Tuesday 1st of july – 14:00
14:00
River health assessment of the Ganga River, India based on geomorphic attributes
AUTHORS
SINHA Rajiv, MOHANTA Haridas
India
Short Abstract: Rivers, particularly large river systems, constitute one of the most fundamental life-support systems that have sustained civilisations and are projected to be a critical determinant for the future sustenance of human civilisations. A river can be termed as a healthy ecosystem only when all flora and fauna in and along the river and the cultivation in flood plains are healthy, and the river form is in equilibrium. The Ganga River system in India is a large river system comprising geodiversity and biodiversity, where about one-third of the population of India depends on the river directly or indirectly. This study focuses on the development of a River health index (RHI) based on geomorphic attributes, where the selected river health parameters are analysed using a multi-criteria decision-making technique, the Analytical Hierarchical Process (AHP), in a GIS framework. We have adopted a five-class (i.e., near pristine, good, fair, poor and degraded) ranking system for the entire Ganga River system from Gomukh to Farakka. Results of the RHI estimation indicate that most of the reaches of the Ganga River in the mountainous stretch are in ‘near pristine’ condition. In the valley interfluve setting, several reaches fall in the ‘good’ RHI class. Most reaches in the alluvial part show ‘poor’ river health, primarily because of flow reduction and sediment accumulation leading to morphological degradation. Several ‘hotspots’ of ‘poor’ river health in the alluvial stretch of the Ganga River are also identified. The geomorphic framework presented in this study can be implemented to understand and evaluate the spatio-temporal scenarios of habitat suitability, environmental flows, and flood risk associated with any fluvial system.
14:20
Aggradation and Widening in a Dam-Regulated Alpine River
AUTHORS
SCHIAVI CAPPELLO Niccolò, BERTOLDI Walter, ZOLEZZI Guido, SOTO PARRA Tulio
Italy
Short Abstract: Dams are known to disrupt natural sediment transport in rivers, leading to negative ecological impacts. However, in the Spöl River in Switzerland, downstream of the unregulated Cluozza River, significant aggradation, widening, and sediment fining have occurred over the past decade, despite dam regulation. This study examines the role of both artificial and natural hydrological events in shaping these changes, with a focus on the effects of an ecological flood program started in 2000. Using high-resolution imagery, digital terrain models, and hydrological data, the study reconstructs the morphological evolution of a 2.6 km reach of the river. It highlights the importance of unregulated tributaries in balancing sediment supply and modified flow regimes, showing how both the 2009 reservoir flushing event and major natural floods have influenced the river’s morphology.
14:40
Valleys and Rivers, River and Valleys: How the interaction of valleys and rivers shape patterns of accommodation space and the implications for management
AUTHORS
MCCORD Jacqui, BRIERLEY Gary, TUNNICLIFFE Jon
New Zealand
Short Abstract: Through mutual interactions, rivers carve out valleys of different shapes and sizes, and valleys shape the way that rivers flow through the landscape. Geologic, geomorphic and anthropogenic histories shape patterns of valley landforms and accommodation space, thereby influencing locations and forms of contemporary river adjustment. As river management embraces space to move and natural flood management interventions, it is important to determine how much space each river needs. As of yet, no well-defined principles have been established to address this question. To assess this, a coherent framework is required to evaluate the cumulative effects of history with the cascading impacts of system change at the catchment scale. Here we develop a geomorphic framework that considers the location of accommodation space, connectivity relationships and the impact of human modifications. Our approach can be used across a range of tectonic settings. We develop and trial our approach to the Tarawera, Rangitāiki and Whakatāne Rivers, adjacent rift zone rivers that drain to the Rangitāiki Plains in Aotearoa New Zealand. These rivers have vastly different patterns of accommodation space and river adjustment, thereby providing a good case study to highlight the importance of catchment-specific contextual considerations.
15:00
Ajustements fluviaux décennaux en réponse à l’exploitation minière extensive dans une rivière à lit sablonneux
AUTHORS
FERRER-BOIX Carles, MARTÍN-VIDE Juan P., SCORPIO Vittoria, PUNTÍ Pau
Spain
Short Abstract: This article presents the results of a long-term research on river adjustments in the sandy Tordera River. We summarize the most important anthropogenic impacts the river has been subjected to, mainly massive extractions, carried out from 1960s to mid-1980s. The results of the research, conducted by comparing historical longitudinal profiles and orthophotos demonstrates that: 1) incision has attained metric figures, exceeding 3-4 m around some bridges. 2) River bed degradation has come along with a continuous reduction in channel width, which in global terms, has narrowed from 136 m to 98 m from 1945 to 2022. 3) The generalized bed erosion has not finished despite massive extractions ended more than 30 years ago, but 4) incision rates have slowed down since 2001. And 5) the upper half of the study reach has not eroded or aggraded significantly but the lower half continued incising from 2016 to 2021. This general degrading trend indicates that sediment supply to the coast continues declining but probably at slower rates. The last major flood in 2020 contributed to widen the channel but did not halt degradation.
15:20
Scorff (Armorican Massif) Silting: Factors, spatial dynamics and effects on the breeding habitats of the marine lamprey (Petromyzon marinus)
AUTHORS
DOUCERAIN Matthieu, ROLLET Anne Julia, KREUTZENBERGER Karl, DUFOUR Simon
France
Short Abstract: The Scorff, a coastal river in the southwestern Armorican Massif, is suspected of becoming over-sanded in recent decades, similar to many other rivers with granitic watersheds. This project, funded and co-led by the MIAME cluster (OFB-INRAE-Institut Agro-UPPA) and LETG, first analyzes spatial relationships between the potential sand production from various sub-watersheds and the rate of sand coverage on flow facies along the river that are suitable for colonization by the sea lamprey. The evolution of these parameters over the past two decades is also examined. Finally, the project explores the potential effects of excessive sandy sediment deposits on sea lamprey spawning grounds. The distribution of sand was found to be primarily influenced by slope and the presence of numerous transverse structures, with localized exacerbation due to complex factors. For example, the Kerustang sub-basin is highly susceptible to sand erosion, and after the opening of the Pont-Calleck dam (13th century) in 2011, it has contributed a substantial sand load. Observations of spawning ground locations over the past decade suggest that, for now, these sand deposits have not reduced the availability of favorable habitats.