GM5.2 | Fluvial systems: dynamics and interactions across scales

GM5.2

EDI

Fluvial systems cover much of the Earth’s surface; they convey water, sediments, and essential nutrients from the uplands to the sea, intermittently transferring these materials from the river channel to the adjacent floodplain. The routing of sediment and water through the channel network initiates complex process-form interactions as the river bed and banks adjust to changes in flow conditions. Despite their ubiquity, little is known about the landform-driven morphodynamic interactions taking place within the channel that ultimately determine patterns of sedimentation and changes of channel form. Furthermore, an understanding of how these process-form interactions scale with the size of the fluvial system is also currently lacking. Recent technological and methodological advances now afford us the opportunity to study and to quantify these process-form interactions in detail across a range of spatial and temporal scales.
This session aims to bring together interdisciplinary researchers working across field, experimental, and numerical modelling approaches who are advancing methods and providing new insights into: (i) sediment transport and morphodynamic functioning of fluvial systems, (ii) evaluating morphological change at variable spatial and temporal scales, such as at event vs. seasonal scales, and (iii) investigating the sedimentology of these river systems. We particularly welcome applications which investigate the morphodynamic response of fluvial systems in all types and sizes and we would specifically like to encourage submissions from early career researchers and students.

Convener: Eliisa Lotsari | Co-conveners: Joshua Ahmed, László BertalanECSECS, Christopher Hackney
Orals
| Thu, 27 Apr, 14:00–17:45 (CEST)
 
Room D3
Posters on site
| Attendance Thu, 27 Apr, 08:30–10:15 (CEST)
 
Hall X3
Orals |
Thu, 14:00
Thu, 08:30

Orals: Thu, 27 Apr | Room D3

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.
Chairpersons: László Bertalan, Christopher Hackney
14:00–14:05
14:05–14:25
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EGU23-7161
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GM5.2
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solicited
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Highlight
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On-site presentation
Zoltán Szalai, Gergely Jakab, Lili Szabó, Anna Vancsik, Gábor Maász, Péter Dobosy, Árpád Ferincz, Tibor Filep, László Bauer, and Attila Kondor

A significant part of the world's population lives around rivers. The riparian zone is not only a source of drinking water for urbanised areas; streams and rivers are also sinks for wastewater. As a result of the increased consumption of pharmaceutically active compounds (PhACs) in past decades, wastewater untreated and treated is a continuous load of these compounds (and their metabolites) to fluvial systems. The water supply for these kinds of urbanised areas is partly provided by riverbank filtration plants which can be significantly affected by PhACs loading. Riverbank filtration is effective for most pollutants. However, the filtering efficiency for these molecules is poorly known. This presentation focuses on the spatial and temporal distribution of more than a hundred PhACs in the streams and rivers of the Budapest Metropolitan Area. Our presentation demonstrates that bank filtration can also be effective for the filtration of organic micro-pollutants in highly urbanised areas.

Samples were collected during five sampling campaigns. The streams, rivers, and drinking water wells were sampled. The stream sediments were also sampled. Altogether 111 PhACs were measured. In small streams and rivers, eighty-one PhACs were systematically detected, while fifty-three PhACs were detected in the Danube. The quantification of 19 PhACs in the Budapest section of the river was without any precedent, and 10 PhACs were present in >80% of the samples. More PhACswere detectable in the small watercourses, and the concentrations were significantly higher than in the Danube. Sediments always contain fewer PhACs than water. This is mainly due to the high sorption capacity of sediments.

The most frequent PhACs showed higher concentrations in winter than in summer. In the drinking water wells 32 PhACs were quantified. For the majority of PhACs, the bank filtration efficiency was higher than 95%. Concentrations of the compounds did not influence the efficiency of filtering. For some PhACs (e.g. carbamazepine lidocaine, tramadol, and lamotrigine), low filtration efficiency was observed. These frequently occurring PhACs in surface waters have a relatively even distribution, and their sporadic appearance in wells is a function of both space and time, which may be caused by the constantly changing environment and micro-biological parameters, the dynamic operating schedule of abstraction wells, and the resulting sudden changes in flow rates.

This research was funded by the National Research, Development, and Innovation Office (NKFIH), grant numbers: K-142865 and 2020-1.1.2-PIACI-KFI-2021-00309.

How to cite: Szalai, Z., Jakab, G., Szabó, L., Vancsik, A., Maász, G., Dobosy, P., Ferincz, Á., Filep, T., Bauer, L., and Kondor, A.: Pharmaceutically active compounds in streams and rivers of urbanised areas: adsorption in sediments and efficiency of the riverbank filtration, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7161, https://doi.org/10.5194/egusphere-egu23-7161, 2023.

14:25–14:35
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EGU23-13987
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GM5.2
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ECS
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On-site presentation
Miloš Rusnák, Ján Kaňuk, Anna Kidová, Milan Lehotský, Ján Sládek, and Lukáš Michaleje

Freely migrating and dynamic rivers are strongly affected by changing natural conditions in industrial Europe and altered by increasing human pressure on the landscape. Anthropogenic modification, grade-control structures and channelization resulted in channel narrowing, transformation and incision in many rivers in Europe. The Belá river is the last multichannel river system in Slovakia and during the 20th century, systematic regulation and human impact on the environment resulted in rapid channel incision. The channel planform evolution and channel bed changes were analysed in the natural, braided-wandering river system of the Belá river. For spatial-temporal analyses of the channel pattern changes and transformation were used long-term historical aerial data (1949 – 2018; 11 horizons) and high-resolution data were collected from UAV (Unmanned Aerial Vehicle) and TLS (Terrestrial Laser Scanning). Both sources were used for detailed topographic models (including bathymetry) and classified point cloud generation. Lidar dataset combined with a floodplain age map was used for tracking incision intensity during the different time periods and in different river sections.  Sediment supply to the channels correlates with the magnitude of flood events and during the TLS survey from March 2016 to November 2018, 25 964 tonnes of fine-grained sediment were delivered into the river channel. Bed incisions achieve 2.5 m in the last 10 years with the propagation of a knickpoint zone by backward erosion upstream conditioned by the system of cross-valley faults and anthropogenic impact. In 2000, a small hydropower plant was constructed in the position of an old abandoned channel. A rapid incision uncovered a bedrock channel bed formed by a clay sequence of Huty formation (inner-Carpathian Paleogene). The abandoned channel is now used as a supply channel for the hydropower plant and the second natural active channel is artificially maintained by heavy machinery to ensure water supply for the hydropower plant. Human impact disturbed the balance of the sediment system leading to the overall degradation of the channel and loss of ecological functions.

How to cite: Rusnák, M., Kaňuk, J., Kidová, A., Lehotský, M., Sládek, J., and Michaleje, L.: Channel degradation: sediment transport acceleration of multi-thread gravel bed river after human interventions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13987, https://doi.org/10.5194/egusphere-egu23-13987, 2023.

14:35–14:45
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EGU23-1236
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GM5.2
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Highlight
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Virtual presentation
Jens Turowski, Aaron Bufe, and Stefanie Tofelde

The width of fluvial valley-floors is a key parameter to quantifying morphology in mountain regions. It is important in diverse fields including sedimentology, fluvial geomorphology, and archaeology. Valley-floor width has been argued to depend on climatic and tectonic conditions, on the hydraulics and hydrology of the river channel that forms the valley, and on sediment supply from the valley walls. Yet, so far, a physically-based model that can be used to predict valley width is lacking. Here, we derive such a model. As has been done before, we assume that valleys are formed by the erosion of the valley walls by a river migrating across the valley floor. We conceptualize river migration as a Poisson process, in which the river changes its direction stochastically, at a rate determined by hydraulic boundary conditions. This approach yields a characteristic timescale of migration into a particular direction. The valley width can then be determined by integrating the speed of migration over this timescale. We develop equations for the timescale and the migration speed and predict that an unconfined valley or channel belt width scales with the square of the flow depth of the river. We expand the model to arrive a single equation that also includes the effects of uplift and lateral hillslope sediment supply. Both of these effects lead to a decrease in valley width in comparison to the unconfined width. The model predicts that at low uplift rates, the valley width tends to the unconfined width, and at high uplift rates to the channel width, and connects these two limits by a logarithmic equation. As a consequence, valley width increases with increasing drainage area, with a scaling exponent that typically lies in the range between 0.4 and 0.8, but can also be lower or higher. Finally, we compare the model to three data sets of valleys in uplifted regions and show that it closely predicts the first order relationship between valley width and uplift rate.

