Thursday 3rd of july – 11h15
11:15
Effects of anthropogenic vegetation removal on channel dynamics: Insights from a meandering river in Croatia
AUTHORS
PAVLEK Katarina, POEPPL Ronald E., GAŠPAROVIĆ Mateo
Croatia
Short Abstract: This study investigates channel changes in the meandering Orljava River in Croatia over the past 50 years, focusing on the river’s response to flood events before and after the anthropogenic removal of riparian vegetation in 2011. Channel features were measured using aerial images, orthophoto and topographic maps. For the 2011–2021 period, object-based land cover classification was applied to the images to automate the vectorization of channel morphology. To determine the factors affecting lateral migration rates (as the primary metric chosen due to the meandering channel pattern), data on flood size and duration, riparian woody vegetation, and channel geometry (width, sinuosity, and slope) were statistically analysed. The results indicate that lateral migration rates increased fourfold while channel widening amounted to 40% following vegetation removal in 2011. Statistical analyses revealed that lateral migration rates were negatively related to the presence of riparian vegetation and positively related to flood duration, magnitude and channel slope. These findings highlight the role of vegetation in stabilizing riverbanks and mitigating lateral erosion, suggesting that its restoration is crucial for reducing flood risks and enhancing channel stability. Additionally, preserving natural sinuosity promotes geomorphological diversity and increases channel stability by reducing slope and stream power.
11:35
Monitoring the re-restablishment of vegetation after clear-cutting and bar lowering: the case of the Isère River in Combe de Savoie
AUTHORS
GODFROY Julien, BORGNIET Laurent, BOISSY Thibault, MELUN Gabriel, PIÉGAY Hervé, JANSSEN Philippe
France
Short Abstract: To understand and characterize the effects of works aimed at limiting vegetation encroachment, it is necessary to rely on accurate data on the trajectories of riparian environments both in the diagnosis phase and after vegetation removal. Remote sensing tools are key in meeting those challenges as they enable standardised monitoring and are increasingly available to river managers. Using a case study on the Isère River in Combe de Savoie where the revegetation of gravel bars is leading to a loss of biodiversity and an increase in flood risks, we demonstrate the value of high spatial and temporal resolution monitoring using drones to characterise the spatio-temporal dynamics of vegetation following clearing, stump removal and the reshaping of gravel bars. To do this, we use bi-annual campaigns during the growing season to retrace the dynamics of fine sediments and vegetation patches that have colonized the gravel bars. By assessing the age, growth and responses of vegetation units to winter floods over time, these data make it possible to characterize the dynamics of vegetation recruitment and establishment and thus to gain a more general understanding of the evolution of fluvial forms following interventions. Coupling these dynamics with the hydrology during the summer season will enable a better assessment of its effects on the recruitment and establishment of vegetation.
11:55
What role can knotweed play in changing alluvial hydrosystems?
AUTHORS
DE LA FORGE Irène, COTTET Marylise, PIOLA Florence
France
Short Abstract: In the context of global change impacting ecosystems, conciliation biology suggests recognizing the presence of invasive alien species as a way to ensure precious ecological functions. This project, based on interviews with scientists and managers experts, aims to assess the relevance of a change in the management paradigm, involving the integration of these species into hydrosystems under significant anthropogenic constraints. For this purpose, we characterized experts’ representations of the role of Asian knotweeds in alluvial ecosystems, and the strategies to manage them. A survey using semi-structured interviews was conducted with 20 managers (river syndicates, environment consultancy firms, compagnies specializing in knotweed management and regional water authority) and 12 scientists (ecologists, hydrobiologist, geographer, chemist, agronomist and economist), to clarify the arguments surrounding the conciliation paradigm. Results show that control interventions, motivated by the will to protect biodiversity, are structured by economic, political and knowledge production and circulation dynamics. Results also indicate that the current knotweed management strategy is based on localized control in key areas. In addition, their functional roles are more often unknow than rejected by a majority of respondents.