Wednesday 2nd of july – from 10:30 to 19:00
Session A3 : Large-scale approaches: from knowledge to action
An interdisciplinary approach to the detection, characterization and quantification of urban impacts on floodplain ecosystems on a global scale, the GloUrb cluster
BOKO Sonagnon Donald, GEORGE Clément, ESTIENNE Louis, MARLAND Jeanne, BELLETTI Barbara, PIEGAY Hervé, CHIU Victoria, POLOME Philippe, CERNESSON Flavie
France
Short abstract : Hydrosystems, particularly alluvial plains, play a key role in providing essential ecosystem services such as water supply, flood regulation and biodiversity. However, these functions and services are increasingly threatened by growing urbanization on a global scale. This internship cluster, part of the GloUrb project, aims to analyze these impacts through a multidisciplinary approach that integrates water quality, sediment mining, socio-economic dynamics, and regulatory frameworks. Sediment mining, essential for construction, causes ecological degradation by altering river morphology and increasing pollution. By combining remote sensing and economic analysis, the project identifies these practices and assesses their impacts on a global scale. In addition, urbanization is exacerbating water pollution, requiring a robust methodology to identify the sources of pollutants, the factors that facilitate their transfer, and their impact on ecosystem services. Regional disparities associated with economic development and environmental regulation underscore the need to integrate law and environmental economics for a global understanding of these impacts. This work highlights the urgent need for global solutions to identify, characterize, quantify and assess the impacts of alluvial plain urbanization on hydrosystems.
Spatio-temporal extrapolation of river temperatures in present and future time on a national scale
MOUSSAY Marion, MOATAR Florentina, ST-HILAIRE André
France
Short abstract : The warming of river temperatures is an undeniable fact due to climate change and human activities1. However, in France, we do not yet have a national network for continuous monitoring of river temperature, representative of all conditions in order to be able to quantify this warming over the entire hydrographic network and for a large number of metrics compatible with biological studies2. Following various droughts and the lack of information on their consequences on aquatic ecosystems, public authorities are becoming increasingly interested in water temperature monitoring in order to better manage water resources. In this work, we will demonstrate a novel methodology for reconstructing temperature time-series, metrics and regimes across France, based on heterogeneous databases. Particular attention will be paid to fish monitoring stations3, enabling analysis of community trends over the last 40 years in relation to river thermal conditions and the use of direct habitat indicators in species distribution models 4. On the other hand, characterization of regimes (natural and altered) could lead to the construction of a thermal quality indicator. The INRAE website “thermie-rivières.inrae.fr” will be enhanced with new indicators and new functionalities as a result of this work.
Unsupervised classification of hydrological conditions in non-perennial rivers
BRICHETTO Isabelle, CAVALLO Carmela, MANFREDA Giammarco, NEGRO Giovanni, PAPA Maria Nicolina, VEZZA Paolo
Italy
Short abstract : Anthropogenic pressures, such as climate change, land use change and water withdrawals, are leading to significant shifts in hydrological cycles, increasing the spatial extension of the non-perennial rivers (NPRs) network. However, knowledge about the frequency and duration of flow intermittency is severely constrained by the small number of streamflow gauges and the limited reliability of hydrological models in predicting surface water presence when discharge is close or equal to zero. In this context, Sentinel-2 images can provide useful information for studying hydrological processes in NPRs, offering effective ways to observe water surface dynamics at an adequate spatial and temporal resolution. The combination of multispectral satellite imagery and Convolutional Neural Networks (CNNs) can be exploited to distinguish the three hydrological conditions which characterize NPRs automatically: “flowing” (F), “ponding” (P) and “dry” (D). In this study, learning on Sentinel-2 false-color images (B11-B8-B4), different CNNs (2-, 3-, 4-class models) were trained to classify hydrological conditions in five river reaches, considering distinct output classes. In some cases, CNNs were also trained to identify the “cloudy” (C) class. Accuracy of CNNs ranged from 0.87-0.98 for 2- and 3-class models, decreasing to 0.71-0.92 range when the distinction between P and D classes was considered (4-class model). Despite the small size of the dataset (1555 images), the obtained results were promising and deserves further refinement, with the purpose of having a more powerful tool for the automatic classification of hydrological conditions in NPRs.
