Tuesday 1st of july – from 14:00 to 19:00
Session D1 : River morphology: from pressures to impacts
Sediment deficit and river restoration in the Montagne Noire : identifying mobilizable sediment sources
BRUN Mathieu, ARNAUD-FASSETTA Gilles, CORENBLIT Dov, MELUN Gabriel
France
Short abstract : The rivers of the Montagne Noire, historically braided during the Little Ice Age, were modified from the 17th century, changing to a single, meandering bed following developments (corseting, weirs). The major floods of the 2000s, coupled with new public policies (WFD and LEMA), initiated river restorations projects. These efforts aim to promote the decompartmentalization of watercourses, allowing natural functioning of active bands, characterized today by a fluvial metamorphosis and a return to braiding.
Studies on the transport of solid load and the sediment balance highlight a marked sediment deficit, contributing to increased incision of river beds, particularly during ordinary hydrological periods (Arnaud-Fassetta et al., 2024). New work explores the sediment sources available in the watersheds, particularly in alluvial banks, in the banks or in the old cultivation terraces of the Montagne Noire. These recent data provide managers with valuable tools to guide and optimize their next ecological restoration operations.
Do the same river engineering works cause the same hydrosedimentary changes? A comparative approach on four bypassed reaches of the Rhône River.
SEIGNEMARTIN Gabrielle, RIQUIER Jérémie, MOURIER Brice, WINIARSKI Thierry, PÉIGAY Hervé
France
Short abstract : Rivers in the Anthropocene have experienced significant hydromorphological changes as a result of engineering interventions (e.g., channelization, hydroelectric infrastructures) which have profoundly disrupted natural hydrosedimentary dynamics. This study examined four channelized (late 19th century) and bypassed (mid-20th century) Rhône River reaches (~60 km, ~13% of its length) to explore whether similar interventions yield comparable hydrosedimentary effects. Using GIS-based planform analysis (historical maps, aerial imagery, and satellite data), we documented channel evolution and margin terrestrialization, supplemented by hydrosedimentary data (longitudinal riverbed profiles and historical water levels). The results revealed active channel narrowing (-43% to -17% after channelization; -32% to -17% after diversion) and margin terrestrialization (27–44% after channelization; 41–66% after diversion). So, the by-passing had a more pronounced impact when post-channelization adjustments were moderate; and vice versa. In all cases, these diversions have profoundly disrupted hydrological sequences (homogenization of topo- and chrono-sequences), altering lateral connectivity patterns (less frequent but more intense), ultimately degrading the remaining elements of the alluvial mosaic, along with the socio-ecosystem functions and services it supported (e.g., habitat diversity). Additionally, gravel mining has exacerbated local bed incision, with cumulative depths reaching up to -4.1 m over the 20th century (-5 cm/year). Inter-reach variations in impact intensity reflect reach-specific factors and cumulative pressures. These findings highlight the need for a thorough assessment of the impacts of these engineering works to effectively guide management and ecological restoration strategies.
Assessing the geomorphic response and sensitivity of a Himalayan river to climate change and anthropogenic pressures
KARNATAK Nikita, KUSHWAHA Anuj Prakash, MISHRA Vimal, JAIN Vikrant
India
Short abstract : Understanding river response to external controls and its geomorphic sensitivity is critical for planning sustainable management strategies. The Yamuna River with 1,376 km length and 366,223 km² basin area is a key Himalayan river supporting 341,628 number of people for their agriculture, industry, and urban needs. This study integrates geomorphic characterization, stream power analysis, hydrological modeling, and remote sensing to assess its response to projected climate scenarios and anthropogenic influences. Geomorphic analysis was carried out using the River Styles framework and segmentation analysis of river channel using the Fluvial Corridor Toolkit. Geomorphic attributes for River Styles were analyzed across spatial scales and were used to classify the river system in thirteen different geomorphic classes. Stream power distributions were derived from historical hydrological records and DEM derived longitudinal profile. Future hydrological scenarios were simulated via the Variable Infiltration Capacity (VIC) semi-distributed hydrological model driven by INM-CM5-0 and MIROC6 climate models. Results reveal spatial variability in climate change impacts, classifying river reaches into sensitive and resilient zones. Reach-scale sensitivity map of the Yamuna River system will provide a fundamental dataset to priorities the stream management efforts. Further, 460 km long channel reach from mountain front to downstream of Delhi megacity was analysed with high-resolution (500 m) segmentation of the river using the Fluvial Corridor Toolkit to understand anthropogenic impacts on river channel. Key geomorphic parameters including channel width, braiding index, water width, and vegetation width were quantified for each segment. Results highlight extensive human-induced modifications. Anthropogenic influences, particularly in the alluvial reaches, have surpassed climatic and geological controls, driving geomorphic transformations. Notably, sand mining, dam construction, and encroachment in the Delhi megacity urban corridor have disrupted natural fluvial dynamics. This multi-scale multidisciplinary study highlights the integration of climate, and anthropogenic drivers that shape Yamuna’s contemporary morphology and its future trajectory. The results provide new insight for integrated, multi-scale management strategies. Synthesizing climate projections, hydrological simulations, and geomorphic analyses provide a comprehensive assessment of evolving fluvial dynamics, advocating for proactive interventions to mitigate human-induced disturbances and preserve riverine functionality under escalating environmental pressures.
