The character and evolution of floodplains with specific reference to the rivers Ouse and Cuckmere, Sussex
Burrin, Paul J.
PublisherLondon School of Economics and Political Science (University of London)
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The genesis, development, character, spatial variability and sedimentary composition of floodplains have been a much neglected study in the geomorphological literature. This is evidenced by the fact that the three most recent authoritative texts on fluvial geomorphology devote less than 2% of available space to this drainage basin component. As floodplains are one of the most extensive and widespread of fluvial landforms, this lack of analysis is important and surprising. It is the objective of this study partially to redress this previous neglect and to provide a better understanding of this important landform. Following a critical review of previous floodplain geomorphological and sedimentological studies, attention is focused on detailed case studies of floodplain development in the Oise and Cuckmere valleys, two small catchments in the southern Weald. Geornorphological maps have been constructed which are used to to describe floodplain form-process relationships. Subsurface investigations by hand-augering techniques at nineteen locations within the two valleys have enabled the form of the underlying sub-alluvial surfaces and the nature and thickness of the overlying litho-stratigraphic units to be described. A classification of the various types of valley rockhead encountered is outlined and form-lithology relationships investigated. Earlier interpretations of sub-alluvial surfaces are rejected for research has indicated that they are better explained as ccaplex, composite, polygenetic, diachronous response surfaces. The alluvial geometry of the fill sequences is discussed and analysed. The sedimentological and mineralogical characteristics of these deposits are analysed by a number of techniques including scanning electron microscopy, infrared spectrophotometry and X-ray diffraction. Results indicate that the fine-grained alluvial fill deposits comprising these floodplain tracts appear to consist largely of reworked aeolian (loe"ss) sediments with varying inclusions of locally derived materials. Further sampling and analyses of the alluvium found in floodplains throughout the Weald have indicated that deposits with characteristics similar to those in the Ouse and Cuckmere valleys are to be found, which provides an indication of the former widespread deposition of loess in this area. A working model of floodplain and valley development is derived for the Holocene period using palynological and radiocarbon evidence. This is then used to re-examine some of the previous concepts regarding the origins and evolution of floodplains, including a re-evaluation of Dury's meandering valley and underfit stream model as it relates to south-east England.