How to cite: Turowski, J., Bufe, A., and Tofelde, S.: A process-based model for fluvial valley width, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1236, https://doi.org/10.5194/egusphere-egu23-1236, 2023.

14:45–14:55
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EGU23-2396
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GM5.2
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On-site presentation
Piret Plink-Bjorklund, Mark Hansford, Haipeng Li, and Kenya Ono

Extreme river floods are among Earth’s most common and most destructive natural hazards and thus have a high impact on society. Their impact on shaping the landscapes and the sedimentary record is, however, less clear. The most common assumption is that moderate flood events build the sedimentary record, because (1) the high frequency moderate events are suggested to be more common and thus do more geomorphic work, (2) river recovery feedback loops are suggested to be negative and thus high-magnitude event effects are reworked, and (3) river sedimentary records are assumed to consist of ripple, dune and bar scale cross strata that indicate normal Froude subcritical flow, bedload transport, and equilibrium conditions for downstream bedform migration. However, there is a large and growing body of work that documents river deposits that are dominated by preserved high-magnitude flood deposits that consist of stacked flood event beds rather than equilibrium bedform strata, and indicate formative Froude supercritical flow conditions with suspension transport of sand and gravel.

Based on a synthesis of ancient and modern river records, modern river discharge records and experimental data, we propose that there are fundamental differences in magnitude-frequency relationships and relaxation times in rivers with distinct hydrology, such that in some rivers channel recovery may be virtually non-existent and larger floods may leave permanent and formative imprints on landscape. Only if the ratio of the mean relaxation time (normal conditions) to the mean recurrence interval of extreme channel disturbing events is <1, and the critical shear stress for sediment motion is exceeded during moderate (normal) conditions can a river recover from extreme flood-induced change before the next major disturbance occurs. This concept helps to explain the observed variability in the sedimentary record of rivers, as well as critical differences in river flood hazards.

How to cite: Plink-Bjorklund, P., Hansford, M., Li, H., and Ono, K.: Geomorphic Effects of Floods – Integrating Ancient, Modern and Experimental Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2396, https://doi.org/10.5194/egusphere-egu23-2396, 2023.

14:55–15:05
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EGU23-17154
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GM5.2
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On-site presentation
Eddy Langendoen, Dylan Shoemaker, Mick Ursic, and Kory Konsoer

Acoustic instruments such as multibeam echosounders (MBES) and acoustic Doppler current profilers (ADCPs) can collect flow and bathymetric data at high spatial and temporal resolutions. Researchers are widely using MBES and ADCP instruments to advance our understanding of meandering river morphodynamics. Whereas MBES instrumentation produces a continuous bathymetric surface, ADCP usage acquires the three-dimensional flow field at a series of cross sections. The spacing of ADCP cross sections has generally been based on a rule of thumb (for example, a multiple of the channel width), but is constrained by the available survey time. Theoretical advances regarding the morphologic adjustment of meandering rivers over the past 50 years have identified two important parameters: channel width-to-depth ratio (W/H) and channel radius of curvature-to-width ratio (R/W). Though, width is a controlling factor, it is its ratios with respect to channel depth and radius of curvature, that are important. In addition, channel curvature and width may vary considerably along the river. Hence, determining ADCP cross section locations based on a multiplication factor of channel width is challenging. We used a suite of wavelet analysis methods to determine the effects of channel curvature and width on flow measured using ADCPs along the Pearl River, LA/MS, Little Tallahatchie River, MS, and Wabash River, IL/IN. For example, for six bends on the Pearl River, curvature varied between 0.01 and -0.01 and top width varied between 80 and 180 m. The analysis showed that the streamwise velocity along the channel centerline was controlled by variations in channel width for most of the study reach. The primary extremes in near-bank streamwise velocity were controlled by channel curvature, but secondary peaks at some compound bends were controlled by changes in channel top width rather than local increases in curvature.  These findings are used to develop a tool combining a constant-width linear model of meandering-river flow with streamwise channel width profiles to determine the optimal placing of ADCP cross sections. Such information is specifically useful for rivers, such as the Little Tallahatchie River, that have a small width-to-depth ratio and a large channel radius of curvature-to-width ratio. To collect ADCP data using spacing equal to channel width for such rivers would lead to unrealistic survey duration.

How to cite: Langendoen, E., Shoemaker, D., Ursic, M., and Konsoer, K.: Resolving river planform and width effects on flow in meandering rivers for optimal placing of ADCP cross sections, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17154, https://doi.org/10.5194/egusphere-egu23-17154, 2023.

15:05–15:15
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EGU23-7339
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GM5.2
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ECS
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On-site presentation
Ellie Vahidi, Andrew Nicholas, Georgie Bennett, Philip J. Ashworth, Richard Boothroyd, Hannah Cloke, Stephen E. Darby, Pauline M. Delorme, Helen Griffith, Solomon Gebrechorkos, Laurence Hawker, Julian Leyland, Yinxue Liu, Stuart J McLelland, Jeffrey C. Neal, Daniel R. Parsons, Louise Slater, Greg Sambrook-Smith, and Andrew J. Tatem and the Ellie Vahidi

Braided rivers are often characterised by dynamic behaviour that is driven by both internal process-form feedbacks and external variations in water and sediment supply. Such behaviour can involve river bed aggradation or degradation, significant channel widening or narrowing, and changes in planform morphology (e.g., braid intensity). Moreover, such dynamics have the potential to drive changes in the flood conveyance capacity of the river, and to propagate downstream over time. These effects have been observed in numerous field case studies. However, as of yet it has proven difficult to develop a general theory or quantitative understanding of how braided rivers respond to environmental change, or how the morphodynamic sensitivity of such channels is controlled by factors such as valley morphology, flood regime or lateral channel stability.

The current study seeks to investigate these phenomena by performing a series of 2D physically-based morphodynamic model simulations of braided river evolution over periods of multiple centuries. Simulations were carried out to model the development of equilibrium channel morphologies, following which environmental perturbations were applied to investigate the effects of: (i) climate change; (ii) increased sediment delivery from hillslopes; and (iii) the impact of dam construction. For each environmental scenario, multiple simulations were conducted to investigate different combinations of variables that control the river morphology. For example, we examine varying degrees of channel confinement (valley width), differences in hydrologic regime, and changes in vegetation dynamics that control floodplain development and river width adjustment.

Model results demonstrate that long-term (decadal to centennial) variations in flow and sediment supply can drive significant changes in channel flow conveyance capacity, stage-discharge relationships and the frequency of overbank flooding in braided rivers. Width adjustment represents a dominant mode of river response to environmental change. For example, braided rivers tend to accommodate downstream increases in discharge primarily through adjustments in total flow width. In contrast, constraints on adjustment in channel width lead to the concentration of floodwaters within a narrower channel belt, thereby amplifying vertical channel responses to change while potentially creating laterally stable channel nodes. While concern over future changes in flood regime tend to focus on increases in flood magnitude and frequency, model results illustrate that flood duration may also exert an important influence on channel morphodynamics and hence flow conveyance capacity.

How to cite: Vahidi, E., Nicholas, A., Bennett, G., Ashworth, P. J., Boothroyd, R., Cloke, H., Darby, S. E., Delorme, P. M., Griffith, H., Gebrechorkos, S., Hawker, L., Leyland, J., Liu, Y., McLelland, S. J., Neal, J. C., Parsons, D. R., Slater, L., Sambrook-Smith, G., and Tatem, A. J. and the Ellie Vahidi: Morphodynamics of braided rivers under environmental change: controls on the evolution of channel flood conveyance capacity , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7339, https://doi.org/10.5194/egusphere-egu23-7339, 2023.

