Irene Manzella, and Aldina Franco

An increase in storminess under climate change and population pressure are resulting in an increase in landslide and flood events, in the UK and globally, and threatening the defences put in place to mitigate these hazards. Monitoring of unstable hillslopes and flood-prone rivers as well as structures designed to protect these is vital. Furthermore, as landslides and floods are both triggered by heavy rainfall, often occurring simultaneously, and may interact to generate cascading hazards, we need integrated approaches for their management.

A key objective of the SENSUM project (Smart SENSing of landscapes Undergoing hazardous hydrogeomorphic Movement, https://sensum.ac.uk) is to develop a smart sensor to be embedded within boulder and wood debris in landslide and flood prone sites to detect and track hazardous movement. These low-power, low-cost devices communicate this in near real time via Internet of Things networks. Several wireless sensor networks (WSNs) have been installed on landslides and in flood-prone rivers around the UK, involving insertion of devices into debris, installation of long-range wireless network gateways, and camera installation for validation of movements. The developed system architecture also permits straightforward integration of additional third-party sensors and open data. We aim to build a dataset with which hazardous movement can be detected using machine learning and communicated in near real time via alerts and web services to relevant stakeholders. This effort will be complemented by laboratory experiments.

How to cite: Roskilly, K., Bennett, G., Curtis, R., Egedusevic, M., Jones, J., Whitworth, M., Dini, B., Luo, C., Manzella, I., and Franco, A.: SENSUM project, Smart SENSing of landscapes Undergoing hazardous hydrogeomorphic Movement, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10289, https://doi.org/10.5194/egusphere-egu22-10289, 2022.

The use of Inertial Measurement Units (IMUs) in geomorphological studies has exploded during the last decade. Scientists are deploying IMUs in a range of settings: from single grain flume experiments to full scale landslide motions and from capturing rock falls to measuring flows in glacial environments.

The vast majority of these experiments deploy sensing units that are partly customised for each application. However, there are limits to the level of IMU customisation geomorphologists can do as they rarely have access to bottom-up sensor assembly and production lines. Commercial IMUs and IMU components are built and calibrated for very different uses than the monitoring of dynamic sediment transport regimes, such as integration into electronic devices, wearables or Internet of Things applications.

Deploying commercial IMUs outside their nominal operational range has two main implications, the first being methodological. As the sensor is partly a "black box", we are obliged to do extensive testing in a trial-and-error manner and think deeply about the underlying physics of IMUs. If such difficulties are not acknowledged the results become difficult to interpret in the context of sediment movement.

The second implication concerns standardisation. The more our community uses commercial sensors and analytical tools, the more apparent becomes the need for open-source pre-processing and processing workflows that are fully validated and universally available to ensure comparability of published results.

This presentation aspires to contribute to this open debate about IMU sensors in geomorphology. The focus will be on the sensing requirements for grain motion detection, force capture and tracking by IMUs in the context of sediment transport. The presented calculations will use results published before the emergence of IMUs in geomorphology for a range of environments (fluvial, coastal, aeolian and glacial).

The above requirements capture will be accompanied by a meta-analysis of published IMU data in geomorphic applications which will be classified according to the exact type of sensor (accelerometer, full IMU, GPS (or equivalent)-aided IMU) and the sensors' specs (mainly sensing range and frequency).

Finally, this presentation will explore the case study of using a commercially available IMU for the capture of fluvial sediment interactions. The deployed IMU will be subjected to a series of simple physical experiments (e.g., drop tests) and then deployed to a flume setting designed to model grain-grain and grain-substrate collisions. The novelty here is the use of an independent very high-speed camera (1μs exposure frame rate) to monitor the sensor during calibration, which allows for the coherent propagation of uncertainty for all the experiments. All the results are presented within a processing workflow based on free, open-source R libraries.

How to cite: Gadd, C. and Maniatis, G.: Smart-pebbles in sediment transport studies: state of the art, future directions, and unsolved problems., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8757, https://doi.org/10.5194/egusphere-egu22-8757, 2022.

EGU22-10198 | Presentations | GM2.1

Investigating boulder motions with smart sensors in lab experiments

Alessandro Sgarabotto, Irene Manzella, Kyle Roskilly, Chunbo Luo, Miles Clark, Aldina M. A. Franco, Georgina L. Bennett, and Alison Raby

Events such as landslides, rockslides, debris flows, and flash floods can have destructive and possibly fatal outcomes. In these events, boulders and cobbles are carried downstream under the action of gravity and the study of their transport and movement can give important insight on the dynamics and hazards related to these processes. Recently, boulder motion has been investigated by the use of smart sensors in geomorphology applications both in lab and field experiments. Smart sensors are small and light-weighted devices that are able to collect different environmental data with low battery consumption communicating to a server through a wireless connection. However, the reliability of smart sensors still needs to be evaluated for monitoring purposes and for developing early warning systems.

In the present study, dedicated laboratory experiments were designed to assess the ability of the sensors to detect movements and distinguish between intensity and type of movement (e.g. sliding or rolling) within a well-constrained setting. For this purpose, a tag equipped with an accelerometer, a gyroscope, and a magnetometer sensor has been installed inside a cobble of 10.0 cm diameter within a borehole of 4.0 cm diameter, closed hermetically before each experiment. The experiments consisted in letting the cobble fall on an experimental table composed of an inclined plane of 1.5 m, followed by a horizontal one of 2.0 m. The inclined plane can be tilted at different angles (18˚- 55˚) and different types of movement have been generated by letting the cobble roll, bounce, or slide. Sliding was generated by embedding the cobble within a layer of sand. The position of the cobble travelling down the slope was derived from camera videos by a tracking algorithm developed within the study.

Raw sensor data allowed detection of movement and separation of two modes of movement, namely rolling and sliding. Furthermore, raw datasets approximated the magnitude of movement even without any calibration. On the other hand, by coupling smart-sensor measurements and camera-based positions, it was possible to develop a filter to derive reliable values for the position, orientation, velocity, and acceleration to fully represent cobble motions. These findings show how the raw data can provide information about the type and an indication of the magnitude of movement, and confirm the potential to use these sensors to improve early warning systems, although further studies are in progress to assess response time in a field setting. At the same time, the development of a filter that gives more precise and reliable data from the sensors enables assessment of the rotational and linear acceleration of the tracked element. If used in more sophisticated lab and field experiments, this has the potential to give new insights on the behaviour of cobbles within different types of processes and can shed new light on the dynamics of complex hazardous flows.

How to cite: Sgarabotto, A., Manzella, I., Roskilly, K., Luo, C., Clark, M., Franco, A. M. A., Bennett, G. L., and Raby, A.: Investigating boulder motions with smart sensors in lab experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10198, https://doi.org/10.5194/egusphere-egu22-10198, 2022.

EGU22-6075 * | Presentations | GM2.1 | Highlight

How does Coastal Gravel get Sorted under Stormy Longshore Transport?

Haggai Eyal, Yehouda Enzel, Eckart Meiburg, Bernhard Vowinckel, and Nadav G Lensky

Storm waves transport and sort coarse gravel along coasts. This fundamental process is important under changing sea-levels and increased storm frequency and intensity. However, limited information on intra-storm clast motion restricts theory development for coastal gravel sorting and coastal management of longshore transport. Here, we use ‘smart boulders’ equipped with loggers recording underwater, real-time, intra-storm clast motion, and measured longshore displacement of varied-mass marked boulders during storms. We utilize the unique setting of the Dead Sea shores where rapidly falling water levels allow isolating boulder transport during individual storms. Guided by these observations, we develop a new model quantifying the critical wave height for a certain clast mass mobilization. Then, we obtain an expression for the longshore clast displacement under the fluid-induced pressure impulse of a given wave. Finally, we formulate the sorting enforced by wave-height distributions during a storm, demonstrating how sorting is a direct manifestation of regional hydroclimatology.

How to cite: Eyal, H., Enzel, Y., Meiburg, E., Vowinckel, B., and G Lensky, N.: How does Coastal Gravel get Sorted under Stormy Longshore Transport?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6075, https://doi.org/10.5194/egusphere-egu22-6075, 2022.

EGU22-8642 | Presentations | GM2.1

Monitoring the stability of leaky dams and their influence on debris transport with innovative sensor technology on the SENSUM project

Martina Egedusevic, Georgina Bennett, Kyle Roskilly, Alessandro Sgarabotto, Irene Manzella, Alison Raby, Sarah J. Boulton, Miles Clark, Robin Curtis, Diego Panici, and Richard E Brazier

Woody debris dams/leaky dams are an increasingly popular Natural Flood Management (NFM) measure in low order tributaries, with preliminary evidence suggesting that they are effective in attenuating flood peaks and reducing flood risk. However, the stability of these dams is not widely monitored, and thus there is a poor evidence base for best design practice with respect to the long-term integrity of such features. This is particularly pertinent given the threat posed to downstream infrastructure by woody debris carried in floodwaters after potentially catastrophic dam failure. There is also a lack of research into how effective dams of different designs are at holding back large wood and sediment transported by the flow and reducing the impact of flood debris on downstream infrastructure, including bridges, culverts etc. In the SENSUM project (Smart SENSing of landscapes Undergoing hazardous hydrogeomorphic Movement, https://sensum.ac.uk), we are developing and applying innovative sensor technology to assess the stability of different woody debris dam designs and build an evidence base to inform policy on this NFM practice locally and nationally. We also use these sensors to track woody debris and assess how effective dams are at trapping and retaining large wood debris and cobble-sized sediment. This paper addresses these questions at several field sites across the UK and in laboratory experiments to report quantitative data which evaluate the literal success/failure of NFM interventions and how these may impact the future design of such approaches.

How to cite: Egedusevic, M., Bennett, G., Roskilly, K., Sgarabotto, A., Manzella, I., Raby, A., Boulton, S. J., Clark, M., Curtis, R., Panici, D., and Brazier, R. E.: Monitoring the stability of leaky dams and their influence on debris transport with innovative sensor technology on the SENSUM project, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8642, https://doi.org/10.5194/egusphere-egu22-8642, 2022.

EGU22-2894 | Presentations | GM2.1

Capturing the Influence of Large Wood on Fluvial Bedload Transport with RFID Tracers and Linear Mixed Modelling

Miles Clark, Georgina Bennett, Sandra Ryan, David Sear, and Aldina Franco

Bedload transport is a fundamental process by which coarse sediment is transferred through landscapes by river networks and may be well described stochastically by distributions of grain step length and rest time obtained through tracer studies. To date, none of these published tracer studies have specifically investigated the influence of large wood in the river channel on distributions of step length or rest time, limiting the applicability of stochastic sediment transport models in these settings. Large wood is a major component of many forested rivers and is increasing due to anthropogenic ‘Natural Flood Management’ (NFM) practices. This study aims to investigate and model the influence of large wood on grain-scale bedload transport. 

We tagged 957 cobble – pebble sized particles (D50 = 73 mm) and 28 pieces of large wood (> 1 m in length) with RFID tracers in an alpine mountain stream. We monitored the transport distance of tracers annually over three years, building distributions of tracer transport distances. Empirical data was used in linear mixed modelling (LMM) statistical analysis, determining the relative influence proximity to wood had on likelihood of entrainment, deposition, and the transport distances of sediments. 

Tracer sediments accumulated both up and downstream of large wood pieces, with LMM analysis confirming a reduction in the probability of entrainment of tracers closer to wood in all three years. Upon remobilisation, tracers entrained from positions closer to large wood had shorter subsequent transport distances in each year. In 2019, large wood also had a trapping effect, significantly reducing the transport distances of tracer particles entrained from upstream, i.e. forcing premature deposition of tracers. This study demonstrates the role of large wood in influencing bedload transport in alpine stream environments, with implications for both natural and anthropogenic addition of wood debris in fluvial environments.

How to cite: Clark, M., Bennett, G., Ryan, S., Sear, D., and Franco, A.: Capturing the Influence of Large Wood on Fluvial Bedload Transport with RFID Tracers and Linear Mixed Modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2894, https://doi.org/10.5194/egusphere-egu22-2894, 2022.

EGU22-9698 | Presentations | GM2.1

Tracing sediment movement using Infra-Red Stimulated Luminescence

Tessa M. C. Spano, Edward J. Rhodes, and Rebecca A. Hodge

Understanding sediment transport dynamics is key to understanding landscape evolution, and has important implications for engineering projects, aquatic ecosystem dynamics, and transmission of water-borne diseases. Multiple elevated temperature infra-red stimulated luminescence (MET-IRSL) has great potential to provide detailed information on the transport of sediments using infra-red light to stimulate the luminescence signal of feldspars. MET-IRSL uses a series of elevated temperature stimulations to access multiple signals with different characteristic rates of signal reduction by light exposure (bleaching), for example, during grain transport. During deposition and storage, trapped charge accumulates, leading to growth of the different IRSL signals, until the grain is again subject to transport. Applied in this manner, MET-IRSL measurements can constrain past sediment burial and exposure histories.

MET-IRSL measurements of different grain and clast sizes (e.g. silt, sand, pebbles and cobbles) can provide a range of sediment transport information, providing further constraint to sediment dynamics and system behaviour. Different clast size groups are associated with varied ways to structure the MET-IRSL measurements, e.g. depth bleaching profiles observed within pebbles and cobbles. In this presentation we demonstrate the potential of combining these approaches, and of constructing time-space equivalence models for real world situations, including the site of Allt Dubhaig, Perthshire, Scotland.

How to cite: Spano, T. M. C., Rhodes, E. J., and Hodge, R. A.: Tracing sediment movement using Infra-Red Stimulated Luminescence, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9698, https://doi.org/10.5194/egusphere-egu22-9698, 2022.

EGU22-13073 | Presentations | GM2.1

From sediment images to travel distances: an estimation of expected accuracy

Alessandro Cattapan, Paolo Paron, and Mário J. Franca

EGU22-7639 | Presentations | GM2.1

Video-Imagery Analysis of Aeolian Sand Transport over a Beach

Andreas Baas

Sand transport by wind displays dynamic structure and organisation in the form of streamers (aka ‘sand snakes’) that appear, meander and intertwine, and then dissipate as they are advected downwind. These patterns of saltating grain populations are thought to be initiated and controlled by eddies in the turbulent boundary layer airflow that scrape over the bed surface raking up sand into entrainment. Streamer behaviour is thus fundamental to understanding sand transport dynamics, in particular its strong spatio-temporal variability, and is equally relevant to granular transport in other geophysical flows (fluvial, submarine).

This paper presents findings on sand transport rates and streamer dynamics observed in a field experiment on a beach, by analysing imagery from 30Hz video footage, combined with 50Hz sand transport data from laser particle counters (‘Wenglors’), all taking place over an area of ~10 m2 and over periods of several minutes.

