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The persistence of oxbow lakes as aquatic habitats: An assessment of rates of change and patterns of alluviation

Dieras, Pauline L. 2013. The persistence of oxbow lakes as aquatic habitats: An assessment of rates of change and patterns of alluviation. PhD Thesis, Cardiff University.
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Abstract

Oxbow lakes are of high ecological importance due to the number and the diversity of habitats they provide. They are created after the abandonment of meanders and subsequent sediment infilling leads to their progressive terrestrialisation, taking from a few months up to several centuries. Nonetheless, little is known about oxbow lake terrestrialisation processes, sediment composition, or why such a disparity exists in lakes’ longevity. To understand the controls on oxbow lakes alluviation, field observations, remotely sensed data and GIS analyses were combined. Sediment transfers in oxbow lakes were documented by topographic and sampling surveys of sites in France and Wales. Aerial photographs and maps were used to date cutoff events, analyse oxbow lakes geometry, and understand the controls on oxbow lake terrestrialisation for eight rivers of different characteristics. Findings from this study illustrate that the specific mechanism by which an oxbow lake is formed is critical to its persistence as a lake and to the sedimentary processes experienced. Chute cutoff oxbow lakes filled in 10 times faster than neck cutoffs and showed significantly different sediment deposits. Results also highlighted that oxbow lakes are not only fine-grained sediment stores, as often referred to, but can be significant bed material sinks since a site on the Ain River sequestered up to 34% of the bed material supply. However, the volume of sediment mobilised in the main channel during cutoff appeared to be larger than the bed-load stored in the former channel within the first decade after abandonment (40%). Sedimentary evidence showed that the terrestrialisation of oxbow lakes is driven by several processes: a flow separation zone at the entrance of the channel creating a sediment plug, sediment sorting by flow gradients and decantation in ponded areas. These results have important implications for the management of meandering rivers by providing a comprehensive analysis of depositional processes which also helps to predict oxbow lake longevity.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Q Science > QH Natural history
Funders: School of Earth and Ocean Sciences
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 23:22
URI: http://orca-mwe.cf.ac.uk/id/eprint/49392

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