15:15–15:25
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EGU23-7423
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GM5.2
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ECS
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On-site presentation
Elizabeth Dingle and Jeremy Venditti

Riverbed sediments often lack fine gravel between 1 and 5 mm, a phenomenon referred to as the ‘grain size gap’. The gap corresponds to the rapid reduction in grain size associated with the gravel-sand transition, where median bed material grain size reduces from ~10 mm gravel to ~1 mm sand. Fine gravel grain sizes are often present in hillslope sediment, so it is not clear why they are absent on riverbed surfaces. We present a phenomenological laboratory experiment examining changes in sediment dynamics across a gravel-sand transition to explore the fate of grain size gap material. Our observations indicate that where sand falls out of washload, forming persistent surficial deposits at the gravel-sand transition, grain size gap material experiences enhanced mobility. This is due to hydraulic smoothing by sand that occurs because of a geometric effect, where medium sand bridges interstitial pockets in fine gravel bed surfaces. Our experiments show that fine gravel flux is enhanced by sand deposition making gravel beds at the threshold of motion, mobile. We are unable to maintain an immobile fine gravel bed when sand is fed, which explains why gravel beds composed of 1 to 5 mm particles are so rare on Earth. Our experiment shows that fine gravel particles mobilized by sand deposition are transported out of the flume. We hypothesize that in natural systems, fine gravel particles are either buried in the diffuse extension of gravel-sand transitions or transported into coastal and marine environments where they are more commonly observed.

How to cite: Dingle, E. and Venditti, J.: Experiments on the grain size gap in river bed sediments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7423, https://doi.org/10.5194/egusphere-egu23-7423, 2023.

15:25–15:35
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EGU23-9664
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GM5.2
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Highlight
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On-site presentation
Gary Parker, Chenge An, Michael Lamb, and Marcelo Garcia

Long rivers extending from the mountains to the sea often undergo a transition from gravel-bed to sand-bed. The grain size dividing “gravel” and “sand”, i.e. 2 mm, has, on an empirical basis, played a special role in fluvial sediment transport and morphology. Sand-bed rivers and gravel-bed rivers have traditionally been treated separately in terms of morphology and sediment transport. For example, the sediment transport relation of Wilcock and Crowe (2003) treats gravel transport as a function of sand content in the bed. While sand is easily suspended in rivers, there are only sparse records of gravel traveling in suspension under purely fluvial conditions (as opposed to debris flows), and these records become vanishing as grain size increases. Here we study the reason for this in terms of sediment entrainment into suspension from the bed. Garcia and Parker (1991) developed a relation for the rate of suspension of sand from an alluvial, non-cohesive bed. This relation was developed exclusively based on empirical data for sand beds. When the relation is extrapolated to gravel beds, it is found to predict copious suspension where there should be none. The key parameter controlling this is a particle Reynolds number, Rep = (RgD)1/2D/n, where D is grain size, n is fluid kinematic viscosity, R is particle submerged specific gravity and g is gravitational acceleration. However, in the case of spheres, there is a unique relation between particle Reynolds number and dimensionless fall velocity Rf = vs/(RgD)1/2. The Garcia-Parker relation can easily be cast in terms of Rf rather than Rep over the range of sand grain sizes used in the derivation. The curve of Rf versus Rep, however, shows a monotonically increasing zone for small Rep but an approximate plateau region for larger values of Rep. The transitional range between the monotonically increasing and plateau region is Rep = 360 to 600. In the case of quartz in 20° water on Earth, this corresponds to the range 2.0 – 2.8 mm. In the plateau region, the modified Garcia-Parker relation is found to predict negligible suspension of sediment (gravel) within the range of shear velocities most commonly found in rivers. Suspension of gravel is not in principle precluded by the relation, but the conditions commonly found on Earth during floods, even megafloods, do not seem to allow it (Larsen and Lamb, 2016). The result is further verified using the relation for entrainment into suspension by deLeeuw et al. (2020). The results have significance for the interpretation of such phenomena as downstream fining in rivers and gravel-sand transitions. The dimensionless form of the result allows for straightforward modification to the case of ice clasts in liquid methane at the gravitational acceleration. 

How to cite: Parker, G., An, C., Lamb, M., and Garcia, M.: Dimensionless Illustration: The Grain Size 2 mm Is Indeed “Special” in the Context of Fluvial Sediment Transport and Morphology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9664, https://doi.org/10.5194/egusphere-egu23-9664, 2023.

15:35–15:45
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EGU23-15950
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GM5.2
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ECS
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Virtual presentation
Ajay Krishnan U, Abhishek Kumar Paswan, Ketan Kumar Nandi, and Subashisa Dutta

Compared to straight and meandering rivers, turbulent flow features around a mid-channel bar in braided rivers are far more complex. It is believed that the continuous expansion of these bar deposits causes the commencement of braiding. This article will therefore address the turbulent flow characteristics around mid-channel bars. In an experimental flume, a scaled-down physical model of a mid-channel bar deposit is built to examine the flow structure. Although the geometry of mid-channel bar deposits is not uniform, an elliptical shape is suggested here for simplicity. Rigid cylindrical vegetation is planted over the bar with submergent and emergent flow condition. An Acoustic Doppler Velocimeter (ADV) has been used to measure the three dimensional velocity component. Results indicate that the fluvial process associated with the flow is greatly influenced by flow velocity and turbulent kinetic energy. A flow divergence above the bar head and a flow convergence at the bar tail make up the bulk of the flow structure. Near the upstream end of the bar, adjacent regions are where the flow is perceived to accelerate. The bar's existence reduces the flow area nearby, leading to increased velocity in parts close to the upstream end of the mid-channel bar. The velocity was reduced by 15 to 20% from upstream section to downstream section of the bar. The velocity incriment was observed to be about 10% in vegetated conditon as of non-vegetated condition. Additionally, it has been observed that the momentum exchange is higher in the top of canopy and gradually reduces as it approaches the lower canopy and bar level. The findings obtained from this study can further utilized to examine braid bar occurrences in alluvial rivers to build an appropriate response through training techniques.

Keywords: Braiding, Flume, Mid-Channel Bar, Turbulent Flow, Rigid Vegetation

How to cite: Krishnan U, A., Kumar Paswan, A., Kumar Nandi, K., and Dutta, S.: Experimental Investigation of Flow-Turbulence Behaviour in a Channel  with Vegetated Mid-Bar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15950, https://doi.org/10.5194/egusphere-egu23-15950, 2023.

Coffee break
Chairpersons: Eliisa Lotsari, Joshua Ahmed
16:15–16:25
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EGU23-4312
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GM5.2
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On-site presentation
Katja Laute and Achim A. Beylich

In cold-climate environments, climate change can cause changes in the precipitation, hydrological and ground frost regimes which affect the activation of sediment sources and sediment transfers.

The upper Driva drainage basin in central Norway (Oppdal-Hjerkinn) is situated in a cold-climate and mountainous environment and ranges with a total drainage basin area of 1630 km2 from 220 to 2286 m a.s.l. The mean annual air temperature at Oppdal (545 m a.s.l.) is 4.3°C, and mean annual precipitation amounts to 532 mm. The lithology in the drainage basin is complex and varied, and is dominated by metamorphic rocks, mostly gneisses and schists. Vegetation cover varies between tundra vegetation in the high and rather flat areas of the uppermost drainage basin area, tree vegetation in the lower parts of the incised tributary valleys of the Driva main river and grasslands in the agriculturally used areas along the main river valley of the Driva. Relevant geomorphological processes include chemical and mechanical weathering, rockfalls, snow avalanches, debris flows, slides, wash processes, fluvial erosion, fluvial stream bank erosion and down-cutting,  and fluvial solute, suspended sediment and bedload transport.

This ongoing GFL research on sediment sources, controls and spatiotemporal variability, and future trends of fluvial bedload transport includes detailed field-based studies with extensive granulometric and shape analyses of bedload material, and high-resolution bedload transport measurements applying different tracer techniques, Helley-Smith samplings, and underwater video filming together with impact sensor measurements. Specific focus is on selected stream channel stretches in the six tributary systems Svone, Kaldvella, Stølåa, Tronda, Vinstra and Ålma, and on three selected stream channel stretches of the Driva main river in the upper Driva drainage basin system. Stationary hydrological stations are monitoring runoff continuously as discharge occurs in all tributary systems year-round. The runoff regime is nival with mean annual runoff amounting to 576 mm for the entire upper Driva drainage basin.

The activation of sediment sources and the temporal variability of fluvial bedload transport are largely controlled by thermally and, to a lower degree, by pluvially determined events. The selected tributary systems display varying intensities of bedload transport and varying particle-size compositions and shape characteristics of the bed surface material. These detected spatial variations are explained by different lithologies, different levels of sediment connectivity and spatially varying sediment availabilities in the different tributary systems. The clearly highest share of annual bedload transport occurs during the snowmelt period in spring. Continuing climate change might lead to less distinct spring snowmelt generated peak discharge events associated with reduced fluvial bedload transport during these events. Continuing climate change also affects processes like debris flows, snow avalanches and permafrost degradation having variable implications for sediment supply into these stream channels.