Assessing Anthropogenic Impacts on River Morphodynamics : A GIS-Based Analysis of three alpine water basins (NW of Turin, Italy)
PASCHETTO Arianna, CASELLE Chiara
Italy
Short abstract : This study evaluates anthropogenic pressures on three water basins using topographic maps and satellite images spanning 1880 to 2024, analyzed through a GIS interface. A novel automated vectorization procedure was developed to extract key features, including riverbeds, urban/industrial areas, and river barriers (e.g., dams and bridges), despite challenges arising from cartographic variability. MATLAB-based methods supported data extraction, facilitating assessments of natural versus anthropogenic riverbed changes. Two spatial indices—the Anabranching Index and a modified Aggregate Migration Rate Index—quantified these changes. Results reveal significant anthropogenic impacts in the Dora Riparia and Sangone basins, with urban expansion driving a shift toward single-thread, confined morphologies. By contrast, the Stura di Lanzo basin showed relatively natural migration patterns, except in localized areas. Across all basins, narrowing channels and reduced sediment mobility were linked to increasing barriers and urban expansion, particularly between 1990 and 2024. These findings highlight the critical interplay between anthropogenic development and riverine morphodynamics.
Connectivity and Soil Erosion: How to identify hot spots in the catchments threatened by torrent rainfall
KOREŇOVÁ Simona
Czech Republic
Short abstract : Extreme rainfall events such as torrential rainfalls are one of the increasingly frequent meteorological phenomena in recent decades. They mostly threaten small watersheds where the drainage/river network does not have sufficient capacity to drain water and sediments eroded by precipitation. In these cases, sediment connectivity and disconnections play a key role. Improper land management, disruption, or, conversely, enhancement of connectivity can support the creation of flash floods with devastating consequences for local residents. Collaboration between scientists, engineers, and local authorities is critical in finding sustainable and nature-based strategies to mitigate the impact of extreme meteorological phenomena. The main goal of our work is to link the issues of agricultural land erosion and sediment transport connectivity to identify hot spots in small watersheds where torrential rainfall occurred in the past. In selected locations in Central Europe, connectivity mapping and soil erosion quantification using UAVs were carried out, and WEPP, GeoWEPP models, connectivity index, and the method of effective catchment areas were used. The WEPP model was validated by comparison with UAV measurement results, and the GeoWEPP and connectivity index results were compared with field connectivity mapping and a database of erosion events. The main result is the map of the most critical hot spots from the point of view of soil erosion and connectivity, which can serve as a basis for improving the management of small catchments, optimizing connectivity, and improving soil protection.
Super-resolution method based on the use of low resolution Landsat and high-resolution Sentinel-2 images to characterize large-scale river landscapes
AUDISIO Pierre, PUSTELNIK Nelly, BELLETTI Barbara
France
Short abstract : River dynamics can be characterized using specific indicators such as the braiding index or the average width of the active band [1], making it possible to monitor geomorphological changes in the river, but also potentially to determine the nature of the elements at the origin of the transformations. In this study, these descriptors are obtained using Landsat and Sentinel-2 satellites.
While the temporal coverage is wider with Landsat data, the spatial resolution is much better with Sentinel-2, enabling much finer descriptor extraction over a shorter period. In order to extract high-resolution descriptors over a long period of time, we propose a super-resolution method to increase the spatial resolution of Landsat archive data, using an informed deep learning strategy based on the exploitation of Sentinel-2/Landsat high- and low-resolution image pairs.