Mapd’O – A new tool for visualization and hydromorphological analysis of river corridor networks at the national scale
HELLING Leo, DUNESME Samuel, VAUDOR Lise, PIÉGAY Hervé, MANIÈRE Louis, MELUN Gabriel
France
Short abstract : The hydro-ecological functioning of river systems is influenced by the physical conditions within their corridors (e.g. topography, land use, geology). A systematic description of the physical functioning has so far been limited due to a lack of data on aspects such as lateral dynamics and floodplain connectivity. The Mapd’O project addresses this by providing datasets and a web interface that allow operators and scientists to analyze these conditions for the entire French river corridor network. Novel datasets such as a national land use map with a resolution of 1 m and the first national valley bottom and lateral continuity maps were created using the Fluvial Corridor Toolbox (FCT), a geographic information system toolbox for network-scale hydromorphic characterisation. Using the Mapd’O app, these datasets can be visualized, analyzed and interpreted to enable hydromorphological diagnosis of river systems at reach to network scales: the entire watershed, but also their sub-catchments and individual river axis level.
The benefits and requirements of long-term macrophyte monitoring on major French rivers.
LAUTERS François, RICHARD Nina, TREGUIER Mikaël, BLANCHARD Matthieu
France
Short abstract : For 12 years, EDF-DTG has been collecting data on macrophytes in five large French rivers and at nuclear power plant. A protocol is used to draw up macrophyte inventories, supplemented by measurements of the environment’s physico-chemical parameters. This database is an invaluable tool for studying the impact of anthropogenic and climatic pressures on the structure and evolution of macrophyte communities. Today, the development of Artificial Intelligence (AI) and the ease of access to new satellite imagery data, provide additional information and offer development potential for monitoring the spatial and temporal evolution of macrophytes. Using these data and new tools, studies have been carried out showing that water temperature and variations in river flow are the main factors influencing macrophyte development. Regarding climate change, evolutionary trends are emerging, with favorable conditions for plant growth and uprooting, as well as changes in the seasonality and composition of macrophyte communities.
These studies highlight the importance of continuing to collect long-term data to confirm trends in macrophyte communities and improve knowledge and monitoring of the environment around nuclear power plants, thereby contributing to their safe operation.
Fine-scale bathymetry assessment from LiDAR data: a practical tool for regional-scale hydraulic modelling
CHONÉ Guénolé, MAZGAREANU Iulia, BIRON Pascale, BUFFIN-BÉLANGER Thomas, NEAL Jeffrey
Canada
Short abstract : Acquiring bathymetric data for rivers is a costly operation, requiring intensive field surveys. However, it is essential for hydraulic modelling. An innovative method for estimating bathymetry from the water surface detected on conventional LiDAR data has been developed to facilitate hydraulic modelling of rivers at the watershed scale. Used in combination with an estimate of stream widths and discharge at the time of LiDAR data acquisition, the water surface on LiDAR data can be used to deduce bed elevation assuming a rectangular bathymetric cross-section, using inverse hydraulic modelling. By integrating this solution into a suite of IT tools, it becomes possible to map flood-prone areas at low cost over a vast territory with unprecedented accuracy. This approach also makes it possible to revise flood zone maps for dynamic rivers at lower cost, and opens up the possibility of characterising river habitats over large territories on the basis of depths and velocities.
Consequences of connectivity on aquatic food webs in Metropolitan France
REYNAUD Nathalie, SENTIS Arnaud, LECLERC Camille, PERRICHER Antoine
France
Short abstract : The fragmentation of natural habitats poses a major threat to biodiversity, particularly in freshwater ecosystems, where dams and weirs block the migration routes of fish essential for spawning and feeding. Theoretically, habitat connectivity influences fish communities and their interactions, but empirical validations remain scarce. This study analyzes standardized fishing data from over 630 sites across metropolitan France to explore the relationships between connectivity and trophic networks. Using mathematical graphs that integrate hydrographic structures and dams, several key findings emerge: downstream-upstream connectivity, consistent with the River Continuum Concept, explains the richness and length of trophic chains, which increase from upstream to downstream, while connectance decreases. The centrality of river segments, as key junctions in the fluvial network, further shapes trophic networks. Impassable dams amplify this influence by reducing connectivity. Finally, the impact of connectivity differs between lotic and lentic ecosystems. These findings advance our understanding of the links between landscape structure and biotic networks, crucial for the sustainable management of aquatic environments.