How to cite: Laute, K. and Beylich, A. A.: Field-based analysis of fluvial bedload transport and its response to climatic changes in the cold-climate and mountainous upper Driva drainage basin in central Norway, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4312, https://doi.org/10.5194/egusphere-egu23-4312, 2023.

16:25–16:35
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EGU23-7197
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GM5.2
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ECS
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On-site presentation
Tuure Takala and Eliisa Lotsari

In present climate, almost all rivers freeze in the northern high latitude regions every year. In the future, this annual freezing cycle may undergo major changes. These changes can already be observed in the current climate. The effects of climate change in cold climate areas are radical and will have a great impact on the environment: Changes in the ice formation, duration and break-up of river ice cover will affect the hydrology of the rivers. Effects will vary from flow rates to sediment transport and discharge levels. For the most part, studies of freezing and thawing have been carried out under laboratory conditions or are outnumbered by open-channel studies depicting river systems in warmer areas. More information on the processes of freezing and thawing and the effects this cycle has on river flow, and vice versa, is needed by monitoring natural sites.

 

Consequently, this study seeks to respond to this lack research and process knowledge, and aims 1)  to examine, whether the freezing and thawing periods affect the river surface velocity and the spatial variations of speed in the partly frozen channel (and vice versa), 2) to detect the differences in the formation of ice, ice cover and the ice break-up between different type of river reaches, and 3) to examine differences in the freezing and thawing cycles and surface velocity connections in hydro-climatically different rivers. The study is conducted in three cold climate region study sites: Boreal and continental, meandering Koitajoki River (Finland), straight reach of more maritime Sävarå River, and sub-arctic Pulmanki River (straight reach of a meandering river).

 

The data for the study has been collected between 2020-2022 using game camera images and videos with georeferenced targets. The velocity of river flow is analyzed with two different methods (STIV and PTV) from the videos. At the same time, efforts will be made to compare how well the different methods work to analyze the situation in question. Reference measurements have also been carried out in the autumn before freezing, in winter during ice cover, and in spring after the break-up of ice, and these measurements are compared with the results of the analyses. The change and duration of the ice cover is analyzed based on the image series. Regional climate data, as well as data collected from research areas (water temperature, air temperature, atmospheric pressure) is used to estimate the winter conditions. In addition for new knowledge of freezing and thawing processes within cold climate region rivers, the results from this study enable advancing hydraulic modelling approaches in ice covered season, and further specify our knowledge on freezing and thawing of river ice.

How to cite: Takala, T. and Lotsari, E.: Surface flow and ice rafting velocities during freezing and thawing periods of three northern rivers., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7197, https://doi.org/10.5194/egusphere-egu23-7197, 2023.

16:35–16:45
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EGU23-9776
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GM5.2
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Highlight
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On-site presentation
Niccolò Ragno, Marta Crivellaro, Riccardo Bonanomi, Guido Zolezzi, Marco Tubino, and Michael Lamb

Meandering is one of the most common morphological pattern through which rivers manifest themselves. Here, the attention is devoted to meandering streams carving their path through permafrost floodplains, which typically characterize cold environments such as the Arctic. Despite meandering rivers have been widely studied in the last fifty years, little is known about the dynamics of streams where banks are composed of perennially frozen material. It is inquired whether there is a morphological signature in the planform of permafrost streams potentially deriving from specific thermo-mechanical processes occurring in Arctic landscapes, like the formation of thermo-erosional niches and sediment slumps caused by thaw-weakened soil. To this aim, a bend scale analysis of the planform geometry of several Arctic streams by means of Landsat satellite imagery is employed. Morphodynamic features such as lateral migration rates, channel curvatures, and width variations, are extracted from multispectral remotely sensed data by combining Google Earth Engine (GEE) with an established process-based software (PyRIS).  Following a methodology based on continuous wavelet transform, a set of metrics quantitatively defining the meander shape, which include fattening and skewing coefficients, are used to compare permafrost streams with a series of natural meandering rivers from tropical and temperate regions obtained from the literature. The present analysis opens the way to a systematic integration between remote sensing and physically-based morphodynamic models able to incorporate thermo-mechanical processes uniquely related to permafrost environments.

How to cite: Ragno, N., Crivellaro, M., Bonanomi, R., Zolezzi, G., Tubino, M., and Lamb, M.: Looking for permafrost signatures in Arctic streams: the case of meandering rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9776, https://doi.org/10.5194/egusphere-egu23-9776, 2023.

16:45–16:55
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EGU23-14478
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GM5.2
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ECS
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On-site presentation
Linnea Blåfield, Amin Sadeqi, Petteri Alho, and Elina Kasvi

In the rapidly warming sub-arctic areas, it is not known how the climate emergency driven changes in hydroclimatic conditions will affect the fluvio-morphological processes like bank erosion, sediment transport and meander migration, and especially their spatial-temporal mechanisms. At the moment, one big spring flood event is controlling the morphodynamics of the northern rivers, but the significance of this event is expected to decrease when the hydroclimatic conditions change and larger amount of the annual precipitation is expected as rainfall during autumn and winter months instead of snow. In this study, we utilize a 50 year hydroclimatic time-series together with 21 years of bank erosion and meander migration observations from two meander bends in Northern Finland. The aim of this study was to find the main controlling hydroclimatic factors for hydro-morphological processes, like meander migration and sediment transport, and analyse the changes and trends of these factors during the past 50 years. These observations were then used to forecast, how these processes will behave in the future under the changing hydroclimatic conditions in the rapidly warming high latitude areas. We used time-series of historical aerial imagery, geometric levelling data, sediment sampling and Terrestrial Laser Scanner to measure and analyse the bank erosion volume, sediment transport and bend migration in the past, present and future. A series of statistical analysis was then performed for the hydroclimatic time-series to recognise trends and to link the annual events with bend migration, erosion and transport volume. The results indicate how these unique northern river systems are responding to hydroclimatic changes and how the hydro-morphodynamics will be in the future. The results help adapting the river management, flood protection, mitigation strategies for extreme fluvial events in present and in the future at high latitudes.

How to cite: Blåfield, L., Sadeqi, A., Alho, P., and Kasvi, E.: Morphodynamic response on hydroclimatic conditions - A 50 year time-series of a northern river system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14478, https://doi.org/10.5194/egusphere-egu23-14478, 2023.

16:55–17:05
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EGU23-10663
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GM5.2
|
Virtual presentation
Jonas Otaviano Praça Souza and Mirelle Oliveira Silva

Tropical drylands show diverse environmental characteristics worldwide, where the high evapotranspiration rates control the water deficit. In this context, water retention areas such as wetlands are hydro-geomorphological elements essential to ecological and social sustainability. The wetland classification on dryland areas allows better management of these socio-ecological hotspots. This research identifies and classifies wetland areas on the Chapada do Araripe and its surroundings in the centre of Brazilian tropical drylands. The geomorphological unit has 6,000 km², altitudes from 500m to 1100m, and comprises limestones on the base and sandstones on the top layer. The Wetlands were identified by remote sensing and fieldwork analysis and characterized by 13 geoindicators elements (e.g., near-surface lithology, flat valley bottom, spring presence, perennial surface water, hydromorphic soils, TWI, curvature, slope). Geomorphological and hydrological conditional factors define the wetland classification. The eleven wetlands identified are distributed on narrow valleys with slopes under 0.2m/m. The rainfall accumulation patterns directly link the surface flow temporality; only two areas show perennial surface flow. The perennial/intermittent hydrological regime seems to be directly linked to land use intensity. The intense deforestation is linked to the agricultural potentiality due to higher water disponibility. Valley bottom morphology was one of the critical elements to wetland classification, and curvature and slope values characterized it. Also, as a hydro-geomorphological feature, vertical incision and incised channels define the flow concentration/diffusion grade. The plan wetlands were defined by curvature values between 0.03-0.07 and slope values under 0.08m/m. Concave wetland show curvature from 0.1 to 0.19 and slope values between 0,08-0.2m/m. Considering these parameters, four classes were delineated for Wetlands in Chapada do Araripe: (1) flat with channelled valley floor;  (2) flat with unchanneled valley bottoms;   (3) Concave with channelled valley floor; and  (4) concave with unchanneled valley bottoms. Vegetated wetlands show the predominance of vertical incision processes and the presence of continuous channels (types 1 and 3). In contrast, deforested wetlands are controlled by valley floor sedimentation/silting process and absence/discontinuity of vertical incision. The vegetation presence was more significant than the curvature characteristics of valley floor vertical incisions. The association of vegetation presence with near surface low-permeable limestone layer controlled perennial hydrological regime. In this sense, it can be concluded that the geomorphological and hydrological parameters are essential for the characterization and classification of Wetlands. Becoming critical to elaborate specific legislation that aims to protect these environments, especially those found in dry lands.

