The width of channel belts and fluvial valleys and its temporal evolution is important for the hydraulics, hydrology, and ecology of landscapes, and for human activities such as farming, protecting infrastructure, and natural hazard mitigation. Channel belts form by the mobilization and deposition of sediments during the lateral migration of rivers. Similarly, the width of a fluvial valley is set by the river undercutting valley walls and evacuating the resulting sediment. Both channel belt and valley width thus depend on the process of lateral channel migration. We have recently developed a model that predicts a steady-state valley or channel-belt width and its temporal evolution. The model builds on the assumption that the switching of direction of a laterally migrating channel can be described by a Poisson process, with a constant rate parameter related to channel hydraulics. As such, the channel’s lateral migration can be viewed as a non-standard one-dimensional random walk. The model connects channel belt and valley evolution to reach-scale hydraulic parameters. In addition to steady state scaling and the average temporal evolution of valley width, it predicts a range of results on the landscape evolution scale, for example, the age distribution of sediment (equivalent to the distribution of return times to the origin), and bounds on the area that the river is unlikely to migrate beyond (the law of the iterated logarithm). Here, we summarize some key model results and compare model predictions to observations of natural and experimental rivers. First, we demonstrate that a random walk process is a reasonable description of the evolution of channel belt width, because the channel belt width increases with the square root of time and the distribution of return times to the origin has a -3/2 scaling . Second, we argue that the observed downstream scaling of valley or channel-belt width with drainage area is consistent with our model predictions. Third, we show that steady state width of fluvial valleys, as observed in field and experimental data, scales with uplift rate and channel mobility as predicted by the model. Finally, we point out further avenues to test the model and constrain parameters using additional field data.
How to cite: Turowski, J., McNab, F., Bufe, A., Tofelde, S., and Zhong, Y.: A random walk perspective on channel belts and fluvial valleys: model and evidence, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6001, https://doi.org/10.5194/egusphere-egu25-6001, 2025.
Knickpoints are prominent geomorphic features, and despite being localized (i.e. 10s of m) within longitudinal river profiles they profoundly influence landscape evolution with impacts occurring both within the channel system and outside of it due to channel-hillslope interactions. Because of this, a thorough mechanistic understanding of knickpoint dynamics is imperative to understanding landscapes, yet the study of knickpoints remains limited. The long geological timescales over which knickpoints evolve in natural settings makes in-situ measurements of knickpoints challenging. The Bedrock River Experimental Incision Tank at the Université de Rennes 1 was used to perform analogue experiments to provide a comprehensive dataset assessing the impact of sediment supply, base-level fall rate and bedrock strength on knickpoint dynamics. Experiments were conducted with a homogenous lithology made up of a mixture of silica and glass beads with ratios ranging from 2.5:1 to 4:1. The mixture was combined with water and used to simulate bedrock, eroded by clear water flow, with the strength of the material set by the ratio of silica to glass beads. The experiments were run with constant water discharge (1.5 l min-1), sediment supply ranging from 0 g l-1 to 20 g l-1,and base-level fall rates between 1.5 cm hr-1 and 5 cm hr-1. We find that knickpoint retreat exists between two end member states: knickpoint replacement and headward migration. It is illustrated that sediment supply impacts the channel’s ability to diffuse the knickpoint lip, whilst protecting the base, and base-level fall rate impacts the time the channel has to tend towards headward migration. Furthermore, we construct a phase diagram to illustrate the intricate interplay of sediment supply and base-level fall rate in shaping knickpoint morphology. Secondly, we find that lithology is the key determinant of knickpoint retreat rate where harder bedrock strengths result in lower knickpoint retreat rates, and channels respond to faster base level fall rates by generating more knickpoints rather than knickpoints retreating faster. This study provides a key insight into important controls on knickpoint morphology and retreat rate and provides a starting point for accurately modelling how knickpoint morphology varies as it migrates through a channel system.
How to cite: Norriss, W., Baynes, E., Hillier, J., Lague, D., and Steer, P.: Understanding the impact of sediment supply, base-level fall rate and bedrock strength on knickpoint dynamics in fluvial environments., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1576, https://doi.org/10.5194/egusphere-egu25-1576, 2025.
The last decades have seen major advances in our understanding of the long-profile evolution of bedrock rivers, whereas constraints on the development of bedrock-river planform and the coupled evolution of long-profiles and planform patterns in tectonically active landscapes remain limited. Here, we quantify how bedrock-valley width and channel sinuosity are modulated by changes in rock uplift rates on the million-year timescale. Using field- and remote sensing data as well as models, we explore the links between rock-uplift rate, bedrock-valley widening, and channel meandering in rivers draining the Ordos Block in Northern China. There, rock uplift rates have increased in the past 1 Ma, and rivers drain a generally uniform substrate under well constrained paleoclimate conditions. We show that the steady state width of bedrock valleys scales with uplift rate and channel mobility, as predicted by a recent physics-based model. We also observe a possible tectonic control on bedrock meandering where the sinuosity of channels scales positively with the uplift and incision rate beyond a critical threshold.
How to cite: Zhong, Y., Turowski, J., Bufe, A., and Schildgen, T.: Impact of rock uplift on bedrock-valley width and channel sinuosity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8301, https://doi.org/10.5194/egusphere-egu25-8301, 2025.
A simple geometric model is proposed to reconstruct the topography of entire catchments in Taiwan, a region characterized by highly active mountain systems. This model will be tested in the Laonong River Valley, a highly dynamic river catchment in southern Taiwan, using high-resolution topographic data. The model assumes a landscape in sustained uplift, incorporates dynamic steady-state parameters, and uses the stream power law to describe bedrock incision. Additionally, it accounts for valley slopes constrained by critical thresholds where landslides occur.
Building on previous models, the elevation profiles of main channels and tributaries are integrated from the catchment outlet, based on a power-law relationship between slope and drainage area. For non-steady-state conditions, elevation changes are calculated using topographic data from different years. Lateral incision is included to simulate river meandering. Beyond the stream network, valley topography is reconstructed by assuming constant slope patches equal to the maximum channel slope. A simple algorithm connects points within the basin to the river network by tracing steepest descent paths.
This model is supported by three years of topographic data, extracted from digital terrain models using elevation-distance plots. Distances are measured either along river channels or along the steepest descent paths. The model’s accuracy is evaluated by comparing the reconstructed elevations and slopes to actual topographic data. Any discrepancies can highlight anomalies such as variations in uplift rates, lithological differences, or remnants of past valley features, including landslide deposits.
How to cite: Liao, T. and Capart, H.: Dynamic Catchment Topography in Active Mountain Regions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12817, https://doi.org/10.5194/egusphere-egu25-12817, 2025.
Sediment connectivity is a critical concept in understanding sediment transfer dynamics and geomorphological evolution. It refers to the degree of linkages between sediment sources and deposition areas, influenced by hydrological processes, topography and climate. This is particularly relevant in India's complex geological setting. This study presents the first national-scale sediment connectivity map of India, derived from SRTM DEM data (~1km resolution), to observe spatial heterogeneity in sediment transfer.
The connectivity map revealed a wide range of connectivity values (approximately +5 to -14.5), indicating 19 distinct connectivity levels and Getis-Ord (Gi*) revealed 14 major hotspots clusters with 99% statistical accuracy reflecting significant spatial heterogeneity. Key findings include a.) dichotomy in connectivity in The Western and Eastern Ghats b.) the significant contribution of highland connectivity vectors from the Kumaon Himalayas and badlands from the Chambal River Basin to the Ganga River Basin's sediment load. The map was divided into three key zones:
1. High Connectivity Zones:
• Himalayan States: Regions like Jammu & Kashmir, Himachal Pradesh, Uttarakhand, Sikkim, and Arunachal Pradesh exhibit high connectivity due to ongoing Himalayan orogeny, erosion, glacial melt, and heavy rainfall. Major rivers (Indus, Ganges, Brahmaputra) transport substantial sediment, contributing to the Indo-Gangetic Plain.
• Northeastern States: Assam, Meghalaya, Nagaland, and other northeastern states also show high connectivity due to high rainfall and steep slopes, leading to rapid soil erosion and high river sediment loads.
2. Moderate Connectivity Zones:
• Himalayan Bordering States: Uttar Pradesh, Bihar and West Bengal, at the Himalayan foothills, act as transition zones. They receive Himalayan sediment but have lower slopes and broader floodplains, slowing water flow and promoting deposition, thus reducing downstream connectivity as part of a "source-to-sink" system.
• Central India: Madhya Pradesh and Chhattisgarh, on the central plateau, display moderate connectivity. Less steep topography results in lower erosion rates, but functional connectivity might increase significantly during the monsoon due to higher runoff.
3. Low Connectivity Zones:
• Peninsular India: The Deccan Plateau (Maharashtra, Karnataka, Andhra Pradesh, Telangana, and Tamil Nadu) typically shows low connectivity due to stable geology (crystalline rocks), moderate slopes, and lower rainfall, resulting in reduced erosion and sediment yields.
• Thar Desert: The arid Thar Desert exhibits low connectivity.
Understanding these patterns, the interplay between structural and functional connectivity, and the influence of human activities and climate change is crucial for sustainable land and water management. Further research at finer scales and assessment of human and climate change impacts are needed. Future studies should consider multi-temporal DEMs to observe spatiotemporal changes for a more comprehensive understanding.
How to cite: Umrani, F. I., Deshmukh, B., and Neeti, N.: Observing spatial heterogeneity in the first national-scale connectivity map of India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16390, https://doi.org/10.5194/egusphere-egu25-16390, 2025.
Human interaction has always influenced the structure of watercourses, often resulting in changes that disrupt their morphological balance and the associated river habitats. In Europe, the earliest river reconfiguration efforts date back to Roman times. Since then, distinct stages of river management have emerged. The most significant alterations to waterways occurred during the 20th century, particularly after World War II, driven by industrial and urban growth.
This project aims to assess the anthropogenic impacts on river morphodynamics in three alpine water basins located northwest of Turin, Italy, focusing on the past 150 years, from the pre-industrial phase to the present.
Using a Geographic Information System (GIS)-based approach, the study investigates how human activities, such as urbanization, agriculture, and infrastructure development, have influenced the physical characteristics and behaviour of river systems. The methodology involves collecting spatial data from 1850 to 2022, digitizing it, and applying morphological indices to evaluate changes in river settings, shapes, and sediment transport. For the entire period, major changes in river morphodynamics were correlated with land use patterns. Statistical analyses were subsequently employed to assess variations in river morphology over time. This approach provides a robust framework for evaluating anthropogenic pressure on river morphodynamics.