Performance of Segmentation Methods Applied to River continuum at Network scale
DE ALMEIDA Thomas, VAUDOR Lise, DRAY Stéphane, PIÉGAY Hervé
France
Short abstract : River segmentation is a crucial step in river characterization to detect discontinuities and delineate homogeneous reaches. With the increasing availability of longitudinal data to describe rivers, the need for automatic univariate segmentation as summary and analysis tool has become critical. Many methods exist, although they are not typically designed to segment a river. We conducted a review of existing methods and selected a set of potentially available techniques based on several practical criteria. We compared the selected methods using simulated data and evaluated the performances of methods based on quality, robustness and efficiency criteria. We concluded that no segmentation technique outperforms all others in all circumstances and described under which specific conditions each method best performs. Lastly, we provide practical advice for selecting the most suitable technique according to the data distribution and the objectives of the study.
Benchmarking fluvial geomorphic processes for river restoration and monitoring
DOWNS Peter, BOOTH Derek, CASSERLY Colm
United-States
Short abstract : connectivity in the hope of a significant and sustained uplift in biodiversity. While there are various means of characterising changes in river forms and river connectivity, there have been few methods for benchmarking fluvial geomorphic processes as a channel evolves. We showcase a rapid assessment protocol developed to quantify the mode and intensity of river channel adjustments and to assess whether the channel is functionally stable. Of note, we separate field observations from their interpretative conversion into ‘adjustment indices’ to reduce inter-surveyor bias and allow for post-survey interpretative improvement. The approach was tested in relatively undisturbed high elevation meadow channels in California and highly modified lowland channels of Ireland. The method estimates 14 indices representing modes of channel adjustment, categorised into 4 levels of apparent intensity, and with integrative outcomes summarising the channel’s sensitivity to change, lateral activity and relative instability. As a rapid assessment, the approach is well-suited to pre- and post-project monitoring to judge the evolutionary trajectory of channel adjustment processes and relative stability as part of benchmarking fluvial geomorphic processes for river management and restoration.
Mapping riverbed conditions at the drainage-network scale in the Perales river basin (Spain)
VÁZQUEZ-TARRÍO Daniel, GARROTE Julio, SANDOVAL-RINCÓN Kelly Patricia, DÍEZ-HERRERO Andrés
Spain
Short abstract : Sediment transport and geomorphic change processes have implications for many river management issues, such as flood hazards, river restoration, hydropower or infrastructure design. For this reason, river managers often require information on the geomorphic and hydro-sedimentary conditions of river channels. In this work, we propose a GIS workflow adapted to the characterisation the bed condition of channels at a drainage network scale in terms of incision, aggradation or vertical equilibrium. We have applied this procedure to the Perales river (central Spain) and we derived a map of the morpho-sedimentary conditions of 113 river segments of this river. We believe that this type of characterisations could contribute to a first assessment of rivers in terms of sediment balances at a catchment scale and help to prioritise sectors for more detailed, further studies.
Prioritisation of river sections for restoration based on evidence of geomorphological adjustments (Saja River, Spain)
ELENA Fernández-Iglesias, MARÍA Fernández-García, VERÓNICA Moro, LARO Incera, GIL González-Rodríguez, DANIEL Vázquez-Tarrío, ROSANA Menéndez-Duarte
Spain
Short abstract : River restoration is a key tool for mitigating anthropogenic impacts on rivers and restoring their ecosystem functions. However, prioritising actions along a river corridor can be complex due, to variability in geomorphological and environmental conditions, among many others. This work propose a categorisation of reaches in the Saja river (NW Spain) based on morphodynamic indicators of possible sediment imbalances in the river channel, with the aim of prioritising restoration actions. The classification is based on two information. First, on present-day channel and floodplain characteristics obtained from field observations and aerial images collected with drone flights. Second indicators of channel changes identified by comparison of diachronic aerial photos (since 1957). The study focuses on 30 km of the Saja River, a wandering river located in northern Spain that has been affected mainly by longitudinal bank protection and flood control works, as well as an increase in tree cover in the basin. We have classified the 10 sections according to different levels of evidence of imbalance and greater potential for recovery, taking into account that the interventions will be directed towards the recovery of processes and forms. The main aim is to increase longitudinal and transversal connectivity to ensure an appropriate long-term sediment balance and geomorphological conditions.