How to cite: Souza, J. O. P. and Silva, M. O.: Wetland classification of sedimentary plateu on tropical drylands - Brazilian Northeast, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10663, https://doi.org/10.5194/egusphere-egu23-10663, 2023.

17:05–17:15
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EGU23-14613
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GM5.2
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ECS
|
On-site presentation
Muriel Brückner, Rolf Aalto, Renato Paes de Almeida, Jim Best, Andrew Nicholas, Phil Ashworth, and Marco Ianniruberto

Large anabranching sand-bed rivers are characterised by dynamic lateral channel migration, bar aggradation and floodplain accretion. On the Amazon River, variations in bank and floodplain sediments exert a primary control on channel migration rates. In a reach near Tefé, Brazil, the Solimões River shows different migration dynamics along its north and south banks, suggesting that bank strength plays a role in the large-scale and long-term channel and floodplain evolution. Here we present measurements of lower bank strength and sediment resuspension in 29 locations along and across the Solimões River to investigate their spatial variability in sediments of different age and origin by means of a cohesion strength meter and a Pilcon Shear Vane. Results show that the north bank consists mainly of late Holocene sandy and silty deposits, whereas the south bank is characterised by frequent Pleistocene outcrops of cohesive muds and diagenetic iron cements and concretions. The south-bank Pleistocene deposits have on average three times higher bank strength than the younger floodplain deposits along the north bank. When comparing the locations of the Pleistocene deposits with lateral migration rates along both banks for two 40 km reaches, we observe that these sediments occur mainly where the south bank has been eroded, suggesting that they are revealed when the river migrates. Our results suggest: (1) that lateral migration uncovers the less erodible layers that can then deflect the flow towards the north bank; (2) that outcrops of resistant Pleistocene deposits might be abundant underneath the northern alluvial floodplain; and (3) spatial variations in bank erodibility exert a first-order local control on the planform morphology and lateral dynamics of the river. We suggest that such variations in erodibility are equally important for the morphodynamics of other large sand bed rivers that show evidence for the presence of resistant Pleistocene sediments, such as the Nile, Mekong and Mississippi Rivers.

How to cite: Brückner, M., Aalto, R., Paes de Almeida, R., Best, J., Nicholas, A., Ashworth, P., and Ianniruberto, M.: Bank strength and erodibility in the Amazon River and their control on large-scale river morphodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14613, https://doi.org/10.5194/egusphere-egu23-14613, 2023.

17:15–17:25
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EGU23-3934
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GM5.2
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ECS
|
On-site presentation
Sebastián Granados-Bolaños and Nicola Surian

The morphology of rivers is the result of complex relationships between sediment supply, hydrological regime, geological and vegetation conditions, and human disturbances. Numerous river channel classifications have been developed in different geographical contexts over the last few decades. Nevertheless, channel characterization in active volcanic environments under humid tropical conditions is almost completely absent in geomorphological research.

We carried out a detailed characterization of river morphology in an active volcanic complex, the Irazú-Turrialba, characterized by extreme rainfall conditions (>7000 mm/yr.), frequent volcanic eruptions (>10/100 yrs.), high-magnitude earthquakes (>Mw5), and dense tropical vegetation. This volcanic complex is located in the central volcanic chain of Costa Rica and at its foothills, most of the country’s population and economic activities (>60%) can be found. A total length of 166.5km of the river network was mapped to understand the occurrence and distribution of channel morphologies in this high-energy and dynamic environment.

Using remote sensing techniques (RGB and multispectral satellite imagery, digital terrain models, spaceborne imaging radar products, and unmanned aerial vehicles), 74 river reaches located on four rivers within the volcanic complex were analyzed using 13 morphometric variables, including channel slope, channel width, confinement index, braided index, and others. Then, channel morphology for each reach was defined referring to four internationally recognized classification schemes, examining how such schemes adapt to the active tropical volcanoes. Further on, to characterize with more detail the river reaches and the volcanic complex, a morphometric index was developed to identify sediment sources and erosion-sedimentation areas. The morphometric index relies on vegetation height, terrain roughness index, slope degree, and average precipitation

Results allow a novel understanding of river morphology and processes in active volcanic environments under humid tropical conditions. The main outcomes are:  (i) channel morphology in this volcanic complex is dominated by steep, confined and coarse sediment river reaches; (ii) there is a strong difference in channel morphology and processes between the north and south parts of the volcanic complex due to climatological, geological, and tectonic aspects; (iii) established classification schemes partially failed when applied in this specific environment which is characterized by very high energy and a large amount of sediments; (iv) the morphometric index developed to analyze the volcanic complex and river reaches turned out to be useful for mapping sediment sources and detecting landforms such as lava flows, debris avalanches, landslides, and volcanic cones. Overall, this study provides novel insights about river morphology under highly dynamic and active volcanoes with extreme rainfall events, resulting in steep, confined, coarse sediment channel morphologies that are quite uncommon in other environments (e.g., boulder and cobble-bed braided rivers).

How to cite: Granados-Bolaños, S. and Surian, N.: Channel morphology in an active volcanic complex under humid tropical conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3934, https://doi.org/10.5194/egusphere-egu23-3934, 2023.

17:25–17:35
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EGU23-6408
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GM5.2
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ECS
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On-site presentation
Chloé Garcia, Boris Brasseur, Lou-Anne Mathieu, Agnès Gauthier, and Pierre Antoine

Fens are common in Northwest Europe in chalky bedrock valleys (from France to Poland). The peat from the valley bottoms of the River Somme basin is a remarkable wetland characterized by a significant organic accumulation (4 to 6 m on average). This alkaline peat sequence provides outstanding archives to describe the environmental evolution of Northwestern France over the last 14,000 years. Fens are also fragile environments forming huge carbon sinks. In the current context of rapid climate change, it is important to better understand and protect this carbon accumulating ecosystem. In this context, a research initiative has been initiated to highlight the respective roles of climatic and anthropogenic forcing factors (drainage, slope soil erosion) on peat formation and degradation processes and the modification of the related fluvial environments. The study focuses on a high-resolution stratigraphic transect of the valley in Morcourt (about 600 m wide) based on more than fifty manual boreholes and mechanical corings. The reconstruction of sedimentation dynamics and palaeoenvironments evolution is based on a multiproxy approach combining sedimentology, geochemistry, palynology, and plant macro-remains identification, supplemented by thirty-five 14C dates. This work reveals that the first peat deposits were restricted to channel filling at the beginning of Lateglacial (14.6 - 14.0 ka cal. BP). This peaty event was then interrupted during the Younger Dryas by the deposition of highly calcareous overbank silts (CaCO3 > 40%) in the whole alluvial plain. Typical peat formation with high TOC values (> 45%) then growth from the beginning of the Preboreal period around 12 ka cal. BP to the Atlantic (6.5 ka cal. BP) and rapidly extended to the entire valley bottom (0.07 cm/year). During the Subboreal, the reactivation of the river flow (climate modification and soil erosion) is then indicated by the development of a deep meandering channel progressively filled in with laminated silty-organic deposits and a slower peat accumulation rate in the alluvial plain (0.03 cm/year) due to lowering of the water table. These modifications are contemporaneous with the generalized opening of the landscape (palynology), associated with the acceleration of anthropic erosion processes on the slopes. Since the Subatlantic (2.9 ka cal. BP) peat deposits have higher mineral component originating from flood and slope erosion (carbonated: 65% of CaCO3; silicated: up to 27% in silty-peat). Since the late Middle Ages, organic silts fed by the erosion of loessic soils have rapidly buried the peat system which, combined with drainage, is now essentially inactive and fossilized.

How to cite: Garcia, C., Brasseur, B., Mathieu, L.-A., Gauthier, A., and Antoine, P.: Paleoenvironmental evolution of an alkaline fluviogenic peatland (fen) from northern France: a 14 kyr bottom valley history between climatic and anthropogenic forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6408, https://doi.org/10.5194/egusphere-egu23-6408, 2023.