The results reveal significant changes in river patterns, sediment transport, and habitat availability. Notably, a general narrowing of channels was observed, along with a transition in their layout from sinuous to straight and from braided to single-thread channel configurations.
By comparing the outputs of different indices with major land use changes in the territory, the study highlights the critical interplay between human development and riverine morphodynamics. These findings contribute to a deeper understanding of how human interventions reshape natural water systems, offering valuable insights for future environmental management and conservation strategies.
How to cite: Paschetto, A., Caselle, C., and Bonetto, S.: Human Influence on River Systems: 150 years of river Morphodynamics change in Alpine water basins (Torino, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18511, https://doi.org/10.5194/egusphere-egu25-18511, 2025.
Ancient sand-rich fluvial systems form critical subsurface reservoirs for hydrocarbon
exploration, carbon storage and a variety of other uses; however, their complex architecture often
hinders the generation of accurate reservoir models. Detailed study of analogous outcrop
exposures is critical for managing exploration risk and developing efficient production strategies,
providing a detailed look at the architecture and potential connectivity of subsurface reservoir
targets.
The Late Triassic – Early Jurassic Grey Beds and lower Åre Formation are fluvial formations
which are being increasingly targeted as potential hydrocarbon reservoirs within the Norwegian
Sea. Reservoirs such as this have the potential to prolong energy production from the Northern
North Sea Basin for decades to come and are the focus of ongoing regional exploration. One of
the challenges this play concept faces is that much of the strata is entirely preserved within the
subsurface, has few wells, and is poorly understood due to limited data.
Here we present an analysis of the Late Cretaceous Iron Springs Formation in Southwest Utah.
These exposures represent an upward-coarsening, high net-to-gross fluvial system deposited
proximal to the Sevier orogenic belt into the Cretaceous Interior Seaway. This depositional
system provides an excellent analog for the Grey Beds and lower Åre Formation in the
Norwegian Sea and other high net-to-gross sandstones in the geologic record.
This study utilizes a combination of traditional and digital field methods to create detailed
outcrop descriptions. Our preliminary field study reveals important details not often apparent in
subsurface datasets. Exposures of the upper Iron Springs near Parowan, Utah, range from 100m
to 150m in thickness. Based on detailed measured stratigraphic sections described as part of this
study, amalgamation surfaces are common and grain size varies appreciably. Lateral and vertical
connectivity of architectural elements is complex, but excellent three-dimensional exposures in
the field area allow for spatial description of these relationships. Often, high net-to-gross systems
are assumed to be braided; however, our initial findings from the Iron Springs Formation show
variability between braided and meandering elements, with suggestion of more distal
environments suggested in the lower part of the formation.
Photogrammetric models built in Agisoft Metashape software using high resolution drone
imagery allow for identification of high-resolution architectural elements in three dimensions
along two kilometers of continuous outcrop. Channel elements are identified from this dataset,
and fine-scale details observed from geolocated measured sections add details regarding the
facies present within these elements. Geobodies delineated within photogrammetric models are
exported into Schlumberger’s Petrel software, and extrapolated models based on outcrop control
suggest a high degree of channel connectivity in this system even in zones of the Iron Springs
Formation interpreted to be dominated by meandering channel morphologies.
This model will be used to build geospatial descriptive and predictive models for subsurface
fluvial systems that may be underrepresented due to limited sampling and poor seismic
resolution of fine-scale reservoir elements.
How to cite: Robinson, J., Hudson, S., Tatum, O., Toner, A., Grover, C., and Nielsen, T.: Decoding subsurface fluvial architecture: an outcrop-based case study of the Iron Springs Formation as an analog for fluvial systems in the North Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20822, https://doi.org/10.5194/egusphere-egu25-20822, 2025.
Building high resolution analog models based on outcrop exposures is a powerful tool for describing complex geologic systems. By creating detailed architectural models, we further our understanding of these sedimentological systems and increase our ability to predict heterogeneity in the subsurface. These same methods can be applied to the overall understanding of the evolution and architecture of fluvial systems worldwide, and reservoirs across the geologic timeline. This study examines the outcrop architecture and connectivity of fluvial depofacies within the Cretaceous lower Castlegate Sandstone of central Utah, USA, a proposed analog for the Mesozoic fluvial sandstones such as the Grey Beds and lower Åre Formation of the Norwegian Sea and Eiriksson Formation of the North Sea.
The Castlegate Sandstone is a well exposed fluvial system that transported sediment eastward from the Sevier Orogeny toward the Cretaceous Interior Seaway. It is a highly progradational package of strata that overlies the proximal and marine deposits of the Blackhawk Formation. It was selected for study due to its similarity to the Late Triassic - Early Jurassic Grey Beds and lower Åre Formation, offshore Norway – a complex system of floodplain, coal-bearing swamps and channel sand deposits. The lower Castlegate Sandstone and underlying Blackhawk Formations exhibit some coal bearing beds, carbonaceous mudstones, and channel sand deposits, indicating proximity to the seaway and a depositional environment like that of the Åre Formation. Preliminary geochemical analyses using Rock-Eval pyrolysis reveal a mix of Type II and III kerogens within the upper Blackhawk, indicating algal marine and terrestrial carbon sources, with terrestrial influences increasing upward. Samples taken within the Castlegate Sandstone do not
show algal influence.
Detailed outcrop descriptions and measured sections are integrated into a multi-kilometer photogrammetric model. From this model, important temporal and spatial trends are defined. At the transition between the Blackhawk Formation and the Castlegate Sandstone there is an abrupt change in the proportion of mudstone versus sandstone while maintaining internal channel organization. This indicates a measurable basinward shift of the depositional system, likely due to increased sediment supply related to tectonism or other allogenic forces. Initial observations of the lower Castlegate Sandstone show fine- to coarse-grained sandstones ranging from <1 to 8 meters thickness, generally thickening upward. Fluvial bedforms exhibit important trends as well. Lower, more isolated channels are dominated by finer grains, frequent soft sediment deformation, and are mostly single-story, while stratigraphically higher sections are dominated by medium- to coarse-grained sandstones with trough cross stratification and are commonly multi-storied. Amalgamation surfaces are present throughout, evident in frequent mud rip ups, pebble lags, and abrupt changes in bedforms/grain size, but are more frequent and dramatic higher in the section. Architectural elements are defined from the photogrammetric model and exported to subsurface modeling software to be further analyzed. Through the integration of traditional field methods, photogrammetry, and predictive three-dimensional modeling, the lower Castlegate Sandstone serves as an important analog for subsurface exploration of fluvial systems in the Norwegian Sea and elsewhere.
How to cite: Tatum, O., Hudson, S., Robinson, J., Toner, A., and Grover, C.: Analogs across the sea – Using detailed outcrop architectural models of the fluvialCastlegate Sandstone of Utah as an analog for hydrocarbon reservoirs of the Norwegian Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21068, https://doi.org/10.5194/egusphere-egu25-21068, 2025.
River systems often display complex and seemingly random behaviors and patterns. This complexity may be due to the non-linear dynamics intrinsic to these systems, making them suitable for analysis through the lens of chaos theory. While natural processes contribute to chaotic behavior, human interventions, such as mining, significantly alter river systems by modifying sediment loads, flow regimes, and riparian vegetation. This study hypothesizes that these alterations, acting as perturbations to the system, can trigger or amplify chaotic dynamics in the Ankobra River. The research will utilize satellite imagery and DEM data to quantify changes in channel morphology over time. Key morphological parameters, including sinuosity, channel width, meander wavelength, bed elevation, and bank erosion rates will be extracted from these data. The analysis will then examine the temporal evolution of these parameters, investigating potential trends and patterns indicative of chaotic behavior. By analyzing these morphological changes alongside historical data on mining activities and other human interventions in the Ankobra River basin, the research aims to identify the specific impacts of these activities on the river's chaotic dynamics. This research seeks to enhance understanding of the interplay between natural and anthropogenic factors in shaping river systems. The findings will provide valuable insights for developing effective river management strategies under increasing human pressure. Keywords: River Channel Dynamics; Chaotic Dynamics; River Morphology; Ankobra River; Ghana.
How to cite: Quaicoe, J.: Investigating the role of chaotic dynamics in shaping river channel patterns and morphologies: The Case of the Ankobra River, Ghana., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-350, https://doi.org/10.5194/egusphere-egu25-350, 2025.
The beauty of river networks has continuously inspired science to elucidate their self-similarity and the underlying organizing principles. In his pioneering work, Robert Horton postulated several laws explaining the scaling of stream networks, which are today widely accepted in fluvial geomorphology. Another avenue to explain the nature of river networks acknowledges that landforms in general and rivers in particular have been shaped by the physical work of surface runoff in the past. Several studies proposed thus that river networks evolve towards energetically optimal steady states, minimizing total dissipation or energy expenditure in the entire network. Here we reconcile both research avenues, by linking Horton’s stream laws with the theories of river hydraulics and of non-linear, dissipative dynamic systems.
By analyzing the confluence rates of 18 of the largest rivers in the world, we found a universal relation between Horton’s laws of stream numbers and the logistic growth model introduced by Bob May. The confluence ratios converge for Strahler orders smaller than 5 regardless of the climate and physiographic setting to the first Feigenbaum constant, characterizing the route of the logistic growth model into deterministic Chaos. Using the concept of entropy we show furthermore that the transition of the classical logistic growth model from determinism to Chaos corresponds to a step-wise transition from a minimum to a maximum entropy state. A Lagrangian perspective tracing the pathways of surface runoff from the watershed downslope into the first order streams and further downstream, reveals that the entropy of the flow path distribution exhibits continuous downstream decline as well. Consistently with the requirement that a downstream decline in entropy requires a downstream increase in free energy, we found that the potential energy flux in rivers does indeed generally increase with downstream distance up to a Strahler order of 4-5. This is because the downstream accumulation of flowing water mass outweighs the decline in topographic elevation.
We finally show that the growth and mortality in the logistic population model are the equivalents to power generation and energy dissipation in the stream. Assuming bank full discharge and using Lacey’s equations we found that the free energy per stream obeys at confluence points a logistic equation as well. We conclude that Horton’s law of stream numbers is a manifestation of the gradual downstream transition of the flow path density from Chaos, seen as state of minimum predictability and thus maximum entropy, to perfect Order, which is mediated by a maximization of energy efficiency at every confluence point.
How to cite: Zehe, E., Schroers, S., and Savenije, H.: Tracing stream flow in confluent rivers – a journey from chaos to order, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5683, https://doi.org/10.5194/egusphere-egu25-5683, 2025.