Mapping of streamers and saltation cloud density is compared with fluctuations in sand transport rate measured at the Wenglors. Large-Scale Particle Image Velocimetry (LSPIV) is applied to determine advection vectors that can be matched against in-situ measurements of airflow and sand transport. Analysing video-imagery of aeolian sand transport faces several challenges, however, most notably the difficulties of background subtraction to differentiate the moving streamers from the underlying beach surface.

How to cite: Baas, A.: Video-Imagery Analysis of Aeolian Sand Transport over a Beach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7639, https://doi.org/10.5194/egusphere-egu22-7639, 2022.

EGU22-10761 | Presentations | GM2.1

Disco Gravel: Image-based bedload tracking in shallow water flume experiments

Fatemeh Asal Montakhab, Megan Iun, and Bruce MacVicar

Previous experiments on the restoration of sediment cover in semi-alluvial channels with irregular boundaries have shown that coarse size fractions of the bedload are dispersed faster over a bare bed than the finer fractions, and that the coarse fraction helps to build a set of skeleton bars that are later covered by finer sediment. Unsteady flow experiments in the same channel confirmed these trends over a bed of mobile sediment and further indicate strong spatial gradients in bedload transport and deposition. Despite these advances, a methodological gap remains in the tracking of bedload sediment during the experiments. In this study we advance a tracking technique for obtaining vectors of particle displacements during unsteady flow experiments. Methods involve painting the coarsest three sediment fractions with different colours of fluorescent paint and illuminating a region of interest within the flume with ultraviolet lights (wavelength 400-410 nm) during the experiment, which results in the painted gravel appearing in bright neon colors while the water remains transparent and dark (i.e. the ‘Disco’). We use a Panasonic BGH1 camera recording at 60 fps and a resolution of 1080 x 1920 pixels to film a region of interest in the channel roughly 0.25 m wide 1.0 m long.  With this technique we are able to identify the displacements of the two coarsest size fractions. For the third size fraction the tracers were too numerous and too small to be tracked with confidence. Analysis of the videos occurred in three steps: 1) color segmentation to isolate the size class of interest, 2) application of TracTrac algorithm (Heyman, 2019) to identify particle paths, and 3) post-processing to reduce two types of error.  The errors are likely related to the irregular water surface, which can result in particles appearing to ‘vibrate’ in place when they are not moving, and also result in a continuous tracer path being broken into a series of shorter discontinuous paths.  Overall the technique appears to be useful for characterizing spatial variability at the threshold of motion and delimiting preferential transport pathways. Future improvements in resolution and tracer concentration should help to reduce the minimum size of tracer that can be tracked with confidence.

How to cite: Montakhab, F. A., Iun, M., and MacVicar, B.: Disco Gravel: Image-based bedload tracking in shallow water flume experiments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10761, https://doi.org/10.5194/egusphere-egu22-10761, 2022.

EGU22-2505 | Presentations | GM2.1

Multi-river Calibration Curve for Passive Acoustic Bedload Transport Monitoring.

Mohamad Nasr, Thomas Geay, Sébastien Zanker, and Alain Recking

Bedload transport estimation is required for a variety of engineering and ecological applications. Measurement of bedload transport by direct sampling is expensive and time-consuming and rarely captures the spatio-temporal variability of bedload transport. Recent research shows that passive acoustic technology, such as hydrophone, has the potential to monitor bedload transport by recording Self Generated Noise (SGN) resulting from particles collision. In this work, we present a calibration curve relating specific bedload flux to cross-sectional acoustic power for 40 experiments conducted on 13 French rivers. We present the measurement protocols for bedload transport and SGN, the results of the campaign, and discuss the physics of the relationship between the measured quantities.

How to cite: Nasr, M., Geay, T., Zanker, S., and Recking, A.: Multi-river Calibration Curve for Passive Acoustic Bedload Transport Monitoring., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2505, https://doi.org/10.5194/egusphere-egu22-2505, 2022.

EGU22-6702 | Presentations | GM2.1

An acoustic model for monitoring bedload transport with microphones array

Zheng Chen, Siming He, Tobias Nicollier, Lorenz Ammann, Alexandre Badoux, and Dieter Rickenmann

Accurate measurements of bedload flux in mountain rivers remain an important issue in hydraulic engineering. Diverse acoustic-based monitoring devices have been utilized to record continuous vibration signals triggered by bedload particle impacts, aiming to translate bedload information such as transport rates and grain size distributions from the generated signals. However, the spatial variability of bedload impacts on the river bed (or on an impact plate) contributes to uncertainty in the calibration relationship between the recorded signal and bedload flux.

The present study develops an acoustic model based on microphone data to determine the characteristics of the air shock waves induced by the bedload particle impacts on the bed. A phased microphone array (PMA) system is established on the plane underside of an impact plate flush with the river bed, which includes a number of mini microphone elements set apart from each other at a specific spacing distance. The model allows for a calculation of the cross-power matrix of the air vibrations recorded by each microphone of the array. The acoustic vibrations recorded on the PMA plane are subsequently reconstructed and transformed to an acoustic image of the sound source on a scanning plane of the plate surface, considering different air propagation models corresponding to monopole, multipole and moving sources. As a result, the locations of the bedload particle impacts can be detected, connecting to the central coordinates of the reconstructed sound source. The signal amplitude extracted from the sound intensity in the reconstructed acoustic image potentially provides a better way for classifying bedload particle size than just utilizing the raw data recorded by one of the microphone elements.

The findings of this study contribute to the measurement and monitoring of the bedload transport with an acoustic system, illustrating a promising way to identify bedload impact locations, which could be helpful in grain size classification during the transport process.

How to cite: Chen, Z., He, S., Nicollier, T., Ammann, L., Badoux, A., and Rickenmann, D.: An acoustic model for monitoring bedload transport with microphones array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6702, https://doi.org/10.5194/egusphere-egu22-6702, 2022.

EGU22-7633 | Presentations | GM2.1

Isolating bed load transport from river induced seismic signals

Bronwyn Matthews, Mark Naylor, Hugh Sinclair, Michael Dietze, Richard Williams, and Calum Cuthill

Bed load transport is a critical parameter in the study of landscape evolution and also provides valuable information for problems in the fields of ecology, river and landuse management, and civil engineering. Bed load transport is difficult to assess due to its stochastic nature and highly variable transport rates, and traditional measurement techniques have struggled to capture the spatial and temporal variability of bed load transport. In recent years, bed load monitoring based on seismological observations has emerged, which allows non-invasive and continuous indirect measurements. However, there still remains a significant challenge to independently characterise the seismic signature of bed load from other sources of noise, such as turbulence. Our study aims to explore seismic data recorded at the highly braided River Feshie in Scotland, which has undergone significant morphological change in its history and has been highly monitored over the last couple decades through Digital Elevation Models. Since the deployment of our seismometers in December 2020 we have captured three independent high flow events plus an isolated earthquake, which are being used to determine the environmental signals and the site specific signal characteristics. In some previous studies, an observed hysteretic relationship between seismic power and hydrological parameters has been interpreted as being characteristic of bed load transport. From the data we have gathered we have observed a hysteresis in the signals, and through Shields calculations it is suggested that bed load transport would be expected during these events. However, without independent constraints we do not feel we can be absolutely certain that this behaviour is a result of bed load transport. Our ongoing study therefore aims to combine multiple physical measurement techniques, such as hydroacoustic measurements, time-lapse imagery and seismic observations, to try and pinpoint what is contributing to the seismic signals recorded and how we can isolate the bed load transport component.

How to cite: Matthews, B., Naylor, M., Sinclair, H., Dietze, M., Williams, R., and Cuthill, C.: Isolating bed load transport from river induced seismic signals, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7633, https://doi.org/10.5194/egusphere-egu22-7633, 2022.

EGU22-8480 | Presentations | GM2.1

What are the key elements that control the seismic signature of highly concentrated sediment flows?

Marco Piantini, Florent Gimbert, Evangelos Korkolis, Romain Rousseau, Hervé Bellot, and Alain Recking

Flowing through the landscape, rivers generate high-frequency ground vibrations (> 1 Hz) by exerting force fluctuations on the bed. The well-established evidence that seismic sensors detect a wide variety of fluvial processes has motivated the use of seismology to indirectly measure sediment transport. In the last decade, numerous efforts have been dedicated to develop physically-based mechanistic models to investigate the link between the river-induced seismic signal and sediment transport properties such as the characteristic diameter of the transported sediments, bedload transport rate, debris flow thickness and velocity. However, most of the existing theories rely on simplistic descriptions of the transport dynamics that may not necessarily be sufficient to capture realistic behaviours. In particular, highly concentrated sediment flows are characterized by complex grain scale physical processes that could have a major impact on their seismic signature (Allstadt et al., 2020; Piantini et al., 2021).

Here, we carry out laboratory experiments to explore the seismic signature of highly concentrated sediment flows. Our scaled experimental setup allows the self-triggering and propagation of sediment pulses in a steep channel (slope of 18%), using a wide bimodal grain size distribution typical of mountain streams. We monitor physical parameters such as flow surface elevation, outlet solid discharge and the corresponding granulometric composition, together with seismically relevant quantities such as basal force fluctuations and flume vibrations using force and ultrasonic sensors, respectively. We observe transport conditions that range from the dilute transport of big grains (sediment pulse front) to dense sediment flows (sediment pulse body). Consistent with previous studies, the passage of the unsaturated front exerts the highest force fluctuations and seismic power. However, we also find that the body, despite having an amount of coarse particles similar to the front, becomes dramatically quieter when bulk density increases and the content of fine particles is maximum. We explain this latter behaviour by two main processes. First, flow stratification prevents a large part of the transported sediments from generating direct impacts to the fixed channel bed. Second, fines allow the formation of a conveyor belt that transport big particles with reduced collisions, as manifested by a considerable increase in their downstream velocity. These findings argue that internal stratification and the presence of a high content of fines may exert a major control on the seismic signature of highly concentrated sediment flows.

References

Allstadt, K. E., Farin, M., Iverson, R. M., Obryk, M. K., Kean, J. W., Tsai, V. C., Rapstine, T. D., and Logan, M.: Measuring Basal Force Fluctuations of Debris Flows Using Seismic Recordings and Empirical Green’s Functions, J. Geophys. Res.-Earth Surf., 125, 9, https://doi.org/10.1029/2020JF005590, 2020

Piantini, M., Gimbert, F., Bellot, H., and Recking, A.: Triggering and propagation of exogenous sediment pulses in mountain channels: insights from flume experiments with seismic monitoring, Earth Surf. Dynam., 9, 1423–1439, https://doi.org/10.5194/esurf-9-1423-2021, 2021

How to cite: Piantini, M., Gimbert, F., Korkolis, E., Rousseau, R., Bellot, H., and Recking, A.: What are the key elements that control the seismic signature of highly concentrated sediment flows?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8480, https://doi.org/10.5194/egusphere-egu22-8480, 2022.

EGU22-7344 | Presentations | GM2.1

Establishing time series of flux and grain size of suspended sand in rivers using an acoustic method

Jessica Laible, Benoît Camenen, Jérôme Le Coz, Guillaume Dramais, Francois Lauters, and Gilles Pierrefeu

Measuring the concentration and grain size of suspended sand in rivers continuously remains a scientific challenge due to its pronounced spatio-temporal variability. Vertical and lateral gradients within a river cross-section require spatially-distributed water sampling at multiple verticals and depths. However, this classical approach is time-consuming and offers limited temporal resolution. Sampling is particularly difficult in presence of a bimodal suspension composed of fine sediment and a sand fraction, notably if the fine/sand ratio varies with time. The aim of this study is to establish time series of sand concentration and grain size by improving temporal resolution using an acoustic multi-frequency method based on acoustic attenuation and backscatter to measure the suspension indirectly. Experiences of Moore et al. (2012) and Topping & Wright (2016) with Horizontal Acoustic Doppler Current Profilers (HADCPs) show that dual-frequency inversion can separate the fine sediment fraction dominating acoustic attenuation from the sand fraction dominating acoustic backscatter. Concentration and grain size of suspended sediment, both the fine and sand fraction, can be quantified by signal inversion after correction for transmission losses.

Applying existing dual-frequency, semi-empirical methods in a typical Piedmont river (River Isère, France) remains a challenge due to the high concentrations and a broad bimodal distribution. Two monostatic HADCPs of 400 and 1000 kHz were installed at a hydrometric station of the Isère at Grenoble Campus where discharge and turbidity have been recorded for more than 20 years. Using frequent isokinetic water samples obtained with US P-72 and US P-06 samplers close to the ensonified volume, a relation between acoustic signal and the sediment concentration and grain size can be determined. Simultaneously, total sand flux and grain size distribution are calculated performing solid gaugings using Delft bottle samples and ADCP measurements in the entire cross-section. The method using index concentration and grain size in the HADCP measurement area is then used to evaluate the total sand flux and average grain size time-series in the cross-section.

First results show good correlations between the fine sediment concentration and the sediment attenuation for both frequencies. Specific extreme events (e.g. debris flows, dam flushes or spring floods) show distinct signatures in acoustic attenuation, backscatter and ratio between the two frequencies. During a debris flow (concentration up to 5.3 g/l), attenuation reached 1.6 and 3 dB/m for 400 respectively 1000 kHz, but no peak in backscatter intensity, whereas a spring flood (up to 4 g/l with at least 50 % sand) caused major peaks in attenuation and backscatter. Pronounced hysteresis during the events and time-varying ratio between attenuation due to sediments measured by 400 and 1000 kHz indicate suggest that the grain size distribution may vary. Relating sand concentration from physical samples with beam-averaged backscatter may elucidate changes in grain size more precisely. Existing heterogeneities of concentration and grain size along the acoustic beam contradict the homogeneous distribution supposed by the method and require local analysis based on local concentration and grain size characteristics.

How to cite: Laible, J., Camenen, B., Le Coz, J., Dramais, G., Lauters, F., and Pierrefeu, G.: Establishing time series of flux and grain size of suspended sand in rivers using an acoustic method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7344, https://doi.org/10.5194/egusphere-egu22-7344, 2022.