17:35–17:45
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EGU23-16624
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GM5.2
|
Virtual presentation
Magaly Cusipuma Ayuque and Julio Isaac Montenegro Gambini

The Nanay Bridge, Peru's largest bridge, is located on the Nanay Rive near its mouth to the Amazon River in the city of Iquitos, connecting different communities. The Nanay Bridge is 2,283.50 m long and 14.80 m wide. The construction of this structure was completed in November 2021, ensuring, and improving transportation. This research is aimed to the numerical investigation of the hydrodynamic conditions in an Amazonian River reach (Nanay) and is interaction with the mentioned bridge. To this end, The IRIC Nays CUBE and HEC-RAS models were used to simulate unsteady fully two and three-dimensional flow with non-hydrostatic water pressure and high vertical accelerations and velocities. It allows to represent the flow characteristics on the different piers as well as the water level at a certain lateral distance. Different experiments using mean, minimum and maximum flows for different return periods were conducted. Field ADCP and flow measurement data was used for characterization and validation purposes. Estimations of scour around the piers were carried out to quantify the impact of different flows in these elements. The three-dimensional flow structure plays an important role for determining the appropriate countermeasures for local scouring and protection. Our simulation results show that two and three-dimensional flow patterns match the conceptual model of river flow in this type of water courses. Our findings provide useful insight to verify the impact that the implantation of different infrastructures around the Amazonian water courses could produce. This contribution is pointed to be a support in river engineering in Amazonian rivers and might be more valuable in conjunction with physical hydraulic model investigation.

How to cite: Cusipuma Ayuque, M. and Montenegro Gambini, J. I.: Numerical investigation of 2D/3D hydrodynamic conditions in the proximity of a bridge in an amazonian river, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16624, https://doi.org/10.5194/egusphere-egu23-16624, 2023.

Posters on site: Thu, 27 Apr, 08:30–10:15 | Hall X3

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.
Chairpersons: Joshua Ahmed, Eliisa Lotsari, László Bertalan
X3.1
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EGU23-1450
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GM5.2
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ECS
Chris Tomsett and Julian Leyland

The importance of vegetation within the river corridor is well known and has been subject to a considerable body of research. The interactions between riparian vegetation and river morphology are typically complex, co-dependent, highly dynamic, and vary across both spatial and temporal scales. Vegetation diversity can typically be attributed to fluvial influences such as flood regimes and morphology, whilst simultaneously influencing the flow of water and sediment transport. However, adequately capturing the spatial and temporal complexity of vegetation characteristics has been a considerable challenge, and so a number of unresolved questions with regard to the spatial and temporal interactions of vegetation and river flow remain.

Within this research, we seek to establish the relationship between vegetation presence and geomorphic response over 2 years of data collection on a 1 km stretch of the River Teme in the United Kingdom. Functional vegetation traits of different plant forms relevant to hydrological research are extracted using UAV based laser scanning and multispectral imagery. These traits are then upscaled to reach scale functional group classifications, whereby they can be compared to geomorphic change occurring throughout the reach. Our framework moves beyond typical species level classification, as vegetation is instead grouped on the potential geomorphic impact that it may have due to their characteristics. Such methods are beginning to be established in fluvial research, but are often constrained by the need for extensive ground surveying or they focus on how traits vary in response to fluvial controls.

Our results show six distinct functional groups are obtained from a mix of laser scanning and imagery data, before being upscaled across the study area with a classification accuracy of 80% using random forest methods. Plant structure was subsequently used to assess spatially varying and seasonal changes in excess vegetative drag based on reference flow depths across the study site during a peak flow event. These variations could be used to assess the aggregated geomorphic response of the system based on flow conditions and vegetation type, and begin to unpick different feedbacks between them. Such methods could be used on similar river systems, to improve wider reach classifications using both airborne laser scanning and imagery, as well as in different geomorphic research where there is interactions between flows and vegetation.

How to cite: Tomsett, C. and Leyland, J.: Exploring the 4D scales of eco-geomorphic interactions along a river corridor using repeat UAV Laser Scanning (UAV-LS), multispectral imagery, and a functional traits framework., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1450, https://doi.org/10.5194/egusphere-egu23-1450, 2023.

X3.2
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EGU23-2759
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GM5.2
Eliisa Lotsari, Marijke de Vet, Brendan Murphy, Stuart McLelland, Anne Baar, Roberto Fernandez, and Dan Parsons

Climatic warming is projected to affect hydrology and change ice-cover periods within river channels, particularly in northern high-latitude regions. These changes will impact sediment transport conditions and longer-term riverine morphology. For example, the duration of the freezing, frozen, thawing and unfrozen periods, may affect river bank erodibility characteristics. However, it is difficult to quantify the combined impact of soil moisture, rates of freezing/thawing, and ambient temperatures on the fluvial bank erosion in addition to altered flow velocity conditions in natural river sites. We therefore present a series of scaled laboratory experiments in a controlled small-scale novel cryolab morphology facility. The flume experiments allow for detection of how these different forcing factors affect riverbank erosion rates. The ultimate goal of the experimental programme is to enhance the process understanding of the sediment transport behaviors in expected future conditions in sub-arctic environments, where the frozen periods are expected to shorten and air temperatures to rise due to climatic change.

 

The experiments presented in this study aimed to detect how the flow velocity, soil moisture content and freezing levels of the bank sediment, affect river bank stability with altered ambient air temperatures. The laboratory experiments were performed using a small-scale Friedkin channel (1945) within a chilled flume system. A suite of experiments were conducted adjusting the ambient air temperature, the water temperature, and the water discharge (flow velocity). As the basis for creating realistic bank characteristics for the experiments, the sediment size, soil moisture and soil temperature parameter values observed in a sub-arctic Pulmanki River during mid-winter, after ice-breakup/before snow-flood peak and non-frozen conditions were used across the experimental set. The sediment bank blocks (2 cm high) were prepared for each of the experimental runs the day before, and kept in the chilled flume room overnight to match ambient temperatures prior to the runs being advanced.

 

Overall ~130 experiments were performed. From each of the experiments the topography was measured before and after the experiment, by taking photos with a semi-automatic Canon camera. Structure from motion methodologies were used to produce surface models, and volumetric change was thus possible to calculate for each experiment. GoPro cameras (HeroBlack 10) were used to film videos of the bank evolution positioned from both nadir and sideways positions, providing linked high-resolution views of the evolving bank morphology. The data was used to detect the bank edge retreat through time. To assess changes in flow structure, buoyant micro-beads were seeded at the beginning and at the end of each experiment, allowing particle tracking velocimetry method to recover and defining the flow velocities of each experiment. Finally, a FLIR A655 thermal camera was used to aid understanding on the thermal transfers between the flow and the banks and the impact this had on morphodynamics.

 

The preliminary results related to the possible links between temperature, moisture, flow velocity and resultant morphodynamics will be presented and the implications for climate change impacts on defrosting landscapes will be discussed. 

How to cite: Lotsari, E., de Vet, M., Murphy, B., McLelland, S., Baar, A., Fernandez, R., and Parsons, D.: Small scale bank erosion experiments in freezing and thawing conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2759, https://doi.org/10.5194/egusphere-egu23-2759, 2023.

X3.3
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EGU23-2820
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GM5.2
Gravel-sand transition in the mixed bedrock-alluvial Congaree River, SC. Preliminary results on gravel mobility
(withdrawn)
Enrica Viparelli, William Logan, Mahsa Ahmadpoor, Raymond Torres, and Steven Dykstra
X3.4
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EGU23-3175
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GM5.2
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ECS
Kerstin Schlobies, Tuure Takala, Juha-Matti Välimäki, Virpi Pauliina Pajunen, and Eliisa Selina Lotsari

A unique large-scale dam removal series with a combined drop height of 18 meters is conducted at Hiitola River, Southeast Finland during the years 2021–2023. Three dams used for power production are replaced by rapids reconnecting longitudinal flows. Here, we concentrate on the hydraulic impacts of the first, lowermost Kangaskoski dam removal site.

Flow features of a river under restoration vary seasonally as well as before and after each dam removal. The magnitude and seasonal variability of flows and the hydraulic capacity of the river to erode and transport the reservoir sediment are crucial in determining the rate of erosion, deposition, and river channel evolution. Thus, the hydrological conditions at Hiitola River upstream, downstream and in the reservoir section of the former Kangaskoski dam, were analyzed using hydroacoustic measurements by a moving-boat ADCP. We used consistent algorithms for quality checking, filtering, and interpolating from QRev software from USGS and automated steps for creating average transects, data post processing and visualization.