Unsteady bedload transport, whereby temporal variations in transport rate occur under constant total discharge and sediment supply, can be generated from interactions between hydraulics, sediment sorting, bedforms and reach-scale morphological variability. At larger scales, the relation between temporal and spatial variability in bedload transport has not been explicitly resolved largely due to the difficulty in obtaining coincident data over large areas and for long time periods. We hypothesise that spatial variability in bedload transport is a function of river pattern, and explore the implications of our results for temporal bedload variability. We combined bathymetric and LiDAR surveys to generate a high-resolution DEM of a 33km reach of the Bislak River, the Philippines. This DEM was then used for two-dimensional hydraulic modelling to predict distributions of flow and shear stress across the entire reach. The reach consists of four contiguous sub-reaches with different (meandering, wandering, braided, and deltaic) channel patterns. Probability distributions of shear stress and predicted bedload transport rates within each sub-reach reveal significant differences between the four channel patterns. From these results, we assess how different channel patterns generate distinct bedload signatures that can be propagated to predict synthetic time series of bedload transport. The properties of these time series are compared with empirical data on the scales of unsteady bedload transport. Improved understanding of bedload transport variability has implications for quantitative definitions of channel pattern, interpretations of alluvial deposits and assessments of channel response to anthropogenic modification.
How to cite: Hoey, T., Williams, R., Quick, L., Boothroyd, R., Tolentino, P., and David, C. P.: How does channel pattern generate unsteady bedload transport?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8484, https://doi.org/10.5194/egusphere-egu25-8484, 2025.
Flood modelling plays a pivotal role in flood forecasting, defence structures design, and risk assessment. Therefore, reliable model descriptions are essential to provide accurate results. Traditionally, flood models consider fixed-bed conditions and assume that resistance coefficients remain constant throughout the event, regardless of hydrodynamic conditions. Despite its success under relatively stable conditions, this approach can fail when the riverbed undergoes rapid morphodynamic changes. Varying hydrodynamic regime, especially under severe flood conditions, influences bedform development, thus appreciably altering the flow resistance, which in turn affects water levels and flow velocity.
For example, in the terminal reach of the Po River, the largest river in Italy, fixed-bed models with constant resistance coefficients have been observed to overestimate the water level by up to 2 meters during flood events. Sand dunes, clearly visible in the bathymetric survey, are widely distributed in the main river channel, but their height and length, which are key factors in determining the total flow resistance, can vary considerably depending on the hydrodynamic regime. Moreover, recent studies have shown that transitioning from sand dune to upper-stage plane bed is possible even at Froude numbers lower than previously thought (i.e., F<0.8). Thus, among the potential causes of the water level overestimation, we identified the changes in flow resistance induced by bedform evolution as one of the most probable.
To test this hypothesis, we developed a 2D finite element hydrodynamic model of the terminal 200-km long reach of the Po River. To quantify flow resistance in the momentum equations the model employs the Gauckler-Strickler formulation and the spatial distribution of the associated resistance coefficient was calibrated using water level and discharge data collected at multiple locations and during multiple flood events. In general, the results of the fix-bed, constant-resistance model were good up to a certain discharge, above which the relevant, systematic overestimation of water levels was confirmed.
We enhanced the 2D hydrodynamic model by dynamically updating the resistance coefficient within the main river channel as a function of bedform evolution. The dune height and length were computed dynamically following the Van Rijn model as a function of the current local flow conditions, introducing a single additional calibration coefficient that scales the height of the dunes. By using this dynamical roughness predictor, combined with an additional resistance component to account for dissipative mechanisms not explicitly addressed by the model, a strict match was achieved between measured and modelled water levels at five different gauging stations along the terminal reach of the Po River under low, intermediate, and severe flood conditions. Despite the challenges in accurately capturing these processes, the results demonstrate that accounting for the dynamic contribution of bedforms can significantly improve the reliability of flood predictions, offering a more robust tool for managing flood risks in complex river systems.
How to cite: Pilbala, A., Lazzarin, T., Tognin, D., Baldasso, F., and Viero, D. P.: The impact of dune evanescence on the Po River conveyance during flood events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1295, https://doi.org/10.5194/egusphere-egu25-1295, 2025.
Understanding the drivers of river mobility - temporal shifts in river channel positions - is critical for managing fluvial landscapes sustainably and for interpreting past river response to climate change. However, direct observations linking river mobility and water discharge variability are scarce. To resolve this challenge, we pair multi-annual measurements of daily water discharge with river mobility, estimated from Landsat, for 48 rivers worldwide. Our results show that, across climates and planforms, river mobility is correlated with water discharge variability over daily, intra-annual, and inter-annual timescales. For similar mean discharge, higher discharge variability is associated with up to an order-of-magnitude faster floodplain reworking. We use a random forest regression model to show that discharge variability is the primary predictor of river mobility, when compared to mean water discharge, sediment concentration, and channel-bed slope. Our results suggest that enhanced hydro-climatic extremes could accelerate future river mobility, and that past changes to discharge variability may explain the fabric of fluvial strata.
How to cite: Leenman, A., Greenberg, E., Moulds, S., Wortmann, M., Slater, L., and Ganti, V.: Water discharge variability drives accelerated river mobility, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5265, https://doi.org/10.5194/egusphere-egu25-5265, 2025.
Gravel-bed rivers exhibit diverse topographies that offer critical habitats and ecosystem services. Previous studies indicated that the geometric effect of channel width variations can significantly influence the morphodynamic processes of gravel-bed rivers. In particular, flume experiments revealed that at the wide sections, riffle topographies build by migrating fronts of bedload sediment. Also, in a gradually widening segment of the upper Xindian River (Taiwan), we observed the migration of a dune-like bedform driven by flood events. However, how the channel widening triggers the dune formation and development of the migrating front are not well known. In this study, we use the Delft3D model to simulate the morphodynamic processes of linearly widening rectangular channels 300 m in length, with the model setting mimicking the prototype Xindian River. The channels have plane bed of a slope 0.002, with constant inflows of water and sediment. A series of simulations were performed to test sensitivity, with the width expansion ratesranging from 0.02 to 0.18 m/m, grain sizes and flowrates giving Shields numbers between 0.11 and 0.22, all correspond to full transport modes. Based on the simulations, we identify two stages of morphodynamic development: (1) geometry-dominated, and (2) topography-dominated stages. At stage 1, flow entering from the upstream narrow cross-section is strongly affected by channel expansion, resulting in the transverse components of velocity and sediment transport, and thus depositions along the sidewalls. Longitudinally, the increase of channel width reduces the velocity and bed shear stress along the centerline, leading to deposition in the central area. These transverse and longitudinal deposits together evolve as a crescent-shaped dune near the entrance. As the dune migrates downstream it continues to grow, and eventually a steep lee face would develop, which defines stage 2. The stoss-lee topography causes a sudden rise in the water surface and thus sudden drops in the velocity and bed shear stress. Over 90% of bedload sediment would deposit on the lee face, forming a migrating front of deformation that aligns with the prograding lee face. Maps of spatial flow concentration reveal that such development of dune is a morphodynamic process that seeks an equilibrium between flow and sediment transport in response to the perturbation of channel widening. At stage 1, the transverse flows toward the sidewalls are redistributed by the side deposits, while the highly concentrated longitudinal flow near the centerline is redistributed by the central deposit, both seek to uniformize the concentration of flow over a cross-section. The migrating front observed at stage 2 represents the cross-section where the uniformity of flow concentration is reestablished. Results further reveal that, once stage 2 is reached, increasing or decreasing the flowrate only aggrades or degrades the stoss slope to seek a new equilibrium between flow and sediment transport, while the migrating front keeps pace with the prograding lee face, as evidenced by its track during the rising or falling limbs of the flood hydrograph in the Xindian River.
How to cite: Lin, H.-Y. and Wu, F.-C.: Dune formation in gradually widening channels as a morphodynamic process seeking equilibrium between flow and sediment transport: Insights from numerical studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7601, https://doi.org/10.5194/egusphere-egu25-7601, 2025.
Suspended sediment is a natural component of rivers, but extreme concentrations can have substantial impacts on water quality, aquatic ecosystems, floods, hydropower production, etc. In mountain environments, sediment availability and transport are modified by a changing climate through changes in erosive precipitation, snow cover and glacier retreat. As it is well known that the majority of suspended sediment load is transported during a few extreme events, it is essential to better understand the spatial and temporal dynamics of suspended sediment concentration (SSC) during extreme events, now and in the future. To date, most studies have attempted to predict SSC dynamics based on catchment characteristics and hydroclimatic factors, however, mostly for individual catchments or specific events, which limits our understanding of SSC dynamics at larger spatial scales. This research aims to identify the main factors that influence the spatio-temporal variability of SSC and the occurrence of SSC extremes in the Alps.
We use 10 years of observed subdaily SSC data from 38 gauging stations in Switzerland and Austria to study the temporal and spatial variability of SSC. First, we examine spatial patterns in the annual SSC regime. We identify three main types of annual SSC regimes after applying hierarchical clustering based on regime differences in magnitude, timing and shape. Our results show that snow and ice significantly influence the annual SSC regime in small mountainous catchments, in contrast to low-elevation and larger catchments where rainfall is more important. The presence of glaciers and the timing and amount of snowmelt play a crucial role in shaping the annual SSC regime and determining when peak SSC occurs, whereas geological and soil characteristics and the annual runoff regime have a smaller influence.
Second, we move from the annual to the event scale at a subdaily time step by analyzing extreme events. We introduce a new classification scheme to categorize the 2,398 extreme SSC events into nine distinct types, based on their dominant transport processes. Our study reveals that rainfall is the main cause of these extremes, responsible for 80% of the events. However, in high-altitude and partially glaciated catchments, up to 40% of the events are driven by snow and glacial melt. Events triggered by both glacial melt and intense rainfall produce the highest sediment concentrations and area-specific yields. These insights into the large-scale and catchment-specific variations in SSC and their extremes are valuable for improving our understanding of the complex hydrology-sediment system response.
How to cite: van Hamel, A., Molnar, P., Janzing, J., and Brunner, M. I.: Suspended sediment dynamics in Alpine rivers: from annual regimes to short-term extremes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8144, https://doi.org/10.5194/egusphere-egu25-8144, 2025.