EGU22-6321 | Presentations | GM2.1

Fast and automatic measurement of grain geometries from 3D point clouds

Laure Guerit, Philippe Steer, Dimitri Lague, Alain Crave, and Aurélie Gourdon

The size distribution of sediments together with their shape inform on their transport history, are important factors controlling the efficiency of erosion and transport, and control the quality of aquatic ecosystems. However, the size distribution of sediments is generally assessed using poorly representative field measurements and determining the grain-scale shape of sediments remains a real challenge in geomorphology. To tackle this issue, we develop a new methodological approach based on the segmentation and geomorphological fitting of 3D point clouds. Point cloud segmentation into individual grains is performed using a watershed algorithm applied here to 3D point clouds. Once the grains are individualized into several sub-clouds, the morphology of each grain is determined by fitting a 3D ellipsoid to each sub-cloud. These 3D models are then used to extract the size distribution and the grain-scale shape of the sediment population. The algorithm is validated against field data acquired by Wolman counts in coastal and fluvial environments. The main benefits of this automatic and non-destructive method are that it provides, with a fast and efficient approach, access to 1) an un-biased estimate of surface grain-size distribution on a large range of scales, from centimeters to tens of meters; 2) a very large number of data, only limited by the number of grains in the point-cloud dataset; 3) the 3D morphology of grains, in turn allowing to develop new metrics characterizing the size and shape of grains; and 4) the in-situ orientation and organization of grains and grain clusters. The main limit of this method is that it is only able to detect grains with a characteristic size significantly greater than the resolution of the point cloud.

How to cite: Guerit, L., Steer, P., Lague, D., Crave, A., and Gourdon, A.: Fast and automatic measurement of grain geometries from 3D point clouds, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6321, https://doi.org/10.5194/egusphere-egu22-6321, 2022.

EGU22-1378 | Presentations | GM2.1

Particle path length estimation: a signal processing approach 

Lindsay Capito, Simone Bizzi, Nicola Surian, and Walter Bertoldi

The structure and function of rivers is directly related to bedload transport which is difficult to measure due to its spatial heterogeneity and the logistic constraints of field measurements. These difficulties have given rise to the morphological method wherein sediment transport is inferred from changes in morphology and estimates of the distance traveled by sediment during a flood, its path length. However, current methods for estimating path length are time and labor intensive, have low recovery rates, and are limited to some morphological units. We propose a method to estimate path length from repeat digital elevation models (DEM’s of difference i.e. DoDs) which are requisite for the morphological method. We interpret the pattern of erosion and deposition downstream as a signal and apply Variational Mode Decomposition (VMD), a signal processing method, to quantify the periodicity as a proxy for path length. We developed this method using flume experiments with measured sediment flux and applied it to published field data with tracer measurements for validation. The preliminary results provide a range of values on the same order of magnitude as measured tracer and flux data and are coherent with channel geometry. This method provides a reasonable estimation of path length based solely on remotely sensed data and a range of plausible sediment fluxes associated with specific channel morphological processes through DoD interpretation.

How to cite: Capito, L., Bizzi, S., Surian, N., and Bertoldi, W.: Particle path length estimation: a signal processing approach , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1378, https://doi.org/10.5194/egusphere-egu22-1378, 2022.

EGU22-11367 | Presentations | GM2.1

Monitoring Gravel Volume Change by Very High Resolution Satellite Image Stereopairs

Li-Shan Lin and Kuo-Hsin Tseng

Taiwan is located on the convergent boundary of the Philippine Sea Plate and the Eurasian Plate. Due to the active orogenic movement, the rock formations are fragmented and the weak joints are developed. In recent years, heavy rainfall accompanied with the occurrence of river surges carry a large amount of broken sand and gravel to the downstream. The accumulation of a large amount of sand and gravel in the river may threaten the safety along the river bank, such as channel diversion and flooding. Therefore, the river channel needs to be dredged regularly to reduce the risk to the residents and properties. Because the dredging area is scattered and difficult to reach, on-site measurement has become a time-consuming and labor-intensive method. With the improvement of satellite technology, it is feasible to use efficient remote sensing technology to generate point clouds and a surface elevation model (DSM) for monitoring purposes. However, several problems still exist in this technology, including the scatteredness of control points and feature points, instability of the platform, varying imaging conditions, and time differences in the matching process. To solve the DSM errors caused by these problems, this study uses 3-D point cloud registration method to align the horizontal and vertical directions and tries to reduce elevation system error due to the failure of co-registration. First, feature description, extraction, and feature matching are performed. Second, the iterative closest point algorithm (ICP) is used to closely match two sets of point clouds after coarse alignment. Finally, elevation difference between two dets of DSM is verified with ground measurement data and the accuracy of the point cloud registration is assessed. We use a dredging area in Laonong River, Taiwan, as an example to monitor gravel volume change in river channel by high resolution Pléiades images and UAV in different time periods. Our preliminary results show that the spaceborne technology could achieve submeter level accuracy in monitoring height changes in each transect.

How to cite: Lin, L.-S. and Tseng, K.-H.: Monitoring Gravel Volume Change by Very High Resolution Satellite Image Stereopairs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11367, https://doi.org/10.5194/egusphere-egu22-11367, 2022.

Today, erosion is increasing in many intensively used agricultural regions with fertile soils. At the same time, scientists expect that the intensity of heavy precipitation events, their erosivity, drought intensity and persistance will increase significantly through climate change. In combination with more strict regulations to protect the natural environment from nutrients and hazardous substances (such as herbicides and micro-plastics), it is challenging to balance the interests of food (and energy) production and environmental protection.

Therefore, we design and establish a worldwide unique measurement plot at the Bavarian Agricultural Institute (LfL) to assess different combinations of four- and six-year crop rotation schemes and machining methods concerning their long-term soil fertility, stability and resilience against climate change effects and environmental impacts, focusing on compound effects. The plot to measure and compare soil-water retention, nutrient fluxes, surface runoff, and erosion masses has an area of four acres and 14 parallel crop strips. Crop cultivation, experiments and measurements with and without artificial rain will be performed for more than ten years after a three-year set-up phase, will have a 4D (3D spatial plus temporal) high-resolution design and combine established and innovative measurement and management techniques, such as artificial intelligence, neural networks, deep learning, and robotics. Finally, up-to-date process-based hydrological modelling will incorporate the measurement data to increase our process understanding and enable upscaling to catchment scales.

This contribution to EGU 2022 will inform and include the scientific community during the set-up phase about the running and planned activities to build an international scientific network, discuss our approaches, efficiently use the existing scientific knowledge, and initiate future collaborations around the measurement financed by the German federal state of Bavaria.

How to cite: Ebertseder, F., Mitterer, J., and Disse, M.: Moving the frontier of comparative erosion measurements under different agricultural schemes – Development of a long-term, high-resolution, 4D erosion measurement site of the Bavarian Agricultural Institute in Lower Bavaria (Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9500, https://doi.org/10.5194/egusphere-egu22-9500, 2022.

EGU22-6666 * | Presentations | GM2.1 | Highlight

Measurement and modeling of slope-wash and rill erosion on hillslopes using a novel combination of instrumented plots and remote sensing

Jon Pelletier, Nathan Abramson, Satya Chataut, Sriram Ananthanarayan, and David Ludwick

We have measured unit sediment fluxes and their relationship to unit water discharges over 7 orders of magnitude on hillslopes of up to 350 m in length in Arizona. Unit sediment and water fluxes were measured using a novel combination of instrumented monitoring plots and repeat photogrammetric surveys analyzed volumetrically. The monitoring plots, which are ideal for measuring sediment fluxes in relatively planar portions of the landscape dominated by slope-wash erosion, funnel water and sediment into a detention basin where bedload sediment fluxes are measured and then into a flume where water discharges and suspended sediment fluxes are measured at 1-minute intervals using a pressure transducer and calibrated turbidity sensor. Repeat photogrammetric surveys complement the monitoring plots by measuring sediment fluxes in rills that tend to form in areas of convergent flow during intense rain events. The volumetric change in each pixel is digitally routed to determine the volumetric sediment flux in each pixel associated with rilling during a rain event. Unit water discharges for every pixel cannot be measured directly but are estimated using a rainfall-runoff model calibrated to the monitoring plot data. The relationship between unit sediment fluxes and unit water dischargees exhibits two piecewise power-function relationships with different exponents characterizing the slope-wash and rill-dominated regimes. We developed a novel landscape evolution model, inspired by the SIBERIA model but improved in specific ways optimized for hillslopes, that uses the measured piecewise power-function relationship between unit sediment fluxes and unit water discharges to predict hillslope evolution from time scales of individual events to decades. The predictions of the model are validated using ten years of observation of rill development at the study site. We provide equations for estimating the parameters of the piecewise power-function relationship for other hillslopes with different cover characteristics. This measurement and modeling framework must be tested at more study sites but is potentially useful for predicting the erosion of any hillslope, including alternative designs for landscape rehabilitations following mining or other anthropogenic disturbances.   

How to cite: Pelletier, J., Abramson, N., Chataut, S., Ananthanarayan, S., and Ludwick, D.: Measurement and modeling of slope-wash and rill erosion on hillslopes using a novel combination of instrumented plots and remote sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6666, https://doi.org/10.5194/egusphere-egu22-6666, 2022.

EGU22-6865 * | Presentations | GM2.1 | Highlight

Modelling the sensitivity of changes in sediment flux and grainsize distributions on flooding in the Kathmandu basin, Nepal

Saraswati Thapa, Hugh D. Sinclair, Maggie Creed, Simon M. Mudd, Mikael Attal, Manoranjan Muthusamy, and Bholanath Sharma

Abstract: Climate change and land-use change impact the sediment flux and grainsize delivered to rivers which influences channel morphologies and hence modifies flood risk; this is particularly the case where channels are fed by high mountain catchments. Here, We studied the Nakkhu River which is the largest southern tributary of the Kathmandu basin, Nepal. The mobility of the channel is well documented in response to bank erosion, down-cutting, and accumulation of bar forms; these processes are particularly important during extreme flood events. Comparing satellite images from 2003 to 2020, the river course, which has a medium channel width of 15 m, has migrated laterally up to 130m. Bank erosion and down-cutting reduce the inundation and water storage upstream, whereas aggradation of river bar forms downstream reduces the channel’s conveyance capacity. These vertical and lateral geomorphological alterations result in significant impact on flood risk downstream.

In this research, we investigate how changes in sediment supply, and grain size affect river morphology and flood inundation in the Nakkhu River. We use the landscape evolution model, CAESAR-Lisflood, combined with a newly generated (2019) 10 m digital elevation model, field-derived grainsize data and 20 years (2001 to 2020) of daily discharge data, to simulate erosion and deposition along a 14 km reach of the river. In a set of experiments, we compare river bed cross-sections, flood extent, and water depths for 15 model scenarios where we vary sediment supply and grain size from fine sand to coarse gravel dominated distributions assessing the geomorphic uncertainty of observation of sediment data.

The model results show that channel morphologies are sensitive to changes in sediment grainsize distribution. The study suggests that lack of consideration of sediment impact in flood hazard mapping could lead to increased flood risk. In addition, this study highlights some of the challenges regarding the significance of grain size parameter and uncertainty to the landscape evolution model that need to be addressed in current research.

Keywords: River morphology, sediment flux, grainsize, flood modelling, Nepal

How to cite: Thapa, S., Sinclair, H. D., Creed, M., Mudd, S. M., Attal, M., Muthusamy, M., and Sharma, B.: Modelling the sensitivity of changes in sediment flux and grainsize distributions on flooding in the Kathmandu basin, Nepal, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6865, https://doi.org/10.5194/egusphere-egu22-6865, 2022.

EGU22-1395 * | Presentations | GM2.1 | Highlight

Network-scale analysis of sedimentary hotspots in dynamic, seismically-active steepland rivers

Niraj Bal Tamang and Jon Tunnicliffe

Seismic shaking in mountain environments introduces the potential for complex fluvial response from a multitude of landslide sources. Stream networks may be impacted in multiple branches, introducing the possibility of interacting sedimentary ‘pulses’ moving through the system. Large quantities of mobile sediment added to the stream network from multiple sources during and after a co-seismic event can overload susceptible river reaches, causing changes in sediment transport and storage. Although past research works have addressed dynamic sediment movement in river networks and identification of sedimentary hotspots, the physiographic factors (e.g. canyons, bends, fans, slope change) that prompt such change remain unexplored. The catchment settings and reach sequences that contribute most to delay/acceleration of the sediment in the active mountain environments are investigated in order to improve hazard assessment in susceptible terrain. In this work, we employ the one-dimensional River Network Bed-Material Sediment model (Czuba & Foufoula-Georgiou, 2014) to explore the landscape factors that may lead to hotspot behaviour for the very coarse sand fraction (2mm), followed by multi-criteria analysis of four basic stream network parameters: slope, sinuosity, channel confinement and tributary influence. Patterns of network topology associated with delay and accumulation of river sediment in the model were systematically identified in 75,400 stream links from 16 major drainages (135 to 6425 km2) of New Zealand’s upper South Island, as assessed by sediment travel time and the cluster persistence index (CPI). Catchment size determines the number of sediment sources, and thus ultimately the magnitude of the sedimentary hotspots i.e., bigger catchments can accommodate more landslides which increases the sediment input, along with the chances of sediment accumulation at susceptible locations. Multi-criteria analysis of the top 10 reaches with highest CPI values in each catchment (160 sites, total), showed that about 30% of the hotspots occurred in partly-confined valley settings with gentle slope (<0.02m/m), moderate sinuosity (1-1.1), downstream from the confluence of two or more tributaries. This combination emerged as the most likely setting for the occurrence of sedimentary hotspots in active mountain river networks. This approach may provide a simple means to map out susceptible sites based upon reach characteristics, which will not only contribute to improved catchment hazard assessment but may also help to augment more sophisticated models of catchment response to co-seismic landslide events.

How to cite: Tamang, N. B. and Tunnicliffe, J.: Network-scale analysis of sedimentary hotspots in dynamic, seismically-active steepland rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1395, https://doi.org/10.5194/egusphere-egu22-1395, 2022.

GM2.2 – Assessing and monitoring geomorphic processes across scales

EGU22-1415 | Presentations | GM2.2

Fully coupled modelling of non-uniform sediment transport in sewer systems

Jinxin Liu, Zhixian Cao, and Xichun Li

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

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

EGU22-1885 | Presentations | GM2.2

A novel two-dimensional numerical model developed for slope soil erosion

Tian Wang, Jingming Hou, Yu Tong, Jiaheng Zhao, and Feng Wang

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

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

EGU22-1951 | Presentations | GM2.2

A new two-phase shallow water hydro-sedi-morphodynamic model with the HLLC solver for inter-grid numerical flux estimation

Peng Hu, Binghan Lyu, Ji Li, Qifeng Liu, Youwei Li, and Zhixian Cao

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

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

EGU22-1463 | Presentations | GM2.2

An integrated two-layer model for simulating shallow flow, sediment transport and overtopping-induced breach processes

Jiaheng Zhao, Jingming Hou, Ilhan Özgen Xian, Tian Wang, and Reinhard Hinkelmann

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

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

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

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

EGU22-10656 | Presentations | GM2.2 | Highlight

Predicting coarse particle displacements due to turbulent flows at near-threshold conditions via LSTM models

Hamed Farhadi, Yi Xu, Panagiotis Michalis, Zaid AlHusban, and Manousos Valyrakis

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

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

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

 

References

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

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

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

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

EGU22-3607 | Presentations | GM2.2

Application of the Shields diagram for evaluating critical shear stress for vegetated flows

Yesheng Lu, Nian-Sheng Cheng, and Maoxing Wei

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

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

EGU22-10068 | Presentations | GM2.2

Analysis of oscillatory flow around a rigidly attached spherical particle to the bottom in a sloshing tank

Oral Yagci, Murat Aksel, Fatih Yorgun, and Manousos Valyrakis

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

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

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

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

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

EGU22-10116 | Presentations | GM2.2

Numerical simulation and experimental validation of the air-water flow in a Hydraulic Test Bench

Zied Driss, Khadija Rahal, Mariem Lajnef, Mohamed Salah Abid, and Manousos Valyrakis

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

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

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

EGU22-4702 | Presentations | GM2.2

Experimental study on sediment deposition and water level surge under unsteady sediment supply

Qihang Zhou, Lu Wang, Xingnian Liu, and Ruihua Nie

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

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

EGU22-6105 | Presentations | GM2.2

Simulating water flow over a rolling bed of non-cohesive materials by using a Hydromorphodynamic model.