Session D2 : Solid transport and bed load
COARSED project: International experience feedback on the integrated management of coarse sediments in large rivers as a response to ecological, safety-security and socio-economic issues
LAVAL Frédéric, COME Jean-Marie, PIEGAY Hervé
France
Short abstract : River sediment management is a key issue in sustainable land management, at the interface between natural processes in watersheds and the development of water uses in valleys. The need for comprehensive, integrated sediment management is gradually becoming apparent in developed systems where natural balances are being altered, as the impacts of past and present developments accumulate, and as better functioning of hydrosystems becomes necessary to make the services provided more sustainable. The Rhône River is directly concerned by these types of issues, and between 2018 and 2022 has been the subject of a study to define a “sediment management master plan”. In this sediment management scheme, the aspect concerning coarse sediments (gravels, pebbles) is particularly sensitive for its structuring role in achieving good ecological status, and for the constraints that emerge at the interface with safety-security issues and socio-economic uses. The main principles of key actions can be defined, but given that the Rhône river is a special case in France, it is necessary to look for feedback from European rivers (Danube, Rhine, Po, Swiss Rhône, Isar, etc.) in order to clarify the feasibility of these actions. The COARSED project has therefore been set up for the period 2024-2026 to analyze these operations from a technical, operational and regulatory point of view, and to draw up recommendations for their implementation. The first analyses will be available at the end of the first half of 2025.
Towards automated grain size mapping of gravel-bed river: UAV-based technique for grain size distribution assessment
MD Ashraf, RUSNÁK Miloš
Slovakia
Short abstract : Recent studies have explored automated grain sizing analysis from UAVs imagery of gravel bars, offering efficient alternatives to traditional field methods to understand the river hydraulics and sedimentological properties. This work compares automatic photosieving of sUAS-based orthophotos with field photographs of sediments processed with object-based methods like BASEGRAIN, and PebbleCountsAuto, have also been evaluated, with varying degrees of accuracy compared to laboratory-analysed sediment samples measurements for gravel-bed river Ondava (Western Carpathians, Eastern Slovakia). These UAV-SfM approach enable rapid characterization of grain sizes at higher spatial and temporal resolution than traditional methods, providing valuable insight into sediment dynamics and river processes. Physical habitat parameters can be extracted from detailed 3D models and the channel bed structure or gravel bars substrate is detectable. A predictive model of the relationship between the sUAS image parameters and field samples is proposed and applied for whole high-resolution orthophotos of the study area. The technique showcases the capabilities of high-resolution sUAS images for processing and analysing grain size parameters of the river system. Our preliminary results shows that statistical models calibrated on image texture were almost very closed in comparison with software and the UAV-SfM approach and show potential approach to access the Grain size distribution of river in future.
AcouSed: a software for acoustic inversion to compute concentrations of suspended-sediments in rivers
MOUDJED Brahim, BERNI Céline, LE COZ Jérôme, DRAMAIS Guillaume, PIERREFEU Gilles, FISCHER Stephane, CAMENEN Benoît
France
Short abstract : Down-looking multi-frequency Acoustic Backscattering Systems (ABS) have been deployed at the surface of rivers for several years, to measure the suspended solids throughout the water column. The acoustic backscatter signal is processed using multi-frequency inversion method to compute suspended sediments concentrations. This method involves both water sample calibration and models to determine the acoustic properties of suspended particles. This document presents a software, named AcouSed, developed to make complex theoretical acoustic inversion methods accessible. Acoustic backscatter signal is visualized and preprocessed in the software. Both, concentration and particle size distribution of water sampling are also plotted and used to calibrate the acoustic signal. AcouSed was designed so that the user can control inversion method options and plot results.
Passive Acoustic Monitoring of Sediment Transport by Bedload: Application on the Drac River
NASR Mohamad, LAVAL Frédéric, ZANKER Sébastien, GODAYER Claire
France
Short abstract : The knowledge of bedload flows in rivers is a challenge for managers involved in controlling the hydrosedimentary balance of rivers, under the influence of anthropogenic developments (dams, impoundment, weirs, embankments, bedload regulation) or as part of hydromorphological restoration operations. This research focuses on the application of passive acoustic methods to address this challenge using calibrated hydrophones that will allow for continuous monitoring of bedload sediment transport. The R&D work which is presented applies to the Drac River, near Grenoble,. Using a hydrophone fixed on the riverbank and coupled with calibration based on acoustic mapping, detailed sediment flow records were obtained from 2019 to 2023. Sediment volumes estimated by this method were compared and validated using conventional approaches, such as bathymetric surveys and 1D modeling. Additionally, the measured bedload flux in this study demonstrated that the passive acoustic measurements can be used to detect changes in sediment transport dynamics, whether occurring naturally or as a result of human interventions. This study highlights that hydrophones could serve as an operational tool for river managers, providing essential data for sediment management plans and the optimization of hydraulic infrastructures.