Meandering rivers are a ubiquitous feature worldwide, exhibiting an extraordinary variety of planform patterns. These patterns, from widely observed point bars to alternating bend widening and narrowing, provide compelling evidence of a pulsed lateral migration of meandering rivers. While these rhythmic migrations have recently been tied to intermittent bank collapses, their morphological impacts over large temporal and spatial scales remains largely unexplored. Here we investigate a globally distributed set of alluvial rivers, using satellite imagery and Fourier analysis to identify low-wavelength width variations caused by bank collapses. Our findings reveal that intermittent bank collapse enhances channel width variation, particularly in narrower and less sinuous meanders, exhibiting a positive correlation with the ratio of channel width to curvature radius. Based on observational evidence, we develop parameterized physics-based relations to optimize the balance between the reliability and numerical efficiency of modeling intermittent bank collapse. These relations are subsequently incorporated into a model of river meandering. We find that intermittent bank collapses play a crucial role in shaping the morphology of meandering rivers, accounting for the observed channel width variations, the shift in bend skewness as sinuosity increases, and the prevalence of low-sinuosity bends. The influence of bank collapses stems from their varying frequency along meander bends, thereby introducing width variations and associated curvature perturbations. Our findings elucidate a long-overlooked mechanism that drives meandering river evolution.
How to cite: Zhao, K., Lanzoni, S., Coco, G., Zhang, K., Townend, I., Darby, S., Xu, F., and Gong, Z.: Intermittent bank collapse as an inherent control on meandering river morphology, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12291, https://doi.org/10.5194/egusphere-egu25-12291, 2025.
In most environments, rainfall infiltrates into the porous ground, and forms a body of groundwater which flows into the neighbouring river network. The groundwater discharge is particularly strong near river heads where it triggers seepage erosion, causing existing channels to grow headward. Occasionally, this process initiates the development of new river branches, leading to the formation of a ramified network. Because seepage erosion is slow, drainage networks take hundreds to thousands of years to build. Therefore, observing their evolution in the field is difficult if not impossible. To bypass this issue, we build a laboratory experiment that allows us to replicate the formation of a drainage network over a few days. The experimental set-up consists of a square box of side 1.5 meter and height 30 cm. We fill the box with a 10 cm layer of cohesionless plastic grains (size 0.8 mm). The layer of grains forms an erodible aquifer. We inject water into the aquifer from below, at a rate controlled by a water tower. Groundwater homogeneously fills the aquifer, and flows towards the outlet of the set-up, positioned along one side of the box. If the discharge is large enough, the flow erodes the aquifer, and entrains sediments out of the system. This process initiates the growth of a drainage network. With time and increasing discharge, the network grows until it covers the entire experiment. Using a simple 2D model to solve the Poisson equation, we compute the shape of the groundwater table as the network changes. The numerical solution, validated by piezometric measurements, reveals the interplay between channel head growth and groundwater flow. Our laboratory experiment thus demonstrates that seepage erosion alone is sufficient to generate a branching network, offering a unique opportunity to observe the formation and evolution of river networks within a confined drainage area.
How to cite: Romon, C., Métivier, F., and Lajeunesse, E.: Growth of a drainage network in the lab, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8818, https://doi.org/10.5194/egusphere-egu25-8818, 2025.
In the present climate, nearly 60% of rivers in the Northern Hemisphere freeze during winter, draining more than a third of the planet's land area and forming a crucial part of the cryosphere. Climate change is altering the river ice regimes, leading to shorter ice-cover durations. These ice covers significantly influence river hydrodynamics, affecting water levels and flow velocities compared to open-channel conditions. A stable ice cover effectively doubles the wetted perimeter, increasing flow resistance. Despite the importance of understanding these dynamics, due to the challenges in acquiring detailed field data, such as ice roughness, flow characteristics, and pressure conditions, the knowledge remains limited from different ice-covered flow situations. Therefore, most laboratory flume experiments rely on smooth ice covers or artificially roughened surfaces, characterized using Manning’s roughness coefficient based on measured flow conditions instead of direct roughness measurements. Recent advancements in acquiring roughness details of subsurface ice provide a more accurate approach to understanding these dynamics between river ice cover and hydraulics. Additionally, previous flume experiments use flexible ice covers, which behave differently from stable ice covers in terms of hydrodynamic impact. As a result, the hydrodynamics beneath stable ice covers, especially under pressurised and non-pressurised flow conditions, remain poorly understood.
This study proposes new flume experiments using a proxy ice material in a 16 m long, 0.6 m wide, 0.6 m deep flume. This setup will allow a more comprehensive exploration of ice cover effects across a range of conditions, informed by field measurements, to enhance our understanding of ice-covered river dynamics. The roughness characteristics of both the subsurface of the ice cover and the flume bed will be derived from mid-winter field measurements collected in the subarctic Pulmanki River in northern Finland. Discharge rates will be systematically varied to replicate conditions observed in the Pulmanki River. Flow velocity and pressure measurements will be collected to assess the dynamics under both pressurised and non-pressurised flow conditions. This approach aims to advance our understanding of the hydrodynamics of ice-covered rivers and their response to a changing climate.
How to cite: de Vet, M., Vaahtera, R., and Lotsari, E.: Hydrodynamics of Ice-Covered Rivers: Insights from Flume Experiments , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10155, https://doi.org/10.5194/egusphere-egu25-10155, 2025.
The morphodynamics of alluvial river systems arise from complex interactions between sediment transport and the resulting morphological changes. The variability of sediment transport across space and time makes predicting the geomorphic trajectories of alluvial rivers challenging, yet essential for improved river management. Advances in high-resolution monitoring techniques now enable continuous tracking of riverbed activity in flume experiments with unprecedented detail. These developments offer new opportunities to unravel the links between bedload transport patterns and morphological changes across various spatial and temporal scales, potentially improving predictions of future river geomorphic behavior.
A key metric in assessing alluvial river dynamics is the active width—the portion of the channel actively involved in sediment transport—which directly connects sediment movement to morphological changes. Despite its importance, active width is often inferred from areas of observed morphological change and has not yet been systematically compared to the actual two-dimensional patterns of bedload transport. This gap limits our understanding of the relationship between sediment transport and channel morphology. Additionally, the definition, quantification, and interpretation of active width are highly dependent on the timescale of analysis (e.g., instantaneous, single flood events, or cumulative flood events). The absence of a robust method to account for this timescale dependency complicates comparisons across different hydrological events
This study investigates the temporal and spatial variability of both the bedload active width (BAW) and the morphological active width (MAW) by simulating flood events for different gravel-bed river types using a physical modelling approach. The flume is 24m long and 0.6 m wide, is filled with a uniform grain size sediment of 1mm of diameter, and the slope is set to 0.01. The flume is equipped with a laser scanner allowing to perform topographic surveys and two cameras taking photos every minute during each experiment. Using both a recently developed time-lapse imagery technique and topographic surveys, 2D spatio-temporal information of sediment transport and morphological changes occurrence and intensity can be obtained.
The experiments explore variability across timescales ranging from instantaneous (minute-by-minute) to multiple flood events. Each experimental duration is designed to maintain consistency in terms of volume of sediment transported under various flow conditions, guided by the conservation of sediment mass (Exner equation), which depends on water depth, wetted width, and sediment flux.
The experiments simulated different river morphologies (braided, transitional, and alternating bar) with varying dimensionless stream power (w*). Results show that MAW systematically underestimates BAW by around 30%, regardless of river type, including braided systems. Laboratory experiments also reveal that the relationship between MAW, the timescale of analysis and w* is best described by a power law with coefficients varying by w* and thus the river type. Quantifications of morphological changes on the Tagliamento (Italy), the Sunwapta (Canada), and the Rees (NZ) rivers corroborate laboratory findings.
These insights enhance our understanding of sediment transport and morphological response of alluvial rivers to hydrological events, with implications in improving future river geomorphic trajectories, river management and flood risk assessment.
How to cite: Bernard, T. G., Pandrin, E., Bertoldi, W., Capito, L., and Bizzi, S.: Variability in bedload and morphological active widths of gravel-bed rivers across timescales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4044, https://doi.org/10.5194/egusphere-egu25-4044, 2025.
Spaceborne techniques offer unprecedented opportunities for monitoring network-scale river changes, providing near-weekly observations of medium-large rivers globally. This data can revolutionize our understanding of river dynamics and inform river management. However, current processing methods often focus on wetted channel changes and centerline migration as proxies for planform dynamics. This approach overlooks the ability to map and quantify changes across the entire geomorphic active channel, which includes not only the wetted surface but also exposed sediment bars and newly established vegetation.
We present an automated methodology based on Sentinel-2 imagery and a Convolutional Neural Network (CNN) for generating time series of geomorphic active channel masks, enabling inter-annual comparisons to identify floodplain reworking and abandonment areas. Lateral channel mobility is then automatically classified as either permanent or transient, based on the spatial extent and temporal persistence of changes.
Application to the Po River (Italy) demonstrates the method's ability to: (i) predict short-term channel trajectory revealing areas abandoned or recently activated by the river channel, (ii) identify reaches with a narrowing/widening trend, or those with limited lateral mobility, and (iii) relate active channel changes to the hydrological forcing and the planform morphology, disclosing morphological behaviors of the river system. The Sentinel-2 historical series available (2017-2023) is used to map stable trends of progressively abandoned or activated areas of the river channel, limiting misclassification errors. Results reveal that confinement, induced by the presence of bank protections and levees, plays a crucial role in river mobility alongside planform morphology. In highly confined reaches, the 7 year-variation in active channel width is limited to 5%, compared to 12% in less confined reaches. Single-thread reaches are particularly affected, with activated areas remaining scarce and abandoned zones showing a more intermittent history, driven by fluctuations in water levels and the variable establishment of new vegetation on sediment bars.
This systematic monitoring provides quantifiable and visually interpretable insights into river dynamics, enhancing our ability to predict future channel trajectories. Such information can be used to monitor medium-large rivers globally and automatically explore their dynamics and morphological response to climate and environmental changes, as well as to inform restoration plans and risk mitigation strategies.
How to cite: Cecchetto, M., Bozzolan, E., Doolaeghe, D., Taffetani, E., Brenna, A., Surian, N., Bertoldi, W., and Bizzi, S.: Automated Quantification of River Dynamics from Sentinel-2 Imagery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9322, https://doi.org/10.5194/egusphere-egu25-9322, 2025.
River confinement is a key factor in determining the river’s morphology and its behavior, affecting flow properties, sediment transport, flood risk and floodplain development. Technological limitations have previously hindered global quantification of river confinement but advances in remote sensing and software now enable direct, automated measurements of river confinements. In this study we present a new method that combines the state-of-the-art global river centerline dataset SWORD, with the elevation model MERIT DEM to quantify river confinement across more than three million kilometer of rivers around the world. Our method measures the “entrenchment ratio”, which is the ratio between the valley width and the channel width. Secondly we measure the “confinement slope”, which is the gradient between the centerline and the surrounding topography. Our method enables us to identify five distinct classes. 1) Aggradational Rivers, with a negative confinement slope, due to sediment depositions raising the riverbed. 2) Flat Rivers, with no significant confinement slope. 3) Obstructed Rivers, partially confined by isolated topographic features. 4) Valley-confined Rivers, with a floodplain constrained by topography. 5) Entrenched Rivers, which have deeply incised V-shaped valleys. Our classification provides a globally consistent framework for quantifying river confinement, offering insights into river-landscape, flood risk, morphological change and fluvial infrastructure development.
