Spatial variability of meander characteristics in an avulsing distributive fluvial system

Norris, Neve Traquair (2025) Spatial variability of meander characteristics in an avulsing distributive fluvial system. MSc(R) thesis, University of Glasgow.

Abstract

Previous studies of meandering fluvial systems have mainly focused on meanders at a localised ‘reach’ scale within a river system, without consideration of the spatial context. As such, much of the research has focused on exhumed meander deposits instead of active meanders. More research is therefore required on the spatial variability of meander deposits across a single system or sedimentary basin. Recent research has found meandering fluvial systems to be a dominant planform type in modern-day sedimentary basins; meander deposits are consequently assumed to be more dominant than originally perceived in the fluvial rock record. Distributive fluvial systems (DFSs) have also been shown to dominate sedimentation patterns in modern-day aggradational sedimentary basins and therefore warrant further study due to their abundance. Due to the prevalence of meandering systems and distributive fluvial systems in modern-day sedimentary basins, this study aims to fill a critical literature gap with regards to the spatial and temporal variability of meander characteristics across a modern-day distributive fluvial system (i.e., from apex to toe of a DFS). This study uses satellite imagery of Brazil, acquired through Google Earth Engine and analysed in ArcGIS software, to conduct a spatial analysis of the meandering Taquari DFS. The Taquari DFS is a well-documented, dominantly meandering system, which provides a good spatial context for the study of meander characteristics across the DFS. Spatial changes in: channel width, channel belt width, meander deposit dimensions and sinuosity are quantified on the Taquari DFS to explore downstream changes in meander characteristics within this system. Polygons are created in ArcGIS using the available satellite imagery, which allows for detailed measurements of meander dimensions downstream. This study also explores the temporal changes in channel width, channel belt width, meander deposit dimensions, and sinuosity on the Taquari DFS since the initiation of the large Caronal avulsion (initiation between 1996 to 1997) by comparing meander dimensions pre-avulsion and during-avulsion. The Caronal avulsion is ongoing and continues to divert flow from the parent channel to the avulsed channel. Using the oldest and most modern satellite imagery available from 1985 and 2022, respectively, fluvial dimensions are compared between pre-avulsion (1985) and during-avulsion (2022) imagery, to understand the impact of the avulsion on the parent channel (active channel) and its associated channel belt and meander deposits. On the modern Taquari DFS (2022), active variables (i.e., active channel width, active channel belt width, and active meander deposit dimensions) show a decrease in dimensions downstream, with a significant decrease in dimensions downstream of the avulsion point (where flow is diverted to the avulsed channel). Pre avulsion variables were also identified on the 2022 satellite imagery including pre avulsion channel belt width and abandoned meander deposit dimensions. Pre-avulsion channel belt width displays weak downstream trends and abandoned meander deposit dimensions display no downstream trends. Important differences in downstream trends were identified between active and abandoned meander deposit dimensions along the Taquari DFS. The active meander deposits are larger in size than the abandoned meander deposits upstream of the Caronal avulsion point and the abandoned meander deposits are larger than active meander deposits downstream of the avulsion point. The active meander deposits also show clear changes in size and shape downstream as they change from larger, more rounded deposits, to much smaller crescent-shaped deposits. The abandoned deposits however, display a range of shapes and sizes downstream and show no clear decrease in size, especially between medial and distal DFS zones. The decrease in active meander dimensions (active channel width, active channel belt width, and active meander deposit dimensions) is due to a decrease in discharge downstream as a result of typical DFS bifurcation processes in addition to the diversion of flow from the parent channel to the avulsed channel. Active meander deposit size and shape change downstream as sediment load, and therefore deposition, decrease as discharge decreases. The weak downstream trends displayed by the channel belt relate to confinement in the upper DFS where channel belt migration capacity is limited. The lack of downstream trends displayed by the abandoned meander deposits is due to the range of conditions under which these deposits were formed over time. This research has important implications for the understanding of avulsing rivers due to the significant decrease in width of the parent channel and the size of active deposit dimensions downstream, which influence the redistribution of water and sediment resources within modern DFS. In addition, this research creates an important database on the spatial variability of meander deposit dimensions on a modern DFS which can contribute to the understanding of sandstone-body reservoir dimensions which is important for resource exploration or hydrocarbon storage.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
• Colleges/Schools: College of Science and Engineering > School of Geographical and Earth Sciences
• Supervisor's Name: Owen, Dr. Amanda, Quick, Dr. Laura and Williams, Professor Richard
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85301
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 04 Jul 2025 11:47
• Last Modified: 04 Jul 2025 11:51
• Thesis DOI: 10.5525/gla.thesis.85301
• URI: https://theses.gla.ac.uk/id/eprint/85301