Zaid Alhusban, Manousos Valyrakis, and Hamed Farhadi

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

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

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

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

EGU22-12828 | Presentations | GM2.2 | Highlight

Experimental characterization of mechanical clogging of dry granular flows through sudden constrictions

Solange Mendes, Rodrigo Farias, Rui Aleixo, Michele Larcher, Teresa Viseu, and Rui Ferreira

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

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

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

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

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

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

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

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

EGU22-6355 | Presentations | GM2.2

Evaluation of riprap failure impact on the downstream scour hole

Robert Fliszar and Gordon Gilja

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

Acknowledgments

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

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

EGU22-12570 | Presentations | GM2.2

Incorporating an instrumented particle to monitor the dynamic processes of bed particle motion from entrainment to low transport stages

Zaid Al-Husban, Hamed Farhadi, Khaldoon AlObaidi, Yi Xu, and Manousos Valyrakis

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

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

 

References

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

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

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

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

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

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

EGU22-10620 | Presentations | GM2.2

Assessing the risk of infrastructure scour due to turbulence, using miniaturized instrumented particles

Yi Xu, Hamed Farhadi, Panagiotis Michalis, and Manousos Valyrakis

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

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

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

 

References

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

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

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

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

EGU22-4631 | Presentations | GM2.2

Verification of the pier scour development in the experimental environment

Gordon Gilja, Robert Fliszar, Antonija Harasti, and Nikola Adžaga

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

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

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

EGU22-4883 | Presentations | GM2.2

Impacts of approach bedforms on live-bed scour at rock weirs

Wen Zhang, Lu Wang, Xingnian Liu, and Ruihua Nie

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

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

EGU22-10252 | Presentations | GM2.2

Some observations on the prediction of bridge scour from first principles

Manish Pandey, Yi Xu, Panagiotis Diplas, and Manousos Valyrakis

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

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

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

 

References

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

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

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

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

EGU22-8006 | Presentations | GM2.2

Using a natural laboratory to quantify sediment mobility in the turbulent wake of instrument frames and offshore infrastructure. 

Christopher Unsworth, Martin Austin, and Katrien Van Landeghem

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

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

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

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

EGU22-8428 | Presentations | GM2.2

Coupling physical and digital built environments for proactive asset management

Fotios Konstantinidis, Panagiotis Michalis, and Manousos Valyrakis

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

 

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

References

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

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

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

EGU22-12375 | Presentations | GM2.2

A New Risk Monitoring Approach to Assess Infrastructure Performance

Khaldoon AlObaidi, Yi Xu, Hamed Farhadi, Panagiotis Michalis, and Manousos Valyrakis

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

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

References

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

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

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

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

EGU22-1685 | Presentations | GM2.2

Impact of embankments for reversing neck cutoff on flow structure in a Zoige meandering river

Zhiwei Li, Peng Gao, and Bang Chen

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

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

EGU22-3387 | Presentations | GM2.2

Large-scale experiment on dike breaching with complex measures on the crown

Wei Huang, Deliang Shi, Hongyan Wei, Yufang Ni, and Wengang Duan

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

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

EGU22-4258 | Presentations | GM2.2

The effects of dredged channel geometry on the barrier lake outburst

Yufang Ni, Wei Huang, and Wengang Duan

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

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

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

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

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

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

EGU22-1419 | Presentations | GM2.2

Flow structure at reservoir-tributary confluence with high sediment load

Junhao Zhang, Yining Sun, Zhixian Cao, and Ji Li

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

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

EGU22-7110 | Presentations | GM2.2

Determination of the appropriate baseflow separation method for gauging stations on the two lowland rivers in Croatia

Martina Lacko, Kristina Potočki, and Gordon Gilja

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

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

EGU22-10189 | Presentations | GM2.2

Assessment of the transport capacity of floating plastics through fluvial systems

Ridwan Raquib, Lukasz Przyborowski, and Manousos Valyrakis

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

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

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

EGU22-3043 | Presentations | GM2.2

Erosional dynamics of a river driven by groundwater seepage

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

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

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

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

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

EGU22-4448 | Presentations | GM2.2

Sediment load determines the shape of rivers 

Predrag Popovic, Olivier Devauchelle, Anais Abramian, and Eric Lajeunesse

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

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

GM2.3 – Novel data, methods and applications in Geomorphometry

EGU22-12447 | Presentations | GM2.3 | Highlight

High resolution topography precision maps for DEM differencing. Have they gone too far?

Florian Strohmaier, Jason Goetz, and Sam McColl

Land surface curvature (LSC) is a basic attribute of topography and influences local effects of gravitational energy and surface material transport. However, the calculation of LSCs based on triangulated irregular networks (TINs) has not been fully studied, which restricts further geoscience studies based on TIN digital elevation models (DEMs). The triangular facets and vertices of a TIN are both expressions of the land surface; therefore, based on their adjacency relationship, the LSCs can be calculated. In this study, we propose a mathematical vector framework to enhance LSC system theory. In this framework, LSC can be calculated based on both triangular facets and vertices, and the selection of weighting methods in the framework is flexible. We use the concept of the curvature tensor to interpret and calculate the commonly used LSC, which provides a new perspective in geoscience research. We also investigate the capacity of the TIN-based method to perform LSCs calculations and compare it with grid-based methods. Based on a mathematically simulated surface, we reach the following conclusions. First, the TIN-based method has similar effects on the scale to the grid-based methods of EVANS and ZEVENBERGEN. Second, the TIN-based method is less error sensitive than the grid-based methods by the EVANS and ZEVENBERGEN polynomials for the high error DEMs. Third, the shape of the TIN triangles exerts a great influence on the LSCs calculation, which means that the accuracy of LSCs calculation can be further improved with the optimized TIN but will be discontinuous. Based on three real landforms with different data sources, we discuss the possible applications of the TIN-based method, e.g., the classification of land surface concavity–convexity and hillslope units. We find that the TIN-based method can produce visually better classification results than the grid-based method. This qualitative comparison reflects the potential of using TINs in multiscale geoscience research and the capacity of the proposed TIN-based LSC calculation methods. Our proposed mathematical vector framework for LSCs calculations from TINs is a preliminary approach to mitigate the multiple-scale problem in geoscience. In addition, this research integrates mathematical vector and geographic theories and provides an important reference for geoscience research.

 

How to cite: Hu, G., Xiong, L., and Tang, G.: Mathematical vector framework for gravity-specific land surface curvatures calculation from triangulated irregular networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13122, https://doi.org/10.5194/egusphere-egu22-13122, 2022.

EGU22-13131 | Presentations | GM2.3

Morphological characteristics and evolution model of loess gully cross section

Lulu Liu, Fayuan Li, Xue Yang, and Jianhua Cheng

Gully morphology is an important part of loess geomorphology research. Along with gully development, the variation of its cross section is the most important aspect, and it can intuitively reflect the characteristics of the lateral widening of the gully slope. Therefore, in-depth research of the variation of the cross-sectional morphology of the gully is important to understanding the development process of the loess gully. Based on the data of nine periods of an indoor simulated loess small watershed, this paper deeply studies the evolution model of a complete branch ditch in the watershed from many aspects by using the theory and method of digital terrain analysis. Firstly, we analyse the morphological characteristics of the gully cross section in the simulated small watershed. The test shows that with the development of the gully, the average slope of the slope decreases continuously, and the slope morphology is mostly a concave slope along the slope direction. The degree of downward concave first increases and then gradually tends to be gentle. The gully erosion mode is gradually transformed from downward cutting erosion to lateral erosion. The more mature the gully development, the lower the depth of gully bottom cutting is compared with the width of gully widening. Furthermore, the surface cutting depth tends to be stable and the slope is stable. Then, the transformation law of the slope morphology of the gully cross section with the development of the gully is studied, and the prediction model of the transformation of the slope morphology of the gully cross section is established by using the Markov chain. The Markov model can better reflect the dynamic change of the slope morphology of the gully cross section, which is of considerable importance to revealing the external performance and internal mechanism of the gully morphology.

How to cite: Liu, L., Li, F., Yang, X., and Cheng, J.: Morphological characteristics and evolution model of loess gully cross section, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13131, https://doi.org/10.5194/egusphere-egu22-13131, 2022.

EGU22-5587 * | Presentations | GM2.3 | Highlight

Comparative analysis of the Copernicus (30 m), TanDEM-X (12 m) and UAV-SfM (0.2 m) DEM to estimate gully volumes and mobilization rates in central Madagascar

Liesa Brosens, Benjamin Campforts, Gerard Govers, Emilien Aldana-Jague, Vao Fenotiana Razanamahandry, Tantely Razafimbelo, Tovonarivo Rafolisy, and Liesbet Jacobs

Over the past decades advanced technology has become available, revolutionizing the assessment of surface topography. At smaller scales (up to a few km²) structure from motion (SfM) algorithms applied to uncrewed aerial vehicle (UAV) imagery now allow sub-meter resolution. On the other hand, spaceborne digital elevation models (DEMs) are becoming increasingly accurate and are available at a global scale. Two recent spaceborne developments are the 12 m TanDEM-X and 30 m Copernicus DEMs. While sub-meter resolution UAV-SfM DEMs generally serve as a reference, their acquisition remains time-consuming and spatially constrained. However, some applications in geomorphology, such as the estimation of regional or national erosion quantities of specific landforms, require data over large areas. TanDEM-X and Copernicus data can be applied at such scales, but this raises the question of how much accuracy is lost because of the lower spatial resolution.

Here, we evaluate the performance of the 12 m TanDEM-X DEM and the 30 m Copernicus DEM to i) estimate gully volumes, ii) establish an area-volume relationship, and iii) determine sediment mobilization rates, through comparison with a higher resolution (0.2 m) UAV-SfM DEM. We did this for six study areas in central Madagascar where lavaka (large gullies) are omnipresent and surface area changes over the period 1949-2010s are available. Copernicus derived lavaka volume estimates were systematically too low, indicating that the Copernicus DEM is not suitable to estimate erosion volumes for geomorphic features at the lavaka scale (100 – 105 m²). The relatively coarser resolution of the DEM prevents to accurately capture complex topography and smaller geomorphic features. Lavaka volumes obtained from the TanDEM-X DEM were similar to UAV-SfM volumes for the largest features, while smaller features were generally underestimated. To deal with this bias we introduce a breakpoint analysis to eliminate volume reconstructions that suffered from processing errors as evidenced by significant fractions of negative volumes. This elimination allowed the establishment of an area-volume relationship for the TanDEM-X data with fitted coefficients within the 95% confidence interval of the UAV-SfM relationship. Combined with surface area changes over the period 1949-2010s, our calibrated area-volume relationship enabled us to obtain lavaka mobilization rates ranging between 18 ± 3 and 311 ± 82 t ha-1 yr-1 for the six study areas, with an average of 108 ± 26 t ha-1 yr-1. This does not only show that the Malagasy highlands are currently rapidly eroding by lavaka, but also that lavaka erosion is spatially variable, requiring the assessment of a large area in order to obtain a meaningful estimate of the average erosion rate.

With this study we demonstrate that medium-resolution global DEMs can be used to accurately estimate the volumes of gullies exceeding 800 m² in size, where the proposed breakpoint-method can be applied without requiring the availability of a higher resolution DEM. This might aid geomorphologists to quantify sediment mobilisation rates by highly variable processes such as gully erosion or landsliding at the regional scale, as illustrated by our first assessment of regional lavaka mobilization rates in the central highlands of Madagascar.

How to cite: Brosens, L., Campforts, B., Govers, G., Aldana-Jague, E., Razanamahandry, V. F., Razafimbelo, T., Rafolisy, T., and Jacobs, L.: Comparative analysis of the Copernicus (30 m), TanDEM-X (12 m) and UAV-SfM (0.2 m) DEM to estimate gully volumes and mobilization rates in central Madagascar, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5587, https://doi.org/10.5194/egusphere-egu22-5587, 2022.

EGU22-8994 | Presentations | GM2.3 | Highlight

FABDEM - A 30m global map of elevation with forests and buildings removed

Peter Uhe, Laurence Hawker, Luntadila Paulo, Jeison Sosa, Christopher Sampson, and Jeffrey Neal

Digital Elevation Models (DEMs) depict the elevation of the Earth’s surface and are fundamental to many applications, particularly in the geosciences. To date, global DEMs contain building and forest artifacts that limit its functionality for applications that require precise measurement of terrain elevation, such as flood inundation modeling. Using machine learning techniques, we remove both building and tree height bias from the recently published Copernicus GLO-30 DEM to create a new dataset called FABDEM (Forest And Buildings removed Copernicus DEM). This new dataset is available at 1 arc second grid spacing (~30m) between 60°S-80°N, and is the first global DEM to remove both buildings and trees.

Our correction algorithm is trained on a comprehensive and unique set of reference elevation data from 12 countries that covers a wide range of climate zones and urban types. This results in a wider applicability compared to previous DEM correction studies trained on data from a single country. As a result, we reduce mean absolute vertical error from 5.15m to 2.88m in forested areas, and from 1.61m to 1.12m in built-up areas, compared to Copernicus GLO-30 DEM. Further statistical and visual comparisons to other global DEMs suggests FABDEM is the most accurate global DEM with median errors ranging from -0.11m to 0.45m for the different landcover types assessed. The biggest improvements were found in areas of dense canopy coverage (>50%), with FABDEM having a median error of 0.45m compared to 2.95m in MERIT DEM and 12.95m for Copernicus GLO-30 DEM.