Implementation of a granulometric measurement protocol using underwater imagery and monitoring of the effects of ecological restoration of the Rhône
THAS Elisa, BENACCHIO Véronique, MORA Christophe, GUÉRIN Stéphane, MOIROUD Christophe, PIÉGAY Hervé, CRAVE Alain
France
Short abstract : Anthropogenic developments on the Rhône have disrupted its hydrosedimentary functioning (Rossignon et al., 2019; Donati et al., 2020). The 1990s saw the development of an ecological restoration program, one of the current aims of which is to restore the river’s morphosedimentary dynamics, enabling diversification and an improvement in the biological quality of the environment. Restoration operations involve removing the Girardon structures, opening up disconnected secondary channels and reinjecting sediment (CNR GRAIE-OHM, 2023). This work forms part of the operational monitoring of the restoration, carried out by CNR, in order to assess its impact on the hydromorphology of the channel, and more specifically on aquatic habitats and biocenoses. In this context, a protocol for analysing the granulometry of the bottom of the main channel of the Rhône is proposed.
Granulometric data were collected using an underwater camera and processed automatically using an AI developed by Styx4D. The present contribution firstly aims to determine the main errors made during automated processing with a view to improving it. The second stage involves optimizing the protocol, by streamlining a maximized sampling plan, while retaining as much information as possible, in order to limit data acquisition and processing time. The results obtained will be used to carry out further research as part of a thesis on the morphological changes brought about by the restoration work, the temperature at the bottom of the channel and changes in habitats with a view to identifying a biological response.
Hybride physical/numerical morpho-dynamical model of the Rhône River at the Neyron breach diffluence to improve the coarse sediment management within the clean water well fields of Lyon City
CASSEL Mathieu, GONZALES DE LINARES Matthieu, GUTA Hélder, RIELLAND Pierre-Alain, RONZANI Florian, LOPEZ Arthur, PERRISSIN-FABERT Anne, GILLES Guillaume
France
Short abstract : The evolutions observed in the equilibrium and hydro-sedimentary functioning of the Neyron breach structure, marking the diffluence between the channels of Miribel canal and the Old-Rhône, have significant consequences on the Crépieux-Charmy well fields and the supply of clean water of the city of Lyon. Among these consequences: (i) low flow rates in the Old-Rhône channel during low water periods and (ii) colossal volumes of sediments supplied during floods, necessitating frequent and costly sediment dredging operations. Despite numerous field studies (topo-bathymetry, sediment tracing by RFID), hydro-sedimentary processes remain poorly understood at infra-flood scale.
Thus, the Eau publique du Grand Lyon commissioned ARTELIA to carry out a study based on a hybrid morpho-sedimentary modeling: physical (1/50th scale model) and numerical (3D), whose objectives are (i) to model and understand the current hydro-sedimentary dynamic at the diffluence, then (ii) test and optimize a new structure configuration of the breach to improve the distribution of liquid and solid flows.
The results of the physical model show remarkable similarity with the field data, which allows their confidence utilization for the calibration of numerical models (hybridation). These numerical models then simulate several scenarios, including with a redevelopment solution at larger spatial (entire field of capture) and temporal scales.
Large-scale automated granulometry through Aerial Imagery and Artificial Intelligence with GALET v2: first feedbacks and perspectives
BENACCHIO Véronique, BARATIER Alexandre, LEMAIRE Pierre, BERTHET Johan
France
Granulometry is a crucial parameter for understanding river dynamics. Yet, measuring it at a large-scale remains challenging due to technical constraints in the field. So far, due to a lack of annotated datasets truly representative of the diversity of conditions, it has not quite benefited from recent technological advancements in imaging (particularly from UAV) and Artificial Intelligence (AI). GALET v2 demonstrates the potential of generative AI to overcome this issue. By combining real and synthetic images, both annotated and generated by AI, we trained two Convolutional Neural Networks. Combined into a multi-scale strategy, they enable the analysis of large surfaces within limited time. Less than 10 minutes are required to extract 25,000 masks from a 48 MP image. GALET v2 has been tested on several types of rivers, such as the Ullion (06) and Büech (04), including ortho images representing more than a kilometer in length. It segments all classes and sizes of particles, even in highly heterogeneous environments. Automatic measurements were validated by assessing their similarity with field values. For hydro-sedimentary modeling purposes, this tool enables a shift from a punctual, localized measurement (such as the Wolman method, which is still the reference) to a surface-based, spatialized, and exhaustive measurement. Conversion methods enable the generation of a spatialized Wolman measurement in a GIS, in raster format. This work opens new perspectives for the study and management of sedimentary processes in rivers. They now aspire to being integrated into the practices of river managers.