How to cite: Collot d'Escury, N., Nienhuis, J., and Beelen, D.: Global quantification of river confinement using MERIT DEM and SWORD centerline tools, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18337, https://doi.org/10.5194/egusphere-egu25-18337, 2025.
The concept of connectivity is a hot-topic in many scientific fields for 20 years ago. This concept refers to the capacity of a system to let flow fluxes of matters, energy (Harvey, 2012) and organisms (Heckmann et al., 2018). In fluvial environments, this connectivity is often studied through the prism of hydrologic connectivity but recent studies focus on sediment dynamics, as it is fundamental factor for a stable and diversified fluvial mosaic (Brierley et al., 2006; Wohl et al., 2019). However, connectivity is easily negatively affected by disturbances such as bed-degradation. Many European rivers experiment a decrease in their connectivity between main and lateral channels (Grill et al., 2019).
Studying the connectivity of riverine ecosystems can be challenging and numerous indices has been developed (Heckman and Vericat, 2018). Many of them focus on the structural aspect of the connectivity or, in other words, they describe the morphological configuration of a river reach. The functional aspect of the connectivity, which refers to the modality and the frequency of connection, is rarely explored.
We propose a method to estimate the connectivity between lateral channels and main channel of a large river using topobathymetric LiDAR data. To achieve this goal, we mobilize a Gaussian Mixture Model (GMM) to identify elevation planes that best fit to the main and lateral channels (Andréault et al., 2024). Then, the gradient between both units, representing the structural connectivity of the reach, is calculated. Functionality of the site is approximated by comparing the waterlevel of diverse hydrological events with the surfaces associated to the median elevation of lateral channel. Compilation of the different comparisons approximate the frequency of inundation or in other words the functionality of the site. However, to better estimates both connectivities, results are analysed according to the entrance of the channel, which is the main limit to bedload transport.
Results of the study show a variability of the structural connectivity along the Loire river according to its main incision sectors. It varies from highly connected to highly disconnected. In-depth analysis of the geomorphological situation highlights the presence of morphological units at the entrance of lateral channels that might be responsible in the case of high structural disconnectivity. The analysis of waterlevels compared to mean plane associated to lateral channels revealed that systems connectivity were not much affected in case of flood but that situation change in case of low flow and average discharge values.
This work highlights a variety of situation and a sensitivity of the methods to characterize objectively the connectivity of the river reaches. It is an innovative approach able to process dense data. The relative ease of the method would also allow river management entities to hierarchize operations of management (re-opening of side channels). In that sense, this work could be of interest in a global change context.
How to cite: Andréault, A., Le Guern, J., Gaudichet, C., and Rodrigues, S.: Evaluating fluvial lateral connectivity from topo-bathymetric LiDAR data and Gaussian mixture model., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20473, https://doi.org/10.5194/egusphere-egu25-20473, 2025.
Understanding the hydrodynamics of river channels and predicting their evolution within the landscape relies on a thorough examination of flow resistance. Flow resistance dictates the distribution of shear stress along channel boundaries, as well as patterns and intensity of erosion on riverbeds and banks. In steep mountain streams, characterized by high relative roughness, flow resistance is predominantly influenced by form drag. Mountain streams often exhibit complex bed morphologies, due to the presence of large immobile boulders, sediment aggregates, and unique channel configurations. Such structures create intricate three-dimensional flow patterns that modify lift and drag forces on sediment, which in turn impact water velocities and sediment transport within the stream. In order to improve hydrodynamic models and better describe bed morphology and roughness, we are exploring new methods for determining bed roughness as well as developing new metrics capable of accounting for clustering, directionality, and water-sediment interactions, while distinguishing between sediment-driven and bedrock-imposed morphological features.
We used an uncrewed aerial vehicle (UAV)-based structure-from-motion (SfM) analysis to determine centimeter-level accurate measurements of 3D river channel morphology, an essential step in studying channel geometry and bed roughness. Utilizing these advancements, we are developing a fully automated workflow to characterize the geometry of natural river reaches, including shape metrics, hydraulic geometry estimates, grain size distribution and various roughness parameters. A standardized workflow to quantify bed roughness across diverse channels will facilitate the development of comprehensive databases, enable comparisons between field sites, and promote the application of measured roughness parameters in flow resistance equations. We analyze hundreds of meters of river channels from Taiwan and New Zealand and present the results obtained through our workflow. The workflow consists of processing raw drone footage into high-resolution 3D models, applying both custom and third-party code to extract and analyze roughness parameters, and conducting two-dimensional depth-averaged flow modelling to derive additional hydrodynamic parameters.
How to cite: Vlatkovic, K., Vetsch, D. F., Deal, E., and Willett, S. D.: Characterizing riverbed morphology and roughness: computational workflow integrating UAV-based 3D mapping and flow modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19685, https://doi.org/10.5194/egusphere-egu25-19685, 2025.
Multi-decade satellite data are increasingly used to assess changes in the wetted extent of large rivers, but few studies rigorously document both system- and reach-scale geomorphic mobility across the entire active width of river systems. Here, we quantify satellite-derived locational probabilities for 15 major rivers across the Ganga basin to systematically appraise geomorphic river mobility. Google Earth Engine (GEE) was used to biennially resolve active river channels from Landsat imagery (1990-2023), which includes the wetted channel and unvegetated alluvial deposits. At the system-scale, results reveal behavioural differences between Himalayan and cratonic rivers. Himalayan rivers are characterised by greater changes in active channel extent (mean locational probability = 0.46) than cratonic rivers (mean locational probability = 0.81). Many rivers show spatially non-uniform variability in along-valley patterns of geomorphic river mobility, with marked differences in mobility between reaches. The Wasserstein distance metric is used to quantify this reach-scale variability and identify locations where the changes are most pronounced. Given the increasing anthropogenic stresses on the Ganga basin (e.g., climate change, hydrological alterations and structural interventions), satellite-derived locational probabilities can be used as an interpretative tool to further investigate specific river dynamics.
How to cite: Boothroyd, R. and Patra, S.: Systematic appraisal of geomorphic river mobility across the Ganga basin , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2343, https://doi.org/10.5194/egusphere-egu25-2343, 2025.
River patterns and planform changes play a pivotal role in shaping planetary surfaces and driving sediment reworking. In the upper high Himalayas, some of the Earth’s highest floodplains have been sculpted by rivers, forming remarkable upland braided and meandering belts in the high Himalayas. While lowland fluvial dynamics are well-studied, the morphodynamics of upland river systems remain poorly understood. This study systematically analyzed river patterns and channel morphodynamics in Himalayan upland alluvial rivers through a combination of remote sensing and comprehensive field investigations. Our results reveal a diverse array of planform behaviors, including meandering, anabranching, braiding, cutoffs, avulsions, and transitions, within these high-altitude systems. Over the past 40 years, meander migration rates have increased by ~78%, accompanied by more frequent cutoffs, avulsions, and pattern transitions—phenomena closely linked to upland climate change. These findings underscore the unique channel morphodynamics and intense lateral movements of sparsely vegetated upland rivers, advancing our understanding of upland river evolution in a warming climate. Additionally, these insights may inform the reconstruction of paleochannels on barren landscapes such as early Earth and Mars.
How to cite: Lin, Z.: Channel planforms and morphodynamic diversity of the upper Himalayan upland rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17202, https://doi.org/10.5194/egusphere-egu25-17202, 2025.
Modeling sediment transport dynamics at the river network scale is challenging. This is due to the uncertainty in quantifying sediment volume entrainment at the reach scale, as well as to the complex way these volumes (that we call here “cascades”) travel to downstream reaches, possibly interacting with other cascades (e.g., sediment input from a tributary). In this context, network-scale (graph-like) numerical models offer a way to integrate these intricate processes, by using simplifying assumptions that allow for simulating sediment routing through networks and potentially for long time periods.
We present the capability of a novel version of the network-scale model D-CASCADE (Dynamic CAtchment Sediment Connectivity And DElivery) in simulating sediment transport in three different (for size and morphological typology) riverine contexts: a mountain stream (the Solda Torrent), a low-anthropized river (the Tagliamento River), and a high-anthropized river (the Po River). Using well-known empirical formulas, the original model simulates the generation and pathways of multi-sized sediment cascades at the reach scale and within a discrete time representation (here daily). In this new version, we add numerical developments regarding the way sediment transport equations are accounted for through the network, and how energy is split among the cascades to respect the sediment mass balance within the simulated time step. These new features allow for a more robust representation of cascade interactions as they move downstream, with the aim of better estimating reach sediment fluxes, velocity, and budgets.
By comparing the model’s results with bedload fluxes measured in different rivers through different techniques (e.g., geophones, the morphological method), we demonstrate the ability of the model to produce a realistic representation of river connectivity both at reach scale (sediment fluxes and budget) and at network scale (sediment traveling velocity and provenance). We also discuss the sensitivity of two core parameters of the model: the active layer depth and the sediment traveling velocity.
The present study demonstrates how D-CASCADE enables the representation of sediment entrainment, transport, and deposition at the reach scale, thereby revealing key aspects of river connectivity functioning at the network scale. It also shows that, despite the scarcity of field data on bedload sediment transport, measurements taken in a few reaches within a network are enough to validate the network functioning generated by D-CASCADE.
How to cite: Doolaeghe, D., Bozzolan, E., Argentin, A.-L., Shrestha, S., Pitscheider, F., Capito, L., Cecchetto, M., Brenna, A., Surian, N., and Bizzi, S.: Capability of the network scale D-CASCADE model in simulating sediment transport dynamics in various riverine contexts, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17155, https://doi.org/10.5194/egusphere-egu25-17155, 2025.
Despite the importance of floodplain vegetation (including dead wood) in fluvial geomorphology and its influence on the aquatic-terrestrial transition zone, current research is dominated by an ecological perspective which misses the bi-directional feedbacks between ecological and geomorphological processes in the river corridor. Prior studies have focused attention on the important roles of climate (light availability and temperature) and fluvial disturbance in controlling river corridor vegetation dynamics, but most of these previous studies have focused not only on trees, but also specific attributes such as canopy height and diameter at breast height. In contrast, much less attention has been paid to the role of understorey vegetation within fluvial systems, despite its potential role in modulating overbank flow (roughness), stabilising banks, and sequestering carbon. Here we define ‘understorey’ vegetation to mean all biomass up to a metre above the ground, irrespective of it being under a canopy or not and we also include large wood and leaf litter.