FABDEM has notable improvements over existing global DEMs, resulting from the use of Copernicus GLO-30 and a powerful machine learning correction of building and tree bias. As such, there will be beneifts in using FABDEM for purposes where depiction of the bare-earth terrain is required, such as in applications in geomorphology, glaciology and hydrology.

How to cite: Uhe, P., Hawker, L., Paulo, L., Sosa, J., Sampson, C., and Neal, J.: FABDEM - A 30m global map of elevation with forests and buildings removed, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8994, https://doi.org/10.5194/egusphere-egu22-8994, 2022.

EGU22-13124 | Presentations | GM2.3

Integrating topographic knowledge into deep learning for the void-filling of digital elevation models

Sijin Li, Liyang Xiong, and Guoan Tang

Digital elevation models (DEMs) contain some of the most important data for providing terrain information and supporting environmental analyses. However, the applications of DEMs are significantly limited by data voids, which are commonly found in regions with rugged terrain. We propose a novel deep learning-based strategy called a topographic knowledge-constrained conditional generative adversarial network (TKCGAN) to fill data voids in DEMs. Shuttle Radar Topography Mission (SRTM) data with spatial resolutions of 3 and 1 arc-seconds are used in experiments to demonstrate the applicability of the TKCGAN. Qualitative topographic knowledge of valleys and ridges is transformed into new loss functions that can be applied in deep learning-based algorithms and constrain the training process. The results show that the TKCGAN outperforms other common methods in filling voids and improves the elevation and surface slope accuracy of the reconstruction results. The performance of TKCGAN is stable in the test areas and reduces the error in the regions with medium and high surface slopes. Furthermore, the analysis of profiles indicates that the TKCGAN achieves better performance according to a visual inspection and quantitative comparison. In addition, the proposed strategy can be applied to DEMs with different resolutions. This work is an endeavour to transform perceptive topographic knowledge into computer-processable rules and benefits future research related to terrain reconstruction and modelling.

How to cite: Li, S., Xiong, L., and Tang, G.: Integrating topographic knowledge into deep learning for the void-filling of digital elevation models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13124, https://doi.org/10.5194/egusphere-egu22-13124, 2022.

The delineation of geomorphometrical objects that can be translated to geomorphological features is one of the most practical aspects of geomorphometry. The concave (closed depressions) or convex features (mounds) are often important to be delineated from multiple points of view: theoretical approaches, planning for practical purposes, or various other aspects. In this work, I have approached sinkholes and burial mounds as representative cases of concave and convex features represented on high-resolution DEMs. Based on manual delineations, several algorithms of object-based delineation were tested for accuracy. The interest was in delineating as much as accurate possible the targeted features. Further, the segments were fed to a multilayer perceptron for the classification of the delineated segments. The results show promising accuracy in regard to both types of features.

How to cite: Niculiță, M.: Machine learning and geomorphometrical objects for convex and concave geomorphological features detection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1853, https://doi.org/10.5194/egusphere-egu22-1853, 2022.

In an area experienced a strong earthquake, the formation of clusters of seismic cracks is considered related to susceptibility to post-seismic slides. However, the relationship between crack distribution and the occurrence of post-seismic slides has rarely been evaluated. This study developed an index representing the spatial density of seismic cracks (dense crack index: DCI) for the area where post-seismic slides were identified after the 2016 Kumamoto earthquake (Mw 7.0). The susceptibility of post-seismic slides was then assessed using models that incorporated the weight of evidence (WoE) and random forest (RF) methods, with the DCI as a conditioning factor. Both the models confirmed the importance of the DCI, although the improvement in model performance as indicated by area under the curve values was marginal or negligible by including the index. This was largely because the combination of features that indicated where open cracks were likely to occur, or ridgelines where seismic waves were prone to be amplified, could compensate for the absence of the index. The contribution of the DCI could be improved if more accurate LiDAR data were used in the analysis.

How to cite: Kasai, M. and Yamaguchi, S.: Assessment of post-seismic landslide susceptibility using an index representative of seismic cracks , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13239, https://doi.org/10.5194/egusphere-egu22-13239, 2022.

EGU22-13325 | Presentations | GM2.3

Evaluating Geomorphometric Variables to Identify Groundwater Potential Zones in Sahel-Doukkala, Morocco

Adnane Habib, Abdelaziz El Arabi, and Kamal Labbassi

Topography and geology are considered the primary factors influencing groundwater flow and accumulation. To evaluate their potential in identifying groundwater potential, an integrated approach was provided and used in this work to delineate groundwater potential zones in Sahel-Doukkala, Morocco, by combining geomorphometric variables and a Multi-Criteria Evaluation (MCE) technique. Aside from lithology, all variables used in this approach were derived from a 10 m Digital Elevation Model (DEM) generated from ALOS-PRISM stereo-images using photogrammetric techniques. The chosen variables were considered to be very closely associated with groundwater circulation and accumulation, namely lithology, topographic wetness index (TWI), convergence index (CI), lineament density, lineament intersection density, and drainage network. These variables were given weights based on their respective importance in the occurrence of groundwater, by using a cumulative effect matrix. This process has shown that lineament density had the most effects on other variables, with the biggest weight (24%), followed by lineament intersection density (20%). TWI and CI succeeded 16% while lithology and drainage network density had the least weight (12%). Later, in a GIS system, an MCE based weight sum method was used for generating the groundwater potential zones map.

The obtained map was classified into three zones, viz. “poor”, “moderate” and “high”. These zones delineate areas where the subsurface has varying degrees of potential to store water and also indicate the availability of groundwater. It was found that the zone with “high” potential covered an area of approximately 714 km2 (44 % of the study area), and it identified areas that are suitable for groundwater storage. These zones showed a high association with low drainage density, low TWI values, and a high density of lineaments and lineament intersections. The groundwater potential zones map produced by the proposed approach was verified using the location and groundwater level depth of 325 existing wells that were categorized as successful, and the result was found satisfactory, with 91% of the successful exiting wells were located at zones that fall in the “moderate” and “high” areas. In addition, the validity of the proposed approach was tested according to the groundwater level depth, which indicates the actual groundwater potential. It was found that places with "high" potential have an average groundwater level depth of approximately 27 m, whereas areas with “moderate” and “poor” potential showed an average of 31 m and 37 m, respectively. The validation results show a good agreement between existing groundwater wells and the obtained groundwater potential zones map and were considered to be reasonable. Therefore, the produced map can be of great help to hydrogeologists to detect, with time and cost-effectively, new zones that may carry a high groundwater potential.

Because DEM data is one of the most widely and easily accessible data, the proposed method is well suited for areas where data is scarce. As result, it can be widely used to develop conceptual models based on geomorphometric variables as primary inputs for similar arid and semi-arid regions suffering from data scarcity.

How to cite: Habib, A., El Arabi, A., and Labbassi, K.: Evaluating Geomorphometric Variables to Identify Groundwater Potential Zones in Sahel-Doukkala, Morocco, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13325, https://doi.org/10.5194/egusphere-egu22-13325, 2022.

Stream morphology is an important indicator for revealing the geomorphological features and evolution of the Yangtze River. Existing studies on the morphology of the Yangtze River focus on planar features. However, the vertical features are also important. Vertical features mainly control the flow ability and erosion intensity. Furthermore, traditional studies often focus on a few stream profiles in the Yangtze River. However, stream profiles are linked together by runoff nodes, thus affecting the geomorphological evolution of the Yangtze River naturally. In this study, a clustering method of stream profiles in the Yangtze River is proposed by plotting all profiles together. Then, a stream evolution index is used to investigate the geomorphological features of the stream profile clusters to reveal the evolution of the Yangtze River. Based on the stream profile clusters, the erosion base of the Yangtze River generally changes from steep to gentle from the upper reaches to the lower reaches, and the evolution degree of the stream changes from low to high. The asymmetric distribution of knickpoints in the Han River Basin supports the view that the boundary of the eastward growth of the Tibetan Plateau has reached the vicinity of the Daba Mountain.

How to cite: Zhao, F. and Xiong, L.: Clustering stream profiles to understand the geomorphological features and evolution of the Yangtze River by using DEMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13121, https://doi.org/10.5194/egusphere-egu22-13121, 2022.

EGU22-8456 | Presentations | GM2.3

Sediment connectivity assessment through a geomorphometric approach: a review of recent applications

Marco Cavalli, Stefano Crema, Sara Cucchiaro, Giorgia Macchi, Sebastiano Trevisani, and Lorenzo Marchi

Sediment connectivity, defined as the degree to which a system facilitates the transfer of sediment through itself by means of coupling relationships between its components, has recently emerged as a paramount property of geomorphic systems. The growing interest of the earth sciences community in connectivity led this property to become a key concept concerning sediment transfer processes analysis and one of the building blocks of modern geomorphology. The increasing availability of high-resolution Digital Elevation Models (DEMs) from different sources as LiDAR and Structure from Motion (SfM) paved the way to quantitative and semi-quantitative approaches for assessing sediment connectivity. A geomorphometric index of sediment connectivity, based on DEM derivatives as drainage area, slope, flow length and surface roughness, has been developed along with related freeware software tool (SedInConnect). The index aims at depicting spatial connectivity patterns at the catchment scale to support the assessment of the contribution of a given part of the catchment as sediment source and define sediment transfer paths. The increasing interest in the quantitative characterization of the linkages between landscape units and the straightforward applicability of this index resulted in numerous applications in different contexts. This work presents and discusses the main applications of the sediment connectivity index along with a recent application in the frame of the Interreg ITAT3032 SedInOut Project (2019-2022). Being a topography-based index, it is focused on structural aspects of connectivity, and quality and resolution of DEMs may have a significant impact on the results. Future development should consider process-based connectivity and incorporate temporal variability directly into the index. Moreover, this work demonstrates that, when carefully applied considering the intrinsic limitations of the topographic-based approach, the index can rapidly provide a spatial characterization of sediment dynamics, thus improving the understanding of geomorphic system behavior and, consequently, hazard and risk assessment.

How to cite: Cavalli, M., Crema, S., Cucchiaro, S., Macchi, G., Trevisani, S., and Marchi, L.: Sediment connectivity assessment through a geomorphometric approach: a review of recent applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8456, https://doi.org/10.5194/egusphere-egu22-8456, 2022.

EGU22-13129 | Presentations | GM2.3

Research on texture features for typical sand dunes using multi-source data

Junfei Ma, Fayuan Li, Lulu Liu, Jianhua Cheng, and Guoan Tang

Deserts have obvious textural features. In detail, different types of sand dunes have significant differences in their morphological texture features. Existing studies on desert texture have mainly focused on extracting dune ridges or sand ripples using remote sensing images. However, comprehensive understanding of desert texture at multiple scales and quantitative representation of texture features are lacking. Our study area is in the Badain Jaran Desert. Four typical sand dunes in this desert are selected, namely, starlike chain megadune, barchans chain, compound chain dune, and schuppen chain megadune. Based on Sentinel-2 and ASTER 30m DEM data, the macroscopic and microscopic texture features of the desert are extracted using positive and negative topography, edge detection and local binary pattern (LBP) methods, respectively. Eight texture indexes based on gray level co-occurrence matrix(GLCM) are calculated for the original data and the abstract texture data respectivelyThen these texture parameters are clustered based on the result of Spearman correlation. Finally, the coefficient of variation is used to determine representative indicators for each cluster in order to construct a geomorphological texture information spectrum library of typical dune types. The results show that the macroscopic and microscopic texture features of the same type of sand dunes have high similarity. And geomorphological texture information spectrum can well distinguish different types of sand dunes by curve features.

How to cite: Ma, J., Li, F., Liu, L., Cheng, J., and Tang, G.: Research on texture features for typical sand dunes using multi-source data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13129, https://doi.org/10.5194/egusphere-egu22-13129, 2022.

EGU22-13343 | Presentations | GM2.3

A scale-independent model for the analysis of geomorphodiversity index

Laura Melelli, Martina Burnelli, and Massimiliano Alvioli

The World Urbanization Prospects (ONU) estimates that within 2050 about 70% of the world's population will live in urban areas. The use of GIS and spatial analysis are essential tools for proper land use planning, which takes into account the geomorphological characteristics of the territory, as the starting point for the safeguard of urban ecosystems.

Several geological and environmental approaches have been proposed, albeit they usually lack a new objective, quantitative and scale independent model. At variance with common approaches, recently a new geomorphodiversity index was proposed which aims at an objective classification of joint geological, hydrological, biotic and ... features, in Italy.

In this work, we show results of a study performed in urban areas in Italy, where we apply systematic spatial analysis for the identification of the geomorphodiversity index. The approach proposed a quantitative assessment of topographic features (i.e., slope and landforms classification) is a spatial analysis in GRASS GIS through the use of geomorphon method and additional morphometric quantities. We aim at the definition of a new scale-independent approach, analyzing all of the morphometric quantities calculated at different scales (i.e., within moving windows of different sizes). We shown that scale- and model-independent selection of such features is possible for most of the considered quantities.

We argue that our work is relevant for the objective selection of quantities to define a geomorphodiversity index, and its calculation in  areas of arbitrary size and geomorphological properties, provided the same input data is available.

How to cite: Melelli, L., Burnelli, M., and Alvioli, M.: A scale-independent model for the analysis of geomorphodiversity index, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13343, https://doi.org/10.5194/egusphere-egu22-13343, 2022.

The concept of terrain visibility is vast and hard to summarise in a single definition. It can be generically said that it is a property that measures how observable a territory is from a single or multiple points of view. 

The estimation or calculation of visibility indices has been used in multiple fields, including architecture, archaeology, communications, tourism, land planning, and military applications. Recently (Meinhardt et al., 2015, Bornaetxea et al., 2018, Knevels et al., 2020, ) the concept of viewshed, i.e. the geographical area that is visible from one or more points of view, has been called into play for applications involving geomorphology.  In particular, it has been used to identify the portions of territory in which existing landslide inventories, carried out through field surveys, can be considered valuable for the calculation of landslide susceptibility. The aim is to delineate the Effective Surveyed Area, i.e. the area that has actually been observed by the operators in the field. 

However, this purely geometric approach cannot guarantee that objects are actually visible just because they are in a direct line-of-sight relationship with the observer. Due to their size and/or orientation in space, they may be (i) poorly or not at all detectable and/or (ii) observable from only a few viewpoints.    

For this reason we have developed r.survey (Bornaetxea & Marchesini, 2021), a plugin (Python script) for GRASS GIS, which allows to simulate (i) from how many observation points each point of the territory is visible, (ii) from which point of observation each point of the territory is most effectively visible, (iii) whether an object of a specific size can be detected. Concerning, in particular, the last element, r.survey calculates the solid angle subtended by a circle of equivalent dimensions to those of the object to be surveyed and assumed to be lying on the territory, oriented according to the slope and aspect derived from a digital terrain model. The solid angle provides a continuous measure of the visibility of the object sought, which can be compared with typical values of a human visual acuity. What happens then is that the concept of 'Effective Surveyed Area' can be reworked into the more accurate 'Size-specific Effective Surveyed Area' (SsESA). The new concept makes it possible to identify those portions of territory in which, during fieldwork, it is possible to observe objects of equal or greater size than those of interest, also considering their orientation in space with respect to the observer. 