The spring and autumn surface flow properties of the 200 m long rapid section constructed in autumn 2021 were derived by using image-based velocimetry approaches from nadir UAV-video data sets. Thus, the following major processing steps were applied: video frame selection, image enhancement, frame stabilization, automatic 3D search area creation, image velocimetry, and statistical outlier filter based on flow characteristics.

The aims are to assess, 1) the spring and autumn variation in discharge, the flow field, and the fluvial forces in 2021 and 2022, and 2) the impact of the Kangaskoski dam and flow routing changes on the flow field and fluvial forces in the three different river zones before and after the removal. Identifying the immediate changes of hydraulics, sediment transport capacity and physical habitat conditions following the step-by-step dam removal and freeing of the Hiitola river may serve as criteria for future dam removal projects.

How to cite: Schlobies, K., Takala, T., Välimäki, J.-M., Pajunen, V. P., and Lotsari, E. S.: Application of hydroacoustics and image velocimetry for determining short-term hydraulic changes associated with a dam removal at Hiitola River, Southeast Finland., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3175, https://doi.org/10.5194/egusphere-egu23-3175, 2023.

X3.5
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EGU23-6241
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GM5.2
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ECS
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David Whitfield, Edwin Baynes, Stephen Rice, and Richard Jeffries

Interactions between sediment mobility and transport capacity are one of the key controls over the geometry and morphology of gravel bed rivers; these drivers are temporally variable, fluctuating in response to changes in channel hydrology - for example, with climate change - and sediment supply - for example, via land use change. Quasi-stable, equilibrium channels occur when transport capacity and bed mobility are in balance. In both field and experimental flume studies, various efforts have been made to predict the relationship between channel hydrology (bankfull discharge, Qbf) and the equilibrium dimensions (channel width and depth). Similarly, recent studies seek to quantify equilibrium state by approximating the ratio of dimensionless bankfull shear stress to dimensionless critical shear stress (τ*bf*c). If robust, these theories can offer a useful approach towards identifying channels that are sensitive to present and future aggradation and/or degradation, and can therefore be valuable tools in applications such as predicting the impacts of climate change and flood risk management. Despite their widespread use in the identification and comparison of channel stability at regional scales, these quantitative methods remain uncertain when investigating the equilibrium state of individual channels, particularly when applied to semi-managed reaches.

Through completing a UK-wide assessment of upland channel stability, this study aims to field-validate hydraulic geometry theories and critically evaluate their appropriateness in river management applications within a UK context. A dataset comprising 50 upland reaches of various sizes (Qbf varied from ~2 to 270 m3s-1) was collected through field survey. Observed evidence for recent aggradation and degradation was compared against hydraulic geometry theory. Where τ*bf << τ*c, channels are predicted to aggrade, typically resulting in geometries wider and shallower than expected (and vice versa for degradational regimes, where τ*bf >> τ*c). However, when compared against field observations, predictions do not always coincide with reality. Here, we identify case study exceptions, and explore process complexities (for example, sediment supply, confinement and bank reinforcement) that lead to deviation from the predicted aggradational/degradational regime. Additionally, to account for deviations from expected channel morphology, we consider temporal variations in bed structure and sediment mobility thresholds under different hydrological regimes.

How to cite: Whitfield, D., Baynes, E., Rice, S., and Jeffries, R.: Hydraulic Geometry of ‘Equilibrium’ Channels: From Theory to Application at the National Scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6241, https://doi.org/10.5194/egusphere-egu23-6241, 2023.

X3.6
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EGU23-279
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GM5.2
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ECS
Bhagwan Das, Zulfequar Ahmad, and Pramod Kumar Sharma

A series of experimental and numerical studies were performed to investigate Critical submergence for square water intakes in an open channel flow in this paper. Diversion of water from rivers has recently become a most important subject of study in hydraulic projects, such as water supply, irrigation, power plants, etc. The formation of an air-entraining vortex in the vicinity of an intake is considered to be a severe problem for water intake. The distance between the water surface level and the intake center level is called the submergence of a water intake. Suppose submergence is below a definite lowest level. In that case, air enters into the intake through an air-entraining vortex developing from the free surface, and that specific submergence is termed as critical submergence. Experiments were performed in a concrete flume of 9.47 m long, 0.5 m wide, and 0.6 m deep with an intake of size 0.04 m×0.04 m under uniform approach flow for different flow conditions. A three-dimensional Multiphase CFD Model was also developed for simulating critical submergence for the intakes. Reynolds-averaged Navier–Stokes (RANS) equation with Standard k-ω and SST k-ω turbulence models were used to simulate the fluid flow inside the test domain. These two models, together with the volume of fluid (VOF) two-phase (water-air) model, were found well capable to simulate the flow at critical submergence. Air entraining vortex at critical conditions was identified using phase volume fraction studies and surface streamlines. Multiphase CFD study helped to understand the flow structure and turbulence characteristics of the vortex flow at the vicinity of intakes. The interface between air-water phases has been simulated with better accuracy for identifying the multiphase interface interaction during the event of an air-entraining surface vortex formation. It should be noted that approach flow Froude number and intake flow Froude number play a vital role in observing critical submergence with both experimental and numerical considerations. A comparison of the numerical and experimental results with the selected turbulent model indicated that the multiphase numerical model is capable for simulating flow for air-entraining vortex formation at critical submergence with an 8 % error.

How to cite: Das, B., Ahmad, Z., and Sharma, P. K.: Experimental and Numerical Modeling of Critical submergence  for  Water Intakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-279, https://doi.org/10.5194/egusphere-egu23-279, 2023.

X3.7
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EGU23-6643
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GM5.2
|
ECS
Andrea Gasparotto, Andrew Nicholas, Gregory Sambrook Smith, Afrah Daham, Julian Clark, and Tahmina Yasmin

Sand is a critical natural resource used in the construction sector, in land reclamation and coastal protection schemes. Global consumption of aggregates is estimated to be c. 40 billion tonnes a year (Peduzzi, 2014) a large proportion of which is derived from fluvial sediment sources. This figure exceeds the mass of sediment delivered annually to the global ocean (Milliman and Syvitski, 1992). Moreover, with urban populations projected to rise substantially over the next 20 years (UN, 2019), unsustainable extraction of alluvial sand represents a critical threat to the morphological and ecological integrity of rivers.

Despite growing awareness amongst the scientific community and policymakers of the deleterious effect that uncontrolled extraction can have on the landscape and local populations, there remains a lack of quantitative understanding concerning the diverse potential impacts of fluvial sand extraction, and the degree to which any level of extraction may be deemed sustainable. Similarly, differences between the impacts of alternative mechanisms of extraction are poorly understood, as are the rates at which these impacts may propagate beyond the immediate extraction zone. These knowledge gaps make effective mitigation and regulation of sand extraction practices extremely challenging.

This study seeks to better understand the impact of mining within large sand-bed rivers using numerical modelling. Two modes of sand extraction were considered: (1) bar-top skimming from the floodplain and mid-channel bars; and (2) wet mining by dredging of the channel thalweg. We carry out 2D physically-based morphodynamic model simulations over spatial and temporal scales of 90 km and 150 years in order to quantify the evolution of river morphology, hydraulics and sediment transport during both the period of sand extraction and an extended post-extraction period. Model simulations were designed to quantify both the fluvial responses within the immediate sand extraction zone, and the downstream propagation of the mining disturbances. Results indicate that there is a clear impact of sand extraction in all the analysed hydromorphic metrics (e.g., braid intensity, variations in the river width-depth, and in the flow patterns) and that there is a different river-evolution style and impact when considering different types of sand mining (dry mining from exposed bars at low-flow conditions or wet mining only from the channel thalweg). For example: (1) for wet mining scenarios, the system shows a very significant deepening of the channel thalweg and a consequent reduction in the mobility of the system, decreasing the inundation period on the bars; (2) in dry mining scenarios, the system develops shallower channels (when compared to wet mining), but experiences an increase in avulsion, with the rapid activation and deactivation of secondary channels and unvegetated bars (in the mining zone), enhancing bank erosion and consequent further river widening. Model results demonstrate that recovery of river systems in the absence of mining is a process that can require decades to centuries. Moreover, the influence and consequences of mining directly within the extraction zone are propagated downstream rapidly, although the contrasting response associated with different mining styles becomes less marked outside the immediate area of extraction.