Within this context, this research aims to quantify how hydraulic roughness and understorey vegetation co-vary seasonally along river corridors representing different disturbance regimes and river types, by quantifying structural aspects of understorey vegetation and its interactions with flow. Here we present work that is focused on Highland Water, a small flashy stream located in the New Forest, UK, which has riparian vegetation comprising predominantly a heavily-grazed deciduous canopy. The stream and its floodplain are also affected by the presence of developed log jams promoting overbank flow with multiple side channels. The study site is being surveyed monthly as well as during high flows to monitor flood extent. The structural complexity of riparian and floodplain understorey vegetation (<1m) is captured from a variety of complementary methods to ensure comprehensive coverage/capture of all relevant components of the above-ground biomass, while hydrological monitoring is being undertaken to evaluate variations in imposed hydraulic forces. The survey methods include Terrestrial Laser Scanning (TLS), alongside Uncrewed Aerial Vehicle (UAV) Light Detection and Ranging (LiDAR), RGB and Multispectral Imagery. Monthly surveying is conducted to capture the transition between leaf-off and leaf-on conditions, enabling links between phenological cycles, light availability, and understorey growth patterns to be explored in the context of variable fluvial disturbance. The interactions between understorey vegetation, fluvial disturbance, and subsequent morphology are being examined to identify the processes occurring within this section of the river corridor and how they vary in both space and time.
Keywords:
Environmental sensing, Fluvial biogeomorphology, Phenology, Disturbance, River corridors, UAV, Laser Scanning, TLS, Flood interactions
How to cite: Goss, D., Leyland, J., Darby, S., and Tomsett, C.: Quantifying seasonal ecohydrological roughness along river corridors using environmental sensing techniques, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1641, https://doi.org/10.5194/egusphere-egu25-1641, 2025.
The role of riparian vegetation in shaping river morphology is widely recognized. The interaction between vegetation growth and channel evolution is characterized by complex, non-linear feedbacks, which complicate direct estimates of the role of key elements in the morphological evolution of non-permanent rivers. Riparian vegetation in non-permanent rivers exhibits growth patterns directly influenced by the flow timing, which controls water availability. Thus, monitoring riparian vegetation is an alternative approach to understanding the ecohydrological complexity and its seasonality in the bio-geomorphological influence of non-permanent rivers. This study evaluated how eco-hydrological and bio-geomorphological seasonality affects the morphology of non-permanent sandy channels in Northeast Brazil. DEMs and orthomosaics, generated from five UAV surveys of a representative section of the basin between October 2021 and August 2022, were analyzed, allowing the study of morphological changes and vegetation cover. Simultaneously, field quadrants were set up to monitor the cover and growth of some riparian plant species in various geomorphic units of the studied stretches. These data were correlated with measurements from six rainfall stations. Riparian vegetation was monitored in two distinct areas, the bar and the channel bed, over three periods. In the bar area, vegetation was sparse in December 2021, followed by a significant increase in April 2022 due to rainfall events, which led to accumulated precipitation between 90 mm and 117 mm. There was a slight decrease in July 2022, but the coverage remained higher than in December 2021. In the channel bed, vegetation was almost nonexistent in December 2021, with considerable recovery in April 2022. Vegetation cover in the bar area was strongly influenced by precipitation, showing peaks after rain events. In the channel bed, vegetation showed little response to precipitation variations, suggesting that the species present are more drought-resistant or receive less water, even during rainfall periods. Vegetation in the bar area varied over time, with peaks in January and April 2022, while cover in the channel bed remained consistently low, ranging from 0% to 10%.
Regarding species, Jatropha mollissima was predominant in both areas throughout the monitored period. Jatropha ribifolia and Vitex gardneriana were also in the bar but had a lower recurrence. In the channel bed, Prosopis juliflora was more common at first, but its presence diminished over time. These results highlight the importance of monitoring riparian vegetation in different bio-geomorphological settings, demonstrating that the vegetation composition in the bar area is more stable than in the riverbed. At the same time, in the channel bed, there is greater variation over time.
How to cite: Santos, C. and Praça de Souza, J. O.: Monitoring Riparian Vegetation and Its Influence on Morphological and Hydrological Processes in Non-Permanent Rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20567, https://doi.org/10.5194/egusphere-egu25-20567, 2025.
The knowledge of supercooling and related frazil ice phenomena in rivers and lakes is critical for purposes of flow control, operation of hydraulic works and estimation of the conveyance capacity of the channels, in particular, at rivers having long and severe winters. Most of the previous studies on supercooling, and related frazil ice and anchor ice development, and further on solid ice development, have been done in flumes. However, there are differences in real river and flume results of temperature effect on supercooling, such as supercooling reaching lower temperatures and establishing equilibrium faster in laboratory than in outdoor conditions. The data of supercooling is still sparse and need for observing the processes in different types of cold region rivers is crucial for also understanding their impacts on natural hazards, such as ice dams and winter flooding, and impacts on hydropower production and land-use planning (such as erosion protection). Studies including field observations would be crucial, but those have been so far rare from rivers of different channel gradient, cross-sectional form and material. Further, in addition to directly gaining more understanding of the supercooling processes, the vast field data sets could enhance the modeling of river ice development, and in particular, the calibration of the models.
Therefore, the aim of this study is to enhance understanding of the supercooling events and related occurrence of frazil ice based on data from Nordic rivers with different channel forms and materials. The study is based on high precision temperature sensors and close-range remote sensing, e.g. time-lapse cameras, installed in three sites: 1) Pulmankijoki River in Finland, 2) Sävarå River in Sweden, and 3) Orkla river in Norway. Also discharge, air temperature, and geomorphological data, e.g. channel form, slope and sedimentological data, are available from each site for understanding the differences in the study site characteristics.
The water temperature sensors and time-lapse cameras were installed to the study sites in autumn 2023, before the freezing period started. The Seabird (Swedish and Norwegian rivers) and RBR solo water temperature sensors (Finnish river) were applied. These sensors were collected from the rivers after the ice melting and flood season in spring 2024. The time-lapse cameras recorded still images and videos, and enabled connecting the frazil ice occurrences to the water temperatures and the supercooling events. These events were also analysed against the air temperature, and thus the energy balance was possible to compare between the different rivers. The preliminary results of the supercooling and frazil ice development processes are presented.
How to cite: Lotsari, E. and Alfredsen, K.: Supercooling and frazil ice development processes at Nordic rivers with different channel forms and materials, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3195, https://doi.org/10.5194/egusphere-egu25-3195, 2025.
River channel migration and bank erosion pose significant challenges for infrastructure, agriculture, and ecosystem management, particularly in the context of climate change. While numerical modeling techniques offer predictive capabilities, their validation often suffers from limited temporal resolution in morphodynamic data collection. This study presents an innovative approach to near-continuous monitoring of river bank erosion and streamflow dynamics along the Hungarian reach of the Sajó River, where intensive bank erosion causes substantial economic damage.
We implement a network of low-cost photogrammetric observation stations using Raspberry-Pi and trail cameras to capture river bank changes and streamflow data at unprecedented temporal resolution. The methodology combines Structure-from-Motion (SfM) photogrammetry with AI-based image segmentation techniques to simultaneously monitor bank erosion processes and water levels. To ensure data quality, we develop specialized processing chains that improve signal-to-noise ratios and enable automatic workflows for volumetric calculations of erosion events. The system's calibration and validation involve comparative analysis with terrestrial laser scanning and ADCP measurements through comprehensive field campaigns.
Our study specifically addresses technical challenges including optimal camera placement strategies in varying vegetation conditions, ground control point optimization, and image overlap variations for SfM-based change detection. For discharge measurements, we enhance existing neural networks with site-specific training data and combine surface flow velocities (derived through optical flow techniques) with regularly updated river cross-sections.
Expected outcomes include: (1) a validated methodology for near-continuous monitoring of bank erosion rates and discharge variations, (2) quantitative characterization of the relationship between variable discharges and composite bank erosion in meandering rivers, and (3) improved understanding of erosion mechanisms during high-flow events. This research represents a significant advancement in fluvial geomorphology monitoring techniques, offering new possibilities for river management and floodplain rehabilitation strategies in the era of climate change extremes.
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Supported by the EKÖP-24-4-II-DE-101 University Research Scholarship Program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund. The research was also funded by the DAAD-2024-2025-000006 project-based research exchange program (DAAD, Tempus Public Foundation).
How to cite: Bertalan, L., Bertalan-Balázs, B., Abriha, D., Krüger, R., Blanch Gorriz, X., and Eltner, A.: Near-continuous change detection of river reaches with image-based approaches, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3640, https://doi.org/10.5194/egusphere-egu25-3640, 2025.
The propensity of meandering rivers to change flow path is a well-observed phenomenon. Meander bends migrate across their floodplains in response bank erosion and point bar deposition, progressively increasing channel sinuosity and decreasing the downstream flow gradient. This process ultimately leads to meander cutoff – where the river forms a localised avulsion to improve the downstream flow and sediment conveyance. On freely meandering rivers, these relict channels – or oxbow lakes – provide a mechanism through which rivers can bypass the excavation of floodplain material, to form a new path, and recycle formerly active sections of river channel. Here, I present observations of channel migration and cutoff formation on two meandering rivers in the Bolivian Amazon Basin and quantify how these fundamental processes evolve in response to the surrounding floodplain relief. I use a semi-automated approach to quantify channel migration and cutoff formation over 3.5 km long river valley segments for a 35-year remote sensing record and couple this to the existing – and evolving – relict channel population in the floodplain. Several hundred relict channels are identified in the floodplains of each river, with cutoff hotspots correlating to areas with the greatest lake presence. Over 100 individual cases of incursion, where the river reoccupies relict channel topography, were identified across the two rivers suggesting that this is a common process along actively evolving river corridors and has implications for the rates and calibre of floodplain material cycling and the remobilisation of particulates (e.g., contaminants) stored in the floodplain.
How to cite: Ahmed, J.: Relict channel topography increases mobility on meandering rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18580, https://doi.org/10.5194/egusphere-egu25-18580, 2025.
The ability to perform measurements in rivers underneath seasonal ice cover is valuable as it allows relatively non-invasive survey of river ice and bed morphology over a large area, during a period when boats or other commonly used survey vessels can’t access the river. Remotely Operated Vehicles (ROVs) have been extensively used for the deployment of sensors in studies of marine ice, to assess ice thickness and properties, krill and algal biomass, and radiation transfer through sea ice, but applications on shallow inland waters, such as rivers, are rarer.