The code of r.survey, which is based on the libraries and modules of GRASS GIS and was written to exploit multi-core processing, is open source and available for downloading (https://doi.org/10.5281/zenodo.3993140) together with a manual and some example data.

How to cite: Marchesini, I. and Bornaetxea, T.: r.survey: a tool to assess whether elements of specific sizes can be visually detected during field surveys, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5715, https://doi.org/10.5194/egusphere-egu22-5715, 2022.

EGU22-13130 | Presentations | GM2.3

Regional differences in gully network connectivity based on graph theory: a case study on the Loess Plateau, China

Jianhua Cheng, Lanhua Luo, Fayuan Li, and Lulu Liu

Gullies are some of the areas with the most frequent material exchanges in loess landforms. By studying the influence of the spatial structure of gully networks on material transport and describing the difficulty of material transport from sources to sinks, it is of great significance to understand the development and evolution of loess landforms. This study is based on graph theory and digital terrain analysis and describes the relationship between gully networks and terrain feature elements via a gully network graph model. The adjacency matrix of the gully network graph model is constructed to quantify the connectivity. Taking six typical small watershed sample areas of the Loess Plateau as the research objects, the changes in the gully network connectivity characteristics in different loess geomorphic areas are analyzed from the aspects of overall network connectivity and node connectivity. The results show that (1) From Shenmu to Chunhua (the sample areas from north to south), the average values of the gully network edge weights first decrease and then increase. The maximum value is 0.253 in the Shenmu sample area, and the minimum value is 0.093 in the Yanchuan sample area. These values show that as the gully development increases, the greater the capacity of the gully network to transport materials is, and the less resistance the material receives during the transfer process. (2) The average node strength reaches the minimum in the Yanchuan sample area, and from Yanchuan to the north and south sides, it gradually increases. It can be concluded that the overall connectivity of the gully network shows a gradually weakening trend from the Yanchuan sample area to the north and south sides. (3) The potential flow (Fi) and network structural connectivity index (NSC) show similar characteristic changes; from north to south, the connectivity of nodes from the Shenmu to Yanchuan sample areas gradually increases, and from the Yanchuan to Chunhua sample areas, it gradually weakens. The accessibility from source to sink (Shi) shows the opposite trend. At the same time, the connectivity index values of the gully network nodes in the six typical areas all show clustered spatial distribution characteristics. (4) By comparing the results of the connectivity indicators calculated by the Euclidian distance used in the previous study and the sediment transport capacity index used in this study and by comparing the variation in the gully network quantitative indicators and the gully network connectivity indicators, this comparison result indicates the rationality of connectivity indicators in this paper. The connectivity of the gully network contains abundant and important information on the development and evolution of loess gullies. Research on the connectivity of the gully network will help deepen the understanding of the evolution process and mechanism of loess gullies.

How to cite: Cheng, J., Luo, L., Li, F., and Liu, L.: Regional differences in gully network connectivity based on graph theory: a case study on the Loess Plateau, China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13130, https://doi.org/10.5194/egusphere-egu22-13130, 2022.

GM2.4 – Dates, Rates and Bytes: Quantifying Geomorphological Processes and Landscape Dynamics

EGU22-10420 | Presentations | GM2.4 | Highlight

Intense precipitation during the African Humid Period inferred from east Saharan fossil rivers: Implications for human dispersal   

Abdallah Zaki, Georgina King, Negar Haghipour, Robert Giegengack, Stephen Watkins, Sanjeev Gupta, Mathieu Schuster, Hossam Khairy, Salah Ahmed, Mostafa El-Wakil, Saleh Eltayeb, Frédéric Herman, and Sébastien Castelltort

During Late Quaternary time, the paleoclimate of the eastern Sahara was punctuated by multiple pluvial periods, then dramatically and cyclically transformed to hyperarid conditions, receiving less than 2 mm/yr of precipitation at present. Geologists, climate modelers, and archaeologists, therefore, have used various proxies to reconstruct past climates during that time, a crucial period for human habitation and migration. These reconstructions, however, lack the precipitation pattern during those pluvial periods, which represents a significant control on weighing the hypotheses of human migrations and occupations. Here we reconstruct the chronology and paleohydrology of a set of fossil rivers expressed by ridges in the modern landscape due to differential erosion. Our 14C and Optically Stimulated Luminescence (OSL) ages of sediments preserved in these ancient rivers cluster within the last African Humid Period (AHP; ca. 14.8 – 5.5 ka BP) and hence support more significant fluvial activity during this distinct humid epoch. Based on median grain size (D50), paleochannel geometry, and drainage area, paleohydraulic reconstructions indicate that typical precipitation intensities of 55–80 mm/h occurred during sediment transport events. When combined with previous annual rainfall estimates, we find that such rainfall intensities were likely 3–4 times more frequent during the AHP. These climatic perturbations may have rendered some parts of the Nile River Valley inhospitable for occupation, driving humans to migrate away in the northwest and west of the Nile Valley between 10.2 and 7.2 ka BP. Ultimately, our results, along with the archeological data, tell a tale from the past of the dramatic climatic changes that our planet undergoes, demonstrating the critical role of climate in sustaining human populations. 

 

How to cite: Zaki, A., King, G., Haghipour, N., Giegengack, R., Watkins, S., Gupta, S., Schuster, M., Khairy, H., Ahmed, S., El-Wakil, M., Eltayeb, S., Herman, F., and Castelltort, S.: Intense precipitation during the African Humid Period inferred from east Saharan fossil rivers: Implications for human dispersal   , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10420, https://doi.org/10.5194/egusphere-egu22-10420, 2022.

EGU22-2141 | Presentations | GM2.4

Decoupling between fluvial aggradation-incision dynamics and paleo-denudation rates during the last glacial cycle, Crete, Greece

Richard Ott, Dirk Scherler, Karl Wegmann, Mitch D'Arcy, Susan Ivy-Ochs, Marcus Christl, and Christoph Vockenhuber

The impact of Quaternary climate cycles on denudation as well as fluvial aggradation and incision is debated, especially in regions that did not experience glaciation. Here we present a record of paleo-denudation rates, and geochronologic data constraining aggradation and incision from the Sfakia and Elafonisi alluvial sequences on the island of Crete, Greece. We report seven new optically stimulated luminescence (OSL) and ten new radiocarbon ages, as well as eight 10Be and eight 36Cl denudation rates from modern and terrace sediments. At the Elafonisi fan system, we identify four periods of aggradation, where marine isotope stages (MIS) 2, 4, and likely 6 correspond to aggradation periods, and MIS 1, 3, and likely 5e are characterized by incision. The dating of paleoshorelines indicates constant uplift over the past 71 ka, at rates of 1.2 mm/a. Aggradation occurred throughout the entire glacial cycle at the Sfakia fan, followed by up to 50 m of incision in the past 10 ka. Chronological constraints indicate that aggradation rates were particularly high during MIS 2 and 4, analogous to the Elafonisi fan system. However, our paleo-denudation rates indicate mostly constant denudation throughout the past 80 ka; with only two samples indicating an up to 50% increase in paleo-denudation rates compared to modern rates. Nearby climate and vegetation records show that MIS 2, 4, and 6 were characterized by cold and dry climate with sparse vegetation, whereas forest cover and wet conditions prevailed during MIS 1, 3, and 5. Our data suggest that variations in climate and vegetation cover were not sufficient to markedly alter landscape-wide denudation rates, but that changes in hydroclimate and vegetation exerted a strong control on the aggradation-incision behavior of the drainages. During relatively cold stages, low vegetation cover and river sediment transport capacity led to aggradation, whereas the increased river transport capacity during relatively warm stages caused subsequent incision. We therefore hypothesize that the studied catchments show a decoupling between transport-limited streams responding to climate forcing and near-steady hillslope denudation.

How to cite: Ott, R., Scherler, D., Wegmann, K., D'Arcy, M., Ivy-Ochs, S., Christl, M., and Vockenhuber, C.: Decoupling between fluvial aggradation-incision dynamics and paleo-denudation rates during the last glacial cycle, Crete, Greece, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2141, https://doi.org/10.5194/egusphere-egu22-2141, 2022.

EGU22-3441 | Presentations | GM2.4

Quantifying drainage-divide migration from orographic rainfall over geologic timescales: Sierra de Aconquija, southern Central Andes

Taylor Schildgen, Peter van der Beek, Mitch D'Arcy, Duna Roda Boluda, Orr Elizabeth, and Wittmann Hella

Drainage-divide migration, controlled by rock-uplift and rainfall patterns, may play a major role in the geomorphic evolution of mountain ranges. However, divide-migration rates over geologic timescales have only been estimated by theoretical studies and remain empirically poorly constrained. Geomorphological evidence suggests that the Sierra de Aconquija, on the eastern side of the southern Central Andes, northwest Argentina, is undergoing active westward drainage-divide migration. The mountain range has been subjected to steep rock trajectories and pronounced orographic rainfall for the last several million years, presenting an ideal setting for using low-temperature thermochronometric data and exhumation rates derived from in situ produced 10Be to explore its topographic evolution.

We perform three-dimensional thermal-kinematic modeling of previously published thermochronometric data spanning the windward and leeward sides of the range to explore the most likely structural and topographic evolution of the range. We find that the thermochronometric data can be explained by scenarios involving drainage-divide migration alone, or by scenarios that also involve changes in the structures that have accommodated deformation through time. By combining new 10Be-derived catchment-average denudation rates with geomorphic and stratigraphic constraints on fault activity, we conclude that the evolution of the range was likely dominated by west-vergent faulting on a high-angle reverse fault underlying the range, together with westward drainage-divide migration at a rate of several km per million years. Our findings place new constraints on the magnitudes and rates of drainage-divide migration in real landscapes, quantify the effects of orographic rainfall and erosion on the topographic evolution of a mountain range, and highlight the importance of considering drainage-divide migration when interpreting thermochronometer age patterns.

How to cite: Schildgen, T., van der Beek, P., D'Arcy, M., Roda Boluda, D., Elizabeth, O., and Hella, W.: Quantifying drainage-divide migration from orographic rainfall over geologic timescales: Sierra de Aconquija, southern Central Andes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3441, https://doi.org/10.5194/egusphere-egu22-3441, 2022.

*Georges Aumaître, Didier L. Bourlès, Karim Keddadouche

Located in northeastern France, the Vosges Mountains (VM) belongs to these Hercynian ranges strewn across the European alpine foreland. Peaking at ~1425 m of elevation, it presents four contrasting primary characteristics. Firstly, the geological basement allows a bipartite N-S subdivision: the Palaeozoic southern part (crystalline Vosges) composed of various igneous, metamorphic and sedimentary rocks contrasts with the much more homogeneous Triassic cover in the northern part (sandstone Vosges). Secondly, a clear E-W topographic gradient is reflected by steep hillslopes on the eastern side (Alsace) and gently-sloping hillslopes on the western side (Lorraine). Thirdly, a sharp W-E precipitation gradient (>1000mm/yr) is recorded between the windward and the leeward side. Finally, the imprint left by Quaternary climatic fluctuations yields a N-S gradient: whereas the crystalline Vosges hosted abundant valley glaciers, the sandstone Vosges were void of ice cover.

Owing to these advantageous characteristics, this contribution aims to present the first data of catchment-wide denudation at the massif scale and to explore the long-term interactions between denudation, lithological control, morphometry and climatic forcing. Modern stream sediments from 21 river catchments draining the whole massif were sampled for in situ 10Be and 26Al concentration measurements at the outlet of their mountainous reach. The mean Channel Steepness Index (ksn) was computed as a morphometric “predictor” of denudation rates. Groups of lithologically uniform catchments were statistically identified based on their lithological surficial proportions.

Catchment-wide denudation rates inferred from cosmogenic 10Be and 26Al concentrations range from 33 to 83 mm/ka and 38 to 337 mm/ka, respectively. The [26Al]/[10Be] ratio range from 1.43 to 7.96, highlighting a complex exposure history for the glaciated catchments. At the massif scale, results show (i) no relation between denudation and steepness, (ii) a strong positive relation between denudation and precipitations when lithological groups are considered and (iii) a negative relation between the surficial proportion of fluvio-glacial deposits in the catchment and the [26Al]/[10Be] ratio.

To our knowledge, this contribution is the first massif-scale attempt to quantify denudation in an European low- to medium-altitude mountain range. This is especially relevant as long-term landscape evolution in the Variscan belt, by contrast to the numerous works focusing on denudation in high-mountains ranges (e.g. the Alps), has been regularly disregarded in recent geomorphological studies. Importantly, whereas a vast majority of studies measuring denudation rates rely on 10Be concentrations only, this study highlights the need of using a pair of cosmogenic nuclides (i.e. 26Al/10Be) to check whether stream sediments in formerly glaciated catchments have experienced complex exposure history.

How to cite: Jautzy, T., Rixhon, G., Braucher, R., Schmitt, L., and Team*, A.: Measuring 10Be and 26Al concentrations in stream sediments from the Vosges Mountains (NE France) to explore the respective role of lithologic, topographic and climatic control on massif-wide denudation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5435, https://doi.org/10.5194/egusphere-egu22-5435, 2022.

In global geochemical cycles, the solid flux from the continent to the ocean is usually reduced to the input of sediments from rivers [1]. However, regional studies have shown that the input of sediments from rocky coast erosion may be a significant part of this flux [2]. So, it is important to consider this input into global cycles and to quantify it over different timescales.

On short-term timescales, from the year to the century, coastal erosion is currently quantified with direct measurement of the coastline recession, between successive time intervals [3]. Extrapolating on timescales longer than a thousand years is difficult. This leads to a lack of data and therefore a gap in knowledge in longer term coastal erosion [4].

A solution to quantify long-term erosion of rocky coast is to reconstruct the initial geometry of the coastline and to know the age of its formation. Volcanic islands are suitable objects for this method. Indeed, their initial shape is simple and can be easily reconstructed, and their maximum extension can be dated [5,6,7], although this age can be difficult to estimate. Thus, the topographic reconstruction of a volcanic island allows, by comparison with its current topography, the quantification of volumes lost by erosion. In turn, it becomes possible to obtain values of the rocky coast total recession on timescales from thousands to hundreds of thousands of years [8]. Moreover, the wide geographic distribution of volcanic islands provides a diversity of climatic and geodynamic settings allowing to analyze the effects of various factors on long-term coastal erosion.