Session A4 : Water as a common good
Are rivers becoming more intermittent in France?
JAOUEN Tristan, SAUQUET Eric, BENOIT Lionel, BEAUFORT Aurélien, TERRIER Benoit
France
Short abstract : The French Office for Biodiversity created the Observatoire National Des Etiages (ONDE) to monitor over 3,300 sites located on headwater rivers prone to no-flow events. Since 2012, the flow or no-flow state of each site has been systematically observed every month from May to September.
Our study aims to project the evolution of no-flow events at the 3,300 ONDE monitoring sites under climate change in the 21st century. This study builds on the national Explore2 project, led by the French Ministry of Ecology, which updates knowledge on the impacts of climate change on hydrology in France through multi-scenario and multi-model climate and hydrological simulations across the country for the 21st century.
We calibrate machine learning models using climate and hydrological data from Explore2 to predict observed no-flow events at ONDE sites between 2012 and 2019. In practice we calibrate random forest on historical data, and after training the models identify no-flow events with a sensitivity of 70% (Q1-Q3: 53%-82%) depending on the region, and flow conditions with a specificity of 97% (Q1-Q3: 93%-99%). Afterwards, the models are fed using Explore2 projections in order to estimate the future trends in no-flow events throughout the 21st century. Results suggest that by 2040 over 20% of the ONDE sites in the Rhône-Mediterranean-Corsica region could experience no-flow conditions for more than half the time between July and October, compared to 7% currently.
Potential evaluation of wetlands for flood risk reduction using rainfall-runoff-inundation numerical model
HASHIMOTO Masakazu, OHTSUKI Kazuaki, ITSUKUSHIMA Rei, NISHIHIRO Jun
Japan
Short abstract : The aim of this research is to quantitatively evaluate the flood control effects of Nbs, specifically the flood control potential of rice paddy fields, and to propose the optimal operational method for the flood control water diversion system. The research area selected was the Takasaki River basin in the Inba-numa River system in Chiba Prefecture, Japan. The RRI model was applied to this basin as a basin-scale simulation. The water storage capacity of individual rice paddies was determined using topographical data at 5 m intervals and a 2D unsteady flow model. With regard to optimization, a shuffled complex evolution algorithm was adopted to examine the optimal operation method for the hydrological model parameters at the catchment scale and the water storage in the wetlands. As a result, an optimal operation method was proposed for efficiently operating multiple wetlands and reducing river water levels. In the future, we plan to consider not only the optimization of the flood control effects of wetlands, but also the optimal operation method that takes into account the impact on the ecosystem.
Adapting to climate change: example of the use of the Explore2 ensemble of climate and hydrological projections in assessing the vulnerability to climate change at local scale.