This methodological study aims to evaluate the effectiveness of different imagery collection (multibeam echosounder and stereo-camera imagery processed with shape-from-motion) and acoustic positioning systems (Doppler Velocimeter Log, DVL, and Ultra Short Base Line, USBL) systems for use in ice-covered rivers for the creation of digital models of both riverbeds and ice.
Two BlueROV2 Remotely Operated Vehicles (ROVs) are tested in a high latitude, ice covered river in northern Finland. Both ROVs are identical other than their equipment load; ROV-a is equipped with an Oculus imaging sonar and DVL while ROV-b is equipped with a pair of stereo-cameras and a USBL system linked to a GPS to determine absolute position. Both imaging systems were used to survey a short reach of the subarctic Pulmanki River (nr 69°55'13.3"N 28°01'58.1"E). The surfaces derived from each ROV’s survey are compared to each other, and to known topographic points taken with sub-centimetre accuracy RTK dGPS to determine their accuracies, and so the potential of these methodologies in studies of the critical dynamics of seasonal ice cover and morpho dynamics in ice covered rivers.
How to cite: Johnson, J., Lotsari, E., Vaahtera, R., and Välimäki, J.-M.: Evaluation of Remotely Operated Vehicle -mounted imaging and positioning techniques for topographic measurements under river ice cover., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17596, https://doi.org/10.5194/egusphere-egu25-17596, 2025.
Starting ~20,000 years ago, the North American Ice-sheet Complex receded. As it did, its meltwater formed proglacial lakes, altered water tables, and flowed through rivers to the sea. These waters in turn shaped the landscape and altered ocean circulation. Here we reconstruct the spatially resolved pattern of lakes, wetlands, and river discharge using an updated modeling approach. We reconstruct the Laurentide Ice Sheet using ICESHEET v2.0, which prescribes a basal stress field and mapped ice margins to produce maps of steady-state ice thickness. After accounting for glacial isostatic adjustment and past climate, we simulate groundwater and surface-water distributions using the Water Table Model (WTM) v2.0.1. Following this reconstruction, we map water routing to the ocean, including river discharge and passage through proglacial lakes. We compare these findings against the dated timing of fluvial aggradation, often driven by ice-sheet-derived sediment supply, and incision, which occurs when river discharges remain high but lakes trap incoming sediment.
How to cite: Wickert, A., Callaghan, K., and Gowan, E.: Reconstructing North American rivers and lakes during the last deglaciation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4656, https://doi.org/10.5194/egusphere-egu25-4656, 2025.
The fluvial dynamics of the Danube in the Mohács Island region (Southern Hungary) were analyzed using historical maps spanning the last 500 years. Battle of Mohács, the defeat of the Hungarian armies by the Ottoman Empire took place here in 1526, in environmental conditions that are quite different from today. To reconstruct these conditions, the behaviour of the Danube, the main influencing factor has been studied.
Numerous historical maps, like Tabula Hungariae (1528), Marsigli’s (1726), Müller’s (1709), Lipszky’s (1803) and Korabinszky’s (1804) maps together with the three Military Surveys of the Habsburg Empire (1782-1887) have been transformed or georeferenced and integrated in QGIS for analysis. River branches have been digitized and compared to the present-day situation represented in satellite imagery and a digital elevation model.
Apart from comparing the channels of different centuries, sinuosity values of the river branches and oxbow lakes were calculated. The results provide insights into the river's meandering behaviour and its environmental evolution. Although meandering is the dominant in this section, historical evidence indicates a period when the Danube exhibited an island-building phase. During this time, unlike today, the eastern branch of the river marked the main channel, shaping the floodplain.
Quantitative analyses demonstrated a general declining trend in sinuosity due to the narrowing of bends, river self-regulation, and recently, human-induced interventions such as river regulation. The persistence of island-building period was likely linked to variations in sediment yield and flow patterns. Historical maps suggest that inflowing streams may have had more discharge during this period, contributing to higher sediment deposition at reduced velocities, particularly when the eastern branch served as the main channel. The eventual reversal of the main branch is attributed to flooding events that redefined the fluvial network.
To ensure the reliability of the reconstructions, the accuracy of old maps was also evaluated. The oldest maps depicted rather the character of the river branches, but advances in cartography significantly reduced distortions, enabling the reconstruction of former river courses with greater precision. Comparisons with contemporaneous maps and topographical models highlighted minor deviations and resulted in revision of a few former interpretations.
The study also identified key areas where flooding or marshland characteristics could have influenced land use and military strategies, underscoring the broader implications of environmental history in shaping the region's past. This work highlights the critical role of historical cartography and environmental analysis in understanding long-term fluvial transformations and their socio-environmental impacts.
How to cite: Herczeg, B., Dávid, Z., Vitai, Á., Molnár, G., and Székely, B.: Five Centuries of Fluvial Dynamics and Environmental History of the Danube Floodplain, Southern Hungary: Insights from Historical Maps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7492, https://doi.org/10.5194/egusphere-egu25-7492, 2025.
Understanding flow resistance in rivers with rough beds and banks is critical in predicting flow velocities and depths for a given discharge; this has important applications in improving estimates of sediment fluxes, flood risk, and the identification of hotspots of geomorphic adjustment in rivers. Previous flume experiments have identified the usefulness of topographically derived bed roughness metrics in evaluating the effect of roughness on flow resistance: (1) standard deviation and (2) skewness of bed elevation distributions, as well as (3) frontal area of in-channel obstacles (σz, γ and λfrespectively). In reality, flow resistance is also provided by channel wall roughness, for example, metre scale fluctuations in bank protrusion, riparian vegetation, or the presence of rough bedrock banks in upland reaches. Here, we extend our physical experiments to include sidewall roughness in addition to bed roughness, to quantify the combined influence of bed and bank roughness on flow hydraulics.
Our experimental arrangement uses varying combinations of both bed and bank roughness, both at 1:10 scale. We used two different rough-bed configurations, which comprised a 3D mould of a bedrock riverbed (River Greta, UK), with added scaled boulders at 10% and 40% cover. For the banks we added vertical battens running at regular spacing down the length of the flume walls. Seven sidewall configurations were used (as well as a smooth-walled configuration), with battens varying in protrusion and spacing, to achieve configurations with different combinations of sidewall versus bed roughness. Depth-averaged roughness metrics, ⟨σz⟩, ⟨γ⟩ and ⟨λf⟩ describe the combined roughness of the wetted channel. For each configuration, average water depths were measured for five discharges. Water depths were used to evaluate the Darcy-Weisbach friction factor, f, for each experimental run. We present initial results for the rough-wall experiments, evaluating the combined influence of bed and bank roughness on bulk flow resistance, as well as the relative influences of bed versus bank roughness in each configuration.
How to cite: Whitfield, D., Houseago, R., Hodge, R., Rice, S., Ferguson, R., Hardy, R., Yager, E., Johnson, J., Hoey, T., Hackney, C., and Yamasaki, T.: Coupled effect of river bed and wall roughness on flow resistance , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12560, https://doi.org/10.5194/egusphere-egu25-12560, 2025.
Wetlands are complex systems and understanding them through hydrological connectivity is necessary to uncover their interrelation with other environmental systems, such as rivers and streams. This study aims to understand the dynamics of hydrological connectivity in headwater wetlands and their influence on associated fluvial environments in the Araripe Sedimentary Plateau, located in the Brazilian northeast dryland. Fieldwork was conducted in two different areas (six analysed points), and surveys using a UAV were carried out during dry and rainy seasons to compare the hydrological dynamics of the systems across these periods. In the geoprocessing phase, drainage extraction was performed to identify and analyse water flow continuity using buffer zones (0–2 km, 3–5 km, and 5–10 km) from the base of the Araripe Sedimentary Plateau, where the headwater wetlands are located, to downstream points. Additionally, the NDVI was applied to analyse ecohydrological seasonality during the same distinct periods, and accumulated rainfall levels were calculated for each buffer zone to assess the ecohydrological context and its influence on the connectivity between wetlands and watercourses. The results showed that the highest NDVI values were obtained during the rainiest months when rainfall peaked. Among the analysed distances, segments within the 0–2 km range exhibited higher NDVI averages, whereas other segments had lower averages, except for a few instances where this trend was reversed. Another noteworthy finding is the influence of land use on the continuity of water flows between wetlands and fluvial channels. UAV-captured images revealed elements that could hinder connectivity, such as land-use-modified areas, altered river channels, and constructing barriers, such as low-water crossings. These alterations occurred particularly in downstream sections between 3–5 km and 5–10 km. Preliminary conclusions indicate that most analysed areas demonstrated connectivity, especially in the 0–2 km segments during periods of higher rainfall accumulation. In these environments, vegetation, slope, and the surface and subsurface water flow of wetlands favoured water flow continuity. Conversely, some wetlands did not maintain connectivity with other fluvial environments. Initial investigations suggest that this disconnection may have been caused by land use and other human interferences in fluvial channels.
Keywords: NDVI; Araripe Sedimentary Plateau; ecohydrology interactions; hydrological connectivity; wetland in drylands.
How to cite: Silva, M. and Souza, J.: Hydrological connectivity in small wetlands in tropical dryland areas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13212, https://doi.org/10.5194/egusphere-egu25-13212, 2025.
Suspended sediment concentration (SSC) plays a critical role in riverine systems, influencing ecosystem health, water quality, and sediment transport and deposition. While reach-scale hydraulics determine the available shear stress during a flood and thus sediment flux, the type and quantity of suspended sediment within a river are derived from watershed processes and near-channel properties. A river’s visual color can be monitored from remote sensed images, where the color is a combination of SSC, organic matter, and other particulate pollutants carried by the river. Here we pair high-resolution records of SSC and remotely sensed imagery to investigate the spatial and temporal patterns within river color along river corridors. Preliminary geospatial analysis reveals that mean SSC weakly increases with drainage area, raising questions about the mechanisms driving SSC changes downstream. We utilize remotely sensed imagery to explore how river color correlated with SSC records changes in relation to discharge, tributary spacing and drainage area contribution, watershed attributes, to determine key mixing distances and whether increases in SSC (changes in color) occur primarily at the node scale, such as tributaries, or as a result of gradual downstream fluxes. We utilize these high-resolution temporal and spatial data to inform probabilistic descriptions of SSC and sediment flux along the river corridor where calibration data may be limited. Understanding the dynamics of water color and its relation to SSC changes within a river corridor represents a critical launching pad for leveraging remotely sensed images to predict sediment flux, monitor concentration patterns, and inform strategies for watershed management.