Here we propose an improvement of this erosion quantification by accounting for the submarine morphology. Applying this approach for different volcanic islands, we carried out a statistical analysis of the impact of several factors that control long-term coastal erosion. This analysis allows us hierarchize these factors. This is the first step towards the formulation of long-term coastal erosion universal laws and towards the quantification of rocky coast sediment influx in global cycles.

 

[1] Milliman and Farnsworth (2013). Cambridge University Press.

[2] Regard et al. (in press).

[3] Bird (2011). John Wiley & Sons.

[4] Prémaillon et al. (2018). Earth Surface Dynamics 6, 651-668.

[5] Lahitte et al. (2012). Geomorphology 136, 148-164.

[6] Ramalho et al. (2013). Earth-Science Reviews 127, 140-170.

[7] Karátson et al. (2016). Geomorphology 253, 123-134.

[8] Bossis et al. (in press).

How to cite: Bossis, R., Regard, V., and Carretier, S.: The hierarchy of factors controlling long-term coastal erosion: a statistical approach from topographic reconstruction of volcanic islands., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8000, https://doi.org/10.5194/egusphere-egu22-8000, 2022.

The Southern Alps of New Zealand are among the world’s most active mountain ranges, with extremely high rates of exhumation and erosion. This place is therefore well suited to observe and comprehend sediment production at catchment scale and to study Quaternary landscape evolution.

Common methods to quantify erosion of a landscape include estimation of the suspended sediment yield (SSY), which is a proxy for short-term erosion rates, or measurement of cosmogenic 10Be concentrations in fluvial sediments, a demanding method that offers reliable erosion rates representative of larger time-span (millennial). Here, we propose single-grain post-infrared luminescence (SG-pIRIR) as a potential new proxy for erosion rates.  We test this approach by comparing SG-pIRIR results with catchment-wide erosion rates obtained using conventional 10Be measurements for eight catchments of the New Zealand Southern Alps.

10Be results demonstrate North-South and East-West gradients in erosion rates, ranging from 0.2 to 4.0 mm/yr, with the fastest towards South-West. The North-South gradient is consistent with existing data of Larsen et al., (2014), that present even higher rates to the south of our study area. We suggest that spatial gradient in erosion rate reflects a tectonic uplift gradient related to northward segmentation of the Alpine fault, coupled to an East-West climatic gradient, related to orographic effect.

Recently, luminescence signals have been proposed as a new tool to study exhumation, exposure histories and erosion, with various approaches including luminescence-depth profiles (Sohbati et al., 2018), luminescence thermochronometry (Herman and King, 2018) or direct relations between quartz luminescence sensitivity and erosion rates (Sawakuchi et al., 2018). Here, we tested the potential of equivalent dose (De) distributions obtained using SG-pIRIR as a proxy for catchment wide erosion rates.

We measured SG-pIRIR De distributions from modern fluvial sediments at the outlets of the eight catchments where we estimated 10Be erosion rates. For each of the samples, we calculated the fraction of grains whose luminescence signal is saturated (Bonnet et al., 2019; Guyez et al., 2022) and the fraction of well-bleached grains from De distributions. In addition, we characterized the De distribution using central age model (CAM; Galbraith et al., 1999) and bootstrapped minimum age model (MAM; Cunningham et al., 2012). We found a relationship between those four proxies and erosion rates obtained from conventional 10Be approaches, but also with SSY (Adams, 1980; Hicks et al., 2011) and channel steepness index. These results confirm the potential for this new tool to inform on catchment-wide erosion rates.

Further work should be undertaken to test this relation in other settings, and also to better comprehend the interplay of processes affecting luminescence signals of feldspar grains in fluvial deposits, with the perspective to use it as an independent reliable tool to reconstruct and possibly quantify erosion and transport processes in a wide range of fluvial settings.

How to cite: Guyez, A., Bonnet, S., Reimann, T., Wilkinson, C., Carretier, S., Norton, K., and Wallinga, J.: Does luminescence of modern fluvial sediments vary according to erosion rate? A comparison between single-grain feldspar p-IRIR dose distributions and 10Be cosmogenic catchment-wide erosion rate in the Southern Alps of New Zealand, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5390, https://doi.org/10.5194/egusphere-egu22-5390, 2022.

EGU22-2762 | Presentations | GM2.4

Biotic, lithologic and geomorphic control on sediment production from detrital apatite geochemistry and thermochronology

Andrea Madella, Christoph Glotzbach, and Todd Ehlers

Where, and how much sediment is produced and transported in hillslope and fluvial systems depends upon the topographic slope, soil production rate, lithology, precipitation, and biota. In this study we investigate the patterns of sediment production in two catchments of the Coastal Cordillera (Chile) situated in semi-arid and mediterranean bioclimates. We do this by measuring 29 bedrock and 6 detrital apatite trace elements and apatite cooling ages with the U/Pb, fission track, U-Th(-Sm)/He thermochronometric systems. Detrital samples were collected from fluvial sediment and provide a catchment-scale view of the upstream areas. The compositional and geochronologic data measured in bedrock are analized with a Principal Component Analysis and a clustering algorithm to find the parameters that are best suited to trace sediment provenance at the sub-catchment scale. Next, we analyse the distribution of the same parameters within the detritus to infer the relative contribution of different areas within the catchments. Results indicate that spatial variations of bedrock cooling age and geochemical composition are significant even within small-scale (10-100 km2) granitoid catchments. Therefore, the combination of detrital apatite geochronology and geochemistry allows discrimination among source areas with acceptable confidence. Preliminary results show that the impact of vegetation distribution, hillslope angles and bedrock weatherability on sediment production differs in the two bioclimatic settings. In particular, hillslope angles and lithology exert a greater impact in the semi-arid catchment.

How to cite: Madella, A., Glotzbach, C., and Ehlers, T.: Biotic, lithologic and geomorphic control on sediment production from detrital apatite geochemistry and thermochronology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2762, https://doi.org/10.5194/egusphere-egu22-2762, 2022.

EGU22-6716 | Presentations | GM2.4

A dammed palaeo-lake at the middle Yarlung Tsangpo River, Tibet

Hai-Ping Hu, Jin-Liang Feng, and Georgina King

The Yarlung Tsangpo River follows the Indus-Tsangpo suture through the southern Tibetan Plateau, and then becomes the Brahmaputra, following a bend into India through the Yarlung Tsangpo Gorge. In the middle reaches, narrow gorges alternate with broad valleys (Zhang, et al. 1998). In the section with steep and narrow gorges, the river is easily dammed by landslides, glaciers and/or moraines, rock avalanches and debris flows. Palaeo-lake sediments were discovered in the broad Xigazê valley and Dazhuka-Yueju gorge in the middle reach of the Yarlung Tsangpo River in Tibet. The river was likely dammed by a glacier and/or moraine at the eastern end of the Dazhuka-Yueju gorge. AMS 14C and OSL ages of lacustrine sediments indicate the palaeo-lake was formed during the period from ~30.2 to 32.3 cal. kyr BP, and failed at ~13.2 cal. kyr BP (Hu et al., 2018). The elevation of the dammed lake was 3811 m a.s.l., and its length, maximum water depth, and volume were 185 km, 211 m, and ~22.55 km3, respectively (Hu et al., 2022). The volume of the sediment was ~11.56 km3, which was calculated from the dam location, sediment surface elevation, and the ASTER GDEM2 data. Therefore, the backwater volume was 10.99 km3, and the peak flood possibly exceeded 3.4 × 105 m3/s during the dam failure. The dammed palaeo-lakes in the vallyes downstream of the middle Yarlung Tsangpo River were also discharged during ~13 ka, and they were likely interconnected by hydrological processes. Hence, the failure of the dam and related flooding from the Dazhuka-Yueju gorge probably triggered a chain reaction of dam failures downstream, forming a megaflood. However, the dammed event in the Dazhuka-Yueju valley probably had a limited effect on the landforms at downstream because of the presence of another dammed palaeo-lake in the broad Zetang valley. So the ages of the dammed palaeo-lakes at the middle Yarlung Tsangpo River need to constrained more precisely.

References

Hu, H.-P., Feng, J.-L., Chen, F., 2018. Sedimentary records of a palaeo-lake in the middle Yarlung Tsangpo: Implications for terrace genesis and outburst flooding. Quaternary Science Reviews, 192, 135-148.

Hu, H.-P., Liu, J.-H., Feng, J.-L., Ye, C.-S., Lv, F., Chen, F., Gong, Z.-J., Chen, L.-Q., Du, D.-D., 2022. Geomorphic processes of a dammed palaeo-lake in the middle Yarlung Tsangpo River, Tibet. Science of the Total Environment, 811C, 151949.

Zhang, D.D., 1998. Geomorphological problems of the middle reaches of the Tsangpo River, Tibet. Earth Surface Processes and Landforms, 23(10): 889-903.

How to cite: Hu, H.-P., Feng, J.-L., and King, G.: A dammed palaeo-lake at the middle Yarlung Tsangpo River, Tibet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6716, https://doi.org/10.5194/egusphere-egu22-6716, 2022.

EGU22-7356 | Presentations | GM2.4

Geomorphometric constraints on the development of the Wutach capture

Wolfgang Schwanghart, Stefanie Tofelde, Dirk Scherler, Richard Ott, Andreas Ludwig, and Angela Landgraf

The Wutach capture is one of the most prominent river captures in central Europe. Subsidence of the Upper Rhine Graben and subsequent incision of tributaries to the Hochrhein led to the piracy of the Danube-Wutach draining the Feldberg region of the Black Forest at ~18 ka. The sudden lowering of the base level led to headward incision of the Wutach and the formation of numerous fluvial knickpoints along the trunk river and its tributaries. These knickpoints represent excellent markers that enable testing several hypotheses including the role of bedrock erodibility, the impact of deglaciation, and mechanisms that control the diversion of the Wutach. Here we present a geomorphometric approach predicated on the stream-power incision model to test these hypotheses. We show that the spatial distribution of knickpoints upstream of the capture is consistent with predictions by the stream-power model. Including proxy information about deglaciation change the parameters of the model, but only slightly increase the fit between modelled and observed knickpoint locations. By comparing estimates of the erodibility derived from knickpoints to those derived from catchment-wide denudation rates in nearby catchments, we observe differences of the order of two magnitudes. The difference in these estimates may can be explained by several processes including channel-bed armouring by sediment. We conclude that stream power parameters derived from the spatial distribution of knickpoints in the Wutach catchment are representative of exceptional (short-term) erosional conditions right after the capture event, rather than of landscape evolution on longer-term geological timescales.

How to cite: Schwanghart, W., Tofelde, S., Scherler, D., Ott, R., Ludwig, A., and Landgraf, A.: Geomorphometric constraints on the development of the Wutach capture, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7356, https://doi.org/10.5194/egusphere-egu22-7356, 2022.

  Quantifying the rate and timing of landscape evolution is required to better understand the interaction between tectonic and surface processes and the potential influence of climate change on million-year time scales. Pecube is a 3D thermo-kinematic model capable of predicting low-temperature thermochronometric ages based on variable rock exhumation within an evolving topography driven by tectonic and surface processes. Pecube has been widely used over the past two decades to constrain the timing and rate of relief development, model paleo topographies, establish robust sampling strategies, and track the evolution of glaciated landscapes. Since its initial development by Braun (2003), many new functionalities have been added to Pecube to incorporate lower-temperature thermochronometers (e.g., OSL), lateral advection along faults, and the ability to provide topography evolution scenarios resulting from a surface processes model (SPM). Although widely used, the current version of Pecube (1) still necessitates the use of a non-user-friendly terminal, and (2) lacks sample-specific thermochronometric predictions, including radiation-damage dependent helium diffusion models for (U-Th)/He-based thermochronometers. These two shortcomings may limit the use of Pecube by the community.

  Here, we introduce a newly developed graphical user-friendly interface for Pecube, called PecubeGUI, which incorporates new tools intended to clearly guide the user through all model input parameters for all functionalities of Pecube. Among them, the user is now able to simply load topographic files from a digital elevation model (DEM) or a SPM, and interactively set (i) the topographic evolution scenario by direct visual inspection, and (ii) the corresponding steady-state geotherm. PecubeGUI also enables the ability to predict ages in specific locations on a DEM with the use of up-to-date models for helium production and diffusion in apatite. For a single synthetic grain, the user can choose between several diffusion models, and can define zonation. In addition, 4He/3He release spectra can be predicted and compared with observed data.

  To illustrate the capabilities of PecubeGUI, we present a case-study that couples a glacial landscape evolution model (iSOSIA, Egholm, 2011) with updated Pecube functionalities. We use a forward modelling approach to assess the capability and sensitivity of apatite (U-Th)/He and 4He/3He thermochronometric data, to constrain the spatial and temporal distribution of glacial erosion at exceptionally high-resolutions in the Rhone valley (Swiss Alps) over multiple Quaternary glaciations. There, apatites show a potential for variable damage accumulation (eU = 12-280 ppm), implying variable single-grain closure temperatures. Previous modelling works suggest glacial incision at 1 Ma (Valla et al., 2011; Valla et al., 2012). With the observed data as constraints, we discuss how single-grain age predictions with detailed production-diffusion models (including the effect of radiation damage), can be used to (1) strategically establish the most effective sampling sites; and (2) constrain the spatial and temporal distribution of glacial erosion at the scale of a landscape, as well as at individual sampling sites.

How to cite: Bernard, M., van der Beek, P., Colleps, C., and Amalberti, J.: PecubeGUI: a new graphical user interface for Pecube, introduction and sample-specific predictions of apatite (U-Th)/He and 4He/3He data in the Rhone valley, Switzerland., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2277, https://doi.org/10.5194/egusphere-egu22-2277, 2022.