GAILLOT Arthur, PELTE Thomas, PRESSUROT Anne, SAUQUET Eric
France
Short abstract : To be effective, measures to adapt to climate change must consider both present and future local specificities. However, the scale on which climate and hydrological models are produced does not correspond to the scales used by managers and operators. In 2023, the Agence de l’eau Rhône Méditerranée Corse (AE-RMC) updated its Basin Plan for Adaptation to Climate Change. This work was an opportunity to illustrate how climate and hydrological projections can be integrated into public policies for adaptation to climate change at local level. An evaluation of vulnerability to climate change was carried out for all AE-RMC sub-basins. Four issues were studied: soil drying, resource availability, resource quality and biodiversity of aquatic environments. For each issue, vulnerability was assessed by combining climate and/or hydrological projection data (exposure factor) with data describing the current state (sensitivity factor) of the watersheds to provide a vulnerability score. Exposure factors were estimated for 2050 using 11 climate models and 2 hydrological models from the project Explore2. As a result, all but two sub-basins are highly to very highly vulnerable for at least 1 issue, and 55% of the sub-basins are highly to very highly vulnerable for 3 or more issues. This work is one of the possible uses for operational purposes of the Explore2 results and shows how climate and hydrological projection data can be used to drive public policies for adapting to climate change
Session A5 : Dynamics of river biodiversity
Integrating Fish Ecology into Environmental Flow Assessments in Central Asia
HAYES Daniel S., HÄGELE Tobias, KOPECKI Ianina, ZEIRINGER Bernhard, KARIMOV Erkin, KARIMOV Bakhtiyor, COECK Johan, VERHELST Pieterjan, DE KEYSER Jan, OMONOV Otabek, SCHNEIDER Mathias
Austria
Short abstract : Hydropower development poses increasing pressure on Central Asia’s pristine high-mountain rivers. This study presents an ecohydraulics-based approach to assess environmental flows (e-flows) for a diversion hydropower project on Uzbekistan’s Koksu River. High-resolution 2D hydrodynamic models were combined with habitat requirements of snow trout (Schizothorax eurystomus), using fuzzy logic rules to determine flow magnitudes for three life stages. The recommended e-flows regime, representing 10.6–17.7% of the mean annual flow, ensures seasonal variability and sustains critical habitats. We discuss these findings within an adaptive management framework supported by preliminary biotelemetry results. This methodology provides a replicable workflow for environmental assessments in Central Asia and beyond.
Thermal variability alters resource intake but not energetic demand in an endangered freshwater fish species, Rhône apron (Zingel asper)
Auteurs : SOUQUES Chloé, FABRA Maé, GUILLARD Ludovic, MORALES-MONTARON Anne, AVERTY Laetitia, CLAIR Angéline, TEULIER Loïc, VOITURON Yann, DECHAUME-MONCHARMONT François-Xavier
France
Short abstract : Despite being concomitant to climate change, the ecological, behavioural and physiological implications of thermal stochasticity on organisms remain largely unexplored. In particular, the sensitivity of bioenergetic metabolic performance to temperature could have large consequences from individual fitness to ecological communities via its influence of resource intake. In this context, we investigated the effect of an ecologically relevant pattern of thermal stochasticity on an endangered freshwater fish, the Rhône apron (Zingel asper). Fish (n=92) were exposed to constant temperatures (13°C, 18°C or 23°C) or experienced a stochastic profile centred on 18°C but randomly oscillating between 13°C and 23°C. We predicted increased energetic cost resulting from a disruption of the acclimation process, associated to an increase in predation allowing to meet such energy demand. Under stable temperatures, energetic expenditure increased with rising temperature, conversely to predation. Under stochastic conditions, metabolic costs matched with those of the group acclimated to 18◦C but feeding competitiveness exhibited a marked decline. Such thermal mismatch between energy demand and intake points out that thermal stress questions the persistence of species in the era of global change and suggests important consequences of stochasticity on trophic networks.
Structural and functional response of benthic macroinvertebrate and fish communities to long-term modifications of the abiotic parameters of the Rhône River.
CARREL Georges, LIZEE Marie-Hélène, FRUGET Jean-François, OLIVIER Jean-Michel, BOULOS Johanna, ARCHAMBAUD Gaït, MALLET Jean-Paul, PERU Nicolas
France
Short abstract : A search for similarities or differencies in the temporal trends of functioning and evolution of long-term series in large rivers was carried out from the confrontation of different hydroclimatic and physicochemical variables put in relation to each other. the temporal evolution and spatial variability of two biological descriptors, fish and benthic macroinvertebrates of the Rhône over the period 2000-2019 over a stretch of nearly 250 km of river, in contrasted sectors both from of geographical point of view than hydromorphological.
The analyzes showed the existence of spatial co-structures and temporal co-dynamics between the abiotic environment of the Rhône and the composition of its populations, making it possible to bring out a set of concomitant evolutions between the latter and the environmental variables characterizing the current functioning of the river. They gradually highlighted marked trends linked to global changes. However, the speed and magnitude of the changes observed require more precise determination of cause and effect relationships in order to identify potential levers for action. These different observations also highlight the complementarity of the biological models studied, such a holistic approach allowing an efficient understanding of the structure and functioning of contemporary large regulated rivers.