How to cite: Sigman, A. and Phillips, C.: High-Resolution Suspended Sediment Concentration Dynamics along River Corridors, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13761, https://doi.org/10.5194/egusphere-egu25-13761, 2025.
Rivers and their drainage networks have been shown to follow distinct patterns of organization in space and time. These patterns manifest on different scales and are related to structural equilibria which have previously been linked to energetic optimality concepts. In this study I have analyzed three different properties which are based on the work of Horton, Leopold and Langbein and Stolum. Here I hypothesize that all three aspects are indeed related to the physics-based concept of minimum energy expenditure. Additionally, they have in common that they represent dimensionless properties of stream networks, representing the water sediment dynamics in phase space. In this study I show how the confluence rate of river networks is related to the Feigenbaum numbers δ and α, how the decline of geopotential along the flow path is related to Euler’s number e, and how the meandering process is related to the number π.
For the largest rivers on earth I found that these transcendental numbers can indeed be identified, although on distinct scales. On average, the Feigenbaum numbers can be found for converging flow in the upper stream network, Eulers number e relates to geopotential decline in the medium reaches, and strong meandering can be found in the lower parts of the stream. This pattern can be found for each of the considered river networks, indicating a general principle, valid across different scales and climates. Although the state strongly oscillates, it is astonishing that the average state of the analyzed river networks can be described within lower single digits percentage error to the mathematical constants.
I interpret this finding as the dynamics of water and sediment to be attracted to states in phase space which can be described by geometric forms that directly relate to the mathematical constants of δ, α, e, and π.
How to cite: Schroers, S.: The perfect river - an analysis of three transcendental properties of river networks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14157, https://doi.org/10.5194/egusphere-egu25-14157, 2025.
River management policies commonly rely on geomorphic classifications to understand the form and function of rivers. The geomorphic reach type can be an important component of river ecological status reports and informs management decisions. However, geomorphic classification at the national level is difficult as field-based geomorphic assessment across large regions is costly and time consuming; thus, we need to find predictors based on remote data to classify geomorphic reach types on large spatial scales. A shortcoming in many geomorphic classification schemes is that they are designed for classification of alluvial rivers. Hence, these classifications may not accurately reflect rivers with a semi-alluvial or non-fluvial history, e.g. glacial legacy. Our objective was to determine which remotely-derived parameters predict channel type in paraglacial regions with past continental glaciation and abundant till deposits. We visually field-classified the channel type of 366 reaches (with drainage areas > 10 km2) in seven catchments across a latitudinal gradient of ca.1,500 km in Sweden. Prior to field work, reaches were stratified to obtain a representative sample of drainage areas, channel slope, valley confinement, and surficial geology type. Here we present results from the two northernmost catchments, the Torne and Vindel River catchments. Reaches were classified using the existing Swedish Agency for Marine and Water Management (SwAM) scheme in addition to a novel Nordic hydromorphological classification that takes into account semi-alluvial channels common in Fennoscandia. Using nationally available data — 50- and 2-m digital elevation (DEM) models and surficial geology and lithology maps — we characterized over 18 parameters for each reach, including DEM-based metrics of channel slope, surface roughness, and valley confinement, and surficial geology at various distances from the reach. We used a Random Forest algorithm to elucidate which parameters best predict reach channel type. Preliminary results show that surficial geology type is more important than most DEM-derived variables for several channel types; however, surficial geology maps are quite coarse and may not reflect the field conditions. Several DEM-derived variables were also important predictors of channel type, including channel slope and surface roughness. These results indicate that the glacial legacy, as reflected by the surficial geology, plays an important role in determining channel morphology and thus channel type. This work also supports the need for a classification system that considers the unique post-glacial legacy of Nordic rivers. Not only does this help our understanding of the physical and biological processes in these rivers, it is a tool for practitioners to understand and implement ecological measures such as restoration projects in dynamic systems.
How to cite: Mzobe, P. and Polvi, L. E.: Controls on channel morphologic reach type in paraglacial regions—a study based on a Nordic channel classification in Sweden, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18079, https://doi.org/10.5194/egusphere-egu25-18079, 2025.
The location of stream channel heads on hillslopes is an important metric to determine cumulative channel length and remotely map channels. However, identification of channel heads can present a challenge in any landscape, where seasonal variations in flow may affect the location of perennial flow, which may not necessarily coincide with the location of a channel with definable banks. The location at which a channel starts usually reflects a point where concentrated water flow exceeds a shear stress threshold that erodes sediment. However, in areas with subsurface flow, these relationships between slope and contributing area at the channel head are much more variable. Furthermore, most studies of channel head locations have been conducted in mountain environments or other landscapes where alluvial processes dominate. Paraglacial regions, especially those formed after continental glaciation, contain depositional glacial landforms with variable till deposits that may not reflect current landscape equilibrium conditions. Abundant peatlands, even high in catchments, also typify paraglacial regions in northern Fennoscandia.
The objective of this study is to determine characteristics of and controls on channel head locations in a paraglacial region that has undergone Pleistocene continental glaciation with mainly depositional glacial landforms and abundant till. We focused on a region in northern Sweden encompassing ca. 500 km2 over an elevation range of >1000m, around the city of Kiruna. We divided the study area into three elevation regions: low (~250-500 m), mid (~500-800 m) and high (~800-1500 m). Channel head identification was conducted remotely for those originating in a peatland, after field-verification of a subset. Thirty-four channel heads originating in unconsolidated sediment, mostly till, were field-identified in the three elevation regions: two at the low elevation, 13 at the mid elevation and 19 at the high elevation. At each channel head, locations were taken using an RTK-GPS and surveys of the longitudinal profile and several channel geometry measurements were taken along a 100-m reach. Nearly double the number of channels originate in peatlands than in unconsolidated sediment.
For the channels originating in unconsolidated sediment, the cumulative area required for channel head formation ranged over three orders of magnitude, ranging from <0.001 to nearly 0.1 km2 at the low elevation sites (median: 0.0075 km2), <0.001 km2 to nearly 1.0 km2 at the mid (median: 0.08 km2) and high elevation sites (median: 0.07 km2). The gradients of the longitudinal profiles showed a weak positive trend with elevation, but the slopes of the high-elevation sites varied considerably from 6 to 40%. Sinuosities ranged from 1 to 1.2. Preliminary results also show highly variable cumulative areas for peatland-initiated channel heads, indicating a strong role of subsurface flow. We also present controls on channel head formation in terms of upstream hillslope gradients, surficial geology type and glacial depositional feature. However, these large and variable ranges of values for contributing areas of channel heads in paraglacial regions highlight challenges for remote prediction of channels heads and thus channel length, which can have broad implications, including for hydrological and biogeochemical modelling.
How to cite: Polvi, L. E., Carrillo, R., Sanchez, R., and Martin Duque, J. F.: Characteristics and controls on stream channel heads in paraglacial regions—a field study from northern Fennoscandia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18140, https://doi.org/10.5194/egusphere-egu25-18140, 2025.
This study investigates the parameterization of flow intermittency and river styles in two hydrographic basins in the semi-arid region of Paraíba: the Paraíba and Piranhas rivers. The research adopts an integrated approach combining the Base Flow Index (BFI) and the analysis of river styles (River Styles—RS) to characterize the basins' hydro-geomorphological dynamics and spatial variability.
The results indicated that both rivers exhibit flow perenniality below 5%, with the Paraíba River showing higher intermittency than the Piranhas River. The analysis revealed different patterns of intermittency, classified into subclasses based on the frequency and duration of zero-flow events. Additionally, river styles were categorized as confined, partially confined, and unconfined, with significant variations in geological controls and morphological characteristics. Among the confined styles, rocky beds associated with high-flow energy and the absence of floodplains were highlighted. Conversely, unconfined styles exhibited extensive depositional areas and greater connectivity.
The analysis of river styles employed tools such as remote sensing and fieldwork to map geomorphic units and determine bed material texture. Confined reaches showed high sediment transport competence, whereas partially confined and unconfined reaches demonstrated greater susceptibility to geomorphic adjustments in response to environmental changes and climatic variability. The identified patterns underscore the importance of flow intermittency as a determining factor in the morphodynamics of semi-arid fluvial systems.
The data also revealed that the São Francisco River's transposition directly influences the studied basins' hydrological dynamics. This artificial water input alters the natural flow regimes and contributes to geomorphic processes and river connectivity changes.
In conclusion, the study contributes to the understanding of intermittent rivers in semi-arid regions, emphasizing the relevance of integrating hydrological and geomorphological aspects into the sustainable management of water resources. The applied methodology provides a robust scientific foundation for future research on the interaction between climate, geomorphology, and hydrology while highlighting gaps in the literature related to fluvial adjustment rates in dry environments.
Keywords: intermittent rivers, semi-arid, river styles, hydro-geomorphology, water resource management.
How to cite: Rodrigues, J. and Souza, J.: Flow intermittency and river styles in tropical non-perennial rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19096, https://doi.org/10.5194/egusphere-egu25-19096, 2025.
Riverbed surface roughness (or topography) modulates channel hydrodynamics, including the velocity and turbulence distributions, which underpin flood risk and sediment transport. Our recent research has presented the diversity of bed surface roughness found in bedrock and boulder-bed channels, prompting an investigation into the subsequent relationships between channel roughness and flow. Here, we investigate the influence of riverbed topography on velocity distributions and bulk flow resistance via physical modelling using 1:10 scaled flume experiments. Three bedrock riverbeds spanning from smooth to rough were reproduced from high-resolution laser scans. For each bed, the addition of boulders was tested for five boulder densities spanning from 5% to 55% coverage. Each combination of bed and boulders was measured at five incoming bulk discharges. Vertical profiles of the streamwise velocity reveal the deviations in velocity distribution over the beds, while depth and discharge measurements enabled the calculation of the Darcy-Weisbach friction factor for each of the five bulk discharges. The results show conditions of wake interference and skimming flow regimes, yet the traditional regime transition thresholds based on boulder coverage are not consistent, indicating the importance of the underlying bed roughness. Topographic data from Structure from Motion (SfM) photogrammetry of the beds was used to calculate surface roughness topographic metrics that correlate to changes in the bulk flow resistance and provide scope for improved predictions.
How to cite: Houseago, R., Hodge, R., Ferguson, R., Rice, S., Whitfield, D., Hackney, C., Hardy, R., Johnson, J., Hoey, T., Yager, E., and Yamasaki, T.: Influence of bed surface roughness on flow in rough-bed rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20329, https://doi.org/10.5194/egusphere-egu25-20329, 2025.