EGU22-3544 | Presentations | GM2.4

Synthesizing uniform 3He concentrations in accessory minerals for 4He/3He thermochronology: Current status, complications, and prospects

Cody Colleps, Peter van der Beek, Julien Amalberti, and Maxime Bernard

High-resolution 4He/3He thermochronometry involves stepped-heat degassing of U and Th-bearing accessory minerals with simultaneous measurement of natural 4He (non-uniform bulk distribution) and synthetically produced 3He (uniform bulk distribution) at each step. The ratio evolution of 4He/3He measured across all heating steps reflects the spatial distribution of 4He within a single crystal, which can be coupled with its (U-Th)/He date to model high-resolution low-temperature thermal histories. Although an exceptionally powerful tool to elucidate disputed drivers of crustal exhumation in various geologic settings (e.g., climatic vs. tectonic mechanisms), the 4He/3He method is commonly hindered by the necessity to uniformly synthesize 3He within crystals at concentrations >1x109 atoms/mg for single grain analysis. This high concentration is required to ensure that the 3He released at initial heating steps—where the most important geological information is preserved—is sufficiently above blank-detection limits of modern, highly-sensitive noble gas mass spectrometers. Synthesis of high 3He concentrations is conventionally achieved via the spallation of targeted nuclei during high-energy proton irradiations to fluences >1x1015 protons/cm2; however, facilities capable of, or willing to, efficiently carry out such anomalously high-fluence irradiations using previously defined methods remain few and far between. Here, we summarize the current state-of-the-art of synthesizing uniform distributions of 3He in geologic materials, and present preliminary 4He/3He measurements on gem-quality Durango apatite using conventional and alternative approaches to induce 3He to sufficient concentrations. Alternative approaches include (1) in-vacuum proton-irradiation with a narrowly focused proton beam to maximize intensities for short-duration experiments, and (2) direct uniform 3He implantation via sample exposure to an energy-modulated 3He beam. We discuss the advantages and disadvantages of both conventional and alternative methods in regards to 3He uniformity, concentration limitations, crystal lattice damage, efficiency, post-experiment ‘cool-down’ times, and accessibility. Both alternative approaches are considerably less demanding on particle accelerator facilities, and can significantly reduce the post-experiment waiting time required to safely handle activated samples. Accordingly, these approaches, if proven successful, yield great promise to improve the accessibility and efficiency of routine 4He/3He analyses for geologic applications.

How to cite: Colleps, C., van der Beek, P., Amalberti, J., and Bernard, M.: Synthesizing uniform 3He concentrations in accessory minerals for 4He/3He thermochronology: Current status, complications, and prospects, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3544, https://doi.org/10.5194/egusphere-egu22-3544, 2022.

We present published bedrock apatite fission track (AFT) and apatite (U-Th)/He (AHe) ages from the Northern Apennines to provide new insights into the spatial and temporal pattern of erosion across the mountain range. The spatial pattern of time-averaged erosion rates derived from AFT ages illustrates similar erosion rates on the Ligurian and Adriatic sides of the range. However, erosion rates derived from AHe ages are higher on the Adriatic side of the range, relative to the Ligurian side. The temporal pattern of time-averaged erosion rates illustrates an overall decrease in erosion through time on the Ligurian side, but suggests an increase in erosion through time on the Adriatic side. These results are corroborated by an analysis of paired AFT and AHe thermochronometer samples, which illustrate that erosion rates have generally increased through time on the Adriatic side, but have decreased through time on the Ligurian side. We infer that such regional scale-differences must be controlled by first-order features of the Northern Apennines, so we present an updated kinematic model to understand what could control these differences. Using imposed erosion rates on the Ligurian side that are a factor of two slower relative to the Adriatic side, we demonstrate that cooling ages and maximum burial depths are able to replicate the pattern of measured cooling ages across the orogen and estimates of burial depth from vitrinite reflectance data. These results suggest that horizontal motion is an important component of the overall rock motion in the wedge, and that the asymmetry of the orogen has existed for at least several million years.

How to cite: Erlanger, E., Fellin, M. G., and Willett, S.: Reexamining the temporal and spatial patterns of exhumation and erosion in the Northern Apennines: new insights from low-temperature thermochronometers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2342, https://doi.org/10.5194/egusphere-egu22-2342, 2022.

EGU22-8054 | Presentations | GM2.4

Deciphering rock cooling histories in the European Alps using ESR and OSL thermochronometry

xiaoxia wen, Melanie Bartz, Leif Anderson, and Georgina King

The impact of Quaternary glaciation on rates of erosion and the timing of Alpine valley incision remains disputed. This is mainly due to a lack of geochronological methods that cover the timespan of 103-106 years. While conventional thermochronometers like (U-Th-He) in apatite can constrain timescales of 106 years, and cosmogenic nuclide (CN) dating timescales of 101-103 years, it remains difficult to resolve changes in erosion rates at the timescale of glacial/interglacial cycles. To fill this temporal gap, we develop electron spin resonance (ESR) thermochronometry using both the Al and Ti centres in quartz. The combination of ESR and optically stimulated luminescence (OSL) thermochronometry, as well as numerical modelling approaches, will allow the development of a multi-thermochronometric system to understand rock cooling histories, enabling changes in erosion rates to be related to glacial advance and retreat.

 

In this study, we focus on the western European Alps, which were intensively glaciated during the Quaternary. Three vertical transects are targeted in the Rhône valley, which is thought to have substantially deepened around 1 million years ago[1]. The first transect consists of seven quartz samples, which were used for (i) optimizing the measurement protocols (i.e., preheat conditions, dose recovery), (ii) analyzing ESR signal growth and thermal stability of the Al and Ti signals to estimate kinetic trap parameters; and (iii) inverting the ESR data to constrain rock cooling histories.

 

A series of laboratory experiments show the potential of the single aliquot regenerative dose protocol. The Al and Ti signals show similar thermal stability between different samples in the same transect and yield mid-Pleistocene ages. Preliminary inversion of the data shows that the low closure temperatures of the Al and Ti signals in quartz allow the Late Quaternary exhumation of the Alpine valleys to be resolved. Our new ESR thermochronometry results will be supported by OSL thermochronometry measurements, CN dating and also the high density of existing thermochronometric data [e.g. 1] providing new insights into the glacial incision history during the Quaternary and especially how erosion rates varied temporally under a changing climate.

 

Keywords glacial erosion; landscape evolution; ESR; European Alps

 

Reference:

[1] Valla, P.G., D.L. Shuster, and P.A. van der Beek. 2011. Significant increase in relief of the European Alps during mid-Pleistocene glaciations, Nature Geoscience. 4(10): p. 688-692.

How to cite: wen, X., Bartz, M., Anderson, L., and King, G.: Deciphering rock cooling histories in the European Alps using ESR and OSL thermochronometry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8054, https://doi.org/10.5194/egusphere-egu22-8054, 2022.

EGU22-7404 | Presentations | GM2.4

Rates of erosion in the Japanese Alps during the Quaternary – Insights from trapped charge thermochronometry

Melanie Bartz, Georgina E. King, Leif S. Anderson, Frédéric Herman, Shigeru Sueoka, Sumiko Tsukamoto, and Takahiro Tagami

EGU22-11065 | Presentations | GM2.4

Combining landscape evolution modelling and low T thermochronology to determine the driving forces of relief rejuvenation

Fabian Dremel, Jörg Robl, Christoph von Hagke, and Kurt Stüwe

The Variscan orogeny lasted from the Late Devonian to the Early Permian and resulted in a mountain range whose remnants can be found today in North America, Northern Africa, Europe and Asia. Although the mountain range was almost completely eroded to peneplains in the Permian, today the Variscan massifs (e.g., Appalachians, Massif Central, the Black Forest, Bohemian Massif) feature hilly to mountainous topography with peak elevations exceeding 1500 metres. This indicates surface uplift during the last million years. Clearly, the latest surface uplift is unrelated to the original mountain building phase, but cause, wavelength, timing and rates are still disputed.

Several Variscan massifs are characterised by low relief surfaces, rounded hilltops and graded river profiles with low channel gradients at higher elevations, but deeply incised rivers with migrating knickpoints and steep valley flanks prone to mass wasting at lower elevations near the base level of the receiving streams. This landscape bimodality may indicate temporal and/or spatial variations in uplift rates. Although these massifs have been studied extensively, the driving forces for relief rejuvenation are still unknown.

We investigate relief rejuvenation using two approaches, landscape metrics and low-temperature thermochronometry. This allows us to constrain landscape dynamics on different timescales, with both approaches covering the post-orogenic period. We use the Bohemian Massif as pilot study area, encompassing parts of Germany, Austria, Czech Republic and Poland. First results from the geomorphic analyses allow quantifying the observed landscape bimodality, with highest ksn values at lower reaches of tributaries of the Danube River. Distinct across divide gradients in χ with low χ values on the Danube side indicate that the Danube tributaries feature a higher channel steepness on average than those of the Vltava. Assuming spatially uniform uplift rates and bedrock properties, across-divide gradients in χ may provide evidence for a northward migration of the watershed. In this case, the Danube catchment would grow at the expense of the Vltava catchment.

In addition, we compiled existing cooling ages from the Bohemian Massif to see if similar patterns can be observed on longer timescales. First results show that in the Sudetes in the NE of the Massif, cooling ages found at high altitude areas are predominantly Late Cretaceous, while in lower areas Late to Middle Paleogene cooling ages prevail. South of the Sudetes, in the Austrian Mühlviertel region, this trend seems to be reversed. Local younger ages (late Mesozoic) are found in the higher reaches, while Jurassic cooling ages dominate in the lower sections. However, the relief rejuvenation identified in the geomorphological analysis does not appear to be reflected in this thermochronological data. To reconcile these findings and determine the spatial extent of the different cooling patterns, more low-T thermochronological data is currently processed.

How to cite: Dremel, F., Robl, J., von Hagke, C., and Stüwe, K.: Combining landscape evolution modelling and low T thermochronology to determine the driving forces of relief rejuvenation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11065, https://doi.org/10.5194/egusphere-egu22-11065, 2022.

GM2.5 – What’s new with cosmogenic nuclides? Technique developments and applications of cosmogenic nuclides

EGU22-3670 | Presentations | GM2.5

Neon isotopic signature applied to detrital provenance assignment in foreland basins

Yan Ma, Dewen Zheng, Huiping Zhang, and Jianzhang Pang

Cosmogenic noble gas isotope 21Ne in terrestrial rocks has been used primarily to determine timing and rates of the Earth’s surface evolution. Here we explore the ability of detrital 21Ne as a provenance tracer, considering that Ne isotopes produced in source rocks could be preserved in minerals over geological time and might be predominant in total Ne inventory of sediments sunk in basins. This ability is predicated on potential source terranes of a given stratigraphic section with distinct neon isotopic signatures. Here we analyze neon isotopes of a well-dated Miocene–Pleistocene sedimentary archives in Kuqa foreland basin of southern Tianshan. The data suggest that the neon isotopic signature, which is expressed as εNe and defined in this work as the excess 21Ne/20Ne-ratio relative to atmospheric ratio, is stratigraphically sensitive to changes in local source terranes. This result is compatible with U/Pb provenance analysis and also supported by evidences from sandstone petrography and heavy mineral analysis. Influence of other non-source related 21Ne components in sedimentary archives on sensitivity of εNe has proven to be negligible. Furthermore, the integrated stratigraphic signatures of neon isotope and U/Pb age permit the detection of differential erosion in drainage basin, by which the tectonic or climatic effects on geomorphic evolution could be deciphered.

How to cite: Ma, Y., Zheng, D., Zhang, H., and Pang, J.: Neon isotopic signature applied to detrital provenance assignment in foreland basins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3670, https://doi.org/10.5194/egusphere-egu22-3670, 2022.

EGU22-7018 | Presentations | GM2.5

Soil dynamics at its extremes: insights from cosmogenic and fallout radioactive nuclides

Markus Egli and Alessandra Musso

Soil production and denudation are important and opposing processes that ultimately determine soil formation trajectories and, thus, the landscape. High mountainous areas are geomorphologically active environments and are strongly shaped by the redistribution of sediments and soils. With global warming and the subsequent retreat of glaciers, these processes become increasingly important. New areas having fresh and mostly unweathered glacial till is exposed and soils start to form. The dynamics of soil production and denudation in these high-mountainous landscapes are, however, not yet fully understood. We therefore aimed at exploring the relationship between soil production and denudation at different stages of soil development. This was done by comparing a calcareous and a siliceous soil chronosequence in the central Swiss Alps over the last about 14 kyr. We calculated element mass balances to determine weathering rates and measured short- and long-term erosion rates based on meteoric 239+240Puand10Be. In both chronosequences, the erosion rates were highest in the young soils (on average 5−10 t ha-1 a-1 soil loss). Erosion rates decreased markedly after 3−5 ka of soil development (on average 1−2.5 t ha-1a-1 soil loss) to reach a more or less stable situation after 10−14 ka (on average 0.3–2 t ha-1a-1). Chemical weathering and soil production rates also decreased over time, particularly on the calcareous soil sequence.

Depending on the relief and vegetational development, it takes up to 10 ka to reach soil and slope stability. Despite the very high erosion rates, particularly at the start of soil formation, mineral dissolution and transformation reactions are detected and a high rate of organic matter accumulation is measured. Soil production rates reach under such conditions extreme values. In the early stages of soil development, the parent material mainly drives soil formation while at later stages the vegetation becomes more dominant as it promotes surface stability, complex hydrological pathways and chemical weathering that determine water drainage and retention dynamics.

How to cite: Egli, M. and Musso, A.: Soil dynamics at its extremes: insights from cosmogenic and fallout radioactive nuclides, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7018, https://doi.org/10.5194/egusphere-egu22-7018, 2022.

EGU22-13085 | Presentations | GM2.5

Long-term survival of detrital gold in glaciated landscape based on cosmogenic 3He in detrital grains from Scotland 

Ana Carracedo Plumed, Luigia di Nicola, Valerie Olive, and Fin Stuart

The ability to measure cosmogenic 3He from individual detrital mineral grains [1] provides the potential to tease out details of sediment storage and transport that are unavailable from bulk sample analysis, and may, for instance, shed light on the conditions necessary to form economic alluvial placer deposits. While extremely long exposure histories have been measured in detrital grains from unglaciated regions [1], the effect of repeated glacial cycles in removing economically valuable detrital minerals is unknown. Here we report the cosmogenic 3He content of 36 (2-50 mg) native gold grains from the beds of 8 streams in upland Scotland in order to determine their ability to survive glaciation.

Measured 4He concentrations vary from 4 to 299 x 1013 atoms/g these variation on the 4He concentrations may be related to the presence of U and Th in the mineral lattice or U- and Th-rich mineral inclusions. Based on measured Li contents (<1 ppb) the nucleogenic 3He contribution in all samples is negligible. Minimum cosmogenic 3He exposure ages have been determined using production rate of 25 atoms/g/year and assuming no shielding.  33 grains yield exposure ages that are consistent with survival of detrital gold from before the Last Glacial Maximum (i.e > 20 Ka). These grains yield ages up to 4 Ma.   This implies that a significant proportion of the detrital gold has survived several glacial cycles and may have implications for long-term preservation of economic minerals in glaciated regions.

 

[1] O. Yakubovich, F.M. Stuart, A. Nesterenok & A. Carracedo (2019). Chemical Geology 517, 22-33.

How to cite: Carracedo Plumed, A., di Nicola, L., Olive, V., and Stuart, F.: Long-term survival of detrital gold in glaciated landscape based on cosmogenic 3He in detrital grains from Scotland , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13085, https://doi.org/10.5194/egusphere-egu22-13085, 2022.