How to cite: Gasparotto, A., Nicholas, A., Sambrook Smith, G., Daham, A., Clark, J., and Yasmin, T.: Hidden Depths: modelling the mining impact on sand-bed rivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6643, https://doi.org/10.5194/egusphere-egu23-6643, 2023.

X3.8
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EGU23-7432
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GM5.2
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ECS
Valeria Ruscitto, Michele Delchiaro, Marta Della Seta, Giulia Iacobucci, Daniela Piacentini, and Francesco Troiani

River terraces, together with their deposits, can provide a great deal of information about the history of a drainage system, from a hydrological and sedimentological perspective. As such, they are functional to understand the influence of tectonics, varying climate and base level change on landscapes, and their relevance as geomorphic markers is widely recognized. Through the complete and accurate analysis by remote sensing and field work of the Marche drainage network, it has been possible to identify and reinterpret the main river terrace staircase and to map its remnants in detail, with the perspective of attempting the detection and interpretation of the tectonic and climatic signals preserved in it.
The selected area is challenging from a geomorphological and geomorphometric standpoint because it is characterized by low-rate tectonic activity and a well-preserved fill terrace staircase, middle-to-upper Pleistocene in age, allowing to analyse this classic climatic signal-bearing feature in a tectonically active setting. This work was based on a relatively innovative approach, that analyses Relative Elevation Models (REMs), converted from 1 m/pixel DEMs collected from a 1x1 LiDAR dataset, to better pinpoint river terraces through the identification of their surfaces with the Surface Classification Model (SCM). Once detected through remote techniques, the fill terraces will also be interpreted basing the analysis on field data and geochronological constraints, with the aim of isolating the climatic and tectonic signal they have recorded.

How to cite: Ruscitto, V., Delchiaro, M., Della Seta, M., Iacobucci, G., Piacentini, D., and Troiani, F.: Identification and analysis of Quaternary alluvial terraces for climatic and tectonic signals detection purposes: a case study from the central Marche Apennines (central Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7432, https://doi.org/10.5194/egusphere-egu23-7432, 2023.

X3.9
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EGU23-10128
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GM5.2
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ECS
Joshua Ahmed and Grigorios Vasilopoulos

Oxbow lakes serve as rich habitats for wildlife, natural contaminant filters, and an essential source of sustenance and prosperity for riverine communities around the world. Despite their significance, little is known about the controls on oxbow lake hydrology and the timescales over which they operate. Without an understanding of how these environments currently function, it will be challenging to protect them from the pressures of climate change and land use conversion, thus threatening their ability to deliver the wealth of ecosystem services they currently provide, in the future. Here we present an analysis of the temporal behaviour of 110 recently formed (1984-2022) oxbow lakes in the near-pristine catchments of three Amazonian tributaries and elucidate the hydrological controls on this behaviour using a combination of band-rationing procedures and tropical rainfall data. We demonstrate that water surface areas (WSA) fluctuate annually, with some increasing in size by >60% compared to the year immediately following formation. We found that seasonal and annual rainfall exerted a strong control on annual variations in WSA, while proximity of the lakes to the mainstem was less important. Proximity of the lake to the mainstem became more important where flow could be directly conveyed through tie channels or breaches in the lake plug. Changes in hydro-climate, flow regulation, and land use will alter the dynamism of lake hydrology, thus potentially altering the functioning of lakes in the future.

How to cite: Ahmed, J. and Vasilopoulos, G.: Discerning hydrological controls on the behaviour of water surface area changes in oxbow lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10128, https://doi.org/10.5194/egusphere-egu23-10128, 2023.

X3.10
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EGU23-13176
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GM5.2
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ECS
Ludovico Agostini, Gabriele Barile, Riccardo Bonanomi, Michele Combatti, Marco Fezzi, Marco Redolfi, Livia Serrao, Elisabeth Slomp, Guido Zolezzi, Nadia Zorzi, Sandro Rigotti, and Marco Tubino

The construction of artificial reservoirs for hydropower production strongly alters sediment connectivity, which often produces significant impacts on the river reaches downstream morphology. Assessing sediment connectivity and transport variations is therefore crucial for predicting possible fluvial morphological trajectories and to define scientifically-based management practices in terms of water and sediment releases from Alpine reservoirs. For this reason APRIE, the agency responsible for hydropower regulation in the Trento Province (Italy), is carrying out a project to assess impacts caused by existing hydropower plants, in collaboration with the University of Trento.

We focused on the study case of the Travignolo River, a tributary of the Avisio River in the Dolomites. The valley longitudinal connectivity has been completely interrupted by the Forte Buso dam construction in 1953 and by a series of smaller derivations from the main tributaries. We aim at understanding to what extent the presence of the dam affects the overall sediment connectivity, by assessing the relative contribution of sediment sources that currently drain into the lake with respect to the sources that are still connected to the Travignolo River, and by evaluating to what extent the disconnectivity has compromised the morphological equilibrium of the river.

To this aim, structural and functional sediment connectivity are analysed through a three step integrated approach, considering connectivity at different spatial scales. First, fluvial morphological trajectories have been studied by investigating a dataset of historical images, which allowed us to identify both morphological changes and vegetation growth. Second, sediment connectivity has been modelled at the hillslope scale through the hydrological index of connectivity calculated by applying the SedInConnect model (Crema, S. & Cavalli, M., 2018, Computational Geosciences) on the basis of terrain elevation data and information on Quaternary deposits. The model allowed us to determine the potential sediment yield contribution from the different subbasins, as well as the position of sediment sources depending on their characteristic grain size. Finally, a quantitative analysis of sediment longitudinal connectivity has been carried on by applying the CASCADE Toolbox model (Tangi, M. et al., 2019, Environmental Modelling & Software) to the main river network of the Travignolo basin. Information on surface and subsurface grain size distribution have been obtained by collecting several samples along the main course of the Travignolo River and along their main tributaries, while channel width was estimated by analysing the high-resolution digital elevation model. To calibrate CASCADE model we have compared the predicted grain size distribution cascades with the measured subsurface composition. Furthermore, we have performed several simulations considering different methods of data spatialization and different choices of the main parameters, to obtain a general assessment of the model uncertainties.

Results highlight the potential sediment contributions of different subbasins to the fluvial system, depending on their geological characteristics, slope and distance from the permanent drainage network. Moreover, the analysis of multiple scenarios reveals how sediment transport processes are strongly affected by the dam presence and how they may change depending on water delivery strategies.

How to cite: Agostini, L., Barile, G., Bonanomi, R., Combatti, M., Fezzi, M., Redolfi, M., Serrao, L., Slomp, E., Zolezzi, G., Zorzi, N., Rigotti, S., and Tubino, M.: Evaluating sediment (dis)connectivity in a study Alpine catchment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13176, https://doi.org/10.5194/egusphere-egu23-13176, 2023.

X3.11
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EGU23-14322
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GM5.2
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ECS
Sarah Betz-Nutz, Toni Himmelstoß, Moritz Altmann, Jakob Rom, Fabian Fleischer, Florian Haas, Michael Becht, and Tobias Heckmann

The system of proglacial streams in the Alps has experienced significant changes since the end of the Little Ice Age. Previous studies showed different patterns of aggradation and degradation in proglacial channels over time. This leads to the question of which factors determine the sediment dynamics in the channels and on their floodplains in the long term with ongoing glacier melting. Possible influencing variables are the distance of a channel section to the recent glacier tongue and the percentage of glaciation in the catchment area. Moreover, we suppose an influence of local topographic characteristics such as the slope gradient and the width or confinement of the channel. In addition to these factors, there is also the question of whether large individual events overlay a trend of aggradation or degradation.

In order to analyse the long-term sediment dynamics in channels and the factors influencing it, we used numerous digital elevation models (DEMs) covering several decades and different streams within three main catchments (Kaunertal and Horlachtal in Tyrol and Martelltal in South Tyrol). The DEMs were generated from aerial images dating back until 1953. From the 2000s on, airborne LiDAR datasets and DEMs based on drone images were available. This data basis enables a comparative investigation and the identification of local topographic influences.

How to cite: Betz-Nutz, S., Himmelstoß, T., Altmann, M., Rom, J., Fleischer, F., Haas, F., Becht, M., and Heckmann, T.: Factors influencing the long-term development of sediment dynamics in proglacial channels in the European Alps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14322, https://doi.org/10.5194/egusphere-egu23-14322, 2023.