Rivers are essential components of the earth surface. The world’s largest rivers have been studied
much less than to smaller rivers. They are dominated by meandering channels – whether these are
individual km-wide meander bends or ‘accessory’ meandering channels in an anabranching system.
Large rivers, specifically ones with laterally migrating bends, can build a variety of floodplain
elements that are represented by a complex surface topography, the dynamics and characteristics
of which are not yet fully understood.
This research brings a greater understanding to, and quantification of, the floodplain topography
and geomorphology of large rivers. The project uses remote sensing imagery of the World’s largest
rivers, LiDAR datasets of meandering scroll bar topography, and global coverage elevation data.
Novel analytical methods are created, involving image manipulation and GIS processing, to quantify
these landforms in a way that was not possible until recent technological and computational
A new hierarchical classification schema of meandering floodplain deposits is presented and
applied to quantify meandering deposits for two large rivers, the Amazon and the Ob. Both
floodplains show similar downstream morphological changes to their floodplains despite their
different sizes and locations. The new classification schema works well to describe meandering
floodplain deposits. The geomorphology of scroll bars is investigated for the Mississippi River,
revealing the heterogeneity of these deposits and that local meander bend conditions are
important in determining scroll bar formation and preservation on the floodplain. The periodicity
of scroll bars from a range of rivers is investigated and it is shown that scroll bars are intrinsically
linked with the width of the adjacent river channel and respond to local planform changes.
Floodplains of large rivers have complex overbank sedimentation processes that create spillage
sedimentation phenomena. Spillage sedimentation was quantified down a 1700 km reach of the
Amazon River and a 1400 km reach for the River Ob, revealing spatial discontinuities in spillage
phenomena. Spillage dominance depends on diverse sediment loadings, hydrological sequencing,
and morphological opportunity. Understanding spillage dynamics is important in quantifying
overbank sedimentation rates and the spatial distribution of fine-grained deposits.
The findings of this thesis highlight that despite the incredible complexity and heterogeneity of
large river floodplains, order can be inferred via classification schemas and fundamental
relationships identified. The thesis uses novel methods and conceptual models to bring a greater
understanding and quantification to this complex floodplain geomorphology.
|Date of Award||Jul 2016|